Mao X R, Kaufman D M, Crowder C M
Department of Anesthesiology, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO 63110, USA.
Medical Scientist Training Program, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, MO 63110, USA.
Cell Death Dis. 2016 Feb 25;7(2):e2113. doi: 10.1038/cddis.2016.5.
Gain-of-function mutations in the mouse nicotinamide mononucleotide adenylyltransferase type 1 (Nmnat1) produce two remarkable phenotypes: protection against traumatic axonal degeneration and reduced hypoxic brain injury. Despite intensive efforts, the mechanism of Nmnat1 cytoprotection remains elusive. To develop a new model to define this mechanism, we heterologously expressed a mouse Nmnat1 non-nuclear-localized gain-of-function mutant gene (m-nonN-Nmnat1) in the nematode Caenorhabditis elegans and show that it provides protection from both hypoxia-induced animal death and taxol-induced axonal pathology. Additionally, we find that m-nonN-Nmnat1 significantly lengthens C. elegans lifespan. Using the hypoxia-protective phenotype in C. elegans, we performed a candidate screen for genetic suppressors of m-nonN-Nmnat1 cytoprotection. Loss of function in two genes, haf-1 and dve-1, encoding mitochondrial unfolded protein response (mitoUPR) factors were identified as suppressors. M-nonN-Nmnat1 induced a transcriptional reporter of the mitoUPR gene hsp-6 and provided protection from the mitochondrial proteostasis toxin ethidium bromide. M-nonN-Nmnat1 was also protective against axonal degeneration in C. elegans induced by the chemotherapy drug taxol. Taxol markedly reduced basal expression of a mitoUPR reporter; the expression was restored by m-nonN-Nmnat1. Taken together, these data implicate the mitoUPR as a mechanism whereby Nmnat1 protects from hypoxic and axonal injury.
小鼠烟酰胺单核苷酸腺苷酸转移酶1型（Nmnat1）的功能获得性突变产生了两种显著的表型：预防创伤性轴突退变和减轻缺氧性脑损伤。尽管付出了巨大努力，Nmnat1细胞保护作用的机制仍然不清楚。为了建立一个新模型来确定这一机制，我们在秀丽隐杆线虫中异源表达了一个小鼠Nmnat1非核定位的功能获得性突变基因（m-nonN-Nmnat1），结果表明它能保护线虫免受缺氧诱导的动物死亡和紫杉醇诱导的轴突病变。此外，我们发现m-nonN-Nmnat1能显著延长秀丽隐杆线虫的寿命。利用秀丽隐杆线虫的缺氧保护表型，我们对m-nonN-Nmnat1细胞保护作用的遗传抑制因子进行了候选筛选。编码线粒体未折叠蛋白反应（mitoUPR）因子的两个基因haf-1和dve-1的功能缺失被鉴定为抑制因子。M-nonN-Nmnat1诱导了mitoUPR基因hsp-6的转录报告基因，并保护线虫免受线粒体蛋白稳态毒素溴化乙锭的损伤。M-nonN-Nmnat1还能预防化疗药物紫杉醇诱导的秀丽隐杆线虫轴突退变。紫杉醇显著降低了mitoUPR报告基因的基础表达；m-nonN-Nmnat1可恢复该表达。综上所述，这些数据表明mitoUPR是Nmnat1预防缺氧和轴突损伤的一种机制。
