Translocation of molecular chaperones to the titin springs is common in skeletal myopathy patients and affects sarcomere function.

Abstract

Myopathies encompass a wide variety of acquired and hereditary disorders. The pathomechanisms include structural and functional changes affecting, e.g., myofiber metabolism and contractile properties. In this study, we observed increased passive tension (PT) of skinned myofibers from patients with myofibrillar myopathy (MFM) caused by FLNC mutations (MFM-filaminopathy) and limb-girdle muscular dystrophy type-2A due to CAPN3 mutations (LGMD2A), compared to healthy control myofibers. Because the giant protein titin determines myofiber PT, we measured its molecular size and the titin-to-myosin ratio, but found no differences between myopathies and controls. All-titin phosphorylation and site-specific phosphorylation in the PEVK region were reduced in myopathy, which would be predicted to lower PT. Electron microscopy revealed extensive ultrastructural changes in myofibers of various hereditary myopathies and also suggested massive binding of proteins to the sarcomeric I-band region, presumably heat shock proteins (HSPs), which can translocate to elastic titin under stress conditions. Correlative immunofluorescence and immunoelectron microscopy showed that two small HSPs (HSP27 and αB-crystallin) and the ATP-dependent chaperone HSP90 translocated to the titin springs in myopathy. The small HSPs, but not HSP90, were upregulated in myopathic versus control muscles. The titin-binding pattern of chaperones was regularly observed in Duchenne muscular dystrophy (DMD), LGMD2A, MFM-filaminopathy, MFM-myotilinopathy, titinopathy, and inclusion body myopathy due to mutations in valosin-containing protein, but not in acquired sporadic inclusion body myositis. The three HSPs also associated with elastic titin in mouse models of DMD and MFM-filaminopathy. Mechanical measurements on skinned human myofibers incubated with exogenous small HSPs suggested that the elevated PT seen in myopathy is caused, in part, by chaperone-binding to the titin springs. Whereas this interaction may be protective in that it prevents sarcomeric protein aggregation, it also has detrimental effects on sarcomere function. Thus, we identified a novel pathological phenomenon common to many hereditary muscle disorders, which involves sarcomeric alterations.

• Authors: Andreas Unger, Lisa Beckendorf, Pierre Böhme, Rudolf Kley, Marion von Frieling-Salewsky, Hanns Lochmüller, Rolf Schröder, Dieter O Fürst, Matthias Vorgerd, Wolfgang A Linke
• Journal: Acta neuropathologica communications (Acta Neuropathol Commun) Vol. 5 Issue 1 Pg. 72 (09 15 2017) ISSN: 2051-5960 [Electronic] England
• PMID: 28915917 (Publication Type: Journal Article)

Chemical References

• Connectin
• FLNC protein, human
• Filamins
• HSP27 Heat-Shock Proteins
• HSP90 Heat-Shock Proteins
• HSPB1 protein, human
• Heat-Shock Proteins
• Molecular Chaperones
• Muscle Proteins
• TTN protein, human
• alpha-Crystallin B Chain
• Protein Kinases
• titin protein, mouse
• CAPN3 protein, human
• Calpain
• Myosins

Topics

• Animals
• Calpain (genetics)
• Connectin (metabolism)
• Disease Models, Animal
• Filamins (genetics)
• Fluorescent Antibody Technique
• HSP27 Heat-Shock Proteins (metabolism)
• HSP90 Heat-Shock Proteins (metabolism)
• Heat-Shock Proteins
• Mice, Inbred C57BL
• Mice, Inbred mdx
• Microscopy, Immunoelectron
• Molecular Chaperones
• Muscle Proteins (genetics)
• Muscle, Skeletal (metabolism, ultrastructure)
• Muscular Dystrophies (genetics, metabolism, pathology)
• Muscular Dystrophies, Limb-Girdle (genetics, metabolism, pathology)
• Myofibrils (metabolism, ultrastructure)
• Myosins (metabolism)
• Phosphorylation
• Protein Kinases (metabolism)
• Sarcomeres (metabolism, ultrastructure)
• alpha-Crystallin B Chain (metabolism)