Ultraviolet B Irradiation of Human Skin Induces an Angiogenic Switch That is Mediated by Upregulation of Vascular Endothelial Growth Factor and by Downregulation of Thrombospondin-1

Background: We have previously demonstrated that skin-specific overexpression of the endogenous angiogenesis inhibitor thrombospondin (TSP)-1 prevented chronic ultraviolet (UV) B-induced angiogenesis, inflammatory cell infiltration and cutaneous photodamage in mice.

Objectives: To elucidate the mechanisms by which acute UVB-induced angiogenesis induces dermal damage, and to study the molecular regulation of acute UVB-induced angiogenesis in human skin.

Methods: We subjected five healthy volunteers to acute UVB irradiation (2 minimal erythema doses) and performed histological analysis at 48 h after UVB irradiation.

Results: Histology revealed epidermal hyperplasia, infiltration of elastase-producing neutrophils and elastin fibre damage. Immunohistochemistry for CD31 demonstrated pronounced angiogenesis with a significant increase in both vascular density and vessel size, associated with increased endothelial cell proliferation. Whereas constitutive expression of TSP-1 but only weak expression of vascular endothelial growth factor (VEGF) were detected in normal human epidermis, pronounced downregulation of TSP-1 and upregulation of VEGF were observed in epidermal keratinocytes after acute UVB irradiation. These findings were confirmed by quantitative reverse transcription-polymerase chain reaction analysis after UVB irradiation of cultured HaCaT keratinocytes in vitro.

Conclusions: Together, these data indicate that a disruption of the balance between VEGF and TSP-1 expression leads to a UVB-induced angiogenic switch, facilitating the infiltration of elastase-producing leucocytes and cutaneous photodamage.