Vockel M.,Max Planck Institute for Molecular Biomedicine
Blood | Year: 2013
The vascular endothelial (VE) receptor protein tyrosine phosphatase (VE-PTP) associates with VE-cadherin and supports endothelial cell contact integrity. This complex is rapidly dissociated by adhesion of leukocytes to endothelial cells or by vascular endothelial growth factor. We have shown recently that this dissociation is indeed required for the opening of endothelial cell contacts during leukocyte extravasation in vivo. The leukocyte receptor and signaling mechanism that stimulates VE-cadherin/VE-PTP dissociation are unknown. Here, we identify vascular cell adhesion molecule 1 as the relevant receptor for lymphocytes in this process. As signaling steps downstream of this receptor, we determined the activation of Rac1, the generation of reactive oxygen species by nicotinamide adenine dinucleotide phosphate oxidase and the activation of the redox-sensitive tyrosine kinase Pyk2 as essential for VE-cadherin/VE-PTP dissociation. These signaling steps are also required for the dissociation induced by VE growth factor. Searching for the molecular mechanism of complex dissociation, we found that a model substrate of VE-PTP represented by a tyrosine-phosphorylated peptide of Tie-2 dissociates VE-PTP from VE-cadherin when introduced with the help of a Tat peptide. We suggest that lymphocyte binding to vascular cell adhesion molecule 1 triggers a signaling process that enables a VE-PTP substrate to dissociate VE-PTP from VE-cadherin, thereby facilitating efficient transmigration.
Drexler H.C.,Max Planck Institute for Molecular Biomedicine
Molecular & cellular proteomics : MCP | Year: 2012
Skeletal muscle tissue contains slow as well as fast twitch muscle fibers that possess different metabolic and contractile properties. Although the distribution of individual proteins in fast and slow fibers has been investigated extensively, a comprehensive proteomic analysis, which is key for any systems biology approach to muscle tissues, is missing. Here, we compared the global protein levels and gene expression profiles of the predominantly slow soleus and fast extensor digitorum longus muscles using the principle of in vivo stable isotope labeling with amino acids based on a fully lysine-6 labeled SILAC-mouse. We identified 551 proteins with significant quantitative differences between slow soleus and fast extensor digitorum longus fibers out of >2000 quantified proteins, which greatly extends the repertoire of proteins differentially regulated between both muscle types. Most of the differentially regulated proteins mediate cellular contraction, ion homeostasis, glycolysis, and oxidation, which reflect the major functional differences between both muscle types. Comparison of proteomics and transcriptomics data uncovered the existence of fiber-type specific posttranscriptional regulatory mechanisms resulting in differential accumulation of Myosin-8 and α-protein kinase 3 proteins and mRNAs among others. Phosphoproteome analysis of soleus and extensor digitorum longus muscles identified 2573 phosphosites on 973 proteins including 1040 novel phosphosites. The in vivo stable isotope labeling with amino acids-mouse approach used in our study provides a comprehensive view into the protein networks that direct fiber-type specific functions and allows a detailed dissection of the molecular composition of slow and fast muscle tissues with unprecedented resolution.
Vestweber D.,Max Planck Institute for Molecular Biomedicine
Annals of the New York Academy of Sciences | Year: 2012
Inflammation and immune surveillance rely on the ability of leukocytes to leave the blood stream and enter tissue. Cytokines and chemokines regulate expression and the activation state of adhesion molecules that enable leukocytes to adhere and arrest at sites of leukocyte exit. Capturing and arrest is followed by the transmigration of leukocytes through the vessel wall-a process called diapedesis. The review will focus on recently published novel approaches to determine the route that leukocytes take in vivo when they migrate through the endothelial layer of blood vessels. This work has revealed the dominant importance of the junctional pathway between endothelial cells in vivo. In addition, recent progress has improved our understanding of the molecular mechanisms that regulate junctional stability, the opening of endothelial junctions during leukocyte extravasation, and the induction of vascular permeability. © 2012 New York Academy of Sciences.
Vestweber D.,Max Planck Institute for Molecular Biomedicine
Current Opinion in Hematology | Year: 2012
Purpose of Review: Leukocyte extravasation is a multistep process that is regulated at various levels. This review will highlight recent findings that define new regulatory mechanisms and novel activities in the process of leukocyte docking to the endothelium and diapedesis of leukocytes through the endothelial barrier of the vessel wall. Recent Findings: Within the past 2-3 years, novel regulatory mechanisms have been identified that control or balance leukocyte extravasation at different steps of the extravasation process. First evidence was established for differences in the roles of intracellular factors that bind to integrins and support their activation. A cytokine was found that counteracts the activation of leukocyte integrins. Not only leukocyte integrins but also their ligands on endothelial cells were shown to arrange in clusters while supporting leukocyte-endothelial interactions. Recent progress was made in determining in vivo the route of leukocyte diapedesis through the endothelium of the blood vessel wall. Finally, novel mechanisms were found that control the opening of the endothelial barrier during diapedesis and others that determine directionality of diapedesis. Summary: Recent progress in our understanding of leukocyte extravasation has unraveled novel steps and mechanisms that control this process in vivo. These findings provide new insights into the mechanisms that balance the entry of leukocytes into tissue. © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins.
Adams R.H.,Max Planck Institute for Molecular Biomedicine
Cold Spring Harbor perspectives in biology | Year: 2010
Endothelial cells (ECs) form extensive, highly branched and hierarchically organized tubular networks in vertebrates to ensure the proper distribution of molecular and cellular cargo in the vertebrate body. The growth of this vascular system during development, tissue repair or in disease conditions involves the sprouting, migration and proliferation of endothelial cells in a process termed angiogenesis. Surprisingly, specialized ECs, so-called tip cells, which lead and guide endothelial sprouts, share many feature with another guidance structure, the axonal growth cone. Tip cells are motile, invasive and extend numerous filopodial protrusions sensing growth factors, extracellular matrix and other attractive or repulsive cues in their tissue environment. Axonal growth cones and endothelial tip cells also respond to signals belonging to the same molecular families, such as Slits and Roundabouts, Netrins and UNC5 receptors, Semaphorins, Plexins and Neuropilins, and Eph receptors and ephrin ligands. Here we summarize fundamental principles of angiogenic growth, the selection and function of tip cells and the underlying regulation by guidance cues, the Notch pathway and vascular endothelial growth factor signaling.