Endoplasmic reticulum stress promotes nuclear translocation of calmodulin, which activates phenotypic switching of vascular smooth muscle cells

• Published in: Biochemical and biophysical research communications 2022-11, Vol.628, p.155-162
• Main Authors: Uchida, Tomoyuki, Oda, Tetsuro, Yamamoto, Takeshi, Inamitsu, Masako, Sakai, Chihiro, Uchinoumi, Hitoshi, Suetomi, Takeshi, Nakamura, Yoshihide, Okamoto, Yoko, Tateda, Satomi, Fujii, Shohei, Tanaka, Shinji, Nawata, Junya, Okamura, Takayuki, Kobayashi, Shigeki, Yano, Masafumi
• Format: Article
• Language: English
• Subjects: Calmodulin; Dantrolene; Endoplasmic reticulum stress; Phenotypic switching; Ryanodine receptor
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2022.08.069

Increased endoplasmic reticulum (ER) stress is strongly associated with the phenotypic switching of vascular smooth muscle cells (VSMCs) in atherosclerosis. Depletion of the ER Ca2+ content is one of the leading causes of increased ER stress in VSMCs. The ryanodine receptor (RyR) is a major Ca2+ release channel in the sarcoplasmic reticulum membrane. Calmodulin (CaM), which binds to RyR (CaM-RyR), stabilizes the closed state of RyR in the resting state in normal cells. Defective CaM-RyR interactions can cause abnormal Ca2+ leakage through RyR, resulting in decreased Ca2+ content, indicating that defective CaM-RyR interactions may be a cause of increased ER stress. Herein, we used a mouse VSMCs to assess whether CaM-RyR plays a pivotal role in VSMCs phenotypic switching, which is caused by ER stress, and whether dantrolene, which enhances the binding affinity of CaM to RyR, affects VSMCs phenotypic switching. Tunicamycin was used to mimic ER stress in vitro. Tunicamycin-induced ER stress caused CaM to dissociate from the RyR and translocate to the nucleus, which stimulated phenotypic switching through the activation of MEF2 and KLF5. Dantrolene suppressed tunicamycin-induced apoptosis, ER stress (restoring ER Ca2+ content), and phenotypic switching of VSMCs. Suramin, which directly unbinds CaM from RyR, promoted nuclear CaM accumulation with parallel VSMCs phenotypic switching, and dantrolene prevented these effects. We observed that ER stress causes CaM translocation to the nucleus and drives the phenotypic switching of VSMCs. Thus, restoration of the binding affinity of CaM to RyR may be a therapeutic target for atherosclerosis. •Tunicamycin-induced ER stress promotes cell death by causing apoptosis, but this tunicamycin-driven apoptosis can be inhibited by dantrolene.•Dantrolene suppresses the expression of GRP78 and CHOP by restoring the ER Ca2+ content.•Tunicamycin-induced ER stress promotes MEF2 and KLF5 expression in the nucleus, which promotes the phenotypic switching of VSMCs, but dantrolene reduces the nuclear MEF2 and KLF5 expressions, suggesting that dantrolene prevents the phenotypic switching of VSMCs.•Tunicamycin-induced ER stress reduces the CaM-RyR binding and accelerates the translocation of CaM to the nucleus.•Direct displacement of CaM from RyR by suramin promotes both the nuclear accumulation of CaM and the nuclear expression of KLF5, leading to the phenotypic switching of VSMCs.•Treatment with dantrolene suppresses the formation of ath