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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Research Article

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 5

Reduced AHO induces loss of lymphatic feature in SC ECs, leading to EndMT.

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Reduced AHO induces loss of lymphatic feature in SC ECs, leading to EndM...
(A–E) Images and comparisons of SC between punctured eyes and sham-operated control eyes. Eyes were punctured daily for 7 days, and corneas were harvested at day 7. (A) Comparison of IOP. n = 4–5, each group. (B and C) Images and comparisons of expressions of Prox1, VEGFR3, vWF, and Klf4 in the CD31+ ECs of SC. n = 4–5, each group. The quantification of control group was normalized to 100%, from which the quantifications of other groups were calculated. (D and E) Images and comparisons of mesenchymal markers α-SMA, FSP-1, vimentin, and desmin in CD31+ SC ECs. Solid-line square is magnified on the right, which reveals α-SMA expression in the CD31+ EC of SC (white arrows). Arrowheads indicate expression of FSP-1, vimentin, and desmin in CD31+ SC ECs, respectively. n = 4–5, each group. (F) Lineage-tracing study in which Prox1-CreERT2 R26mTmG mice were treated with tamoxifen 3 times from 8 weeks. Then eyes were punctured daily for 7 days, and corneas were harvested at day 7. Solid-line square is magnified in the bottom right corner. Arrows indicate coexpression of FSP-1 in GFP+ SC ECs. *P < 0.05 versus control. Scale bars: 100 μm; 20 μm (enlarged squares).