@article{PfeifferGoetzXiangetal.2013, author = {Pfeiffer, Verena and G{\"o}tz, Rudolf and Xiang, Chaomei and Camarero, Guadelupe and Braun, Attila and Zhang, Yina and Blum, Robert and Heinsen, Helmut and Nieswandt, Bernhard and Rapp, Ulf R.}, title = {Ablation of BRaf Impairs Neuronal Differentiation in the Postnatal Hippocampus and Cerebellum}, series = {PLoS ONE}, volume = {8}, journal = {PLoS ONE}, number = {3}, doi = {10.1371/journal.pone.0058259}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-130304}, pages = {e58259}, year = {2013}, abstract = {This study focuses on the role of the kinase BRaf in postnatal brain development. Mice expressing truncated, non-functional BRaf in neural stem cell-derived brain tissue demonstrate alterations in the cerebellum, with decreased sizes and fuzzy borders of the glomeruli in the granule cell layer. In addition we observed reduced numbers and misplaced ectopic Purkinje cells that showed an altered structure of their dendritic arborizations in the hippocampus, while the overall cornus ammonis architecture appeared to be unchanged. In male mice lacking BRaf in the hippocampus the size of the granule cell layer was normal at postnatal day 12 (P12) but diminished at P21, as compared to control littermates. This defect was caused by a reduced ability of dentate gyrus progenitor cells to differentiate into NeuN positive granule cell neurons. In vitro cell culture of P0/P1 hippocampal cells revealed that BRaf deficient cells were impaired in their ability to form microtubule-associated protein 2 positive neurons. Together with the alterations in behaviour, such as autoaggression and loss of balance fitness, these observations indicate that in the absence of BRaf all neuronal cellular structures develop, but neuronal circuits in the cerebellum and hippocampus are partially disturbed besides impaired neuronal generation in both structures.}, language = {en} } @article{NieswandtMorowskiBrachsetal.2014, author = {Nieswandt, Bernhard and Morowski, Martina and Brachs, Sebastian and Mielenz, Dirk and D{\"u}tting, Sebastian}, title = {The Adaptor Protein Swiprosin-1/EFhd2 Is Dispensable for Platelet Function in Mice}, doi = {10.1371/journal.pone.0107139}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-113316}, year = {2014}, abstract = {Background Platelets are anuclear cell fragments derived from bone marrow megakaryocytes that safeguard vascular integrity, but may also cause pathological vessel occlusion. Reorganizations of the platelet cytoskeleton and agonist-induced intracellular Ca2+-mobilization are crucial for platelet hemostatic function. EF-hand domain containing 2 (EFhd2, Swiprosin-1) is a Ca2+-binding cytoskeletal adaptor protein involved in actin remodeling in different cell types, but its function in platelets is unknown. Objective Based on the described functions of EFhd2 in immune cells, we tested the hypothesis that EFhd2 is a crucial adaptor protein for platelet function acting as a regulator of Ca2+-mobilization and cytoskeletal rearrangements. Methods and Results We generated EFhd2-deficient mice and analyzed their platelets in vitro and in vivo. Efhd2-/- mice displayed normal platelet count and size, exhibited an unaltered in vivo life span and showed normal Ca2+-mobilization and activation/aggregation responses to classic agonists. Interestingly, upon stimulation of the immunoreceptor tyrosine-based activation motif-coupled receptor glycoprotein (GP) VI, Efhd2-/- platelets showed a slightly increased coagulant activity. Furthermore, absence of EFhd2 had no significant impact on integrin-mediated clot retraction, actomyosin rearrangements and spreading of activated platelets on fibrinogen. In vivo EFhd2-deficiency resulted in unaltered hemostatic function and unaffected arterial thrombus formation. Conclusion These results show that EFhd2 is not essential for platelet function in mice indicating that other cytoskeletal adaptors may functionally compensate its loss.}, language = {en} } @article{AmmarThahoulyHanaueretal.2015, author = {Ammar, Mohamed Raafet and Thahouly, Tamou and Hanauer, Andr{\´e} and Stegner, David and Nieswandt, Bernhard and Vitale, Nicolas}, title = {PLD1 participates in BDNF-induced signalling in cortical neurons}, series = {Scientific Reports}, volume = {5}, journal = {Scientific Reports}, number = {14778}, doi = {10.1038/srep14778}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-139962}, year = {2015}, abstract = {The brain-derived neurotrophic factor BDNF plays a critical role in neuronal development and the induction of L-LTP at glutamatergic synapses in several brain regions. However, the cellular and molecular mechanisms underlying these BDNF effects have not been firmly established. Using in vitro cultures of cortical neurons from knockout mice for Pld1 and Rsk2, BDNF was observed to induce a rapid RSK2-dependent activation of PLD and to stimulate BDNF ERK1/2-CREB and mTor-S6K signalling pathways, but these effects were greatly reduced in Pld1\(^{-/-}\) neurons. Furthermore, phospho-CREB did not accumulate in the nucleus, whereas overexpression of PLD1 amplified the BDNF-dependent nuclear recruitment of phospho-ERK1/2 and phospho-CREB. This BDNF retrograde signalling was prevented in cells silenced for the scaffolding protein PEA15, a protein which complexes with PLD1, ERK1/2, and RSK2 after BDNF treatment. Finally PLD1, ERK1/2, and RSK2 partially colocalized on endosomal structures, suggesting that these proteins are part of the molecular module responsible for BDNF signalling in cortical neurons.}, language = {en} } @article{WolfBraunHainingetal.2016, author = {Wolf, Karen and Braun, Attila and Haining, Elizabeth J. and Tseng, Yu-Lun and Kraft, Peter and Schuhmann, Michael K. and Gotru, Sanjeev K. and Chen, Wenchun and Hermanns, Heike M. and Stoll, Guido and Lesch, Klaus-Peter and Nieswandt, Bernhard}, title = {Partially Defective Store Operated Calcium Entry and Hem(ITAM) Signaling in Platelets of Serotonin Transporter Deficient Mice}, series = {PLoS One}, volume = {11}, journal = {PLoS One}, number = {1}, doi = {10.1371/journal.pone.0147664}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-146399}, pages = {e0147664}, year = {2016}, abstract = {Background Serotonin (5-hydroxytryptamin, 5-HT) is an indolamine platelet agonist, biochemically derived from tryptophan. 5-HT is secreted from the enterochromaffin cells into the gastrointestinal tract and blood. Blood 5-HT has been proposed to regulate hemostasis by acting as a vasoconstrictor and by triggering platelet signaling through 5-HT receptor 2A (5HTR2A). Although platelets do not synthetize 5-HT, they take 5-HT up from the blood and store it in their dense granules which are secreted upon platelet activation. Objective To identify the molecular composite of the 5-HT uptake system in platelets and elucidate the role of platelet released 5-HT in thrombosis and ischemic stroke. Methods: 5-HT transporter knockout mice (5Htt\(^{-/-}\)) were analyzed in different in vitro and in vivo assays and in a model of ischemic stroke. Results In 5Htt\(^{-/-}\) platelets, 5-HT uptake from the blood was completely abolished and agonist-induced Ca2+ influx through store operated Ca\(^{2+}\) entry (SOCE), integrin activation, degranulation and aggregation responses to glycoprotein VI (GPVI) and C-type lectin-like receptor 2 (CLEC-2) were reduced. These observed in vitro defects in 5Htt\(^{-/-}\) platelets could be normalized by the addition of exogenous 5-HT. Moreover, reduced 5-HT levels in the plasma, an increased bleeding time and the formation of unstable thrombi were observed ex vivo under flow and in vivo in the abdominal aorta and carotid artery of 5Htt\(^{-/-}\) mice. Surprisingly, in the transient middle cerebral artery occlusion (tMCAO) model of ischemic stroke 5Htt\(^{-/-}\) mice showed nearly normal infarct volume and the neurological outcome was comparable to control mice. Conclusion Although secreted platelet 5-HT does not appear to play a crucial role in the development of reperfusion injury after stroke, it is essential to amplify the second phase of platelet activation through SOCE and plays an important role in thrombus stabilization.}, language = {en} } @article{ChilloKleinertLautzetal.2016, author = {Chillo, Omary and Kleinert, Eike Christian and Lautz, Thomas and Lasch, Manuel and Pagel, Judith-Irina and Heun, Yvonn and Troidl, Kerstin and Fischer, Silvia and Caballero-Martinez, Amelia and Mauer, Annika and Kurz, Angela R. M. and Assmann, Gerald and Rehberg, Markus and Kanse, Sandip M. and Nieswandt, Bernhard and Walzog, Barbara and Reichel, Christoph A. and Mannell, Hanna and Preissner, Klaus T. and Deindl, Elisabeth}, title = {Perivascular Mast Cells Govern Shear Stress-Induced Arteriogenesis by Orchestrating Leukocyte Function}, series = {Cell Reports}, volume = {16}, journal = {Cell Reports}, number = {8}, doi = {10.1016/j.celrep.2016.07.040}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-164800}, pages = {2197-2207}, year = {2016}, abstract = {The body has the capacity to compensate for an occluded artery by creating a natural bypass upon increased fluid shear stress. How this mechanical force is translated into collateral artery growth (arteriogenesis) is unresolved. We show that extravasation of neutrophils mediated by the platelet receptor GPIbα and uPA results in Nox2-derived reactive oxygen radicals, which activate perivascular mast cells. These c-kit+/CXCR-4+ cells stimulate arteriogenesis by recruiting additional neutrophils as well as growth-promoting monocytes and T cells. Additionally, mast cells may directly contribute to vascular remodeling and vascular cell proliferation through increased MMP activity and by supplying growth-promoting factors. Boosting mast cell recruitment and activation effectively promotes arteriogenesis, thereby protecting tissue from severe ischemic damage. We thus find that perivascular mast cells are central regulators of shear stress-induced arteriogenesis by orchestrating leukocyte function and growth factor/cytokine release, thus providing a therapeutic target for treatment of vascular occlusive diseases.}, language = {en} } @article{StrittNurdenFavieretal.2016, author = {Stritt, Simon and Nurden, Paquita and Favier, Remi and Favier, Marie and Ferioli, Silvia and Gotru, Sanjeev K. and van Eeuwijk, Judith M.M. and Schulze, Harald and Nurden, Alan T. and Lambert, Michele P. and Turro, Ernest and Burger-Stritt, Stephanie and Matsushita, Masayuki and Mittermeier, Lorenz and Ballerini, Paola and Zierler, Susanna and Laffan, Michael A. and Chubanov, Vladimir and Gudermann, Thomas and Nieswandt, Bernhard and Braun, Attila}, title = {Defects in TRPM7 channel function deregulate thrombopoiesis through altered cellular Mg\(^{2+}\) homeostasis and cytoskeletal architecture}, series = {Nature Communications}, volume = {7}, journal = {Nature Communications}, doi = {10.1038/ncomms11097}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173843}, year = {2016}, abstract = {Mg\(^{2+}\) plays a vital role in platelet function, but despite implications for life-threatening conditions such as stroke or myocardial infarction, the mechanisms controlling [Mg\(^{2+}\)]i in megakaryocytes (MKs) and platelets are largely unknown. Transient receptor potential melastatin-like 7 channel (TRPM7) is a ubiquitous, constitutively active cation channel with a cytosolic α-kinase domain that is critical for embryonic development and cell survival. Here we report that impaired channel function of TRPM7 in MKs causes macrothrombocytopenia in mice (Trpm7\(^{fl/fl-Pf4Cre}\)) and likely in several members of a human pedigree that, in addition, suffer from atrial fibrillation. The defect in platelet biogenesis is mainly caused by cytoskeletal alterations resulting in impaired proplatelet formation by Trpm7\(^{fl/fl-Pf4Cre}\) MKs, which is rescued by Mg\(^{2+}\) supplementation or chemical inhibition of non-muscle myosin IIA heavy chain activity. Collectively, our findings reveal that TRPM7 dysfunction may cause macrothrombocytopenia in humans and mice.}, language = {en} } @article{VieraElMerahbiNieswandtetal.2016, author = {Viera, Jonathan Trujillo and El-Merahbi, Rabih and Nieswandt, Bernhard and Stegner, David and Sumara, Grzegorz}, title = {Phospholipases D1 and D2 Suppress Appetite and Protect against Overweight}, series = {PLoS ONE}, volume = {11}, journal = {PLoS ONE}, number = {6}, doi = {10.1371/journal.pone.0157607}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-179729}, year = {2016}, abstract = {Obesity is a major risk factor predisposing to the development of peripheral insulin resistance and type 2 diabetes (T2D). Elevated food intake and/or decreased energy expenditure promotes body weight gain and acquisition of adipose tissue. Number of studies implicated phospholipase D (PLD) enzymes and their product, phosphatidic acid (PA), in regulation of signaling cascades controlling energy intake, energy dissipation and metabolic homeostasis. However, the impact of PLD enzymes on regulation of metabolism has not been directly determined so far. In this study we utilized mice deficient for two major PLD isoforms, PLD1 and PLD2, to assess the impact of these enzymes on regulation of metabolic homeostasis. We showed that mice lacking PLD1 or PLD2 consume more food than corresponding control animals. Moreover, mice deficient for PLD2, but not PLD1, present reduced energy expenditure. In addition, deletion of either of the PLD enzymes resulted in development of elevated body weight and increased adipose tissue content in aged animals. Consistent with the fact that elevated content of adipose tissue predisposes to the development of hyperlipidemia and insulin resistance, characteristic for the pre-diabetic state, we observed that Pld1\(^{-/-}\) and Pld2\(^{-/-}\) mice present elevated free fatty acids (FFA) levels and are insulin as well as glucose intolerant. In conclusion, our data suggest that deficiency of PLD1 or PLD2 activity promotes development of overweight and diabetes.}, language = {en} } @article{DuettingGaitsIacovoniStegneretal.2017, author = {D{\"u}tting, Sebastian and Gaits-Iacovoni, Frederique and Stegner, David and Popp, Michael and Antkowiak, Adrien and van Eeuwijk, Judith M.M. and Nurden, Paquita and Stritt, Simon and Heib, Tobias and Aurbach, Katja and Angay, Oguzhan and Cherpokova, Deya and Heinz, Niels and Baig, Ayesha A. and Gorelashvili, Maximilian G. and Gerner, Frank and Heinze, Katrin G. and Ware, Jerry and Krohne, Georg and Ruggeri, Zaverio M. and Nurden, Alan T. and Schulze, Harald and Modlich, Ute and Pleines, Irina and Brakebusch, Cord and Nieswandt, Bernhard}, title = {A Cdc42/RhoA regulatory circuit downstream of glycoprotein Ib guides transendothelial platelet biogenesis}, series = {Nature Communications}, volume = {8}, journal = {Nature Communications}, number = {15838}, doi = {10.1038/ncomms15838}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170797}, year = {2017}, abstract = {Blood platelets are produced by large bone marrow (BM) precursor cells, megakaryocytes (MKs), which extend cytoplasmic protrusions (proplatelets) into BM sinusoids. The molecular cues that control MK polarization towards sinusoids and limit transendothelial crossing to proplatelets remain unknown. Here, we show that the small GTPases Cdc42 and RhoA act as a regulatory circuit downstream of the MK-specific mechanoreceptor GPIb to coordinate polarized transendothelial platelet biogenesis. Functional deficiency of either GPIb or Cdc42 impairs transendothelial proplatelet formation. In the absence of RhoA, increased Cdc42 activity and MK hyperpolarization triggers GPIb-dependent transmigration of entire MKs into BM sinusoids. These findings position Cdc42 (go-signal) and RhoA (stop-signal) at the centre of a molecular checkpoint downstream of GPIb that controls transendothelial platelet biogenesis. Our results may open new avenues for the treatment of platelet production disorders and help to explain the thrombocytopenia in patients with Bernard-Soulier syndrome, a bleeding disorder caused by defects in GPIb-IX-V.}, language = {en} } @article{StegnervanEeuwijkAngayetal.2017, author = {Stegner, David and van Eeuwijk, Judith M.M. and Angay, Oğuzhan and Gorelashvili, Maximilian G. and Semeniak, Daniela and Pinnecker, J{\"u}rgen and Schmithausen, Patrick and Meyer, Imke and Friedrich, Mike and D{\"u}tting, Sebastian and Brede, Christian and Beilhack, Andreas and Schulze, Harald and Nieswandt, Bernhard and Heinze, Katrin G.}, title = {Thrombopoiesis is spatially regulated by the bone marrow vasculature}, series = {Nature Communications}, volume = {8}, journal = {Nature Communications}, number = {127}, doi = {10.1038/s41467-017-00201-7}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170591}, year = {2017}, abstract = {In mammals, megakaryocytes (MKs) in the bone marrow (BM) produce blood platelets, required for hemostasis and thrombosis. MKs originate from hematopoietic stem cells and are thought to migrate from an endosteal niche towards the vascular sinusoids during their maturation. Through imaging of MKs in the intact BM, here we show that MKs can be found within the entire BM, without a bias towards bone-distant regions. By combining in vivo two-photon microscopy and in situ light-sheet fluorescence microscopy with computational simulations, we reveal surprisingly slow MK migration, limited intervascular space, and a vessel-biased MK pool. These data challenge the current thrombopoiesis model of MK migration and support a modified model, where MKs at sinusoids are replenished by sinusoidal precursors rather than cells from a distant periostic niche. As MKs do not need to migrate to reach the vessel, therapies to increase MK numbers might be sufficient to raise platelet counts.}, language = {en} } @article{SchuhmannGuthmannStolletal.2017, author = {Schuhmann, Michael K. and Guthmann, Josua and Stoll, Guido and Nieswandt, Bernhard and Kraft, Peter and Kleinschnitz, Christoph}, title = {Blocking of platelet glycoprotein receptor Ib reduces "thrombo-inflammation" in mice with acute ischemic stroke}, series = {Journal of Neuroinflammation}, volume = {14}, journal = {Journal of Neuroinflammation}, number = {18}, doi = {10.1186/s12974-017-0792-y}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-157582}, year = {2017}, abstract = {Background: Ischemic stroke causes a strong inflammatory response that includes T cells, monocytes/macrophages, and neutrophils. Interaction of these immune cells with platelets and endothelial cells facilitates microvascular dysfunction and leads to secondary infarct growth. We recently showed that blocking of platelet glycoprotein (GP) receptor Ib improves stroke outcome without increasing the risk of intracerebral hemorrhage. Until now, it has been unclear whether GPIb only mediates thrombus formation or also contributes to the pathophysiology of local inflammation. Methods: Focal cerebral ischemia was induced in C57BL/6 mice by a 60-min transient middle cerebral artery occlusion (tMCAO). Animals were treated with antigen-binding fragments (Fab) against the platelet surface molecules GPIb (p0p/B Fab). Rat immunoglobulin G (IgG) Fab was used as control treatment. Stroke outcome, including infarct size and functional deficits as well as the local inflammatory response, was assessed on day 1 after tMCAO. Results: Blocking of GPIb reduced stroke size and improved functional outcome on day 1 after tMCAO without increasing the risk of intracerebral hemorrhage. As expected, disruption of GPIb-mediated pathways in platelets significantly reduced thrombus burden in the cerebral microvasculature. In addition, inhibition of GPIb limited the local inflammatory response in the ischemic brain as indicated by lower numbers of infiltrating T cells and macrophages and lower expression levels of inflammatory cytokines compared with rat IgG Fab-treated controls. Conclusion: In acute ischemic stroke, thrombus formation and inflammation are closely intertwined ("thrombo-inflammation"). Blocking of platelet GPIb can ameliorate thrombo-inflammation.}, language = {en} }