title: FLNC myofibrillar myopathy results from impaired autophagy and protein insufficiency.
abstract: Myofibrillar myopathy is a progressive muscle disease characterized by the disintegration of muscle fibers and formation of protein aggregates. Causative mutations have been identified in nine genes encoding Z-disk proteins, including the actin binding protein filamin C (FLNC). To investigate the mechanism of disease in FLNCW2710Xmyopathy we overexpressed fluorescently tagged FLNC or FLNCW2710Xin zebrafish. Expression of FLNCW2710Xcauses formation of protein aggregates but surprisingly, our studies reveal that the mutant protein localizes correctly to the Z-disk and is capable of rescuing the fiber disintegration phenotype that results from FLNC knockdown. This demonstrates that the functions necessary for muscle integrity are not impaired, and suggests that it is the formation of protein aggregates and subsequent sequestration of FLNC away from the Z-disk that results in myofibrillar disintegration. Similar to those found in patients, the aggregates in FLNCW2710Xexpressing fish contain the co-chaperone BAG3. FLNC is a target of the BAG3-mediated chaperone assisted selective autophagy (CASA) pathway and therefore we investigated its role, and the role of autophagy in general, in clearing protein aggregates. We reveal that despite BAG3 recruitment to the aggregates they are not degraded via CASA. Additionally, recruitment of BAG3 is sufficient to block alternative autophagy pathways which would otherwise clear the aggregates. This blockage can be relieved by reducing BAG3 levels or by stimulating autophagy. This study therefore identifies both BAG3 reduction and autophagy promotion as potential therapies for FLNCW2710Xmyofibrillar myopathy, and identifies protein insufficiency due to sequestration, compounded by impaired autophagy, as the cause.
authors.affiliation: School of Biological Sciences.
authors.forename: Avnika A
authors.initials: AA
authors.lastname: Ruparelia
authors.affiliation: The Clive and Vera Ramaciotti Centre for Structural Cryo-Electron Microscopy and and.
authors.forename: Viola
authors.initials: V
authors.lastname: Oorschot
authors.affiliation: The Clive and Vera Ramaciotti Centre for Structural Cryo-Electron Microscopy and and Department of Biochemistry and Molecular Biology, Monash University, Melbourne, VIC 3800, Australia.
authors.forename: Georg
authors.initials: G
authors.lastname: Ramm
authors.affiliation: School of Biological Sciences, robert.bryson-richardson@monash.edu.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Bryson-Richardson
mesh_terms: D000818:Animals; D001343:Autophagy / Q000235:genetics*; D064448:Filamins / Q000235:genetics*; D005786:Gene Expression Regulation; D006801:Humans; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000473:pathology*; D018482:Muscle, Skeletal / Q000473:pathology; D009154:Mutation; D009210:Myofibrils / Q000235:genetics / Q000473:pathology; D020914:Myopathies, Structural, Congenital / Q000235:genetics*; D010641:Phenotype; D066263:Protein Aggregation, Pathological / Q000235:genetics; D012518:Sarcomeres / Q000235:genetics / Q000473:pathology; D015027:Zebrafish / Q000235:genetics
chemical_list: D064448:Filamins