HIF-1α limits myocardial infarction by promoting mitophagy in mouse hearts adapted to chronic hypoxia.

AIM: The transcriptional factor HIF-1α is recognized for its contribution to cardioprotection against acute ischemia/reperfusion injury. Adaptation to chronic hypoxia (CH) is known to stabilize HIF-1α and increase myocardial ischemic tolerance. However, the precise role of HIF-1α in mediating the protective effect remains incompletely understood. METHODS: Male wild-type (WT) mice and mice with partial Hif1a deficiency (hif1a +/-) were exposed to CH for 4 weeks, while their respective controls were kept under normoxic conditions. Subsequently, their isolated perfused hearts were subjected to ischemia/reperfusion to determine infarct size, while RNA-sequencing of isolated cardiomyocytes was performed. Mitochondrial respiration was measured to evaluate mitochondrial function, and western blots were performed to assess mitophagy. RESULTS: We demonstrated enhanced ischemic tolerance in WT mice induced by adaptation to CH compared with their normoxic controls and chronically hypoxic hif1a +/- mice. Through cardiomyocyte bulk mRNA sequencing analysis, we unveiled significant reprogramming of cardiomyocytes induced by CH emphasizing mitochondrial processes. CH reduced mitochondrial content and respiration and altered mitochondrial ultrastructure. Notably, the reduced mitochondrial content correlated with enhanced autophagosome formation exclusively in chronically hypoxic WT mice, supported by an increase in the LC3-II/LC3-I ratio, expression of PINK1, and degradation of SQSTM1/p62. Furthermore, pretreatment with the mitochondrial division inhibitor (mdivi-1) abolished the infarct size-limiting effect of CH in WT mice, highlighting the key role of mitophagy in CH-induced cardioprotection. CONCLUSION: These findings provide new insights into the contribution of HIF-1α to cardiomyocyte survival during acute ischemia/reperfusion injury by activating the selective autophagy pathway.

Glycopolymer Inhibitors of Galectin-3 Suppress the Markers of Tissue Remodeling in Pulmonary Hypertension.

Pulmonary hypertension is a cardiovascular disease with a low survival rate. The protein galectin-3 (Gal-3) binding ß-galactosides of cellular glycoproteins plays an important role in the onset and development of this disease. Carbohydrate-based drugs that target Gal-3 represent a new therapeutic strategy in the treatment of pulmonary hypertension. Here, we present the synthesis of novel hydrophilic glycopolymer inhibitors of Gal-3 based on a polyoxazoline chain decorated with carbohydrate ligands. Biolayer interferometry revealed a high binding affinity of these glycopolymers to Gal-3 in the subnanomolar range. In the cell cultures of cardiac fibroblasts and pulmonary artery smooth muscle cells, the most potent glycopolymer 18 (Lac-high) caused a decrease in the expression of markers of tissue remodeling in pulmonary hypertension. The glycopolymers were shown to penetrate into the cells. In a biodistribution and pharmacokinetics study in rats, the glycopolymers accumulated in heart and lung tissues, which are most affected by pulmonary hypertension.

Epitranscriptomic regulation in fasting hearts: implications for cardiac health.

Cardiac tolerance to ischaemia can be increased by dietary interventions such as fasting, which is associated with significant changes in myocardial gene expression. Among the possible mechanisms of how gene expression may be altered are epigenetic modifications of RNA - epitranscriptomics. N6-methyladenosine (m6A) and N6,2'-O-dimethyladenosine (m6Am) are two of the most prevalent modifications in mRNA. These methylations are reversible and regulated by proteins called writers, erasers, readers, and m6A-repelled proteins. We analysed 33 of these epitranscriptomic regulators in rat hearts after cardioprotective 3-day fasting using RT-qPCR, Western blot, and targeted proteomic analysis. We found that the most of these regulators were changed on mRNA or protein levels in fasting hearts, including up-regulation of both demethylases - FTO and ALKBH5. In accordance, decreased methylation (m6A+m6Am) levels were detected in cardiac total RNA after fasting. We also identified altered methylation levels in Nox4 and Hdac1 transcripts, both of which play a role in the cytoprotective action of ketone bodies produced during fasting. Furthermore, we investigated the impact of inhibiting demethylases ALKBH5 and FTO in adult rat primary cardiomyocytes (AVCMs). Our findings indicate that inhibiting these demethylases reduced the hypoxic tolerance of AVCMs isolated from fasting rats. This study showed that the complex epitranscriptomic machinery around m6A and m6Am modifications is regulated in the fasting hearts and might play an important role in cardiac adaptation to fasting, a well-known cardioprotective intervention.

In vitro and in vivo investigation of cardiotoxicity associated with anticancer proteasome inhibitors and their combination with anthracycline.

Although proteasome inhibitors (PIs) are modern targeted anticancer drugs, they have been associated with a certain risk of cardiotoxicity and heart failure (HF). Recently, PIs have been combined with anthracyclines (ANTs) to further boost their anticancer efficacy. However, this raised concerns regarding cardiac safety, which were further supported by several in vitro studies on immature cardiomyocytes. In the present study, we investigated the toxicity of clinically used PIs alone (bortezomib (BTZ), carfilzomib (CFZ)) as well as their combinations with an ANT (daunorubicin (DAU)) in both neonatal and adult ventricular cardiomyocytes (NVCMs and AVCMs) and in a chronic rabbit model of DAU-induced HF. Using NVCMs, we found significant cytotoxicity of both PIs around their maximum plasma concentration (cmax) as well as significant augmentation of DAU cytotoxicity. In AVCMs, BTZ did not induce significant cytotoxicity in therapeutic concentrations, whereas the toxicity of CFZ was significant and more profound. Importantly, neither PI significantly augmented the cardiotoxicity of DAU despite even more profound proteasome-inhibitory activity in AVCMs compared with NVCMs. Furthermore, in young adult rabbits, no significant augmentation of chronic ANT cardiotoxicity was noted with respect to any functional, morphological, biochemical or molecular parameter under study, despite significant inhibition of myocardial proteasome activity. Our experimental data show that combination of PIs with ANTs is not accompanied by an exaggerated risk of cardiotoxicity and HF in young adult animal cardiomyocytes and hearts.

Anti-arrhythmic Cardiac Phenotype Elicited by Chronic Intermittent Hypoxia Is Associated With Alterations in Connexin-43 Expression, Phosphorylation, and Distribution.

Remodeling of the cellular distribution of gap junctions formed mainly by connexin-43 (Cx43) can be related to the increased incidence of cardiac arrhythmias. It has been shown that adaptation to chronic intermittent hypobaric hypoxia (IHH) attenuates the incidence and severity of ischemic and reperfusion ventricular arrhythmias and increases the proportion of anti-arrhythmic n-3 polyunsaturated fatty acids (n-3 PUFA) in heart phospholipids. Wistar rats were exposed to simulated IHH (7,000 m, 8-h/day, 35 exposures) and compared with normoxic controls (N). Cx43 expression, phosphorylation, localization and n-3 PUFA proportion were analyzed in left ventricular myocardium. Compared to N, IHH led to higher expression of total Cx43, its variant phosphorylated at Ser368 [p-Cx43(Ser368)], which maintains "end to end" communication, as well as p-Cx43(Ser364/365), which facilitates conductivity. By contrast, expression of non-phosphorylated Cx43 and p-Cx43(Ser278/289), attenuating intercellular communication, was lower in IHH than in N. IHH also resulted in increased expression of protein kinase A and protein kinase G while casein kinase 1 did not change compared to N. In IHH group, which exhibited reduced incidence of ischemic ventricular arrhythmias, Cx43 and p-Cx43(Ser368) were more abundant at "end to end" gap junctions than in N group and this difference was preserved after acute regional ischemia (10 min). We further confirmed higher n-3 PUFA proportion in heart phospholipids after adaptation to IHH, which was even further increased by ischemia. Our results suggest that adaptation to IHH alters expression, phosphorylation and distribution of Cx43 as well as cardioprotective n-3PUFA proportion suggesting that the anti-arrhythmic phenotype elicited by IHH can be at least partly related to the stabilization of the "end to end" conductivity between cardiomyocytes during brief ischemia.

Antioxidant tempol suppresses heart cytosolic phospholipase A2α stimulated by chronic intermittent hypoxia.

Adaptation to chronic intermittent hypoxia (CIH) is associated with reactive oxygen species (ROS) generation implicated in the improved cardiac tolerance against acute ischemia-reperfusion injury. Phospholipases A2 (PLA2s) play an important role in cardiomyocyte phospholipid metabolism influencing membrane homeostasis. Here we aimed to determine the effect of CIH (7000 m, 8 h/day, 5 weeks) on the expression of cytosolic PLA2 (cPLA2α), its phosphorylated form (p-cPLA2α), calcium-independent (iPLA2), and secretory (sPLA2IIA) at protein and mRNA levels, as well as fatty acids (FA) profile in left ventricular myocardium of adult male Wistar rats. Chronic administration of antioxidant tempol was used to verify the ROS involvement in CIH effect on PLA2s expression and phospholipid FA remodeling. While CIH did not affect PLA2s mRNA levels, it increased the total cPLA2α protein in cytosol and membranes (by 191% and 38%, respectively) and p-cPLA2α (by 23%) in membranes. On the contrary, both iPLA2 and sPLA2IIA were downregulated by CIH. CIH further decreased phospholipid n-6 polyunsaturated FA (PUFA) and increased n-3 PUFA proportion. Tempol treatment prevented only CIH-induced cPLA2α up-regulation and its phosphorylation on Ser505. Our results show that CIH diversely affect myocardial PLA2s and suggest that ROS are responsible for the activation of cPLA2α under these conditions.

Myocardial ischemic tolerance in rats subjected to endurance exercise training during adaptation to chronic hypoxia.

Chronic hypoxia and exercise are natural stimuli that confer sustainable cardioprotection against ischemia-reperfusion (I/R) injury, but it is unknown whether they can act in synergy to enhance ischemic resistance. Inflammatory response mediated by tumor necrosis factor-α (TNF-α) plays a role in the infarct size limitation by continuous normobaric hypoxia (CNH), whereas exercise is associated with anti-inflammatory effects. This study was conducted to determine if exercise training performed under conditions of CNH (12% O2) affects myocardial ischemic resistance with respect to inflammatory and redox status. Adult male Wistar rats were assigned to one of the following groups: normoxic sedentary, normoxic trained, hypoxic sedentary, and hypoxic trained. ELISA and Western blot analysis, respectively, were used to quantify myocardial cytokines and the expression of TNF-α receptors, nuclear factor-κB (NF-κB), and selected components of related signaling pathways. Infarct size and arrhythmias were assessed in open-chest rats subjected to I/R. CNH increased TNF-α and interleukin-6 levels and the expression of TNF-α type 2 receptor, NF-κB, inducible nitric oxide synthase (iNOS), cytosolic phospholipase A2α, cyclooxygenase-2, manganese superoxide dismutase (MnSOD), and catalase. None of these effects occurred in the normoxic trained group, whereas exercise in hypoxia abolished or significantly attenuated CNH-induced responses, except for NF-κB, iNOS, and MnSOD. Both CNH and exercise reduced infarct size, but their combination provided the same degree of protection as CNH alone. In conclusion, exercise training does not amplify the cardioprotection conferred by CNH. High ischemic tolerance of the CNH hearts persists after exercise, possibly by maintaining the increased antioxidant capacity despite attenuating TNF-α-dependent protective signaling.NEW & NOTEWORTHY Chronic hypoxia and regular exercise are natural stimuli that confer sustainable myocardial protection against acute ischemia-reperfusion injury. Signaling mediated by TNF-α via its type 2 receptor plays a role in the cardioprotective mechanism of chronic hypoxia. In the present study, we found that exercise training of rats during adaptation to hypoxia does not amplify the infarct size-limiting effect. Ischemia-resistant phenotype is maintained in the combined hypoxia-exercise setting despite exercise-induced attenuation of TNF-α-dependent protective signaling.

Chronic intermittent hypoxia affects the cytosolic phospholipase A2α/cyclooxygenase 2 pathway via ß2-adrenoceptor-mediated ERK/p38 stimulation.

Cardiac resistance against acute ischemia/reperfusion (I/R) injury can be enhanced by adaptation to chronic intermittent hypoxia (CIH), but the changes at the molecular level associated with this adaptation are still not fully explored. Phospholipase A2 (PLA2) plays an important role in phospholipid metabolism and may contribute to membrane destruction under conditions of energy deprivation during I/R. The aim of this study was to determine the effect of CIH (7000 m, 8 h/day, 5 weeks) on the expression of cytosolic PLA2α (cPLA2α) and its phosphorylated form (p-cPLA2α), as well as other related signaling proteins in the left ventricular myocardium of adult male Wistar rats. Adaptation to CIH increased the total content of cPLA2α by 14 % in myocardial homogenate, and enhanced the association of p-cPLA2α with the nuclear membrane by 85 %. The total number of ß-adrenoceptors (ß-ARs) did not change but the ß2/ß1 ratio markedly increased due to the elevation of ß2-ARs and drop in ß1-ARs. In parallel, the amount of adenylyl cyclase decreased by 49 % and Giα proteins increased by about 50 %. Besides that, cyclooxygenase 2 (COX-2) and prostaglandin E2 (PGE2) increased by 36 and 84 %, respectively. In parallel, we detected increased phosphorylation of protein kinase Cα, ERK1/2 and p38 (by 12, 48 and 19 %, respectively). These data suggest that adaptive changes induced in the myocardium by CIH may include activation of cPLA2α and COX-2 via ß2-AR/Gi-mediated stimulation of the ERK/p38 pathway.