Wound healing defect of Vav3−/− mice due to impaired β2-integrin–dependent macrophage phagocytosis of apoptotic neutrophils

Abstract

AbstractVav proteins are guanine-nucleotide exchange factors implicated in leukocyte functions by relaying signals from immune response receptors and integrins to Rho-GTPases. We here provide first evidence for a role of Vav3 for β2-integrins–mediated macrophage functions during wound healing. Vav3−/− and Vav1−/−/Vav3−/− mice revealed significantly delayed healing of full-thickness excisional wounds. Furthermore, Vav3−/− bone marrow chimeras showed an identical healing defect, suggesting that Vav3 deficiency in leukocytes, but not in other cells, is causal for the impaired wound healing. Vav3 was required for the phagocytotic cup formation preceding macrophage phagocytosis of apoptotic neutrophils. Immunoprecipitation and confocal microscopy revealed Vav3 activation and colocalization with β2-integrins at the macrophage membrane upon adhesion to ICAM-1. Moreover, local injection of Vav3−/−or β2-integrin(CD18)−/− macrophages into wound margins failed to restore the healing defect of Vav3−/− mice, suggesting Vav3 to control the β2-integrin–dependent formation of a functional phagocytic synapse. Impaired phagocytosis of apoptotic neutrophils by Vav3−/− macrophages was causal for their reduced release of active transforming growth factor (TGF)-β1, for decreased myofibroblasts differentiation and myofibroblast-driven wound contraction. TGF-β1 deficiency in Vav3−/− macrophages was causally responsible for the healing defect, as local injection of either Vav3-competent macrophages or recombinant TGF-β1 into wounds of Vav3−/− mice fully rescued the delayed wound healing.