The Schlemm’s canal is a VEGF-C/VEGFR-3–responsive lymphatic-like vessel
Aleksanteri Aspelund, … , Ilkka Immonen, Kari Alitalo
Aleksanteri Aspelund, … , Ilkka Immonen, Kari Alitalo
Published July 25, 2014
Citation Information: J Clin Invest. 2014;124(9):3975-3986. https://doi.org/10.1172/JCI75395.
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Research Article

The Schlemm’s canal is a VEGF-C/VEGFR-3–responsive lymphatic-like vessel

Abstract

In glaucoma, aqueous outflow into the Schlemm’s canal (SC) is obstructed. Despite striking structural and functional similarities with the lymphatic vascular system, it is unknown whether the SC is a blood or lymphatic vessel. Here, we demonstrated the expression of lymphatic endothelial cell markers by the SC in murine and zebrafish models as well as in human eye tissue. The initial stages of SC development involved induction of the transcription factor PROX1 and the lymphangiogenic receptor tyrosine kinase VEGFR-3 in venous endothelial cells in postnatal mice. Using gene deletion and function-blocking antibodies in mice, we determined that the lymphangiogenic growth factor VEGF-C and its receptor, VEGFR-3, are essential for SC development. Delivery of VEGF-C into the adult eye resulted in sprouting, proliferation, and growth of SC endothelial cells, whereas VEGF-A obliterated the aqueous outflow system. Furthermore, a single injection of recombinant VEGF-C induced SC growth and was associated with trend toward a sustained decrease in intraocular pressure in adult mice. These results reveal the evolutionary conservation of the lymphatic-like phenotype of the SC, implicate VEGF-C and VEGFR-3 as critical regulators of SC lymphangiogenesis, and provide a basis for further studies on therapeutic manipulation of the SC with VEGF-C in glaucoma treatment.

Authors

Aleksanteri Aspelund, Tuomas Tammela, Salli Antila, Harri Nurmi, Veli-Matti Leppänen, Georgia Zarkada, Lukas Stanczuk, Mathias Francois, Taija Mäkinen, Pipsa Saharinen, Ilkka Immonen, Kari Alitalo

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Figure 5

VEGF-C overexpression induces directional sprouting, proliferation, and migration of SC ECs in adults.

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VEGF-C overexpression induces directional sprouting, proliferation, and ...
(A–E) AdVEGF-C, AdVEGF, or an AdControl was injected into the anterior chamber, as indicated. (A) Immunofluorescence staining of the SC with antibodies against PECAM-1 (green), BrdU (red), and PROX1 (blue) at days 4 and 14 after injection. Mice were injected with 100 mg/kg BrdU 2 hours prior to sacrifice. Sprouts of SC ECs (asterisks) are indicated. Changes in limbal vascular anatomy on day 14 are illustrated. C, cornea; S, sclera; AC, anterior chamber; PC, posterior chamber. (B and C) Quantitative analysis of SC area (B) and SC sprouts extending toward the cornea or sclera (C). Each symbol represents data from 1 eye. (D and E) IOP before and 3 (D) and 14 (E) days after injection. (F and G) AAV–VEGF-C or AAV-HSA was injected into the anterior chamber. (F) Immunofluorescence staining of the SC with indicated antibodies at week 6 after transduction, and illustration of changes in limbal vascular anatomy. (G) IOP before and after injection. (H) X-gal staining in mice injected with AdLacZ. (I) Immunofluorescence in mice injected with reporter AAV vectors encoding EGFP and staining with antibodies against GFP (red) and PECAM-1 (blue). Scale bars: 200 μm (A, F, and I). *P < 0.05; **P < 0.01; ***P < 0.001; #P < 0.0001.