Culturing Cardiac Tissue Slices Under Continuous Physiological Mechanical Stretches.

Testing drugs in vivo and in vitro have been essential elements for the discovery of new therapeutics. Due to the recent advances in in vitro cell culture models, such as human-induced pluripotent stem cell-derived cardiomyocytes and 3D multicell type organoid culture methods, the detection of adverse cardiac events prior to human clinical trials has improved. However, there are still numerous therapeutics whose adverse cardiac effects are not detected until human trials due to the inability of these cell cultures to fully model the complex multicellular organization of an intact human myocardium. Cardiac tissue slices are a possible alternative solution. Myocardial slices are a 300-micron thin snapshot of the myocardium, capturing a section of the adult heart in a 1 × 1 cm section. Using a culture method that incorporates essential nutrients and electrical stimulation, tissue slices can be maintained in culture for 6 days with full viability and functionality. With the addition of mechanical stimulation and humoral cues, tissue slices can be cultured for 12 days. Here we provide detailed methods for how to culture cardiac tissue slices under continuous mechanical stimulation in the cardiac tissue culture model (CTCM) device. The CTCM incorporates four essential factors for maintaining tissue slices in culture for 12 days: mechanical stimulation, electrical stimulation, nutrients, and humoral cues. The CTCM can also be used to model disease conditions, such as overstretch-induced cardiac hypertrophy. The versatility of the CTCM illustrates its potential to be a medium-throughput screening platform for personalized drug testing.

Gene therapy encoding cell cycle factors to treat chronic ischemic heart failure in rats.

AIMS: Gene therapies to induce cardiomyocyte (CM) cell cycle re-entry have shown a potential to treat subacute ischaemic heart failure (IHF) but have not been tested in the more relevant setting of chronic IHF. Our group recently showed that polycistronic non-integrating lentivirus encoding Cdk1/CyclinB1 and Cdk4/CyclinD1 (TNNT2-4Fpolycistronic-NIL) is effective in inducing CM cell cycle re-entry and ameliorating subacute IHF models and preventing the subsequent IHF-induced congestions in the liver, kidneys, and lungs in rats and pigs. Here, we aim to test the long-term efficacy of TNNT2-4Fpolycistronic-NIL in a rat model of chronic IHF, a setting that differs pathophysiologically from subacute IHF and has greater clinical relevance. METHODS AND RESULTS: Rats were subjected to a 2-h coronary occlusion followed by reperfusion; 4 weeks later, rats were injected intramyocardially with either TNNT2-4Fpolycistronic-NIL or LacZ-NIL. Four months post-viral injection, TNNT2-4Fpolycistronic-NIL-treated rats showed a significant reduction in scar size and a significant improvement in left ventricular (LV) systolic cardiac function but not in the LV dilatation associated with chronic IHF. A mitosis reporter system developed in our lab showed significant induction of CM mitotic activity in TNNT2-4Fpolycistronic-NIL-treated rats. CONCLUSION: This study demonstrates, for the first time, that TNNT2-4Fpolycistronic-NIL gene therapy induces CM cell cycle re-entry in chronic IHF and improves LV function, and that this salubrious effect is sustained for at least 4 months. Given the high prevalence of chronic IHF, these results have significant clinical implications for developing a novel treatment for this deadly disease.

Pharmacological or genetic inhibition of LTCC promotes cardiomyocyte proliferation through inhibition of calcineurin activity.

Cardiomyocytes (CMs) lost during ischemic cardiac injury cannot be replaced due to their limited proliferative capacity, which leads to progressive heart failure. Calcium (Ca2+) is an important signal transducer that regulates key cellular processes, but its role in regulating CM proliferation is incompletely understood. A drug screen targeting proteins involved in CM calcium cycling in human embryonic stem cell-derived cardiac organoids (hCOs) revealed that only the inhibition of L-Type Calcium Channel (LTCC), but not other Ca2+ regulatory proteins (SERCA or RYR), induced the CM cell cycle. Furthermore, overexpression of Ras-related associated with Diabetes (RRAD), an endogenous inhibitor of LTCC, induced CM cell cycle activity in vitro, in human cardiac slices, and in vivo. Mechanistically, LTCC inhibition by RRAD induces the cell cycle in CMs by modulating calcineurin activity and translocating Hoxb13 to the CM nucleus. Together, this represents a robust pathway for regenerative strategies.

Development of new adeno-associated virus capsid variants for targeted gene delivery to human cardiomyocytes.

Recombinant adeno-associated viruses (rAAVs) have emerged as one of the most promising gene therapy vectors that have been successfully used in pre-clinical models of heart disease. However, this has not translated well to humans due to species differences in rAAV transduction efficiency. As a result, the search for human cardiotropic capsids is a major contemporary challenge. We used a capsid-shuffled rAAV library to perform directed evolution in human iPSC-derived cardiomyocytes (hiPSC-CMs). Five candidates emerged, with four presenting high sequence identity to AAV6, while a fifth divergent variant was related to AAV3b. Functional analysis of the variants was performed in vitro using hiPSC-CMs, cardiac organoids, human cardiac slices, non-human primate and porcine cardiac slices, as well as mouse heart and liver in vivo. We showed that cell entry was not the best predictor of transgene expression efficiency. The novel variant rAAV.KK04 was the best-performing vector in human-based screening platforms, exceeding the benchmark rAAV6. None of the novel capsids demonstrate a significant transduction of liver in vivo. The range of experimental models used revealed the value of testing for tropism differences under the conditions of human specificity, bona fide, myocardium and cell type of interest.

Improved Cardiac Function in Postischemic Rats Using an Optimized Cardiac Reprogramming Cocktail Delivered in a Single Novel Adeno-Associated Virus.

BACKGROUND: Cardiac reprogramming is a technique to directly convert nonmyocytes into myocardial cells using genes or small molecules. This intervention provides functional benefit to the rodent heart when delivered at the time of myocardial infarction or activated transgenically up to 4 weeks after myocardial infarction. Yet, several hurdles have prevented the advancement of cardiac reprogramming for clinical use. METHODS: Through a combination of screening and rational design, we identified a cardiac reprogramming cocktail that can be encoded in a single adeno-associated virus. We also created a novel adeno-associated virus capsid that can transduce cardiac fibroblasts more efficiently than available parental serotypes by mutating posttranslationally modified capsid residues. Because a constitutive promoter was needed to drive high expression of these cell fate-altering reprogramming factors, we included binding sites to a cardiomyocyte-restricted microRNA within the 3' untranslated region of the expression cassette that limits expression to nonmyocytes. After optimizing this expression cassette to reprogram human cardiac fibroblasts into induced cardiomyocyte-like cells in vitro, we also tested the ability of this capsid/cassette combination to confer functional benefit in acute mouse myocardial infarction and chronic rat myocardial infarction models. RESULTS: We demonstrated sustained, dose-dependent improvement in cardiac function when treating a rat model 2 weeks after myocardial infarction, showing that cardiac reprogramming, when delivered in a single, clinically relevant adeno-associated virus vector, can support functional improvement in the postremodeled heart. This benefit was not observed with GFP (green fluorescent protein) or a hepatocyte reprogramming cocktail and was achieved even in the presence of immunosuppression, supporting myocyte formation as the underlying mechanism. CONCLUSIONS: Collectively, these results advance the application of cardiac reprogramming gene therapy as a viable therapeutic approach to treat chronic heart failure resulting from ischemic injury.

A novel small molecule inhibitor of p38⍺ MAP kinase augments cardiomyocyte cell cycle entry in response to direct cell cycle stimulation.

BACKGROUND AND PURPOSE: Myocardial infarction (MI) is the leading cause of mortality globally due in part to the limited ability of cardiomyocytes (CMs) to regenerate. Recently, we demonstrated that overexpression of four-cell cycle factors, CDK1, CDK4, cyclin B1 and cyclin D1 (4F), induced cell division in ~20% of the post-mitotic CMs overexpressed 4F. The current study aims to identify a small molecule that augments 4F-induced CM cycle induction. EXPERIMENTAL APPROACH, KEY RESULTS: Screening of small molecules with a potential to augment 4F-induced cell-cycle induction in 60-day-old mature human induced pluripotent cardiomyocytes (hiPS-CMs) revealed N-(4,6-Dimethylpyridin-2-yl)-4-(pyridine-4-yl)piperazine-1-carbothioamide (NDPPC), which activates cell cycle progression in 4F-transduced hiPS-CMs. Autodock tool and Autodock vina computational methods showed that NDPPC has a potential interaction with the binding site at the human p38⍺ mitogen-activated protein kinase (p38⍺ MAP kinase), a critical negative regulator of the mammalian cell cycle. A p38 MAP kinase activity assay showed that NDPPC inhibits p38⍺ with 5-10 times lower IC50 compared to the other P38 isoforms in a dose-dependent manner. Overexpression of p38⍺ MAP kinase in CMs inhibited 4F cell cycle induction, and treatment with NDPPC reversed the cell cycle inhibitory effect. CONCLUSION AND IMPLICATIONS: NDPPC is a novel inhibitor for p38 MAP kinase and is a promising drug to augment CM cell cycle response to the 4F. NDPPC could become an adjunct treatment with other cell cycle activators for heart failure treatment.

Restored autophagy is protective against PAK3-induced cardiac dysfunction.

Despite the development of clinical treatments, heart failure remains the leading cause of mortality. We observed that p21-activated kinase 3 (PAK3) was augmented in failing human and mouse hearts. Furthermore, mice with cardiac-specific PAK3 overexpression exhibited exacerbated pathological remodeling and deteriorated cardiac function. Myocardium with PAK3 overexpression displayed hypertrophic growth, excessive fibrosis, and aggravated apoptosis following isoprenaline stimulation as early as two days. Mechanistically, using cultured cardiomyocytes and human-relevant samples under distinct stimulations, we, for the first time, demonstrated that PAK3 acts as a suppressor of autophagy through hyper-activation of the mechanistic target of rapamycin complex 1 (mTORC1). Defective autophagy in the myocardium contributes to the progression of heart failure. More importantly, PAK3-provoked cardiac dysfunction was mitigated by administering an autophagic inducer. Our study illustrates a unique role of PAK3 in autophagy regulation and the therapeutic potential of targeting this axis for heart failure.

FGF21/FGFR1-ß-KL cascade in cardiomyocytes modulates angiogenesis and inflammation under metabolic stress.

Diabetes is a metabolic disorder with an increased risk of developing heart failure. Inflammation and damaged vasculature are the cardinal features of diabetes-induced cardiac damage. Moreover, systemic metabolic stress triggers discordant intercellular communication, thus culminating in cardiac dysfunction. Fibroblast growth factor 21 (FGF21) is a pleiotropic hormone transducing cellular signals via fibroblast growth factor receptor 1 (FGFR1) and its co-receptor beta-klotho (ß-KL). This study first demonstrated a decreased expression or activity of FGFR1 and ß-KL in both human and mouse diabetic hearts. Reinforcing cardiac FGFR1 and ß-KL expression can alleviate pro-inflammatory response and endothelial dysfunction upon diabetic stress. Using proteomics, novel cardiomyocyte-derived anti-inflammatory and proangiogenic factors regulated by FGFR1-ß-KL signaling were identified. Although not exhaustive, this study provides a unique insight into the protective topology of the cardiac FGFR1-ß-KL signaling-mediated intercellular reactions in the heart in response to metabolic stress.

Literature Review: Pathophysiology of Heart Failure with Preserved Ejection Fraction.

Heart failure with preserved ejection fraction is a growing public health concern, a disease with poor health outcomes, and is showing increased prevalence globally. This review paper explores the literature with a focus on the pathophysiology and microbiology of preserved ejection fraction heart failure while drawing connections between preserved and reduced ejection fraction states. The discussion teases out the cellular level changes that affect the overall dysfunction of the cardiac tissue, including the clinical manifestations, microbiological changes (endothelial cells, fibroblasts, cardiomyocytes, and excitation-contraction coupling), and the burden of structural diastolic dysfunction. The goal of this review is to summarize the pathophysiological disease state of heart failure with preserved ejection fraction to enhance understanding, knowledge, current treatment models of this pathology.

Transient gene therapy using cell cycle factors reverses renin-angiotensin-aldosterone system activation in heart failure rat model.

The loss of cardiomyocytes after myocardial infarction (MI) leads to heart failure. Recently, we demonstrated that transient overexpression of 4 cell cycle factors (4F), using a polycistronic non-integrating lentivirus (TNNT2-4F-NIL) resulted in significant improvement in cardiac function in a rat model of MI. Yet, it is crucial to demonstrate the reversal of the heart failure-related pathophysiological manifestations, such as renin-angiotensin-aldosterone system activation (RAAS). To assess that, Fisher 344 rats were randomized to receive TNNT2-4F-NIL or control virus seven days after coronary occlusion for 2 h followed by reperfusion. 4 months after treatment, N-terminal pro-brain natriuretic peptide, plasma renin activity, and aldosterone levels returned to the normal levels in rats treated with TNNT2-4F-NIL but not in vehicle-treated rats. Furthermore, the TNNT2-4F-NIL-treated group showed significantly less liver and kidney congestion than vehicle-treated rats. Thus, we conclude that in rat models of MI, TNNT2-4F-NIL reverses RAAS activation and subsequent systemic congestion.

The impact of senescence on muscle wasting in chronic kidney disease.

BACKGROUND: Muscle wasting is a common complication of chronic kidney disease (CKD) that is associated with higher mortality. Although the mechanisms of myofibre loss in CKD has been widely studied, the contribution of muscle precursor cell (MPC) senescence remains poorly understood. Senescent MPCs no longer proliferate and can produce proinflammatory factors or cytokines. In this study, we tested the hypothesis that the senescence associated secretory phenotype (SASP) of MPCs contributes to CKD-induced muscle atrophy and weakness. METHODS: CKD was induced in mice by 5/6th nephrectomy. Kidney function, muscle size, and function were measured, and markers of atrophy, inflammation, and senescence were evaluated using immunohistochemistry, immunoblots, or qPCR. To study the impact of senescence, a senolytics cocktail of dasatinib + quercetin (D&Q) was given orally to mice for 8 weeks. To investigate CKD-induced senescence at the cellular level, primary MPCs were incubated with serum from CKD or control subjects. The roles of specific proteins in MPC senescence were studied using adenoviral transduction, siRNA, and plasmid transfection. RESULTS: In the hindlimb muscles of CKD mice, (i) the senescence biomarker SA-ß-gal was sharply increased (~30-fold); (ii) the DNA damage response marker γ-H2AX was increased 1.9-fold; and (iii) the senescence pathway markers p21 and p16INK4a were increased 1.99-fold and 2.82-fold, respectively (all values, P < 0.05), whereas p53 was unchanged. γ-H2AX, p21, and p16INK4A were negatively correlated at P < 0.05 with gastrocnemius weight, suggesting a causal relationship with muscle atrophy. Administration of the senolytics cocktail to CKD mice for 8 weeks eliminated the disease-related elevation of p21, p16INK4a , and γ-H2AX, abolished positive SA-ß-gal, and depressed the high levels of the SASP cytokines, TNF-α, IL-6, IL-1ß, and IFN (all values, P < 0.05). Skeletal muscle weight, myofibre cross-sectional area, and grip function were improved in CKD mice receiving D&Q. Markers of protein degradation, inflammation, and MPCs dysfunction were also attenuated by D&Q treatment compared with the vehicle treatment in 5/6th nephrectomy mice (all values, P < 0.05). Uraemic serum induced senescence in cultured MPCs. Overexpression of FoxO1a in MPCs increased the number of p21+ senescent cells, and p21 siRNA prevented uraemic serum-induced senescence (P < 0.05). CONCLUSIONS: Senescent MPCs are likely to contribute to the development of muscle wasting during CKD by producing inflammatory cytokines. Limiting senescence with senolytics ameliorated muscle wasting and improved muscle strength in vivo and restored cultured MPC functions. These results suggest potential new therapeutic targets to improve muscle health and function in CKD.

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.

Paracrine signal emanating from stressed cardiomyocytes aggravates inflammatory microenvironment in diabetic cardiomyopathy.

Myocardial inflammation contributes to cardiomyopathy in diabetic patients through incompletely defined underlying mechanisms. In both human and time-course experimental samples, diabetic hearts exhibited abnormal ER, with a maladaptive shift over time in rodents. Furthermore, as a cardiac ER dysfunction model, mice with cardiac-specific p21-activated kinase 2 (PAK2) deletion exhibited heightened myocardial inflammatory response in diabetes. Mechanistically, maladaptive ER stress-induced CCAAT/enhancer-binding protein homologous protein (CHOP) is a novel transcriptional regulator of cardiac high-mobility group box-1 (HMGB1). Cardiac stress-induced release of HMGB1 facilitates M1 macrophage polarization, aggravating myocardial inflammation. Therapeutically, sequestering the extracellular HMGB1 using glycyrrhizin conferred cardioprotection through its anti-inflammatory action. Our findings also indicated that an intact cardiac ER function and protective effects of the antidiabetic drug interdependently attenuated the cardiac inflammation-induced dysfunction. Collectively, we introduce an ER stress-mediated cardiomyocyte-macrophage link, altering the macrophage response, thereby providing insight into therapeutic prospects for diabetes-associated cardiac dysfunction.

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.

Artificial Intelligence Based Framework to Quantify the Cardiomyocyte Structural Integrity in Heart Slices.

PURPOSE: Drug induced cardiac toxicity is a disruption of the functionality of cardiomyocytes which is highly correlated to the organization of the subcellular structures. We can analyze cellular structures by utilizing microscopy imaging data. However, conventional image analysis methods might miss structural deteriorations that are difficult to perceive. Here, we propose an image-based deep learning pipeline for the automated quantification of drug induced structural deteriorations using a 3D heart slice culture model. METHODS: In our deep learning pipeline, we quantify the induced structural deterioration from three anticancer drugs (doxorubicin, sunitinib, and herceptin) with known adverse cardiac effects. The proposed deep learning framework is composed of three convolutional neural networks that process three different image sizes. The results of the three networks are combined to produce a classification map that shows the locations of the structural deteriorations in the input cardiac image. RESULTS: The result of our technique is the capability of producing classification maps that accurately detect drug induced structural deterioration on the pixel level. CONCLUSION: This technology could be widely applied to perform unbiased quantification of the structural effect of the cardiotoxins on heart slices.

Cell cycle induction in human cardiomyocytes is dependent on biosynthetic pathway activation.

AIMS: The coordinated gene and metabolic programs that facilitate cardiomyocyte entry and progression in the cell cycle are poorly understood. The purpose of this study was to identify the metabolic changes that influence myocyte proliferation. METHODS AND RESULTS: In adult mouse cardiomyocytes and human induced pluripotent stem cell cardiomyocytes (hiPS-CMs), cell cycle initiation by ectopic expression of Cyclin B1, Cyclin D1, CDK1, and CDK4 (termed 4F) downregulated oxidative phosphorylation genes and upregulated genes that regulate ancillary biosynthetic pathways of glucose metabolism. Results from metabolic analyses and stable isotope tracing experiments indicate that 4F-mediated cell cycle induction in hiPS-CMs decreases glucose oxidation and oxidative phosphorylation and augments NAD+, glycogen, hexosamine, phospholipid, and serine biosynthetic pathway activity. Interventions that diminish NAD+ synthesis, serine synthesis, or protein O-GlcNAcylation decreased 4F-mediated cell cycle entry. In a gain of function approach, we overexpressed phosphoenolpyruvate carboxykinase 2 (PCK2), which can drive carbon from the Krebs cycle to the glycolytic intermediate pool, and found that PCK2 augments 4F-mediated cell cycle entry. CONCLUSIONS: These findings suggest that a metabolic shift from catabolic to anabolic activity is a critical step for cardiomyocyte cell cycle entry and is required to facilitate proliferation.

Induced Cardiomyocyte Proliferation: A Promising Approach to Cure Heart Failure.

Unlike some lower vertebrates which can completely regenerate their heart, the human heart is a terminally differentiated organ. Cardiomyocytes lost during cardiac injury and heart failure cannot be replaced due to their limited proliferative capacity. Therefore, cardiac injury generally leads to progressive failure. Here, we summarize the latest progress in research on methods to induce cardiomyocyte cell cycle entry and heart repair through the alteration of cardiomyocyte plasticity, which is emerging as an effective strategy to compensate for the loss of functional cardiomyocytes and improve the impaired heart functions.