Project description:Skeletal muscle atrophy is a serious and highly prevalent condition that remains poorly understood at the molecular level. Previous work found that skeletal muscle atrophy involves an increase in skeletal muscle Gadd45a expression, which is necessary and sufficient for skeletal muscle fiber atrophy. However, the direct mechanism by which Gadd45a promotes skeletal muscle atrophy was unknown. To address this question, we biochemically isolated skeletal muscle fiber proteins that associate with Gadd45a as it induces skeletal muscle atrophy in living mice. We found that Gadd45a interacts with multiple proteins in skeletal muscle fibers, including, most prominently, the MAP kinase kinase kinase MEKK4. Furthermore, by forming a complex with MEKK4 in skeletal muscle fibers, Gadd45a increases MEKK4 protein kinase activity, which is sufficient to induce skeletal muscle fiber atrophy and required for Gadd45a-mediated skeletal muscle fiber atrophy. Together, these results identify a direct biochemical mechanism by which Gadd45a induces skeletal muscle atrophy and provide new insight into way that skeletal muscle atrophy occurs at the molecular level.
Project description: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.
Project description:FOXO1, a member of the FOXO forkhead type transcription factors, is markedly up-regulated in skeletal muscle during atrophy. Previously, we created transgenic mice specifically overexpressing FOXO1 in skeletal muscle (FOXO1 Tg mice). These mice weighed less than the wildtype control mice, had a reduced skeletal muscle mass. In this study, to better understand changes in skeletal muscle during atrophy, we performed a microarray analysis of skeletal muscle in wild-type control and FOXO1 Tg mice. The microarray data shows that in the skeletal muscles of FOXO1 Tg mice, gene expression of PGC-1β, a transcriptional regulator whose increased expression activates energy-expenditure-related genes in skeletal muscles, is decreased.
Project description:Injury of skeletal muscle is a common occurence affecting millions worldwide. Injuries usually are not major incisions into daily life, however, the underlying health varies e. g. due to obesity. Obesity is usually accompanied by excessive and dysfunctional lipid depots, chronic low-grade inflammation as well as several co-morbidities, which are able to impair the regeneration of skeletal muscle. A blunt injury approach was used to damage mouse skeletal muscle of the extensor iliotibialis anticus in both obese and normal weight C57BL/6J mice. Microarray analysis was used to assess the molecular fingerprint in different stages of muscle regeneration while observing different health conditions.
Project description:To investigate the possible changes of genes expression during muscle atrophy, we performed bulk RNA-seq of skeletal muscle from C57 BL/6 mice with or without denervation (2 weeks).
Project description:In skeletal muscle, the pattern of electrical activity regulates the expression of proteins involved in synaptic transmission, contraction and metabolism. Disruptions in electrical activity, resulting from prolonged bed-rest, cast-immobilization or trauma, inevitably lead to muscle atrophy. The mechanisms that regulate muscle atrophy are poorly understood, but it seems likely that changes in gene expression play a key role in initiating and maintaining a muscle atrophy program. Previously, we found that Runx1, a transcription factor previously termed AML1, was substantially induced in muscle following denervation. More recently, we sought to determine whether this increase in Runx1 expression may be causally related to the morphological changes in skeletal muscle that accompany muscle disuse, notably muscle atrophy. We found that Runx1 is indeed required to sustain muscle and to minimize atrophy following denervation. Experiments described here are designed to identify the genes that are regulated by Runx1 in skeletal muscle with the particular goal of identifying genes that regulate muscle atrophy. We propose to use microarray analysis to identify genes, expressed in skeletal muscle, that are mis-regulated in mice lacking Runx1. We inactivated runx1 selectively in skeletal muscle and found that denervated myofibers in mutant mice atrophy far more (90% atrophy) than in wild-type mice (30% atrophy). We therefore reason that Runx1 activates and/or represses genes that are required to sustain muscle and to minimize atrophy. We generated MCK::cre; runx1f/- and runx1f/- control mice. In normal mice, an increase in runx1 expression is detected by two days after denervation and is maximal by five days after denervation. Muscle atrophy is first evident between one and two weeks after denervation. As we wish to avoid detecting global changes in gene expression that are associated with late stages of muscle atrophy, we plan to denervate muscle for three or five days and to compare gene expression in dissected innervated and denervated muscles from mutant and control mice. We will generate thirty samples for comparison-5 replicates per condition: Samples 1-3 from runx1f/- control mice. (1) innervated tibialis anterior muscles (TA); (2) 3-day-denervated TA; (3) 5-day-denervated TA. Samples 4-6 from MCK::cre; runx1f/- mice. (4) innervated TA; (5) 3-day-denervated TA; (6) 5-day-denervated TA. We obtain sufficient total RNA (10 micrograms) from each dissected muscle to avoid pooling samples. We will analyze adult mice of the same age (~six weeks after birth; most will be littermates) and sex-male. It is difficult to anticipate how many genes will be identified in this screen, as few target genes for Runx1 have been identified in any cell type and none in skeletal muscle. Moreover, although we would prefer to focus our attention on genes that are strongly dependent upon Runx1 expression (e.g. more than 5-fold difference in expression in wild-type and mutant mice), we do not know the extent to which target gene expression will depend upon Runx1. For these reasons, in these experiments, we will analyze expression from five âidenticalâ samples, so that we can be confident that even small (e.g. three-fold) differences in expression can be reliably determined. Importantly, in order to confirm results obtained from the microarray data, we will use other assays (RNase protection) to measure RNA expression of candidate genes in innervated and denervated muscles of wild-type and mutant mice.
Project description:Endogenous retroviruses (ERVs) are transposable elements that cause host genome instability and usually play deleterious roles such as tumorigenesis. Recent advances also suggest that this 'enemy within' may encode viral mimic to induce antiviral immune responses through viral sensors. Here, through whole genome RNA-seq we discovered a full-length ERV-derived long non-coding RNA (lncRNA), designated lnc-EPAV (ERV-derived lncRNA positively regulates antiviral responses), as a positive regulator of NF-κB signaling. Lnc-EPAV expression was rapidly up-regulated by viral RNA mimic or RNA viruses to facilitate the expression of RELA, an NF-κB subunit that plays a critical role in antiviral responses. In turn, RELA promoted the transcription of lnc-EPAV to form a positive feedback loop. Transcriptome analysis of lnc-EPAV-silenced macrophages, combined with gain- and loss-of-function experiments, showed that lnc-EPAV was critical for induction of type I interferon (IFN) and inflammatory cytokine expression by RNA viruses. Consistently, lnc-EPAV-deficient mice exhibited reduced expression of type I IFNs, and consequently increased viral loads and mortality following lethal RNA virus infection. Mechanistically, lnc-EPAV promoted expression of RELA by competitively binding to and displacing SFPQ, a transcriptional repressor of RELA. The binding between ERV-derived RNAs and SFPQ also existed in human cells. Altogether, our work demonstrates an alternative mechanism by which ERVs regulate antiviral immune responses.