Parathyroid hormone-induced vascular smooth muscle cells calcification by endoplasmic reticulum stress

Vascular smooth muscle cells (VSMCs) play a key role in vascular calcification, which is associated with enhanced mortality in chronic kidney disease. To ascertain the concentration of parathyroid hormone (PTH) that induces apoptosis of VSMCs and to explore whether the mechanism of endoplasmic reticulum (ER) stress is involved in PTH-induced calcification of VSMCs. The appropriate concentration and intervention time of PTH-inducing apoptosis of VSMCs were screened by flow cytometry. To investigate the effects of PTH on ER stress-related and apoptotic proteins in VSMCs, they were divided into four groups. These were the control group, the PTH group, the siC/EBP homologous protein (CHOP) + PTH group (in which siCHOP was used to knockdown the expression of CHOP at first), and the sp600125 + PTH group (in which the cells were pretreated with sp600125 at a concentration of 10 ng/ml for 24 h at first). Then, all groups except the control group were given 1x10^-6 mol/L PTH to stimulate VSMCs. The changes in ER stress and apoptosis-related proteins in each group were detected, and the cell calcification was tested by Alizarin Red staining. Flow cytometry showed that the concentration of 1x10^-6 mol/L PTH induced apoptosis most significantly. The apoptosis rate of the cells increased with the extension of stimulation time. The apoptosis of VSMCs pretreated with the Jun-N-terminal kinase (JNK) antagonist sp600125 was significantly reduced. The expression of cleaved caspase-3, PERK, IRE1, and CHOP was detected by Western blot analysis when cells were stimulated with 10^-6 mol/L PTH for 14 days. After the knockdown of the CHOP expression by siCHOP, cleaved caspase-3 expression was significantly reduced. Alizarin Red staining showed siCHOP and sp600125 inhibits the VSMCs' calcification induced by PTH. In conclusion: the ER stress mechanism is involved in VSMCs' calcification induced by PTH.