Ankyrin repeat and SOCS box protein 15 regulates protein synthesis in skeletal muscle

Deletion of Asb15b gene can lead to a significant decrease in zebrafish intermuscular bone

Intermuscular bones, which are present in numerous economically significant fish species, have a negative impact on the development of aquaculture. The Asb15b gene, primarily expressed in skeletal muscle, plays a crucial role in regulating protein turnover and the development of muscle fibers. It stimulates protein synthesis and controls the differentiation of muscle fibers. In this study, we employed CRISPR/Cas9 technology to generate homozygous zebrafish strains with 7 bp and 49 bp deletions in the Asb15b gene. Subsequent analyses using skeleton staining demonstrated a substantial reduction in the number of intermuscular bones in adult Asb15b-/- -7 bp and Asb15b-/- -49 bp mutants compared to the wild-type zebrafish, with decreases of 30 % (P < 0.001) and 40 % (P < 0.0001), respectively. Histological experiments further revealed that the diameter and number of muscle fibers in adult Asb15b-/- mutants did not exhibit significant changes when compared to wild-type zebrafish. Moreover, qRT-PCR experiments demonstrated significant differences in the expression of bmp6 and runx2b genes, which are key regulators of intermuscular bone development, during different stages of intermuscular bone development in Asb15b-/- mutants. This study strongly suggests that the Asb15b gene plays a crucial role in regulating intermuscular bone development in fish and lays the groundwork for further exploration of the role of the Asb15b gene in zebrafish intermuscular bone development.

Subregion-specific transcriptomic profiling of rat brain reveals sex-distinct gene expression impacted by adolescent stress

Stress during adolescence clearly impacts brain development and function. Sex differences in adolescent stress-induced or exacerbated emotional and metabolic vulnerabilities could be due to sex-distinct gene expression in hypothalamic, limbic, and prefrontal brain regions. However, adolescent stress-induced whole-genome expression changes in key subregions of these brain regions were unclear. In this study, female and male adolescent Sprague Dawley rats received one-hour restraint stress daily from postnatal day (PD) 32 to PD44. Corticosterone levels, body weights, food intake, body composition, and circulating adiposity and sex hormones were measured. On PD44, brain and blood samples were collected. Using RNA-sequencing, sex-specific differences in stress-induced differentially expressed (DE) genes were identified in subregions of the hypothalamus, limbic system, and prefrontal cortex. Canonical pathways reflected well-known sex-distinct maladies and diseases, substantiating the therapeutic potential of the DE genes found in the current study. Thus, we proposed specific sex distinct, adolescent stress-induced transcriptional changes found in the current study as examples of the molecular bases for sex differences witnessed in stress induced or exacerbated emotional and metabolic disorders. Future behavioral studies and single-cell studies are warranted to test the implications of the DE genes identified in this study in sex-distinct stress-induced susceptibilities.

Exercise-induced expression of genes associated with aging in the hippocampus of rats

Recent research has underscored the influence of aging and exercise on brain function. In this study, we aimed to explore alterations in the expression of novel molecular factors and gain insight into underlying molecular mechanisms in the hippocampus of rats engaged in voluntary wheel running. We assessed the expression of aging-related genes in the hippocampus using a high-throughput whole genome DNA microarray approach in rats engaged in voluntary running for four weeks. The results indicated that compared to the control group, wheel running significantly altered the expressions of aging-related genes in the hippocampus. Functional categorization, utilizing pathway-focused gene classifications and disease state-focused gene classifications, along with Ingenuity Pathway Analysis (IPA), revealed changes in expression pattern in major categories of cell death and survival, renal necrosis/cell death, and cardiovascular disease genes. These findings suggest that exercise may mitigate the risk of age-related cognitive decline by regulating of aging-related genes in the hippocampus. Further research is warranted to elucidate the mechanisms driving changes in gene expression and to determine the long-term effects of exercise on brain function.

Mining of chicken muscle growth genes and the function of important candidate gene RPL3L in muscle development

The birth weight of chickens does not significantly affect the weight at slaughter, while the different growth rate after birth was one of the important reasons for the difference in slaughter weight. Also, the increase in chickens' postnatal skeletal muscle weight is the main cause of the slaughter weight gain, but which genes are involved in this biological process is still unclear. In this study, by integrating four transcriptome datasets containing chicken muscles at different developmental times or different chicken tissues in public databases, a total of nine candidate genes that may be related to postnatal muscle development in chickens were obtained, including RPL3L, FBP2, ASB4, ASB15, CKMT2, PGAM1, YIPF7, PFKM, and LDHA. One of these candidate genes is RPL3L, whose 42 bp insertion/deletion (indel) mutation significantly correlated with multiple carcass traits in the F2 resource population from Xinghua chickens crossing with White Recessive Rock (WRR) chickens, including live weight, carcass weight, half eviscerated weight, eviscerated weight, breast meat weight, wing weight, leg muscle shear force, and breast muscle shear force. Also, there was a very significant difference between different genotypes of the RPL3L 42 bp indel mutation in these trains. Further experiments showed that RPL3L was highly expressed in chicken skeletal muscle, and its overexpression could promote the proliferation and inhibit the differentiation of chicken myoblasts by regulating ASB4 and ASB15 expression. Our findings demonstrated that the RPL3L 42 bp indel may be one of the molecular markers of chicken weight-related traits.

SNP within the bovine ASB-3 gene and their association analysis with stature traits in three Chinese cattle breeds

ASB-3 is one of the 18 members of ASB gene family. As a special negative regulation factor of TNF-R2, ASB-3 inhibits the signal transduction of JNK-TNF-R2 and JNK-STAT signaling pathway by TNF-R2 protein. In this study, the genetic polymorphisms of ASB-3 were detected in total of 637 from Qinchuan, Jinnan and Xianan cattle using the sequence of mixed DNA pool, Tetra-primer ARMS-PCR and PCR-RFLP methods. Four mutation sites were detected including the g.C41255T, g.G74754A, and g.T75438C were synonymous mutation, whereas the g.C115213T was missense mutation (Pro > Ser). The associated analysis of four polymorphic loci of ASB-3 gene respectively with growth traits in the three cattle breeds. The result showed that SNP1 site was significantly related with Qinchuan cattle height and TT was the dominant genotype; SNP2 had a significant relationship with body length of Xianan cattle and cross department height of Qinchuan cattle, AA was the dominant genotype; SNP3 was significantly related to cross height of Xianan cattle, TT was the dominant genotype; SNP4 site was significantly correlated with body height of Xianan cattle and cross height of Jinnan cattle. Genotype combinations were only significantly correlated with the hucklebone width in the adult Qinchuan cattle. The combination genotype CTAGCTCC was outperformed other combination genotypes of Qinchuan cattle. The results showed that ASB-3 could be an important candidate gene and the four SNPs in ASB-3 can be used for molecular marker-assisted selection of four beef cattle breeds.

Identification of muscle-specific candidate genes in Simmental beef cattle using imputed next generation sequencing

Genome-wide association studies (GWAS) have commonly been used to identify candidate genes that control economically important traits in livestock. Our objective was to detect potential candidate genes associated mainly with muscle development traits related to dimension of hindquarter in cattle. A next generation sequencing (NGS) dataset to imputed to 12 million single nucleotide polymorphisms (SNPs) (from 1252 Simmental beef cattle) were used to search for genes affecting hindquarter traits using a linear, mixed model approach. We also used haplotype and linkage disequilibrium blocks to further support our identifications. We identified 202 significant SNPs in the bovine BTA4 chromosome region associated with width of hind leg, based on a stringent statistical threshold (p = 0.05/ effective number of SNPs identified). After exploring the region around these SNPs, we found candidate genes that were potentially related to the associated markers. More importantly, we identified a region of approximately 280 Kb on the BTA4 chromosome that harbored several muscle specific candidate genes, genes to be in a potential region for muscle development. However, we also found candidate gene SLC13A1 on BTA4, which seems to be associated with bone disorders (such as chondrodysplasia) in Simmental beef cattle.

Identification of multiple risk loci and regulatory mechanisms influencing susceptibility to multiple myeloma

Genome-wide association studies (GWAS) have transformed our understanding of susceptibility to multiple myeloma (MM), but much of the heritability remains unexplained. We report a new GWAS, a meta-analysis with previous GWAS and a replication series, totalling 9974 MM cases and 247,556 controls of European ancestry. Collectively, these data provide evidence for six new MM risk loci, bringing the total number to 23. Integration of information from gene expression, epigenetic profiling and in situ Hi-C data for the 23 risk loci implicate disruption of developmental transcriptional regulators as a basis of MM susceptibility, compatible with altered B-cell differentiation as a key mechanism. Dysregulation of autophagy/apoptosis and cell cycle signalling feature as recurrently perturbed pathways. Our findings provide further insight into the biological basis of MM.

Genes Whose Gain or Loss-Of-Function Increases Skeletal Muscle Mass in Mice: A Systematic Literature Review

Skeletal muscle mass differs greatly in mice and humans and this is partially inherited. To identify muscle hypertrophy candidate genes we conducted a systematic review to identify genes whose experimental loss or gain-of-function results in significant skeletal muscle hypertrophy in mice. We found 47 genes that meet our search criteria and cause muscle hypertrophy after gene manipulation. They are from high to small effect size: Ski, Fst, Acvr2b, Akt1, Mstn, Klf10, Rheb, Igf1, Pappa, Ppard, Ikbkb, Fstl3, Atgr1a, Ucn3, Mcu, Junb, Ncor1, Gprasp1, Grb10, Mmp9, Dgkz, Ppargc1a (specifically the Ppargc1a4 isoform), Smad4, Ltbp4, Bmpr1a, Crtc2, Xiap, Dgat1, Thra, Adrb2, Asb15, Cast, Eif2b5, Bdkrb2, Tpt1, Nr3c1, Nr4a1, Gnas, Pld1, Crym, Camkk1, Yap1, Inhba, Tp53inp2, Inhbb, Nol3, Esr1. Knock out, knock down, overexpression or a higher activity of these genes causes overall muscle hypertrophy as measured by an increased muscle weight or cross sectional area. The mean effect sizes range from 5 to 345% depending on the manipulated gene as well as the muscle size variable and muscle investigated. Bioinformatical analyses reveal that Asb15, Klf10, Tpt1 are most highly expressed hypertrophy genes in human skeletal muscle when compared to other tissues. Many of the muscle hypertrophy-regulating genes are involved in transcription and ubiquitination. Especially genes belonging to three signaling pathways are able to induce hypertrophy: (a) Igf1-Akt-mTOR pathway, (b) myostatin-Smad signaling, and (c) the angiotensin-bradykinin signaling pathway. The expression of several muscle hypertrophy-inducing genes and the phosphorylation of their protein products changes after human resistance and high intensity exercise, in maximally stimulated mouse muscle or in overloaded mouse plantaris.

Promoter analysis and tissue expression of the chicken ASB15 gene

1. This study was conducted to explore the promoter region of the chicken ASB15 gene by detecting the activities of the dual luciferase reporter gene and to assess expression profiles of the ASB15 gene in 10 different tissues from Gushi chickens. 2. Five dual luciferase reporter gene vectors were constructed and transfected into DF1 cells. The activities of recombined plasmids were measured and the core promoter was confirmed by bioinformatic analysis. Total RNA was extracted and the relative expression of the ASB15 gene was examined. 3. Data analysis indicated that the promoter was located from -955 to -212 bp. Results showed that the chicken ASB15 gene was expressed in heart, breast muscle and leg muscle. 4. This study has confirmed the promoter region and the expression profile of the chicken ASB15 gene, which provides a foundation for further exploring its transcriptional regulation and function.

Polymorphisms of Flanking Region of the ASB15 Gene and Their Associations with Performance Traits in Chicken

Research on the identity of genes and their relationship with traits of economic importance in chickens could assist in the selection of poultry. In this study, an F₂ resource population of Gushi chickens crossed with Anka broilers was used to detect single-nucleotide polymorphisms (SNPs) in the flanking region of the ASB15 gene by DNA sequencing and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). One SNP of -1271 C>T in 5' flanking region of the chicken ASB15 gene and two SNPs of the 10618 A>G and 10716 G>A in 3' flanking region were identified. Furthermore, the 10618 A>G and 10716 G>A in 3' flanking region were in complete linkage. Association analysis results showed that -1271 C>T was not associated with performance traits, while the 10618 A>G and 10716 G>A were significantly associated with BW2, 4, 6, 8, 10, 12, SL12, CD8, CW4, 8, 12, BSL4, 8, 12, and SEW, EW, WW, BMW, LW, CW, SFT. Our results suggest that the ASB15 gene profoundly affects chicken performance traits.

Transcriptomic effects of adenosine 2A receptor deletion in healthy and endotoxemic murine myocardium

Influences of adenosine 2A receptor (A_2AR) activity on the cardiac transcriptome and genesis of endotoxemic myocarditis are unclear. We applied transcriptomic profiling (39 K Affymetrix arrays) to identify A_2AR-sensitive molecules, revealed by receptor knockout (KO), in healthy and endotoxemic hearts. Baseline cardiac function was unaltered and only 37 A_2AR-sensitive genes modified by A_2AR KO (≥1.2-fold change, <5 % FDR); the five most induced are Mtr, Ppbp, Chac1, Ctsk and Cnpy2 and the five most repressed are Hp, Yipf4, Acta1, Cidec and Map3k2. Few canonical paths were impacted, with altered Gnb1, Prkar2b, Pde3b and Map3k2 (among others) implicating modified G protein/cAMP/PKA and cGMP/NOS signalling. Lipopolysaccharide (LPS; 20 mg/kg) challenge for 24 h modified >4100 transcripts in wild-type (WT) myocardium (≥1.5-fold change, FDR < 1 %); the most induced are Lcn2 (+590); Saa3 (+516); Serpina3n (+122); Cxcl9 (+101) and Cxcl1 (+89) and the most repressed are Car3 (-38); Adipoq (-17); Atgrl1/Aplnr (-14); H19 (-11) and Itga8 (-8). Canonical responses centred on inflammation, immunity, cell death and remodelling, with pronounced amplification of toll-like receptor (TLR) and underlying JAK-STAT, NFκB and MAPK pathways, and a 'cardio-depressant' profile encompassing suppressed ß-adrenergic, PKA and Ca²⁺ signalling, electromechanical and mitochondrial function (and major shifts in transcripts impacting function/injury including Lcn2, S100a8/S100a9, Icam1/Vcam and Nox2 induction, and Adipoq, Igf1 and Aplnr repression). Endotoxemic responses were selectively modified by A_2AR KO, supporting inflammatory suppression via A_2AR sensitive shifts in regulators of NFκB and JAK-STAT signalling (IκBζ, IκBα, STAT1, CDKN1a and RRAS2) without impacting the cardio-depressant gene profile. Data indicate A_2ARs exert minor effects in un-stressed myocardium and selectively suppress NFκB and JAK-STAT signalling and cardiac injury without influencing cardiac depression in endotoxemia.

Genome-wide association study of short-acting β2-agonists. A novel genome-wide significant locus on chromosome 2 near ASB3

RATIONALE

β2-Agonists are the most common form of treatment of asthma, but there is significant variability in response to these medications. A significant proportion of this responsiveness may be heritable.

OBJECTIVES

To investigate whether a genome-wide association study (GWAS) could identify novel pharmacogenetic loci in asthma.

METHODS

We performed a GWAS of acute bronchodilator response (BDR) to inhaled β2-agonists. A total of 444,088 single-nucleotide polymorphisms (SNPs) were examined in 724 individuals from the SNP Health Association Resource (SHARe) Asthma Resource Project (SHARP). The top 50 SNPs were carried forward to replication in a population of 444 individuals.

MEASUREMENTS AND MAIN RESULTS

The combined P value for four SNPs reached statistical genome-wide significance aftercorrecting for multiple comparisons. Combined P values for rs350729, rs1840321, rs1384918, and rs1319797 were 2.21 × 10(-10), 5.75 × 10(-8), 9.3 × 10(-8), and 3.95 × 10(-8), respectively. The significant variants all map to a novel genetic region on chromosome 2 near the ASB3 gene, a region associated with smooth muscle proliferation. As compared with the wild type, the presence of the minor alleles reduced the degree of BDR by 20% in the original population and by a similar percentage in the confirmatory population.

CONCLUSIONS

These GWAS findings for BDR in subjects with asthma suggest that a gene associated with smooth muscle proliferation may influence a proportion of the smooth muscle relaxation that occurs in asthma.

asb11 is a regulator of embryonic and adult regenerative myogenesis

The specific molecular determinants that govern progenitor expansion and final compartment size in the myogenic lineage, either during gestation or during regenerative myogenesis, remain largely obscure. Recently, we retrieved d-asb11 from a zebrafish screen designed to identify gene products that are downregulated during embryogenesis upon terminal differentiation and identified it as a potential regulator of compartment size in the ectodermal lineage. A role in mesodermal derivatives remained, however, unexplored. Here we report pan-vertebrate expression of Asb11 in muscle compartments, where it highly specifically localizes to the Pax7(+) muscle satellite cell compartment. Forced expression of d-asb11 impaired terminal differentiation and caused enhanced proliferation in the myogenic progenitor compartment both in in vivo and in vitro model systems. Conversely, introduction of a germline hypomorphic mutation in the zebrafish d-asb11 gene produced premature differentiation of the muscle progenitors and delayed regenerative responses in adult injured muscle. Thus, the expression of d-asb11 is necessary for muscle progenitor expansion, whereas its downregulation marks the onset of terminal differentiation. Hence, we provide evidence that d-asb11 is a principal regulator of embryonic as well as adult regenerative myogenesis.

Chromatin immunoprecipitation-promoter microarray identification of genes regulated by PRDM16 in murine embryonic palate mesenchymal cells

The transcription factor PRDM16 regulates differentiation of brown adipocyte tissue in mice. Recently, however, it has been demonstrated that genetic knockout of Prdm16 in mice leads to a complete cleft of the secondary palate in offspring. To identify genes whose promoters bind PRDM16 in mouse embryonic palate/maxillary mesenchymal cells, we have conducted a chromatin immunoprecipitation-promoter microarray analysis (ChIP-Chip). One hundred and twenty-two gene promoters were identified as capable of binding PRDM16. These could be functionally grouped to include those on genes linked to muscle development, chondrogenesis and osteogenesis, in addition to many transcription factors. These results suggest that PRDM16 may play a role in differentiation of mesenchymal cells in the embryonic secondary palate that contribute to the anterior, bony palate and posterior, muscular palate.

Gene expression profiling in gastric mucosa from Helicobacter pylori-infected and uninfected patients undergoing chronic superficial gastritis

Helicobacter pylori infection reprograms host gene expression and influences various cellular processes, which have been investigated by cDNA microarray using in vitro culture cells and in vivo gastric biopsies from patients of the Chronic Abdominal Complaint. To further explore the effects of H. pylori infection on host gene expression, we have collected the gastric antral mucosa samples from 6 untreated patients with gastroscopic and pathologic confirmation of chronic superficial gastritis. Among them three patients were infected by H. pylori and the other three patients were not. These samples were analyzed by a microarray chip which contains 14,112 cloned cDNAs, and microarray data were analyzed via BRB ArrayTools software and Ingenuity Pathways Analysis (IPA) website. The results showed 34 genes of 38 differentially expressed genes regulated by H. pylori infection had been annotated. The annotated genes were involved in protein metabolism, inflammatory and immunological reaction, signal transduction, gene transcription, trace element metabolism, and so on. The 82% of these genes (28/34) were categorized in three molecular interaction networks involved in gene expression, cancer progress, antigen presentation and inflammatory response. The expression data of the array hybridization was confirmed by quantitative real-time PCR assays. Taken together, these data indicated that H. pylori infection could alter cellular gene expression processes, escape host defense mechanism, increase inflammatory and immune responses, activate NF-κB and Wnt/β-catenin signaling pathway, disturb metal ion homeostasis, and induce carcinogenesis. All of these might help to explain H. pylori pathogenic mechanism and the gastroduodenal pathogenesis induced by H. pylori infection.

The E3 ubiquitin ligase specificity subunit ASB2α targets filamins for proteasomal degradation by interacting with the filamin actin-binding domain

Filamins are an important family of actin-binding and crosslinking proteins that mediate remodeling of the actin cytoskeleton and maintain extracellular matrix connections by anchoring transmembrane proteins to actin filaments and linking them to intracellular signaling cascades. We recently found that filamins are targeted for proteasomal degradation by the E3 ubiquitin ligase specificity subunit ASBα and that acute degradation of filamins through this ubiquitin-proteasome pathway correlates with cell differentiation. Specifically, in myeloid leukemia cells retinoic-acid-induced expression of ASB2α triggers filamin degradation and recapitulates early events crucial for cell differentiation. ASB2α is thought to link substrates to the ubiquitin transferase machinery; however, the mechanism by which ASB2α interacts with filamin to induce degradation remained unknown. Here, we use cell-based and biochemical assays to show that the subcellular localization of ASB2α to actin-rich structures is dependent on filamin and that the actin-binding domain (ABD) of filamin mediates the interaction with ASB2α. Furthermore, we show that the ABD is necessary and sufficient for ASB2α-mediated filamin degradation. We propose that ASB2α exerts its effect by binding the ABD and mediating its polyubiquitylation, so targeting filamins for degradation. These studies provide the molecular basis for ASB2α-mediated filamin degradation and unravel an important mechanism by which filamin levels can be acutely regulated.

Essential role for the d-Asb11 cul5 Box domain for proper notch signaling and neural cell fate decisions in vivo

ECS (Elongin BC-Cul2/Cul5-SOCS-box protein) ubiquitin ligases recruit substrates to E2 ubiquitin-conjugating enzymes through a SOCS-box protein substrate receptor, an Elongin BC adaptor and a cullin (Cul2 or Cul5) scaffold which interacts with the RING protein. In vitro studies have shown that the conserved amino acid sequence of the cullin box in SOCS-box proteins is required for complex formation and function. However, the in vivo importance of cullin boxes has not been addressed. To explore the biological functions of the cullin box domain of ankyrin repeat and SOCS-box containing protein 11 (d-Asb11), a key mediator of canonical Delta-Notch signaling, we isolated a zebrafish mutant lacking the Cul5 box (Asb11^Cul). We found that homozygous zebrafish mutants for this allele were defective in Notch signaling as indicated by the impaired expression of Notch target genes. Importantly, asb11^Cul fish were not capable to degrade the Notch ligand DeltaA during embryogenesis, a process essential for the initiation of Notch signaling during neurogenesis. Accordingly, proper cell fate specification within the neurogenic regions of the zebrafish embryo was impaired. In addition, Asb11^Cul mRNA was defective in the ability to transactivate a her4::gfp reporter DNA when injected in embryos. Thus, our study reporting the generation and the characterization of a metazoan organism mutant in the conserved cullin binding domain of the SOCS-box demonstrates a hitherto unrecognized importance of the SOCS-box domain for the function of this class of cullin-RING ubiquitin ligases and establishes that the d-Asb11 cullin box is required for both canonical Notch signaling and proper neurogenesis.

ASB9 interacts with ubiquitous mitochondrial creatine kinase and inhibits mitochondrial function

BACKGROUND

The ankyrin repeat and suppressor of cytokine signalling (SOCS) box proteins (Asbs) are a large protein family implicated in diverse biological processes including regulation of proliferation and differentiation. The SOCS box of Asb proteins is important in a ubiquitination-mediated proteolysis pathway. Here, we aimed to evaluate expression and function of human Asb-9 (ASB9).

RESULTS

We found that a variant of ASB9 that lacks the SOCS box (ASB9DeltaSOCS) was naturally detected in human cell lines but not in peripheral blood mononuclear cells or normal hepatocytes. We also identified ubiquitous mitochondrial creatine kinase (uMtCK) as a new target of ASB9 in human embryonic kidney 293 (HEK293) cells. The ankyrin repeat domains of ASB9 can associate with the substrate binding site of uMtCK in a SOCS box-independent manner. The overexpression of ASB9, but not ASB9DeltaSOCS, induces ubiquitination of uMtCK. ASB9 and ASB9DeltaSOCS can interact and colocalise with uMtCK in the mitochondria. However, only expression of ASB9 induced abnormal mitochondrial structure and a decrease of mitochondrial membrane potential. Furthermore, the creatine kinase activities and cell growth were significantly reduced by ASB9 but not by ASB9DeltaSOCS.

CONCLUSIONS

ASB9 interacts with the creatine kinase system and negatively regulates cell growth. The differential expression and function of ASB9 and ASB9DeltaSOCS may be a key factor in the growth of human cell lines and primary cells.

Comparative gene expression profiling between human cultured myotubes and skeletal muscle tissue

Background

A high-sensitivity DNA microarray platform requiring nanograms of RNA input facilitates the application of transcriptome analysis to individual skeletal muscle (SM) tissue samples. Culturing myotubes from SM-biopsies enables investigating transcriptional defects and assaying therapeutic strategies. This study compares the transcriptome of aneurally cultured human SM cells versus that of tissue biopsies.

Results

We used the Illumina expression BeadChips to determine the transcriptomic differences between tissue and cultured SM samples from five individuals. Changes in the expression of several genes were confirmed by QuantiGene Plex assay or reverse transcription real-time PCR. In cultured myotubes compared to the tissue, 1216 genes were regulated: 583 down and 633 up. Gene ontology analysis showed that downregulated genes were mainly associated with cytoplasm, particularly mitochondria, and involved in metabolism and the muscle-system/contraction process. Upregulated genes were predominantly related to cytoplasm, endoplasmic reticulum, and extracellular matrix. The most significantly regulated pathway was mitochondrial dysfunction. Apoptosis genes were also modulated. Among the most downregulated genes detected in this study were genes encoding metabolic proteins AMPD1, PYGM, CPT1B and UCP3, muscle-system proteins TMOD4, MYBPC1, MYOZ1 and XIRP2, the proteolytic CAPN3 and the myogenic regulator MYF6. Coordinated reduced expression of five members of the GIMAP gene family, which form a cluster on chromosome 7, was shown, and the GIMAP4-reduction was validated. Within the most upregulated group were genes encoding senescence/apoptosis-related proteins CDKN1A and KIAA1199 and potential regulatory factors HIF1A, TOP2A and CCDC80.

Conclusions

Cultured muscle cells display reductive metabolic and muscle-system transcriptome adaptations as observed in muscle atrophy and they activate tissue-remodeling and senescence/apoptosis processes.

Expression profiling of skeletal muscle following acute and chronic beta2-adrenergic stimulation: implications for hypertrophy, metabolism and circadian rhythm

Background

Systemic administration of β-adrenoceptor (β-AR) agonists has been found to induce skeletal muscle hypertrophy and significant metabolic changes. In the context of energy homeostasis, the importance of β-AR signaling has been highlighted by the inability of β_1-3-AR-deficient mice to regulate energy expenditure and susceptibility to diet induced obesity. However, the molecular pathways and gene expression changes that initiate and maintain these phenotypic modulations are poorly understood. Therefore, the aim of this study was to identify differential changes in gene expression in murine skeletal muscle associated with systemic (acute and chronic) administration of the β₂-AR agonist formoterol.

Results

Skeletal muscle gene expression (from murine tibialis anterior) was profiled at both 1 and 4 hours following systemic administration of the β₂-AR agonist formoterol, using Illumina 46K mouse BeadArrays. Illumina expression profiling revealed significant expression changes in genes associated with skeletal muscle hypertrophy, myoblast differentiation, metabolism, circadian rhythm, transcription, histones, and oxidative stress. Differentially expressed genes relevant to the regulation of muscle mass and metabolism (in the context of the hypertrophic phenotype) were further validated by quantitative RT-PCR to examine gene expression in response to both acute (1-24 h) and chronic administration (1-28 days) of formoterol at multiple timepoints. In terms of skeletal muscle hypertrophy, attenuation of myostatin signaling (including differential expression of myostatin, activin receptor IIB, phospho-Smad3 etc) was observed following acute and chronic administration of formoterol. Acute (but not chronic) administration of formoterol also significantly induced the expression of genes involved in oxidative metabolism, including hexokinase 2, sorbin and SH3 domain containing 1, and uncoupling protein 3. Interestingly, formoterol administration also appeared to influence some genes associated with the peripheral regulation of circadian rhythm (including nuclear factor interleukin 3 regulated, D site albumin promoter binding protein, and cryptochrome 2).

Conclusion

This is the first study to utilize gene expression profiling to examine global gene expression in response to acute β₂-AR agonist treatment of skeletal muscle. In summary, systemic administration of a β₂-AR agonist had a profound effect on global gene expression in skeletal muscle. In terms of hypertrophy, β₂-AR agonist treatment altered the expression of several genes associated with myostatin signaling, a previously unreported effect of β-AR signaling in skeletal muscle. This study also demonstrates a β₂-AR agonist regulation of circadian rhythm genes, indicating crosstalk between β-AR signaling and circadian cycling in skeletal muscle. Gene expression alterations discovered in this study provides insight into many of the underlying changes in gene expression that mediate β-AR induced skeletal muscle hypertrophy and altered metabolism.

The E3 ubiquitin ligase specificity subunit ASB2beta is a novel regulator of muscle differentiation that targets filamin B to proteasomal degradation

Ubiquitin-mediated protein degradation is the main mechanism for controlled proteolysis, which is crucial for muscle development and maintenance. The ankyrin repeat-containing protein with a suppressor of cytokine signaling box 2 gene (ASB2) encodes the specificity subunit of an E3 ubiquitin ligase complex involved in differentiation of hematopoietic cells. Here, we provide the first evidence that a novel ASB2 isoform, ASB2beta, is important for muscle differentiation. ASB2beta is expressed in muscle cells during embryogenesis and in adult tissues. ASB2beta is part of an active E3 ubiquitin ligase complex and targets the actin-binding protein filamin B (FLNb) for proteasomal degradation. Thus, ASB2beta regulates FLNb functions by controlling its degradation. Knockdown of endogenous ASB2beta by shRNAs during induced differentiation of C2C12 cells delayed FLNb degradation as well as myoblast fusion and expression of muscle contractile proteins. Finally, knockdown of FLNb in ASB2beta knockdown cells restores myogenic differentiation. Altogether, our results suggest that ASB2beta is involved in muscle differentiation through the targeting of FLNb to destruction by the proteasome.

Role of beta-adrenoceptor signaling in skeletal muscle: implications for muscle wasting and disease

The importance of beta-adrenergic signaling in the heart has been well documented, but it is only more recently that we have begun to understand the importance of this signaling pathway in skeletal muscle. There is considerable evidence regarding the stimulation of the beta-adrenergic system with beta-adrenoceptor agonists (beta-agonists). Although traditionally used for treating bronchospasm, it became apparent that some beta-agonists could increase skeletal muscle mass and decrease body fat. These so-called "repartitioning effects" proved desirable for the livestock industry trying to improve feed efficiency and meat quality. Studying beta-agonist effects on skeletal muscle has identified potential therapeutic applications for muscle wasting conditions such as sarcopenia, cancer cachexia, denervation, and neuromuscular diseases, aiming to attenuate (or potentially reverse) the muscle wasting and associated muscle weakness, and to enhance muscle growth and repair after injury. Some undesirable cardiovascular side effects of beta-agonists have so far limited their therapeutic potential. This review describes the physiological significance of beta-adrenergic signaling in skeletal muscle and examines the effects of beta-agonists on skeletal muscle structure and function. In addition, we examine the proposed beneficial effects of beta-agonist administration on skeletal muscle along with some of the less desirable cardiovascular effects. Understanding beta-adrenergic signaling in skeletal muscle is important for identifying new therapeutic targets and identifying novel approaches to attenuate the muscle wasting concomitant with many diseases.

Changes in skeletal muscle gene expression following clenbuterol administration

Background

Beta-adrenergic receptor agonists (BA) induce skeletal muscle hypertrophy, yet specific mechanisms that lead to this effect are not well understood. The objective of this research was to identify novel genes and physiological pathways that potentially facilitate BA induced skeletal muscle growth. The Affymetrix platform was utilized to identify gene expression changes in mouse skeletal muscle 24 hours and 10 days after administration of the BA clenbuterol.

Results

Administration of clenbuterol stimulated anabolic activity, as indicated by decreased blood urea nitrogen (BUN; P < 0.01) and increased body weight gain (P < 0.05) 24 hours or 10 days, respectively, after initiation of clenbuterol treatment. A total of 22,605 probesets were evaluated with 52 probesets defined as differentially expressed based on a false discovery rate of 10%. Differential mRNA abundance of four of these genes was validated in an independent experiment by quantitative PCR. Functional characterization of differentially expressed genes revealed several categories that participate in biological processes important to skeletal muscle growth, including regulators of transcription and translation, mediators of cell-signalling pathways, and genes involved in polyamine metabolism.

Conclusion

Global evaluation of gene expression after administration of clenbuterol identified changes in gene expression and overrepresented functional categories of genes that may regulate BA-induced muscle hypertrophy. Changes in mRNA abundance of multiple genes associated with myogenic differentiation may indicate an important effect of BA on proliferation, differentiation, and/or recruitment of satellite cells into muscle fibers to promote muscle hypertrophy. Increased mRNA abundance of genes involved in the initiation of translation suggests that increased levels of protein synthesis often associated with BA administration may result from a general up-regulation of translational initiators. Additionally, numerous other genes and physiological pathways were identified that will be important targets for further investigations of the hypertrophic effect of BA on skeletal muscle.