Background: Histone deacetylases (HDACs) play a critical role in modulating myocardial protection and cardiomyocyte survivals. However, Specific HDAC isoforms in mediating myocardial ischemia/reperfusion injury remain currently unknown. We used cardiomyocyte-specific overexpression of active HDAC4 to determine the functional role of activated HDAC4 in regulating myocardial ischemia and reperfusion in isovolumetric perfused hearts. Methods: In this study, we created myocyte-specific active HDAC4 transgenic mice to examine the functional role of active HDAC4 in mediating myocardial I/R injury. Ventricular function was determined in the isovolumetric heart, and infarct size was determined using tetrazolium chloride staining. Results: Myocyte-specific overexpressing activated HDAC4 in mice promoted myocardial I/R injury, as indicated by the increases in infarct size and reduction of ventricular functional recovery following I/R injury. Notably, active HDAC4 overexpression led to an increase in LC-3 and active caspase 3 and decrease in SOD-1 in myocardium. Delivery of chemical HDAC inhibitor attenuated the detrimental effects of active HDAC4 on I/R injury, revealing the pivotal role of active HDAC4 in response to myocardial I/R injury. Conclusions: Taken together, these findings are the first to define that activated HDAC4 as a crucial regulator for myocardial ischemia and reperfusion injury.

Background: Erythropoietin (EPO) can reduce myocardial ischemia/reperfusion (I/R) injury. However, the cellular mechanisms have not been elucidated entirely. The present study was to investigate whether transcription factor GATA-4 could be involved in EPO-induced cardioprotection when it was administered after ischemia, immediately before reperfusion. Methods and results: Male Balb/c mice treated with or without EPO were subjected to ischemia (45 min) followed by reperfusion (4 h). TTC staining showed that the infarct size in EPO-treated mice was significantly reduced compared with untreated I/R mice (P < 0.05). Echocardiography examination suggested that EPO administration significantly improved cardiac function following I/R. TUNEL assay indicated that EPO treatment decreased apoptosis. EPO administration also significantly increased the level of nuclear GATA-4 phosphorylation in the myocardium which was positively correlated with the reduction of myocardial infarction. In vitro hypoxia/re-oxygenation study showed that EPO treatment increased the levels of phospho-GATA-4 and decreased cardiomyocyte apoptosis. More significantly, blocking GATA-4 by transfection of a dominant-negative form of GATA-4 (dnGATA-4) abolished EPO-induced cardioprotective effects. Conclusion: EPO administration after ischemia, just before reperfusion induced cardioprotection and stimulated GATA-4 phosphorylation. Activation of GATA-4 may be one of the mechanisms by which EPO induced protection against myocardial I/R injury.

Inhibitors of apoptosis proteins (IAPs) are key intrinsic regulators of caspases-3 and -7. During ischemia, IAP-2 is upregulated dramatically, while the other IAPs show little or no change. To test whether IAP-2 prevents cardiac apoptosis and injury following ischemia/reperfusion, we generated a line of transgenic mice that carried a mouse IAP-2 transgene. High levels of mouse IAP-2 transcripts and 70 kDa IAP-2 were expressed in the hearts of transgenic mice, whereas IAP-1 and XIAP levels remained the same. Immunohistochemical studies revealed more intense staining of IAP-2 in the myocytes of transgenic mouse hearts. To assess the role of IAP-2 in I/R injury, the transgenic mice were subjected to ligation of the left descending anterior coronary artery ligation followed by reperfusion. The infarct sizes, expressed as the percentage of the area at risk, were significantly smaller in the transgenic mice than in the non-transgenic mice (30 ± 2% vs. 44 ± 2%, respectively, P < 0.05). This protection was accompanied by a decrease of the serum level of troponin I in the transgenic mice. IAP-2 transgenic hearts had significantly fewer TUNEL-positive cardiac cells, which indicated an attenuation of apoptosis. Our results demonstrate that overexpression of IAP-2 renders the heart more resistant to apoptosis and I/R injury.

Generation of free radicals upon reperfusion has been cited as one of the major causes of ischaemia/reperfusion injury. The following series of experiments was designed to study the effect of manganese superoxide dismutase (MnSOD) overexpression in transgenic mice on ischemia/reperfusion injury. A species of 1.4 kb human MnSOD mRNA was expressed, and a 325% increase in MnSOD activity was detected in the hearts of transgenic mice with no changes in the other antioxidant enzymes or heat shock proteins. Immunocytochemical study indicated an increased labeling of MnSOD mainly in the heart mitochondria of the transgenic mice. When these hearts were perfused as Langendorff preparations for 45 min after 35 min of global ischemia, the functional recovery of the hearts, expressed as heart rate x left ventricular developed pressure, was 52 ± 4% in the transgenic hearts as compared to 31 ± 4% in the non-transgenic hearts. This protection was accompanied by a significant decrease in lactate dehydrogenase release from the transgenic hearts. Overexpression of MnSOD limited the infarct size in vivo in a left coronary artery ligation model. Our results demonstrate that overexpression of MnSOD renders the heart more resistant to ischemia/reperfusion injury.

PURPOSE: Previous work suggests that Dihydroorotate dehydrogenase (DHODH) inhibition via teriflunomide (TERI) may provide protection in multiple disease models. To date, little is known about the effect of TERI on the heart. This study was performed to assess the potential effects of TERI on cardiac ischemia reperfusion injury. METHODS: Male and female rat hearts were subjected to global ischemia (25 min) and reperfusion (120 min) on a Langendorff apparatus. Hearts were given either DMSO (VEH) or teriflunomide (TERI) for 5 min prior to induction of ischemia and during the reperfusion period. Left ventricular pressure, ECG, coronary flow, and infarct size were determined using established methods. Mitochondrial respiration was assessed via respirometry. RESULTS: Perfusion of hearts with TERI led to no acute effects in any values measured across 500 pM-50 nM doses. However, following ischemia-reperfusion injury, we found that 50 nM TERI-treated hearts had an increase in myocardial infarction (p < 0.001). In 50 nM TERI-treated hearts, we also observed a marked increase in the severity of contracture (p < 0.001) at an earlier time-point (p = 0.004), as well as reductions in coronary flow (p = 0.037), left ventricular pressure development (p = 0.025), and the rate-pressure product (p = 0.008). No differences in mitochondrial respiration were observed with 50 nM TERI treatment (p = 0.24-0.87). CONCLUSION: This study suggests that treatment with TERI leads to more negative outcomes following cardiac ischemia reperfusion, and administration of TERI to at-risk populations should receive special considerations.

No description available.

Neutrophils are thought to orchestrate myocardial remodeling during the early progression to cardiac failure through the release of reactive oxygen species, antimicrobial peptides, and proteases. Although neutrophil activation may be beneficial at early stages of disease, excessive neutrophil infiltration detrimentally leads to cardiomyocyte death and tissue damage. The neutrophil-derived serine protease cathepsin G (CG) has been shown to induce neonatal rat cardiomyocyte detachment and apoptosis by anoikis1. However the role of inflammatory serine proteases in cardiac remodeling and cardiac regeneration in-vivo is still unknown. We showed that cardiac injection of neutrophil derived protease led to early cardiac dilatation and dysfunction characterized by an increase in matrix metalloprotease (MMP) activation and extracellular matrix degradation along with an increase in myocyte death by apoptosis. To assess the role of these serine proteases, we used mice lacking dipeptidyl peptidase I (DPPI), an enzyme involved in major inflammatory protease activation. DPPI deficient mice demonstrated a more robust functional recovery after ischemia reperfusion (IR) and myocardial infarction (MI) injury, as well as significantly reduced myocyte apoptosis, cardiac dilatation, infarct size and mortality rate. Meanwhile, our data showed increased groups of cardiac stem cells and proliferating cardiac cells in the MI 7-days DPPI knockout mice. We also found enhanced DPPI expression in response to pathological stress stimuli in mice. These findings reveal an unrecognized role of DPPI as a key mediator of post-ischemia cardiac injury and show that inflammatory derived proteases may contribute to the pathological cardiac remodeling and cardiac regeneration, and may be considered as novel target for future therapies. / Physiology

Acute myocardial infarction (AMI) is a leading cause of morbidity and mortality in the world (4). Restoration of coronary flow to the ischemic myocardium by interventions such as angioplasty, thrombolytic treatment or coronary bypass surgery is the current standard therapy for AMI (5). However, reperfusion of the ischemic myocardium may result in paradoxical cardiomyocyte dysfunction and worsen tissue damage, in a process known as “reperfusion injury” (6). Ischemic reperfusion (IR) injury may intensify pathological processes that contribute to the generation of oxyradicals, disturbances in cation homeostasis, and depletion of cellular energy stores, which may elicit arrhythmias, contractile dysfunction, and ultrastructural damage of the myocardium. These changes can lead to heart failure and ultimately sudden death. The exact mechanisms of IR injury are not fully known (7). Molecular, cellular, and tissue alterations such as cell death, inflammation, neurohumoral activation, and oxidat / Bioengineering

Mitochondrial structure and function are inextricably linked ("structure-function"), with decrements in structure-function evident across diseases. Barriers to new therapies include a complete understanding of the underlying molecular culprits, as well as effective mitochondria-targeted therapies that mitigate injury. In these works, we investigate the role of cristae-shaping factors like cardiolipin in health and disease. In a series of studies, we tested the effects of the cell-permeable tetrapeptides, elamipretide and a postulated peptide, (arginine-tyrosine-lysine-phenylalanine; "RYKF"), on the recovery of mitochondrial structure-function after injury. Elamipretide is a clinical-stage compound currently under investigation for genetic and age-related mitochondrial diseases, yet the mechanism of action is not completely understood. We used a combination of physiological models, mitochondrial imaging, and biomimetic membrane studies to test the hypothesis that elamipretide and RYKF-cardiolipin interactions improved mitochondrial structure-function. Post-ischemic treatment with elamipretide sustained mitochondrial function across electron transport chain complexes. Endogenous RYKF expression similarly improved mitochondrial respiration after peroxide and hypoxia nutrient deprivation injuries. Using two parallel electron microscopy paradigms, we show elamipretide and RYKF treatment led to maintenance of mitochondrial ultrastructure and notably, improved cristae interconnectedness. Finally, we utilized a novel biomimetic membrane system to model the pathological mitochondrial membrane and found that elamipretide and RYKF both improved biophysical pressure-area relationships through a mechanism that appears to involve aggregating cardiolipin. Our data indicate that targeting pathophysiological mitochondrial membranes with cationic, lipophilic peptides can improve bioenergetics by sustaining cristae networks and support interdependent relationships between mitochondrial structure and function. / Doctor of Philosophy / Mitochondria, the powerhouses of the cell, form energy networks that produce over 90% of the body’s energy. Mitochondrial dysfunction is implicated across diseases, yet no FDA-approved treatments exist that improve mitochondrial energy production. In this study, we tested the effects of elamipretide, a peptide that localizes to mitochondria. Although elamipretide is currently in clinical trials for several diseases characterized by energetic deficiencies, its mechanism of action is not fully understood. Since mitochondrial structure and function are directly linked, we modeled heart attacks in cultured cells and rat hearts to test the hypothesis that elamipretide and a postulated analog, RYKF, glue damaged mitochondrial membranes back together to preserve structure and function during disease. In hearts subjected to a heart attack, elamipretide significantly protected mitochondrial energy production. Similarly, RYKF protected mitochondrial function in muscle cells exposed to peroxide stress. In damaged hearts imaged with electron microscopy, elamipretide and RYKF treatment significantly improved mitochondrial structure and notably, improved the interconnectedness of mitochondrial energy networks. Furthermore, elamipretide and RYKF improved the integrity of diseased mitochondrial membranes. Together, these data support our hypothesis that elamipretide and RYKF act as mitochondrial adhesion molecules to protect mitochondrial structure and sustain energy production during disease.

Dysfunction within complex I (CI) of the mitochondrial electron transport system has been implicated in a number of disease states ranging from cardiovascular diseases to neuro-ophthalmic indications. Herein, we provide three novel approaches to model and study the impacts of injury on the function of CI. Cardiovascular ischemia/reperfusion (I/R) injury has long been recognized as a leading contributor to CI dysfunction. Aside from the physical injury that occurs in the tissue during the ischemic period, the production of high levels of reactive oxygen species (ROS) upon reperfusion, led by reverse electron transport (RET) from CI, causes significant damage to the cell. With over 700,000 people in the US set to experience an ischemic cardiac event annually, the need for a pharmacological intervention is paramount. Unfortunately, current pharmacological approaches to treat I/R related injury are limited and the ones that have shown efficacy have often done so with mixed results. Among the current approaches to treat I/R injury antioxidants have shown some promise to help preserve mitochondrial function and assuage tissue death. The studies described herein have provided new, more physiologically matched, methods for assessing the impact of potential therapeutic interventions in I/R injury. With these methods we evaluated the efficacy of the coenzyme-Q derivative idebenone, a proposed antioxidant. Surprisingly, in both chemically induced models of I/R and I/R in the intact heart, we see no antioxidant-based mechanism for rescue. The mechanistic insight we gained from these models of I/R injury directed us to further examine CI dysfunction in greater detail. Through the use of two cutting edge genetic engineering approaches, CRISPR/Cas9 and Artificial Site-specific RNA Endonucleases (ASRE), we have been able to directly edit the mitochondria to accurately model CI dysfunction in disease. The use of these genetic engineering technologies have provided first in class methods for modeling three unique mitochondrial diseases. The culmination of these projects has provided tremendous insight into the role of CI in disease and have taken a significant step towards elucidating potential therapeutic avenues for targeting decrements in mitochondrial function. / Doctor of Philosophy / Within the mitochondria, “the powerhouse of the cell,” exists a series of five enzyme complexes that produce 90% of the energy for our cells need to function. The largest of these enzymes, complex I (CI), plays an important role in ensuring proper mitochondrial function. Injury to CI contributes to a number of diseases, but surprisingly few options exist to treat complex I. One of the most prevalent forms of CI dysfunction can be seen in ischemia/ reperfusion injury, a form of which is most commonly recognized as a heart attack. Surprisingly, the American Heart Association reports that in the next year over 700,000 people in the US will suffer from an ischemic event. With such a profound impact on the population, the need for new therapeutic developments is extremely high. Some current therapeutic approaches have been shown to be effective at treating cardiac dysfunction, but few address the dysfunction that occurs in the mitochondria. Here we test both a method for modeling these ischemia/reperfusion-based injuries and a potential therapeutic for treating these injuries within the context of CI dysfunction. We further evaluate CI dysfunction by using both established genetic engineering approaches as well as a completely new method to model CI disease. Through the use of two cutting edge genetic engineering approaches, we have been able to directly edit components of the mitochondria to accurately model CI dysfunction in disease. The use of these genetic engineering technologies have provided a first-in-class method for modeling three unique mitochondrial diseases. The culmination of these projects has provided tremendous insight into the role of CI in disease and have taken a significant step towards elucidating potential therapeutic avenues for targeting decrements in mitochondrial function.