Both TGF-β1 and Smad4 regulate type I collagen expression in the muscle of grass carp, Ctenopharyngodon idella.

Type I collagen is proven to make an important contribution to fish muscle quality. Our previous study has shown the Smad4-dependent regulation of type I collagen expression in the muscle of crisp grass carp fed with faba bean. However, the regulatory roles of TGF-β1 or TGF-β1/Smad4 on type I collagen remain unclear in ordinary grass carp fed with normal diets or in other fish species. To clarify this point, the effect of TGF-β1 and Smad4 over-expression and RNAi knockdown on type I collagen (COL1-α1 and COL1-α2) expression were tested in vitro (zebrafish ZF4 cells) and in vivo (grass carp) along with the TGF-β1/Smad4 co-expression and co-knockdown. The mRNA levels of TGF-β1, Smad4, and type I collagen were upregulated in the groups with over-expressed TGF-β1 and Smad4 and downregulated in the groups of TGF-β1 and Smad4 RNAi in comparison to controls in vitro (P < 0.05). Similarly, in the in vivo experiment, the mRNA abundance of TGF-β1, Smad4, and type I collagen of over-expression group was higher than the controls at 36 h (P < 0.05). Co-injection of TGF-β1/Smad4 over-expression and RNAi vectors generally showed the higher efficacy. This study revealed that TGF-β1 and Smad4 genes regulated type I collagen expression in grass carp muscle and zebrafish. These findings will provide references for the collagen regulation of other freshwater fishes.