Caroline Barisch, PhD
phone +49 (0)541 969 7232
Molecular Infection Biology
Mykobakteria and Lipids
Tuberculosis (Tb) is caused by Mycobacterium tuberculosis (Mtb) and remains one of the deadliest infectious diseases. The World Health Organization (WHO) estimates that in 2016, Tb killed 1.6 million people emphasizing the importance to develop new drugs, vaccines and diagnostic tools to reduce this burden in the future.
There is an increasing body of literature demonstrating that pathogenic mycobacteria are especially dependent on the lipids of their host. This importance is highlighted by the fact that mycobacteria use fatty acids released from host lipids and sterols as sole nutrient and energy source during infection. However, central mechanisms by which pathogenic mycobacteria exploit host lipids are still poorly understood.
My lab uses the Dictyostelium discoideum/Mycobacterium marinum system to identify the molecular mechanisms by which mycobacteria exploit host lipids.
During infection, M. marinum acquires Dictyostelium TAGs by hijacking lipid droplets (LDs). Shortly after bacteria uptake LDs are transferred to the mycobacterium-containing vacuole (MCV), eventually leading to an accumulation of neutral lipids inside the bacteria-containing compartment at later infection stages and to the formation of intracytosolic lipid inclusions (ILIs) inside M. marinum (Fig. 1A and B). Importantly, the acquisition of LDs is not the only route by which host lipids are transferred to vacuolar bacteria, since M. marinum also exploits host phospholipids.
Figure 1. ILI formation in M. marinum during infection. LDs are transferred to the MCV leading to the accumulation of ILIs in M. marinum (A). ILIs (stained by Bodipy 493/503) are formed when Dictyostelium is cultured in FA-supplemented medium before infection (B). From Barisch et al., 2015.
Characterization of the lipid flow from Dictyostelium to M. marinum
In my lab we will launch a first systematic effort to unravel the molecular mechanisms by which mycobacteria acquire and exploit host lipids using the Dictyostelium/Mycobacterium marinum infection model (Fig. 2).
Figure 2. Lipid flow from Dictyostelium to M. marinum.
In addition to known the lipid species (TAGs, sterols and phospholipids) mycobacteria probably manipulate other lipid species such as sphingolipids and ceramides. These lipids are used by intracellular mycobacteria to gain and save energy but also as building blocks for membrane lipids with a role in bacteria virulence (black arrow in Fig. 2 above). On the other hand, mycobacteria are also known to share their lipids with the host (red arrow in Fig. 2).
We will chart the lipid flows between mycobacteria and their host that are potentially relevant for infection and identify lipid species acquired by intracellular mycobacteria using metabolic tracing studies and mass spectrometry lipidomics.
In addition, we will monitor the presence of lipid metabolic enzymes and lipid transfer proteins at the MCV and in the vicinity of cytosolic bacteria (Fig. 3).
Figure 3. Localization of lipid-synthesizing enzymes during infection. Dgat2-decorated LDs (green) stick to cytosolic bacteria (red). From Barisch and Soldati, 2017.
In the future, we plan to disrupt lipid flows from the host to the pathogen during infection using genetics or drugs. With the help of fluorescent and clickable lipid probes, we will first analyze the impact of these disruptions on host-to-pathogen lipid flows (Fig. 4).
Finally, we will determine the consequences of blocking specific lipid supply routes on various stages of the mycobacterial infection course. Collectively, these efforts may uncover novel therapeutic targets to fight mycobacteria infection.
Video clip (French) on Radio Television Suisse: https://avisdexperts.ch/experts/caroline_barisch
Figure 4. Visualization of the lipid dynamics during infection. Bottom right: Fluctuations of PI(3,4,5)P3 / PI(3,4)P2 (green) at the MCV of non-pathogenic mycobacteria (red). Left: Topfluor-LysoPC-tagged host lipids (green) first label the membrane of the MCV at early infection stages and are finally found inside the bacteria (red) at later stages. From Barisch and Soldati, 2017. Center: Thin layer chromatography showing that M. marinum incorporates fatty acids released from host phospholipids into TAGs. From Barisch and Soldati, 2017.
- *Luscher A, *Fröhlich F, Barisch C, Littlewood C, Metcalfe J, Leuba F, Palma A, Pirruccello M, Cesareni G, Stagi M, Walther TC, Soldati T, De Camilli P and Swan LE (2019). Lowe syndrome-linked endocytic adaptors direct membrane cycling kinetics with OCRL in Dictyostelium discoideum. Mol Biol Cell.
- Koliwer-Brandl H, Knobloch P, Barisch C, Welin A, Hanna N, Soldati T and Hilbi H (2019). Distinct Mycobacterium marinum phosphatases determine pathogen vacuole phosphoinositide pattern, phagosome maturation, and escape to the cytosol. Cell Microbiol.
- López-Jiménez AT, Cardenal-Muñoz E, Leuba F, Gerstenmaier L, Barisch C, Hagedorn M, King JS and Soldati T. (2019). The ESCRT and autophagy machineries cooperate to repair ESX-1-dependent damage at the Mycobacterium-containing vacuole but have opposite impact on containing the infection. PLoS Pathog.
- Barisch C and Soldati T. (2017) Breaking fat! How mycobacteria and other intracellular pathogens manipulate host lipid droplets. Biochimie. REVIEW.
- Barisch C and Soldati T. (2017). Mycobacterium marinum Degrades Both Triacylglycerols and Phospholipids from Its Dictyostelium Host to Synthesise Its Own Triacylglycerols and Generate Lipid Inclusions. PLoS Pathog.
- *Barisch C, *López-Jiménez AT and Soldati T. (2015). Live imaging of Mycobacterium marinum infection in Dictyostelium discoideum. Methods Mol Biol. BOOK CHAPTER.
- Barisch C, Paschke P, Hagedorn M, Maniak M and Soldati T. (2015). Lipid droplet dynamics at early stages of Mycobacterium marinum infection in Dictyostelium. Cell Microbiol.
(* equal contribution)