host-pathogen interaction; intracellular pathogens; antimicrobial activity; lipid droplet; 3D electron cryomicroscopy; correlative light and electron microscopic
Bosch Marta, Sánchez-Álvarez Miguel, Fajardo Alba, Kapetanovic Ronan, Steiner Bernhard, Dutra Filipe, Moreira Luciana, López Juan Antonio, Campo Rocío, Marí Montserrat, Morales-Paytuví Frederic, Tort Olivia, Gubern Albert, Templin Rachel M, Curson James E B, Martel Nick, Català Cristina, Lozano Francisco, Tebar Francesc, Enrich Carlos, Vázquez Jesús, Del Pozo Miguel A, Sweet Matthew J, Bozza Patricia T, Gross Steven P, Parton Robert G, Pol Albert (2020), Mammalian lipid droplets are innate immune hubs integrating cell metabolism and host defense., in Science (New York, N.Y.)
, 370(6514), 1-12.
Parton Robert G., Bosch Marta, Steiner Bernhard, Pol Albert (2020), Novel contact sites between lipid droplets, early endosomes, and the endoplasmic reticulum, in Journal of Lipid Research
Mammalian lipid droplets are innate immune hubs integrating cell metabolism and host defense
||Bosch, Marta; Sánchez-Álvarez, Miguel; Fajardo, Alba; Kapetanovic, Ronan; Steiner, Bernhard; Dutra, Filipe; Moreira, Luciana; López, Juan Antonio; Campo, Rocío; Marí, Montserrat; Morales-Paytuví, Frederic; Tort, Olivia; Gubern, Albert; Templin, Rachel M.; Curson, James E. B.; Martel, Nick; Català, Cristina; Lozano, Francisco; Tebar, Francesc; Enrich, Carlos; Vázquez, Jesús; Del Pozo, Miguel A.; Sweet, Matthew J.; Bozza, Patricia T.; et al.,
|Persistent Identifier (PID)
Research Data Manager (RDM) at The University of Queensland: RGPEM2020-Q1895
Lipid droplets (LDs) are the major lipid storage organelles of eukaryotic cells and a source of nutrients for intracellular pathogens. We demonstrate that mammalian LDs are endowed with a protein-mediated antimicrobial capacity, which is up-regulated by danger signals. In response to lipopolysaccharide (LPS), multiple host defense proteins, including interferon-inducible guanosine triphosphatases and the antimicrobial cathelicidin, assemble into complex clusters on LDs. LPS additionally promotes the physical and functional uncoupling of LDs from mitochondria, reducing fatty acid metabolism while increasing LD-bacterial contacts. Thus, LDs actively participate in mammalian innate immunity at two levels: They are both cell-autonomous organelles that organize and use immune proteins to kill intracellular pathogens as well as central players in the local and systemic metabolic adaptation to infection.
Novel contact sites between lipid droplets, early endosomes, and the endoplasmic reticulum
Lipid droplets (LDs) play a crucial role in the storage and distribution of lipids to control cellular metabolism and bioenergetics (1). How LDs organize the lipid supply to different cellular fates is just starting to be elucidated. Formation of membrane contact sites (MCSs; defined as regions where the two membranes of similar or different organelles are <30 nm from each other) between LDs and target organelles, such as the endoplasmic reticulum (ER) or mitochondria, is emerging as an important mechanism regulating lipid transfer (1, 2). MCSs can ensure timely and local lipid supply, avoiding lipotoxicity and missorting of valuable energetic and metabolic substrates. In support of the biological relevance of these mechanisms, up to 26 different Rab GTPases reside on LDs, representing 20% of the LD proteome (3). Interestingly, a subpopulation of these proteins [e.g., Rab5 (a, b, and c), Rab8 (a and b), Rab11 (a), Rab13, Rab14, Rab15, and Rab21] is also associated with the early endosomal system. Early endosomes (EEs) are the major endocytic compartments mediating sorting of proteins, lipids, and lipoproteins. Early biochemical studies proposed the existence of physical interactions between LDs and EEs (4). The existence of these contacts in mammalian cells has not been further explored. The figure illustrates that EE tubules, defined by the presence of internalized transferrin, interact with LDs in mammalian cells. BHK cells were cotransfected with a plasmid encoding human transferrin receptor (TfR plus plasmid encoding GFP) and then incubated with transferrin-HRP for 30 min at 37°C. Cells were then processed for HRP detection and processed for electron microscopy using a mild fixation/low membrane-contrast staining method to optimize transferrin-HRP visualization. Transferrin-HRP-labeled EE tubules (arrows) were specifically associated with LDs (asterisks) as shown in the low magnification overview (left panel) and at higher magnification in the lower right panel. The two pseudocolored panels show higher magnification views of the neighboring panels, with ER in blue and the LD monolayer in orange; note the tripartite interaction with the EE tubule (EE, arrows). The images clearly demonstrate that LDs can form a distinct MCS with tubules of the EE but also that LD-EE contacts can interact in tripartite fashion with the ER. While hitherto elusive in mammalian cells, the existence and function of three-way contacts between lysosomes, LDs, and ER have been well described in yeast (2). With EEs acting as central hubs in lipid trafficking, these observations provide a new perspective on the complexity of LD interactions in mammalian cells.
Cytosolic lipid droplets (LDs) are storage compartment for neutral lipids in eukaryotic cells and represent an attractive target rich in membrane precursors or nutrients for various intracellular pathogens, including parasites, bacteria and viruses. Recent data suggests that Drosophila LDs attract bacteria and strikingly, this interaction seems to represent a novel and potent form of a cellular antibacterial defense system. I propose that equivalent mechanisms function in mammalian and protozoan cells and I plan to characterize the physiological relevance as well as the ultra-structural and molecular details underlying this previously unexplored antimicrobial mechanism. My research proposal combines LD-purification protocols, bacterial growth assays, correlative light and electron microscopic (CLEM) analyses as well as novel high-resolution 3D imaging techniques, including 3D electron cryomicroscopy (cryo-EM). With these techniques I aim to analyze in real-time the interactions between LDs and bacteria to characterize the protein or lipid components involved in LD-mediated bacterial killing and to quantitate the killing of various (non)-pathogenic bacteria by LDs of eukaryotic cells. This will allow me to gather unique 3D details and volumetric quantifications of the ultra-structure of LD-pathogen contact sites in whole-cells and at a resolution rarely seen yet. My research proposal addresses a new innate defense mechanism, which is conserved in evolution and mediated by LDs. The ultra-structural and molecular insights gained by studying LD-bacterial contact sites have the potential to improve our understanding of the cellular response of host cells towards bacterial infection and have a considerable impact on the fundamental understanding of LD-biology and host-pathogen interactions.