Promotes Cardiomyocyte Survival Research Articles

Design, Synthesis, and Preclinical Evaluation of a High-Affinity 18F-Labeled Radioligand for Myocardial Growth Hormone Secretagogue Receptor Before and After Myocardial Infarction.

The peptide hormone ghrelin is produced in cardiomyocytes and acts through the myocardial growth hormone secretagogue receptor (GHSR) to promote cardiomyocyte survival. Administration of ghrelin may have therapeutic effects on post-myocardial infarction (MI) outcomes. Therefore, there is a need to develop molecular imaging probes that can track the dynamics of GHSR in health and disease to better predict the effectiveness of ghrelin-based therapeutics. We designed a high-affinity GHSR ligand labeled with 18F for imaging by PET and characterized its invivo properties in a canine model of MI. Methods: We rationally designed and radiolabeled with 18F a quinazolinone derivative ([18F]LCE470) with subnanomolar binding affinity to GHSR. We determined the sensitivity and invivo and ex vivo specificity of [18F]LCE470 in a canine model of surgically induced MI using PET/MRI, which allowed for anatomic localization of tracer uptake and simultaneous determination of global cardiac function. Uptake of [18F]LCE470 was determined by time-activity curve and SUV analysis in 3 regions of the left ventricle-area of infarct, territory served by the left circumflex coronary artery, and remote myocardium-over a period of 1.5 y. Changes in cardiac perfusion were tracked by [13N]NH3 PET. Results: The receptor binding affinity of LCE470 was measured at 0.33 nM, the highest known receptor binding affinity for a radiolabeled GHSR ligand. In vivo blocking studies in healthy hounds and ex vivo blocking studies in myocardial tissue showed the specificity of [18F]LCE470, and sensitivity was demonstrated by a positive correlation between tracer uptake and GHSR abundance. Post-MI changes in [18F]LCE470 uptake occurred independently of perfusion tracer distributions and changes in global cardiac function. We found that the regional distribution of [18F]LCE470 within the left ventricle diverged significantly within 1 d after MI and remained that way throughout the 1.5-y duration of the study. Conclusion: [18F]LCE470 is a high-affinity PET tracer that can detect changes in the regional distribution of myocardial GHSR after MI. In vivo PET molecular imaging of the global dynamics of GHSR may lead to improved GHSR-based therapeutics in the treatment of post-MI remodeling.

Abstract Tu090: P21-activated kinase 1 safeguards cardiac function from impairment during fasting

Excessive calorie intake poses a heightened risk for cardiovascular disease, while caloric restriction and intermittent fasting have demonstrated benefits in enhancing cardiovascular health and improving cardiometabolic risk profiles. Despite this knowledge, the precise mechanisms underlying the cardioprotective effects of these dietary regimens remain inadequately understood. P21-activated kinase 1 (PAK1) is a serine/threonine protein kinase known to play a crucial role in promoting cardiomyocyte survival in response to various stressors. In this study, we aimed to elucidate the role of PAK1 in maintaining cardiac function during fasting, utilizing mice with modified PAK1 activity in the heart. Under normal feeding conditions, heart function exhibited no discernible differences among wild type (WT), transgenic (TG), and knockout (KO) mice, as evidenced by consistent fractional shortening (FS), ejection fraction (EF), E/A ratio, and isovolumic relaxation time (IVRT). After a one-day fast, systolic contractile function remained robust across all groups of mice. However, the E/A ratio decreased in KO mice, and IVRT was prolonged in KO mice, while shortened in TG mice, highlighting the crucial role of PAK1 in maintaining diastolic cardiac function. Upon a two-day fast, systolic function was compromised in both WT and KO mice, whereas TG mice exhibited preserved function, as evidenced by FS and EF measurements, emphasizing PAK1's equal significance in sustaining systolic cardiac function. Furthermore, fasting accelerated mitophagy, a process eliminating dysfunctional mitochondria through lysosomal degradation, as observed by mitochondria-associated LC3-II and a dual fluorescent mitophagy reporter. Additionally, we established PAK1 as a positive regulator of mitophagy, suggesting its potential protective role in the heart during fasting via mitophagy modulation. In summary, PAK1 emerges as a critical mediator of cardiac function during fasting, presenting promising avenues for therapeutic interventions aimed at improving cardiovascular health.

P85α deficiency alleviates ischemia-reperfusion injury by promoting cardiomyocyte survival

Myocardial ischemia-reperfusion (I/R) injury is a prevalent cause of myocardial injury, involving a series of interconnected pathophysiological processes. However, there is currently no clinical therapy for effectively mitigating myocardial I/R injury. Here, we show that p85α protein levels increase in response to I/R injury through a comprehensive analysis of cardiac proteomics, and confirm this in the I/R-injured murine heart and failing human myocardium. Genetic inhibition of p85α in mice activates the Akt-GSK3β/Bcl-x(L) signaling pathway and ameliorates I/R-induced cardiac dysfunction, apoptosis, inflammation, and mitochondrial dysfunction. p85α silencing in cardiomyocytes alleviates hypoxia-reoxygenation (H/R) injury through activating the Akt-GSK3β/Bcl-x(L) signaling pathway, while its overexpression exacerbates the damage. Mechanistically, the interaction between MG53 and p85α triggers the ubiquitination and degradation of p85α, consequently enhancing Akt phosphorylation and ultimately having cardioprotective effects. Collectively, our findings reveal that substantial reduction of p85α and subsequently activated Akt signaling have a protective effect against cardiac I/R injury, representing an important therapeutic strategy for mitigating myocardial damage.

Inhibition of Hmbox1 Promotes Cardiomyocyte Survival and Glucose Metabolism Through Gck Activation in Ischemia/Reperfusion Injury.

Exercise-induced physiological cardiac growth regulators may protect the heart from ischemia/reperfusion (I/R) injury. Homeobox-containing 1 (Hmbox1), a homeobox family member, has been identified as a putative transcriptional repressor and is downregulated in the exercised heart. However, its roles in exercise-induced physiological cardiac growth and its potential protective effects against cardiac I/R injury remain largely unexplored. We studied the function of Hmbox1 in exercise-induced physiological cardiac growth in mice after 4 weeks of swimming exercise. Hmbox1 expression was then evaluated in human heart samples from deceased patients with myocardial infarction and in the animal cardiac I/R injury model. Its role in cardiac I/R injury was examined in mice with adeno-associated virus 9 (AAV9) vector-mediated Hmbox1 knockdown and in those with cardiac myocyte-specific Hmbox1 ablation. We performed RNA sequencing, promoter prediction, and binding assays and identified glucokinase (Gck) as a downstream effector of Hmbox1. The effects of Hmbox1 together with Gck were examined in cardiomyocytes to evaluate their cell size, proliferation, apoptosis, mitochondrial respiration, and glycolysis. The function of upstream regulator of Hmbox1, ETS1, was investigated through ETS1 overexpression in cardiac I/R mice in vivo. We demonstrated that Hmbox1 downregulation was required for exercise-induced physiological cardiac growth. Inhibition of Hmbox1 increased cardiomyocyte size in isolated neonatal rat cardiomyocytes and human embryonic stem cell-derived cardiomyocytes but did not affect cardiomyocyte proliferation. Under pathological conditions, Hmbox1 was upregulated in both human and animal postinfarct cardiac tissues. Furthermore, both cardiac myocyte-specific Hmbox1 knockout and AAV9-mediated Hmbox1 knockdown protected against cardiac I/R injury and heart failure. Therapeutic effects were observed when sh-Hmbox1 AAV9 was administered after I/R injury. Inhibition of Hmbox1 activated the Akt/mTOR/P70S6K pathway and transcriptionally upregulated Gck, leading to reduced apoptosis and improved mitochondrial respiration and glycolysis in cardiomyocytes. ETS1 functioned as an upstream negative regulator of Hmbox1 transcription, and its overexpression was protective against cardiac I/R injury. Our studies unravel a new role for the transcriptional repressor Hmbox1 in exercise-induced physiological cardiac growth. They also highlight the therapeutic potential of targeting Hmbox1 to improve myocardial survival and glucose metabolism after I/R injury.

Vascular Endothelial Cell-Derived Exosomal Sphingosylphosphorylcholine Attenuates Myocardial Ischemia-Reperfusion Injury through NR4A2-Mediated Mitophagy.

Cardiomyocyte survival is a critical contributing process of host adaptive responses to cardiovascular diseases (CVD). Cells of the cardiovascular endothelium have recently been reported to promote cardiomyocyte survival through exosome-loading cargos. Sphingosylphosphorylcholine (SPC), an intermediate metabolite of sphingolipids, mediates protection against myocardial infarction (MI). Nevertheless, the mechanism of SPC delivery by vascular endothelial cell (VEC)-derived exosomes (VEC-Exos) remains uncharacterized at the time of this writing. The present study utilized a mice model of ischemia/reperfusion (I/R) to demonstrate that the administration of exosomes via tail vein injection significantly diminished the severity of I/R-induced cardiac damage and prevented apoptosis of cardiomyocytes. Moreover, SPC was here identified as the primary mediator of the observed protective effects of VEC-Exos. In addition, within this investigation, in vitro experiments using cardiomyocytes showed that SPC counteracted myocardial I/R injury by activating the Parkin and nuclear receptor subfamily group A member 2/optineurin (NR4A2/OPTN) pathways, in turn resulting in increased levels of mitophagy within I/R-affected myocardium. The present study highlights the potential therapeutic effects of SPC-rich exosomes secreted by VECs on alleviating I/R-induced apoptosis in cardiomyocytes, thereby providing strong experimental evidence to support the application of SPC as a potential therapeutic target in the prevention and treatment of myocardial infarction.

β-Arrestin-1 reduces acute myocardial infarction via promoting autophagy in cardiomyocytes

Background and purpose: β-Arrestins are key regulators of G protein–coupled receptor (GPCR) signaling. Through their function as scaffolding proteins, β-arrestins mediate a range of cellular signaling events. However, the role of β-arrestins during myocardial ischemia remains incompletely understood. In this study, we explored the regulatory effects of β-arrestin-1 on autophagy following myocardial infarction and sought to identify the underlying mechanism. Methods: Acute myocardial infarction was induced by permanent left anterior descending coronary artery ligation. Cardiac function was assessed using echocardiography. β-Arrestin-1, autophagy-related 5 (ATG5), and liver kinase B1 (LKB1) were overexpressed or knocked down using lentivirus-mediated transduction of the gene or short hairpin RNA (shRNA) in cultured primary cardiomyocytes. Oxygen-glucose deprivation (OGD) in cardiomyocytes was used to simulate cardiac ischemia in vitro. Autophagy and apoptosis were assessed by western blot, flow cytometry, and transmission electron microscopy. Cell survival and lactate dehydrogenase (LDH) release were evaluated using the respective kits. Results: β-Arrestin-1 knockout (KO) increased myocardial infarction size, an effect that was associated with decreased autophagy and deterioration of cardiac function. The overexpression of β-arrestin-1 significantly increased autophagy levels and decreased cell apoptosis in cardiomyocytes exposed to OGD, whereas the knockdown of β-arrestin-1 exerted the opposite effect. The protective effect of β-arrestin-1 overexpression was abrogated by ATG5 knockdown. β-Arrestin-1 KO attenuated the myocardial infarction–induced phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK). In cultured myocytes, the blockade of AMPK or the knockdown of LKB1 inhibited the β-arrestin-1–induced increase in the LC3-II/LC3-I ratio and beclin 1 expression levels and attenuated β-arrestin-1–mediated cardioprotective effects. Conclusions: Collectively, our findings suggested that β-arrestin-1 promotes cardiomyocyte survival under ischemic conditions via the regulation of LKB1/AMPK-dependent autophagy. These findings may be helpful in designing novel therapeutic strategies for myocardial ischemia.

Exercise improves cardiac function and attenuates myocardial inflammation and apoptosis by regulating APJ/STAT3 in mice with stroke

Stroke can induce cardiac dysfunction without a primary cardiac disease. Exercise can promote the overall rehabilitation of stroke patients and be beneficial for all kinds of heart diseases. However, the mechanisms underlying the protective effects of exercise in stroke-induced cardiac dysfunction are poorly understood. Hence, we aimed to distinguish the different effects of acute and long-term exercise and further study the mechanism of protection against cardiomyopathy caused by stroke. Mice underwent a single acute session or long-term exercise for 30 days, followed by middle cerebral artery occlusion surgery. The expression of apoptosis-related proteins and proinflammatory factors in the heart was evaluated. Then, overexpression of apelin peptide jejunum (APJ) transfected adeno-associated virus type 9 (AAV9) and inhibition of signal transducer and activator of transcription 3 (STAT3) by Stattic were used in stroke mice or hypoxic cardiomyocytes. ML221 were used to inhibit APJ activity in exercise mouse. Thereafter, changes in apoptotic and proinflammatory factors were evaluated. The results demonstrated that chronic exercise prevented myocardial inflammation, apoptosis and cardiac dysfunction after stroke. However, acute exercise did not have similar effects. Exercise maintained the levels of APJ expression and decreased phosphorylated-STAT3 (p-STAT3) activation to protect cardiomyocytes. Moreover, APJ overexpression promoted cardiomyocyte survival and reduced p-STAT3 levels. STAT3 inhibition also reduced apoptosis and proinflammatory factors in mice hearts. Conversely, the protective effect of exercise was eliminated by APJ inhibition. This study showed that exercise can maintain APJ expression and inhibit p-STAT3, thus, conferring protection against myocardial inflammation and apoptosis induced by stroke.

Abstract P1149: Junctophilin-2 Promotes Cardiomyocyte Survival By Blocking Murf1-mediated Junctin Ubiquitination And Proteasome-dependent Degradation

Background: Junctophilin-2 is required for the development, maturation and integrity of the t-tubule system and the gating stability of RyR2 in cardiomyocytes. This study investigated whether and how junctophilin-2 maintained junctin, a scaffold protein stabilizing RyR2, to prevent cardiomyocyte death under stress. Methods: Cardiomyocytes were exposed to conditions of stress including palmitate, doxorubicin, or hypoxia/re-oxygenation. Adenoviral vectors were employed to manipulate expression of junctophilin-2 and junctin in cardiomyocytes. Molecular/cellular/biochemical analyses were conducted. Results: Different conditions of stress decreased junctophilin-2 expression through aberrant autophagy and concomitantly induced a reduction of junctin protein in cardiomyocytes. Over-expression of junctophilin-2 preserved the protein levels of junctin and attenuated cytosolic Ca 2+ and apoptosis in cardiomyocytes under stress. Knockdown of junctophilin-2 reproduced the detrimental phenotypes of stress in cardiomyocytes. Notably, over-expression of junctin prevented cardiomyocyte death under stress whereas knockdown of junctin offset the protective effects conferred by junctophilin-2 over-expression. Mechanistically, junctophilin-2 blocked MURF1-junctin interaction thereby preventing junctin ubiquitination and proteasome-dependent degradation. Mass spectrometry analysis identified multiple ubiquitination sites on the junctin protein and the non-ubiquitinated junctin mutant (K8R/K102R/K107R/K140R) was resistant to degradation. Conclusions: This study uncovers an unrecognized role of junctophilin-2 in preventing junctin ubiquitination and degradation in maintaining cytosolic Ca 2+ homeostasis. Junctophilin-2 and junctin represent two new survival factors of cardiomyocytes and thus, may be new therapeutic targets for cardiac protection.

ER stress induces upregulation of transcription factor Tbx20 and downstream Bmp2 signaling to promote cardiomyocyte survival

In the mammalian heart, fetal cardiomyocytes proliferate prior to birth; however, they exit the cell cycle shortly after birth. Recent studies show that adult cardiomyocytes re-enters the cell cycle postinjury to promote cardiac regeneration. The endoplasmic reticulum (ER) orchestrates the production and assembly of different types of proteins, and a disruption in this machinery leads to the generation of ER stress, which activates the unfolded protein response. There is a very fine balance between ER stress-mediated protective and proapoptotic responses. T-box transcription factor 20 (Tbx20) promotes embryonic and adult cardiomyocyte proliferation postinjury to restore cardiac homeostasis. However, the function and regulatory interactions of Tbx20 in ER stress-induced cardiomyopathy have not yet been reported. We show here that ER stress upregulates Tbx20, which activates downstream bone morphogenetic protein 2 (Bmp2)-pSmad1/5/8 signaling to induce cardiomyocyte proliferation and limit apoptosis. However, augmenting ER stress reverses this protective response. We also show that increased expression of tbx20 during ER stress is mediated by the activating transcription factor 6 arm of the unfolded protein response. Cardiomyocyte-specific loss of Tbx20 results in decreased cardiomyocyte proliferation and increased apoptosis. Administration of recombinant Bmp2 protein during ER stress upregulates Tbx20 leading to augmented proliferation, indicating a feed-forward loop mechanism. In in vivo ER stress, as well as in diabetic cardiomyopathy, the activity of Tbx20 is increased with concomitant increased cardiomyocyte proliferation and decreased apoptosis. These data support a critical role of Tbx20-Bmp2 signaling in promoting cardiomyocyte survival during ER stress-induced cardiomyopathies.

Exosomes derived from mir-214-3p overexpressing mesenchymal stem cells promote myocardial repair

AimsExosomes are known as nanovesicles that are naturally secreted, playing an essential role in stem-mediated cardioprotection. This study mainly focused on investigating if exosomes derived from miR-214 overexpressing mesenchymal stem cells (MSCs) show more valid cardioprotective ability in a rat model of acute myocardial infarction (AMI) and its potential mechanisms.MethodsExosomes were isolated from control MSCs (Ctrl-Exo) and miR-214 overexpressing MSCs (miR-214OE-Exo) and then they were delivered to cardiomyocytes and endothelial cells in vitro under hypoxia and serum deprivation (H/SD) condition or in vivo in an acutely infarcted Sprague-Dawley rat heart. Regulated genes and signal pathways by miR-214OE-Exo treatment were explored using western blot analysis and luciferase assay.Results in vitro, miR-214OE-Exo enhanced migration, tube-like formation in endothelial cells. In addition, miR-214OE-Exo ameliorated the survival of cardiomyocytes under H/SD. In the rat AMI model, compared to Ctrl-Exo, miR-214OE-Exo reduced myocardial apoptosis, and therefore reduced infarct size and improved cardiac function. Besides, miR-214OE-Exo accelerated angiogenesis in peri-infarct region. Mechanistically, we identified that exosomal miR-214-3p promoted cardiac repair via targeting PTEN and activating p-AKT signal pathway.ConclusionExosomes derived from miR-214 overexpressing MSCs have greatly strengthened the therapeutic efficacy for treatment of AMI by promoting cardiomyocyte survival and endothelial cell function.Graphical abstract

Ablation of CXCR4 expression in cardiomyocytes exacerbates isoproterenol‑induced cell death and heart failure.

CXCR4 is a seven‑transmembrane‑spanning Gi‑coupled receptor for the SDF‑1 chemokine and plays a critical role in cardiovascular development and post‑injury repair. However, the specific role of CXCR4 in cardiomyocytes is incompletely understood. It was hypothesized that CXCR4 activation in cardiomyocytes antagonizes β‑adrenoceptor/Gs signaling‑induced cardiac dysfunction. Cardiomyocyte‑specific CXCR4 knockout (CXCR4‑CMKO) mice were generated by crossing CXCR4fl/fl and MHC‑Cre+/‑ mice. Their cardiac structure and function in the basal state are equivalent to that of the control MHC‑Cre+/‑ littermates until at least 4months old. However, following continuous subcutaneous administration of isoproterenol (Iso) via an osmotic mini‑pump, the ventricular myocardial contractility, dilation, cardiomyocyte apoptosis, and interstitial fibrosis are worse in CXCR4‑CMKO mice than in MHC‑Cre+/‑ littermates. In the cultured H9C2 cardiomyocytes, SDF‑1 treatment markedly attenuated Iso‑induced apoptosis and reduction in phospho‑Akt, and this protective effect was lost by knockdown of CXCR4 or by co‑treatment with Gi inhibitors. In conclusion, CXCR4 promotes cardiomyocyte survival and heart function during β‑adrenergic stress.

Dual specificity phosphatase 1 attenuates inflammation-induced cardiomyopathy by improving mitophagy and mitochondrial metabolism

ObjectivesDual specificity phosphatase 1 (DUSP1) is regarded as an anti-inflammatory factor in cardiovascular disorders. Mitophagy removes damaged mitochondria and thus promotes mitochondrial regeneration. We investigated whether DUSP1 could attenuate inflammation-induced cardiomyopathy by improving mitophagy. MethodsLipopolysaccharide was used to induce septic cardiomyopathy in wild-type (WT) and DUSP1 transgenic (DUSP1TG) mice. ResultsEchocardiography revealed that lipopolysaccharide impaired heart function by reducing the cardiac systolic and diastolic capacities of WT mice. Freshly isolated single cardiomyocytes from lipopolysaccharide-treated WT mice also exhibited reduced contractile/relaxation parameters. However, DUSP1 overexpression not only maintained the mechanical properties of cardiomyocytes, but also improved heart performance. Lipopolysaccharide upregulated myocardial inflammatory gene transcription and adhesive factor expression, which increased myocardial neutrophil accumulation and cardiomyocyte apoptosis in WT mice. DUSP1 overexpression inhibited the inflammatory response and therefore promoted cardiomyocyte survival. Lipopolysaccharide disrupted mitochondrial respiration and metabolism in WT cardiomyocytes, but DUSP1 overexpression restored mitochondrial metabolism, maintained the mitochondrial membrane potential and inhibited mitochondrial reactive oxygen species production, possibly by increasing FUN14 domain-containing 1 (FUNDC1)-dependent mitophagy. Silencing of FUNDC1 abolished the protective effects of DUSP1 overexpression on cardiomyocytes and their mitochondria following lipopolysaccharide treatment. ConclusionThese results demonstrated that DUSP1 is a novel anti-inflammatory factor that protects against septic cardiomyopathy by improving FUNDC1-induced mitophagy.

Poly(I:C) attenuates myocardial ischemia/reperfusion injury by restoring autophagic function.

Polyinosinic-polycytidylic acid (poly(I:C)) is the agonist of Toll-like receptor 3 (TLR3), which participates in innate immune responses under the condition of myocardial ischemia/reperfusion injury (MIRI). It has been shown that poly(I:C) exhibited cardioprotective activities through the PI3K/Akt pathway, which is the main signal transduction pathway during autophagy. However, the precise mechanism by whether poly(I:C) regulates autophagy remains poorly understood. Thus, this study was designed to investigate the therapeutic effect of poly(I:C) against MIRI and the underlying pathway connection with autophagy. We demonstrated that 1.25 and 5mg/kg poly(I:C) preconditioning significantly reduced myocardial infarct size and cardiac dysfunction. Moreover, poly(I:C) significantly promoted cell survival by restoring autophagy flux and then regulating it to an adequate level Increased autophagy protein Beclin1 and LC3II together with p62degradation after additional chloroquine. In addition, mRFP-GFP-LC3 adenoviruses exhibited autophagy activity in neonatal rat cardiac myocytes (NRCMs). Mechanistically, poly(I:C) activated the PI3K/AKT/mTOR pathway to induce autophagy, which was abolished by LY294002 (PI3K antagonist), rapamycin (autophagy activator and mTOR inhibitor), or 3-methyladenine (autophagy inhibitor), suggesting either inhibition of the PI3K/Akt/mTOR pathway or autophagy activity interrupt the beneficial effect of poly(I:C) preconditioning. In conclusion, poly(I:C) promotes cardiomyocyte survival from ischemia/reperfusion injury by regulating autophagy via the PI3K/Akt/mTOR pathway.

Interleukin-10 Mitigates Doxorubicin-Induced Endoplasmic Reticulum Stress as Well as Cardiomyopathy.

The use of doxorubicin (Dox) in cancer patients carries the risk of cardiotoxicity via an increase in oxidative stress, mitochondrial dysfunction, and disturbed endoplasmic reticulum (ER) homeostasis in cardiomyocytes. The present study explores which of the ER transmembrane sensors is involved in Dox-induced apoptosis and whether interleukin-10 (IL-10) has any mitigating effect. There was a time-related increase in apoptosis in cardiomyocytes exposed to 5.43 µg/mL Dox for 0 to 48 h. Dox treatment for 24 h significantly upregulated glucose-regulated proteins 78 and 94, protein disulfide isomerase, cleavage of activating transcription factor 6α, and X-box binding protein 1. These Dox-induced changes in ER stress proteins as well as apoptosis were blunted by IL-10 (10 ng/mL). In Dox-exposed cardiomyocytes, IL-10 also promoted expression of protein kinase-like endoplasmic reticulum kinase and inositol-requiring kinase 1α, which helped in maintaining ER homeostasis. Additionally, under Dox-treatment, IL-10 downregulated caspase-12 activation as well as phosphorylation of c-JUN NH2-terminal kinase, thereby promoting cardiomyocyte survival. IL-10 was able to reduce the overexpression of mitochondrial apoptotic proteins caspase-3 as well as Bax, which were upregulated upon Dox treatment. Thus, a reduction in Dox-induced ER stress as well as apoptosis through IL-10 may provide a significant benefit in improving cardiac function.

Zyxin protects from hypertension-induced cardiac dysfunction

Arterial hypertension causes left ventricular hypertrophy leading to dilated cardiomyopathy. Following compensatory cardiomyocyte hypertrophy, cardiac dysfunction develops due to loss of cardiomyocytes preceded or paralleled by cardiac fibrosis. Zyxin acts as a mechanotransducer in vascular cells that may promote cardiomyocyte survival. Here, we analyzed cardiac function during experimental hypertension in zyxin knockout (KO) mice. In zyxin KO mice, made hypertensive by way of deoxycorticosterone acetate (DOCA)-salt treatment telemetry recording showed an attenuated rise in systolic blood pressure. Echocardiography indicated a systolic dysfunction, and isolated working heart measurements showed a decrease in systolic elastance. Hearts from hypertensive zyxin KO mice revealed increased apoptosis, fibrosis and an upregulation of active focal adhesion kinase as well as of integrins α5 and β1. Both interstitial and perivascular fibrosis were even more pronounced in zyxin KO mice exposed to angiotensin II instead of DOCA-salt. Stretched microvascular endothelial cells may release collagen 1α2 and TGF-β, which is characteristic for the transition to an intermediate mesenchymal phenotype, and thus spur the transformation of cardiac fibroblasts to myofibroblasts resulting in excessive scar tissue formation in the heart of hypertensive zyxin KO mice. While zyxin KO mice per se do not reveal a cardiac phenotype, this is unmasked upon induction of hypertension and owing to enhanced cardiomyocyte apoptosis and excessive fibrosis causes cardiac dysfunction. Zyxin may thus be important for the maintenance of cardiac function in spite of hypertension.

Prevention of Fibrosis and Pathological Cardiac Remodeling by Salinomycin.

[Figure: see text].

Inhibition of endoplasmic reticulum stress through activation of MAPK/ERK signaling pathway attenuates hypoxia-mediated cardiomyocyte damage

The pathogenesis of post-infarction ischemia-induced myocardial damage is related to hypoxia-mediated cardiomyocyte damage. In the present study, we explored the roles of ERK signaling pathway and endoplasmic reticulum (ER) stress in hypoxia-related cardiomyocyte damage. H9c2 cells were cultured under hypoxia condition in the presence of the ERK activator. Our data demonstrated that ER stress was significantly activated by hypoxia in cardiomyocyte, as evidenced by increased expression of PERK and CHOP through immunofluorescence. Interestingly, application of ERK activator significantly reduced hypoxia-mediated ER stress. Besides, ERK activation also sustained cardiomyocyte viability in the presence of hypoxia, as evidenced by decreased activities of caspase-3 and caspase-9. Altogether, our results demonstrated that ERK activation significantly promoted cardiomyocyte survival through inhibition of ER stress. This finding provides a novel insight into the molecular mechanism underlying hypoxia-mediated cardiomyocyte damage. Besides, our results also offer a potential target for the treatment and prevention of post-infarction ischemia-related myocardial damage.

Parkin overexpression reduces inflammation-mediated cardiomyocyte apoptosis through activating Nrf2/ARE signaling pathway

Inflammation has been acknowledged as one of the pathological alterations in various cardiovascular disorders. Parkin has been found to be associated with mitochondrial protection. In the present study, we explored the influence of Parkin overexpression on cardiomyocyte induced by LPS-mediated inflammation response. Our results demonstrated that cardiomyocyte viability was reduced and apoptotic rate was increased upon LPS treatment, an effect that may be caused by cardiomyocyte oxidative stress. At the molecular levels, LPS treatment promoted ROS production, a result that was followed by a drop in the levels of anti-oxidants. Interestingly, Parkin overexpression significantly promoted cardiomyocyte survival and this cardioprotective was attributable to the anti-oxidative property. Parkin overexpression enhanced the expression of anti-oxidative factors such as GSH, SOD and GPX, resulting into depressed ROS production. Further, we found that Parkin modulated cellular anti-oxidative capacity through the Nrf2/ARE signaling pathway. This finding demonstrates that oxidative stress could be considered as the core of inflammation response. Further, therapeutic approaches targeting Parkin would improve cardiomyocyte anti-oxidative capacity through activating Nrf2/ARE signaling pathway.

PIM1 Promotes Survival of Cardiomyocytes by Upregulating c-Kit Protein Expression.

Enhancing cardiomyocyte survival is crucial to blunt deterioration of myocardial structure and function following pathological damage. PIM1 (Proviral Insertion site in Murine leukemia virus (PIM) kinase 1) is a cardioprotective serine threonine kinase that promotes cardiomyocyte survival and antagonizes senescence through multiple concurrent molecular signaling cascades. In hematopoietic stem cells, PIM1 interacts with the receptor tyrosine kinase c-Kit upstream of the ERK (Extracellular signal-Regulated Kinase) and Akt signaling pathways involved in cell proliferation and survival. The relationship between PIM1 and c-Kit activity has not been explored in the myocardial context. This study delineates the interaction between PIM1 and c-Kit leading to enhanced protection of cardiomyocytes from stress. Elevated c-Kit expression is induced in isolated cardiomyocytes from mice with cardiac-specific overexpression of PIM1. Co-immunoprecipitation and proximity ligation assay reveal protein–protein interaction between PIM1 and c-Kit. Following treatment with Stem Cell Factor, PIM1-overexpressing cardiomyocytes display elevated ERK activity consistent with c-Kit receptor activation. Functionally, elevated c-Kit expression confers enhanced protection against oxidative stress in vitro. This study identifies the mechanistic relationship between PIM1 and c-Kit in cardiomyocytes, demonstrating another facet of cardioprotection regulated by PIM1 kinase.

Long noncoding RNA UCA1 from hypoxia-conditioned hMSC-derived exosomes: a novel molecular target for cardioprotection through miR-873-5p/XIAP axis

Exosomes (Exo) secreted from mesenchymal stem cells (hMSCs) are protective against myocardial injury. The purpose of the study was to investigate the role and mechanisms by which exosomes promote cardiomyocyte survival and function following myocardial infarction (MI). hMSCs were cultured under hypoxic and normoxic conditions. Hypoxia-conditioned hMSC-derived exosomes (Hypo-Exo) and normoxic-conditioned hMSC-derived exosomes (Nor-Exo) were collected and intramyocardially injected into rats with MI. The therapeutic effects of Hypo-Exo and Nor-Exo were evaluated after 4 weeks. Quantitative real-time PCR (qRT-PCR) was used to detect the expression of candidate long noncoding RNA urothelial carcinoma associated 1 (lncRNA-UCA1) in Nor-Exo and Hypo-Exo. Intramyocardial injection of lncRNA-UCA1-knockdown-Hypo-Exo in a rat model of MI was then performed and the cardiac function was characterized. The target and downstream of the molecular mechanism lncRNA-UCA1 was disclosed by luciferase reporter assays and western blot. Circulating exosomal lncRNA-UCA1 level in AMI patients and healthy volunteers was assessed. We found that (1) hMSC exosomal (from hypoxic and normoxic conditions) cardioprotection in vitro and in vivo correlated with the presence of encapsulated lncRNA-UCA1 in exosomes; (2) lncRNA-UCA1 targeted miR-873 via sponging, reducing the latter’s suppressive effects on its target XIAP, and this translated into AMPK phosphorylation and increased level of the antiapoptotic protein BCL2; and (3) plasma derived from patients with AMI contained exosomes enriched with the lncRNA-UCA1, unlike that from normal subjects. This study demonstrates that Hypo-Exo lncRNA-UCA1 plays a cardioprotective role via the miR-873-5p/XIAP axis and circulating exosomal lncRNA-UCA1 may be a promising novel biomarker for the diagnosis of AMI.