Phospholipid Scramblase 1 (PLSCR1) Regulates Interferon-Lambda Receptor 1 (IFN-λR1) and IFN-λ Signaling in Influenza A Virus (IAV) Infection.

Phospholipid scramblase 1 (PLSCR1) is an antiviral interferon-stimulated gene (ISG) that has several known anti-influenza functions such as interfering with viral nuclear import, regulating toll-like receptor (TLR) 9 and potentiating the expression of other ISGs. However, the exact mechanisms of anti-flu activity of PLSCR1 in relation to its expression compartment and enzymatic activity, and the molecular and cellular mechanisms involved have not been completely explored. Moreover, only limited animal models have been studied to delineate its role at the tissue level in influenza infections. We hypothesize that PLSCR1 protects hosts against IAV infection by regulating type 3 interferon (IFN-λ) signaling pathways. Our results showed that Plscr1 expression was highly induced by IAV infection and in epithelial cells treated with IFN-λ. We found that knockout (KO) mice exhibited exacerbated body weight loss, decreased survival rates, heightened viral replication, and increased lung damage. Interestingly, transcriptomic analyses demonstrated that Plscr1 was required for type 3 interferon receptor (Ifn-λr1) expression, and impaired expression of Ifn-λr1 and downstream ISGs may be responsible for delayed viral clearance in Plscr1 KO mice. In addition, Plscr1 interacted with Ifn-λr1 within the epithelial compartment following IAV infection, suggesting Plscr1 may modulate IFN-λ signaling via protein-protein interactions. Finally, single-cell RNA sequencing data indicated that expression was significantly upregulated in ciliated airway epithelial cells in mice following IAV infection. Consistently, mice with ciliated epithelial cell-specific Plscr1 overexpression showed reduced susceptibility, less inflammation and enhanced Ifn-λr1 expression in IAV infection. Our research will elucidate virus-host interactions and pave the way for the development of novel anti-influenza drugs that target human elements like PLSCR1, thereby mitigating the emergence of drug-resistant IAV strains.