@article{BrennerGeigerSchlegeletal.2023, author = {Brenner, Daniela and Geiger, Nina and Schlegel, Jan and Diesendorf, Viktoria and Kersting, Louise and Fink, Julian and Stelz, Linda and Schneider-Schaulies, Sibylle and Sauer, Markus and Bodem, Jochen and Seibel, J{\"u}rgen}, title = {Azido-ceramides, a tool to analyse SARS-CoV-2 replication and inhibition — SARS-CoV-2 is inhibited by ceramides}, series = {International Journal of Molecular Sciences}, volume = {24}, journal = {International Journal of Molecular Sciences}, number = {8}, issn = {1422-0067}, doi = {10.3390/ijms24087281}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-313581}, year = {2023}, abstract = {Recently, we have shown that C6-ceramides efficiently suppress viral replication by trapping the virus in lysosomes. Here, we use antiviral assays to evaluate a synthetic ceramide derivative α-NH2-ω-N3-C6-ceramide (AKS461) and to confirm the biological activity of C6-ceramides inhibiting SARS-CoV-2. Click-labeling with a fluorophore demonstrated that AKS461 accumulates in lysosomes. Previously, it has been shown that suppression of SARS-CoV-2 replication can be cell-type specific. Thus, AKS461 inhibited SARS-CoV-2 replication in Huh-7, Vero, and Calu-3 cells up to 2.5 orders of magnitude. The results were confirmed by CoronaFISH, indicating that AKS461 acts comparable to the unmodified C6-ceramide. Thus, AKS461 serves as a tool to study ceramide-associated cellular and viral pathways, such as SARS-CoV-2 infections, and it helped to identify lysosomes as the central organelle of C6-ceramides to inhibit viral replication.}, language = {en} } @article{EderHollmannMandasarietal.2022, author = {Eder, Sascha and Hollmann, Claudia and Mandasari, Putri and Wittmann, Pia and Schumacher, Fabian and Kleuser, Burkhard and Fink, Julian and Seibel, J{\"u}rgen and Schneider-Schaulies, J{\"u}rgen and Stigloher, Christian and Beyersdorf, Niklas and Dembski, Sofia}, title = {Synthesis and characterization of ceramide-containing liposomes as membrane models for different T cell subpopulations}, series = {Journal of Functional Biomaterials}, volume = {13}, journal = {Journal of Functional Biomaterials}, number = {3}, issn = {2079-4983}, doi = {10.3390/jfb13030111}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-286130}, year = {2022}, abstract = {A fine balance of regulatory (T\(_{reg}\)) and conventional CD4\(^+\) T cells (T\(_{conv}\)) is required to prevent harmful immune responses, while at the same time ensuring the development of protective immunity against pathogens. As for many cellular processes, sphingolipid metabolism also crucially modulates the T\(_{reg}\)/T\(_{conv}\) balance. However, our understanding of how sphingolipid metabolism is involved in T cell biology is still evolving and a better characterization of the tools at hand is required to advance the field. Therefore, we established a reductionist liposomal membrane model system to imitate the plasma membrane of mouse T\(_{reg}\) and T\(_{conv}\) with regards to their ceramide content. We found that the capacity of membranes to incorporate externally added azide-functionalized ceramide positively correlated with the ceramide content of the liposomes. Moreover, we studied the impact of the different liposomal preparations on primary mouse splenocytes in vitro. The addition of liposomes to resting, but not activated, splenocytes maintained viability with liposomes containing high amounts of C\(_{16}\)-ceramide being most efficient. Our data thus suggest that differences in ceramide post-incorporation into T\(_{reg}\) and T\(_{conv}\) reflect differences in the ceramide content of cellular membranes.}, language = {en} } @phdthesis{Fink2023, author = {Fink, Julian}, title = {Synthese von molekularen Werkzeugen zur Visualisierung und Untersuchung des Sphingolipidmetabolismus und weiterer biologischer Prozesse}, doi = {10.25972/OPUS-28699}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-286992}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {Die Zelle stellt die kleinste Einheit des Lebens dar und zeichnet sich durch die hoch koordinierte Anordnung von mehreren Millionen (Bio-)Molek{\"u}len zu einem mikrometergroßen Objekt aus. Als struktureller Bestandteil der Lipiddoppelschicht eukaryotischer Zellen spielt neben Sterolen und Glycerolipiden die Verbindungsklasse der Sphingolipide eine zentrale Rolle bei der Aufrechterhaltung der Membranintegrit{\"a}t.[472] Dar{\"u}ber hinaus sind bioaktive Sphingolipide bei vielen grundlegenden zellul{\"a}ren Prozessen wie Apoptose, Wachstum, Differenzierung, Migration und Adh{\"a}sion entscheidend beteiligt.[87,120] Ein gest{\"o}rtes Gleichgewicht des Sphingolipidmetabolismus und Defekte der entsprechenden Stoffwechselwege stehen im Zusammenhang mit vielen Krankheiten wie Krebs, Diabetes, Adipositas, Arteriosklerose, chronischen Entz{\"u}ndungen und Autoimmunerkrankungen sowie viraler und bakterieller Pathogenese.[22,143,473,474] Die Entwicklung und Anwendung von Sphingolipidanaloga als potenzielle Wirkstoffe r{\"u}ckten in den letzten Jahren immer weiter in den Fokus der interdisziplin{\"a}ren Forschung von Biologen, Chemikern und Medizinern. Als bekanntestes Beispiel ist Fingolimod (FTY720) zu nennen, das als Sphingosin-1-phosphat-Mimetikum heute unter dem Markennamen Gilenya® erfolgreich als Arzneistoff zur Behandlung von Multipler Sklerose eingesetzt wird.[475] Es besteht jedoch die Gefahr, dass Fingolimod zur Sch{\"a}digung anderer Zellfunktionen und zu gravierenden Nebeneffekten wie Bradykardie f{\"u}hren kann.[476] Da Sphingolipide ebenfalls in der Kontrolle von bakteriellen und viralen Infektionen essentiell beteiligt sind, spielen Sphingolipide und deren synthetisch dargestellte Derivate vermehrt eine Rolle in der Wirkstoffentwicklung im Kampf gegen pathogene Krankheitserreger.[175,477-479] Die Wirkweise von antimikrobiellen Sphingolipiden ist bisher nicht vollst{\"a}ndig aufgekl{\"a}rt. F{\"u}r eine Weiterentwicklung von bekannten Medikamenten gegen verschiedene Krankheiten oder f{\"u}r die Entwicklung neuartiger Wirkstoffe gegen Erreger ist eine umfassende Untersuchung der zugrundeliegenden zellul{\"a}ren Mechanismen auf molekularer Ebene entscheidend. Hierf{\"u}r finden aufgrund der relativ einfachen Detektion mittels Fluoreszenzmikroskopie h{\"a}ufig fluoreszenzmarkierte Sphingolipidderivate breite Anwendung.[480] Die kovalent gebundene Farbstoffeinheit bringt jedoch wesentliche Nachteile mit sich, da sich die Biomolek{\"u}le durch die ver{\"a}nderte Struktur und Polarit{\"a}t in ihren biologischen Eigenschaften von den nat{\"u}rlichen Substraten unterscheiden k{\"o}nnen. Die Verwendung von bioorthogonal funktionalisierten Biomolek{\"u}len umgeht dieses Problem, da die strukturellen {\"A}nderungen minimal gehalten werden. Nach dem zellul{\"a}ren Einbau dieser Derivate ist eine schnelle und spezifische Konjugation mit einem komplement{\"a}ren Fluorophor zu einem gew{\"u}nschten Zeitpunkt durch sogenannte Click-Reaktionen wie CuAAC oder SPAAC m{\"o}glich.[12,46] Das Prinzip der Click-Chemie wurde bereits auf eine Vielzahl an Biomolek{\"u}len wie Sphingolipide, Fetts{\"a}uren, Aminos{\"a}uren, Proteine, Kohlenhydrate, Nukleoside oder Nukleins{\"a}uren (DNA und RNA) {\"u}bertragen.[47,280] Jedoch bedarf es weiterer spezifisch modifizierter Verbindungen, die vielf{\"a}ltige bioorthogonale Reaktionen f{\"u}r die Untersuchung von Zellprozessen zulassen ‒ sowohl in vitro als auch in vivo. Um neue Therapieans{\"a}tze gegen verschiedene Krankheiten zu entwickeln und schwerwiegende Nebenwirkungen zu vermeiden, ist die detaillierte Erforschung hochkomplexer Zellvorg{\"a}nge auf molekularer Ebene von entscheidender Bedeutung. Das Ziel dieser Arbeit war daher die Synthese und Charakterisierung von molekularen Werkzeugen, die in Kombination mit verschiedenen aktuellen Mikroskopie- und Massenspektrometriemethoden die Visualisierung und Untersuchung des Sphingolipidmetabolismus und weiterer biologischer Prozesse erm{\"o}glichen. Zusammenfassend wurde in dieser Arbeit eine Vielzahl an Sphingolipiden und deren bioorthogonal funktionalisierte Analoga ausgehend von der Aminos{\"a}ure L-Serin erfolgreich synthetisiert. Die vorgestellten Verbindungen eignen sich in Kombination mit Massenspektrometrie und Fluoreszenz- oder Elektronenmikroskopie als molekulare Werkzeuge zur Untersuchung des komplexen Sphingolipidmetabolismus sowie des Einbaus und der Dynamik von Sphingolipiden in Modell- und Zellmembranen. Sowohl in humanen und tierischen Zellen als auch in Bakterien wurden die azidmodifizierten Sphingolipide durch Click-Reaktionen visualisiert, um ein verbessertes Verst{\"a}ndnis von bakteriellen und viralen Infektionsprozessen zu erhalten. Der modulare Ansatz der Click-Chemie erm{\"o}glicht die Verwendung verschiedener komplement{\"a}r funktionalisierter Farbstoffe, die unterschiedliche Eigenschaften bez{\"u}glich der Membrandurchg{\"a}ngigkeit oder Absorptions- und Emissionswellenl{\"a}ngen besitzen und somit je nach biologischer Fragestellung gezielt eingesetzt werden k{\"o}nnen. Alles in allem tragen die in dieser Arbeit synthetisierten Verbindungen dazu bei, die Rolle von Sphingolipiden bei Infektionsprozessen und Krankheitsverl{\"a}ufen auf subzellul{\"a}rer Ebene aufzukl{\"a}ren. Dadurch wird ein entscheidender Beitrag f{\"u}r die Entwicklung neuartiger Wirkstoffe gegen bakterielle oder virale Erreger sowie innovativer Therapien gegen verschiedene humane Krankheiten geliefert.}, subject = {Chemische Synthese}, language = {de} } @article{GoetzKunzFinketal.2020, author = {G{\"o}tz, Ralph and Kunz, Tobias C. and Fink, Julian and Solger, Franziska and Schlegel, Jan and Seibel, J{\"u}rgen and Kozjak-Pavlovic, Vera and Rudel, Thomas and Sauer, Markus}, title = {Nanoscale imaging of bacterial infections by sphingolipid expansion microscopy}, series = {Nature Communications}, volume = {11}, journal = {Nature Communications}, doi = {10.1038/s41467-020-19897-1}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-231248}, year = {2020}, abstract = {Expansion microscopy (ExM) enables super-resolution imaging of proteins and nucleic acids on conventional microscopes. However, imaging of details of the organization of lipid bilayers by light microscopy remains challenging. We introduce an unnatural short-chain azide- and amino-modified sphingolipid ceramide, which upon incorporation into membranes can be labeled by click chemistry and linked into hydrogels, followed by 4x to 10x expansion. Confocal and structured illumination microscopy (SIM) enable imaging of sphingolipids and their interactions with proteins in the plasma membrane and membrane of intracellular organelles with a spatial resolution of 10-20nm. As our functionalized sphingolipids accumulate efficiently in pathogens, we use sphingolipid ExM to investigate bacterial infections of human HeLa229 cells by Neisseria gonorrhoeae, Chlamydia trachomatis and Simkania negevensis with a resolution so far only provided by electron microscopy. In particular, sphingolipid ExM allows us to visualize the inner and outer membrane of intracellular bacteria and determine their distance to 27.6 +/- 7.7nm. Imaging of lipid bilayers using light microscopy is challenging. Here the authors label cells using a short chain click-compatible ceramide to visualize mammalian and bacterial membranes with expansion microscopy.}, language = {en} } @article{HollmannWieseDennstaedtetal.2019, author = {Hollmann, Claudia and Wiese, Teresa and Dennst{\"a}dt, Fabio and Fink, Julian and Schneider-Schaulies, J{\"u}rgen and Beyersdorf, Niklas}, title = {Translational approaches targeting ceramide generation from sphingomyelin in T cells to modulate immunity in humans}, series = {Frontiers in Immunology}, volume = {10}, journal = {Frontiers in Immunology}, number = {2363}, issn = {1664-3224}, doi = {10.3389/fimmu.2019.02363}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198806}, year = {2019}, abstract = {In T cells, as in all other cells of the body, sphingolipids form important structural components of membranes. Due to metabolic modifications, sphingolipids additionally play an active part in the signaling of cell surface receptors of T cells like the T cell receptor or the co-stimulatory molecule CD28. Moreover, the sphingolipid composition of their membranes crucially affects the integrity and function of subcellular compartments such as the lysosome. Previously, studying sphingolipid metabolism has been severely hampered by the limited number of analytical methods/model systems available. Besides well-established high resolution mass spectrometry new tools are now available like novel minimally modified sphingolipid subspecies for click chemistry as well as recently generated mouse mutants with deficiencies/overexpression of sphingolipid-modifying enzymes. Making use of these tools we and others discovered that the sphingolipid sphingomyelin is metabolized to ceramide to different degrees in distinct T cell subpopulations of mice and humans. This knowledge has already been translated into novel immunomodulatory approaches in mice and will in the future hopefully also be applicable to humans. In this paper we are, thus, summarizing the most recent findings on the impact of sphingolipid metabolism on T cell activation, differentiation, and effector functions. Moreover, we are discussing the therapeutic concepts arising from these insights and drugs or drug candidates which are already in clinical use or could be developed for clinical use in patients with diseases as distant as major depression and chronic viral infection.}, 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{SolgerKunzFinketal.2020, author = {Solger, Franziska and Kunz, Tobias C. and Fink, Julian and Paprotka, Kerstin and Pfister, Pauline and Hagen, Franziska and Schumacher, Fabian and Kleuser, Burkhard and Seibel, J{\"u}rgen and Rudel, Thomas}, title = {A Role of Sphingosine in the Intracellular Survival of Neisseria gonorrhoeae}, series = {Frontiers in Cellular and Infection Microbiology}, volume = {10}, journal = {Frontiers in Cellular and Infection Microbiology}, issn = {2235-2988}, doi = {10.3389/fcimb.2020.00215}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-204111}, year = {2020}, abstract = {Obligate human pathogenic Neisseria gonorrhoeae are the second most frequent bacterial cause of sexually transmitted diseases. These bacteria invade different mucosal tissues and occasionally disseminate into the bloodstream. Invasion into epithelial cells requires the activation of host cell receptors by the formation of ceramide-rich platforms. Here, we investigated the role of sphingosine in the invasion and intracellular survival of gonococci. Sphingosine exhibited an anti-gonococcal activity in vitro. We used specific sphingosine analogs and click chemistry to visualize sphingosine in infected cells. Sphingosine localized to the membrane of intracellular gonococci. Inhibitor studies and the application of a sphingosine derivative indicated that increased sphingosine levels reduced the intracellular survival of gonococci. We demonstrate here, that sphingosine can target intracellular bacteria and may therefore exert a direct bactericidal effect inside cells.}, language = {en} } @article{WieseDennstaedtHollmannetal.2021, author = {Wiese, Teresa and Dennst{\"a}dt, Fabio and Hollmann, Claudia and Stonawski, Saskia and Wurst, Catherina and Fink, Julian and Gorte, Erika and Mandasari, Putri and Domschke, Katharina and Hommers, Leif and Vanhove, Bernard and Schumacher, Fabian and Kleuser, Burkard and Seibel, J{\"u}rgen and Rohr, Jan and Buttmann, Mathias and Menke, Andreas and Schneider-Schaulies, J{\"u}rgen and Beyersdorf, Niklas}, title = {Inhibition of acid sphingomyelinase increases regulatory T cells in humans}, series = {Brain Communications}, volume = {3}, journal = {Brain Communications}, number = {2}, doi = {10.1093/braincomms/fcab020}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-259868}, year = {2021}, abstract = {Genetic deficiency for acid sphingomyelinase or its pharmacological inhibition has been shown to increase Foxp3\(^+\) regulatory T-cell frequencies among CD4\(^+\) T cells in mice. We now investigated whether pharmacological targeting of the acid sphingomyelinase, which catalyzes the cleavage of sphingomyelin to ceramide and phosphorylcholine, also allows to manipulate relative CD4\(^+\) Foxp3\(^+\) regulatory T-cell frequencies in humans. Pharmacological acid sphingomyelinase inhibition with antidepressants like sertraline, but not those without an inhibitory effect on acid sphingomyelinase activity like citalopram, increased the frequency of Foxp3\(^+\) regulatory T cell among human CD4\(^+\) T cells in vitro. In an observational prospective clinical study with patients suffering from major depression, we observed that acid sphingomyelinase-inhibiting antidepressants induced a stronger relative increase in the frequency of CD4\(^+\) Foxp3\(^+\) regulatory T cells in peripheral blood than acid sphingomyelinase-non- or weakly inhibiting antidepressants. This was particularly true for CD45RA\(^-\) CD25\(^{high}\) effector CD4\(^+\) Foxp3\(^+\) regulatory T cells. Mechanistically, our data indicate that the positive effect of acid sphingomyelinase inhibition on CD4\(^+\) Foxp3\(^+\) regulatory T cells required CD28 co-stimulation, suggesting that enhanced CD28 co-stimulation was the driver of the observed increase in the frequency of Foxp3+ regulatory T cells among human CD4\(^+\) T cells. In summary, the widely induced pharmacological inhibition of acid sphingomyelinase activity in patients leads to an increase in Foxp3+ regulatory T-cell frequencies among CD4\(^+\) T cells in humans both in vivo and in vitro.}, language = {en} }