Impaired insulin signaling limits osteogenic potential of bone marrow stromal cells in type 2 diabetes

Objective: Type 2 diabetes (T2D) is associated with low bone turnover and increased fracture risk. Although impaired insulin signaling is a hallmark of T2D in classical metabolic tissues, it remains unclear whether similar defects occur in bone-forming cells and contribute to impaired bone formation in T2D. Design: Observational study using primary human bone marrow stromal cells (BMSCs). Methods: Insulin signaling and osteogenic capacity were assessed in BMSCs isolated from 16 adult male and female patients with long-standing T2D. In vitro osteogenic differentiation was quantified by bone alkaline phosphatase activity, and in vivo bone formation rate was assessed in iliac crest bone biopsies. Quantitative phosphoproteomics was performed in BMSCs from patients with T2D and age- and sex-matched healthy controls to define basal and insulin-stimulated signaling responses. Finally, single-cell RNA sequencing was used to characterize cellular distribution of BMSCs, including correlation with fasting insulin levels and HbA1c. Results: Single-cell RNA sequencing identified a BMSC subset enriched for inflammatory genes that correlated with fasting insulin levels. Insulin responsiveness in BMSCs correlated positively with in vitro osteogenic differentiation and in vivo bone formation rate. Phosphoproteomic analyses revealed a shared molecular signature in T2D BMSCs characterized by baseline hyperphosphorylation and attenuated insulin-stimulated canonical Wnt signaling compared with healthy controls. Conclusion: These findings demonstrate impaired insulin signaling in human BMSCs from patients with T2D and link reduced insulin responsiveness to diminished osteogenic potential and bone formation. Disrupted insulin-Wnt pathway signaling in BMSCs may contribute to the low bone turnover phenotype observed in T2D.