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Appropriate coordination of smooth muscle contraction and relaxation is essential for normal colonic motility. The impact of perturbed motility ranges from moderate, in conditions such as colitis, to potentially fatal in the case of pseudo-obstruction. The mechanisms underlying aberrant motility and the extent to which they can be targeted pharmacologically are incompletely understood. This study identified colonic smooth muscle as a major site of expression of neuropilin 2 (Nrp2) in mice and humans. Mice with inducible smooth muscle-specific knockout of Nrp2 had an increase in evoked contraction of colonic rings in response to carbachol at 1 and 4 weeks following initiation of deletion. KCl-induced contractions were also increased at 4 weeks. Colonic motility was similarly enhanced, as evidenced by faster bead expulsion in Nrp2-deleted mice versus Nrp2-intact controls. In length-tension analysis of the distal colon, passive tension was similar in Nrp2-deficient and Nrp2-intact mice, but at low strains, active stiffness was greater in Nrp2-deficient animals. Consistent with the findings in conditional Nrp2 mice, Nrp2-null mice showed increased contractility in response to carbachol and KCl. Evaluation of selected proteins implicated in smooth muscle contraction revealed no significant differences in the level of α-smooth muscle actin, myosin light chain, calponin, or RhoA. Together, these findings identify Nrp2 as a novel regulator of colonic contractility that may be targetable in conditions characterized by dysmotility., (Copyright © 2022 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

The vasculature influences the progression and resolution of tissue inflammation. Capillaries express vascular endothelial growth factor (VEGF) receptors, including neuropilins (NRPs), which regulate interstitial fluid flow. NRP2, a receptor of VEGFA and semaphorin (SEMA) 3F ligands, is expressed in the vascular and lymphatic endothelia. Previous studies have demonstrated that blocking VEGF receptor 2 attenuates VEGFA-induced vascular permeability. The inhibition of NRP2 was hypothesized to decrease vascular permeability as well. Unexpectedly, massive tissue swelling and edema were observed in Nrp2 -/- mice compared with wild-type littermates after delayed-type hypersensitivity reactions. Vascular permeability was twofold greater in inflamed blood vessels in Nrp2-deficient mice compared to those in Nrp2-intact littermates. The addition of exogenous SEMA3F protein inhibited vascular permeability in Balb/cJ mice, suggesting that the loss of endogenous Sema3F activity in the Nrp2-deficient mice was responsible for the enhanced vessel leakage. Functional lymphatic capillaries are necessary for draining excess fluid after inflammation; however, Nrp2-mutant mice lacked superficial lymphatic capillaries, leading to 2.5-fold greater fluid retention and severe lymphedema after inflammation. In conclusion, Nrp2 deficiency increased blood vessel permeability and decreased lymphatic vessel drainage during inflammation, highlighting the importance of the NRP2/SEMA3F pathway in the modulation of tissue swelling and resolution of postinflammatory edema., (Copyright © 2016 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Neuropilins (NRPs) are transmembrane receptors that bind class 3 semaphorins and VEGF family members to regulate axon guidance and angiogenesis. Although expression of NRP1 by vascular smooth muscle cells (SMCs) has been reported, NRP function in smooth muscle (SM) in vivo is unexplored. Using Nrp2(+/LacZ) and Nrp2(+/gfp) transgenic mice, we observed robust and sustained expression of Nrp2 in the SM compartments of the bladder and gut, but no expression in vascular SM, skeletal muscle, or cardiac muscle. This expression pattern was recapitulated in vitro using primary human SM cell lines. Alterations in cell morphology after treatment of primary visceral SMCs with the NRP2 ligand semaphorin-3F (SEMA3F) were accompanied by inhibition of RhoA activity and myosin light chain phosphorylation, as well as decreased cytoskeletal stiffness. Ex vivo contractility testing of bladder muscle strips exposed to electrical stimulation or soluble agonists revealed enhanced tension generation of tissues from mice with constitutive or SM-specific knockout of Nrp2, compared with controls. Mice lacking Nrp2 also displayed increased bladder filling pressures, as assessed by cystometry in conscious mice. Together, these findings identify Nrp2 as a mediator of prorelaxant stimuli in SMCs and suggest a novel function for Nrp2 as a regulator of visceral SM contractility., (Copyright © 2012 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Vascular endothelial growth factor-3 (VEGFR-3) plays a critical role in embryonic cardiovascular development and is thought to be expressed exclusively on the lymphatic endothelium, high endothelial venules, and rarely on adult vascular endothelium. Recent evidence also suggests expression of VEGFR-3 on some tumor-associated macrophages. We have studied the expression of VEGFR-3, its ligand VEGF-C and the co-receptor neuropilin-2, in normal and inflamed corneas and characterized the phenotype and distribution of VEGFR-3(+) cells. Our data demonstrate, for the first time, the expression of VEGFR-3 on corneal dendritic cells (DC) and its up-regulation in inflammation. VEGFR-3(+) DC are CD11c(+)CD45(+)CD11b(+), and are mostly major histocompatibility (MHC) class II(-)CD80(-)CD86(-), indicating immature DC of a monocytic lineage. During inflammation, there is rapid increase in the number of VEGFR-3(+) DC in the cornea associated with heightened membranous expression as compared to a mostly intracellular expression in uninflamed tissue. VEGFR-3(+) DC in normal corneas are VEGF-C(-)neuropilin-2(-), but express VEGF-C in inflammation. Interestingly, similar cells are absent both in the normal and inflamed skin. These data demonstrate, for the first time, the expression of VEGFR-3 and VEGF-C on tissue DC, which implicate a novel potential relationship between lymphangiogenesis and leukocyte trafficking in the eye.