Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous disease of cardiomyocytes, and with an unclear mechanism underlying HCM progression [11–12]. In recent years, there is overwhelming evidence that sex differences in clinical presentation might contribute to the phenotypic heterogeneity of HCM individuals, showing the prevalence is higher in men, while women suffered from higher risk of cardiovascular outcomes and worse survival [13–15].
With a growing awareness that HCM is due to a complex interaction between genetic and environmental factors, it is considered sarcomere genes have the most robustly genetic disorders associated with HCM, including MYBPC3, MYH7, TNNT2, TNNI3, TPM1, ACTC1, MYL2, MYL3, MYH6, TTN, and TNNC1. Butters et al. have reported the sex-specific interaction of genetics and the environment on outcomes of HCM, finding that women are more likely to have a disease-causing variant identified and more likely to be sarcomere-positive [16]. There still lacks detailed molecular mechanisms leading to sex differences of HCM, with some mechanisms underlying physiological differences and social factors. Here, we identified 208 DEGs in HCM females. GO analysis showed that the regulated genes were mainly involved in regulating response to external stimulus, inflammatory response, collagen-containing extracellular matrix, platelet alpha granule lumen, intergrin binding, and endopeptidase inhibitor activity. Meanwhile, the KEGG pathway analysis showed the DEGs were significantly enriched in phagosome.
Furthermore, in order to obtain female specific genes causing HCM with higher risk of cardiovascular events, LASSO regression and SVM-RFE algorithm were applied, and 7 genes (S100A9, CEBPD, S1PR3, CDC42EP4, ZFP36, RASD1 and MYH6) were identified. GSEA analysis of core genes indicated signaling pathways involved in fatty acid β-oxidation, tricarboxylic acid cycle enzyme complex, autophagy, and ribosome pathways. After a verification in HCM males, outcomes proved a significantly greater reduction of MYH6 and RASD1 expressions in female-specific HCM.
It is reported that two types of cardiac mosin heavy chain (MyHC) informs (alpha and beta) were in humans. The MYH6 gene encodes the alpha heavy chain subunit of cardiac myosin (MyHC) while β-MyHc was encoded by MYH7 gene. Normally, a-MyHC protein may represent about 7% of the total MyHC in normal hearts of mammals, while with a significantly down-regulation at Erna and protein levels in failing hearts [17–19]. Although MYH7 and MYBPC3, encoding a-imposing heavy chain and imposing binding protein C, are responsible for probably 40% of all HCM cases [10], it is further discovered that an out-of-balance of MYH6 and MYH7 transcription is important [20]. Some viewpoints also indicated MYH6 variant is associated with HCM onset [21–22]. Currently, outcomes have demonstrated that a down-regulation of MYH6 expressions in HCM females may be closely related to the occurrence of a higher risk of cardiovascular outcomes.
RASD1, namely Ras dexamethasone-induced protein 1 or AGS1, encodes Dexamethasone-induced Ras-related protein 1 (Dexras1), commonly as a protein with a critical role in signal transduction in neurons[23]. Interestingly, according to the bioinformatic analysis in female-specific HCM, the RASD1 mRNA levels significantly down-regulated. Based on the previous studies, it discovered the unique expression profiles in the atria for G protein signaling including Galphao1, Ggamma2, Ggamma3, AGS1, et al by transcriptional analysis between the atrial and ventricular tissues in rats [24]. In 2012, McGrath et al found that temporal mRNA expression of RASD1 expression levels decreased significantly when cardiac hypertrophy developed. Meanwhile, in vitro, RASD1 knockdown did not affect ANF expression levels, but possibly increasing ANF secretion[25]. A clinical research found that in HCM, female was associated with higher plasma B-type natriuretic peptide (BNP) levels, a predictor of prognosis, than male [26]. Based on the report that RASD1 expression in the heart is important to modulate cardiac hormone secretion (ANF and BNP) by PTX sensitive Gα i/o [27]. Additionally, RASD1 has been reported as a novel physiologic nitric oxide (NO) effector, and it suggested that anchoring of neuronal nitric oxide synthase (nNOS) could contribute to an enhanced NO signaling pathway [28]. Hence, a great down-regulation of RASD1 in cardiac tissues of HCM females probably leads to an impairment of cardiac natriuretic hormones and vasodilator function via NO signaling pathway. These changes negatively impact cardiovascular homeostasis and myocardial remodeling.
Previous studies demonstrated that dysregulated autophagy promoting the progression of cardiac remodeling, while little focus on the alteration of autophagy in HCM [29]. This study reported that imbalance of cardiac autophagy might be involved in sex differences of HCM, according to KEGG and GSEA data. The shared genes by DEGs in HCM females and autophagy-related genes included MYC, NAMPT, CCL2, CDKN1A and FOS, while there existed a significant difference only in NAMPT expressions when compared HCM males with females. NAMPT (nicotinamide phosphoribosyltransferase), is a regulator of the intracellular nicotinamide adenine dinucleotide (NAD) pool, and it influences the activity of NAD-dependent enzymes, thereby regulating cellular metabolism. It was assessed the role of NAMPT expressions in autophagy and extracellular matrix degradation, which demonstrated the NAMPT silencing could inhibit autophagic flux[30]. Expression of NAMPT and its contribution to NAD + synthesis are cell type-dependent. Under stress, expression of NAMPT is significantly down-regulated at both mRNA and protein levels, contributing to decreases in NAD + during pathological conditions in the heart. During the failing hearts, NAMPT is down-regulated, causing increases in cell death in cardiac myocytes. Furthermore, downreguation of NAMPT causes suppression of Sirt1 activity, a NAD+-dependent histone deacetylase. Our analyses suggest that down-regulation of NAMPT has a causative role in mediating myocardial remodeling, by decreasing cellular ATP content, inhibiting autophagy and increasing apoptosis of cardiomyocytes in HCM.