Activation of the Connective Tissue Growth Factor (CTGF)- Transforming Growth Factor

Background: The pro-fibrogenic cytokine connective tissue growth factor (CTGF) plays an important role in the development and progression of fibrosis in many organ systems, including liver. However, its role in the pathogenesis of hepatitis C virus (HCV)-induced liver fibrosis remains unclear. Methods: In the present study, we assessed CTGF expression in HCV-infected hepatocytes using replicon cells containing full-length HCV genotype 1 and the infectious HCV clone JFH1 (HCV genotype 2) by real-time PCR, Western blot analysis and confocal microscopy. We evaluated transforming growth factor b1 (TGF-b1) as a key upstream mediator of CTGF production using neutralizing antibodies and shRNAs. We also determined the signaling molecules involved in CTGF production using various immunological techniques. Results: We demonstrated an enhanced expression of CTGF in two independent models of HCV infection. We also demonstrated that HCV induced CTGF expression in a TGF-b1-dependent manner. Further dissection of the molecular mechanisms revealed that CTGF production was mediated through sequential activation of MAPkinase and Smaddependent pathways. Finally, to determine whether CTGF regulates fibrosis, we showed that shRNA-mediated knock-down of CTGF resulted in reduced expression of fibrotic markers in HCV replicon cells. Conclusion: Our studies demonstrate a central role for CTGF expression in HCV-induced liver fibrosis and highlight the potential value of developing CTGF-based anti-fibrotic therapies to counter HCV-induced liver damage. Citation: Nagaraja T, Chen L, Balasubramanian A, Groopman JE, Ghoshal K, et al. (2012) Activation of the Connective Tissue Growth Factor (CTGF)-Transforming Growth Factor b 1 (TGF-b 1) Axis in Hepatitis C Virus-Expressing Hepatocytes. PLoS ONE 7(10): e46526. doi:10.1371/journal.pone.0046526 Editor: Ashok Chauhan, University of South Carolina School of Medicine, United States of America Received July 29, 2011; Accepted September 5, 2012; Published October 4, 2012 Copyright: 2012 Nagaraja et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by grants National Institutes of Health RO1 HL087576 to RKG, R01AA016003 to DRB and a collaborative seed grant from The Ohio State University’and Nationwide Children’s Hospital, Columbus, OH to RKG and DRB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected] (RKG); [email protected] (ARA); [email protected] (DRB) . These authors contributed equally to this work. " These authors also contributed equally to this work.