Abstract
ABSTRACTLipid droplets (LDs) are lipid-carrying multifunctional organelles, which might also interact with pathogens and influence the host immune response. However, the exact nature of these interactions remains currently unexplored. Here we show that systemic infection of Drosophila adult flies with non-pathogenic Escherichia coli, the extracellular bacterial pathogen Photorhabdus luminescens or the facultative intracellular pathogen Photorhabdus asymbiotica results in intestinal steatosis marked by lipid accumulation in the midgut. Accumulation of LDs in the midgut also correlates with increased whole-body lipid levels characterized by increased expression of genes regulating lipogenesis. The lipid-enriched midgut further displays reduced expression of the enteroendocrine-secreted hormone, Tachykinin. The observed lipid accumulation requires the Gram-negative cell wall pattern recognition molecule, PGRP-LC, but not PGRP-LE, for the humoral immune response. Altogether, our findings indicate that Drosophila LDs are inducible organelles, which can serve as markers for inflammation and, depending on the nature of the challenge, they can dictate the outcome of the infection.
Highlights
Lipid droplets (LDs) are specialized lipid-storing organelles which are found in almost all organisms ranging from bacteria to yeast and humans (Walther and Farese, 2009; Guo et al, 2009; Farese and Walther, 2009)
Infection of Drosophila with P. asymbiotica or P. luminescens resulted in increased mortality with 50% of the infected flies dying by 30 h (P. asymbiotica) and 24 h (P. luminescens) post infection, respectively (Fig. S1)
Peptidoglycan Recognition Proteins (PGRPs)-LE, we found no accumulation of LDs in the midgut of PGRP-LC mutants after infection with E. coli, P. asymbiotica or P. luminescens (Fig. 4D)
Summary
Lipid droplets (LDs) are specialized lipid-storing organelles which are found in almost all organisms ranging from bacteria to yeast and humans (Walther and Farese, 2009; Guo et al, 2009; Farese and Walther, 2009). LDs consist of a fatty acid monolayer and structural proteins surrounding a hydrophobic core of neutral lipids, mainly sterol and triglycerides (TGs) (Walther and Farese, 2009; Guo et al, 2009; Farese and Walther, 2009). LDs were originally shown to play a passive role in lipid homeostasis, they are increasingly perceived as dynamic, multifunctional organelles. Their proteome contains key components that imply interactions with a variety of cell-specialized structures
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