Effect of cAMP on TGFβ1-Induced Corneal Keratocyte-Myofibroblast Transformation

PURPOSE. TGF beta is the major mediator to induce myofibroblast differentiation in the corneal wound-healing process. Elevated cAMP can reduce TGF beta-induced fibrosis in other tissues. This study was conducted to determine whether elevated cAMP can inhibit TGF beta 1-induced rabbit corneal keratocyte-myofibroblast transformation. METHODS. Primary isolated rabbit corneal keratocytes were cultured in serum-free medium. The effects of the adenylate cyclase agonist forskolin (FSK; 2 mu M) on TGF beta 1 (5 ng/mL)-induced alpha-smooth muscle actin (alpha-SMA) expression was examined by immunofluorescence, flow cytometry, and immunochemistry 72 hours after treatment. The effects of TGF beta+FSK on activated pSmad3, CREB binding protein (CBP), MAPKs, and RhoA were determined by coimmunoprecipitation and Western blot. RESULTS. FSK significantly reduced the myofibroblast phenotype and alpha-SMA expression induced by TGF beta 1 in rabbit corneal keratocytes. TGF beta 1 increased the phosphorylation of ERK and Smad3. TGF beta 1-induced alpha-SMA expression was reduced by MEK inhibition (U0126); however, the levels of pERK, pSmad3, or the extent of the interaction between pSmad3 and CBP induced by TGF beta 1 were not affected by FSK. TGF beta 1 also activated RhoA and ROCK (Y27632) inhibition reduced alpha-SMA expression. Activation of RhoA was significantly reduced by FSK. CONCLUSIONS. Raising cAMP by FSK treatment inhibits the TGF beta 1-induced corneal myofibroblast transformation and alpha-SMA expression and thereby provides a promising method to control corneal fibrosis. The data suggest that cAMP-dependent inhibition does not occur by altering Smads or MAPK signaling, but possibly by reducing the activation of RhoA. (Invest Ophthalmol Vis Sci. 2009;50:626-633) DOI:10.1167/iovs.08-2444