Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP): Estimation of pathological lesion stage from brain images.

BACKGROUND: Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is a disease responsible for cognitive impairment in adult humans. It is caused by mutations in the colony stimulating factor 1 receptor gene (CSF1R) or alanyl-transfer (t) RNA synthetase 2 (AARS2) gene and affects brain white matter. Settlement of stages of the pathological brain lesions (Oyanagi et al. 2017) from the findings of brain imaging will be inevitably essential for prognostication. METHODS: MRI images of eight patients with ALSP were analyzed semiquantitatively. White matter degeneration was assessed on a scale of 0 to 4 (none, patchy, large patchy, confluent, and diffuse) at six anatomical points, and brain atrophy on a scale 0 to 4 (none, slight, mild, moderate, and severe) in four anatomical areas. The scores of the two assessments were then summed to give total MRI scores of 0-40 points. Based on the scores, the MRI features were classified as Grades (0-4). Regression analysis was applied to mutual association between mRS, white matter degeneration score, brain atrophy score, the total MRI score and disease duration. RESULTS: White matter degeneration score, brain atrophy score, and the total MRI score were significantly correlated with the disease duration. MRI Grades (2-4) based on the total MRI scores and the features of the images were well correlated with the pathological lesion stages (II - IV); i.e., 'large patchy' white matter degeneration in the frontal and parietal lobes (MRI Grade 2) corresponded to pathological Stage II, 'confluent' degeneration (Grade 3) to Stage III, and 'diffuse' degeneration (Grade 4) to Stage IV. CONCLUSION: MRI Grades (2-4) resulted from the total MRI scores were well correlated with the pathological lesion Stages (II - IV).

Selective extension of cerebral vascular calcification in an autopsy case of Fahr's syndrome associated with asymptomatic hypoparathyroidism.

We report an autopsy case of Fahr's syndrome in an 85-year-old woman associated with asymptomatic hypoparathyroidism. The patient was diagnosed as having brain calcification at 65 years of age. She developed mild dementia at 75, parkinsonism at 76, and severe dementia at 82. Computed tomography revealed extensive, symmetric intracranial calcification, involving both sides of the basal ganglia and cerebellar dentate nuclei, and severe cerebral atrophy that developed afterwards. A neuropathological examination revealed intracranial calcification, particularly in the wall of the arterioles and capillaries having numerous calcium deposits. Severe vascular calcification and severe neuronal loss without α-synuclein accumulation were found in the substantia nigra. There were high-level neuropathological changes indicative of Alzheimer's disease. Although the colocalization of calcium and amyloid-ß deposits in the same arterial wall was rare, both of them were located in a similar layer of the arterial wall. The vascular calcification in the basal ganglia spread continuously through the corona radiata into the selective cerebral areas along the medullary arteries, but did not involve the corpus callosum or insular region. Stone formation was observed at the corona radiata adjacent to the superolateral angles of the lateral ventricles. We hypothesized that there would be a stereotypical extension pattern of vascular calcification related to the arrangement of penetrating arteries in Fahr's syndrome.

Intracranial vascular calcification with extensive white matter changes in an autopsy case of pseudopseudohypoparathyroidism.

We herein report an autopsy case of a 69-year-old man with pseudopseudohypoparathyroidism. The patient suffered from mental retardation and spastic tetraparesis and had all the features of Albright's hereditary osteodystrophy with a normal response to parathyroid hormone in the Ellsworth-Howard test. Computed tomography demonstrated symmetrical massive brain calcification involving the bilateral basal ganglia, thalami, dentate nuclei and cerebral gray/white matter junctions, which was consistent with Fahr's syndrome. Magnetic resonance imaging revealed extensive white matter changes sparing the corpus callosum. Severe ossification of the posterior longitudinal ligament of the cervical spine was also demonstrated. A neuropathological examination revealed massive intracranial calcification within the walls of the blood vessels and capillaries with numerous calcium deposits. The calcium deposits aligned along the capillaries, and deposits in the vessel wall at the initial stage were confined to the border between the tunica media and adventitia. The vascular calcification in the basal ganglia continuously spread over the surrounding white matter into the cortex. The area of vascular calcification in the white matter was very well correlated with the area of the attenuated myelin staining. Axonal loss, myelin sheath loss and gliosis were observed in the white matter with severe vascular calcification. We should recognize the continuous area of vascular calcification and its correlation with extensive white matter changes as possible causes of neuropsychiatric symptoms in pseudopseudohypoparathyroidism with Fahr's syndrome.

Adult onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) and Nasu-Hakola disease: lesion staging and dynamic changes of axons and microglial subsets.

The brains of 10 Japanese patients with adult onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) encompassing hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) and pigmentary orthochromatic leukodystrophy (POLD) and eight Japanese patients with Nasu-Hakola disease (N-HD) and five age-matched Japanese controls were examined neuropathologically with special reference to lesion staging and dynamic changes of microglial subsets. In both diseases, the pathognomonic neuropathological features included spherically swollen axons (spheroids and globules), axon loss and changes of microglia in the white matter. In ALSP, four lesion stages based on the degree of axon loss were discernible: Stage I, patchy axon loss in the cerebral white matter without atrophy; Stage II, large patchy areas of axon loss with slight atrophy of the cerebral white matter and slight dilatation of the lateral ventricles; Stage III, extensive axon loss in the cerebral white matter and dilatation of the lateral and third ventricles without remarkable axon loss in the brainstem and cerebellum; Stage IV, devastated cerebral white matter with marked dilatation of the ventricles and axon loss in the brainstem and/or cerebellum. Internal capsule and pontine base were relatively well preserved in the N-HD, even at Stage IV, and the swollen axons were larger with a higher density in the ALSP. Microglial cells immunopositive for CD68, CD163 or CD204 were far more obvious in ALSP, than in N-HD, and the shape and density of the cells changed in each stage. With progression of the stage, clinical symptoms became worse to apathetic state, and epilepsy was frequently observed in patients at Stages III and IV in both diseases. From these findings, it is concluded that (i) shape, density and subsets of microglia change dynamically along the passage of stages and (ii) increase of IBA-1-, CD68-, CD163- and CD204-immunopositive cells precedes loss of axons in ALSP.

Characterization of spheroids in hereditary diffuse leukoencephalopathy with axonal spheroids.

Hereditary diffuse leukoencephalopathy with axonal spheroids (HDLS) is a neurodegenerative disease clinically characterized by slowly progressive cognitive decline and motor dysfunction. Neuropathology shows diffuse degeneration in the white matter, with prominent presence of widespread axonal spheroids. To investigate the mechanism underlying HDLS neurodegeneration, we characterized spheroids and examined their development in the degenerated white matter. Analysis revealed that the spheroids are an early neuropathological manifestation in the white matter degeneration and involve axonal component proteins and α-synuclein. The development of spheroids facilitates in initiating neurodegeneration in HDLS.

ß-III Tubulin fragments inhibit α-synuclein accumulation in models of multiple system atrophy.

Multiple system atrophy (MSA) is a neurodegenerative disease caused by α-synuclein aggregation in oligodendrocytes and neurons. Using a transgenic mouse model overexpressing human α-synuclein in oligodendrocytes, we previously demonstrated that oligodendrocytic α-synuclein inclusions induce neuronal α-synuclein accumulation and progressive neuronal degeneration. α-Synuclein binds to ß-III tubulin, leading to the neuronal accumulation of insoluble α-synuclein in an MSA mouse model. The present study demonstrates that α-synuclein co-localizes with ß-III tubulin in the brain tissue from patients with MSA and MSA model transgenic mice as well as neurons cultured from these mice. Accumulation of insoluble α-synuclein in MSA mouse neurons was blocked by the peptide fragment ß-III tubulin (residues 235-282). We have determined the α-synuclein-binding domain of ß-III tubulin and demonstrated that a short fragment containing this domain can suppress α-synuclein accumulation in the primary cultured cells. Administration of a short α-synuclein-binding fragment of ß-III tubulin may be a novel therapeutic strategy for MSA.

Corpus callosum atrophy in patients with hereditary diffuse leukoencephalopathy with neuroaxonal spheroids: an MRI-based study.

OBJECTIVE: Hereditary diffuse leukoencephalopathy with neuroaxonal spheroids (HDLS) is an adult-onset white matter disease that presents clinically with cognitive, mental and motor dysfunction. Several autopsy reports have indicated that the corpus callosum (CC), the largest bundle of white matter, is severely affected in patients with HDLS. The aim of this study was to evaluate corpus callosum atrophy (CCA) quantitatively in HDLS patients. METHODS: We assessed CCA in six genetically-proven HDLS patients (HDLS group), in comparison with that observed in 20 patients with vascular dementia (VaD group) and 24 age-matched patients without organic central nervous system (CNS) disease (non-CNS group). Using midsagittal MR images, five measurements of the CC were obtained: the width of the rostrum (aa'), body (bb') and splenium (cc'), the anterior to posterior length (ab) and the maximum height (cd). Next, the corpus callosum index (CCI) was calculated as (aa' + bb' + cc')/ab. RESULTS: All HDLS patients had white matter lesions in the CC and frontoparietal lobes on the initial MRI scans. Compared with that observed in the VaD and age-matched non-CNS groups, the CCI was significantly decreased in the HDLS group (with VaD group, p<0.01; with non-CNS group, p<0.01). CONCLUSION: This study showed significant atrophy of the CC in all HDLS patients on the initial MRI scans obtained 6-36 months after onset. We propose that the early appearance of CCA, frequently accompanied by high-intensity in the genu and/or splenium, on T2 images is an important diagnostic clue to HDLS.

Cystatin C triggers neuronal degeneration in a model of multiple system atrophy.

Multiple system atrophy is an intractable neurodegenerative disease caused by α-synuclein (α-syn) accumulation in oligodendrocytes and neurons. With the use of a transgenic mouse model overexpressing human α-syn in oligodendrocytes, we demonstrated that oligodendrocytic α-syn inclusions induce neuronal α-syn accumulation, resulting in progressive neuronal degeneration. The mechanism through which oligodendrocytic α-syn inclusions trigger neuronal α-syn accumulation leading to multiple system atrophy is unknown. In this study, we identified cystatin C, an oligodendrocyte-derived secretory protein that triggers α-syn up-regulation and insoluble α-syn accumulation, in neurons of the mouse central nervous system. Cystatin C was released by mouse oligodendrocytes overexpressing human α-syn, and extracellular cystatin C increased the expression of the endogenous α-syn gene in wild-type mouse neurons. These neurons then accumulate insoluble α-syn and may undergo apoptosis. Cystatin C is a potential pathogenic signal triggering neurodegeneration in multiple system atrophy.

Increased aggregation of polyleucine compared with that of polyglutamine in dentatorubral-pallidoluysian atrophy protein.

Polyglutamine (polyQ) diseases result from expansion of CAG trinucleotide repeats in their responsible genes. Although gene products with polyQ expansions undergo conformational changes to aggregate in neurons, the relationship between inclusions and neurotoxicity remains unclear. Dentatorubral-pallidoluysian atrophy (DRPLA) is a polyQ disease, and DRPLA protein, also known as atrophin-1 (ATN1), carries an expanded polyQ tract. To investigate how an expanded polyQ tract influences ATN1 aggregation and localization, we compared the aggregation of ATN1 with a polyQ tract to that of ATN1 with a polyleucine (polyL) tract. In COS-7 cells, polyL-ATN1 triggered more aggregation than polyQ-ATN1 of similar repeat sizes. Immunocytochemical and biochemical studies revealed that replacement of the polyQ tract with polyL alters ATN1 localization, leading to retention of polyL-ATN1 in the cytoplasm. Despite this change in localization, polyL-ATN1 and polyQ-ATN1 demonstrate comparable repeat length dependent toxicity. These results suggest that expanded polyQ repeats in ATN1 may contribute to neurodegeneration via alterations in both protein aggregation and intracellular localization.

α-Synuclein accumulation reduces GABAergic inhibitory transmission in a model of multiple system atrophy.

Multiple system atrophy is a neurodegenerative disease caused by abnormal α-synuclein (α-syn) accumulation in oligodendrocytes and neurons. We previously demonstrated that transgenic (Tg) mice that selectively overexpressed human α-syn in oligodendrocytes exhibited neuronal α-syn accumulation. Microtubule ß-III tubulin binds to endogenous neuronal α-syn to form an insoluble complex, leading to progressive neuronal degeneration. α-Syn accumulation is increased in the presynaptic terminals of Tg mice neurons and may reduce neurotransmitter release. To clarify the mechanisms underlying its involvement in neuronal dysfunction, in the present study, we investigated the effects of neuronal α-syn accumulation on synaptic function in Tg mice. Using whole-cell patch-clamp recording, we found that the frequency of miniature inhibitory postsynaptic currents was reduced in Tg mice. Furthermore, a microtubule depolymerizing agent restored normal frequencies of miniature inhibitory postsynaptic currents in Tg mice. These findings suggest that α-syn and ß-III tubulin protein complex plays roles for regulation of synaptic vesicle release in GABAergic interneurons, and it causes to reduce GABAergic inhibitory transmission.

Binding of neuronal α-synuclein to ß-III tubulin and accumulation in a model of multiple system atrophy.

Multiple system atrophy (MSA) is a neurodegenerative disease caused by α-synuclein (α-syn) accumulation in oligodendrocytes and neurons. We generated a transgenic (Tg) mouse model in which human α-syn was overexpressed in oligodendrocytes. Our previous studies have revealed that oligodendrocytic α-syn inclusions induced neuronal α-syn accumulation, thereby resulting in progressive neuronal degeneration in mice. We also demonstrated that an insoluble complex of α-syn and ß-III tubulin in microtubules progressively accumulated in neurons, thereby leading to neuronal degeneration. In the present study, we demonstrated that neuronal accumulation of the insoluble complex was derived from binding of α-syn to ß-III tubulin and not from α-syn self-aggregation. Thus, interaction between α-syn and ß-III tubulin plays an important role in neuronal α-syn accumulation in an MSA mouse model.

Pathological accumulation of atrophin-1 in dentatorubralpallidoluysian atrophy.

Dentatorubral-pallidoluysian atrophy (DRPLA) is caused by the expansion of polyglutamine (polyQ) in atrophin-1 (ATN1), also known as DRPLA protein. ATN1 is ubiquitously expressed in the central nervous system (CNS), although selective regions of CNS are degenerated in DRPLA, and this selective neuronal damage gives rise to the specific clinical features of DRPLA. Accumulation of mutant ATN1 that carries an expanded polyQ tract seems to be the primary cause of DRPLA neurodegeneration, but it is still unclear how the accumulation of ATN1 leads to neu-rodegeneration. Recently, cleaved fragments of ATN1 were shown to accumulate in the disease models and the brain tissues of patients with DRPLA. Furthermore, proteolytic processing of ATN1 may regulate the intracellular localization of ATN1 and its fragments. Therefore, proteolytic processing of ATN1 may provide clues to disease pathogenesis and hopefully aid in the determination of molecular targets for effective therapeutic approaches for DRPLA.

Proteolytic processing regulates pathological accumulation in dentatorubral-pallidoluysian atrophy.

Dentatorubral-pallidoluysian atrophy is caused by polyglutamine (polyQ) expansion in atrophin-1 (ATN1). Recent studies have shown that nuclear accumulation of ATN1 and cleaved fragments with expanded polyQ is the pathological process underlying neurodegeneration in dentatorubral-pallidoluysian atrophy. However, the mechanism underlying the proteolytic processing of ATN1 remains unclear. In the present study, we examined the proteolytic processing of ATN1 aiming to understand the mechanisms of ATN1 accumulation with polyQ expansion. Using COS-7 and Neuro2a cells that express the ATN1 gene, in which ATN1 was accumulated by increasing the number of polyQs, we identified a novel C-terminal fragment containing a polyQ tract. The mutant C-terminal fragment with expanded polyQ selectively accumulated in the cells, and this was also demonstrated in the brain tissues of patients with dentatorubral-pallidoluysian atrophy. Immunocytochemical and biochemical studies revealed that full-length ATN1 and C-terminal fragments displayed individual localization. The mutant C-terminal fragment was preferentially found in the cytoplasmic membrane/organelle and insoluble fractions. Accordingly, it is assumed that the proteolytic processing of ATN1 regulates the localization of C-terminal fragments. Accumulation of the C-terminal fragment was enhanced by inhibition of caspases in the cytoplasm of COS-7 cells. Collectively, these results suggest that the C-terminal fragment plays a principal role in the pathological accumulation of ATN1 in dentatorubral-pallidoluysian atrophy.

Microtubule depolymerization suppresses alpha-synuclein accumulation in a mouse model of multiple system atrophy.

Multiple system atrophy (MSA) is a neurodegenerative disease caused by an accumulation of alpha-synuclein (alpha-syn) in oligodendrocytes. Little is known about the cellular mechanisms by which alpha-syn accumulation causes neuronal degeneration in MSA. Our previous research, however, revealed that in a mouse model of MSA, oligodendrocytic inclusions of alpha-syn induced neuronal accumulation of alpha-syn, as well as progressive neuronal degeneration. Here we identify the mechanisms that underlie neuronal accumulation of alpha-syn in a mouse MSA model. We found that the alpha-syn protein binds to beta-III tubulin in microtubules to form an insoluble complex. The insoluble alpha-syn complex progressively accumulates in neurons and leads to neuronal dysfunction. Furthermore, we demonstrated that the neuronal accumulation of insoluble alpha-syn is suppressed by treatment with a microtubule depolymerizing agent. The underlying pathological process appeared to also be inhibited by this treatment, providing promise for future therapeutic approaches.

Severe neurological phenotypes of Q129 DRPLA transgenic mice serendipitously created by en masse expansion of CAG repeats in Q76 DRPLA mice.

We herein provide a thorough description of new transgenic mouse models for dentatorubral-pallidoluysian atrophy (DRPLA) harboring a single copy of the full-length human mutant DRPLA gene with 76 and 129 CAG repeats. The Q129 mouse line was unexpectedly obtained by en masse expansion based on the somatic instability of 76 CAG repeats in vivo. The mRNA expression levels of both Q76 and Q129 transgenes were each 80% of that of the endogenous mouse gene, whereas only the Q129 mice exhibited devastating progressive neurological phenotypes similar to those of juvenile-onset DRPLA patients. Electrophysiological studies of the Q129 mice demonstrated age-dependent and region-specific presynaptic dysfunction in the globus pallidus and cerebellum. Progressive shrinkage of distal dendrites of Purkinje cells and decreased currents through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and gamma-aminobutyrate type A receptors in CA1 neurons were also observed. Neuropathological studies of the Q129 mice revealed progressive brain atrophy, but no obvious neuronal loss, associated with massive neuronal intranuclear accumulation (NIA) of mutant proteins with expanded polyglutamine stretches starting on postnatal day 4, whereas NIA in the Q76 mice appeared later with regional specificity to the vulnerable regions of DRPLA. Expression profile analyses demonstrated age-dependent down-regulation of genes, including those relevant to synaptic functions and CREB-dependent genes. These results suggest that neuronal dysfunction without neuronal death is the essential pathophysiologic process and that the age-dependent NIA is associated with nuclear dysfunction including transcriptional dysregulations. Thus, our Q129 mice should be highly valuable for investigating the mechanisms of disease pathogenesis and therapeutic interventions.

Convergence of heat shock protein 90 with ubiquitin in filamentous alpha-synuclein inclusions of alpha-synucleinopathies.

Heat shock proteins (Hsps) facilitate refolding of denatured polypeptides, but there is limited understanding about their roles in neurodegenerative diseases characterized by misfolded proteins. Because Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy are alpha-synucleinopathies characterized by filamentous alpha-synuclein (alpha-syn) inclusions, we assessed which Hsps might be implicated in these disorders by examining human brain samples, transgenic mouse models, and cell culture systems. Light and electron microscopic multiple-label immunohistochemistry showed Hsp90 was the predominant Hsp examined that co-localized with alpha-syn in Lewy bodies, Lewy neurites, and glial cell inclusions and that Hsp90 co-localized with alpha-syn filaments of Lewy bodies in PD. Hsp90 levels were most predominantly increased in PD brains, which correlated with increased levels of insoluble alpha-syn. These alterations in Hsp90 were recapitulated in a transgenic mouse model of PD-like alpha-syn pathologies. Cell culture studies also revealed that alpha-syn co-immunoprecipitated preferentially with Hsp90 and Hsc70 relative to other Hsps, and exposure of cells to proteasome inhibitors resulted in increased levels of Hsp90. These data implicate predominantly Hsp90 in the formation of alpha-syn inclusions in PD and related alpha-synucleinopathies.

Mouse model of multiple system atrophy alpha-synuclein expression in oligodendrocytes causes glial and neuronal degeneration.

Transgenic (Tg) mice overexpressing human wild-type alpha-synuclein in oligodendrocytes under the control of the 2,' 3'-cyclic nucleotide 3'-phosphodiesterase (CNP) promoter are shown here to recapitulate features of multiple system atrophy (MSA), including the accumulation of filamentous human alpha-synuclein aggregates in oligodendrocytes linked to their degeneration and autophagocytosis of myelin. Significantly, endogenous mouse alpha-synuclein also accumulated in normal and degenerating axons and axon terminals in association with oligodendroglia and neuron loss and slowly progressive motor impairments. Our studies demonstrate that overexpression of alpha-synuclein in oligodendrocytes of mice results in MSA-like degeneration in the CNS and that alpha-synuclein inclusions in oligodendrocytes participate in the degeneration of neurons in MSA.

[A case of skeletal muscle type very-long-chain-acyl CoA dehydrogenase(VLCAD) deficiency with repeated rhabdomyolysis].

We experienced a 24-year-old male patient with myalgia and myoglobuinuria followed by severe exercise from childhood. In 18 years old, he had severe myaglia after a long time-night trip by bus. He was diagnosed as acute renal failure induced by rhabdomyolysis and treated with hemodialysis. In 24 years old, he was admitted to our hospital because of repeated rhabdomyolysis. We performed muscle biopsy from right quadriceps femoris, however histological and immunohistochemistological studies were normal. Ischemic forearm exercise test showed the elevation of lactic acid in serum. Therefore, we performed the analysis of acylcarnitine in serum, and the measurement of enzyme in beta-oxidation in muscle and white blood cells. These showed the lack of very-long-chain-acyl coA dehydrogenase (VLCAD) activity. He was diagnosed as skeletal muscle type VLCAD deficiency. Under the guidance of high carbohydrate and low fat diet, creatine kinase was controlled around 400 IU/l. VLCAD deficiency is important to make a differential diagnosis of young cases with recurrent elevation of creatine kinase.

Histone H3 is aberrantly phosphorylated in glutamine-repeat diseases.

Double-labeling immunohistochemical studies staining with anti-ubiquitin and anti-phosphoserine antibodies and application of an enzymatic dephosphorylation technique reveal neuronal inclusions and affected nuclei to be aberrantly phosphorylated in brain tissues with patients with glutamine-repeat diseases. Regional distribution of the phosphorylated nuclei in neurons correlates with the pathology. To identify the target nuclear protein, transient expression of Huntington's disease exon 1 gene containing an expanded glutamine repeat was generated in a cell culture and nuclear inclusions were isolated with a fluorescence-activated cell sorting system. Immunoblotting studies of the aggregated nuclear proteins using anti-phosphoserine antibody demonstrate the protein of the aberrant phosphorylation as histone H3. The immunoblots of control and diseased brain tissues demonstrate that the phosphorylation of histone H3 is commonly increased in the diseased brains. Aberrant phosphorylation of histone H3 is surmised to be a shared pathological process in glutamine-repeat diseases.

Ultrastructure of nuclear aggregates formed by expressing an expanded polyglutamine.

Intranuclear inclusions have been observed in the brains of patients affected with Huntington's disease (HD). Neuro 2A cells that transiently expressed HD exon 1 bearing 74 glutamine repeats linked to the green fluorescent protein (GFP) and the nuclear localization sequence (NLS) contained aggregates in nuclei. The aggregates were purified by fractionation with centrifugation followed by fluorescence-activated cell sorting (FACS). Heat treatment of the aggregate in an SDS sample buffer caused the dense aggregate cores to disappear and generated a basket-like structure composed of fibrils. Biochemical analysis of the aggregates revealed that the HD exon 1-GFP fusion protein was the major component. The heterogeneous nuclear ribonucleoproteins F and H, histones and ubiquitin were found to be associated with the aggregates. Our observations suggest that the N-terminal fragment of huntingtin may organize the skeletal structure of the aggregates and may disturb normal cellular functions by trapping other proteins within the aggregates.