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Myocardial hypertrophy is associated with a significant increase in intracellular Ca

Cardiopulmonary arrest (CA) is the leading cause of death and disability in the United States. CA-induced brain injury is influenced by multifactorial processes, including reduced cerebral blood flow (hypoperfusion) and neuroinflammation, which can lead to neuronal cell death and functional deficits. We have identified serum and glucocorticoid-regulated kinase-1 (SGK1) as a new target in brain ischemia previously described in the heart, liver, and kidneys (i.e., diabetes and hypertension). Our data suggest brain SGK1 mRNA and protein expression (i.e., hippocampus), presented with hypoperfusion (low cerebral blood flow) and neuroinflammation, leading to further studies of the potential role of SGK1 in CA-induced brain injury. We used a 6-min asphyxia cardiac arrest (ACA) rat model to induce global cerebral ischemia. Modulation of SGK1 was implemented via GSK650394, a SGK1-specific inhibitor (1.2 μg/kg icv). Accordingly, treatment with GSK650394 attenuated cortical hypoperfusion and neuroinflammation (via Iba1 expression) after ACA, whereas neuronal survival was enhanced in the CA1 region of the hippocampus. Learning/memory deficits were observed 3 days after ACA but ameliorated with GSK650394. In conclusion, SGK1 is a major contributor to ACA-induced brain injury and neurological deficits, while inhibition of SGK1 with GSK650394 provided neuroprotection against CA-induced hypoperfusion, neuroinflammation, neuronal cell death, and learning/memory deficits. Our studies could lead to a novel, therapeutic target for alleviating brain injury following cerebral ischemia. NEW & NOTEWORTHY Upregulation of SGK1 exacerbates brain injury during cerebral ischemia. Inhibition of SGK1 affords neuroprotection against cardiac arrest-induced hypoperfusion, neuroinflammation, neuronal cell death, and neurological deficits.

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a type of post-translational modification which is important for numerous cellular processes, including mRNA splicing, DNA repair, signal transduction, protein interaction, and transport. PRMTs have been extensively associated with various pathologies, including cancer, inflammation, and immunity response. However, the role of PRMTs has not been well described in vascular and neurological function. Aberrant expression of PRMTs can alter its metabolic products, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). Increased ADMA levels are recognized as an independent risk factor for cardiovascular disease and mortality. Recent studies have provided considerable advances in the development of small-molecule inhibitors of PRMTs to study their function under normal and pathological states. In this review, we aim to elucidate the particular roles of PRMTs in vascular and neuronal function as a potential target for cardiovascular and neurological diseases.

Atherosclerotic cardiovascular diseases (ASCVDs), associated with vascular inflammation and lipid dysregulation, are responsible for high morbidity and mortality rates globally. For ASCVD treatment, cholesterol efflux plays an atheroprotective role in ameliorating inflammation and lipid dysregulation. To develop a multidisciplinary agent for promoting cholesterol efflux, octimibate derivatives were screened and investigated for the expression of ATP-binding cassette transporter A1 (ABCA1). Western blotting and qPCR analysis were conducted to determine the molecular mechanism associated with ABCA1 expression in THP-1 macrophages; results revealed that Oxa17, an octimibate derivative, enhanced ABCA1 expression through liver X receptors alpha (LXRα) activation but not through the microRNA pathway. We also investigated the role of Oxa17 in high-fat diet (HFD)-fed mice used as an in vivo atherosclerosis-prone model. In ldlr-/- mice, Oxa17 increased plasma high-density lipoprotein (HDL) and reduced plaque formation in the aorta. Plaque stability improved via reduction of macrophage accumulation and via narrowing of the necrotic core size under Oxa17 treatment. Our study demonstrates that Oxa17 is a novel and potential agent for ASCVD treatment with atheroprotective and anti-inflammatory properties.

Intermittent hypoxia (IH) has been shown to exert cardioprotective effects against ischemia/reperfusion (I/R) injury through the preservation of ion homeostasis. I/R dramatically elevated cytosolic Zn2+ and caused cardiomyocyte death. However, the role of IH exposure in the relationship between Zn2+ regulation and cardioprotection is still unclear. The aim of the present study was to study whether IH exposure could help in intracellular Zn2+ regulation, hence contributing to cardioprotection against I/R injury. Adult rat cardiomyocytes were exposed to IH (5% O2, 5% CO2 and balanced N2) for 30 min followed by 30 min of normoxia (21% O2, 5% CO2 and balanced N2). Changes in intracellular Zn2+ concentration were determined using a Zn2+-specific fluorescent dye, FluoZin-3 or RhodZin-3. Fluorescence was monitored under an inverted fluorescent or confocal microscope. The results demonstrated that I/R or 2,2′-dithiodipyridine (DTDP), a reactive disulphide compound, induced Zn2+ release from metallothioneins (MTs), subsequently causing cytosolic Zn2+ overload, which in turn increased intracellular Zn2+ entry into the mitochondria via a Ca2+ uniporter, hence inducing mitochondrial membrane potential loss, and eventually led to cell death. However, the cytosolic Zn2+ overload and cell death caused by I/R or DTDP was significantly reduced by treatment of cardiomyocytes with IH. The findings from this study suggest that IH might exert its cardioprotective effect through reducing the I/R-induced cytosolic Zn2+ overload and cell death in cardiomyocytes.

Background/Aims: Intermittent hypoxia (IH) has been shown to exert preconditioning-like cardioprotective effects. It also has been reported that IH preserves intracellular pH (pHi) during ischemia and protects cardiomyocytes against ischemic reperfusion injury. However, the exact mechanism is still unclear. Methods: In this study, we used proton indicator BCECF-AM to analyze the rate of pHi recovery from acidosis in the IH model of rat neonatal cardiomyocytes. Neonatal cardiomyocytes were first treated with repetitive hypoxia-normoxia cycles for 1-4 days. Cells were then acid loaded with NH4Cl, and the rate of pHi recovery from acidosis was measured. Results: We found that the pHi recovery rate from acidosis was much slower in the IH group than in the room air (RA) group. When we treated cardiomyocytes with Na+-H+ exchange (NHE) inhibitors (Amiloride and HOE642) or Na+-free Tyrode solution during the recovery, there was no difference between RA and IH groups. We also found intracellular Na+ concentration ([Na+]i) significantly increased after IH exposure for 4 days. However, the phenomenon could be abolished by pretreatment with ROS inhibitors (SOD and phenanathroline), intracellular calcium chelator or Na+-Ca2+ exchange (NCX) inhibitor. Furthermore, the pHi recovery rate from acidosis became faster in the IH group than in the RA group when inhibition of NCX activity. Conclusions: These results suggest that IH would induce the elevation of ROS production. ROS then activates Ca2+-efflux mode of NCX and results in intracellular Na+ accumulation. The rise of [Na+]i further inhibits the activity of NHE-mediated acid extrusion and retards the rate of pHi recovery from acidosis during IH.

Background/Aims: Intermittent hypoxia (IH) may exert pre-conditioning-like cardioprotective effects and alter Ca2+ regulation; however, the exact mechanism of these effects remains unclear. Thus, we examined Ca2+-handling mechanisms induced by IH in rat neonatal cardiomyocytes. Methods: Cardiomyocytes were exposed to repetitive hypoxia-re-oxygenation cycles for 1-4 days. Mitochondrial reactive oxygen species (ROS) generation was determined by flow cytometry, and intracellular Ca2+ concentrations were measured using a live-cell fluorescence imaging system. Protein kinase C (PKC) isoforms and Ca2+-handling proteins were analysed using immunofluorescence and western blotting. Results: After IH exposure for 4 days, the rate of Ca2+ extrusion from the cytosol to the extracellular milieu during 40-mM KCl-induced Ca2+ mobilization increased significantly, whereas ROS levels increased mildly. IH activated PKC isoforms, which translocated to the membrane from the cytosol, and Na+/Ca2+ exchanger-1, leading to enhanced Ca2+ efflux capacity. Simultaneously, IH increased sarcoplasmic reticulum (SR) Ca2+-ATPase and ryanodine receptor 2 (RyR-2) activities and RyR-2 expression, resulting in improved Ca2+ uptake and release capacity of SR in cardiomyocytes. Conclusions: IH-induced mild elevations in ROS generation can enhance Ca2+ efflux from the cytosol to the extracellular milieu and Ca2+-mediated SR regulation in cardiomyocytes, resulting in enhanced Ca2+-handling ability.

It has been documented that reactive oxygen species (ROS) contribute to oxidative stress, leading to diseases such as ischemic heart disease. Recently, increasing evidence has indicated that short-term intermittent hypoxia (IH), similar to ischemia preconditioning, could yield cardioprotection. However, the underlying mechanism for the IH-induced cardioprotective effect remains unclear. The aim of this study was to determine whether IH exposure can enhance antioxidant capacity, which contributes to cardioprotection against oxidative stress and ischemia/reperfusion (I/R) injury in cardiomyocytes. Primary rat neonatal cardiomyocytes were cultured in IH condition with an oscillating O2 concentration between 20% and 5% every 30 min. An MTT assay was conducted to examine the cell viability. Annexin V-FITC and SYTOX green fluorescent intensity and caspase 3 activity were detected to analyze the cell death. Fluorescent images for DCFDA, Fura-2, Rhod-2, and TMRM were acquired to analyze the ROS, cytosol Ca2+, mitochondrial Ca2+, and mitochondrial membrane potential, respectively. RT-PCR, immunocytofluorescence staining, and antioxidant activity assay were conducted to detect the expression of antioxidant enzymes. Our results show that IH induced slight increases of O2&minus, &middot, and protected cardiomyocytes against H2O2- and I/R-induced cell death. Moreover, H2O2-induced Ca2+ imbalance and mitochondrial membrane depolarization were attenuated by IH, which also reduced the I/R-induced Ca2+ overload. Furthermore, treatment with IH increased the expression of Cu/Zn SOD and Mn SOD, the total antioxidant capacity, and the activity of catalase. Blockade of the IH-increased ROS production abolished the protective effects of IH on the Ca2+ homeostasis and antioxidant defense capacity. Taken together, our findings suggest that IH protected the cardiomyocytes against H2O2- and I/R-induced oxidative stress and cell death through maintaining Ca2+ homeostasis as well as the mitochondrial membrane potential, and upregulation of antioxidant enzymes.

Sleep apnea syndrome, characterized by intermittent hypoxia (IH), is linked with increased oxidative stress. This study investigates the mechanisms underlying IH and the effects of IH-induced oxidative stress on cerebellar astrocytes. Rat primary cerebellar astrocytes were kept in an incubator with an oscillating O2 concentration between 20% and 5% every 30 min for 1–4 days. Although the cell loss increased with the duration, the IH incubation didn’t induce apoptosis or necrosis, but rather a G0/G1 cell cycle arrest of cerebellar astrocytes was noted. ROS accumulation was associated with cell loss during IH. PARP activation, resulting in p21 activation and cyclin D1 degradation was associated with cell cycle G0/G1 arrest of IH-treated cerebellar astrocytes. Our results suggest that IH induces cell loss by enhancing oxidative stress, PARP activation and cell cycle G0/G1 arrest in rat primary cerebellar astrocytes.

Background Episodic cessation of airflow during sleep in patients with sleep apnea syndrome results in intermittent hypoxia (IH). Our aim was to investigate the effects of IH on cerebellar granule cells and to identify the mechanism of IH-induced cell death. Methods Cerebellar granule cells were freshly prepared from neonatal Sprague-Dawley rats. IH was created by culturing the cerebellar granule cells in the incubators with oscillating O2 concentration at 20% and 5% every 30 min for 1-4 days. The results of this study are based on image analysis using a confocal microscope and associated software. Cellular oxidative stress increased with increase in IH. In addition, the occurrence of cell death (apoptosis and necrosis) increased as the duration of IH increased, but decreased in the presence of an iron chelator (phenanthroline) or poly (ADP-ribose) polymerase (PARP) inhibitors [3-aminobenzamide (3-AB) and DPQ]. The fluorescence of caspase-3 remained the same regardless of the duration of IH, and Western blots did not detect activation of caspase-3. However, IH increased the ratio of apoptosis-inducing factor (AIF) translocation to the nucleus, while PARP inhibitors (3-AB) reduced this ratio. Results According to our findings, IH increased oxidative stress and subsequently leading to cell death. This effect was at least partially mediated by PARP activation, resulting in ATP depletion, calpain activation leading to AIF translocation to the nucleus. Conclusions We suggest that IH induces cell death in rat primary cerebellar granule cells by stimulating oxidative stress PARP-mediated calpain and AIF activation.