scholarly journals Activating transcription factor 4 (ATF4) promotes skeletal muscle atrophy by forming a heterodimer with the transcriptional regulator C/EBPβ

2020 ◽  
Vol 295 (9) ◽  
pp. 2787-2803 ◽  
Author(s):  
Scott M. Ebert ◽  
Steven A. Bullard ◽  
Nathan Basisty ◽  
George R. Marcotte ◽  
Zachary P. Skopec ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Transcription Factor ◽  
Muscle Atrophy ◽  
Molecular Level ◽  
Muscle Fibers ◽  
Skeletal Muscle Atrophy ◽  
Skeletal Muscle Fibers ◽  
Activating Transcription Factor 4 ◽  
Activating Transcription Factor ◽  
Transcription Factor 4

Skeletal muscle atrophy is a highly-prevalent and debilitating condition that remains poorly understood at the molecular level. Previous work found that aging, fasting, and immobilization promote skeletal muscle atrophy via expression of activating transcription factor 4 (ATF4) in skeletal muscle fibers. However, the direct biochemical mechanism by which ATF4 promotes muscle atrophy is unknown. ATF4 is a member of the basic leucine zipper transcription factor (bZIP) superfamily. Because bZIP transcription factors are obligate dimers, and because ATF4 is unable to form highly-stable homodimers, we hypothesized that ATF4 may promote muscle atrophy by forming a heterodimer 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 forms at least five distinct heterodimeric bZIP transcription factors in skeletal muscle fibers. Furthermore, one of these heterodimers, composed of ATF4 and CCAAT enhancer-binding protein β (C/EBPβ), mediates muscle atrophy. Within skeletal muscle fibers, the ATF4–C/EBPβ heterodimer interacts with a previously unrecognized and evolutionarily conserved ATF–C/EBP composite site in exon 4 of the Gadd45a gene. This three-way interaction between ATF4, C/EBPβ, and the ATF–C/EBP composite site activates the Gadd45a gene, which encodes a critical mediator of muscle atrophy. Together, these results identify a biochemical mechanism by which ATF4 induces skeletal muscle atrophy, providing molecular-level insights into the etiology of skeletal muscle atrophy.

scholarly journals Induction of autophagy through the activating transcription factor 4 (ATF4)-dependent amino acid response pathway in maternal skeletal muscle may function as the molecular memory in response to gestational protein restriction to alert offspring to maternal nutrition

2015 ◽  
Vol 114 (4) ◽  
pp. 519-532 ◽  
Author(s):  
Huan Wang ◽  
Gabriel J. Wilson ◽  
Dan Zhou ◽  
Stéphane Lezmi ◽  
Xiuwen Chen ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Transcription Factor ◽  
Amino Acid ◽  
Protein Expression ◽  
Mrna Expression ◽  
Protein Restriction ◽  
Activating Transcription Factor 4 ◽  
Activating Transcription Factor ◽  
Transcription Factor 4

The aim of the present study was to investigate the mechanistic basis of protein deficiency during pregnancy in mother that is transduced to offspring. To this end, timed-pregnant Sprague–Dawley rats were fed either a control (20 % of energy from protein) or low-protein (LP, 8 % of energy from protein) diet during gestation. Tissues were collected after delivery from rat dams, and skeletal muscle was collected at postnatal day 38 from the offspring. Quantitative RT-PCR and Western blot analyses were performed to determine mRNA and protein levels. Histological analysis was performed to evaluate myofibre size. LP dams gained significantly less weight during pregnancy, developed muscle atrophy, and had significantly lower circulating threonine and histidine levels than control dams. The mRNA expression of the well-known amino acid response (AAR) pathway-related target genes was increased only in the skeletal muscle of LP dams, as well as the protein expression levels of activating transcription factor 4 (ATF4) and phosphorylated eukaryotic translation initiation factor 2α (p-eIF2α). The mRNA expression of autophagy-related genes was significantly increased in the skeletal muscle of LP dams. Moreover, the mRNA expression of genes involved in both AAR and autophagy pathways remained elevated and was memorised in the muscle of LP offspring that consumed a post-weaning control diet. Additionally, the LP diet increased an autophagy marker, microtubule-associated proteins 1A/1B light chain 3B (LC3B) protein expression in the skeletal muscle of rat dams, consistent with the initiation of autophagy. The LP diet further increased ATF4 binding at the predicted regions of AAR and autophagy pathway-related genes. Increased binding of ATF4 unveils the crucial role of ATF4 in the activation of autophagy in response to protein restriction. Our data suggest that molecular changes in maternal muscle are memorised in the offspring long after gestational protein restriction, reinforcing the role of maternal signalling in programming offspring health.

scholarly journals Elevated nuclear Foxo1 suppresses excitability of skeletal muscle fibers

2013 ◽  
Vol 305 (6) ◽  
pp. C643-C653 ◽  
Author(s):  
Erick O. Hernández-Ochoa ◽  
Tova Neustadt Schachter ◽  
Martin F. Schneider
Keyword(s):  
Skeletal Muscle ◽  
Electrical Stimulation ◽  
Muscle Atrophy ◽  
Action Potentials ◽  
Muscle Fibers ◽  
Calcium Transients ◽  
Skeletal Muscle Atrophy ◽  
Nuclear Activity ◽  
Ec Coupling ◽  
Skeletal Muscle Fibers

Forkhead box O 1 (Foxo1) controls the expression of proteins that carry out processes leading to skeletal muscle atrophy, making Foxo1 of therapeutic interest in conditions of muscle wasting. The transcription of Foxo1-regulated proteins is dependent on the translocation of Foxo1 to the nucleus, which can be repressed by insulin-like growth factor-1 (IGF-1) treatment. The role of Foxo1 in muscle atrophy has been explored at length, but whether Foxo1 nuclear activity affects skeletal muscle excitation-contraction (EC) coupling has not yet been examined. Here, we use cultured adult mouse skeletal muscle fibers to investigate the effects of Foxo1 overexpression on EC coupling. Fibers expressing Foxo1-green fluorescent protein (GFP) exhibit an inability to contract, impaired propagation of action potentials, and ablation of calcium transients in response to electrical stimulation compared with fibers expressing GFP alone. Evaluation of the transverse (T)-tubule system morphology, the membranous system involved in the radial propagation of the action potential, revealed an intact T-tubule network in fibers overexpressing Foxo1-GFP. Interestingly, long-term IGF-1 treatment of Foxo1-GFP fibers, which maintains Foxo1-GFP outside the nucleus, prevented the loss of normal calcium transients, indicating that Foxo1 translocation and the atrogenes it regulates affect the expression of proteins involved in the generation and/or propagation of action potentials. A reduction in the sodium channel Nav1.4 expression in fibers overexpressing Foxo1-GFP was also observed in the absence of IGF-1. We conclude that increased nuclear activity of Foxo1 prevents the normal muscle responses to electrical stimulation and that this indicates a novel capability of Foxo1 to disable the functional activity of skeletal muscle.

scholarly journals Human and Rodent Skeletal Muscles Express Angiotensin II Type 1 Receptors

Cells ◽  
2020 ◽  
Vol 9 (7) ◽  
pp. 1688
Author(s):  
Rafael Deminice ◽  
Hayden Hyatt ◽  
Toshinori Yoshihara ◽  
Mustafa Ozdemir ◽  
Branden Nguyen ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Angiotensin Ii ◽  
Muscle Atrophy ◽  
Muscle Fibers ◽  
Skeletal Muscle Atrophy ◽  
Type I ◽  
Single Muscle ◽  
Rat Skeletal Muscle ◽  
Skeletal Muscle Fibers

Abundant evidence reveals that activation of the renin-angiotensin system promotes skeletal muscle atrophy in several conditions including congestive heart failure, chronic kidney disease, and prolonged mechanical ventilation. However, controversy exists about whether circulating angiotensin II (AngII) promotes skeletal muscle atrophy by direct or indirect effects; the centerpiece of this debate is the issue of whether skeletal muscle fibers express AngII type 1 receptors (AT1Rs). While some investigators assert that skeletal muscle expresses AT1Rs, others argue that skeletal muscle fibers do not contain AT1Rs. These discordant findings in the literature are likely the result of study design flaws and additional research using a rigorous experimental approach is required to resolve this issue. We tested the hypothesis that AT1Rs are expressed in both human and rat skeletal muscle fibers. Our premise was tested using a rigorous, multi-technique experimental design. First, we established both the location and abundance of AT1Rs on human and rat skeletal muscle fibers by means of an AngII ligand-binding assay. Second, using a new and highly selective AT1R antibody, we carried out Western blotting and determined the abundance of AT1R protein within isolated single muscle fibers from humans and rats. Finally, we confirmed the presence of AT1R mRNA in isolated single muscle fibers from rats. Our results support the hypothesis that AT1Rs are present in both human and rat skeletal muscle fibers. Moreover, our experiments provide the first evidence that AT1Rs are more abundant in fast, type II muscle fibers as compared with slow, type I fibers. Together, these discoveries provide the foundation for an improved understanding of the mechanism(s) responsible for AngII-induced skeletal muscle atrophy.

scholarly journals Activating Transcription Factor 4 Is Translationally Regulated by Hypoxic Stress

2004 ◽  
Vol 24 (17) ◽  
pp. 7469-7482 ◽  
Author(s):  
Jaime D. Blais ◽  
Vasilisa Filipenko ◽  
Meixia Bi ◽  
Heather P. Harding ◽  
David Ron ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Microarray Analysis ◽  
Initiation Factor ◽  
Hypoxic Stress ◽  
Unfolded Protein ◽  
Activating Transcription Factor 4 ◽  
Activating Transcription Factor ◽  
The Unfolded Protein Response ◽  
Protein Response ◽  
Transcription Factor 4

ABSTRACT Hypoxic stress results in a rapid and sustained inhibition of protein synthesis that is at least partially mediated by eukaryotic initiation factor 2α (eIF2α) phosphorylation by the endoplasmic reticulum (ER) kinase PERK. Here we show through microarray analysis of polysome-bound RNA in aerobic and hypoxic HeLa cells that a subset of transcripts are preferentially translated during hypoxia, including activating transcription factor 4 (ATF4), an important mediator of the unfolded protein response. Changes in mRNA translation during the unfolded protein response are mediated by PERK phosphorylation of the translation initiation factor eIF2α at Ser-51. Similarly, PERK is activated and is responsible for translational regulation under hypoxic conditions, while inducing the translation of ATF4. The overexpression of a C-terminal fragment of GADD34 that constitutively dephosphorylates eIF2α was able to attenuate the phosphorylation of eIF2α and severely inhibit the induction of ATF4 in response to hypoxic stress. These studies demonstrate the essential role of ATF4 in the response to hypoxic stress, define the pathway for its induction, and reveal that GADD34, a target of ATF4 activation, negatively regulates the eIF2α-mediated inhibition of translation. Taken with the concomitant induction of additional ER-resident proteins identified by our microarray analysis, this study suggests an important integrated response between ER signaling and the cellular adaptation to hypoxic stress.

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