Cardioprotection of exercise preconditioning involving heat shock protein 70 and concurrent autophagy: a potential chaperone-assisted selective macroautophagy effect

Glycophagy is involved in cardiac glycogen regulation in response to exercise

Cardiac glycogen-autophagy ('glycophagy') is disturbed in cardiometabolic pathologies. The physiological role of cardiac glycophagy is unclear. Exercise induces transient cardiac glycogen accumulation. Thus, this study experimentally examined glycophagy involvement during recovery from an exhaustive exercise protocol. Peak myocardial glycogen accumulation in mice was evident at 2 h post-exercise, preceded by transient activation of glycogen synthase. At 4 and 16 h post-exercise, glycogen degradation was associated with decreased STBD1 (glycophagy tagging protein) and increased GABARAPL1 (Atg8 protein), suggesting that glycophagy activity was increased. These findings provide the first evidence that glycophagy is involved in cardiac glycogen physiologic homeostasis post-exercise.

Heat Shock Protein 70 Constitutes a Promising Novel Biomarker in Differential Diagnosis between Takotsubo Syndrome and Non-ST-Segment Elevation Myocardial Infarction

(1) Background: Due to similar clinical presentation and a lack of specific biomarkers, initial differentiation between Takotsubo syndrome (TTS) and non-ST-segment elevation myocardial infarction (NSTEMI) remains challenging in daily practice. Heat Shock Protein 70 (HSP70) is a novel biomarker that is recognized for its potential in the diagnosis and differentiation of cardiovascular conditions. (2) Methods: Data from a total of 156 patients were analyzed (32.1% NSTEMI, 32.7% TTS, and 35.3% controls). Serum concentrations of HSP70 were determined using ELISA and compared between patients and controls. ROC curve analysis, logistic regression analysis and propensity-score-weighted logistic regression were conducted. (3) Results: Concentrations of HSP70 were highest in patients with TTS (median 1727 pg/mL vs. ACS: median 1545 pg/mL vs. controls: median 583 pg/mL, p < 0.0001). HSP70 was predictive for TTS in binary logistic regression analysis (B(SE) = 0.634(0.22), p = 0.004), which even remained significant after correction for possible confounders in propensity-score-weighted analysis. ROC curve analysis also revealed a significant association of HSP70 with TTS (AUC: 0.633, p = 0.008). (4) Conclusions: Based on our findings, HSP70 constitutes a promising biomarker for discrimination between TTS and NSTEMI, especially in combination with established cardiovascular biomarkers like pBNP or high-sensitivity cardiac troponin.

Exercise preconditioning inhibits doxorubicin-induced cardiotoxicity via YAP/STAT3 signaling

Doxorubicin (DOX) possesses strong anti-tumor effects but is limited by its irreversible cardiac toxicity. The relationship between exercise, a known enhancer of cardiovascular health, and DOX-induced cardiotoxicity has been a focus of recent research. Exercise has been suggested to mitigate DOX's cardiac harm by modulating the Yes-associated protein (YAP) and Signal transducer and activator of transcription 3 (STAT3) pathways, which are crucial in regulating cardiac cell functions and responses to damage. This study aimed to assess the protective role of exercise preconditioning against DOX-induced cardiac injury. We used Sprague-Dawley rats, divided into five groups (control, DOX, exercise preconditioning (EP), EP-DOX, and verteporfin + EP + DOX), to investigate the potential mechanisms. Our findings, including echocardiography, histological staining, Western blot, and q-PCR analysis, demonstrated that exercise preconditioning could alleviate DOX-induced cardiac dysfunction and structural damage. Notably, exercise preconditioning enhanced the nuclear localization and co-localization of YAP and STAT3. Our study suggests that exercise preconditioning may counteract DOX-induced cardiotoxicity by activating the YAP/STAT3 pathway, highlighting a potential therapeutic approach for reducing DOX's cardiac side effects.

Exercise preconditioning improves electrocardiographic signs of myocardial ischemic/hypoxic injury and malignant arrhythmias occurring after exhaustive exercise in rats

Exercise preconditioning (EP) has a good myocardial protective effect. This study explored whether EP improves electrocardiographic (ECG) signs of myocardial ischemic/hypoxic injury and the occurrence of malignant arrhythmia after exhaustive exercise. A total of 120 male SD rats were randomly divided into the control group (group C), early exercise preconditioning group (group EEP), late exercise preconditioning group (group LEP), exhaustive exercise group (group EE), early exercise preconditioning + exhaustive exercise group (group EEP + EE) and late exercise preconditioning + exhaustive exercise group (group LEP + EE). Changes in heart rate (HR), ST segment, T wave and QT corrected (QTc) intervals on ECG; hematoxylin-basic fuchsin-picric acid (HBFP) staining; and cTnI levels were used to study myocardial injury and the protective effect of EP. Compared with those in group C, the levels of plasma markers of myocardial injury, HBFP staining and ECG in group EE were significantly increased (P < 0.05). Compared with those in group EE, the levels of plasma markers of myocardial injury, HBFP staining and ECG in group EEP + EE and group LEP + EE were significantly decreased (P < 0.05). The results suggested that EP improved ECG signs of myocardial ischemic/hypoxic injury and malignant arrhythmias that occur after exhaustive exercise. The ST segment and T wave could also serve as indexes for evaluating exhaustive exercise-induced myocardial ischemia/hypoxia.

Sevoflurane Postconditioning Reduces Hypoxia/Reoxygenation Injury in Cardiomyocytes via Upregulation of Heat Shock Protein 70

Sevoflurane postconditioning (SPostC) has been proved effective in cardioprotection against myocardial ischemia/reperfusion injury. It was also reported that heat shock protein 70 (HSP70) could be induced by sevoflurane, which played a crucial role in hypoxic/reoxygenation (HR) injury of cardiomyocytes. However, the mechanism by which sevoflurane protects cardiomyocytes via HSP70 is still not understood. Here, we aimed to investigate the related mechanisms of SPostC inducing HSP70 expression to reduce the HR injury of cardiomyocytes. After the HR cardiomyocytes model was established, the cells transfected with siRNA for HSP70 (siHSP70) or not were treated with sevoflurane during reoxygenation. The lactate dehydrogenase (LDH) level was detected by colorimetry while cell viability and apoptosis were detected by MTT and flow cytometry. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blotting were used to detect HSP70, apoptosis-, cell cycle-associated factors, iNOS, and Cox-2 expressions. Enzyme-linked immuno sorbent assay (ELISA) was used to measure malondialdehyde (MDA) and superoxide dismutase (SOD). SPostC decreased apoptosis, cell injury, oxidative stress and inflammation and increased viability of HR-induced cardiomyocytes. In addition, SPostC downregulated Bax and cleaved caspase-3 levels, while SPostC upregulated Bcl-2, CDK-4, Cyclin D1, and HSP70 levels. SiHSP70 had the opposite effect that SPostC had on HR-induced cardiomyocytes. Moreover, siHSP70 further reversed the effect of SPostC on apoptosis, cell injury, oxidative stress, inflammation, viability and the expressions of HSP70, apoptosis-, and cell cycle-associated factors in HR-induced cardiomyocytes. In conclusion, this study demonstrates that SPostC can reduce the HR injury of cardiomyocytes by inducing HSP70 expression.

Exercise Preconditioning Increases Beclin1 and Induces Autophagy to Promote Early Myocardial Protection via Intermittent Myocardial Ischemia-Hypoxia

Exercise preconditioning (EP) provides protective effects for acute cardiovascular stress; however, its mechanisms need to be further investigated. Autophagy is a degradation pathway essential for myocardium health. Therefore, we investigated whether intermittent myocardial ischemia-hypoxia affected Beclin1 and whether the changes in autophagy levels contribute to EP-induced early myocardial protective effects. Rats were trained on a treadmill using an EP model (four cycles of 10 minutes of running/10 minutes of rest). Exhaustive exercise (EE) was performed to induce myocardial injury. Cardiac troponin I (cTnI) and ischemia-hypoxia staining were used to evaluate myocardial injury and protection. Double-labeled immunofluorescence staining and western blot analysis were employed to examine related markers. EP attenuated the myocardial ischemic-hypoxic injury induced by EE. Compared with the control (C) group, the dissociations of Beclin1/Bcl-2 ratio and Beclin1 expression were both higher in all other groups. Compared with the C group, PI3KC3 and the LC3-II/LC3-I ratio were higher in all other groups, whereas LC3-II was higher in the EE and EEP + EE groups. p62 was higher in the EE group than in the C group but lower in the EEP + EE group than in the EE group. We concluded that EP increases Beclin1 via intermittent myocardial ischemia-hypoxia and induces autophagy, which exerts early myocardial protective effects and reduces the myocardial ischemic-hypoxic injury induced by exhaustive exercise.

Heat Shock Proteins in Oxidative Stress and Ischemia/Reperfusion Injury and Benefits from Physical Exercises: A Review to the Current Knowledge

Heat shock proteins (HSPs) are molecular chaperones produced in response to oxidative stress (OS). These proteins are involved in the folding of newly synthesized proteins and refolding of damaged or misfolded proteins. Recent studies have been focused on the regulatory role of HSPs in OS and ischemia/reperfusion injury (I/R) where reactive oxygen species (ROS) play a major role. ROS perform many functions, including cell signaling. Unfortunately, they are also the cause of pathological processes leading to various diseases. Biological pathways such as p38 MAPK, HSP70 and Akt/GSK-3β/eNOS, HSP70, JAK2/STAT3 or PI3K/Akt/HSP70, and HSF1/Nrf2-Keap1 are considered in the relationship between HSP and OS. New pathophysiological mechanisms involving ROS are being discovered and described the protein network of HSP interactions. Understanding of the mechanisms involved, e.g., in I/R, is important to the development of treatment methods. HSPs are multifunctional proteins because they closely interact with the antioxidant and the nitric oxide generation systems, such as HSP70/HSP90/NOS. A deficiency or excess of antioxidants modulates the activation of HSF and subsequent HSP biosynthesis. It is well known that HSPs are involved in the regulation of several redox processes and play an important role in protein-protein interactions. The latest research focuses on determining the role of HSPs in OS, their antioxidant activity, and the possibility of using HSPs in the treatment of I/R consequences. Physical exercises are important in patients with cardiovascular diseases, as they affect the expression of HSPs and the development of OS.

Exercise combined with trimetazidine improves anti-fatal stress capacity through enhancing autophagy and heat shock protein 70 of myocardium in mice

Background: Anti-stress capacity is important to resist the occurrence of adverse events. To observe the effects of exercise, trimetazidine alone or combined on the anti-stress capacity of mice, and further explore its potential mechanism. Methods: Forty-four C57BL/6 male mice aged 8 weeks were randomly divided into four groups (n=11 for each group): control group (group C), exercise group (group E), trimetazidine group (group T), exercise combined with trimetazidine group (group TE). After the intervention, each group was randomly subdivided into the exhaustive exercise (EE, n=6) and the non-EE (n=5) subgroups. The mice in the EE-subgroup underwent EE. Mice were sacrificed 12 hours later after EE. The myocardial ultrastructure and autophagosomes were observed under an electron microscope. The expression of autophagy-related proteins: BNIP3, LC3-II, and P62 were analyzed and the heat shock protein 70 mRNA transcription and protein expression were also investigated. Results: Exercise or trimetazidine increased the expression of BNIP3, LC3-II, and heat shock protein 70, decreased the expression of P62 pre- and post-EE while the combination has the synergistic effect. Conclusion: Exercise and trimetazidine, alone or combined enhanced the anti-stress capacity of mice significantly. The underlying mechanism may be associated with the promotion of autography and the expression of heat shock protein 70.

Moderate Fever Cycles as a Potential Mechanism to Protect the Respiratory System in COVID-19 Patients

Mortality in COVID-19 patients predominantly results from an acute respiratory distress syndrome (ARDS), in which lungs alveolar cells undergo programmed cell death. Mortality in a sepsis-induced ARDS rat model is reduced by adenovirus over-expression of the HSP70 chaperone. A natural rise of body temperature during mild fever can naturally accumulate high cellular levels of HSP70 that can arrest apoptosis and protect alveolar lung cells from inflammatory damages. However, beyond 1-2 h of fever, no HSP70 is being further produced and a decreased in body temperature required to the restore cell's ability to produce more HSP70 in a subsequent fever cycle. We suggest that antipyretics may be beneficial in COVID-19 patients subsequent to several hours of mild (<38.8°C) advantageous fever, allowing lung cells to accumulate protective HSP70 against damages from the inflammatory response to the virus SARS-CoV-2. With age, the ability to develop fever and accumulate HSP70 decreases. This could be ameliorated, when advisable to do so, by thermotherapies and/or physical training.

Mechanisms Involved in Cardioprotection Induced by Physical Exercise

Significance: Regular exercise training can reduce myocardial damage caused by acute ischemia/reperfusion (I/R). Exercise can reproduce the phenomenon of ischemic preconditioning, due to the capacity of brief periods of ischemia to reduce myocardial damage caused by acute I/R. In addition, exercise may also activate the multiple kinase cascade responsible for cardioprotection even in the absence of ischemia. Recent Advances: Animal and human studies highlighted the fact that, besides to reduce risk factors related to cardiovascular disease, the beneficial effects of exercise are also due to its ability to induce conditioning of the heart. Exercise behaves as a physiological stress that triggers beneficial adaptive cellular responses, inducing a protective phenotype in the heart. The factors contributing to the exercise-induced heart preconditioning include stimulation of the anti-radical defense system and nitric oxide production, opioids, myokines, and adenosine-5'-triphosphate (ATP) dependent potassium channels. They appear to be also involved in the protective effect exerted by exercise against cardiotoxicity related to chemotherapy. Critical Issues and Future Directions: Although several experimental evidences on the protective effect of exercise have been obtained, the mechanisms underlying this phenomenon have not yet been fully clarified. Further studies are warranted to define precise exercise prescriptions in patients at risk of myocardial infarction or undergoing chemotherapy.

Neuromuscular Diseases Due to Chaperone Mutations: A Review and Some New Results

Skeletal muscle and the nervous system depend on efficient protein quality control, and they express chaperones and cochaperones at high levels to maintain protein homeostasis. Mutations in many of these proteins cause neuromuscular diseases, myopathies, and hereditary motor and sensorimotor neuropathies. In this review, we cover mutations in DNAJB6, DNAJB2, αB-crystallin (CRYAB, HSPB5), HSPB1, HSPB3, HSPB8, and BAG3, and discuss the molecular mechanisms by which they cause neuromuscular disease. In addition, previously unpublished results are presented, showing downstream effects of BAG3 p.P209L on DNAJB6 turnover and localization.

Altered expression levels of autophagy-associated proteins during exercise preconditioning indicate the involvement of autophagy in cardioprotection against exercise-induced myocardial injury

Exercise has been reported to induce autophagy. We hypothesized that exercise preconditioning (EP)-related autophagy in cardiomyocytes could be attributed to intermittent ischemia-hypoxia, allowing the heart to be protected for subsequent high-intensity exercise (HE). We applied approaches, chromotrope-2R brilliant green (C-2R BG) staining and plasma cTnI levels measuring, to characterize two periods of cardioprotection after EP: early EP (EEP) and late EP (LEP). Further addressing the relationship between ischemia-hypoxia and autophagy, key proteins, Beclin1, LC3, Cathepsin D, and p62, were determined by immunohistochemical staining, western blotting, and by their adjacent slices with C-2R BG. Results indicated that exercise-induced ischemia-hypoxia is a key factor in Beclin1-dependent autophagy. High-intensity exercise was associated with the impairment of autophagy due to high levels of LC3II and unchanged levels of p62, intermittent ischemia-hypoxia by EP itself plays a key role in autophagy, which resulted in more favorable cellular effects during EEP-cardioprotection compared to LEP.

Alpha-Lipoic Acid Protects Cardiomyocytes against Heat Stroke-Induced Apoptosis and Inflammatory Responses Associated with the Induction of Hsp70 and Activation of Autophagy

Heat stroke (HS) is a life-threatening illness and defined as when body temperature elevates above 40°C accompanied by the systemic inflammatory response syndrome that results in multiple organ dysfunctions. α-Lipoic acid (ALA) acts as a cofactor of mitochondrial enzymes and exerts anti-inflammatory and antioxidant properties in a variety of diseases. This study investigates the beneficial effects of ALA on myocardial injury and organ damage caused by experimental HS and further explores its underlying mechanism. Male Wistar rats were exposed to 42°C until their rectal core temperature reached 42.9°C and ALA was pretreared 40 or 80 mg/kg (i.v.) 1.5 h prior to heat exposure. Results showed that HS-induced lethality and hypothermia were significantly alleviated by ALA treatment that also improved plasma levels of CRE, LDH, and CPK and myocardial injury biomarkers myoglobin and troponin. In addition, ALA reduced cardiac superoxide anion formation and protein expression of cleaved caspase 3 caused by HS. Proinflammatory cytokine TNF-α and NF-κB pathways were significantly reduced by ALA treatment which may be associated with the upregulation of Hsp70. ALA significantly increased the Atg5-12 complex and LC3B II/LC3B I ratio, whereas the p62 and p-mTOR expression was attenuated in HS rats, indicating the activation of autophagy by ALA. In conclusion, ALA ameliorated the deleterious effects of HS by exerting antioxidative and anti-inflammatory capacities. Induction of Hsp70 and activation of autophagy contribute to the protective effects of ALA in HS-induced myocardial injury.

Late Exercise Preconditioning Promotes Autophagy against Exhaustive Exercise-Induced Myocardial Injury through the Activation of the AMPK-mTOR-ULK1 Pathway

Accumulating evidence shows that the AMPK-mTOR pathway modulates autophagy via coordinated phosphorylation of ULK1. The aim of the present study was to investigate the relationship between AMPK, mTOR, and ULK1 during late exercise preconditioning (LEP), and to explore whether LEP-induced myocardial protection is related to the autophagy. The exercise preconditioning (EP) protocol was as follows: rats were instructed to for run four repeated in duration of 10 minutes (including 10 minutes rest between each period) on a treadmill. Exhaustive exercise (EE) after LEP pretreatment and administration of wortmannin (an autophagy inhibitor that suppresses Class III PI3K-kinase (PI3KC3) activity) were added to test the protective effect. Cardiac troponin I (cTnI), and transmission electron microscopy (TEM), along with hematoxylin-basic fuchsin-picric acid (HBFP) staining, were used to evaluate the myocardial ischemic-hypoxic injury and protection. Western blot was used to analyze the relationship of autophagy-associated proteins. Exhaustive exercise caused severe myocardial ischemic-hypoxic injury, which led to an increase in cTnI levels, changes of ischemia–hypoxia, and cells ultrastructure. Compared with the EE group, LEP significantly suppressed exhaustive exercise-induced myocardial injury. However, wortmannin attenuated LEP-induced myocardial protection by inhibiting autophagy. Compared with the C group, AMPK was increased in the LEP, EE, and LEP+EE groups, but phosphorylation of AMPK at Thr172 was not significantly changed. Exercise did not have any effect on mTOR expression. Compared with the C group, ULK1 was increased and the ULK1^ser757/ULK1 ratio was decreased in the LEP and LEP+EE groups. ULK1 was not significantly affected in the EE group, however, phosphorylation of ULK1 at Ser757 was remarkably decreased. To sum up, our results suggested that LEP promoted autophagy through the activation of AMPK-mTOR-ULK1 pathway, and that activated autophagy was partially involved in myocardial protection against EE-induced myocardial ischemic-hypoxic injury.

Long-term moderate intensity exercise alleviates myocardial fibrosis in type 2 diabetic rats via inhibitions of oxidative stress and TGF-β1/Smad pathway

Exercise has an effect on the reduction of myocardial fibrosis in diabetic rats as previously reported, in which oxidative stress and the TGF-β1/Smad signaling pathway may play key roles. There is little direct experimental evidence that exercise alleviates myocardial fibrosis in type 2 diabetes mellitus (T2DM). Here we established a type 2 diabetic model by using streptozotocin and a high-fat diet. Rats were divided into groups of normal control (NC), T2DM and T2DM plus exercise (T2DME). The T2DME group received further treadmill training at moderate intensity for 8 weeks. Histological and biochemical methods were used to detect the benefits of exercise to T2DM. Results showed that the weight of rats in the T2DM group dropped dramatically, along with significant increases in blood glucose, myocardial fibrosis and oxidative stress, associated with upregulated expression of factors of myocardial fibrosis, except Smad7. Exercise largely reversed T2DM-induced alterations in factors of myocardial fibrosis, including suppressing expression of MMP-2, CTGF, TGF-β1, p-Smad2 and p-Smad3, and increased expression of TIMP-1 and Smad7. Therefore, exercise might be considered an alternative therapeutic remedy for diabetic cardiomyopathy.

Cardiac basal autophagic activity and increased exercise capacity

To investigate whether high-intensity interval training (HIIT) and continuous moderate-intensity training (CMT) have different impacts on exercise performance and cardiac function and to determine the influence of these exercise protocols on modulating basal autophagy in the cardiac muscle of rats. Rats were assigned to three groups: sedentary control (SC), CMT, and HIIT. Total exercise volume and mean intensity were matched between the two protocols. After a 10-week training program, rats were evaluated for exercise performance, including exercise tolerance and grip strength. Blood lactate levels were measured after an incremental exercise test. Cardiac function and morphology were assessed by echocardiography. Western blotting was used to evaluate the expression of autophagy and mitochondrial markers. Transmission electron microscopy was used to evaluate mitochondrial content. The results showed that time to exhaustion and grip strength increased significantly in the HIIT group compared with the SC and CMT groups. Both training interventions significantly increased time to exhaustion, reduced blood lactate level (after an incremental exercise test) and induced adaptive changes in cardiac morphology, but without altering cardiac systolic function. The greater improvements in exercise performance with the HIIT than with the CMT protocol were related to improvement in basal autophagic adaptation and mitochondria function in cardiac muscle. Mitochondria markers were positively correlated with autophagy makers. This study shows that HIIT is more effective for improving exercise performance than CMT and this improvement is related to mitochondrial function and basal autophagic adaptation in cardiac muscle.

The effects of high-intensity interval training on reverse cholesterol transport elements: A way of cardiovascular protection against atherosclerosis

AIMS

Reverse cholesterol transport (RCT) is a process that prevents atherosclerosis. Studies showed that exercise training for strengthening cardiac muscle, increasing heart lipid metabolism and its potency against risk factors could protect cardiovascular health. Thus, the present study aims to investigate the effects of high intensity interval training (HIIT) on RCT and its related elements in plasma and tissues (liver and intestine) of rats.

MATERIALS AND METHODS

Twenty adult male Wistar rats were randomly divided into control (n = 10) and trained (n = 10) groups. The trained group undertook HIIT (90%-95% of VO₂max, five days/week, for 10 weeks) on a treadmill. The rats were killed five days after the last training session to minimize the effects of the last training session.

KEY FINDINGS

A higher and significant ABCA1 mRNA was observed in the liver and intestine of trained rats. However, ABCG1 and LXR expressions only increased in the liver following the HIIT. These changes in the expression of the trained rats were accompanied by higher changes in plasma LCAT and HDL levels.

SIGNIFICANCE

The responses of ABCA1, as a key player in plasma HDL biogenesis, are similar in liver and intestine tissues after the HIIT program. However, different responses of ABCG1 and LXR in the liver and intestine tissues of the trained rats confirm the main role of the liver than the intestine in HDL biogenes. Therefore, HIIT modality result in cardiovascular protection by increasing the expression of genes involved in RCT and biogenesis of HDL.

Hypoxic conditioning in blood vessels and smooth muscle tissues: effects on function, mechanisms, and unknowns

Hypoxic preconditioning, the protective effect of brief, intermittent hypoxic or ischemic episodes on subsequent more severe hypoxic episodes, has been known for 30 yr from studies on cardiac muscle. The concept of hypoxic preconditioning has expanded; excitingly, organs beyond the heart, including the brain, liver, and kidney, also benefit. Preconditioning of vascular and visceral smooth muscles has received less attention despite their obvious importance to health. In addition, there has been no attempt to synthesize the literature in this field. Therefore, in addition to overviewing the current understanding of hypoxic conditioning, in the present review, we consider the role of blood vessels in conditioning and explore evidence for conditioning in other smooth muscles. Where possible, we have distinguished effects on myocytes from other cell types in the visceral organs. We found evidence of a pivotal role for blood vessels in conditioning and for conditioning in other smooth muscle, including the bladder, vascular myocytes, and gastrointestinal tract, and a novel response in the uterus of a hypoxic-induced force increase, which helps maintain contractions during labor. To date, however, there are insufficient data to provide a comprehensive or unifying mechanism for smooth muscles or visceral organs and the effects of conditioning on their function. This also means that no firm conclusions can be drawn as to how differences between smooth muscles in metabolic and contractile activity may contribute to conditioning. Therefore, we have suggested what may be general mechanisms of conditioning occurring in all smooth muscles and tabulated tissue-specific mechanistic findings and suggested ideas for further progress.

Redox Aspects of Chaperones in Cardiac Function

Molecular chaperones are stress proteins that allow the correct folding or unfolding as well as the assembly or disassembly of macromolecular cellular components. Changes in expression and post-translational modifications of chaperones have been linked to a number of age- and stress-related diseases including cancer, neurodegeneration, and cardiovascular diseases. Redox sensible post-translational modifications, such as S-nitrosylation, glutathionylation and phosphorylation of chaperone proteins have been reported. Redox-dependent regulation of chaperones is likely to be a phenomenon involved in metabolic processes and may represent an adaptive response to several stress conditions, especially within mitochondria, where it impacts cellular bioenergetics. These post-translational modifications might underlie the mechanisms leading to cardioprotection by conditioning maneuvers as well as to ischemia/reperfusion injury. In this review, we discuss this topic and focus on two important aspects of redox-regulated chaperones, namely redox regulation of mitochondrial chaperone function and cardiac protection against ischemia/reperfusion injury.

Proteostasis, oxidative stress and aging

The production of reactive species is an inevitable by-product of metabolism and thus, life itself. Since reactive species are able to damage cellular structures, especially proteins, as the most abundant macromolecule of mammalian cells, systems are necessary which regulate and preserve a functional cellular protein pool, in a process termed “proteostasis”. Not only the mammalian protein pool is subject of a constant turnover, organelles are also degraded and rebuild. The most important systems for these removal processes are the “ubiquitin-proteasomal system” (UPS), the central proteolytic machinery of mammalian cells, mainly responsible for proteostasis, as well as the “autophagy-lysosomal system”, which mediates the turnover of organelles and large aggregates.

Many age-related pathologies and the aging process itself are accompanied by a dysregulation of UPS, autophagy and the cross-talk between both systems. This review will describe the sources and effects of oxidative stress, preservation of cellular protein- and organelle-homeostasis and the effects of aging on proteostasis in mammalian cells.

Cardiac Ischemia/Reperfusion Injury: The Beneficial Effects of Exercise

Cardiac ischemia reperfusion injury (IRI) occurs when the myocardium is revascularized after an episode of limited or absent blood supply. Many changes, including free radical production, calcium overload, protease activation, altered membrane lipids and leukocyte activation, contribute to IRI-induced myocardium damage. Aerobic exercise is the only countermeasure against IRI that can be sustained on a regular basis in clinical practice. Interestingly, both short-term (3-5 days) and long-term (several weeks) exercise increase myocardial tolerance, reduce infarct size area and arrhythmias induced by IRI. Exercise protects the heart against IRI in a biphasic manner. The early phase of cardioprotection occurs between 30 min and 3 h following an acute exercise bout, whilst the late phase is achieved within 24 h after the exercise bout and persists for several days. As for the exercise intensity, although controversial data exists, it is feasible that the amount of cardioprotection is proportional to exercise intensity and only achieved above a critical threshold. It is known that aerobic exercise produces a cardioprotective phenotype, however the mechanisms responsible for this phenomenon remain unclear. Apparently, aerobic exercise-induced preconditioning is dependent on several factors that work together to protect the heart. Altered nitric oxide (NO) signaling, increased levels of heat shock proteins (HSPs), enhanced function of ATP-sensitive potassium channels, increased activation of opioids system, and enhanced antioxidant capacity may contribute to exercise-induced cardioprotection. Much has been discovered from animal models involving exercise-induced cardioprotection against cardiac IRI, however translating these findings to clinical practice still represents the major challenge in this field.