Abstract
Purpose: :
The normal cornea, but not conjunctiva, is devoid of lymphatic vessels. Corneal lymphangiogenesis occurs during neovascularization, as lymphangiogenesis is believed to depend on angiogenesis. Growth factor-induced angiogenesis in various mouse strains differs significantly. However, strain dependency of growth factor-induced lymphangiogenesis remains to be investigated.
Methods: :
Using the corneal micropocket assay, VEGF-A, FGF-2, or control pellets were implanted in corneas of C57BL/6 and BALB/c mice. Lymphangiogenesis and angiogenesis were quantified using immunostaining of LYVE-1 and CD31, respectively.
Results: :
The area of pre-existing lymphatics was significantly higher in untreated corneas of C57BL/6 (0.85±0.08 mm2) compared to BALB/c mice (0.44±0.09 mm2) (n=6 and 11, P=0.007), while the area of pre-existing vasculature did not differ significantly (0.88±0.11 and 0.79±0.07 mm2, n=4 and 11 respectively, P=0.5). The number of pre-existing lymphatic tips as well as the number of lymphatics that overreached pre-existing limbal vessels were significantly higher in normal C57BL/6 corneas than in BALB/c corneas (Total tips: 22.2±1.4 vs 15.4±2.0, Tips over vessels; 15.4±0.9 vs 2.9±0.5, n=12 and 11, P=0.006 and 1.0X10-11, respectively). VEGF-A or FGF-2 induced lymphangiogenesis did not differ significantly between C57BL/6 and BALB/c mice (VEGF-A: 0.82±0.19 vs 0.78±0.10 mm2, n=9 and 7, P=0.9; FGF-2: 1.88±0.39 vs 2.08±0.42 mm2, n=6 and 10, P=0.7). Corneal lymphangiogenesis was significantly greater in VEGF-A-implanted BALB/c mice with preexisting conjunctival lymphatics (1.35±0.13 mm2, n=4), compared to those without (0.39±0.08 mm2, n=7, P=0.00007). In contrast, VEGF-A-induced corneal angiogenesis in mice with and without pre-existing conjunctival lymphatics did not differ significantly (2.07±0.09 mm2 and 2.29±0.10 mm2, n=4 and 7, P=0.18).
Conclusions: :
Growth factor-induced lymphangiogenesis differs significantly among mouse strains. The extent of growth factor-induced corneal lymphangiogenesis depends on pre-existing lymphatics, while growth factor-induced angiogenesis does not.
Keywords: cornea: basic science • vascular endothelial growth factor • inflammation