Chapter: Role of Paracrine Mechanisms
- [Show abstract] [Hide abstract] ABSTRACT: In the past decade, substantial evidence supports the paradigm that stem cells exert their reparative and regenerative effects, in large part, through the release of biologically active molecules acting in a paracrine fashion on resident cells. The data suggest the existence of a tissue microenvironment where stem cell factors influence cell survival, inflammation, angiogenesis, repair, and regeneration in a temporal and spatial manner.
- [Show abstract] [Hide abstract] ABSTRACT: High-resolution tracking of stem cells remains a challenging task. An ultra-bright contrast agent with extended intracellular retention is suitable for in vivo high-resolution tracking of stem cells following the implantation. Here, a plasmonic-active nanoplatform was developed for tracking mesenchymal stromal cells (MSCs) in mice. The nanoplatform consisted of TAT peptide-functionalized gold nanostars (TAT-GNS) that emit ultra-bright two-photon photoluminescence capable of tracking MSCs under high-resolution optical imaging. In vitro experiment showed TAT-GNS-labeled MSCs retained a similar differentiability to that of non-labeled MSCs controls. Due to their star shape, TAT-GNS exhibited greater intracellular retention than that of commercial Q-Tracker. In vivo imaging of TAT-GNS-labeled MSCs five days following intra-arterial injections in mice kidneys showed possible MSCs implantation in juxta-glomerular (JG) regions, but non-specifically in glomeruli and afferent arterioles as well. With future design to optimize GNS labeling specificity and clearance, plasmonic-active nanoplatforms may be a useful intracellular tracking tool for stem cell research.
- [Show abstract] [Hide abstract] ABSTRACT: Inappropriate activation of the type 1A angiotensin (AT1A) receptor contributes to the pathogenesis of hypertension and its associated complications. To define the role for actions of vascular AT1A receptors in BP regulation and hypertension pathogenesis, we generated mice with cell-specific deletion of AT1A receptors in smooth muscle cells (SMKO mice) using Loxp technology and Cre transgenes with robust expression in both conductance and resistance arteries. We found that elimination of AT1A receptors from vascular smooth muscle cells (VSMCs) caused a modest (approximately 7 mmHg) yet significant reduction in baseline BP and exaggerated sodium sensitivity in mice. Additionally, the severity of angiotensin II (Ang II)-dependent hypertension was dramatically attenuated in SMKO mice, and this protection against hypertension was associated with enhanced urinary excretion of sodium. Despite the lower BP, acute vasoconstrictor responses to Ang II in the systemic vasculature were largely preserved (approximately 80% of control levels) in SMKO mice because of exaggerated activity of the sympathetic nervous system rather than residual actions of AT1B receptors. In contrast, Ang II-dependent responses in the renal circulation were almost completely eliminated in SMKO mice (approximately 5%-10% of control levels). These findings suggest that direct actions of AT1A receptors in VSMCs are essential for regulation of renal blood flow by Ang II and highlight the capacity of Ang II-dependent vascular responses in the kidney to effect natriuresis and BP control. Copyright © 2015 by the American Society of Nephrology.
- [Show abstract] [Hide abstract] ABSTRACT: Familial forms of focal segmental glomerulosclerosis (FSGS) have been linked to gain-of-function mutations in the gene encoding the transient receptor potential channel C6 (TRPC6). GPCRs coupled to Gq signaling activate TRPC6, suggesting that Gq-dependent TRPC6 activation underlies glomerular diseases. Here, we developed a murine model in which a constitutively active Gq α subunit (GqQ209L, referred to herein as GqQ>L) is specifically expressed in podocytes and examined the effects of this mutation in response to puromycin aminonucleoside (PAN) nephrosis. We found that compared with control animals, animals expressing GqQ>L exhibited robust albuminuria, structural features of FSGS, and reduced numbers of glomerular podocytes. Gq activation stimulated calcineurin (CN) activity, resulting in CN-dependent upregulation of TRPC6 in murine kidneys. Deletion of TRPC6 in GqQ>L-expressing mice prevented FSGS development and inhibited both tubular damage and podocyte loss induced by PAN nephrosis. Similarly, administration of the CN inhibitor FK506 reduced proteinuria and tubular injury but had more modest effects on glomerular pathology and podocyte numbers in animals with constitutive Gq activation. Moreover, these Gq-dependent effects on podocyte injury were generalizable to diabetic kidney disease, as expression of GqQ>L promoted albuminuria, mesangial expansion, and increased glomerular basement membrane width in diabetic mice. Together, these results suggest that targeting Gq/TRPC6 signaling may have therapeutic benefits for the treatment of glomerular diseases.
- [Show abstract] [Hide abstract] ABSTRACT: Despite the importance of juxtaglomerular cell recruitment in the pathophysiology of cardiovascular diseases, the mechanisms that underlie renin production under conditions of chronic stimulation remain elusive. We have previously shown that CD44+ mesenchymal-like cells (CD44+ cells) exist in the adult kidney. Under chronic sodium deprivation, these cells are recruited to the juxtaglomerular area and differentiate to new renin-expressing cells. Given the proximity of macula densa to the juxtaglomerular area and the importance of macula densa released prostanoids in renin synthesis and release, we hypothesized that chronic sodium deprivation induces macula densa release of prostanoids, stimulating renal CD44+ cell activation and differentiation. CD44+ cells were isolated from adult kidneys and cocultured with the macula densa cell line, MMDD1, in normal or low-sodium medium. Low sodium stimulated prostaglandin E2 production by MMDD1 and induced migration of CD44+ cells. These effects were inhibited by addition of a cyclooxygenase 2 inhibitor (NS398) or an E-prostanoid receptor 4 antagonist (AH23848) to MMDD1 or CD44+ cells, respectively. Addition of prostaglandin E2 to CD44+ cells increased cell migration and induced renin expression. In vivo activation of renal CD44+ cells during juxtaglomerular recruitment was attenuated in wild-type mice subjected to salt restriction in the presence of cyclooxygenase 2 inhibitor rofecoxib. Similar results were observed in E-prostanoid receptor 4 knockout mice subjected to salt restriction. These results show that the prostaglandin E2/E-prostanoid receptor 4 pathway plays a key role in the activation of renal CD44+ mesenchymal stromal cell-like cells during conditions of juxtaglomerular recruitment; highlighting the importance of this pathway as a key regulatory mechanism of juxtaglomerular recruitment. © 2015 American Heart Association, Inc.
- [Show abstract] [Hide abstract] ABSTRACT: Rationale: Cardiac progenitor cells (CPCs) are thought to differentiate into the major cell types of the heart: cardiomyocytes, smooth muscle cells, and endothelial cells. We have recently identified ABI family, member 3 (NESH) binding protein (Abi3bp) as a protein important for mesenchymal stem cell biology. Because CPCs share several characteristics with mesenchymal stem cells, we hypothesized that Abi3bp would similarly affect CPC differentiation and proliferation. Objective: To determine whether Abi3bp regulates CPC proliferation and differentiation. Methods and results: In vivo, genetic ablation of the Abi3bp gene inhibited CPC differentiation, whereas CPC number and proliferative capacity were increased. This correlated with adverse recovery after myocardial infarction. In vitro, CPCs, either isolated from Abi3bp knockout mice or expressing an Abi3bp shRNA construct, displayed a higher proliferative capacity and, under differentiating conditions, reduced expression of both early and late cardiomyocyte markers. Abi3bp controlled CPC differentiation via integrin-β1, protein kinase C-ζ, and v-akt murine thymoma viral oncogene homolog. Conclusions: We have identified Abi3bp as a protein important for CPC differentiation and proliferation.
- [Show abstract] [Hide abstract] ABSTRACT: In a wide array of kidney diseases, type 1 angiotensin (AT1) receptors are present on the immune cells that infiltrate the renal interstitium. Here, we examined the actions of AT1 receptors on macrophages in progressive renal fibrosis and found that macrophage-specific AT1 receptor deficiency exacerbates kidney fibrosis induced by unilateral ureteral obstruction (UUO). Macrophages isolated from obstructed kidneys of mice lacking AT1 receptors solely on macrophages had heightened expression of proinflammatory M1 cytokines, including IL-1. Evaluation of isolated AT1 receptor-deficient macrophages confirmed the propensity of these cells to produce exaggerated levels of M1 cytokines, which led to more severe renal epithelial cell damage via IL-1 receptor activation in coculture compared with WT macrophages. A murine kidney crosstransplantation concomitant with UUO model revealed that augmentation of renal fibrosis instigated by AT1 receptor-deficient macrophages is mediated by IL-1 receptor stimulation in the kidney. This study indicates that a key role of AT1 receptors on macrophages is to protect the kidney from fibrosis by limiting activation of IL-1 receptors in the kidney.
- [Show abstract] [Hide abstract] ABSTRACT: Mesenchymal stem cells (MSCs) transplanted into injured myocardium promote repair through paracrine mechanisms. We have previously shown that MSCs overexpressing AKT1 (Akt-MSCs) exhibit enhanced properties for cardiac repair. In this study, we investigated the relevance of Abi3bp towards MSC biology. Abi3bp formed extracellular deposits with expression controlled by Akt1 and ubiquitin-mediated degradation. Abi3bp knockdown/knockout stabilized focal adhesions and promoted stress-fiber formation. Furthermore, MSCs from Abi3bp knockout mice displayed severe deficiencies in osteogenic and adipogenic differentiation. Knockout or stable knockdown of Abi3bp increased MSC and Akt-MSC proliferation, promoting S-phase entry via cyclin-d1, ERK1/2 and Src. Upon Abi3bp binding to integrin-β1 Src associated with paxillin which inhibited proliferation. In vivo, Abi3bp knockout increased MSC number and proliferation in bone marrow, lung, and liver. In summary, we have identified a novel extracellular matrix protein necessary for the switch from proliferation to differentiation in MSCs.
- [Show abstract] [Hide abstract] ABSTRACT: The renin-angiotensin-aldosterone system (RAAS) regulates BP and salt-volume homeostasis. Juxtaglomerular (JG) cells synthesize and release renin, which is the first and rate-limiting step in the RAAS. Intense pathologic stresses cause a dramatic increase in the number of renin-producing cells in the kidney, termed JG cell recruitment, but how this occurs is not fully understood. Here, we isolated renal CD44(+) mesenchymal stem cell (MSC)-like cells and found that they differentiated into JG-like renin-expressing cells both in vitro and in vivo. Sodium depletion and captopril led to activation and differentiation of these cells into renin-expressing cells in the adult kidney. In summary, CD44(+) MSC-like cells exist in the adult kidney and can differentiate into JG-like renin-producing cells under conditions that promote JG cell recruitment.
- [Show abstract] [Hide abstract] ABSTRACT: Human clinical trials using type 1 angiotensin (AT(1)) receptor antagonists indicate that angiotensin II is a critical mediator of cardiovascular and renal disease. However, recent studies have suggested that individual tissue pools of AT(1) receptors may have divergent effects on target organ damage in hypertension. We examined the role of AT(1) receptors on T lymphocytes in the pathogenesis of hypertension and its complications. Deficiency of AT(1) receptors on T cells potentiated kidney injury during hypertension with exaggerated renal expression of chemokines and enhanced accumulation of T cells in the kidney. Kidneys and purified CD4(+) T cells from "T cell knockout" mice lacking AT(1) receptors on T lymphocytes had augmented expression of Th1-associated cytokines including interferon-γ and tumor necrosis factor-α. Within T lymphocytes, the transcription factors T-bet and GATA-3 promote differentiation toward the Th1 and Th2 lineages, respectively, and AT(1) receptor-deficient CD4(+) T cells had enhanced T-bet/GATA-3 expression ratios favoring induction of the Th1 response. Inversely, mice that were unable to mount a Th1 response due to T-bet deficiency were protected from kidney injury in our hypertension model. The current studies identify an unexpected role for AT(1) receptors on T lymphocytes to protect the kidney in the setting of hypertension by favorably modulating CD4(+) T helper cell differentiation.
Dataset: Supplementary Material 2
- [Show abstract] [Hide abstract] ABSTRACT: Podocytes are highly differentiated cells that play an important role in maintaining glomerular filtration barrier integrity; a function regulated by small GTPase proteins of the Rho family. To investigate the role of Rho A in podocyte biology, we created transgenic mice expressing doxycycline-inducible constitutively active (V14 Rho) or dominant-negative Rho A (N19 Rho) in podocytes. Specific induction of either Rho A construct in podocytes caused albuminuria and foot process effacement along with disruption of the actin cytoskeleton as evidenced by decreased expression of the actin-associated protein synaptopodin. The mechanisms of these adverse effects, however, appeared to be different. Active V14 Rho enhanced actin polymerization, caused a reduction in nephrin mRNA and protein levels, promoted podocyte apoptosis, and decreased endogenous Rho A levels. In contrast, the dominant-negative N19 Rho caused a loss of podocyte stress fibers, did not alter the expression of either nephrin or Rho A, and did not cause podocyte apoptosis. Thus, our findings suggest that Rho A plays an important role in maintaining the integrity of the glomerular filtration barrier under basal conditions, but enhancement of Rho A activity above basal levels promotes podocyte injury.
Dataset: Supplementary Material 1
Dataset: Supplementary Material 3
- [Show abstract] [Hide abstract] ABSTRACT: The use of stem cells for tissue regeneration and repair is advancing both at the bench and bedside. Stem cells isolated from bone marrow are currently being tested for their therapeutic potential in a variety of clinical conditions including cardiovascular injury, kidney failure, cancer, and neurological and bone disorders. Despite the advantages, stem cell therapy is still limited by low survival, engraftment, and homing to damage area as well as inefficiencies in differentiating into fully functional tissues. Genetic engineering of mesenchymal stem cells is being explored as a means to circumvent some of these problems. This review presents the current understanding of the use of genetically engineered mesenchymal stem cells in human disease therapy with emphasis on genetic modifications aimed to improve survival, homing, angiogenesis, and heart function after myocardial infarction. Advancements in other disease areas are also discussed.