In our lab we are interested in lipid homeostasis at both the organismal and cellular level.
In mammals the brain controls the systemic energy status and global parameters of metabolism including lipid metabolism. For assessment of the metabolic situation circulating metabolites like lipids are taken up into specific brain areas, e.g. the hypothalamus, and locally sensed. Depending on that read-out adaptations to systemic metabolism are executed by various brain regions to maintain homeostasis.
These processes and the underlying cellular mechanisms are the focus of our junior group.
We recently discovered that the hypothalamus differentially processes various lipids. Specific hypothalamic cells, tanycytes and astrocytes, are involved and change in an adaptive manner the local lipid trafficking and local lipid metabolism. We continue to study this delicate interplay of cells and its consequences for the maintenance of body energy homeostasis.
Tanycytes and astrocytes in the murine hypothalamus have been identified by specific markers and light up (green) using immunofluorescence microscopy, while the nuclei of all hypothalamic cells are marked in magenta. The Tanycytes border the lumen of the 3rd ventricle and project their extensions into deeper regions of the hypothalamus.
In association with the lab of Christoph Thiele we have been interested in cellular organelles commonly associated with the storage of fat, lipid droplets. Although most cells contain lipid droplets, it is adipoytes, the cells of adipose tissue (fat tissue), which are specialized to store most of our energy resources as triglycerides (fat) in their lipid droplets.
An adipocyte with large lipid droplets (shadow cast discs) observed by DIC-microscopy.
The mechanism by which cells pack triglycerides into lipid droplets is poorly understood. The use of polyene lipids developed by the Thiele lab allowed for following triglyceride biosynthesis and the flux of lipids to the lipid droplets in living cells. The underlying mechanisms are of significant importance as their understanding may facilitate the development of treatments for certain lipid storage diseases.
Adipocytes used fluorescent polyene fatty acids to generate fluorescent triglyceride, which is stored in lipid droplets. The spherical lipid droplets light up when observed by two-photon fluorescence microscopy.
We have discovered that the enzyme Diacylglycerol:AcylCoA-Acyltransferase 2 (DGAT2), which is essential for life and produces triglyceride, is found on lipid droplets and is active there. This finding emphasizes the essential role DGAT2 plays for the process of lipid storage and renders this enzyme a prime target for biomedical research seeking to control this process.
An adipocyte, which transiently expresses tagged DGAT2 (green) that localizes around lipid droplets (purple) observed by confocal fluorescence microscopy.
We also used polyene analogues of ether lipids, a lipid class of special importance for the brain, in microscopy tracing experiments. This study has highlighted a role for mitochondria in ether lipid metabolism.
Endothelial cells incubated with a polyene ether lipid show a prominent staining of mitochondria as observed by two-photon fluorescence microscopy.
To study cellular lipid metabolism we apply biochemical, spectroscopic, microscopic, cell and molecular biological techniques. Fluorescence microscopy of living cells yields valuable information on dynamic processes, while electron microscopy provides the highest resolution data.
Electron micrograph of lipid droplets and mitochondria in adipocytes.
Only a small part of the cell is shown.
Lipid analogues such as the polyene lipids or alkyne lipids are valuable tools to track cellular lipid metabolism both kinetically and spatially. In our laboratory we have been developing these tools and the respective microscopy routines for high resolution lipid imaging.
An artistic illustration of how lipid metabolism can be followed by fluorescence microscopy or chromatographic lipid analysis employing a alkyne lipids and the CLiCK reaction with a fluorescent reporter molecule.
Polyene lipids are fluorescent lipids with a unique similarity to natural lipids. The polyene fluorophore does not interfere with biological or biophysical properties of natural lipids, such as metabolism or the preference for ordered or disordered phases. This makes polyene lipids the reagent of choice for studying lipid localization in living cells.
We offer interesting projects and are always looking for curious, creative and talented people at all levels, including rotation students and graduate students. Please contact us by email and send a meaningful CV highlighting your various skills and interests.
Hofmann, K.; Thiele, C.; Schött, H.F.; Gaebler, A.; Schoene, M.; Kiver, Y.; Friedrichs, S.; Lütjohann, D.; Kuerschner, L. A novel alkyne cholesterol to trace cellular cholesterol metabolism and localization. J Lipid Res. 2014, 55, 583-91.
Thiele, C.; Papan, C.; Hoelper, C.; Kusserow, K.; Gaebler, A.; Schoene, M.; Piotrowitz, K.; Lohmann, D.; Spandl, J.; Stevanovic, A.; Shevchenko, A.; Kuerschner, L. Tracing Fatty Acid metabolism by Click chemistry. ACS Chem. Biol. 2012, 7, 2004-11.
Kuerschner, L.*; Richter, D.; Hannibal-Bach, H.K.; Gaebler, A.; Shevchenko, A.; Eijsing, C.S.; Thiele, C. Exogenous ether lipids predominantly target mitochondria. PLoS One. 2012, 7, e31342. *corresponding author
Fairn, G. D.; Schieber, N. L.; Ariotti, N.; Murphy, S.; Kuerschner, L.; Webb, R. I.; Grinstein, S.; Parton, R. G. High-resolution mapping reveals topologically distinct cellular pools of phosphatidylserine. J. Cell Biol. 2011, 194, 257-75.
Moessinger, C.; Kuerschner, L.; Spandl, J.; Shevchenko, A.; Thiele, C. Human lysophosphatidylcholine acyltransferase 1 and 2 are located to lipid droplets, where they catalyze the formation of phosphatidylcholine. J. Biol. Chem. 2011, 286, 21330-9.
Spandl, J.; Lohmann, D.; Kuerschner, L.; Moessinger, C.; Thiele, C. Ancient ubiquitous protein 1 (AUP1) localizes to lipid droplets and binds the E2 ubiquitin conjugase G2 (Ube2g2) via its G2 binding region. J. Biol. Chem. 2011, 286, 5599-5606.
Fei, W.; Shui, G.; Gaeta, B.; Du, X.; Kuerschner, L.; Li, P.; Brown, A. J.; Wenk, M. R.; Parton, R. G.; Yang, H. Fld1p, a functional homologue of human seipin, regulates the size of lipid droplets in yeast. J. Cell Biol. 2008, 180, 473-482.
Gütschow, M.; Kuerschner, L.; Pietsch, M.; Ambrozak, A.; Neumann, U.; Günther, R.; Hofmann, H.-J. Inhibition of cathepsin G by 2-amino-3,1-benzoxazin-4-ones: Kinetic investigations and docking studies. Arch. Biochem. Biophys. 2002 , 402, 180-191.
Kuerschner, L. Untersuchungen zu Cathepsin G-Inhibitoren. Apothekenmagazin. 2000, 10, 8-10.
Gütschow, M.; Kuerschner, L.; Neumann, U.; Pietsch, M.; Löser, R.; Koglin, N.; Eger, K. 2-(Diethylamino)[1,3]oxazin-4-ones as Stable Inhibitors of Human Leukocyte Elastase. J. Med. Chem. 1999, 42, 5437-5447.