Fak/src Suppresses Early Chondrogenesis: Central Role of CCN2

Objectives: Adhesive signaling plays a key role in cellular differentiation including chondrogenesis. In this report, we probe the contribution to early chondrogenesis of two key modulators of adhesion, namely FAK/src and CCN2 (Connective tissue growth factor, CTGF).

Methods: We use the established micromass model of early chondrogenesis and gene expression, as well as protein expression assays, such as Real Time Rt-PCR, western blot, immunoflourescence, PNA and Alcian Blue staining.

Results: Our data show that FAK/src signaling, which normally mediates cell/matrix attachment, suppresses chondrogenesis including the induction of Ccn2, Agc and Sox6. Whereas the FAK/src inhibitor PP2 elevates Ccn2, Agc and Sox6 expression in micromass culture, induction of these genes does not occur in the absence of CCN2.

Conclusions: Our results suggest a critical feature permitting chondrogenic differentiation is a reduction in FAK/src signaling, and that CCN2 operates downstream of this loss to promote features of chondrogenesis.

This work was supported by the Canadian Foundation for Innovation, the Arthritis Society, the Canadian Institute of Health Research (CIHR) and the Scleroderma Society. A.L. is an Arthritis Society (Scleroderma Society of Ontario) New Investigator and a recipient of an Early Investigator Award. D.P. was the recipient of an OGSST Graduate Fellowship and a NORTH Summer Undergraduate Dental Student. L.K. is the recipient of a NSERC Graduate Fellowship. L.B. and A.W. were recipients of Canadian Arthritis Network graduate scholarships, A.W. received a Canada Graduate Scholarship from CIHR, and F.B. is a Canada Research Chair.