Smad4-dependent regulation of type I collagen expression in the muscle of grass carp fed with faba bean.

Smad4 is the key regulator in the transforming growth factor β1 (TGF-β1)/Smads signal pathway, and is also the crux of the regulation of type I collagen expression in mammals. In fish, however, the relationship between Smad4 and type I collagen is still unknown. Given the widely accepted importance of type I collagen in fish muscle hardness, we seek to explore this issue by analyzing the expressions of the TGF-β1/Smads pathway molecules and type I collagen in the muscle of crisp grass carp fed with faba bean, which shows increased muscle hardness. The study found that (1) in the process of feeding the grass carp with faba bean, the mRNA and protein expressions of TGF-β1, Smad2 and Smad4 all increased along with the increase of type I collagen expression (Col1α1 and Col1α2); (2) one day after the injection of Smad4 over-expression vector, both mRNA and protein expressions of Col1α1 and Col1α2 significantly increased, reaching the maximum on the 2nd and 5th day, respectively; (3) one day after the injection of Smad4 RNAi interference vector, the mRNA and protein expressions of Col1α1 and Col1α2 decreased, reaching the minimum on the 5th day. These results revealed that Smad4 is the major regulator of type I collagen in the muscle of grass carp fed with faba bean. This study would provide an important mechanistic basis for nutritional regulation of type I collagen in the muscle of fish.