Prostaglandin F2alpha involves heparan sulfate sugar chains and FGFRs to modulate osteoblast growth and differentiation

The present investigation extends our previous studies on PGF2α-mediated signalling in osteoblast metabolism. In particular, the role of PGF2α as modulator of heparan sulphate proteoglycans (HSPGs), fibroblast growth factor 2 (FGF-2) and fibroblast growth factor receptors (FGFRs) was evaluated. We hereby reported the novel observation that PGF2α was able to promote the formation of HSPGs/FGF-2/FGFRs complexes. Moreover, our data suggested that PGF2α could induce new synthesis of heparan sulphate (HS) chains on osteoblasts by a mechanism involving a modulation of MAPK signalling and that HS is required for the regulation of FGF-2 induced by PGF2α. Indeed, a proteolytic cleavage of HSPGs with heparinase III (Hep III) prior to PGF2α administration down-regulated the basal expression of phospho-p44/42, likely inhibiting FGFRs tyrosine kinase activity. Interestingly, MAPK signalling influenced syntheses and subcellular localization of FGF-2, its specific receptor and HS. In addition, the proteolytic cleavage by Hep III and the MAPK kinase inhibition by PD-98059 also revealed that PGF2α induced cell proliferation is dependent on HSPGs and FGF-2 specific receptor, respectively. Of further relevance of this study, we demonstrated, by using a specific siRNA for FGFR1, that PGF2α modulates Runx2 expression by FGFR1 and HS.