Cell-to-cell communication is essential for coordination of biological processes such as viral infections, and this is often facilitated by the exchange of small particles. Lipid enclosed particles, including extracellular vesicles (EVs), mediate intercellular communication through transfer of their cargo and are actively explored for their role in various diseases and potential therapeutic and diagnostic applications. Our lab has shown that lipid droplets (LDs) are integral intracellular organelles in the early host response and are required for an efficient interferon response.
We can now show that LDs leave cells in vitro and can directly influence the antiviral response of neighboring cells against ZIKV. To elucidate LD transport mechanisms, we mined published databases to reveal an overlap of up to 96% in the proteomes of EVs and LDs, with both groups sharing proteins involved in biogenesis, cargo recruitment and transport. To understand if LDs are utilising EV secretion pathways, proteomic comparative analysis using a primary immortalised astrocyte model was performed before and following ZIKV infection (24 hpi). Western blot and super resolution microscopy were used to confirm protein targets. There was approximately a 75% proteome overlap; with 48 of the 50 common EV protein markers present in varying abundances in astrocyte EVs also observed in their LD proteome. Notably, proteins involved in EV secretion pathways (ESCRT), ALIX and TSG101 were found to be localised to LDs with an increased association during ZIKV infection.
To date, there has been no studies investigating the similarities of protein cargo between LDs and EVs and their potential interactions, and we believe this will be important in determining the antiviral mechanisms of LDs. Here, we have demonstrated for the first time that LDs carry proteins involved in EV biogenesis and release which may allude to their transport between cells.