Article

A Myopathy-linked Desmin Mutation Perturbs Striated Muscle Actin Filament Architecture

Department of Cell Biology and Anatomy, University of Arizona, Tucson, AZ 85724, USA.
Molecular biology of the cell (Impact Factor: 4.47). 12/2008; 20(3):834-45. DOI: 10.1091/mbc.E08-07-0753
Source: PubMed

ABSTRACT

Desmin interacts with nebulin establishing a direct link between the intermediate filament network and sarcomeres at the Z-discs. Here, we examined a desmin mutation, E245D, that is located within the coil IB (nebulin-binding) region of desmin and that has been reported to cause human cardiomyopathy and skeletal muscle atrophy. We show that the coil IB region of desmin binds to C-terminal nebulin (modules 160-164) with high affinity, whereas binding of this desmin region containing the E245D mutation appears to enhance its interaction with nebulin in solid-phase binding assays. Expression of the desmin-E245D mutant in myocytes displaces endogenous desmin and C-terminal nebulin from the Z-discs with a concomitant increase in the formation of intracellular aggregates, reminiscent of a major histological hallmark of desmin-related myopathies. Actin filament architecture was strikingly perturbed in myocytes expressing the desmin-E245D mutant because most sarcomeres contained elongated or shorter actin filaments. Our findings reveal a novel role for desmin intermediate filaments in modulating actin filament lengths and organization. Collectively, these data suggest that the desmin E245D mutation interferes with the ability of nebulin to precisely regulate thin filament lengths, providing new insights into the potential molecular consequences of expression of certain disease-associated desmin mutations.

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    • "Desmin is the major IF protein found in skeletal and heart muscle that has a vital role in maintaining the structural integrity of myocytes and contributes to force transmission. Actin forms the microfilaments and is also an integral part of the cytoskeleton and contractile apparatus (Gloria et al. 2009). Engler and coworkers have shown that the elasticity and rigidity of scaffolds directly affects the maintenance and differentiation of cells (Engler et al. 2006). "
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    ABSTRACT: Electrospinning is a well-established technique that uses a high electric field to fabricate ultrafine fibrous scaffolds from both natural and synthetic polymers to mimic the cellular microenvironment. Collagen is one of the most preferred biopolymers, due to its widespread occurrence in nature and its biocompatibility. Electrospinning of collagen alone has been reported, with fluoroalcohols such as hexafluoroisopropanol (HFIP) and trifluoroethanol (TFE), but the resultant collagen lost its characteristic ultrastructural integrity of D-periodicity 67 nm banding, confirmed by transmission electron microscopy (TEM), and the fluoroalcohols used were toxic to the environment. In this study, we describe the use of glacial acetic acid and DMSO to dissolve collagen and generate electrospun nanofibers of collagen type 1, which is non-toxic and economical. TEM analysis revealed the characteristic feature of native collagen triple helical repeats, showing 67 nm D-periodicity banding pattern and confirming that the ultrastructural integrity of the collagen was maintained. Analysis by scanning electron microscopy (SEM) showed fiber diameters in the range of 200-1100 nm. Biocompatibility of the three-dimensional (3D) scaffolds was established by MTT assays using rat skeletal myoblasts (L6 cell line) and confocal microscopic analysis of immunofluorescent-stained sections of collagen scaffolds for muscle-specific markers such as desmin and actin. Primary neonatal rat ventricular cardiomyocytes (NRVCM) seeded onto the collagen scaffolds were able to maintain their contractile function for a period of 17 days and also expressed higher levels of desmin when compared with 2D cultures. We report for the first time that collagen type 1 can be electrospun without blending with copolymers using the novel benign solvent combination, and the method can be potentially explored for applications in tissue engineering.
    Full-text · Article · May 2015 · Artificial Cells
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    • "That desmin tethers adjacent Z-disks is supported by work on a desmin KO mouse in which Z-disk misalignment was shown to occur in stretched muscle (Shah et al., 2002). In vitro work, using a yeast two-hybrid approach, suggested that desmin binds to the C-terminal region of nebulin (Bang et al., 2002), which is anchored in the Z-disk, and recently it was shown that nebulin modules M160–170 are involved in this interaction (Conover et al., 2009; Conover and Gregorio, 2011). These findings lead Bang et al. to speculate that this desmin-nebulin interaction links myofibrillar Z-disks to the intermediate filament system, thereby forming a lateral linkage system which maintains adjacent Z-disks in register. "
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    ABSTRACT: The sliding filament model of the sarcomere was developed more than half a century ago. This model, consisting only of thin and thick filaments, has been successful in explaining many, but not all, features of skeletal muscle. Work during the 1980s revealed the existence of two additional filaments: the giant filamentous proteins titin and nebulin. Whereas the role of titin rapidly progressed, nebulin's role in muscle structure and function remained long nebulous. An important feature of muscle structure and function that has remained relatively obscure concerns the mechanisms that are involved in regulating thin filament length. Filament length is an important aspect of muscle function as force production is proportional to the amount of overlap between thick and thin filaments. Recent advances, due in part to the generation of nebulin KO models, reveal that nebulin plays an important role in the regulation of thin filament length, most likely by stabilizing F-actin assemblies. Another structural feature of skeletal muscle that has been incompletely understood concerns the mechanisms involved in maintaining Z-disk structure and the regular lateral alignment of adjacent sarcomeres during contraction. Recent studies indicate that nebulin is part of a protein complex that mechanically links adjacent myofibrils. In addition to these structural roles in support of myofibrillar force generation, nebulin has been also shown to regulate directly muscle contraction at the level of individual crossbridges: cycling kinetics and the calcium sensitivity of force producing crossbridges is enhanced in the presence of nebulin. Thus, these recent data all point to nebulin being important for muscle force optimization. Consequently, muscle weakness as the lead symptom develops in the case of patients with nemaline myopathy that have mutations in the nebulin gene. Here, we discuss these important novel insights into the role of nebulin in skeletal muscle function.
    Full-text · Article · Feb 2012 · Frontiers in Physiology
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    • "That desmin tethers adjacent Z-disks is supported by work on a desmin KO mouse in which Z-disk misalignment was shown to occur in stretched muscle [24]. In vitro work, using a yeast two-hybrid approach, suggested that desmin binds to the C-terminal region of nebulin [25], which is anchored in the Z-disk, and recently it was shown that nebulin modules M160–164 are involved in this interaction [26]. These findings lead Bang et al. to speculate that this desmin-nebulin interaction links myofibrillar Zdisks to the intermediate filament system, thereby forming a lateral linkage system which maintains adjacent Z-disks in register. "
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    ABSTRACT: One important feature of muscle structure and function that has remained relatively obscure is the mechanism that regulates thin filament length. Filament length is an important aspect of muscle function as force production is proportional to the amount of overlap between thick and thin filaments. Recent advances, due in part to the generation of nebulin KO models, reveal that nebulin plays an important role in the regulation of thin filament length. Another structural feature of skeletal muscle that is not well understood is the mechanism involved in maintaining the regular lateral alignment of adjacent sarcomeres, that is, myofibrillar connectivity. Recent studies indicate that nebulin is part of a protein complex that mechanically links adjacent myofibrils. Thus, novel structural roles of nebulin in skeletal muscle involve the regulation of thin filament length and maintaining myofibrillar connectivity. When these functions of nebulin are absent, muscle weakness ensues, as is the case in patients with nemaline myopathy with mutations in nebulin. Here we review these new insights in the role of nebulin in skeletal muscle structure.
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