3β-hydroxysteroid-Δ24 reductase integrates cholesterol metabolism and innate immune to promote PRRSV replication

Cholesterol metabolism is a strategy used by PRRSV to inhibit host antiviral innate immunity. However, the key enzymes or the natural products and mechanisms involved have not been well elucidated. Here, we show that PRRSV infection upregulated DHCR24, the rate-limiting enzyme in the cholesterol synthesis pathway, to increase virus proliferation. We further elucidated that PRRSV Nsp4 interacts with the FAD domain of DHCR24, promoting its expression and increasing cellular cholesterol levels. In addition, U18666A treatment inhibited DHCR24 enzyme activity, significantly reduced cell cholesterol content and PRRSV replication, and exogenous cholesterol supplementation could rescued this effect. We also found that DHCR24 is a negative regulator of type I interferon (IFN-I) production upon viral infection. Mechanistically, DHCR24 interacts with TBK1 and disrupts the interaction of TBK1-IRF3, thereby inhibiting IRF3 phosphorylation and nuclear translocation. Taken together, these findings elucidate that DHCR24 is utilized by PRRSV to regulate host cholesterol content, inhibit the innate immune response, and promote virus proliferation.