Cardioprotective adaptation to chronic hypoxia stimulates the ROS-dependent/cytosolic phospholipase A2a pathway in rat heart

Abstract

Adaptation to chronic intermittent hypoxia (CIH) is associated with reactive oxygen species (ROS) generation implicated in the cardiac ischemia-resistant phenotype. Phospholipases A2 (PLA2s) belong to ROS-dependent enzymes and are the key enzymes that take part in the repairing and remodeling of the cell membranes. The aim was to study the effect of CIH on PLA2s isoform expression and β-adrenoceptors (β-AR) signaling in the rat heart. Chronic administration of antioxidant tempol was used to verify the ROS involvement in CIH effect on PLA2s expression. Selected proteins were analysed in the left ventricular (LV) myocardium of adult male Wistar rats adapted to CIH (7,000 m, 8h/day, 5 weeks). CIH increased the total cPLA2α protein in cytosol and membranes (by 191% and 38%, respectively) and p-cPLA2α (by 23%) in membranes. On the other hand, both iPLA2 and sPLA2IIA were down-regulated. Tempol treatment prevented only CIH-induced cPLA2α up-regulation and its phosphorylation on Ser505.The total number of β-AR did not change. Nevertheless, the proportion of β2-AR significantly increased from 30% in normoxic LV to 40% in CIH. Concomitantly, the protein abundance of Gi1,2 and Gi3 increased by 39% and 35%, respectively, by CIH, whereas there was no significant change in the expression of the stimulatory Gsα protein; adenylyl cyclase 5/6 was down-regulated. Furthermore, active/phosphorylated forms of upstream cPLA2 activating signaling molecules (PKCα, ERK1/2 and p38) were increased by CIH. The protein level of cyclooxygenase 2 (COX-2) and the concentration of prostaglandin E2 increased by 36% and 84%, respectively. Our results show that CIH diversely affects myocardial PLA2s and suggest that ROS are responsible for the activation of cPLA2α under these conditions. Moreover, CIH enhances β2-AR-Gi signaling which activates the cPLA2α-COX-2 pathway via ERK/p38. Further experiments should assess the potential role of this pathway in the induction of protected phenotype of CIH hearts.