Figure 8. CCN2 overexpression reduces cyclic tension stress (CTS)-induced gene expression changes in cultured chondrocytes.

(A) Gene expression analysis of cartilage matrix constituents and proteases of GFP-CCN2 overexpressing rib chondrocytes or mock transfectants after application of cyclic tension stress (CTS) (+). Control cells without CTS (−). Primary cultures of mouse rib chondrocytes overexpressing GFP-CCN2 or GFP as a control were subjected to CTS at 0.5 Hz, with 6% elongation, for 12 hours; and gene expression was then measured by RT-PCR. The expression of transfected Ccn2 was decreased after CTS. The expression of Col2a1, Aggrecan, ColXa1, Col1a1, Mmp13, and Mmp9 genes was stimulated after CTS application to mock cells, but was slightly reduced or remained equal when CTS was applied to CCN2-overexpressing rib chondrocytes after CTS. *: p<0.05 **: p<0.01 ***: p<0.005 (B) Gene expression analysis of cartilage matrix constituents and proteases in cultures of epiphyseal chondrocytes from 6-day-old TG and WT mice, subjected to after CTS as in (A). Contrary to that in rib chondrocytes, the expression of Col2a1 and Aggrecan was decreased when CTS was applied to WT cells. The expression of Col1a1, ColXa1, and Mmp9 genes was stimulated by CTS in WT cells, but down-regulated in the TG chondrocytes. Mmp13 gene was also reduced in the TG chondrocytes by CTS. *: p<0.05 **: p<0.01 ***: p<0.005 (C) Cartilage-specific overexpression of CCN2 under the control of type II collagen promoter alleviated the development of degenerative changes in aging articular cartilage such as decreases in proteoglycan and type II collagen and enhanced expression of type X and I collagens and MMP-13.