Endoplasmic Reticulum (ER) stress‐generated microparticles self‐perpetuate ER stress and mediate endothelial cell dysfunction independently of cell survival

Abstract

Microparticles (MPs) are nanosized membrane‐shed vesicles released from activated cells. MPs can induce endothelial dysfunction, the first step in atherosclerosis, through endoplasmic reticulum (ER) stress. However, it is not known whether ER stress can lead to MPs release and what biological messages these MPs would carry. Therefore, we aimed to assess the impact of ER stress on MPs shedding from endothelial cells, and to investigate their effects on endothelial function.Human umbilical vein endothelial cells (HUVECs) were treated for 24h with ER stress inducer, thapsigargin, in the presence or absence of 4‐Phenylbutyric acid (PBA), a chemical chaperone to inhibit ER stress. Then, MPs were isolated and used to treat naïve HUVECs (20 g/mL) for 24‐48h before assessing ER‐stress response, autophagy and apoptosis.MPs generated under ER stress conditions did not differ quantitatively from controls; however, they carried deleterious messages for endothelial function. The treatment of naïve HUVECs with ER stress‐generated MPs (48h) increased mRNA and protein expression of key ER stress markers [activating transcription factor (ATF)‐4, and Binding immunoglobulin protein (BiP)], indicating a vicious circle between MPs production and ER stress activation. ER stress‐generated MPs impaired the angiogenic capacity of HUVECs to form tube‐like structures, indicating an impaired endothelial function. However, ER stress‐generated MPs did not affect autophagy (no changes in protein expression of LC3‐II) or apoptosis in HUVECs.Our data show that ER stress activation caused the shedding of MPs, which were capable of activating ER stress in HUVECs in a vicious circle and impaired angiogenic capacity of these cells. These MPs impaired endothelial function in a mechanism independent from cell death and autophagy.Support or Funding InformationThis work was supported by awards from Qatar University (QUUG‐CPH‐CPH‐15/16‐6; QUST‐2‐CPH‐2017‐19; QUST‐1‐CPH‐2018‐1) to Dr Abdelali Agouni. The findings achieved herein are solely the responsibility of the authors.