KLHL40 deficiency destabilizes thin filament proteins and promotes nemaline myopathy
Ankit Garg, … , Rhonda Bassel-Duby, Eric N. Olson
Ankit Garg, … , Rhonda Bassel-Duby, Eric N. Olson
Published June 24, 2014
Citation Information: J Clin Invest. 2014;124(8):3529-3539. https://doi.org/10.1172/JCI74994.
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Research Article

KLHL40 deficiency destabilizes thin filament proteins and promotes nemaline myopathy

Abstract

Nemaline myopathy (NM) is a congenital myopathy that can result in lethal muscle dysfunction and is thought to be a disease of the sarcomere thin filament. Recently, several proteins of unknown function have been implicated in NM, but the mechanistic basis of their contribution to disease remains unresolved. Here, we demonstrated that loss of a muscle-specific protein, kelch-like family member 40 (KLHL40), results in a nemaline-like myopathy in mice that closely phenocopies muscle abnormalities observed in KLHL40-deficient patients. We determined that KLHL40 localizes to the sarcomere I band and A band and binds to nebulin (NEB), a protein frequently implicated in NM, as well as a putative thin filament protein, leiomodin 3 (LMOD3). KLHL40 belongs to the BTB-BACK-kelch (BBK) family of proteins, some of which have been shown to promote degradation of their substrates. In contrast, we found that KLHL40 promotes stability of NEB and LMOD3 and blocks LMOD3 ubiquitination. Accordingly, NEB and LMOD3 were reduced in skeletal muscle of both Klhl40–/– mice and KLHL40-deficient patients. Loss of sarcomere thin filament proteins is a frequent cause of NM; therefore, our data that KLHL40 stabilizes NEB and LMOD3 provide a potential basis for the development of NM in KLHL40-deficient patients.

Authors

Ankit Garg, Jason O’Rourke, Chengzu Long, Jonathan Doering, Gianina Ravenscroft, Svetlana Bezprozvannaya, Benjamin R. Nelson, Nadine Beetz, Lin Li, She Chen, Nigel G. Laing, Robert W. Grange, Rhonda Bassel-Duby, Eric N. Olson

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Figure 3

KO mice have disrupted muscle structure and function.

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KO mice have disrupted muscle structure and function. (A) Longitudinal s...
(A) Longitudinal sections of P8 diaphragm muscles from WT and KO mice stained with desmin (red), DAPI (blue), and wheat germ agglutinin (green). The white arrow indicates disrupted myofibers. The white arrowhead denotes fibers staining abnormally for desmin that are more frequent in, but not specific to, KO muscles. Insets show normal striated pattern of Z lines in WT muscles but that some KO fibers have complete loss of sarcomere organization. Scale bar: 20 μm. (B) Electron microscopy analysis of longitudinal sections of P8 diaphragms from WT and KO mice shows some highly disorganized fibers. The red “Z” with red arrowhead indicates representative Z line in WT section. The yellow arrowhead denotes representative nemaline-like body. Scale bar: 1 μm. (C) Maximum contractile force of P1 WT, Klhl40+/– (HET), and KO hind limb following 150-Hz stimulation, normalized to limb mass. KO muscle shows greater than 50% loss of force compared with that of both WT and HET mice (WT, n = 6; HET, n = 17; and KO, n = 8). *P < 0.05, FDR = 0.05. Data are presented as mean ± SEM.