Lymphatic regulator PROX1 determines Schlemm’s canal integrity and identity
Dae-Young Park, … , Young-Kwon Hong, Gou Young Koh
Dae-Young Park, … , Young-Kwon Hong, Gou Young Koh
Published July 25, 2014
Citation Information: J Clin Invest. 2014;124(9):3960-3974. https://doi.org/10.1172/JCI75392.
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Lymphatic regulator PROX1 determines Schlemm’s canal integrity and identity

Abstract

Schlemm’s canal (SC) is a specialized vascular structure in the eye that functions to drain aqueous humor from the intraocular chamber into systemic circulation. Dysfunction of SC has been proposed to underlie increased aqueous humor outflow (AHO) resistance, which leads to elevated ocular pressure, a factor for glaucoma development in humans. Here, using lymphatic and blood vasculature reporter mice, we determined that SC, which originates from blood vessels during the postnatal period, acquires lymphatic identity through upregulation of prospero homeobox protein 1 (PROX1), the master regulator of lymphatic development. SC expressed lymphatic valve markers FOXC2 and integrin α9 and exhibited continuous vascular endothelial–cadherin (VE-cadherin) junctions and basement membrane, similar to collecting lymphatics. SC notably lacked luminal valves and expression of the lymphatic endothelial cell markers podoplanin and lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1). Using an ocular puncture model, we determined that reduced AHO altered the fate of SC both during development and under pathologic conditions; however, alteration of VEGF-C/VEGFR3 signaling did not modulate SC integrity and identity. Intriguingly, PROX1 expression levels linearly correlated with SC functionality. For example, PROX1 expression was reduced or undetectable under pathogenic conditions and in deteriorated SCs. Collectively, our data indicate that PROX1 is an accurate and reliable biosensor of SC integrity and identity.

Authors

Dae-Young Park, Junyeop Lee, Intae Park, Dongwon Choi, Sunju Lee, Sukhyun Song, Yoonha Hwang, Ki Yong Hong, Yoshikazu Nakaoka, Taija Makinen, Pilhan Kim, Kari Alitalo, Young-Kwon Hong, Gou Young Koh

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Figure 1

SC drains out aqueous humor into BVs and exhibits lymphatic markers but does not perfectly match the features of terminally differentiated LVs.

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SC drains out aqueous humor into BVs and exhibits lymphatic markers but ...
(A) Schematic diagram of cornea showing SC (light green), AV (dark green), limbal LVs (light blue), and BVs (red). The square portion, immunostained and highly magnified, is shown in B. (B and C) Image and schematic diagram showing Prox1-GFP+ SC, AV, and CD31+ BV networks. Dashed lines demarcate limbal LV and AV, while dashed arrows indicate the AHO from SC into BVs. (D) H&E staining of corneal limbus in section. Arrow indicates SC. (E) Cross-sectioned image showing Prox1-GFP+ SC, PDGFR-β+ TM, and α-SMA+ CM in corneal limbus. (F) Perfused red fluorescent microbeads (diameter, 1 μm) in Prox1-GFP+ SC. Prox1-GFP mice were given 0.5 μl of the microbeads by intraocular injection; sample was harvested after 1 hour. (G) Image showing VEGFR3 expression in CD31+ SC. (H) Cross-sectioned image showing Itga9 (arrowhead), CD31+ SC, and α-SMA+ CM in corneal limbus. Magnification of the square portion is shown in the top right corner. (I) Comparison of expression and distribution of endomucin between SC (left panel) and limbal LVs (right panel). Arrows indicate limbal veins, while arrowheads indicate limbal artery. (J–L) Comparisons of expressions and distributions of podoplanin, VE-cadherin, Prox1-GFP, LYVE-1, and collagen IV+ basement membrane between SC (upper panels) and limbal LVs (lower panels). Dashed lines demarcate SC or limbal LVs (I–L).The square portions are magnified on the right. Scale bars: 100 μm; 20 μm (enlarged squares).