👤 Michael S Glennon

Activation of cell cycle regulatory pathways has been detected during pathological cardiomyocyte growth. However, it has remained unclear whether DNA synthesis pathways play a direct role in cardiomyocyte hypertrophy. We previously discovered in a mouse model of hypertrophic cardiomyopathy that there was increased DNA synthesis, which led to cardiomyocyte endoreplication and replication stress-induced DNA damage. We hypothesized that targeting cardiomyocyte endoreplication pathways could reduce pathological myocardial hypertrophy. We utilized murine models of hypertrophic cardiomyopathy secondary to mutations in cardiac Mybpc3 (myosin-binding protein C3) We discovered that p21 protein peaked during the early stages of hypertrophic growth in both murine hypertrophic cardiomyopathy models and a pressure overload hypertrophy model. Using genetic manipulation of p21 expression, we discovered that cardiomyocyte endoreplication and hypertrophic growth were negatively correlated with p21 expression. Mechanistically, we discovered that p21 bound to PCNA (proliferating cell nuclear antigen), which led to a reduction of PCNA binding to POLD1 (DNA polymerase delta 1). Directly targeting PCNA or POLD1 prevented cardiomyocyte DNA synthesis and hypertrophic cardiomyocyte growth. Cardiomyocyte-selective overexpression of p21 using an adeno-associated virus vector reduced long-term pathological left ventricular hypertrophy and improved diastolic function in a preclinical murine model of hypertrophic cardiomyopathy (Myh6 Our results demonstrate that PCNA-POLD1-mediated cardiomyocyte endoreplication drives hypertrophic cardiomyocyte growth, and p21 serves as a negative regulator of this process. Targeting these pathways demonstrates therapeutic potential in preventing pathological myocardial hypertrophy. Show less

Microvasculature dysfunction is a common finding in pathologic remodeling of the heart and is thought to play an important role in the pathogenesis of hypertrophic cardiomyopathy (HCM), a disease caused by sarcomere gene mutations. We hypothesized that microvascular dysfunction in HCM was secondary to abnormal microvascular growth and could occur independent of ventricular hypertrophy. We used multimodality imaging methods to track the temporality of microvascular dysfunction in HCM mouse models harboring mutations in the sarcomere genes We found that microvascular dysfunction in our HCM models occurred secondary to reduced myocardial capillary growth during the early postnatal time period and could occur before the onset of myocardial hypertrophy. We discovered that the E3 ubiquitin protein ligase MDM2 (murine double minute 2) dynamically regulates the protein stability of both HIF1α (hypoxia-inducible factor 1 alpha) and HIF2α (hypoxia-inducible factor 2 alpha)/EPAS1 (endothelial PAS domain protein 1) through canonical and noncanonical mechanisms. The resulting HIF imbalance leads to reduced proangiogenic gene expression during a key period of myocardial capillary growth. Reducing MDM2 protein levels by genetic or pharmacological methods normalized HIF protein levels and prevented the development of microvascular dysfunction in both HCM models. Our results show that sarcomere mutations induce cardiomyocyte MDM2 signaling during the earliest stages of disease, and this leads to long-term changes in the myocardial microenvironment. Show less

Background Sarcomere gene mutations lead to cardiomyocyte hypertrophy and pathological myocardial remodeling. However, there is considerable phenotypic heterogeneity at both the cellular and the organ level, suggesting modifiers regulate the effects of these mutations. We hypothesized that sarcomere dysfunction leads to cardiomyocyte genotoxic stress, and this modifies pathological ventricular remodeling. Methods and Results Using a murine model deficient in the sarcomere protein, Mybpc3 Show less

It remains unclear how perturbations in cardiomyocyte sarcomere function alter postnatal heart development. We utilized murine models that allowed manipulation of cardiac myosin-binding protein C (MYBPC3) expression at critical stages of cardiac ontogeny to study the response of the postnatal heart to disrupted sarcomere function. We discovered that the hyperplastic to hypertrophic transition phase of mammalian heart development was altered in mice lacking MYBPC3 and this was the critical period for subsequent development of cardiomyopathy. Specifically, MYBPC3-null hearts developed evidence of increased cardiomyocyte endoreplication, which was accompanied by enhanced expression of cell cycle stimulatory cyclins and increased phosphorylation of retinoblastoma protein. Interestingly, this response was self-limited at later developmental time points by an upregulation of the cyclin-dependent kinase inhibitor p21. These results provide valuable insights into how alterations in sarcomere protein function modify postnatal heart development and highlight the potential for targeting cell cycle regulatory pathways to counteract cardiomyopathic stimuli. Show less