Department of Neurology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Veterans Affairs Medical Center, Baltimore, MD 21201, USA.
Brain. 2019 Dec 1;142(12):3737-3752. doi: 10.1093/brain/awz324.
In diabetic neuropathy, there is activation of axonal and sensory neuronal degeneration pathways leading to distal axonopathy. The nicotinamide-adenine dinucleotide (NAD+)-dependent deacetylase enzyme, Sirtuin 1 (SIRT1), can prevent activation of these pathways and promote axonal regeneration. In this study, we tested whether increased expression of SIRT1 protein in sensory neurons prevents and reverses experimental diabetic neuropathy induced by a high fat diet (HFD). We generated a transgenic mouse that is inducible and overexpresses SIRT1 protein in neurons (nSIRT1OE Tg). Higher levels of SIRT1 protein were localized to cortical and hippocampal neuronal nuclei in the brain and in nuclei and cytoplasm of small to medium sized neurons in dorsal root ganglia. Wild-type and nSIRT1OE Tg mice were fed with either control diet (6.2% fat) or a HFD (36% fat) for 2 months. HFD-fed wild-type mice developed neuropathy as determined by abnormal motor and sensory nerve conduction velocity, mechanical allodynia, and loss of intraepidermal nerve fibres. In contrast, nSIRT1OE prevented a HFD-induced neuropathy despite the animals remaining hyperglycaemic. To test if nSIRT1OE would reverse HFD-induced neuropathy, nSIRT1OE was activated after mice developed peripheral neuropathy on a HFD. Two months after nSIRT1OE, we observed reversal of neuropathy and an increase in intraepidermal nerve fibre. Cultured adult dorsal root ganglion neurons from nSIRT1OE mice, maintained at high (30 mM) total glucose, showed higher basal and maximal respiratory capacity when compared to adult dorsal root ganglion neurons from wild-type mice. In dorsal root ganglion protein extracts from nSIRT1OE mice, the NAD+-consuming enzyme PARP1 was deactivated and the major deacetylated protein was identified to be an E3 protein ligase, NEDD4-1, a protein required for axonal growth, regeneration and proteostasis in neurodegenerative diseases. Our results indicate that nSIRT1OE prevents and reverses neuropathy. Increased mitochondrial respiratory capacity and NEDD4 activation was associated with increased axonal growth driven by neuronal overexpression of SIRT1. Therapies that regulate NAD+ and thereby target sirtuins may be beneficial in human diabetic sensory polyneuropathy.
在糖尿病性神经病中，轴突和感觉神经元退化途径被激活，导致远端轴突病。烟酰胺腺嘌呤二核苷酸（NAD+）依赖性脱乙酰酶酶，Sirtuin 1（SIRT1），可以防止这些途径的激活并促进轴突再生。在这项研究中，我们测试了感觉神经元中 SIRT1 蛋白的表达增加是否可以预防和逆转高脂肪饮食（HFD）诱导的实验性糖尿病性神经病。我们生成了一种可诱导的转基因小鼠，该小鼠可在神经元中过表达 SIRT1 蛋白（nSIRT1OE Tg）。更高水平的 SIRT1 蛋白定位于大脑皮质和海马神经元核以及背根神经节中小到中型神经元的核和细胞质中。野生型和 nSIRT1OE Tg 小鼠分别用对照饮食（6.2%脂肪）或高脂肪饮食（36%脂肪）喂养 2 个月。高脂肪饮食喂养的野生型小鼠出现神经病，表现为运动和感觉神经传导速度异常、机械性痛觉过敏和表皮内神经纤维丧失。相比之下，nSIRT1OE 尽管动物仍保持高血糖，但可预防高脂肪饮食引起的神经病。为了测试 nSIRT1OE 是否会逆转高脂肪饮食诱导的神经病，在动物发生周围神经病后，在高脂肪饮食上激活 nSIRT1OE。在 nSIRT1OE 两个月后，我们观察到神经病的逆转和表皮内神经纤维的增加。与野生型小鼠的成年背根神经节神经元相比，来自 nSIRT1OE 小鼠的培养成年背根神经节神经元在高（30 mM）总葡萄糖下显示出更高的基础和最大呼吸能力。在 nSIRT1OE 小鼠的背根神经节蛋白提取物中，NAD+-消耗酶 PARP1 被失活，主要的脱乙酰化蛋白被鉴定为 E3 蛋白连接酶 NEDD4-1，这是一种在神经退行性疾病中促进轴突生长、再生和蛋白质平衡所必需的蛋白。我们的结果表明，nSIRT1OE 可预防和逆转神经病。增加的线粒体呼吸能力和 NEDD4 激活与神经元过表达 SIRT1 驱动的轴突生长有关。调节 NAD+并因此靶向 Sirtuins 的疗法可能对人类糖尿病性感觉性多发性神经病有益。
