Ischaemic preconditioning improves proteasomal activity and increases the degradation of deltaPKC during reperfusion

Mitochondrial Kinase Signaling for Cardioprotection

Myocardial ischemia/reperfusion injury is reduced by cardioprotective adaptations such as local or remote ischemic conditioning. The cardioprotective stimuli activate signaling cascades, which converge on mitochondria and maintain the function of the organelles, which is critical for cell survival. The signaling cascades include not only extracellular molecules that activate sarcolemmal receptor-dependent or -independent protein kinases that signal at the plasma membrane or in the cytosol, but also involve kinases, which are located to or within mitochondria, phosphorylate mitochondrial target proteins, and thereby modify, e.g., respiration, the generation of reactive oxygen species, calcium handling, mitochondrial dynamics, mitophagy, or apoptosis. In the present review, we give a personal and opinionated overview of selected protein kinases, localized to/within myocardial mitochondria, and summarize the available data on their role in myocardial ischemia/reperfusion injury and protection from it. We highlight the regulation of mitochondrial function by these mitochondrial protein kinases.

An Update on Protein Kinases as Therapeutic Targets-Part I: Protein Kinase C Activation and Its Role in Cancer and Cardiovascular Diseases

Protein kinases are one of the most significant drug targets in the human proteome, historically harnessed for the treatment of cancer, cardiovascular disease, and a growing number of other conditions, including autoimmune and inflammatory processes. Since the approval of the first kinase inhibitors in the late 1990s and early 2000s, the field has grown exponentially, comprising 98 approved therapeutics to date, 37 of which were approved between 2016 and 2021. While many of these small-molecule protein kinase inhibitors that interact orthosterically with the protein kinase ATP binding pocket have been massively successful for oncological indications, their poor selectively for protein kinase isozymes have limited them due to toxicities in their application to other disease spaces. Thus, recent attention has turned to the use of alternative allosteric binding mechanisms and improved drug platforms such as modified peptides to design protein kinase modulators with enhanced selectivity and other pharmacological properties. Herein we review the role of different protein kinase C (PKC) isoforms in cancer and cardiovascular disease, with particular attention to PKC-family inhibitors. We discuss translational examples and carefully consider the advantages and limitations of each compound (Part I). We also discuss the recent advances in the field of protein kinase modulators, leverage molecular docking to model inhibitor-kinase interactions, and propose mechanisms of action that will aid in the design of next-generation protein kinase modulators (Part II).

Changes in Skeletal Muscle Protein Metabolism Signaling Induced by Glutamine Supplementation and Exercise

AIM

To evaluate the effects of resistance exercise training (RET) and/or glutamine supplementation (GS) on signaling protein synthesis in adult rat skeletal muscles.

METHODS

The following groups were studied: (1) control, no exercise (C); (2) exercise, hypertrophy resistance exercise training protocol (T); (3) no exercise, supplemented with glutamine (G); and (4) exercise and supplemented with glutamine (GT). The rats performed hypertrophic training, climbing a vertical ladder with a height of 1.1 m at an 80° incline relative to the horizontal with extra weights tied to their tails. The RET was performed three days a week for five weeks. Each training session consisted of six ladder climbs. The extra weight load was progressively increased for each animal during each training session. The G groups received daily L-glutamine by gavage (one g per kilogram of body weight per day) for five weeks. The C group received the same volume of water during the same period. The rats were euthanized, and the extensor digitorum longus (EDL) muscles from both hind limbs were removed and immediately weighed. Glutamine and glutamate concentrations were measured, and histological, signaling protein contents, and mRNA expression analyses were performed.

RESULTS

Supplementation with free L-glutamine increased the glutamine concentration in the EDL muscle in the C group. The glutamate concentration was augmented in the EDL muscles from T rats. The EDL muscle mass did not change, but a significant rise was reported in the cross-sectional area (CSA) of the fibers in the three experimental groups. The levels of the phosphorylated proteins (pAkt/Akt, pp70S6K/p70S6K, p4E-BP1/4E-BP1, and pS6/S6 ratios) were significantly increased in EDL muscles of G rats, and the activation of p4E-BP1 was present in T rats. The fiber CSAs of the EDL muscles in T, G, and GT rats were increased compared to the C group. These changes were accompanied by a reduction in the 26 proteasome activity of EDL muscles from T rats.

CONCLUSION

Five weeks of GS and/or RET induced muscle hypertrophy, as indicated by the increased CSAs of the EDL muscle fibers. The increase in CSA was mediated via the upregulated phosphorylation of Akt, 4E-BP1, p70S6k, and S6 in G animals and 4E-BP1 in T animals. In the EDL muscles from T animals, a decrease in proteasome activity, favoring a further increase in the CSA of the muscle fibers, was reported.

Chaperone-mediated autophagy protects cardiomyocytes against hypoxic-cell death

Chaperone-mediated autophagy (CMA) is a chaperone-dependent process of selective cytosolic protein turnover that targets specific proteins to lysosomes for degradation. Enhancing protein degradation mechanisms has been shown to be beneficial in multiple models of cardiac disease, including myocardial infarction (MI) and ischemia-reperfusion (I/R) injury. However, the causal role of CMA in cardiomyocyte injury and death is largely unknown. Hypoxia is an important contributor to both MI and I/R damage, which are major, precedent causes of heart failure. Upregulating CMA was hypothesized to protect against hypoxia-induced cardiomyocyte death. Lysosome-associated membrane protein 2a (Lamp2a) overexpression and knockdown were used to causally study CMA's role in hypoxically stressed cardiomyocytes. LAMP2a protein levels were used as both a primary indicator and driver of CMA function. Hypoxic stress was stimulated by CoCl2 treatment, which increased LAMP2a protein levels (+1.4-fold) and induced cardiomyocyte apoptosis (+3.2-4.0-fold). Lamp2a siRNA knockdown (-3.2-fold) of control cardiomyocytes increased apoptosis (+1.8-fold) suggesting that loss of CMA is detrimental for cardiomyocyte survival. However, there was neither an additive nor a synergistic effect on cell death when Lamp2a-silenced cells were treated with CoCl2. Conversely, Lamp2a overexpression (+3.0-fold) successfully reduced hypoxia-induced apoptosis by ∼50%. LAMP2a was also significantly increased (+1.7-fold) in ischemic heart failure patient samples, similar to hypoxically stressed cardiomyocytes. The failing ischemic hearts may have had insufficient CMA activation. To our knowledge, this study for the first time establishes a protective role for CMA (via Lamp2a overexpression) against hypoxia-induced cardiomyocyte loss and reveals the intriguing possibility that CMA activation may offer a cardioprotective treatment for ischemic heart disease.

Krüppel-like factor (KLF)5: An emerging foe of cardiovascular health

Krüppel-like factors (KLFs) are DNA-binding transcriptional factors, which regulate various pathways that pertain to development, metabolism and other cellular mechanisms. KLF5 was first cloned in 1993 and by 1999, it was reported as the intestinal-enriched KLF. Beyond findings that have associated KLF5 with normal development and cancer, it has been associated with various types of cardiovascular (CV) complications and regulation of metabolic pathways in the liver, heart, adipose tissue and skeletal muscle. Specifically, increased KLF5 expression has been linked with cardiomyopathy in diabetes, end-stage heart failure, and as well as in vascular atherosclerotic lesions. In this review article, we summarize research findings about transcriptional, post-transcriptional and post-translational regulation of KLF5, as well as the role of KLF5 in the biology of cells and organs that affect cardiovascular health either directly or indirectly. Finally, we propose KLF5 inhibition as an emerging approach for cardiovascular therapeutics.

Protein lysine acetylation and its role in different human pathologies: a proteomic approach

INTRODUCTION

Lysine acetylation is a reversible post-translational modification (PTM) regulated through the action of specific types of enzymes: lysine acetyltransferases (KATs) and lysine deacetylases (HDACs), in addition to bromodomains, which are a group of conserved domains which identify acetylated lysine residues, several of the players in the process of protein acetylation, including enzymes and bromodomain-containing proteins, have been related to the progression of several diseases. The combination of high-resolution mass spectrometry-based proteomics, and immunoprecipitation to enrich acetylated peptides has contributed in recent years to expand the knowledge about this PTM described initially in histones and nuclear proteins, and is currently reported in more than 5000 human proteins, that are regulated by this PTM.

AREAS COVERED

This review presents an overview of the main participant elements, the scenario in the development of protein lysine acetylation, and its role in different human pathologies.

EXPERT OPINION

Acetylation targets are practically all cellular processes in eukaryotes and prokaryotes organisms. Consequently, this modification has been linked to many pathologies like cancer, viral infection, obesity, diabetes, cardiovascular, and nervous system-associated diseases, to mention a few relevant examples. Accordingly, some intermediate mediators in the acetylation process have been projected as therapeutic targets.

Intracellular ATP Concentration and Implication for Cellular Evolution

Crystalline lens and striated muscle exist at opposite ends of the metabolic spectrum. Lens is a metabolically quiescent tissue, whereas striated muscle is a mechanically dynamic tissue with high-energy requirements, yet both tissues contain millimolar levels of ATP (>2.3 mM), far exceeding their underlying metabolic needs. We explored intracellular concentrations of ATP across multiple cells, tissues, species, and domains to provide context for interpreting lens/striated muscle data. Our database revealed that high intracellular ATP concentrations are ubiquitous across diverse life forms including species existing from the Precambrian Era, suggesting an ancient highly conserved role for ATP, independent of its widely accepted view as primarily "metabolic currency". Our findings reinforce suggestions that the primordial function of ATP was non-metabolic in nature, serving instead to prevent protein aggregation.

Impact of Aldosterone on the Failing Myocardium: Insights from Mitochondria and Adrenergic Receptors Signaling and Function

The mineralocorticoid aldosterone regulates electrolyte and blood volume homeostasis, but it also adversely modulates the structure and function of the chronically failing heart, through its elevated production in chronic human post-myocardial infarction (MI) heart failure (HF). By activating the mineralocorticoid receptor (MR), a ligand-regulated transcription factor, aldosterone promotes inflammation and fibrosis of the heart, while increasing oxidative stress, ultimately induding mitochondrial dysfunction in the failing myocardium. To reduce morbidity and mortality in advanced stage HF, MR antagonist drugs, such as spironolactone and eplerenone, are used. In addition to the MR, aldosterone can bind and stimulate other receptors, such as the plasma membrane-residing G protein-coupled estrogen receptor (GPER), further complicating it signaling properties in the myocardium. Given the salient role that adrenergic receptor (ARs)—particularly βARs—play in cardiac physiology and pathology, unsurprisingly, that part of the impact of aldosterone on the failing heart is mediated by its effects on the signaling and function of these receptors. Aldosterone can significantly precipitate the well-documented derangement of cardiac AR signaling and impairment of AR function, critically underlying chronic human HF. One of the main consequences of HF in mammalian models at the cellular level is the presence of mitochondrial dysfunction. As such, preventing mitochondrial dysfunction could be a valid pharmacological target in this condition. This review summarizes the current experimental evidence for this aldosterone/AR crosstalk in both the healthy and failing heart, and the impact of mitochondrial dysfunction in HF. Recent findings from signaling studies focusing on MR and AR crosstalk via non-conventional signaling of molecules that normally terminate the signaling of ARs in the heart, i.e., the G protein-coupled receptor-kinases (GRKs), are also highlighted.

Insulin directly stimulates mitochondrial glucose oxidation in the heart

Background

Glucose oxidation is a major contributor to myocardial energy production and its contribution is orchestrated by insulin. While insulin can increase glucose oxidation indirectly by enhancing glucose uptake and glycolysis, it also directly stimulates mitochondrial glucose oxidation, independent of increasing glucose uptake or glycolysis, through activating mitochondrial pyruvate dehydrogenase (PDH), the rate-limiting enzyme of glucose oxidation. However, how insulin directly stimulates PDH is not known. To determine this, we characterized the impacts of modifying mitochondrial insulin signaling kinases, namely protein kinase B (Akt), protein kinase C-delta (PKC-δ) and glycogen synthase kinase-3 beta (GSK-3β), on the direct insulin stimulation of glucose oxidation.

Methods

We employed an isolated working mouse heart model to measure the effect of insulin on cardiac glycolysis, glucose oxidation and fatty acid oxidation and how that could be affected when mitochondrial Akt, PKC-δ or GSK-3β is disturbed using pharmacological modulators. We also used differential centrifugation to isolate mitochondrial and cytosol fraction to examine the activity of Akt, PKC-δ and GSK-3β between these fractions. Data were analyzed using unpaired t-test and two-way ANOVA.

Results

Here we show that insulin-stimulated phosphorylation of mitochondrial Akt is a prerequisite for transducing insulin’s direct stimulation of glucose oxidation. Inhibition of mitochondrial Akt completely abolishes insulin-stimulated glucose oxidation, independent of glucose uptake or glycolysis. We also show a novel role of mitochondrial PKC-δ in modulating mitochondrial glucose oxidation. Inhibition of mitochondrial PKC-δ mimics insulin stimulation of glucose oxidation and mitochondrial Akt. We also demonstrate that inhibition of mitochondrial GSK3β phosphorylation does not influence insulin-stimulated glucose oxidation.

Conclusion

We identify, for the first time, insulin-stimulated mitochondrial Akt as a prerequisite transmitter of the insulin signal that directly stimulates cardiac glucose oxidation. These novel findings suggest that targeting mitochondrial Akt is a potential therapeutic approach to enhance cardiac insulin sensitivity in condition such as heart failure, diabetes and obesity.

Inhibition of the proteasome preserves Mitofusin-2 and mitochondrial integrity, protecting cardiomyocytes during ischemia-reperfusion injury

Cardiomyocyte loss is the main cause of myocardial dysfunction following an ischemia-reperfusion (IR) injury. Mitochondrial dysfunction and altered mitochondrial network dynamics play central roles in cardiomyocyte death. Proteasome inhibition is cardioprotective in the setting of IR; however, the mechanisms underlying this protection are not well-understood. Several proteins that regulate mitochondrial dynamics and energy metabolism, including Mitofusin-2 (Mfn2), are degraded by the proteasome. The aim of this study was to evaluate whether proteasome inhibition can protect cardiomyocytes from IR damage by maintaining Mfn2 levels and preserving mitochondrial network integrity. Using ex vivo Langendorff-perfused rat hearts and in vitro neonatal rat ventricular myocytes, we showed that the proteasome inhibitor MG132 reduced IR-induced cardiomyocyte death. Moreover, MG132 preserved mitochondrial mass, prevented mitochondrial network fragmentation, and abolished IR-induced reductions in Mfn2 levels in heart tissue and cultured cardiomyocytes. Interestingly, Mfn2 overexpression also prevented cardiomyocyte death. This effect was apparently specific to Mfn2, as overexpression of Miro1, another protein implicated in mitochondrial dynamics, did not confer the same protection. Our results suggest that proteasome inhibition protects cardiomyocytes from IR damage. This effect could be partly mediated by preservation of Mfn2 and therefore mitochondrial integrity.

Ubiquitin and Ubiquitin-like proteins in cardiac disease and protection

Post-translational modification represents an important mechanism to regulate protein function in cardiac cells. Ubiquitin (Ub) and ubiquitin-like proteins (UBLs) are a family of protein modifiers that share a certain extent of sequence and structure similarity. Conjugation of Ub or UBLs to target proteins is dynamically regulated by a set of UBL-specific enzymes and modulates the physical and physiological properties of protein substrates. Ub and UBLs control a strikingly wide spectrum of cellular processes and not surprisingly are involved in the development of multiple human diseases including cardiac diseases. Further identification of novel UBL targets will expand our understanding of the functional diversity of UBL pathways in physiology and pathology. Here we review recent findings on the mechanisms, proteome and functions of a subset of UBLs and highlight their potential impacts on the development and progression of various forms of cardiac diseases.

Cardioprotection induced by a brief exposure to acetaldehyde: role of aldehyde dehydrogenase 2

Aims

We previously demonstrated that acute ethanol administration protects the heart from ischaemia/reperfusion (I/R) injury thorough activation of aldehyde dehydrogenase 2 (ALDH2). Here, we characterized the role of acetaldehyde, an intermediate product from ethanol metabolism, and its metabolizing enzyme, ALDH2, in an ex vivo model of cardiac I/R injury.

Methods and results

We used a combination of homozygous knock-in mice (ALDH2*2), carrying the human inactivating point mutation ALDH2 (E487K), and a direct activator of ALDH2, Alda-1, to investigate the cardiac effect of acetaldehyde. The ALDH2*2 mice have impaired acetaldehyde clearance, recapitulating the human phenotype. Yet, we found a similar infarct size in wild type (WT) and ALDH2*2 mice. Similar to ethanol-induced preconditioning, pre-treatment with 50 μM acetaldehyde increased ALDH2 activity and reduced cardiac injury in hearts of WT mice without affecting cardiac acetaldehyde levels. However, acetaldehyde pre-treatment of hearts of ALDH2*2 mice resulted in a three-fold increase in cardiac acetaldehyde levels and exacerbated I/R injury. Therefore, exogenous acetaldehyde appears to have a bimodal effect in I/R, depending on the ALDH2 genotype. Further supporting an ALDH2 role in cardiac preconditioning, pharmacological ALDH2 inhibition abolished ethanol-induced cardioprotection in hearts of WT mice, whereas a selective activator, Alda-1, protected ALDH2*2 against ethanol-induced cardiotoxicity. Finally, either genetic or pharmacological inhibition of ALDH2 mitigated ischaemic preconditioning.

Conclusion

Taken together, our findings suggest that low levels of acetaldehyde are cardioprotective whereas high levels are damaging in an ex vivo model of I/R injury and that ALDH2 is a major, but not the only, regulator of cardiac acetaldehyde levels and protection from I/R.

Targeting mitochondrial dysfunction and oxidative stress in heart failure: Challenges and opportunities

Mitochondrial dysfunction characterized by impaired bioenergetics, oxidative stress and aldehydic load is a hallmark of heart failure. Recently, different research groups have provided evidence that selective activation of mitochondrial detoxifying systems that counteract excessive accumulation of ROS, RNS and reactive aldehydes is sufficient to stop cardiac degeneration upon chronic stress, such as heart failure. Therefore, pharmacological and non-pharmacological approaches targeting mitochondria detoxification may play a critical role in the prevention or treatment of heart failure. In this review we discuss the most recent findings on the central role of mitochondrial dysfunction, oxidative stress and aldehydic load in heart failure, highlighting the most recent preclinical and clinical studies using mitochondria-targeted molecules and exercise training as effective tools against heart failure.

Protein kinase C and cardiac dysfunction: a review

Heart failure (HF) is a physiological state in which cardiac output is insufficient to meet the needs of the body. It is a clinical syndrome characterized by impaired ability of the left ventricle to either fill or eject blood efficiently. HF is a disease of multiple aetiologies leading to progressive cardiac dysfunction and it is the leading cause of deaths in both developed and developing countries. HF is responsible for about 73,000 deaths in the UK each year. In the USA, HF affects 5.8 million people and 550,000 new cases are diagnosed annually. Cardiac remodelling (CD), which plays an important role in pathogenesis of HF, is viewed as stress response to an index event such as myocardial ischaemia or imposition of mechanical load leading to a series of structural and functional changes in the viable myocardium. Protein kinase C (PKC) isozymes are a family of serine/threonine kinases. PKC is a central enzyme in the regulation of growth, hypertrophy, and mediators of signal transduction pathways. In response to circulating hormones, activation of PKC triggers a multitude of intracellular events influencing multiple physiological processes in the heart, including heart rate, contraction, and relaxation. Recent research implicates PKC activation in the pathophysiology of a number of cardiovascular disease states. Few reports are available that examine PKC in normal and diseased human hearts. This review describes the structure, functions, and distribution of PKCs in the healthy and diseased heart with emphasis on the human heart and, also importantly, their regulation in heart failure.

Macroautophagy and Chaperone-Mediated Autophagy in Heart Failure: The Known and the Unknown

Cardiac diseases including hypertrophic and ischemic cardiomyopathies are increasingly being reported to accumulate misfolded proteins and damaged organelles. These findings have led to an increasing interest in protein degradation pathways, like autophagy, which are essential not only for normal protein turnover but also in the removal of misfolded and damaged proteins. Emerging evidence suggests a previously unprecedented role for autophagic processes in cardiac physiology and pathology. This review focuses on the major types of autophagic processes, the genes and protein complexes involved, and their regulation. It discusses the key similarities and differences between macroautophagy, chaperone-mediated autophagy, and selective mitophagy structures and functions. The genetic models available to study loss and gain of macroautophagy, mitophagy, and CMA are discussed. It defines the markers of autophagic processes, methods for measuring autophagic activities, and their interpretations. This review then summarizes the major studies of autophagy in the heart and their contribution to cardiac pathology. Some reports suggest macroautophagy imparts cardioprotection from heart failure pathology. Meanwhile, other studies find macroautophagy activation may be detrimental in cardiac pathology. An improved understanding of autophagic processes and their regulation may lead to a new genre of treatments for cardiac diseases.

Balanced Diet-Fed Fat-1 Transgenic Mice Exhibit Lower Hindlimb Suspension-Induced Soleus Muscle Atrophy

The consequences of two-week hindlimb suspension (HS) on skeletal muscle atrophy were investigated in balanced diet-fed Fat-1 transgenic and C57BL/6 wild-type mice. Body composition and gastrocnemius fatty acid composition were measured. Skeletal muscle force, cross-sectional area (CSA), and signaling pathways associated with protein synthesis (protein kinase B, Akt; ribosomal protein S6, S6, eukaryotic translation initiation factor 4E-binding protein 1, 4EBP1; glycogen synthase kinase3-beta, GSK3-beta; and extracellular-signal-regulated kinases 1/2, ERK 1/2) and protein degradation (atrophy gene-1/muscle atrophy F-box, atrogin-1/MAFbx and muscle RING finger 1, MuRF1) were evaluated in the soleus muscle. HS decreased soleus muscle wet and dry weights (by 43% and 26%, respectively), muscle isotonic and tetanic force (by 29% and 18%, respectively), CSA of the soleus muscle (by 36%), and soleus muscle fibers (by 45%). Fat-1 transgenic mice had a decrease in the ω-6/ω-3 polyunsaturated fatty acids (PUFAs) ratio as compared with C57BL/6 wild-type mice (56%, p < 0.001). Fat-1 mice had lower soleus muscle dry mass loss (by 10%) and preserved absolute isotonic force (by 17%) and CSA of the soleus muscle (by 28%) after HS as compared with C57BL/6 wild-type mice. p-GSK3B/GSK3B ratio was increased (by 70%) and MuRF-1 content decreased (by 50%) in the soleus muscle of Fat-1 mice after HS. Balanced diet-fed Fat-1 mice are able to preserve in part the soleus muscle mass, absolute isotonic force and CSA of the soleus muscle in a disuse condition.

Angiotensin II-preconditioning is associated with increased PKCε/PKCδ ratio and prosurvival kinases in mitochondria

Angiotensin II-preconditioning (APC) has been shown to reproduce the cardioprotective effects of ischaemic preconditioning (IPC), however, the molecular mechanisms mediating the effects of APC remain unknown. In this study, Langendorff-perfused rat hearts were subjected to IPC, APC or both (IPC/APC) followed by ischaemia-reperfusion (IR), to determine translocation of PKCε, PKCδ, Akt, Erk1/2, JNK, p38 MAPK and GSK-3β to mitochondria as an indicator of activation of the protein kinases. In agreement with previous observations, IPC, APC and IPC/APC increased the recovery of left ventricular developed pressure (LVDP), reduced infarct size (IS) and lactate dehydrogenase (LDH) release, compared to controls. These effects were associated with increased mitochondrial PKCε/PKCδ ratio, Akt, Erk1/2, JNK, and inhibition of permeability transition pore (mPTP) opening. Chelerythrine, a pan-PKC inhibitor, abolished the enhancements of PKCε but increased PKCδ expression, and inhibited Akt, Erk1/2, and JNK protein levels. The drug had no effect on the APC- and IPC/APC-induced cardioprotection as previously reported, but enhanced the post-ischaemic LVDP in controls. Losartan, an angiotensin II type 1 receptor (AT1-R) blocker, abolished the APC-stimulated increase of LVDP and reduced PKCε, Akt, Erk1/2, JNK, and p38. Both drugs reduced ischaemic contracture and LDH release, and abolished the inhibition of mPTP by the preconditioning. Chelerythrine also prevented the reduction of IS by APC and IPC/APC. These results suggest that the cardioprotection induced by APC and IPC/APC involves an AT1-R-dependent translocation of PKCε and survival kinases to the mitochondria leading to mPTP inhibition. In chelerythrine-treated hearts, however, alternate mechanisms appear to maintain cardiac function.

Hyperosmotic environment blunts effectivity of ischemic preconditioning against ischemia-reperfusion injury and improves ischemic tolerance in non-preconditioned isolated rat hearts

Several studies have shown that diabetes mellitus modulates heart resistance to ischemia and abrogates effectivity of cardioprotective interventions, such as ischemic preconditioning (IP). The aim of this study was to evaluate whether the effect of hyperglycemic conditions on the severity of ischemia-reperfusion (I/R) injury in preconditioned and non-preconditioned hearts (controls, C) is related to changes in osmotic activity of glucose. Experiments were performed in isolated rat hearts perfused according to Langendorff exposed to 30-min coronary occlusion/120-min reperfusion. IP was induced by two cycles of 5-min coronary occlusion/5-min reperfusion, prior to the long-term I/R. Hyperosmotic (HO) state induced by an addition of mannitol (11 mmol/l) to a standard Krebs-Henseleit perfusion medium significantly decreased the size of infarction and also suppressed a release of heart fatty acid binding protein (h-FABP - biomarker of cell injury) from the non-IP hearts nearly to 50 %, in comparison with normoosmotic (NO) mannitol-free perfusion. However, IP in HO conditions significantly increased the size of infarction and tended to elevate the release of h-FABP to the effluent from the heart. The results indicate that HO environment plays a cardioprotective role in the ischemic myocardium. On the other hand, increased osmolarity, similar to that in the hyperglycemic conditions, may play a pivotal role in a failure of IP to induce cardioprotection in the diabetic myocardium.

Therapeutic Effects of Ischemic-Preconditioned Exosomes in Cardiovascular Diseases

Despite years of researches, cardiovascular disease (CVD) remains the most common cause of death around the world. Lots of studies showed that by pretreating with short nonfatal ischemia in in situ organ or distant organ, one could develop tolerance to the following fatal ischemia. The process is called ischemic preconditioning (IPC). IPC prepare the heart for damage by producing inflammatory signals, miRNA, neuro system stimulation and exosomes. Among them, exosomes have been gaining increasing interest since it is characterized by its capability to carry information and its specific ligand-receptor system. Here we will discuss IPC induced exosomes and its protective effects during ischemic heart disease.

Subnormothermic Perfusion in the Isolated Rat Liver Preserves the Antioxidant Glutathione and Enhances the Function of the Ubiquitin Proteasome System

The reduction of oxidative stress is suggested to be one of the main mechanisms to explain the benefits of subnormothermic perfusion against ischemic liver damage. In this study we investigated the early cellular mechanisms induced in isolated rat livers after 15 min perfusion at temperatures ranging from normothermia (37°C) to subnormothermia (26°C and 22°C). Subnormothermic perfusion was found to maintain hepatic viability. Perfusion at 22°C raised reduced glutathione levels and the activity of glutathione reductase; however, lipid and protein oxidation still occurred as determined by malondialdehyde, 4-hydroxynonenal-protein adducts, and advanced oxidation protein products. In livers perfused at 22°C the lysosomal and ubiquitin proteasome system (UPS) were both activated. The 26S chymotrypsin-like (β5) proteasome activity was significantly increased in the 26°C (46%) and 22°C (42%) groups. The increased proteasome activity may be due to increased Rpt6 Ser120 phosphorylation, which is known to enhance 26S proteasome activity. Together, our results indicate that the early events produced by subnormothermic perfusion in the liver can induce oxidative stress concomitantly with antioxidant glutathione preservation and enhanced function of the lysosomal and UPS systems. Thus, a brief hypothermia could trigger antioxidant mechanisms and may be functioning as a preconditioning stimulus.

Effects of high EPA and high DHA fish oils on changes in signaling associated with protein metabolism induced by hindlimb suspension in rats

The effects of either eicosapentaenoic (EPA)- or docosahexaenoic (DHA)-rich fish oils on hindlimb suspension (HS)-induced muscle disuse atrophy were compared. Daily oral supplementations (0.3 mL/100 g b.w.) with mineral oil (MO) or high EPA or high DHA fish oils were performed in adult rats. After 2 weeks, the animals were subjected to HS for further 2 weeks. The treatments were maintained alongside HS At the end of 4 weeks, we evaluated: body weight gain, muscle mass and fat depots, composition of fatty acids, cross-sectional areas (CSA) of the soleus muscle and soleus muscle fibers, activities of cathepsin L and 26S proteasome, and content of carbonylated proteins in the soleus muscle. Signaling pathway activities associated with protein synthesis (Akt, p70S6K, S6, 4EBP1, and GSK3-beta) and protein degradation (atrogin-1/MAFbx, and MuRF1) were evaluated. HS decreased muscle mass, CSA of soleus muscle and soleus muscle fibers, and altered signaling associated with protein synthesis (decreased) and protein degradation (increased). The treatment with either fish oil decreased the ratio of omega-6/omega-3 fatty acids and changed protein synthesis-associated signaling. EPA-rich fish oil attenuated the changes induced by HS on 26S proteasome activity, CSA of soleus muscle fibers, and levels of p-Akt, total p70S6K, p-p70S6K/total p70S6K, p-4EBP1, p-GSK3-beta, p-ERK2, and total ERK 1/2 proteins. DHA-rich fish oil attenuated the changes induced by HS on p-4EBP1 and total ERK1 levels. The effects of EPA-rich fish oil on protein synthesis signaling were more pronounced. Both EPA- and DHA-rich fish oils did not impact skeletal muscle mass loss induced by non-inflammatory HS.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Multifunctional roles of PKCδ: Opportunities for targeted therapy in human disease

The serine-threonine protein kinase, protein kinase C-δ (PKCδ), is emerging as a bi-functional regulator of cell death and proliferation. Studies in PKCδ-/- mice have confirmed a pro-apoptotic role for this kinase in response to DNA damage and a tumor promoter role in some oncogenic contexts. In non-transformed cells, inhibition of PKCδ suppresses the release of cytochrome c and caspase activation, indicating a function upstream of apoptotic pathways. Data from PKCδ-/- mice demonstrate a role for PKCδ in the execution of DNA damage-induced and physiologic apoptosis. This has led to the important finding that inhibitors of PKCδ can be used therapeutically to reduce irradiation and chemotherapy-induced toxicity. By contrast, PKCδ is a tumor promoter in mouse models of mammary gland and lung cancer, and increased PKCδ expression is a negative prognostic indicator in Her2+ and other subtypes of human breast cancer. Understanding how these distinct functions of PKCδ are regulated is critical for the design of therapeutics to target this pathway. This review will discuss what is currently known about biological roles of PKCδ and prospects for targeting PKCδ in human disease.

Damaging effects of hyperglycemia on cardiovascular function: spotlight on glucose metabolic pathways

The incidence of cardiovascular complications associated with hyperglycemia is a growing global health problem. This review discusses the link between hyperglycemia and cardiovascular diseases onset, focusing on the role of recently emerging downstream mediators, namely, oxidative stress and glucose metabolic pathway perturbations. The role of hyperglycemia-mediated activation of nonoxidative glucose pathways (NOGPs) [i.e., the polyol pathway, hexosamine biosynthetic pathway, advanced glycation end products (AGEs), and protein kinase C] in this process is extensively reviewed. The proposal is made that there is a unique interplay between NOGPs and a downstream convergence of detrimental effects that especially affect cardiac endothelial cells, thereby contributing to contractile dysfunction. In this process the AGE pathway emerges as a crucial mediator of hyperglycemia-mediated detrimental effects. In addition, a vicious metabolic cycle is established whereby hyperglycemia-induced NOGPs further fuel their own activation by generating even more oxidative stress, thereby exacerbating damaging effects on cardiac function. Thus NOGP inhibition, and particularly that of the AGE pathway, emerges as a novel therapeutic intervention for the treatment of cardiovascular complications such as acute myocardial infarction in the presence hyperglycemia.

Xenon Treatment Protects against Remote Lung Injury after Kidney Transplantation in Rats

BACKGROUND

Ischemia-reperfusion injury (IRI) of renal grafts may cause remote organ injury including lungs. The authors aimed to evaluate the protective effect of xenon exposure against remote lung injury due to renal graft IRI in a rat renal transplantation model.

METHODS

For in vitro studies, human lung epithelial cell A549 was challenged with H2O2, tumor necrosis factor-α, or conditioned medium from human kidney proximal tubular cells (HK-2) after hypothermia-hypoxia insults. For in vivo studies, the Lewis renal graft was stored in 4°C Soltran preserving solution for 24 h and transplanted into the Lewis recipient, and the lungs were harvested 24 h after grafting. Cultured lung cells or the recipient after engraftment was exposed to 70% Xe or N2. Phospho (p)-mammalian target of rapamycin (mTOR), hypoxia-inducible factor-1α (HIF-1α), Bcl-2, high-mobility group protein-1 (HMGB-1), TLR-4, and nuclear factor κB (NF-κB) expression, lung inflammation, and cell injuries were assessed.

RESULTS

Recipients receiving ischemic renal grafts developed pulmonary injury. Xenon treatment enhanced HIF-1α, which attenuated HMGB-1 translocation and NF-κB activation in A549 cells with oxidative and inflammatory stress. Xenon treatment enhanced p-mTOR, HIF-1α, and Bcl-2 expression and, in turn, promoted cell proliferation in the lung. Upon grafting, HMGB-1 translocation from lung epithelial nuclei was reduced; the TLR-4/NF-κB pathway was suppressed by xenon treatment; and subsequent tissue injury score (nitrogen vs. xenon: 26 ± 1.8 vs. 10.7 ± 2.6; n = 6) was significantly reduced.

CONCLUSION

Xenon treatment confers protection against distant lung injury triggered by renal graft IRI, which is likely through the activation of mTOR-HIF-1α pathway and suppression of the HMGB-1 translocation from nuclei to cytoplasm.

Increased clearance of reactive aldehydes and damaged proteins in hypertension-induced compensated cardiac hypertrophy: impact of exercise training

Background. We previously reported that exercise training (ET) facilitates the clearance of damaged proteins in heart failure. Here, we characterized the impact of ET on cardiac protein quality control during compensated ventricular hypertrophy in spontaneously hypertensive rats (SHR). Methods and Results. SHR were randomly assigned into sedentary and swimming-trained groups. Sedentary SHR displayed cardiac hypertrophy with preserved ventricular function compared to normotensive rats, characterizing a compensated cardiac hypertrophy. Hypertensive rats presented signs of cardiac oxidative stress, depicted by increased lipid peroxidation. However, these changes were not followed by accumulation of lipid peroxidation-generated reactive aldehydes and damaged proteins. This scenario was explained, at least in part, by the increased catalytic activity of both aldehyde dehydrogenase 2 (ALDH2) and proteasome. Of interest, ET exacerbated cardiac hypertrophy, improved ventricular function, induced resting bradycardia, and decreased blood pressure in SHR. These changes were accompanied by reduced cardiac oxidative stress and a consequent decrease in ALDH2 and proteasome activities, without affecting small chaperones levels and apoptosis in SHR. Conclusion. Increased cardiac ALDH2 and proteasomal activities counteract the deleterious effect of excessive oxidative stress in hypertension-induced compensated cardiac hypertrophy in rats. ET has a positive effect in reducing cardiac oxidative stress without affecting protein quality control.

Targeting the ubiquitin-proteasome system in heart disease: the basis for new therapeutic strategies

SIGNIFICANCE

Novel therapeutic strategies to treat heart failure are greatly needed. The ubiquitin-proteasome system (UPS) affects the structure and function of cardiac cells through targeted degradation of signaling and structural proteins. This review discusses both beneficial and detrimental consequences of modulating the UPS in the heart.

RECENT ADVANCES

Proteasome inhibitors were first used to test the role of the UPS in cardiac disease phenotypes, indicating therapeutic potential. In early cardiac remodeling and pathological hypertrophy with increased proteasome activities, proteasome inhibition prevented or restricted disease progression and contractile dysfunction. Conversely, enhancing proteasome activities by genetic manipulation, pharmacological intervention, or ischemic preconditioning also improved the outcome of cardiomyopathies and infarcted hearts with impaired cardiac and UPS function, which is, at least in part, caused by oxidative damage.

CRITICAL ISSUES

An understanding of the UPS status and the underlying mechanisms for its potential deregulation in cardiac disease is critical for targeted interventions. Several studies indicate that type and stage of cardiac disease influence the dynamics of UPS regulation in a nonlinear and multifactorial manner. Proteasome inhibitors targeting all proteasome complexes are associated with cardiotoxicity in humans. Furthermore, the type and dosage of proteasome inhibitor impact the pathogenesis in nonuniform ways.

FUTURE DIRECTIONS

Systematic analysis and targeting of individual UPS components with established and innovative tools will unravel and discriminate regulatory mechanisms that contribute to and protect against the progression of cardiac disease. Integrating this knowledge in drug design may reduce adverse effects on the heart as observed in patients treated with proteasome inhibitors against noncardiac diseases, especially cancer.

Transcriptional regulation of oncogenic protein kinase Cϵ (PKCϵ) by STAT1 and Sp1 proteins

Overexpression of PKCϵ, a kinase associated with tumor aggressiveness and widely implicated in malignant transformation and metastasis, is a hallmark of multiple cancers, including mammary, prostate, and lung cancer. To characterize the mechanisms that control PKCϵ expression and its up-regulation in cancer, we cloned an ∼ 1.6-kb promoter segment of the human PKCϵ gene (PRKCE) that displays elevated transcriptional activity in cancer cells. A comprehensive deletional analysis established two regions rich in Sp1 and STAT1 sites located between -777 and -105 bp (region A) and -921 and -796 bp (region B), respectively, as responsible for the high transcriptional activity observed in cancer cells. A more detailed mutagenesis analysis followed by EMSA and ChIP identified Sp1 sites in positions -668/-659 and -269/-247 as well as STAT1 sites in positions -880/-869 and -793/-782 as the elements responsible for elevated promoter activity in breast cancer cells relative to normal mammary epithelial cells. RNAi silencing of Sp1 and STAT1 in breast cancer cells reduced PKCϵ mRNA and protein expression, as well as PRKCE promoter activity. Moreover, a strong correlation was found between PKCϵ and phospho-Ser-727 (active) STAT1 levels in breast cancer cells. Our results may have significant implications for the development of approaches to target PKCϵ and its effectors in cancer therapeutics.

Transduction of PEP-1-heme oxygenase-1 fusion protein reduces myocardial ischemia/reperfusion injury in rats

Recent studies have uncovered that overexpression of heme oxygenase-1 (HO-1) by induction or gene transfer provides myocardial protection. In the present study, we investigated whether HO-1 protein mediated by cell-penetrating peptide PEP-1 could confer cardioprotection in a rat model of myocardial ischemia/reperfusion (I/R) injury. Male Sprague-Dawley rats were subjected to 30 minutes of ischemia by occluding the left anterior descending coronary artery and to 120 minutes of reperfusion to prepare the model of I/R. Animals were randomized to receive PEP-1-HO-1 fusion protein or saline 30 minutes before a 30-minute occlusion. I/R increased myocardial infarct size and levels of malondialdehyde, serum tumor necrosis factor alpha, and interleukin 6 and reduced myocardial superoxide dismutase activity. Administration of PEP-1-HO-1 reduced myocardial infarct size and levels of malondialdehyde, serum tumor necrosis factor alpha, and interleukin 6 and increased myocardial superoxide dismutase and HO-1 activities. His-probe protein was only detected in PEP-1-HO-1-transduced hearts. In addition, transduction of PEP-1-HO-1 markedly reduced elevated myocardial tissue nuclear factor-κB induced by I/R. The results suggested that transduction of PEP-1-HO-1 fusion protein decreased myocardial reperfusion injury, probably by attenuating the production of oxidants and proinflammatory cytokines regulated by nuclear factor-κB.

PREINFARCTION ANGINA AS A CLINICAL FORM OF THE ISCHEMIC PRECONDITIONING PHENOMENON

Brief episodes of myocardial ischemia initiate a cascade of endogenous mechanisms which protect the heart during further ischemic attack. This phenomenon is called an ischemic preconditioning. Preinfarction angina is a clinical model of this phenomenon. Clinical studies have demonstrated that preinfarction angina is associated with: lower incidence of cardiogenic shock, pulmonary edema, ventricular tachycardia and ventricular fibrillation, reduced infarct size, less severe left ventricular dysfunction, better results of thrombolytic therapy, less severe myocardial reperfusion injury, better hospital and long-term prognosis. There is evidence that elderly age, presence of diabetes mellitus, left ventricular hypertrophy and hypercholesterolemia do reduce the cardioprotective effect of preinfarction angina. Preinfarction angina may be an additional criterion of risk stratification in myocardial infarction patients. This review summarizes data from the literature on the most important aspects of preinfarction angina.

Aldehyde dehydrogenase 2 activation in heart failure restores mitochondrial function and improves ventricular function and remodelling

AIMS

We previously demonstrated that pharmacological activation of mitochondrial aldehyde dehydrogenase 2 (ALDH2) protects the heart against acute ischaemia/reperfusion injury. Here, we determined the benefits of chronic activation of ALDH2 on the progression of heart failure (HF) using a post-myocardial infarction model.

METHODS AND RESULTS

We showed that a 6-week treatment of myocardial infarction-induced HF rats with a selective ALDH2 activator (Alda-1), starting 4 weeks after myocardial infarction at a time when ventricular remodelling and cardiac dysfunction were present, improved cardiomyocyte shortening, cardiac function, left ventricular compliance and diastolic function under basal conditions, and after isoproterenol stimulation. Importantly, sustained Alda-1 treatment showed no toxicity and promoted a cardiac anti-remodelling effect by suppressing myocardial hypertrophy and fibrosis. Moreover, accumulation of 4-hydroxynonenal (4-HNE)-protein adducts and protein carbonyls seen in HF was not observed in Alda-1-treated rats, suggesting that increasing the activity of ALDH2 contributes to the reduction of aldehydic load in failing hearts. ALDH2 activation was associated with improved mitochondrial function, including elevated mitochondrial respiratory control ratios and reduced H2O2 release. Importantly, selective ALDH2 activation decreased mitochondrial Ca(2+)-induced permeability transition and cytochrome c release in failing hearts. Further supporting a mitochondrial mechanism for ALDH2, Alda-1 treatment preserved mitochondrial function upon in vitro aldehydic load.

CONCLUSIONS

Selective activation of mitochondrial ALDH2 is sufficient to improve the HF outcome by reducing the toxic effects of aldehydic overload on mitochondrial bioenergetics and reactive oxygen species generation, suggesting that ALDH2 activators, such as Alda-1, have a potential therapeutic value for treating HF patients.

Protein kinase C delta modulates endothelial nitric oxide synthase after cardiac arrest

We previously showed that inhibition of protein kinase C delta (PKCδ) improves brain perfusion 24 hours after asphyxial cardiac arrest (ACA) and confers neuroprotection in the cortex and CA1 region of the hippocampus 7 days after arrest. Therefore, in this study, we investigate the mechanism of action of PKCδ-mediated hypoperfusion after ACA in the rat by using the two-photon laser scanning microscopy (TPLSM) to observe cortical cerebral blood flow (CBF) and laser Doppler flowmetry (LDF) detecting regional CBF in the presence/absence of δV1-1 (specific PKCδ inhibitor), nitric oxide synthase (NOS) substrate (L-arginine, L-arg) and inhibitor (N(ω)-Nitro-L-arginine, NLA), and nitric oxide (NO) donor (sodium nitroprusside, SNP). There was an increase in regional LDF and local (TPLSM) CBF in the presence of δV1-1+L-arg, but only an increase in regional CBF under δV1-1+SNP treatments. Systemic blood nitrite levels were measured 15 minutes and 24 hours after ACA. Nitrite levels were enhanced by pretreatment with δV1-1 30 minutes before ACA possibly attributable to enhanced endothelial NOS protein levels. Our results suggest that PKCδ can modulate NO machinery in cerebral vasculature. Protein kinase C delta can depress endothelial NOS blunting CBF resulting in hypoperfusion, but can be reversed with δV1-1 improving brain perfusion, thus providing subsequent neuroprotection after ACA.

Muscarinic 2 receptors modulate cardiac proteasome function in a protein kinase G-dependent manner

Proteasome function insufficiency and inadequate protein quality control are strongly implicated in a large subset of cardiovascular disease and may play an important role in their pathogenesis. Protein degradation by the ubiquitin proteasome system can be physiologically regulated. Cardiac muscarinic 2 (M2) receptors were pharmacologically interrogated in intact mice and cultured neonatal rat ventricular myocytes (NRVMs). Proteasome-mediated proteolysis was measured with a surrogate misfolded protein, proteasome peptidase assay, and by characterizing key proteasome subunits. Successful M2 receptor manipulation in cardiomyocytes was determined by measuring an endogenous protein substrate, and in mice, the cardiovascular physiological response. M2 receptor stimulation was associated with increased proteasome-mediated proteolysis and enhanced peptidase activities, while M2 receptor inhibition yielded opposing results. Additionally, M2 receptor manipulation did not alter abundance of the key proteasome subunits, Rpt6 and β5, but significantly shifted their isoelectric points. Inhibition of protein kinase G abrogated the stimulatory effects on proteasome-mediated proteolysis from M2 receptor activation. We conclude that M2 receptor stimulation enhances, whereas M2 receptor inhibition reduces, proteasome-mediated proteolysis likely through posttranslational modifications. Protein kinase G appears to be the mediator of the M2 receptors actions.

Detrimental effects of acute hyperglycaemia on the rat heart

AIM

Hyperglycaemia is an important risk factor for acute myocardial infarction. It can lead to increased induction of non-oxidative glucose pathways (NOGPs) - polyol and hexosamine biosynthetic pathways, advanced glycation end products and protein kinase C - that may contribute to cardiovascular diseases onset. However, the precise underlying mechanisms remain poorly understood. Here we hypothesized that acute hyperglycaemia increases myocardial oxidative stress and NOGP activation resulting in cardiac dysfunction during ischaemia-reperfusion and that inhibition of, and/or shunting flux away from NOGPs [by benfotiamine (BFT) treatment], leads to cardioprotection.

METHODS

We employed several experimental systems: (i) Isolated rat hearts were perfused ex vivo with Krebs-Henseleit buffer containing 33 mm glucose vs. controls (11 mm glucose) ± global ischaemia and reperfusion ± BFT (first 20 min of reperfusion); (ii) Infarct size determination as per the ischaemic protocol, but with regional ischaemia and reperfusion ± BFT treatment; in separate experiments, NOGP inhibitors were also employed for (i) and (ii); and (iii) In vivo coronary ligations performed on streptozotocin-treated rats ± BFT treatment (early reperfusion).

RESULTS

Acute hyperglycaemia generated myocardial oxidative stress, NOGP activation and apoptosis, but caused no impairment of cardiac function during pre-ischaemia, thereby priming hearts for later damage. Following ischaemia-reperfusion (under hyperglycaemic conditions), such effects were exacerbated together with cardiac contractile dysfunction. Moreover, inhibition of respective NOGPs and shunting away by BFT treatment (in part) improved cardiac function during ischaemia-reperfusion.

CONCLUSION

Coordinate NOGP activation in response to acute hyperglycaemia results in contractile dysfunction during ischaemia-reperfusion, allowing for the development of novel cardioprotective agents.

Targeting aldehyde dehydrogenase 2: new therapeutic opportunities

A family of detoxifying enzymes called aldehyde dehydrogenases (ALDHs) has been a subject of recent interest, as its role in detoxifying aldehydes that accumulate through metabolism and to which we are exposed from the environment has been elucidated. Although the human genome has 19 ALDH genes, one ALDH emerges as a particularly important enzyme in a variety of human pathologies. This ALDH, ALDH2, is located in the mitochondrial matrix with much known about its role in ethanol metabolism. Less known is a new body of research to be discussed in this review, suggesting that ALDH2 dysfunction may contribute to a variety of human diseases including cardiovascular diseases, diabetes, neurodegenerative diseases, stroke, and cancer. Recent studies suggest that ALDH2 dysfunction is also associated with Fanconi anemia, pain, osteoporosis, and the process of aging. Furthermore, an ALDH2 inactivating mutation (termed ALDH2*2) is the most common single point mutation in humans, and epidemiological studies suggest a correlation between this inactivating mutation and increased propensity for common human pathologies. These data together with studies in animal models and the use of new pharmacological tools that activate ALDH2 depict a new picture related to ALDH2 as a critical health-promoting enzyme.

Adenosine transport blockade restores attenuated cardioprotective effects of adenosine preconditioning in the isolated diabetic rat heart: potential crosstalk with opioid receptors

Considering the reduced ability of cardiac fibroblasts to release adenosine and increased ability of interstitial adenosine uptake during diabetes mellitus, the present study investigated the effect of adenosine preconditioning and the existence of cross-talk with opioid receptor activation in the diabetic rat heart subjected to ischemia-reperfusion (I/R). Langendorff-perfused normal and streptozotocin (65 mg/kg, i.p., once)-administered diabetic (after 8-weeks) rat hearts were subjected to 30-min global ischemia and 120-min reperfusion. Myocardial infarct size using triphenyltetrazolium chloride staining, markers of cardiac injury such as lactate dehydrogenase (LDH) and creatine kinase (CK-MB) release, coronary flow rate (CFR) and myocardial oxidative stress were assessed. The diabetic rat heart showed high degree of I/R injury with increased LDH and CK-MB release, high oxidative stress and reduced CFR as compared to the normal rat heart. The adenosine preconditioning (10 μM) afforded cardioprotection against I/R injury in the normal rat heart that was prevented by naloxone (100 μM) pre-treatment. Conversely, adenosine preconditioning-induced cardioprotection was abolished in the diabetic rat heart. However, co-administration of dipyridamole (100 μM), adenosine reuptake inhibitor, markedly restored the cardioprotective effect of adenosine preconditioning in the diabetic rat heart, and this effect was also abolished by naloxone pre-treatment. The reduced myocardial availability of extracellular adenosine might explain the inability of adenosine preconditioning to protect the diabetic myocardium. The pharmacological elevation of extracellular adenosine restores adenosine preconditioning-mediated cardioprotection in the diabetic myocardium by possibly involving opioid receptor activation.

Regulation of acetylation restores proteolytic function of diseased myocardium in mouse and human

Proteasome complexes play essential roles in maintaining cellular protein homeostasis and serve fundamental roles in cardiac function under normal and pathological conditions. A functional detriment in proteasomal activities has been recognized as a major contributor to the progression of cardiovascular diseases. Therefore, approaches to restore proteolytic function within the setting of the diseased myocardium would be of great clinical significance. In this study, we discovered that the cardiac proteasomal activity could be regulated by acetylation. Histone deacetylase (HDAC) inhibitors (suberoylanilide hydroxamic acid and sodium valproate) enhanced the acetylation of 20S proteasome subunits in the myocardium and led to an elevation of proteolytic capacity. This regulatory paradigm was present in both healthy and acutely ischemia/reperfusion (I/R) injured murine hearts, and HDAC inhibition in vitro restored proteolytic capacities to baseline sham levels in injured hearts. This mechanism of regulation was also viable in failing human myocardium. With 20S proteasomal complexes purified from murine myocardium treated with HDAC inhibitors in vivo, we confirmed that acetylation of 20S subunits directly, at least in part, presents a molecular explanation for the improvement in function. Furthermore, using high-resolution LC-MS/MS, we unraveled the first cardiac 20S acetylome, which identified the acetylation of nine N-termini and seven internal lysine residues. Acetylation on four lysine residues and four N-termini on cardiac proteasomes were novel discoveries of this study. In addition, the acetylation of five lysine residues was inducible via HDAC inhibition, which correlated with the enhancement of 20S proteasomal activity. Taken as a whole, our investigation unveiled a novel mechanism of proteasomal function regulation in vivo and established a new strategy for the potential rescue of compromised proteolytic function in the failing heart using HDAC inhibitors.

Impact of exercise training on redox signaling in cardiovascular diseases

Reactive oxygen and nitrogen species regulate a wide array of signaling pathways that governs cardiovascular physiology. However, oxidant stress resulting from disrupted redox signaling has an adverse impact on the pathogenesis and progression of cardiovascular diseases. In this review, we address how redox signaling and oxidant stress affect the pathophysiology of cardiovascular diseases such as ischemia-reperfusion injury, hypertension and heart failure. We also summarize the benefits of exercise training in tackling the hyperactivation of cellular oxidases and mitochondrial dysfunction seen in cardiovascular diseases.

Role of Protein Kinase C in Ischemic “Conditioning”

Since the discovery of ischemic preconditioning (IPC) 26 years ago, numerous studies attempted to determine the mechanism of this powerful form of cardioprotection. One of the first proposed pathways of IPC suggested that the preconditioning stimulus activated phospholipase C via G-protein, and diacylglycerol released from phospholipid moieties activated protein kinase C (PKC) by translocating it from the cytosol to the sarcolemmal membranes. The major protective isoform of PKC was found to be the PKC-∊. Despite some contradictions and controversies, today even the most skeptical opponents acknowledge that PKC plays a significant role in the mechanism of IPC. During recent years, both the role and the place of PKC-∊ in the mechanism of IPC have been revised. The current review presents the evolution of the “PKC theory” and summarizes the most recent data regarding the role of PKC in IPC. In addition to classical IPC, PKC appears to play a role in the mechanisms of newer conditioning protocols, that is, remote IPC and ischemic postconditioning.

Protein kinase g positively regulates proteasome-mediated degradation of misfolded proteins

BACKGROUND

Proteasome functional insufficiency is implicated in a large subset of cardiovascular diseases and may play an important role in their pathogenesis. The regulation of proteasome function is poorly understood, hindering the development of effective strategies to improve proteasome function.

METHODS AND RESULTS

Protein kinase G (PKG) was manipulated genetically and pharmacologically in cultured cardiomyocytes. Activation of PKG increased proteasome peptidase activities, facilitated proteasome-mediated degradation of surrogate (enhanced green fluorescence protein modified by carboxyl fusion of degron CL1) and bona fide (CryAB(R120G)) misfolded proteins, and attenuated CryAB(R120G) overexpression-induced accumulation of ubiquitinated proteins and cellular injury. PKG inhibition elicited the opposite responses. Differences in the abundance of the key 26S proteasome subunits Rpt6 and β5 between the PKG-manipulated and control groups were not statistically significant, but the isoelectric points were shifted by PKG activation. In transgenic mice expressing a surrogate substrate (GFPdgn), PKG activation by sildenafil increased myocardial proteasome activities and significantly decreased myocardial GFPdgn protein levels. Sildenafil treatment significantly increased myocardial PKG activity and significantly reduced myocardial accumulation of CryAB(R120G), ubiquitin conjugates, and aberrant protein aggregates in mice with CryAB(R120G)-based desmin-related cardiomyopathy. No discernible effect on bona fide native substrates of the ubiquitin-proteasome system was observed from PKG manipulation in vitro or in vivo.

CONCLUSIONS

PKG positively regulates proteasome activities and proteasome-mediated degradation of misfolded proteins, likely through posttranslational modifications to proteasome subunits. This may be a new mechanism underlying the benefit of PKG stimulation in treating cardiac diseases. Stimulation of PKG by measures such as sildenafil administration is potentially a new therapeutic strategy to treat cardiac proteinopathies.

Mitochondria as a source of reactive oxygen and nitrogen species: from molecular mechanisms to human health

Mitochondrially generated reactive oxygen species are involved in a myriad of signaling and damaging pathways in different tissues. In addition, mitochondria are an important target of reactive oxygen and nitrogen species. Here, we discuss basic mechanisms of mitochondrial oxidant generation and removal and the main factors affecting mitochondrial redox balance. We also discuss the interaction between mitochondrial reactive oxygen and nitrogen species, and the involvement of these oxidants in mitochondrial diseases, cancer, neurological, and cardiovascular disorders.

Altered ubiquitin-proteasome signaling in right ventricular hypertrophy and failure

Alterations in the ubiquitin-proteasome system (UPS) have been described in left ventricular hypertrophy and failure, although results have been inconsistent. The role of the UPS in right ventricular (RV) hypertrophy (RVH) and RV failure (RVF) is unknown. Given the greater percent increase in RV mass associated with RV afterload stress, as present in many congenital heart lesions, we hypothesized that alterations in the UPS could play an important role in RVH/RVF. UPS expression and activity were measured in the RV from mice with RVH/RVF secondary to pulmonary artery constriction (PAC). Epoxomicin and MG132 were used to inhibit the proteasome, and overexpression of the 11S PA28α subunit was used to activate the proteasome. PAC mice developed RVH (109.3% increase in RV weight to body weight), RV dilation with septal shift, RV dysfunction, and clinical RVF. Proteasomal function (26S β₅ chymotrypsin-like activity) was decreased 26% (P < 0.05). Protein expression of 19S subunit Rpt5 (P < 0.05), UCHL1 deubiquitinase (P < 0.0001), and Smurf1 E3 ubiquitin ligase (P < 0.01) were increased, as were polyubiquitinated proteins (P < 0.05) and free-ubiquitins (P = 0.05). Pro-apoptotic Bax was increased (P < 0.0001), whereas anti-apoptotic Bcl-2 decreased (P < 0.05), resulting in a sixfold increase in the Bax/Bcl-2 ratio. Proteasomal inhibition did not accelerate RVF. However, proteasome enhancement by cardiac-specific proteasome overexpression partially improved survival. Proteasome activity is decreased in RVH/RVF, associated with upregulation of key UPS regulators and pro-apoptotic signaling. Enhancement of proteasome function partially attenuates RVF, suggesting that UPS dysfunction contributes to RVF.

Regulation of the proteasome by ATP: implications for ischemic myocardial injury and donor heart preservation

Several lines of evidence suggest that proteasomes are involved in multiple aspects of myocardial physiology and pathology, including myocardial ischemia-reperfusion injury. It is well established that the 26S proteasome is an ATP-dependent enzyme and that ischemic heart disease is associated with changes in the ATP content of the cardiomyocyte. A functional link between the 26S proteasome, myocardial ATP concentrations, and ischemic cardiac injury, however, has been suggested only recently. This review discusses the currently available data on the pathophysiological role of the cardiac proteasome during ischemia and reperfusion in the context of the cellular ATP content. Depletion of the myocardial ATP content during ischemia appears to activate the 26S proteasome via direct regulatory effects of ATP on 26S proteasome stability and activity. This implies pathological degradation of target proteins by the proteasome and could provide a pathophysiological basis for beneficial effects of proteasome inhibitors in various models of myocardial ischemia. In contrast to that in the ischemic heart, reduced and impaired proteasome activity is detectable in the postischemic heart. The paradoxical findings that proteasome inhibitors showed beneficial effects when administered during reperfusion in some studies could be explained by their anti-inflammatory and immune suppressive actions, leading to reduction of leukocyte-mediated myocardial reperfusion injury. The direct regulatory effects of ATP on the 26S proteasome have implications for the understanding of the contribution of the 26S proteasome to the pathophysiology of the ischemic heart and its possible role as a therapeutic target.

Role of various proteases in cardiac remodeling and progression of heart failure

It is believed that cardiac remodeling due to geometric and structural changes is a major mechanism for the progression of heart failure in different pathologies including hypertension, hypertrophic cardiomyopathy, dilated cardiomyopathy, diabetic cardiomyopathy, and myocardial infarction. Increases in the activities of proteolytic enzymes such as matrix metalloproteinases, calpains, cathepsins, and caspases contribute to the process of cardiac remodeling. In addition to modifying the extracellular matrix, both matrix metalloproteinases and cathepsins have been shown to affect the activities of subcellular organelles in cardiomyocytes. The activation of calpains and caspases has been identified to induce subcellular remodeling in failing hearts. Proteolytic activities associated with different proteins including caspases, calpain, and the ubiquitin-proteasome system have been shown to be involved in cardiomyocyte apoptosis, which is an integral part of cardiac remodeling. This article discusses and compares how the activities of various proteases are involved in different cardiac abnormalities with respect to alterations in apoptotic pathways, cardiac remodeling, and cardiac dysfunction. An imbalance appears to occur between the activities of some proteases and their endogenous inhibitors in various types of hypertrophied and failing hearts, and this is likely to further accentuate subcellular remodeling and cardiac dysfunction. The importance of inhibiting the activities of both extracellular and intracellular proteases specific to distinct etiologies, in attenuating cardiac remodeling and apoptosis as well as biochemical changes of subcellular organelles, in heart failure has been emphasized. It is suggested that combination therapy to inhibit different proteases may prove useful for the treatment of heart failure.

Protein kinase C, an elusive therapeutic target?

Protein kinase C (PKC) has been a tantalizing target for drug discovery ever since it was first identified as the receptor for the tumour promoter phorbol ester in 1982. Although initial therapeutic efforts focused on cancer, additional indications--including diabetic complications, heart failure, myocardial infarction, pain and bipolar disorder--were targeted as researchers developed a better understanding of the roles of eight conventional and novel PKC isozymes in health and disease. Unfortunately, both academic and pharmaceutical efforts have yet to result in the approval of a single new drug that specifically targets PKC. Why does PKC remain an elusive drug target? This Review provides a short account of some of the efforts, challenges and opportunities in developing PKC modulators to address unmet clinical needs.

Mitochondrial pathways, permeability transition pore, and redox signaling in cardioprotection: therapeutic implications

Reperfusion therapy is the indispensable treatment of acute myocardial infarction (AMI) and must be applied as soon as possible to attenuate the ischemic insult. However, reperfusion is responsible for additional myocardial damage likely involving opening of the mitochondrial permeability transition pore (mPTP). A great part of reperfusion injury occurs during the first minute of reperfusion. The prolonged opening of mPTP is considered one of the endpoints of the cascade to myocardial damage, causing loss of cardiomyocyte function and viability. Opening of mPTP and the consequent oxidative stress due to reactive oxygen and nitrogen species (ROS/RNS) are considered among the major mechanisms of mitochondrial and myocardial dysfunction. Kinases and mitochondrial components constitute an intricate network of signaling molecules and mitochondrial proteins, which interact in response to stressors. Cardioprotective pathways are activated by stimuli such as preconditioning and postconditioning (PostC), obtained with brief intermittent ischemia or with pharmacological agents, which drastically reduce the lethal ischemia/reperfusion injury. The protective pathways converging on mitochondria may preserve their function. Protection involves kinases, adenosine triphosphate-dependent potassium channels, ROS signaling, and the mPTP modulation. Some clinical studies using ischemic PostC during angioplasty support its protective effects, and an interesting alternative is pharmacological PostC. In fact, the mPTP desensitizer, cyclosporine A, has been shown to induce appreciable protections in AMI patients. Several factors and comorbidities that might interfere with cardioprotective signaling are considered. Hence, treatments adapted to the characteristics of the patient (i.e., phenotype oriented) might be feasible in the future.