Myelination process in the rat sciatic nerve during regeneration and development: Molecular species composition and acyl group biosynthesis of choline-, ethanolamine-, and serine-glycerophospholipids of myelin fractions

The content of alkenyl-acyl, alkyl-acyl and diacyl types of the three major myelin glycerophospholipids such as PtdCho, PtdEtn and PtdSer was determined in myelin fractions prepared from sciatic nerve segments of rats at 12, 25 and 45 days after birth, and of adult rats (6-month-old) 90 days after crush injury. The biosynthesis and metabolic heterogeneity of lipid classes and types were also studied by incubation with 1-¹⁴C] acetate of nerve segments of young rats at different ages as well as crushed and sham-operated control nerve segments of adult rats. The analysis of composition and positional distribution in major individual molecular species extracted from light myelin and myelin-related fraction suggest that the metabolism of alkenyl-acyl-glycerophosphorylethanolamines and unsaturated species of PtdCho and PtdSer may not be regulated in the same manner during peripheral nerve myelination of developing rat and remyelination of regenerating nerve in the adult animal. The¹⁴C-radioactivity incorporation into lipid classes and alkyl and acyl moieties of the three major phospholipids of sciatic nerve segments during the developmental period investigated revealed that Schwann cells were capable of synthesizing acyl-linked fatty acids in both myelin fractions at a decreasing rate and with different patterns during development. In regenerating sciatic nerve of adult animals the labeling of myelin lipid classes and types of remyelinating nerve segment distal to the crush site was markedly higher than that of sham-operated normal one; however, the magnitude and the pattern of the specific radioactivity never approached those observed during active myelination of the nerve in young animals. These observations show that the remyelinating process of injured nerve during regeneration seems not to recapitulate nerve myelin ensheathment occurring during development.Abbreviations used PtdEtn Phosphatidylethanolamine - PtdCho Phosphatidylcholine - PtdSer Phosphatidylserine - GPE Glycero(3)phosphoethanolamine - GPC Glycero(3)phosphocholine - GPS Glycero(3)phosphoserine - DG-acetates 1,2-diradyl-3-acetyl-sn-glycerols - HPLC High performance liquid chromatography - TLC Thin-layer chromatography - BHT 2,6-di-tert-butyl-4-methylphenol