SMURF1 Affects Dental Implant Integration in Diabetes By Regulating PKG2 Expression.

Background: Poor dental implant has been reported in type II diabetes mellitus (T2DM), which seriously affects the patients' quality of life. The protein kinase type 2 (PKG2) is a target to regulate osteogenic differentiation. We aimed to investigate the effect and mechanisms of SMAD Specific E3 Ubiquitin Protein Ligase 1 (SMURF1, E3 ubiquitin ligase) on bone integration of dental implants in T2DM by regulating PKG2 in a ubiquitination-dependent manner.

Methods: The dental implant model of diabetic rats and the high-glucose-induced bone marrow mesenchymal stem cell (BMSC) model were constructed. The changes in osteogenic differentiation indices were determined by immunohistochemical staining and alizarin red staining. The levels of insulin and glucose tolerance were assessed by glucose and insulin tolerance tests. Hematoxylin-eosin staining was performed to detect alveolar bone inflammation. PKG2, PERK, CHOP, SMURF1, p-PERK, GRP78, and ATF4 levels were examined via quantitative real-time PCR or western blot. The interaction between SMURF1 and PKG2 and PKG2 ubiquitination was analyzed by co-immunoprecipitation.

Results: The T2DM model rats exhibited enhanced glucose tolerance and insulin resistance. PKG2 expression and Runx2 signal were reduced in T2DM rats following the dental implant. After treatment with high glucose in BMSCs, the expression of PKG2 and osteogenic differentiation were reduced. The proteasome inhibitor MG132 recovered PKG2 expression. The reduction of PKG2 was related to ubiquitination. SMURF1 is the key E3 ubiquitin ligase for PKG2. SMURF1 expression was increased in T2DM rats and BMSC cells induced by high glucose. Overexpression SMURF1 was downregulated the expression of PKG2 protein. SMURF1 regulated PKG2 expression via ubiquitination. PKG2 overexpression reversed the inhibition of osteogenic differentiation by SMURF1 overexpression, and inhibits the expression of endoplasmic reticulum stress related proteins. Additionally, these changes caused by SMURF1 overexpression were reversed by cinaciguat (PKG2 generator).

Conclusions: In T2DM, SMURF1 regulated PKG2 expression through ubiquitination, thereby interfering with osteogenic differentiation and affecting the integration of dental transplantation.