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Background and Purpose Activation of PKC‐ζ is closely linked to the pathogenesis of cardiac hypertrophy. PKC‐ζ can be activated by certain lipid metabolites such as phosphatidylinositol (3,4,5)‐trisphosphate and ceramide. However, its endogenous negative regulators are not well defined. Here, the role of the sirtuin1‐PKC‐ζ signalling axis and the underlying molecular mechanisms were investigated in cardiac hypertrophy. Experimental Approach Cellular hypertrophy in cultures of cardiac myocytes, from neonatal Sprague‐Dawley rats, was monitored by measuring cell surface area and the mRNA levels of hypertrophic biomarkers. Interaction between sirtuin1 and PKC‐ζ was investigated by co‐immunoprecipitation and confocal immunofluorescence microscopy. Sirtuin1 activation was enhanced by resveratrol treatment or Ad‐sirtuin1 transfection. A model of cardiac hypertrophy in Sprague‐Dawley rats was established by abdominal aortic constriction surgery or induced by isoprenaline in vivo. Key Results Overexpression of PKC‐ζ led to cardiac hypertrophy and increased activity of NF‐κB, ERK1/2 and ERK5, which was ameliorated by sirtuin1 overexpression. Enhancement of sirtuin1 activity suppressed acetylation of PKC‐ζ, hindered its binding to phosphoinositide‐dependent kinase 1 and inhibited PKC‐ζ phosphorylation in cardiac hypertrophy. Consequently, the downstream pathways of PKC‐ζ' were suppressed in cardiac hypertrophy. This regulation loop suggests a new role for sirtuin1 in mediation of cardiac hypertrophy. Conclusions and Implications Sirtuin1 is an endogenous negative regulator for PKC‐ζ and mediates its activity via regulating the acetylation and phosphorylation in the pathogenesis of cardiac hypertrophy. Targeting the sirtuin1‐PKC‐ζ signalling axis may suggest a novel therapeutic approach against cardiac hypertrophy.

The bromodomain and extraterminal (BET) family member BRD4 is pivotal in the pathogenesis of cardiac hypertrophy. BRD4 induces hypertrophic gene expression by binding to the acetylated chromatin, facilitating the phosphorylation of RNA polymerases II (Pol II) and leading to transcription elongation. The present study identified a novel post-translational modification of BRD4: poly(ADP-ribosyl)ation (PARylation), that was mediated by poly(ADP-ribose)polymerase-1 (PARP1) in cardiac hypertrophy. BRD4 silencing or BET inhibitors JQ1 and MS417 prevented cardiac hypertrophic responses induced by isoproterenol (ISO), whereas overexpression of BRD4 promoted cardiac hypertrophy, confirming the critical role of BRD4 in pathological cardiac hypertrophy. PARP1 was activated in ISO-induced cardiac hypertrophy and facilitated the development of cardiac hypertrophy. BRD4 was involved in the prohypertrophic effect of PARP1, as implied by the observations that BRD4 inhibition or silencing reversed PARP1-induced hypertrophic responses, and that BRD4 overexpression suppressed the anti-hypertrophic effect of PARP1 inhibitors. Interactions of BRD4 and PARP1 were observed by co-immunoprecipitation and immunofluorescence. PARylation of BRD4 induced by PARP1 was investigated by PARylation assays. In response to hypertrophic stimuli like ISO, PARylation level of BRD4 was elevated, along with enhanced interactions between BRD4 and PARP1. By investigating the PARylation of truncation mutants of BRD4, the C-terminal domain (CTD) was identified as the PARylation modification sites of BRD4. PARylation of BRD4 facilitated its binding to the transcription start sites (TSS) of hypertrophic genes, resulting in enhanced phosphorylation of RNA Pol II and transcription activation of hypertrophic genes. The present findings suggest that strategies targeting inhibition of PARP1-BRD4 might have therapeutic potential for pathological cardiac hypertrophy.

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Jumonji domain-containing 3 (JMJD3) protein, a histone demethylase protein, specifically catalyzes the demethylation of H3K27 (H3K27me3) and regulates gene expression. Sestrin2 (SESN2), a stress-inducible protein, protected against doxorubicin (DOX)-induced cardiomyopathy by regulating mitophagy and mitochondrial function. Here, the expression of JMJD3 was increased and that of SESN2 was decreased in both the heart samples from patients with dilated cardiomyopathy and chronic DOXstimulation induced cardiomyopathy. Inhibition or knockdown of JMJD3 attenuated DOX-induced cardiomyocytes apoptosis, mitochondrial injury and cardiac dysfunction. However, JMJD3 overexpression aggravated DOX-induced cardiomyopathy, which were relieved by SESN2 overexpression. JMJD3 inhibited the transcription of SESN2 by reducing tri-methylation of H3K27 in the promoter region of SESN2. In conclusion, JMJD3 negatively regulated SESN2 via decreasing H3K27me3 enrichment in the promoter region of SESN2, subsequently inducing mitochondrial dysfunction and cardiomyocytes apoptosis. Targeting the JMJD3-SESN2 signaling axis may be a potential therapeutic strategy to protect against DOX-mediated cardiomyopathy.