CCN2 induces cellular senescence in fibroblasts

The expression of Ccn2 (CTGF) has been linked to fibrosis in many tissues and pathologies, although its activities in fibroblastic cells and precise mechanism of action in fibrogenesis are still controversial. Here, we showed that CCN2 can induce cellular senescence in fibroblasts both in vitro and in vivo, whereupon senescent cells express an anti-fibrotic "senescence-associated secretory phenotype" (SASP) that includes upregulation of matrix metalloproteinases and downregulation of collagen. Mechanistically, CCN2 induces fibroblast senescence through integrin α₆β₁-mediated accumulation of reactive oxygen species, leading to activation of p53 and induction of p16^INK4a. In cutaneous wound healing, Ccn2 expression is highly elevated only during the initial inflammatory phase and quickly declines thereafter to a low level during the proliferation and maturation phases of healing when myofibroblasts play a major role. Consistent with this expression kinetics, knockdown of Ccn2 has little effect on the rate of wound closure, formation of senescent cells, or collagen content of the wounds. However, application of purified CCN2 protein on cutaneous wounds leads to induction of senescent cells, expression of SASP, and reduction of collagen content. These results show that CCN2 can induce cellular senescence in fibroblasts and is capable of exerting an anti-fibrotic effect in a context-dependent manner.