Cardiac fibrosis is considered the initial change of diabetic cardiomyopathy (DCM).We have shown that curcumin alleviates collagen deposition in DCM,but the mechanism remains unknown.In this study we sought to investigate the effects of curcumin on cardiac fibrosis in vivo and in vitro and to elucidate the underlying mechanisms.Experimental diabetes was induced in rats by injection of lowdose streptozotocin (STZ) combined with high energy diet.The rats were orally treated with curcumin (300 mg·kg1·d-1) for 16 weeks.Curcumin administration significantly suppressed the deposition of type Ⅰ and type Ⅲ collagens in the heart tissues of diabetic rats,accompanied by markedly reduced TGF-β1 production,suppressed TβR Ⅱ levels and Smad2/3 phosphorylation,and increased Smad7 expression.Similar effects were observed in human cardiac fibroblasts exposed to high glucose (HG,30 mmol/L) or exogenous TGF-β1 (5 ng/mL).Furthermore,TGF-β1 or HG treatment significantly increased the phosphorylation levels of AMPK and p38 MAPK in the fibroblasts.Application of curcumin (25 μmol/L) inhibited TGF-β1-or HG-induced AMPK/p38 MAPK activation and suppressed collagen synthesis in the fibroblasts.These effects were similar to those of the AMPK inhibitor compound C (10 μmol/L) but opposite to the effects of the AMPK activator metformin (2 mmol/L) in the fibroblasts.Our results demonstrate that curcumin suppresses diabetesassociated collagen synthesis in rat myocardium not only by inhibiting TGF-β1 production and canonical Smad signaling but also by blocking the non-canonical AMPK/p38 MAPK pathway.