Lin28a Regulates Pathological Cardiac Hypertrophic Growth Through Pck2-Mediated Enhancement of Anabolic Synthesis

Epigenetic Regulation of Cardiomyocyte Maturation by Arginine Methyltransferase CARM1

BACKGROUND

During the neonatal stage, the cardiomyocyte undergoes a constellation of molecular, cytoarchitectural, and functional changes known collectively as cardiomyocyte maturation to increase myocardial contractility and cardiac output. Despite the importance of cardiomyocyte maturation, the molecular mechanisms governing this critical process remain largely unexplored.

METHODS

We leveraged an in vivo mosaic knockout system to characterize the role of Carm1, the founding member of protein arginine methyltransferase, in cardiomyocyte maturation. Using a battery of assays, including immunohistochemistry, immuno-electron microscopy imaging, and action potential recording, we assessed the effect of loss of Carm1 function on cardiomyocyte cell growth, myofibril expansion, T-tubule formation, and electrophysiological maturation. Genome-wide transcriptome profiling, H3R17me2a chromatin immunoprecipitation followed by sequencing, and assay for transposase-accessible chromatin with high-throughput sequencing were used to investigate the mechanisms by which CARM1 (coactivator-associated arginine methyltransferase 1) regulates cardiomyocyte maturation. Finally, we interrogated the human syntenic region to the H3R17me2a chromatin immunoprecipitation followed by sequencing peaks for single-nucleotide polymorphisms associated with human heart diseases.

RESULTS

We report that mosaic ablation of Carm1 disrupts multiple aspects of cardiomyocyte maturation cell autonomously, leading to reduced cardiomyocyte size and sarcomere thickness, severe loss and disorganization of T tubules, and compromised electrophysiological maturation. Genomics study demonstrates that CARM1 directly activates genes that underlie cardiomyocyte cytoarchitectural and electrophysiological maturation. Moreover, our study reveals significant enrichment of human heart disease-associated single-nucleotide polymorphisms in the human genomic region syntenic to the H3R17me2a chromatin immunoprecipitation followed by sequencing peaks.

CONCLUSIONS

This study establishes a critical and multifaceted role for CARM1 in regulating cardiomyocyte maturation and demonstrates that deregulation of CARM1-dependent cardiomyocyte maturation gene expression may contribute to human heart diseases.

Analysis of immunoinfiltration and EndoMT based on TGF-β signaling pathway-related genes in acute myocardial infarction

Acute myocardial infarction (AMI), a critical manifestation of coronary heart disease, presents a complex and not entirely understood etiology. This study investigates the potential role of immune infiltration and endothelial-mesenchymal transition (EndoMT) in AMI pathogenesis. We conducted an analysis of the GSE24519 and MSigDB datasets to identify differentially expressed genes associated with the TGF-β signaling pathway (DE-TSRGs) and carried out a functional enrichment analysis. Additionally, we evaluated immune infiltration in AMI and its possible link to myocardial fibrosis. Key genes were identified using machine learning and LASSO logistic regression. The expression of MEOX1 in the ventricular muscles and endothelial cells of Sprague-Dawley rats was assessed through RT-qPCR, immunohistochemical and immunofluorescence assays, and the effect of MEOX1 overexpression on EndoMT was investigated. Our study identified five DE-TSRGs, among which MEOX1, SMURF1, and SPTBN1 exhibited the most significant associations with AMI. Notably, we detected substantial immune infiltration in AMI specimens, with a marked increase in neutrophils and macrophages. MEOX1 demonstrated consistent expression patterns in rat ventricular muscle tissue and endothelial cells, and its overexpression induced EndoMT. Our findings suggest that the TGF-β signaling pathway may contribute to AMI progression by activating the immune response. MEOX1, linked to the TGF-β signaling pathway, appears to facilitate myocardial fibrosis via EndoMT following AMI. These novel insights into the mechanisms of AMI pathogenesis could offer promising therapeutic targets for intervention.

Single-cell chromatin profiling reveals genetic programs activating proregenerative states in nonmyocyte cells

Cardiac regeneration requires coordinated participation of multiple cell types whereby their communications result in transient activation of proregenerative cell states. Although the molecular characteristics and lineage origins of these activated cell states and their contribution to cardiac regeneration have been studied, the extracellular signaling and the intrinsic genetic program underlying the activation of the transient functional cell states remain largely unexplored. In this study, we delineated the chromatin landscapes of the noncardiomyocytes (nonCMs) of the regenerating heart at the single-cell level and inferred the cis-regulatory architectures and trans-acting factors that control cell type-specific gene expression programs. Moreover, further motif analysis and cell-specific genetic manipulations suggest that the macrophage-derived inflammatory signal tumor necrosis factor-α, acting via its downstream transcription factor complex activator protein-1, functions cooperatively with discrete transcription regulators to activate respective nonCM cell types critical for cardiac regeneration. Thus, our study defines the regulatory architectures and intercellular communication principles in zebrafish heart regeneration.

Valerenic acid attenuates pathological myocardial hypertrophy by promoting the utilization of multiple substrates in the mitochondrial energy metabolism

INTRODUCTION

Valerenic acid (VA) is a unique and biologically active component in Valeriana officinalis L., which has been reported to have a regulatory effect on the cardiovascular system. However, its therapeutic effects on pathological myocardial hypertrophy (PMH) and the underlying mechanisms are undefined.

OBJECTIVES

Our study aims to elucidate how VA improves PMH, and preliminarily discuss its mechanism.

METHODS

The efficacy of VA on PMH was confirmed by in vivo and in vitro experiments and the underlying mechanism was investigated by molecular dynamics (MD) simulations and specific siRNA interference.

RESULTS

VA enhanced cardiomyocyte fatty acid oxidation (FAO), inhibited hyper-activated glycolysis, and improved the unbalanced pyruvate-lactate axis. VA could significantly improve impaired mitochondrial function and reduce the triglyceride (TG) in the hypertrophic myocardium while reducing the lactate (LD) content. Molecular mechanistic studies showed that VA up-regulated the expression of peroxisome proliferator-activated receptor-α (PPARα) and downstream FAO-related genes including CD36, CPT1A, EHHADH, and MCAD. VA reduced the expression of ENO1 and PDK4, the key enzymes in glycolysis. Meanwhile, VA improved the pyruvate-lactate axis and promoted the aerobic oxidation of pyruvate by inhibiting LDAH and MCT4. MD simulations confirmed that VA can bind with the F273 site of PPARα, which proposes VA as a potential activator of the PPARα.

CONCLUSION

Our results demonstrated that VA might be a potent activator for the PPARα-mediated pathway. VA directly targets the PPARα and subsequently promotes energy metabolism to attenuate PMH, which can be applied as a potentially effective drug for the treatment of HF.

Advances in Metabolic Remodeling and Intervention Strategies in Heart Failure

The heart is the most energy-demanding organ throughout the whole body. Perturbations or failure in energy metabolism contributes to heart failure (HF), which represents the advanced stage of various heart diseases. The poor prognosis and huge economic burden associated with HF underscore the high unmet need to explore novel therapies targeting metabolic modulators beyond conventional approaches focused on neurohormonal and hemodynamic regulators. Emerging evidence suggests that alterations in metabolic substrate reliance, metabolic pathways, metabolic by-products, and energy production collectively regulate the occurrence and progression of HF. In this review, we provide an overview of cardiac metabolic remodeling, encompassing the utilization of free fatty acids, glucose metabolism, ketone bodies, and branched-chain amino acids both in the physiological condition and heart failure. Most importantly, the latest advances in pharmacological interventions are discussed as a promising therapeutic approach to restore cardiac function, drawing insights from recent basic research, preclinical and clinical studies.

Metabolic adaptations in pressure overload hypertrophic heart

This review article offers a detailed examination of metabolic adaptations in pressure overload hypertrophic hearts, a condition that plays a pivotal role in the progression of heart failure with preserved ejection fraction (HFpEF) to heart failure with reduced ejection fraction (HFrEF). The paper delves into the complex interplay between various metabolic pathways, including glucose metabolism, fatty acid metabolism, branched-chain amino acid metabolism, and ketone body metabolism. In-depth insights into the shifts in substrate utilization, the role of different transporter proteins, and the potential impact of hypoxia-induced injuries are discussed. Furthermore, potential therapeutic targets and strategies that could minimize myocardial injury and promote cardiac recovery in the context of pressure overload hypertrophy (POH) are examined. This work aims to contribute to a better understanding of metabolic adaptations in POH, highlighting the need for further research on potential therapeutic applications.

Activation of the integrated stress response rewires cardiac metabolism in Barth syndrome

Barth Syndrome (BTHS) is an inherited cardiomyopathy caused by defects in the mitochondrial transacylase TAFAZZIN (Taz), required for the synthesis of the phospholipid cardiolipin. BTHS is characterized by heart failure, increased propensity for arrhythmias and a blunted inotropic reserve. Defects in Ca2+-induced Krebs cycle activation contribute to these functional defects, but despite oxidation of pyridine nucleotides, no oxidative stress developed in the heart. Here, we investigated how retrograde signaling pathways orchestrate metabolic rewiring to compensate for mitochondrial defects. In mice with an inducible knockdown (KD) of TAFAZZIN, and in induced pluripotent stem cell-derived cardiac myocytes, mitochondrial uptake and oxidation of fatty acids was strongly decreased, while glucose uptake was increased. Unbiased transcriptomic analyses revealed that the activation of the eIF2α/ATF4 axis of the integrated stress response upregulates one-carbon metabolism, which diverts glycolytic intermediates towards the biosynthesis of serine and fuels the biosynthesis of glutathione. In addition, strong upregulation of the glutamate/cystine antiporter xCT increases cardiac cystine import required for glutathione synthesis. Increased glutamate uptake facilitates anaplerotic replenishment of the Krebs cycle, sustaining energy production and antioxidative pathways. These data indicate that ATF4-driven rewiring of metabolism compensates for defects in mitochondrial uptake of fatty acids to sustain energy production and antioxidation.

Cardiac-specific BACH1 ablation attenuates pathological cardiac hypertrophy by inhibiting the Ang II type 1 receptor expression and the Ca2+/CaMKII pathway

AIMS

BACH1 is up-regulated in hypertrophic hearts, but its function in cardiac hypertrophy remains largely unknown. This research investigates the function and mechanisms of BACH1 in the regulation of cardiac hypertrophy.

METHODS AND RESULTS

Male cardiac-specific BACH1 knockout mice or cardiac-specific BACH1 transgenic (BACH1-Tg) mice and their respective wild-type littermates developed cardiac hypertrophy induced by angiotensin II (Ang II) or transverse aortic constriction (TAC). Cardiac-specific BACH1 knockout in mice protected the hearts against Ang II- and TAC-induced cardiac hypertrophy and fibrosis, and preserved cardiac function. Conversely, cardiac-specific BACH1 overexpression markedly exaggerated cardiac hypertrophy and fibrosis and reduced cardiac function in mice with Ang II- and TAC-induced hypertrophy. Mechanistically, BACH1 silencing attenuated Ang II- and norepinephrine-stimulated calcium/calmodulin-dependent protein kinase II (CaMKII) signalling, the expression of hypertrophic genes, and hypertrophic growth of cardiomyocytes. Ang II stimulation promoted the nuclear localization of BACH1, facilitated the recruitment of BACH1 to the Ang II type 1 receptor (AT1R) gene promoter, and then increased the expression of AT1R. Inhibition of BACH1 attenuated Ang II-stimulated AT1R expression, cytosolic Ca2+ levels, and CaMKII activation in cardiomyocytes, whereas overexpression of BACH1 led to the opposite effects. The increased expression of hypertrophic genes induced by BACH1 overexpression upon Ang II stimulation was suppressed by CaMKII inhibitor KN93. The AT1R antagonist, losartan, significantly attenuated BACH1-mediated CaMKII activation and cardiomyocyte hypertrophy under Ang II stimulation in vitro. Similarly, Ang II-induced myocardial pathological hypertrophy, cardiac fibrosis, and dysfunction in BACH1-Tg mice were blunted by treatment with losartan.

CONCLUSION

This study elucidates a novel important role of BACH1 in pathological cardiac hypertrophy by regulating the AT1R expression and the Ca2+/CaMKII pathway, and highlights potential therapeutic target in pathological cardiac hypertrophy.

RNA-Binding Proteins as Critical Post-Transcriptional Regulators of Cardiac Regeneration

Myocardial injury causes death to cardiomyocytes and leads to heart failure. The adult mammalian heart has very limited regenerative capacity. However, the heart from early postnatal mammals and from adult lower vertebrates can fully regenerate after apical resection or myocardial infarction. Thus, it is of particular interest to decipher the mechanism underlying cardiac regeneration that preserves heart structure and function. RNA-binding proteins, as key regulators of post-transcriptional gene expression to coordinate cell differentiation and maintain tissue homeostasis, display dynamic expression in fetal and adult hearts. Accumulating evidence has demonstrated their importance for the survival and proliferation of cardiomyocytes following neonatal and postnatal cardiac injury. Functional studies suggest that RNA-binding proteins relay damage-stimulated cell extrinsic or intrinsic signals to regulate heart regenerative capacity by reprogramming multiple molecular and cellular processes, such as global protein synthesis, metabolic changes, hypertrophic growth, and cellular plasticity. Since manipulating the activity of RNA-binding proteins can improve the formation of new cardiomyocytes and extend the window of the cardiac regenerative capacity in mammals, they are potential targets of therapeutic interventions for cardiovascular disease. This review discusses our evolving understanding of RNA-binding proteins in regulating cardiac repair and regeneration, with the aim to identify important open questions that merit further investigations.

Dynamic interplay between RPL3- and RPL3L-containing ribosomes modulates mitochondrial activity in the mammalian heart

The existence of naturally occurring ribosome heterogeneity is now a well-acknowledged phenomenon. However, whether this heterogeneity leads to functionally diverse 'specialized ribosomes' is still a controversial topic. Here, we explore the biological function of RPL3L (uL3L), a ribosomal protein (RP) paralogue of RPL3 (uL3) that is exclusively expressed in skeletal muscle and heart tissues, by generating a viable homozygous Rpl3l knockout mouse strain. We identify a rescue mechanism in which, upon RPL3L depletion, RPL3 becomes up-regulated, yielding RPL3-containing ribosomes instead of RPL3L-containing ribosomes that are typically found in cardiomyocytes. Using both ribosome profiling (Ribo-seq) and a novel orthogonal approach consisting of ribosome pulldown coupled to nanopore sequencing (Nano-TRAP), we find that RPL3L modulates neither translational efficiency nor ribosome affinity towards a specific subset of transcripts. In contrast, we show that depletion of RPL3L leads to increased ribosome-mitochondria interactions in cardiomyocytes, which is accompanied by a significant increase in ATP levels, potentially as a result of fine-tuning of mitochondrial activity. Our results demonstrate that the existence of tissue-specific RP paralogues does not necessarily lead to enhanced translation of specific transcripts or modulation of translational output. Instead, we reveal a complex cellular scenario in which RPL3L modulates the expression of RPL3, which in turn affects ribosomal subcellular localization and, ultimately, mitochondrial activity.

LIN28 expression and function in medulloblastoma

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. Current treatment modalities are not completely effective and can lead to severe neurological and cognitive adverse effects. In addition to urgently needing better treatment approaches, new diagnostic and prognostic biomarkers are required to improve the therapy outcomes of MB patients. The RNA-binding proteins, LIN28A and LIN28B, are known to regulate invasive phenotypes in many different cancer types. However, the expression and function of these proteins in MB had not been studied to date. This study identified the expression of LIN28A and LIN28B in MB patient samples and cell lines and assessed the effect of LIN28 inhibition on MB cell growth, metabolism and stemness. LIN28B expression was significantly upregulated in MB tissues compared to normal brain tissues. This upregulation, which was not observed in other brain tumors, was specific for the aggressive MB subgroups and correlated with patient survival and metastasis rates. Functionally, pharmacological inhibition of LIN28 activity concentration-dependently reduced LIN28B expression, as well as the growth of D283 MB cells. While LIN28 inhibition did not affect the levels of intracellular ATP, it reduced the expression of the stemness marker CD133 in D283 cells and the sphere formation of CHLA-01R cells. LIN28B, which is highly expressed in the human cerebellum during the first few months after birth, subsequently decreased with age. The results of this study highlight the potential of LIN28B as a diagnostic and prognostic marker for MB and open the possibility to utilize LIN28 as a pharmacological target to suppress MB cell growth and stemness.

Lin28a induced mitochondrial dysfunction in human granulosa cells via suppressing LARS2 expression

Granulosa cells surround the oocytes as a component of ovarian follicles and produce sex steroids and growth factors to support oocyte development. Mitochondria is one of the multiple factors regulating granulosa cell function by modulating bioenergetic pathways and maintaining cells' metabolic needs. Lin28a was reported to regulate the primordial germ cell development in the ovary and affect the fertility rate in females. However, whether Lin28a modulated mitochondria function in granulosa cells to regulate steroidogenesis remains a further exploration. In this study, we utilized immortal human granulosa cells (HGrC1) to overexpress or suppress the protein level of Lin28a. Results showed that overexpression of Lin28a could decrease the estrogen level, ATP content, mitochondrial membrane potential and Glutathione (GSH) level, while silencing Lin28a caused the opposite effect. Further, we found that overexpression of LARS2, a mitochondrial leucyl-tRNA synthetase, could increase the estrogen level, ATP content, mitochondrial membrane potential and GSH level while silencing LARS2 caused adverse results. Overexpression of LARS2 reversed Lin28a-induced estrogen downregulation and mitochondrial dysfunction. Moreover, overexpression of LARS2 increased the mRNA level of Pgc1α and Nrf2, which were involved in mitochondrial biogenesis. Besides, Lin28a could directly bind to the mRNA of Lars2 to suppress its translation. Taken together, overexpression of Lin28a caused mitochondrial dysfunction in granulosa cells via suppressing LARS2 expression. This study can provide new insights into how Lin28a regulates mitochondrial function in granulosa cells and influences female fertility.

Association between placental DNA methylation and fetal congenital heart disease

Congenital heart disease (CHD) is a worldwide problem with high morbidity and mortality. Early diagnosis of congenital heart disease is still a challenge in clinical work. In recent years, few studies indicated that placental methylation may be predictors of CHD. More studies are needed to confirm the association between placental methylation and CHD. The aim of this study was to investigate the association between prenatal placental DNA methylation and CHD. Placental tissues were obtained from four fetuses during the second trimester with isolated, non-syndromic congenital heart disease, including three cases with double outlet right ventricle (DORV) and one case with tetralogy of Fallot (TOF), and four unaffected fetuses as controls. The Illumina Infinium Human Methylation 850K BeadChip assay was employed to identify differential methylation sites (DMSs) and differential methylation regions (DMRs). Differential methylation was evaluated by comparing the β-values for individual CpG loci in cases vs. controls. In addition, the function of genes was assessed through KEGG enrichment analysis, Gene Ontology (GO) analysis and KEGG pathway analysis. Compared with the control group, we identified 9625 differential methylation genes on 26,202 DMSs (p < 0.05), of which 6997 were hyper-methylation and 2628 were hypo-methylation. The top 30 terms of GO biological process and KEGG enrichment analysis of DMSs were connected with multiple important pathways of heart development and disease. Ten differentially methylated regions and the genes related to DMRs, such as TLL1, CRABP1, FDFT1, and PCK2, were identified. The deformity caused by the loss of function of these genes is remarkably consistent with the clinical phenotype of our cases. The DNA methylation level of placental tissue is closely associated with fetal congenital heart disease.

The sodium-glucose co-transporter-2 inhibitor ertugliflozin modifies the signature of cardiac substrate metabolism and reduces cardiac mTOR signalling, endoplasmic reticulum stress and apoptosis

AIM

To investigate cardiac signalling pathways connecting substrate utilization with left ventricular remodelling in a murine pressure overload model.

METHODS

Cardiac hypertrophy was induced by transverse aortic constriction surgery in 20-week-old C57BL/6J mice treated with or without the sodium-glucose co-transporter 2 (SGLT2) inhibitor ertugliflozin (225 mg kg^-1 chow diet) for 10 weeks.

RESULTS

Ertugliflozin improved left ventricular function and reduced myocardial fibrosis. This occurred simultaneously with a fasting-like response characterized by improved glucose tolerance and increased ketone body concentrations. While cardiac insulin signalling was reduced in response to SGLT2 inhibition, AMP-activated protein kinase (AMPK) signalling was increased with induction of the fatty acid transporter cluster of differentiation 36 and phosphorylation of acetyl-CoA carboxylase (ACC). Further, enzymes responsible for ketone body catabolism (β-hydroxybutyrate dehydrogenase, succinyl-CoA:3-oxoacid-CoA transferase and acetyl-CoA acetyltransferase 1) were induced by SGLT2 inhibition. Ertugliflozin led to more cardiac abundance of fatty acids, tricarboxylic acid cycle metabolites and ATP. Downstream mechanistic target of rapamycin (mTOR) pathway, relevant for protein synthesis, cardiac hypertrophy and adverse cardiac remodelling, was reduced by SGLT2 inhibition, with alleviation of endoplasmic reticulum (ER) stress and unfolded protein response (UPR) providing a potential mechanism for abundant reduced left ventricular apoptosis and fibrosis.

CONCLUSION

SGLT2 inhibition reduced left ventricular fibrosis in a murine model of cardiac hypertrophy. Mechanistically, this was associated with reduced cardiac insulin and increased AMPK signalling as a potential mechanism for less cardiac mTOR activation with alleviation of downstream ER stress, UPR and apoptosis.

Predicting Heart Cell Types by Using Transcriptome Profiles and a Machine Learning Method

The heart is an essential organ in the human body. It contains various types of cells, such as cardiomyocytes, mesothelial cells, endothelial cells, and fibroblasts. The interactions between these cells determine the vital functions of the heart. Therefore, identifying the different cell types and revealing the expression rules in these cell types are crucial. In this study, multiple machine learning methods were used to analyze the heart single-cell profiles with 11 different heart cell types. The single-cell profiles were first analyzed via light gradient boosting machine method to evaluate the importance of gene features on the profiling dataset, and a ranking feature list was produced. This feature list was then brought into the incremental feature selection method to identify the best features and build the optimal classifiers. The results suggested that the best decision tree (DT) and random forest classification models achieved the highest weighted F1 scores of 0.957 and 0.981, respectively. The selected features, such as NPPA, LAMA2, DLC1, and the classification rules extracted from the optimal DT classifier played a crucial role in cardiac structure and function in recent research and enrichment analysis. In particular, some lncRNAs (LINC02019, NEAT1) were found to be quite important for the recognition of different cardiac cell types. In summary, these findings provide a solid academic foundation for the development of molecular diagnostics and biomarker discovery for cardiac diseases.

Identification of Rare Variants in Right Ventricular Outflow Tract Obstruction Congenital Heart Disease by Whole-Exome Sequencing

Background

Pulmonary atresia (PA) is a kind of congenital heart disease characterized by right ventricular outflow tract obstruction. It is divided into PA with intact ventricular septum (PA/IVS) whose favorable form is pulmonary valvular stenosis (PS), and PA with ventricular septal defect (PA/VSD) whose favorable form is tetralogy of Fallot (TOF). Due to limitations in genetics etiology, whole-exome sequencing (WES) was utilized to identify new variants associated with the diseases.

Methods

The data from PS-PA/IVS (n = 74), TOF-PA/VSD (n = 100), and 100 controls were obtained. The common sites between PS and PA/IVS, PA/VSD and TOF, were compared. The novel rare damage variants, and candidate genes were identified by gene-based burden analysis. Finally, the enrichment analysis of differential genes was conducted between case and control groups.

Results

Seventeen rare damage variants located in seven genes were predicted to be associated with the PS through burden analysis. Enrichment analysis identified that the Wnt and cadherin signaling pathways were relevant to PS-PA/IVS.

Conclusion

This study put forth seven candidate genes (APC, PPP1R12A, PCK2, SOS2, TNR, MED13, and TIAM1), resulting in PS-PA/IVS. The Wnt and cadherin signaling pathways were identified to be related to PS-PA/IVS by enrichment analysis. This study provides new evidence for exploring the genetic mechanism of PS-PA/IVS.

Harmine is an effective therapeutic small molecule for the treatment of cardiac hypertrophy

Harmine is a β-carboline alkaloid isolated from Banisteria caapi and Peganum harmala L with various pharmacological activities, including antioxidant, anti-inflammatory, antitumor, anti-depressant, and anti-leishmanial capabilities. Nevertheless, the pharmacological effect of harmine on cardiomyocytes and heart muscle has not been reported. Here we found a protective effect of harmine on cardiac hypertrophy in spontaneously hypertensive rats in vivo. Further, harmine could inhibit the phenotypes of norepinephrine-induced hypertrophy in human embryonic stem cell-derived cardiomyocytes in vitro. It reduced the enlarged cell surface area, reversed the increased calcium handling and contractility, and downregulated expression of hypertrophy-related genes in norepinephrine-induced hypertrophy of human cardiomyocytes derived from embryonic stem cells. We further showed that one of the potential underlying mechanism by which harmine alleviates cardiac hypertrophy relied on inhibition of NF-κB phosphorylation and the stimulated inflammatory cytokines in pathological ventricular remodeling. Our data suggest that harmine is a promising therapeutic agent for cardiac hypertrophy independent of blood pressure modulation and could be a promising addition of current medications for cardiac hypertrophy.

PKM1 Exerts Critical Roles in Cardiac Remodeling Under Pressure Overload in the Heart

BACKGROUND

Metabolic remodeling precedes most alterations during cardiac hypertrophic growth under hemodynamic stress. The elevation of glucose utilization has been recognized as a hallmark of metabolic remodeling. However, its role in cardiac hypertrophic growth and heart failure in response to pressure overload remains to be fully illustrated. Here, we aimed to dissect the role of cardiac PKM1 (pyruvate kinase muscle isozyme 1) in glucose metabolic regulation and cardiac response under pressure overload.

METHODS

Cardiac-specific deletion of PKM1 was achieved by crossing the floxed PKM1 mouse model with the cardiomyocyte-specific Cre transgenic mouse. PKM1 transgenic mice were generated under the control of tetracycline response elements, and cardiac-specific overexpression of PKM1 was induced by doxycycline administration in adult mice. Pressure overload was triggered by transverse aortic constriction. Primary neonatal rat ventricular myocytes were used to dissect molecular mechanisms. Moreover, metabolomics and nuclear magnetic resonance spectroscopy analyses were conducted to determine cardiac metabolic flux in response to pressure overload.

RESULTS

We found that PKM1 expression is reduced in failing human and mouse hearts. It is important to note that cardiomyocyte-specific deletion of PKM1 exacerbates cardiac dysfunction and fibrosis in response to pressure overload. Inducible overexpression of PKM1 in cardiomyocytes protects the heart against transverse aortic constriction-induced cardiomyopathy and heart failure. At the mechanistic level, PKM1 is required for the augmentation of glycolytic flux, mitochondrial respiration, and ATP production under pressure overload. Furthermore, deficiency of PKM1 causes a defect in cardiomyocyte growth and a decrease in pyruvate dehydrogenase complex activity at both in vitro and in vivo levels.

CONCLUSIONS

These findings suggest that PKM1 plays an essential role in maintaining a homeostatic response in the heart under hemodynamic stress.

Phosphoenolpyruvate carboxykinase in cell metabolism: Roles and mechanisms beyond gluconeogenesis

BACKGROUND

Phosphoenolpyruvate carboxykinase (PCK) has been almost exclusively recognized as a critical enzyme in gluconeogenesis, especially in the liver and kidney. Accumulating evidence has shown that the enhanced activity of PCK leads to increased glucose output and exacerbation of diabetes, whereas the defects of PCK result in lethal hypoglycemia. Genetic mutations or polymorphisms are reported to be related to the onset and progression of diabetes in humans.

SCOPE OF REVIEW

Recent studies revealed that the PCK pathway is more complex than just gluconeogenesis, depending on the health or disease condition. Dysregulation of PCK may contribute to the development of obesity, cardiac hypertrophy, stroke, and cancer. Moreover, a regulatory network with multiple layers, from epigenetic regulation, transcription regulation, to posttranscription regulation, precisely tunes the expression of PCK. Deciphering the molecular basis that regulates PCK may pave the way for developing practical strategies to treat metabolic dysfunction.

MAJOR CONCLUSIONS

In this review, we summarize the metabolic and non-metabolic roles of the PCK enzyme in cells, especially beyond gluconeogenesis. We highlight the distinct functions of PCK isoforms (PCK1 and PCK2), depict a detailed network regulating PCK's expression, and discuss its clinical relevance. We also discuss the therapeutic potential targeting PCK and the future direction that is highly in need to better understand PCK-mediated signaling under diverse conditions.

Molecular and cellular basis of embryonic cardiac chamber maturation

Heart malformation is the leading cause of human birth defects, and many of the congenital heart diseases (CHDs) originate from genetic defects that impact cardiac development and maturation. During development, the vertebrate heart undergoes a series of complex morphogenetic processes that increase its ability to pump blood. One of these processes leads to the formation of the sheet-like muscular projections called trabeculae. Trabeculae increase cardiac output and permit nutrition and oxygen uptake in the embryonic myocardium prior to coronary vascularization without increasing heart size. Cardiac trabeculation is also crucial for the development of the intraventricular fast conduction system. Alterations in cardiac trabecular development can manifest as a variety of congenital defects such as left ventricular noncompaction. In this review, we discuss the latest advances in understanding the molecular and cellular mechanisms underlying cardiac trabecular development.

Lin28a attenuates cerebral ischemia/reperfusion injury through regulating Sirt3-induced autophagy

Cerebral ischemia-reperfusion injury causes damage to local brain tissue and its function, but its specific pathogenesis is still unclear. Autophagy is an important catabolic pathway in eukaryotic cells, which is mainly used to remove damaged intracellular organelles, misfolded long-acting macromolecules and participate in cerebral ischemia-reperfusion injury. Lin28 is a highly conserved RNA-binding protein that plays a role in regulating gene translation, which is important for the growth and maintenance of pluripotent cells. Lin28a has been reported to have a clear protective effect on post-ischemic reperfusion injury of the heart. However, whether Lin28a has an effect on nerve injury after cerebral ischemia-reperfusion needs further study. In this study, we found that the expression of Lin28a was decreased in cerebral ischemia-reperfusion mice model. Upregulation of Lin28a could alleviate the nerve injury caused by ischemia-reperfusion, and promote autophagy of nerve cells. Upregulation of Lin28a reduced nerve cell apoptosis and relieved nerve cell injure induced by oxygen-glucose deprivation/reoxygenation. Lin28a increased the LC3-II levels in nerve cells, suggesting the promotion of autophagy. Mechanism studies indicated that Lin28a promoted autophagy mainly through regulating Sirt3 expression and activating AMPK-mTOR pathway. In conclusion, our study revealed the important role of Lin28a in cerebral ischemia-reperfusion and suggested that Lin28a was a protective factor for cerebral ischemia-induced injury.

Quantitative Analysis of the Physiological Contributions of Glucose to the TCA Cycle

The nutritional source for catabolism in the tricarboxylic acid (TCA) cycle is a fundamental question in metabolic physiology. Limited by data and mathematical analysis, controversy exists. Using isotope-labeling data in vivo across several experimental conditions, we construct multiple models of central carbon metabolism and develop methods based on metabolic flux analysis (MFA) to solve for the preferences of glucose, lactate, and other nutrients used in the TCA cycle. We show that in nearly all circumstances, glucose contributes more than lactate as a substrate to the TCA cycle. This conclusion is verified in different animal strains from different studies and different administrations of ¹³C glucose, and is extended to multiple tissue types. Thus, this quantitative analysis of organismal metabolism defines the relative contributions of nutrient fluxes in physiology, provides a resource for analysis of in vivo isotope tracing data, and concludes that glucose is the major nutrient used in mammals.

Restoring the epigenetically silenced PCK2 suppresses renal cell carcinoma progression and increases sensitivity to sunitinib by promoting endoplasmic reticulum stress

Rationale: Tumors have significant abnormalities in various biological properties. In renal cell carcinoma (RCC), metabolic abnormalities are characteristic biological dysfunction that cannot be ignored. Despite this, many aspects of this dysfunction have not been fully explained. The purpose of this study was to reveal a new mechanism of metabolic and energy-related biological abnormalities in RCC.

Methods: Molecular screening and bioinformatics analysis were performed in RCC based on data from The Cancer Genome Atlas (TCGA) database. Regulated pathways were investigated by qRT-PCR, immunoblot analysis and immunohistochemistry. A series of functional analyses was performed in cell lines and xenograft models.

Results: By screening the biological abnormality core dataset-mitochondria-related dataset and the metabolic abnormality core dataset-energy metabolism-related dataset in public RCC databases, PCK2 was found to be differentially expressed in RCC compared with normal tissue. Further analysis by the TCGA database showed that PCK2 was significantly downregulated in RCC and predicted a poor prognosis. Through additional studies, it was found that a low expression of PCK2 in RCC was caused by methylation of its promoter region. Restoration of PCK2 expression in RCC cells repressed tumor progression and increased their sensitivity to sunitinib. Finally, mechanistic investigations indicated that PCK2 mediated the above processes by promoting endoplasmic reticulum stress.

Conclusions: Collectively, our results identify a specific mechanism by which PCK2 suppresses the progression of renal cell carcinoma (RCC) and increases sensitivity to sunitinib by promoting endoplasmic reticulum stress. This finding provides a new biomarker for RCC as well as novel targets and strategies for the treatment of RCC.

Peroxiredoxin-1 Overexpression Attenuates Doxorubicin-Induced Cardiotoxicity by Inhibiting Oxidative Stress and Cardiomyocyte Apoptosis

Background. Previous research has shown that peroxiredoxin 1 (Prdx1) is an important modulator of physiological and pathophysiological cardiovascular events. This study is aimed at investigating the role and underlying mechanism of Prdx1 in doxorubicin- (DOX-) induced cardiotoxicity. Cardiac-specific expression of Prdx1 was induced in mice, and the mice received a single dose of DOX (15 mg/kg) to generate cardiotoxicity. First, our study demonstrated that Prdx1 expression was upregulated in the heart and in cardiomyocytes after DOX treatment. Second, we provided direct evidence that Prdx1 overexpression ameliorated DOX-induced cardiotoxicity by attenuating oxidative stress and cardiomyocyte apoptosis. Mechanistically, we found that DOX treatment increased the phosphorylation level of apoptosis signal-regulating kinase-1 (ASK1) and the downstream protein p38 in the heart and in cardiomyocytes, and these effects were decreased by Prdx1 overexpression. In contrast, inhibiting Prdx1 promoted DOX-induced cardiac injury via the ASK1/p38 pathway. These results suggest that Prdx1 may be an effective therapeutic option to prevent DOX-induced cardiotoxicity.

Role of YAP/TAZ in Energy Metabolism in the Heart

The heart requires a high amount of energy, in the form of adenosine triphosphate, to maintain its viability and pump function. Anaerobic glycolysis and mitochondrial oxidative phosphorylation are the two main metabolic pathways by which adenosine triphosphate is generated, using fatty acids, glucose, lactate, and ketone bodies as primary substrates. Previous studies have demonstrated that, in response to stress, the heart undergoes alterations in metabolism, ranging from changes in substrate utilization to mitochondrial function, collectively called metabolic remodeling. However, the molecular mechanism mediating metabolic remodeling in the heart remains unclear. Yes-associated protein 1 (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), which are major downstream effectors of the Hippo signaling pathway, play an important role in the regulation of heart size and cellular homeostasis of cardiomyocytes through the regulation of various transcriptional factors under both physiological and pathophysiological conditions. Recent findings in various organs and cell types have revealed that YAP and TAZ play an important role in energy metabolism. Here, we summarize what is currently known about YAP/TAZ in the regulation of metabolism of various substrates and mitochondrial function in various organs and cell types and discuss the potential role of YAP/TAZ in mediating metabolic remodeling of the heart during stress and heart failure.

Metabolic Remodeling Promotes Cardiac Hypertrophy by Directing Glucose to Aspartate Biosynthesis

RATIONALE

Hypertrophied hearts switch from mainly using fatty acids (FAs) to an increased reliance on glucose for energy production. It has been shown that preserving FA oxidation (FAO) prevents the pathological shift of substrate preference, preserves cardiac function and energetics, and reduces cardiomyocyte hypertrophy during cardiac stresses. However, it remains elusive whether substrate metabolism regulates cardiomyocyte hypertrophy directly or via a secondary effect of improving cardiac energetics.

OBJECTIVE

The goal of this study was to determine the mechanisms of how preservation of FAO prevents the hypertrophic growth of cardiomyocytes.

METHODS AND RESULTS

We cultured adult rat cardiomyocytes in a medium containing glucose and mixed-chain FAs and induced pathological hypertrophy by phenylephrine. Phenylephrine-induced hypertrophy was associated with increased glucose consumption and higher intracellular aspartate levels, resulting in increased synthesis of nucleotides, RNA, and proteins. These changes could be prevented by increasing FAO via deletion of ACC2 (acetyl-CoA-carboxylase 2) in phenylephrine-stimulated cardiomyocytes and in pressure overload-induced cardiac hypertrophy in vivo. Furthermore, aspartate supplementation was sufficient to reverse the antihypertrophic effect of ACC2 deletion demonstrating a causal role of elevated aspartate level in cardiomyocyte hypertrophy. 15N and 13C stable isotope tracing revealed that glucose but not glutamine contributed to increased biosynthesis of aspartate, which supplied nitrogen for nucleotide synthesis during cardiomyocyte hypertrophy.

CONCLUSIONS

Our data show that increased glucose consumption is required to support aspartate synthesis that drives the increase of biomass during cardiac hypertrophy. Preservation of FAO prevents the shift of metabolic flux into the anabolic pathway and maintains catabolic metabolism for energy production, thus preventing cardiac hypertrophy and improving myocardial energetics.