The origin of tubular aggregates in human myopathies.
Tubular aggregates are morphological abnormalities characterized by the accumulation of densely packed tubules in skeletal muscle fibres. To improve knowledge of tubular aggregates, the formation and role of which are still unclear, the present study reports the electron microscopic analysis and protein characterization of tubular aggregates in six patients with 'tubular aggregate myopathy'. Three of the six patients also presented with myasthenic features. A large panel of immunochemical markers located in the sarcoplasmic reticulum, T-tubules, mitochondria, and nucleus was used. Despite differences in clinical phenotype, the composition of tubular aggregates, which contained proteins normally segregated differently along the sarcoplasmic reticulum architecture, was similar in all patients. All of these proteins, calsequestrin, RyR, triadin, SERCAs, and sarcalumenin, are involved in calcium uptake, storage, and release. The dihydropyridine receptor, DHPR, specifically located in the T-tubule, was also present in tubular aggregates in all patients. COX-2 and COX-7 mitochondrial proteins were not found in tubular aggregates, despite being observed close to them in the muscle fibre. The nuclear membrane protein emerin was found in only one case. Electron microscopy revealed vesicular budding from nuclei, and the presence of SAR-1 GTPase protein in tubular aggregates shown by immunochemistry, in all patients, suggests that tubular aggregates could arise from endoplasmic reticulum exit sites. Taken together, these results cast new light on the composition and significance of tubular aggregates.
Chevessier
Frédéric
F
INSERM U582, IFR 14, Institut de Myologie, Hôpital de la Salpêtrière and Université Pierre et Marie Curie, Paris, France.
Bauché-Godard
Stéphanie
S
Leroy
Jean-Paul
JP
Koenig
Jeanine
J
Paturneau-Jouas
Marion
M
Eymard
Bruno
B
Hantaï
Daniel
D
Verdière-Sahuqué
Martine
M
D000328:Adult; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000032:analysis; D002467:Cell Nucleus / Q000473:pathology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D008854:Microscopy, Electron / Q000379:methods; D008875:Middle Aged; D008931:Mitochondria, Muscle / Q000473:pathology; D024101:Mitochondrial Proteins / Q000032:analysis; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D009124:Muscle Proteins / Q000032:analysis; D018482:Muscle, Skeletal / Q000473:pathology*; D020914:Myopathies, Structural, Congenital / Q000473:pathology* / Q000503:physiopathology; D012519:Sarcoplasmic Reticulum / Q000473:pathology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D024101:Mitochondrial Proteins; D009124:Muscle Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D002118:Calcium