Zhuang L, Wang B, Shinder G A, Shivji G M, Mak T W, Sauder D N
Division of Dermatology, Sunnybrook Health Science Centre, University of Toronto, Toronto, ON, Canada.
J Immunol. 1999 Feb 1;162(3):1440-7.
Excess exposure of skin to ultraviolet B (UVB) results in the appearance of so-called sunburn cells. Although it has been demonstrated that sunburn cells represent apoptotic keratinocytes, the molecular mechanisms for UVB-induced apoptosis in keratinocytes have not been fully elucidated. The cytokine, TNF-alpha, has been shown to induce apoptosis in a variety of cell types. Since UVB induces keratinocytes to release TNF-alpha, we hypothesized that TNF-alpha is involved in UVB-induced apoptosis in keratinocytes. In order to confirm this hypothesis and to further delineate which type of TNF receptor signaling mediates the apoptosis pathway, we performed both in vivo and in vitro experiments using gene-targeted knockout mice lacking either the TNF p55 receptor or the TNF p75 receptor. In the in vivo study, wild-type and mutant mice were exposed to UVB, and apoptotic keratinocytes were detected by examining DNA fragmentation using in situ nick-end labeling. For the in vitro experiments, keratinocytes derived from the wild-type and mutant mice were irradiated with UVB, and the degree of apoptosis was determined by flow cytometry, nick-end labeling of DNA, and a DNA ladder assay. Both in vivo and in vitro studies demonstrated that the deletion of TNF receptor p55 could suppress UVB-induced apoptosis in keratinocytes. Our observations support the notion that TNF-alpha is involved in UVB-induced keratinocyte apoptosis, and demonstrate that p55 receptor signaling plays a pivotal role in this event.
皮肤过度暴露于紫外线B（UVB）会导致所谓晒伤细胞的出现。尽管已经证明晒伤细胞代表凋亡的角质形成细胞，但UVB诱导角质形成细胞凋亡的分子机制尚未完全阐明。细胞因子肿瘤坏死因子-α（TNF-α）已被证明可在多种细胞类型中诱导凋亡。由于UVB诱导角质形成细胞释放TNF-α，我们推测TNF-α参与了UVB诱导的角质形成细胞凋亡。为了证实这一假设并进一步确定哪种类型的TNF受体信号传导介导凋亡途径，我们使用缺乏TNF p55受体或TNF p75受体的基因靶向敲除小鼠进行了体内和体外实验。在体内研究中，将野生型和突变型小鼠暴露于UVB，并通过使用原位缺口末端标记检测DNA片段化来检测凋亡的角质形成细胞。对于体外实验，用UVB照射源自野生型和突变型小鼠的角质形成细胞，并通过流式细胞术、DNA缺口末端标记和DNA梯状条带分析来确定凋亡程度。体内和体外研究均表明，TNF受体p55的缺失可抑制UVB诱导的角质形成细胞凋亡。我们的观察结果支持TNF-α参与UVB诱导的角质形成细胞凋亡的观点，并证明p55受体信号传导在这一过程中起关键作用。
