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

Abstract 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 (MSCsBMP‐9) enhances the osteoblast differentiation of MSCs and the bone formation in calvarial defects. CM of either MSCsBMP‐9 (CM‐MSCsBMP‐9) or MSCs without BMP‐9 overexpression (CM‐MSCsVPR) were obtained at different periods. As the CM‐MSCsBMP‐9 generated after 1 h presented the highest BMP‐9 concentration, CM‐MSCsBMP‐9 and CM‐MSCsVPR were collected at this time point and used to culture MSCs and to be injected into mouse calvarial defects. The CM‐MSCsBMP‐9 enhanced the osteoblast differentiation of MSC by upregulating RUNX2, alkaline phosphatase (ALP) and osteopontin protein expression, and ALP activity, compared with CM‐MSCsVPR. The CM‐MSCsBMP‐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‐MSCsVPR or even with MSCsBMP‐9 themselves. In conclusion, the potential of the MSCBMP‐9‐secretome to induce osteoblast differentiation and bone formation shed lights on novel cell‐free‐based therapies to promote bone regeneration of challenging defects.