Metformin attenuates diabetes-induced osteopenia in rats is associated with down-regulation of the RAGE-JAK2-STAT1 signal axis

Osteopenia and fragile fractures are diabetes-associated complications. Many hypoglycemic drugs have effects on bone metabolism. Metformin, as is a prescribed medication for type 2 diabetes mellitus (T2DM), had been reported to have osteoprotective effects beyond its hypoglycemic effect, however the potential mechanism behind these effects remains unclear. In this study, we aimed to investigate the comprehensive effects of metformin on bone metabolism in T2DM rat model and elucidate the potential mechanism. Goto-Kakizaki spontaneous T2DM rats with significant hyperglycemia were treated with/without metformin for 20 weeks. Glucose tolerance was tested and all rats were weighed every two weeks. The osteoprotective effects of metformin in diabetic rats were determined by quantifying serum bone biomarkers, μ-CT imaging, histological staining, bone histomorphometry, and biomechanical properties analyses. Potential targets of metformin in the treatment of T2DM and osteoporosis were predicted using network pharmacology. The effects of metformin on mesenchymal stem cells (C3H10) cultured in high glucose medium were evaluated by CCK-8 assay, alkaline phosphatase (ALP) staining, qPCR and western blotting. This study demonstrated that metformin significantly attenuated osteopenia, decreased serum glucose and glycated serum protein (GSP) levels, improved bone microarchitecture, and biomechanical properties in GK rats with T2DM. Metformin significantly increased biomarkers of bone formation, and significantly decreased muscle ubiquitin C (Ubc) expression. Network pharmacology analysis found that signal transducer and activator of transcription1 (STAT1) would be a potential target of metformin for regulating bone metabolism. Metformin increased C3H10 ​cell viability in vitro, alleviated ALP inhibition caused by hyperglycemia, increased the osteogenic gene expression of runt-related transcription factor 2 (RUNX2), collagen type I alpha 1 (Col1a1), osteocalcin (OCN), and ALP, while suppressing RAGE and STAT1 expression. Metformin also increased the protein expression of Osterix and decreased that of RAGE, p-JAK2, and p-STAT1. Our results demonstrate that metformin attenuated osteopenia and improved bone microarchitecture in GK rats with T2DM and significantly promoted stem cell osteogenic differentiation under high glucose condition. The effects of metformin on bone metabolism are closely associated with the suppression of RAGE-JAK2-STAT1 signaling axis. Our research provides experiment evidence and potential mechanistic rationale for the use of metformin as an effective candidate for diabetes-induced osteopenia treatment.