Biochemistry of Melanins and Photoprotection of the Skin

黑色素的生物化学和皮肤的光保护

• 批准号: 8349158
• 负责人: VINCENT J HEARING
• 金额: $ 41.17万
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8349158
• 关键词: Acute; Affect; Apoptosis; Appearance; Asians; Biochemistry; Cell Survival; Cells; Collaborations; Color; Cutaneous Melanoma; DNA; DNA Damage; DNA Microarray Chip; DNA Repair; DNA lesion; DNA photoproducts; Data; Diffuse; Dose; Epidermis; Ethnic Origin; Excision; Fontana-Masson stain; Hispanics; Human; Immunohistochemistry; In Situ; In Vitro; Incidence; Industry; Light; Link; Malignant Neoplasms; Measurement; Measures; Melanins; Nature; Photobiology; Pigmentation physiologic function; Pigments; Play; Population; Process; Production; Property; Proteins; Pyrimidine Dimers; Reactive Oxygen Species; Regulation; Research; Resistance; Risk; Role; Skin; Skin Cancer; Skin Pigmentation; Skin tanning; Solar Energy; Source; Specimen; Squamous cell carcinoma; Stratum Basale; Stress; Sum; System; TYRP1 gene; Testing; UV Radiation Exposure; UV carcinogenesis; UV induced; UV induced DNA damage; UV sensitive; UVA induced; Ultraviolet B Radiation; Work; base; cell injury; chemical property; density; eumelanin; falls; follow-up; gene function; in vivo; insight; melanocyte; melanoma; oxidation; oxidative damage; pheomelanin; photoprotection; racial and ethnic; racial/ethnic difference; repaired; response; ultraviolet damage; ultraviolet irradiation

Constitutive skin pigmentation dramatically affects the incidence of skin cancers, and in the US, rates of basal and squamous cell carcinomas and melanomas are dramatically higher in Whites than in Blacks. Cyclobutane pyrimidine dimers (CPD) and (6-4)-photoproducts (64PP), the two major types of DNA lesions resulting from UVB exposure, are potentially carcinogenic as is the oxidative damage resulting from UVA exposure. Melanin reduces DNA photoproducts in vivo and in vitro and can scavenge reactive oxygen species. Thus, melanin content of melanocytes plays a significant role in minimizing UV damage and in enhancing cell survival. However, much remains unknown about relationships between DNA damage/repair and different types, quantities, forms and distribution of melanin in skin of different racial/ethnic origin and different phototypes. Our collaborations with the FDA have been highly productive and have provided some insights into these basic questions. Several key observations have evolved from these studies: (1) DNA damage is greatest immediately following UV exposure in all subjects and is gradually repaired thereafter; (2) rates and efficiencies of removal of DNA lesions differs dramatically between subjects in all groups; (3) while DNA damage is most severe in light, UV-sensitive skin, even the darkest, UV-resistant skin incurs significant DNA damage after UV exposure at levels less than 1 MED; and (4) there is an inverse correlation between skin pigmentation and DNA damage. Thus, even very low UV exposures cause significant damage to DNA in all types of skin, underscoring the contention that there is no such thing as totally UV-resistant human skin. Our studies, combined with others on this topic, suggest that at least 5 factors contribute to UV-induced carcinogenesis and the various risks seen in human populations: (1) the amount of UV-induced DNA damage, (2) the identity and function of gene(s) damaged, (3) the nature of cells damaged, (4) the efficiency of post-exposure removal/repair of DNA damage, and (5) the removal of irreversibly UV-damaged cells by apoptosis or other mechanisms. The sum of those processes may explain the dramatically higher incidence of skin cancers in light-skinned subjects compared to dark-skinned subjects. We have completed our studies on the effects of acute or repetitive UV exposure on human skin of various phototypes. Such work has gained urgency since repeated UV exposure by sunlamps has been linked with squamous cell carcinoma and cutaneous melanoma. Our results on the effects of repetitive UV exposure further emphasize that the distribution of melanin is important to the appearance of visible color and to photoprotection of the skin; however DNA damage is not eliminated during UV-induced pigmentation. Important issues that we are now studying include defining: (1) whether production of eumelanin versus pheomelanin has any consequence on photoprotection, (2) whether facultative (induced) pigmentation of the skin provides added protection against UV damage, (3) the role of DNA repair in minimizing long-term damage to the skin and subsequent photocarcinogenesis, and (4) the identity and regulation of UV-induced factors that modulate responses to that environmental stress. Given the importance of skin pigmentation to reduce the risk of photocarcinogenesis, these studies are critical to understanding parameters involved in photocarcinogenesis, as well as to developing effective strategies to minimize such risk. We have now measured parameters that had been characterized in our single UV dose study to determine levels of DNA damage and melanogenic functions in the skin during tanning elicited by repetitive UV exposure. Increased expression of MITF occurs most quickly after repetitive UV exposure (within 1-2 d), increased expression of melanosomal proteins such as TYR, TYRP1, Pmel17 and DCT is slower (1 wk), while increases in melanin synthesis take longer (3 wk) and increases in melanocyte density take even longer (4-5 wk). The distribution of melanin in the skin is important to visible pigmentation and to its photoprotective capacity. It is clear that relatively small changes in melanin content and/or distribution can make relatively large changes in visible pigmentation. Those affect not only constitutive pigmentation that defines racial/ethnic differences, but also responses to UV exposure. Long-term follow-up studies have revealed a new type of UV-induced pigmentation, termed LLP (long-lasting pigmentation), which is defined as skin pigmentation that persists more than 9 months after the end of UV exposure, in some cases up to 3 or 4 years later. We are currently studying the mechanisms involved in LLP and whether that is associated (positively or negatively) with increased risk for skin photocarcinogenesis. The data from our studies suggest that the induction of DNA damage as a by-product of tanning is a significant source of delayed risks, including skin cancer. The induction/removal of DNA photoproducts in fair skin (phototypes 2 or 3) were measured for repeated UV exposures 1 day after the final exposure. Following repeated UV exposure, redistribution of melanin to upper layers of the skin is an immediate response followed by de novo melanin synthesis. Based on diffuse reflectance measurements and melanin content assessed by Fontana-Masson staining, repeated UV doses produce a moderate to dark brown tan which reaches a plateau after several exposures, indicating that the pigment system reaches saturation. Pigmentation remains elevated for >4 wk after the final exposure showing that once a tan develops, continued frequent UV exposure is not necessary to maintain it. The 2-3 fold increase in melanin content of each layer of the epidermis elicited by repetitive UV exposure is consistent with the increased density of melanocytes in the basal layer of the skin. We have also examined UV-irradiated specimens obtained 3 days after a 2 week course of repeated doses of SSR, UVA or UVB. It has been proposed that melanin protects against UVB more efficiently than against UVA, and that eumelanin absorbs UV more efficiently than pheomelanin, but those assumptions need to be tested. According to our UV reflectance analysis, different types of UV affect melanin content in human skin in different manners. We analyzed the relationship between CPD damage and melanin content using immunohistochemistry and Fontana Masson staining. Those results are consistent with our earlier studies and confirm that different subjects with apparently identical skin phototype have distinct responses to repetitive UVA and/or UVB radiation. UVB stimulates the melanogenic system, increasing factors involved in melanin production and eventually in melanin content, and provides a small measure of added photoprotection. In contrast, repetitive UVA exposure, while leading to comparable visible skin tanning, has no detectable effect on the melanogenic system and elicits no increase in melanin content, thus providing absolutely no photoprotective benefit. We have completed our DNA microarray analyses of human skin exposed to repetitive UVA and/or UVB which provides important clues as to the in situ responses of human skin to different types of UV, and also adds to our understanding of the mechanisms of skin tanning in response to UVA and/or UVB. We hypothesize that the visible tan elicited by UVA results from oxidation of existing melanin (or its precursors) and that UVA-induced tans (such as those promoted by the tanning industry) give tanners a false sense of protection against subsequent UV exposure, which may be worsening skin cancer incidence.

构成性皮肤色素沉着极大地影响了皮肤癌的发生率，在美国，白人的基础和鳞状细胞癌的发生率显着高于黑人。环丁烷嘧啶二聚体（CPD）和（6-4） - 吞噬作用（64pp），这是UVB暴露引起的两种主要类型的DNA病变，可能是致癌性的，因为UVA暴露造成的氧化损害是氧化损伤。黑色素在体内和体外降低了DNA光药物，可以清除活性氧。因此，黑素细胞的黑色素含量在最大程度地减少紫外线损伤和增强细胞存活方面起着重要作用。然而，关于DNA损伤/修复与不同种族/种族血统和不同光型皮肤中黑色素不同类型，数量，形式和分布之间的关系之间的关系，尚不清楚。 我们与FDA的合作效率很高，并为这些基本问题提供了一些见解。从这些研究中得出了几种关键观察结果：（1）所有受试者紫外线暴露后立即最大的DNA损伤，此后逐渐修复； （2）所有组受试者之间的DNA病变去除率和效率在所有组中都有很大不同； （3）虽然在光线，对紫外线敏感的皮肤中，DNA损伤最为严重，甚至最黑暗，耐紫外线的皮肤在紫外线暴露于水平小于1 MED的情况下会造成明显的DNA损伤； （4）皮肤色素沉着与DNA损伤之间存在逆相关性。因此，即使是非常低的紫外线暴露在所有类型的皮肤中都会对DNA造成重大损害，强调了没有完全抗紫外线的人皮肤的观点。 Our studies, combined with others on this topic, suggest that at least 5 factors contribute to UV-induced carcinogenesis and the various risks seen in human populations: (1) the amount of UV-induced DNA damage, (2) the identity and function of gene(s) damaged, (3) the nature of cells damaged, (4) the efficiency of post-exposure removal/repair of DNA damage, and (5) the removal of irreversibly凋亡或其他机制通过紫外线损害细胞。与深色皮肤受试者相比，这些过程的总和可以解释皮肤癌中皮肤癌的发生率明显更高。 我们已经完成了有关急性或重复紫外线暴露对各种光型人类皮肤的影响的研究。由于Sunlamps反复暴露于鳞状细胞癌和皮肤黑色素瘤，因此这种工作已经急切地升高。我们对重复紫外线暴露的影响的结果进一步强调，黑色素的分布对于可见颜色的出现和皮肤的光保护很重要。但是，在紫外线诱导的色素沉着过程中，DNA损伤并未消除。我们现在正在研究的重要问题包括：（1）依美酸酯与苯烷蛋白的产生是否对光保护有任何影响，（2）（2）皮肤的辅导性（诱导）色素是否提供了额外的保护，可抵抗UV损害，（3）DNA修复在对皮肤的长期损害中的长期损害和后期的识别率和（4）识别率和（4）识别率和（4））的作用（4）对这种环境压力的反应。鉴于皮肤色素沉着在降低光钙局发生的风险方面的重要性，这些研究对于理解参与光的参数至关重要，以及制定有效的策略以最大程度地降低这种风险。 现在，我们已经测量了在单个UV剂量研究中表征的参数，以确定通过重复的紫外线暴露引起的晒黑过程中皮肤中DNA损伤的水平和黑色素的功能。 MITF的表达增加在重复紫外线暴露后最快发生（在1-2 d之内），Tyr，TyrP1，PMEL17和DCT等黑色素体蛋白的表达增加的表达较慢（1周），而黑色素合成的增加则增加了（3 WK）（3 WK），而黑色素密度则增加了更长的（4-5 Wk）。黑色素在皮肤中的分布对于可见色素沉着及其光保护能力很重要。显然，黑色素含量和/或分布的变化相对较小，可以使可见色素沉着的变化相对较大。这些影响不仅影响定义种族/种族差异的构成色素沉着，还影响对紫外线暴露的反应。长期的随访研究表明，一种新型的紫外线诱导的色素沉着，称为LLP（持久色素沉着），在紫外线暴露结束后的9个月以上，在某些情况下，最多3或4年后，它被定义为皮肤色素沉着。我们目前正在研究LLP中涉及的机制，以及这是否与皮肤光碳促发生的风险增加有关（正面还是负面）。 我们研究的数据表明，将DNA损伤作为晒黑的副产品的诱导是包括皮肤癌在内的延迟风险的重要来源。在最终暴露后1天，测量了在白皙皮肤（光型2或3）中的DNA光产物的诱导/去除（光型2或3）。反复暴露紫外线后，黑色素重新分布到皮肤的上层是立即反应，然后是从头黑色素合成。基于通过Fontana-Masson染色评估的弥漫性反射率测量和黑色素含量，重复的紫外线剂量会产生中等至深棕色的棕褐色，该棕褐色棕褐色在几次暴露后达到平稳，表明色素系统达到饱和度。在最终暴露后，色素沉着保持> 4周的升高，表明一旦棕褐色发展，维持棕褐色的频繁持续暴露是不需要的。通过重复性紫外线暴露引起的表皮每一层的黑色素含量的2-3倍增加与皮肤基础层中黑色素细胞的密度增加一致。 我们还检查了2周重复剂量的SSR，UVA或UVB后3天获得的UV-IRRADAID样品。有人提出，黑色素比违反UVA更有效地预防UVB，而eumelanin比苯烷蛋白更有效地吸收了紫外线，但是这些假设需要测试。根据我们的UV反射分析，不同类型的紫外线以不同的方式影响人类皮肤中的黑色素含量。我们使用免疫组织化学和Fontana Masson染色分析了CPD损伤与黑色素含量之间的关系。这些结果与我们的早期研究一致，并确认皮肤光谱型显然相同的受试者对重复的UVA和/或UVB辐射具有不同的反应。 UVB刺激黑色素产生的黑色素生成系统，最终与黑色素含量涉及的因素越来越多，并提供了一小部分添加的光保护。相反，重复的UVA暴露虽然导致可比的可见皮肤晒黑，但对黑色素发电系统没有可检测的影响，也没有引起黑色素含量的增加，因此绝对没有光保护益处。我们已经完成了暴露于重复性UVA和/或UVB的人体皮肤的DNA微阵列分析，该分析提供了有关人皮肤对不同类型紫外线的原位反应的重要线索，还增加了我们对响应于UVA和/或UVB的皮肤晒黑机制的理解。我们假设UVA引起的可见棕褐色是由于现有黑色素（或其前体）氧化而引起的，并且UVA诱导的TAN（例如由晒黑行业促进的棕褐色）使晒黑剂具有虚假的保护感，以防止随后的UV暴露，这可能会使皮肤癌症癌症发生率更高。