Viperin suppresses goose astrovirus type 2 replication through inhibition of viral RdRP activity

Goose astrovirus 2 (GAstV-2) infection induces visceral gout in goslings, resulting in high mortality rates in birds aged 3 to 15 days. Despite extensive research since the virus was first identified in 2018, the innate immune defense mechanisms of the host against GAstV-2 remain incompletely characterized, impeding the development of effective vaccines and therapeutics. Here, we demonstrated that GAstV-2 infection upregulated Viperin expression both in vitro and in vivo, suggesting a potential role for Viperin as a host restriction factor. Further studies revealed that the P2 domain of viral ORF2 contributed to stimulate Viperin. Overexpression and knockdown experiments confirmed that Viperin exerts antiviral activity against GAstV-2. However, Viperin did not affect attachment or internalization. Mechanistic studies revealed that Viperin inhibits GAstV-2 by attenuating viral RNA-dependent RNA polymerase (RdRp) activity in a manner dependent on its S-adenosylmethionine (SAM) domain. The SAM domain was found to promote the production of ddhCTP, which correlated with reduced RdRp activity and suppression of viral replication. Furthermore, intramuscular administration of ddhCTP reduced mortality and viral loads, and ameliorated GAstV-2-induced pathological injury in the kidney, spleen, and liver of goslings. Collectively, these findings identify Viperin as a key host restriction factor against GAstV-2 and highlight its potential as a target for antiviral strategies.