Pathogenetic mechanisms and genotype-phenotype correlations in nemaline myopathies and related disorders caused by mutations in tropomyosin genes and nebulin
Year: 2014
Type: dissertation
Abstract: We collected all mutations in TPM2 and TPM3 genes hitherto found to cause congenital myopathies, to perform genotype-phenotype correlations, and to increase our understanding of the pathogenetic mechanisms of congenital myopathies caused by mutations in the tropomyosin and nebulin genes. Nemaline myopathy (NM), a rare, genetic muscle disorder defined on the basis of muscle dysfunction and the presence of structural abnormalities in the muscle fibres (i.e. nemaline bodies), is caused by mutations in ten genes known to date: Nebulin (NEB), α-actin (ACTA1), α-tropomyosin (TPM3), β-tropomyosin (TPM2), troponin T (TNNT1), cofilin 2 (CFL2), KBTBD13, KLHL40, KLHL41 and leiomodin 3 (LMOD 3). Tropomyosin controls muscle contraction by inhibiting the actin myosin interaction in a calcium-sensitive manner. Mutations in tropomyosin genes may cause NM, cap myopathy, congenital fibre-type disproportion, distal arthrogryposes and Escobar syndrome. We correlated the clinical picture of these diseases to novel and previously published mutations to the TPM2 (30 mutations) and TPM3 (20 mutations) genes. Mutations in TPM2 and TPM3 caused an increased Ca2+ sensitivity, resulting in a hypercontractile molecular phenotype. We studied the pathogenetic mechanisms to which five disease-causing mutations in β-tropomyosin (p.Glu41Lys, p.Lys49del, p.Glu117Lys, p.Glu139del and p.Gln147Pro) lead. We showed that four of the mutations cause changes in the affinity for actin leading to muscle weakness in patients, while two mutations show defective Ca2+ activation of contractility. Nebulin (NEB) is a giant 600 900-kDa filamentous protein in thin filament. We produced four wild-type nebulin super-repeats and five corresponding mutation constructs (p.Glu2431Lys, p.Ser4665Ile, p.Thr5681Pro, p.Arg2478_Asp2512del and p.Val3681_Asn3686del) in the study. The mutations were identified in patients with NM or distal myopathy. We performed F-actin and tropomyosin-binding experiments for the nebulin fragments. Our results demonstrate actin nebulin interactions and, for the first time, tropomyosin nebulin interactions in vitro, and show that the interactions are altered by disease-causing mutations. This suggests that an abnormal interaction between aberrant thin filament proteins is a pathogenetic mechanism in NM and related disorders.
Source: Työväentutkimus Vuosikirja
Author: M. Marttila
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1495130248