Connective Tissue Growth Factor Promotes Fibrosis Downstream of TGFβ and IL-6 in Chronic Cardiac Allograft Rejection

Cardiac transplantation is an effective treatment for multiple types of heart failure refractive to therapy. Although immunosuppressive therapeutics have increased survival rates within the first year posttransplant, chronic rejection (CR) remains a significant barrier to long-term graft survival. Indicators of CR include patchy interstitial fibrosis, vascular occlusion and progressive loss of graft function. Multiple factors have been implicated in the onset and progression of CR, including TGF beta, IL-6 and connective tissue growth factor (CTGF). While associated with CR, the role of CTGF in CR and the factors necessary for CTGF induction in vivo are not understood. To this end, we utilized forced expression and neutralizing antibody approaches. Transduction of allografts with CTGF significantly increased fibrotic tissue development, though not to levels observed with TGF beta transduction. Further, intragraft CTGF expression was inhibited by IL-6 neutralization whereas TGF beta expression remained unchanged, indicating that IL-6 effects may potentiate TGF beta-mediated induction of CTGF. Finally, neutralizing CTGF significantly reduced graft fibrosis without reducing TGF beta and IL-6 expression levels. These findings indicate that CTGF functions as a downstream mediator of fibrosis in CR, and that CTGF neutralization may ameliorate fibrosis and hypertrophy associated with CR.