Formation Of Intranuclear Inclusions Research Articles

Neuronal Intranuclear Inclusion Disease with a Corneal Disorder: A Case Report

Background: Neuronal intranuclear inclusion disease (NIID) is a progressive neurodegenerative disorder characterized by the formation of intranuclear inclusions in cells. Adult-type NIID usually develops in elderly patients with various clinical manifestations and is sometimes accompanied by ocular symptoms. A case of adult-onset NIID with early and unique manifestations, including a progressive corneal defect and retinal changes, which are concerning at a young age, is reported. Case Presentation: A 29-year-old woman with adult sporadic NIID presented to our department with a progressive corneal disorder. Her neurological symptoms started at the age of 22 years, and she was diagnosed with NIID by skin biopsy and genetic testing. Ocular examination revealed bilateral corneal superficial punctate keratitis, right corneal opacity, decreased vision, nocturnal lagophthalmos, and early retinal changes. Corneal nerve fiber atrophy was detected by in vivo confocal microscopy. With a Cochet–Bonnet aesthesiometer, the progression of NIID and decreased corneal sensation were confirmed. Findings consistent with neurotrophic keratitis and keratoconjunctivitis due to nocturnal lagophthalmos were both suggested as being complications of her underlying NIID. Treatment with punctal plugs, sodium hyaluronate eye drops, diquafosol sodium eye drops, systemic and local antivirals, and local steroid medications resulted in the gradual improvement in the irregularity and opacity of the epithelium. Conclusions: NIID may lead to neurotrophic keratopathy due to impairment of the corneal sensory nerves. Nocturnal lagophthalmos is a remarkable finding in a case of NIID. The findings in the present case highlight the complex and multifaceted nature of NIID, with neurological and ocular manifestations requiring a multidisciplinary approach to management.

Pathologic changes in neuronal intranuclear inclusion disease are linked to aberrant FUS interaction under hyperosmotic stress

CGG repeat expansion in NOTCH2NLC is the genetic cause of neuronal intranuclear inclusion disease (NIID). Previous studies indicated that the CGG repeats can be translated into polyglycine protein (N2CpolyG) which was toxic to neurons by forming intranuclear inclusions (IIs). However, little is known about the factors governing polyG IIs formation as well as its molecular pathogenesis. Considering that neurogenetic disorders usually involve interactions between genetic and environmental stresses, we investigated the effect of stress on the formation of IIs. Our results revealed that under hyperosmotic stress, N2CpolyG translocated from the cytoplasm to the nucleus and formed IIs in SH-SY5Y cells, recapitulating the pathological hallmark of NIID patients. Furthermore, N2CpolyG interacted/ co-localized with an RNA-binding protein FUS in the IIs of cellular model and NIID patient tissues, thereby disrupting stress granule formation in cytoplasm under hyperosmotic stress. Consequently, dysregulated expression of microRNAs was found both in NIID patients and cellular model, which could be restored by FUS overexpression in cultured cells. Overall, our findings indicate a mechanism of stress-induced pathological changes as well as neuronal damage, and a potential strategy for the treatment of NIID.

Trehalose consumption ameliorates pathogenesis in an inducible mouse model of the Fragile X-associated tremor/ataxia syndrome

ABSTRACT Trehalose is a naturally occurring sugar found in various food and pharmaceutical preparations with the ability to enhance cellular proteostasis and reduce the formation of toxic intracellular protein aggregates, making it a promising therapeutic candidate for various neurodegenerative disorders. Objectives Here, we explored the effectiveness of nutritional trehalose supplementation in ameliorating symptoms in a mouse model of Fragile X-associated tremor/ataxia syndrome (FXTAS), an incurable late onset manifestation of moderately expanded trinucleotide CGG repeat expansion mutations in the 5’ untranslated region of the fragile X messenger ribonucleoprotein 1 gene (FMR1). Methods An inducible mouse model of FXTAS expressing 90 CGG repeats in the brain had been previously developed, which faithfully captures hallmarks of the disorder, the formation of intracellular inclusions, and the disturbance of motor function. Taking advantage of the inducible nature of the model, we investigated the therapeutic potential of orally administered trehalose under two regimens, modelling disease prevention and disease treatment. Results and Discussion Trehalose's effectiveness in combating protein aggregation is frequently attributed to its ability to induce autophagy. Accordingly, trehalose supplementation under the prevention regimen ameliorated the formation of intranuclear inclusions and improved the motor deficiencies resulting from the induced expression of 90 CGG repeats, but it failed to reverse the existing nuclear pathology as a treatment strategy. Given the favorable safety profile of trehalose, it is promising to further explore the potential of this agent for early stage FXTAS.

Assessment of PABPN1 nuclear inclusions on a large cohort of patients and in a human xenograft model of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare muscle disease characterized by an onset of weakness in the pharyngeal and eyelid muscles. The disease is caused by the extension of a polyalanine tract in the Poly(A) Binding Protein Nuclear 1 (PABPN1) protein leading to the formation of intranuclear inclusions or aggregates in the muscle of OPMD patients. Despite numerous studies stressing the deleterious role of nuclear inclusions in cellular and animal OPMD models, their exact contribution to human disease is still unclear. In this study, we used a large and unique collection of human muscle biopsy samples to perform an in-depth analysis of PABPN1 aggregates in relation to age, genotype and muscle status with the final aim to improve our understanding of OPMD physiopathology. Here we demonstrate that age and genotype influence PABPN1 aggregates: the percentage of myonuclei containing PABPN1 aggregates increases with age and the chaperone HSP70 co-localize more frequently with PABPN1 aggregates with a larger polyalanine tract. In addition to the previously described PRMT1 and HSP70 co-factors, we identified new components of PABPN1 aggregates including GRP78/BiP, RPL24 and p62. We also observed that myonuclei containing aggregates are larger than myonuclei without. When comparing two muscles from the same patient, a similar amount of aggregates is observed in different muscles, except for the pharyngeal muscle where fewer aggregates are observed. This could be due to the peculiar nature of this muscle which has a low level of PAPBN1 and contains regenerating fibers. To confirm the fate of PABPN1 aggregates in a regenerating muscle, we generated a xenograft model by transplanting human OPMD muscle biopsy samples into the hindlimb of an immunodeficient mouse. Xenografts from subjects with OPMD displayed regeneration of human myofibers and PABPN1 aggregates were rapidly present—although to a lower extent-after muscle fiber regeneration. Our data obtained on human OPMD samples add support to the dual non-exclusive models in OPMD combining toxic PABPN1 intranuclear inclusions together with PABPN1 loss of function which altogether result in this late-onset and muscle selective disease.

TMT-based quantitative proteomics analysis reveals the role of Notch signaling in FAdV-4-infected LMH cell.

Fowl adenovirus serotype 4 (FAdV-4) is recognized as a pathogen that causes hydropericardium syndrome. Irrespective of the pathway used by the virus to invade the chicken, the pathological characteristics of the disease include degeneration and necrosis of hepatocytes, formation of intranuclear inclusions, as well as inflammatory cell infiltration. Liver dysfunction constitutes one of the critical factors leading to death. Therefore, it is vital to investigate the virus-mediated severe pathological liver damage to further understand the pathogenesis of FAdV-4. Here, proteomics, a tandem mass tag (TMT)-based approach to directly analyze protein expression, was used to determine the protein expression during FAdV-4 proliferation in leghorn male hepatoma (LMH) cells. We identified 177 differentially expressed proteins associated with various biological processes and pathways. The functional enrichment analysis revealed that FAdV-4 could downregulate some signaling pathways in LMH cells, including NOD-like receptor signaling, RIG-I-like receptor signaling, NF-κB signaling, TNF signaling pathway, and Notch signaling, FoxO signaling, PI3K-Akt signaling, and autophagy. The results of proteomics screening suggested an association between FAdV-4 infection and Notch signaling in LMH in vitro, indicating that Notch signaling regulated the expression of inflammatory cytokines and interferons but not viral replication in LMH cells. These data contributed to the understanding of the immunopathogenesis and inflammopathogenesis of FAdV-4 infection and also provided valuable information for the further analysis of the molecular mechanisms underlying viral pathogenesis.

Expression of mutant exon 1 huntingtin fragments in human neural stem cells and neurons causes inclusion formation and mitochondrial dysfunction.

Robust cellular models are key in determining pathological mechanisms that lead to neurotoxicity in Huntington's disease (HD) and for high throughput pre‐clinical screening of potential therapeutic compounds. Such models exist but mostly comprise non‐human or non‐neuronal cells that may not recapitulate the correct biochemical milieu involved in pathology. We have developed a new human neuronal cell model of HD, using neural stem cells (ReNcell VM NSCs) stably transduced to express exon 1 huntingtin (HTT) fragments with variable length polyglutamine (polyQ) tracts. Using a system with matched expression levels of exon 1 HTT fragments, we investigated the effect of increasing polyQ repeat length on HTT inclusion formation, location, neuronal survival, and mitochondrial function with a view to creating an in vitro screening platform for therapeutic screening. We found that expression of exon 1 HTT fragments with longer polyQ tracts led to the formation of intra‐nuclear inclusions in a polyQ length‐dependent manner during neurogenesis. There was no overt effect on neuronal viability, but defects of mitochondrial function were found in the pathogenic lines. Thus, we have a human neuronal cell model of HD that may recapitulate some of the earliest stages of HD pathogenesis, namely inclusion formation and mitochondrial dysfunction.

Astroglial-targeted expression of the fragile X CGG repeat premutation in mice yields RAN translation, motor deficits and possible evidence for cell-to-cell propagation of FXTAS pathology

The fragile X premutation is a CGG trinucleotide repeat expansion between 55 and 200 repeats in the 5′-untranslated region of the fragile X mental retardation 1 (FMR1) gene. Human carriers of the premutation allele are at risk of developing the late-onset neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS). Characteristic neuropathology associated with FXTAS includes intranuclear inclusions in neurons and astroglia. Previous studies recapitulated these histopathological features in neurons in a knock-in mouse model, but without significant astroglial pathology. To determine the role of astroglia in FXTAS, we generated a transgenic mouse line (Gfa2-CGG99-eGFP) that selectively expresses a 99-CGG repeat expansion linked to an enhanced green fluorescent protein (eGFP) reporter in astroglia throughout the brain, including cerebellar Bergmann glia. Behaviorally these mice displayed impaired motor performance on the ladder-rung test, but paradoxically better performance on the rotarod. Immunocytochemical analysis revealed that CGG99-eGFP co-localized with GFAP and S-100ß, but not with NeuN, Iba1, or MBP, indicating that CGG99-eGFP expression is specific to astroglia. Ubiquitin-positive intranuclear inclusions were found in eGFP-expressing glia throughout the brain. In addition, intracytoplasmic ubiquitin-positive inclusions were found outside the nucleus in distal astrocyte processes. Intriguingly, intranuclear inclusions, in the absence of eGFP mRNA and eGFP fluorescence, were present in neurons of the hypothalamus and neocortex. Furthermore, intranuclear inclusions in both neurons and astrocytes displayed immunofluorescent labeling for the polyglycine peptide FMRpolyG, implicating FMRpolyG in the pathology found in Gfa2-CGG99 mice. Considered together, these results show that Gfa2-CGG99 expression in mice is sufficient to induce key features of FXTAS pathology, including formation of intranuclear inclusions, translation of FMRpolyG, and deficits in motor function.

Impaired Nuclear Export of Polyglutamine-Expanded Androgen Receptor in Spinal and Bulbar Muscular Atrophy

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by polyglutamine (polyQ) expansion in the androgen receptor (AR). Prior studies have highlighted the importance of AR nuclear localization in SBMA pathogenesis; therefore, in this study, we sought to determine the role of AR nuclear export in the pathological manifestations of SBMA. We demonstrate here that the nuclear export of polyQ-expanded AR is impaired, even prior to the formation of intranuclear inclusions of aggregated AR. Additionally, we find that promoting AR export with an exogenous nuclear export signal substantially reduces its aggregation and blocks hormone-induced toxicity. Moreover, we show that these protective effects are conferred by destabilization of the mutant protein due to an increase in proteasomal degradation of the cytoplasmic AR. Despite a growing body of evidence that global disruption of nucleo/cytoplasmic transport occurs in ALS and HD, our data suggest that no such global disruption occurs in models of SBMA; rather, AR-specific mechanisms, including reduced phosphorylation at Serine 650, are likely responsible for the impaired nuclear export of polyQ-expanded AR.

Molecular Imaging in Huntington's Disease.

Huntington's disease (HD) is a rare monogenic neurodegenerative disorder caused by a trinucleotide CAG repeat expansion in the huntingtin gene resulting in the formation of intranuclear inclusions of mutated huntingtin. The accumulation of mutated huntingtin leads to loss of GABAergic medium spiny neurons (MSNs); subsequently resulting in the development of chorea, cognitive dysfunction and psychiatric symptoms. Premanifest HD gene expansion carriers, provide a unique cohort to examine very early molecular changes, occurring before the development of overt symptoms, to elucidate disease pathophysiology and identify reliable biomarkers of HD progression. Positron emission tomography (PET) is a non-invasive molecular imaging technique allowing the evaluation of specific molecular targets in vivo. Selective PET radioligands provide invaluable tools to investigate the role of the dopaminergic system, brain metabolism, microglial activation, phosphodiesterase 10A, and cannabinoid, GABA, adenosine and opioid receptors in HD. PET has been employed to monitor disease progression aiming to identify a reliable biomarker to predict phenoconversion from premanifest to manifest HD.

The Inhibition of Heat Shock Protein 90 Facilitates the Degradation of Poly-Alanine Expanded Poly (A) Binding Protein Nuclear 1 via the Carboxyl Terminus of Heat Shock Protein 70-Interacting Protein.

BackgroundSince the identification of poly-alanine expanded poly(A) binding protein nuclear 1 (PABPN1) as the genetic cause of oculopharyngeal muscular dystrophy (OPMD), considerable progress has been made in our understanding of the pathogenesis of the disease. However, the molecular mechanisms that regulate the onset and progression of the disease remain unclear.ResultsIn this study, we show that PABPN1 interacts with and is stabilized by heat shock protein 90 (HSP90). Treatment with the HSP90 inhibitor 17-AAG disrupted the interaction of mutant PABPN1 with HSP90 and reduced the formation of intranuclear inclusions (INIs). Furthermore, mutant PABPN1 was preferentially degraded in the presence of 17-AAG compared with wild-type PABPN1 in vitro and in vivo. The effect of 17-AAG was mediated through an increase in the interaction of PABPN1 with the carboxyl terminus of heat shock protein 70-interacting protein (CHIP). The overexpression of CHIP suppressed the aggregation of mutant PABPN1 in transfected cells.ConclusionsOur results demonstrate that the HSP90 molecular chaperone system plays a crucial role in the selective elimination of abnormal PABPN1 proteins and also suggest a potential therapeutic application of the HSP90 inhibitor 17-AAG for the treatment of OPMD.

Chromosome substitution strain assessment of a Huntington's disease modifier locus.

Huntington’s disease (HD) is a dominant neurodegenerative disorder that is due to expansion of an unstable HTT CAG repeat for which genome-wide genetic scans are now revealing chromosome regions that contain disease-modifying genes. We have explored a novel human–mouse cross-species functional prioritisation approach, by evaluating the HD modifier 6q23–24 linkage interval. This unbiased strategy employs C57BL/6J (B6J) HdhQ111 knock-in mice, replicates of the HD mutation, and the C57BL/6J-chr10A/J/NaJ chromosome substitution strain (CSS10), in which only chromosome 10 (chr10), in synteny with the human 6q23–24 region, is derived from the A/J (AJ) strain. Crosses were performed to assess the possibility of dominantly acting chr10 AJ-B6J variants of strong effect that may modulate CAG-dependent HdhQ111/+ phenotypes. Testing of F1 progeny confirmed that a single AJ chromosome had a significant effect on the rate of body weight gain and in HdhQ111 mice the AJ chromosome was associated subtle alterations in somatic CAG instability in the liver and the formation of intra-nuclear inclusions, as well as DARPP-32 levels, in the striatum. These findings in relatively small cohorts are suggestive of dominant chr10 AJ-B6 variants that may modify effects of the CAG expansion, and encourage a larger study with CSS10 and sub-strains. This cross-species approach may therefore be suited to functional in vivo prioritisation of genomic regions harbouring genes that can modify the early effects of the HD mutation.Electronic supplementary materialThe online version of this article (doi:10.1007/s00335-014-9552-9) contains supplementary material, which is available to authorized users.

The design and delivery of a PKA inhibitory polypeptide to treat SCA1.

Spinocerebellar ataxia-1 (SCA1) is a neurodegenerative disease that primarily targets Purkinje cells (PCs) of the cerebellum. The exact mechanism of PC degeneration is unknown, however, it is widely believed that mutant ataxin-1 becomes toxic because of the phosphorylation of its serine 776 (S776) residue by cAMP-dependent protein kinase A (PKA). Therefore, to directly modulate mutant ATXN1 S776 phosphorylation and aggregation, we designed a therapeutic polypeptide to inhibit PKA. This polypeptide comprised of a thermally responsive elastin-like peptide (ELP) carrier, which increases peptide half-life, a PKA inhibitory peptide (PKI), and a cell-penetrating peptide (Synb1). We observed that our therapeutic polypeptide, Synb1-ELP-PKI, inhibited PKA activity at concentrations similar to the PKI peptide. Additionally, Synb1-ELP-PKI significantly suppressed mutant ATXN1 S776 phosphorylation and intranuclear inclusion formation in cell culture. Further, Synb1-ELP-PKI treatment improved SCA1 PC morphology in cerebellar slice cultures. Furthermore, the Synb1-ELP peptide carrier crossed the blood-brain barrier and localized to the cerebellum via the i.p. or intranasal route. Here, we show the intranasal delivery of ELP-based peptides to the brain as a novel delivery strategy. We also demonstrate that our therapeutic polypeptide has a great potential to target the neurotoxic S776 phosphorylation pathway in the SCA1 disease.

Intranuclear Aggregation of Mutant FUS/TLS as a Molecular Pathomechanism of Amyotrophic Lateral Sclerosis

Dominant mutations in FUS/TLS cause a familial form of amyotrophic lateral sclerosis (fALS), where abnormal accumulation of mutant FUS proteins in cytoplasm has been observed as a major pathological change. Many of pathogenic mutations have been shown to deteriorate the nuclear localization signal in FUS and thereby facilitate cytoplasmic mislocalization of mutant proteins. Several other mutations, however, exhibit no effects on the nuclear localization of FUS in cultured cells, and their roles in the pathomechanism of fALS remain obscure. Here, we show that a pathogenic mutation, G156E, significantly increases the propensities for aggregation of FUS in vitro and in vivo. Spontaneous in vitro formation of amyloid-like fibrillar aggregates was observed in mutant but not wild-type FUS, and notably, those fibrils functioned as efficient seeds to trigger the aggregation of wild-type protein. In addition, the G156E mutation did not disturb the nuclear localization of FUS but facilitated the formation of intranuclear inclusions in rat hippocampal neurons with significant cytotoxicity. We thus propose that intranuclear aggregation of FUS triggered by a subset of pathogenic mutations is an alternative pathomechanism of FUS-related fALS diseases.

Ubiquitin‐related proteins in neuronal and glial intranuclear inclusions in intranuclear inclusion body disease

Recent studies have shown that eosinophilic intranuclear inclusions (INI) in the brain of patients with intranuclear inclusion body disease (INIBD) are immunopositive for ubiquitin and ubiquitin-related proteins (URP). However, the extent and frequency of URP-immunoreactive inclusions in INIBD are uncertain. We immunohistochemically examined the brain, spinal cord and dorsal root ganglia from five patients with INIBD, using a virtual slide system with sequential staining of the same sections with hematoxylin and eosin and by immunolabeling with antibodies against ubiquitin and URP (NEDD8, NUB1, SUMO-1 and SUMO-2). Intranuclear inclusions were widely distributed in neurons and glial cells in all the cases. Sequential staining revealed that 100% of INI in neurons and glial cells were positive for ubiquitin. Moreover, the majority or a significant proportion of INI were positive for NEDD8, NUB1, SUMO-1 and SUMO-2. However, the proportions of NEDD8-, NUB1- and SUMO-1-positive inclusions were significantly higher in neurons than in glial cells (P < 0.05). These findings suggest that proteins related to ubiquitination and proteasomal degradation are involved in the formation of INI in INIBD.

Reprogramming Huntington Monkey Skin Cells into Pluripotent Stem Cells

Induced pluripotent Huntington's disease monkey stem cells (rHD-iPSCs) were established by the overexpression of rhesus macaque transcription factors (Oct4, Sox2, and Klf4) in transgenic Huntington's monkey skin fibroblasts. The rHD-iPSCs were pluripotent and capable of differentiating into neuronal cell types in vitro and developed teratoma in immune compromised mice. We also demonstrated the upregulation of endogenous Oct4 and Sox2 after successful reprogramming to pluripotency in rHD-iPSCs, which was not expressed in skin fibroblasts. rHD-iPSCs also developed cellular features comparable to Huntington's disease (HD), including the accumulation of mutant huntingtin (htt) aggregate and the formation of intranuclear inclusions (NIs) paralleling neural differentiation in vitro. Induced pluripotent stem cells from transgenic HD monkeys open a new era of nonhuman primate modeling of human diseases. rHD-iPSCs that develop key HD cellular features and parallel neural differentiation can be a powerful platform for investigating the developmental impact on HD pathogenesis and developing new therapies, which can be evaluated in HD monkeys from whom the rHD-iPSCs were derived.

Monkey hybrid stem cells develop cellular features of Huntington's disease

BackgroundPluripotent stem cells that are capable of differentiating into different cell types and develop robust hallmark cellular features are useful tools for clarifying the impact of developmental events on neurodegenerative diseases such as Huntington's disease. Additionally, a Huntington's cell model that develops robust pathological features of Huntington's disease would be valuable for drug discovery research.ResultsTo test this hypothesis, a pluripotent Huntington's disease monkey hybrid cell line (TrES1) was established from a tetraploid Huntington's disease monkey blastocyst generated by the fusion of transgenic Huntington's monkey skin fibroblast and a wild-type non-transgenic monkey oocyte. The TrES1 developed key Huntington's disease cellular pathological features that paralleled neural development. It expressed mutant huntingtin and stem cell markers, was capable of differentiating to neural cells, and developed teratoma in severely compromised immune deficient (SCID) mice. Interestingly, the expression of mutant htt, the accumulation of oligomeric mutant htt and the formation of intranuclear inclusions paralleled neural development in vitro , and even mutant htt was ubiquitously expressed. This suggests the development of Huntington's disease cellular features is influenced by neural developmental events.ConclusionsHuntington's disease cellular features is influenced by neural developmental events. These results are the first to demonstrate that a pluripotent stem cell line is able to mimic Huntington's disease progression that parallels neural development, which could be a useful cell model for investigating the developmental impact on Huntington's disease pathogenesis.

Evidence for RNA-Mediated Toxicity in the Fragile X-Associated Tremor/Ataxia Syndrome

Fragile X premutation carriers are at risk for developing a late-onset, progressive neurodegenerative disorder termed fragile X-associated tremor/ataxia syndrome (FXTAS). A growing body of evidence suggests the characteristic excess CGG repeat containing FMR1 mRNA observed in premutation carriers is pathogenic and leads to clinical features of FXTAS. The current model suggests premutation mRNA transcripts can induce the formation of intranuclear inclusions by the sequestration of RNA-binding proteins and other proteins. The sequestered proteins are prevented from performing their normal functions, which is thought to lead to the neuropathology-observed FXTAS. This paper discusses the existing evidence that microsatellite expansions at the level of RNA play a role in the disease pathogenesis of FXTAS and some of the approaches that may uncover downstream effects of expanded riboCGG expression.

Phosphodiesterase type IV inhibition prevents sequestration of CREB binding protein, protects striatal parvalbumin interneurons and rescues motor deficits in the R6/2 mouse model of Huntington’s disease

The phosphodiesterase type IV inhibitor rolipram increases cAMP response element-binding protein (CREB) phosphorylation and exerts neuroprotective effects in both the quinolinic acid rat model of Huntington's disease (DeMarch et al., 2007) and the R6/2 mouse including sparing of striatal neurons, prevention of neuronal intranuclear inclusion formation and attenuation of microglial reaction (DeMarch et al., 2008). In this study, we sought to determine if rolipram has a beneficial role in the altered distribution of CREB binding protein in striatal spiny neurons and in the motor impairments shown by R6/2 mutants. Moreover, we investigated whether rolipram treatment altered the degeneration of parvalbuminergic interneurons typical of Huntington's disease (Fusco et al., 1999). Transgenic mice and their wild-type controls from a stable colony maintained in our laboratory were treated with rolipram (1.5 mg/kg) or saline daily starting from 4 weeks of age. The cellular distribution of CREB binding protein in striatal spiny neurons was assessed by immunofluorescence, whereas parvalbuminergic neuron degeneration was evaluated by cell counts of immunohistochemically labeled tissue. Motor coordination and motor activity were also examined. We found that rolipram was effective in preventing CREB binding protein sequestration into striatal neuronal intranuclear inclusions, sparing parvalbuminergic interneurons of R6/2 mice, and rescuing their motor coordination and motor activity deficits. Our findings demonstrate the possibility of reversing pharmacologically the behavioral and neuropathological abnormalities of symptomatic R6/2 mice and underline the potential therapeutic value of phosphodiesterase type IV inhibitors in Huntington's disease.

Fragile X–Associated Tremor/Ataxia Syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-adult-onset neurodegenerative disorder affecting primarily male (and occasionally female) carriers of a premutation expansion (55-200 CGG repeats) of the fragile X mental retardation 1 gene (FMR1). FXTAS is principally characterized as a movement disorder with progressive intention tremor and gait ataxia, with more variable associated features of parkinsonism, dysautonomia, peripheral neuropathy, and dementia. The pathogenic basis of FXTAS is overexpression of the expanded CGG repeat FMR1 RNA, which leads to neural cell dysregulation, formation of intra-nuclear inclusions in neurons and astrocytes, and disruption of the nuclear lamin architecture. By contrast, larger CGG repeat expansions (> 200 CGG repeats, full mutation) generally result in FMR1 silencing and absence of FMR1 RNA and protein (FMRP). The lack of FMRP is the pathogenic basis of the developmental disorder fragile X syndrome, the leading heritable form of mental impairment. Thus, the same gene presents 2 opposing faces: a neurodegenerative syndrome (FXTAS) in older adults, caused by excess gene activity and production of a toxic RNA, and a childhood-onset disorder (fragile X syndrome), caused by absence of gene activity. This review will focus on FXTAS, the aging face of the fragile X gene.

CAG repeat disorder models and human neuropathology: similarities and differences

CAG repeat diseases are hereditary neurodegenerative disorders caused by expansion of a polyglutamine tract in each respective disease protein. They include at least nine disorders, including Huntington's disease (HD), dentatorubral pallidoluysian atrophy (DRPLA), spinal and bulbar muscular atrophy (SBMA), and the spinocerebellar ataxias SCA1, SCA2, SCA3 (also known as Machado-Joseph disease), SCA6, SCA7, and SCA17. It is thought that a gain of toxic function resulting from the protein mutation plays important and common roles in the pathogenesis of these diseases. Recent studies have disclosed that, in addition to the presence of clinical phenotypes and conventional neuropathology in each disease, human brains affected by CAG repeat diseases share several polyglutamine-related changes in their neuronal nuclei and cytoplasm including the formation of intranuclear inclusions. Although these novel pathologic changes also show a distribution pattern characteristic to each disease, they are generally present beyond the lesion distribution of neuronal loss, suggesting that neurons are affected much more widely than has been recognized previously. Various mouse models of CAG repeat diseases have revealed that CAG repeat lengths, which are responsible for polyglutamine diseases in humans, are not sufficient for creating the conditions characteristic of each disease in mice. Although high expression of mutant proteins in mice results in the successful generation of polyglutamine-related changes in the brain, there are still some differences from human pathology in the lesion distribution or cell types that are affected. In addition, no model has yet successfully reproduced the specific neuronal loss observed in humans. Although there are no models that fully represent the neuropathologic changes present in humans, the data obtained have provided evidence that clinical onset is not clearly associated with neuronal cell death, but depends on intranuclear accumulation of mutant proteins in neurons.