PLP/DM20 expression and turnover in a transgenic mouse model of Pelizaeus-Merzbacher disease.
The most common cause of Pelizaeus-Merzbacher (PMD) is due to duplication of the PLP1 gene but it is unclear how increased gene dosage affects PLP turnover and causes dysmyelination. We have studied the dynamics of PLP/DM20 in a transgenic mouse model of PMD with increased gene dosage of the proteolipid protein gene (Plp1). The turnover of PLP/DM20 were investigated using an ex-vivo brain slice system and cultured oligodendrocytes. Homozygous mice have reduced PLP translation, markedly enhanced PLP degradation, and markedly reduced incorporation of PLP into myelin. Proteasome inhibition (MG132) prevented the enhanced degradation. Numerous autophagic vesicles are present in homozygous transgenic mice that may influence protein dynamics. Surprisingly, promoting autophagy with rapamycin decreases the degradation of nascent PLP suggesting autophagic vacuoles serve as a cellular storage compartment. We suggest that there are multiple subcellular fates of PLP/DM20 when overexpressed: the vast majority being degraded by the proteasome, a proportion sequestered into autophagic vacuoles, probably fused with endolysosomes, and only a small proportion entering the myelin sheath, where its association with lipid rafts is perturbed. Transgenic oligodendrocytes have fewer membrane sheets and this phenotype is improved with siRNA-mediated knockdown of PLP expression that promotes the formation of MBP+ myelin-like sheets. This finding suggests that RNAi technology is in principle applicable to improve CNS myelination when compromised by PLP/DM20 overexpression.
Karim
Saadia A
SA
The Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Bearsden, Glasgow, G61 1BD, Scotland.
Barrie
Jennifer A
JA
McCulloch
Mailis C
MC
Montague
Paul
P
Edgar
Julia M
JM
Iden
Debrah L
DL
Anderson
Thomas J
TJ
Nave
Klaus-Armin
KA
Griffiths
Ian R
IR
McLaughlin
Mark
M
D000818:Animals; D002478:Cells, Cultured; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000235:genetics; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D018991:Myelin Proteolipid Protein / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D009186:Myelin Sheath / Q000235:genetics* / Q000378:metabolism*; D009924:Organ Culture Techniques; D020371:Pelizaeus-Merzbacher Disease / Q000235:genetics* / Q000378:metabolism*; D034622:RNA Interference / Q000502:physiology; D014617:Vacuoles / Q000378:metabolism / Q000648:ultrastructure
D018991:Myelin Proteolipid Protein; C047516:Plp1 protein, mouse