Mustn1 ablation in skeletal muscle results in functional alterations

Mustn1, a gene expressed exclusively in the musculoskeletal system, was shown in previous in vitro studies to be a key regulator of myogenic differentiation and myofusion. Other studies also showed Mustn1 expression associated with skeletal muscle development and hypertrophy. However, its specific role in skeletal muscle function remains unclear. This study sought to investigate the effects of Mustn1 in a conditional knockout (KO) mouse model in Pax7 positive skeletal muscle satellite cells. Specifically, we investigated the potential effects of Mustn1 on myogenic gene expression, grip strength, alterations in gait, ex vivo investigations of isolated skeletal muscle isometric contractions, and potential changes in the composition of muscle fiber types. Results indicate that Mustn1 KO mice did not present any substantial phenotypic changes or significant variations in genes related to myogenic differentiation and fusion. However, an approximately 10% decrease in overall grip strength was observed in the 2-month-old KO mice in comparison to the control wild type (WT), but this decrease was not significant when normalized by weight. KO mice also generated approximately 8% higher vertical force than WT at 4 months in the hindlimb. Ex vivo experiments revealed decreases in about 20 to 50% in skeletal muscle contractions and about 10%-20% fatigue in soleus of both 2- and 4-month-old KO mice, respectively. Lastly, immunofluorescent analyses showed a persistent increase of Type IIb fibers up to 15-fold in the KO mice while Type I fibers decreased about 20% and 30% at both 2 and 4 months, respectively. These findings suggest a potential adaptive or compensatory mechanism following Mustn1 loss, as well as hinting at an association between Mustn1 and muscle fiber typing. Collectively, Mustn1's complex roles in skeletal muscle physiology requires further research, particularly in terms of understanding the potential role of Mustn1 in muscle repair and regeneration, as well as with influence of exercise. Collectively, these will offer valuable insights into Mustn1's key biological functions and regulatory pathways.

asb5a/asb5b Double Knockout Affects Zebrafish Cardiac Contractile Function

Ankyrin repeat and suppression-of-cytokine-signaling box (Asb) proteins, a subset of ubiquitin ligase E3, include Asb5 with six ankyrin-repeat domains. Zebrafish harbor two asb5 gene isoforms, asb5a and asb5b. Currently, the effects of asb5 gene inactivation on zebrafish embryonic development and heart function are unknown. Using CRISPR/Cas9, we generated asb5a-knockout zebrafish, revealing no abnormal phenotypes at 48 h post-fertilization (hpf). In situ hybridization showed similar asb5a and asb5b expression patterns, indicating the functional redundancy of these isoforms. Morpholino interference was used to target asb5b in wild-type and asb5a-knockout zebrafish. Knocking down asb5b in the wild-type had no phenotypic impact, but simultaneous asb5b knockdown in asb5a-knockout homozygotes led to severe pericardial cavity enlargement and atrial dilation. RNA-seq and cluster analyses identified significantly enriched cardiac muscle contraction genes in the double-knockout at 48 hpf. Moreover, semi-automatic heartbeat analysis demonstrated significant changes in various heart function indicators. STRING database/Cytoscape analyses confirmed that 11 cardiac-contraction-related hub genes exhibited disrupted expression, with three modules containing these genes potentially regulating cardiac contractile function through calcium ion channels. This study reveals functional redundancy in asb5a and asb5b, with simultaneous knockout significantly impacting zebrafish early heart development and contraction, providing key insights into asb5's mechanism.

Paraspinal Muscle Health is Related to Fibrogenic, Adipogenic, and Myogenic Gene Expression in Patients with Lumbar Spine Pathology

BACKGROUND

Lumbar spine pathology is a common feature of lower back and/or lower extremity pain and is associated with observable degenerative changes in the lumbar paraspinal muscles that are associated with poor clinical prognosis. Despite the commonly observed phenotype of muscle degeneration in this patient population, its underlying molecular mechanisms are not well understood. The aim of this study was to investigate the relationships between groups of genes within the atrophic, myogenic, fibrogenic, adipogenic, and inflammatory pathways and multifidus muscle health in individuals undergoing surgery for lumbar spine pathology.

METHODS

Multifidus muscle biopsies were obtained from patients (n = 59) undergoing surgery for lumbar spine pathology to analyze 42 genes from relevant adipogenic/metabolic, atrophic, fibrogenic, inflammatory, and myogenic gene pathways using quantitative polymerase chain reaction. Multifidus muscle morphology was examined preoperatively in these patients at the level and side of biopsy using T2-weighted magnetic resonance imaging to determine whole muscle compartment area, lean muscle area, fat cross-sectional areas, and proportion of fat within the muscle compartment. These measures were used to investigate the relationships between gene expression patterns and muscle size and quality.

RESULTS

Relationships between gene expression and imaging revealed significant associations between decreased expression of adipogenic/metabolic gene (PPARD), increased expression of fibrogenic gene (COL3A1), and lower fat fraction on MRI (r = -0.346, p = 0.018, and r = 0.386, p = 0.047 respectively). Decreased expression of myogenic gene (mTOR) was related to greater lean muscle cross-sectional area (r = 0.388, p = 0.045).

CONCLUSION

Fibrogenic and adipogenic/metabolic genes were related to pre-operative muscle quality, and myogenic genes were related to pre-operative muscle size. These findings provide insight into molecular pathways associated with muscle health in the presence of lumbar spine pathology, establishing a foundation for future research that addresses how these changes impact outcomes in this patient population.

Transcriptome Profile Reveals Genetic and Metabolic Mechanisms Related to Essential Fatty Acid Content of Intramuscular Longissimus thoracis in Nellore Cattle

Beef is a source of essential fatty acids (EFA), linoleic (LA) and alpha-linolenic (ALA) acids, which protect against inflammatory and cardiovascular diseases in humans. However, the intramuscular EFA profile in cattle is a complex and polygenic trait. Thus, this study aimed to identify potential regulatory genes of the essential fatty acid profile in Longissimus thoracis of Nellore cattle finished in feedlot. Forty-four young bulls clustered in four groups of fifteen animals with extreme values for each FA were evaluated through differentially expressed genes (DEG) analysis and two co-expression methodologies (WGCNA and PCIT). We highlight the ECHS1, IVD, ASB5, and ERLIN1 genes and the TF NFIA, indicated in both FA. Moreover, we associate the NFYA, NFYB, PPARG, FASN, and FADS2 genes with LA, and the RORA and ELOVL5 genes with ALA. Furthermore, the functional enrichment analysis points out several terms related to FA metabolism. These findings contribute to our understanding of the genetic mechanisms underlying the beef EFA profile in Nellore cattle finished in feedlot.

Epigenetics of Skeletal Muscle-Associated Genes in the ASB, LRRC, TMEM, and OSBPL Gene Families

Much remains to be discovered about the intersection of tissue-specific transcription control and the epigenetics of skeletal muscle (SkM), a very complex and dynamic organ. From four gene families, Leucine-Rich Repeat Containing (LRRC), Oxysterol Binding Protein Like (OSBPL), Ankyrin Repeat and Socs Box (ASB), and Transmembrane Protein (TMEM), we chose 21 genes that are preferentially expressed in human SkM relative to 52 other tissue types and analyzed relationships between their tissue-specific epigenetics and expression. We also compared their genetics, proteomics, and descriptions in the literature. For this study, we identified genes with little or no previous descriptions of SkM functionality (ASB4, ASB8, ASB10, ASB12, ASB16, LRRC14B, LRRC20, LRRC30, TMEM52, TMEM233, OSBPL6/ORP6, and OSBPL11/ORP11) and included genes whose SkM functions had been previously addressed (ASB2, ASB5, ASB11, ASB15, LRRC2, LRRC38, LRRC39, TMEM38A/TRIC-A, and TMEM38B/TRIC-B). Some of these genes have associations with SkM or heart disease, cancer, bone disease, or other diseases. Among the transcription-related SkM epigenetic features that we identified were: super-enhancers, promoter DNA hypomethylation, lengthening of constitutive low-methylated promoter regions, and SkM-related enhancers for one gene embedded in a neighboring gene (e.g., ASB8-PFKM, LRRC39-DBT, and LRRC14B-PLEKHG4B gene-pairs). In addition, highly or lowly co-expressed long non-coding RNA (lncRNA) genes probably regulate several of these genes. Our findings give insights into tissue-specific epigenetic patterns and functionality of related genes in a gene family and can elucidate normal and disease-related regulation of gene expression in SkM.

Gene expression profiling of porcine skeletal muscle satellite cells after poly(I:C) stimulation

Porcine satellite cells (PSCs) play a vital role in the construction, development and self-renewal of skeletal muscle. In this study, PSCs were exposed to poly(I:C) stimulation to mimic viral infection during the proliferation and differentiation phases at 0, 12, 24 and 48 hours (h) of the stimulation. The untreated and treated PSCs were analyzed by the RNA-Seq technology. There were 88, 119, 104 and 95 genes being differentially expressed in 0 h vs 12 h treated, 12 h vs 24 h treated, 0 h vs 24 h treated and 24 h vs 48 h untreated comparison libraries, respectively. The GO terms analysis results showed that during the proliferation phase of treated PSCs, the up-regulated genes related to the immune system were highly expressed. In addition, the gene expressions associated with muscle structure development in response to growth factor emerged during the differentiation phase of untreated PSCs. The biological pathways associated with Influenza A, Toll-like receptor and chemokine signaling were revealed in PSCs following poly(I:C) stimulation. The differentially expressed genes were confirmed by quantitative real-time PCR. These findings expanded our understanding of gene expressions and signaling pathways about the infiltrated mechanism of the virus into PSCs.

Signaling Size: Ankyrin and SOCS Box-Containing ASB E3 Ligases in Action

Ankyrin repeat and suppressor of cytokine signaling (SOCS) box (Asb) proteins are ubiquitin E3 ligases. The subfamily of six-ankyrin repeat domain-containing Asb proteins (Asb5, Asb9, Asb11, and Asb13) is of specific interest because they display unusual strong evolutionary conservation (e.g., urochordate and human ASB11 are >49% similar at the amino acid level) and mediate compartment size expansion, regulating, for instance, the size of the brain and muscle compartment. Thus, they may be involved in the explanation of the differences in brain size between humans and apes. Mechanistically, many questions remain, but it has become clear that regulation of canonical Notch signaling and also mitochondrial function are important effectors. Here, we review the action and function of six ankyrin repeat domain-containing Asb proteins in physiology and pathophysiology.

Cysteine- and glycine-rich protein 3 regulates glucose homeostasis in skeletal muscle

Skeletal muscle is the major site of postprandial peripheral glucose uptake, but in obesity-induced insulin-resistant states insulin-stimulated glucose disposal is markedly impaired. Despite the importance of skeletal muscle in regulating glucose homeostasis, the specific transcriptional changes associated with insulin-sensitive vs. -resistant states in muscle remain to be fully elucidated. Herein, using an RNA-seq approach we identified 20 genes differentially expressed in an insulin-resistant state in skeletal muscle, including cysteine- and glycine-rich protein 3 ( Csrp3), which was highly expressed in insulin-sensitive conditions but significantly reduced in the insulin-resistant state. CSRP3 has diverse functional roles including transcriptional regulation, signal transduction, and cytoskeletal organization, but its role in glucose homeostasis has yet to be explored. Thus, we investigated the role of CSRP3 in the development of obesity-induced insulin resistance in vivo. High-fat diet-fed CSRP3 knockout (KO) mice developed impaired glucose tolerance and insulin resistance as well as increased inflammation in skeletal muscle compared with wild-type (WT) mice. CSRP3-KO mice had significantly impaired insulin signaling, decreased GLUT4 translocation to the plasma membrane, and enhanced levels of phospho-PKCα in muscle, which all contributed to reduced insulin-stimulated glucose disposal in muscle in HFD-fed KO mice compared with WT mice. CSRP3 is a highly inducible protein and its expression is acutely increased after fasting. After 24h fasting, glucose tolerance was significantly improved in WT mice, but this effect was blunted in CSRP3-KO mice. In summary, we identify a novel role for Csrp3 expression in skeletal muscle in the development of obesity-induced insulin resistance.

MEF2 as upstream regulator of the transcriptome signature in human skeletal muscle during unloading

Our understanding of skeletal muscle structural and functional alterations during unloading has increased in recent decades, yet the molecular mechanisms underpinning these changes have only started to be unraveled. The purpose of the current investigation was to assess changes in skeletal muscle gene expression after 21 days of bed rest, with a particular focus on predicting upstream regulators of muscle disuse. Additionally, the association between differential microRNA expression and the transcriptome signature of bed rest were investigated. mRNAs from musculus vastus lateralis biopsies obtained from 12 men before and after the bed rest were analyzed using a microarray. There were 54 significantly upregulated probesets after bed rest, whereas 103 probesets were downregulated (false discovery rate 10%; fold-change cutoff ≥1.5). Among the upregulated genes, transcripts related to denervation-induced alterations in skeletal muscle were identified, e.g., acetylcholine receptor subunit delta and perinatal myosin. The most downregulated transcripts were functionally enriched for mitochondrial genes and genes involved in mitochondrial biogenesis, followed by a large number of contractile fiber components. Upstream regulator analysis identified a robust inhibition of the myocyte enhancer factor-2 (MEF2) family, in particular MEF2C, which was suggested to act upstream of several key downregulated genes, most notably peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α)/peroxisome proliferator-activated receptors (PPARs) and CRSP3. Only a few microRNAs were identified as playing a role in the overall transcriptome picture induced by sustained bed rest. Our results suggest that the MEF2 family is a key regulator underlying the transcriptional signature of bed rest and, hence, ultimately also skeletal muscle alterations induced by systemic unloading in humans.

Mustn1: A Developmentally Regulated Pan-Musculoskeletal Cell Marker and Regulatory Gene

The Mustn1 gene encodes a small nuclear protein (~9.6 kDa) that does not belong to any known family. Its genomic organization consists of three exons interspersed by two introns and it is highly homologous across vertebrate species. Promoter analyses revealed that its expression is regulated by the AP family of transcription factors, especially c-Fos, Fra-2 and JunD. Mustn1 is predominantly expressed in the major tissues of the musculoskeletal system: bone, cartilage, skeletal muscle and tendon. Its expression has been associated with normal embryonic development, postnatal growth, exercise, and regeneration of bone and skeletal muscle. Moreover, its expression has also been detected in various musculoskeletal pathologies, including arthritis, Duchenne muscular dystrophy, other skeletal muscle myopathies, clubfoot and diabetes associated muscle pathology. In vitro and in vivo functional perturbation revealed that Mustn1 is a key regulatory molecule in myogenic and chondrogenic lineages. This comprehensive review summarizes our current knowledge of Mustn1 and proposes that it is a new developmentally regulated pan-musculoskeletal marker as well as a key regulatory protein for cell differentiation and tissue growth.

Differential regulation of mRNAs and lncRNAs related to lipid metabolism in two pig breeds

Long non-coding RNAs (lncRNAs) can regulate lipid metabolism and adipogenesis. However, there is little research on the role of lncRNAs in fat deposition in pig. In this study, RNA-seq technology was used to analyze the gene expression profiles of subcutaneous adipose tissue in Laiwu (LW) and Large White (LY) pigs. Then, key lncRNAs and genes associated with lipid metabolism and adipogenic differentiation were identified. Fifty four lncRNAs and 482 known mRNAs were differentially expressed in the two pig breeds. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analyses revealed that differentially expressed genes and the target genes of differentially expressed lncRNAs were significantly enriched in PPAR signaling pathway and biological processes including fat cell differentiation and fatty acid metabolism. Key lncRNAs might regulate adipogenic differentiation and fatty acid metabolism by regulating genes involved in above signaling pathway and biological processes. Specifically, XLOC_014379, XLOC_011279, XLOC_064871, XLOC_019518 and XLOC_013639 might target SCD, LPIN1, TRIB3, EGR2 and FABP3, respectively, and then play critical regulatory role. These results are useful for understanding fat deposition in pig, breeding livestock with high quality meat, and preventing and treating lipid metabolic disease.

Differential Gene Expression Profiling of Dystrophic Dog Muscle after MuStem Cell Transplantation

BACKGROUND

Several adult stem cell populations exhibit myogenic regenerative potential, thus representing attractive candidates for therapeutic approaches of neuromuscular diseases such as Duchenne Muscular Dystrophy (DMD). We have recently shown that systemic delivery of MuStem cells, skeletal muscle-resident stem cells isolated in healthy dog, generates the remodelling of muscle tissue and gives rise to striking clinical benefits in Golden Retriever Muscular Dystrophy (GRMD) dog. This global effect, which is observed in the clinically relevant DMD animal model, leads us to question here the molecular pathways that are impacted by MuStem cell transplantation. To address this issue, we compare the global gene expression profile between healthy, GRMD and MuStem cell treated GRMD dog muscle, four months after allogenic MuStem cell transplantation.

RESULTS

In the dystrophic context of the GRMD dog, disease-related deregulation is observed in the case of 282 genes related to various processes such as inflammatory response, regeneration, calcium ion binding, extracellular matrix organization, metabolism and apoptosis regulation. Importantly, we reveal the impact of MuStem cell transplantation on several molecular and cellular pathways based on a selection of 31 genes displaying signals specifically modulated by the treatment. Concomitant with a diffuse dystrophin expression, a histological remodelling and a stabilization of GRMD dog clinical status, we show that cell delivery is associated with an up-regulation of genes reflecting a sustained enhancement of muscle regeneration. We also identify a decreased mRNA expression of a set of genes having metabolic functions associated with lipid homeostasis and energy. Interestingly, ubiquitin-mediated protein degradation is highly enhanced in GRMD dog muscle after systemic delivery of MuStem cells.

CONCLUSIONS

Overall, our results provide the first high-throughput characterization of GRMD dog muscle and throw new light on the complex molecular/cellular effects associated with muscle repair and the clinical efficacy of MuStem cell-based therapy.

The long non-coding RNA NEAT1 is increased in IUGR placentas, leading to potential new hypotheses of IUGR origin/development

INTRODUCTION

Intrauterine Growth Restriction (IUGR) is a multifactorial disease defined by an inability of the fetus to reach its growth potential. IUGR not only increases the risk of neonatal mortality/morbidity, but also the risk of metabolic syndrome during adulthood. Certain placental proteins have been shown to be implicated in IUGR development, such as proteins from the GH/IGF axis and angiogenesis/apoptosis processes.

METHODS

Twelve patients with term IUGR pregnancy (birth weight < 10th percentile) and 12 CTRLs were included. mRNA was extracted from the fetal part of the placenta and submitted to a subtraction method (Clontech PCR-Select cDNA Subtraction).

RESULTS

One candidate gene identified was the long non-coding RNA NEAT1 (nuclear paraspeckle assembly transcript 1). NEAT1 is the core component of a subnuclear structure called paraspeckle. This structure is responsible for the retention of hyperedited mRNAs in the nucleus. Overall, NEAT1 mRNA expression was 4.14 (±1.16)-fold increased in IUGR vs. CTRL placentas (P = 0.009). NEAT1 was exclusively localized in the nuclei of the villous trophoblasts and was expressed in more nuclei and with greater intensity in IUGR placentas than in CTRLs. PSPC1, one of the three main proteins of the paraspeckle, co-localized with NEAT1 in the villous trophoblasts. The expression of NEAT1_2 mRNA, the long isoform of NEAT1, was only modestly increased in IUGR vs. CTRL placentas.

DISCUSSION/CONCLUSION

The increase in NEAT1 and its co-localization with PSPC1 suggests an increase in paraspeckles in IUGR villous trophoblasts. This could lead to an increased retention of important mRNAs in villous trophoblasts nuclei. Given that the villous trophoblasts are crucial for the barrier function of the placenta, this could in part explain placental dysfunction in idiopathic IUGR fetuses.

To pull or be pulled: parsing the multiple modes of mechanotransduction

A cell embedded in a multicellular organism will experience a wide range of mechanical stimuli over the course of its life. Fluid flows and neighboring cells actively exert stresses on the cell, while the cell's environment presents a set of passive mechanical properties that constrain its physical behavior. Cells respond to these varied mechanical cues through biological responses that regulate activities such as differentiation, morphogenesis, and proliferation, as well as material responses involving compression, stretching, and relaxation. Here, we break down recent studies of mechanotransduction on the basis of the input mechanical stimuli acting upon the cell and the output response of the cell. This framework provides a useful starting point for identifying overlaps in molecular players and sensing modalities, and it highlights how different timescales involved in biological and material responses to mechanical inputs could serve as a means for filtering important mechanical signals from noise.

A novel GFP reporter mouse reveals Mustn1 expression in adult regenerating skeletal muscle, activated satellite cells and differentiating myoblasts

AIM

Mustn1 has been implicated in myofusion as well as skeletal muscle growth and repair; however, the exact role and spatio-temporal expression of Mustn1 have yet to be fully defined.

METHODS

Transgenic mice were generated with a 1512-bp sequence of the Mustn1 promoter directing the expression of GFP (Mustn1(PRO) -GFP). These mice were used to investigate the spatio-temporal expression of Mustn1(PRO) -GFP during skeletal muscle development and adult skeletal muscle repair, as well as various phases of the satellite cell lifespan (i.e. quiescence, activation, proliferation, differentiation).

RESULTS

Mustn1(PRO) -GFP expression was observed within somites at embryonic day 12 and developing skeletal muscles at embryonic day 15 and 18. While uninjured adult tibialis anterior muscle displayed no detectable Mustn1(PRO) -GFP expression, cardiotoxin injury robustly elevated Mustn1(PRO) -GFP expression at 3 days post-injury with decreasing levels observed at 5 days and minimal, focal expression seen at 10 days. The expression of Mustn1(PRO) -GFP at 3 days post-injury consistently overlaid with MyoD although the strongest expression of Mustn1(PRO) -GFP was noted in newly formed myotubes that were expressing minimal levels of MyoD. By 5 days post-injury, Mustn1(PRO) -GFP overlaid in all myotubes expressing myogenin although cells were present expressing Mustn1(PRO) -GFP alone. The expression patterns of Mustn1(PRO) -GFP in regenerating muscle preceded the expression of desmin throughout the regenerative time course consistent with Mustn1 being upstream of this myogenic protein. Further, quiescent satellite cells located on freshly isolated, single myofibers rarely expressed Mustn1(PRO) -GFP, but within 24 h of isolation, all activated satellite cells expressed Mustn1(PRO) -GFP. Expression of Mustn1(PRO) -GFP in primary myoblasts diminished with prolonged time in proliferation media. However, in response to serum withdrawal, the expression of Mustn1(PRO) -GFP increased during myofusion (day 2) followed by declining expression thereafter.

CONCLUSION

Mustn1(PRO) -GFP is expressed in activated satellite cells and myoblasts but continued time in proliferation media diminished Mustn1(PRO) -GFP expression. However, myoblasts exposed to serum withdrawal increased Mustn1(PRO) -GFP expression consistent with its demonstrated role in myofusion. The in vivo expression pattern of Mustn1 observed in regenerating and developing skeletal muscle is consistent with its presence in satellite cells and its critical role in myofusion.

Pronounced effects of acute endurance exercise on gene expression in resting and exercising human skeletal muscle

Regular physical activity positively influences whole body energy metabolism and substrate handling in exercising muscle. While it is recognized that the effects of exercise extend beyond exercising muscle, it is unclear to what extent exercise impacts non-exercising muscles. Here we investigated the effects of an acute endurance exercise bouts on gene expression in exercising and non-exercising human muscle. To that end, 12 male subjects aged 44–56 performed one hour of one-legged cycling at 50% W_max. Muscle biopsies were taken from the exercising and non-exercising leg before and immediately after exercise and analyzed by microarray. One-legged cycling raised plasma lactate, free fatty acids, cortisol, noradrenalin, and adrenalin levels. Surprisingly, acute endurance exercise not only caused pronounced gene expression changes in exercising muscle but also in non-exercising muscle. In the exercising leg the three most highly induced genes were all part of the NR4A family. Remarkably, many genes induced in non-exercising muscle were PPAR targets or related to PPAR signalling, including PDK4, ANGPTL4 and SLC22A5. Pathway analysis confirmed this finding. In conclusion, our data indicate that acute endurance exercise elicits pronounced changes in gene expression in non-exercising muscle, which are likely mediated by changes in circulating factors such as free fatty acids. The study points to a major influence of exercise beyond the contracting muscle.