OBJECTIVEMammalian target of rapamycin (mTOR) plays a central role in controlling cell proliferation, survival and growth. We investigated the role of mTOR signal transduction on viral myocarditis by observing the effect of mTOR inhibitor rapamycin on Smad 3 and collagen type I expression in rat myocardial fibroblasts infected with coxsackievirus B 3 (CVB 3).

METHODSPrimary cultured myocardial fibroblasts of SD rats infected with CVB 3 were treated with or without rapamycin. The Smad 3 and collagen type I expression of the cells were determined by RT-PCR and Western blot.

RESULTS(1) mTOR/beta-actin ratio was dose-dependently reduced (1 nmol/L, 0.381 +/- 0.022; 10 nmol/L, 0.282 +/- 0.014; 100 nmol/L, 0.263 +/- 0.012 vs. control 1.45 +/- 0.04, all P < 0.05 vs. control) after 48 hours rapamycin treatments and time-dependently reduced after 10 nmol/L rapamycin treatment (24 h, 0.203 +/- 0.021; 48 h, 0.163 +/- 0.022; 72 h, 0.144 +/- 0.013 vs. 0 h, 0.341 +/- 0.022, all P < 0.05 vs.0 h) in CVB 3 infected myocardial fibroblasts. (2) Smad 3/beta-actin ratio of myocardial fibroblasts was significantly increased in CVB 3 infected cardial fibroblasts and this increase could be significantly attenuated by rapamycin (control, 0.63 +/- 0.06; CVB 3, 1.18 +/- 0.03; CVB 3 + Rapamycin, 0.77 +/- 0.08 by RT-PCR and 0.89 +/- 0.07, 2.27 +/- 0.13 and 0.131 +/- 0.013 by Western blot). Collagen type I/beta-actin ratio was also significantly increased by CVB 3 and this increase could be reversed by rapamycin (1.13 +/- 0.06, 1.303 +/- 0.012, 0.82 +/- 0.03 by RT-PCR).

CONCLUSIONRapamycin can inhibit the Smad 3 and collagen type I expressions in CVB 3 infected myocardial fibroblasts suggesting that the mTOR signal pathway may play an important role in the pathogenesis of CVB 3 induced myocardial fibrosis.