HDAC inhibition induces autophagy and mitochondrial biogenesis to maintain mitochondrial homeostasis during cardiac ischemia/reperfusion injury

Disentangling the epigenetic landscape in cardiovascular patients: a path toward personalized medicine

Despite significant advances in our understanding of cardiovascular disease (CVD) we are still far from having developed breakthrough strategies to combat coronary atherosclerosis and heart failure, which account for most of CV deaths worldwide. Available cardiovascular therapies have failed to show to be equally effective in all patients, suggesting that inter-individual diversity is an important factor when it comes to conceive and deliver effective personalized treatments. Genome mapping has proved useful in identifying patients who could benefit more from specific drugs depending on genetic variances; however, our genetic make-up determines only a limited part of an individual's risk profile. Recent studies have demonstrated that epigenetic changes - defined as dynamic changes of DNA and histones which do not affect DNA sequence - are key players in the pathophysiology of cardiovascular disease and may participate to delineate cardiovascular risk trajectories over the lifetime. Epigenetic modifications include changes in DNA methylation, histone modifications and non-coding RNAs and these epigenetic signals have shown to cooperate in modulating chromatin accessibility to transcription factors and gene expression. Environmental factors such as air pollution, smoking, psychosocial context, and unhealthy diet regimens have shown to significantly modify the epigenome thus leading to altered transcriptional programs and CVD phenotypes. Therefore, the integration of genetic and epigenetic information might be invaluable to build individual maps of cardiovascular risk and hence, could be employed for the design of customized diagnostic and therapeutic strategies. In the present review, we discuss the growing importance of epigenetic information and its putative implications in cardiovascular precision medicine.

Cardioprotective Effects of Sirtuin-1 and Its Downstream Effectors: Potential Role in Mediating the Heart Failure Benefits of SGLT2 (Sodium-Glucose Cotransporter 2) Inhibitors

The cardioprotective effects of SGLT2 (sodium-glucose cotransporter 2) inhibitors may be related to their ability to induce a fasting-like paradigm, which triggers the activation of nutrient deprivation pathways to promote cellular homeostasis. The most distinctive metabolic manifestations of this fasting mimicry are enhanced gluconeogenesis and ketogenesis, which are not seen with other antihyperglycemic drugs. The principal molecular stimulus to gluconeogenesis and ketogenesis is activation of SIRT1 (sirtuin-1) and its downstream mediators: PGC-1α (proliferator-activated receptor gamma coactivator 1-alpha) and FGF21 (fibroblast growth factor 21). These three nutrient deprivation sensors exert striking cardioprotective effects in a broad range of experimental models. This benefit appears to be related to their actions to alleviate oxidative stress and promote autophagy-a lysosome-dependent degradative pathway that disposes of dysfunctional organelles that are major sources of cellular injury. Nutrient deprivation sensors are suppressed in states of perceived energy surplus (ie, type 2 diabetes mellitus and chronic heart failure), but SGLT2 inhibitors activate SIRT1/PGC-1α/FGF21 signaling and promote autophagy. This effect may be related to their action to trigger the perception of a system-wide decrease in environmental nutrients, but SGLT2 inhibitors may also upregulate SIRT1, PGC-1α, and FGF21 by a direct effect on the heart. Interestingly, metformin-induced stimulation of AMP-activated protein kinase (a nutrient deprivation sensor that does not promote ketogenesis) has not been shown to reduce heart failure events in clinical trials. Therefore, promotion of ketogenic nutrient deprivation signaling by SGLT2 inhibitors may explain their cardioprotective effects, even though SGLT2 is not expressed in the heart.

AMPKα2 Overexpression Reduces Cardiomyocyte Ischemia-Reperfusion Injury Through Normalization of Mitochondrial Dynamics

Cardiac ischemia-reperfusion (I/R) injury is associated with mitochondrial dysfunction. Recent studies have reported that mitochondrial function is determined by mitochondrial dynamics. Here, we hypothesized that AMPKα2 functions as an upstream mediator that sustains mitochondrial dynamics in cardiac I/R injury and cardiomyocyte hypoxia-reoxygenation (H/R) in vitro. To test this, we analyzed cardiomyocyte viability and survival along with mitochondrial dynamics and function using western blots, qPCR, immunofluorescence, and ELISA. Our results indicated that both AMPKα2 transcription and translation were reduced by H/R injury in cardiomyocytes. Decreased AMPKα2 levels were associated with cardiomyocyte dysfunction and apoptosis. Adenovirus-mediated AMPKα2 overexpression dramatically inhibited H/R-mediated cardiomyocyte damage, possibly by increasing mitochondrial membrane potential, inhibiting cardiomyocyte oxidative stress, attenuating intracellular calcium overload, and inhibiting mitochondrial apoptosis. At the molecular level, AMPKα2 overexpression alleviated abnormal mitochondrial division and improved mitochondrial fusion through activation of the Sirt3/PGC1α pathway. This suggests AMPKα2 contributes to maintaining normal mitochondrial dynamics. Indeed, induction of mitochondrial dynamics disorder abolished the cardioprotective effects afforded by AMPKα2 overexpression. Thus, cardiac I/R-related mitochondrial dynamics disorder can be reversed by AMPKα2 overexpression in a manner dependent on the activation of Sirt3/PGC1α signaling.

Histone Deacetylase Inhibitors: A Novel Strategy for Neuroprotection and Cardioprotection Following Ischemia/Reperfusion Injury

Ischemia/reperfusion injury is a complex molecular cascade that causes deleterious cellular damage and organ dysfunction. Stroke, sudden cardiac arrest, and acute myocardial infarction are the most common causes of ischemia/reperfusion injury without effective pharmacologic therapies. Existing preclinical evidence suggests that histone deacetylase inhibitors may be an efficacious, affordable, and clinically feasible therapy that can improve neurologic and cardiac outcomes following ischemia/reperfusion injury. In this review, we discuss the pathophysiology and epigenetic modulations of ischemia/reperfusion injury and focus on the neuroprotective and cardioprotective effects of histone deacetylase inhibitors. We also summarize the protective effects of histone deacetylase inhibitors for other vital organs and highlight the key research priorities for their successful translation to the bedside.

Melatonin improves mitochondrial biogenesis through the AMPK/PGC1α pathway to attenuate ischemia/reperfusion-induced myocardial damage

Cardiac ischemia/reperfusion injury is associated with reduced mitochondrial turnover and regeneration. There is currently no effective approach to stimulate mitochondrial biogenesis in the reperfused myocardium. In this study, we investigated whether melatonin could increase mitochondrial biogenesis and thus promote mitochondrial homeostasis in cardiomyocytes. Cardiomyocytes were subjected to hypoxia/reoxygenation (H/R) injury with or without melatonin treatment, and various mitochondrial functions were measured. H/R injury repressed mitochondrial biogenesis in cardiomyocytes, whereas melatonin treatment restored mitochondrial biogenesis through the 5’ adenosine monophosphate-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α) pathway. Melatonin enhanced mitochondrial metabolism, inhibited mitochondrial oxidative stress, induced mitochondrial fusion and prevented mitochondrial apoptosis in cardiomyocytes subjected to H/R injury. The melatonin-induced improvement in mitochondrial biogenesis was associated with increased cardiomyocyte survival during H/R injury. On the other hand, silencing of PGC1α attenuated the protective effects of melatonin on cardiomyocyte viability, thereby impairing mitochondrial bioenergetics, disrupting the mitochondrial morphology, and activating mitochondrial apoptosis. Thus, H/R injury suppressed mitochondrial biogenesis, while melatonin activated the AMPK/PGC1α pathway and restored mitochondrial biogenesis, ultimately protecting the reperfused heart.

Suberoylanilide hydroxamic acid alleviates orthotopic liver transplantation‑induced hepatic ischemia‑reperfusion injury by regulating the AKT/GSK3β/NF‑κB and AKT/mTOR pathways in rat Kupffer cells

Multiple mechanisms are involved in regulating hepatic ischemia-reperfusion injury (IRI), in which Kupffer cells (KCs), which are liver-resident macrophages, play critical roles by regulating inflammation and the immune response. Suberoylanilide hydroxamic acid (SAHA), a pan-histone deacetylase inhibitor, has anti-inflammatory effects and induces autophagy. To investigate whether SAHA ameliorates IRI and the mechanisms by which SAHA exerts its effects, an orthotopic liver transplantation (OLT) rat model was established after treatment with SAHA. The results showed that SAHA effectively ameliorated OLT-induced IRI by reducing M1 polarization of KCs through inhibition of the AKT/glycogen synthase kinase (GSK)3β/NF-κB signaling pathway. Furthermore, the present study found that SAHA upregulates autophagy 5 protein (ATG5)/LC3B in KCs through the AKT/mTOR signaling pathway and inhibition of autophagy by knockdown of ATG5 in KCs partly impaired the protective effect of SAHA on IR-injured liver. Therefore, the current study demonstrated that SAHA reduces M1 polarization of KCs by inhibiting the AKT/GSK3β/NF-κB pathway and upregulates autophagy in KCs through the AKT/mTOR signaling pathway, which both alleviate OLT-induced IRI. The present study revealed that SAHA may be a novel treatment for the amelioration of OLT-induced IRI.

Epigenetic Control of Mitochondrial Function in the Vasculature

The molecular signatures of epigenetic regulation and chromatin architecture are emerging as pivotal regulators of mitochondrial function. Recent studies unveiled a complex intersection among environmental factors, epigenetic signals, and mitochondrial metabolism, ultimately leading to alterations of vascular phenotype and increased cardiovascular risk. Changing environmental conditions over the lifetime induce covalent and post-translational chemical modification of the chromatin template which sensitize the genome to establish new transcriptional programs and, hence, diverse functional states. On the other hand, metabolic alterations occurring in mitochondria affect the availability of substrates for chromatin-modifying enzymes, thus leading to maladaptive epigenetic signatures altering chromatin accessibility and gene transcription. Indeed, several components of the epigenetic machinery require intermediates of cellular metabolism (ATP, AcCoA, NADH, α-ketoglutarate) for enzymatic function. In the present review, we describe the emerging role of epigenetic modifications as fine tuners of gene transcription in mitochondrial dysfunction and vascular disease. Specifically, the following aspects are described in detail: (i) mitochondria and vascular function, (ii) mitochondrial ROS, (iii) epigenetic regulation of mitochondrial function; (iv) the role of mitochondrial metabolites as key effectors for chromatin-modifying enzymes; (v) epigenetic therapies. Understanding epigenetic routes may pave the way for new approaches to develop personalized therapies to prevent mitochondrial insufficiency and its complications.