2. 神經系統疾病
▼ 致病機理：神經細胞中由于遺傳缺陷導致的疾病
▼ 代表工作：同時另一項突破性的工作則使用一種SunTag（dCas9-10xGCN4）系統融合多個拷貝的轉錄激活蛋白（p65-HSF1），構建了一種Cre依賴性的SunTag-p65-HSF1（SPH）轉基因小鼠模型。使用AAV8將Cre和sgRNAs遞送到SPH轉基因小鼠中，通過激活內源性神經源性轉錄因子的表達，在小鼠體內成功地實現了星形膠質細胞直接轉化為功能性的神經元[17]。這一研究表明，在不需要使用外源重編程因子或轉錄因子的前提下，通過轉錄調控的CRISPR系統可以實現特定細胞的重編程或不同細胞類型之間的轉分化，為體外細胞基因治療遺傳疾病提供了新的策略。
圖5. Cre誘導的dCas9小鼠[21]
3. 單倍體劑量不足引起的疾病
▼ 致病機理：單倍劑量不足(haploinsufficiency )指一個等位基因突變后，另一個等位基因能正常表達，但這只有正常水平50%的蛋白質不足以維持細胞正常的生理功能。
▼ 代表工作：近日，Science在線發表了一篇使用CRISPRa系統在小鼠中成功修復一種因單倍劑量不足引起的肥胖。研究人員通過AAV在SIM1基因或MC4R基因部分功能喪失的小鼠腦部遞送dCas9-vp64和sgRNA的方式成功激活了SIM1或MC4R蛋白的表達，成功抑制了肥胖的表型[18]。這一策略給罹患單倍體劑量不足引起的疾病患者帶來轉機。
圖6. 通過CRISPRa治療單倍體劑量不足相關疾病[18]
4. 異常甲基化引起的疾病
▼ 致病機理：基因中CpG島中的5' C經常突變引起高甲基化、羥甲基化等修飾，研究表明這些異常修飾會影響基因的表達調控，最終引起疾病[19]。
▼ 代表工作：脆性X綜合征（Fragile X syndrome, FXS）就是一種由FMR1基因5' UTR 區中CGG三核甘酸重復序列擴增突變并高甲基化，使FMR基因沉默而導致的疾病。最近的一項研究通過利用dCas9融合Tet甲基胞嘧啶雙加氧酶1（Tet methylcytosine dioxygenase 1, Tet1）轉染FXS iPSCs 細胞系，成功靶向誘導FMR基因5' UTR CpG島去甲基化，為這些因異常甲基化引起的疾病的治療奠定了基礎[20]。
圖7. 脆性X綜合征相關疾病的表觀遺傳治療[20]
怎么樣，這次的公眾號是不是讓大家大開眼界呢？相信通過這四期的公眾號，大家已經對基因編輯在疾病治療中的研究應用有了較為系統的了解，不過“路漫漫其修遠兮”，從實驗室走到臨床還有較為漫長的距離要走。但是大量的實驗已經給我們看到了未來疾病治療的新曙光，相信終有一天，基因編輯治療的大時代終會到來。
參考文獻：（向下滑動查看）
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