Abstract 1219: The Kruppel-like factor KLF15 inhibits connective tissue growth factor (CTGF) expression in cardiac fibroblasts.
Background: Cardiac hypertrophy and fibrosis characterize adaptive remodeling of the heart in response to hemodynamic or neurohormonal stress. Accumulating evidence implicates connective tissue growth factor (CTGF), expressed in cardiomyocytes and fibroblasts, as a key mediator of cardiac fibrosis. We hypothesized Kruppel-like Factor 15 (KLF15), a transcription factor implicated as a negative regulator of cardiac hypertrophy, may also regulate cardiac fibrosis.
Methods and Results: KLF15 is expressed in cardiac fibroblasts and myocytes in vitro and in vivo. Treatment of neonatal rat ventricular fibroblasts (NRVFs) with pro-fibrotic stimuli such as angiotensin II and transforming growth factor β 1 (TGFβ1) strongly reduced KLF15 expression while inducing the pro-fibrotic factor CTGF. Adenoviral overexpression of KLF15 inhibited basal and TGFβ1-induced CTGF expression in NRVFs and myocytes and also reduced the expression of critical extracellular matrix components collagen III, collagen IV and fibronectin. Furthermore, hearts from KLF15 (−/ −) mice subjected to aortic banding exhibited increased CTGF levels. Trichrome staining also suggested elevated deposition of collagen protein in KLF15 (−/ −) heart in response to mechanical stress. To determine the molecular basis for KLF15’s ability to inhibit CTGF expression, promoter analyses were undertaken. KLF15 inhibited basal and TGFβ1-mediated induction of the CTGF promoter activities. Previous studies indicate that TGFb1-mediated induction of CTGF occurs via Smad3 as well as via the co-activator P/CAF. Using a combination of ChIP and electrophoretic mobility shift assays, we show that that while KLF15 has no significant effect on Smad3 binding to CTGF promoter, it strongly inhibits recruitment of P/CAF to CTGF promoter. Consistently with this observation, KLF15 mediated inhibition of CTGF was rescued by overexpression of P/CAF.
Conclusion: KLF15 is a novel negative regulator of CTGF expression. These data coupled with previous observations from our lab that KLF15 is a negative regulator of hypertrophy support an important role for this factor in adaptive remodeling of the heart in response to injury and stress.