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

The regulation of protein acetylation influences the redox homeostasis to protect the heart

The cellular damage caused by redox imbalance is involved in the pathogenesis of many cardiovascular diseases. Besides, redox imbalance is related to the alteration of protein acetylation processes, causing not only chromatin remodeling but also disturbances in so many processes where protein acetylation is involved, such as metabolism and signal transduction. The modulation of acetylases and deacetylases enzymes aids in maintaining the redox homeostasis, avoiding the deleterious cellular effects associated with the dysregulation of protein acetylation. Of note, regulation of protein acetylation has shown protective effects to ameliorate cardiovascular diseases. For instance, HDAC inhibition has been related to inducing cardiac protective effects and it is an interesting approach to the management of cardiovascular diseases. On the other hand, the upregulation of SIRT protein activity has also been implicated in the relief of cardiovascular diseases. This review focuses on the major protein acetylation modulators described, involving pharmacological and bioactive compounds targeting deacetylase and acetylase enzymes contributing to heart protection through redox homeostasis.

Mzb1 protects against myocardial infarction injury in mice via modulating mitochondrial function and alleviating inflammation

Myocardial infarction (MI) leads to the loss of cardiomyocytes, left ventricle dilation and cardiac dysfunction, eventually developing into heart failure. Mzb1 (Marginal zone B and B1 cell specific protein 1) is a B-cell-specific and endoplasmic reticulum-localized protein. Mzb1 is an inflammation-associated factor that participates a series of inflammatory processes, including chronic periodontitis and several cancers. In this study we investigated the role of Mzb1 in experimental models of MI. MI was induced in mice by ligation of the left descending anterior coronary artery, and in neonatal mouse ventricular cardiomyocytes (NMVCs) by H2O2 treatment in vitro. We showed that Mzb1 expression was markedly reduced in the border zone of the infarct myocardium of MI mice and in H2O2-treated NMVCs. In H2O2-treated cardiomyocytes, knockdown of Mzb1 decreased mitochondrial membrane potential, impaired mitochondrial function and promoted apoptosis. On contrary, overexpression of Mzb1 improved mitochondrial membrane potential, ATP levels and mitochondrial oxygen consumption rate (OCR), and inhibited apoptosis. Direct injection of lentiviral vector carrying Len-Mzb1 into the myocardial tissue significantly improved cardiac function and alleviated apoptosis in MI mice. We showed that Mzb1 overexpression significantly decreased the levels of Bax/Bcl-2 and cytochrome c and improved mitochondrial function in MI mice via activating the AMPK-PGC1α pathway. In addition, we demonstrated that Mzb1 recruited the macrophages and alleviated inflammation in MI mice. We conclude that Mzb1 is a crucial regulator of cardiomyocytes after MI by improving mitochondrial function and reducing inflammatory signaling pathways, implying a promising therapeutic target in ischemic cardiomyopathy.

Protein acetylation in cardiac aging

Biological aging is attributed to progressive dysfunction in systems governing genetic and metabolic integrity. At the cellular level, aging is evident by accumulated DNA damage and mutation, reactive oxygen species, alternate lipid and protein modifications, alternate gene expression programs, and mitochondrial dysfunction. These effects sum to drive altered tissue morphology and organ dysfunction. Protein-acylation has emerged as a critical mediator of age-dependent changes in these processes. Despite decades of research focus from academia and industry, heart failure remains a leading cause of death in the United States while the 5 year mortality rate for heart failure remains over 40%. Over 90% of heart failure deaths occur in patients over the age of 65 and heart failure is the leading cause of hospitalization in Medicare beneficiaries. In 1931, Cole and Koch discovered age-dependent accumulation of phosphates in skeletal muscle. These and similar findings provided supporting evidence for, now well accepted, theories linking metabolism and aging. Nearly two decades later, age-associated alterations in biochemical molecules were described in the heart. From these small beginnings, the field has grown substantially in recent years. This growing research focus on cardiac aging has, in part, been driven by advances on multiple public health fronts that allow population level clinical presentation of aging related disorders. It is estimated that by 2030, 25% of the worldwide population will be over the age of 65. This review provides an overview of acetylation-dependent regulation of biological processes related to cardiac aging and introduces emerging non-acetyl, acyl-lysine modifications in cardiac function and aging.

Investigation into the difference in mitochondrial-cytosolic calcium coupling between adult cardiomyocyte and hiPSC-CM using a novel multifunctional genetic probe

Ca2+ cycling plays a critical role in regulating cardiomyocyte (CM) function under both physiological and pathological conditions. Mitochondria have been implicated in Ca2+ handling in adult cardiomyocytes (ACMs). However, little is known about their role in the regulation of Ca2+ dynamics in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). In the present study, we developed a multifunctional genetically encoded Ca2+ probe capable of simultaneously measuring cytosolic and mitochondrial Ca2+ in real time. Using this novel probe, we determined and compared mitochondrial Ca2+ activity and the coupling with cytosolic Ca2+ dynamics in hiPSC-CMs and ACMs. Our data showed that while ACMs displayed a highly coordinated beat-by-beat response in mitochondrial Ca2+ in sync with cytosolic Ca2+, hiPSC-CMs showed high cell-wide variability in mitochondrial Ca2+ activity that is poorly coordinated with cytosolic Ca2+. We then revealed that mitochondrial-sarcoplasmic reticulum (SR) tethering, as well as the inter-mitochondrial network connection, is underdeveloped in hiPSC-CM compared to ACM, which may underlie the observed spatiotemporal decoupling between cytosolic and mitochondrial Ca2+ dynamics. Finally, we showed that knockdown of mitofusin-2 (Mfn2), a protein tethering mitochondria and SR, led to reduced cytosolic-mitochondrial Ca2+ coupling in ACMs, albeit to a lesser degree compared to hiPSC-CMs, suggesting that Mfn2 is a potential engineering target for improving mitochondrial-cytosolic Ca2+ coupling in hiPSC-CMs. Physiological relevance: The present study will advance our understanding of the role of mitochondria in Ca2+ handling and cycling in CMs, and guide the development of hiPSC-CMs for healing injured hearts.

A novel danshensu/tetramethypyrazine derivative attenuates oxidative stress-induced autophagy injury via the AMPK-mTOR-Ulk1 signaling pathway in cardiomyocytes

Myocardial ischemia/reperfusion injury (MIRI) is an inevitable and unsolved clinical problem in the treatment of ischemic heart diseases. Compound DT-010 is a novel danshensu/tetramethylpyrazine derivative and was examined as a candidate for treating MIRI. In the present study, MTT, lactate dehydrogenase assay and Hoechst staining data indicated that DT-010 attenuated tert-butylhydroperoxide (t-BHP)-induced oxidative damage by increasing cell survival, reducing cell damage and decreasing apoptosis in H9c2 cardiomyocytes. Autophagy was assessed by western blotting for microtubule-associated protein 1A/1B-light chain 3 (LC3-II and LC3-I) expression, acridine orange and monodansylcadaverine staining for autophagosome formation and the monomeric red fluorescent protein-green fluorescent protein-LC3 assay for autophagic flow. t-BHP-induced cell damage was aggravated by the autophagy agonist rapamycin and alleviated by the autophagy blocker hydroxy-chloroquine, suggesting that autophagy was involved in t-BHP-induced cardiomyocyte injury. DT-010 pretreatment significantly prevented t-BHP-induced cell damage, which was partially but significantly abolished by rapamycin and significantly improved by hydroxy-chloroquine treatment. DT-010 treatment inhibited t-BHP-induced autophagy in H9c2 cells, reduced phosphorylation of 5'-AMP-activated protein kinase (AMPK) and promoted the phosphorylation of mTOR and unc-51 like autophagy activating kinase 1 (Ulk1). To conclude, DT-010 can serve as a potential candidate for myocardial ischemia-reperfusion injury therapy. The cardioprotective effects of DT-010 could be partially attributed to its inhibition of autophagy via the AMPK-mTOR-Ulk1 signaling pathway.

Therapeutic effects of histone deacetylase inhibitors on heart disease

A wide range of histone deacetylase (HDAC) inhibitors have been studied for their therapeutic potential because the excessive activity and expression of HDACs have been implicated in the pathogenesis of cardiac diseases. An increasing number of preclinical studies have demonstrated the cardioprotective effects of numerous HDAC inhibitors, suggesting a wide variety of mechanisms by which the inhibitors protect against cardiac stress, such as the suppression of cardiac fibrosis and fetal gene expression, enhancement of angiogenesis and mitochondrial biogenesis, prevention of electrical remodeling, and regulation of apoptosis, autophagy, and cell cycle arrest. For the development of isoform-selective HDAC inhibitors with high efficacy and low toxicity, it is important to identify and understand the mechanisms responsible for the effects of the inhibitors. This review highlights the preclinical effects of HDAC inhibitors that act against Zn²⁺-dependent HDACs and the underlying mechanisms of their protective effects against cardiac hypertrophy, hypertension, myocardial infarction, heart failure, and atrial fibrillation.

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.