부산대학교 도서관

Aims Sporadic inclusion-body myositis (s- IBM) is an age-associated degenerative muscle disease. Characteristic features are muscle-fibre vacuolization and intramuscle-fibre accumulations of multiprotein aggregates, which may result from the demonstrated impairments of the 26 S proteasome and autophagy. Chaperone-mediated autophagy ( CMA) is a selective form of lysosomal degradation targeting proteins carrying the KFERQ motif. Lysosome-associated membrane protein type 2 A ( LAMP2 A) and the heat-shock cognate protein 70 ( Hsc70) constitute specific CMA components. Neither CMA components nor CMA activity has been studied in normal or disease human muscle, to our knowledge. Methods We studied CMA components by immunocytochemistry, immunoblots, real-time PCR and immunoprecipitation in: (a) 16 s- IBM, nine aged-matched normal and nine disease control muscle biopsies; and (b) cultured human muscle fibres ( CHMFs) with experimentally inhibited activities of either the 26 S proteasome or autophagy. Results Compared with age-matched controls, in s- IBM muscle, LAMP2 A and Hsc70 were on a given transverse section accumulated as aggregates in approximately 5% of muscle fibres, where they (a) colocalized with each other and α-synuclein (α-syn), a CMA-targeted protein; and (b) were bound to each other and to α-syn by immunoprecipitation. By immunoblots, LAMP2 A was increased sevenfold P < 0.001 and Hsc70 2.6-fold P < 0.05. LAMP2 A mRNA was increased 4.4-fold P < 0.001 and Hsc70 mRNA 1.9-fold P < 0.05. In CHMFs inhibition of either the 26 S proteasome or autophagy induced CMA, evidenced by a significant increase of both LAMP2 A and Hsc70. Conclusions Our study demonstrates, for the first time, up-regulation of CMA components in s- IBM muscle, and it provides further evidence that altered protein degradation is likely an important pathogenic aspect in s- IBM. [ABSTRACT FROM AUTHOR]