VEGF promotes acute photodamage and UVB-induced skin angiogenesis. Macroscopic appearance of ears in sham-irradiated wild-type (A) and VEGF-overexpressing (B) mice is shown as control. No major changes were seen in the ear skin of wild-type mice (C) 48 hours after UVB irradiation with 3.6 × 10-2 J/cm2, whereas VEGF transgenic mice developed marked erythema (D). Histologic analysis revealed that the ear skin of wild-type mice was normal, with (top) or without (bottom) UVB irradiation (E; hematoxylin-eosin stain). In contrast, the ear skin of VEGF-overexpressing mice showed epidermal hyperplasia, dermal edema, inflammatory cell infiltration, and vessel dilation after UVB irradiation (top) compared with the nonirradiated skin (bottom) (F). Double immunofluorescence staining revealed dilated CD31+ vessels (red) that contained proliferating endothelial cells (Ki-67 stain; yellow; arrowheads) in the skin of VEGF-overexpressing mice and in proliferating epidermal keratinocytes, labeled with Ki-67 (green; arrows; H). No such changes were seen in the skin of wild-type littermates (G). Scale bars, 200 μm. A Plan Fluor 10 × objective with an aperture of 0.30 was used for panels E-H. (I) VEGF-overexpressing mice showed significant ear swelling 48 hours after irradiation with 3.6 × 10-2 J/cm2 UVB (▪) but not with 1.8 × 10-2 J/cm2 UVB (•). No ear swelling was observed in wild-type littermates irradiated with 1.8 × 10-2 J/cm2 (○) or 3.6 × 10-2 J/cm2 UVB (□). Ear thickness in VEGF transgenic mice returned to original levels 7 days after UVB irradiation (I). Ear swelling is expressed as the increase (Δ) over the original ear thickness in micrometers. (J) VEGF ELISA of skin lysates revealed enhanced VEGF protein levels in the ear skin of VEGF-overexpressing mice (▪) 48 hours after UVB irradiation compared with transgenic mice that did not undergo UVB irradiation or with wild-type mice (□). Data are expressed as mean ± SEM (n = 3 per condition and time point). ***P < .001; **P < .01.
