Inhibition of vascular permeability by semaphorin 3F in acute inflammation
Li, David Joseph
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Edema or tissue swelling is exacerbated during inflammation due to increased leukocyte infiltration and vascular permeability, after which resolution returns the tissue to homeostasis. In acute inflammatory reactions, upregulated levels of vascular endothelial growth factor (VEGF) is shown to increase vascular permeability. Vascular endothelial cells (EC) form a selective barrier regulating the degree of microvascular exchange and permeability in normal physiological and pathological settings. Vascular EC express pro-permeability VEGF receptors and neuropilin co-receptors that can mediate both stimulatory and inhibitory signals. Secreted class 3 semaphorin-3F (SEMA3F) is a high affinity ligand for the NRP2 receptor and has been shown to be anti-angiogenic through its ability to inhibit cell migration and attachment. Importantly, SEMA3F has been shown to compete for binding with VEGF to the NRP2 receptor. However, the role, if any, of SEMA3F in inflammation has yet to be fully elucidated. We hypothesize that SEMA3F reduces edema by inhibiting vascular permeability thereby promoting a quickened resolution of inflammation. To generate inflammatory lesions, delayed-type hypersensitivity cutaneous reactions were induced on the ear skin of C57BL/6 mice through topical applications of oxazolone. Total ear thickness as a readout of tissue swelling was compared to baseline (Day 0). To determine the effects of depleting SEMA3F during inflammation, ear thickness was measured after SEMA3F antibody or control IgG intraperitoneal injection into Nrp2+/- mice. To assess the effects of increased systemic SEMA3F on edema, ear thickness was measured after intravenous delivery of SEMA3F adenovirus (Ad-3F) or control adenovirus into wild-type mice. We report that SEMA3F depletion via SEMA3F antibodies led to significantly prolonged edema compared to controls. Ad-3F treated mice exhibit lower levels of inflammatory edema compared to control. We demonstrate that the SEMA3F signaling cascade is a key mediator of fluid homeostasis in inflammation. Likely, SEMA3F serves as an anti-inflammatory mechanism preventing excessive edema.