Rapamycin Inhibits the mTOR/p70S6K Pathway and Attenuates Cardiac Fibrosis in Adriamycin-induced Dilated Cardiomyopathy

BACKGROUND: The objective of the present study was to investigate whether mTOR is involved in cardiac fibrosis evident in dilated cardiomyopathy, and whether rapamycin provides therapeutic potential for cardiac fibrosis. METHODS: Forty-five rats were divided into three groups. Fifteen rats in the Adriamycin group underwent 8 weeks of Adriamycin treatment (2.5 mg/kg, twice per week; i.v.) to induce cardiac fibrosis and dilated cardiomyopathy. Fifteen rats in the rapamycin group received rapamycin (2 mg/kg, per day, orally) and i.v. Adriamycin simultaneously for 8 weeks. Fifteen untreated rats served as controls. Cardiac morphology and function were quantified using echocardiography. mTOR and p70S6K1 mRNA expression were assessed using reverse transcription-PCR. RESULTS: Collagen volume fraction (CVF) was significantly elevated in the adriamycin group (3.36 ± 0.75) compared with controls (1.51 ± 0.31), whereas mTOR and p70S6K mRNA expression were significantly increased in the adriamycin group (0.68 ± 0.03 and 0.69 ± 0.03) compared with controls (0.38 ± 0.03 and 0.34 ± 0.02). The Adriamycin group was associated with cardiac dilation and decreased contractile function. The rapamycin group showed significantly decreased CVF (1.87 ± 0.45), accompanied with a significant decrease in mTOR and p70S6K mRNA expression (0.42 ± 0.05 and 0.45 ± 0.04) relative to the Adriamycin group. In addition, treatment with rapamycin recovered impairments in cardiac morphology and function. CONCLUSION: The mTOR/p70S6K pathway plays an important role in adriamycin-induced cardiac fibrosis resulting from dilated cardiomyopathy. Rapamycin is a potential therapeutic treatment that can be used to attenuate cardiac fibrosis and improve cardiac function.