title: Sporadic inclusion body myositis correlates with increased expression and cross-linking by transglutaminases 1 and 2.
abstract: Sporadic inclusion body myositis (SIBM) is characterized by vacuolar degeneration of muscle fibers and intrafiber clusters of paired helical filaments with abnormal amyloid deposition. Because of their potential involvement in other degenerative disorders, we have examined the expression of transglutaminases (TGases) in normal and SIBM tissues. We report that at least two different enzymes, the ubiquitous TGase 2 as well as the TGase 1 enzyme, are present in muscle tissues. However, in comparison with normal tissue, the expression of TGases 1 and 2 was increased 2.5- and 4-fold in SIBM, accompanied by about a 20-fold higher total TGase activity. By immunohistochemical staining, in normal muscle, TGase 2 expression was restricted to some endomysial connective tissue elements, whereas TGase 1 and beta-amyloid proteins were not detectable. In SIBM muscle, both TGases 1 and 2 as well as amyloid proteins were brightly expressed and co-localized in the vacuolated muscle fibers, but none of these proteins colocalized with inflammatory cell markers. Next, we isolated high molecular weight insoluble proteins from SIBM muscle tissue and showed that they were cross-linked by about 6 residues/1000 residues of the isopeptide bond. Furthermore, by amino acid sequencing of solubilized tryptic peptides, they contain amyloid and skeletal muscle proteins. Together, these findings suggest that elevated expression of TGases 1 and 2 participate in the formation of insoluble amyloid deposits in SIBM tissue and in this way may contribute to progressive and debilitating muscle disease.
authors.affiliation: Department of Neurology, College of Medicine, Yonsei University, Seoul 135-270, Republic of Korea. ycchoi@yumc.yonsei.ac.kr
authors.forename: Y C
authors.initials: YC
authors.lastname: Choi
authors.forename: G T
authors.initials: GT
authors.lastname: Park
authors.forename: T S
authors.initials: TS
authors.lastname: Kim
authors.forename: I N
authors.initials: IN
authors.lastname: Sunwoo
authors.forename: P M
authors.initials: PM
authors.lastname: Steinert
authors.forename: S Y
authors.initials: SY
authors.lastname: Kim
mesh_terms: D016564:Amyloid beta-Protein Precursor / Q000302:isolation & purification; D001706:Biopsy; D004151:Dipeptides / Q000302:isolation & purification* / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000302:isolation & purification* / Q000378:metabolism; D006801:Humans; D009124:Muscle Proteins / Q000737:chemistry*; D018482:Muscle, Skeletal / Q000201:enzymology; D018979:Myositis, Inclusion Body / Q000201:enzymology*; D010446:Peptide Fragments / Q000302:isolation & purification; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011499:Protein Processing, Post-Translational; D012995:Solubility; D013848:Thigh; D014018:Tissue Distribution; D011503:Transglutaminases / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D016564:Amyloid beta-Protein Precursor; D004151:Dipeptides; D009124:Muscle Proteins; D010446:Peptide Fragments; C001299:epsilon-(gamma-glutamyl)-lysine; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; C105804:transglutaminase 1; D019204:GTP-Binding Proteins