Cellular characterization of MPZ mutations presenting with diverse clinical phenotypes

Abstract

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.

Neuropathy-related mutations alter the membrane binding properties of the human myelin protein P0 cytoplasmic tail

“…The mutation results in a loosened repeat structure without a major impact on protein folding. Arg227 might be involved in electrostatic anchoring of the protein to the lipid headgroups – the R227S mutation likely has low impact on ER stress and UPR, as mutated P0 correctly localizes to the plasma membrane (Lee et al 2010).…”

Protein misfolding and clearance in demyelinating peripheral neuropathies

“…The accumulation of misfolded PMP22 and MPZ at the ER 19,20 suggests that ERAD dysfunction and subsequent ER stress may be involved in causing demyelinating CMT. Our recent finding that endosome to the cytosol ( Fig.…”

A novel Gly137Asp MPZ mutation in a Charcot-Marie-Tooth disease type 1B family

“…Hayasaka et al (1993) first identified MPZ mutations as the underlying cause of CMT1B, and until recently, more than a hundred MPZ mutations have been reported to be relevant for CMT. Mutations in MPZ are shown to be responsible for a wide range of CMT phenotypes, which could be categorized into early or late onset neuropathy (Shy et al, 2004;Zschüntzschet al, 2009;Lee et al, 2010). Based on the clinical and electrophysiological features, the present family members with the Gly137Asp MPZ mutation was compatible with demyelinating CMT1B neuropathy.…”

“…These variable clinical phenotypes are usually associated with specific MPZ mutations, namely different phenotypes by different mutation sites (Lee et al, 2010). Moreover, some MPZ mutations have been associated with divergent types of nerve pathologies and the same mutationsproduce a spectrum of CMT disorders.…”