P2095SIRT4 regulates fatty acid utilisation and cardiac function in the normal and diabetic heart

Abstract

Background: Obesity is a major risk factor for the development of heart failure. The pathophysiology of obesity cardiomyopathy is complex, and the exact mechanisms of disease remain poorly understood. The accumulation of lipids in the heart, caused by a mismatch between uptake and oxidation of fatty acids, is a powerful determinant of lipotoxic damage, apoptosis and impaired contractile function. The transcription factor JunD -a component of the Activator Protein-1 (AP-1) complex -has recently emerged as a pivotal modulator of triglyceride metabolism in the liver of obese mice. Purpose: To investigate whether JunD participates to cardiac lipid accumulation and myocardial damage. Methods: JunD transcriptional activity as well as the expression of genes involved in triglyceride uptake and storage were assessed in neonatal rat ventricular myocytes (NRVM) and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) exposed to palmitic acid (PA, 200uM) and vehicle for 48 hours. Gene silencing of JunD was perfomed by siRNA technology. Western blot and real-time PCR were used to assess JunD expression and lipid-related genes. Binding of JunD to peroxisome proliferator-activated receptor gamma (PPARγ) promoter was investigated by chromatin immunoprecipitation (ChIP) assay. Apoptosis and oxidative stress were investigated by caspase-3 and 3-nitrotyrosine (3-NT) assays. The impact of JunD on cardiac lipid uptake and PPARγ signaling was also investigated in the heart of JunD knockout (JunD−/−) mice as well as in transgenic mice with cardiac-specific overexpression of JunD via the α-myosin heavy chain promoter (α-MHC-JunDtg). Myocardial triglyceride content was assessed on crude heart homogenates. Results: Exposure of NRVM and hiPSC-CMs to PA significantly increased JunD expression and transcriptional activity. ChIP assays in PA-treated cells showed that JunD binds PPARγ promoter, leading to its upregulation and subsequent overexpression of PPARγ-dependent genes, namely CD36, fatty acid synthase (FAS) and Perilipin 5 (Plin5). Interestingly, JunD knockdown abolished PA-induced PPARγ transcriptional programs and intracellular lipid uptake both in rat and human cardiomyocytes. Caspase-3 activity and 3-NT levels were also significantly reduced by JunD silencing. Consistently, PPARγ signaling and intramyocardial lipid content were blunted in the heart of JunD−/− mice as compared to wild-type littermates. By contrast, α-MHC-JunDtg mice displayed cardiac steatosis due to massive upreguation of PPARγ and its downstream genes CD36, FAS and Plin5. Lipid accumulation in α-MHC-JunDtg mice was associated with apoptosis and oxidative stress. Conclusions: JunD drives the expression of PPARγ-related genes, leading to cardiac lipid accumulation and damage. This study -which employs JunD gainand loss of function mouse models -provides insights into new anti-steatotic therapies for the prevention of obesity cardiomyopathy phenotype.

SIRT6 transcriptionally regulates fatty acid transport by suppressing PPARγ

“…Similarly, SIRT5KO mice develop cardiac dysfunction associated with hyper-succinylation and reduction in the activities of key enzymes in the b-oxidation pathway (Sadhukhan et al, 2016). SIRT4 deficiency improves cardiac function and protects from lipid accumulation due to increased fatty acid oxidation (Hoelscher et al, 2017).…”