Alpha-5 Integrin Mediates Simvastatin-Induced Osteogenesis of Bone Marrow Mesenchymal Stem Cells

Simvastatin (SVS) promotes the osteogenic differentiation of mesenchymal stem cells (MSCs) and has been studied for MSC-based bone regeneration. However, the mechanism underlying SVS-induced osteogenesis is not well understood. We hypothesize that α5 integrin mediates SVS-induced osteogenic differentiation. Bone marrow MSCs (BMSCs) derived from BALB/C mice, referred to as D1 cells, were used. Alizarin red S (calcium deposition) and alkaline phosphatase (ALP) staining were used to evaluate SVS-induced osteogenesis of D1 cells. The mRNA expression levels of α5 integrin and osteogenic marker genes (bone morphogenetic protein-2 (BMP-2), runt-related transcription factor 2 (Runx2), collagen type I, ALP and osteocalcin (OC)) were detected using quantitative real-time PCR. Surface-expressed α5 integrin was detected using flow cytometry analysis. Protein expression levels of α5 integrin and phosphorylated focal adhesion kinase (p-FAK), which is downstream of α5 integrin, were detected using Western blotting. siRNA was used to deplete the expression of α5 integrin in D1 cells. The results showed that SVS dose-dependently enhanced the gene expression levels of osteogenic marker genes as well as subsequent ALP activity and calcium deposition in D1 cells. Upregulated p-FAK was accompanied by an increased protein expression level of α5 integrin after SVS treatment. Surface-expressed α5 integrin was also upregulated after SVS treatment. Depletion of α5 integrin expression significantly suppressed SVS-induced osteogenic gene expression levels, ALP activity, and calcium deposition in D1 cells. These results identify a critical role of α5 integrin in SVS-induced osteogenic differentiation of BMSCs, which may suggest a therapeutic strategy to modulate α5 integrin/FAK signaling to promote MSC-based bone regeneration.