Mild functional effects of a novel GFAP mutant allele identified in a familial case of adult-onset Alexander disease.
Alexander disease is a neurological genetic disorder characterized by progressive white-matter degeneration, with astrocytes containing cytoplasmic aggregates, called Rosenthal fibers, including the intermediate filament glial fibrillary acidic protein (GFAP). The age of onset of the disease defines three different forms, infantile, juvenile and adult, all due to heterozygous GFAP mutations and characterized by a progressive less severe phenotype from infantile to adult forms. In an Italian family with a recurrent mild adult onset of Alexander disease, we have identified two GFAP mutations, coupled on a same allele, leading to p.[R330G; E332K]. Functional studies on this complex allele revealed less severe aggregation patterns compared to those observed with p.R239C GFAP mutant, associated with a severe Alexander disease phenotype. Moreover, in addition to confirming the involvement of the ubiquitin-proteasome system in cleaning cells from aggregates and a dominant effect of the novel mutant protein, in cells expressing the mild p.[R330G; E332K] mutant we have observed that indirect alphaB-crystallin overexpression, induced by high extracellular potassium concentration, could completely rescue the correct filament organization while, under the same experimental conditions, in cells expressing the severe p.R239C mutant only a partial rescue effect could be achieved.
Bachetti
Tiziana
T
Laboratory of Molecular Genetics, G Gaslini Institute, Genoa, Italy.
Caroli
Francesco
F
Bocca
Paola
P
Prigione
Ignazia
I
Balbi
Pietro
P
Biancheri
Roberta
R
Filocamo
Mirella
M
Mariotti
Caterina
C
Pareyson
Davide
D
Ravazzolo
Roberto
R
Ceccherini
Isabella
I
D000328:Adult; D017668:Age of Onset; D038261:Alexander Disease / Q000235:genetics* / Q000503:physiopathology; D000483:Alleles; D045744:Cell Line, Tumor; D003599:Cytoskeleton / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D005904:Glial Fibrillary Acidic Protein / Q000235:genetics* / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D025801:Ubiquitin / Q000378:metabolism; D014746:Vimentin / Q000378:metabolism; D038203:alpha-Crystallin B Chain / Q000378:metabolism
D005904:Glial Fibrillary Acidic Protein; D025801:Ubiquitin; D014746:Vimentin; D038203:alpha-Crystallin B Chain; D049452:Green Fluorescent Proteins