Reduction in Disease Progression by Inhibition of Transforming Growth Factor α–CCL2 Signaling in Experimental Posttraumatic Osteoarthritis

Objective. Transforming growth factor alpha (TGF alpha) is increased in osteoarthritic (OA) cartilage in rats and humans and modifies chondrocyte phenotype. CCL2 is increased in OA cartilage and stimulates proteoglycan loss. This study was undertaken to test whether TGF alpha and CCL2 cooperate to promote cartilage degradation and whether inhibiting either reduces disease progression in a rat model of posttraumatic OA. Methods. Microarray analysis was used to profile expression of messenger RNA (mRNA) for Tgfa, Ccl2, and related genes in a rat model of posttraumatic OA. Rat primary chondrocytes and articular cartilage explants were treated with TGF alpha in the presence or absence of MEK-1/ 2, p38, phosphatidylinositol 3-kinase, Rho-associated protein kinase, or CCR2 inhibitors and immunostained for markers of cartilage degradation. The rat model was used to administer pharmacologic inhibitors of TGF alpha (AG1478) and CCL2 (RS504393) signaling for up to 10 weeks and assess histopathology and serum biomarkers of cartilage synthesis (C-propeptide of type II collagen [CPII]) and breakdown (C2C). Results. Tgfa and Ccl2 mRNA were simultaneously up-regulated in articular cartilage in the rat model of posttraumatic OA. TGFa induced expression of CCL2, Mmp3, and Tnf in primary chondrocytes. Cleavage of type II collagen and aggrecan (by matrix metalloproteinases and ADAMTS-4/ 5, respectively) induced by TGF alpha was blocked by pharmacologic inhibition of CCL2 in cartilage explants. In vivo pharmacologic inhibition of TGF alpha or CCL2 signaling reduced Osteoarthritis Research Society International cartilage histopathology scores and increased serum CPII levels, but only TGF alpha inhibition reduced C2C levels intreated versus untreated rat OA cartilage. Conclusion. TGF alpha signaling stimulates cartilage degradation via a CCL2-dependent mechanism, but pharmacologic inhibition of the TGF alpha-CCL2 axis reduces experimental posttraumatic OA progression in vivo.