High‐mobility group box‐1 promotes vascular calcification in diabetic mice via endoplasmic reticulum stress

Abstract Several studies reported the role of endoplasmic reticulum stress (ERS) in vascular calcification. High‐mobility group box‐1 (HMGB‐1) plays a substantial role in diabetes and its complications. However, relatively little information is available regarding the association between HMGB‐1 and calcification, and the underlying mechanism has still remained elusive. Therefore, in the present study, we attempted to indicate whether HMGB‐1 could promote vascular calcification via ERS in diabetes. After induction of diabetes by Streptozotocin (STZ), mice were treated with glycyrrhizin (Gly) or 4‐phenylbutyrate (4‐PBA). Mineral deposition was confirmed by reverse transcription‐polymerase chain reaction (RT‐PCR) and calcium assay. In cell experiments, calcification of vascular smooth muscle cells (VSMCs) was performed with Alizarin Red staining, alkaline phosphatase (ALP) activity and RT‐PCR. Expression and location of HMGB‐1 in aortic tissue were detected by Western blotting, immunocytochemistry (ICC) and immunohistochemistry (IHC). Diabetic mice demonstrated increased HMGB‐1 expression, ERS and vascular calcification. However, inhibition of HMGB‐1 with Gly or inhibition of ERS with 4‐PBA ameliorated the enhanced vascular calcification and ERS in diabetic mice. In vitro experiments unveiled that inhibition of HMGB‐1 attenuated advanced glycation end products (AGEs)‐induced ERS in VSMCs. In addition, AGEs promoted translocation and secretion of HMGB‐1 in VSMCs, which was reversed by 4‐PBA. Moreover, VSMCs exhibited increased mineralization and osteogenic gene expressions in response to HMGB‐1 and AGEs. However, inhibition of ERS with 4‐PBA partially, although noticeably, attenuated VSMC calcification induced by HMGB‐1. Thus, diabetes induced translocation and secretion of HMGB‐1 via ERS, which resulted in calcification in diabetic mice and in AGEs‐treated VSMCs.