Effect of advanced glycation end product on paraoxonase 2 expression: Its impact on endoplasmic reticulum stress and inflammation in HUVECs

Background: Paraoxonase (PON), an antioxidant enzyme, comprises of three members (PON1, 2 and 3). Hyperglycemia accelerates formation of AGE in diabetes which mediates endothelial dysfunction. PON1 is studied in diabetes due to its association with HDL, lipid peroxidation and vascular complications but PON2 is not explored much. Recently decreased PON2 activity is reported in monocytes of Type 2 diabetes mellitus (T2DM) patients but its regulation by factors like high glucose and AGE has not been studied. Aim: The aim of the current study is to identify the effect of AGEs on PON2 expression and activity and its implications on endothelial dysfunction in HUVECs. Main methods: HUVECs were exposed to Glycated albumin (GA)/Carboxymethyl lysine (CML) for 24 h to check for PON2 expression. The ER stress markers GRP78 and IRE1 alpha, pro-inflammatory genes MCP-1, IL-6, IL-8, ICAM1, VCAM1 were assessed by qPCR, western blotting/ELISA. Endothelial-leukocyte adhesion and ROS were assessed using Calcein AM and DCFDA method. One-way ANOVA and student's t-test was done using Graphpad Prism. Key findings: AGE exposure significantly decreased PON2 expression and activity with increased oxidative stress, ER stress and inflammation. PON2 overexpression significantly reduced ROS, ER stress and inflammation as well as inhibited NF kappa B, and ERK1/2, phosphorylation induced by GA/CML treatment. Concomitantly, silencing of PON2 accelerated AGEs induced effects. Significance: This is the first study to show that both GA and CML down regulates the PON2 expression and activity in HUVECs and over expression of PON2 alleviates AGEs induced endothelial dysfunction.