The Role Of Lipid Metabolism In Drosophila Innate Immunity

Drosophila relies on a variety of innate immune responses to adapt to the complex external environment,including humoral immunity and cellular immunity.Recognition of bacteria is achieved through the sensing of specific forms of peptidoglycan(PGN),an essential glucopeptidic polymer restricted to the cell wall of both Gram-negative and Grampositive bacteria,by peptidoglycan recognition proteins(PGRPs)to activate the humoral immune system and produce antimicrobial peptides(AMPs)eliminating pathogens.Fat body is one of the important humoral immune organs in the humoral immunity.Cellular immunity mainly includes melanization and phagocytosis to ensure the normal life activities of Drosophila.The methods of infection include intestinal infection and systemic infection.In this paper,using the needle pricking as the screening method to activate the humoral immune system of Drosophila.Then,by recording the mortality rate of Drosophila RNAi different strains after infection,and some new genes related to immunity were quickly and efficiently screened out.From more than 400 experimental screening datas,we found that cytidine diphosphate-diacylglycerol synthetase(CdsA)was knocked down in the fat body of Drosophila,the mortality rate of Pectinobacterium carotovora15(Ecc15)and Enterococcus faecalis(E.faecalis)infection was higher than the control group.CdsA is a very important gene in the process of synthesizing phosphatidylglycerol(PG)and phosphatidylinositol(PI),and it can also convert phosphatidic acid(PA)from synthesizing phospholipids to synthesizing triacylglyceride(TAG).Using qPCR found that:(1)by mutating the transcription factor Relish in the Imd pathway,the infection of Ecc15 after the interference of the Imd pathway will inhibit the expression of CdsA gene in the fat body,so the normal expression of CdsA in the fat body requires Relish;(2)infecting Ecc15 after interfering with the expression of CdsA in the fat body,the mortality rate of Drosophila will increase,and the expression level of the antimicrobial peptide gene Diptericin(Dpt)will decrease;(3)interfering with the expression of CdsA in the fat body,the of Drosophila increases after being infected by E.faecalis,but the expression of the antimicrobial peptide gene Drosomycin(Drs)is normal.It is speculated that the increased mortality rate is not due to the activation of the Toll pathway,but may be due to insufficient phospholipid synthesis.And phospholipids are the main component of cell membranes.The PA in the process of phospholipid synthesis is also an important part of the process of TAG synthesis,so this study further explores whether TAG plays a role in the innate immunity of Drosophila.We also use Ecc15 and E.faecalis to infect related strains of Drosophila,and it was found that Drosophila strains that inhibited the synthesis of TAG and overexpressed the corresponding lipolytic enzyme gene to decompose TAG in the fat body have a lower survival rate after infection with E.faecalis,but the expression level of antimicrobial peptide gene Drs don't change significantly compared with the control group.After,by oil red O staining,we analysis that TAG may help Drosophila innate immune system to resist pathogenic bacteria.In summary,this study has discovered and preliminarily studied the role of lipid metabolism in the innate immunity of Drosophila through genetic screening of Drosophila,laying a foundation for understanding the relationship between lipid metabolism and animal innate immunity in the future.