Vance J E, Campenot R B, Vance D E
Department of Medicine, University of Alberta, Edmonton, Canada.
Biochim Biophys Acta. 2000 Jun 26;1486(1):84-96. doi: 10.1016/s1388-1981(00)00050-0.
Neurons are unique polarized cells in which the growing axon is often located up to a meter or more from the cell body. Consequently, the intracellular movement of membrane lipids and proteins between cell bodies and axons poses a special challenge. The mechanisms of lipid transport within neurons are, for the most part, unknown although lipid transport via vesicles and via cholesterol- and sphingolipid-rich 'rafts' are considered likely mechanisms. Very active anterograde and retrograde transport of lipid-containing vesicles occurs between the cell body and distal axons. However, it is becoming clear that the axon need not obtain all of its membrane constituents from the cell body. For example, the synthesis of phosphatidylcholine, the major membrane phospholipid, occurs in axons, and its synthesis at this location is required for axonal elongation. In contrast, cholesterol synthesis appears to occur only in cell bodies, and cholesterol is efficiently delivered from cell bodies to axons by anterograde transport. Cholesterol that is required for axonal growth can also be exogenously supplied from lipoproteins to axons of cultured neurons. Several studies have suggested a role for apolipoprotein E in lipid delivery for growth and regeneration of axons after a nerve injury. Alternatively, or in addition, apolipoprotein E has been proposed to be a ligand for receptors that mediate signal transduction cascades. Lipids are also transported from axons to myelin, although the importance of this process for myelination is not clear.
神经元是独特的极化细胞，其生长的轴突通常距离细胞体一米或更远。因此，膜脂和蛋白质在细胞体与轴突之间的细胞内移动带来了特殊挑战。尽管通过囊泡以及富含胆固醇和鞘脂的“筏”进行脂质转运被认为是可能的机制，但神经元内脂质转运的机制在很大程度上仍不清楚。含脂质囊泡在细胞体和轴突远端之间进行非常活跃的顺行和逆行转运。然而，越来越清楚的是，轴突不必从细胞体获得其所有膜成分。例如，主要的膜磷脂磷脂酰胆碱在轴突中合成，其在此位置的合成是轴突伸长所必需的。相比之下，胆固醇合成似乎仅发生在细胞体中，并且胆固醇通过顺行转运从细胞体有效地输送到轴突。轴突生长所需的胆固醇也可以从脂蛋白外源性地供应给培养神经元的轴突。几项研究表明载脂蛋白E在神经损伤后轴突生长和再生的脂质递送中起作用。另外，或者除此之外，有人提出载脂蛋白E是介导信号转导级联反应的受体的配体。脂质也从轴突转运到髓磷脂，尽管这一过程对髓鞘形成的重要性尚不清楚。
