Protein Tyrosine Phosphatase (PTP) 1B Inhibition Improves Endoplasmic Reticulum Stress‐Induced Apoptosis in Endothelial Cells
Authors: Agouni Abdelali , Pasha Mazhar , Abdelsalam Shahenda , El Gamal Heba 
Published: June 2021

BackgroundEndoplasmic Reticulum (ER) stress response, which is activated in obesity and diabetes, contributes to the development of endothelial dysfunction in a complex interplay with insulin resistance. Previously, the inhibition of Protein Tyrosine Phosphatase 1B (PTP1B), a negative regulator of insulin receptor anchored to the ER membrane, was found to improved endothelial dysfunction; however, the role of PTP1B in ER stress‐mediated endothelial cell death and dysfunction is not fully understood.MethodsHuman Umbilical Vein Endothelial Cells (HUVECs) were exposed to Thapsigargin (100 nM; 5–24 h), a pharmacological ER stressor, in the presence and absence of PTP1B inhibitor (BML‐267; 20 μM) or PTP1B‐specific siRNA duplexes. Then, we have assessed the expression of ER stress markers [CCAAT‐enhancer‐binding protein homologous protein (CHOP) and Binding immunoglobulin protein (BiP)], angiogenic capacity of cells (Matrigel assay), cell cycle and apoptosis. Furthermore, we evaluated the expression of apoptotic effectors [cleaved caspases 3, 9, 12 and poly ADP ribose polymerase (PARP)‐1] and signaling pathways associated with cellular inflammation, cell survival and apoptosis: c‐Jun N‐terminal kinase (JNK), p42/p44 and p‐38 mitogen activated protein kinase (MAPK) in addition to autophagy (LC3‐II).ResultsOur findings highlighted a protective effect of PTP1B silencing on ER stress‐mediated endothelial cell apoptosis. Exposure of HUVECs with Thapsigargin caused as expected an increase in mRNA and protein expression of ER stress markers; however, the pharmacological inhibition of PTP1B partially prevented these effects. ER stress induction reduced the capacity of HUVECs to form tube‐like structures on a Matrigel matrix, a hallmark of endothelial dysfunction, while cells pre‐treated with PTP1B inhibitor were protected. The blockade of PTP1B using PTP1B inhibitor or specific siRNA, prevented ER stress‐induced apoptosis and cell cycle arrest at the G2/M phase. This focal effect of PTP1B inhibition on apoptosis was associated with reduced expression of cleaved caspases 9 and 12 and PARP‐1. The inhibition of PTP1B caused a concomitant increase in the phosphorylation of pro‐proliferative p42/p44 MPAK and a decrease in that of pro‐apoptotic p‐38 MAPK. Furthermore, the inhibition of PTP1B was associated with suppression of autophagy (low expression of LC3‐II) activated by Thapsigargin.ConclusionOur data bring further insight into the molecular mechanisms underpinning endothelial dysfunction in metabolic disorders such as obesity and diabetes. We specifically harnessed here the critical role of PTP1B, located at the surface of the ER, in ER stress‐mediated cell death and endothelial dysfunction through the activation of a complex signaling pathway involving multiple inflammatory responses including JNK, MPAK and autophagy.Support or Funding InformationThis work was funded by grants QUST‐1‐CPH‐2018‐2, QUST‐2‐CPH‐2017‐18 and QUUGCPH\2017‐1 from Qatar University to Dr. Abdelali Agouni.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.