Department of Internal Medicine, University of Texas Medical Branch, Galveston, TX 77555.
Department of Neurology, Mitchell Center for Neurodegenerative Diseases, University of Texas Medical Branch, Galveston, TX 77555.
Proc Natl Acad Sci U S A. 2024 Sep 24;121(39):e2406308121. doi: 10.1073/pnas.2406308121. Epub 2024 Sep 19.
Huntington's disease (HD) and spinocerebellar ataxia type 3 (SCA3) are the two most prevalent polyglutamine (polyQ) neurodegenerative diseases, caused by CAG (encoding glutamine) repeat expansion in the coding region of the huntingtin (HTT) and ataxin-3 (ATXN3) proteins, respectively. We have earlier reported that the activity, but not the protein level, of an essential DNA repair enzyme, polynucleotide kinase 3'-phosphatase (PNKP), is severely abrogated in both HD and SCA3 resulting in accumulation of double-strand breaks in patients' brain genome. While investigating the mechanistic basis for the loss of PNKP activity and accumulation of DNA double-strand breaks leading to neuronal death, we observed that PNKP interacts with the nuclear isoform of 6-phosphofructo-2-kinase fructose-2,6-bisphosphatase 3 (PFKFB3). Depletion of PFKFB3 markedly abrogates PNKP activity without changing its protein level. Notably, the levels of both PFKFB3 and its product fructose-2,6 bisphosphate (F2,6BP), an allosteric modulator of glycolysis, are significantly lower in the nuclear extracts of postmortem brain tissues of HD and SCA3 patients. Supplementation of F2,6BP restored PNKP activity in the nuclear extracts of patients' brain. Moreover, intracellular delivery of F2,6BP restored both the activity of PNKP and the integrity of transcribed genome in neuronal cells derived from the striatum of the HD mouse. Importantly, supplementing F2,6BP rescued the HD phenotype in Drosophila, suggesting F2,6BP to serve in vivo as a cofactor for the proper functionality of PNKP and thereby, of brain health. Our results thus provide a compelling rationale for exploring the therapeutic use of F2,6BP and structurally related compounds for treating polyQ diseases.
亨廷顿病（HD）和脊髓小脑性共济失调 3 型（SCA3）是两种最常见的多聚谷氨酰胺（polyQ）神经退行性疾病，分别由亨廷顿（HTT）和ataxin-3（ATXN3）蛋白编码区的 CAG（编码谷氨酰胺）重复扩展引起。我们之前报道称，一种必需的 DNA 修复酶，多核苷酸激酶 3′-磷酸酶（PNKP）的活性而非其蛋白水平在 HD 和 SCA3 中均严重降低，导致患者大脑基因组中双链断裂的积累。在研究导致神经元死亡的 PNKP 活性丧失和双链断裂积累的机制基础时，我们观察到 PNKP 与 6-磷酸果糖-2-激酶果糖-2,6-双磷酸酶 3 的核同工型（PFKFB3）相互作用。PFKFB3 的耗竭可显著降低 PNKP 的活性而不改变其蛋白水平。值得注意的是，在 HD 和 SCA3 患者死后脑组织的核提取物中，PFKFB3 及其产物果糖-2,6-双磷酸（F2,6BP）的水平均显著降低，F2,6BP 是糖酵解的别构调节剂。F2,6BP 的补充恢复了患者大脑核提取物中的 PNKP 活性。此外，F2,6BP 的细胞内递送恢复了来自 HD 小鼠纹状体的神经元细胞中 PNKP 的活性和转录基因组的完整性。重要的是，F2,6BP 补充挽救了果蝇中的 HD 表型，表明 F2,6BP 在体内作为 PNKP 及其脑健康适当功能的辅助因子。我们的结果因此为探索 F2,6BP 和结构相关化合物在治疗 polyQ 疾病中的治疗用途提供了强有力的理由。
