Short-chain fatty acid, acylation and cardiovascular diseases

JMJD1A Represses the Development of Cardiomyocyte Hypertrophy by Regulating the Expression of Catalase

The histone demethylase JMJD family is involved in various physiological and pathological functions. However, the roles of JMJD1A in the cardiovascular system remain unknown. Here, we studied the function of JMJD1A in cardiac hypertrophy. The mRNA and protein levels of JMJD1A were significantly downregulated in the hearts of human patients with hypertrophic cardiomyopathy and the hearts of C57BL/6 mice underwent cardiac hypertrophy induced by transverse aortic constriction (TAC) surgery or isoproterenol (ISO) infusion. In neonatal rat cardiomyocytes (NRCMs), siRNA-mediated JMJD1A knockdown facilitated ISO or angiotensin II-induced increase in cardiomyocyte size, protein synthesis, and expression of hypertrophic fetal genes, including atrial natriuretic peptide (Anp), brain natriuretic peptide (Bnp), and Myh7. By contrast, overexpression of JMJD1A with adenovirus repressed the development of ISO-induced cardiomyocyte hypertrophy. We observed that JMJD1A reduced the production of total cellular and mitochondrial levels of reactive oxygen species (ROS), which was critically involved in the effects of JMJD1A because either N-acetylcysteine or MitoTEMPO treatment blocked the effects of JMJD1A deficiency on cardiomyocyte hypertrophy. Mechanism study demonstrated that JMJD1A promoted the expression and activity of Catalase under basal condition or oxidative stress. siRNA-mediated loss of Catalase blocked the protection of JMJD1A overexpression against ISO-induced cardiomyocyte hypertrophy. These findings demonstrated that JMJD1A loss promoted cardiomyocyte hypertrophy in a Catalase and ROS-dependent manner.

FBXW7 promotes pathological cardiac hypertrophy by targeting EZH2-SIX1 signaling

F-box and WD repeat domain-containing 7 (FBXW7) is an E3-ubiquitin ligase, which serves as one of the components of the SKP1, CUL1, and F-box protein type ubiquitin ligase (SCF) complex. Previous studies reveal that FBXW7 participates in cancer, inflammation and Parkinson's disease. FBXW7 also contributes to angiogenesis of endothelial cells. However, the function of FBXW7 in cardiac homeostasis remains to elucidate. Here we identified the critical role of FBXW7 during cardiac hypertrophy in humans and rodents. Quantitative real-time PCR (qRT-PCR) and Western blot revealed that the mRNA and protein levels of FBXW7 were upregulated significantly in hypertrophic hearts in human and mouse as well as Angiotensin II (Ang II)-induced hypertrophic neonatal rat cardiomyocytes (NRCM). Gain-of-function (adenovirus) and loss-of-function (siRNA) experiments provided evidence that FBXW7 promoted Ang II-induced cardiomyocyte hypertrophy as demonstrated by the increase in the size of cardiomyocytes and overexpression of hypertrophic fetal genes myosin heavy chain 7 (Myh7) natriuretic peptide a (Nppa), brain natriuretic peptide (Nppb). Further mechanism study revealed that FBXW7 promoted the expression of sine oculis homeobox homolog 1 (SIX1) in cardiomyocytes, which relied on regulation of the stability of the histone methyltransferase EZH2 (Enhancer of zeste homolog 2). Previous work revealed the pro-hypertrophic role of the EZH2-SIX1 axis in rodents. Indeed, our genetic and pharmacological evidence showed that the EZH2-SIX1 signaling was critically involved in FBXW7 functions in Ang II-induced cardiomyocyte hypertrophy. Therefore, we identified FBWX7 as an important regulator of cardiac hypertrophy via modulating the EZH2-SIX1 axis.

Cardiomyocyte Senescence and Cellular Communications Within Myocardial Microenvironments

Cardiovascular diseases have become the leading cause of human death. Aging is an independent risk factor for cardiovascular diseases. Cardiac aging is associated with maladaptation of cellular metabolism, dysfunction (or senescence) of cardiomyocytes, a decrease in angiogenesis, and an increase in tissue scarring (fibrosis). These events eventually lead to cardiac remodeling and failure. Senescent cardiomyocytes show the hallmarks of DNA damage, endoplasmic reticulum stress, mitochondria dysfunction, contractile dysfunction, hypertrophic growth, and senescence-associated secreting phenotype (SASP). Metabolism within cardiomyocytes is essential not only to fuel the pump function of the heart but also to maintain the functional homeostasis and participate in the senescence of cardiomyocytes. The senescence of cardiomyocyte is also regulated by the non-myocytes (endothelial cells, fibroblasts, and immune cells) in the local microenvironment. On the other hand, the senescent cardiomyocytes alter their phenotypes and subsequently affect the non-myocytes in the local microenvironment and contribute to cardiac aging and pathological remodeling. In this review, we first summarized the hallmarks of the senescence of cardiomyocytes. Then, we discussed the metabolic switch within senescent cardiomyocytes and provided a discussion of the cellular communications between dysfunctional cardiomyocytes and non-myocytes in the local microenvironment. We also addressed the functions of metabolic regulators within non-myocytes in modulating myocardial microenvironment. Finally, we pointed out some interesting and important questions that are needed to be addressed by further studies.