THE ANTIVIRAL ROLES OF ATG1 IN DROSOPHILA MELANOGASTER: IMMUNE RESPONSES AGAINST DROSOPHILA X VIRUS

Abstract

In mammals, autophagy is important for the immune response against select viruses and is responsible for delivering virus to the lysosome for degradation. In <italic>Drosophila melanogaster</italic>, the roles of autophagy genes in an antiviral immune response are not fully understood. Here we identify a novel antiviral role for <italic>Atg1</italic> in <italic>Drosophila melanogaster</italic> upon infection with <italic>Drosophila</italic> X virus (DXV). Flies with a decreased level of <italic>Atg1</italic> expression in the fat body developed an increased susceptibility to DXV and have a higher viral load compared to wildtype. However, silencing of other autophagy components (<italic>Atg7, Atg8</italic>) does not have the same effect. Moreover, we could find no evidence that classical autophagy is directly associated with DXV upon viral infection. This suggests that the antiviral function of <italic>Atg1</italic> may be independent of classical autophagy. To address this, we examined the effect of <italic>Atg1</italic> knockdown on the fly transcriptome in both DXV infected and uninfected flies. Interestingly, lipid droplet lipolysis and &beta;-oxidation, two major processes responsible for energy production, are induced upon DXV infection. Facilitating lipolysis by knocking down <italic>lsd2</italic>, a positive regulator of lipase bmm, results in

an increased host susceptibility to DXV, together with an increased viral load. In contrast, blocking lipolysis in the negative regulator <italic>lsd1</italic> null mutant renders the host more resistant to the virus. This indicates that the increased energy production favors the virus for active replication and does not favor the elimination of virus. Surprisingly, silencing of <italic>Atg1</italic>, even in the absence of infection, also increases the rates of lipolysis and &beta-oxidation, shown by an increased expression of genes that are involved in lipid metabolism and an decreased lipid droplet size in the <italic>Atg1</italic>-silenced flies. The differences in gene expression and lipid droplet size between <italic>Atg1</italic> RNAi flies and WT flies become more apparent as the infection progresses. In summary, we identify a novel role for <italic>Atg1</italic> in restricting energy production and limiting DXV replication. This finding may shed light on antiviral studies against other dsRNA viruses that manipulate host energy homeostasis. Finally, our data reveal an important and unexpected role for <italic>Atg1</italic> in innate immune antiviral responses independent of autophagy.