TLQP-21 Protects Human Umbilical Vein Endothelial Cells against High-Glucose-Induced Apoptosis by Increasing G6PD Expression

Hyperglycemia causes oxidative stress that could damage vascular endothelial cells, leading to cardiovascular complications. The Vgf gene was identified as a nerve growth factor-responsive gene, and its protein product, VGF, is characterized by the presence of partially cleaved products. One of the VGF-derived peptides is TLQP-21, which is composed of 21 amino acids (residues 556–576). Past studies have reported that TLQP-21 could stimulate insulin secretion in pancreatic cells and protect these cells from apoptosis, which suggests that TLQP-21 has a potential function in diabetes therapy. Here, we explore the protective role of TLQP-21 against the high glucose-mediated injury of vascular endothelial cells. Using human umbilical vascular endothelial cells (HUVECs), we demonstrated that TLQP-21 (10 or 50 nM) dose-dependently prevented apoptosis under high-glucose (30 mmol/L) conditions (the normal glucose concentration is 5.6 mmol/L). TLQP-21 enhanced the expression of NAPDH, resulting in upregulation of glutathione (GSH) and a reduction in the levels of reactive oxygen species (ROS). TLQP-21 also upregulated the expression of glucose-6-phosphate dehydrogenase (G6PD), which is known as the main source of NADPH. Knockdown of G6PD almost completely blocked the increase of NADPH induced by TLQP-21, indicating that TLQP-21 functions mainly through G6PD to promote NADPH generation. In conclusion, TLQP-21 could increase G6PD expression, which in turn may increase the synthesis of NADPH and GSH, thereby partially restoring the redox status of vascular endothelial cells under high glucose injury. We propose tha