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Loss of Hectd1 disrupts muscle sarcomere assembly and causes combined desmin-nemaline myopathy

ABSTRACT: The sarcomere is the muscle contractile unit, whose assembly and disassembly are intimately linked to changes in myofiber size and function. Mutations in sarcomeric proteins are common causes of myopathies, ranging from severe neonatal to adult-onset forms. Here, we identify HECTD1 as an E3 ubiquitin ligase necessary for sarcomere maintenance. We show that silencingHectd1 in myotubesreduces the levels of proteins critical for sarcomere integrity including a-actin, titin, troponins, tropomyosins, and several myosin heavy chain isoforms. We further establish that Hectd1 ubiquitylates and stabilizes the molecular chaperones KLHL40/41, that when dysfunctional destabilize nebulin and other sarcomere thin filament proteins (causing nemaline myopathy). Consequently, skeletal muscle-specific Hectd1 knockout mice (Hectd1 mKO) show progressive muscle weakness, exercise intolerance, and unresolved tissue remodeling. Molecular and histological analysis of Hectd1 mKO muscle revealed subsarcolemmal storage of the scaffold protein desmin, mitochondrial abnormalities, and severe sarcomere disorganization. This work uncovers Hectd1 as an E3 ligase critical for sarcomere assembly, and a novel diagnostic gene for myopathy with features of nemaline and desmin myopathy.

ORGANISM(S): Mus musculus

PROVIDER: GSE272775 | GEO | 2024/07/26

REPOSITORIES: GEO

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Project description:Desmin, the major intermediate filament (IF) protein in muscle cells, interlinks neighboring myofibrils and connects the whole myofibrillar apparatus to myonuclei, mitochondria, and the sarcolemma. However, desmin is also known to be enriched at postsynaptic membranes of neuromuscular junctions (NMJs). The pivotal role of the desmin IF cytoskeletal network is underscored by the fact that over 100 mutations of the human DES gene cause hereditary and sporadic myopathies and cardiomyopathies. A subgroup of human desminopathies comprises autosomal recessive cases resulting in complete abolition of desmin protein. In these patients, who display a more severe phenotype than the autosomal dominant cases, it has been reported that some individuals also suffer from a myasthenic syndrome in addition to the classical occurrence of myopathy and cardiomyopathy. Since further studies on the NMJ pathology is hampered by the lack of available human striated muscle biopsy specimens, we exploited homozygous desmin knock-out mice which closely mirror the striated muscle pathology of human patients lacking desmin protein. Here, we report on the impact of the lack of desmin on the structure and function of NMJs and on the transcription of genes coding for postsynaptic proteins. Desmin knock-out mice display a fragmentation of NMJs in soleus, but not in extensor digitorum longus muscle. Moreover, soleus muscle fibers show larger NMJs. Further, transcription levels of acetylcholine receptor (AChR) genes are increased in muscles from desmin knock-out mice, especially of the AChR subunit, which is known as a marker of muscle fiber regeneration. Electrophysiological recordings depicted a pathological decrement of nerve-dependent endplate potentials and a faster rise time of the nerve-independent miniature endplate potentials. The latter is indicating an enhanced opening time of the AChR channels. Our study highlights the essential role of desmin for the structural and functional integrity of mammalian neuromuscular junctions.

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Loss of Hectd1 disrupts muscle sarcomere assembly and causes combined desmin-nemaline myopathy

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