Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Federal Research Center "Kazan Scientific Center of RAS", 2/31 Lobachevsky Street, box 30, Kazan 420111, Russia; Institute of Neuroscience, Kazan State Medial University, 49 Butlerova Street, Kazan, 420012, Russia.
Department of Normal Physiology, Kazan State Medial University, 49 Butlerova Street, Kazan 420012, Russia.
Life Sci. 2021 May 15;273:119300. doi: 10.1016/j.lfs.2021.119300. Epub 2021 Mar 2.
Plasma hyperlipidemia is a protective factor in amyotrophic lateral sclerosis (ALS) while cholesterol-lowering drugs aggravate the pathology. We hypothesize that this phenomenon can be linked with membrane lipid alterations in the neuromuscular junctions (NMJs) occurring before motor neuron loss.
Neurotransmitter release in parallel with lipid membrane properties in diaphragm NMJs of SOD1G93A (mSOD) mice at nine weeks of age (pre-onset stage) were assessed.
Despite on slight changes in spontaneous and evoked quantum release of acetylcholine, extracellular levels of choline at resting conditions, an indicator of non-quantum release, were significantly increased in mSOD mice. The use of lipid-sensitive fluorescent probes points to lipid raft disruption in the NMJs of mSOD mice. However, content of cholesterol, a key raft component was unchanged implying another pathway responsible for the loss of raft integrity. In the mSOD mice we found marked increase in levels of raft-destabilizing lipid ceramide. This was accompanied by enhanced ability to uptake of exogenous ceramide in NMJs. Acute and chronic administration of 25-hydroxycholesterol, whose levels increase due to hypercholesterolemia, recovered early alterations in membrane properties. Furthermore, chronic treatment with 25-hydroxycholesterol prevented increase in ceramide and extracellular choline levels as well as suppressed lipid peroxidation of NMJ membranes and fragmentation of end plates.
Thus, lipid raft disruption likely due to ceramide accumulation could be early event in ALS which may trigger neuromuscular abnormalities. Cholesterol derivative 25-hydroxycholesterol may serve as a molecule restoring the membrane and functional properties of NMJs at the early stage.
血浆高脂血症是肌萎缩侧索硬化症 (ALS) 的保护因素，而降胆固醇药物则会加重病情。我们假设这种现象可能与运动神经元丧失前发生在神经肌肉接头 (NMJ) 中的膜脂改变有关。
评估了 9 周龄（发病前阶段）SOD1G93A (mSOD) 小鼠膈肌 NMJ 中的神经递质释放与脂质膜特性的平行变化。
尽管自发性和诱发性乙酰胆碱量子释放略有变化，但在 mSOD 小鼠中，静息状态下的胆碱细胞外水平（非量子释放的指标）显著增加。脂质敏感荧光探针的使用表明 mSOD 小鼠 NMJ 中的脂质筏破坏。然而，胆固醇含量（关键筏成分）不变，表明存在另一条导致筏完整性丧失的途径。在 mSOD 小鼠中，我们发现脂质筏不稳定的神经酰胺水平明显增加。这伴随着 NMJ 中摄取外源性神经酰胺能力的增强。由于高胆固醇血症，25-羟胆固醇的急性和慢性给药恢复了早期的膜特性改变。此外，25-羟胆固醇的慢性治疗可防止神经酰胺和细胞外胆碱水平的增加，并抑制 NMJ 膜的脂质过氧化和终板的碎片化。
因此，由于神经酰胺积累导致的脂质筏破坏可能是 ALS 的早期事件，这可能引发神经肌肉异常。胆固醇衍生物 25-羟胆固醇可能作为一种分子，在早期恢复 NMJ 的膜和功能特性。
