Abstract:

Objective To investigate the expression of cathepsin B in photoaging skin and its significance. Methods Skin specimens were obtained from the right forearm （sun-exposed sites） and buttock （unexposed sites） of 6 healthy volunteers with informed consent and subjected to immunohistochemistry for the detection of cathepsin B expression. Primary human fibroblasts derived from the prepuce of children aged 3 to 6 years were cultured in vitro; after 10 to 15 passages, cells were divided into four groups to be treated with methoxsalen of 50 mg/L for 24 hours followed by ultraviolet A （UVA） exposure （premature senescence group）, phosphate buffered saline （PBS） only （control group）, UVA exposure only （UVA group）, methoxsalen only （methoxsalen group）. Then, the protein and mRNA expressions of cathepsin B were detected by Western blot and RT-PCR, respectively, in these fibroblasts 1, 2, 3 weeks after the treatment. Results Cathepsin B was observed in both exposed and unexposed sites of all volunteers, and the average absorbence of cathepsin B was significantly lower in exposed sites than in unexposed sites （0.2130 ± 0.7997 vs 0.4520 ± 0.5921, t = 5.37, P < 0.05）. Decreased protein expression of cathepsin B was also noted in the premature senescence group compared with the other three groups. Moreover, the gray ratio between cathepsin B protein and glyceraldehyde phosphate dehydrogenase （GAPDH） in premature senescence group reduced from 28.099 ± 0.054 before treatment to 25.103 ± 0.102 in week 1 and 17.693 ± 0.099 in week 3 after UVA exposure. RT-PCR revealed that the mRNA expression level of cathepsin B in fibroblasts of premature senescence group decreased by 36 percent compared with that in the control group. Conclusions The expression of cathepsin B decreases in photoaged skin as well as in UVA-exposed fibroblasts in a time-dependent manner, which may be associated with the self-repair of photoaged skin.

Key words: Skin Aging, Cathepsin B, Fibroblasts