Hepatic nephroblastoma overexpressed (NOV/CCN3) in experimental liver fibrosis models

NOV/CCN3 is a matricellular protein of the CCN family, comprising CCN1 (CYR61), CCN2 (CTGF), CCN4 (WISP-1), CCN5 (WISP-2), and CCN6 (WISP-3). CCN proteins are involved in mitosis, adhesion, apoptosis, extracellular matrix production, growth arrest and migration of multiple cell types. Compared with CTGF, NOV has been studied to a lesser degree and its biological role in liver fibrosis remains primarily unknown. We therefore investigated hepatic expression of NOV in chronic liver injury upon long term CCl4 treatment and bile duct ligation (BDL) rat models. NOV gene expression was quantified by TaqMan RT-PCR, immunohistochemistry and ELISA. In both models of chronic liver injury, NOV mRNA showed significant and sustained upregulation. Specifically in BDL models, immunohistochemistry revealed clear expression of NOV protein in portal myofibroblasts, HSC and proliferative bile ducts along the fibrotic septa. Additionally, CCL4 models showed positive staining in particular regenerative hepatocytes. By contrast, TaqMan RT-PCR demonstrated no NOV expression in cultured hepatocytes isolated from naive and CCl4 treated rats. Culture-activated HSC however showed significant upregulation of NOV, reaching the highest levels in MFB.

Upon HSC stimulation with TGF-beta and PDGF isoforms, only PDGF-B and –D (known to induce HSC proliferation) significantly reduced NOV expression in both mRNA and protein levels (Western blot and ELISA) while TGF-beta showed but modest effects. Since NOV forms physiological complexes with fibulin-1 in blood, we set to analyze rat serum NOV through ELISA, finding a serum concentration of 5–10 ng/ml but no significant difference between the control and BDL rats. The indifference found in serum concentration may result from NOV being produced by different organs, specifically adrenal cortex, and secreted into the blood circulation.

Conclusion: NOV appears to play its role in liver fibrogenesis, the functionality of which merits to be further established.