UVA causes dysfunction of ETBR and BMPR2 in vascular endothelial cells, resulting in structural abnormalities of the skin capillaries

•Capillary structural abnormalities on sun-exposed skin with skin redness unevenness.•Capillary structural abnormalities include dilation and disappearance.•Capillaries are excessively dilated by increased ETBR expression on HUVECs by UVA.•Capillary migration disappears under decreased BMPR2 expression on HUVECs by UVA. Capillary structural abnormalities cause skin disorders. Mottled redness, i.e., skin redness unevenness, may appear on the sun-exposed skin, suggesting capillary structural abnormalities, although its mechanism remains unclear. To observe the capillary structures in the sun-exposed skin where skin redness unevenness is likely to occur, and clarify the mechanism of capillary structural abnormalities. The tissue structures in the skin with skin redness unevenness were observed by LC-OCT. Subsequently, immunostaining of the sun-exposed skin where skin redness unevenness is often observed, was performed. Vascular endothelial cells were UV-irradiated to analyze the expression and functions of genes involved in the capillary structures and morphogenesis. The skin with skin redness unevenness exhibited scattering of dilated tubular tissue and disturbance of distribution uniformity. Immunostaining of the sun-exposed skin that were more likely to be exposed to UV rays also revealed similarly disorder of capillary structures. In addition, UVA-irradiated vascular endothelial cells exhibited increased expression of ETBR, involved in telangiectasia, decreased expression of BMPR2, involved in the morphogenesis and maintenance of the blood vessels, and reduced migration of the capillaries. UV rays alter ETBR and BMPR2 expression in the skin capillaries, and cause partial dilation and decreased migration, resulting in capillary structural abnormalities and causing skin redness unevenness.