Conditional depletion of the acetyltransferase Tip60 protects against the damaging effects of myocardial infarction

Emerging Epigenetic Therapies for the Treatment of Cardiac Fibrosis

Fibrosis is a pathological process characterized by excessive extracellular matrix (ECM) deposition, leading to tissue stiffening and organ dysfunction. It is a major contributor to chronic diseases affecting various organs, with limited therapeutic options available. Among the different forms of fibrosis, cardiac fibrosis is particularly relevant due to its impact on cardiovascular diseases (CVDs), which remain the leading cause of morbidity and mortality worldwide. This process is driven by activated cardiac fibroblasts (CFs), which promote ECM accumulation in response to chronic stressors. Epigenetic mechanisms, including DNA methylation, histone modifications, and chromatin remodeling, are key regulators of fibroblast activation and fibrotic gene expression. Enzymes such as DNA methyltransferases (DNMTs), histone methyltransferases (HMTs), histone acetyltransferases (HATs), and histone deacetylases (HDACs) have emerged as potential therapeutic targets, and epigenetic inhibitors have shown promise in modulating these enzymes to attenuate fibrosis by controlling fibroblast function and ECM deposition. These small-molecule compounds offer advantages such as reversibility and precise temporal control, making them attractive candidates for therapeutic intervention. This review aims to provide a comprehensive overview of the mechanisms by which epigenetic regulators influence cardiac fibrosis and examines the latest advances in preclinical epigenetic therapies. By integrating recent data from functional studies, single-cell profiling, and drug development, it highlights key molecular targets, emerging therapeutic strategies, and current limitations, offering a critical framework to guide future research and clinical translation.

Mitigation of Injury from Myocardial Infarction by Pentamidine, an Inhibitor of the Acetyltransferase Tip60

PURPOSE

There is an urgent unmet need for new pharmacologic approaches that promote re-muscularization and repair following myocardial infarction (MI). We previously reported that genetic depletion of the acetyltransferase Tip60 after MI in a mouse model activates the CM cell-cycle, reduces scarring, and restores cardiac function, and that these beneficial effects are mimicked by the Tip60-selective inhibitor TH1834. Here, we investigated whether the FDA-approved anti-microbial agent pentamidine, a Tip60 inhibitor from which TH1834 is derived, also protects from the damaging effects of MI.

METHODS

Adult (10-14 weeks old) C57Bl/6 mice were subjected to permanent left coronary artery ligation to induce MI. Subsequently, echocardiography, electrocardiography, cardiac staining, and molecular analyses were performed to monitor the effects of treatment with pentamidine on cardiac injury and function.

RESULTS

We report that transient systemic administration of pentamidine on days 3-16 post-MI at a daily dose of 3 mg/kg efficiently improved cardiac function for up to ten months. This was accompanied by improved survival, diminished scarring, and increased activation of cell-cycle markers in CMs located in the infarct border zone in the absence of hypertrophy. Histological assessments suggested that post-MI treatment with pentamidine reduced site-specific acetylation of the minor histone variant H2A.Z at lysines K4 and K7 in CMs, indicative of the dedifferentiation process which must occur prior to CM proliferation. Treating mice with pentamidine post-MI produced no prominent electrophysiological changes.

CONCLUSIONS

These findings support the translational potential of pentamidine for treatment of MI, and provide evidence that functional improvement is mediated, in part, by CM renewal due to inhibition of the acetyltransferase activity of Tip60.

Histone H2A.Z Deacetylation and Dedifferentiation in Infarcted/Tip60-depleted Cardiomyocytes

Myocardial infarction (MI) results in the loss of billions of cardiomyocytes (CMs), resulting in cardiac dysfunction. To re-muscularize injured myocardium, new CMs must be generated via renewed proliferation of surviving CMs. Approaches to induce proliferation of CMs after injury have been insufficient. Toward this end we are targeting the acetyltransferase Tip60, encoded by the Kat5 gene, based on the rationale that its pleiotropic functions combine to block CM proliferation at multiple checkpoints. We previously demonstrated that genetic depletion of Tip60 in a mouse model after MI reduces scarring, retains cardiac function, and activates the CM cell-cycle, although it remains unclear whether this culminates in the generation of daughter CMs. In order for pre-existing CMs in the adult heart to undergo proliferation, it has become accepted that they must first dedifferentiate, a process highlighted by loss of maturity, epithelial to mesenchymal transitioning (EMT), and reversion from fatty acid oxidation to glycolytic metabolism, accompanied by softening of the myocardial extracellular matrix (ECM). Based on recently published findings that Tip60 induces and maintains the differentiated state of hematopoietic stem cells and neurons via site-specific acetylation of the histone variant H2A.Z, we assessed levels of acetylated H2A.Z and dedifferentiation markers after depleting Tip60 in CMs post-MI. We report that genetic depletion of Tip60 from CMs after MI results in the near obliteration of acetylated H2A.Z in CM nuclei, accompanied by the altered expression of genes indicative of EMT induction, ECM softening, decreased fatty acid oxidation, and depressed expression of genes that regulate the TCA cycle. In accord with the possibility that site-specific acetylation of H2A.Z maintains adult CMs in a mature state of differentiation, CUT&Tag revealed enrichment of H2A.ZacK4/K7 in genetic motifs and in GO terms respectively associated with CM transcription factor binding and muscle development/differentiation. Along with our previous findings, these results support the notion that Tip60 has multiple targets in CMs that combine to maintain the differentiated state and prevent proliferation.

Acetyltransferase in cardiovascular disease and aging

Acetyltransferases are enzymes that catalyze the transfer of an acetyl group to a substrate, a modification referred to as acetylation. Loss-of-function variants in genes encoding acetyltransferases can lead to congenital disorders, often characterized by intellectual disability and heart and muscle defects. Their activity is influenced by dietary nutrients that alter acetyl coenzyme A levels, a key cofactor. Cardiovascular diseases, including ischemic, hypertensive, and diabetic heart diseases - leading causes of mortality in the elderly - are largely attributed to prolonged lifespan and the growing prevalence of metabolic syndrome. Acetyltransferases thus serve as a crucial link between lifestyle modifications, cardiometabolic disease, and aging through both epigenomic and non-epigenomic mechanisms. In this review, we discuss the roles and relevance of acetyltransferases. While the sirtuin family of deacetylases has been extensively studied in longevity, particularly through fasting-mediated NAD+ metabolism, recent research has brought attention to the essential roles of acetyltransferases in health and aging-related pathways, including cell proliferation, DNA damage response, mitochondrial function, inflammation, and senescence. We begin with an overview of acetyltransferases, classifying them by domain structure, including canonical and non-canonical lysine acetyltransferases, N-terminal acetyltransferases, and sialic acid O-acetyltransferases. We then discuss recent advances in understanding acetyltransferase-related pathologies, particularly focusing on cardiovascular disease and aging, and explore their potential therapeutic applications for promoting health in older individuals.

A meta-analysis and systematic review of myocardial infarction-induced cardiomyocyte proliferation in adult mouse heart

BACKGROUND

The proliferation capacity of adult cardiomyocytes is very limited in the normal adult mammalian heart. Previous studies implied that cardiomyocyte proliferation increases after injury stimulation, but the result is controversial partly due to different methodologies. We aim to evaluate whether myocardial infarction (MI) stimulates cardiomyocyte proliferation in adult mice.

METHODS

A comprehensive literature search was conducted through PubMed/Medline, Embase, and Web of Science databases from 1 January 2000 to 21 December 2023. The SYRCLE's Risk of Bias tool for animal experiments was used to evaluate the quality of the literature by two independent reviewers. Twenty-six studies with cell cycle indicators (Ki67+, PH3+, BrdU/EdU+, and AurkB+) to evaluate cycling cardiomyocytes were collected for a meta-analysis. Another 10 studies with genetic reporter/tracing systems to evaluate cardiomyocyte proliferation were collected for a systematic review.

RESULTS

Evaluating cardiomyocyte proliferation by immunostaining of the cell cycle indicators on heart tissue, the meta-analysis showed that differences of Ki67+, PH3+, and BrdU/EdU+ cycling cardiomyocytes between MI and Sham groups were not statistically significant. In the post-MI heart, the percentages of PH3+, BrdU/EdU+, and AurkB+ cardiomyocytes were not significantly different between the infarct border zone and remote zone. The percentage of Ki67+ cardiomyocytes in the infarct border zone was statistically higher than that in the remote zone. Most of the studies (6 out of 10) using genetic reporter/tracing mouse systems showed that the difference in cardiomyocyte proliferation between MI and Sham groups was not statistically significant. Among the other 4 studies, at least 3 studies could not demonstrate that MI stimulates bona fide cardiomyocyte proliferation because of methodological shortages.

CONCLUSIONS

MI injury increases Ki67+ cycling adult mouse cardiomyocytes in infarct border zone. Very little overwhelming evidence shows that MI stimulates bona fide proliferation in the adult heart.

Targeting cardiomyocyte cell cycle regulation in heart failure

Heart failure continues to be a significant global health concern, causing substantial morbidity and mortality. The limited ability of the adult heart to regenerate has posed challenges in finding effective treatments for cardiac pathologies. While various medications and surgical interventions have been used to improve cardiac function, they are not able to address the extensive loss of functioning cardiomyocytes that occurs during cardiac injury. As a result, there is growing interest in understanding how the cell cycle is regulated and exploring the potential for stimulating cardiomyocyte proliferation as a means of promoting heart regeneration. This review aims to provide an overview of current knowledge on cell cycle regulation and mechanisms underlying cardiomyocyte proliferation in cases of heart failure, while also highlighting established and novel therapeutic strategies targeting this area for treatment purposes.

Polyploidy Promotes Hypertranscription, Apoptosis Resistance, and Ciliogenesis in Cancer Cells and Mesenchymal Stem Cells of Various Origins: Comparative Transcriptome In Silico Study

Mesenchymal stem cells (MSC) attract an increasing amount of attention due to their unique therapeutic properties. Yet, MSC can undergo undesirable genetic and epigenetic changes during their propagation in vitro. In this study, we investigated whether polyploidy can compromise MSC oncological safety and therapeutic properties. For this purpose, we compared the impact of polyploidy on the transcriptome of cancer cells and MSC of various origins (bone marrow, placenta, and heart). First, we identified genes that are consistently ploidy-induced or ploidy-repressed through all comparisons. Then, we selected the master regulators using the protein interaction enrichment analysis (PIEA). The obtained ploidy-related gene signatures were verified using the data gained from polyploid and diploid populations of early cardiomyocytes (CARD) originating from iPSC. The multistep bioinformatic analysis applied to the cancer cells, MSC, and CARD indicated that polyploidy plays a pivotal role in driving the cell into hypertranscription. It was evident from the upregulation of gene modules implicated in housekeeping functions, stemness, unicellularity, DNA repair, and chromatin opening by means of histone acetylation operating via DNA damage associated with the NUA4/TIP60 complex. These features were complemented by the activation of the pathways implicated in centrosome maintenance and ciliogenesis and by the impairment of the pathways related to apoptosis, the circadian clock, and immunity. Overall, our findings suggest that, although polyploidy does not induce oncologic transformation of MSC, it might compromise their therapeutic properties because of global epigenetic changes and alterations in fundamental biological processes. The obtained results can contribute to the development and implementation of approaches enhancing the therapeutic properties of MSC by removing polyploid cells from the cell population.

The genetics of cardiomyocyte polyploidy

The regulation of ploidy in cardiomyocytes is a complex and tightly regulated aspect of cardiac development and function. Cardiomyocyte ploidy can range from diploid (2N) to 8N or even 16N, and these states change during key stages of development and disease progression. Polyploidization has been associated with cellular hypertrophy to support normal growth of the heart, increased contractile capacity, and improved stress tolerance in the heart. Conversely, alterations to ploidy also occur during cardiac pathogenesis of diseases, such as ischemic and non-ischemic heart failure and arrhythmia. Therefore, understanding which genes control and modulate cardiomyocyte ploidy may provide mechanistic insight underlying cardiac growth, regeneration, and disease. This chapter summarizes the current knowledge regarding the genes involved in the regulation of cardiomyocyte ploidy. We discuss genes that have been directly tested for their role in cardiomyocyte polyploidization, as well as methodologies used to identify ploidy alterations. These genes encode cell cycle regulators, transcription factors, metabolic proteins, nuclear scaffolding, and components of the sarcomere, among others. The general physiological and pathological phenotypes in the heart associated with the genetic manipulations described, and how they coincide with the respective cardiomyocyte ploidy alterations, are further discussed in this chapter. In addition to being candidates for genetic-based therapies for various cardiac maladies, these genes and their functions provide insightful evidence regarding the purpose of widespread polyploidization in cardiomyocytes.

Myocardial ischemia/reperfusion: Translational pathophysiology of ischemic heart disease

Ischemic heart disease is the greatest health burden and most frequent cause of death worldwide. Myocardial ischemia/reperfusion is the pathophysiological substrate of ischemic heart disease. Improvements in prevention and treatment of ischemic heart disease have reduced mortality in developed countries over the last decades, but further progress is now stagnant, and morbidity and mortality from ischemic heart disease in developing countries are increasing. Significant problems remain to be resolved and require a better pathophysiological understanding. The present review attempts to briefly summarize the state of the art in myocardial ischemia/reperfusion research, with a view on both its coronary vascular and myocardial aspects, and to define the cutting edges where further mechanistic knowledge is needed to facilitate translation to clinical practice.

RGS7 balances acetylation/de-acetylation of p65 to control chemotherapy-dependent cardiac inflammation

Cardiotoxicity remains a major limitation in the clinical utility of anthracycline chemotherapeutics. Regulator of G-protein Signaling 7 (RGS7) and inflammatory markers are up-regulated in the hearts of patients with a history of chemotherapy particularly those with reduced left-ventricular function. RGS7 knockdown in either the murine myocardium or isolated murine ventricular cardiac myocytes (VCM) or cultured human VCM provided marked protection against doxorubicin-dependent oxidative stress, NF-κB activation, inflammatory cytokine production, and cell death. In exploring possible mechanisms causally linking RGS7 to pro-inflammatory signaling cascades, we found that RGS7 forms a complex with acetylase Tip60 and deacetylase sirtuin 1 (SIRT1) and controls the acetylation status of the p65 subunit of NF-κB. In VCM, the detrimental impact of RGS7 could be mitigated by inhibiting Tip60 or activating SIRT1, indicating that the ability of RGS7 to modulate cellular acetylation capacity is critical for its pro-inflammatory actions. Further, RGS7-driven, Tip60/SIRT1-dependent cytokines released from ventricular cardiac myocytes and transplanted onto cardiac fibroblasts increased oxidative stress, markers of transdifferentiation, and activity of extracellular matrix remodelers emphasizing the importance of the RGS7-Tip60-SIRT1 complex in paracrine signaling in the myocardium. Importantly, while RGS7 overexpression in heart resulted in sterile inflammation, fibrotic remodeling, and compromised left-ventricular function, activation of SIRT1 counteracted the detrimental impact of RGS7 in heart confirming that RGS7 increases acetylation of SIRT1 substrates and thereby drives cardiac dysfunction. Together, our data identify RGS7 as an amplifier of inflammatory signaling in heart and possible therapeutic target in chemotherapeutic drug-induced cardiotoxicity.

Pharmacological inhibition of the acetyltransferase Tip60 mitigates myocardial infarction injury

Pharmacologic strategies that target factors with both pro-apoptotic and anti-proliferative functions in cardiomyocytes (CMs) may be useful for the treatment of ischemic heart disease. One such multifunctional candidate for drug targeting is the acetyltransferase Tip60, which is known to acetylate both histone and non-histone protein targets that have been shown in cancer cells to promote apoptosis and to initiate the DNA damage response, thereby limiting cellular expansion. Using a murine model, we recently published findings demonstrating that CM-specific disruption of the Kat5 gene encoding Tip60 markedly protects against the damaging effects of myocardial infarction (MI). In the experiments described here, in lieu of genetic targeting, we administered TH1834, an experimental drug designed to specifically inhibit the acetyltransferase domain of Tip60. We report that, similar to the effect of disrupting the Kat5 gene, daily systemic administration of TH1834 beginning 3 days after induction of MI and continuing for 2 weeks of a 4-week timeline resulted in improved systolic function, reduced apoptosis and scarring, and increased activation of the CM cell cycle, effects accompanied by reduced expression of genes that promote apoptosis and inhibit the cell cycle and reduced levels of CMs exhibiting phosphorylated Atm. These results support the possibility that drugs that inhibit the acetyltransferase activity of Tip60 may be useful agents for the treatment of ischemic heart disease.

The Tip60/Ep400 chromatin remodeling complex impacts basic cellular functions in cranial neural crest-derived tissue during early orofacial development

The cranial neural crest plays a fundamental role in orofacial development and morphogenesis. Accordingly, mutations with impact on the cranial neural crest and its development lead to orofacial malformations such as cleft lip and palate. As a pluripotent and dynamic cell population, the cranial neural crest undergoes vast transcriptional and epigenomic alterations throughout the formation of facial structures pointing to an essential role of factors regulating chromatin state or transcription levels. Using CRISPR/Cas9-guided genome editing and conditional mutagenesis in the mouse, we here show that inactivation of Kat5 or Ep400 as the two essential enzymatic subunits of the Tip60/Ep400 chromatin remodeling complex severely affects carbohydrate and amino acid metabolism in cranial neural crest cells. The resulting decrease in protein synthesis, proliferation and survival leads to a drastic reduction of cranial neural crest cells early in fetal development and a loss of most facial structures in the absence of either protein. Following heterozygous loss of Kat5 in neural crest cells palatogenesis was impaired. These findings point to a decisive role of the Tip60/Ep400 chromatin remodeling complex in facial morphogenesis and lead us to conclude that the orofacial clefting observed in patients with heterozygous KAT5 missense mutations is at least in part due to disturbances in the cranial neural crest.

Measuring cardiomyocyte cell-cycle activity and proliferation in the age of heart regeneration

During the past two decades, the field of mammalian myocardial regeneration has grown dramatically, and with this expanded interest comes increasing claims of experimental manipulations that mediate bona fide proliferation of cardiomyocytes. Too often, however, insufficient evidence or improper controls are provided to support claims that cardiomyocytes have definitively proliferated, a process that should be strictly defined as the generation of two de novo functional cardiomyocytes from one original cardiomyocyte. Throughout the literature, one finds inconsistent levels of experimental rigor applied, and frequently the specific data supplied as evidence of cardiomyocyte proliferation simply indicate cell-cycle activation or DNA synthesis, which do not necessarily lead to the generation of new cardiomyocytes. In this review, we highlight potential problems and limitations faced when characterizing cardiomyocyte proliferation in the mammalian heart, and summarize tools and experimental standards, which should be used to support claims of proliferation-based remuscularization. In the end, definitive establishment of de novo cardiomyogenesis can be difficult to prove; therefore, rigorous experimental strategies should be used for such claims.