Different cellular and molecular mechanisms for early and late-onset myelin protein zero mutations.
Mutations in the gene MPZ, encoding myelin protein zero (MPZ), cause inherited neuropathies collectively called Charcot-Marie-Tooth type 1B (CMT1B). Based on the age of onset, clinical and pathological features, most MPZ mutations are separable into two groups: one causing a severe, early-onset, demyelinating neuropathy and a second, causing a late-onset neuropathy with prominent axonal loss. To investigate potential pathomechanisms underlying the two phenotypes, we transiently transfected HeLa cells with two late-onset (T95M, H10P) and two early-onset (H52R, S22_W28 deletion) mutations and analyzed their effects on intracellular protein trafficking, glycosylation, cell viability and intercellular adhesion. We found that the two late-onset mutations were both transported to the cell membrane and moderately reduced MPZ-mediated intercellular adhesion. The two early-onset mutations caused two distinct abnormalities. H52R was correctly glycosylated and trafficked to the plasma membrane, but strongly affected intercellular adhesion. When co-expressed with wild-type MPZ (wtMPZ), a functional dominant negative effect was observed. Alternatively, S22_W28 deletion was retained within the cytoplasm and reduced both adhesion caused by wtMPZ and cellular viability. Since the same trafficking patterns were observed in transfected murine Schwann cells, they are not an artifact of heterologous cell expression. Our results suggest that at least some late-onset mutations cause a partial loss of function in the transfected cells, whereas multiple abnormal gain of function pathways can result in early-onset neuropathy. Further characterization of these pathways will lead to a better understanding of the pathogenesis of CMT1B and a rational basis for treating these debilitating inherited neuropathies.
Grandis
Marina
M
Department of Neurosciences, Ophthalmology and Genetics, Universityof Genova, 16132 Genova, Italy. mgrandis@neurologia.unige.it
Vigo
Tiziana
T
Passalacqua
Mario
M
Jain
Manisha
M
Scazzola
Sara
S
La Padula
Veronica
V
Brucal
Michelle
M
Benvenuto
Federica
F
Nobbio
Lucilla
L
Cadoni
Angela
A
Mancardi
Gian Luigi
GL
Kamholz
John
J
Shy
Michael E
ME
Schenone
Angelo
A
D017668:Age of Onset; D000818:Animals; D017209:Apoptosis; D002449:Cell Aggregation; D002470:Cell Survival; D002607:Charcot-Marie-Tooth Disease / Q000453:epidemiology* / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D017930:Genes, Reporter; D006031:Glycosylation; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D020125:Mutation, Missense; D018993:Myelin P0 Protein / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D017510:Protein Folding; D021381:Protein Transport
D018993:Myelin P0 Protein; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins