title: The UNC-45 chaperone is critical for establishing myosin-based myofibrillar organization and cardiac contractility in the Drosophila heart model.
abstract: UNC-45 is a UCS (UNC-45/CRO1/She4P) class chaperone necessary for myosin folding and/or accumulation, but its requirement for maintaining cardiac contractility has not been explored. Given the prevalence of myosin mutations in eliciting cardiomyopathy, chaperones like UNC-45 are likely to be equally critical in provoking or modulating myosin-associated cardiomyopathy. Here, we used the Drosophila heart model to examine its role in cardiac physiology, in conjunction with RNAi-mediated gene silencing specifically in the heart in vivo. Analysis of cardiac physiology was carried out using high-speed video recording in conjunction with movement analysis algorithms. unc-45 knockdown resulted in severely compromised cardiac function in adults as evidenced by prolonged diastolic and systolic intervals, and increased incidence of arrhythmias and extreme dilation; the latter was accompanied by a significant reduction in muscle contractility. Structural analysis showed reduced myofibrils, myofibrillar disarray, and greatly decreased cardiac myosin accumulation. Cardiac unc-45 silencing also dramatically reduced life-span. In contrast, third instar larval and young pupal hearts showed mild cardiac abnormalities, as severe cardiac defects only developed during metamorphosis. Furthermore, cardiac unc-45 silencing in the adult heart (after metamorphosis) led to less severe phenotypes. This suggests that UNC-45 is mostly required for myosin accumulation/folding during remodeling of the forming adult heart. The cardiac defects, myosin deficit and decreased life-span in flies upon heart-specific unc-45 knockdown were significantly rescued by UNC-45 over-expression. Our results are the first to demonstrate a cardiac-specific requirement of a chaperone in Drosophila, suggestive of a critical role of UNC-45 in cardiomyopathies, including those associated with unfolded proteins in the failing human heart. The dilated cardiomyopathy phenotype associated with UNC-45 deficiency is mimicked by myosin knockdown suggesting that UNC-45 plays a crucial role in stabilizing myosin and possibly preventing human cardiomyopathies associated with functional deficiencies of myosin.
authors.affiliation: Department of Biology, Molecular Biology Institute and Heart Institute, San Diego State University, San Diego, California, United States of America.
authors.forename: Girish C
authors.initials: GC
authors.lastname: Melkani
authors.forename: Rolf
authors.initials: R
authors.lastname: Bodmer
authors.forename: Karen
authors.initials: K
authors.lastname: Ocorr
authors.forename: Sanford I
authors.initials: SI
authors.lastname: Bernstein
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D029721:Drosophila Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology* / Q000378:metabolism* / Q000502:physiology; D005260:Female; D055785:Gene Knockdown Techniques; D020868:Gene Silencing; D006321:Heart / Q000502:physiology*; D007814:Larva / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D008297:Male; D023421:Models, Animal; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D009119:Muscle Contraction / Q000235:genetics; D009206:Myocardium / Q000378:metabolism; D009210:Myofibrils / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D009218:Myosins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D012518:Sarcomeres / Q000378:metabolism / Q000502:physiology
chemical_list: D029721:Drosophila Proteins; D018832:Molecular Chaperones; C550552:UNC-45 protein, Drosophila; D018995:Myosin Heavy Chains; D009218:Myosins