Effects of UV irradiation on the sebaceous gland and sebum secretion in hamsters

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Abstract

Background: Although an understanding of the photobiology of the skin has been extensively advanced recently, the effect of ultraviolet (UV) radiation on sebaceous glands is not well known. Objective: In this study, we examined the direct effect of UV radiation on cultured sebocytes from hamsters in vitro experimental system. Moreover, we examined whether UV-induced peroxidation of skin surface lipids may affect barrier function of horney layer. Methods: We irradiated cultured sebocytes from hamsters, which have similar biological characteristics to the human sebocytes, with UV radiation. Moreover, transepidermal water loss (TEWL) was examined after topical application of cholesterol or triglyceride (TG) and UV exposures on the back of hamsters. Results: The number of sebocytes were increased significantly (120–140%) after 4 days as compared with the non-irradiated controls. Lipid production in sebocytes was also increased on day 7 in an irradiation-dependent manner up to 4.1 times of the pre-irradiated level. When UVB was irradiated to TG- or cholesterol-applied skin at the minimum ear-swelling dose, TEWL increased twice or more as compared with UVB irradiation to unapplied sites. When in vitro-irradiated TG, in vitro-irradiated cholesterol, TG-peroxide (TG-OOH), and cholesterol-peroxide (CHO-OOH) were applied to the skin, TEWL increased significantly. Conclusion: These results suggest that UVB may directly activate the functions of the sebaceous gland in vivo to produce increased amounts of sebum, which may undergo peroxidation by UV light and damage the barrier functions of the skin.

Introduction

Much is known about the acute and chronic effects of UV radiation on epidermis and dermis [1], [2], [3], [4]. In contrast, only limited investigations have been aimed at the effects on the skin appendage such as the sebaceous gland. The DNA, RNA, and protein syntheses of keratinocytes are depressed shortly after UV exposure, but recover and accelerate thereafter [3]. These findings may explain the epidermal hyperplasia after UV irradiation. Chronic exposures to the sunlight clinically cause sebaceous gland hyperplasia on the face as one of the manifestations of the photoaging in human. However, the dynamics of sebocytes after UV irradiation has not been fully understood. It has been reported that, when hairless mice or hamsters were exposed to UVB in vivo, the sebaceous glands showed hyperplasia and the number of sebocytes increased [5], [6]. These studies suggest that UV radiation in the sunlight can directly or indirectly influence the sebaceous gland. In this study, we examined the direct effect of UV radiation on cultured sebocytes from hamsters in vitro experimental system. We also examine the effect of UV radiation on the sebum production because there are some reports that UVB phototherapy or PUVA photochemotherapy increased the amount of skin surface lipids [7], [8].

It has been shown that hamsters are useful as an experimental animal to examine the functions of sebaceous gland because the hamster sebaceous gland is similar to the human gland with regard to its size, response to androgens, and turnover time in vivo [9]. Recently, we established a tissue culture system for hamster sebaceous glands without damaging their functions [10]. Furthermore, it has been demonstrated that these hamster sebocytes are similar to human sebocytes in the proliferation and lipid synthesis [11]. Moreover, we examined whether UV-induced peroxidation of skin surface lipids may affect barrier function of horney layer.

Section snippets

Culture of sebocytes

Earlobes removed from 5-week-old golden male hamsters were incubated in Dulbecco's modified Eagle's medium (DMEM; Nikken Biomedical Laboratory, Kyoto, Japan) with 100 IU/ml penicillin and 100 μg/ml streptomycin (Flow laboratories Ltd., Ayrshire, Scotland) for 3 h at 4 °C, and were successively washed with Ca2+- and Mg2+-free phosphate-buffered saline (PBS(−)), then cut into 5×5 mm2 pieces. They were incubated for 14 h in 2.4 U/ml dispase (Godoshusei Co. Ltd., Tokyo, Japan) at 4 °C to separate

Effects of UVB on proliferation of cultured sebocytes and keratinocytes

Proliferation of sebocytes was inhibited on day 2 depending on the dose of UVB. The number of 10 or 20 mJ/cm2 UVB-irradiated cells was about 2/3 (P<0.001) or 1/2 (P<0.001) of non-irradiated cells, respectively. On day 4, on the contrary, proliferation of the cells was accelerated depending on the irradiated dose. The number of 10 or 20 mJ/cm2 UVB-irradiated cells was about 1.2 times (P<0.05) or 1.4 times (P<0.01) higher than that of non-irradiated cells, respectively. On day 7, however, there

Discussion

The sebaceous gland is a holocrine gland. The sebocytes produce lipid droplets with differentiation and finally rupture to excrete sebum to the skin surface. The amount of excreted sebum changes according to the degrees of proliferation and differentiation of sebocytes. The functions of sebaceous gland are controlled by endocrine factors such as several hormones produced in pituitary gland, adrenal cortex, and gonad [15], [16], [17]. Among them, androgen is the most important hormone. It is

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