Leiomodin-3 dysfunction results in thin filament disorganization and nemaline myopathy
Michaela Yuen, et al.
Michaela Yuen, et al.
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Research Article

Leiomodin-3 dysfunction results in thin filament disorganization and nemaline myopathy

Abstract

Nemaline myopathy (NM) is a genetic muscle disorder characterized by muscle dysfunction and electron-dense protein accumulations (nemaline bodies) in myofibers. Pathogenic mutations have been described in 9 genes to date, but the genetic basis remains unknown in many cases. Here, using an approach that combined whole-exome sequencing (WES) and Sanger sequencing, we identified homozygous or compound heterozygous variants in LMOD3 in 21 patients from 14 families with severe, usually lethal, NM. LMOD3 encodes leiomodin-3 (LMOD3), a 65-kDa protein expressed in skeletal and cardiac muscle. LMOD3 was expressed from early stages of muscle differentiation; localized to actin thin filaments, with enrichment near the pointed ends; and had strong actin filament-nucleating activity. Loss of LMOD3 in patient muscle resulted in shortening and disorganization of thin filaments. Knockdown of lmod3 in zebrafish replicated NM-associated functional and pathological phenotypes. Together, these findings indicate that mutations in the gene encoding LMOD3 underlie congenital myopathy and demonstrate that LMOD3 is essential for the organization of sarcomeric thin filaments in skeletal muscle.

Authors

Michaela Yuen, Sarah A. Sandaradura, James J. Dowling, Alla S. Kostyukova, Natalia Moroz, Kate G. Quinlan, Vilma-Lotta Lehtokari, Gianina Ravenscroft, Emily J. Todd, Ozge Ceyhan-Birsoy, David S. Gokhin, Jérome Maluenda, Monkol Lek, Flora Nolent, Christopher T. Pappas, Stefanie M. Novak, Adele D’Amico, Edoardo Malfatti, Brett P. Thomas, Stacey B. Gabriel, Namrata Gupta, Mark J. Daly, Biljana Ilkovski, Peter J. Houweling, Ann E. Davidson, Lindsay C. Swanson, Catherine A. Brownstein, Vandana A. Gupta, Livija Medne, Patrick Shannon, Nicole Martin, David P. Bick, Anders Flisberg, Eva Holmberg, Peter Van den Bergh, Pablo Lapunzina, Leigh B. Waddell, Darcée D. Sloboda, Enrico Bertini, David Chitayat, William R. Telfer, Annie Laquerrière, Carol C. Gregorio, Coen A.C. Ottenheijm, Carsten G. Bönnemann, Katarina Pelin, Alan H. Beggs, Yukiko K. Hayashi, Norma B. Romero, Nigel G. Laing, Ichizo Nishino, Carina Wallgren-Pettersson, Judith Melki, Velia M. Fowler, Daniel G. MacArthur, Kathryn N. North, Nigel F. Clarke

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Figure 9

Levels of LMOD2 and TMOD4 are altered in LMOD3-NM.

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Levels of LMOD2 and TMOD4 are altered in LMOD3-NM. (A) Western blot anal...
(A) Western blot analysis of thin filament pointed end proteins LMOD2, TMOD1, and TMOD4 in patients with LMOD3-NM and age-matched controls. Coomassie-stained MHC, sarcomeric actin, GAPDH, and α-actinin-2 served as loading controls. (B) Histograms show normalized protein levels for TMOD1, TMOD4, and LMOD2 in patients with LMOD3-NM and controls. TMOD1 expression levels are variable in both patients and controls, with no consistent difference between these groups. TMOD4 levels are consistently reduced in patients with LMOD3-NM compared with age-matched controls. LMOD2 expression is upregulated in patients. Densitometry was performed using ImageJ, and values were normalized to α-actinin-2 levels and are scaled to mean control level = 1.0. Patients with low or no expression of muscle proteins were excluded from analysis (e.g., patient 4). Dotted lines show the average results for patients and controls, respectively.