Background: Transforming growth factor (TGF)-beta1 has been associated with cranial suture fusion, whereas TGF-beta3 has been associated with suture patency. The mouse posterofrontal suture, analogous to the human metopic suture, fuses through endochondral ossification.
Methods: TGF-beta1 and TGF-beta3 expression in the posterofrontal suture was examined by immunohistochemistry. Next, the authors established cultures of suture-derived mesenchymal cells from the posterofrontal suture and examined the cellular responses to TGF-beta1 and TGF-beta3. Proliferation in response to TGF-beta isoforms was examined by bromodeoxyuridine incorporation. High-density micromass culture of posterofrontal mesenchymal cells was used to study the effect of TGF-beta1 and TGF-beta3 on chondrogenic differentiation.
Results: TGF-beta1 but not TGF-beta3 protein was highly expressed in chondrocytes within the posterofrontal suture. Significant increases in posterofrontal cell proliferation were observed with TGF-beta3 but not TGF-beta1. TGF-beta1 led to significant increases in chondrogenic-specific gene expression (including Sox9, Col II, Aggrecan, and Col X) as compared with moderate effects of TGF-beta3. TGF-beta1 increased cellular adhesion molecule expression (N-cadherin and fibronectin) and promoted cellular condensation, whereas TGF-beta3 increased cellular proliferation (PCNA expression). Finally, TGF-beta1 and, to a lesser extent, TGF-beta3 induced the expression of fibroblast growth factors (FGF-2 and FGF-18).
Conclusions: TGF-beta1 and TGF-beta3 exhibit marked differences in their effects on chondrogenesis in posterfrontal suture-derived mesenchymal cells, influencing different stages of chondrogenic differentiation. TGF-beta3 significantly increased cellular proliferation, whereas TGF-beta1 induced precartilage condensation, promoting chondrocyte differentiation.