Differential effects of TGF-β isoforms on murine fetal dural cells and calvarial osteoblasts

Background: Proteins within the transforming growth factor (TGF)-beta family play a central role in both normal and pathologic calvarial morphogenesis. Previous work has suggested differential functions of the TGF-beta isoforms in these processes. Little is known, however, about effects of TGF-beta s on the underlying dura. Furthermore, studies on the effects of TGF-beta isoforms on osteoblasts have been conflicting. The purpose of this study was to determine the effect of TGF-beta isoforms, specifically TGF-beta 1 and TGF-beta 3, on fetal calvarial osteoblast and dural cell differentiation, proliferation, and apoptosis. Methods: Primary cultures of fetal calvarial osteoblasts and dural cells were established from embryonic day-18 CD-I mice. Cells were treated for 48 hours with TGF-beta 1 or TGF-beta 3. Northern blot analysis, cell counts, and apoptosis assays were performed. Results: In dural cells, TGF-beta 1 stimulated the expression of early osteodifierentiation genes and resulted in a slight decrease in cell number and no effect on apoptosis. Similar results were observed in osteoblasts. TGF-beta 3 had little or no effect on the genes studied in both cell types but resulted in increased apoptosis and concomitant decreases in cell number in both cell types. Conclusions: This study demonstrates that dural cells respond to TGF-beta and that this response is isoform-specific. TGF-beta 1 stimulates osteodifferentiation of previously uncommitted cells in the dura. It also stimulates early events in bone matrix deposition and has little effect on late markers of bone differentiation in osteoblasts and dural cells. Both isoforms result in decreases in cell number. TGF-beta 3 results in greater decreases in cell number and isoform-specific stimulation of apoptosis in both dural cells and calvarial osteoblasts.