FATTY-ACIDS FROM DEGENERATING MYELIN LIPIDS ARE CONSERVED AND REUTILIZED FOR MYELIN SYNTHESIS DURING REGENERATION IN PERIPHERAL-NERVE

Following nerve crush, cholesterol from degenerating myelin is conserv ed and reutilized for new myelin synthesis during nerve regeneration. The possibility that other myelin lipids are salvaged and reutilized h as not been investigated previously. We examined the fate of myelin ph ospholipids and their fatty acyl moieties following nerve crush by ele ctron microscopic autoradiography of myelin lipids prelabeled with [H- 3]oleate or [2-H-3]-glycerol. Both precursors were incorporated predom inantly (> 90%) into phospholipids; > 85% of the [H-3]-oleate was inco rporated as oleate, with the remainder in longer-chain fatty acids. Be fore nerve crush, both labels were restricted to myelin sheaths. Follo wing nerve crush and subsequent regeneration, over half the label from [H-3]oleate, but little from [2-H-3]glycerol, remained in nerve. The oleate label was present as fatty acyl moieties in phospholipids and w as localized to newly formed myelin sheaths. Among the extracellular s oluble lipids within the degenerating nerve, the bulk of the labeled p hospholipids floated at the same density as lipoprotein particles. The se data indicate that myelin phospholipids are completely hydrolyzed d uring nerve degeneration, that at least half the resultant free fatty acids are salvaged and reutilized for new myelin synthesis, and that t hese salvaged fatty acids are transported by a lipoprotein-mediated me chanism similar to that functioning in cholesterol reutilization.