Sphingolipids and Innate Immunity - SUMMARY Type I interferon (IFN) is the first line of defense in innate antiviral immunity, orchestrating transcriptional and metabolic responses that restrict viral replication. While IFN signaling is known to modulate sterol and glycerolipid pathways, its impact on sphingolipids (SPLs)—a class of bioactive lipids involved in immune signaling and cell stress responses—remains poorly understood. Mounting evidence suggests that infections by RNA viruses, including flaviviruses and coronaviruses, induce the accumulation of ceramide (Cer), but whether this promotes viral replication or enhances antiviral defenses is unclear. Our preliminary studies show that Zika virus (ZIKV) triggers overall changes in SPL composition and relies on Cer biosynthesis for successful infection. However, other studies implicate Cer in restricting viral replication and promoting cell survival, raising the possibility that these lipids are upregulated by the host response rather than the virus. The central goal of this proposal is to uncover how type I IFN affects SPL metabolism and to determine whether these lipids, in turn, control the IFN response and infection outcomes. We hypothesize that SPLs, particularly Cer, play a dual role in infection and immunity. Viruses may induce Cer to suppress innate immune responses, including IFN production, as suggested by the known roles of Cer in modulating host signaling pathways. However, we also propose that IFN itself alters SPL metabolism, as it does with other lipid classes, and that these IFN-induced lipid changes may contribute to antiviral defense. To disentangle these possibilities, we will use a combination of untargeted lipidomics, innovative SPL probes, CRISPR gene editing, and organelle-targeted lipid perturbation to systematically determine the causes and consequences of SPL dysregulation in infection. Aim 1 will define how IFN-β alters SPL content and distribution in infected and uninfected cells. In doing so, we will generate the first comprehensive map of IFN-driven changes in the cellular lipidome—including SPLs—across multiple cell types, providing a foundational resource for the broader virology and immunometabolism communities. Aim 2 will determine whether Cer regulates IFN-β signaling and antiviral defense, and whether the subcellular location of Cer influences its role as a pro- or anti-viral signal. Together, these studies will determine how IFN shapes and is shaped by SPLs, providing fundamental insight into the role of these lipids in the earliest steps of antiviral innate immunity.
