Loss Of Cardiomyocytes Research Articles

Cardioprotective effects of nicorandil on mitochondrial apoptosis signaling in the failing heart of cardiac-specific Bcl-2-associated athanogene (BAG) 3 knockout mice

Abstract Background Bcl-2-associated athanogene (BAG) 3 is a known regulator of mitochondrial apoptotic cell death and autophagic protein degradation in the heart. Disruption of the BAG3 gene in a cardiac-specific manner can lead to cardiac failure in mice. However, therapeutic approaches for cardiac failure induced by BAG3 gene disruption remain poorly understood. Method and results We characterized mice with the ablated BAG3 gene using the Cre-recombinase-loxp site system in a cardiac-specific manner (BAG3f/f crossbred with cardiac specific Cre transgenic mice; BAG3 cKO) and examined the therapeutic effect of nicorandil, an antianginal drug, in BAG3 cKO mice. Cardiac BAG3 levels were markedly reduced in the cytoplasmic and mitochondrial fractions from the hearts of BAG3 cKO mice compared to BAG3f/f mice. BAG3cKO mice exhibited cardiac disease such as a reduction in fractional shortening detected by echocardiography, cardiac fibrosis at 6 months of age, and approximately 40% premature death by 6 months of age. Electron microscopy analysis confirmed cardiomyocyte loss and mitochondrial abnormalities in some areas of the heart section from BAG3cKO mice at 4.5 months of age. A marked decrease in the level of cytochrome C in the mitochondrial fraction and a slight increase in the cytoplasmic fraction, along with apoptotic cell death, were observed in hearts from BAG3 cKO mice at 4.5 months. Mitochondrial levels of anti-apoptotic factors, such as Bcl-2 and Bcl-xl, were reduced, while there was a marked increase in Bak1, an apoptotic inducible factor, in hearts from BAG3 cKO mice at 4.5 months of age. These results suggest that cardiac mitochondrial impairment and subsequent apoptotic cell death occurred in BAG3cKO mice. Nicorandil treatment (81 mg/L drinking water) initiated at 2 months of age prevented the reduction of fractional shortening, cardiac fibrosis, ultrastructural cardiac abnormalities, and premature death. Furthermore, nicorandil treatment prevented the decrease in mitochondrial cytochrome C and the increase in cytoplasmic cytochrome C in hearts from BAG3 cKO mice at 4.5 months of age. Nicorandil treatment also inhibited the elevation of mitochondrial Bak1 levels, reduction in Bcl-2 levels, and occurrence of apoptotic cell death in hearts from BAG3 cKO mice at 4.5 months of age. Conclusion Long-term treatment with nicorandil can inhibit cardiac disease induced by cardiac- specific BAG3 ablation through mitochondrial protection via the prevention of activation of mitochondrial apoptosis signaling.

Lats-IN-1 protects cardiac function and promotes regeneration after myocardial infarction by targeting the hippo pathway.

Myocardial infarction (MI), a leading cause of heart failure, is characterized by the loss of cardiomyocytes, which severely limits the heart's regenerative capacity. The Hippo pathway, which regulates cell proliferation and apoptosis, presents a therapeutic target for cardiac regeneration. This study explores the efficacy of Lats-IN-1, a LATS1/2 kinase inhibitor targeting the Hippo pathway, as a novel treatment for MI. Using male C57BL/6 mice subjected to surgically induced MI, we administered Lats-IN-1 and evaluated the effects on cardiac function, infarct size, cardiomyocyte proliferation, and apoptosis through various assays and echocardiographic assessments. Our results demonstrate that Lats-IN-1 significantly improves cardiac function, as evidenced by enhanced ejection fraction and reduced ventricular dimensions. Additionally, Lats-IN-1 decreased infarct size and apoptosis rates while promoting cardiomyocyte proliferation. These findings suggest that Lats-IN-1 promotes cardiac repair and regeneration. By modulating the Hippo pathway and reducing apoptosis markers, Lats-IN-1 represents a promising therapeutic strategy for improving outcomes in heart diseases characterized by cardiomyocyte loss. This study highlights the critical role of the Hippo pathway in facilitating cardiac regeneration.

Bridging the Gap: Advances and Challenges in Heart Regeneration from In Vitro to In Vivo Applications.

Cardiovascular diseases, particularly ischemic heart disease, area leading cause of morbidity and mortality worldwide. Myocardial infarction (MI) results in extensive cardiomyocyte loss, inflammation, extracellular matrix (ECM) degradation, fibrosis, and ultimately, adverse ventricular remodeling associated with impaired heart function. While heart transplantation is the only definitive treatment for end-stage heart failure, donor organ scarcity necessitates the development of alternative therapies. In such cases, methods to promote endogenous tissue regeneration by stimulating growth factor secretion and vascular formation alone are insufficient. Techniques for the creation and transplantation of viable tissues are therefore highly sought after. Approaches to cardiac regeneration range from stem cell injections to epicardial patches and interposition grafts. While numerous preclinical trials have demonstrated the positive effects of tissue transplantation on vasculogenesis and functional recovery, long-term graft survival in large animal models is rare. Adequate vascularization is essential for the survival of transplanted tissues, yet pre-formed microvasculature often fails to achieve sufficient engraftment. Recent studies report success in enhancing cell survival rates in vitro via tissue perfusion. However, the transition of these techniques to in vivo models remains challenging, especially in large animals. This review aims to highlight the evolution of cardiac patch and stem cell therapies for the treatment of cardiovascular disease, identify discrepancies between in vitro and in vivo studies, and discuss critical factors for establishing effective myocardial tissue regeneration in vivo.

PPARγ drives mitochondrial stress signaling and the loss of atrial cardiomyocytes in newborn mice exposed to hyperoxia

Diastolic dysfunction is increasingly common in preterm infants exposed to supplemental oxygen (hyperoxia). Previous studies in neonatal mice showed hyperoxia suppresses fatty acid synthesis genes required for proliferation and survival of atrial cardiomyocytes. The loss of atrial cardiomyocytes creates a hypoplastic left atrium that inappropriately fills the left ventricle during diastole. Here, we show that hyperoxia stimulates adenosine monophosphate-activated kinase (AMPK) and peroxisome proliferator activated receptor-gamma (PPARγ) signaling in atrial cardiomyocytes. While both pathways can regulate lipid homeostasis, PPARγ was the primary pathway by which hyperoxia inhibits fatty acid gene expression and inhibits proliferation of mouse atrial HL-1 cells. It also enhanced the toxicity of hyperoxia by increasing expression of activating transcription factor (ATF) 5 and other mitochondrial stress response genes. Silencing PPARγ signaling restored proliferation and survival of HL-1 cells as well as atrial cardiomyocytes in neonatal mice exposed to hyperoxia. Our findings reveal PPARγ enhances the toxicity of hyperoxia on atrial cardiomyocytes, thus suggesting inhibitors of PPARγ signaling may prevent diastolic dysfunction in preterm infants.

Vectorcardiography Predicts Heart Failure in Patients Following ST Elevation Myocardial Infarction.

Modeling outcomes, such as onset of heart failure (HF) or mortality, in patients following ST elevation myocardial infarction (STEMI) is challenging but clinically very useful. The acute insult following a myocardial infarction and chronic degeneration seen in HF involve a similar process where a loss of cardiomyocytes and abnormal remodeling lead to pump failure. This process may alter the strength and direction of the heart's net depolarization signal. We hypothesize that changes over time in unique parameters extracted using vectorcardiography (VCG) have the potential to predict outcomes in patients post-STEMI and could eventually be used as a noninvasive and cost-effective surveillance tool for characterizing the severity and progression of HF to guide evidence-based therapies. We identified 162 patients discharged from Michigan Medicine between 2016 and 2021 with a diagnosis of acute STEMI. For each patient, a single 12-lead ECG > 1 week pre-STEMI and > 1 week post-STEMI were collected. A set of unique VCG parameters were derived by analyzing features of the QRS complex. We used LASSO regression analysis incorporating clinical variables and VCG parameters to create a predictive model for HF, mortality, or the composite at 90, 180, and 365 days post-STEMI. The VCG model is most predictive for HF onset at 90 days with a robust AUC. Variables from the HF model mitigating or driving risk, at a p < 0.05, were primarily parameters that assess the area swept by the depolarization vector including the 3D integral and convex hull in select spatial octants and quadrants.

Potential Role of Gene Therapy Targeting Hippo Signaling with Adeno-Associated Virus Based Vectors in Heart Failure Post-Myocardial Infarction

Heart failure is a condition that occurs when the heart cannot pump enough blood for the body's needs. This disease is caused by loss of cardiomyocytes and fibrosis, and is a leading cause of death worldwide. Current therapeutic treatments cannot generally directly replace lost cardiomyocytes in the myocardium, so the prognosis for patients with post-myocardial infarction heart failure remains poor. Based on the results of recent research, deactivating the Salvador (Sav) function in the Hippo pathway can regenerate cardiomyocyte cells. Gene therapy using Sav knockdown with adeno-associated virus (AAV) vector-based short hairpin RNA (shRNA), and restricted to cardiomyocytes by using the cTnT promoter, can specifically target cardiomyocyte cells in the infarction area so that it can become a new therapy for heart failure after myocardial infarction. Keywords: AAV, gene therapy, hippo pathway, post-myocardial infarction heart failure

Novel Insights into Post-Myocardial Infarction Cardiac Remodeling through Algorithmic Detection of Cell-Type Composition Shifts.

Recent advances in single cell sequencing have led to an increased focus on the role of cell-type composition in phenotypic presentation and disease progression. Cell-type composition research in the heart is challenging due to large, frequently multinucleated cardiomyocytes that preclude most single cell approaches from obtaining accurate measurements of cell composition. Our in silico studies reveal that ignoring cell type composition when calculating differentially expressed genes (DEGs) can have significant consequences. For example, a relatively small change in cell abundance of only 10% can result in over 25% of DEGs being false positives. We have implemented an algorithmic approach that uses snRNAseq datasets as a reference to accurately calculate cell type compositions from bulk RNAseq datasets through robust data cleaning, gene selection, and multi-sample cross-subject and cross-cell-type deconvolution. We applied our approach to cardiomyocyte-specific α1A adrenergic receptor (CM-α1A-AR) knockout mice. 8-12 week-old mice (either WT or CM-α1A-KO) were subjected to permanent left coronary artery (LCA) ligation or sham surgery (n=4 per group). Transcriptomes from the infarct border zones were collected 3 days later and analyzed using our algorithm to determine cell-type abundances, corrected differential expression calculations using DESeq2, and validated these findings using RNAscope. Uncorrected DEGs for the CM-α1A-KO X LCA interaction term featured many cell-type specific genes such as Timp4 (fibroblasts) and Aplnr (cardiomyocytes) and overall GO enrichment for terms pertaining to cardiomyocyte differentiation (P=3.1E-4). Using our algorithm, we observe a striking loss of cardiomyocytes and gain in fibroblasts in the α1A-KO + LCA mice that was not recapitulated in WT + LCA animals, although we did observe a similar increase in macrophage abundance in both conditions. This recapitulates prior results that showed a much more severe heart failure phenotype in CM-α1A-KO + LCA mice. Following correction for cell-type, our DEGs now highlight a novel set of genes enriched for GO terms such as cardiac contraction (P=3.7E-5) and actin filament organization (P=6.3E-5). Our algorithm identifies and corrects for cell-type abundance in bulk RNAseq datasets opening new avenues for research on novel genes and pathways as well as an improved understanding of the role of cardiac cell types in cardiovascular disease.

Abstract We131: Systems-Enabled Drug Repurposing to Regulate Cardiomyocyte Proliferation

Introduction: The inability of the adult heart to regenerate results in prevalent morbidity and mortality related to myocardial infarction and heart failure. This lack of cardiac regeneration is driven by the loss of cardiomyocytes (CMs), with limited supporting endogenous CM renewal. While many individual regulators of CM proliferation have been implicated, the field lacks strategies to identify druggable proliferative signaling pathways and prioritize candidate therapeutics. Our goal is to predict and experimentally validate FDA-approved drugs and their respective mechanisms that regulate CM proliferation. Methods: A logic-based differential equation model of CM proliferation signaling was integrated with drug-target interactions from a publicly available database (DrugBank) to simulate the effect of drugs on CM proliferation phenotypes (Binucleation, Cytokinesis, DNA Replication, Mitosis, and Polyploid). A virtual screen with knockdown combinations of regulators identified signaling mechanisms responsible for mediating the effect of drugs, and literature validation was performed against published experimental data investigating the drugs or the drug targets in CMs. Neonatal rat CMs were treated with the YAP-activating drug TT10 or drugs predicted to increase CM proliferation. Proliferation was measured by high-content microscopy and DNA replication and mitosis positive cells were identified from image analysis (CellProfiler) to discern CM proliferation from endoreplication. Results: We identified 16 unique drug-target interactions predicted to regulate CM proliferation phenotypes. Four drugs were predicted to increase CM phenotypic proliferation outputs. Experimental validation confirmed lithium, a GSK3beta-antagonist, induces cell cycle activity in neonatal rat CMs as evidenced by increased Ki67 expression in cardiac Troponin T positive cells. The model predicts cyclin D is critical in mediating this response and subsequent experiments measured changes in cyclin D expression in response to lithium treatment. Retrospective analysis of clinical data (TriNetX and AERSMine) indicates more adverse events of congenital cardiac disorders were reported in patients exposed to lithium. Conclusion: We identified lithium to promote DNA replication in CMs by upregulating cyclin D. This study advances the current knowledge of CM proliferation regulators by providing insight into new pathways targeted with existing drugs that can ultimately impact cardiac regeneration.

Abstract We034: Hjurp Promotes Cardiomyocyte Proliferation and Heart Regeneration by Mediating CenpA Assembly

Background: Loss of cardiomyocytes without replenishment is one of the main cellular mechanisms leading to heart failure. Promoting cardiomyocyte proliferation and heart regeneration has become a therapeutic strategy to rescue heart failure. Therefore, we need to understand the differences between neonatal cardiomyocytes and adult cardiomyocytes, summarize the mechanism of cardiomyocyte exit from the cell cycle, and find potential intervention targets. Method: Combined analysis of bulk RNA-seq, ATAC-seq, and histone CUT&amp;Tag of 1-day-old mouse and 7-day-old mouse cardiomyocytes to screen for Hjurp . In vitro , siRNA was used to knock down Hjurp in neonatal rat cardiomyocytes, and adenovirus was used to overexpress Hjurp . RT-qPCR and immunofluorescence were used to detect cardiomyocyte proliferation and cardiomyocyte number. In vivo , adenovirus was injected into the mouse heart in situ to knock down Hjurp . Immunofluorescence was used to detect cardiomyocyte proliferation. Masson staining was used to detect the proportion of myocardial fibrosis and echocardiography was used to detect cardiac function to reflect cardiac regeneration and repair. Results: HJURP was identified by RNA-seq, ATAC-seq, and histone CUT&amp;Tag as a key regulator of cardiomyocyte proliferation during neonatal heart regeneration in mice. The expression levels of Hjurp and Cenp-A decrease with the weakening of cardiomyocyte proliferation ability. In vitro , Hjurp overexpression promoted whereas Hjurp knockdown attenuated cardiomyocyte proliferation. In vivo , cardiomyocyte proliferation and heart regeneration were suspended in neonatal mice after cardiac injury when Hjurp was knockdown in cardiomyocytes. Conclusion: Our study confirms that HJURP is necessary for cardiomyocyte proliferation and cardiac regeneration after cardiac injury. As an assembly element of centromeres during the cell cycle, overexpression of HJURP is sufficient to promote cardiomyocyte proliferation, which may be accomplished by promoting CENP-A assembly. Thus, HJURP might serve as a potential novel target in heart regeneration after myocardial infarction.

Abstract Mo046: GJA1-20k Restores Connexin-43 Trafficking and β-Catenin Signaling in Myocytes Lacking Desmoplakin

Background: Arrhythmogenic Cardiomyopathy (ACM) is an insidious hereditary heart disease that results in structural and electrical cardiac abnormalities leading to arrhythmogenesis and heart failure. ACM is characterized by cardiomyocyte loss, decreased cellular coupling, and fibrofatty replacement. The disease arises from mutations in desmosomal genes, such as plakophilin (PKP), desmoglein (DSG), and desmoplakin (DSP). The pathogenesis of this disease is linked to dysfunction at the level of several cellular processes and pathways, including Wnt/β-catenin signaling. Recent evidence has shown that GJA1-20k, a truncated isoform of Connexin-43 (Cx43) generated by internal translation, has a therapeutic role in preserving Cx43 trafficking and cell-cell coupling in ACM of DSG origin. This study aims to investigate the role of GJA1-20k in protecting against ACM of DSP origin by evaluating its effect in cell models on Cx43 trafficking and Wnt/β-catenin signaling. Methods: DSP knockdown was performed on HEK cells and mouse neonatal cardiomyocytes. The role of GJA1-20k was determined using imaging, biochemical, and molecular biology techniques. Results: Protein levels of Cx43 and β-catenin were decreased on Western blot (WB) upon DSP knockdown. These findings were corroborated through imaging wherein the signal intensity for Cx43 at cellular junctions and β-catenin at the membrane was significantly decreased compared to the control group. β-catenin signal intensity was also decreased within the nucleus. Upon administration of GJA1-20k, protein levels of Cx43 were normalized on WB. Moreover, the ratio of phosphorylated β-catenin (inactive) to total β-catenin was decreased. Imaging studies identified a significant increase in Cx43 and β-catenin at the membrane in ACM models treated with GJA1-20k. This was also accompanied by an increase in β-catenin signal intensity within the nucleus. A TOP-flash luciferase assay was performed and revealed a significant increase in β-catenin transcriptional activity in the presence of GJA1-20k despite DSP knockdown. Conclusions: These results suggest that GJA1-20k is able to rescue Cx43 trafficking and recover Wnt/β-catenin signaling in cells and cardiomyocytes lacking DSP. The ability of GJA1-20k to restore dysfunctional genetic pathways involved in arrhythmogenesis and fibro-adipogenesis make it an attractive potential candidate for targeted therapy against ACM.

Abstract We022: Depletion of Tip60 After Myocardial Infarction Induces Histone H2A.Z Deacetylation Followed by Cardiomyocyte Dedifferentiation/Cell-Cycle Activation

Myocardial infarction (MI) leads to cardiomyocyte (CM) loss, resulting in cardiac dysfunction and heart failure. Remuscularization of injured myocardium requires proliferation of surviving CMs. However, approaches aimed at inducing CM regeneration following MI have been inadequate. To this end, we are targeting the acetyltransferase Tip60 (Tat-interactive protein 60 kD), a pleiotropic tumor suppressor encoded by the Kat5 gene. Using a murine genetic model, we previously reported that disruption of Kat5 promotes CM cell-cycle re-entry, and protects against the damaging effects of MI. It is becoming increasingly recognized that pre-existing CMs must undergo dedifferentiation accompanied by reversion to glycolytic metabolism in order to resume proliferation. The site-specific acetylation of the histone variant H2A.Z at lysine K4/K7 (H2A.Zac K4/K7 ) has been shown to maintain the differentiated state in hematopoietic stem cells (HSCs), neurons, and skeletal myocytes. Here, we report that Tip60 depletion post-MI results in the near-complete absence of H2A.Zac K4/K7 in CMs. This is associated with the enrichment of differentially expressed genes (DEGs) in epithelial to mesenchymal transitioning (EMT), cytoskeletal disassembly, extracellular matrix (ECM) softening, and metabolic reprogramming. To assess therapeutic relevance, we have begun to evaluate the potential cardioprotective effects of the anti-parasitic drug pentamidine, a known Tip60 inhibitor. Systemic administration of pentamidine on days 3-16 post-MI preserved cardiac function, accompanied by CM cell-cycle activation. These data suggest that pentamidine treatment enhances remuscularization, thereby promoting the retention of post-MI function, supporting the translational promise of targeting Tip60 as an innovative therapy for ischemic heart disease.

Abstract We115: Modified mRNA Therapeutics Inhibits Cardiomyocyte Apoptosis and Induces Cardiac Protection in Ischemic Heart Diseases

Introduction: Cardiovascular diseases are the leading cause of mortality worldwide. After myocardial infarction (MI), there is a permanent loss of cardiomyocytes (CMs), and as the mammalian heart has limited regenerative capacity, it leads to Heart Failure. Extracellular vesicles (EVs) derived from induced pluripotent stem cells (iPSCs) have emerged as potential therapeutic agents, yet their precise mechanism of CM survival and cardiac repair remains elusive. Hypothesis: The myocardial delivery of hiPSC-EV-specific protein improves cardiac function and mice survival post-MI by inhibiting CM apoptosis and oxidative stress molecular pathways. Methods and Results: Our preliminary studies confirmed that hiPSC-EVs promote CM survival post-MI in mice, and through proteomic analysis, we identified a novel protein uniquely expressed in hiPSC-EVs. We showed that the myocardial delivery of hiPSC-EVs specific protein in the form of modRNA inhibited CM apoptosis and induced CM survival post-MI. This increase in the CM's survival by hiPSC-EVs specific protein expression was associated with reduced scar size, improved cardiac function, and mice survival 28 days post-MI. Furthermore, using the siRNA and small molecule inhibition of hiPSC-EVs specific protein, we found enhanced MI-induced CM apoptosis post-MI. Mechanistic insights reveal the hiPSC-EVs specific protein induced STAT3 pathway, while STAT3 pathway inhibition by small molecule repressed hiPSC-EVs specific protein induced CM survival in vitro . Additionally, our preliminary study shows this protein translocates to the nucleus post-MI or ischemic injury. Conclusion: Taken together, the myocardial injection of hiPSC-EVs specific protein through a highly therapeutic modRNA tool improves cardiac function by inhibiting CMs apoptosis, and reactivating cardiac repair post-injury. Moreover, our studies demonstrate that the modRNA (protein) approach in mouse models is potentially adaptable for mRNA therapeutics in a clinical setup.

Abstract We122: Suppression of defender against cell death 1 (Dad1) induces cardiomyocyte death by regulating cell adhesion proteins.

Introduction: Suppression of cardiomyocyte loss is considered a promising strategy for the prevention of the onset of heart failure (HF). Previously, defender against cell death 1 ( Dad1 ) was identified as a cytoprotective gene. Dad1 forms a complex with staurosporine and temperature sensitive 3A (Stt3A), a catalytic subunit of oligosaccharyltransferase (OST) complex which is responsible for N-glycosylation. However, the function of Dad1 in cardiomyocytes remains unknown. Hypothesis: The disruption of cell-extracellular matrix interactions results in cell death, known as anoikis. Because various cell adhesion proteins are N-glycosylated, we hypothesized that Dad1 suppressed anoikis by regulating N-glycosylation of cell adhesion proteins in cardiomyocytes. Methods: Neonatal rat cardiomyocytes were cultured and the expression of Dad1 or Stt3A was knocked down using siRNA. The protein expression was assessed with immunoblot analysis, and cell viability was evaluated using a CellTiter-Blue assay kit. Results: The suppression of Dad1 using siRNAs reduced cardiomyocyte viability ( p &lt;0.01, n=4). Interestingly, suppression of Dad1 impaired the N-glycosylation of integrin β1 and decreased the expression of mature integrin β1 ( p &lt;0.01, n=3). These changes inactivated integrin-mediated signal transduction through dephosphorylation of focal adhesion kinase ( p &lt;0.01, n=5). In addition, enhanced cell-extracellular matrix interactions by using adhesamine rescued the cardiomyocyte death by Dad1 knockdown ( p &lt;0.01, n=4). Next, we pursued the relationship between Dad1 and Stt3A. Dad1 knockdown decreased the expression of Stt3A ( p &lt;0.01, n=6). Suppression of Stt3A induced cardiomyocyte death accompanied by the changes of cell adhesion proteins ( p &lt;0.01, n=4). Finally, double knockdown of Dad1 and Stt3A did not induce a further reduction in cell viability compared with the knockdown of only Dad1 ( p &lt;0.05, n=4), suggesting that cardiomyocyte death by Dad1 knockdown was dependent on Stt3A. Conclusion: Dad1 is required for the stabilization of Stt3A and suppresses cardiomyocyte anoikis by regulating N-glycosylation of cell adhesion proteins in an OST-dependent manner. Dad1-mediated cardiomyocyte survival could be a therapeutic target against HF.

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

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. 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. 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.

Anti-Ferroptotic Treatment Deteriorates Myocardial Infarction by Inhibiting Angiogenesis and Altering Immune Response.

Mammalian cardiomyocytes have limited regenerative ability. Cardiac disease, such as congenital heart disease and myocardial infarction, causes an initial loss of cardiomyocytes through regulated cell death (RCD). Understanding the mechanisms that govern RCD in the injured myocardium is crucial for developing therapeutics to promote heart regeneration. We previously reported that ferroptosis, a non-apoptotic and iron-dependent form of RCD, is the main contributor to cardiomyocyte death in the injured heart. To investigate the mechanisms underlying the preference for ferroptosis in cardiomyocytes, we examined the effects of anti-ferroptotic reagents in infarcted mouse hearts. The results revealed that the anti-ferroptotic reagent did not improve neonatal heart regeneration, and further compromised the cardiac function of juvenile hearts. On the other hand, ferroptotic cardiomyocytes played a supportive role during wound healing by releasing pro-angiogenic factors. The inhibition of ferroptosis in the regenerating mouse heart altered the immune and angiogenic responses. Our study provides insights into the preference for ferroptosis over other types of RCD in stressed cardiomyocytes, and guidance for designing anti-cell-death therapies for treating heart disease.

Downregulation of RIP3 ameliorates the left ventricular mechanics and function after myocardial infarction via modulating NF-κB/NLRP3 pathway.

Adverse cardiac mechanical remodeling is critical for the progression of heart failure following myocardial infarction (MI). We previously demonstrated the involvement of RIP3-mediated necroptosis in the loss of functional cardiomyocytes and cardiac dysfunction post-MI. Herein, we investigated the role of RIP3 in NOD-like receptor protein 3 (NLRP3)-mediated inflammation and evaluated the effects of RIP3 knockdown on myocardial mechanics and functional changes after MI. Our findings revealed that mice with MI for 4 weeks exhibited impaired left ventricular (LV) myocardial mechanics, as evidenced by a significant decrease in strain and strain rate in each segment of the LV wall during both systole and diastole. However, RIP3 knockdown ameliorated cardiac dysfunction by improving LV myocardial mechanics not only in the anterior wall but also in other remote nonischemic segments of the LV wall. Mechanistically, knockdown of RIP3 effectively inhibited the activation of the nuclear factor kappa-B (NF-κB)/NLRP3 pathway, reduced the levels of interleukin-1β (IL-1β) and interleukin-18 (IL-18) in the heart tissues, and mitigated adverse cardiac remodeling following MI. These results suggest that downregulation of RIP3 holds promise for preventing myocardial inflammation and cardiac mechanical remodeling following MI by regulating the NF-κB/NLRP3 pathway.

The Role of High-Sensitivity Troponin T Regarding Prognosis and Cardiovascular Outcome across Heart Failure Spectrum.

Background: Cardiac troponin release is related to the cardiomyocyte loss occurring in heart failure (HF). The prognostic role of high-sensitivity cardiac troponin T (hs-cTnT) in several settings of HF is under investigation. The aim of the study is to assess the prognostic role of intrahospital hs-cTnT in patients admitted due to HF. Methods: In this observational, single center, prospective study, patients hospitalized due to HF have been enrolled. Admission, in-hospital peak, and discharge hs-cTnT have been assessed. Patients were followed up for 6 months. Cardiovascular (CV) death, HF hospitalization (HFH), and worsening HF (WHF) (i.e., urgent ambulatory visit/loop diuretics escalation) events have been assessed at 6-month follow up. Results: 253 consecutive patients have been enrolled in the study. The hs-cTnT median values at admission and discharge were 0.031 ng/mL (IQR 0.02-0.078) and 0.031 ng/mL (IQR 0.02-0.077), respectively. The risk of CV death/HFH was higher in patients with admission hs-cTnT values above the median (p = 0.02) and in patients who had an increase in hs-cTnT during hospitalization (p = 0.03). Multivariate Cox regression analysis confirmed that hs-cTnT above the median (OR: 2.06; 95% CI: 1.02-4.1; p = 0.04) and increase in hs-cTnT during hospitalization (OR:1.95; 95%CI: 1.006-3.769; p = 0.04) were predictors of CV death/HFH. In a subgroup analysis of patients with chronic HF, hs-cTnT above the median was associated with increased risk of CV death/HFH (p = 0.03), while in the subgroup of patients with HFmrEF/HFpEF, hs-cTnT above the median was associated with outpatient WHF events (p = 0.03). Conclusions: Inpatient hs-cTnT levels predict CV death/HFH in patients with HF. In particular, in the subgroup of chronic HF patients, hs-cTnT is predictive of CV death/HFH; while in patients with HFmrEF/HFpEF, hs-cTnT predicts WHF events.

The influence of endurance exercise training on myocardial fibrosis and arrhythmogenesis in a coxsackievirus B3 myocarditis mouse model

Nonischaemic myocardial fibrosis is associated with cardiac dysfunction, malignant arrhythmias and sudden cardiac death. In the absence of a specific aetiology, its finding as late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging is often attributed to preceding viral myocarditis. Athletes presenting with ventricular arrhythmias often have nonischaemic LGE. Previous studies have demonstrated an adverse effect of exercise on the course of acute viral myocarditis. In this study, we have investigated, for the first time, the impact of endurance training on longer-term outcomes such as myocardial fibrosis and arrhythmogenicity in a murine coxsackievirus B3 (CVB)-induced myocarditis model. Male C57BL/6J mice (n = 72) were randomly assigned to 8 weeks of forced treadmill running (EEX) or no exercise (SED). Myocarditis was induced 2 weeks later by a single intraperitoneal injection with CVB, versus vehicle in the controls (PBS). In a separate study, mice (n = 30) were subjected to pretraining for 13 weeks (preEEX), without continuation of exercise during myocarditis. Overall, continuation of exercise resulted in a milder clinical course of viral disease, with less weight loss and better preserved running capacity. CVB-EEX and preEEX-CVB mice tended to have a lower mortality rate. At sacrifice (i.e. 6 weeks after inoculation), the majority of virus was cleared from the heart. Histological assessment demonstrated prominent myocardial inflammatory infiltration and cardiomyocyte loss in both CVB groups. Inflammatory lesions in the CVB-EEX group contained higher numbers of pro-inflammatory cells (iNOS-reactive macrophages and CD8+ T lymphocytes) compared to these in CVB-SED. Treadmill running during myocarditis increased interstitial fibrosis [82.4% (CVB-EEX) vs. 56.3% (CVB-SED); P = 0.049]. Additionally, perivascular and/or interstitial fibrosis with extensive distribution was more likely to occur with exercise [64.7% and 64.7% (CVB-EEX) vs. 50% and 31.3% (CVB-SED); P = 0.048]. There was a numerical, but not significant, increase in the number of scars per cross-section (1.9 vs. 1.2; P = 0.195), with similar scar distribution and histological appearance in CVB-EEX and CVB-SED. In vivo electrophysiology studies did not induce sustained monomorphic ventricular tachycardia, only nonsustained (usually polymorphic) runs. Their cumulative beat count and duration paralleled the increased fibrosis between CVB-EEX and CVB-SED, but the difference was not significant (P = 0.084 for each). Interestingly, in mice that were subjected to pretraining only without continuation of exercise during myocarditis, no differences between pretrained and sedentary mice were observed at sacrifice (i.e. 6 weeks after inoculation and training cessation) with regard to myocardial inflammation, fibrosis, and ventricular arrhythmogenicity. In conclusion, endurance exercise during viral myocarditis modulates the inflammatory process with more pro-inflammatory cells and enhances perivascular and interstitial fibrosis development. The impact on ventricular arrhythmogenesis requires further exploration.

MYH7 R453C induced cardiac remodelling via activating TGF-β/Smad2/3, ERK1/2 and Nox4/ROS/NF-κB signalling pathways.

Hypertrophic cardiomyopathy (HCM) is a monogenic cardiac disorder commonly induced by sarcomere gene mutations. However, the mechanism for HCM is not well defined. Here, we generated transgenic MYH7 R453C and MYH6 R453C piglets and found both developed typical cardiac hypertrophy. Unexpectedly, we found serious fibrosis and cardiomyocyte loss in the ventricular of MYH7 R453C, not MYH6 R453C piglets, similar to HCM patients. Then, RNA-seq analysis and western blotting identified the activation of ERK1/2 and PI3K-Akt pathways in MYH7 R453C. Moreover, we observed an increased expression of fetal genes and an excess of reactive oxygen species (ROS) in MYH7 R453C piglet models, which was produced by Nox4 and subsequently induced inflammatory response. Additionally, the phosphorylation levels of Smad2/3, ERK1/2 and NF-kB p65 proteins were elevated in cardiomyocytes with the MYH7 R453C mutation. Furthermore, epigallocatechin gallate, a natural bioactive compound, could be used as a drug to reduce cell death by adjusting significant downregulation of the protein expression of Bax and upregulated Bcl-2 levels in the H9C2 models with MYH7 R453C mutation. In conclusion, our study illustrated that TGF-β/Smad2/3, ERK1/2 and Nox4/ROS pathways have synergistic effects on cardiac remodelling and inflammation in MYH7 R453C mutation.

Alcohol exposure during pregnancy induces cardiac mitochondrial damage in offspring mice.

Prenatal alcohol exposure (PAE) has been linked to congenital heart disease and fetal alcohol syndrome. The heart primarily relies on mitochondria to generate energy, so impaired mitochondrial function due to alcohol exposure can significantly affect cardiac development and function. Our study aimed to investigate the impact of PAE on myocardial and mitochondrial functions in offspring mice. We administered 30% alcohol (3 g/kg) to pregnant C57BL/6 mice during the second trimester. We assessed cardiac function by transthoracic echocardiography, observed myocardial structure and fibrosis through staining tests and electron transmission microscopy, and detected cardiomyocyte apoptosis with dUTP nick end labeling assay and real-time quantitative PCR. Additionally, we measured the reactive oxygen species content, ATP level, and mitochondrial DNA copy number in myocardial mitochondria. Mitochondrial damage was evaluated by assessing the level of mitochondrial membrane potential and the opening degree of mitochondrial permeability transition pores. Our findings revealed that PAE caused cardiac systolic dysfunction, ventricular enlargement, thinned ventricular wall, cardiac fibrosis in the myocardium, scattered loss of cardiomyocytes, and disordered arrangement of myocardial myotomes in the offspring. Furthermore, we observed a significant increase in mitochondrial reactive oxygen species content, a decrease in mitochondrial membrane potential, ATP level, and mitochondrial DNA copy number, and sustained opening of mitochondrial permeability transition pores in the heart tissues of the offspring. These results indicated that PAE had adverse effects on the cardiac structure and function of the newborn mice and could trigger oxidative stress in their myocardia and contribute to mitochondrial dysfunction.