Effect of the secretome of mesenchymal stem cells overexpressing BMP-9 on osteoblast differentiation and bone repair.

The secretome present in the conditioned medium (CM) of mesenchymal stem cells (MSCs) is a promising tool to be used in therapies to promote bone regeneration. Considering the high osteogenic potential of the bone morphogenetic protein 9 (BMP-9), we hypothesized that the secretome of MSCs overexpressing BMP-9 (MSCs BMP-9 ) enhances the osteoblast differentiation of MSCs and the bone formation in calvarial defects. CM of either MSCs BMP-9 (CM-MSCs BMP-9 ) or MSCs without BMP-9 overexpression (CM-MSCs VPR ) were obtained at different periods. As the CM-MSCs BMP-9 generated after 1 h presented the highest BMP-9 concentration, CM-MSCs BMP-9 and CM-MSCs VPR were collected at this time point and used to culture MSCs and to be injected into mouse calvarial defects. The CM-MSCs BMP-9 enhanced the osteoblast differentiation of MSC by upregulating RUNX2, alkaline phosphatase (ALP) and osteopontin protein expression, and ALP activity, compared with CM-MSCs VPR . The CM-MSCs BMP-9 also enhanced the bone repair of mouse calvarial defects, increasing bone volume, bone volume/total volume, bone surface, and trabecular number compared with untreated defects and defects treated with CM-MSCs VPR or even with MSCs BMP-9 themselves. In conclusion, the potential of the MSC BMP-9 -secretome to induce osteoblast differentiation and bone formation shed lights on novel cell-free-based therapies to promote bone regeneration of challenging defects.