Myelin extracellular leaflet compaction requires apolipoprotein D membrane management to optimize lysosomal ‐dependent recycling and glycocalyx removal

Abstract To compact the extracellular sides of myelin, an important transition must take place: from membrane sliding, while building the wraps, to membrane adhesion and water exclusion. Removal of the negatively charged glycocalyx becomes the limiting factor in such transition. What is required to initiate this membrane‐zipping process? Knocking‐out the Lipocalin Apolipoprotein D (ApoD), essential for lysosomal functional integrity in glial cells, results in a specific defect in myelin extracellular leaflet compaction in peripheral and central nervous system, which results in reduced conduction velocity and suboptimal behavioral outputs: motor learning is compromised. Myelination initiation, growth, intracellular leaflet compaction, myelin thickness or internodal length remain unaltered. Lack of ApoD specifically modifies Plp and P0 protein expression, but not Mbp or Mag. Late in myelin maturation period, ApoD affects lipogenic and growth‐related, but not stress‐responsive, signaling pathways. Without ApoD, the sialylated glycocalyx is maintained and ganglioside content remains high. In peripheral nervous system, Neu3 membrane sialidase and lysosomal Neu1 are coordinately expressed with ApoD in subsets of Schwann cells. ApoD‐KO myelin becomes depleted of Neu3 and enriched in Fyn, a kinase with pivotal roles in transducing axon‐derived signals into myelin properties. In the absence of ApoD, partial permeabilization of lysosomes alters Neu1 location as well. Exogen...
Source: Glia - Category: Neurology Authors: Tags: RESEARCH ARTICLE Source Type: research