@article{11588, abstract = {Visualizing cell behavior and effector function on a single cell level has been crucial for understanding key aspects of mammalian biology. Due to their small size, large number and rapid recruitment into thrombi, there is a lack of data on fate and behavior of individual platelets in thrombosis and hemostasis. Here we report the use of platelet lineage restricted multi-color reporter mouse strains to delineate platelet function on a single cell level. We show that genetic labeling allows for single platelet and megakaryocyte (MK) tracking and morphological analysis in vivo and in vitro, while not affecting lineage functions. Using Cre-driven Confetti expression, we provide insights into temporal gene expression patterns as well as spatial clustering of MK in the bone marrow. In the vasculature, shape analysis of activated platelets recruited to thrombi identifies ubiquitous filopodia formation with no evidence of lamellipodia formation. Single cell tracking in complex thrombi reveals prominent myosin-dependent motility of platelets and highlights thrombus formation as a highly dynamic process amenable to modification and intervention of the acto-myosin cytoskeleton. Platelet function assays combining flow cytrometry, as well as in vivo, ex vivo and in vitro imaging show unaltered platelet functions of multicolor reporter mice compared to wild-type controls. In conclusion, platelet lineage multicolor reporter mice prove useful in furthering our understanding of platelet and MK biology on a single cell level.}, author = {Nicolai, Leo and Kaiser, Rainer and Escaig, Raphael and Hoffknecht, Marie Louise and Anjum, Afra and Leunig, Alexander and Pircher, Joachim and Ehrlich, Andreas and Lorenz, Michael and Ishikawa-Ankerhold, Hellen and Aird, William C. and Massberg, Steffen and Gärtner, Florian R}, issn = {1592-8721}, journal = {Haematologica}, number = {7}, pages = {1669--1680}, publisher = {Ferrata Storti Foundation}, title = {{Single platelet and megakaryocyte morpho-dynamics uncovered by multicolor reporter mouse strains in vitro and in vivo}}, doi = {10.3324/haematol.2021.278896}, volume = {107}, year = {2022}, } @article{12119, abstract = {Intravascular neutrophils and platelets collaborate in maintaining host integrity, but their interaction can also trigger thrombotic complications. We report here that cooperation between neutrophil and platelet lineages extends to the earliest stages of platelet formation by megakaryocytes in the bone marrow. Using intravital microscopy, we show that neutrophils “plucked” intravascular megakaryocyte extensions, termed proplatelets, to control platelet production. Following CXCR4-CXCL12-dependent migration towards perisinusoidal megakaryocytes, plucking neutrophils actively pulled on proplatelets and triggered myosin light chain and extracellular-signal-regulated kinase activation through reactive oxygen species. By these mechanisms, neutrophils accelerate proplatelet growth and facilitate continuous release of platelets in steady state. Following myocardial infarction, plucking neutrophils drove excessive release of young, reticulated platelets and boosted the risk of recurrent ischemia. Ablation of neutrophil plucking normalized thrombopoiesis and reduced recurrent thrombosis after myocardial infarction and thrombus burden in venous thrombosis. We establish neutrophil plucking as a target to reduce thromboischemic events.}, author = {Petzold, Tobias and Zhang, Zhe and Ballesteros, Iván and Saleh, Inas and Polzin, Amin and Thienel, Manuela and Liu, Lulu and Ul Ain, Qurrat and Ehreiser, Vincent and Weber, Christian and Kilani, Badr and Mertsch, Pontus and Götschke, Jeremias and Cremer, Sophie and Fu, Wenwen and Lorenz, Michael and Ishikawa-Ankerhold, Hellen and Raatz, Elisabeth and El-Nemr, Shaza and Görlach, Agnes and Marhuenda, Esther and Stark, Konstantin and Pircher, Joachim and Stegner, David and Gieger, Christian and Schmidt-Supprian, Marc and Gärtner, Florian R and Almendros, Isaac and Kelm, Malte and Schulz, Christian and Hidalgo, Andrés and Massberg, Steffen}, issn = {1074-7613}, journal = {Immunity}, keywords = {Infectious Diseases, Immunology, Immunology and Allergy}, number = {12}, pages = {2285--2299.e7}, publisher = {Elsevier}, title = {{Neutrophil “plucking” on megakaryocytes drives platelet production and boosts cardiovascular disease}}, doi = {10.1016/j.immuni.2022.10.001}, volume = {55}, year = {2022}, } @article{9294, abstract = {In this issue of Developmental Cell, Doyle and colleagues identify periodic anterior contraction as a characteristic feature of fibroblasts and mesenchymal cancer cells embedded in 3D collagen gels. This contractile mechanism generates a matrix prestrain required for crawling in fibrous 3D environments.}, author = {Gärtner, Florian R and Sixt, Michael K}, issn = {18781551}, journal = {Developmental Cell}, number = {6}, pages = {723--725}, publisher = {Elsevier}, title = {{Engaging the front wheels to drive through fibrous terrain}}, doi = {10.1016/j.devcel.2021.03.002}, volume = {56}, year = {2021}, } @article{7885, abstract = {Eukaryotic cells migrate by coupling the intracellular force of the actin cytoskeleton to the environment. While force coupling is usually mediated by transmembrane adhesion receptors, especially those of the integrin family, amoeboid cells such as leukocytes can migrate extremely fast despite very low adhesive forces1. Here we show that leukocytes cannot only migrate under low adhesion but can also transmit forces in the complete absence of transmembrane force coupling. When confined within three-dimensional environments, they use the topographical features of the substrate to propel themselves. Here the retrograde flow of the actin cytoskeleton follows the texture of the substrate, creating retrograde shear forces that are sufficient to drive the cell body forwards. Notably, adhesion-dependent and adhesion-independent migration are not mutually exclusive, but rather are variants of the same principle of coupling retrograde actin flow to the environment and thus can potentially operate interchangeably and simultaneously. As adhesion-free migration is independent of the chemical composition of the environment, it renders cells completely autonomous in their locomotive behaviour.}, author = {Reversat, Anne and Gärtner, Florian R and Merrin, Jack and Stopp, Julian A and Tasciyan, Saren and Aguilera Servin, Juan L and De Vries, Ingrid and Hauschild, Robert and Hons, Miroslav and Piel, Matthieu and Callan-Jones, Andrew and Voituriez, Raphael and Sixt, Michael K}, issn = {14764687}, journal = {Nature}, pages = {582–585}, publisher = {Springer Nature}, title = {{Cellular locomotion using environmental topography}}, doi = {10.1038/s41586-020-2283-z}, volume = {582}, year = {2020}, } @article{8787, abstract = {Breakdown of vascular barriers is a major complication of inflammatory diseases. Anucleate platelets form blood-clots during thrombosis, but also play a crucial role in inflammation. While spatio-temporal dynamics of clot formation are well characterized, the cell-biological mechanisms of platelet recruitment to inflammatory micro-environments remain incompletely understood. Here we identify Arp2/3-dependent lamellipodia formation as a prominent morphological feature of immune-responsive platelets. Platelets use lamellipodia to scan for fibrin(ogen) deposited on the inflamed vasculature and to directionally spread, to polarize and to govern haptotactic migration along gradients of the adhesive ligand. Platelet-specific abrogation of Arp2/3 interferes with haptotactic repositioning of platelets to microlesions, thus impairing vascular sealing and provoking inflammatory microbleeding. During infection, haptotaxis promotes capture of bacteria and prevents hematogenic dissemination, rendering platelets gate-keepers of the inflamed microvasculature. Consequently, these findings identify haptotaxis as a key effector function of immune-responsive platelets.}, author = {Nicolai, Leo and Schiefelbein, Karin and Lipsky, Silvia and Leunig, Alexander and Hoffknecht, Marie and Pekayvaz, Kami and Raude, Ben and Marx, Charlotte and Ehrlich, Andreas and Pircher, Joachim and Zhang, Zhe and Saleh, Inas and Marel, Anna-Kristina and Löf, Achim and Petzold, Tobias and Lorenz, Michael and Stark, Konstantin and Pick, Robert and Rosenberger, Gerhild and Weckbach, Ludwig and Uhl, Bernd and Xia, Sheng and Reichel, Christoph Andreas and Walzog, Barbara and Schulz, Christian and Zheden, Vanessa and Bender, Markus and Li, Rong and Massberg, Steffen and Gärtner, Florian R}, issn = {20411723}, journal = {Nature Communications}, publisher = {Springer Nature}, title = {{Vascular surveillance by haptotactic blood platelets in inflammation and infection}}, doi = {10.1038/s41467-020-19515-0}, volume = {11}, year = {2020}, } @article{6824, abstract = {Platelets are small anucleate cellular fragments that are released by megakaryocytes and safeguard vascular integrity through a process termed ‘haemostasis’. However, platelets have important roles beyond haemostasis as they contribute to the initiation and coordination of intravascular immune responses. They continuously monitor blood vessel integrity and tightly coordinate vascular trafficking and functions of multiple cell types. In this way platelets act as ‘patrolling officers of the vascular highway’ that help to establish effective immune responses to infections and cancer. Here we discuss the distinct biological features of platelets that allow them to shape immune responses to pathogens and tumour cells, highlighting the parallels between these responses.}, author = {Gärtner, Florian R and Massberg, Steffen}, issn = {1474-1741}, journal = {Nature Reviews Immunology}, number = {12}, pages = {747–760}, publisher = {Springer Nature}, title = {{Patrolling the vascular borders: Platelets in immunity to infection and cancer}}, doi = {10.1038/s41577-019-0202-z}, volume = {19}, year = {2019}, } @article{6988, abstract = {Platelets are central players in thrombosis and hemostasis but are increasingly recognized as key components of the immune system. They shape ensuing immune responses by recruiting leukocytes, and support the development of adaptive immunity. Recent data shed new light on the complex role of platelets in immunity. Here, we summarize experimental and clinical data on the role of platelets in host defense against bacteria. Platelets bind, contain, and kill bacteria directly; however, platelet proinflammatory effector functions and cross-talk with the coagulation system, can also result in damage to the host (e.g., acute lung injury and sepsis). Novel clinical insights support this dichotomy: platelet inhibition/thrombocytopenia can be either harmful or protective, depending on pathophysiological context. Clinical studies are currently addressing this aspect in greater depth.}, author = {Nicolai, Leo and Gärtner, Florian R and Massberg, Steffen}, issn = {1471-4906}, journal = {Trends in Immunology}, number = {10}, pages = {922--938}, publisher = {Cell Press}, title = {{Platelets in host defense: Experimental and clinical insights}}, doi = {10.1016/j.it.2019.08.004}, volume = {40}, year = {2019}, } @article{6354, abstract = {Blood platelets are critical for hemostasis and thrombosis, but also play diverse roles during immune responses. We have recently reported that platelets migrate at sites of infection in vitro and in vivo. Importantly, platelets use their ability to migrate to collect and bundle fibrin (ogen)-bound bacteria accomplishing efficient intravascular bacterial trapping. Here, we describe a method that allows analyzing platelet migration in vitro, focusing on their ability to collect bacteria and trap bacteria under flow.}, author = {Fan, Shuxia and Lorenz, Michael and Massberg, Steffen and Gärtner, Florian R}, issn = {2331-8325}, journal = {Bio-Protocol}, keywords = {Platelets, Cell migration, Bacteria, Shear flow, Fibrinogen, E. coli}, number = {18}, publisher = {Bio-Protocol}, title = {{Platelet migration and bacterial trapping assay under flow}}, doi = {10.21769/bioprotoc.3018}, volume = {8}, year = {2018}, } @article{15, abstract = {Although much is known about the physiological framework of T cell motility, and numerous rate-limiting molecules have been identified through loss-of-function approaches, an integrated functional concept of T cell motility is lacking. Here, we used in vivo precision morphometry together with analysis of cytoskeletal dynamics in vitro to deconstruct the basic mechanisms of T cell migration within lymphatic organs. We show that the contributions of the integrin LFA-1 and the chemokine receptor CCR7 are complementary rather than positioned in a linear pathway, as they are during leukocyte extravasation from the blood vasculature. Our data demonstrate that CCR7 controls cortical actin flows, whereas integrins mediate substrate friction that is sufficient to drive locomotion in the absence of considerable surface adhesions and plasma membrane flux.}, author = {Hons, Miroslav and Kopf, Aglaja and Hauschild, Robert and Leithner, Alexander F and Gärtner, Florian R and Abe, Jun and Renkawitz, Jörg and Stein, Jens and Sixt, Michael K}, journal = {Nature Immunology}, number = {6}, pages = {606 -- 616}, publisher = {Nature Publishing Group}, title = {{Chemokines and integrins independently tune actin flow and substrate friction during intranodal migration of T cells}}, doi = {10.1038/s41590-018-0109-z}, volume = {19}, year = {2018}, } @article{571, abstract = {Blood platelets are critical for hemostasis and thrombosis and play diverse roles during immune responses. Despite these versatile tasks in mammalian biology, their skills on a cellular level are deemed limited, mainly consisting in rolling, adhesion, and aggregate formation. Here, we identify an unappreciated asset of platelets and show that adherent platelets use adhesion receptors to mechanically probe the adhesive substrate in their local microenvironment. When actomyosin-dependent traction forces overcome substrate resistance, platelets migrate and pile up the adhesive substrate together with any bound particulate material. They use this ability to act as cellular scavengers, scanning the vascular surface for potential invaders and collecting deposited bacteria. Microbe collection by migrating platelets boosts the activity of professional phagocytes, exacerbating inflammatory tissue injury in sepsis. This assigns platelets a central role in innate immune responses and identifies them as potential targets to dampen inflammatory tissue damage in clinical scenarios of severe systemic infection. In addition to their role in thrombosis and hemostasis, platelets can also migrate to sites of infection to help trap bacteria and clear the vascular surface.}, author = {Gärtner, Florian R and Ahmad, Zerkah and Rosenberger, Gerhild and Fan, Shuxia and Nicolai, Leo and Busch, Benjamin and Yavuz, Gökce and Luckner, Manja and Ishikawa Ankerhold, Hellen and Hennel, Roman and Benechet, Alexandre and Lorenz, Michael and Chandraratne, Sue and Schubert, Irene and Helmer, Sebastian and Striednig, Bianca and Stark, Konstantin and Janko, Marek and Böttcher, Ralph and Verschoor, Admar and Leon, Catherine and Gachet, Christian and Gudermann, Thomas and Mederos Y Schnitzler, Michael and Pincus, Zachary and Iannacone, Matteo and Haas, Rainer and Wanner, Gerhard and Lauber, Kirsten and Sixt, Michael K and Massberg, Steffen}, issn = {00928674}, journal = {Cell Press}, number = {6}, pages = {1368 -- 1382}, publisher = {Cell Press}, title = {{Migrating platelets are mechano scavengers that collect and bundle bacteria}}, doi = {10.1016/j.cell.2017.11.001}, volume = {171}, year = {2017}, } @article{3957, author = {Riedl, Julia and Flynn, Kevin C and Raducanu, Aurelia and Florian Gärtner and Beck, Gisela and Bosl, Michael and Bradke, Frank and Massberg, Steffen and Aszodi, Attila and Michael Sixt and Wedlich-Söldner, Roland}, journal = {Nature Methods}, number = {3}, pages = {168 -- 169}, publisher = {Nature Publishing Group}, title = {{Lifeact mice for studying F-actin dynamics}}, doi = {10.1038/nmeth0310-168}, volume = {7}, year = {2010}, }