Enhanced Vascular Calcification and Stiffness in Diabetic Mice with SMC‐specific STIM1 deficiency

Abstract

Vasculopathy is a devastating complication in patients with diabetes mellitus, which increases the risk of morbidity and mortality. Vascular smooth muscle cells (VSMC) are the main vascular cells that regulate vascular tone and contribute predominantly to the development of vasculopathy. We have demonstrated an important role of VSMC in the development of vascular calcification and stiffness in diabetes. The present study investigated the function of stromal interaction molecule 1 (STIM1), an important regulator for intracellular calcium homeostasis, in regulating VSMC calcification in mouse model of diabetes, and uncovered the underlying molecular mechanisms.The effect of SMC‐expressed STIM1 in regulating vascular function in diabetes was determined in a SMC‐specific STIM1‐deficient mouse (STIM1Δ/Δ SMC), generated by breeding SM22α‐Cre mice with STIM1 floxed mice (STIM1f/f). SMC‐specific deletion in the STIM1Δ/Δ SMC mice was confirmed by immunohistochemical staining. Using the low‐dose streptozotocin (STZ)‐induced mouse model of diabetes, we found that SMC‐specific STIM1 deletion did not affect STZ‐induced hyperglycemia in mice. STZ‐induced vascular calcification and stiffness were enhanced in SMC‐specific STIM1 deficient mice comparing with their control littermates (STIM1f/f), which was associated with increased aortic expression of Runx2, the master osteogenic regulator. Furthermore, aortas from the STIM1Δ/Δ SMC mice exhibited increased protein O‐GlcNAcylation, an important post‐translational modulation that we have shown to promote vascular calcification and stiffness. Increased protein O‐GlcNAcylation was also determined in primary VSMC isolated from STIM1Δ/Δ SMC mice compared with those form the control littermates. STIM1 deficiency in VSMC promoted osteogenic differentiation and calcification of VSMC cultured in osteogenic media, which was attenuation by inhibition of protein O‐GlcNAcylation. Osteogenic media‐induced elevation of intracellular calcium flux was demonstrated in the STIM1 deficiency VSMC, which induced endoplasmic reticulum stress and activation of p38 MAPK pathway that contributed to increased O‐GlcNAcylation and VSMC calcification.In summary, our studies have determined a new causative effect of SMC‐expressed STIM1 on diabetic vascular calcification and stiffness, and identified a novel link connecting STIM1 and protein O‐GlcNAcylation in regulating endoplasmic reticulum stress and VSMC calcification.