University of Glasgow, Institute of Infection, Immunity and Inflammation Glasgow G12 8TA, United Kingdom.
University of Glasgow, School of Veterinary Biosciences, Glasgow G61 1QH, United Kingdom, and.
J Neurosci. 2019 Jan 2;39(1):63-77. doi: 10.1523/JNEUROSCI.2095-18.2018. Epub 2018 Nov 16.
Sulfatides and gangliosides are raft-associated glycolipids essential for maintaining myelinated nerve integrity. Mice deficient in sulfatide (cerebroside sulfotransferase knock-out, ) or complex gangliosides (β-1,4--acetylegalactosaminyltransferase1 knock-out, ) display prominent disorganization of proteins at the node of Ranvier (NoR) in early life and age-dependent neurodegeneration. Loss of neuronal rather than glial complex gangliosides underpins the phenotype, as shown by neuron- or glial-specific rescue, whereas sulfatide is principally expressed and functional in glial membranes. The similarities in NoR phenotype of , , and axo-glial protein-deficient mice suggests that these glycolipids stabilize membrane proteins including neurofascin155 (NF155) and myelin-associated glycoprotein (MAG) at axo-glial junctions. To assess the functional interactions between sulfatide and gangliosides, and genotypes were interbred. × mice develop normally to postnatal day 10 (P10), but all die between P20 and P25, coinciding with peak myelination. Ultrastructural, immunohistological, and biochemical analysis of either sex revealed widespread axonal degeneration and disruption to the axo-glial junction at the NoR. In addition to sulfatide-dependent loss of NF155, × mice exhibited a major reduction in MAG protein levels in CNS myelin compared with WT and single-lipid-deficient mice. The × phenotype was fully restored to that of mice by neuron-specific expression of complex gangliosides, but not by their glial-specific expression nor by the global expression of -series gangliosides. These data indicate that sulfatide and complex -series gangliosides on the glial and neuronal membranes, respectively, act in concert to promote NF155 and MAG in maintaining the stable axo-glial interactions essential for normal nerve function. Sulfatides and complex gangliosides are membrane glycolipids with important roles in maintaining nervous system integrity. Node of Ranvier maintenance in particular requires stable compartmentalization of multiple membrane proteins. The axo-glial adhesion molecules neurofascin155 (NF155) and myelin-associated glycoprotein (MAG) require membrane microdomains containing either sulfatides or complex gangliosides to localize and function effectively. The cooperative roles of these microdomains and associated proteins are unknown. Here, we show vital interdependent roles for sulfatides and complex gangliosides because double (but not single) deficiency causes a rapidly lethal phenotype at an early age. These findings suggest that sulfatides and complex gangliosides on opposing axo-glial membranes are responsible for essential tethering of the axo-glial junction proteins NF155 and MAG, which interact to maintain the nodal complex.
硫酸脑苷脂和神经节苷脂是与筏相关的糖脂，对于维持有髓神经的完整性至关重要。硫酸脑苷脂（半乳糖脑苷脂硫转移酶敲除）或复合神经节苷脂（β-1,4--乙酰半乳糖胺基转移酶 1 敲除）缺陷的小鼠在生命早期和年龄依赖性神经退行性变中表现出神经节蛋白在Ranvier 结（NoR）处的明显紊乱。神经元而非神经胶质复合神经节苷脂的缺失是这种表型的基础，如神经元或神经胶质特异性拯救所表明的那样，而硫酸脑苷脂主要在神经胶质膜中表达和发挥功能。NoR 表型在 、 和轴突-胶质蛋白缺陷型小鼠中的相似性表明，这些糖脂在轴突-神经胶质连接处稳定包括神经束蛋白 155（NF155）和髓鞘相关糖蛋白（MAG）在内的膜蛋白。为了评估硫酸脑苷脂和神经节苷脂之间的功能相互作用， 和 基因型进行了杂交。× 雄性和雌性小鼠在出生后第 10 天（P10）发育正常，但均在 P20 至 P25 之间死亡，此时正是髓鞘形成的高峰期。对两性的超微结构、免疫组织化学和生化分析显示，NoR 处广泛的轴突变性和轴突-神经胶质连接中断。与 WT 和单脂质缺陷型小鼠相比，× 小鼠中枢神经系统髓鞘中的 NF155 依赖于硫酸脑苷脂的丢失，同时 MAG 蛋白水平也显著降低。通过神经元特异性表达复合神经节苷脂，完全恢复了 × 小鼠的表型，但通过其神经胶质特异性表达或 - 系列神经节苷脂的全局表达均未恢复。这些数据表明，硫酸脑苷脂和复合 - 系列神经节苷脂分别在神经胶质和神经元膜上发挥作用，共同促进 NF155 和 MAG 的稳定轴突-神经胶质相互作用，这对于正常的神经功能至关重要。硫酸脑苷脂和复合神经节苷脂是具有重要作用的膜糖脂，可维持神经系统的完整性。Ranvier 结的维持特别需要多种膜蛋白的稳定区室化。轴突-神经胶质粘附分子神经束蛋白 155（NF155）和髓鞘相关糖蛋白（MAG）需要含有硫酸脑苷脂或复合神经节苷脂的膜微区室才能有效定位和发挥功能。这些微区室和相关蛋白的协同作用尚不清楚。在这里，我们发现硫酸脑苷脂和复合神经节苷脂之间存在重要的相互依存作用，因为双重（而非单一）缺陷会导致在幼年时出现快速致命表型。这些发现表明，在相对的轴突-神经胶质膜上的硫酸脑苷脂和复合神经节苷脂负责将轴突-神经胶质连接蛋白 NF155 和 MAG 有效地固定在一起，它们相互作用以维持节点复合物。
