Dietary Branched Chain Amino Acids Modify Post-Infarct Cardiac Remodeling and Function in the Murine Heart.

Introduction: Branch-chain amino acids (BCAA) are markedly elevated in the heart following myocardial infarction (MI) in both humans and animal models. Nevertheless, it remains unclear whether dietary BCAA levels influence post-MI remodeling. We hypothesize that lowering dietary BCAA levels prevents adverse cardiac remodeling after MI. Methods and Results: To assess whether altering dietary BCAA levels would impact circulating BCAA concentrations, mice were fed a low (1/3×), normal (1×), or high (2×) BCAA diet over a 7-day period. We found that mice fed the low BCAA diet had >2-fold lower circulating BCAA concentrations when compared with normal and high BCAA diet feeding strategies; notably, the high BCAA diet did not further increase BCAA levels over the normal chow diet. To investigate the impact of dietary BCAAs on cardiac remodeling and function after MI, male and female mice were fed either the low or high BCAA diet for 2 wk prior to MI and for 4 wk after MI. Although body weights or heart masses were not different in female mice fed the custom diets, male mice fed the high BCAA diet had significantly higher body and heart masses than those on the low BCAA diet. Echocardiographic assessments revealed that the low BCAA diet preserved stroke volume and cardiac output for the duration of the study, while the high BCAA diet led to progressive decreases in cardiac function. Although no discernible differences in cardiac fibrosis, scar collagen topography, or cardiomyocyte cross-sectional area were found between the dietary groups, male mice fed the high BCAA diet showed longer cardiomyocytes and higher capillary density compared with the low BCAA group. Conclusions: Provision of a diet low in BCAAs to mice mitigates eccentric cardiomyocyte remodeling and loss of cardiac function after MI, with dietary effects more prominent in males.

Exercise-induced changes in myocardial glucose utilization during periods of active cardiac growth.

Exercise training can promote physiological cardiac growth, which has been suggested to involve changes in glucose metabolism to facilitate hypertrophy of cardiomyocytes. In this study, we used a dietary, in vivo isotope labeling approach to examine how exercise training influences the metabolic fate of carbon derived from dietary glucose in the heart during acute, active, and established phases of exercise-induced cardiac growth. Male and female FVB/NJ mice were subjected to treadmill running for up to 4 weeks and cardiac growth was assessed by gravimetry. Cardiac metabolic responses to exercise were assessed via in vivo tracing of [13C6]-glucose via mass spectrometry and nuclear magnetic resonance. We found that the half-maximal cardiac growth response was achieved by approximately 1 week of daily exercise training, with near maximal growth observed in male mice with 2 weeks of training; however, female mice were recalcitrant to exercise-induced cardiac growth and required a higher daily intensity of exercise training to achieve significant, albeit modest, increases in cardiac mass. We also found that increases in the energy charge of adenylate and guanylate nucleotide pools precede exercise-induced changes in cardiac size and were associated with higher glucose tracer enrichment in the TCA pool and in amino acids (aspartate, glutamate) sourced by TCA intermediates. Our data also indicate that the activity of collateral biosynthetic pathways of glucose metabolism may not be markedly altered by exercise. Overall, this study provides evidence that metabolic remodeling in the form of heightened energy charge and increased TCA cycle activity and cataplerosis precedes cardiac growth caused by exercise training in male mice.

Cardiac mitochondrial metabolism during pregnancy and the postpartum period.

The goal of the present study was to characterize changes in mitochondrial respiration in the maternal heart during pregnancy and after birth. Timed pregnancy studies were performed in 12-wk-old female FVB/NJ mice, and cardiac mitochondria were isolated from the following groups of mice: nonpregnant (NP), midpregnancy (MP), late pregnancy (LP), and 1-wk postbirth (PB). Similar to our previous studies, we observed increased heart size during all stages of pregnancy (e.g., MP and LP) and postbirth (e.g., PB) compared with NP mice. Differential cardiac gene and protein expression analyses revealed changes in several mitochondrial transcripts at LP and PB, including several mitochondrial complex subunits and members of the Slc family, important for mitochondrial substrate transport. Respirometry revealed that pyruvate- and glutamate-supported state 3 respiration was significantly higher in PB vs. LP mitochondria, with respiratory control ratio (RCR) values higher in PB mitochondria. In addition, we found that PB mitochondria respired more avidly when given 3-hydroxybutyrate (3-OHB) than mitochondria from NP, MP, and LP hearts, with no differences in RCR. These increases in respiration in PB hearts occurred independent of changes in mitochondrial yield but were associated with higher abundance of 3-hydroxybutyrate dehydrogenase 1. Collectively, these findings suggest that, after birth, maternal cardiac mitochondria have an increased capacity to use 3-OHB, pyruvate, and glutamate as energy sources; however, increases in mitochondrial efficiency in the postpartum heart appear limited to carbohydrate and amino acid metabolism.NEW & NOTEWORTHY Few studies have detailed the physiological adaptations that occur in the maternal heart. We and others have shown that pregnancy-induced cardiac growth is associated with significant changes in cardiac metabolism. Here, we examined mitochondrial respiration and substrate preference in isolated mitochondria from the maternal heart. We show that following birth, cardiac mitochondria are "primed" to respire on carbohydrate, amino acid, and ketone bodies. However, heightened respiratory efficiency is observed only with carbohydrate and amino acid sources. These results suggest that significant changes in mitochondrial respiration occur in the maternal heart in the postpartum period.

CFD-based design optimization of ducted hydrokinetic turbines.

Hydrokinetic turbines extract kinetic energy from moving water to generate renewable electricity, thus contributing to sustainable energy production and reducing reliance on fossil fuels. It has been hypothesized that a duct can accelerate and condition the fluid flow passing the turbine blades, improving the overall energy extraction efficiency. However, no substantial evidence has been provided so far for hydrokinetic turbines. To investigate this problem, we perform a CFD-based optimization study with a blade-resolved Reynolds-averaged Navier-Stokes (RANS) solver to explore the design of a ducted hydrokinetic turbine that maximizes the efficiency of energy extraction. A gradient-based optimization approach is utilized to effectively deal with the high-dimensional design space of the blade and duct geometry, with gradients being calculated through the adjoint method. The final design is re-evaluated through higher-fidelity unsteady RANS (URANS) simulations. Our optimized ducted turbine achieves an efficiency of about 54% over a range of operating conditions, higher than the typical 46% efficiency of unducted turbines.

Coordinated Metabolic Responses Facilitate Cardiac Growth in Pregnancy and Exercise.

PURPOSE OF REVIEW: Pregnancy and exercise are systemic stressors that promote physiological growth of the heart in response to repetitive volume overload and maintenance of cardiac output. This type of remodeling is distinct from pathological hypertrophy and involves different metabolic mechanisms that facilitate growth; however, it remains unclear how metabolic changes in the heart facilitate growth and if these processes are similar in both pregnancy- and exercise-induced cardiac growth. RECENT FINDINGS: The ability of the heart to metabolize a myriad of substrates balances cardiac demands for energy provision and anabolism. During pregnancy, coordination of hormonal status with cardiac reductions in glucose oxidation appears important for physiological growth. During exercise, a reduction in cardiac glucose oxidation also appears important for physiological growth, which could facilitate shuttling of glucose-derived carbons into biosynthetic pathways for growth. Understanding the metabolic underpinnings of physiological cardiac growth could provide insight to optimize cardiovascular health and prevent deleterious remodeling, such as that which occurs from postpartum cardiomyopathy and heart failure. This short review highlights the metabolic mechanisms known to facilitate pregnancy-induced and exercise-induced cardiac growth, both of which require changes in cardiac glucose metabolism for the promotion of growth. In addition, we mention important similarities and differences of physiological cardiac growth in these models as well as discuss current limitations in our understanding of metabolic changes that facilitate growth.

The metabolic state of the heart regulates mitochondrial supercomplex abundance in mice.

Mitochondrial supercomplexes are observed in mammalian tissues with high energy demand and may influence metabolism and redox signaling. Nevertheless, the mechanisms that regulate supercomplex abundance remain unclear. In this study, we examined the composition of supercomplexes derived from murine cardiac mitochondria and determined how their abundance changes with substrate provision or by genetically induced changes to the cardiac glucose-fatty acid cycle. Protein complexes from digitonin-solubilized cardiac mitochondria were resolved by blue-native polyacrylamide gel electrophoresis and were identified by mass spectrometry and immunoblotting to contain constituents of Complexes I, III, IV, and V as well as accessory proteins involved in supercomplex assembly and stability, cristae architecture, carbohydrate and fat oxidation, and oxidant detoxification. Respiratory analysis of high molecular mass supercomplexes confirmed the presence of intact respirasomes, capable of transferring electrons from NADH to O2. Provision of respiratory substrates to isolated mitochondria augmented supercomplex abundance, with fatty acyl substrate (octanoylcarnitine) promoting higher supercomplex abundance than carbohydrate-derived substrate (pyruvate). Mitochondria isolated from transgenic hearts that express kinase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (GlycoLo), which decreases glucose utilization and increases reliance on fatty acid oxidation for energy, had higher mitochondrial supercomplex abundance and activity compared with mitochondria from wild-type or phosphatase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-expressing hearts (GlycoHi), the latter of which encourages reliance on glucose catabolism for energy. These findings indicate that high energetic reliance on fatty acid catabolism bolsters levels of mitochondrial supercomplexes, supporting the idea that the energetic state of the heart is regulatory factor in supercomplex assembly or stability.

Fine Particulate Matter (PM2.5)-Induced Pulmonary Oxidative Stress Contributes to Changes in the Plasma Lipidome and Liver Transcriptome in Mice.

Fine particulate matter (PM2.5) air pollution exposure increases the cardiovascular disease risk. Although the specific mechanisms remain elusive, it is thought that PM2.5-induced oxidative stress and endothelial dysfunction contribute to this pathogenesis. Our previous findings indicate that PM2.5 impairs vascular health via a circulating factor and that plasma lipid changes contribute to the observed vascular effects. In the current study, we extend on these findings by further characterizing PM2.5-induced changes in circulating lipids and examining whether the observed changes were accompanied by related alterations in the liver transcriptome. To address the role of pulmonary oxidative stress, we exposed wild-type (WT) mice and mice that overexpress extracellular superoxide dismutase (ecSOD-Tg) in the lungs to concentrated ambient PM2.5 (CAP, 9 days). We found that CAP decreased circulating complex lipids and increased free fatty acids and acylcarnitines in WT, but not ecSOD-Tg mice. These plasma lipid changes were accompanied by transcriptional changes in genes that regulate lipid metabolism (e.g., upregulation of lipid biosynthesis, downregulation of mitochondrial/peroxisomal FA metabolism) in the liver. The CAP-induced changes in lipid homeostasis and liver transcriptome were accompanied by pulmonary but not hepatic oxidative stress and were largely absent in ecSOD-Tg mice. Our results suggest that PM2.5 impacts hepatic lipid metabolism; however, it remains unclear whether the transcriptional changes in the liver contribute to PM2.5-induced changes in plasma lipids. Regardless, PM2.5-induced changes in the plasma lipidome and hepatic transcriptome are, at least in part, mediated by pulmonary oxidative stress.

Exercise-induced specialized proresolving mediators stimulate AMPK phosphorylation to promote mitochondrial respiration in macrophages.

OBJECTIVE: Physical activity has been shown to reduce the risk of CVD mortality in large-cohort longitudinal studies; however, the mechanisms underpinning the beneficial effects of exercise remain incompletely understood. Emerging data suggest that the risk reducing effect of exercise extends beyond changes in traditional CVD risk factors alone and involves alterations in immunity and reductions in inflammatory mediator production. Our study aimed to determine whether exercise-enhanced production of proresolving lipid mediators contribute to alterations in macrophage intermediary metabolism, which may contribute to the anti-inflammatory effects of exercise. METHODS: Changes in lipid mediators and macrophage metabolism were assessed in C57Bl/6 mice following 4 weeks of voluntary exercise training. To investigate whether exercise-stimulated upregulation of specialized proresolving lipid mediators (SPMs) was sufficient to enhance mitochondrial respiration, both macrophages from control mice and human donors were incubated in vitro with SPMs and mitochondrial respiratory parameters were measured using extracellular flux analysis. Compound-C, an ATP-competitive inhibitor of AMPK kinase activity, was used to investigate the role of AMPK activity in SPM-induced mitochondrial metabolism. To assess the in vivo contribution of 5-lipoxygenase in AMPK activation and exercise-induced mitochondrial metabolism in macrophages, Alox5-/- mice were also subjected to exercise training. RESULTS: Four weeks of exercise training enhanced proresolving lipid mediator production, while also stimulating the catabolism of inflammatory lipid mediators (e.g., leukotrienes and prostaglandins). This shift in lipid mediator balance following exercise was associated with increased macrophage mitochondrial metabolism. We also find that treating human and murine macrophages in vitro with proresolving lipid mediators enhances mitochondrial respiratory parameters. The proresolving lipid mediators RvD1, RvE1, and MaR1, but not RvD2, stimulated mitochondrial respiration through an AMPK-dependent signaling mechanism. Additionally, in a subset of macrophages, exercise-induced mitochondrial activity in vivo was dependent upon 5-lipoxygenase activity. CONCLUSION: Collectively, these results suggest that exercise stimulates proresolving lipid mediator biosynthesis and mitochondrial metabolism in macrophages via AMPK, which might contribute to the anti-inflammatory and CVD risk reducing effect of exercise.

PON2 mediates mitochondrial dysfunction in tracheal epithelial cells in response to a quorum sensing molecule N-(-3-oxododecanoyl)-l-homoserine lactone.

The opportunistic bacterium Pseudomonas aeruginosa secretes the quorum-sensing molecule N-(3-oxododecanoyl)-l-homoserine lactone (C12) to co-ordinate gene expression profiles favorable for infection. Recent studies have demonstrated that high concentrations of C12 impair many aspects of host cell physiology, including mitochondrial function and cell viability. The cytotoxic effects of C12 are mediated by the lactonase enzyme, Paraoxonase 2 (PON2), which hydrolyzes C12 to a reactive metabolite. However, the influence of C12 on host cell physiology at concentrations observed in patients infected with P. aeruginosa is largely unknown. Since the primary site of P. aeruginosa infections is the mammalian airway, we sought to investigate how PON2 modulates the effects of C12 at subtoxic concentrations using immortalized murine tracheal epithelial cells (TECs) isolated from wild-type (WT) or PON2-knockout (PON2-KO) mice. Our data reveal that C12 at subtoxic concentrations disrupts mitochondrial bioenergetics to hinder cellular proliferation in TECs expressing PON2. Subtoxic concentrations of C12 disrupt normal mitochondrial network morphology in a PON2-dependent manner without affecting mitochondrial membrane potential. In contrast, higher concentrations of C12 depolarize mitochondrial membrane potential and subsequently trigger caspase signaling and apoptotic cell death. These findings demonstrate that different concentrations of C12 impact distinct aspects of host airway epithelial cell physiology through PON2 activity in mitochondria.

Biomimetic cardiac tissue culture model (CTCM) to emulate cardiac physiology and pathophysiology ex vivo.

There is need for a reliable in vitro system that can accurately replicate the cardiac physiological environment for drug testing. The limited availability of human heart tissue culture systems has led to inaccurate interpretations of cardiac-related drug effects. Here, we developed a cardiac tissue culture model (CTCM) that can electro-mechanically stimulate heart slices with physiological stretches in systole and diastole during the cardiac cycle. After 12 days in culture, this approach partially improved the viability of heart slices but did not completely maintain their structural integrity. Therefore, following small molecule screening, we found that the incorporation of 100 nM tri-iodothyronine (T3) and 1 µM dexamethasone (Dex) into our culture media preserved the microscopic structure of the slices for 12 days. When combined with T3/Dex treatment, the CTCM system maintained the transcriptional profile, viability, metabolic activity, and structural integrity for 12 days at the same levels as the fresh heart tissue. Furthermore, overstretching the cardiac tissue induced cardiac hypertrophic signaling in culture, which provides a proof of concept for the ability of the CTCM to emulate cardiac stretch-induced hypertrophic conditions. In conclusion, CTCM can emulate cardiac physiology and pathophysiology in culture for an extended time, thereby enabling reliable drug screening.

Glutamine uptake and catabolism is required for myofibroblast formation and persistence.

BACKGROUND: Fibrosis and extracellular matrix remodeling are mediated by resident cardiac fibroblasts (CFs). In response to injury, fibroblasts activate, differentiating into specialized synthetic and contractile myofibroblasts producing copious extracellular matrix proteins (e.g., collagens). Myofibroblast persistence in chronic diseases, such as HF, leads to progressive cardiac dysfunction and maladaptive remodeling. We recently reported that an increase in αKG (alpha-ketoglutarate) bioavailability, which contributes to enhanced αKG-dependent lysine demethylase activity and chromatin remodeling, is required for myofibroblast formation. Therefore, we aimed to determine the substrates and metabolic pathways contributing to αKG biosynthesis and their requirement for myofibroblast formation. METHODS: Stable isotope metabolomics identified glutaminolysis as a key metabolic pathway required for αKG biosynthesis and myofibroblast formation, therefore we tested the effects of pharmacologic inhibition (CB-839) or genetic deletion of glutaminase (Gls1-/-) on myofibroblast formation in both murine and human cardiac fibroblasts. We employed immunofluorescence staining, functional gel contraction, western blotting, and bioenergetic assays to determine the myofibroblast phenotype. RESULTS: Carbon tracing indicated enhanced glutaminolysis mediating increased αKG abundance. Pharmacological and genetic inhibition of glutaminolysis prevented myofibroblast formation indicated by a reduction in αSMA+ cells, collagen gel contraction, collagen abundance, and the bioenergetic response. Inhibition of glutaminolysis also prevented TGFß-mediated histone demethylation and supplementation with cell-permeable αKG rescued the myofibroblast phenotype. Importantly, inhibition of glutaminolysis was sufficient to prevent myofibroblast formation in CFs isolated from the human failing heart. CONCLUSIONS: These results define glutaminolysis as necessary for myofibroblast formation and persistence, providing substantial rationale to evaluate several new therapeutic targets to treat cardiac fibrosis.

Influence of biological sex and exercise on murine cardiac metabolism.

Although the structural and functional effects of exercise on the heart are well established, the metabolic changes that occur in the heart during and after exercise remain unclear. In this study, we used metabolomics to assess time-dependent changes in the murine cardiac metabolome following 1 session of treadmill exercise. After the exercise bout, we also recorded blood lactate, glucose, and ketone body levels and measured cardiac mitochondrial respiration. In both male and female mice, moderate- and high-intensity exercise acutely increased blood lactate levels. In both sexes, low- and moderate-intensity exercise augmented circulating 3-hydroxybutryrate levels immediately after the exercise bout; however, only in female mice did high-intensity exercise increase 3-hydroxybutyrate levels, with significant increases occurring 1 h after the exercise session. Untargeted metabolomics analyses of sedentary female and male hearts suggest considerable sex-dependent differences in basal cardiac metabolite levels, with female hearts characterized by higher levels of pantothenate, pyridoxamine, homoarginine, tryptophan, and several glycerophospholipid and sphingomyelin species and lower levels of numerous metabolites, including acetyl coenzyme A, glucuronate, gulonate, hydroxyproline, prolyl-hydroxyproline, carnosine, anserine, and carnitinylated and glycinated species, as compared with male hearts. Immediately after a bout of treadmill exercise, both male and female hearts had higher levels of corticosterone; however, female mice showed more extensive exercise-induced changes in the cardiac metabolome, characterized by significant, time-dependent changes in amino acids (e.g., serine, alanine, tyrosine, tryptophan, branched-chain amino acids) and the ketone body 3-hydroxybutyrate. Results from experiments using isolated cardiac mitochondria suggest that high-intensity treadmill exercise does not acutely affect respiration or mitochondrial coupling; however, female cardiac mitochondria demonstrate generally higher adenosine diphosphate sensitivity compared with male cardiac mitochondria. Collectively, these findings in mice reveal key sex-dependent differences in cardiac metabolism and suggest that the metabolic network in the female heart is more responsive to physiological stress caused by exercise.

Metabolic signatures of pregnancy-induced cardiac growth.

The goal of this study was to develop an atlas of the metabolic, transcriptional, and proteomic changes that occur with pregnancy in the maternal heart. Timed pregnancy studies in FVB/NJ mice revealed a significant increase in heart size by day 8 of pregnancy (midpregnancy; MP), which was sustained throughout the rest of the term compared with nonpregnant control mice. Cardiac hypertrophy and myocyte cross-sectional area were highest 7 days after birth (postbirth; PB) and were associated with significant increases in end-diastolic and end-systolic left ventricular volumes and higher cardiac output. Metabolomics analyses revealed that by day 16 of pregnancy (late pregnancy; LP) metabolites associated with nitric oxide production as well as acylcholines, sphingomyelins, and fatty acid species were elevated, which coincided with a lower activation state of phosphofructokinase and higher levels of pyruvate dehydrogenase kinase 4 (Pdk4) and ß-hydroxybutyrate dehydrogenase 1 (Bdh1). In the postpartum period, urea cycle metabolites, polyamines, and phospholipid levels were markedly elevated in the maternal heart. Cardiac transcriptomics in LP revealed significant increases in not only Pdk4 and Bdh1 but also genes that regulate glutamate and ketone body oxidation, which were preceded in MP by higher expression of transcripts controlling cell proliferation and angiogenesis. Proteomics analysis of the maternal heart in LP and PB revealed significant reductions in several contractile filament and mitochondrial subunit complex proteins. Collectively, these findings describe the coordinated molecular changes that occur in the maternal heart during and after pregnancy.NEW & NOTEWORTHY Little is known of the underlying molecular and cellular mechanisms that contribute to pregnancy-induced cardiac growth. Several lines of evidence suggest that changes in cardiac metabolism may contribute. Here, we provide a comprehensive metabolic atlas of the metabolomic, proteomic, and transcriptomic changes occurring in the maternal heart. We show that pregnancy-induced cardiac growth is associated with changes in glycerophospholipid, nucleotide, and amino acid metabolism, with reductions in cardiac glucose catabolism. Collectively, these results suggest that substantial metabolic changes occur in the maternal heart during and after pregnancy.

Pyridine nucleotide redox potential in coronary smooth muscle couples myocardial blood flow to cardiac metabolism.

Adequate oxygen delivery to the heart during stress is essential for sustaining cardiac function. Acute increases in myocardial oxygen demand evoke coronary vasodilation and enhance perfusion via functional upregulation of smooth muscle voltage-gated K+ (Kv) channels. Because this response is controlled by Kv1 accessory subunits (i.e., Kvß), which are NAD(P)(H)-dependent aldo-keto reductases, we tested the hypothesis that oxygen demand modifies arterial [NAD(H)]i, and that resultant cytosolic pyridine nucleotide redox state influences Kv1 activity. High-resolution imaging mass spectrometry and live-cell imaging reveal cardiac workload-dependent increases in NADH:NAD+ in intramyocardial arterial myocytes. Intracellular NAD(P)(H) redox ratios reflecting elevated oxygen demand potentiate native coronary Kv1 activity in a Kvß2-dependent manner. Ablation of Kvß2 catalysis suppresses redox-dependent increases in Kv1 activity, vasodilation, and the relationship between cardiac workload and myocardial blood flow. Collectively, this work suggests that the pyridine nucleotide sensitivity and enzymatic activity of Kvß2 controls coronary vasoreactivity and myocardial blood flow during metabolic stress.

Metabolic Determinants of Cardiomyocyte Proliferation.

The adult mammalian heart is recalcitrant to regeneration after injury, in part due to the postmitotic nature of cardiomyocytes. Accumulating evidence suggests that cardiomyocyte proliferation in fetal or neonatal mammals and in regenerative non-mammalian models depends on a conducive metabolic state. Results from numerous studies in adult hearts indicate that conditions of relatively low fatty acid oxidation, low reactive oxygen species generation, and high glycolysis are required for induction of cardiomyocyte proliferation. Glycolysis appears particularly important because it provides branchpoint metabolites for several biosynthetic pathways that are essential for synthesis of nucleotides and nucleotide sugars, amino acids, and glycerophospholipids, all of which are required for daughter cell formation. In addition, the proliferative cardiomyocyte phenotype is supported in part by relatively low oxygen tensions and through the actions of critical transcription factors, coactivators, and signaling pathways that promote a more glycolytic and proliferative cardiomyocyte phenotype, such as hypoxia inducible factor 1α (Hif1α), Yes-associated protein (Yap), and ErbB2. Interventions that inhibit glycolysis or its integrated biosynthetic pathways almost universally impair cardiomyocyte proliferative capacity. Furthermore, metabolic enzymes that augment biosynthetic capacity such as phosphoenolpyruvate carboxykinase 2 and pyruvate kinase M2 appear to be amplifiers of cardiomyocyte proliferation. Collectively, these studies suggest that acquisition of a glycolytic and biosynthetic metabolic phenotype is a sine qua non of cardiomyocyte proliferation. Further knowledge of the regulatory mechanisms that control substrate partitioning to coordinate biosynthesis with energy provision could be leveraged to prompt or augment cardiomyocyte division and to promote cardiac repair.

Transient Cell Cycle Induction in Cardiomyocytes to Treat Subacute Ischemic Heart Failure.

BACKGROUND: The regenerative capacity of the heart after myocardial infarction is limited. Our previous study showed that ectopic introduction of 4 cell cycle factors (4F; CDK1 [cyclin-dependent kinase 1], CDK4 [cyclin-dependent kinase 4], CCNB [cyclin B1], and CCND [cyclin D1]) promotes cardiomyocyte proliferation in 15% to 20% of infected cardiomyocytes in vitro and in vivo and improves cardiac function after myocardial infarction in mice. METHODS: Using temporal single-cell RNA sequencing, we aimed to identify the necessary reprogramming stages during the forced cardiomyocyte proliferation with 4F on a single cell basis. Using rat and pig models of ischemic heart failure, we aimed to start the first preclinical testing to introduce 4F gene therapy as a candidate for the treatment of ischemia-induced heart failure. RESULTS: Temporal bulk and single-cell RNA sequencing and further biochemical validations of mature human induced pluripotent stem cell-derived cardiomyocytes treated with either LacZ or 4F adenoviruses revealed full cell cycle reprogramming in 15% of the cardiomyocyte population at 48 hours after infection with 4F, which was associated mainly with sarcomere disassembly and metabolic reprogramming (n=3/time point/group). Transient overexpression of 4F, specifically in cardiomyocytes, was achieved using a polycistronic nonintegrating lentivirus (NIL) encoding 4F; each is driven by a TNNT2 (cardiac troponin T isoform 2) promoter (TNNT2-4Fpolycistronic-NIL). TNNT2-4Fpolycistronic-NIL or control virus was injected intramyocardially 1 week after myocardial infarction in rats (n=10/group) or pigs (n=6-7/group). Four weeks after injection, TNNT2-4Fpolycistronic-NIL-treated animals showed significant improvement in left ventricular ejection fraction and scar size compared with the control virus-treated animals. At 4 months after treatment, rats that received TNNT2-4Fpolycistronic-NIL still showed a sustained improvement in cardiac function and no obvious development of cardiac arrhythmias or systemic tumorigenesis (n=10/group). CONCLUSIONS: This study provides mechanistic insights into the process of forced cardiomyocyte proliferation and advances the clinical feasibility of this approach by minimizing the oncogenic potential of the cell cycle factors owing to the use of a novel transient and cardiomyocyte-specific viral construct.