a Centre for Research and Development, Uppsala University/Region Gävleborg, Gävle, Sweden.
b Department of Immunology, Genetics and Pathology, Experimental and Clinical Oncology, Uppsala University, Uppsala, Sweden.
Radiat Res. 2019 Jan;191(1):93-106. doi: 10.1667/RR15078.1. Epub 2018 Nov 8.
To date, the response activated in melanocytes by repeated genotoxic insults from radiotherapy has not been explored. We hypothesized that the molecular pathways involved in the response of melanocytes to ionizing radiation and ultraviolet radiation (UVR) are similar. Skin punch biopsies, not sun-exposed, were collected from prostate cancer patients before, as well as at 1 and 6.5 weeks after daily doses of 0.05-1.1 Gy. Interfollicular melanocytes were identified by ΔNp63- and eosin-periodic acid Schiff staining. Immunohistochemistry and immunofluorescence were performed to detect molecular markers of the melanocyte lineage. Melanocytes were negative for ΔNp63, and the number remained unchanged over the treatment period. At radiation doses as low as 0.05 Gy, melanocytes express higher protein levels of microphthalmia-associated transcription factor (MITF) and Bcl-2. Subsets of MITF- and Bcl-2-negative melanocytes were identified among interfollicular melanocytes in unexposed skin; the cell number in both subsets was reduced after irradiation in a way that indicates low-dose hyperradiosensitivity. A corresponding increase in MITF- and Bcl-2-positive cells was observed. PAX3 and SOX10 co-localized to some extent with MITF in unexposed skin, more so with radiation exposure. Low doses of ionizing radiation also intensified c-KIT and DCT staining. Nuclear p53 and p21 were undetectable in melanocytes. Apoptosis and proliferation could not be observed. In conclusion, undifferentiated interfollicular melanocytes were identified, and responded with differentiation in a hypersensitive manner at 0.05 Gy doses. Radioresistance regarding cell death was maintained up to fractionated doses of 1.1 Gy, applied for 7 weeks. The results suggest that the initial steps of melanin synthesis are common to ionizing radiation and UVR, and underline the importance of keratinocyte-melanocyte interaction behind hyperpigmentation and depigmentation to radiotherapy.
迄今为止，尚未探讨放疗引起的反复遗传毒性损伤在黑素细胞中引发的反应。我们假设，黑素细胞对电离辐射和紫外线辐射（UVR）的反应所涉及的分子途径是相似的。采集前列腺癌患者的非暴露于阳光的皮肤穿刺活检标本，在每天接受 0.05-1.1 Gy 剂量照射之前、照射 1 周和 6.5 周后进行采集。通过 ΔNp63 和曙红过碘酸希夫（periodic acid Schiff，PAS）染色鉴定毛囊间黑素细胞。进行免疫组织化学和免疫荧光检测以检测黑素细胞谱系的分子标志物。黑素细胞 ΔNp63 染色阴性，且在治疗期间数量保持不变。即使在低至 0.05 Gy 的辐射剂量下，黑素细胞也会表达更高水平的小眼畸形相关转录因子（microphthalmia-associated transcription factor，MITF）和 Bcl-2。在未暴露于阳光的皮肤中，毛囊间黑素细胞中鉴定出 MITF 和 Bcl-2 阴性的黑素细胞亚群；在照射后，这两个亚群的细胞数量减少，表明存在低剂量超辐射敏感性。观察到 MITF 和 Bcl-2 阳性细胞相应增加。在未暴露于阳光的皮肤中，PAX3 和 SOX10 与 MITF 部分共定位，暴露于辐射后共定位更多。低剂量电离辐射还增强了 c-KIT 和 DCT 染色。p53 和 p21 的核蛋白在黑素细胞中无法检测到。未观察到细胞凋亡和增殖。总之，鉴定出未分化的毛囊间黑素细胞，在 0.05 Gy 剂量下以超敏感方式对分化作出反应。在 7 周内应用 1.1 Gy 的分割剂量时，保持对细胞死亡的辐射抗性。结果表明，黑色素合成的初始步骤与电离辐射和 UVR 共同发生，并且强调了角质形成细胞-黑素细胞相互作用在放射治疗后的色素沉着和退色中的重要性。
