@phdthesis{Schlegel2021,
  author    = {Schlegel, Jan},
  title     = {Super-Resolution Microscopy of Sphingolipids and Protein Nanodomains},
  doi       = {10.25972/OPUS-22959},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-229596},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {The development of cellular life on earth is coupled to the formation of lipid-based biological membranes. Although many tools to analyze their biophysical properties already exist, their variety and number is still relatively small compared to the field of protein studies. One reason for this, is their small size and complex assembly into an asymmetric tightly packed lipid bilayer showing characteristics of a two-dimensional heterogenous fluid. Since membranes are capable to form dynamic, nanoscopic domains, enriched in sphingolipids and cholesterol, their detailed investigation is limited to techniques which access information below the diffraction limit of light. In this work, I aimed to extend, optimize and compare three different labeling approaches for sphingolipids and their subsequent analysis by the single-molecule localization microscopy (SMLM) technique direct stochastic optical reconstruction microscopy (dSTORM). First, I applied classical immunofluorescence by immunoglobulin G (IgG) antibody labeling to detect and quantify sphingolipid nanodomains in the plasma membrane of eukaryotic cells. I was able to identify and characterize ceramide-rich platforms (CRPs) with a size of ~ 75nm on the basal and apical membrane of different cell lines. Next, I used click-chemistry to characterize sphingolipid analogs in living and fixed cells. By using a combination of fluorescence microscopy and anisotropy experiments, I analyzed their accessibility and configuration in the plasma membrane, respectively. Azide-modified, short fatty acid side chains, were accessible to membrane impermeable dyes and localized outside the hydrophobic membrane core. In contrast, azide moieties at the end of longer fatty acid side chains were less accessible and conjugated dyes localized deeper within the plasma membrane. By introducing photo-crosslinkable diazirine groups or chemically addressable amine groups, I developed methods to improve their immobilization required for dSTORM. Finally, I harnessed the specific binding characteristics of non-toxic shiga toxin B subunits (STxBs) and cholera toxin B subunits (CTxBs) to label and quantify glycosphingolipid nanodomains in the context of Neisseria meningitidis infection. Under pyhsiological conditions, these glycosphingolipids were distributed homogenously in the plasma membrane but upon bacterial infection CTxB detectable gangliosides accumulated around invasive Neisseria meningitidis. I was able to highlight the importance of cell cycle dependent glycosphingolipid expression for the invasion process. Blocking membrane accessible sugar headgroups by pretreatment with CTxB significantly reduced the number of invasive bacteria which confirmed the importance of gangliosides for bacterial uptake into cells. Based on my results, it can be concluded that labeling of sphingolipids should be carefully optimized depending on the research question and applied microscopy technique. In particular, I was able to develop new tools and protocols which enable the characterization of sphingolipid nanodomains by dSTORM for all three labeling approaches.},
  subject      = {Sphingolipide},
  language  = {en}
}
@article{PetersKaiserFinketal.2021,
  author    = {Peters, Simon and Kaiser, Lena and Fink, Julian and Schumacher, Fabian and Perschin, Veronika and Schlegel, Jan and Sauer, Markus and Stigloher, Christian and Kleuser, Burkhard and Seibel, Juergen and Schubert-Unkmeir, Alexandra},
  title     = {Click-correlative light and electron microscopy (click-AT-CLEM) for imaging and tracking azido-functionalized sphingolipids in bacteria},
  series = {Scientific Reports},
  volume    = {11},
  journal   = {Scientific Reports},
  number    = {1},
  doi       = {10.1038/s41598-021-83813-w},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-259147},
  pages     = {4300},
  year      = {2021},
  abstract  = {Sphingolipids, including ceramides, are a diverse group of structurally related lipids composed of a sphingoid base backbone coupled to a fatty acid side chain and modified terminal hydroxyl group. Recently, it has been shown that sphingolipids show antimicrobial activity against a broad range of pathogenic microorganisms. The antimicrobial mechanism, however, remains so far elusive. Here, we introduce 'click-AT-CLEM', a labeling technique for correlated light and electron microscopy (CLEM) based on the super-resolution array tomography (srAT) approach and bio-orthogonal click chemistry for imaging of azido-tagged sphingolipids to directly visualize their interaction with the model Gram-negative bacterium Neisseria meningitidis at subcellular level. We observed ultrastructural damage of bacteria and disruption of the bacterial outer membrane induced by two azido-modified sphingolipids by scanning electron microscopy and transmission electron microscopy. Click-AT-CLEM imaging and mass spectrometry clearly revealed efficient incorporation of azido-tagged sphingolipids into the outer membrane of Gram-negative bacteria as underlying cause of their antimicrobial activity.},
  language  = {en}
}
@article{HaackBaikerSchlegeletal.2021,
  author    = {Haack, Stephanie and Baiker, Sarah and Schlegel, Jan and Sauer, Markus and Sparwasser, Tim and Langenhorst, Daniela and Beyersdorf, Niklas},
  title     = {Superagonistic CD28 stimulation induces IFN-γ release from mouse T helper 1 cells in vitro and in vivo},
  series = {European Journal of Immunology},
  volume    = {51},
  journal   = {European Journal of Immunology},
  number    = {3},
  doi       = {10.1002/eji.202048803},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-239028},
  pages     = {738 -- 741},
  year      = {2021},
  abstract  = {Like human Th1 cells, mouse Th1 cells also secrete IFN-γ upon stimulation with a superagonistic anti-CD28 monoclonal antibody (CD28-SA). Crosslinking of the CD28-SA via FcR and CD40-CD40L interactions greatly increased IFN-γ release. Our data stress the utility of the mouse as a model organism for immune responses in humans.},
  language  = {en}
}
@article{SchneiderSchauliesSchumacherWiggeretal.2021,
  author    = {Schneider-Schaulies, Sibylle and Schumacher, Fabian and Wigger, Dominik and Sch{\"o}l, Marie and Waghmare, Trushnal and Schlegel, Jan and Seibel, J{\"u}rgen and Kleuser, Burkhard},
  title     = {Sphingolipids: effectors and Achilles heals in viral infections?},
  series = {Cells},
  volume    = {10},
  journal   = {Cells},
  number    = {9},
  issn      = {2073-4409},
  doi       = {10.3390/cells10092175},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-245151},
  year      = {2021},
  abstract  = {As viruses are obligatory intracellular parasites, any step during their life cycle strictly depends on successful interaction with their particular host cells. In particular, their interaction with cellular membranes is of crucial importance for most steps in the viral replication cycle. Such interactions are initiated by uptake of viral particles and subsequent trafficking to intracellular compartments to access their replication compartments which provide a spatially confined environment concentrating viral and cellular components, and subsequently, employ cellular membranes for assembly and exit of viral progeny. The ability of viruses to actively modulate lipid composition such as sphingolipids (SLs) is essential for successful completion of the viral life cycle. In addition to their structural and biophysical properties of cellular membranes, some sphingolipid (SL) species are bioactive and as such, take part in cellular signaling processes involved in regulating viral replication. It is especially due to the progress made in tools to study accumulation and dynamics of SLs, which visualize their compartmentalization and identify interaction partners at a cellular level, as well as the availability of genetic knockout systems, that the role of particular SL species in the viral replication process can be analyzed and, most importantly, be explored as targets for therapeutic intervention.},
  language  = {en}
}