The clinicopathological spectrum of Rosenthal fibre encephalopathy and Alexander's disease: a case report and review of the literature.
Alexander's disease is a leucodystrophy that usually presents in early childhood, but can infrequently arise in adults. It is characterised pathologically by megalencephaly, demyelination, and the presence of numerous Rosenthal fibres. Most cases have been shown to be due to mutations in the gene encoding glial fibrillary acidic protein. In rare instances, numerous Rosenthal fibres have been found at autopsy in patients who have suffered protracted debilitating systemic illnesses, some with associated brain stem signs, and in very rare instances in patients with no apparent neurological abnormality. The term "Rosenthal fibre encephalopathy" is used to distinguish these cases from those of Alexander's disease. We report the first case of Rosenthal fibre encephalopathy in a young man with AIDS, and review the literature. (+info)
Alexander-disease mutation of GFAP causes filament disorganization and decreased solubility of GFAP.
Alexander disease is a fatal neurological illness characterized by white-matter degeneration and the formation of astrocytic cytoplasmic inclusions called Rosenthal fibers, which contain the intermediate filament glial fibrillary acidic protein (GFAP), the small heat-shock proteins HSP27 and alphaB-crystallin, and ubiquitin. Many Alexander-disease patients are heterozygous for one of a set of point mutations in the GFAP gene, all of which result in amino acid substitutions. The biological effects of the most common alteration, R239C, were tested by expressing the mutated protein in cultured cells by transient transfection. In primary rat astrocytes and Cos-7 cells, the mutant GFAP was incorporated into filament networks along with the endogenous GFAP and vimentin, respectively. In SW13Vim(-) cells, which have no endogenous cytoplasmic intermediate filaments, wild-type human GFAP frequently formed filamentous bundles, whereas the R239C GFAP formed 'diffuse' and irregular patterns. Filamentous bundles of R239C GFAP were sometimes formed in SW13Vim(-) cells when wild-type GFAP was co-transfected. Although the presence of a suitable coassembly partner (vimentin or GFAP) reduced the potential negative effects of the R239C mutation on GFAP network formation, the mutation affected the stability of GFAP in cells in a dominant fashion. Extraction of transfected SW13Vim(-) cells with Triton-X-100-containing buffers showed that the mutant GFAP was more resistant to solubilization at elevated KCl concentrations. Both wild-type and R239C GFAP assembled into 10 nm filaments with similar morphology in vitro. Thus, although the R239C mutation does not appear to affect filament formation per se, the mutation alters the normal solubility and organization of GFAP networks. (+info)
Gene expression analysis in mice with elevated glial fibrillary acidic protein and Rosenthal fibers reveals a stress response followed by glial activation and neuronal dysfunction.
Alexander disease is a fatal neurodegenerative disorder resulting from missense mutations of the intermediate filament protein, GFAP. The pathological hallmark of this disease is the formation of cytoplasmic protein aggregates within astrocytes known as Rosenthal fibers. Transgenic mice engineered to over-express wild-type human GFAP develop an encephalopathy with identical aggregates, suggesting that elevated levels of GFAP in addition to mutant protein contribute to the pathogenesis of this disorder. To study further the effects of elevated GFAP and Rosenthal fibers per se, independent of mutations, we performed gene expression analysis on olfactory bulbs of transgenic mice at two different ages to follow the progression of pathology. The expression profiles reveal a stress response that includes genes involved in glutathione metabolism, peroxide detoxification and iron homeostasis. Many of these genes are regulated by the transcription factor Nfe2l2, which is also increased in expression at 3 weeks. An immune-related response occurs with activation of cytokine and cytokine receptor genes, complement components and acute phase response genes. These transcripts are further elevated with age, with additional induction of macrophage-specific markers such as Mac1 and CD68, suggesting activation of microglia. At 4 months, decreased expression of genes for microtubule-associated proteins, vesicular trafficking proteins and neurotransmitter receptors becomes apparent. Interneuron-specific transcription factors including Dlx family members and Pax6 are downregulated as well as Gad1 and Gad2, suggesting impairment of GABAergic granule cells. Together, these data implicate an initial stress response by astrocytes, which results in the activation of microglia and compromised neuronal function. (+info)
Plectin regulates the organization of glial fibrillary acidic protein in Alexander disease.
Alexander disease (AxD) is a rare but fatal neurological disorder caused by mutations in the astrocyte-specific intermediate filament protein glial fibrillary acidic protein (GFAP). Histologically, AxD is characterized by cytoplasmic inclusion bodies called Rosenthal fibers (RFs), which contain GFAP, small heat shock proteins, and other undefined components. Here, we describe the expression of the cytoskeletal linker protein plectin in the AxD brain. RFs displayed positive immunostaining for plectin and GFAP, both of which were increased in the AxD brain. Co-localization, co-immunoprecipitation, and in vitro overlay analyses demonstrated direct interaction of plectin and GFAP. GFAP with the most common AxD mutation, R239C (RC GFAP), mainly formed abnormal aggregates in human primary astrocytes and murine plectin-deficient fibroblasts. Transient transfection of full-length plectin cDNA converted these aggregates to thin filaments, which exhibited diffuse cytoplasmic distribution. Compared to wild-type GFAP expression, RC GFAP expression lowered plectin levels in astrocytoma-derived stable transfectants and plectin-positive fibroblasts. A much higher proportion of total GFAP was found in the Triton X-insoluble fraction of plectin-deficient fibroblasts than in wild-type fibroblasts. Taken together, our results suggest that insufficient amounts of plectin, due to RC GFAP expression, promote GFAP aggregation and RF formation in AxD. (+info)
Neuropathology for the neuroradiologist: Rosenthal fibers.
Distinctive intracellular structures known as inclusions may be occasionally observed on stained tissue preparations and may further suggest a specific diagnosis. Pathologists rely on these findings much as radiologists rely on findings revealed in the gray-scale patterns of densities and intensities on images. Appreciation of these inclusions can enhance the interactions of the neuroradiologist with the neuropathologist and deepen understanding of certain conditions. This report reviews the neuropathologically observed intracellular inclusions known as Rosenthal fibers in the context of Alexander disease and slow-growing tumors such as pilocytic astrocytoma. (+info)
The Alexander disease-causing glial fibrillary acidic protein mutant, R416W, accumulates into Rosenthal fibers by a pathway that involves filament aggregation and the association of alpha B-crystallin and HSP27.
Here, we describe the early events in the disease pathogenesis of Alexander disease. This is a rare and usually fatal neurodegenerative disorder whose pathological hallmark is the abundance of protein aggregates in astrocytes. These aggregates, termed "Rosenthal fibers," contain the protein chaperones alpha B-crystallin and HSP27 as well as glial fibrillary acidic protein (GFAP), an intermediate filament (IF) protein found almost exclusively in astrocytes. Heterozygous, missense GFAP mutations that usually arise spontaneously during spermatogenesis have recently been found in the majority of patients with Alexander disease. In this study, we show that one of the more frequently observed mutations, R416W, significantly perturbs in vitro filament assembly. The filamentous structures formed resemble assembly intermediates but aggregate more strongly. Consistent with the heterozygosity of the mutation, this effect is dominant over wild-type GFAP in coassembly experiments. Transient transfection studies demonstrate that R416W GFAP induces the formation of GFAP-containing cytoplasmic aggregates in a wide range of different cell types, including astrocytes. The aggregates have several important features in common with Rosenthal fibers, including the association of alpha B-crystallin and HSP27. This association occurs simultaneously with the formation of protein aggregates containing R416W GFAP and is also specific, since HSP70 does not partition with them. Monoclonal antibodies specific for R416W GFAP reveal, for the first time for any IF-based disease, the presence of the mutant protein in the characteristic histopathological feature of the disease, namely Rosenthal fibers. Collectively, these data confirm that the effects of the R416W GFAP are dominant, changing the assembly process in a way that encourages aberrant filament-filament interactions that then lead to protein aggregation and chaperone sequestration as early events in Alexander disease. (+info)
Synergistic effects of the SAPK/JNK and the proteasome pathway on glial fibrillary acidic protein (GFAP) accumulation in Alexander disease.
Protein aggregates in astrocytes that contain glial fibrillary acidic protein (GFAP), small heat shock proteins, and ubiquitinated proteins are termed Rosenthal fibers and characterize Alexander disease, a leukodystrophy caused by heterozygous mutations in GFAP. The mechanisms responsible for the massive accumulation of GFAP in Alexander disease remain unclear. In this study, we show that overexpression of both wild type and R239C mutant human GFAP led to cytoplasmic inclusions. GFAP accumulation also led to a decrease of proteasome activity and an activation of the MLK2-JNK pathway. In turn, the expression of activated mixed lineage kinases (MLKs) induced JNK activation and increased GFAP accumulation, whereas blocking the JNK pathway decreased GFAP accumulation. Activated MLK also inhibited proteasome function. A direct inhibition of proteasome function pharmacologically further activated JNK. Our data suggest a synergistic interplay between the proteasome and the SAPK/JNK pathway in the context of GFAP accumulation. Feedback interactions among GFAP accumulation, SAPK/JNK activation, and proteasomal hypofunction cooperate to produce further protein accumulation and cellular stress responses. (+info)
A case of infantile Alexander disease accompanied by infantile spasms diagnosed by DNA analysis.
Alexander disease (AD) is a rare leukodystrophy of the central nervous system of unknown etiology. AD is characterized by progressive failure of central myelination and the accumulation of Rosenthal fibers in astrocytes, and is inevitably lethal in nature. Symptomatically, AD is associated with leukoencephalopathy with macrocephaly, seizures, and psychomotor retardation in infants, and usually leads to death within the first decade. Its characteristic magnetic resonance imaging (MRI) findings have been described as demyelination predominantly in the frontal lobe. Moreover, dominant mutations in the GFAP gene, coding for glial fibrillary acidic protein (GFAP), a principal astrocytic intermediate filament protein, have been shown to lead to AD. The disease can now be detected by genetic diagnosis. We report the Korean case of an 8-month-old male patient with AD. He was clinically characterized due to the presence of psychomotor retardation, megalencephaly, spasticity, and recurrent seizures including infantile spasms which is a remarkable presentation. Demyelination in the frontal lobe and in a portion of the temporal lobe was demonstrated by brain MRI. Moreover, DNA analysis of peripheral blood showed the presence of a R239L mutation in the GFAP gene, involving the replacement of guanine with thymine. (+info)