Transforming growth factor-beta promotes recruitment of bone marrow cells and bone marrow-derived mesenchymal stem cells through stimulation of MCP-1 production in vascular smooth muscle cells.

Bone marrow-derived progenitor cells have recently been shown to be involved in the development of intimal hyperplasia after vascular injury. Transforming growth factor-beta (TGF-beta) has profound stimulatory effects on intimal hyperplasia, but it is unknown whether these effects involve progenitor cell recruitment. In this study we found that although TGF-beta had no direct effect on progenitor cell recruitment, conditioned media derived from vascular smooth muscle cells (VSMC) stimulated with TGF-beta induced migration of both total bone marrow (BM) cells and BM-mesenchymal stem cells (MSC) and also induced MSC differentiation into smooth muscle like cells. Furthermore, overexpression of the signaling molecule Smad3 in VSMC via adenovirus-mediated gene transfer (AdSmad3) enhanced the TGF-beta's chemotactic effect. Microarray analysis of VSMC stimulated by TGF-beta/AdSmad3 revealed monocyte chemoattractant protein-1 (MCP-1) as a likely factor responsible for progenitor cell recruitment. We then demonstrated that TGF-beta through Smad3 phosphorylation induced a robust expression of MCP-1 in VSMC. Recombinant MCP-1 mimicked the stimulatory effect of conditioned media on BM and MSC migration. In the rat carotid injury model, Smad3 overexpression significantly increased MCP-1 expression after vascular injury, consistent with our in vitro results. Interestingly, TGF-beta/Smad3-induced MCP-1 was completely blocked by both Ro-32-0432 and rotterlin, suggesting protein kinase C-delta (PKCdelta) may play a role in TGF-beta/Smad3-induced MCP-1 expression. In summary, our data demonstrate that TGF-beta, through Smad3 and PKCdelta, stimulates VSMC production of MCP-1, which is a chemoattractant for bone marrow-derived cells, specifically MSC. Manipulation of this signaling system may provide a novel approach to inhibition of intimal hyperplasia.