Madecassic Acid protects against hypoxia-induced oxidative stress in retinal microvascular endothelial cells via ROS-mediated endoplasmic reticulum stress

Abstract

Madecassic acid (MA) is an abundant triterpenoid in Centella asiatica (L.) Urban. (Apiaceae) that has been used as a wound-healing, anti-inflammatory and anti-cancer agent. Up to now, the effects of MA against oxidative stress remain unclear. In this study, we investigated the effect of MA and its mechanisms on hypoxia-induced human Retinal Microvascular Endothelial Cells (hRMECs). hRMECs were pre-treated with different concentrations of MA (0-50μM) for 30min before being incubated under hypoxia condition (37°C, 5% CO₂ and 95% N₂). Cell apoptosis was evaluated with MTT assay and TUNEL staining, and the expression of apoptosis- and endoplasmic reticulum (ER) stress-related molecules was assessed with western blotting and RT-PCR analysis. Intracellular ROS level was evaluated using DCFH-DA. Intracellular malondialdehyde (MDA), dehydrogenase (LDH), glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD) were evaluated using related Kits. Activating transcription factor 4 (ATF4) nuclear translocation was assessed with western blotting analysis and immunofluorescence staining. MA significantly reduced oxidative stress in hypoxia-induced hRMECs, as shown by increased cell viability, SOD and GSH-PX leakage, decreased TUNEL- and ROS-positive cell ratio, LDH and MDA leakage, caspase-3 and -9 activity, and Bax/Bcl-2 ratio. In addition, MA also attenuated hypoxia-induced ER stress in hRMECs, as shown by reduced mRNA levels of glucose-regulated protein 78 (GRP78), C/EBP homologous transcription factor (CHOP), protein levels of cleaved activating transcription factor 6 (ATF6) and inositol-requiring kinase/endonuclease 1 alpha (IRE1α), phosphorylation of pancreatic ER stress kinase (PERK) and eukaryotic initiation factor 2 alpha (eIF2α), cleaved caspase-12 and ATF4 translocation to nucleus. The current study indicated that the regulation of oxidative stress and ER stress by MA would be a promising therapy to reverse the process and development of hypoxia-induced hRMECs dysfunction.

Keywords: ATF4; Apoptosis; Endoplasmic reticulum stress; Human retinal microvascular endothelial cells; Madecassic acid; Oxidative stress; ROS.