title: Glial fibrillary acidic protein exhibits altered turnover kinetics in a mouse model of Alexander disease.
abstract: Mutations in the astrocyte-specific intermediate filament glial fibrillary acidic protein (GFAP) lead to the rare and fatal disorder, Alexander disease (AxD). A prominent feature of the disease is aberrant accumulation of GFAP. It has been proposed that this accumulation occurs because of an increase in gene transcription coupled with impaired proteasomal degradation, yet this hypothesis remains untested. We therefore sought to directly investigate GFAP turnover in a mouse model of AxD that is heterozygous for a disease-causing point mutation (GfapR236H/+) (and thus expresses both wild-type and mutant protein). Stable isotope labeling by amino acids in cell culture, using primary cortical astrocytes, indicated that thein vitrohalf-lives of total GFAP in astrocytes from wild-type and mutant mice were similar at ∼3-4 days. Surprisingly, results obtained with stable isotope labeling of mammals revealed that,in vivo, the half-life of GFAP in mutant mice (15.4 ± 0.5 days) was much shorter than that in wild-type mice (27.5 ± 1.6 days). These unexpectedin vivodata are most consistent with a model in which synthesis and degradation are both increased. Our work reveals that an AxD-causing mutation alters GFAP turnover kineticsin vivoand provides an essential foundation for future studies aimed at preventing or reducing the accumulation of GFAP. In particular, these data suggest that elimination of GFAP might be possible and occurs more quickly than previously surmised.
authors.affiliation: From the Waisman Center.
authors.forename: Laura R
authors.initials: LR
authors.lastname: Moody
authors.affiliation: the Biotechnology Center, and.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Barrett-Wilt
authors.affiliation: the Biotechnology Center, and.|the Departments of Biochemistry and.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Sussman
authors.affiliation: From the Waisman Center, amessing@wisc.edu.|Comparative Biosciences, University of Wisconsin-Madison, Madison, Wisconsin 53705.
authors.forename: Albee
authors.identifier: 0000-0001-6049-0521
authors.initials: A
authors.lastname: Messing
mesh_terms: D038261:Alexander Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019943:Amino Acid Substitution; D000818:Animals; D001253:Astrocytes / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D005904:Glial Fibrillary Acidic Protein / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D017354:Point Mutation
chemical_list: D005904:Glial Fibrillary Acidic Protein; C528900:glial fibrillary astrocytic protein, mouse
keywords: Alexander disease; SILAC; SILAM; astrocyte; gfap; glial cell; glial fibrillary acidic protein; intermediate filament; mouse; protein turnover