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ATF4 Promotes Skeletal Muscle Atrophy by Forming a Heterodimer with C/EBPbeta

ABSTRACT: Skeletal muscle atrophy is a highly prevalent and debilitating condition that remains poorly understood at the molecular level. Previous work found that skeletal muscle atrophy involves activating transcription factor 4 (ATF4), a protein in the basic leucine zipper (bZIP) transcription factor family. However, the direct biochemical mechanism by which ATF4 promotes muscle atrophy was unknown. Because bZIP proteins such as ATF4 must dimerize to bind and activate genes, and because ATF4 is unable to form highly stable homodimers, we hypothesized that ATF4 may promote muscle atrophy by heterodimerizing with another bZIP family member. To test this hypothesis, we biochemically isolated skeletal muscle proteins that associate with the dimerization- and DNA-binding domain of ATF4 (the bZIP domain) in mouse skeletal muscle fibers in vivo. Interestingly, we found that ATF4 makes up one half of at least 5 distinct heterodimeric bZIP transcription factors in skeletal muscle fibers. This three-way interaction between ATF4, C/EBPbeta and the ATF4-C/EBP composite site activates the Gadd45a gene, which encodes a known mediator of muscle atrophy (Gadd45a). Together, these results identify a direct biochemical mechanism by which ATF4 induces skeletal muscle atrophy and provide new insight into the way that skeletal muscle atrophy occurs at the molecular level.

INSTRUMENT(S): TripleTOF 6600

ORGANISM(S): Mus Musculus (ncbitaxon:10090)

SUBMITTER: Birgit Schilling

PROVIDER: MSV000084538 | MassIVE | Mon Nov 04 17:33:00 GMT 2019

SECONDARY ACCESSION(S): PXD016139

REPOSITORIES: MassIVE

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Project description:The degenerative loss of muscle associated with aging leading to muscular atrophy is called sarcopenia. Currently, practicing regular physical exercise is the only efficient way to delay the onset of sarcopenia. To identify therapeutic targets to suppress the symptoms of aging, there is a need for in vivo model organisms of accelerated muscle degeneration and atrophy. The zebrafish harbors hallmarks of aging, notably mitochondrial dysfunction, telomeres shortening and accumulation of senescent cells. Unfortunately, zebrafish aged slowly, and no specific zebrafish models of accelerated muscle atrophy associated with aging or sarcopenia are currently available. We have developed a new genetic tool to efficiently accelerate muscle fibers degeneration and muscle tissue atrophy in zebrafish larvae and adults. We used a gain-of-function strategy with a molecule that has been shown to be necessary and sufficient to induce muscle atrophy and a sarcopenia phenotype in mammals: Atrogin1 (also named Fbxo32). We report the generation, validation, and characterization of a zebrafish genetic model of accelerated muscle atrophy, the sarcofish. We demonstrated that specific expression of Atrogin1 in skeletal muscle tissue induces a muscle atrophic phenotype associated with locomotion dysfunctions in both larvae and adult fish. We identified that degradation of the myosin light chain as an event occurring before the degeneration of muscle fibers. Biological processes associated with muscle aging such as inflammation, proteolysis, apoptosis and stress response are upregulated in the sarcofish. Surprisingly, we observed a strong correlation between muscle fibers degeneration and a reduction of neuromuscular junctions in the peripheral nervous system, as well as neuronal cell bodies in the spinal cord, suggesting that muscle atrophy could underly a neurodegenerative phenotype in the central nervous system. Finally, while sarcofish larvae harbor regeneration of muscle fibers, spinal neurons and recover locomotive functions, adult sarcofish have impaired regenerative capacities as observed in mammals during muscle aging. In the future, the sarcofish could open new strategies in the fight against the sarcopenia disease to test therapeutic molecules aiming to treat or alleviate the symptoms of muscle aging.

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ATF4 Promotes Skeletal Muscle Atrophy by Forming a Heterodimer with C/EBPbeta

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