G.P.55 Evaluation of pathogenicity of a novel BAG3 mutation by using transgenic medaka

Abstract

Myofibrillar myopathy (MFM) is a group of hereditary myopathies pathologically characterized as markedly disorganized myofibrils with cytoplasmic inclusions. Six disease-related genes have been identified, including DES, CRYAB, MYOT, ZASP, FLNC, and BAG3, all of which encode proteins closely associated with Z-line. We performed mutation screening in Japanese patients with MFM. In this study, we focus on a novel heterozygous mutation in BAG3 (p.261_265RAASPdel), and evaluate whether the mutation is causative or not. Transgenic animal is a powerful tool for evaluating protein function in vivo. Japanese small teleost fish, medaka (Olyzias latipes) is known as a useful model organism for vertebrate organogenesis and methodology of transgenesis is well established. We generated transgenic medaka models expressing human BAG3 (WT, RAASPdel, and a previously reported P209L mutant) under control of the medaka α-actin promoter. Each transgenic fish was histologically analyzed. The RAASPdel fishes displayed lateral curvature of body axis similar to the P209L fishes at hatching stage. Histological analysis revealed marked variation in muscle fiber size with increased interstitial fibrous tissues in both mutant BAG3 transgenic fishes, but not in WT. Confocal microscopic analysis revealed that RAASPdel and P209L mutant BAG3, but not WT, were accumulated in some muscle fibers, although all transgenic BAG3 were predominantly detected as striated patterns. Similar to the human patients’ muscles, accumulations of BAG3 were co-localized with other Z-line proteins such as Filamin C and Desmin. Our results strongly suggested that the p.261_265RAASPdel is a causative mutation of BAG3opathy. Transgenic medaka is a useful model for evaluating pathogenicity of human mutation.