Intranuclear inclusions in oculopharyngeal muscular dystrophy among Bukhara Jews

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.

Oculopharyngeal Muscular Dystrophy and Inherited Retinal Dystrophy in Bukhara Jews Due to Linked Mutations in the PABPN1 and NRL Genes

AIM

We have previously described two unrelated Bukhara Jews (BJs) with a combination of oculopharyngeal muscular dystrophy (OPMD) and inherited retinal dystrophy (IRD), because of mutations in two linked genes: PABPN1 and NRL. Here we investigated the prevalence of the NRL mutation among BJs with OPMD.

MATERIALS AND METHODS

PABPN1 and NRL mutation testing were performed by polymerase chain reaction amplification and direct sequencing on two cohorts of Bukhara Jewish patients: OPMD patients (with or without IRD) and IRD patients (without OPMD).

RESULTS

Of 24 unrelated chromosomes from Bukhara Jewish OPMD patients, 19 (79%) harbored the NRL mutation. In contrast, the NRL mutation was not detected in Bukhara Jewish patients diagnosed with IRD but without OPMD.

CONCLUSIONS

Our findings provide an explanation for the reoccurrence of IRD in Bukhara Jewish OPMD homozygotes. Moreover, they indicate that Bukhara Jewish OPMD patients are at high risk for carrying the NRL mutation, and should be offered appropriate genetic counseling and testing.

Correlation between PABPN1 genotype and disease severity in oculopharyngeal muscular dystrophy

OBJECTIVE

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant adult-onset disease characterized by progressive ptosis, dysphagia, and proximal limb weakness. The genetic cause is an expanded (GCN)n mutation in the PABPN1 gene encoding for the polyadenylate-binding protein nuclear 1. We hypothesized a potential correlation between the size of the (GCN)n expansion and the severity of the phenotype. To do this, we characterized the distribution of the genotypes as well as their correlation with age at diagnosis and phenotypical features in a large cohort of heterozygous and homozygous patients with OPMD in France with a confirmed molecular diagnosis of PABPN1.

METHODS

We explored 354 unrelated index cases recruited between 1999 and 2014 in several neuromuscular centers in France.

RESULTS

This cohort allowed us to characterize the frequency of mutated alleles in the French population and to demonstrate a statistical correlation between the size of the expansion and the mean age at diagnosis. We also confirmed that homozygous patients present with a more severe disease.

CONCLUSIONS

It has been difficult to establish phenotype-genotype correlations because of the rare nature of this disease. Our work demonstrates that patients with OPMD with longer PABPN1 expansion are on average diagnosed at an earlier age than patients with a shorter expansion, confirming that polyalanine expansion size plays a role in OPMD, with an effect on disease severity and progression.

Conformational behavior of polyalanine peptides with and without protecting groups of varying chain lengths: population of PP-II structure!

Oculopharyngeal muscular dystrophy (OPMD), a polyalanine myopathy, occurs due to expansion of homo-polyalanine stretch in normal polyadenylating binding protein nuclear 1 (PABPN1) protein from Ala10 to Ala11-17. Therefore, the conformational behavior of polyalanine peptides with n = 10-17, with and without terminal protecting groups, have been investigated with different starting geometries in water by molecular dynamics simulation studies. Alanine peptides are shown to give rise to unordered structure irrespective of starting geometry and not more than two residues at a stretch have the same/similar set of φ, ψ values. However, the final structure with terminal protecting groups look like β-strand. Unprotected poly-Ala peptides adopt twisted β-hairpin/multi hairpin like structure with increasing chain length. The number of residues having φ, ψ values in collagen region is found to be less in peptides with unprotected termini as compared to peptides with protected termini of same chain length. The results have been supported by recent synchrotron radiation circular dichroism spectroscopy of polyproline II and unordered secondary structures. Opening of the helical structure in poly-Ala peptides with protecting groups has been shown to take place from C-terminal and in peptides without protecting groups opening of helix starts from both terminals. Further, opening of helix takes more time in poly-Ala peptides without terminal protecting groups. The deviations in amide bond planarity have been discussed and compared with available experimental and computational results.

Cricopharyngeal myotomy in the treatment of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant myopathic disease which provokes oropharyngeal dysphagia, palpabral ptosis and proximal limb weakness. It is the abnormal expression of the GCG triplet in the PABPN1 gene on chromosome 14 that causes this disease. The study of the oropharyngeal dysphagia that these patients suffer from should include upper gastrointestinal endoscopy, barium video-radiology and oesophageal manometry. Genetic study confirms the diagnosis. We report 6 patients (3 of whom were siblings) referred to our department with a confirmed diagnosis of OPMD, who underwent cricopharyngeal myotomy to achieve normal swallowing.

Oculopharyngeal muscular dystrophy: Recent advances in the understanding of the molecular pathogenic mechanisms and treatment strategies

Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive eyelid drooping, swallowing difficulties and proximal limb weakness. OPMD is caused by a small expansion of a short polyalanine tract in the poly (A) binding protein nuclear 1 protein (PABPN1). The mechanism by which the polyalanine expansion mutation in PABPN1 causes disease is unclear. PABPN1 is a nuclear multi-functional protein which is involved in pre-mRNA polyadenylation, transcription regulation, and mRNA nucleocytoplasmic transport. The distinct pathological hallmark of OPMD is the presence of filamentous intranuclear inclusions (INIs) in patient's skeletal muscle cells. The exact relationship between mutant PABPN1 intranuclear aggregates and pathology is not clear. OPMD is a unique disease sharing common pathogenic features with other polyalanine disorders, as well as with polyglutamine and dystrophic disorders. This chapter aims to review the rapidly growing body of knowledge concerning OPMD. First, we outline the background of OPMD. Second, we compare OPMD with other trinucleotide repeat disorders. Third, we discuss the recent advances in the understanding of the molecular mechanisms underlying OPMD pathogenesis. Finally, we review recent therapeutic strategies for OPMD.

Reconstructive rhytidectomy?

Muscular dystrophies are commonly considered hereditary progressive degenerative diseases that affect skeletal and cardiac muscles. Oculopharyngeal muscular dystrophy is a rare hereditary disorder of later onset consisting of progressive dysphagia and bilateral blepharoptosis unlike the peripheral muscular weakness common to other muscular dystrophies. The symptoms of progressive dysphagia, with bilateral ptosis, usually occur after the age of 40 years. The authors present a patient with oculopharyngeal muscular dystrophy and chronic facial pain relieved by midface soft tissue support, namely, the reconstructive rhytidectomy.

Premature proliferative arrest of cricopharyngeal myoblasts in oculo-pharyngeal muscular dystrophy: Therapeutic perspectives of autologous myoblast transplantation

Cultures of myoblasts isolated from cricopharyngeal muscles from patients with oculopharyngeal muscular dystrophy (OPMD) have been performed to study the effect of the expanded (GCG)8-13 repeat, located on the poly(A) binding protein nuclear-1 (PABPN1), on satellite cell phenotype. Cell cultures exhibited a reduced myogenicity, as well as a rapid decrease in proliferative lifespan, as compared to controls. The incorporation of BrdU decreased during the proliferative lifespan, due to a progressive accumulation of non-dividing cells. A lower fusion index was also observed, but myoblasts were able to form large myotubes when OPMD cultures were purified, although a rapid loss of myogenicity during successive passages was also observed. Myoblasts isolated from unaffected muscles did not show the defects observed in cricopharyngeal muscle cultures. The PABPN1 was predominantly located in nuclei of myoblasts and in both the nuclei and cytoplasm of myotubes in OPMD cultures. In vivo analysis of OPMD muscles showed that the number of satellite cells was slightly higher than that observed in age matched controls. Mutation of the PABPN1 in OPMD provokes premature senescence in dividing myoblasts, that may be due to intranuclear toxic aggregates. These results suggest that myoblast autografts, isolated from unaffected muscles, and injected into the dystrophic pharyngeal muscles, may be a useful therapeutic strategy to restore muscular function. Its tolerance and feasibility has been preclinically demonstrated in the dog.

Progress in understanding the pathogenesis of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is an adult-onset disorder characterized by progressive eyelid drooping (ptosis), swallowing difficulties (dysphagia), and proximal limb weakness. The autosomal dominant form of this disease is caused by expansions of a (GCG)6 repeat to (GCG)8-13 in the PABPN1 gene. These mutations lead to the expansion of a polyalanine stretch from 10 to 12-17 alanines in the N-terminal domain of PABPN1. Mutated PABPN1 (mPABPN1) induces the formation of muscle intranuclear inclusions that are thought to be the hallmark of this disease. In this review, we discuss: 1) OPMD genetics and PABPN I function studies; 2) diseases caused by polyalanine expansions and cellular polyalanine toxicity; 3) mPABPN1-induced intranuclear inclusion toxicity; 4) role of oligomerization of mPABPNI in the formation and toxicity of OPMD intranuclear inclusions and; 5) recruitment of subcellular components to the OPMD inclusions. We present a potential molecular mechanism for OPMD pathogenesis that accounts for these observations.

Correction of blepharoptosis in oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy is a hereditary, autosomal dominant, slowly progressive disorder with onset that occurs during middle age. Major symptoms are ptosis and dysphagia resulting primarily from selectively involved levator palpebrae and the pharyngeal muscles. Progressive, usually symmetrical blepharoptosis, with or without dysphagia, appears during middle age. Muscular weakness in the limbs can be noted in some patients. The guidelines for surgery in myopathic ptosis are conservative in view of the increased risk of postoperative corneal complications. However, orbicularis function remains intact in oculopharyngeal muscular dystrophy; therefore, corrective surgery is performed in most patients. This report describes four cases of ptosis correction in patients with oculopharyngeal muscular dystrophy in one family. The frontalis action was very poor to qualify for frontalis transfer; therefore, the authors performed moderate to large levator resection in all patients. The follow-up results 5 years postoperatively are promising to date and all the patients are satisfied with the results.

GCG repeats and phenotype in oculopharyngeal muscular dystrophy

Short GCG repeat expansions in the PABP2 gene were recently shown to cause oculopharyngeal muscular dystrophy (OPMD) in French-Canadian and Italian pedigrees. We diagnosed OPMD in 16 German patients by the detection of GCG repeat expansions, confirming genetic homogeneity. Myopathic and neurogenic changes were found in skeletal muscle biopsies. Age of onset and severity of disease were not correlated with the number of repeats.

Autosomal recessive oculopharyngodistal myopathy in light of distal myopathy with rimmed vacuoles and oculopharyngeal muscular dystrophy

We investigated two Japanese siblings presenting with oculopharyngodistal myopathy, whose healthy parents were consanguineous. To clarify their disease characteristics, we compared them with four patients with distal myopathy with rimmed vacuoles linked to chromosome 9p1-q1, and 36 patients with oculopharyngeal muscular dystrophy linked to 14q11.2-q13. The first symptom in the patients with autosomal recessive oculopharyngodistal myopathy was weakness of the tibialis anterior muscle. Their biceps muscles showed initial and advanced myogenic changes, with rimmed vacuoles in 3% and 6% of the muscle fibers, respectively. In contrast, patients with distal myopathy with rimmed vacuoles revealed many rimmed vacuoles, on average in 20% of the fibers, and their oculopharyngeal muscles were spared. None of the patients with oculopharyngeal muscular dystrophy showed distal dominant weakness and the occurrence of rimmed vacuoles was rare. Ultrastructural studies in groups of autosomal recessive oculopharyngodistal myopathy and distal myopathy with rimmed vacuoles disclosed a collection of cytoplasmic filaments of 16-18 nm, but oculopharyngeal muscular dystrophy-specific intranuclear inclusions of 8.5 nm were not found. Thus, the phenotype of autosomal recessive oculopharyngodistal myopathy is distinct from distal myopathy with rimmed vacuoles and oculopharyngeal muscular dystrophy, but shares some ultrastructural characteristics with distal myopathy with rimmed vacuoles and hereditary inclusion body myopathy.

Oculopharyngeal muscular dystrophy in Italy

Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant myopathy particularly frequent in Québec. The few Italian cases thus far described with bilateral ptosis, dysphagia and variable muscle weakness, show non-specific dystrophic findings on muscle biopsies by light microscopy. We describe a 70-year-old Italian woman with an adult-onset ptosis, mild dysphagia and proximal muscle weakness belonging to a family segregating OPMD according to an autosomal dominant mode of inheritance. Clinical features of four of her relatives are reviewed. Muscle biopsy studied by electron microscopy showed the typical 8.5 nm in diameter intranuclear filamentous inclusions (INI). To our knowledge, this is the first Italian report of OPMD with INI. The identification of nuclear inclusions is mandatory in order to confirm the diagnosis prior to linkage analysis.

Morphological changes in muscle fibers in oculopharyngeal muscular dystrophy

The study of muscle biopsies of 29 cases of oculopharyngeal muscular dystrophy (OPMD) showed the two main morphological features of this disease: rimmed vacuoles (in 26 cases) and intranuclear inclusions (in all cases). These inclusions are made of 8.5 nm tubular filaments and the areas occupied by them are lighter than the surrounded nucleoplasm. This can be seen by light microscopy, facilitating the detection of the tubulo-filamentous inclusions which can only be identified with certitude by electron microscopy. In a given ultrathin section the area occupied by these inclusions varied from 2% to 5% of the nuclei. The intranuclear inclusions are the morphological marker of OPMD and their finding in a muscle biopsy allows the exact diagnosis of this disease. The origin and biochemical nature of the intranuclear inclusions is unknown.

Epidemiology and inheritance of oculopharyngeal muscular dystrophy in Israel

Oculopharyngeal muscular dystrophy (OPMD) is considered frequent among French Canadians. Our previous observations suggested it is common also among the Jews originating from Bukhara in Uzbekistan, many of whom are now living in Israel. One hundred and seventeen OPMD patients were identified in a population of 70,000 people of Bukharian descent, resulting in a calculated minimal prevalence of 1:600. In all but three families age dependent autosomal dominant inheritance was documented. There is some evidence for genetic anticipation. Three young, severely ill, patients from two different families may be homozygotes, their parents being both affected. Bukhara Jews present the second largest known cluster and the prevalence is the highest in the world. The existence of very large families, intermarriage among carriers and probably homozygote offspring may be useful for genetic studies. A 'founder effect' may explain the high prevalence of OPMD in this population.

Intranuclear inclusions of expanded polyglutamine protein in spinocerebellar ataxia type 3

The mechanism of neurodegeneration in CAG/polyglutamine repeat expansion diseases is unknown but is thought to occur at the protein level. Here, in studies of spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/MJD), we show that the disease protein ataxin-3 accumulates in ubiquitinated intranuclear inclusions selectively in neurons of affected brain regions. We further provide evidence in vitro for a model of disease in which an expanded polyglutamine-containing fragment recruits full-length protein into insoluble aggregates. Together with recent findings from transgenic models, our results suggest that intranuclear aggregation of the expanded protein is a unifying feature of CAG/polyglutamine diseases and may be initiated or catalyzed by a glutamine-containing fragment of the disease protein.

Clinical features of oculopharyngeal muscular dystrophy among Bukhara Jews

Oculopharyngeal muscular dystrophy (OPMD), a late onset autosomal dominant myopathy, is common among the French-Canadians and the Jews from Bukhara (Uzbekistan); most clinical histologic and genetic data published until now, as well as the recently suggested diagnostic criteria, are based on studies among the former. We studied 79 patients with OPMD belonging to the newly described Jewish-Bukhara cluster. The disease began between the ages of 21 and 78 yr (median 53 yr). In 11 patients (15%) it began before the age of 40. Ptosis was the first symptom in 59 patients and dysphagia in the remaining 20. Eight patients (10%) were monosymptomatic (ptosis) after more than 7 yr from the start of the disease; however, other family members had additional signs/symptoms. The patients belong to 29 families; in 26 age-dependent autosomal dominant inheritance could be documented. Among them there is certain evidence for genetic anticipation. This clinical study is the largest published concerning patients other than French-Canadians.