Hedgehog proteins stimulate chondrogenic cell differentiation and cartilage formation

Sonic hedgehog (Shh) and Indian hedgehog (Ihh) are important regulators of skeletogenesis, but their roles in this complex multistep process are not f ully understood. Recent studies have suggested that the proteins participat e in the differentiation of chondrogenic precursor cells into chondrocytes, In the present study, we have tested this possibility more directly. We fo und that implantation of dermal fibroblasts expressing hedgehog proteins in to nude mice induces ectopic cartilage and bone formation. Immunohistologic al and reverse-transcription polymerase chain reaction (RT-PCR) analyses re vealed that the ectopic tissues derived largely if not exclusively from hos t cells. We found also that treatment of clonal prechondrogenic RMD-1 and A TDC5 cells in culture with Ihh or recombinant amino half of Shh (recombinan t N-terminal portion of Shh [rShh-N]) induced their differentiation into ch ondrocytes, as revealed by cytoarchitectural changes, Alcian blue staining and proteoglycan synthesis. Induction of RMD-1 cell differentiation by kh o r rShh-N was synergistically enhanced by cotreatment with bone morphogeneti c protein 2 (BMP-2) but was blocked by cotreatment with fibroblast growth f actor 2 (FGF-2). Our findings indicate that hedgehog proteins have the abil ity to promote differentiation of chondrogenic precursor cells and that the ir action in this process can be influenced and modified by synergistic or antagonist cofactors.