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 2

Acquisition of lymphatic characteristics in SC dependent on AHO during postnatal development.

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Acquisition of lymphatic characteristics in SC dependent on AHO during p...
Unless otherwise noted, for the bar graphs, the quantification of the control group was normalized to 100%, from which the quantifications of other groups were calculated. (A and B) Temporal changes and quantifications of SC area and expression of Prox1, VEGFR2, VEGFR3, and Tie2 in SC during postnatal development. Dashed lines indicate the buds of SC derived from the CVs. Arrowheads demarcate the remnant communication between SC and CVs. Mean ± SD are shown (n = 4). Scale bars: 50 μm. For the quantifications, the group with the highest value was normalized to 100%, from which the relative values of other groups are shown. (C) Schematic diagram showing generation of the ocular puncture. Upper panel: a puncture on the sclera through 31-gauge syringe needle; lower panel: reduction of AHO achieved by leakage through the puncture. (D–G) Images and comparisons of the SC between the punctured eyes (puncture) and the sham-operated control eyes. Eyes were punctured from P5 to P6, and the corneas were harvested at P7. (D) Comparison of IOP. Each group, n = 4–5. (E) Images showing Prox1+, Prox1-GFP+, or VEGFR3+ cells in CD31+ SC. Arrowheads indicate the remnant communication between SC and CVs. Scale bars: 100 μm. (F and G) Comparisons of relative area and expressions of Prox1, Prox1-GFP, and VEGFR3 in SC. Each group, n = 4–5. *P < 0.05 versus control.