Abstract
Most diabetic cardiovascular complications are mediated by endothelial dysfunction and impaired angiogenesis. Endoplasmic Reticulum [ER] and oxidative stresses were shown to play a pivotal role in the development of endothelial dysfunction in diabetes. The cytoprotective effects of Hemeoxygenase-1 [HO-1] were extensively studied; however, its role in alleviating ER stress-induced endothelial dysfunction remains elusive. We aim here to test the role of HO-1 against high glucose-mediated ER stress response and endothelial dysfunction and understand the underlying mechanisms with special emphasis on oxidative stress, inflammation and cell death. Primary Human Umbilical Vein Endothelial cells [HUVECs] were harbored in culture medium containing high glucose (33 mM) for 5 days with 8 hrs intermittent recovery periods to mimic the diabetic milieu. Using a wide array of molecular biology techniques, we were able to show that this chronic and intermittent exposure of HUVECs to high glucose significantly increased mRNA and protein expression of key ER stress markers namely, binding immunoglobulin protein [BiP], activation transcription factor-4 [ATF-4], CCAAT-enhancer-binding protein homologous protein [CHOP], and phosphorylated eukaryotic initiation factor2α [p-eIF-2α]. In addition, there was a significant elevation in ROS associated with significant increased phosphorylation of p47phox regulatory subunit of NADPH oxidase [NOX]. Moreover, inflammatory and apoptotic responses were also elicited, featured mainly by significant increase in phosphorylation/activation of IκB kinase [IKK] and c-Jun, and upregulation of IL-6, whereas apoptosis was featured by showing significantly increased caspase3/7 activity and cell death. Vascular endothelial growth factor-A [VEGF-A] expression, Nitric Oxide [NO] production, and tube formation capacity were also significantly inhibited by high glucose. Pre-treatment by HO-1 inducer Cobalt protoporphyrin IX [CoPP] significantly abolished all the observed effects with high glucose. Altogether, to the best of our knowledge, we present for the first time the role of HO-1 induction as a potential antagonist to ER stress response against high glucose mediated endothelial dysfunction and impaired angiogenesis.