We have previously demonstrated that lipid droplets (LDs) are upregulated as a host repose to viral infections of IAV, ZIKV, DENV and HSV-1 both in vitro and in vivo, and this upregulation of LDs helps drive an effective interferon response. However, the mechanism by which they do this, and their role during a host antiviral repose has not been examined.
Microscopic examination of LDs very early following activation of antiviral signaling pathways showed a significant upregulation in both LD velocity and distance traveled, as well as displayed directional movement of LDs. As LDs are known to interact with other organelles, and transfer both lipid species and protein cargo, we developed techniques to determine the changing lipidome and protein landscape of LDs at early time points following activation of both dsRNA and dsDNA signalling pathways. Lipidome analysis revealed limited alterations in the cellular lysates at early time points, in direct contrast to the significant changes observed in multiple major lipid species within LDs themselves. Additionally, an upregulation of long chain fatty acids was also observed in virally driven LDs. Proteomics analysis demonstrated a significant upregulation of 83 proteins, including multiple antiviral proteins, and members of the early innate antiviral signaling pathways, demonstrating for the first time that the lipid droplet may act as a signaling platform during an effective antiviral response.
We believe that LDs play vital roles in facilitating the magnitude of the early anti-viral immune response, in particular the production of IFN following viral infection, and control of viral replication. Here we characterise for the first time that the lipidome and proteome of LDs changes during an early antiviral response. This data represents a paradigm shift in our understanding of the molecular mechanisms which coordinate an effective antiviral response by implicating LDs as a critical signaling organelle.