Expression of metallothionein-I and II in skin ageing and its association with skin proliferation

Background Metallothioneins (MT) are important antioxidants involved in the ageing process of many tissues and organs. To our knowledge, the role of MT in skin ageing has not been reported. Objectives To investigate the expression of MT in ageing skin. Methods The protein levels of MT-I and MT-II in sun-exposed and sun-protected skin specimens obtained from healthy individuals were detected by immunohistochemistry using tissue microarray and expressed as average integrated optical density (AIOD). Proliferating cell nuclear antigen (PCNA) and Ki-67 protein levels in these specimens were also detected to study the possible link between the proliferation of keratinocytes and expression of MT. Results The protein levels of MT-I and MT-II decreased significantly with increasing age of sun-exposed and sun-protected skin (r = −0·73 and −0·98, respectively, P < 0·01) but was more prominent in sun-exposed skin. In sex- and age-matched specimens, the intensity of MT-I and MT-II in sun-exposed skin was much lower than in sun-protected skin (9·46 ± 2·39 vs. 22·25 ± 8·04, mean ± SD of AIOD, P < 0·01, Student’s t-test). The expression of PCNA and Ki-67 showed the same trend. Conclusions The expression of MT-I and MT-II declined with the decrease of keratinocyte proliferation in the process of skin ageing, and this decline was more significant in sun-exposed skin. Whether MT-I and MT-II supplementation could inhibit skin ageing, especially photoageing, merits further study.