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Agnieszka Dejda, Gaelle-Stephanie Mawambo-Tagne, Jean-Francois Daudelin, Naoufal Akla, Chintan Patel, khalil Miloudi, Nathalie Labrecque, Przemyslaw Sapieha; Myeloid cell-resident neuropilin-1 is dispensable for retinal vascular development.. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5406.
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Neuropilin-1 (Nrp-1) is a transmembrane receptor that mediates developmental angiogenesis. It binds both vascular endothelial growth factor 165 and Semaphorin 3A. Nrp-1 is expressed in neurons and endothelial tip and stalk cells. In addition, it has been shown that Nrp-1 positive macrophages comprise the major population of tissue macrophages during brain vascularization, and that they interact with endothelial tip cells to promote vascular anastomosis. Our analysis of mouse retinal cell suspensions revealed a subpopulation of microglia cells that are Nrp-1-positive. Here we investigated the role of myeloid cell-resident Nrp-1 in mouse retinal angiogenesis.
We generated transgenic mice with Nrp-1 specifically knocked out in myeloid cells by breading LyzMcre mice (Cre-recombinase is expressed in myeloid cell lineage) with Nrp-1 floxed mice. Eyes from control (C57BL/6 and LyzMcre) and LyzMcre/Nrp-1-/- mice were collected between postnatal day 2 (P2) and 7 (P7). We investigated distribution patterns of Nrp-1-positive microglia and performed a comprehensive morphometric analysis of retinal vasculature throughout its development. Isolated retinas were fluorescently labeled for microglia (Iba1), vessels (lectin) and Nrp-1 and images were acquired by confocal microscopy. Numbers of total microglia and Nrp-1-positive microglia, rates of vascularization, numbers of branch points and tip cells were quantified. In addition to superficial plexus, development of intermediate and deep vascular retinal layers were investigated in cryosectioned eyes collected at P14 and P21.
Nrp-1-positive microglia cells are present throughout the retina during vascular development. LyzMcre/Nrp-1-/- mice show a 70% reduction in the number of Nrp-1-positive retinal microglia. However, at all time points analyzed, no significant difference was noted in superficial plexus development with respect to rates of retinal vascularization, vascular branch points or tip cells between LyzMcre/Nrp-1-/- and control mice. In addition, the intermediate plexus was appropriately formed by the end of the second week after birth and deep vascular plexus in the third week in both control and knockout mice.
Cell-specific knockout of Nrp-1 in the myeloid cell lineage does not impair development of mouse retinal vasculature. Macrophage/microglia-resident Nrp-1 is therefore not required for adequate vascularization of mouse retina.
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