Cellular characterization of MPZ mutations presenting with diverse clinical phenotypes

Mutations in MPZ, which encodes myelin protein zero (P(0)), may lead to different subtypes of Charcot-Marie-Tooth disease (CMT). The aim of this study was to characterize the cellular manifestations of various MPZ mutations associated with CMT1, Dejerine-Sottas syndrome (DSS) and CMT2, and to correlate their cellular and clinical phenotypes. Nine P(0) mutants associated with CMT1 (P(0)S63F, R98H, R277S, and S233fs), DSS (P(0) I30T and R98C), and CMT2 (P(0)S44F, D75V, and T124M), were investigated. Wild-type and mutant P(0) fused with fluorescent proteins were expressed in vitro to monitor their intracellular localization. An adhesiveness assay was used to evaluate the adhesiveness of the transfected cells. Protein localization and cell adhesiveness of each mutant protein were compared and correlated with their clinical phenotypes. Three different intracellular localization patterns of the mutant P(0) were observed. Wild-type P(0), P(0)I30T, S44F, S63F, D75V, T124M, and R227S were mostly localized on the cell membrane, P(0)R98H, and R98C were found in the endoplasmic reticulum (ER) or Golgi apparatus, and P(0)S233fs formed aggregates within the ER. Cells expressing mutant P(0), as compared with those expressing wild-type P(0), demonstrated variable degrees of reduction in the cell adhesiveness. The molecular patho-mechanisms of MPZ mutations are likely very complex and the clinical phenotype must be influenced by many genetic or environmental factors. This complexity may contribute to the highly variable clinical manifestations resulting from different MPZ mutations.