Smad3 gene C-terminal phosphorylation site mutation aggravates CCl₄ -induced inflammation in mice

The expression of C-terminal phosphorylated Smad3 (pSmad3C) is down-regulated with the progression of liver disease. Thus, we hypothesized that pSmad3C expression may be negatively related to liver disease. To develop novel therapeutic strategies, a suitable animal model is required that will allow researchers to study the effect of Smad3 domain-specific phosphorylation on liver disease progression. The current study aimed to construct a new mouse model with the Smad3 C-terminal phosphorylation site mutation and to explore the effects of this mutation on CCl₄ -induced inflammation. Smad3 C-terminal phosphorylation site mutant mice were generated using TetraOne™ gene fixed-point knock-in technology and embryonic stem cell microinjection. Resulting mice were identified by genotyping, and the effects on inflammation were explored in the presence or absence of CCl₄ . No homozygous mice were born, indicating that the mutation is embryonic lethal. There was no significant difference in liver phenotype and growth between the wild-type (WT) and heterozygous (HT) mice in the absence of reagent stimulation. After CCl₄ -induced acute and chronic liver damage, liver pathology, serum transaminase (ALT/AST) expression and levels of inflammatory factors (IL-6/TNF-α) were more severely altered in HT mice than in WT mice. Furthermore, pSmad3C protein levels were lower in liver tissue from HT mice. These results suggest that Smad3 C-terminal phosphorylation may have a protective effect during the early stages of liver injury. In summary, we have generated a new animal model that will be a novel tool for future research on the effects of Smad3 domain-specific phosphorylation on liver disease progression.