Insulin-like Growth Factor 2 (IGF-2) Potentiates BMP-9-Induced Osteogenic Differentiation and Bone Formation

Efficient osteogenic differentiation and bone formation from mesenchymal stem cells (MSCs) should have clinical applications in treating nonunion fracture healing MSCs are adherent bone marrow stromal cells that can self renew and differentiate into osteogenic chondrogenic adipogenic and myogenic lineages We have identified bone morphogenetic protein 9 (BMP-9) as one of the most osteogenic BMPs Here we investigate the effect of insulin like growth factor 2 (IGF 2) on BMP-9 induced bone formation We have found that endogenous IGF 2 expression is low in MSCs Expression of IGF 2 can potentiate BMP 9 induced early osteogenic marker alkaline phosphatase (ALP) activity and the expression of later markers IGF 2 has been shown to augment BMP 9-induced ectopic bone formation in the stem cell implantation assay In perinatal limb explant culture assay IGF 2 enhances BMP 9 induced endochondral ossification whereas IGF-2 itself can promote the expansion of the hypertropic chondrocyte zone of the cultured limb explants Expression of the IGF antagonists IGFBP3 and IGFBP4 leads to inhibition of the IGF 2 effect on BMP 9 induced ALP activity and matrix mineralization Mechanistically IGF 2 is further shown to enhance the BMP-9 induced BMPR Smad reporter activity and Smad1/5/8 nuclear translocation PI3 kinase (PI3K) inhibitor LY294002 abolishes the IGF 2 potentiation effect on BMP-9 mediated osteogenic signaling and can directly inhibit BMP 9 activity These results demonstrate that BMP 9 crosstalks with IGF 2 through PI3K/AKT signaling pathway during osteogenic differentiation of MSCs Taken together our findings suggest that a combination of BMP 9 and IGF 2 may be explored as an effective bone regeneration agent to treat large segmental bony defects nonunion fracture and/or osteoporotic fracture (C) 2010 American Society for Bone and Mineral Research