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Down-regulation of MEIS1 promotes the maturation of oxidative phosphorylation in perinatal cardiomyocytes
Abstract
Fetal cardiomyocytes shift from glycolysis to oxidative phosphorylation around the time of birth. Myeloid ecotropic viral integration site 1 (MEIS1) is a transcription factor that promotes glycolysis in hematopoietic stem cells. We reasoned that MEIS1 could have a similar role in the developing heart. We hypothesized that suppression of MEIS1 expression in fetal sheep cardiomyocytes leads to a metabolic switch as found at birth. Expression of MEIS1 was assayed in left ventricular cardiac tissue and primary cultures of cardiomyocytes from fetal (100- and 135-d gestation, term = 145 d), neonatal, and adult sheep. Cultured cells were treated with short interfering RNA (siRNA) to suppress MEIS1. Oxygen consumption rate was assessed with the Seahorse metabolic flux analyzer, and mitochondrial activity was assessed by staining cells with MitoTracker Orange. Cardiomyocyte respiratory capacity increased with advancing age concurrently with decreased expression of MEIS1. MEIS1 suppression with siRNA increased maximal oxygen consumption in fetal cells but not in postnatal cells. Mitochondrial activity was increased and expression of glycolytic genes decreased when MEIS1 expression was suppressed. Thus, we conclude that MEIS1 is a key regulator of cardiomyocyte metabolism and that the normal down-regulation of MEIS1 with age underlies a gradual switch to oxidative metabolism.-Lindgren, I. M., Drake, R. R., Chattergoon, N. N., Thornburg, K. L. Down-regulation of MEIS1 promotes the maturation of oxidative phosphorylation in perinatal cardiomyocytes.
... Meis1 has previously been found to play vital roles in cardiogenesis and heart development in zebrafish and murine [26,76], suggesting it is a conserved cardiac-specific gene across species; however, its expression level in heart changes dramatically from the embryonic stage to the adult stage, with very low level of Meis1 protein in adult heart [77]. The implication of stage-dependent Meis1 expression remains largely unknown in mammalian heart development and maintenance (Table 1). ...
... Suppression of Meis1 expression leads to increased oxygen consumption in fetal CMs, presumably mimicking the characteristics of adult stage, but no effect was found in the CMs isolated from neonatal sheep in contrast to the results by Mahmoud et al. [6], which is probably due to the difference in the nature of CMs at the postnatal stage between murine and sheep. siRNA mediated Meis1 knockdown resulted in downregulation of important metabolic genes glycolytic genes aldolase (ALDO), enolase (ENO) and post-glycolytic gene lactate dehydrogenase B (LDHB), which may underscore its role as CM metabolic regulator [77]. This observation implicates a normal downregulation of Meis1 with age to provide a switch in oxidative metabolism [77]. ...
... siRNA mediated Meis1 knockdown resulted in downregulation of important metabolic genes glycolytic genes aldolase (ALDO), enolase (ENO) and post-glycolytic gene lactate dehydrogenase B (LDHB), which may underscore its role as CM metabolic regulator [77]. This observation implicates a normal downregulation of Meis1 with age to provide a switch in oxidative metabolism [77]. ...
Regeneration of cardiomyocytes, endothelial cells and vascular smooth muscle cells (three major lineages of cardiac tissues) following myocardial infarction is the critical step to recover the function of the damaged heart. Myeloid ecotropic viral integration site 1 (Meis1) was first discovered in leukemic mice in 1995 and its biological function has been extensively studied in leukemia, hematopoiesis, the embryonic pattering of body axis, eye development and various genetic diseases, such as restless leg syndrome. It was found that Meis1 is highly associated with Hox genes and their cofactors to exert its regulatory effects on multiple intracellular signaling pathways. Recently with the advent of bioinformatics, biochemical methods and advanced genetic engineering tools, new function of Meis1 has been found to be involved in the cell cycle regulation of cardiomyocytes and endothelial cells. For example, inhibition of Meis1 expression increases the proliferative capacity of neonatal mouse cardiomyocytes, whereas overexpression of Meis1 results in the reduction in the length of cardiomyocyte proliferative window. Interestingly, downregulation of one of the circular RNAs, which acts downstream of Meis1 in the cardiomyocytes, promotes angiogenesis and restores the myocardial blood supply, thus reinforcing better regeneration of the damaged heart. It appears that Meis1 may play double roles in modulating proliferation and regeneration of cardiomyocytes and endothelial cells post-myocardial infarction. In this review, we propose to summarize the major findings of Meis1 in modulating fetal development and adult abnormalities, especially focusing on the recent discoveries of Meis1 in controlling the fate of cardiomyocytes and endothelial cells.
... Meis1. Meis1 is a transcription factor that regulates CM proliferation and is essential for cardiac development Porrello & Olson, 2014) and promotes glycolysis in haematopoietic stem cells (Lindgren et al., 2019). It has been found that Meis1 is a critical regulator of the CM cell cycle. ...
... Deletion of Meis1 allows for an extension of the proliferative window in mice after birth at P14 and can re-activate CMs to enter the cell cycle in adult mice . Interestingly in fetal sheep CMs, down-regulation of Meis1 increased mitochondrial activity and expression of oxygen consumption genes and decreased expression of glycolytic genes (Lindgren et al., 2019). ...
Mammalian cardiomyocytes undergo major maturational changes in preparation for birth and postnatal life. Immature cardiomyocytes contribute to cardiac growth via proliferation and thus the heart has the capacity to regenerate. To prepare for postnatal life, structural and metabolic changes associated with increased cardiac output and function must occur. This includes exit from the cell cycle, hypertrophic growth, mitochondrial maturation and sarcomeric protein isoform switching. However, these changes come at a price; the loss of cardiac regenerative capacity such that damage to the heart in postnatal life is permanent. This is a significant barrier in the development of new treatments for cardiac repair and contributes to heart failure. The transitional period of cardiomyocyte growth is a complex and multifaceted event. In this review, we focus on studies that have investigated this critical transition period as well as novel factors that may regulate and drive this process. We also discuss the potential use of new biomarkers for the detection of myocardial infarction and in the broader sense, cardiovascular disease. Abstract figure legend In the mammalian fetal (immature) heart, cardiomyocytes proliferate and can regenerate in a low oxygen environment. In the lead up to and after birth, major changes occur to cardiomyocytes that result in regeneration no longer being possible; however, timing of these events varies across species. Factors that regulate this cardiomyocyte transition include nutrient and oxygen availability, hormones and microRNAs. An emerging field of research is the use of biomarkers as a non‐invasive detection method for cardiovascular disease. This article is protected by copyright. All rights reserved
... The myocardium of the postnatal day 1 (P1) mouse can be completely regenerated after surgical resection of the apex of heart, this regenerative ability is lost at P7 [7,8]. Although the underlying mechanisms of the lost ability remain unknown, these including cardiac polyploidy, multi-levelled early innate immune system, "cancer risk" suppression and cardiac thyroxin signaling activation may likely be a barrier for cardiomyocyte proliferation [9][10][11][12][13]. Thus, studying the changes of myocardial regeneration ability during the neonatal-to-adult mouse heart transition may help to elucidate the mechanism of myocardium regeneration. ...
... However, this capacity is operative only during the first week after birth [7]. After which, its regenerative capability was lost and that may likely be due to the underlying mechanisms of ex utero relative hyperxia-induced DNA damage, cardiac polyploidy, multi-levelled early innate immune system, "cancer risk" suppression mechanism and cardiac thyroxin signaling activation [9][10][11][12][13]40]. Interestingly, m 6 A modification, as the most common modification in mRNA and lncRNA, is involved in a variety of biological processes [14,15]. ...
Long non-coding RNAs (lncRNAs) were reported to potentially play a regulatory role in the process of myocardial regeneration in the neonatal mouse. N6-methyladenosine (m ⁶ A) modification may play a key role in myocardial regeneration in mice and regulates a variety of biological processes through affecting the stability of lncRNAs. However, the map of m ⁶ A modification of lncRNAs in mouse cardiac development still remains unknown. We aimed to investigate the differences in the m ⁶ A status of lncRNAs during mouse cardiac development and reveal a potential role of m ⁶ A modification modulating lncRNAs in cardiac development and myocardial regeneration during cardiac development in mice. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-seq) of the heart tissue in C57BL/6 J mice at postnatal day 1 (P1), P7 and P28 were performed to produce stagewise cardiac lncRNA m ⁶ A-methylomes in a parallel timeframe with the established loss of an intrinsic cardiac regeneration capacity and early postnatal development. There were significant differences in the distribution and abundance of m ⁶ A modifications in lncRNAs in the P7 vs P1 mice. In addition, the functional role of m ⁶ A in regulating lncRNA levels was established for selected transcripts with METTL3 silencing in neonatal cardiomyocytes in vitro. Based on our MeRIP-qPCR experiment data, both lncGm15328 and lncRNA Zfp597 , that were not previously associated with cardiac regeneration, were found to be the most differently methylated at P1-P7. These two lncRNAs sponged several miRNAs which further regulated multiple mRNAs, including some of which have previously been linked with cardiac regeneration ability. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that differential m ⁶ A modifications were more enriched in functions and cellular signalling pathways related to cardiomyocyte proliferation. Our data suggested that the m ⁶ A modification on lncRNAs may play an important role in the regeneration of myocardium and cardiac development.
... Mechanistically, Meis1 regulates transcription of the CDK inhibitors p15, p16, and p21 (Mahmoud et al., 2013) and regulates cardiac metabolism. Knockdown of Meis1 in cultured CMs increased respiratory capacity and mitochondrial activity while decreasing glycolytic gene expression (Lindgren et al., 2019). ...
Pathological heart injuries such as myocardial infarction induce adverse ventricular remodeling and progression to heart failure owing to widespread cardiomyocyte death. The adult mammalian heart is terminally differentiated unlike those of lower vertebrates. Therefore, the proliferative capacity of adult cardiomyocytes is limited and insufficient to restore an injured heart. Although current therapeutic approaches can delay progressive remodeling and heart failure, difficulties with the direct replenishment of lost cardiomyocytes results in a poor long-term prognosis for patients with heart failure. However, it has been revealed that cardiac function can be improved by regulating the cell cycle or changing the cell state of cardiomyocytes by delivering specific genes or small molecules. Therefore, manipulation of cardiomyocyte plasticity can be an effective treatment for heart disease. This review summarizes the recent studies that control heart regeneration by manipulating cardiomyocyte plasticity with various approaches including differentiating pluripotent stem cells into cardiomyocytes, reprogramming cardiac fibroblasts into cardiomyocytes, and reactivating the proliferation of cardiomyocytes.
... A research found that myocardium-specific knockout of MEIS1 in neonatal mice could extend the proliferation window of cardiomyocytes and that these cardiomyocytes could re-enter the cell cycle (79). Conversely, another finding indicated that inhibiting MEIS1 expression in primary fetal and neonatal sheep cardiomyocytes resulted in the increased mitochondrial activity and decreased glycolytic genes, leading to the enhanced cardiomyocyte maturation (80). The discrepancy in MEIS1 function between mice and sheep may be related to the differences in cardiomyocytes themselves from these two species. ...
The mortality due to heart diseases remains highest in the world every year, with ischemic cardiomyopathy being the prime cause. The irreversible loss of cardiomyocytes following myocardial injury leads to compromised contractility of the remaining myocardium, adverse cardiac remodeling, and ultimately heart failure. The hearts of adult mammals can hardly regenerate after cardiac injury since adult cardiomyocytes exit the cell cycle. Nonetheless, the hearts of early neonatal mammals possess a stronger capacity for regeneration. To improve the prognosis of patients with heart failure and to find the effective therapeutic strategies for it, it is essential to promote endogenous regeneration of adult mammalian cardiomyocytes. Mitochondrial metabolism maintains normal physiological functions of the heart and compensates for heart failure. In recent decades, the focus is on the changes in myocardial energy metabolism, including glucose, fatty acid, and amino acid metabolism, in cardiac physiological and pathological states. In addition to being a source of energy, metabolites are becoming key regulators of gene expression and epigenetic patterns, which may affect heart regeneration. However, the myocardial energy metabolism during heart regeneration is majorly unknown. This review focuses on the role of energy metabolism in cardiac regeneration, intending to shed light on the strategies for manipulating heart regeneration and promoting heart repair after cardiac injury.
... It is known that during heart development significant changes occur in different aspects such as growth, cell proliferation, function, and other metabolic characteristics. Accordingly, in this study the transcriptome profiles (RNAseq) of the sheep heart were characterized in three stages: adult (non-proliferative differentiated CMs) and fetus of two gestational ages (both proliferative CMs in process of differentiation) (28). This comparative transcriptomic analysis can provide information on varying levels of expression of specific transcripts that, in turn, can be used as possible targets in cardiac regeneration strategies. ...
Adult mammalian cardiomyocytes show scarce division ability, which makes the heart ineffective in replacing lost contractile cells after ischemic cardiomyopathy. In the past decades, there have been increasing efforts in the search for novel strategies to regenerate the injured myocardium. Among them, gene therapy is one of the most promising ones, based on recent and emerging studies that support the fact that functional cardiomyocyte regeneration can be accomplished by the stimulation and enhancement of the endogenous ability of these cells to achieve cell division. This capacity can be targeted by stimulating several molecules, such as cell cycle regulators, noncoding RNAs, transcription, and metabolic factors. Therefore, the proposed target, together with the selection of the vector used, administration route, and the experimental animal model used in the development of the therapy would determine the success in the clinical field.
... Additional regulators can affect both the cell cycle and the metabolic switch in cardiomyocytes. MEIS1, a transcription factor that stimulates cell cycle activity in cardiomyocytes [216], also supports a less mature metabolic phenotype in cardiomyocytes by promoting glycolysis, while MEIS1 siRNA in fetal sheep cardiomyocytes triggers a metabolic switch from glycolysis to oxidative phosphorylation [217]. Deletion of endonuclease G, a mitochondrial enzyme that promotes apoptosis during oxidative stress, increases ROS levels, reduces proliferative capacity of cardiomyocytes in mice, and increases cardiomyocyte size, with cell cycle arrest in the G1 phase [218]. ...
Current methods to differentiate cardiomyocytes from human pluripotent stem cells (PSCs) inadequately recapitulate complete development and result in PSC-derived cardiomyocytes (PSC-CMs) with an immature or fetal-like phenotype. Embryonic and fetal development are highly dynamic periods during which the developing embryo or fetus is exposed to changing nutrient, oxygen, and hormone levels until birth. It is becoming increasingly apparent that these metabolic changes initiate developmental processes to mature cardiomyocytes. Mitochondria are central to these changes, responding to these metabolic changes and transitioning from small, fragmented mitochondria to large organelles capable of producing enough ATP to support the contractile function of the heart. These changes in mitochondria may not simply be a response to cardiomyocyte maturation; the metabolic signals that occur throughout development may actually be central to the maturation process in cardiomyocytes. Here, we review methods to enhance maturation of PSC-CMs and highlight evidence from development indicating the key roles that mitochondria play during cardiomyocyte maturation. We evaluate metabolic transitions that occur during development and how these affect molecular nutrient sensors, discuss how regulation of nutrient sensing pathways affect mitochondrial dynamics and function, and explore how changes in mitochondrial function can affect metabolite production, the cell cycle, and epigenetics to influence maturation of cardiomyocytes.
... Furthermore, overexpression of certain oncogenes has been found to increase adult CM proliferation. Meis1 (Myeloid ecotropic viral integration site 1) promotes glycolysis in hematopoietic stem cells, is upregulated in various cancers, and is naturally downregulated in the neonatal heart as CMs exit the cell cycle; fetal Meis1 suppression pushes fetal CMs from glycolysis to oxidative phosphorylation prematurely (Lindgren et al. 2019). Likewise, oncogene and NRG1 co-receptor ERBB2 overexpression in juvenile and adult mice resulted in cardiomegaly & increased CM proliferation, and transient ERBB2 induction post-MI improves adult cardiac regeneration (D'Uva et al. 2015). ...
Cardiac regeneration is an ancestral trait in vertebrates that is lost both as more recent vertebrate lineages evolved to adapt to new environments and selective pressures, and as members of certain species developmentally progress towards their adult forms. While higher vertebrates like humans and rodents resolve cardiac injury with permanent fibrosis and loss of cardiac output as adults, neonates of these same species can fully regenerate heart structure and function after injury - as can adult lower vertebrates like many teleost fish and urodele amphibians. Recent research has elucidated several broad factors hypothesized to contribute to this loss of cardiac regenerative potential both evolutionarily and developmentally: an oxygen-rich environment, vertebrate thermogenesis, a complex adaptive immune system, and cancer risk trade-offs. In this review, we discuss the evidence for these hypotheses as well as the cellular participators and molecular regulators by which they act to govern heart regeneration in vertebrates.
... With the inhibition of Meis1 expression by siRNA in cultured cardiomyocytes, the respiratory capacity and the mitochondrial activity were increased, while the expression of glycolytic genes was decreased. This also promotes cardiomyocyte proliferation [25]. Mechanically, Meis1 is a vital transcriptional regulator for cardiomyocyte proliferation, and it may be a potential target to regulate mature cardiomyocytes to reboot cell cycle and promote cardiac regeneration post-cardiac injuries. ...
Myocardial infarction leads to cardiomyocyte loss, ensuing ventricular pathological remodeling, dramatic impairment of cardiac function, and ultimately heart failure. Unfortunately, the existing therapeutical treatments cannot directly replenish the lost myocytes in the injured myocardium and the long-term prognosis of heart failure after myocardial infarction remains poor. Growing investigations have demonstrated that the adult mammalian cardiomyocytes possess very limited proliferation capacity, and that was not enough to restore the injured heart. Recently, many studies were targeting to promote cardiomyocyte proliferation via inducing cardiomyocyte cell cycle re-entry for cardiac repair after myocardial infarction. Indeed, these results showed it is a feasible way to stimulate terminally differentiated cardiomyocyte proliferation. Here, we reviewed the major mechanisms and the potential targets for stimulating mammalian adult cardiomyocyte proliferation specifically. This will provide a new therapeutic strategy for the clinical treatment of myocardial infarction by activating the endogenous regeneration.
Graphical abstract
... Chromatin immunoprecipitation and luciferase reporter assay demonstrated that MEIS1 binds to a number of cyclin-dependent kinase inhibitors including p16INK4a/p19ARF/p15INK4b as well as p21CDKN1A promoters and regulates their expression [3]. Interestingly, in a separate report, MEIS1 downregulation during the postnatal development has been linked to the metabolic shift from glycolytic to oxidative metabolism [61]. ...
Purpose of review:
This review provides an overview of the molecular mechanisms underpinning the cardiac regenerative capacity during the neonatal period and the potential targets for developing novel therapies to restore myocardial loss.
Recent findings:
We present recent advances in the understanding of the molecular mechanisms of neonatal cardiac regeneration and the implications for the development of new cardiac regenerative therapies. During the early postnatal period, several cell types and pathways are involved in cardiomyocyte proliferation including immune response, nerve signaling, extracellular matrix, mitochondria substrate utilization, gene expression, miRNAs, and cell cycle progression. The early neonatal mammalian heart has remarkable regenerative capacity, which is mediated by proliferation of endogenous cardiomyocytes, and is lost when cardiomyocytes stop dividing shortly after birth. A wide array of mechanisms that regulate this regenerative process have been proposed.
... Experiments carried out in sheep-derived cell lines showed that MEIS1, a master transcriptional regulator, positively regulates the expression of HIF-1α. Inhibition of MEIS1 in cardiomyocytes with siRNA resulted in downregulation of multiple glycolytic genes, with concomitant increases in mitochondrial activity and oxidative phosphorylation (OXPHOS; see Glossary) [8]. ...
The heart pumps blood throughout the whole life of an organism, without rest periods during which to replenish energy or detoxify. Hence, cardiomyocytes, the working units of the heart, have mechanisms to ensure constitutive production of energy and detoxification to preserve fitness and function for decades. Even more challenging, the heart must adapt to the varying conditions of the organism from fetal life to adulthood, old age, and pathological stress. Mitochondria are at the nexus of these processes by producing not only energy but also metabolites and oxidative byproducts that can activate alarm signals and be toxic to the cell. We review basic concepts about cardiac mitochondria with a focus on their remarkable adaptations, including elimination, throughout the mammalian lifetime.
... Amazingly, four 1 factors (Cdk1, Cdk4, Cyclin B1, Cyclin D1) were sufficient to drive post-mitotic cardiomyocytes through cytokinesis and improve myocardial function post-infarction 27 . Downregulation of Meis1 was shown to increase cardiomyocyte proliferation and was later found to play a role in the switch from glycolytic to oxidative metabolism 28 , a key event in the maturation of cardiomyocytes driven in large part by thyroid signaling 29 . ...
Adult mammalian cardiomyocytes exit the cell cycle during the neonatal period, commensurate with the loss of regenerative capacity in adult mammalian hearts. We established conditions for long-term culture of adult mouse cardiomyocytes that are genetically labeled with fluorescence. This technique permits reliable analyses of proliferation of pre-existing cardiomyocytes without complications from cardiomyocyte marker expression loss due to dedifferentiation or significant contribution from cardiac progenitor cell expansion and differentiation in culture. Using this system, we took a candidate gene approach to screen for fetal-specific proliferative gene programs that can induce proliferation of adult mouse cardiomyocytes. Using pooled gene delivery and subtractive gene elimination, we identified a novel functional interaction between E2f Transcription Factor 2 (E2f2) and Brain Expressed X-Linked (Bex)/Transcription elongation factor A-like (Tceal) superfamily members Bex1 and Tceal8. Specifically, Bex1 and Tceal8 both preserved cell viability during E2f2-induced cell cycle re-entry. Although Tceal8 inhibited E2f2-induced S-phase re-entry, Bex1 facilitated DNA synthesis while inhibiting cell death. In sum, our study provides a valuable method for adult cardiomyocyte proliferation research and suggests that Bex family proteins may function in modulating cell proliferation and death decisions during cardiomyocyte development and maturation.
Heart disease is the primary cause of death worldwide. Even though extensive research has been done, and many pharmacological and surgical treatments have been introduced to treat heart disease, the mortality rate still remains high. Gene therapy is widely used to understand molecular mechanisms of myocardial infarction and to treat cardiomyocyte loss. It was reported that adult cardiomyocytes proliferate at a very low rate; thus, targeting their proliferation has become a new regenerative therapeutic approach. Currently, re-activating cardiomyocyte proliferation appears to be one of the most promising methods to promote adult cardiomyocyte renewal. In this article, we highlight gene therapeutic targets of cell proliferation presently being pursued to re-activate the cell cycle of cardiomyocytes, including cell cycle regulators, transcription factors, microRNAs, signal transduction, and other contributing factors. We also summarize gene delivery vectors that have been used in cardiac research and major challenges to be overcome in the translation to the clinical approach and future directions.
The advent of methods for efficient generation and cardiac differentiation of pluripotent stem cells opened new avenues for disease modelling, drug testing, and cell therapies of the heart. However, cardiomyocytes obtained from such cells demonstrate an immature, fetal‐like phenotype that involves spontaneous contractions, irregular morphology, expression of embryonic isoforms of sarcomere components, and low level of ion channels. These and other features may affect cellular response to putative therapeutic compounds and the efficient integration into the host myocardium after in vivo delivery. Therefore, novel strategies to increase the maturity of pluripotent stem cell‐derived cardiomyocytes are of utmost importance. Several approaches have already been developed relying on molecular changes that occur during fetal and postnatal maturation of the heart, its electromechanical activity, and the cellular composition. As a better understanding of these determinants may facilitate the generation of efficient protocols for in vitro acquisition of an adult‐like phenotype by immature cardiomyocytes, this review summarizes the most important molecular factors that govern cardiomyogenesis during embryonic development, postnatal changes that trigger heart maturation, as well as protocols that are currently used to generate mature pluripotent stem cell‐derived cardiomyocytes. This article is protected by copyright. All rights reserved.
The postnatal development and maturation of the liver, the major metabolic organ, are inadequately understood. We have analyzed 52,834 single-cell transcriptomes and identified 31 cell types or states in mouse livers at postnatal days 1, 3, 7, 21, and 56. We observe unexpectedly high levels of hepatocyte heterogeneity in the developing liver and the progressive construction of the zonated metabolic functions from pericentral to periportal hepatocytes, which is orchestrated with the development of sinusoid endothelial, stellate, and Kupffer cells. Trajectory and gene regulatory analyses capture 36 transcription factors, including a circadian regulator, Bhlhe40, in programming liver development. Remarkably, we identified a special group of macrophages enriched at day 7 with a hybrid phenotype of macrophages and endothelial cells, which may regulate sinusoidal construction and Treg-cell function. This study provides a comprehensive atlas that covers all hepatic cell types and is instrumental for further dissection of liver development, metabolism, and disease.
In a prospective study, 48 fetuses were evaluated with Doppler ultrasound after 34 weeks and classified, according to the cerebroplacental ratio (CPR) and estimated fetal weight (EFW), into fetuses with normal growth and fetuses with late-onset fetal growth restriction (LO-FGR). Overexpression of miRNAs from neonatal cord blood belonging to LO-FGR fetuses, was validated by real-time PCR. In addition, functional characterization of overexpressed miRNAs was performed by analyzing overrepresented pathways, gene ontologies, and prioritization of synergistically working miRNAs. Three miRNAs: miR-25-3p, miR-185-5p and miR-132-3p, were significantly overexpressed in cord blood of LO-FGR fetuses. Pathway and gene ontology analysis revealed over-representation of certain molecular pathways associated with cardiac development and neuron death. In addition, prioritization of synergistically working miRNAs highlighted the importance of miR-185-5p and miR-25-3p in cholesterol efflux and starvation responses associated with LO-FGR phenotypes. Evaluation of miR-25-3p; miR-132-3p and miR-185-5p might serve as molecular biomarkers for the diagnosis and management of LO-FGR; improving the understanding of its influence on adult disease.
Key points:
The fetal heart relies on carbohydrates in utero and must be prepared to metabolize fatty acids after birth but the effects of compromised fetal growth on the maturation of this metabolic system are unknown. Plasma fatty-acylcarnitines are elevated in intrauterine growth restricted (IUGR) fetuses over control fetuses, indicative of impaired fatty acid metabolism in fetal organs. Fatty acid uptake and storage are not different in IUGR cardiomyocytes compared to controls. mRNA levels of genes regulating fatty acid transporter and metabolic enzymes are suppressed in the IUGR myocardium compared to controls, while protein levels remain unchanged. Mismatches in gene and protein expression, and increased circulating fatty acylcarnitines may have long term implications for offspring heart metabolism and adult health in IUGR individuals. This requires further investigation.
Abstract:
At birth, the mammalian myocardium switches from using carbohydrates as the primary energy substrate to free fatty acids as the primary fuel. Thus, a compromised switch could jeopardize normal heart function in the neonate. Placental embolization in sheep is a reliable model of intrauterine growth restriction (IUGR). It leads to suppression of both proliferation and terminal differentiation of cardiomyocytes. We hypothesized that the expression of genes regulating cardiac fatty acid metabolism would be similarly suppressed in IUGR, leading to compromised processing of lipids. Following 10 days of umbilicoplacental embolization in fetal sheep, IUGR fetuses had elevated circulating long chain fatty acylcarnitines compared to controls (C14: CTRL 0.012 ± 0.005 nmol/mL vs IUGR 0.018 ± 0.005 nmol/mL, p<0.05; C18: CTRL 0.027 ± 0.009 nmol/mol vs IUGR 0.043 ± 0.024 nmol/mol, p<0.05, n = 12 control, n = 12 IUGR) indicative of impaired fatty acid metabolism. Uptake studies using fluorescently tagged BODIPY-C12 saturated free fatty acid in live, isolated cardiomyocytes showed lipid droplet area and number were not different between control and IUGR cells. mRNA levels of sarcolemmal fatty acid transporters (CD36, FATP6), acylation enzymes (ACSL1, ACSL3), mitochondrial transporter (CPT1), ß-oxidation enzymes (LCAD, HADH, ACAT1), tricarboxylic acid cycle enzyme (IDH), esterification enzymes (PAP, DGAT) and regulator of lipid droplet formation (BSCL2) gene were all suppressed in IUGR myocardium (p<0.05). However, protein levels for these regulatory genes were not different between groups. This discordance between mRNA and protein levels in the stressed myocardium suggests an adaptive protection of key myocardial enzymes under conditions of placental insufficiency. Abstract figure. We investigated to degree to which the cardiac genes that regulate fatty acid metabolism were altered in growth restricted fetuses compared to those that grew normally. As shown by the red arrows, messenger RNA levels for the genes studied were suppressed compared to controls. However, the double headed arrows show that protein levels were unaffected. Circulating long chain fatty acylcarnitines in the fetus were elevated suggesting incomplete metabolism of free fatty acids. Whether these experimental conditions portend adverse outcomes in the postnatal period as the heart transitions to fatty acid metabolism requires further study. This article is protected by copyright. All rights reserved.
Cell proliferation and differentiation are the foundation of reproduction and growth. Mistakes in these processes may affect cell survival, or cause cell cycle dysregulation, such as tumorigenesis, birth defects and degenerative diseases, or cell death. Myeloid ecotropic viral integration site 1 (MEIS1) was initially discovered in leukemic mice. Recent research identified MEIS1 as an important transcription factor that regulates cell proliferation and differentiation during cell fate commitment. MEIS1 has a pro-proliferative effect in leukemia cells; however, its overexpression in cardiomyocytes restrains neonatal and adult cardiomyocyte proliferation. Additionally, MEIS1 has carcinogenic or tumor suppressive effects in different neoplasms. Thus, this uncertainty suggests that MEIS1 has a unique function in cell proliferation and differentiation. In this review, we summarize the primary findings of MEIS1 in regulating cell proliferation and differentiation. Correlations between MEIS1 and cell fate specification might suggest MEIS1 as a therapeutic target for diseases.
The adult mammalian cardiomyocyte has a very limited capacity to re-enter the cell cycle and advance into mitosis. Therefore, diseases characterized by lost contractile tissue usually evolve into myocardial remodeling and heart failure. Analyzing the cardiac transcriptome at different developmental stages in a large mammal closer to the human than laboratory rodents may serve to disclose positive and negative cardiomyocyte cell cycle regulators potentially targetable to induce cardiac regeneration in the clinical setting. We thus aimed at characterizing the transcriptomic profiles of the early fetal, late fetal and adult sheep heart employing RNA-seq technique and bioinformatic analysis to detect protein encoding genes that in some of the stages were turned-off, turned-on or differentially expressed. Genes earlier proposed as positive cell cycle regulators such as cyclin A, cdk2, meis2, meis3 and PCNA showed higher expression in fetal hearts and lower in AH, as expected. In contrast, genes previously proposed as cell cycle inhibitors such as meis1, p16 and sav1 tended to be higher in fetal than in adult hearts, suggesting that these genes are involved in cell processes other than cell cycle regulation. Additionally, we described Gene Ontology (GO) enrichment of different sets of genes. GO analysis revealed that differentially expressed gene sets were mainly associated with metabolic and cellular processes. The cell cycle-related genes fam64a, cdc20 and cdk1, and the metabolism-related genes pitx and adipoq showed strong differential expression between fetal and adult hearts, thus being potent candidates to be targeted in human cardiac regeneration strategies.
Introduction:
In a recent report, the American Heart Association estimated that medical costs and productivity losses of cardiovascular disease (CVD) are expected to grow from $555 billion in 2015 to $1.1 trillion in 2035. Although the burden is significant, the estimate does not include the costs of family, informal, or unpaid caregiving provided to patients with CVD. In this analysis, we estimated projections of costs of informal caregiving attributable to CVD for 2015 to 2035.
Methods:
We used data from the 2014 Health and Retirement Survey to estimate hours of informal caregiving for individuals with CVD by age/sex/race using a zero-inflated binomial model and controlling for sociodemographic factors and health conditions. Costs of informal caregiving were estimated separately for hypertension, coronary heart disease, heart failure, stroke, and other heart disease. We analyzed data from a nationally representative sample of 16 731 noninstitutionalized adults ≥54 years of age. The value of caregiving hours was monetized by the use of home health aide workers' wages. The per-person costs were multiplied by census population counts to estimate nation-level costs and to be consistent with other American Heart Association analyses of burden of CVD, and the costs were projected from 2015 through 2035, assuming that within each age/sex/racial group, CVD prevalence and caregiving hours remain constant.
Results:
The costs of informal caregiving for patients with CVD were estimated to be $61 billion in 2015 and are projected to increase to $128 billion in 2035. Costs of informal caregiving of patients with stroke constitute more than half of the total costs of CVD informal caregiving ($31 billion in 2015 and $66 billion in 2035). By age, costs are the highest among those 65 to 79 years of age in 2015 but are expected to be surpassed by costs among those ≥80 years of age by 2035. Costs of informal caregiving for patients with CVD represent an additional 11% of medical and productivity costs attributable to CVD.
Conclusions:
The burden of informal caregiving for patients with CVD is significant; accounting for these costs increases total CVD costs to $616 billion in 2015 and $1.2 trillion in 2035. These estimates have important research and policy implications, and they may be used to guide policy development to reduce the burden of CVD on patients and their caregivers.
Immediately following birth, the mammalian heart switches from generating ATP via glycolysis to β-oxidation of lipid. Coincident with this metabolic remodeling, cardiomyocyte mitosis ceases and regenerative capacity is lost. Recently, our understanding of the molecular pathways linking physiological stimuli with gene expression and phenotype changes around birth has increased, although fundamental gaps remain. This review discusses recent work that sheds light on this important area of mammalian cardiovascular development.
Fetal cardiomyocyte adaptation to low levels of oxygen in utero is incompletely understood, and is of interest as hypoxia tolerance is lost after birth, leading to vulnerability of adult cardiomyocytes. It is known that cardiac mitochondrial morphology, number and function change significantly following birth, although the underlying molecular mechanisms and physiological stimuli are undefined. Here we show that the decrease in cardiomyocyte HIF-signaling in cardiomyocytes immediately after birth acts as a physiological switch driving mitochondrial fusion and increased postnatal mitochondrial biogenesis. We also investigated mechanisms of ATP generation in embryonic cardiac mitochondria. We found that embryonic cardiac cardiomyocytes rely on both glycolysis and the tricarboxylic acid cycle to generate ATP, and that the balance between these two metabolic pathways in the heart is controlled around birth by the reduction in HIF signaling. We therefore propose that the increase in ambient oxygen encountered by the neonate at birth acts as a key physiological stimulus to cardiac mitochondrial adaptation.
Cardiomyocytes are vulnerable to hypoxia in the adult, but adapted to hypoxia in utero. Current understanding of endogenous cardiac oxygen sensing pathways is limited. Myocardial oxygen consumption is determined by regulation of energy metabolism, which shifts from glycolysis to lipid oxidation soon after birth, and is reversed in failing adult hearts, accompanying re-expression of several "fetal" genes whose role in disease phenotypes remains unknown. Here we show that hypoxia-controlled expression of the transcription factor Hand1 determines oxygen consumption by inhibition of lipid metabolism in the fetal and adult cardiomyocyte, leading to downregulation of mitochondrial energy generation. Hand1 is under direct transcriptional control by HIF1α. Transgenic mice prolonging cardiac Hand1 expression die immediately following birth, failing to activate the neonatal lipid metabolising gene expression programme. Deletion of Hand1 in embryonic cardiomyocytes results in premature expression of these genes. Using metabolic flux analysis, we show that Hand1 expression controls cardiomyocyte oxygen consumption by direct transcriptional repression of lipid metabolising genes. This leads, in turn, to increased production of lactate from glucose, decreased lipid oxidation, reduced inner mitochondrial membrane potential, and mitochondrial ATP generation. We found that this pathway is active in adult cardiomyocytes. Up-regulation of Hand1 is protective in a mouse model of myocardial ischaemia. We propose that Hand1 is part of a novel regulatory pathway linking cardiac oxygen levels with oxygen consumption. Understanding hypoxia adaptation in the fetal heart may allow development of strategies to protect cardiomyocytes vulnerable to ischaemia, for example during cardiac ischaemia or surgery.
The neonatal mammalian heart is capable of substantial regeneration following injury through cardiomyocyte proliferation. However, this regenerative capacity is lost by postnatal day 7 and the mechanisms of cardiomyocyte cell cycle arrest remain unclear. The homeodomain transcription factor Meis1 is required for normal cardiac development but its role in cardiomyocytes is unknown. Here we identify Meis1 as a critical regulator of the cardiomyocyte cell cycle. Meis1 deletion in mouse cardiomyocytes was sufficient for extension of the postnatal proliferative window of cardiomyocytes, and for re-activation of cardiomyocyte mitosis in the adult heart with no deleterious effect on cardiac function. In contrast, overexpression of Meis1 in cardiomyocytes decreased neonatal myocyte proliferation and inhibited neonatal heart regeneration. Finally, we show that Meis1 is required for transcriptional activation of the synergistic CDK inhibitors p15, p16 and p21. These results identify Meis1 as a critical transcriptional regulator of cardiomyocyte proliferation and a potential therapeutic target for heart regeneration.
The transcription factor Meis1 is preferentially expressed in hematopoietic stem cells (HSCs) and over-expressed in certain leukemias. However, the functions of Meis1 in hematopoiesis remain largely unknown. Using inducible knock-out mice, we found that Meis1 is required for the maintenance of hematopoiesis under stress and over long term while steady-state hematopoiesis was sustained in the absence of Meis1. Bone marrow cells of Meis1 deficient mice showed reduced colony formation, contained significantly fewer numbers of long- term HSCs and these Meis1-deficient HSCs exhibited loss of quiescence. Further, we found that Meis1 deletion led to the accumulation of reactive oxygen species (ROS) in HSCs and decreased expression of genes implicated in hypoxia response. Finally, ROS scavenging by N-acetyl cysteine or stabilization of hypoxia-signaling by knockdown of the VHL protein led to reversal of the effects of Meis1-deletion. Taken together, these results demonstrate that Meis1 protects and preserves HSCs by restricting oxidative metabolism.
The role of Meis1 in leukemia is well established, but its role in hematopoietic stem cells (HSCs) remains poorly understood. Previously, we showed that HSCs utilize glycolytic metabolism to meet their energy demands. However, the mechanism of regulation of HSC metabolism, and the importance of maintaining this distinct metabolic phenotype on HSC function has not been determined. More importantly, the primary function of Meis1 in HSCs remains unknown. Here we examined the effect of loss of Meis1 on HSC function and metabolism. Inducible Meis1 deletion in adult mice resulted in apoptosis, loss of HSC quiescence and failure of bone marrow repopulation following transplantation. While we previously showed that Meis1 regulates Hif-1α transcription in vitro, we demonstrate here that loss of Meis1 results in downregulation of both Hif-1α and Hif-2α in HSCs. This resulted in a shift to mitochondrial metabolism, increased reactive oxygen species (ROS) production, and apoptosis of HSCs. Finally, we demonstrate that the effect of Meis1 KO on HSCs is entirely mediated through ROS where treatment of the Meis1 KO mice with the scavenger N-acetylcystein (NAC) restored HSC quiescence and rescued HSC function. These results uncover an important transcriptional network that regulates metabolism, oxidant defense, and maintenance of HSCs.
Tri-iodo-l-thyronine (T(3)) suppresses the proliferation of near-term serum-stimulated fetal ovine cardiomyocytes in vitro. Thus, we hypothesized that T(3) is a major stimulant of cardiomyocyte maturation in vivo. We studied 3 groups of sheep fetuses on gestational days 125-130 (term ∼145 d): a T(3)-infusion group, to mimic fetal term levels (plasma T(3) levels increased from ∼0.1 to ∼1.0 ng/ml; t(1/2)∼24 h); a thyroidectomized group, to produce low thyroid hormone levels; and a vehicle-infusion group, to serve as intact controls. At 130 d of gestation, sections of left ventricular freewall were harvested, and the remaining myocardium was enzymatically dissociated. Proteins involved in cell cycle regulation (p21, cyclin D1), proliferation (ERK), and hypertrophy (mTOR) were measured in left ventricular tissue. Evidence that elevated T(3) augmented the maturation rate of cardiomyocytes included 14% increased width, 31% increase in binucleation, 39% reduction in proliferation, 150% reduction in cyclin D1 protein, and 500% increase in p21 protein. Increased expression of phospho-mTOR, ANP, and SERCA2a also suggests that T(3) promotes maturation and hypertrophy of fetal cardiomyocytes. Thyroidectomized fetuses had reduced cell cycle activity and binucleation. These findings support the hypothesis that T(3) is a prime driver of prenatal cardiomyocyte maturation.
Fetal hearts show a remarkable ability to develop under hypoxic conditions. The metabolic flexibility of fetal hearts allows sustained development under low oxygen conditions. In fact, hypoxia is critical for proper myocardial formation. Particularly, hypoxia inducible factor 1 (HIF-1) and vascular endothelial growth factor play central roles in hypoxia-dependent signaling in fetal heart formation, impacting embryonic outflow track remodeling and coronary vessel growth. Although HIF is not the only gene involved in adaptation to hypoxia, its role places it as a central figure in orchestrating events needed for adaptation to hypoxic stress. Although "normal" hypoxia (lower oxygen tension in the fetus as compared with the adult) is essential in heart formation, further abnormal hypoxia in utero adversely affects cardiogenesis. Prenatal hypoxia alters myocardial structure and causes a decline in cardiac performance. Not only are the effects of hypoxia apparent during the perinatal period, but prolonged hypoxia in utero also causes fetal programming of abnormality in the heart's development. The altered expression pattern of cardioprotective genes such as protein kinase c epsilon, heat shock protein 70, and endothelial nitric oxide synthase, likely predispose the developing heart to increased vulnerability to ischemia and reperfusion injury later in life. The events underlying the long-term changes in gene expression are not clear, but likely involve variation in epigenetic regulation.
Members of the homeobox family of transcription factors are major regulators of hematopoiesis. Overexpression of either HOXB4
or HOXA9 in primitive marrow cells enhances the expansion of hematopoietic stem cells (HSCs). However, little is known of
how expression or function of these proteins is regulated during hematopoiesis under physiological conditions. In our previous
studies we demonstrated that thrombopoietin (TPO) enhances levels of HOXB4 mRNA in primitive hematopoietic cells (K. Kirito,
N. Fox, and K. Kaushansky, Blood 102:3172-3178, 2003). To extend our studies, we investigated the effects of TPO on HOXA9 in this same cell population. Although
overall levels of the transcription factor were not affected, we found that TPO induced the nuclear import of HOXA9 both in
UT-7/TPO cells and in primitive Sca-1+/c-kit+/Gr-1− hematopoietic cells in a mitogen-activated protein kinase-dependent fashion. TPO also controlled MEIS1 expression at mRNA
levels, at least in part due to phosphatidylinositol 3-kinase activation. Collectively, TPO modulates the function of HOXA9
by leading to its nuclear translocation, likely mediated by effects on its partner protein MEIS1, and potentially due to two
newly identified nuclear localization signals. Our data suggest that TPO controls HSC development through the regulation of
multiple members of the Hox family of transcription factors through multiple mechanisms.
Low birth weight is a risk factor for coronary heart disease. It is uncertain how postnatal growth affects disease risk.
We studied 8760 people born in Helsinki from 1934 through 1944. Childhood growth had been recorded. A total of 357 men and 87 women had been admitted to the hospital with coronary heart disease or had died from the disease. Coronary risk factors were measured in a subset of 2003 people.
The mean body size of children who had coronary events as adults was below average at birth. At two years of age the children were thin; subsequently, their body-mass index (BMI) increased relative to that of other children and had reached average values by 11 years of age. In simultaneous regressions, the hazard ratios associated with a 1 SD increase in BMI were 0.76 (95 percent confidence interval, 0.66 to 0.87; P<0.001) at 2 years and 1.14 (95 percent confidence interval, 1.00 to 1.31; P=0.05) at 11 years among the boys. The corresponding figures for the girls were 0.62 (95 percent confidence interval, 0.46 to 0.82; P=0.001) and 1.35 (95 percent confidence interval, 1.02 to 1.78; P=0.04). Low BMI at 2 years of age and increased BMI from 2 to 11 years of age were also associated with raised fasting insulin concentrations (P<0.001 for both).
On average, adults who had a coronary event had been small at birth and thin at two years of age and thereafter put on weight rapidly. This pattern of growth during childhood was associated with insulin resistance in later life. The risk of coronary events was more strongly related to the tempo of childhood gain in BMI than to the BMI attained at any particular age.
The generation of new myocytes is an essential process of in utero heart growth. Most, or all, cardiac myocytes lose their capacity for proliferation during the perinatal period through the process of terminal differentiation. An increasing number of studies focus on how experimental interventions affect cardiac myocyte growth in the fetal sheep. Nevertheless, fundamental questions about normal growth of the fetal heart remain unanswered. In this study, we determined that during the last third of gestation the hearts of fetal sheep grew primarily by four processes. 1) Myocyte proliferation contributed substantially to daily cardiac mass gain, and the number of cardiac myocytes continued to increase to term. 2) The (hitherto unrecognized) contribution to cardiac growth by the increase in myocyte size associated with the transition from mononucleation to binucleation (terminal differentiation) became considerable from approximately 115 days of gestational age (dGA) until term (145dGA). Because binucleation became the more frequent outcome of myocyte cell cycle activity after approximately 115dGA, the number of binucleated myocytes increased at the expense of the number of mononucleated myocytes. Both the interval between nuclear divisions and the duration of cell cycle activity in myocytes decreased substantially during this same period. Finally, cardiac growth was in part due to enlargement of 3) mononucleated and 4) binucleated myocytes, which grew in cross-sectional diameter but not length during the last third of gestation. These data on normal cardiac growth may enable a more detailed understanding of the consequences of experimental and pathological interventions in prenatal life.
Cardiogenesis within embryos or associated with heart repair requires stem cell differentiation into energetically competent, contracting cardiomyocytes. While it is widely accepted that the coordination of genetic circuits with developmental bioenergetics is critical to phenotype specification, the metabolic mechanisms that drive cardiac transformation are largely unknown. Here, we aim to define the energetic requirements for and the metabolic microenvironment needed to support the cardiac differentiation of embryonic stem cells. We demonstrate that anaerobic glycolytic metabolism, while sufficient for embryonic stem cell homeostasis, must be transformed into the more efficient mitochondrial oxidative metabolism to secure cardiac specification and excitation-contraction coupling. This energetic switch was programmed by rearrangement of the metabolic transcriptome that encodes components of glycolysis, fatty acid oxidation, the Krebs cycle, and the electron transport chain. Modifying the copy number of regulators of mitochondrial fusion and fission resulted in mitochondrial maturation and network expansion, which in turn provided an energetic continuum to supply nascent sarcomeres. Disrupting respiratory chain function prevented mitochondrial organization and compromised the energetic infrastructure, causing deficient sarcomerogenesis and contractile malfunction. Thus, establishment of the mitochondrial system and engagement of oxidative metabolism are prerequisites for the differentiation of stem cells into a functional cardiac phenotype. Mitochondria-dependent energetic circuits are thus critical regulators of de novo cardiogenesis and targets for heart regeneration.
Two different methods of presenting quantitative gene expression exist: absolute and relative quantification. Absolute quantification calculates the copy number of the gene usually by relating the PCR signal to a standard curve. Relative gene expression presents the data of the gene of interest relative to some calibrator or internal control gene. A widely used method to present relative gene expression is the comparative C(T) method also referred to as the 2 (-DeltaDeltaC(T)) method. This protocol provides an overview of the comparative C(T) method for quantitative gene expression studies. Also presented here are various examples to present quantitative gene expression data using this method.
Significance
Engineered cardiac muscle can be used to promote the structural and functional maturation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs). However, previous studies have not yet produced cardiac tissues with metabolic and proliferative maturation. Here, we develop a 96-well screening platform and screen for cardiac maturation conditions in engineered cardiac muscle. We found that simulating the postnatal switch in metabolic substrates from carbohydrates to fatty acids promoted a switch in metabolism, DNA damage response, and cell cycle arrest in hPSC-CM. Our study shows that this mechanism can be harnessed to enhance the maturation of human hPSC-CM and cardiac tissues, which has major implications for stem cell sciences, drug discovery, and regenerative medicine.
Immature contractile cardiomyocytes proliferate to rapidly increase cell number, establishing cardiomyocyte endowment in the perinatal period. Developmental changes in cellular maturation, size and attrition further contribute to cardiac anatomy. These physiological processes occur concomitant with a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. There are complex interactions between endocrine, hemodynamic and nutritional regulators of cardiac development. Birth has been long assumed to be the trigger for major differences between the fetal and postnatal cardiomyocyte growth patterns, but investigations in normally growing sheep and rodents suggest this may not be entirely true; in sheep, these differences are initiated before birth, while in rodents they occur after birth. The aim of this review is to draw together our understanding of the temporal regulation of these signals and cardiomyocyte responses relative to birth. Further, we consider how these dynamics are altered in stressed and suboptimal intrauterine environments.
Studies in altricial rodents attribute dramatic changes in perinatal cardiomyocyte growth, maturation, and attrition to stimuli associated with birth. Our purpose was to determine whether birth is a critical trigger controlling perinatal cardiomyocyte growth, maturation and attrition in a precocial large mammal, sheep (Ovis aries). Hearts from 0-61 d postnatal lambs were dissected or enzymatically dissociated. Cardiomyocytes were measured by micromorphometry, cell cycle activity assessed by immunohistochemistry, and nuclear number counted after DNA staining. Integration of this new data with published fetal data from our laboratory demonstrate that a newly appreciated >30% decrease in myocyte number occurred in the last 10 d of gestation (P < 0.0005) concomitant with an increase in cleaved poly (ADP-ribose) polymerase 1 (P < 0.05), indicative of apoptosis. Bisegmental linear regressions show that most changes in myocyte growth kinetics occur before birth (median = 15.2 d; P < 0.05). Right ventricular but not left ventricular cell number increases in the neonate, by 68% between birth and 60 d postnatal (P = 0.028). We conclude that in sheep few developmental changes in cardiomyocytes result from birth, excepting the different postnatal degrees of free wall hypertrophy between the ventricles. Furthermore, myocyte number is reduced in both ventricles immediately before term, but proliferation increases myocyte number in the neonatal right ventricle.-Jonker, S. S., Louey, S., Giraud, G. D., Thornburg, K. L., Faber, J. J. Timing of cardiomyocyte growth, maturation, and attrition in perinatal sheep.
© FASEB.
Significance:
Metabolism-dependent generation of reactive oxygen species (ROS) and associated oxidative damage have been traditionally linked to impaired homeostasis and cellular death. Beyond the adverse effects of ROS accumulation, increasing evidence implicates redox status as a regulator of vital cellular processes.
Recent advances:
Emerging studies on the molecular mechanisms guiding stem cell fate decisions indicate a role for energy metabolism in regulating the fundamental ability of maintaining stemness versus undergoing lineage-specific differentiation. Stem cells have evolved protective metabolic phenotypes to minimize reactive oxygen generation through oxidative metabolism and support antioxidant scavenging through glycolysis and the pentose phosphate pathway.
Critical issues:
While the dynamics in ROS generation has been correlated with stem cell function, the intimate mechanisms by which energy metabolism regulates ROS to impact cellular fate remain to be deciphered.
Future directions:
Decoding the linkage between nutrient sensing, energy metabolism, and ROS in regulating cell fate decisions would offer a redox-dependent strategy to regulate stemness and lineage specification.
Rapidly proliferating and neoplastically transformed cells generate the energy required to support rapid cell division by increasing glycolysis and decreasing flux through the oxidative phosphorylation pathway (OXPHOS), usually without alterations in mitochondrial function. In contrast, little is known of the metabolic alterations, if any, which occur in cells harboring mutations that prime their neoplastic transformation. To address this question, we used a Pten-deficient mouse model to examine thyroid cells where a mild hyperplasia progresses slowly to follicular thyroid carcinoma. Using this model, we report that constitutive PI3K activation caused by PTEN deficiency in non-transformed thyrocytes results in a global down-regulation of Krebs cycle and OXPHOS gene expression, defective mitochondria, reduced respiration and an enhancement in compensatory glycolysis. We found that this process does not involve any of the pathways classically associated with the Warburg effect. Moreover, this process was independent of proliferation but contributed directly to thyroid hyperplasia. Our findings define a novel metabolic switch to glycolysis driven by PI3K-dependent AMPK inactivation with a consequent repression in the expression of key metabolic transcription regulators.
Significance:
The effect of redox signaling on hematopoietic stem cell (HSC) function is not clearly understood.
Recent advances:
A growing body of evidence suggests that adult HSCs reside in the hypoxic bone marrow microenvironment or niche during homeostasis. It was recently shown that primitive HSCs in the bone marrow prefer to utilize anaerobic glycolysis to meet their energy demands and have lower rates of oxygen consumption and lower ATP levels. Hypoxia-inducible factor-α (Hif-1α) is a master regulator of cellular metabolism. With hundreds of downstream target genes and crosstalk with other signaling pathways, it regulates various aspects of metabolism from the oxidative stress response to glycolysis and mitochondrial respiration. Hif-1α is highly expressed in HSCs, where it regulates their function and metabolic phenotype. However, the regulation of Hif-1α in HSCs is not entirely understood. The homeobox transcription factor myeloid ecotropic viral integration site 1 (Meis1) is expressed in the most primitive HSCs populations, and it is required for primitive hematopoiesis. Recent reports suggest that Meis1 is required for normal adult HSC function by regulating the metabolism and redox state of HSCs transcriptionally through Hif-1α and Hif-2α.
Critical issues:
Given the profound effect of redox status on HSC function, it is critical to fully characterize the intrinsic, and microenvironment-related mechanisms of metabolic and redox regulation in HSCs.
Future directions:
Future studies will be needed to elucidate the link between HSC metabolism and HSC fates, including quiescence, self-renewal, differentiation, apoptosis, and migration.
Plasticity in energy metabolism allows stem cells to match the divergent demands of self-renewal and lineage specification. Beyond a role in energetic support, new evidence implicates nutrient-responsive metabolites as mediators of crosstalk between metabolic flux, cellular signaling, and epigenetic regulation of cell fate. Stem cell metabolism also offers a potential target for controlling tissue homeostasis and regeneration in aging and disease. In this Perspective, we cover recent progress establishing an emerging relationship between stem cell metabolism and cell fate control.
The "fetal origin of adult disease Hypothesis" originally described by Barker et al. identified the relationship between impaired in utero growth and adult cardiovascular disease risk and death. Since then, numerous clinical and experimental studies have confirmed that early developmental influences can lead to cardiovascular, pulmonary, metabolic, and psychological diseases during adulthood with and without alterations in birth weight. This so called "fetal programming" includes developmental disruption, immediate adaptation, or predictive adaptation and can lead to epigenetic changes affecting a specific organ or overall health. The intrauterine environment is dramatically impacted by the overall maternal health. Both premature birth or low birth weight can result from a variety of maternal conditions including undernutrition or dysnutrition, metabolic diseases, chronic maternal stresses induced by infections and inflammation, as well as hypercholesterolemia and smoking. Numerous animal studies have supported the importance of both maternal health and maternal environment on the long term outcomes of the offspring. With increasing rates of obesity and diabetes and survival of preterm infants born at early gestational ages, the need to elucidate mechanisms responsible for programming of adult cardiovascular disease is essential for the treatment of upcoming generations.
Bone marrow transplantation is the primary therapy for numerous hematopoietic disorders. The efficiency of bone marrow transplantation depends on the function of long-term hematopoietic stem cells (LT-HSCs), which is markedly influenced by their hypoxic niche. Survival in this low-oxygen microenvironment requires significant metabolic adaptation. Here, we show that LT-HSCs utilize glycolysis instead of mitochondrial oxidative phosphorylation to meet their energy demands. We used flow cytometry to identify a unique low mitochondrial activity/glycolysis-dependent subpopulation that houses the majority of hematopoietic progenitors and LT-HSCs. Finally, we demonstrate that Meis1 and Hif-1alpha are markedly enriched in LT-HSCs and that Meis1 regulates HSC metabolism through transcriptional activation of Hif-1alpha. These findings reveal an important transcriptional network that regulates HSC metabolism.
Dramatic maturational changes occur in cardiac energy metabolism during cardiac development, differentiation, and postnatal growth. These changes in energy metabolism have important impacts on the ability of the cardiomyocyte to proliferate during early cardiac development, as well as when cardiomyocytes terminally differentiate during later development. During early cardiac development, glycolysis is a major source of energy for proliferating cardiomyocytes. As cardiomyocytes mature and become terminally differentiated, mitochondrial oxidative capacity increases, with fatty acid beta-oxidation becoming a major source of energy for the heart. The increase in mitochondrial oxidative capacity seems to coincide with a decrease in the proliferative ability of the cardiomyocyte. The switch from glycolysis to mitochondrial oxidative metabolism during cardiac development includes both alterations in the transcriptional control and acute alterations in the control of each pathway. Interestingly, if a hypertrophic stress is placed on the adult heart, cardiac energy metabolism switches to a more fetal phenotype, which includes an increase in glycolysis and decrease in mitochondrial fatty acid beta-oxidation. In this article, we review the impact of alterations in energy substrate metabolism on cardiomyocyte proliferation, differentiation, and postnatal maturation.
According to many experts in neonatal nutrition, the goal for nutrition of the preterm infant should be to achieve a postnatal growth rate approximating that of the normal fetus of the same gestational age. Unfortunately, most preterm infants, especially those born very preterm with extremely low birth weight, are not fed sufficient amounts of nutrients to produce normal fetal rates of growth and, as a result, end up growth-restricted during their hospital period after birth. Growth restriction is a significant problem, as numerous studies have shown definitively that undernutrition, especially of protein, at critical stages of development produces long-term short stature, organ growth failure, and both neuronal deficits of number and dendritic connections as well as later behavioral and cognitive outcomes. Furthermore, clinical follow-up studies have shown that among infants fed formulas, the nutrient content of the formula is directly and positively related to mental and motor outcomes later in life. Nutritional requirements do not stop at birth. Thus, delaying nutrition after birth ‘until the infant is stable’ ignores the fundamental point that without nutrition starting immediately after birth, the infant enters a catabolic condition, and catabolism does not contribute to normal development and growth. Oxygen is necessary for all metabolic processes. Recent trends to limit oxygen supply to prevent oxygen toxicity have the potential, particularly when the blood hemoglobin concentration falls to less than 8 g/dl, to develop growth failure. Glucose should be provided at 6–8 mg/min/kg as soon after birth as possible and adjusted according to frequent measurements of plasma glucose to achieve and maintain concentrations >45 mg/dl but
The authors examined postnatal circulatory changes in three groups of lambs at 1,4 and 6 weeks after birth. Five lambs in each group were instrumented chronically with electromagnetic flow transducers on the ascending aorta and catheters in the aorta, left ventricle, left atrium, and superior vena cava. After recovery for 2 days, measurements were made daily at rest and during intravenous infusion of 0.9% NaCl solution (25 ml/kg per min) for 2 minutes into the superior vena cava to increase mean left atrial pressure to about 25 mm Hg. Resting heart rate fell progressively, from 210 ± 27/min (mean ± SD) at 1 week to 141 ± 26 at 6 weeks, whereas arterial pressure increased from 71 ± 8 mm Hg during the 4th week to 80 ± 10 at 6 weeks. Aortic flow per kilogram body weight fell from the high level of 425 ± 86 ml during the 1st week to 147 ± 28 ml by the 6th week. This reduction in cardiac output probably is associated with alterations of oxygen consumption per kilogram body weight in the neonatal period. During infusion of saline, left ventricular output increased by a modest 35% over control levels in the 1-week-old lambs, but rose more (58%) in the other two groups. The maximal cardiac output achieved during saline infusion was greater during isoproterenol and less after propranolol administration in each group. The authors therefore, suggest that since the neonatal lamb has a high resting cardiac output it has less capacity to respond to volume loading than does the older lamb.
Right and left ventricular function were investigated in 12 fetal lambs (127-140 days gestation) instrumented with electromagnetic flow sensors on the ascending aorta and the main pulmonary artery, and with vascular catheters. Nine fetuses were equipped with a postductal aortic occluder and the trachea was cannulated in eight. Control arterial blood values were pH 7.36 +/- 0.02 (SD), PCO2 49.3 +/- 2.3 torr, PO2 18.4 +/- 1.7 torr, and hematocrit 37.3 +/- 4.4%. Biventricular function curves relating stroke volume to mean right and left atrial pressure were generated by rapid withdrawal and reinfusion of fetal blood. Both function curves were composed of steep ascending and plateau limbs that intersected at a breakpoint. Stroke volumes at the breakpoints were 0.94 +/- 0.19 ml.kg-1 and 0.63 +/- 0.15 ml.kg-1 for right and left ventricle, respectively (p less than 0.001). During postductal aortic occlusion, arterial pressure increased by 19.3 +/- 7.9 torr while right ventricular stroke volume decreased by approximately 48% and left ventricular stroke volume decreased by approximately 9%. In utero ventilation increased arterial pressure, heart rate, PO2, and oxygen content. Right atrial pressure increased from 3.9 +/- 1.3 to 5.8 +/- 2.9 torr (p less than 0.05); left atrial pressure from 3.5 +/- 1.5 to 10.0 +/- 4.4 torr (p less than 0.05). Aortic flow nearly doubled (112 +/- 29 to 211 +/- 35 ml.min-1.kg-1) (p less than 0.05), and the left ventricular function curve shifted upward. The right ventricular function curve was shifted downward during ventilation. We conclude that the fetal ventricles differ significantly in their outputs, response to changes in arterial pressure, and to the onset of in utero ventilation.
Muscle fiber groups from fetal, neonatal, infant, and adult rhesus monkeys (Macaca mulatta) were incubated in glycylglycine and bicarbonate buffered media plus glucose-C14. Results obtained with these two media were similar. The metabolic data were calculated with noncollagenous nitrogen as a reference base. Under aerobic conditions the QO2 and CO2 productions were higher at 89 to 90 days fetal age, similar at 120 to 129 days, and lower at 150 to 160 days than those of adult muscle. Glucose uptake was higher at 89 to 90 days and 120 to 129 days fetal age than that of the adult series. Variations in the above parameters demonstrate that results on fetal metabolism must be reported for specific gestational periods. Lactate and lactate-C14 productions were higher in all three fetal series, and pyruvate and pyruvate-C14 productions were higher in the earlier fetal series than in those of the adult. The sum of C14 activities appearing in lactate, pyruvate, and CO2 was higher in rapidly growing muscle than in adult muscle. These data suggest that aerobic glycolysis is more active in fetal and neonatal than in adult muscle. Birth did not cause a significant change in any metabolic parameter. The relative increases, under hypoxic conditions, in glucose uptake and lactate and lactate-C14 productions in fetal compared with the increases in adult muscle suggest that the glycolytic pathway of fetal muscle does not respond more effectively to hypoxia.
1. Changes in the composition of foetal and maternal blood have been followed during the last 5-10 days of gestation and throughout parturition in the conscious sheep.2. Catheters were placed in the foetal inferior vena cava through a tarsal vein and in a maternal uterine vein in ten ewes under sodium pentobarbitone anaesthesia. In four of the foetuses blood pressure and heart rates were recorded before and during parturition from an arterial catheter.3. Foetal blood gas tensions, pH and PCV remained stable during the latter part of gestation and throughout labour until 15 min before delivery, when P(O) (2) and pH fell while PCV and P(CO) (2) rose in about 50% of the foetuses examined.4. Metabolite levels were also relatively stable at the end of gestation. Plasma glucose in both maternal and foetal blood rose during the hour before birth, while foetal plasma lactate was elevated as early as 4 hr before birth and was unrelated to any maternal changes. Foetal fructose levels were maintained until after delivery.5. Rises in foetal blood pressure before birth were associated with uterine contractions. Foetal heart rate changes during labour varied in different individuals. The heart rate either fell gradually before birth or there was little change until a sudden drop at delivery.6. The most striking changes in the lamb occurred at, or a few minutes after, birth; pH and P(O) (2) fell, P(CO) (2) and PCV rose, and bradycardia at delivery was succeeded by prolonged tachycardia. There were marked increases in plasma glucose and lactic acid at this time.7. P(O) (2) rose rapidly once respiration was established, while pH and P(CO) (2) levels were restored within (1/2)-1 hr. Plasma FFA levels rose rapidly in the lambs 10-30 min after birth and remained high, while plasma glucose, lactate and fructose concentrations declined slowly in the 1-2 hr after birth, although suckling raised the plasma glucose levels. Considerable individual variation in the metabolite levels was found in both ewes and lambs.8. In the majority of ewes delivery was associated with an abrupt maternal hyperglycaemia, with a much smaller rise in lactate and virtually no change in maternal blood gases or pH.9. These findings are discussed in relation to existing information on new-born lambs and the human infant during birth.
Circulatory changes at birth have a profound influence on the physiology of the circulation in normal infants and those with congenital heart disease. Since the concept that cardiac defects are fixed entities is being superseded by an appreciation of the changing nature of physiologic disturbances and their clinical consequence, the course and distribution of the fetal circulation with the influences of the major changes at birth, including changes in pulmonary vascular resistance, and closure of the ductus arteriosus and foramen ovale, require study. This lecture traces these and other changes and discusses their influences on congenital heart disease.
My colleagues and I compared the biochemical status and rates of growth of three groups of preterm infants: one group was fed milk obtained early from mothers of preterm infants; one group received milk produced during the mature stage of lactation by mothers of term infants; and one group received a whey-based infant formula. Sixty healthy preterm infants with birth weights of 1600 g or less were randomly assigned to one of the three feedings groups. The 20 infants in each group were followed until they reached a weight of 1800 g. The mean (+/- S.E.M.) number of days required to regain birth weight was similar for infants receiving the formula (10.3 +/- 0.8) and those receiving milk from mothers of preterm infants (11.4 +/- 0.8); both were significantly less than the number (18.8 +/- 1.7) for infants receiving milk from mothers of term infants (P less than 0.001). Subsequent rates of weight gain were greater for the groups receiving formula (27.0 +/- 0.8 g per day) and milk from mothers of preterm infants (23.7 +/- 1.1) than for the group receiving milk from mothers of term infants (15.8 +/- 0.8) (P less than 0.001). Similarly, the average increments in crown-to-heel length and in the head circumference were significantly greater for the groups given formula and milk from mothers of preterm infants (P less than 0.005 and P less than 0.001, respectively). These data indicate that feeding with either milk from mothers of preterm infants or a whey-based infant formula results in more appropriate growth in preterm infants than feeding with milk from mothers of term infants.
Lactic acid represents a major exogenous nutrient for the developing fetal lamb in utero. Our study was undertaken (a) to quantitate the net consumption of lactate by the fetus, (b) to quantitate the net lactate production and metabolism by the placenta, and (c) to compare the net fetal lactate consumption with fetal lactate use, measured simultaneously with radioactive tracers. 14 pregnant sheep were prepared with catheters in the maternal femoral artery and uterine vein and in the fetal aorta and umbilical vein. By simultaneous application of the Fick principle to the uterine and umbilical circulations, placental glucose consumption and placental lactate production were rapid, averaging 39.8 +/- 5.1 and 11.8 +/- 0.7 mg.min-1. Net lactate umbilical uptake averaged 1.95 +/- 0.16 mg-1.kg.min-1. During infusion of L-[14C(U)]lactate, fetal lactate turnover was much more rapid, averaging 6.5 +/- 0.8 mg.kg-1.min-1, and lactate utilization within the anatomic fetus was 5.9 +/- 0.7 mg.kg-1.min-1. During infusion of tracer glucose, endogenous fetal lactate production from glucose and nonglucose substrates averaged 3.0 and 1.5 mg.kg-1.min-1, respectively. The present studies have quantitated under well oxygenated, steady-state conditions, the rapid placental metabolism and production of lactate, the net fetal consumption of lactate, and the rapid endogenous fetal lactate production from glucose and nonglucose substrates.
We measured blood flow to the myocardium of the left ventricular free wall, and blood glucose, lactate, pyruvate, and oxygen concentrations simultaneously in the aorta and coronary sinus 13 times in seven previously instrumented newborn sheep, 4 to 25 days after birth. We calculated arteriovenous difference and consumption of oxygen, glucose, lactate, and pyruvate by the newborn myocardium. Results were compared with recently obtained measurements in the myocardium of fetal and adult sheep (6). Myocardial consumption of oxygen in the newborn (577 +/- 38 microM.min-1.100 g LV-1) was higher than in either the fetuses or the adults. This was associated with a greater myocardial blood flow (201 +/- 21 mm.min-1.100 g LV-1) in the newborns. However, the increased myocardial oxygen consumption in the newborns was commensurate with their increased cardiac work as compared with both the fetuses and adults. Although there is an abrupt postnatal increase in arterial glucose concentration, there was no significant difference in either the myocardial consumption of glucose or the contribution of glucose to the total myocardial energy supply among fetal, newborn or adult sheep. Postnatal decreases in myocardial consumption of lactate and pyruvate are not compensated for by an increase in glucose consumption. In newborn sheep, carbohydrates including glucose, lactate, and pyruvate supply the substrate for no more than approximately one-fourth of the total myocardial energy demands (carbohydrate/oxygen quotient was 0.26).
1. Baroreflex activity was assessed in nine fetal, four new-born and six adult sheep, using the relationship between heart period and arterial pressure. Arterial pressure was raised either by inflating a balloon in the dorsal aorta, by rapid intravenous injection of phenylephrine or methoxamine, or by slow intravenous infusion of methoxamine. 2. In the fetus the three methods gave different estimates of baroreflex sensitivity (balloon, 1.3 +/- 0.7 mmHg; injections, 5.4 +/- 0.5 msec mmHg; infusions, 7.2 +/- 0.9 msec/mmHg) whereas they were comparable in the new-born and adult. 3. Estimates of baroreflex sensitivity were significantly lower in the fetus and new-born than in the adult whichever method was used. 4. In the fetus there were variable changes of heart period when arterial pressure was raised by inflation of the balloon. The responses to injection of phenylephrine or methoxamine were also variable. 5. This variability was not associated with changes in electrocortical activity, the presence or absence of breathing movements or limb movements, or changes of blood gases. 6. In the fetus the heart period frequently did not change unless the arterial pressure was raised by approximately 15 mmHg (to 61 mmHg), suggesting that the threshold for baroreflex activity is above the normal range of arterial pressure before birth.
We measured myocardial oxygen, glucose, lactate, and pyruvate consumption in chronically instrumented fetal and adult sheep. Although ascending aortic blood concentration of oxygen was significantly lower in fetuses, myocardial consumption of oxygen was similar in the two groups. This was accomplished by a significantly greater myocardial blood flow in the fetuses. Although ascending aortic blood glucose concentration was significantly lower in fetuses, myocardial consumption of glucose was significantly greater in fetuses. Complete oxidative combustion of all glucose consumed by the fetal heart would supply only one-third of myocardial energy demands, as measured by oxygen consumption. Ascending aortic blood concentration of lactate was similar in fetuses and adults, but myocardial consumption of lactate was significantly greater in fetuses. Complete oxidative combustion of all lactate consumed by fetal hearts would supply almost 60% of myocardial energy demands. Small, but significant, amounts of pyruvate are consumed by both fetuses and adults. Our data indicate that fetal lamb myocardium requires substrates other than glucose alone. The large amount of lactate consumed indicates that there is oxidative metabolism in addition to glycolysis and that lactate is of equal, or perhaps greater, importance as a myocardial energy substrate.
Cardiomyocyte DNA synthesis and binucleation indexes were determined during murine development. Cardiomyocyte DNA synthesis occurred in two temporally distinct phases. The first phase occurred during fetal life and was associated exclusively with cardiomyocyte proliferation. The second phase occurred during early neonatal life and was associated with binucleation. Collectively, these results suggest that cardiomyocyte reduplication ceases during late fetal life. Northern and Western blot analyses identified several candidate genes that were differentially expressed during the reduplicative and binucleation phases of cardiomyocyte growth.
Increasingly, neonatologists are realizing that current feeding practices for preterm infants are insufficient to produce reasonable rates of growth, and earlier and larger quantities of both parenteral and enteral feeding should be provided to these infants. Unfortunately, there is very little outcome data to recommend any particular nutritional strategy to achieve better growth. Instead, the rationale for feeding regimens in many nurseries has been quite variably extrapolated from animal data and human studies conducted in gestationally more mature and/or stable neonates. Additionally, there are no well-controlled, prospective studies that validate any nutritional regimen for the very preterm and or sick, unstable neonate. The goal of this review is to present available data to help define the risks and benefits of early parenteral and enteral nutrition, particularly in very preterm neonates, concluding with a more aggressive approach to feeding these infants than has been customary practice.
Rat and sheep cardiac myocytes become binucleate as they complete the 'terminal differentiation' process soon after birth and are not able to divide thereafter. Angiotensin II (Ang II) is known to stimulate hypertrophic changes in rodent cardiomyocytes under both in vivo and in vitro conditions via the AT1 receptor and intracellular extracellular regulated kinase (ERK) signalling cascade. We sought to develop culture methods for immature sheep cardiomyocytes in order to test the hypothesis that Ang II is a hypertrophic agent in the immature myocardium of the sheep. We isolated fetal sheep cardiomyocytes and cultured them for 96 h, added Ang II and phenylephrine (PE) for 48 h, and measured footprint area and proliferation (5-bromo-2'-deoxyuridine (BrdU) uptake) separately in mono- vs. binucleate myocytes. We found that neither Ang II nor PE changed the footprint area of mononucleated cells. PE stimulated an increase in footprint area of binucleate cells but Ang II did not. Ang II increased myocyte BrdU uptake compared to serum free conditions, but PE did not affect BrdU uptake. The MAP kinase kinase (MEK) inhibitor UO126 prevented BrdU uptake in Ang II-stimulated cells and prevented cell hypertrophy in PE-stimulated cells. This paper establishes culture methods for immature sheep cardiomyocytes and reports that: (1) Ang II is not a hypertrophic agent; (2) Ang II stimulates hyperplastic growth among mononucleate myocytes; (3) PE is a hypertrophic agent in binucleate myocytes; and (4) the ERK cascade is required for the proliferation effect of Ang II and the hypertrophic effect of PE.
Right (RVFW) and left (LVFW) ventricular free wall cardiac myocytes were collected from 25 fetal sheep aged 77-146 days gestation (term = 150 days gestation), six saline-infused catheterized fetal sheep (129 GD), and five lambs to measure gestational changes in uni- and binucleated cardiac myocyte numbers and cell volumes by confocal microscopy. At 77 days gestation, 2% of the myocytes were binucleated, which increased to 50% at 135 days gestation and 90% at 4-6 weeks after birth. RVFW uni- and binucleated myocytes were larger than those in the LVFW, and cell volumes of RVFW uni- and binucleated and LVFW binucleated myocytes (but not LVFW uninucleated myocytes) increased with gestation. Before birth, the approximate number of myocytes was greater in the LVFW than in the RVFW (P < 0.001). Before 110 GD, cardiac growth appeared to be due to myocyte hyperplasia, as approximate myocyte numbers and VFW weight increased at the same rate. After 110 days gestation, the approximate myocyte number/g VFW weight decreased, which suggests that myocyte hypertrophy, as well as hyperplasia, was occurring in association with the appearance of a greater proportion of binucleated cells after that time. By 4-6 weeks of age, there was marked hypertrophy of myocytes and an apparent reduction in myocyte number.
The HIF-1 transcription factor drives hypoxic gene expression changes that are thought to be adaptive for cells exposed to a reduced-oxygen environment. For example, HIF-1 induces the expression of glycolytic genes. It is presumed that increased glycolysis is necessary to produce energy when low oxygen will not support oxidative phosphorylation at the mitochondria. However, we find that while HIF-1 stimulates glycolysis, it also actively represses mitochondrial function and oxygen consumption by inducing pyruvate dehydrogenase kinase 1 (PDK1). PDK1 phosphorylates and inhibits pyruvate dehydrogenase from using pyruvate to fuel the mitochondrial TCA cycle. This causes a drop in mitochondrial oxygen consumption and results in a relative increase in intracellular oxygen tension. We show by genetic means that HIF-1-dependent block to oxygen utilization results in increased oxygen availability, decreased cell death when total oxygen is limiting, and reduced cell death in response to the hypoxic cytotoxin tirapazamine.
Accelerated neonatal growth increases the later propensity to cardiovascular disease (CVD) in animals, whereas slower growth is thought to have a beneficial effect. To test this hypothesis in humans, we measured flow-mediated endothelium-dependent dilation (FMD) in a population subject to slower early growth and in healthy controls.
High-resolution vascular ultrasound was used to measure the change in brachial artery diameter in response to reactive hyperemia in adolescents age 13 to 16 years who were either part of a cohort born preterm and followed up prospectively (n=216) or controls born at term (n=61). Greater weight gain or linear growth in the first 2 weeks postnatally was associated with lower FMD at adolescence (regression coefficient, -0.026-mm change in mean arterial diameter per 100-g increase in weight; 95% CI, -0.040 to -0.012 mm; P=0.0003) independent of birthweight and potential confounding factors. Mean FMD in the half of the preterm population with the lowest rates of early growth was higher than in both the half with the greatest growth (P=0.001) and subjects born at term (P=0.03).
FMD was 4% lower in adolescents with the highest compared with the lowest rate of weight gain in the first 2 weeks after birth, a substantial negative effect similar to that for insulin-dependent diabetes mellitus or smoking in adults. Our findings are consistent with the adverse effects of accelerated neonatal growth on long-term cardiovascular health and suggest that postnatal growth patterns could explain the previously reported association between birthweight and later CVD.
premature birth report card
- March Of Dimes
March of Dimes. (2016) 2016 premature birth report card. Accessed
August 1, 2018, at: https://www.marchofdimes.org/materials/
premature-birth-report-card-united-states.pdf
Projected costs of informal caregiving for cardiovascular disease
- S B Dunbar
- O A Khavjou
- T Bakas
- G Hunt
- R A Kirch
- A R Leib
- R S Morrison
- D C Poehler
- V L Roger
- L P Whitsel
Dunbar, S. B., Khavjou, O. A., Bakas, T., Hunt, G., Kirch, R. A., Leib,
A. R., Morrison, R. S., Poehler, D. C., Roger, V. L., and Whitsel, L. P.
(2018) Projected costs of informal caregiving for cardiovascular
disease: 2015 to 2035: a policy statement from the American Heart
Association. Circulation 137:e558-e577
Projections of cardiovascular disease prevalence and costs
American Heart Association. (2016) Projections of cardiovascular disease
prevalence and costs: 2015-2035. Accessed August 1, 2018, at:
http://www.heart.org/idc/groups/heart-public/%40wcm/%40adv/
documents/downloadable/ucm_491513.pdf
Fetal lamb ventricles respond differently to filling and arterial pressures and to in utero ventilation
- Relier M. D.
Hypoxic regulation of hand1 controls the fetal-neonatal switch in cardiac metabolism
- Breckenridge R. A.