Involvement of PKCε in Cardioprotection Induced by Adaptation to Chronic Continuous Hypoxia

Myocardial m6A regulators in postnatal development: effect of sex

N6-methyladenosine (m6A) is an abundant mRNA modification affecting mRNA stability and protein expression. It is a highly dynamic process, and its outcomes during postnatal heart development are poorly understood. Here we studied m6A machinery in the left ventricular myocardium of Fisher344 male and female rats (postnatal days one to ninety; P1-P90) using Western Blot. A downward pattern of target protein levels (demethylases FTO and ALKBH5, methyltransferase METTL3, reader YTHDF2) was revealed in male and female rat during postnatal development. On P1, the FTO protein level was significantly higher in male compared to females.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

The roles of PKC-δ and PKC-ε in myocardial ischemia/reperfusion injury

Ischemia and reperfusion (I/R) cause a reduction in arterial blood supply to tissues, followed by the restoration of perfusion and consequent reoxygenation. The reestablishment of blood flow triggers further damage to ischemic tissue through reactive oxygen species (ROS) accumulation, interference with cellular ion homeostasis, opening of mitochondrial permeability transition pores (mPTPs) and promotion of cell death (apoptosis or necrosis). PKC-δ and PKC-ε, belonging to a family of serine/threonine kinases, have been demonstrated to play important roles during I/R injury in cardiovascular diseases. However, the cardioprotective mechanisms of PKC-δ and PKC-ε in I/R injury have not been elaborated until now. This article discusses the roles of PKC-δ and PKC-ε during myocardial I/R in redox regulation (redox signaling and oxidative stress), cell death (apoptosis and necrosis), Ca²⁺ overload, and mitochondrial dysfunction.

The involvement of protein kinases in the cardioprotective effect of chronic hypoxia

The purpose of this review is to analyze the involvement of protein kinases in the cardioprotective mechanism induced by chronic hypoxia. It has been reported that chronic intermittent hypoxia contributes to increased expression of the following kinases in the myocardium: PKCdelta, PKCalpha, p-PKCepsilon, p-PKCalpha, AMPK, p-AMPK, CaMKII, p-ERK1/2, p-Akt, PI3-kinase, p-p38, HK-1, and HK-2; whereas, chronic normobaric hypoxia promotes increased expression of the following kinases in the myocardium: PKCepsilon, PKCbetaII, PKCeta, CaMKII, p-ERK1/2, p-Akt, p-p38, HK-1, and HK-2. However, CNH does not promote enhanced expression of the AMPK and JNK kinases. Adaptation to hypoxia enhances HK-2 association with mitochondria and causes translocation of PKCdelta, PKCbetaII, and PKCeta to the mitochondria. It has been shown that PKCdelta, PKCepsilon, ERK1/2, and MEK1/2 are involved in the cardioprotective effect of chronic hypoxia. The role of other kinases in the cardioprotective effect of adaptation to hypoxia requires further research.

Cardiac Cx43 and ECM Responses to Altered Thyroid Status Are Blunted in Spontaneously Hypertensive versus Normotensive Rats

Heart function and its susceptibility to arrhythmias are modulated by thyroid hormones (THs) but the responsiveness of hypertensive individuals to thyroid dysfunction is elusive. We aimed to explore the effect of altered thyroid status on crucial factors affecting synchronized heart function, i.e., connexin-43 (Cx43) and extracellular matrix proteins (ECM), in spontaneously hypertensive rats (SHRs) compared to normotensive Wistar Kyoto rats (WKRs). Basal levels of circulating THs were similar in both strains. Hyperthyroid state (HT) was induced by injection of T3 (0.15 mg/kg b.w. for eight weeks) and hypothyroid state (HY) by the administration of methimazol (0.05% for eight weeks). The possible benefit of omega-3 polyunsaturated fatty acids (Omacor, 200 mg/kg for eight weeks) intake was examined as well. Reduced levels of Cx43 in SHRs were unaffected by alterations in THs, unlike WKRs, in which levels of Cx43 and its phosphorylated form at serine368 were decreased in the HT state and increased in the HY state. This specific Cx43 phosphorylation, attributed to enhanced protein kinase C-epsilon signaling, was also increased in HY SHRs. Altered thyroid status did not show significant differences in markers of ECM or collagen deposition in SHRs. WKRs exhibited a decrease in levels of profibrotic transforming growth factor β1 and SMAD2/3 in HT and an increase in HY, along with enhanced interstitial collagen. Short-term intake of omega-3 polyunsaturated fatty acids did not affect any targeted proteins significantly. Key findings suggest that myocardial Cx43 and ECM responses to altered thyroid status are blunted in SHRs compared to WKRs. However, enhanced phosphorylation of Cx43 at serine368 in hypothyroid SHRs might be associated with preservation of intercellular coupling and alleviation of the propensity of the heart to malignant arrhythmias.

Cardioprotection by intermittent hypoxia conditioning: evidence, mechanisms, and therapeutic potential

The calibrated application of limited-duration, cyclic, moderately intense hypoxia-reoxygenation increases cardiac resistance to ischemia-reperfusion stress. These intermittent hypoxic conditioning (IHC) programs consistently produce striking reductions in myocardial infarction and ventricular tachyarrhythmias after coronary artery occlusion and reperfusion and, in many cases, improve contractile function and coronary blood flow. These IHC protocols are fundamentally different from those used to simulate sleep apnea, a recognized cardiovascular risk factor. In clinical studies, IHC improved exercise capacity and decreased arrhythmias in patients with coronary artery or pulmonary disease and produced robust, persistent, antihypertensive effects in patients with essential hypertension. The protection afforded by IHC develops gradually and depends on β-adrenergic, δ-opioidergic, and reactive oxygen-nitrogen signaling pathways that use protein kinases and adaptive transcription factors. In summary, adaptation to intermittent hypoxia offers a practical, largely unrecognized means of protecting myocardium from impending ischemia. The myocardial and perhaps broader systemic protection provided by IHC clearly merits further evaluation as a discrete intervention and as a potential complement to conventional pharmaceutical and surgical interventions.

Cardioprotective Regimen of Adaptation to Chronic Hypoxia Diversely Alters Myocardial Gene Expression in SHR and SHR-mtBN Conplastic Rat Strains

Adaptation to continuous normobaric hypoxia (CNH) protects the heart against acute ischemia/reperfusion injury. Recently, we have demonstrated the infarct size-limiting effect of CNH also in hearts of spontaneously hypertensive rats (SHR) and in conplastic SHR-mt^BN strain characterized by the selective replacement of the mitochondrial genome of SHR with that of more ischemia-resistant Brown Norway rats. Importantly, cardioprotective effect of CNH was more pronounced in SHR-mt^BN than in SHR. Thus, here we aimed to identify candidate genes which may contribute to this difference between the strains. Rats were adapted to CNH (FiO₂ 0.1) for 3 weeks or kept at room air as normoxic controls. Screening of 45 transcripts was performed in left ventricles using Biomark Chip. Significant differences between the groups were analyzed by univariate analysis (ANOVA) and the genes contributing to the differences between the strains unmasked by CNH were identified by multivariate analyses (PCA, SOM). ANOVA with Bonferroni correction revealed that transcripts differently affected by CNH in SHR and SHR-mt^BN belong predominantly to lipid metabolism and antioxidant defense. PCA divided four experimental groups into two main clusters corresponding to chronically hypoxic and normoxic groups, and differences between the strains were more pronounced after CNH. Subsequently, the following 14 candidate transcripts were selected by PCA, and confirmed by SOM analyses, that can contribute to the strain differences in cardioprotective phenotype afforded by CNH: Alkaline ceramidase 2 (Acer2), Fatty acid translocase (Cd36), Aconitase 1 (Aco1), Peroxisome proliferator activated receptor gamma (Pparg), Hemoxygenase 2 (Hmox2), Phospholipase A2 group IIA (Ppla2g2a), Dynamin-related protein (Drp), Protein kinase C epsilon (Pkce), Hexokinase 2 (Hk2), Sphingomyelin synthase 2 (Sgms2), Caspase 3 (Casp3), Mitofussin 1 (Mfn1), Phospholipase A2 group V (Pla2g5), and Catalase (Cat). Our data suggest that the stronger cardioprotective phenotype of conplastic SHR-mt^BN strain afforded by CNH is associated with either preventing the drop or increasing the expression of transcripts related to energy metabolism, antioxidant response and mitochondrial dynamics.

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

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

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 iPLA2and 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.

Selective replacement of mitochondrial DNA increases the cardioprotective effect of chronic continuous hypoxia in spontaneously hypertensive rats

Mitochondria play an essential role in improved cardiac ischaemic tolerance conferred by adaptation to chronic hypoxia. In the present study, we analysed the effects of continuous normobaric hypoxia (CNH) on mitochondrial functions, including the sensitivity of the mitochondrial permeability transition pore (MPTP) to opening, and infarct size (IS) in hearts of spontaneously hypertensive rats (SHR) and the conplastic SHR-mt^BN strain, characterized by the selective replacement of the mitochondrial genome of SHR with that of the more ischaemia-resistant brown Norway (BN) strain. Rats were adapted to CNH (10% O₂, 3 weeks) or kept at room air as normoxic controls. In the left ventricular mitochondria, respiration and cytochrome c oxidase (COX) activity were measured using an Oxygraph-2k and the sensitivity of MPTP opening was assessed spectrophotometrically as Ca²⁺-induced swelling. Myocardial infarction was analysed in anaesthetized open-chest rats subjected to 20 min of coronary artery occlusion and 3 h of reperfusion. The IS reached 68±3.0% and 65±5% of the area at risk in normoxic SHR and SHR-mt^BN strains, respectively. CNH significantly decreased myocardial infarction to 46±3% in SHR. In hypoxic SHR-mt^BN strain, IS reached 33±2% and was significantly smaller compared with hypoxic SHR. Mitochondria isolated from hypoxic hearts of both strains had increased detergent-stimulated COX activity and were less sensitive to MPTP opening. The maximum swelling rate was significantly lower in hypoxic SHR-mt^BN strain compared with hypoxic SHR, and positively correlated with myocardial infarction in all experimental groups. In conclusion, the mitochondrial genome of SHR modulates the IS-limiting effect of adaptation to CNH by affecting mitochondrial energetics and MPTP sensitivity to opening.

Lazaroid U83836E protects the heart against ischemia reperfusion injury via inhibition of oxidative stress and activation of PKC

Oxidative stress has been demonstrated to be important during myocardial ischemia/reperfusion injury (MIRI). The lazaroid U83836E, which combines the amino functionalities of the 21‑aminosteroids with the antioxidant ring portion of vitamin E, is a reactive oxygen species scavenger. The aim of the current study was to investigate the effect of U83836E on MIRI and its mechanisms of action. Rat hearts were subjected to 30 min ligation of the left anterior descending coronary artery, followed by 2 h reperfusion. The results demonstrated that at 5 mg/kg, U83836E markedly protected cardiac function in ischemia/reperfusion rat models, decreased the malondialdehyde content and creatinine kinase activity, while increasing superoxide dismutase and glutathione peroxidase activity. Additionally, U83836E significantly decreased the histological damage to the myocardium, reduced the area of myocardial infarction in the left ventricle and modified the mitochondrial dysfunction. Furthermore, U83836E enhanced the translocation of protein kinase Cε (PKCε) from the cytoplasm to the membrane. However, the cardioprotective effects of U83836E were reduced in the presence of the PKC inhibitor, chelerythrine (1 mg/kg). Therefore, the results of the present study suggest that U83836E has a potent protective effect against MIRI in rat models through the direct anti‑oxidative stress mechanisms and the activation of PKC signaling.