Fibulin-5 deposition in human skin: decrease with ageing and ultraviolet B exposure and increase in solar elastosis

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Abstract
Background Fibulin‐5 was recently found as a secreted extracellular matrix protein that functions as a scaffold for elastic fibres. However, the distribution of fibulin‐5 in human skin and its changes during the ageing process are not known. Objectives To explore the involvement of fibulin‐5 in skin ageing, the age‐dependent changes in fibulin‐5 localization in human skin were examined compared with those of other elastic fibre components including elastin, fibrillin‐1 and fibulin‐2. Methods The distribution of elastin, fibrillin‐1, fibrillin‐2, fibulin‐2 and fibulin‐5 was investigated by means of immunohistochemistry using their specific antibodies. Skin samples were recovered from 12 healthy subjects undergoing plastic surgery. Ultraviolet (UV) B‐irradiated or control nonirradiated buttock skin samples were obtained from two healthy volunteers at 2 days after the irradiation at 2 minimal erythemal doses. Results In the reticular dermis of young sun‐protected skin from the upper arm, fibulin‐5 colocalized with the other elastic fibre components, while in the papillary dermis fibulin‐5 showed candelabra‐like structures perpendicular to the epidermis with an unstained area just beneath the epidermis, which was similar to that of elastin but not fibrillin‐1. Fibulin‐5 in the reticular dermis decreased and disappeared with age even in sun‐protected skin from the thigh, abdomen and upper arm. In sun‐exposed skin, fibulin‐5 was extremely reduced in the dermis of cheek skin even from a 20‐year‐old man. UVB irradiation reduced fibulin‐5, fibulin‐2 and elastin markedly, moderately and weakly, respectively, compared with levels in control nontreated skin. Interestingly, the deposition of fibulin‐5 was increased in solar elastosis, like that of other elastic fibre components. Conclusions These results suggest that fibulin‐5 is a good marker of skin ageing and that the earlier loss of fibulin‐5 may involve age‐dependent changes in other elastic fibre components.