IRX2 activated by jumonji domain-containing protein 2A is crucial for cardiac hypertrophy and dysfunction in response to the hypertrophic stimuli

JMJD2A mediates transcriptional activation of SFRP4 and regulates oxidative stress and mitochondrial dysfunction in heart failure

The importance of mitochondrial dysfunction and oxidative stress has been indicated in the progression of heart failure (HF). The molecular mechanisms, however, remain to be fully elucidated. This study aimed to explore the role and underlying mechanism of secreted frizzled-related protein 4 (SFRP4) in these two events in HF. Mice with HF were developed using transverse aortic constriction, and hematoxylin-eosin staining, MASSON staining, and Terminal deoxynucleotidyl transferase (TdT)-mediated 2'-Deoxyuridine 5'- Triphosphate nick end labeling (TUNEL assays) were conducted to detect morphological damage in the myocardial tissues of mice. HL-1 mouse cardiomyocytes were induced with isoproterenol (ISO), and cell viability and apoptosis were examined using cell counting kit-8 and TUNEL assays. SFRP4 and Jumonji domain-containing protein 2A (JMJD2A) were highly expressed in myocardial tissues. Suppression of SFRP4 alleviated apoptosis and fibrosis in myocardial tissues of mice. In addition, the extent of mitochondrial dysfunction and oxidative stress in damaged myocardial tissues and HL-1 cells was mitigated by SFRP4 inhibition as well. JMJD2A catalyzed demethylation modification of the SFRP4 promoter, thus promoting SFRP4 transcription in the development of HF. JMJD2A is responsible for SFRP4 transcription activation in the failing hearts of mice. Blockade of JMJD2A or SFRP4 might be a novel therapy effective in mitigating HF progression.

The JMJD family of histone demethylase and their intimate links to cardiovascular disease

The incidence rate and mortality rate of cardiovascular disease rank first in the world. It is associated with various high-risk factors, and there is no single cause. Epigenetic modifications, such as DNA methylation or histone modification, actively participate in the initiation and development of cardiovascular diseases. Histone lysine methylation is a type of histone post-translational modification. The human Jumonji C domain (JMJD) protein family consists of more than 30 members. JMJD proteins participate in many key nuclear processes and play a key role in the specific regulation of gene expression, DNA damage and repair, and DNA replication. Importantly, increasing evidence shows that JMJD proteins are abnormally expressed in cardiovascular diseases, which may be a potential mechanism for the occurrence and development of these diseases. Here, we discuss the key roles of JMJD proteins in various common cardiovascular diseases. This includes histone lysine demethylase, which has been studied in depth, and less-studied JMJD members. Furthermore, we focus on the epigenetic changes induced by each JMJD member, summarize recent research progress, and evaluate their relationship with cardiovascular diseases and therapeutic potential.

Slow down my beating heart: induction of cardiac fibrosis by Iroquois homeobox 2

Cardiovascular diseases are a significant global health challenge and pervasive cause of mortality worldwide. Heart failure due to cardiovascular disease is characterized by the inability of the heart to pump blood efficiently to meet the metabolic demands of the body. The pathophysiology of heart failure involves myocardial remodeling due to excessive deposition of extracellular matrix proteins by cardiac myofibroblasts - structural changes which impair contractility, reduce compliance, and ultimately reduce stroke volume. Now, a recent report has uncovered an essential role for Iroquois homeobox 2 in the transcriptional regulation of cardiac fibrosis, illuminating new mechanistic insights that can be applied to developing future clinical therapies.

IRX2 regulates angiotensin II-induced cardiac fibrosis by transcriptionally activating EGR1 in male mice

Cardiac fibrosis is a common feature of chronic heart failure. Iroquois homeobox (IRX) family of transcription factors plays important roles in heart development; however, the role of IRX2 in cardiac fibrosis has not been clarified. Here we report that IRX2 expression is significantly upregulated in the fibrotic hearts. Increased IRX2 expression is mainly derived from cardiac fibroblast (CF) during the angiotensin II (Ang II)-induced fibrotic response. Using two CF-specific Irx2-knockout mouse models, we show that deletion of Irx2 in CFs protect against pathological fibrotic remodelling and improve cardiac function in male mice. In contrast, Irx2 gain of function in CFs exaggerate fibrotic remodelling. Mechanistically, we find that IRX2 directly binds to the promoter of the early growth response factor 1 (EGR1) and subsequently initiates the transcription of several fibrosis-related genes. Our study provides evidence that IRX2 regulates the EGR1 pathway upon Ang II stimulation and drives cardiac fibrosis.

Single-cell transcriptional profiling of hearts during cardiac hypertrophy reveals the role of MAMs in cardiomyocyte subtype switching

Pathological cardiac hypertrophy is the main predecessor of heart failure. Its pathology is sophisticated, and its progression is associated with multiple cellular processes. To explore new therapeutic approaches, more precise examination of cardiomyocyte subtypes and involved biological processes is required in response to hypertrophic stimuli. Mitochondria and the endoplasmic reticulum (ER) are two crucial organelles associated with the progression of cardiac hypertrophy and are connected through junctions known as mitochondria-associated endoplasmic reticulum membranes (MAMs). Although MAM genes are altered in cardiac hypertrophy, the importance of MAMs in cardiac hypertrophy and the expression pattern of MAMs in certain cardiac cell types require a comprehensive analysis. In this study, we analyzed the temporal expression of MAM proteins in the process of cardiac hypertrophy and observed that MAM-related proteins preferentially accumulated in cardiomyocytes at the initial stage of cardiac hypertrophy and underwent a gradual decline, which was synchronized with the proportion of two cardiomyocyte subtypes (CM2 and CM3). Meanwhile, these subtypes went through a functional switch during cardiac hypertrophy. Trajectory analysis suggested that there was a differentiation trajectory of cardiomyocyte subtypes from high to low MAM protein expression. Distinct regulon modules across different cardiomyocyte cell types were revealed by transcriptional regulatory network analysis. Furthermore, scWGCNA revealed that MAM-related genes were clustered into a module that correlated with diabetic cardiomyopathy. Altogether, we identified cardiomyocyte subtype transformation and the potential critical transcription factors involved, which may serve as therapeutic targets in combating cardiac hypertrophy.