Background: Evidence from animal studies has associated transforming growth factor (TGF)-beta signaling with both normal and premature cranial suture fusion. However, the mechanisms whereby this pleiotropic cytokine mediates suture fusion remain uncertain. The authors established cultures of suture-derived mesenchymal cells from normally fusing (posterofrontal) and patent (sagittal) sutures and examined the in vitro effects of TGF-beta1 on these distinct cell populations.
Methods: Skulls were harvested from 80 5-day-old mice. Posterofrontal and sagittal sutures were dissected, and cultures of suture-derived mesenchymal cells were established. The mitogenic, osteogenic, and chondrogenic effects of recombinant TGF-beta1 were then assessed on posterofrontal and sagittal suture-derived mesenchymal cells (1 to 10 ng/ml). Quantitative real-time polymerase chain reaction was used to examine the effects of TGF-beta1 on gene expression.
Results: TGF-beta1 significantly decreased proliferation of both posterofrontal and sagittal suture-derived mesenchymal cells, by bromodeoxyuridine incorporation assays (n = 6). TGF-beta1 also inhibited osteogenesis in both suture-derived mesenchymal cells determined by alkaline phosphatase activity and mineralization (n = 3 for all assays). During chondrogenic differentiation, TGF-beta1 markedly increased expression of chondrocyte-specific gene markers in posterofrontal suture-derived mesenchymal cells (Sox9, Col II, Aggrecan, and Col X) (p <or= 0.05). In contrast, TGF-beta1 did not increase chondrocyte-specific gene expression in sagittal suture-derived mesenchymal cells (n = 3).
Conclusions: Posterofrontal suture-derived mesenchymal cells retain significant capability for both osteogenic and chondrogenic differentiation in vitro. TGF-beta1 induces in vitro chondrogenesis in posterofrontal but not sagittal suture-derived mesenchymal cells. Future studies will focus on elucidating the mechanisms whereby TGF-beta signaling mediates chondrogenesis in posterofrontal suture-derived mesenchymal cells.