CCN3 (NOV) Is a Negative Regulator of CCN2 (CTGF) and a Novel Endogenous Inhibitor of the Fibrotic Pathway in an in Vitro Model of Renal Disease

Abstract

Fibrosis is a major cause of end-stage renal disease, and although initiation factors have been elucidated, uncertainty concerning the downstream pathways has hampered the development of anti-fibrotic therapies. CCN2 (CTGF) functions downstream of transforming growth factor (TGF)-beta, driving increased extracellular matrix (ECM) accumulation and fibrosis. We examined the possibility that CCN3 (NOV), another CCN family member with reported biological activities that differ from CCN2, might act as an endogenous negative regulator of ECM and fibrosis. We show that cultured rat mesangial cells express CCN3 mRNA and protein, and that TGF-beta treatment reduced CCN3 expression levels while increasing CCN2 and collagen type I activities. Conversely, either the addition of CCN3 or CCN3 overexpression produced a marked down-regulation of CCN2 followed by virtual blockade of both collagen type I transcription and its accumulation. This finding occurred in both growth-arrested and CCN3-transfected cells under normal growth conditions after TGF-beta treatment. These effects were not attributable to altered cellular proliferation as determined by cell cycle analysis, nor were they attributable to interference of Smad signaling as shown by analysis of phosphorylated Smad3 levels. In conclusion, both CCN2 and CCN3 appear to act in a yin/yang manner to regulate ECM metabolism. CCN3, acting downstream of TGF-beta to block CCN2 and the up-regulation of ECM, may therefore serve to naturally limit fibrosis in vivo and provide opportunities for novel, endogenous-based therapeutic treatments.

Spatial-temporal modulation of CCN proteins during wound healing in human skin in vivo

“…It is interesting to note that, as discussed above for CCN5, a similar CCN2-antagonizing function has been described for CCN3 in murine cartilage (Kawaki et al 2008) and in kidney mesangial cells (Riser et al 2009). Additional experiments will be needed to determine if CCN3 and CCN5 inhibit CCN2 function similarly but at different locations, or if their inhibitory activity is mechanistically different due to their intrinsic structural differences (CCN5 is the only CCN family member that lacks the entire C-terminal module).…”

CCN2 requires TGF-β signalling to regulate CCAAT/enhancer binding proteins and inhibit fat cell differentiation

“…In example, rhTGF-β1, acting through the TGF-β type 1 receptor, has recently been shown to induce CCN1 and CCN2, and in a reciprocal fashion to inhibit CCN3 gene expression in skin fibroblasts (Thompson et al 2014). In some cases differing CCN family members have been shown to have balancing, and antagonistic cell and tissue effects; for example, CCN3 may suppress CCN1 and CCN2-dependent activities (Riser et al 2009;Perbal 2013). We have previously shown that rhTGF-β1 induces CCN2 in adipocyte differentiation (Tan et al 2008).…”

Possible strategies for anti-fibrotic drug intervention in scleroderma

“…Moreover, as some members of the CCN family, notably CCN3 and CCN5 block the fibrogenic action of CCN2, it is possible that CCN3 and CCN5 may be used in the future to treat fibrotic diseases such as SSc (Riser et al 2009;Leask 2009;Yoon et al 2010). …”