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Michael Walch

Bio: Michael Walch is an academic researcher from University of Fribourg. The author has contributed to research in topics: Granzyme & Granulysin. The author has an hindex of 21, co-authored 42 publications receiving 1599 citations. Previous affiliations of Michael Walch include Boston Children's Hospital & Harvard University.

Papers
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Journal ArticleDOI
TL;DR: It is shown that perforin formed pores in the gigantosome membrane, allowing endosomal cargo, including granzymes, to be gradually released.
Abstract: How the pore-forming protein perforin delivers apoptosis-inducing granzymes to the cytosol of target cells is uncertain. Perforin induces a transient Ca2+ flux in the target cell, which triggers a process to repair the damaged cell membrane. As a consequence, both perforin and granzymes are endocytosed into enlarged endosomes called 'gigantosomes'. Here we show that perforin formed pores in the gigantosome membrane, allowing endosomal cargo, including granzymes, to be gradually released. After about 15 min, gigantosomes ruptured, releasing their remaining content. Thus, perforin delivers granzymes by a two-step process that involves first transient pores in the cell membrane that trigger the endocytosis of granzyme and perforin and then pore formation in endosomes to trigger cytosolic release.

264 citations

Journal ArticleDOI
TL;DR: These findings provide a mechanistic link between EVs and vascular dysfunction during malaria infection and show that EVs are efficiently internalized by endothelial cells, where the miRNA-Argonaute 2 complexes modulate target gene expression and barrier properties.
Abstract: Malaria remains one of the greatest public health challenges worldwide, particularly in sub-Saharan Africa. The clinical outcome of individuals infected with Plasmodium falciparum parasites depends on many factors including host systemic inflammatory responses, parasite sequestration in tissues and vascular dysfunction. Production of pro-inflammatory cytokines and chemokines promotes endothelial activation as well as recruitment and infiltration of inflammatory cells, which in turn triggers further endothelial cell activation and parasite sequestration. Inflammatory responses are triggered in part by bioactive parasite products such as hemozoin and infected red blood cell-derived extracellular vesicles (iRBC-derived EVs). Here we demonstrate that such EVs contain functional miRNA-Argonaute 2 complexes that are derived from the host RBC. Moreover, we show that EVs are efficiently internalized by endothelial cells, where the miRNA-Argonaute 2 complexes modulate target gene expression and barrier properties. Altogether, these findings provide a mechanistic link between EVs and vascular dysfunction during malaria infection.

174 citations

Journal ArticleDOI
05 Jun 2014-Cell
TL;DR: Mice expressing transgenic granulysin are better able to clear Listeria monocytogenes and play an unexpected role in bacterial defense, suggesting that granzymes disrupt multiple vital bacterial pathways.

152 citations

Journal ArticleDOI
TL;DR: The capacity of the proximal tubule to rapidly recruit cells into division relies on a large reserve pool of cells in G(1) and on the shortening of the obligatory period of quiescence that follows division.
Abstract: We investigated the proliferative capacity of renal proximal tubular cells in healthy rats. Previously, we observed that tubular cells originate from differentiated cells. We now found 1) by application of bromo-deoxyuridine (BrdU) for 14 days and costaining for BrdU, and the G(1)-phase marker cyclin D1 that the bulk of cells in the S3 segment of juvenile rats were involved in proliferation; 2) that although the proliferation rate was about 10-fold higher in juvenile rats compared with adult rats, roughly 40% of S3 cells were in G(1) in both groups; 3) that after a strong mitotic stimulus (lead acetate), proliferation was similar in juveniles and adults; 4) that there was a high incidence of cyclin D1-positive cells also in the healthy human kidney; and 5) by labeling dividing cells with BrdU for 2 days before the application of lead acetate and subsequent costaining for BrdU and cell cycle markers, that, although a strong mitotic stimulus does not abolish the period of quiescence following division, it shortens it markedly. Thus the capacity of the proximal tubule to rapidly recruit cells into division relies on a large reserve pool of cells in G(1) and on the shortening of the obligatory period of quiescence that follows division.

149 citations

Journal ArticleDOI
TL;DR: GNLY-transgenic mice are protected against infection by T. cruzi and T. gondii, and survive infections that are lethal to wild-type mice, and GNLY, PFN- and Gzm-mediated elimination of intracellular protozoan parasites is an unappreciated immune defense mechanism.
Abstract: Protozoan infections are a serious global health problem. Natural killer (NK) cells and cytolytic T lymphocytes (CTLs) eliminate pathogen-infected cells by releasing cytolytic granule contents--granzyme (Gzm) proteases and the pore-forming perforin (PFN)--into the infected cell. However, these cytotoxic molecules do not kill intracellular parasites. CD8(+) CTLs protect against parasite infections in mice primarily by secreting interferon (IFN)-γ. However, human, but not rodent, cytotoxic granules contain the antimicrobial peptide granulysin (GNLY), which selectively destroys cholesterol-poor microbial membranes, and GNLY, PFN and Gzms rapidly kill intracellular bacteria. Here we show that GNLY delivers Gzms into three protozoan parasites (Trypanosoma cruzi, Toxoplasma gondii and Leishmania major), in which the Gzms generate superoxide and inactivate oxidative defense enzymes to kill the parasite. PFN delivers GNLY and Gzms into infected cells, and GNLY then delivers Gzms to the intracellular parasites. Killer cell-mediated parasite death, which we term 'microbe-programmed cell death' or 'microptosis', is caspase independent but resembles mammalian apoptosis, causing mitochondrial swelling, transmembrane potential dissipation, membrane blebbing, phosphatidylserine exposure, DNA damage and chromatin condensation. GNLY-transgenic mice are protected against infection by T. cruzi and T. gondii, and survive infections that are lethal to wild-type mice. Thus, GNLY-, PFN- and Gzm-mediated elimination of intracellular protozoan parasites is an unappreciated immune defense mechanism.

146 citations


Cited by
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Journal ArticleDOI
TL;DR: The atomic force microscope (AFM) is not only used to image the topography of solid surfaces at high resolution but also to measure force-versus-distance curves as discussed by the authors, which provide valuable information on local material properties such as elasticity, hardness, Hamaker constant, adhesion and surface charge densities.

3,281 citations

Journal ArticleDOI
07 Jul 2016-Nature
TL;DR: It is shown that GSDMD-NT oligomerizes in membranes to form pores that are visible by electron microscopy and kills cell-free bacteria in vitro and may have a direct bactericidal effect within the cytosol of host cells, but the importance of direct bacterial killing in controlling in vivo infection remains to be determined.
Abstract: Inflammatory caspases (caspases 1, 4, 5 and 11) are activated in response to microbial infection and danger signals. When activated, they cleave mouse and human gasdermin D (GSDMD) after Asp276 and Asp275, respectively, to generate an N-terminal cleavage product (GSDMD-NT) that triggers inflammatory death (pyroptosis) and release of inflammatory cytokines such as interleukin-1β. Cleavage removes the C-terminal fragment (GSDMD-CT), which is thought to fold back on GSDMD-NT to inhibit its activation. However, how GSDMD-NT causes cell death is unknown. Here we show that GSDMD-NT oligomerizes in membranes to form pores that are visible by electron microscopy. GSDMD-NT binds to phosphatidylinositol phosphates and phosphatidylserine (restricted to the cell membrane inner leaflet) and cardiolipin (present in the inner and outer leaflets of bacterial membranes). Mutation of four evolutionarily conserved basic residues blocks GSDMD-NT oligomerization, membrane binding, pore formation and pyroptosis. Because of its lipid-binding preferences, GSDMD-NT kills from within the cell, but does not harm neighbouring mammalian cells when it is released during pyroptosis. GSDMD-NT also kills cell-free bacteria in vitro and may have a direct bactericidal effect within the cytosol of host cells, but the importance of direct bacterial killing in controlling in vivo infection remains to be determined.

1,902 citations

Journal ArticleDOI
Jonas Schulte-Schrepping1, Nico Reusch1, Daniela Paclik2, Kevin Baßler1, Stephan Schlickeiser2, Bowen Zhang3, Benjamin Krämer4, Tobias Krammer, Sophia Brumhard2, Lorenzo Bonaguro1, Elena De Domenico5, Daniel Wendisch2, Martin Grasshoff3, Theodore S. Kapellos1, Michael Beckstette3, Tal Pecht1, Adem Saglam5, Oliver Dietrich, Henrik E. Mei6, Axel Schulz6, Claudia Conrad2, Désirée Kunkel2, Ehsan Vafadarnejad, Cheng-Jian Xu3, Cheng-Jian Xu7, Arik Horne1, Miriam Herbert1, Anna Drews5, Charlotte Thibeault2, Moritz Pfeiffer2, Stefan Hippenstiel2, Andreas C. Hocke2, Holger Müller-Redetzky2, Katrin-Moira Heim2, Felix Machleidt2, Alexander Uhrig2, Laure Bosquillon de Jarcy2, Linda Jürgens2, Miriam Stegemann2, Christoph R. Glösenkamp2, Hans-Dieter Volk2, Christine Goffinet2, Markus Landthaler8, Emanuel Wyler8, Philipp Georg2, Maria Schneider2, Chantip Dang-Heine2, Nick Neuwinger2, Kai Kappert2, Rudolf Tauber2, Victor M. Corman2, Jan Raabe4, Kim Melanie Kaiser4, Michael To Vinh4, Gereon Rieke4, Christian Meisel2, Thomas Ulas5, Matthias Becker5, Robert Geffers, Martin Witzenrath2, Christian Drosten2, Norbert Suttorp2, Christof von Kalle2, Florian Kurth2, Florian Kurth9, Florian Kurth10, Kristian Händler5, Joachim L. Schultze1, Joachim L. Schultze5, Anna C. Aschenbrenner1, Anna C. Aschenbrenner7, Yang Li7, Yang Li3, Jacob Nattermann4, Birgit Sawitzki2, Antoine-Emmanuel Saliba, Leif E. Sander2, Angel Angelov, Robert Bals, Alexander Bartholomäus, Anke Becker, Daniela Bezdan, Ezio Bonifacio, Peer Bork, Thomas Clavel, Maria Colomé-Tatché, Andreas Diefenbach, Alexander T. Dilthey, Nicole Fischer, Konrad U. Förstner, Julia-Stefanie Frick, Julien Gagneur, Alexander Goesmann, Torsten Hain, Michael Hummel, Stefan Janssen, Jörn Kalinowski, René Kallies, Birte Kehr, Andreas Keller, Sarah Kim-Hellmuth, Christoph Klein, Oliver Kohlbacher, Jan O. Korbel, Ingo Kurth, Kerstin U. Ludwig, Oliwia Makarewicz, Manja Marz, Alice C. McHardy, Christian Mertes, Markus M. Nöthen, Peter Nürnberg, Uwe Ohler, Stephan Ossowski, Jörg Overmann, Silke Peter, Klaus Pfeffer, Anna R. Poetsch, Alfred Pühler, Nikolaus Rajewsky, Markus Ralser, Olaf Rieß, Stephan Ripke, Ulisses Nunes da Rocha, Philip Rosenstiel, Philipp H. Schiffer, Eva-Christina Schulte, Alexander Sczyrba, Oliver Stegle, Jens Stoye, Fabian J. Theis, Janne Vehreschild, Jörg Vogel, Max von Kleist, Andreas Walker, Jörn Walter, Dagmar Wieczorek, John Ziebuhr 
17 Sep 2020-Cell
TL;DR: This study provides detailed insights into the systemic immune response to SARS-CoV-2 infection and it reveals profound alterations in the myeloid cell compartment associated with severe COVID-19.

1,042 citations

Journal ArticleDOI
TL;DR: The transfer of gene products from injured cells may explain stem cell functional and phenotypic changes without the need of transdifferentiation into tissue cells, and the evidence supporting a bidirectional exchange of genetic information between stem and injured cells is discussed.

1,029 citations

Journal ArticleDOI
TL;DR: The current understanding of the structural, cellular and clinical aspects of perforin and granzyme biology is discussed, beginning to define and understand a range of human diseases that are associated with a failure to deliver active per forin to target cells.
Abstract: A defining property of cytotoxic lymphocytes is their expression and regulated secretion of potent toxins, including the pore-forming protein perforin and serine protease granzymes. Until recently, mechanisms of pore formation and granzyme transfer into the target cell were poorly understood, but advances in structural and cellular biology have now begun to unravel how synergy between perforin and granzymes brings about target cell death. These and other advances are demonstrating the surprisingly broad pathophysiological roles of the perforin–granzyme pathway, and this has important implications for understanding immune homeostasis and for developing immunotherapies for cancer and other diseases. In particular, we are beginning to define and understand a range of human diseases that are associated with a failure to deliver active perforin to target cells. In this Review, we discuss the current understanding of the structural, cellular and clinical aspects of perforin and granzyme biology.

785 citations