Chromatin remodeling and mitochondrial biogenesis underlie the improved cardiac function in heart failure induced by ketogenic diet and beta‐hydroxibutiyrate supplementation

Abstract

Background : Beta Hydroxybutyrate (BHB) is the main ketone body produced during fasting or carbohydrate deprivation as an alternative fuel. A key aspect of metabolic remodeling in heart failure (HF) is the down-regulation of fatty acid utilization. Moreover, the myocardial metabolic profile reveals that the failing heart shift towards oxidizing ketones bodies. Emerging evidence suggests that after myocardial infarction (MI) the metabolic failure coincides with increased levels and utilization of BHB; equally important, the key enzyme involved in BHB catabolism, BHB-dehydrogenase 1, is up-regulated in HF. However, whether such modifications are adaptive or maladaptive in the damaged myocardium has never been evaluated. On these grounds, our main aim is to explore the effects of BHB on cardiac function after ischemic injury in vivo, in vitro, and ex vivo. Methods and Results A layout of the experimental design is shown in Figure 1. Our in vitro experiments, performed in cultured H9C2 cardiac cells, demonstrated that the administration of BHB (3 mM) reduced the activation of caspase 3 in response to ischemia, as well as the number of TUNEL+ nuclei. Specifically, the mitochondrial apoptotic pathway was affected, as BHB reduced mitochondrial cytochrome-C release in the cytosol induced by ischemia. Mitochondrial structure and interconnections, markedly affected by ischemia, were significantly retained in presence of BHB, as well as mitochondrial membrane potential (assessed via TMRE). The preserved mitochondrial health was further supported by higher levels of PGC-1α detected in cells exposed to ischemia plus BHB compared to ischemia alone. Then, in order to investigate the in vivo effects of BHB on ischemia-damaged myocardium, we administrated carbohydrate-null diet (ketogenic diet, KD) or standard diet-supplemented with BHB, to post-MI mice. The MI was obtained by permanent ligation of the left anterior descending coronary artery. Both groups treated with KD and BHB-supplemented diet displayed a significantly preserved left ventricular ejection fraction compared to untreated infarcted mice. The protective effects of BHB on cardiac phenotype were mirrored by increased levels of PGC-1α in the myocardium of treated mice, both in terms of protein and transcription levels. Additionally, in the hearts of mice fed KD and BHB supplemented diet, we observed a distinct difference in chromatin remodeling and in the histone acetylation pattern. Strikingly, these results were confirmed both in our ex vivo and in vitro assays. Conclusions BHB protects cardiac cells from apoptotic and mitochondrial damage induced by ischemia. Through its ability to regulate fundamental epigenetic modifications, BHB activates a gene expression program that specifically supports mitochondrial biogenesis and function, thereby representing an unprecedented and powerful therapeutic strategy in heart failure.