Key Publications
Endothelial cell-matrix adhesion in health and disease
Endothelial cells regulate blood vessel formation and barrier function. Crucial herein are cell-cell adhesion by adherens junctions, and integrin-mediated cell adhesion to extracellular matrix proteins such as fibronectin. In this paper we discuss endothelial cell-matrix adhesion complexes and associated signaling pathways, and their crosstalk with adherens junctions in response to hemodynamic stress and in (patho)physiological conditions like angiogenesis and inflammation. Regulators of endothelial cell-matrix adhesion may constitute novel targets for clinical conditions characterized by barrier disruption and vascular leak, which are associated with severe morbidity and high mortality rates.
Image: Human endothelial cells on a matrix of fibronectin fibrils. Yellow, actin filaments/nuclei; Magenta, fibronectin.
Depletion of Arg/Abl2 improves cell adhesion and protects against vascular leak
Endothelial barrier disruption and vascular leak contribute to organ dysfunction and mortality in inflammatory conditions like sepsis and acute respiratory distress syndrome. In this study we show that the kinase Arg is activated in the endothelium during inflammation and promotes loss of cell adhesion and endothelial barrier disruption. Suppression or deletion of Arg improves endothelial cell-matrix and cell-cell adhesion, and reduces inflammatory vascular leak in the skin and lungs. Therapeutic inhibition of Arg may provide a strategy for the treatment of clinical conditions characterized by vascular leak.
Image: Endothelial cells during barrier disruption (Red, actin stress fibers; Green, focal adhesions; Blue, adherens junctions).
RIN2/Rab5C protect VEGF receptor levels and promote angiogenic tip cell formation
Angiogenesis depends on signaling through VEGF receptor 2 (VEGFR2). Here we show that the early endosomal Rab GTPase Rab5C and its activator (the guanine nucleotide exchange factor RIN2) prevent lysosomal degradation of VEGF-bound, internalized VEGFR2 which is crucial for VEGF signaling, induction of target genes, and tip cell formation during angiogenesis. Using overexpression of Rab mutants, knockdown and CRISPR/Cas9-mediated gene editing, and live-cell imaging in zebrafish, we further show that endosomal stabilization of VEGFR2 levels is required for developmental angiogenesis in vivo.
Movie: Actin dynamics in a sprouting endothelial tip cell during developmental angiogenesis in zebrafish (Yuki Wakayama).
Maternal antibodies against β3 integrins cause fetal defects
Mismatch between maternal and fetal platelet antigens can cause an alloimmune response during pregnancy in which the mother generates antibodies against her own fetus. The most frequently affected antigen is HPA1a on β3 integrins, which are found on platelets, endothelial cells, and placental trophoblasts. The clinical effects range from no symptoms to thrombocytopenia and bleedings including fatal intracranial hemorrhage, but underlying determinants are poorly understood.
In this paper we discuss current insights into the diversity and actions of these antibodies and their effects on hemostasis, angiogenesis, and placental development.
Image: The HPA1a epitope recognized by maternal antibodies on the αIIbβ3 integrin (Figure by Jose Maria de Pereda).
Reciprocal repression of integrin function by integrins
Fibronectin-binding integrins α5β1 and αvβ3 have different effects on cell-matrix adhesion, cell migration, and signaling. While α5β1 induces random single-cell motility, αvβ3 promotes collective and directional movement. In this work we show that these two integrins actively repress each other, due to competition for integrin binding partners such as kindlins, and controls activation of Rho GTPases Rac1 and RhoA, cytoskeletal organization and contractility, and cell-cell adhesion. Antagonism between α5β1 and αvβ3 may be a universal mechanism to regulate tissue morphogenesis, endothelial barrier function, trophoblast invasion, and sprouting angiogenesis.
Movies and cell tracks: Random single-cell migration is promoted by integrin α5β1 (top), while αvβ3 promotes collective directional migration (bottom).
Vps3/8 regulate integrin trafficking
Cell migration requires endocytosis and recycling of integrins by the endosomal system. In this paper we show that Vps3 and Vps8 proteins, members of the CORVET tethering complex, regulate transport of internalized integrins from early to recycling endosomes and their subsequent return to the plasma membrane. Defects in this recycling route lead to reduced integrin recycling and aberrant cell migration. These data reveal a role for Vps3 and Vps8 in a specialised recycling pathway important for integrin trafficking.
Image: Pseudo-colored EM image of internalized integrins (Klumperman lab). BSA (5 nm gold), Vps3 (10 nm gold), β1 integrins (15 nm gold). E, endosome; G, Golgi network; RV, recycling vesicles.