Mitochondrial localization of PABPN1 in oculopharyngeal muscular dystrophy.

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset disorder characterized by ptosis, dysphagia, and weakness of proximal limbs. OPMD is caused by the expansion of polyalanine in poly(A)-binding protein, nuclear 1 (PABPN1). Although mitochondrial abnormality has been proposed as the possible etiology, the molecular pathogenesis is still poorly understood. The aim of the study was to specify the mechanism by which expanded PABPN1 causes mitochondrial dysfunction in OPMD. We evaluated whether transgenic mouse model of OPMD, by expressing expanded PABPN1, indeed causes mitochondrial abnormality associated with muscle degeneration. We also investigated the mechanism by which expanded PABPN1 would cause mitochondrial dysfunction in the mouse and cell models of OPMD. Mitochondrial localization of PABPN1 was observed in the muscle fibers of patients with OPMD. Moreover, abnormal accumulation of PABPN1 on the inner membrane of mitochondria and reduced expression of OXPHOS complexes were detected in the muscle fibers of the transgenic mice expressing expanded human PABPN1 with a 13-alanine stretch. In cells expressing PABPN1 with a 10-alanine or 18-alanine stretch, both types of PABPN1 accumulated in the mitochondria and interacted with TIM23 mitochondrial protein import complex, but PABPN1 with 18-alanine stretch decreased the cell viability and aggresome formation. We proposed that the abnormal accumulation of expanded PABPN1 in mitochondria may be associated with mitochondrial abnormality in OPMD.

[Successful treatment of Epstein-Barr virus-related encephalomyelitis with steroid and ganciclovir].

We report a 56-year-old man with encephalomyelitis due to Epstein-Barr virus (EBV). The patient suffered from fever and headache, and become somnolent on day 10. On day 18, following treatment with an antibiotic and aciclovir, a cerebrospinal fluid (CSF) examination revealed increased protein levels and lymphocytic pleocytosis. On day 25, he developed progressive tetraplegia, hypesthesia of Th l0 dermatomes, difficulty in defecating, and urinary retention. Magnetic resonance (MR) T2-weighted images showed a high-signal lesion in the center of the medulla oblongata, patchy high-signal lesions throughout the spinal cord, and swelling of the cervical spinal cord. A polymerase chain reaction test for EBV DNA in the CSF was positive. After treatment with high-dose methyl-predonisolone, the neurological symptoms improved rapidly and the high-signal lesions in the spinal cord improved. EBV DNA in the CSF was not detected after treatment with ganciclovir. This case suggests that steroid and ganciclovir are effective for the treatment of EBV-related encephalomyelitis.

Distal myopathy with rimmed vacuoles: impaired O-glycan formation in muscular glycoproteins.

Distal myopathy with rimmed vacuoles (DMRV), is an autosomal recessive disorder with early adult onset, displays distal dominant muscular involvement and is characterized by the presence of numerous rimmed vacuoles in the affected muscle fibers. The pathophysiology of DMRV has not been clarified yet, although the responsible gene was identified as that encoding UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase involved in the biosynthesis of sialic acids. To identify defective carbohydrate moieties of muscular glycoproteins from DMRV patients, frozen skeletal muscle sections from seven patients with DMRV, as well as normal and pathological controls, were treated with or without sialidase or N-glycosidase F followed by lectin staining and lectin blotting analysis. The sialic acid contents of the O-glycans in the skeletal muscle specimens from the DMRV patients were also measured. We found that Arachis hypogaea agglutinin (PNA) lectin reacted strongly with sarcolemmal glycoproteins in the DMRV patients but not with those in control subjects. alpha-Dystroglycan from the DMRV patients strongly associated with PNA lectin, although that from controls did not. The sialic acid level of the O-glycans in the DMRV muscular glycoproteins with molecular weights of 30 to 200 kd was reduced to 60 to 80% of the control level. The results show that impaired sialyl O-glycan formation in muscular glycoproteins, including alpha-dystroglycan, occurs in DMRV.

Myopathy phenotype in transgenic mice expressing mutated PABPN1 as a model of oculopharyngeal muscular dystrophy.

Autosomal dominant oculopharyngeal muscular dystrophy (OPMD) is a late-onset disorder characterized clinically by progressive ptosis, dysphagia and limb weakness, and by unique intranuclear inclusions in the skeletal muscle fibers. The disease is caused by the expansion of a 10-alanine stretch to 12-17 alanine residues in the poly(A)-binding protein, nuclear 1 (PABPN1; PABP2). While PABPN1 is a major component of the inclusions in OPMD, the exact cause of the disease is unknown. To elucidate the molecular mechanism and to construct a useful model for therapeutic trials, we have generated transgenic mice expressing the hPABPN1. Transgenic mice lines expressing a normal hPABPN1 with 10-alanine stretch did not reveal myopathic changes, whereas lines expressing high levels of expanded hPABPN1 with a 13-alanine stretch showed an apparent myopathy phenotype, especially in old age. Pathological studies in the latter mice disclosed intranuclear inclusions consisting of aggregated mutant hPABPN1 product. Furthermore, some TUNEL positive nuclei were shown around degenerating fibers and a cluster of it in the lesion in necrotic muscle fibers. Interestingly, the degree of myopathic changes was more prominent in the eyelid and pharyngeal muscles. Further, muscle weakness in the limbs was apparent as shown by the fatigability test. Nuclear inclusions seemed to develop gradually with aging, at least after 1 week of age, in model mouse muscles. We established the first transgenic mouse model of OPMD by expressing mutated PABPN1, and our model mice appear to have more dramatic alternations in myofiber viability.