Decreased fatty acylation of myelin proteolipid protein in the twitcher mouse

We examined chronological changes of myelin proteins of the brainstem and spinal cord of the twitcher mouse (15, 20, and 30 days old), a murine model of human globoid cell leukodystrophy caused by a genetic deficiency of galactosylceramidase I activity. The yield of myelin was normal until postnatal day 20, whereas galactosylsphingosine (psychosine) accumulated with age in myelin. The protein profiles of myelin and the activity of 2',3'-cyclic nucleotide 3'-phosphodiesterase in the myelin remained normal throughout the experimental period. Fatty acylation of proteolipid protein (PLP) was examined in a cell-free system by incubation of myelin with [3H]palmitic acid, CoA, and ATP, and was normal at postnatal day 15, but decreased after postnatal day 20. Decreased fatty acylation of PLP was also observed in the twitcher mouse at postnatal day 20 when the isolated myelin was incubated with [14C]palmitoyl-CoA in the absence of ATP and CoA, or the slices of brainstem and spinal cord were incubated with [3H]palmitic acid. The activity of fatty acid:CoA ligase was reduced in myelin. These data suggest that decreased acylation of PLP in twitcher mouse myelin is probably due to reduced activities for both activation and transfer of fatty acid into PLP and that metabolic disturbance is present in myelin because acylation of PLP has been shown to occur in myelin membrane. Although psychosine (200 microM) inhibited only 17% of the acylation in vitro, it may be responsible for the reduced acylation of PLP in vivo.