PERK-eIF2α-ATF4-CHOP Signaling Contributes to TNFα-Induced Vascular Calcification

Background-Vascular calcification is a common feature in patients with chronic kidney disease (CKD). CKD increases serum levels of tumor necrosis factor- alpha (TNF alpha), a critical mediator of vascular calcification. However, the molecular mechanism by which TNFa promotes CKD-dependent vascular calcification remains obscure. The purpose of the present study was to investigate whether TNF alpha-induced vascular calcification in CKD is caused by the endoplasmic reticulum response involving protein kinase RNA-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2 alpha (eIF2 alpha), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP). Methods and Results-We examined the effects of TNF alpha on the endoplasmic reticulum (ER) stress response of vascular smooth muscle cells (VSMCs). TNF alpha treatment drastically induced the PERK-eIF2 alpha-ATF4-CHOP axis of the ER stress response in VSMCs. PERK, ATF4, and CHOP shRNA-mediated knockdowns drastically inhibited mineralization and osteogenesis of VSMCs induced by TNF alpha. CKD induced by 5/6 nephrectomies activated the PERK-eIF2 alpha-ATF4-CHOP axis of the ER stress response in the aortas of ApoE(-/-) mice with increased aortic TNFa expression and vascular calcification. Treatment of 5/6 nephrectomized ApoE(-/-) mice with the TNF alpha neutralizing antibody or chemical Chaperones reduced aortic PERK-eIF2 alpha-ATF4-CHOP signaling of the ER stress increased by CKD. This resulted in the inhibition of CKD-dependent vascular calcification. Conclusions-These results suggest that TNF alpha induces the PERK-eIF2 alpha-ATF4-CHOP axis of the ER stress response, leading to CKD-dependent vascular calcification.