Connective Tissue Growth Factor in Meckel's Cartilage Development

Connective tissue growth factor (CTGF) is thought to regulate chondrogenesis in the limb and other sites. In this study, we analyzed whether CTGF is involved in Meckel's cartilage development and what roles it may have. In situ hybridization and immunohistochemistry revealed that CTGF was strongly expressed at the mesenchymal condensation stage, decreased during differentiation of type II collagen positive chondrocytes, and was again increased in chondrocytes at late embryonic stages. At each stage analyzed, strong CTGF expression characterized perichondrium.When mesenchymal cells from E10 mouse first branchyal arch were isolated and micromass-cultured in DMEM containing 10% serum, the cells aggregated and formed CTGF positive cartilage nodules by 4-8 day. Interestingly, when the cells were cultured in the presence of recombinant CTGF at 10, 100 or 1000 ng/ml, a dose dependent increase in cartilage nodule formation was observed. In good agreement, nodule formation was inhibited by treatment with neutralizing CTGF antibodies. To clarify the mechanisms of endogenous CTGF action in nodule formation, mesenchymal cells from first branchyal arch were reared in micromass-culture in DMEM containing 10% serum for 48 hrs and then switched to DMEM containing 0.5 % serum for 24 hrs. The cells were then treated with different concentrations of recombinant CTGF. We found that recombinant CTGF treatment increased fibronectin mRNA levels, a matrix molecule which is known to be up-regulated during chondrogenic cell aggregation and differentiation. The effect was consistent and was similar to seen after treatment with TGF-b. Taken together, our data demonstrate for the first time that CTGF is expressed during Meckel's cartilage development. The possible role CTGF appears to play in this process is to promote mesenchymal cell aggregation via stimulation of fibronectin gene expression and cell-cell interactions. Supported by NIDCR grant RO1DE13206 to E.K.