Contribution of Lipid Droplet Breakdown to Coxiella Burnetii Infection
Coxiella burnetii is an obligate intracellular bacterium and causative agent of culture-negative endocarditis. Although Coxiella initially infects alveolar macrophages, it is found in lipid droplet (LD)-containing foamy macrophages in endocarditis patients. LDs are host lipid storage organelles containing cholesterol esters (CE) and triacylglycerols (TAG). Our previous studies show that Coxiella actively manipulates host LD metabolism via its Type 4 Secretion System (T4SS), which secretes bacterial effectors in the host cell cytoplasm to manipulate cellular processes. Further, specifically blocking adipose triglyceride lipase (ATGL)-mediated LD breakdown inhibits Coxiella growth suggesting importance of LD-derived lipids for bacterial growth. However, how Coxiella regulates LD breakdown and the composition of LD-derived lipids is unknown. Our preliminary fluorescence microscopy studies using CRISPR knockouts and LD inhibitors indicate presence of TAG-rich LDs in Coxiella-infected cells. ATGL-mediated breakdown of TAG-rich LDs releases arachidonic acids, precursors for lipid immune mediators important for immunomodulation during bacterial infections. Hence we hypothesize that Coxiella manipulates ATGL via its T4SS to initiate TAG-rich LD breakdown and subsequently modulate the immune response to promote bacterial survival. To test this hypothesis, we analyzed ATGL gene expression in differentially infected cells using qRT-PCR. Compared to uninfected and T4SS-infected cells, Coxiella infection increased ATGL expression indicating T4SS-dependent regulation of ATGL. Ongoing studies are elucidating the Coxiella T4SS-ATGL interaction. To identify cellular CE and TAG levels and the breakdown products at different times post-infection, we are performing thin layer chromatography (TLC). Completion of our studies will identify the LD breakdown-derived lipids and how Coxiella regulates LD breakdown of to promote its intracellular survival.
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"Contribution of Lipid Droplet Breakdown to Coxiella Burnetii Infection" (2018). MU-COM Research Day. 85.