The transcriptome landscape of the carcinogenic treatment response in the blind mole rat: Insights into cancer resistance mechanisms [RNA-seq]

Background: Spalax, the blind mole rat, developed an extraordinary cancer resistance during 40 million years of evolution in a subterranean, hypoxic, thus DNA damaging, habitat. In 50 years of Spalax research, no spontaneous cancer development has been observed. The mechanisms underlying this resistance are still not clarified. We investigated the genetic difference between Spalax and mice that might enable the Spalax relative resistance to cancer development. We compared Spalax and mice responses to a treatment with the carcinogen 3-Methylcholantrene, as a model to assess Spalax’ cancer-resistance. Results: We compared RNA-Seq data of untreated Spalax to Spalax with a tumor and identified a high number of differentially expressed genes. We filtered these genes by their expression in tolerant Spalax that resisted the 3MCA, and in mice, and found 25 genes with a consistent expression pattern in the samples susceptible to cancer among species. Contrasting the expressed genes in Spalax with benign granulomas to those in Spalax with malignant fibrosarcomas elucidated significant differences in several pathways, mainly the extracellular matrix and the immune system. We found a central cluster of ECM genes that differ greatly between conditions. Further analysis of these genes revealed potential drug targets and associated microRNAs.We also show that in Spalax has higher levels of gene expression of some DNA repair pathways than other murines, like the majority of Fanconi Anemia pathway. Conclusion: The comparison of the treated with the untreated tissue revealed a regulatory complex that might give an answer how Spalax is able to restrict the tumor growth. By strengthening the extracellular matrix, the possible growth is limited, and the proliferation of cancer cells was prevented. We hypothesize that this regulatory cluster plays a major role in the cancer resistance of Spalax. Furthermore, we identified 25 additional candidate genes that show a distinct expression pattern in untreated or tolerant Spalax compared to animals that developed a growth, either benign or malignant. While further study is necessary, we believe that these genes may be used as markers in cancer detection. 12 Spalax and 6 mice were used. Animals were treated with a single injection of 3MCA as follows: 200 μg/200 μl for mice; 1 mg/500 μl for Spalax. Animals used in this experiment were: six approximately 2-year-old Spalax individuals; six 10-year old or older Spalax individuals; six 3- to 4- month-old mice. Animals were observed once a week until tumors could be palpated, and then two to three times a week.

背景：盲鼹形鼠（Spalax）在地下低氧且由此造成DNA损伤的生境中经历了4000万年的演化，演化出了极强的抗癌能力。在长达50年的盲鼹形鼠研究中，从未观察到其自发发生肿瘤的情况。但其抗癌背后的分子机制仍未阐明。本研究旨在探究盲鼹形鼠与小鼠之间的遗传差异，该差异可能赋予盲鼹形鼠相对较强的抗癌能力。我们以致癌物3-甲基胆蒽（3-Methylcholantrene）处理盲鼹形鼠与小鼠，通过对比二者的响应，以此评估盲鼹形鼠的抗癌抗性。
结果：我们对比了未处理盲鼹形鼠与荷瘤盲鼹形鼠的转录组测序（RNA-Seq）数据，鉴定出大量差异表达基因（differentially expressed genes）。随后，我们依据耐受3-甲基胆蒽的盲鼹形鼠以及小鼠中的基因表达水平对这些基因进行筛选，最终在不同物种的癌症易感样本中发现了25个表达模式一致的基因。对比患有良性肉芽肿的盲鼹形鼠与患有恶性纤维肉瘤的盲鼹形鼠的表达基因，我们阐明了多条通路的显著差异，主要集中在细胞外基质（extracellular matrix, ECM）与免疫系统通路。我们发现了一组核心的细胞外基质基因，其在两种状态下表达差异显著。对这些基因的进一步分析揭示了潜在的药物靶点以及相关的微小RNA（microRNAs）。此外，我们发现盲鼹形鼠的部分DNA修复通路（如大多数范可尼贫血（Fanconi Anemia）通路）的基因表达水平高于其他鼠类。
结论：对比处理组与未处理组的组织，我们发现了一个调控复合体，该复合体或许可以解释盲鼹形鼠如何抑制肿瘤生长。通过强化细胞外基质，其可以限制肿瘤潜在的增殖，并阻止癌细胞的扩散。我们推测该调控簇在盲鼹形鼠的抗癌能力中发挥核心作用。此外，我们还鉴定出25个额外的候选基因，与发生了良性或恶性增生的动物相比，这些基因在未处理或耐受的盲鼹形鼠中呈现出独特的表达模式。尽管还需要进一步的研究，但我们认为这些基因可作为癌症检测的标志物。
本实验共使用12只盲鼹形鼠与6只小鼠：按照如下方式单次注射3-甲基胆蒽：小鼠剂量为200 μg/200 μl，盲鼹形鼠剂量为1 mg/500 μl。实验所用动物包括6只约2岁龄的盲鼹形鼠、6只10岁及以上的盲鼹形鼠，以及6只3~4月龄的小鼠。实验期间每周观察一次动物，直至可触诊到肿瘤，随后改为每周观察2~3次。