Intermittent heat stress facilitates the autophagy and apoptosis of the vascular endothelium in spontaneously hypertensive rats via the AMPK/mTOR/ULK1 pathway

This study examined the autophagy and apoptosis of vascular endothelial cells in spontaneously hypertensive rats (SHRs) under intermittent heat stress and determined whether the AMP-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR)/Unc-51 like autophagy activating kinase (ULK1) pathway is involved in autophagy regulation. Wistar-Kyoto (WKY) rats were assigned to control (WKY-CN), intermittent heat stress (WKY-8), and continuous heat stress (WKY-24) groups. SHRs were also assigned to three groups: SHR-CN, SHR-8, and SHR-24. Western blotting assay, immunohistochemical assay, and immunofluorescence assay were performed for observing expression of proteins related to autophagy and apoptosis and the AMPK/mTOR/ULK1 pathway. Vascular endothelial cells underwent autophagy and apoptosis following heat stress, as revealed by high expression of autophagy- and apoptosis-related proteins. Heat stress elevated AMPK and ULK1 expression levels, whereas it decreased mTOR phosphorylation in SHR-8 and SHR-24 groups. Finally, the rats in SHR-8 group were administered an autophagy inducer (rapamycin, Rapa) and inhibitor (3-Methyladenine, 3-MA), respectively, for evaluating autophagy induction and inhibition. Following Rapa administration, LC3-II/LC3-I and Caspase-3 expression levels were elevated in the intermittent heat stress groups as compared to those in the control groups; in contrast, 3-MA attenuated cell death in the intermittent heat stress groups. Overall, this study demonstrated that intermittent heat stress elicits autophagy and apoptosis processes in vascular endothelial cells and that the AMPK/mTOR/ULK1 pathway participates in regulating autophagy and apoptosis.