Harald F Langer

Publications of Harald F Langer

• Platelets Contribute to the Pathogenesis of Experimental Autoimmune Encephalomyelitis.

  Authors: Harald F Langer, Eun Young Choi, Hong Zhou, Rebecca Schleicher, Kyoung-Jin Chung, Zhongshu Tang, Kerstin Göbel, Khalil Bdeir, Antonios Chatzigeorgiou, Connie Wong [......] Elin Lehrmann, Kevin G Becker, Yunmei Wang, Daniel I Simon, Bernhard Nieswandt, John D Lambris, Xuri Li, Sven G Meuth, Paul Kubes, Triantafyllos Chavakis

  Circulation research. 03/2012;

  Rationale:Multiple sclerosis (MS) and its mouse model, experimental autoimmune encephalomyelitis (EAE), are inflammatory disorders of the central nervous system (CNS). The function of platelets inRationale:Multiple sclerosis (MS) and its mouse model, experimental autoimmune encephalomyelitis (EAE), are inflammatory disorders of the central nervous system (CNS). The function of platelets in inflammatory and autoimmune pathologies is thus far poorly defined.Objective:We addressed the role of platelets in mediating CNS inflammation in EAE.Methods and Results:We found that platelets were present in human MS lesions as well as in the CNS of mice subjected to EAE but not in the CNS from control nondiseased mice. Platelet depletion at the effector-inflammatory phase of EAE in mice resulted in significantly ameliorated disease development and progression. EAE suppression on platelet depletion was associated with reduced recruitment of leukocytes to the inflamed CNS, as assessed by intravital microscopy, and with a blunted inflammatory response. The platelet-specific receptor glycoprotein Ibα (GPIbα) promotes both platelet adhesion and inflammatory actions of platelets and targeting of GPIbα attenuated EAE in mice. Moreover, targeting another platelet adhesion receptor, glycoprotein IIb/IIIa (GPIIb/IIIa), also reduced EAE severity in mice.Conclusions:Platelets contribute to the pathogenesis of EAE by promoting CNS inflammation. Targeting platelets may therefore represent an important new therapeutic approach for MS treatment.

• Platelets in Angiogenesis.

  Authors: Johannes Patzelt, Harald F Langer

  Current vascular pharmacology. 02/2012;

  Platelets hold an important function as first line of response to seal wounds after vascular and tissue injury. However, they are much more than just a component of the haemostatic system. They arePlatelets hold an important function as first line of response to seal wounds after vascular and tissue injury. However, they are much more than just a component of the haemostatic system. They are involved in tissue regeneration and play a role in different pathologic conditions such as atherosclerosis or tumour progression. Angiogenesis being involved in these processes, as well, may represent one of the (patho-) physiological mechanisms, which are modulated by platelets thereby affecting disease. In other diseases involving inflammation, the role of platelets for endothelial cells, which are the most important cell type in angiogenesis, is well established. Recent effort has now highlighted a potential role of platelets and platelet derived mediators for angiogenesis. This article reviews our current understanding of the role of platelets for angiogenesis and how this knowledge could affect future directions in research and therapy.

• Engagement of αIIbβ3 (GPIIb/IIIa) with ανβ3 integrin mediates interaction of melanoma cells with platelets: a connection to hematogenous metastasis.

  Authors: Anke S Lonsdorf, Björn F Krämer, Manuela Fahrleitner, Tanja Schönberger, Stephan Gnerlich, Sabine Ring, Sarah Gehring, Stefan W Schneider, Michael J Kruhlak, Sven G Meuth, Bernhard Nieswandt, Meinrad Gawaz, Alexander H Enk, Harald F Langer

  The Journal of biological chemistry. 11/2011; 287(3):2168-78.

  A mutual relationship exists between metastasizing tumor cells and components of the coagulation cascade. The exact mechanisms as to how platelets influence blood-borne metastasis, however, remainA mutual relationship exists between metastasizing tumor cells and components of the coagulation cascade. The exact mechanisms as to how platelets influence blood-borne metastasis, however, remain poorly understood. Here, we used murine B16 melanoma cells to observe functional aspects of how platelets contribute to the process of hematogenous metastasis. We found that platelets interfere with a distinct step of the metastasis cascade, as they promote adhesion of melanoma cells to the endothelium in vitro under shear conditions. Constitutively active platelet receptor GPIIb/IIIa (integrin αIIbβ3) expressed on Chinese hamster ovary cells promoted melanoma cell adhesion in the presence of fibrinogen, whereas blocking antibodies to aνβ3 integrin on melanoma cells or to GPIIb/IIIa significantly reduced melanoma cell adhesion to platelets. Furthermore, using intravital microscopy, we observed functional platelet-melanoma cell interactions, as platelet depletion resulted in significantly reduced melanoma cell adhesion to the injured vascular wall in vivo. Using a mouse model of hematogenous metastasis to the lung, we observed decreased metastasis of B16 melanoma cells to the lung by treatment with a mAb blocking the aν subunit of aνβ3 integrin. This effect was significantly reduced when platelets were depleted in vivo. Thus, the engagement of GPIIb/IIIa with aνβ3 integrin interaction mediates tumor cell-platelet interactions and highlights how this interaction is involved in hematogenous tumor metastasis.

• A novel function of junctional adhesion molecule-C in mediating melanoma cell metastasis.

  Authors: Harald F Langer, Valeria V Orlova, Changping Xie, Sunil Kaul, Darius Schneider, Anke S Lonsdorf, Manuela Fahrleitner, Eun Young Choi, Vanessa Dutoit, Manuela Pellegrini, Sylvia Grossklaus, Peter P Nawroth, Gustavo Baretton, Sentot Santoso, Sam T Hwang, Bernd Arnold, Triantafyllos Chavakis

  Cancer research. 06/2011; 71(12):4096-105.

  Hematogenous dissemination of melanoma is a life-threatening complication of this malignant tumor. Here, we identified junctional adhesion molecule-C (JAM-C) as a novel player in melanoma metastasisHematogenous dissemination of melanoma is a life-threatening complication of this malignant tumor. Here, we identified junctional adhesion molecule-C (JAM-C) as a novel player in melanoma metastasis to the lung. JAM-C expression was identified in human and murine melanoma cell lines, in human malignant melanoma, as well as in metastatic melanoma including melanoma lung metastasis. JAM-C expressed on both murine B16 melanoma cells as well as on endothelial cells promoted the transendothelial migration of the melanoma cells. We generated mice with inactivation of JAM-C. JAM-C(-/-) mice as well as endothelial-specific JAM-C-deficient mice displayed significantly decreased B16 melanoma cell metastasis to the lung, whereas treatment of mice with soluble JAM-C prevented melanoma lung metastasis. Together, JAM-C represents a novel therapeutic target for melanoma metastasis.

• Blockade of the kinin receptor B1 protects from autoimmune CNS disease by reducing leukocyte trafficking.

  Authors: Kerstin Göbel, Susann Pankratz, Tilman Schneider-Hohendorf, Stefan Bittner, Michael K Schuhmann, Harald F Langer, Guido Stoll, Heinz Wiendl, Christoph Kleinschnitz, Sven G Meuth

  Journal of autoimmunity. 01/2011; 36(2):106-14.

  Disruption of the blood brain barrier (BBB) and transendothelial trafficking of immune cells into the central nervous system (CNS) are pathophysiological hallmarks of Multiple Sclerosis (MS) and itsDisruption of the blood brain barrier (BBB) and transendothelial trafficking of immune cells into the central nervous system (CNS) are pathophysiological hallmarks of Multiple Sclerosis (MS) and its animal model, Experimental Autoimmune Encephalomyelitis (EAE). Kinins are proinflammatory peptides which are released during tissue injury including EAE. They increase vascular permeability and enhance inflammation by acting on distinct bradykinin receptors, B1R and B2R. We studied the expression of B1R and B2R and the effect of their inhibition on the disease course, BBB integrity and T cell migration following myelin oligodendrocyte glycoprotein (MOG(35-55))-induced EAE. B1R, but not B2R expression was markedly enhanced in inflammatory CNS lesions in mice and humans. Brain endothelial cells could be identified as major source of B1R protein. The severity of EAE was significantly alleviated in B1R(-/-) mice compared with wild-type (WT) controls (P<0.05). Treatment of WT mice with the B1R antagonist R715 before and after disease onset was equally effective (P<0.05) while B1R activation by R838 promoted EAE (P<0.05). B1R inhibition was accompanied by a remarkable reduction of BBB disruption and tissue inflammation. In vitro analyses revealed that B1R suppression reverses the upregulation of ICAM-I and VCAM-I at the inflamed BBB thereby limiting T cell transmigration. In contrast, blocking B2R had no significant impact on EAE. We conclude that B1R inhibition can reduce BBB damage and cell invasion during autoimmune CNS disease and may offer a novel anti-inflammatory strategy for the treatment of MS.

• Complement-mediated inhibition of neovascularization reveals a point of convergence between innate immunity and angiogenesis.

  Authors: Harald F Langer, Kyoung-Jin Chung, Valeria V Orlova, Eun Young Choi, Sunil Kaul, Michael J Kruhlak, Markella Alatsatianos, Robert A Deangelis, Paul A Roche, Paola Magotti, Xuri Li, Matina Economopoulou, Stavros Rafail, John D Lambris, Triantafyllos Chavakis

  Blood. 11/2010; 116(22):4395-403.

  Beyond its role in immunity, complement mediates a wide range of functions in the context of morphogenetic or tissue remodeling processes. Angiogenesis is crucial during tissue remodeling in multipleBeyond its role in immunity, complement mediates a wide range of functions in the context of morphogenetic or tissue remodeling processes. Angiogenesis is crucial during tissue remodeling in multiple pathologies; however, the knowledge about the regulation of neovascularization by the complement components is scarce. Here we studied the involvement of complement in pathological angiogenesis. Strikingly, we found that mice deficient in the central complement component C3 displayed increased neovascularization in the model of retinopathy of prematurity (ROP) and in the in vivo Matrigel plug assay. In addition, antibody-mediated blockade of C5, treatment with C5aR antagonist, or C5aR deficiency in mice resulted in enhanced pathological retina angiogenesis. While complement did not directly affect angiogenesis-related endothelial cell functions, we found that macrophages mediated the antiangiogenic activity of complement. In particular, C5a-stimulated macrophages were polarized toward an angiogenesis-inhibitory phenotype, including the up-regulated secretion of the antiangiogenic soluble vascular endothelial growth factor receptor-1. Consistently, macrophage depletion in vivo reversed the increased neovascularization associated with C3- or C5aR deficiency. Taken together, complement and in particular the C5a-C5aR axes are potent inhibitors of angiogenesis.

• Capture of endothelial progenitor cells by a bispecific protein/monoclonal antibody molecule induces reendothelialization of vascular lesions.

  Authors: Harald F Langer, Jürgen W von der Ruhr, Karin Daub, Tanja Schoenberger, Konstantinos Stellos, Andreas E May, Hannah Schnell, Alexandra Gauss, Ramona Hafner, Peter Lang, Michael Schumm, Hans-Jörg Bühring, Karin Klingel, Sabine Conrad, Martin Schaller, Marc van Zandvoort, Gundram Jung, Stefanie Dimmeler, Thomas Skutella, Meinrad Gawaz

  Journal of molecular medicine (Berlin, Germany). 04/2010; 88(7):687-99.

  Tissue injury is inevitably accompanied by disruption of the endothelium and exposure of the subendothelial matrix. To generate a guidance molecule directing progenitor cells to sites of vascularTissue injury is inevitably accompanied by disruption of the endothelium and exposure of the subendothelial matrix. To generate a guidance molecule directing progenitor cells to sites of vascular lesions, we designed a bifunctional protein. The protein consists of the soluble platelet collagen receptor glycoprotein VI and an antibody to CD133 (hereafter called GPVI-CD133). In vitro and in vivo, this construct substantially mediates endothelial progenitor cell (EPC) homing to vascular lesions. Exposure of EPCs to GPVI-CD133 did not impair their capability to differentiate toward mature endothelial cells as verified by the formation of colony-forming units, the upregulation of endothelial markers CD31 and CD146 analyzed by flow cytometry or von Willebrand factor and endoglin assessed by immunofluorescence microscopy, as well as the presence of Weibel-Palade bodies using transmission electron microscopy. In vivo, GPVI-CD133 augments reendothelialization of vascular lesions. Thus, this bifunctional protein could be a potential new therapeutic option for cardiovascular diseases.

• Interaction of platelets and inflammatory endothelium in the development and progression of coronary artery disease.

  Authors: Harald F Langer, Boris Bigalke, Peter Seizer, Konstantinos Stellos, Suzanne Fateh-Moghadam, Meinrad Gawaz

  Seminars in thrombosis and hemostasis. 03/2010; 36(2):131-8.

  An expanding body of evidence emphasizes the role of platelets as initial actors in inflammatory diseases such as atherosclerosis. Platelets interact with leukocytes and endothelial cells and enforceAn expanding body of evidence emphasizes the role of platelets as initial actors in inflammatory diseases such as atherosclerosis. Platelets interact with leukocytes and endothelial cells and enforce monocyte transformation into macrophages. Platelets not only mediate the recruitment of leukocytes. They also bind oxidized phospholipids and may promote foam cell formation. Platelets furthermore recruit progenitor cells to the scene, which are able to differentiate into foam cells or endothelial cells, presumably depending on the local microenvironment. Furthermore, platelets are capable of promoting the recruitment of circulating dendritic cells and influencing their functions, thereby presumably modulating immune reactions in atherogenesis. Taken together, platelets may participate in the initiation, development, and total extent of atherosclerotic lesions.

• Platelets in regeneration.

  Authors: Konstantinos Stellos, Sebastian Kopf, Angela Paul, Jens U Marquardt, Meinrad Gawaz, Johnny Huard, Harald F Langer

  Seminars in thrombosis and hemostasis. 03/2010; 36(2):175-84.

  Platelets, as the first cellular response after disruption of vascular and/or tissue integrity, cover any existing injury within our body. But is the regenerative potential of platelets limited toPlatelets, as the first cellular response after disruption of vascular and/or tissue integrity, cover any existing injury within our body. But is the regenerative potential of platelets limited to providing a cellular patch for wounds? This review highlights the recent advance in our understanding of platelets being distinctly regulated and regulating cells that contribute immensely to the healing process from the very initial stage to the late events of tissue regeneration. For instance, the intrinsic actions of platelets as a regenerative cell, the participation of platelets in angiogenic processes, and the interplay of platelets and circulating stem and progenitor cells, as well as potential therapeutic implications, are addressed. Although we are starting to understand the underlying mechanisms connecting platelets to the components of tissue regeneration just mentioned, many aspects remain to be elucidated. The demand to invest research in this area is underscored by the fact that platelets or platelet-derived molecules are already applied in clinical contexts such as connective tissue regeneration, whereas other research fields have largely neglected platelet effects going beyond their participation in the coagulation cascade. Understanding the mechanisms connecting platelets to tissue regeneration, however, will inevitably open novel options in regenerative medicine.

• Cytotoxic CD8+ T cell-neuron interactions: perforin-dependent electrical silencing precedes but is not causally linked to neuronal cell death.

  Authors: Sven G Meuth, Alexander M Herrmann, Ole J Simon, Volker Siffrin, Nico Melzer, Stefan Bittner, Patrick Meuth, Harald F Langer, Stefan Hallermann, Nadia Boldakowa, Josephine Herz, Thomas Munsch, Peter Landgraf, Orhan Aktas, Manfred Heckmann, Volkmar Lessmann, Thomas Budde, Bernd C Kieseier, Frauke Zipp, Heinz Wiendl

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 12/2009; 29(49):15397-409.

  Cytotoxic CD8(+) T cells are considered important effector cells contributing to neuronal damage in inflammatory and degenerative CNS disorders. Using time-lapse video microscopy and two-photonCytotoxic CD8(+) T cells are considered important effector cells contributing to neuronal damage in inflammatory and degenerative CNS disorders. Using time-lapse video microscopy and two-photon imaging in combination with whole-cell patch-clamp recordings, we here show that major histocompatibility class I (MHC I)-restricted neuronal antigen presentation and T cell receptor specificity determine CD8(+) T-cell locomotion and neuronal damage in culture and hippocampal brain slices. Two separate functional consequences result from a direct cell-cell contact between antigen-presenting neurons and antigen-specific CD8(+) T cells. (1) An immediate impairment of electrical signaling in single neurons and neuronal networks occurs as a result of massive shunting of the membrane capacitance after insertion of channel-forming perforin (and probably activation of other transmembrane conductances), which is paralleled by an increase of intracellular Ca(2+) levels (within <10 min). (2) Antigen-dependent neuronal apoptosis may occur independently of perforin and members of the granzyme B cluster (within approximately 1 h), suggesting that extracellular effects can substitute for intracellular delivery of granzymes by perforin. Thus, electrical silencing is an immediate consequence of MHC I-restricted interaction of CD8(+) T cells with neurons. This mechanism is clearly perforin-dependent and precedes, but is not causally linked, to neuronal cell death.

• A possible crosstalk between DNA repair pathways and angiogenesis.

  Authors: Triantafyllos Chavakis, Valeria V Orlova, Harald F Langer

  Cell cycle (Georgetown, Tex.). 11/2009; 8(21):3438-9.

• EMMPRIN and its ligand cyclophilin A regulate MT1-MMP, MMP-9 and M-CSF during foam cell formation.

  Authors: Peter Seizer, Tanja Schönberger, Moritz Schött, Michael R Lang, Harald F Langer, Boris Bigalke, Björn F Krämer, Oliver Borst, Karin Daub, Olaf Heidenreich, Roland Schmidt, Stephan Lindemann, Yared Herouy, Meinrad Gawaz, Andreas E May

  Atherosclerosis. 08/2009;

  Upon coincubation with platelets, CD34(+) progenitor cells have the potential to differentiate into foam cells, and thereby may promote the progression of atherosclerosis. The exact mechanism ofUpon coincubation with platelets, CD34(+) progenitor cells have the potential to differentiate into foam cells, and thereby may promote the progression of atherosclerosis. The exact mechanism of MMP-regulation during the cellular differentiation process to foam cells is still unclear. Thus, we investigated the role of EMMPRIN (CD147) and its ligand cyclophilin A (CyPA) during foam cell formation originating from both monocytes/macrophages and CD34(+) progenitor cells. METHODS AND RESULTS: Differentiation of CD34(+) progenitor to foam cells was analyzed in a coculture model of progenitor cells and platelets. While CD34(+) cells did not express EMMPRIN or MT1-MMP, mature foam cells strongly expressed EMMPRIN, which was associated with MT1-MMP expression as well as MMP-9. Gene silencing of EMMPRIN by siRNA during the cell differentiation process hindered not only the upregulation of MMPs (MT1-MMP, MMP-9), but also the secretion of the cytokine M-CSF. During the differentiation process CyPA was substantially released into the supernatant. The presence of the CyPA inhibitor NIM811 significantly reduced MMP-9 secretion during the differentiation process. Similar results were obtained using the classical pathway of foam cell formation by coincubating human macrophages with AcLDL. Additionally, the presence of soluble EMMPRIN ligands (CyPA, recombinant EMMPRIN) further enhanced MMP-9 secretion by mature foam cells. Consistently, CyPA and EMMPRIN were found in atherosclerotic plaques of ApoE-deficient mice by immunohistochemistry. CONCLUSION: EMMPRIN is upregulated during the differentiation process from CD34(+) progenitor cells to foam cells, whereas its ligand, CyPA, is released. The CyPA/EMMPRIN activation pathway may play a relevant role in promoting the vulnerability of atherosclerotic plaques.

• Leukocyte-Endothelial Interactions in Inflammation.

  Authors: Harald F Langer, Triantafyllos Chavakis

  Journal of cellular and molecular medicine. 07/2009;

  Abstract At sites of inflammation, infection or vascular injury local proinflammatory or pathogen-derived stimuli render the luminal vascular endothelial surface attractive for leukocytes. ThisAbstract At sites of inflammation, infection or vascular injury local proinflammatory or pathogen-derived stimuli render the luminal vascular endothelial surface attractive for leukocytes. This innate immunity response consists of a well defined and regulated multistep cascade involving consecutive steps of adhesive interactions between the leukocytes and the endothelium. During the initial contact with the activated endothelium leukocytes roll along the endothelium via a loose bond which is mediated by selectins. Subsequently leukocytes are activated by chemokines presented on the luminal endothelial surface, which results in the activation of leukocyte integrins and the firm leukocyte arrest on the endothelium. After their firm adhesion, leukocytes make use of two transmigration processes to pass the endothelial barrier, the transcellular route through the endothelial cell body or the paracellular route through the endothelial junctions. In addition, further circulating cells, such as platelets arrive early at sites of inflammation contributing to both coagulation and to the immune response in parts by facilitating leukocyte-endothelial interactions. Platelets have thereby been implicated in several inflammatory pathologies. This review summarizes the major mechanisms and molecules involved in leukocyte-endothelial and leukocyte-platelet interactions in inflammation.

• Platelet interactions as therapeutic targets for prevention of atherothrombosis.

  Authors: Jan Smid, Ruediger Braun-Dullaeus, Meinrad Gawaz, Harald F Langer

  Future cardiology. 06/2009; 5(3):285-96.

  Physiologically, platelets perform important tasks to maintain the homeostasis of the vascular wall and the surrounding environment. In pathologic conditions, however, platelets contribute to thePhysiologically, platelets perform important tasks to maintain the homeostasis of the vascular wall and the surrounding environment. In pathologic conditions, however, platelets contribute to the formation of atherosclerotic plaques as well as to atherothrombotic events (i.e., acute myocardial infarction). This review aims to elucidate the role of platelets in atherogenesis and atherothrombosis and to provide an insight into current and future strategies for platelet inhibition.

• EMMPRIN (CD147) is a novel receptor for platelet GPVI and mediates platelet rolling via GPVI-EMMPRIN interaction.

  Authors: Peter Seizer, Oliver Borst, Harald F Langer, Andreas Bültmann, Götz Münch, Yared Herouy, Konstantinos Stellos, Björn Krämer, Boris Bigalke, Berthold Büchele, Max G Bachem, Dietmar Vestweber, Thomas Simmet, Meinrad Gawaz, Andreas E May

  Thrombosis and haemostasis. 05/2009; 101(4):682-6.

  The Extracellular Matrix Metalloproteinase Inducer (EMMPRIN, CD147, basigin) is an immunoglobulin-like receptor expressed in various cell types. During cellular interactions homotypic EMMPRIN-EMMPRINThe Extracellular Matrix Metalloproteinase Inducer (EMMPRIN, CD147, basigin) is an immunoglobulin-like receptor expressed in various cell types. During cellular interactions homotypic EMMPRIN-EMMPRIN interactions are known to induce the synthesis of matrix metalloproteinases. Recently, we have identified EMMPRIN as a novel receptor on platelets. To our knowledge EMMPRIN has not been shown to serve as adhesion receptor, yet. Here we characterise platelet glycoprotein VI (GPVI) as a novel adhesion receptor for EMMPRIN. Human platelets were prestimulated with ADP and perfused over immobilised recombinant EMMPRIN-Fc or Fc-fragments under arterial shear conditions. ADP-stimulated platelets showed significantly enhanced rolling (but not enhanced firm adhesion) on immobilised EMMPRIN-Fc compared to Fc. Pretreatment of platelets with blocking mAbs anti-EMMPRIN or anti-GPVI leads to a significant reduction of rolling platelets on immobilised EMMPRIN-Fc, whereas pretreatment with blocking mAbs anti-p-selectin, anti-alpha4-integrin or anti-GPIIb/IIIa complex (20 microg/ml each) had no effect. Consistently, chinese hamster ovary (CHO) cells stably transfected with GPVI showed enhanced rolling (but not adhesion) on immobilised EMMPRIN-Fc in comparison to non-transfected CHO cells. Similarly, CHO cells stably transfected with EMMPRIN showed enhanced rolling on immobilised GPVI-Fc (or EMMPRIN-Fc) compared to non transfected CHO-cells. Finally, specific binding of EMMPRIN to GPVI was demonstrated by a modified ELISA and surface plasmon resonance technology with a dissociation constant of 88 nM. Platelet GPVI is a novel receptor for EMMPRIN and can mediate platelet rolling via GPVI-EMMPRIN interaction.

• Histone H2AX is integral to hypoxia-driven neovascularization.

  Authors: Matina Economopoulou, Harald F Langer, Arkady Celeste, Valeria V Orlova, Eun Young Choi, Mingchao Ma, Athanassios Vassilopoulos, Elsa Callen, Chuxia Deng, Craig H Bassing, Manfred Boehm, Andre Nussenzweig, Triantafyllos Chavakis

  Nature medicine. 05/2009;

  H2A histone family member X (H2AX, encoded by H2AFX) and its C-terminal phosphorylation (gamma-H2AX) participates in the DNA damage response and mediates DNA repair. Hypoxia is a physiological stressH2A histone family member X (H2AX, encoded by H2AFX) and its C-terminal phosphorylation (gamma-H2AX) participates in the DNA damage response and mediates DNA repair. Hypoxia is a physiological stress that induces a replication-associated DNA damage response. Moreover, hypoxia is the major driving force for neovascularization, as the hypoxia-mediated induction of vascular growth factors triggers endothelial cell proliferation. Here we studied the role of the hypoxia-induced DNA damage response in endothelial cell function and in hypoxia-driven neovascularization in vivo. Hypoxia induced replication-associated generation of gamma-H2AX in endothelial cells in vitro and in mice. Both in cultured cells and in mice, endothelial cell proliferation under hypoxic conditions was reduced by H2AX deficiency. Whereas developmental angiogenesis was not affected in H2afx(-/-) mice, hypoxia-induced neovascularization during pathologic proliferative retinopathy, in response to hind limb ischemia or during tumor angiogenesis was substantially lower in H2afx(-/-) mice. Moreover, endothelial-specific H2afx deletion resulted in reduced hypoxia-driven retina neovascularization and tumor neovascularization. Our findings establish that H2AX, and hence activation of the DNA repair response, is needed for endothelial cells to maintain their proliferation under hypoxic conditions and is crucial for hypoxia-driven neovascularization.

• Platelet derived bFGF mediates vascular integrative mechanisms of mesenchymal stem cells in vitro.

  Authors: Harald F Langer, Konstantinos Stellos, Caroline Steingen, Amrei Froihofer, Tanja Schönberger, Boris Bigalke, Andreas E May, Peter Seizer, Iris Müller, Friederike Gieseke, Dorothea Siegel-Axel, Sven G Meuth, Annette Schmidt, Hans P Wendel, Ingo Müller, Wilhelm Bloch, Meinrad Gawaz

  Journal of molecular and cellular cardiology. 04/2009;

  Patients with myocardial infarction reveal an increased number of circulating mesenchymal stem cells (MSCs). Recently, it was shown that MSCs are able to regenerate myocardial tissue and toPatients with myocardial infarction reveal an increased number of circulating mesenchymal stem cells (MSCs). Recently, it was shown that MSCs are able to regenerate myocardial tissue and to differentiate into endothelial cells. The homing mechanisms of MSCs from the circulation into the target tissue, however, are not understood so far. In this study, we evaluated the impact of platelets on MSC recruitment, proliferation, migration and integration into the endothelium. MSCs expressing alpha(v)beta(3)-integrin were recruited to human arterial endothelial cells exposed to isolated platelets or IL-1beta under high shear conditions. Furthermore, induction of vascular injury in vivo resulted in increased recruitment of injected MSCs as assessed by intravital microscopy and depletion of platelets significantly reduced this adhesion. The interaction of platelets and MSCs was inhibited by preincubation with the mAb 7E3 or an RGD protein both blocking beta(3)-integrin mediated adhesion. Platelets had a chemotactic effect on MSCs, promoted a migratory MSC phenotype and dose- and activation-dependently enhanced migration of MSCs, a process, which was mediated by basic fibroblast growth factor (bFGF). Similarly, platelet derived bFGF increased proliferation of MSCs. Co-incubation of MSCs with platelets facilitated integration into an endothelial monolayer, which was significantly reduced by pre-incubation with a blocking mAb to bFGF. We conclude that platelets may play a critical part in the recruitment of MSCs to the endothelium, influence MSC function and promote integration of MSCs into the endothelium.

• Del-1, an endogenous leukocyte-endothelial adhesion inhibitor, limits inflammatory cell recruitment.

  Authors: Eun Young Choi, Emmanouil Chavakis, Marcus A Czabanka, Harald F Langer, Line Fraemohs, Matina Economopoulou, Ramendra K Kundu, Alessia Orlandi, Ying Yi Zheng, Darue A Prieto [......] Stephanie L Constant, William C Aird, Thalia Papayannopoulou, Carl G Gahmberg, Mark C Udey, Peter Vajkoczy, Thomas Quertermous, Stefanie Dimmeler, Christian Weber, Triantafyllos Chavakis

  Science (New York, N.Y.). 12/2008; 322(5904):1101-4.

  Leukocyte recruitment to sites of infection or inflammation requires multiple adhesive events. Although numerous players promoting leukocyte-endothelial interactions have been characterized,Leukocyte recruitment to sites of infection or inflammation requires multiple adhesive events. Although numerous players promoting leukocyte-endothelial interactions have been characterized, functionally important endogenous inhibitors of leukocyte adhesion have not been identified. Here we describe the endothelially derived secreted molecule Del-1 (developmental endothelial locus-1) as an anti-adhesive factor that interferes with the integrin LFA-1-dependent leukocyte-endothelial adhesion. Endothelial Del-1 deficiency increased LFA-1-dependent leukocyte adhesion in vitro and in vivo. Del-1-/- mice displayed significantly higher neutrophil accumulation in lipopolysaccharide-induced lung inflammation in vivo, which was reversed in Del-1/LFA-1 double-deficient mice. Thus, Del-1 is an endogenous inhibitor of inflammatory cell recruitment and could provide a basis for targeting leukocyte-endothelial interactions in disease.

• Radionuclide imaging: a molecular key to the atherosclerotic plaque.

  Authors: Harald F Langer, Roland Haubner, Bernd J Pichler, Meinrad Gawaz

  Journal of the American College of Cardiology. 08/2008; 52(1):1-12.

  Despite primary and secondary prevention, serious cardiovascular events such as unstable angina or myocardial infarction still account for one-third of all deaths worldwide. Therefore, identifyingDespite primary and secondary prevention, serious cardiovascular events such as unstable angina or myocardial infarction still account for one-third of all deaths worldwide. Therefore, identifying individual patients with vulnerable plaques at high risk for plaque rupture is a central challenge in cardiovascular medicine. Several noninvasive techniques, such as magnetic resonance imaging, multislice computed tomography, and electron beam tomography are currently being tested for their ability to identify such patients by morphological criteria. In contrast, molecular imaging techniques use radiolabeled molecules to detect functional aspects in atherosclerotic plaques by visualizing their biological activity. Based upon the knowledge about the pathophysiology of atherosclerosis, various studies in vitro and in vivo and the first clinical trials have used different tracers for plaque imaging studies, including radioactive-labeled lipoproteins, components of the coagulation system, cytokines, mediators of the metalloproteinase system, cell adhesion receptors, and even whole cells. This review gives an update on the relevant noninvasive plaque imaging approaches using nuclear imaging techniques to detect atherosclerotic vascular lesions.

• Platelets in regenerative medicine.

  Authors: Harald F Langer, Meinrad Gawaz

  Basic research in cardiology. 07/2008; 103(4):299-307.

  Stem and progenitor cells have evolved as the central cell type in regenerative medicine. This focussed approach may, however, sometimes narrow the point of view. Recently, platelets have been shownStem and progenitor cells have evolved as the central cell type in regenerative medicine. This focussed approach may, however, sometimes narrow the point of view. Recently, platelets have been shown to strongly influence progenitor cell biology and to serve as regenerative cells themselves. Platelets represent an important recruitment factor for circulating progenitor cells. Furthermore, they modulate progenitor cell chemotaxis, migration and differentiation. Platelets are crucial for the regeneration of parenchymatous organs such as the liver. Moreover, in the clinical setting, platelets are already applied for the restoration of connective and bone tissue. However, also adverse effects can be mediated by platelets and progenitor cells exposed to platelets, including the induction of pro-inflammatory processes. This review gives an update on platelets as regenerative cells and as modulators of progenitor cell biology in (patho-) physiological conditions. Abundant data obtained during the last decade have linked progenitor and stem cells to tissue repair. Very recent accumulating results from different groups revealed that platelets may have a strong influence on central functions of these progenitor cells. Only little is known about the impact of platelets themselves on tissue regeneration. Therefore, this review highlights the role of platelets themselves as a potential effector cell for tissue regeneration and their impact on progenitor cell biology.