No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Vascular Extracellular Matrix and Arterial Mechanics
Abstract
An important factor in the transition from an open to a closed circulatory system was a change in vessel wall structure and composition that enabled the large arteries to store and release energy during the cardiac cycle. The component of the arterial wall in vertebrates that accounts for these properties is the elastic fiber network organized by medial smooth muscle. Beginning with the onset of pulsatile blood flow in the developing aorta, smooth muscle cells in the vessel wall produce a complex extracellular matrix (ECM) that will ultimately define the mechanical properties that are critical for proper function of the adult vascular system. This review discusses the structural ECM proteins in the vertebrate aortic wall and will explore how the choice of ECM components has changed through evolution as the cardiovascular system became more advanced and pulse pressure increased. By correlating vessel mechanics with physiological blood pressure across animal species and in mice with altered vessel compliance, we show that cardiac and vascular development are physiologically coupled, and we provide evidence for a universal elastic modulus that controls the parameters of ECM deposition in vessel wall development. We also discuss mechanical models that can be used to design better tissue-engineered vessels and to test the efficacy of clinical treatments.
... Without those, the comparatively thick aortal wall would get necrotic due to a barrier problem for oxygen and nutrients. This principle is important when developing a TEVG with bigger dimensions by TE, and one would have to provide tiny little vasa vasorum inside the printed wall to sustain the structure alive [9]. ...
... For vessels, collagen type I is the most frequent compared to collagen types III, VI, VIII (the latter one predominantly in tunica media), XIII, and XXI (the latter one secreted by VSMCs). Other structural proteins are elastin, diverse laminins, lecticans, fibronectin, diverse fibrillins, and unbranched, typically anionic polysaccharide chains known as glycosaminoglycans (GAGs) covalently attached to protein cores, namely proteoglycans [9]. More than 100 different proteins have been identified in ECM of the human aorta [24]. ...
... The formation of a vascular functional ECM results from the secretory function of all contributing vascular cells, i.e., ECs, VSMCs, and AFs [9,13]. This means that all these cell types are capable of producing ECM. ...
Three-dimensional (3D) printing and bioprinting have come into view for a plannable and standardizable generation of implantable tissue-engineered constructs that can substitute native tissues and organs. These tissue-engineered structures are intended to integrate with the patient’s body. Vascular tissue engineering (TE) is relevant in TE because it supports the sustained oxygenization and nutrition of all tissue-engineered constructs. Bioinks have a specific role, representing the necessary medium for printability and vascular cell growth. This review aims to understand the requirements for the design of vascular bioinks. First, an in-depth analysis of vascular cell interaction with their native environment must be gained. A physiological bioink suitable for a tissue-engineered vascular graft (TEVG) must not only ensure good printability but also induce cells to behave like in a native vascular vessel, including self-regenerative and growth functions. This review describes the general structure of vascular walls with wall-specific cell and extracellular matrix (ECM) components and biomechanical properties and functions. Furthermore, the physiological role of vascular ECM components for their interaction with vascular cells and the mode of interaction is introduced. Diverse currently available or imaginable bioinks are described from physiological matrix proteins to nonphysiologically occurring but natural chemical compounds useful for vascular bioprinting. The physiological performance of these bioinks is evaluated with regard to biomechanical properties postprinting, with a view to current animal studies of 3D printed vascular structures. Finally, the main challenges for further bioink development, suitable bioink components to create a self-assembly bioink concept, and future bioprinting strategies are outlined. These concepts are discussed in terms of their suitability to be part of a TEVG with a high potential for later clinical use.
... Conversely, proteoglycans and glycoproteins form a looser network capable of withstanding compressive stress. At the vascular level, the high proportion of collagen and elastin molecules in the wall allows large arteries (i.e., elastic arteries) to resist to stretch caused by systolic pressure [10] and to smooth the discontinuous blood pressure and ow induced by the heart, namely the Windkessel effect [11]. Maintenance of arterial ECM ensures proper arterial function and is essential. ...
... From adolescence to death, an individual lives with a de ned stock of EFs, which is progressively degraded [11]. Indeed, elastogenesis begins in utero and stops at the end of childhood in mice and humans. ...
Background
The approximately fifteen-year reduction in life expectancy observed in diabetic patients, compared to non-diabetic individuals, is believed to be attributed to the early onset of cardiovascular diseases. Among the molecular actors involved in the occurrence of cardiovascular complications, the remodeling of elastic fibers (EFs) in favor of degradation rather than neosynthesis is significant.
Objective
This study aims to modulate the elastogenesis/elastolysis balance in the arterial wall of diabetic db/db mice (a diabetic model where the leptin receptor is deficient) to limit the premature aging of their EFs and aortic stiffening.
Methods
Mice are treated with two antihypertensive agents: minoxidil (an ATP-sensitive potassium (KATP) channel opener) or nebivolol (a β-blocker also active on KATP channels). The degree of wear and functionality of EF are assessed after these treatments. We complement this analysis by identifying molecular actors from smooth muscle cell cultures.
Results
Our data show that by applying these antihypertensive agents in cultured vascular smooth muscle cells in vitro and in diabetic mice, we efficiently stimulate elastogenesis and inhibit elastolysis. Therefore, treatments restore functional EFs and limit their degradation. This brings blood pressure values of diseased mice close to normal ones (as in unaffected mice). Elastogenesis pathway stimulation and elastolysis inhibition are induced by the opening of sensitive KATP channels and the regulation of the forkhead box transcription factor (FOXO1).
Conclusion
Monitoring these two pathways could, therefore, be sufficient to limit the premature aging of the aorta and to reduce the occurrence of hypertension, atherosclerosis, and aneurysms in diabetic patients.
... Soluble elastin precursors are deposited on microfibers during the assembly of elastic fibers in the aortic wall. They are crosslinked by m-LOX into insoluble mature elastin called elastic fibers [33][34][35]. Therefore, we investigated the effect of S100A4 on LOX expression. ...
... The disruption of ECM homeostasis is one of the most important components of aortic dissection [1,9]. During aorta development, once blood flow occurs, VSMCs begin to produce ECM [33], which not only provides structural support for the main artery under physiological conditions but also affects the pathophysiological process of blood vessels [52]. Importantly, elastic fibers are the largest and most stable structures within ECM. ...
Background: Thoracic aortic dissection (TAD) is one of the cardiovascular diseases with high incidence and fatality rates. Vascular smooth muscle cells (VSMCs) play a vital role in TAD formation. Recent studies have shown that extracellular S100A4 may participate in VSMCs regulation. However, the mechanism(s) underlying this association remains elusive. Consequently, this study investigated the role of S100A4 in VSMCs regulation and TAD formation.
Methods: Hub genes were screened based on the transcriptome data of aortic dissection in the Gene Expression Synthesis database. Three-week-old male S100A4 overexpression (AAV9- S100A4 OE) and S100A4 knockdown (AAV9- S100A4 KD) mice were exposed to β-aminopropionitrile monofumarate through drinking water for 28 days to create the murine TAD model.
Results: S100A4 was observed to be the hub gene in aortic dissection. Furthermore, overexpression of S100A4 was exacerbated, whereas inhibition of S100A4 significantly improved TAD progression. In the TAD model, the S100A4 was observed to aggravate the phenotypic transition of VSMCs. Additionally, lysyl oxidase (LOX) was an important target of S100A4 in TAD. S100A4 interacted with LOX in VSMCs, reduced mature LOX (m-LOX), and decreased elastic fiber deposition, thereby disrupting extracellular matrix homeostasis and promoting TAD development. Elastic fiber deposition in human aortic tissues was negatively correlated with the expression of S100A4, which in turn, was negatively correlated with LOX.
Conclusions: Our data showed that S100A4 modulates TADprogression, induces lysosomal degradation of m-LOX, and reduces the deposition of elastic fibers by interacting with LOX, thus contributing to the disruption of extracellular matrix homeostasis in TAD. These findings suggest that S100A4 may be a new target for the prevention and treatment of TAD.
... Stenosis is a major cause of late-stage graft failure and is due primarily to neointimal hyperplasia at the anastomoses [74]. This is attributed to the compliance mismatch between the graft and native vessel, a lack of luminal endothelialization, altered blood flow, and chronic inflammation, which are associated with SMC activation, including their proliferation and migration and ECM synthesis [75] (Figure I). ...
... The endothelial basement membrane provides structural support, mediates EC signaling, and serves as a reservoir for growth factors and enzymes [80]. ECs are a source of signaling molecules that regulate vascular cell growth and maturation, including SMC quiescence and the formation of new blood vessels [75]. The internal and external elastic laminae separate intima-media (all arteries) and media-adventitia (large arteries only), respectively. ...
... In addition to elastolysis, ECM stiffness may further increase in pathological conditions via extensive collagen expression and deposition or enzymatic or non-enzymatic cross-linking of fibers by lysyl oxidases (LOXs) or advanced glycation end-products (AGEs), respectively 7,8,[10][11][12][13] . As a result of these processes, arterial biomechanical competences progressively deteriorate, accelerating vascular disease. ...
... dysregulation of genes controlling elastic fiber formation (FBN3, MFAP1, MFAP2, MFAP5, and EMILIN2) 47,75,76 and elastolysis (CTSV and TIMP1) 10,13,77 . Microscopic analyses revealed elastic fiber fragmentation and degradation and increased fiber tortuosity, presumably as progressive fragmentation will result in the retraction of residual fiber pieces. ...
Pulmonary hypertension worsens outcome in left heart disease. Stiffening of the pulmonary artery may drive this pathology by increasing right ventricular dysfunction and lung vascular remodeling. Here we show increased stiffness of pulmonary arteries from patients with left heart disease that correlates with impaired pulmonary hemodynamics. Extracellular matrix remodeling in the pulmonary arterial wall, manifested by dysregulated genes implicated in elastin degradation, precedes the onset of pulmonary hypertension. The resulting degradation of elastic fibers is paralleled by an accumulation of fibrillar collagens. Pentagalloyl glucose preserves arterial elastic fibers from elastolysis, reduces inflammation and collagen accumulation, improves pulmonary artery biomechanics, and normalizes right ventricular and pulmonary hemodynamics in a rat model of pulmonary hypertension due to left heart disease. Thus, targeting extracellular matrix remodeling may present a therapeutic approach for pulmonary hypertension due to left heart disease.
... NRI indicates the extent to which a biomarker improves diagnostic accuracy, which in the current analyses was not significant, indicating that the discriminatory performance of PWV on top of commonly measured risk factors, in particular sex, age, various BP indexes (Table S4), and dyslipidemia, is small. A risk calculator is made available as Supplemental Material 2. The SPARTE (Strategy for Preventing Cardiovascular and Renal Events Based on Arterial Stiffness) Investigators 34 and the pathophysiology of aortic stiffness [35][36][37] provide the interpretation of these findings. Aortic stiffness, as captured by PWV, integrates the lifetime injury to the arterial wall. ...
... 35 This process already starts in young adulthood, but the deposition of elastin by vascular smooth muscle cells only occurs during fetal development and in early infancy, and is switchedoff thereafter. 36 This implies that elastin fiber damage is basically irreversible. 37 In the SPARTE trial, 34 hypertensive patients were randomized to a therapeutic strategy targeting the normalization of PWV, measured every 6 months (N=264) or to a therapeutic strategy only implementing the European Hypertension Guidelines 3 (N=272). ...
Background:
Aortic pulse wave velocity (PWV) predicts cardiovascular events (CVEs) and total mortality (TM), but previous studies proposing actionable PWV thresholds have limited generalizability. This individual-participant meta-analysis is aimed at defining, testing calibration, and validating an outcome-driven threshold for PWV, using 2 populations studies, respectively, for derivation IDCARS (International Database of Central Arterial Properties for Risk Stratification) and replication MONICA (Monitoring of Trends and Determinants in Cardiovascular Disease Health Survey - Copenhagen).
Methods:
A risk-carrying PWV threshold for CVE and TM was defined by multivariable Cox regression, using stepwise increasing PWV thresholds and by determining the threshold yielding a 5-year risk equivalent with systolic blood pressure of 140 mm Hg. The predictive performance of the PWV threshold was assessed by computing the integrated discrimination improvement and the net reclassification improvement.
Results:
In well-calibrated models in IDCARS, the risk-carrying PWV thresholds converged at 9 m/s (10 m/s considering the anatomic pulse wave travel distance). With full adjustments applied, the threshold predicted CVE (hazard ratio [CI]: 1.68 [1.15-2.45]) and TM (1.61 [1.01-2.55]) in IDCARS and in MONICA (1.40 [1.09-1.79] and 1.55 [1.23-1.95]). In IDCARS and MONICA, the predictive accuracy of the threshold for both end points was ≈0.75. Integrated discrimination improvement was significant for TM in IDCARS and for both TM and CVE in MONICA, whereas net reclassification improvement was not for any outcome.
Conclusions:
PWV integrates multiple risk factors into a single variable and might replace a large panel of traditional risk factors. Exceeding the outcome-driven PWV threshold should motivate clinicians to stringent management of risk factors, in particular hypertension, which over a person's lifetime causes stiffening of the elastic arteries as waypoint to CVE and death.
... The main building component of the adventitia is collagen, accompanied by other constituents such as elastin fibers and fibroblasts [1,11] . Regardless of this, the passive mechanical behavior of the aortic tissue mainly depends on collagen and elastin [2,12,13] . In particular, collagen and elastin contribute to the nonlinear mechanical behavior of the aortic tissue at high and low stretch [14][15][16][17] . ...
... This inconsistency could originate from different densities of collagen and elastin in the two layers. In contrast to the adventitia, the media has a higher density of elastin than collagen [12] . Consequently, the relatively higher intensity of the elastin signal compared to the collagen signal was observed in the media but not in the adventitia. ...
... The elastic component of the vascular wall is primarily needed in elastic arteries, comprising the aorta and its first ramifications. These high-caliber arteries allow the smoothing of the cardiac pulsatile blood flow into a continuous flow so that all organs are optimally perfused at all times [2,3]. ...
... Eln −/− mice have normal cardiovascular development in utero up to an embryonic day (E) 18, but die just a few days later, between day (P) 0 and P4.5, due to the inward proliferation of medial smooth muscle cells resulting in obliteration of the large vessel lumen [2,57]. On the contrary, mice haploinsufficient for elastin (Eln +/− ) live a normal life span despite significant hypertension. ...
Elastic fibers are extracellular macromolecules that provide resilience and elastic recoil to elastic tissues and organs in vertebrates. They are composed of an elastin core surrounded by a mantle of fibrillin-rich microfibrils and are essentially produced during a relatively short period around birth in mammals. Thus, elastic fibers have to resist many physical, chemical, and enzymatic constraints occurring throughout their lives, and their high stability can be attributed to the elastin protein. Various pathologies, called elastinopathies, are linked to an elastin deficiency, such as non-syndromic supravalvular aortic stenosis (SVAS), Williams-Beuren syndrome (WBS), and autosomal dominant cutis laxa (ADCL). To understand these diseases, as well as the aging process related to elastic fiber degradation, and to test potential therapeutic molecules in order to compensate for elastin impairments, different animal models have been proposed. Considering the many advantages of using zebrafish, we here characterize a zebrafish mutant for the elastin a paralog (elnasa12235) with a specific focus on the cardiovascular system and highlight premature heart valve defects at the adult stage.
... The standard interpretation of the relationship between vascular stiffness and blood pressure is that it increases blood pressure (BP). Pulse pressure (PP) increases pulsatile aortic wall stress, advancing elastic fibre degeneration [4,5]. Importantly, several studies have demonstrated that increased local carotid and aortic stiffness levels in normotensive individuals are associated with an increased risk of incidental higher BP and progressive development of hypertensive BP over time [4,6,7]. ...
Increased aortic and carotid stiffness are independent predictors of adverse cardiovascular events. Arterial stiffness is not uniform across the arterial tree and its accurate assessment is challenging. The complex interactions and influence of aortic stiffness on carotid stiffness have not been investigated. The aim of this study was to evaluate the effect of aortic stiffness on carotid stiffness under physiological pressure conditions. A realistic patient-specific geometry was used based on magnetic resonance images obtained from the OsiriX library. The luminal aortic–carotid model was reconstructed from magnetic resonance images using 3D Slicer. A series of aortic stiffness simulations were performed at different regional aortic areas (levels). By applying variable Young's modulus to the aortic wall under two pulse pressure conditions, one could examine the deformation, compliance and von Mises stress between the aorta and carotid arteries. An increase of Young's modulus in an aortic area resulted in a notable difference in the mechanical properties of the aortic tree. Regional deformation, compliance and von Mises stress changes across the aorta and carotid arteries were noted with an increase of the aortic Young's modulus. Our results indicate that increased carotid stiffness may be associated with increased aortic stiffness. Large-scale clinical validation is warranted to examine the influence of aortic stiffness on carotid stiffness.
... Natural arteries have three distinct layers: the adventitia, the media, and the intima. The adventitia layer has a high percentage of collagen fibers, which increases the strength of the natural blood vessels and inhibits excessive dilation and rupture under physiological pressure [12,13]. The media mainly comprises smooth muscle cells (SMCs), collagen, and elastin and can adapt to the contraction and relaxation of blood vessels under physiological pressures [14]. ...
Synthetic vascular grafts suitable for small-diameter arteries (< 6 mm) are in great need. However, there are still no commercially available small-diameter vascular grafts (SDVGs) in clinical practice due to thrombosis and stenosis after in vivo implantation. When designing SDVGs, many studies emphasized reendothelization but ignored the importance of reconstruction of the smooth muscle layer (SML). To facilitate rapid SML regeneration, a high-resolution 3D printing method was used to create a novel bilayer SDVG with structures and mechanical properties mimicking natural arteries. Bioinspired by the collagen alignment of SML, the inner layer of the grafts had larger pore sizes and high porosity to accelerate the infiltration of cells and their circumferential alignment, which could facilitate SML reconstruction for compliance restoration and spontaneous endothelialization. The outer layer was designed to induce fibroblast recruitment by low porosity and minor pore size and provide SDVG with sufficient mechanical strength. One month after implantation, the arteries regenerated by 3D-printed grafts exhibited better pulsatility than electrospun grafts, with a compliance (8.9%) approaching that of natural arteries (11.36%) and significantly higher than that of electrospun ones (1.9%). The 3D-printed vascular demonstrated a three-layer structure more closely resembling natural arteries while electrospun grafts showed incomplete endothelium and immature SML. Our study shows the importance of SML reconstruction during vascular graft regeneration and provides an effective strategy to reconstruct blood vessels through 3D-printed structures rapidly.
... Alterations in wall structure of blood vessels leading to the elevation in arterial stiffness are accompanied by an increase in CYM. [22][23][24][25] We had previously reported sex-specific changes in CYM in small resistance arteries between male and female hypertensive rats due to high salt consumption following exposure to phenylephrine (vasoconstrictor) and sodium nitroprusside (vasodilator). 9 At baseline, we found no differences in CYM among the experimental groups in our current study, and as we had previously reported. ...
Changes in vascular biomechanics leading to increase in arterial stiffness play a pivotal role in circulatory dysfunction. Our objectives were to examine sex‐specific pharmacological changes related to the biomechanics and any structural modifications in small resistance arteries of Dahl salt‐sensitive male and female rats. The composite Young modulus (CYM) was determined using pressure myograph recordings, and immunohistochemistry was used for the evaluation of any structural changes in the third‐order mesenteric arteries ( n = 6). Animals on high‐salt diet developed hypertension with significant elevation in central and peripheral blood pressures and pulse wave velocity compared to those on regular diet. There were no significant differences observed in the CYM between any of the groups (i.e., males and females) in vehicle‐treated time‐control studies. The presence of verapamil (0.3 μM) significantly reduced CYM in hypertensive males without changes within females compared to vehicle. This effect was abolished by phenylephrine (0.3 μM). BaCl 2 (100 μM), ouabain (100 μM), and L‐NAME (0.3 μM) combined significantly increased CYM in vessels from in normotensive males and females but not in hypertensive males compared to vehicle. The increase in CYM was abolished in the presence of phenylephrine. Sodium nitroprusside (0.3 μM), in the presence of phenylephrine, significantly reduced CYM in male normotensive versus hypertensive, with no differences within females. Significant differences were observed in immunohistochemical assessment of biomechanical markers of arterial stiffness between males and females. Our findings suggest sex possibly due to pressure differences to be responsible for adaptive changes in biomechanics, and varied pharmacological responses in hypertensive state.
... It is well established that mechanical factors such as increased wall stress, caused by high BP; biochemical factors including oxidative stress; and inflammation associated with aging, diabetes, and activation of the renin-angiotensin system contribute to the development of arterial stiffness (5,6). In response to these challenges, blood vessels undergo a collection of structural modifications, for instance, increased deposition and cross-linking of extracellular matrix (ECM) (7,8). Vascular smooth muscle cells (SMCs) also promote arterial stiffness by proliferation, calcification, and increase of cellular stiffness (9,10). ...
... The adventitial layer is comprised of fibroblasts, pericytes, immune cells, nerves and lymphatics (8). Key to normal function is the high level of compliance within the aortic wall (9). Increased stiffness results in wall weakness and elevated cardiac afterload resulting in higher cardiovascular events (10) as well as increasing risk for type A aortic dissection when combined with high wall stress (11). ...
Thoracic aortic disease (TAD) is often silent until a life-threatening complication occurs. However, genetic information can inform both identification and treatment at an early stage. Indeed, a diagnosis is important for personalised surveillance and intervention plans, as well as cascade screening of family members. Currently, only 20% of heritable TAD patients have a causative mutation identified and, consequently, further advances in genetic coverage are required to define the remaining molecular landscape. The rapid expansion of next generation sequencing technologies is providing a huge resource of genetic data, but a critical issue remains in functionally validating these findings. Induced pluripotent stem cells (iPSCs) are patient-derived, reprogrammed cell lines which allow mechanistic insights, complex modelling of genetic disease and a platform to study aortic genetic variants. This review will address the need for iPSCs as a frontline diagnostic tool to evaluate variants identified by genomic discovery studies and explore their evolving role in biological insight through to drug discovery.
... Unlike elastic conduit arteries, whose mechanical properties are largely defined by the composition of the extracellular matrix, muscular arterial stiffness is rather related to smooth muscle cell tone. 24 As such, the effects of antifibrotic interventions (eg, ARNI) may be functionally less effective/relevant in muscular arteries and may therefore not necessarily translate in decreased peripheral vascular resistance and blood pressure. ...
Background
Increasing arterial stiffness is a prominent feature of the aging cardiovascular system. Arterial stiffening leads to fundamental alterations in central hemodynamics with widespread detrimental implications for organ function resulting in significant morbidity and death, and specific therapies to address the underlying age‐related structural arterial remodeling remain elusive. The present study investigates the potential of the recently clinically available dual angiotensin receptor–neprilysin inhibitor (ARNI) sacubitril/valsartan (LCZ696) to counteract age‐related arterial fibrotic remodeling and stiffening in 1‐year‐old mice.
Methods and Results
Treatment of in 1‐year‐old mice with ARNI (sacubitril/valsartan), in contrast to angiotensin receptor blocker monotherapy (valsartan) and vehicle treatment (controls), significantly decreases structural aortic stiffness (as measured by in vivo pulse‐wave velocity and ex vivo aortic pressure myography). This phenomenon appears, at least partly, independent of (indirect) blood pressure effects and may be related to a direct antifibrotic interference with aortic smooth muscle cell collagen production. Furthermore, we find aortic remodeling and destiffening due to ARNI treatment to be associated with improved parameters of cardiac diastolic function in aged mice.
Conclusions
This study provides preclinical mechanistic evidence indicating that ARNI‐based interventions may counteract age‐related arterial stiffening and may therefore be further investigated as a promising strategy to improve cardiovascular outcomes in the elderly.
... The primary function of large arteries lies in their ability to serve as energy reservoirs, storing elastic energy during systole and using that energy to maintain blood circulation during diastole [63,64]. Loss or decrease of this energy is an indicator of vascular dysfunction and has been connected to aortic disease [24,39,65]. ...
Maternal mortality due to cardiovascular disease is a rising concern in the U.S. Pregnancy triggers changes in the circulatory system, potentially influencing the structure of the central vasculature. Evidence suggests a link between a woman's pregnancy history and future cardiovascular health, but our understanding remains limited. To fill this gap, we examined the passive mechanics of the murine ascending thoracic aorta during late gestation. By performing biaxial mechanical testing on the ascending aorta, we were able to characterize the mechanical properties of both control and late-gestation tissues. By examining mechanical, structural, and geometric properties, we confirmed that a remodeling of the aortic wall occurred. Morphological and mechanical properties of the tissue indicated an outward expansion of the tissue, as reflected in changes in wall thickness (~ 12% increase) and luminal diameter (~ 6% increase) at its physiologically loaded state in the pregnant group. With these geometric adaptations and despite increased hemodynamic loads, pregnancy did not induce significant changes in the tensile wall stress at the similar physiological pressure levels of the pregnant and control tissues. The geometric alterations also included reduced intrinsic stiffness in the circumferential direction (~ 18 %) and reduced structural stiffness (~ 26 %) in the pregnant group. The observed vascular remodeling maintained the elastic stored energy of the aortic wall under systolic loads, indicating preservation of vascular function. Data from our study of pregnancy-related vascular remodeling will provide valuable insights for future investigations of maternal cardiovascular health.
... Molecular determinants of large artery stiffness in ageing may thus be ECM proteins governing collagen breakdown and production, such as matrix metalloproteinases (MMPs), tissue inhibitors of MMPs (TIMPs), transforming growth factor-β1 (TGF-β1), and transglutaminases (TGMs). In addition, proteins responsible for elastin or elastic fiber expression, coherence, and functional characteristics, such as fibrillins and fibulins [8,9], may be involved in age-related arterial stiffness. However, increasing attention is given to smooth muscle phenotypic changes related to various stressors, such as mechano-transduction, oxidative stress, genetic and epigenetic factors [10][11][12]. ...
The normal ageing process significantly affects resistance arteries, leading to various biological and physiological consequences. Systolic hypertension is a common occurrence in ageing individuals, accompanied by increased large artery stiffening, heightened pulsatility, small artery remodeling, and damage to critical microvascular structures. Starting from young adulthood, there is a progressive elevation in mean arterial pressure, supported by clinical and epidemiological evidence as well as findings from animal models. The myogenic response, a protective mechanism for the microcirculation, may face disruptions during ageing. Dysregulation of calcium entry channels (T-type, L-type, TRP channels), dysfunction in intracellular calcium storage and extrusion mechanisms, altered expression of potassium channels, and a change in smooth muscle calcium sensitization may contribute to age-related dysregulation of myogenic tone. Flow-mediated vasodilatation, a hallmark of endothelial function, is compromised in ageing. This result of endothelial dysfunction is related to oxidative stress, lower nitric oxide bioavailability and a low-grade inflammatory response, further exacerbating vascular dysfunction. Resistance artery remodeling in ageing emerges as a hypertrophic response of the vessel wall, often seen in conjunction with outward remodeling (in normotension), but can also present as inward hypertrophic remodeling (in hypertension). The remodeling process involves oxidative stress, inflammation, reorganization of extracellular matrix fiber proteins and actin cytoskeletal components. Reactive oxygen species (ROS) signaling and chronic low-grade inflammation, often referred to as "inflammaging”, play substantial roles in age-related vascular dysfunction. Due to its role in regulation of vascular tone as well as structural proteins, the RhoA/Rho-kinase pathway becomes a new target in age-related vascular dysfunction and associated diseases. Understanding the intricate interplay of these factors is crucial for developing targeted interventions to mitigate the consequences of ageing on resistance arteries and enhance overall vascular health.
... Although the use of DCB in patients with small vessel disease has been extensively investigated, evidence for the optimal method of revascularization for large coronary lesions remains inadequate. It has been suggested previously that large coronary arteries have more smooth muscle fibers than small vessel arteries and are more prone to recoil and dissection, which may lead to acute occlusion or restenosis of blood vessels [24]. In a retrospective study, although optimal lesion preparation for the use of DCB has been taken, 10% of patients remain need to be bailout stenting due to recoil and dissection [11]. ...
Purpose
Although a number of studies involving small-vessel de novo coronary disease showed clinical benefits of drug-coated balloons (DCB), the role of DCB in large vessel lesions is still unclear.
Methods
We searched main electronic databases for randomized controlled trials (RCTs) comparing DCB with stents for large vessel de novo coronary artery disease. The primary endpoint was major cardiovascular adverse events (MACE), composite cardiovascular death (CD), myocardial infarction (MI), or target lesion revascularization (TLR).
Results
This study included 7 RCTs with 770 participants. DCB were associated with a marked risk reduction in MACE [Risk Ratio (RR): 0.48; 95% confidence interval [CI]: 0.24 to 0.97; P = 0.04], TLR (RR: 0.53; 95% CI: 0.25 to 1.14; P = 0.10), and late lumen loss [standard mean difference (SMD): -0.57; 95% CI: -1.09 to -0.05; P = 0.03] as compared with stents. There is no significant difference in MI (RR: 0.58; 95% CI: 0.21 to 1.54; P = 0.27), CD (RR: 0.33; 95% CI: 0.06 to 1.78; P = 0.19), and minimal lumen diameter (SMD: -0.34; 95% CI: -0.72 to 0.05; P = 0.08) between groups. In subgroup analyses, the risk reduction of MACE persisted in patients with chronic coronary syndrome (RR: 0.25; 95% CI: 0.07 to 0.89; P = 0.03), and patients receiving DCB vs. bare metal stent (RR: 0.19; 95% CI: 0.05 to 0.73; P = 0.01). In addition, there was no significant difference between the DCB group and the drug eluting stent group for MACE (RR: 0.69; 95% CI: 0.30 to 1.60; P = 0.38).
Conclusion
DCB may be an effective therapeutic option in patients with large vessel de novo coronary artery disease.
... Notably, endothelial stiffening is distinct from arterial stiffening, or stiffening of the vascular wall, a known predictor of cardiovascular disease. Arterial stiffening is a result primarily of the remodeling of the extracellular matrix 39 and is typically observed after a prolonged WD 40,41 or during ageing 42 . Earlier studies suggested that the pathological effect of arterial stiffening is at least in part due to its effect on the endothelium. ...
Background
To determine the impact of endothelial stiffening induced by CD36-mediated lipid uptake in the disruption of aortic endothelial barrier and development of atherosclerosis in mouse models of obesity and hypercholesterolemia.
Approach and Results
Endothelial-specific inducible downregulation of CD36 results in abrogating the stiffening of aortic endothelium induced by a short-term (6-8 weeks) high-fat Western diet in intact freshly isolated mouse aortas of Cdh5.CreER T2 CD36 fl/fl mice, as assessed by atomic force microscopy. No effect was observed on the stiffness of aortic vascular wall assessed in the same groups of mice by echocardiography. Prevention of WD-induced endothelial stiffening by the downregulation of endothelial CD36 was associated with a protective effect against endothelial barrier disruption, assessed by morphological analysis of VE-cadherin junctions and penetration of Evans blue dye into the aortic wall. These protective effects were independent of the changes in the serum lipid profiles. Furthermore, endothelial specific downregulation of CD36 in hypercholesterolemic Cdh5.CreER T2 CD36 fl/fl LDLR -/- mice also led to significant decrease in endothelial stiffening after 4-5 months of high fat diet and a significant decrease in the areas of atherosclerotic lesion. In both models, significant endothelial stiffening was observed specifically in male mice, while female mice exhibited less endothelial stiffening and less severe atherosclerosic phenotype, consistent with endothelial stiffening playing an important role in aortic vascular disease in a sex-dependent way. Mechanistically, we show in vitro that CD36-mdiated uptake of long chain saturated fatty acids, particularly palmitic acid, induces endothelial stiffening via activation of RhoA/ROCK pathway. Moreover, palmitic acid-induced endothelial stiffening critically depends on the expression of a RhoA inhibitory protein, Rho-GDI-1.
Conclusions
We conclude that stiffening of the aortic endothelium by CD36-mediated uptake of fatty acids contributes significantly to WD-induced vascular dysfunction and atherosclerosis. We further propose that fatty acids may activate RhoA by inducing its dissociation from Rho-GDI-1.
... Fibrillin-1 is a component of the extracellular matrix (ECM) and encloses elastin, which is a main component of elastic arteries [8]. Additional components critically impacting the integrity of the vasculature, i.e., the basement membrane, are the family of collagens [9]. ...
... Fibrillin-1 is a component of the extracellular matrix (ECM) and encloses elastin, which is a main component of elastic arteries [8]. Additional components critically impacting the integrity of the vasculature, i.e., the basement membrane, are the family of collagens [9]. ...
An impaired integrity of vascular elements and the extracellular matrix (ECM) has been discussed to play a critical role in the pathophysiology of spontaneous cervical artery dissection (sCAD). This study aimed to explore the temporal course of circulating elastin, collagen type I, and collagen type III in patients with sCAD and evaluated their eligibility as diagnostic biomarkers. Patients with sCAD were prospectively enrolled in four German stroke centers. Blood samples were collected at baseline (acute phase), at day 10 ± 3 (subacute phase), and after 6 ± 1 months (chronic phase). Patients with acute ischemic stroke not related to sCAD, healthy probands, and patients undergoing thromboendarterectomy of the carotid artery served as control groups. Serum levels of elastin and collagen types I and III were determined by ELISAs. Fifty-seven patients with sCAD were enrolled. Compared to all three control groups, patients with sCAD had significantly lower levels of elastin and collagen type III at baseline and after 6 months. Compared to healthy probands, patients with sCAD showed similar collagen type I levels at baseline and in the subacute phase, but significantly increased levels after 6 months. As serum levels of elas-tin, collagen types I and III were not elevated in the acute phase, they do not appear eligible as biomarkers for the diagnosis of sCAD. Persisting low serum levels of elastin and collagen type III towards the chronic phase of sCAD strengthens the hypothesis of a subtle, in most cases clinically inapparent affection of the ECM in patients with sCAD.
... As a degradation product, oligosaccha rides can efficiently regulate the pathological microenvironment and therapeutically alleviate inflammatory responses (23), oxidative stress (24), and hypertension (25) in the treatment of ischemic diseases. Apart from that, oligosaccharides also play pivotal roles in maintaining the arterial wall integrity and regulating cellular behavior within it (26,27). However, the mechanisms by which oligosaccharides interact with host cells and modulate endogenous growth factors to induce in situ arteriogenesis remain largely elusive. ...
Ischemic diseases lead to considerable morbidity and mortality, yet conventional clinical treatment strategies for therapeutic angiogenesis fall short of being impactful. Despite the potential of biomaterials to deliver pro-angiogenic molecules at the infarct site to induce angiogenesis, their efficacy has been impeded by aberrant vascular activation and off-target circulation. Here, we present a semisynthetic low-molecular sulfated chitosan oligosaccharide (SCOS) that efficiently induces therapeutic arteriogenesis with a spontaneous generation of collateral circulation and blood reperfusion in rodent models of hind limb ischemia and myocardial infarction. SCOS elicits anti-inflammatory macrophages’ (Mφs’) differentiation into perivascular Mφs, which in turn directs artery formation via a cell-to-cell communication rather than secretory factor regulation. SCOS-mediated arteriogenesis requires a canonical Notch signaling pathway in Mφs via the glycosylation of protein O-glucosyltransferases 2, which results in promoting arterial differentiation and tissue repair in ischemia. Thus, this highly bioactive oligosaccharide can be harnessed to direct efficiently therapeutic arteriogenesis and perfusion for the treatment of ischemic diseases.
... The aorta should not be considered only a passive conduit for the bloodstream, 29,30 but also as an elastic reservoir, enabling the arterial tree to undergo large volume changes with little pressure changes. 31 The viscoelasticity of the aorta is a critical yet overlooked physical property that should be considered when designing new biomaterials for aortic treatments. ...
Highlights
•Two-faced polycaprolactone patches were electrospun. The luminal face consisted of aligned fibers designed to align with blood flow, to promote endothelial cell migration and to stop underlying smooth muscle cell colonization. The abluminal face of the patch was comprised of random fibers with high porosity, aimed at promoting smooth muscle cell colonization and macrophage clustering. This structure guarantees full integration within the native vascular tissue, promoting differential colonization by endothelial and smooth muscle cells.
•The aorta has viscoelastic properties, and these are not met by any available grafts or stents nowadays. Mimicking the aorta’s mechanical properties is critical to avoid mechanical mismatches and consequent device failure. Our mechanical testing indicates that the patch design is able to mimic those properties, and echocardiographic measurements validate that indeed we are in the range of natural tissue properties, because the patch is fully compliant with the natural motion of the aorta.
•Patch and adhesive biocompatibility was assessed in vivo and ex vivo. The patch-adhesive system failed to cause any thrombogenicity in standardized tests. Cytotoxicity was very low in vitro, and animal studies showed minimal to no inflammation and thrombogenicity up to 90 days in large animals. Together, these results show that neither the patch nor the adhesive compromise cell viability.
... Features of CAD include plaque buildup within the arterial wall, disappearance of the intima layer, and increasing inflammation corresponding to disease progression 14,15 . In aneurysms, the vessel wall becomes dysfunctional due to the loss of vascular SMC and destruction of matrix elastic fibers 16,17 . ...
In this study, organ‐on‐chip technology is used to develop an in vitro model of medium‐to‐large size arteries, the artery‐on‐a‐chip ( AoC ), with the objective to recapitulate the structure of the arterial wall and the relevant hemodynamic forces affecting luminal cells. AoCs exposed either to in vivo‐like shear stress values or kept in static conditions are assessed to generate a panel of novel genes modulated by shear stress. Considering the crucial role played by shear stress alterations in carotid arteries affected by atherosclerosis (CAD) and abdominal aortic aneurysms (AAA) disease development/progression, a patient cohort of hemodynamically relevant specimens was utilized, consisting of diseased and non‐diseased (internal control) vessel regions from the same patient. Genes activated by shear stress followed the same expression pattern in non‐diseased segments of human vessels. Single cell RNA sequencing enables us to discriminate the unique cell subpopulations between non‐diseased and diseased vessel portions, revealing an enrichment of flow activated genes in structural cells originating from non‐diseased specimens. Furthermore, the AoC served as a platform for drug‐testing. It reproduced the effects of a therapeutic agent (lenvatinib) previously used in preclinical AAA studies, therefore extending our understanding of its therapeutic effect through a multicellular structure.
This article is protected by copyright. All rights reserved
... ECM is the main determinant of the mechanical properties of the arterial wall (4,29). A change in stiffness thus points toward altered ECM. ...
It is widely believed that tissue mechanical properties, determined mainly by the extracellular matrix (ECM), are actively maintained. However, despite its broad importance to biology and medicine, tissue mechanical homeostasis is poorly understood. To explore this hypothesis, we developed mutations in the mechanosensitive protein talin1 that alter cellular sensing of ECM stiffness. Mutation of a novel mechanosensitive site between talin1 rod domain helix bundles 1 and 2 (R1 and R2) shifted cellular stiffness sensing curves, enabling cells to spread and exert tension on compliant substrates. Opening of the R1-R2 interface promotes binding of the ARP2/3 complex subunit ARPC5L, which mediates the altered stiffness sensing. Ascending aortas from mice bearing these mutations show increased compliance, less fibrillar collagen, and rupture at lower pressure. Together, these results demonstrate that cellular stiffness sensing regulates ECM mechanical properties. These data thus directly support the mechanical homeostasis hypothesis and identify a novel mechanosensitive interaction within talin that contributes to this mechanism.
... Vascular extracellular matrix (ECM) contains an array of structural matrix proteins. These include elastin, fibrillar collagens as well as adhesive glycoproteins such as, fibronectin, and basement membrane components including Type IV collagen and laminins that are synthesized by vascular smooth muscle cells (VSMC), fibroblasts and endothelial cells (Hallmann et al., 2005;Wagenseil and Mecham, 2009) Collectively these macromolecules are vital for tissue mechanical integrity and are importantly linked to cell movement and cell-matrix adhesive interactions (Kelleher et al., 2004;Hynes and Naba, 2012) and together contribute to the overall mechanical function of large elastic vessels, such as aorta (Wagenseil, 2011), and small muscular arteries. Of these ECM proteins, changes in elastin, in particular, have been shown to play an important role in aging and vascular disease (Duca et al., 2016;Le Page et al., 2019;Yanagisawa and Wagenseil, 2020;Adeva-Andany et al., 2021). ...
Introduction: Vascular extracellular matrix (ECM) is dominated by elastic fibers (elastin with fibrillin-rich microfibrils) and collagens. Current understanding of ECM protein development largely comes from studies of conduit vessels (e.g., aorta) while resistance vessel data are sparse. With an emphasis on elastin, we examined whether changes in postnatal expression of arteriolar wall ECM would correlate with development of local vasoregulatory mechanisms such as the myogenic response and endothelium-dependent dilation.
Methods: Rat cerebral and mesenteric arteries were isolated at ages 3, 7, 11, 14, 19 days, 2 months, and 2 years. Using qPCR mRNA expression patterns were examined for elastin, collagen types I, II, III, IV, fibrillin-1, and -2, lysyl oxidase (LOX), and transglutaminase 2.
Results: Elastin, LOX and fibrillar collagens I and III mRNA peaked at day 11–14 in both vasculatures before declining at later time-points. 3D confocal imaging for elastin showed continuous remodeling in the adventitia and the internal elastic lamina for both cerebral and mesenteric vessels. Myogenic responsiveness in cannulated cerebral arteries was detectable at day 3 with constriction shifted to higher intraluminal pressures by day 19. Myogenic responsiveness of mesenteric vessels appeared fully developed by day 3. Functional studies were performed to investigate developmental changes in endothelial-dependent dilation. Endothelial-dependent dilation to acetylcholine was less at day 3 compared to day 19 and at day 3 lacked an endothelial-derived hyperpolarizing factor component that was evident at day 19.
Conclusion: Collectively, in the rat small artery structural remodeling and aspects of functional control continue to develop in the immediate postnatal period.
... Challenging the aorta with a single risk factor such as Ang II infusion, hypertension, or hypercholesterolemia alone can elicit phenotypic changes of VSMCs but is not insufficient to induce AAs [105][106][107][108][109][110]. Extreme agents such as calcium chloride and elastase, which directly destroy the aortic wall, do induce AAs [167][168][169]. However, such "one-hit" models failed to reproduce the progression of human AAs, indicating that a stable adaptive state can be established [118,165]. ...
Vascular smooth muscle cells (VSMCs) are the predominant cell type in the medial layer of the aorta, which plays a critical role in the maintenance of aortic wall integrity. VSMCs have been suggested to have contractile and synthetic phenotypes and undergo phenotypic switching to contribute to the deteriorating aortic wall structure. Recently, the unprecedented heterogeneity and diversity of VSMCs and their complex relationship to aortic aneurysms (AAs) have been revealed by high-resolution research methods, such as lineage tracing and single-cell RNA sequencing. The aortic wall consists of VSMCs from different embryonic origins that respond unevenly to genetic defects that directly or indirectly regulate VSMC contractile phenotype. This difference predisposes to hereditary AAs in the aortic root and ascending aorta. Several VSMC phenotypes with different functions, for example, secreting VSMCs, proliferative VSMCs, mesenchymal stem cell-like VSMCs, immune-related VSMCs, proinflammatory VSMCs, senescent VSMCs, and stressed VSMCs are identified in non-hereditary AAs. The transformation of VSMCs into different phenotypes is an adaptive response to deleterious stimuli but can also trigger pathological remodeling that exacerbates the pathogenesis and development of AAs. This review is intended to contribute to the understanding of VSMC diversity in health and aneurysmal diseases. Papers that give an update on VSMC phenotype diversity in health and aneurysmal disease are summarized and recent insights on the role of VSMCs in AAs are discussed.
... Hence, the normally slow turnover rate of elastin, less than 1% per year (Wagenseil & Mecham, 2009), is typically negligible. By contrast, fibrillar collagens endow the arterial wall with stiffness and strength. ...
The production, removal, and remodeling of fibrillar collagen is fundamental to mechanical homeostasis in arteries, including dynamic morphological and microstructural changes that occur in response to sustained changes in blood flow and pressure under physiological conditions. These dynamic processes involve complex, coupled biological, chemical, and mechanical mechanisms that are not completely understood. Nevertheless, recent simulations using constrained mixture models with phenomenologically motivated constitutive relations have proven able to predict salient features of the progression of certain vascular adaptations as well as disease processes. Collagen turnover is modeled, in part, via stress-dependent changes in collagen half-life, typically within the range of 10–70 days. By contrast, in this work we introduce a biochemomechanical approach to model the cellular synthesis of procollagen as well as its transition from an intermediate state of assembled microfibrils to mature cross-linked fibers, with mechano-regulated removal. The resulting model can simulate temporal changes in geometry, composition, and stress during early vascular adaptation (weeks to months) for modest changes in blood flow or pressure. It is shown that these simulations capture salient features from data presented in the literature from different animal models.
... becomes stiffer, it loses its ability to distend elastically, compromising its capacity to store and release energy. As a result, the continuous perfusion of blood flow is disrupted, leading to other cardiovascular complications (Wagenseil and Mecham, 2009;Cocciolone et al., 2018). Therefore, accurately quantifying aortic wall stiffness is an essential step in bridging our knowledge gap with regards to vascular remodeling in normal and hypertensive pregnancies. ...
With the rise in maternal mortality rates and the growing body of epidemiological evidence linking pregnancy history to maternal cardiovascular health, it is essential to comprehend the vascular remodeling that occurs during gestation. The maternal body undergoes significant hemodynamic alterations which are believed to induce structural remodeling of the cardiovascular system. Yet, the effects of pregnancy on vascular structure and function have not been fully elucidated. Such a knowledge gap has limited our understanding of the etiology of pregnancy-induced cardiovascular disease. Towards bridging this gap, we measured the biaxial mechanical response of the murine descending thoracic aorta during a normotensive late-gestation pregnancy. Non-invasive hemodynamic measurements confirmed a 50% increase in cardiac output in the pregnant group, with no changes in peripheral blood pressure. Pregnancy was associated with significant wall thickening ( ∼14%), an increase in luminal diameter ( ∼6%), and material softening in both circumferential and axial directions. This expansive remodeling of the tissue resulted in a reduction in tensile wall stress and intrinsic tissue stiffness. Collectively, our data indicate that an increase in the geometry of the vessel may occur to accommodate for the increase in cardiac output and blood flow that occurs in pregnancy. Similarly, wall thickening accompanied by increased luminal diameter, without a change in blood pressure may be a necessary mechanism to decrease the tensile wall stress, and avoid pathophysiological events following late gestation.
... For example, direct contact between ECs and VSMCs via junctional molecules such as N-cadherin, connexin 43, intercellular adhesion molecule 1, and vascular cell adhesion molecule 1 contribute to vessel identity and vasculature formation [11][12][13]. In addition, various secreted ECM components from ECs and VSMCs can alter each other's functions and disrupt their interactions [14,15]. Extracellular vesicles, microRNAs, and cytokines secreted from both cell types are also known to regulate EC-VSMC interactions, leading to the induction of atherogenesis [16][17][18][19]. ...
Abnormal communication between endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) promotes vascular diseases, including atherogenesis. ETS variant transcription factor 2 (ETV2) plays a substantial role in pathological angiogenesis and the reprogramming of ECs; however, the role of ETV2 in the communication between ECs and VSMCs has not been revealed. To investigate the interactive role of ETV2 in the EC to VSMC phenotype, we first showed that treatment with a conditioned medium from ETV2-overexpressed ECs (Ad-ETV2 CM) significantly increased VSMC migration. The cytokine array showed altered levels of several cytokines in Ad-ETV2 CM compared with those in normal CM. We found that C-X-C motif chemokine 5 (CXCL5) promoted VSMC migration using the Boyden chamber and wound healing assays. In addition, an inhibitor of C-X-C motif chemokine receptor 2 (CXCR2) (the receptor for CXCL5) significantly inhibited this process. Gelatin zymography showed that the activities of matrix metalloproteinase (MMP)-2 and MMP-9 increased in the media of VSMCs treated with Ad-ETV2 CM. Western blotting revealed a positive correlation between Akt/p38/c-Jun phosphorylation and CXCL5 concentration. The inhibition of Akt and p38-c-Jun effectively blocked CXCL5-induced VSMC migration. In conclusion, CXCL5 from ECs induced by ETV2 promotes VSMC migration via MMP upregulation and the activation of Akt and p38/c-Jun.
Understanding the growth-induced deformation of soft materials in viscous environments is important for a variety of problems in nature and engineering. Here, we focus on the fluid–structure interaction of a hyperelastic sheet growing in an incompressible Newtonian fluid in the Stokes flow regime. We develop a computational framework for simulating this problem, where the isogeometric boundary integral method is used with the Kirchhoff–Love shell formulation and elastic–plastic decomposition of the deformation gradient tensor. We quantify the relative effects of the growth rate, the sheet bending rigidity, and the fluid viscosity on the fold formation and development of the growing sheet. Our results suggest that the viscous resistance to in-plane deformation promotes fold formation, whereas the viscous resistance to out-of-plane deformation suppresses fold development. We also investigate the effects of the thickness and aspect ratio of the rectangular sheet. Finally, we compare the growth- and prestrain-induced deformations to find a common behavior of sheets under viscous environments.
Heart disease is a pressing public health problem and the leading cause of death worldwide. The heart is the first organ to gain function during embryogenesis in mammals. Heart development involves cell determination, expansion, migration, and crosstalk, which are orchestrated by numerous signaling pathways, such as the Wnt, TGF-β, IGF, and Retinoic acid signaling pathways. Human-induced pluripotent stem cell-based platforms are emerging as promising approaches for modeling heart disease in vitro. Understanding the signaling pathways that are essential for cardiac development has shed light on the molecular mechanisms of congenital heart defects and postnatal heart diseases, significantly advancing stem cell-based platforms to model heart diseases. This review summarizes signaling pathways that are crucial for heart development and discusses how these findings improve the strategies for modeling human heart disease in vitro.
An essential aspect of cardiovascular in situ tissue engineering (TE) is to ensure balance between scaffold degradation and neo-tissue formation. We evaluated the rate of degradation and neo-tissue formation of three electrospun supramolecular bisurea-based biodegradable scaffolds that differ in their soft-block backbone compositions only. Scaffolds were implanted as interposition grafts in the abdominal aorta in rats, and evaluated at different time points (t = 1, 6, 12, 24, and 40 weeks) on function, tissue formation, strength, and scaffold degradation. The fully carbonate-based biomaterial showed minor degradation after 40 weeks in vivo, whereas the other two ester-containing biomaterials showed (near) complete degradation within 6-12 weeks. Local dilatation was only observed in these faster degrading scaffolds. All materials showed to some extent mineralization, at early as well as late time points. Histological evaluation showed equal and non-native-like neo-tissue formation after total degradation. The fully carbonate-based scaffolds lagged in neo-tissue formation, presumably as its degradation was (far from) complete at 40 weeks. A significant difference in vessel wall contrast enhancement was observed by magnetic resonance imaging between grafts with total compared with minimal-degraded scaffolds.
The normal ageing process affects resistance arteries, leading to various functional and structural changes. Systolic hypertension is a common occurrence in human ageing, and it is associated with large artery stiffening, heightened pulsatility, small artery remodeling, and damage to critical microvascular structures. Starting from young adulthood, a progressive elevation in the mean arterial pressure is evidenced by clinical and epidemiological data as well as findings from animal models. The myogenic response, a protective mechanism for the microcirculation, may face disruptions during ageing. The dysregulation of calcium entry channels (L-type, T-type, and TRP channels), dysfunction in intracellular calcium storage and extrusion mechanisms, altered expression of potassium channels, and a change in smooth muscle calcium sensitization may contribute to the age-related dysregulation of myogenic tone. Flow-mediated vasodilation, a hallmark of endothelial function, is compromised in ageing. This endothelial dysfunction is related to increased oxidative stress, lower nitric oxide bioavailability, and a low-grade inflammatory response, further exacerbating vascular dysfunction. Resistance artery remodeling in ageing emerges as a hypertrophic response of the vessel wall that is typically observed in conjunction with outward remodeling (in normotension), or as inward hypertrophic remodeling (in hypertension). The remodeling process involves oxidative stress, inflammation, reorganization of actin cytoskeletal components, and extracellular matrix fiber proteins. Reactive oxygen species (ROS) signaling and chronic low-grade inflammation play substantial roles in age-related vascular dysfunction. Due to its role in the regulation of vascular tone and structural proteins, the RhoA/Rho-kinase pathway is an important target in age-related vascular dysfunction and diseases. Understanding the intricate interplay of these factors is crucial for developing targeted interventions to mitigate the consequences of ageing on resistance arteries and enhance the overall vascular health.
Aortic diseases such as atherosclerosis, aortic aneurysms, and aortic stiffening are significant complications that can have significant impact on end-stage cardiovascular disease. With limited pharmacological therapeutic strategies that target the structural changes in the aorta, surgical intervention remains the only option for some patients with these diseases. Although there have been significant contributions to our understanding of the cellular architecture of the diseased aorta, particularly in the context of atherosclerosis, furthering our insight into the cellular drivers of disease is required. The major cell types of the aorta are well defined; however, the advent of single-cell RNA sequencing provides unrivaled insights into the cellular heterogeneity of each aortic cell type and the inferred biological processes associated with each cell in health and disease. This review discusses previous concepts that have now been enhanced with recent advances made by single-cell RNA sequencing with a focus on aortic cellular heterogeneity.
Cell encapsulation within three‐dimensional hydrogels is a promising approach to mimic tissues. However, true biomimicry of the intricate microenvironment, biophysical and biochemical gradients, and the macroscale hierarchical spatial organisations of native tissues is an unmet challenge within tissue engineering. This review provides an overview of the macromolecular chemistries that have been applied towards the design of cell‐friendly hydrogels, as well as their application towards controlling biophysical and biochemical bulk and gradient properties of the microenvironment. Furthermore, biofabrication technologies provide the opportunity to simultaneously replicate macroscale features of native tissues. Biofabrication strategies are reviewed in detail with a particular focus on the compatibility of these strategies with the current macromolecular toolkit described for hydrogel design and the challenges associated with their clinical translation. This review identifies that the convergence of the ever‐expanding macromolecular toolkit and technological advancements within the field of biofabrication, along with an improved biological understanding, represents a promising strategy towards the successful tissue regeneration.
This article is protected by copyright. All rights reserved
Vascular ageing, characterized by structural and functional changes in blood vessels of which arterial stiffness and endothelial dysfunction are key components, is associated with increased risk of cardiovascular and other age-related diseases. As the global population continues to age, understanding the underlying mechanisms and developing effective therapeutic interventions to mitigate vascular ageing becomes crucial for improving cardiovascular health outcomes. Therefore, this review provides an overview of the current knowledge on pharmacological modulation of vascular ageing, highlighting key strategies and promising therapeutic targets. Several molecular pathways have been identified as central players in vascular ageing, including oxidative stress and inflammation, the renin-angiotensin-aldosterone system, cellular senescence, macroautophagy, extracellular matrix remodelling, calcification, and gasotransmitter-related signalling. Pharmacological and dietary interventions targeting these pathways have shown potential in ameliorating age-related vascular changes. Nevertheless, the development and application of drugs targeting vascular ageing is complicated by various inherent challenges and limitations, such as certain preclinical methodological considerations, interactions with exercise training and sex/gender-related differences, which should be taken into account. Overall, pharmacological modulation of endothelial dysfunction and arterial stiffness as hallmarks of vascular ageing, holds great promise for improving cardiovascular health in the ageing population. Nonetheless, further research is needed to fully elucidate the underlying mechanisms and optimize the efficacy and safety of these interventions for clinical translation.
BACKGROUND
The regional heterogeneity of vascular components and transcriptomes is an important determinant of aortic biology. This notion has been explored in multiple mouse studies. In the present study, we examined the regional heterogeneity of aortas in nonhuman primates.
METHODS
Aortic samples were harvested from the ascending, descending, suprarenal, and infrarenal regions of young control monkeys and adult monkeys provided with high fructose for 3 years. The regional heterogeneity of aortic structure and transcriptomes was examined by histological and bulk RNA sequencing analyses.
RESULTS
Immunostaining of CD31 and αSMA (alpha-smooth muscle actin) revealed that endothelial and smooth muscle cells were distributed homogeneously across the aortic regions. In contrast, elastic fibers were less abundant and dispersed in the infrarenal aorta compared with other regions and associated with collagen deposition. Bulk RNA sequencing identified a distinct transcriptome related to the Notch signaling pathway in the infrarenal aorta with significantly increased NOTCH3 mRNA compared with other regions. Immunostaining revealed that NOTCH3 protein was increased in the media of the infrarenal aorta. The abundance of medial NOTCH3 was positively correlated with the dispersion of elastic fibers. Adult cynomolgus monkeys provided with high fructose displayed vascular wall remodeling, such as smooth muscle cell loss and elastic fiber disruption, predominantly in the infrarenal region. The correlation between NOTCH3 and elastic fiber dispersion was enhanced in these monkeys.
CONCLUSIONS
Aortas of young cynomolgus monkeys display regional heterogeneity of their transcriptome and the structure of elastin and collagens. Elastic fibers in the infrarenal aorta are dispersed along with upregulation of medial NOTCH3.
Recent advances recognize that the viscoelastic properties of epithelial structures play important roles in biology and disease modeling. However, accessing the viscoelastic properties of multicellular structures in mechanistic or drug-screening applications has challenges in repeatability, accuracy, and practical implementation. Here, we present a microfluidic platform that leverages elastohydrodynamic phenomena, sensed by strain sensors made from graphene decorated with palladium nanoislands, to measure the viscoelasticity of cellular monolayers in situ, without using chemical labels or specialized equipment. We demonstrate platform utility with two systems: cell dissociation following trypsinization, where viscoelastic properties change over minutes, and epithelial-to-mesenchymal transition, where changes occur over days. These cellular events could only be resolved with our platform's higher resolution: viscoelastic relaxation time constants of λ = 14.5 ± 0.4 s-1 for intact epithelial monolayers, compared to λ = 13.4 ± 15.0 s-1 in other platforms, which represents a 30-fold improvement. By rapidly assessing combined contributions from cell stiffness and intercellular interactions, we anticipate that the platform will hasten the translation of new mechanical biomarkers.
Biological tissues are fed by arterial networks whose task is to set blood flow delivery in accordance with energetic demand. Coordinating vasomotor activity among hundreds of neighboring segments is an essential process, one dependent upon electrical information spreading among smooth muscle and endothelial cells. The "Conducted Vasomotor Response" is a functional expression of electrical spread and it's this process that lies at the heart of this critical review. Written in a narrative format, this review will first highlight historical manuscripts and then characterize the conducted response across a range of preparations. Trends will be highlighted and used to guide subsequent sections, focused on cellular foundations, biophysical underpinnings, and regulation in health and disease. Key information has been tabulated in table format; illustrative figures reinforce grounding concepts and reveal a framework within which theoretical and experimental work can be rationalized. This summative review highlights that despite thirty years of concerted experimentation, key aspects of the conducted response remain ill-defined. Of note is the need to rationalize the regulation and deterioration of conduction in pathobiological settings. New quantitative tools, along with transgenic technology, will be discussed as a means of propelling this investigative field forward.
Because of structural and cellular differences (ie, degrees of matrix abundance and cross-linking, mural cell density, and adventitia), large and medium-sized vessels, in comparison to capillaries, react in a unique manner to stimuli that induce vascular disease. A stereotypical vascular injury response is ECM (extracellular matrix) remodeling that occurs particularly in larger vessels in response to injurious stimuli, such as elevated angiotensin II, hyperlipidemia, hyperglycemia, genetic deficiencies, inflammatory cell infiltration, or exposure to proinflammatory mediators. Even with substantial and prolonged vascular damage, large- and medium-sized arteries, persist, but become modified by (1) changes in vascular wall cellularity; (2) modifications in the differentiation status of endothelial cells, vascular smooth muscle cells, or adventitial stem cells (each can become activated); (3) infiltration of the vascular wall by various leukocyte types; (4) increased exposure to critical growth factors and proinflammatory mediators; and (5) marked changes in the vascular ECM, that remodels from a homeostatic, prodifferentiation ECM environment to matrices that instead promote tissue reparative responses. This latter ECM presents previously hidden matricryptic sites that bind integrins to signal vascular cells and infiltrating leukocytes (in coordination with other mediators) to proliferate, invade, secrete ECM-degrading proteinases, and deposit injury-induced matrices (predisposing to vessel wall fibrosis). In contrast, in response to similar stimuli, capillaries can undergo regression responses (rarefaction). In summary, we have described the molecular events controlling ECM remodeling in major vascular diseases as well as the differential responses of arteries versus capillaries to key mediators inducing vascular injury.
The vasa vasorum (vessels of vessels) are a dynamic microvascular system uniquely distributed to maintain physiological homeostasis of the artery wall by supplying nutrients and oxygen to the outer layers of the artery wall, adventitia, and perivascular adipose tissue (PVAT), and in large arteries, to the outer portion of the medial layer. Vasa vasorum endothelium and contractile mural cells regulate direct access of bioactive cells and factors present both in the systemic circulation and in the arterial PVAT and adventitia to the artery wall. Experimental and human data show that proatherogenic factors and cells gain direct access to the artery wall via the vasa vasorum and may initiate, promote, and destabilize the plaque. Activation and growth of vasa vasorum occurs in all blood vessel layers primarily by angiogenesis, producing fragile and permeable new microvessels that may cause plaque hemorrhage and fibrous cap rupture. Ironically, invasive therapies such as angioplasty and coronary artery bypass grafting injure the vasa vasorum leading to treatment failures. The vasa vasorum function as a master integrator of both arterial homeostasis and once perturbed or injured, as a promotor of atherogenesis. Future studies need to be directed at establishing reliable in vivo and in vitro models to investigate the cellular and molecular regulation of the function and dysfunction of the arterial vasa vasorum.
The fine distribution of the extracellular matrix glycoprotein emilin (previously known as glycoprotein gp115) (Bressan, G. M., I. Castellani, A. Colombatti, and D. Volpin. 1983. J. Biol. Chem. 258: 13262-13267) has been studied at the ultrastructural level with specific antibodies. In newborn chick aorta the protein was exclusively found within elastic fibers. In both post- and pre-embedding immunolabeling emilin was mainly associated with regions where elastin and microfibrils are in close contact, such as the periphery of the fibers. This localization of emilin in aorta has been confirmed by quantitative evaluation of the distribution of gold particles within elastic fibers. In other tissues, besides being associated with typical elastic fibers, staining for emilin was found in structures lacking amorphous elastin, but where the presence of tropoelastin has been demonstrated by immunoelectron microscopy. This was particularly evident in the oxitalan fibers of the corneal stroma, in the Descemet's membrane, and in the ciliary zonule. Analysis of embryonic aorta revealed the presence of emilin at early stages of elastogenesis, before the appearance of amorphous elastin. Immunofluorescence studies have shown that emilin produced by chick embryo aorta cells in culture is strictly associated with elastin and that the process of elastin deposition is severely altered by the presence of antiemilin antibodies in the culture medium. The name of the protein was derived from its localization at sites where elastin and microfibrils are in proximity (emilin, elastin microfibril interface located protein).
In the mechanically active environment of the artery, cells sense mechanical stimuli and regulate extracellular matrix structure.
In this study, we explored the changes in synthesis of proteoglycans by vascular smooth muscle cells in response to precisely
controlled mechanical strains. Strain increased mRNA for versican (3.2-fold), biglycan (2.0-fold), and perlecan (2.0-fold),
whereas decorin mRNA levels decreased to a third of control levels. Strain also increased versican, biglycan, and perlecan
core proteins, with a concomitant decrease in decorin core protein. Deformation did not alter the hydrodynamic size of proteoglycans
as evidenced by molecular sieve chromatography but increased sulfate incorporation in both chondroitin/dermatan sulfate proteoglycans
and heparan sulfate proteoglycans (p < 0.05 for both). Using DNA microarrays, we also identified the gene for the hyaluronan-linking protein TSG6 as mechanically
induced in smooth muscle cells. Northern analysis confirmed a 4.0-fold increase in steady state mRNA for TSG6 following deformation.
Size exclusion chromatography under associative conditions showed that versican-hyaluronan aggregation was enhanced following
deformation. These data demonstrate that mechanical deformation increases specific vascular smooth muscle cell proteoglycan
synthesis and aggregation, indicating a highly coordinated extracellular matrix response to biomechanical stimulation.
Mice heterozygous for the elastin gene (ELN(+/-)) show unique cardiovascular properties, including increased blood pressure and smaller, thinner arteries with an increased number of lamellar units. Some of these properties are also observed in humans with supravalvular aortic stenosis, a disease caused by functional heterozygosity of the elastin gene. The arterial geometry in ELN(+/-) mice is contrary to the increased thickness that would be expected in an animal demonstrating hypertensive remodeling. To determine whether this is due to a decreased capability for cardiovascular remodeling or to a novel adaptation of the ELN(+/-) cardiovascular system, we increased blood pressure in adult ELN(+/+) and ELN(+/-) mice using the two-kidney, one-clip Goldblatt model of hypertension. Successfully clipped mice have a systolic pressure increase of at least 15 mmHg over sham-operated animals. ELN(+/+) and ELN(+/-)-clipped mice show significant increases over sham-operated mice in cardiac weight, arterial thickness, and arterial cross-sectional area with no changes in lamellar number. There are no significant differences in most mechanical properties with clipping in either genotype. These results indicate that ELN(+/+) and ELN(+/-) hearts and arteries remodel similarly in response to adult induced hypertension. Therefore, the cardiovascular properties of ELN(+/-) mice are likely due to developmental remodeling in response to altered hemodynamics and reduced elastin levels.
Mutations in fibrillin-1 (FBN1) result in Marfan syndrome, demonstrating a critical requirement for microfibrils in vessel structure and function. However, the identity and function of many microfibril-associated molecules essential for vascular development and function have yet to be characterized. In our morpholino-based screen for members of the secretome required for vascular development, we identified a key player in microfibril formation in zebrafish embryogenesis. Microfibril-associated glycoprotein-1 (MAGP1) is a conserved protein found in mammalian and zebrafish microfibrils. Expression of magp1 mRNA is detected in microfibril-producing cells. Analysis of a functional Magp1-mRFP fusion protein reveals localization along the midline and in the vasculature during embryogenesis. Underexpression and overexpression analyses demonstrate that specific Magp1 protein levels are critical for vascular development. Integrin function is compromised in magp1 morphant embryos, suggesting that reduced integrin-matrix interaction is the main mechanism for the vascular defects in magp1 morphants. We further show that Magp1 and fibrillin-1 interact in vivo. This study implicates MAGP1 as a key player in microfibril formation and integrity during development. The essential role for MAGP1 in vascular morphogenesis and function also supports a wide range of clinical applications, including therapeutic targets in vascular disease and cardiovascular tissue engineering.
MAGP1 is an extracellular matrix protein that, in vertebrates, is a ubiquitous component of fibrillin-rich microfibrils. We previously reported that aged MAGP1-deficient mice (MAGP1Delta) develop lesions that are the consequence of spontaneous bone fracture. We now present a more defined bone phenotype found in MAGP1Delta mice. A longitudinal DEXA study demonstrated age-associated osteopenia in MAGP1Delta animals and muCT confirmed reduced bone mineral density in the trabecular and cortical bone. Further, MAGP1Delta mice have significantly less trabecular bone, the trabecular microarchitecture is more fragmented, and the diaphyseal cross-sectional area is significantly reduced. The remodeling defect seen in MAGP1Delta mice is likely not due to an osteoblast defect, because MAGP1Delta bone marrow stromal cells undergo osteoblastogenesis and form mineralized nodules. In vivo, MAGP1Delta mice exhibit normal osteoblast number, mineralized bone surface, and bone formation rate. Instead, our findings suggest increased bone resorption is responsible for the osteopenia. The number of osteoclasts derived from MAGP1Delta bone marrow macrophage cells is increased relative to the wild type, and osteoclast differentiation markers are expressed at earlier time points in MAGP1Delta cells. In vivo, MAGP1Delta mice have more osteoclasts lining the bone surface. RANKL (receptor activator of NF-kappaB ligand) expression is significantly higher in MAGP1Delta bone, and likely contributes to enhanced osteoclastogenesis. However, bone marrow macrophage cells from MAGP1Delta mice show a higher propensity than do wild-type cells to differentiate to osteoclasts in response to RANKL, suggesting that they are also primed to respond to osteoclast-promoting signals. Together, our findings suggest that MAGP1 is a regulator of bone remodeling, and its absence results in osteopenia associated with an increase in osteoclast number.
Mutations in the COL3A1 gene that encodes the chains of type III procollagen result in the vascular form of Ehlers-Danlos syndrome (EDS), EDS type IV, if they alter the sequence in the triple-helical domain. Although other fibrillar collagen–gene mutations that lead to allele instability or failure to incorporate proα-chains into trimers—and that thus reduce the amount of mature molecules produced—result in clinically apparent phenotypes, no such mutations have been identified in COL3A1. Furthermore, mice heterozygous for Col3a1 “null” alleles have no identified phenotype. We have now found three frameshift mutations (1832delAA, 413delC, and 555delT) that lead to premature termination codons (PTCs) in exons 27, 6, and 9, respectively, and to allele-product instability. The mRNA from each mutant allele was transcribed efficiently but rapidly degraded, presumably by the mechanisms of nonsense-mediated decay. In a fourth patient, we identified a point mutation, in the final exon, that resulted in a PTC (4294C→T [Arg1432Ter]). In this last instance, the mRNA was stable but led to synthesis of a truncated protein that was not incorporated into mature type III procollagen molecules. In all probands, the presenting feature was vascular aneurysm or rupture. Thus, in contrast to mutations in genes that encode the dominant protein of a tissue (e.g., COL1A1 and COL2A1), in which “null” mutations result in phenotypes milder than those caused by mutations that alter protein sequence, the phenotypes produced by these mutations in COL3A1 overlap with those of the vascular form of EDS. This suggests that the major effect of many of these dominant mutations in the “minor” collagen genes may be expressed through protein deficiency rather than through incorporation of structurally altered molecules into fibrils.
The extracellular matrix protein fibulin-1 is a distinct component of vessel walls and can be associated with other ligands
present in basement membranes, microfibrils, and elastic fibers. Its biological role was investigated by the targeted inactivation
of the fibulin-1 gene in mice. This led to massive hemorrhages in several tissues starting at midgestation, ultimately resulting
in the death of almost all homozygous embryos upon birth. Histological analysis demonstrated dilation and ruptures in the
endothelial lining of various small vessels but not in that of larger vessels. Kidneys displayed a distinct malformation of
glomeruli and disorganization of podocytes. A delayed development of lung alveoli suggested impairment in lung inflation.
Immunohistology demonstrated the absence of fibulin-1 in its typical localizations but no aberrant patterns for several other
extracellular matrix proteins. Electron microscopy revealed intact basement membranes but very irregular cytoplasmic processes
of capillary endothelial cells in the organs that were most severely affected. Absence of fibulin-1 caused considerable blood
loss but did not compromise blood clotting. The data indicate a strong but restricted abnormality in some endothelial compartments
which, together with some kidney and lung defects, may be responsible for early death.
The vitality of the cardiovascular system, which consists of the heart, vas culature, and blood, depends on its response to a host of complex stimuli, including biological, chemical, electrical, mechanical, and thermal. The focus of this book, however, is on the response of the heart and arteries to mechanical loads from the perspective of nonlinear solid mechanics. Through my own research in this field, I have come to realize that study ing the complex responses of cardiovascular cells, tissues, and organs nec essarily requires a combined theoretical, experimental, and computational approach. Theory is needed to guide the performance and interpretation of experiments as well as to synthesize the results; experiment is needed to study the responses of the system to well-controlled loads and to test can didate hypotheses and theories; and due to the geometric and material non linearities inherent to cardiovascular mechanics, computation is needed to analyze data as well as to solve boundary and initial value problems that correspond to either experimental or in vivo conditions. One of the primary goals of this book is to introduce together basic analytical, experimental, and computational methods and to illustrate how these methods can and must be integrated to gain a more complete understanding of the bio mechanics of the heart and vasculature. Despite the focus on cardiovascu lar mechanics, the fundamental methods, indeed many of the specific results, are generally applicable to many different soft tissues.
It is characteristic of arteries that they do not obey Hooke's law, but resist further stretch more strongly, the more they are stretched. It appears that this might be due to the combination of elastin fibers in the elastic laminae, with the much less distensible collagenous libers in the media and adventitia, more and more of which reach their 'unstretched length' as distension is increased. This has been verified on human iliac arteries, from autopsy, by comparing the 'elastic diagrams' (tension vs. circumference) before and after differential digestion of collagen by formic acid, and digestion of elastin by crude trypsin (containing an elastase). This proved that the resistance to stretch at low pressures was almost entirely due to elastin fibers, that at physiological pressures due to both collagenous and elastin fibers, but dominantly to collagen, and that at high pressures almost entirely due to collagenous fibers. In future work on the effect of age on the elasticity of iliac arteries, the initial slope of the elastic diagram can be taken as an index of the state, or number, of the elastin fibers, and the final slope as an index of the state, or number, of collagenous fibers.
Dilation of the ascending aorta, associated with Marfan Syndrome, bicuspid aortic valve, or advanced age, may lead to aortic dissection and rupture. Mathematical models can be used to assess the relative importance of increased wall stresses and decreased strength in these mechanical failures. To obtain needed inputs for such models, mechanical properties of dilated human ascending aorta were measured in vitro. Specimens for opening angle, biaxial elastic, and uniaxial circumferential strength tests were cut from excised tissue obtained from 54 patients (age 18-81 years) undergoing elective aortic graft replacement surgery. Opening angle was significantly greater in patients older than 50 years (262degrees+/-76degrees, n = 21) compared to younger patients (202degrees+/-70degrees, n = 13). All biaxial elastic specimens (n = 40) exhibited nonlinear stress-strain behavior. Rapid increases in circumferential and axial stresses occurred at lower strains in the older patient group than in the younger. Mean strength was significantly lower in older patients (1.35+/-0.37 MPa, n = 14) than younger (2.04+/-0.46 MPa, n = 11, age <50 years). These changes in mechanical properties suggest that age may influence the risk of aortic dissection or rupture of dilated ascending aorta. (C) 2002 Biomedical Engineering Society.
To study the effects of smooth muscle contraction and relaxation on the strain and stress distribution in the vascular wall, a mathematical model was proposed. The artery was assumed to be a thick-walled orthotropic tube made of nonlinear, incompressible elastic material. Considering that the contraction of smooth muscle generates an active circumferential stress in the wall, a numerical study was performed using data available in the literature. The results obtained showed that smooth muscle contraction affects the residual strains which exist in a ring segment cut out from the artery and exposed to no external load. When the ring specimen is cut radially, it springs open with an opening angle. The predicted monotonic increase of the opening angle with increasing muscular tone was in agreement with recent experimental results reported in the literature. It was shown that basal muscular tone, which exists under physiological conditions, reduces the strain gradient in the arterial wall and yields a near uniform stress distribution. During temporary changes in blood pressure, the increase in muscular tone induced by elevated pressure tends to restore the distribution of circumferential strain in the arterial wall, and to maintain the flow-induced wall shear stress to normal level. 1999 Biomedical Engineering Society.
PAC99: 8719Rr, 8719Ff, 8710+e
The effects of hypertension on the stress and strain distributions through the wall thickness were studied in the rat thoracic aorta. Goldblatt hypertension was induced by constricting the left renal artery for 8 weeks. Static pressure-diameter-axial force relations were determined on excised tubular segments. The segments were then sliced into thin ring specimens. Circumferential strain distributions were determined from the cross-sectional shape of the ring specimens observed before and after releasing residual stresses by radial cutting. Stress distributions were calculated using a logarithmic type of strain energy density function. The wall thickness at the systolic blood pressure, P(sys) significantly correlated with P(sys). The mean stress and strain developed by P(sys) in the circumferential direction were not significantly different between the hypertensive and control aortas, while those in the axial direction were significantly smaller in the hypertensive aorta than in the control. The opening angles of the stress free ring specimens correlated well with P(sys). The stress concentration factor in the circumferential direction was almost constant and independent of P(sys) although the stress distributions were not uniform through the wall thickness. Histological observation showed that the wall thickening caused by hypertension is mainly due to the hypertrophy of the lamellar units of the media, especially in the subintimal layer where the stress increase developed by hypertension is larger than in the other layers. These results indicate that: (a) the aortic wall adapts itself to the mechanical field by changing not only the wall dimensions but also the residual stresses, (b) this adaptation is primarily related to the circumferential stress but not to the axial stress, and (c) the aortic smooth muscle cells seem to change their morphology in response to the mechanical stress.
Acute and long-term (up to 56 days) evolution of geometry, structural properties, vascular smooth muscle (VSM) tone and histomorphometric properties of the rat common carotid arteries under induced hypertension were investigated. Hypertension was induced in 8-week old male Wistar rats by total ligation of the aorta between the two kidneys. Rats were sacrificed 2, 4, 8 and 56 days postsurgery. The arterial wall layers thicken non-uniformly during the adaptation process, the inner layers thicken more in the acute phase of hypertension, whereas the outer layers of the wall are thicker than the inner layers at the end of the adaptation phase. Collagen content in the wall media exhibits a non-linear evolution, with a rapid increase in the acute hypertension phase followed by a slower increase at long-term. The elastin content increase is slight and steady, whereas VSM shows a steady but considerable increase which outdoes the collagen increase in long-term phase. VSM tone increases rapidly in the acute phase of remodelling (0-8 days) and this increase in tone contributes to a considerable increase in arterial compliance in the operating pressure range. At long-term (56 days) VSM tone returns to near control level, but compliance is even further increased, which suggests that at long-term the compliance increase is attributed primarily to structural remodelling.
Stress distribution through the wall thickness of the canine carotid artery was analyzed on the basis of the uniform strain hypothesis in which the wall circumferential strain was assumed to be constant over the wall cross-section under physiological loading condition. A newly proposed logarithmic type of strain energy density function was used to describe the wall properties. In contrast with other studies, this hypothesis gave almost uniform distribution of wall stresses under the physiological condition and non-zero residual stresses when all external forces were removed.
This chapter discusses that there is now abundant evidence in favor of the view that elastic fibers are composed of bundles of thin homogeneous microfibrils, and that the substance of these microfibrils is a unique protein. This protein contains in its structure a chromophoric residue, which gives elastin its characteristic as yellow and fluorescence color. The microfibrils of all elastic fibers in different tissues of the same animal species have a similar analytical composition, although they may differ to some extent in details of molecular structure. The elastic properties of the wet fiber may best be understood on the basis that the component microfibrils are composed of a protein with inherent elastic properties brought about by a cross-linked structure. These cross-links are not the familiar S S bridges since elastin contains little, if any cystine, but if the linkages are indeed of covalent character, they must be due to bridges of a hitherto unknown type. Finally, evidence has been presented leading to the view that the radical comprising the chromophore in elastin may also be involved in bridging adjacent peptide chains.
Publisher Summary
This chapter illustrates the expression patterns of several cytoskeletal, contractile, extracellular matrix proteins, and integrins in smooth muscle cells of developing, adult, and atherosclerotic human aorta. This chapter intends to describe the phenotypic properties of smooth muscle cells during development and in disease states; to characterize the diversity of human vascular smooth muscle cells; and to analyze possible strategies for the regulation of individual gene expression used during smooth muscle development and phenotypic transitions of smooth muscle cells in adult, and the role of genetic (intrinsic) and environmental (extrinsic) factors in smooth-muscle-cell phenotypic expression. Whereas intrinsic control plays a major role in the early events of smooth-muscle-cell differentiation, extrinsic factors probably serve as signals for morphogenetic events and determine the phenotypic transitions of mature smooth muscle cells. This chapter focuses on analyzing the coordinate changes in the expression of extracellular matrix components, laminin, fibronectin, extracellular matrix receptors, integrins, and cytoskeletal differentiation markers of smooth muscle cells.
A new connective tissue protein, which we call fibrillin, has been isolated from the medium of human fibroblast cell cultures. Electrophoresis of the disulfide bond-reduced protein gave a single band with an estimated molecular mass of 350,000 D. This 350-kD protein appeared to possess intrachain disulfide bonds. It could be stained with periodic acid-Schiff reagent, and after metabolic labeling, it contained [3H]glucosamine. It could not be labeled with [35S]sulfate. It was resistant to digestion by bacterial collagenase. Using mAbs specific for fibrillin, we demonstrated its widespread distribution in the connective tissue matrices of skin, lung, kidney, vasculature, cartilage, tendon, muscle, cornea, and ciliary zonule. Electron microscopic immunolocalization with colloidal gold conjugates specified its location to a class of extracellular structural elements described as microfibrils. These microfibrils possessed a characteristic appearance and averaged 10 nm in diameter. Microfibrils around the amorphous cores of the elastic fiber system as well as bundles of microfibrils without elastin cores were labeled equally well with antibody. Immunolocalization suggested that fibrillin is arrayed periodically along the individual microfibril and that individual microfibrils may be aligned within bundles. The periodicity of the epitope appeared to match the interstitial collagen band periodicity. In contrast, type VI collagen, which has been proposed as a possible microfibrillar component, was immunolocalized with a specific mAb to small diameter microfilaments that interweave among the large, banded collagen fibers; it was not associated with the system of microfibrils identified by the presence of fibrillin.
Fibrillins are large, cysteine-rich glycoproteins that form microfibrils and play a central role in elastic fibrillogenesis. Fibrillin-1 and fibrillin-2, encoded by FBN1 on chromosome 15q21.1 and FBN2 on chromosome 5q23-q31, are highly similar proteins. The finding of mutations in FBN1 and FBN2 in the autosomal dominant microfibrillopathies Marfan syndrome (MFS) and congenital contractural arachnodactyly (CCA), respectively, has highlighted their essential role in the development and homeostasis of elastic fibres. MFS is characterized by cardiovascular, skeletal and ocular abnormalities, and CCA by long, thin, flexed digits, crumpled ears and mild joint contractures. Although mutations arise throughout FBN1, those clustering within exons 24-32 are associated with the most severe form of MFS, so-called neonatal MFS. All the mutations described in CCA occur in the 'neonatal region' of FBN2. Both MFS and CCA are thought to arise via a dominant negative mechanism. The analysis of mouse mutations has demonstrated that fibrillin-1 microfibrils are mainly engaged in tissue homeostasis rather than elastic matrix assembly. In the current investigation, we have analysed the classical mouse mutant shaker-with-syndactylism using a positional candidate approach and demonstrated that loss-of-function mutations outside the 'neonatal region' of FBn2 cause syndactyly in mice. These results suggest that phenotypes distinct from CCA may result in man as a consequence of mutations outside the 'neonatal region' of FBN2.
Evidence from diverse investigations suggests that arterial growth and remodeling correlates well with changes in mechanical stresses from their homeostatic values. Ultimately, therefore, there is a need for a comprehensive theory that accounts for changes in the 3-D distribution of stress within the arterial wall, including residual stress, and its relation to the mechanisms of mechanotransduction. Here, however, we consider a simpler theory that allows competing hypotheses to be tested easily, that can provide guidance in the development of a 3-D theory, and that may be useful in modeling solid-fluid interactions and interpreting clinical data. Specifically, we present a 2-D constrained mixture model for the adaptation of a cylindrical artery in response to a sustained alteration in flow. Using a rule-of-mixtures model for the stress response and first order kinetics for the production and removal of the three primary load-bearing constituents within the wall, we illustrate capabilities of the model by comparing responses given complete versus negligible turnover of elastin. Findings suggest that biological constraints may result in suboptimal adaptations, consistent with reported observations. To build upon this finding, however, there is a need for significantly more data to guide the hypothesis testing as well as the formulation of specific constitutive relations within the model.
Extracellular microfibrils, alone or in association with elastin, confer critical biomechanical properties on a variety of connective tissues. Little is known about the composition of the microfibrils or the factors responsible for their spatial organization into tissue-specific macroaggregates. Recent work has revealed the existence of two structurally related microfibrillar components, termed fibrillin-1 and fibrillin-2. The functional relationships between these glycoproteins and between them and other components of the microfibrils and elastic fibers are obscure. As a first step toward elucidating these important points, we compared the expression pattern of the fibrillin genes during mammalian embryogenesis. The results revealed that the two genes are differentially expressed, in terms of both developmental stages and tissue distribution. In the majority of cases, fibrillin-2 transcripts appear earlier and accumulate for a shorter period of time than fibrillin-1 transcripts. Synthesis of fibrillin-1 correlates with late morphogenesis and the appearance of well-defined organ structures; fibrillin-2 synthesis, on the other hand, coincides with early morphogenesis and, in particular, with the beginning of elastogenesis. The findings lend indirect support to our original hypothesis stating that fibrillins contribute to the compositional and functional heterogeneity of the microfibrils. The available evidence is also consistent with the notion that the fibrillins might have distinct, but related roles in microfibril physiology. Accordingly, we propose that fibrillin-1 provides mostly force-bearing structural support, whereas fibrillin-2 predominantly regulates the early process of elastic fiber assembly.
The two morphologically different constituents of the mature elastic fiber, the central amorphous and the peripheral microfibrillar components, have been separated and partially characterized. A pure preparation of elastic fibers was obtained from fetal bovine ligamentum nuchae by extraction of the homogenized ligament with 5 M guanidine followed by digestion with collagenase. The resultant preparation consisted of elastic fibers which were morphologically identical with those seen in vivo. The microfibrillar components of these elastic fibers were removed either by proteolytic enzymes or by reduction of disulfide bonds with dithioerythritol in 5 M guanidine. The microfibrils solubilized by both methods were rich in polar, hydroxy, and sulfur-containing amino acids and contained less glycine, valine, and proline than the amorphous component of the elastic fiber. In contrast, the amino acid composition of the amorphous component was identical with that previously described for elastin. This component demonstrated selective susceptibility to elastase digestion, but was relatively resistant to the action of other proteolytic enzymes and to reduction. These observations establish that the microfibrils consist of a different connective tissue protein (or proteins) that is neither collagen nor elastin. During embryologic development the microfibrils form an aggregate structure before the amorphous component is secreted. These microfibrils may therefore play a primary role in the morphogenesis of the elastic fiber.
Versican is an extracellular matrix (ECM) proteoglycan that is synthesized as multiple splice variants. In a recent study, we demonstrated that retroviral-mediated overexpression of the variant V3, which lacks chondroitin sulfate (CS) chains, altered arterial smooth muscle cell (ASMC) phenotype in short-term cell culture. We now report that V3-overexpressing ASMCs exhibit significantly increased expression of tropoelastin and increased formation of elastic fibers in long-term cell cultures. In addition, V3-overexpressing ASMCs seeded into ballooned rat carotid arteries continued to overexpress V3 and, at 4 weeks after seeding, produced a highly structured neointima significantly enriched in elastic fiber lamellae. In contrast to the hydrated, myxoid neointima produced by rounded or stellate vector-alone–transduced cells, V3-expressing cells produced a compact and highly ordered neointima, which contained elongated ASMCs that were arranged in parallel arrays and separated by densely packed collagen bundles and elastic fibers. These results indicate that a variant of versican is involved in elastic fiber assembly and may represent a novel therapeutic approach to facilitate the formation of elastic fibers.
Application of cyclic stretch (10% at 1 hertz) to vascular smooth muscle cells (SMC) increased L-arginine uptake and this was associated with a specific increase in cationic amino acid transporter-2 (CAT-2) mRNA. In addition, cyclic stretch stimulated L-arginine metabolism by inducing arginase I mRNA and arginase activity. In contrast, cyclic stretch inhibited the catabolism of L-arginine to nitric oxide (NO) by blocking inducible NO synthase expression. Exposure of SMC to cyclic stretch markedly increased the capacity of SMC to generate L-proline from L-arginine while inhibiting the formation of polyamines. The stretch-mediated increase in L-proline production was reversed by methyl-L-arginine, a competitive inhibitor of L-arginine transport, by hydroxy-L-arginine, an arginase inhibitor, or by the ornithine aminotransferase inhibitor L-canaline. Finally, cyclic stretch stimulated collagen synthesis and the accumulation of type I collagen, which was inhibited by L-canaline. These results demonstrate that cyclic stretch coordinately stimulates L-proline synthesis by regulating the genes that modulate the transport and metabolism of L-arginine. In addition, they show that stretch-stimulated collagen production is dependent on L-proline formation. The ability of hemodynamic forces to up-regulate L-arginine transport and direct its metabolism to L-proline may play an important role in stabilizing vascular lesions by promoting SMC collagen synthesis.—Durante, W., Liao, L., Reyna, S. V., Peyton, K. J., Schafer, A. I. Physiological cyclic stretch directs L-arginine transport and metabolism to collagen synthesis in vascular smooth muscle.
: In recent years, it has become increasingly clear that vascular structures readily remodel in response to hemodynamic cues associated with changes in blood flows. These remodeling processes are invoked by a wealth of developmental, physiologic, and pathologic phenomena. Current work is providing novel clues concerning flow sensing by endothelial cells, the signal transduction pathways that translate flow detection into endothelial responses, and some of the signals that are transmitted to the effector cells, the vascular smooth muscle cells in the media. However, most of these mechanisms relate to acute responses to altered flow, and we remain ignorant of how important they are in eliciting tissue remodeling. Also, there is very little information on the processes that accomplish "remodeling" beyond evidence that modulation of new tissue synthesis occurs. There is a potential for imaginative experiments to provide fundamental information on the genesis of the vascular structure-function relations, which now clearly span much of the pre- and postnatal life.
A number of important questions remain to be answered concerning our understanding of elastic tissues. The size and molecular weight of the elastin precursor remains to be clearly established. The number of proteins involved in the microfibrillar component of the elastic fiber are as yet undetermined, although it would appear that they are glycoproteins that may represent a species of reasonably high molecular weight. Clearly the elastic fiber contains two morphologic components. During morphogenesis, the elastic fiber begins to appear in the form of aggregates of microfibrils that take the shape and direction of the presumptive elastic fiber. With increasing maturity elastin begins to form within the interstices of each bundle of microfibrils. By the time the elastic fiber is fully formed it consists largely of the amorphous component, elastin, surrounded by an envelope of microfibrils with microfibrils embedded within its interstices.
It has been suggested that the microfibrils form and take their shape extracellularly under the influence of the cells that have secreted their precursors. After the aggregates of microfibrils have taken their shape Ross and Bornstein (22) have suggested that the elastin may interact ionically with the surface of the microfibrils, since each of these two components has an opposite net charge, and may be held in position while desmosine cross-links are established through the action of the enzyme, lysyl oxidase. Thus the microfibrils would serve as a scaffolding to determine morphogenetically the shape and direction to be later taken by the mature elastic fiber.
The reason for the elastic properties of the elastin is still yet poorly understood, and the means by which the cells synthesize and secrete both of these components remain to be investigated.
This chapter discusses the vascular smooth muscle cell (SMC) phenotype and extracellular matrix (ECM) molecules made by vessel wall cells during vascular development, with the primary focus on the developing mouse aorta, and focuses on ECM gene expression during mouse aortic development. The structural matrix proteins, which are important for vascular strength and compliance, are produced during a relatively narrow developmental window in the mouse that begins around the last trimester of development and continues for only a few weeks after birth. Prior to this synthetic ‘‘matrix phase,’’ the cells in the vessel wall are highly proliferative and express matrix proteins that support cell motility, establish polarity, and bind and sequester growth factors. As the cells shift out of the matrix phase, the spectrum of contractile proteins changes as the SMC prepares for its unique contractile function and general cell maintenance genes are expressed. It is shown in the chapter that the vascular SMC can exhibit a wide range of phenotypes at different stages of development. Developing a molecular snapshot of normal development provides new avenues of investigation into vascular cell phenotypic modulation in health and disease.
Guidelines for submitting commentsPolicy: Comments that contribute to the discussion of the article will be posted within approximately three business days. We do not accept anonymous comments. Please include your email address; the address will not be displayed in the posted comment. Cell Press Editors will screen the comments to ensure that they are relevant and appropriate but comments will not be edited. The ultimate decision on publication of an online comment is at the Editors' discretion. Formatting: Please include a title for the comment and your affiliation. Note that symbols (e.g. Greek letters) may not transmit properly in this form due to potential software compatibility issues. Please spell out the words in place of the symbols (e.g. replace “α” with “alpha”). Comments should be no more than 8,000 characters (including spaces ) in length. References may be included when necessary but should be kept to a minimum. Be careful if copying and pasting from a Word document. Smart quotes can cause problems in the form. If you experience difficulties, please convert to a plain text file and then copy and paste into the form.
1.1. Reconstruction of the amino acid composition of an hypothetical, ancestral elastin which arose at some time after divergence of the cyclostome and gnathostome lines revealed a protein which was similar in composition and in degree of crosslinking to the present-day mammalian elastin.2.2. There has been a positive trend toward increasing hydrophobicity in the evolution of elastin.3.3. Present evidence does not support a common genetic origin for elastin and other structural proteins such as collagen and silk fibroin. However, the existence of distinct genetic types of elastin which diverged from a common ancestral gene or genes is suggested by marked interspecies variation in elastin amino acid composition.
1. INTRODUCTION. 1.1 Historical Prelude, 1.2 Basic Cell Biology, 1.3 The Extracellular Matrix, 1.4 Soft Tissue Behavior, 1.5 Needs and General Approach, 1.6 Exercises, 1.7 References. 2. MATHEMATICAL PRELIMINARIES 2.1 A Direct Tensor Notation, 2.2 Cartesian Components, 2.3 Further Results in Tensor Calculus, 2.4 Orthogonal Curvilinear Components, 2.5 Matrix Methods, 2.6 Exercises, 2.7 References, 3. CONTINUUM MECHANICS 3.1 Kinematics, 3.2 Forces, Tractions and Stresses, 3.3 Balance Relations, 3.4 Constitutive Formulations, 3.5 Boundary and Initial Conditions, 3.6 Exercises, 3.7 References, 4. FINITE ELASTICITY 4.1 Introduction, 4.2 Incompressible Isotropic Elasticity, 4.3 Solutions in 3-D Incompressible Elasticity, 4.4 Compressible Isotropic Elasticity, 4.5 Membrane Hyperelasticity, 4.6 Exercises, 4.7 References 5. EXPERIMENTAL METHODS 5.1 General Philosophy, 5.2 Measurement of Strain, 5.3 Measurement of Applied Loads, 5.4 Testing Conditions, 5.5 Parameter Estimation and Statistics, 5.6 Exercises, 5.7 References 6. Finite Element Methods 6.1 Fundamental Equations, 6.2 Interpolation, Integration, and Solvers, 6.3 An Illustrative Formulation, 6.4 Inflation of a Membrane, 6.5 Inverse Finite Elements, 6.6 Exercises, 6.7 References PART II - VASCULAR MECHANICS 7. THE NORMAL ARTERIAL WALL 7.1 Structure and Function, 7.2 General Characteristics, 7.3 Constitutive Framework, 7.4 Experimental Methods, 7.5 Specific Constitutive Relations, 7.6 Stress Analyses, 7.7 Exercises, 7.8 References 8. VASCULAR DISORDERS 8.1 Hypertension, 8.2 Intracranial Aneurysms, 8.3 Atherosclerosis, 8.4 Aortic Aneurysms, 8.5 Additional Topics, 8.6 Exercises, 8.7 References 9. VASCULAR ADAPTATION 9.1 Mechanical Preliminaries, 9.2 Cellular Responses to Applied Loads, 9.3 Arterial Response to Hypertension, 9.4 Arterial Response to Altered Flow, 9.5 Vessel Response to Injury, 9.6 Veins as Arterial Grafts, 9.7 Aging, 9.8 Exercises, 9.9 References PART III CARDIAC MECHANICS 10. THE NORMAL HEART 10.1 Structure and Function, 10.2 General Characteristics, 10.3 Constitutive Framework, 10.4 Constitutive Relations, 10.5 Stress Analyses, 10.6 Exercises, 10.7 References 11. EPILOGUE APPENDICES I. Nomenclature, Abbreviations, and Conversions II. Results for Curvilinear Coordinates III. Material Frame Indifference 11. CARDIAC DISORDERS 11.1 Ischemia 11.2 Volume Overload 11.3 Hypertrophy 11.4 Cardiac Aneurysms 11.5 Additional Topics
Elastogenesis in the ligamentum nuchae of the fetal calf commences with the extracellular deposition of hollow-appearing filaments, 130 Å in diameter, showing a banding pattern consisting of alternating segments, 50 Å and 130 Å long, respectively. Similar filaments are found in the crude extract of the ligament. Mature elastin forms within these masses of filaments and displays an internal, branching tangle of 30 Å filaments. Elastogenesis is accompanied by a high level of cellular activity involving acanthosomes, which have been interpreted as a mechanism of secretion of protein-polysaccharide complexes.
Smooth muscle cell (SMC) phenotype can be altered by physical forces as demonstrated by cyclic strain-induced changes in proliferation, orientation, and secretion of macromolecules. However, the magnitude of strain required and the intracellular coupling pathways remain ill defined. To examine the strain requirements for SMC proliferation, we selectively seeded bovine aortic SMC either on the center or periphery of silastic membranes which were deformed with 150 mm Hg vacuum (0–7% center; 7–24% periphery). SMC located in either the center or peripheral regions showed enhanced proliferation compared to cells grown under the absence of cyclic strain. Moreover, SMC located in the center region demonstrated significantly (P < 0.005) greater proliferation as compared to those in the periphery. In contrast, SMC exposed to high strain (7–24%) demonstrated alignment perpendicular to the strain gradient, whereas SMC in the center (0–7%) remained aligned randomly. To determine the mechanisms of these phenomena, we examined the effect of cyclic strain on bovine aortic SMC signaling pathways. We observed strain-induced stimulation of the cyclic AMP pathway including adenylate cyclase activity and cyclic AMP accumulation. In addition, exposure of SMC to cyclic strain caused a significant increase in protein kinase C (PKC) activity and enzyme translocation from the cytosol to a particulate fraction. Further study was conducted to examine the effect of strain magnitude on signaling, particularly protein kinase A (PKA) activity as well as cAMP response element (CRE) binding protein levels. We observed significantly (P < 0.05) greater PKA activity and CRE binding protein levels in SMC located in the center as compared to the peripheral region. However, inhibition of PKA (with 10 μM Rp-cAMP) or PKC (with 5–20 ng/ml staurosporine) failed to alter either the strain-induced increase in SMC proliferation or alignment. These data characterize the strain determinants for activation of SMC proliferation and alignment. Although strain activated both the AC/cAMP/PKA and the PKC pathways in SMC, singular inhibition of PKA and PKC failed to prevent strain-induced alignment and proliferation, suggesting either their lack of involvement or the multifactorial nature of these responses. J. Cell. Physiol. 170:228–234, 1997. © 1997 Wiley-Liss, Inc.
A 1.4-kb EST clone encoding mouse microfibril-associated glycoprotein-2 (MAGP-2), identified by its similarity with the reported
human cDNA, was used to screen a mouse 129 genomic bacterial artificial chromosome (BAC) library. The mouse gene contains
10 exons spanning 16 kb, located on the distal region of Chromosome (Chr) 6. The exons range in size from 24 to 963 bp, with
the ATG located in exon 2. The tenth and largest exon contains 817 bp of 3′ untranslated sequence, including a B2 repetitive
element. Northern analysis demonstrates abundant expression of MAGP-2 mRNA in skeletal muscle, lung, and heart. Sequence analysis
of additional cDNA clones suggests that the two mRNA forms of MAGP-2 in the mouse arise from alternative polyadenylation site
usage. The promoter does not contain an obvious TATA box, and the sequence surrounding the start site does not conform to
the consensus for an initiator promoter element. Additionally, the mouse promoter contains 22 copies of a CT dinucleotide
repeat sequence located ∼155 bp 5′ to exon 1.
Dynamic mechanical conditioning is investigated as a means of improving the mechanical properties of tissue-engineered blood vessel constructs composed of living cells embedded in a collagen-gel scaffold. This approach attempts to elicit a unique response from the embedded cells so as to reorganize their surrounding matrix, thus improving the overall mechanical stability of the constructs. Mechanical conditioning, in the form of cyclic strain, was applied to the tubular constructs at a frequency of 1 Hz for 4 and 8 days. The response to conditioning thus evinced involved increased contraction and mechanical strength, as compared to statically cultured controls. Significant increases in ultimate stress and material modulus were seen over an 8 day culture period. Accompanying morphological changes showed increased circumferential orientation in response to the cyclic stimulus. We conclude that dynamic mechanical conditioning during tissue culture leads to an improvement in the properties of tissue-engineered blood vessel constructs in terms of mechanical strength and histological organization. This concept, in conjunction with a proper biochemical environment, could present a better model for engineering vascular constructs. 2000 Biomedical Engineering Society.
PAC00: 8719Rr, 8714Ee, 8718-h, 8768+z
The thoracic aorta of the rat was investigated by electron microscopy. A form of smooth muscle is the only cell type to be found in the tunica media. Successive layers of cells alternate with elastic lamellae. Each cell diagonally spans the interspace from one elastic lamella to the next. The muscle of the tunica media is without specific innervation. A three-dimensional network of elastic cords intersperced between the cells helps tie together the principal elastic lamellae. Substantial numbers of collagenous fibers are also found.The basement membrane system (sarcolemma) of the muscle is quite poorly developed in the rat aorta. Muscle is directly attached to elastin by a thin (200 Å) layer of “cement substance”. There is no evidence of any direct attachment of smooth muscle to collagen, nor is there evident any specific connection or fusion of collagen with elastin.The only cell type in the tunica intima is the endothelium. Intimal connective tissue sometimes contains thin strands and tiny units of elastin, associated with mucopolysaccharide, which are thought to represent active centers of elastin deposition.
A monoclonal antibody generated against the isolated extracellular matrix (ECM) of the medusa Podocoryne carnea M. Sarz (Coelenterata, Cnidaria, Hydrozoa) stains a fibrillar component of the Podocoryne ECMs in immunohistochemical preparations. The antigen shows a different staining pattern according to the type of ECMs from the animals life cycle. In ontogeny the epitope first appears after gastrulation in the planula larva as single widely dispersed small fibrils, which later accumulate to form a dense meshwork in the larval ECM. The distribution of the antigen strongly suggests an important role of the molecule to cover the biomechanical needs of the animal. In immunoblots one band with a size of 330 kDa is detectable in the polyp ECM, whereas in the outer ECM of the medusa a 340-kDa band is observed. Both the 330- and the 340-kDa bands appear when probed on the inner ECM of the medusa or on ECMs of the larva. The antibody was used to isolate a cDNA clone from an expression library. The deduced amino acid sequence of this cDNA fragment reveals a molecular structure composed of tandemly repeated epidermal growth factor-like repeats interrupted by a second cystein-rich motif first found in the latent transforming growth factor β binding protein. Comparison of the sequence to the data bases indicates >40% identity to human fibrillins. The presence of fibrillin-like beaded microfibrils in the ECM of P. carnea is furthermore demonstrated by electron microscopy after rotary shadowing. Our results demonstrate for the first time the existence of this noncollagenous interstitial ECM protein in invertebrates and suggest that the structure and the function of fibrillin have been conserved during evolution.
The nuchal ligament of bovines is a useful system in which to study elastic fibre formation since it contains up to 83% elastin and undergoes a period of rapid elastinogenesis during the last trimester of fetal development and in the first four post-natal months. To identify proteoglycans (PGs) which may be involved in this process we initially investigated changes in the glycosaminoglycan (GAG) profiles during nuchal ligament development. In contrast to the collagenous Achilles tendon, nuchal ligament exhibited: (a) elevated hyaluronan (HA) levels in the peak period of elastin-associated microfibril (fibrillin) synthesis (130–200 days) which precedes elastinogenesis; and (b) markedly increased synthesis of a glucuronate-rich copolymeric form of dermatan sulfate (DS) in the period corresponding to elastin formation (200–270 days). Analysis of DSPGs isolated from 230-day nuchal ligament showed that this copolymer was predominantly associated with a glycoform of biglycan which was specifically elevated at this stage in development. This finding was consistent with Northern blot analysis which showed that steady-state biglycan mRNA levels increased significantly during the elastinogenic period. In contrast, the mRNA levels for decorin, the only other DSPG detected in this tissue, declined rapidly after 140 days of fetal development. In conclusion, the results suggest that HA may play a role in microfibril assembly and that a specific glycoform of biglycan may be associated with the elastinogenic phase of elastic fibre formation.
The thoracic aortas of mice ranging in age from 3 days to 17 months were studied in thin sections by means of the electron microscope. A few small arterial blood vessels from mouse lung and the aorta of a young rabbit were also examined. All tissues were fixed in osmium tetroxide. The length of fixation and the embedding procedures were varied in different preparations. The mouse aorta consists of an endothelium (tunica intima), a tunica media composed of about five elastic laminae and alternating layers of smooth muscle cells, and a tunica adventitia containing fibroblasts and fibers. Notable aging changes in the tunica media are: a gradually increasing amount of collagen, rarifications and interruptions of elastic laminae, disconnections between smooth muscle cells and elastic laminae, and a peculiar fraying or fragmentation of the innermost elastica. In recessive-obese mice, subendothelial deposition of collagen was also found. A subendothelial proliferative “lesion” consisting of elongated cells and newly formed collagen and elastin is interpreted as a possible parallel to the initial lesions seen in atherosclerosis.Additional evidence demonstrates that there is probably a filamentous component present within elastic fibers and elastic laminae. These filaments can be seen at the surface of small elastic fibers and, less frequently, within the elastic laminae. In addition, it appears that collagen fibrils and possibly cell fragments are incorporated into the outermost elastic laminae in the young aortas.The cells within the media are recognized as a variety of smooth muscle cells which probably arise from fibroblasts present during embryonic development. It is assumed that these smooth muscle cells are responsible for the gradual production of collagen, although the fine structure of their cytoplasm is not typical of cells engaging in fibrogenesis.
Lysyl oxidase (LOX) plays a key role in the maturation of the extra-cellular matrix, by inducing the formation of lysyl cross-links in collagen and elastin molecules. Beside its enzymic activity, LOX is able to regulate the promoter of collagen III, one of its natural substrates. In this paper we demonstrated that LOX regulates also the promoter of elastin, inducing an important activation of its activity. In order to define the pathways used by LOX to achieve its effect, we activated some of the main fibrogenic signal pathways and studied the consequences on LOX effects on the promoter. TGF-beta1 activated most of the elastin promoter constructs that we studied, except for an inhibitory region contained in the region between -1500 and -1000 bp. The treatment with TGF-beta1 abolished completely the activation induced by LOX. LOX-over-expression coupled with TGF treatment abolished both effects in the -500 bp region. The treatment with CTGF also inhibited LOX effect, although to a lesser extent. However, CTGF behaved quite differently from TGF-beta1 suggesting that it is not necessarily the mediator of TGF effects. Basic FGF, the other fibrogenic factor that we tested, again abolished LOX-dependent activation, but by itself did not affect elastin promoter activity. Because TGF-beta1 activating effects, we used EMSA to examine the transcription factor binding patterns in presence of LOX, TGF-beta1 or both. The study showed that LOX reverted the patterns of several DNA-protein complexes along the 1.5 kb of the studied promoter region. Most were affected by both LOX and TGF-beta1, while on some only TGF-beta1 was effective. LOX presence mostly inhibited the TGF-regulated complexes. Many of those included SMAD transcription factors. Two more restricted regions binding AP1 and SMAD were identified as mediators of LOX effects and of LOX and TGF-beta1 cross-inhibition.