Corneal avascularity—the absence of blood vessels in the cornea—is required for optical clarity and optimal vision, and has led to the cornea being widely used for validating pro- and anti-angiogenic therapeutic strategies for many disorders1,2,3,4. But the molecular underpinnings of the avascular phenotype have until now remained obscure5,6,7,8,9,10 and are all the more remarkable given the presence in the cornea of vascular endothelial growth factor (VEGF)-A, a potent stimulator of angiogenesis, and the proximity of the cornea to vascularized tissues. Here we show that the cornea expresses soluble VEGF receptor-1 (sVEGFR-1; also known as sflt-1) and that suppression of this endogenous VEGF-A trap11 by neutralizing antibodies, RNA interference or Cre-lox-mediated gene disruption abolishes corneal avascularity in mice. The spontaneously vascularized corneas of corn1 and Pax6+/- mice12,13 and Pax6+/- patients with aniridia14 are deficient in sflt-1, and recombinant sflt-1 administration restores corneal avascularity in corn1 and Pax6+/- mice. Manatees, the only known creatures uniformly to have vascularized corneas15, do not express sflt-1, whereas the avascular corneas of dugongs, also members of the order Sirenia, elephants, the closest extant terrestrial phylogenetic relatives of manatees, and other marine mammals (dolphins and whales) contain sflt-1, indicating that it has a crucial, evolutionarily conserved role. The recognition that sflt-1 is essential for preserving the avascular ambit of the cornea can rationally guide its use as a platform for angiogenic modulators, supports its use in treating neovascular diseases, and might provide insight into the immunological privilege of the cornea.

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  1. 1.

    Susruta-Samhita (Chaukhambha Visvabharati, Varanasi, India, 2001)

  2. 2.

    Ophthalmology of the Ancients (J. P. Wayenborgh, Oostende, Belgium, 1999)

  3. 3.

    & The mucopolysaccharide acid of the cornea and its enzymatic hydrolysis. Am. J. Ophthalmol. 23, 1320–1325 (1940)

  4. 4.

    , , & Tumor growth and neovascularization: an experimental model using the rabbit cornea. J. Natl Cancer Inst. 52, 413–427 (1974)

  5. 5.

    , , & Corneal neovascularization. Curr. Opin. Ophthalmol. 12, 242–249 (2001)

  6. 6.

    et al. Genetic modulation of pigment epithelium-derived factor (PEDF) expression does not alter normal or pathological angiogenesis in the eye, or tumor growth. Invest. Ophthalmol. Vis. Sci. 45, abstr. 1884. (2004)

  7. 7.

    et al. Roles of thrombospondin-1 and -2 in regulating corneal and iris angiogenesis. Invest. Ophthalmol. Vis. Sci. 45, 1117–1124 (2004)

  8. 8.

    , , & Plasminogen deficiency causes severe thrombosis but is compatible with development and reproduction. Genes Dev. 9, 794–807 (1995)

  9. 9.

    et al. Lack of collagen XVIII/endostatin results in eye abnormalities. EMBO J. 21, 1535–1544 (2002)

  10. 10.

    , , & Functions of interleukin 1 receptor antagonist in gene knockout and overproducing mice. Proc. Natl Acad. Sci. USA 93, 11008–11013 (1996)

  11. 11.

    & Inhibition of vascular endothelial cell growth factor activity by an endogenously encoded soluble receptor. Proc. Natl Acad. Sci. USA 90, 10705–10709 (1993)

  12. 12.

    et al. Corn1: a mouse model for corneal surface disease and neovascularization. Invest. Ophthalmol. Vis. Sci. 37, 397–404 (1996)

  13. 13.

    et al. Corneal abnormalities in Pax6+/- small eye mice mimic human aniridia-related keratopathy. Invest. Ophthalmol. Vis. Sci. 44, 1871–1878 (2003)

  14. 14.

    et al. The human PAX6 gene is mutated in two patients with aniridia. Nature Genet. 1, 328–332 (1992)

  15. 15.

    , & Corneal vascularization in the Florida manatee (Trichechus manatus latirostris) and three-dimensional reconstruction of vessels. Vet. Ophthalmol. 8, 89–99 (2005)

  16. 16.

    , , , & Flt-1 lacking the tyrosine kinase domain is sufficient for normal development and angiogenesis in mice. Proc. Natl Acad. Sci. USA 95, 9349–9354 (1998)

  17. 17.

    , , & Role of the Flt-1 receptor tyrosine kinase in regulating the assembly of vascular endothelium. Nature 376, 66–70 (1995)

  18. 18.

    et al. Rapid ocular angiogenic control via naked DNA delivery to cornea. Invest. Ophthalmol. Vis. Sci. 42, 1975–1979 (2001)

  19. 19.

    , , & Enhanced cell-permeant Cre protein for site-specific recombination in cultured cells. BMC Biotechnol. 4, 25 (2004)

  20. 20.

    et al. Epigenetic regulation of gene structure and function with a cell-permeable Cre recombinase. Nature Biotechnol. 19, 929–933 (2001)

  21. 21.

    et al. Membrane fixation of vascular endothelial growth factor receptor 1 ligand-binding domain is important for vasculogenesis and angiogenesis in mice. Mol. Cell. Biol. 25, 346–354 (2005)

  22. 22.

    , , & Differential transcriptional regulation of the two vascular endothelial growth factor receptor genes. Flt-1, but not Flk-1/KDR, is up-regulated by hypoxia. J. Biol. Chem. 272, 23659–23667 (1997)

  23. 23.

    et al. Aberrant actin cytoskeleton leads to accelerated proliferation of corneal epithelial cells in mice deficient for destrin (actin depolymerizing factor). Hum. Mol. Genet. 12, 1029–1036 (2003)

  24. 24.

    et al. Sustained inhibition of corneal neovascularization by genetic ablation of CCR5. Invest. Ophthalmol. Vis. Sci. 44, 590–593 (2003)

  25. 25.

    , , , & Inhibition of corneal neovascularization by genetic ablation of CCR2. Cornea 22, 465–467 (2003)

  26. 26.

    , , , & Vascular repair after menstruation involves regulation of vascular endothelial growth factor-receptor phosphorylation by sFLT-1. Am. J. Pathol. 158, 1399–1410 (2001)

  27. 27.

    , , , & The VEGF receptor flt-1 (VEGFR-1) is a positive modulator of vascular sprout formation and branching morphogenesis. Blood 103, 4527–4535 (2004)

  28. 28.

    et al. Circulating angiogenic factors and the risk of preeclampsia. N. Engl. J. Med. 350, 672–683 (2004)

  29. 29.

    et al. Matrix metalloproteinase-9 triggers the angiogenic switch during carcinogenesis. Nature Cell Biol. 2, 737–744 (2000)

  30. 30.

    & Loss and restoration of immune privilege in eyes with corneal neovascularization. Invest. Ophthalmol. Vis. Sci. 37, 2485–2494 (1996)

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We thank the various aquaria, zoos and wildlife rehabilitation centres that donated tissues for comparative studies; R. Groom, S. Joshi, M. Kellogg, R. King, C. K. Lau, P. Lewis, N. Mezei, K.K. Smith and L. Xu for technical assistance; R. J. Kryscio for statistical guidance; and R. Mohan, S. Bondada, M. W. Fannon, L. Mazzaro, Y. Nozaki, P. A. Pearson, L. Peichl, A. M. Rao, G. S. Rao and K. Ambati for discussions. J.A. was supported by the NEI/NIH, the Lew R. Wasserman Merit Award (Research to Prevent Blindness), the Dennis W. Jahnigen Career Development Award (American Geriatrics Society, John A. Hartford Foundation, Atlantic Philanthropies), the Macula Vision Research Foundation, the International Retinal Research Foundation, the E. Matilda Ziegler Foundation for the Blind, the Dr E. Vernon Smith and Eloise C. Smith Macular Degeneration Endowed Chair, a physician–scientist award from University of Kentucky, and a departmental challenge grant from Research to Prevent Blindness; M.N. by ARVO/Japan National Society for the Prevention of Blindness; E.S. by Fight For Sight; R.J.C.A by Research to Prevent Blindness; J.Z.B. and B.R. by the NIDCD/NIH; A.T. by a Japan Young Scientist Award; B.K.A. by a VA Career Development Award, the Knights-Templar Eye Foundation and Fight for Sight; N.S by ARVO/Alcon; S.I. by the NEI/NIH; J.M.C. by the Wellcome Trust and the Birth Defects Foundation; T.S.K by the NEI/NIH and the NIAMS/NIH; S.B. by the Muscular Dystrophy Association; and S.D.F. by the AIRC (Italian Association for Cancer Research). Author Contributions B.K.A. and J.A. conceived and designed the experiments, wrote the manuscript, and are joint senior authors. M.N., N.S., A.T., P.D.J., J.Z.B. and B.J.R. contributed equally.

Author information

Author notes

    • Dalen W. Agnew
    •  & Hans-Peter Gerber

    Present addresses: Diagnostic Center for Population and Animal Health, Michigan State University, Lansing, Michigan 48910, USA (D.W.A.); Department of Translational Biology, Seattle Genetics, Bothell, Washington 98021, USA (H.-P.G.).


  1. Departments of Ophthalmology and

    • Balamurali K. Ambati
    • , Nirbhai Singh
    • , Pooja D. Jani
    • , Tushar Suthar
    •  & Elizabeth Richter
  2. Cell Biology, Medical College of Georgia & Augusta Veterans Affairs Medical Center, Augusta, Georgia 30907, USA

    • Balamurali K. Ambati
    •  & Ruth B. Caldwell
  3. Departments of Ophthalmology & Visual Sciences,

    • Miho Nozaki
    • , Atsunobu Takeda
    • , Romulo J. C. Albuquerque
    • , Eiji Sakurai
    • , Michael T. Newcomb
    • , Mark E. Kleinman
    • , Judit Z. Baffi
    • , Brian J. Raisler
    •  & Jayakrishna Ambati
  4. Internal Medicine and

    • Jassir Witta
  5. Physiology, University of Kentucky, Lexington, Kentucky 40506, USA

    • Brian J. Raisler
    •  & Jayakrishna Ambati
  6. Department of Ophthalmology, Nagoya City University Medical School, Nagoya 467-8601, Japan

    • Eiji Sakurai
    •  & Yuichiro Ogura
  7. Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, Tennesee 37232, USA

    • Qing Lin
  8. Molecular and Cell Biology Laboratory, IDI-IRCCS, Rome 00167, Italy

    • Angela Orecchia
  9. Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Gainesville, Florida 32610, USA

    • Don A. Samuelson
  10. Department of Pathology, Microbiology and Immunology, University of California, Davis, California 95616, USA

    • Dalen W. Agnew
  11. Department of Pathology, Sea World, San Diego, California 92109, USA

    • Judy St. Leger
  12. The Eye Pathology Laboratory, Wilmer Institute and Department of Pathology, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205, USA

    • W. Richard Green
  13. Division of Human Gene Therapy, The Gene Therapy Center, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA

    • Parameshwar J. Mahasreshti
    •  & David T. Curiel
  14. School of Tropical Environment Studies and Geography, James Cook University, Townsville, Queensland 4811, Australia

    • Donna Kwan
    •  & Helene Marsh
  15. Department of Medical Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA

    • Sakae Ikeda
  16. School of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK

    • Lucy J. Leiper
    •  & J. Martin Collinson
  17. Department of Physiology & Pennsylvania Muscle Institute, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

    • Sasha Bogdanovich
    •  & Tejvir S. Khurana
  18. Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan

    • Masabumi Shibuya
  19. Department of Molecular Oncology, Genentech Inc., South San Francisco, California 94080, USA

    • Megan E. Baldwin
    • , Napoleone Ferrara
    •  & Hans-Peter Gerber
  20. Institute of Genetics and Biophysics, Consiglio Nazionale delle Ricerche, Naples 80131, Italy

    • Sandro De Falco


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Competing interests

B.K.A, J.A. and N.S. are listed as inventors on a patent application describing these findings.

Corresponding author

Correspondence to Jayakrishna Ambati.

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