Drug screening for Pelizaeus-Merzbacher disease by quantifying the total levels and membrane localization of PLP1

BACKGROUND: Pelizaeus-Merzbacher disease (PMD) is caused by point mutations or copy number changes in the proteolipid protein 1 gene (PLP1). PLP1 is exclusively localized in the myelin sheath of oligodendrocytes. Amino acid-substituted PLP1 protein is unable to fold properly and is subsequently degraded and/or restrictedly translated, resulting in a decrease in the PLP1 protein level and a failure to localize to the membrane. Furthermore, misfolded proteins increase the burden on the intracellular quality control system and trafficking, finally resulting in cell apoptosis. The objective of this study was to identify therapeutic chemicals for PMD by quantifying the total levels and membrane localization of PLP1. METHOD: We established a cell line stably expressing PLP1(A243V) fused with green fluorescent protein in oligodendrocyte-derived MO3.13 cells. We screened a chemical library composed of drugs approved for central nervous system disorders that increased both the total intensity of PLP1(A243V) in the whole cell and the cell membrane localization. We analyzed the change in the endoplasmic reticulum (ER) stress and the gene expression of candidate chemicals using a micro-array analysis. Finally, we tested the in vivo effectiveness using myelin synthesis deficient (msd) mice with Plp(A243V). RESULTS AND CONCLUSION: Piracetam significantly increased the PLP1(A243V) intensity and membrane localization and decreased the ER stress. It was also shown to reverse the gene expression changes induced by PLP1(A243V) in a micro-array analysis. However, in vivo treatment of piracetam did not improve the survival of msd mice (Plp1(A243V)).