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Katy Liu, Darren Schuman, Guorong Li, W. Daniel Stamer, Daniel R Saban; Macrophage Ontogeny and Distribution within the Conventional Outflow Tract. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2247.
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Macrophages reside in tissues throughout the eye and their phenotypes and functions are shaped by both their sub-anatomic location in tissue as well as their respective developmental origins (ontogeny). Developmentally, macrophages are mostly either (a) derived prenatally and are long-lived; or, (b) from circulating monocytes and are short-lived. The purpose of this study was to characterize the presence and distribution of long-lived versus short-lived macrophages in the conventional outflow tract.
We took advantage of Cx3cr1-YFPCreER/+ transgenic mice with various Cre reporters to tamoxifen-induce conditional labeling of tissue resident macrophages in anterior segment tissues. Mice were tamoxifen pulsed (60 mg/kg) and rested. Fixed anterior segment whole mounts were prepared. Tissues were labelled with antibodies against cluster of differentiation 31 (CD31), alpha-smooth muscle actin (Sma-1) and DAPI, along with their isotype controls in separate cohorts. We categorized long-lived macrophages as YFP+ cells that retained the Cre reporter labeling (>2 weeks post tamoxifen pulse), whereas short-lived macrophages did not (O’Koren, 2019). Immunolabelled tissue samples were imaged by confocal microscopy.
Macrophages were found throughout the conventional outflow tract, including the trabecular meshwork (TM), Schlemm’s canal (SC), collector channels and surrounding distal vessels (DVs). Macrophage density was measured in the DVs (84 ±42 cells per high-powered field (HPF), 40X magnification) and in the SC and TM (103 ± 32 cells per HPF). Macrophages were counted and averaged over 6-7 randomly selected HPFs imaged from anterior segment whole mounts from 3 mice. Long-lived macrophages comprised a subpopulation of macrophages in the TM, SC, and around the DVs. In the SC and TM, macrophages generally retained a dendritic morphology, whereas DV-associated macrophages were largely elongated or rounded in appearance and in close apposition to the vessels.
Macrophages are present throughout the conventional outflow tract of TM, SC and DVs. The presence of short-lived and long-lived or tissue resident macrophages suggests two distinct populations of macrophages reside in the outflow tract.
This is a 2021 ARVO Annual Meeting abstract.
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