Expression of expanded GGC repeats within NOTCH2NLC causes behavioral deficits and neurodegeneration in a mouse model of neuronal intranuclear inclusion disease

Heat-shock chaperone HSPB1 mitigates poly-glycine-induced neurodegeneration via restoration of autophagic flux

The CGG repeat expansions in the 5'-UTR regions of certain genes have been implicated in various neurodegenerative and muscular disorders. However, the underlying pathogenic mechanisms are not well understood. In this study, we explore the role of the small molecular chaperone HSPB1 in counteracting neurodegeneration induced by poly-glycine (poly-G) aggregates. Employing a reporter system, we demonstrate that CGG repeat expansions within the 5'-UTR of the GIPC1 gene produce poly-G proteins, by repeat-associated non-AUG (RAN) translation. Through proximity labeling and subsequent mass spectrometry analysis, we characterize the composition of poly-G insoluble aggregates and reveal that these aggregates sequester key macroautophagy/autophagy receptors, SQSTM1/p62 and TOLLIP. This sequestration disrupts MAP1LC3/LC3 recruitment and impairs autophagosome formation, thereby compromising the autophagic pathway. Importantly, we show that HSPB1 facilitates the dissociation of these receptors from poly-G aggregates and consequently restores autophagic function. Overexpressing HSPB1 alleviates poly-G-induced neurodegeneration in mouse models. Taken together, these findings highlight a mechanistic basis for the neuroprotective effects of HSPB1 and suggest its potential as a therapeutic target in treating poly-G-associated neurodegenerative diseases.Abbreviations: AD: Alzheimer disease; AIF1/Iba1: allograft inflammatory factor 1; Baf A1: bafilomycin A1; BFP: blue fluorescent protein; CQ: chloroquine; EIF2A/eIF-2α: eukaryotic translation initiation factor 2A; FRAP: fluorescence recovery after photobleaching; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary acidic protein; GFP: green fluorescent protein; HSPB1: heat shock protein family B (small) member 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; NOTCH2NLC: notch 2 N-terminal like C; PD: Parkinson disease; PFA: paraformaldehyde; poly-A: poly-alanine; poly-G: poly-glycine; poly-R: poly-arginine; RAN translation: repeat-associated non-AUG translation; RBFOX3/NeuN: RNA binding fox-1 homolog 3; STED: stimulated emission depletion; TARDBP/TDP-43: TAR DNA binding protein; TG: thapsigargin; TOLLIP: toll interacting protein.

Recent progress in oculopharyngodistal myopathy research from clinical and genetic viewpoints

Oculopharyngodistal myopathy (OPDM) is a rare muscular disorder characterized by ocular symptoms, pharyngeal symptoms, facial weakness, and distal predominant limb muscle weakness. The cause of the disease was unknown for a long time. Recently, however, it has been reported that expansions of CGG or CCG repeats in LRP12, LOC642361/NUTM2B-AS1, GIPC1, NOTCH2NLC, RILPL1, and ABCD3 are the causes of the disease. Cases sometimes present with neurological symptoms, and the clinical spectrum of diseases caused by expansions of CGG or CCG repeats has been proposed to be called FNOP-spectrum disorder after the names of fragile X-associated tremor/ataxia syndrome, neuronal intranuclear inclusion disease, oculopharyngeal myopathy with leukoencephalopathy, and OPDM. In this article, the recent progress in the field of OPDM is reviewed, and remaining issues in OPDM are discussed.

uN2CpolyG-mediated p65 nuclear sequestration suppresses the NF-κB-NLRP3 pathway in neuronal intranuclear inclusion disease

BACKGROUND

Neuronal intranuclear inclusion disease (NIID) is genetically linked to CGG repeat expansion in the 5'-untranslated region of the NOTCH2NLC gene, with nascent polyglycine-containing protein (uN2CpolyG) identified as a primary pathogenic factor. Emerging clinical evidence suggests that inflammation contributes to NIID pathogenesis, yet the underlying molecular mechanisms remain elusive. This study aimed to elucidate the molecular interaction between uN2CpolyG and the NF-κB-NLRP3 pathway.

METHODS

Single-cell RNA sequencing was conducted on the skin tissues of NIID patients to assess changes in the expression of genes involved in inflammatory pathways. Cell models (HEK-293T and U87-MG) transfected with CGG9/69/100 expansion vectors were used to investigate alterations in the NF-κB-NLRP3-autophagy pathway. Additionally, the therapeutic potential of NF-κB activators was evaluated in a Drosophila model with a CGG expansion knock-in.

RESULTS

Single-cell sequencing revealed a significant reduction in the expression of NFKBIA, encoding NF-κB inhibitor alpha (IkBa), which facilitates the nuclear translocation of p65, a key NF-κB component. uN2CpolyG directly interacted with and sequestered p65 in nuclear inclusions, leading to reduced phosphorylated p65 (p-p65) levels. This sequestration significantly downregulated the NF-κB-NLRP3 pathway, impairing autophagy, as indicated by decreased LC3II/LC3I ratios. Treatment of CGG100 cells with lipopolysaccharide (LPS) significantly increased p-p65, NLRP3, and LC3II/LC3I levels while reducing insoluble uN2CpolyG levels and intranuclear inclusions. In the Drosophila knock-in model, LPS significantly reduced the number of intranuclear inclusions and improved phenotypic manifestations.

CONCLUSIONS

This study revealed that uN2CpolyG directly interacts with and sequesters p65, thereby inhibiting the NF-κB-NLRP3 pathway and impairing autophagy. This mechanism highlights a novel therapeutic target for NIID and provides potentially broader insights into similar mechanisms in other neurodegenerative diseases characterized by misfolded protein aggregates.

NOTCH2NLC GGC intermediate repeat with serine induces hypermyelination and early Parkinson's disease-like phenotypes in mice

BACKGROUND

The expansion of GGC repeats (typically exceeding 60 repeats) in the 5' untranslated region (UTR) of the NOTCH2NLC gene (N2C) is linked to N2C-related repeat expansion disorders (NREDs), such as neuronal intranuclear inclusion disease (NIID), frontotemporal dementia (FTD), essential tremor (ET), and Parkinson's disease (PD). These disorders share common clinical manifestations, including parkinsonism, dementia, seizures, and muscle weakness. Intermediate repeat sizes ranging from 40 to 60 GGC repeats, particularly those with AGC-encoded serine insertions, have been reported to be associated with PD; however, the functional implications of these intermediate repeats with serine insertion remain unexplored.

METHODS

Here, we utilized cellular models harbouring different sizes of N2C variant 2 (N2C2) GGC repeat expansion and CRISPR-Cas9 engineered transgenic mouse models carrying N2C2 GGC intermediate repeats with and without serine insertion to elucidate the underlying pathophysiology associated with N2C intermediate repeat with serine insertion in NREDs.

RESULTS

Our findings revealed that the N2C2 GGC intermediate repeat with serine insertion (32G13S) led to mitochondrial dysfunction and cell death in vitro. The neurotoxicity was influenced by the length of the repeat and was exacerbated by the presence of the serine insertion. In 12-month-old transgenic mice, 32G13S intensified intranuclear aggregation and exhibited early PD-like characteristics, including the formation of α-synuclein fibers in the midbrain and the loss of tyrosine hydroxylase (TH)-positive neurons in both the cortex and striatum. Additionally, 32G13S induced neuronal hyperexcitability and caused locomotor behavioural impairments. Transcriptomic analysis of the mouse cortex indicated dysregulation in calcium signaling and MAPK signaling pathways, both of which are critical for mitochondrial function. Notably, genes associated with myelin sheath components, including MBP and MOG, were dysregulated in the 32G13S mouse. Further investigations using immunostaining and transmission electron microscopy revealed that the N2C intermediate repeat with serine induced mitochondrial dysfunction-related hypermyelination in the cortex.

CONCLUSIONS

Our in vitro and in vivo investigations provide the first evidence that the N2C-GGC intermediate repeat with serine promotes intranuclear aggregation of N2C, leading to mitochondrial dysfunction-associated hypermyelination and neuronal hyperexcitability. These changes contribute to motor deficits in early PD-like neurodegeneration in NREDs.

Evolutionarily new genes in humans with disease phenotypes reveal functional enrichment patterns shaped by adaptive innovation and sexual selection

New genes (or young genes) are genetic novelties pivotal in mammalian evolution. However, their phenotypic impacts and evolutionary patterns over time remain elusive in humans due to the technical and ethical complexities of functional studies. Integrating gene age dating with Mendelian disease phenotyping, our research shows a gradual rise in disease gene proportion as gene age increases. Logistic regression modeling indicates that this increase in older genes may be related to their longer sequence lengths and higher burdens of deleterious de novo germline variants (DNVs). We also find a steady integration of new genes with biomedical phenotypes into the human genome over macroevolutionary timescales (~0.07% per million years). Despite this stable pace, we observe distinct patterns in phenotypic enrichment, pleiotropy, and selective pressures across gene ages. Notably, young genes show significant enrichment in diseases related to the male reproductive system, indicating strong sexual selection. Young genes also exhibit disease-related functions in tissues and systems potentially linked to human phenotypic innovations, such as increased brain size, musculoskeletal phenotypes, and color vision. We further reveal a logistic growth pattern of pleiotropy over evolutionary time, indicating a diminishing marginal growth of new functions for older genes due to intensifying selective constraints over time. We propose a "pleiotropy-barrier" model that delineates higher potentials for phenotypic innovation in young genes compared to older genes, a process that is subject to natural selection. Our study demonstrates that evolutionarily new genes are critical in influencing human reproductive evolution and adaptive phenotypic innovations driven by sexual and natural selection, with low pleiotropy as a selective advantage.

Encephalitis-like episodes with cortical edema and enhancement in patients with neuronal intranuclear inclusion disease

OBJECTIVES

Neuronal intranuclear inclusion disease (NIID) exhibited significant clinical heterogeneities. However, the clinical features, radiographic changes, and prognosis of patients with encephalitis-like NIID have yet to be systematically elucidated.

METHODS

Clinical data including medical history, physical examination, and laboratory examinations were collected and analyzed. Skin and sural nerve biopsies were conducted on the patient. Repeat-primed PCR (RP-PCR) and fluorescence amplicon length PCR (AL-PCR) were used to detect the expansion of CGG repeat. We also reviewed the clinical and genetic data of NIID patients with cortical enhancement.

RESULTS

A 54-year-old woman presented with encephalitis-like NIID, characterized by severe headache and agitative psychiatric symptoms. The brain MRI showed cortical swelling in the temporo-occipital lobes and significant enhancement of the cortical surface and dura, but without hyperintensities along the corticomedullary junction on diffusion-weighted image (DWI). A biopsy of the sural nerve revealed a demyelinating pathological change. The intranuclear inclusions were detected in nerve and skin tissues using the p62 antibody and electron microscopy. RP-PCR and AL-PCR unveiled the pathogenic expansion of CGG repeats in the NOTCH2NLC gene. A review of the literature indicated that nine out of the 16 patients with cortical lesions and linear enhancement exhibited encephalitis-like NIID.

CONCLUSION

This study indicated that patients with encephalitis-like NIID typically exhibited headache and excitatory psychiatric symptoms, often accompanied by cortical edema and enhancement of posterior lobes, and responded well to glucocorticoid treatment. Furthermore, some patients may not exhibit hyperintensities along the corticomedullary junction on DWI, potentially leading to misdiagnosis.

A family with neuronal intranuclear inclusion disease with focal segmental glomerulosclerosis

BACKGROUND

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disease caused by the expansion of GGC repeats in the 5'-untranslated region (5'-UTR) of NOTCH2NLC. Although increasing evidence suggests that NIID affects various organs, its association with renal involvement remains unclear. We studied the genetic background of a family with NIID, in which four of five members presented with proteinuria as the initial manifestation. The renal pathology of three patients was diagnosed as focal segmental glomerulosclerosis (FSGS) at a previous hospital. These patients also presented with tremors, retinal degeneration, and episodic neurological events. Finally, one patient exhibited reversible bilateral thalamic high-intensity signal changes on diffusion-weighted imaging during episodic neurological events.

METHODS

Exome sequencing (ES) and nanopore long-read whole-genome sequencing (LR-WGS) were performed on the index case, followed by nanopore target sequencing using Cas9-mediated PCR-free enrichment and methylation analysis.

RESULTS

ES revealed no candidate variants; however, nanopore LR-WGS in the index case revealed expansion of short tandem repeats (STR) in NOTCH2NLC. Subsequent nanopore target sequencing using Cas9-mediated PCR-free enrichment showed STR expansion of NOTCH2NLC in an affected sibling and asymptomatic father. Methylation analysis using nanopore data revealed hypermethylation of the expanded allele in the asymptomatic father and partial hypermethylation in a mildly symptomatic sibling, whereas the expanded allele was hypomethylated in the index case.

CONCLUSIONS

This investigation expands the clinical spectrum of NIID, suggesting that STR expansion of NOTCH2NLC is a cause of renal diseases, including FSGS.

Microglia contribute to polyG-dependent neurodegeneration in neuronal intranuclear inclusion disease

Neuronal intranuclear inclusion disease (NIID) is a neurodegenerative disorder caused by the expansion of GGC trinucleotide repeats in NOTCH2NLC gene. Despite identifying uN2CpolyG, a toxic polyglycine (polyG) protein translated by expanded GGC repeats, the exact pathogenic mechanisms of NIID remain unclear. In this study, we investigated the role of polyG by expressing various forms of NOTCH2NLC in mice: the wild-type, the expanded form with 100 GGC repeats (either translating or not translating into uN2CpolyG), and the mutated form that encodes a pure polyG without GGC-repeat RNA and the C-terminal stretch (uN2CpolyG-dCT). Both uN2CpolyG and uN2CpolyG-dCT induced the formation of inclusions composed by filamentous materials and resulted in neurodegenerative phenotypes in mice, including impaired motor and cognitive performance, shortened lifespan, and pathologic lesions such as white-matter lesions, microgliosis, and astrogliosis. In contrast, expressing GGC-repeat RNA alone was non-pathogenic. Through bulk and single-nuclei RNA sequencing, we identified common molecular signatures linked to the expression of uN2CpolyG and uN2CpolyG-dCT, particularly the upregulation of inflammation and microglia markers, and the downregulation of immediate early genes and splicing factors. Importantly, microglia-mediated inflammation was visualized in NIID patients using positron emission tomography, correlating with levels of white-matter atrophy. Furthermore, microglia ablation ameliorated neurodegenerative phenotypes and transcriptional alterations in uN2CpolyG-expressing mice but did not affect polyG inclusions. Together, these results demonstrate that polyG is crucial for the pathogenesis of NIID and highlight the significant role of microglia in polyG-induced neurodegeneration.

Deep learning-enhanced R-loop prediction provides mechanistic implications for repeat expansion diseases

R-loops play diverse functional roles, but controversial genomic localization of R-loops have emerged from experimental approaches, posing significant challenges for R-loop research. The development and application of an accurate computational tool for studying human R-loops remains an unmet need. Here, we introduce DeepER, a deep learning-enhanced R-loop prediction tool. DeepER showcases outstanding performance compared to existing tools, facilitating accurate genome-wide annotation of R-loops and a deeper understanding of the position- and context-dependent effects of nucleotide composition on R-loop formation. DeepER also unveils a strong association between certain tandem repeats and R-loop formation, opening a new avenue for understanding the mechanisms underlying some repeat expansion diseases. To facilitate broader utilization, we have developed a user-friendly web server as an integral component of R-loopBase. We anticipate that DeepER will find extensive applications in the field of R-loop research.

Clinical features of neuronal intranuclear inclusion disease with seizures: a systematic literature review

Background

Infant, junior, and adult patients with neuronal intranuclear inclusion disease (NIID) present with various types of seizures. We aimed to conduct a systematic literature review on the clinical characteristics of NIID with seizures to provide novel insight for early diagnosis and treatment and to improve prognosis of these patients.

Methods

We used keywords to screen articles related to NIID and seizures, and data concerning the clinical characteristics of patients, including demographic features, disease characteristics of the seizures, treatment responses, imaging examinations, and other auxiliary examination results were extracted.

Results

The included studies comprised 21 patients with NIID with seizures. The most common clinical phenotypes were cognitive impairment (76.20%) and impaired consciousness (57.14%), and generalized onset motor seizures (46.15%) represented the most common type. Compared with infantile and juvenile cases, the use of antiepileptic drugs in adults led to significant seizure control and symptom improvement, in addition to providing a better prognosis. The number of GGC sequence repeats in the NOTCH2NLC gene in six NIID patients with seizures who underwent genetic testing ranged 72-134.

Conclusion

The most common clinical phenotypes in patients with NIID with seizures were cognitive impairment and consciousness disorders. Patients with NIID presented with various types of seizures, with the most common being generalized onset motor seizures. Adult patients had a better prognosis and were relatively stable. The early diagnosis of NIID with seizures is of great significance for treatment and to improve prognosis.

Review of Phenotypic Heterogeneity of Neuronal Intranuclear Inclusion Disease and NOTCH2NLC-Related GGC Repeat Expansion Disorders

Neuronal intranuclear inclusion disease (NIID) is an underdiagnosed neurodegenerative disorder caused by pathogenic GGC expansions in NOTCH2NLC. However, an increasing number of reports of NOTCH2NLC GGC expansions in patients with Alzheimer disease, essential tremor, Parkinson disease, amyotrophic lateral sclerosis, and oculopharyngodistal myopathy have led to the proposal of a new concept known as NOTCH2NLC-related GGC repeat expansion disorders (NREDs). The majority of studies have mainly focused on screening for NOTCH2NLC GGC repeat variation in populations previously diagnosed with the associated disease, subsequently presenting it as a novel causative gene for the condition. These studies appear to be clinically relevant but do have their limitations because they may incorrectly regard the lack of MRI abnormalities as an exclusion criterion for NIID or overlook concomitant clinical presentations not typically observed in the associated diseases. Besides, in many instances within these reports, patients lack pathologic evidence or undergo long-term follow-up to conclusively rule out NIID. In this review, we will systematically review the research on NOTCH2NLC 5' untranslated region GGC repeat expansions and their association with related neurologic disorders, explaining the limitations of the relevant reports. Furthermore, we will integrate subsequent studies to further demonstrate that these patients actually experienced distinct clinical phenotypes of NIID.

GGC expansions in NOTCH2NLC contribute to Parkinson disease and dopaminergic neuron degeneration

BACKGROUND AND PURPOSE

The role of GGC repeat expansions within NOTCH2NLC in Parkinson's disease (PD) and the substantia nigra (SN) dopaminergic neuron remains unclear. Here, we profile the NOTCH2NLC GGC repeat expansions in a large cohort of patients with PD. We also investigate the role of GGC repeat expansions within NOTCH2NLC in the dopaminergic neurodegeneration of SN.

METHODS

A total of 2,522 patients diagnosed with PD and 1,085 health controls were analyzed for the repeat expansions of NOTCH2NLC by repeat-primed PCR and GC-rich PCR assay. Furthermore, the effects of GGC repeat expansions in NOTCH2NLC on dopaminergic neurons were investigated by using recombinant adeno-associated virus (AAV)-mediated overexpression of NOTCH2NLC with 98 GGC repeats in the SN of mice by stereotactic injection.

RESULTS

Four PD pedigrees (4/333, 1.2%) and three sporadic PD patients (3/2189, 0.14%) were identified with pathogenic GGC repeat expansions (larger than 60 GGC repeats) in the NOTCH2NLC gene, while eight PD patients and one healthy control were identified with intermediate GGC repeat expansions ranging from 41 to 60 repeats. No significant difference was observed in the distribution of intermediate NOTCH2NLC GGC repeat expansions between PD cases and controls (Fisher's exact test p-value = 0.29). Skin biopsy showed P62-positive intranuclear NOTCH2NLC-polyGlycine (polyG) inclusions in the skin nerve fibers of patient. Expanded GGC repeats in NOTCH2NLC produced widespread intranuclear and perinuclear polyG inclusions, which led to a severe loss of dopaminergic neurons in the SN. Consistently, polyG inclusions were presented in the SN of EIIa-NOTCH2NLC-(GGC)98 transgenic mice and also led to dopaminergic neuron loss in the SN.

CONCLUSIONS

Overall, our findings provide strong evidence that GGC repeat expansions within NOTCH2NLC contribute to the pathogenesis of PD and cause degeneration of nigral dopaminergic neurons.

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.

Evolutionarily new genes in humans with disease phenotypes reveal functional enrichment patterns shaped by adaptive innovation and sexual selection

New genes (or young genes) are structural novelties pivotal in mammalian evolution. Their phenotypic impact on humans, however, remains elusive due to the technical and ethical complexities in functional studies. Through combining gene age dating with Mendelian disease phenotyping, our research reveals that new genes associated with disease phenotypes steadily integrate into the human genome at a rate of ~ 0.07% every million years over macroevolutionary timescales. Despite this stable pace, we observe distinct patterns in phenotypic enrichment, pleiotropy, and selective pressures between young and old genes. Notably, young genes show significant enrichment in the male reproductive system, indicating strong sexual selection. Young genes also exhibit functions in tissues and systems potentially linked to human phenotypic innovations, such as increased brain size, bipedal locomotion, and color vision. Our findings further reveal increasing levels of pleiotropy over evolutionary time, which accompanies stronger selective constraints. We propose a "pleiotropy-barrier" model that delineates different potentials for phenotypic innovation between young and older genes subject to natural selection. Our study demonstrates that evolutionary new genes are critical in influencing human reproductive evolution and adaptive phenotypic innovations driven by sexual and natural selection, with low pleiotropy as a selective advantage.

Expression of expanded GGC repeats within NOTCH2NLC causes cardiac dysfunction in mouse models

BACKGROUND

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder characterized by widespread intranuclear inclusions in the nervous system as well as multiple visceral organs. In 2019, expanded GGC repeats within the 5' untranslated region of the NOTCH2NLC gene was identified as the causative factor. NIID is a heterogeneous disorder with variable clinical manifestations including cognitive impairment, cerebellar ataxia, parkinsonism, paroxysmal symptoms, autonomic dysfunction, and muscle weakness. Although NIID primarily affects the central and peripheral nervous systems, growing evidence suggests potential cardiac abnormalities in NIID. However, the link between expanded GGC repeats within NOTCH2NLC and cardiac dysfunction remains uncertain.

RESULTS

In this study, we utilized two transgenic mouse models, expressing NOTCH2NLC-(GGC)98 ubiquitously or specifically in cardiomyocytes, and identified p62 (also known as sequestosome 1, SQSTM1)-positive intranuclear NOTCH2NLC-polyG inclusions in cardiomyocytes in two mouse models. We observed that both models exhibited cardiac-related pathological and echocardiographic changes, albeit exhibiting varying degrees of severity. Transcriptomic analysis revealed shared downregulation of genes related to ion channels and mitochondria in both models, with the cardiomyocyte-specific mice showing a more pronounced downregulation of mitochondria and energy metabolism-related pathways. Further investigations revealed decreased expression of mitochondria-related genes and electron transport chain activity. At last, we conducted a retrospective review of cardiac-related examination results from NIID patients at our hospital and also identified some cardiac abnormalities in NIID patients.

CONCLUSIONS

Our study provided the first in vivo evidence linking GGC repeat expansions within NOTCH2NLC to cardiac abnormalities and highlighted the contribution of mitochondrial dysfunction in the development of cardiac abnormalities.

Native functions of short tandem repeats

Over a third of the human genome is comprised of repetitive sequences, including more than a million short tandem repeats (STRs). While studies of the pathologic consequences of repeat expansions that cause syndromic human diseases are extensive, the potential native functions of STRs are often ignored. Here, we summarize a growing body of research into the normal biological functions for repetitive elements across the genome, with a particular focus on the roles of STRs in regulating gene expression. We propose reconceptualizing the pathogenic consequences of repeat expansions as aberrancies in normal gene regulation. From this altered viewpoint, we predict that future work will reveal broader roles for STRs in neuronal function and as risk alleles for more common human neurological diseases.

Clinical, radiological, and molecular analyses of neuronal intranuclear inclusion disease with polyglycine inclusions

Neuronal intranuclear inclusion disease (NIID) is a clinically complex neurological disorder that appears sporadically or autosomally. Expansions of intronic GGC trinucleotide repeats in the NOTCH2 N-terminal-like C (NOTCH2NLC) gene cause NIID. In this study, to clarify the clinical characteristics useful for the differential diagnosis of NIID, clinical data of neurological examination, neuroimaging, and nerve conduction studies of six NIID patients diagnosed by pathological or genetic investigations were analyzed. Clinically useful characteristics for diagnosing NIID include general hyporeflexia, episodic disturbance of consciousness, sensory disturbance, miosis, and dementia. Furthermore, neuroimaging findings, such as leukoencephalopathy in T2-weighted magnetic resonance imaging and a linear high intensity of subcortical U-fibers in diffusion-weighted imaging (DWI), as well as decreased motor nerve conduction velocity, are especially important biomarkers for NIID. However, it is necessary to remember that these features may not always be present, as shown in one of the cases who did not have a DWI abnormality in this study. This study also investigated whether expanded GGC repeats were translated into polyglycine. Immunohistochemical analysis using a custom antibody raised against putative C-terminal polypeptides followed by polyglycine of uN2CpolyG revealed that polyglycines were localized in the intranuclear inclusions in skin biopsy specimens from all six patients, suggesting its involvement in the pathogenesis of NIID.

Current advances in neuronal intranuclear inclusion disease

Neuronal intranuclear inclusion disease (NIID) is a rare but probably underdiagnosed neurodegenerative disorder due to pathogenic GGC expansions in the NOTCH2NLC gene. In this review, we summarize recent developments in the inheritance features, pathogenesis, and histopathologic and radiologic features of NIID that subvert the previous perceptions of NIID. GGC repeat sizes determine the age of onset and clinical phenotypes of NIID patients. Anticipation may be absent in NIID but paternal bias is observed in NIID pedigrees. Eosinophilic intranuclear inclusions in skin tissues once considered pathological hallmarks of NIID can also present in other GGC repeat diseases. Diffusion-weighted imaging (DWI) hyperintensity along the corticomedullary junction once considered the imaging hallmark of NIID can frequently be absent in muscle weakness and parkinsonism phenotype of NIID. Besides, DWI abnormalities can appear years after the onset of predominant symptoms and may even disappear completely with disease progression. Moreover, continuous reports of NOTCH2NLC GGC expansions in patients with other neurodegenerative diseases lead to the proposal of a new concept of NOTCH2NLC-related GGC repeat expansion disorders (NRED). However, by reviewing the previous literature, we point out the limitations of these studies and provide evidence that these patients are actually suffering from neurodegenerative phenotypes of NIID.

Proteomic profile of nuclei containing p62-positive inclusions in a patient with neuronal intranuclear inclusion disease

Neuronal intranuclear inclusion disease (NIID) is a neurodegenerative disease characterized by eosinophilic hyaline intranuclear inclusions in the neurons, glial cells, and other somatic cells. Although CGG repeat expansions in NOTCH2NLC have been identified in most East Asian patients with NIID, the pathophysiology of NIID remains unclear. Ubiquitin- and p62-positive intranuclear inclusions are the pathological hallmark of NIID. Targeted immunostaining studies have identified several other proteins present in these inclusions. However, the global molecular changes within nuclei with these inclusions remained unclear. Herein, we analyzed the proteomic profile of nuclei with p62-positive inclusions in a NIID patient with CGG repeat expansion in NOTCH2NLC to discover candidate proteins involved in the NIID pathophysiology. We used fluorescence-activated cell sorting and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to quantify each protein identified in the nuclei with p62-positive inclusions. The distribution of increased proteins was confirmed via immunofluorescence in autopsy brain samples from three patients with genetically confirmed NIID. Overall, 526 proteins were identified, of which 243 were consistently quantified using MS. A 1.4-fold increase was consistently observed for 20 proteins in nuclei with p62-positive inclusions compared to those without. Fifteen proteins identified with medium or high confidence in the LC-MS/MS analysis were further evaluated. Gene ontology enrichment analysis showed enrichment of several terms, including poly(A) RNA binding, nucleosomal DNA binding, and protein binding. Immunofluorescence studies confirmed that the fluorescent intensities of increased RNA-binding proteins identified by proteomic analysis, namely hnRNP A2/B1, hnRNP A3, and hnRNP C1/C2, were higher in the nuclei with p62-positive inclusions than in those without, which were not confined to the intranuclear inclusions. We identified several increased proteins in nuclei with p62-positive inclusions. Although larger studies are needed to validate our results, these proteomic data may form the basis for understanding the pathophysiology of NIID.