The nuclear receptor NOR-1 regulates the small muscle protein, X-linked (SMPX) and myotube differentiation

Loss of NOR-1 represses muscle metabolism through mTORC1-mediated signaling and mitochondrial gene expression in C2C12 myotubes

Gene expression of the NR4A nuclear orphan receptor NOR-1 is reduced in obesity and in human skeletal muscle during disuse. It has been well established that NOR-1 is highly responsive to both aerobic and resistance exercise and NOR-1 overexpression is coincident with a plethora of metabolic benefits. However, it is unclear whether loss of NOR-1 contributes to inappropriate metabolic signaling in skeletal muscle that could lead to insulin resistance. The purpose of this study was to elucidate the impact of NOR-1 deficiency on C2C12 metabolic signaling. Changes in gene expression after siRNA-mediated NOR-1 knockdown in C2C12 myotubes were determined by qPCR and bioinformatic analysis of RNA-Seq data. Our RNA-Seq data identified several metabolic targets regulated by NOR-1 and implicates NOR-1 as a modulator of mTORC1 signaling via Akt-independent mechanisms. Furthermore, pathway analysis revealed NOR-1 knockdown perturbs the insulin resistance and insulin sensitivity pathways. Taken together, these data suggest skeletal muscle NOR-1 deficiency may contribute to altered metabolic signaling that is consistent with metabolic disease. We postulate that strategies that improve NOR-1 may be important to offset the negative impact that inactivity, obesity, and type 2 diabetes have on mitochondria and muscle metabolism.

Genome-wide identification of SNPs associated with body weight in yak

BACKGROUND

The yak is the most important livestock in the Qinghai-Tibet Plateau, and body weight directly affects the economic values of yak. Up to date, the genome-wide profiling of single-nucleotide polymorphisms (SNPs) associating with body weight has not been reported in yak. In the present study, the SNPs in 480 yaks from three breeds were analyzed using the commercial high-density (600 K) yak SNP chips.

RESULTS

The results identified 12 and 4 SNPs potentially associated with body weight in male and female yaks, respectively. Among them, 9 and 2 SNPs showed significant difference in yak body weight between different genotypes at each locus in male and female yaks, respectively. Further exploration found 33 coding genes within the 100 kbp upstream or downstream to the SNP loci, which might be potentially affected by the variation of SNPs. Among them, G protein-coupled receptor kinase 4 (GRK4) might be potentially affected by the SNP AX-174555047, which has been reported to affect the functioning of two body-weight associated hormones (parathyroid hormone, PTH, and adrenomedullin, ADM). Determination of PTH and ADM levels in yak revealed positive relationship between PTH level and body weight, negative relationship between ADM level and body weight along with the variation of AX-174555047 mutation.

CONCLUSIONS

These results suggested that the SNP AX-174555047 might potentially affect body weight through mediating GRK4 expression and then PTH and ADM functioning. Thus, the SNP AX-174555047 might be used as a biomarker for molecular breeding of yak. More investigations are required to validate this point.

Druggability Evaluation of the Neuron Derived Orphan Receptor (NOR-1) Reveals Inverse NOR-1 Agonists

The neuron derived orphan receptor (NOR-1, NR4A3) is among the least studied nuclear receptors. Its physiological role and therapeutic potential remain widely elusive which is in part due to the lack of chemical tools that can directly modulate NOR-1 activity. To probe the possibility of pharmacological NOR-1 modulation, we have tested a drug fragment library for NOR-1 activation and repression. Despite low hit-rate (<1 %), we have obtained three NOR-1 ligand chemotypes one of which could be rapidly expanded to an analogue comprising low micromolar inverse NOR-1 agonist potency and altering NOR-1 regulated gene expression in a cellular setting. It confirms druggability of the transcription factor and may serve as an early tool to assess the role and potential of NOR-1.

Targeting Nuclear Receptors in Neurodegeneration and Neuroinflammation

Nuclear receptors, also known as ligand-activated transcription factors, regulate gene expression upon ligand signals and present as attractive therapeutic targets especially in chronic diseases. Despite the therapeutic relevance of some nuclear receptors in various pathologies, their potential in neurodegeneration and neuroinflammation is insufficiently established. This perspective gathers preclinical and clinical data for a potential role of individual nuclear receptors as future targets in Alzheimer's disease, Parkinson's disease, and multiple sclerosis, and concomitantly evaluates the level of medicinal chemistry targeting these proteins. Considerable evidence suggests the high promise of ligand-activated transcription factors to counteract neurodegenerative diseases with a particularly high potential of several orphan nuclear receptors. However, potent tools are lacking for orphan receptors, and limited central nervous system exposure or insufficient selectivity also compromises the suitability of well-studied nuclear receptor ligands for functional studies. Medicinal chemistry efforts are needed to develop dedicated high-quality tool compounds for the therapeutic validation of nuclear receptors in neurodegenerative pathologies.

Temporomandibular Disorders Slow Down the Regeneration Process of Masticatory Muscles: Transcriptomic Analysis

Background and Objectives: Musculoskeletal injuries represent a pathological condition due to limited joint motility and morphological and functional alterations of the muscles. Temporomandibular disorders (TMDs) are pathological conditions due to alterations in the musculoskeletal system. TMDs mainly cause temporomandibular joint and masticatory muscle dysfunctions following trauma, along with various pathologies and inflammatory processes. TMD affects approximately 15% of the population and causes malocclusion problems and common symptoms such as myofascial pain and migraine. The aim of this work was to provide a transcriptomic profile of masticatory muscles obtained from TMD migraine patients compared to control. Materials and Methods: We used Next Generation Sequencing (NGS) technology to evaluate transcriptomes in masseter and temporalis muscle samples. Results: The transcriptomic analysis showed a prevalent downregulation of the genes involved in the myogenesis process. Conclusions: In conclusion, our findings suggest that the muscle regeneration process in TMD migraine patients may be slowed, therefore therapeutic interventions are needed to restore temporomandibular joint function and promote healing processes.

A novel missense mutation in SMPX causes a rare form of X-linked postlingual sensorineural hearing loss in a Chinese family

BACKGROUND

X-linked deafness-4 (DFNX4) caused by the functional loss of the SMPX gene is one form of nonsyndromic hearing loss with postlingual onset. This study aimed to investigate the cause of X-linked inherited sensorineural nonsyndromic hearing loss in a four-generation Chinese family and to explain the reason for extremely different hearing phenotypes between the proband and other family members.

METHODS

Whole-exome sequencing (WES) and co-segregation analysis were used to identify the pathogenic variants. Furthermore, methylation differences among the androgen receptor genes were utilized to investigate whether the severe phenotype of the proband is related to X-chromosome inactivation (Xi).

RESULTS

We described in detail the clinical characteristics of the family and identified a novel missense mutation (c.262C>G: p.Gln88Glu) in SMPX by WES. This variant was co-segregated with the postlingual hearing loss phenotype and was absent in 300 normal controls. Also, we found that the proband, a 4-year-old female, carries two new compound heterozygous mutations (c.9259G>A: p.Val3087Ile and c.8576G>A: p.Arg2859His) in the USH2A gene, but to date without any other symptoms except profound sensorineural hearing loss. Additionally, analysis of X-chromosome inactivation indicated moderate skewing in the proband, which is probably related to the heterogeneity of clinical characteristics.

CONCLUSIONS

This is the first study to report a missense mutation of SMPX in a Chinese family. Our findings have enriched the mutation and phenotypic spectrum of the SMPX gene.

Neuron-derived orphan receptor-1 modulates cardiac gene expression and exacerbates angiotensin II-induced cardiac hypertrophy

Hypertensive cardiac hypertrophy (HCH) is a common cause of heart failure (HF), a major public health problem worldwide. However, the molecular bases of HCH have not been completely elucidated. Neuron-derived orphan receptor-1 (NOR-1) is a nuclear receptor whose role in cardiac remodelling is poorly understood. The aim of the present study was to generate a transgenic mouse over-expressing NOR-1 in the heart (TgNOR-1) and assess the impact of this gain-of-function on HCH. The CAG promoter-driven transgenesis led to viable animals that over-expressed NOR-1 in the heart, mainly in cardiomyocytes and also in cardiofibroblasts. Cardiomyocytes from TgNOR-1 exhibited an enhanced cell surface area and myosin heavy chain 7 (Myh7)/Myh6 expression ratio, and increased cell shortening elicited by electric field stimulation. TgNOR-1 cardiofibroblasts expressed higher levels of myofibroblast markers than wild-type (WT) cells (α 1 skeletal muscle actin (Acta1), transgelin (Sm22α)) and were more prone to synthesise collagen and migrate. TgNOR-1 mice experienced an age-associated remodelling of the left ventricle (LV). Angiotensin II (AngII) induced the cardiac expression of NOR-1, and NOR-1 transgenesis exacerbated AngII-induced cardiac hypertrophy and fibrosis. This effect was associated with the up-regulation of hypertrophic (brain natriuretic peptide (Bnp), Acta1 and Myh7) and fibrotic markers (collagen type I α 1 chain (Col1a1), Pai-1 and lysyl oxidase-like 2 (Loxl2)). NOR-1 transgenesis up-regulated two key genes involved in cardiac hypertrophy (Myh7, encoding for β-myosin heavy chain (β-MHC)) and fibrosis (Loxl2, encoding for the extracellular matrix (ECM) modifying enzyme, Loxl2). Interestigly, in transient transfection assays, NOR-1 drove the transcription of Myh7 and Loxl2 promoters. Our findings suggest that NOR-1 is involved in the transcriptional programme leading to HCH.

Expression pattern of the small muscle protein, X-linked (smpx) gene during zebrafish embryonic and larval developmental stages

The small muscle protein, X-linked (SMPX) gene encodes a cytoskeleton-associated protein, highly expressed in both cardiac and skeletal muscles, as well as in fetal inner ears, with suggested roles as mechanotransductor. Recently, several mutations in the SMPX gene have been associated with X-chromosomal progressive deafness in human. However, very little information is known concerning the roles of SMPX, and no in-vivo models are currently available. Therefore, we characterized the zebrafish ortholog of SMPX to pave the way towards the establishment of a biotool for future functional studies. Despite the genome duplication occurred in the ancestry of teleosts, zebrafish retain only one copy of smpx which shares a high degree of similarity with the mammalian counterpart in terms of genomic organization, syntenic map, and encoded protein. RT-PCR, as well as whole-mount in-situ hybridization and immunofluorescence analyses, revealed that smpx is expressed in several embryonic areas starting from the 4-somite stage. Specifically, smpx mRNA marked the Kupffer's vesicle (KV), the somites, the myocardium, the hair cells of the anterior and the posterior macula of the inner ear, the pronephric ducts, and the muscles of the branchial arches, eyes and pectoral fins. According to our data, zebrafish smpx expression pattern closely resembles that observed in mouse and human, supporting the notion that zebrafish might represent a suitable in-vivo model to disclose the cellular and molecular mechanisms underlying the involvement of SMPX in development and disease.

RNA-Seq Analysis Reveals Spatial and Sex Differences in Pectoralis Major Muscle of Broiler Chickens Contributing to Difference in Susceptibility to Wooden Breast Disease

Wooden Breast Disease (WBD) is a novel myopathy affecting the pectoralis major muscle of modern broiler chickens. The etiology of WBD is not currently known, but has been linked to increased feed efficiency, growth rate, and muscle yield in broiler chickens. Differential effect of WBD has been detected between regions of the P. major and between sexes of broilers-male birds and the cranial aspect of the muscle tend to be more severely affected by the disease than females and the caudal aspect. This study aimed to characterize biological differences in the P. major between regions of the muscle and sexes of birds. Samples were taken from the cranial and caudal aspects of P. major muscles of 3-week-old, unaffected male and female birds for RNA sequencing. RNA was extracted and used for preparation of cDNA libraries, which were sequenced by the Delaware Biotechnology Institute (DBI) using HiSeq2500. Sequence reads were aligned to the chicken reference genome with HISAT, and genes were analyzed for differential expression between regions of the breast muscle and sexes of birds using CuffDiff. Functional analysis was performed on differentially expressed genes (DEGs) between sex groups using DAVID and Ingenuity Pathway Analysis (IPA). There were 12 DEGs between cranial and caudal samples, and 260 between male and female birds. Out of the 260 genes differentially expressed between sexes, 189 were upregulated in males. Of this subset, 103 genes (55%) were located on the Z-chromosome. There was increased expression of genes involved in fat metabolism and oxidative stress responses in the cranial region of the P. major muscle, as well as increased expression of fat metabolism, oxidative stress response, antiangiogenesis, and connective tissue proliferation genes in male broilers. These results support the hypothesis that there are biological characteristics in male broilers and the cranial region of the breast muscle that may make them more susceptible to WBD, as well as raising the possibility of a metabolic switch in modern broiler chickens that may be more prominent in males.

The Nuclear Receptor Nor-1 Is a Pleiotropic Regulator of Exercise-Induced Adaptations

Exercise induces various physical and metabolic changes in skeletal muscle that adaptively reprograms this tissue to current physiological and environmental demands. Underlying these changes are broad modifications to gene expression. We postulate that the nuclear hormone receptor, Nor-1, is activated after exercise, and this transcription factor modifies gene expression to drive the molecular and cellular adaptations associated with contractile reorganization.

Genome Architecture Mediates Transcriptional Control of Human Myogenic Reprogramming

Genome architecture has emerged as a critical element of transcriptional regulation, although its role in the control of cell identity is not well understood. Here we use transcription factor (TF)-mediated reprogramming to examine the interplay between genome architecture and transcriptional programs that transition cells into the myogenic identity. We recently developed new methods for evaluating the topological features of genome architecture based on network centrality. Through integrated analysis of these features of genome architecture and transcriptome dynamics during myogenic reprogramming of human fibroblasts we find that significant architectural reorganization precedes activation of a myogenic transcriptional program. This interplay sets the stage for a critical transition observed at several genomic scales reflecting definitive adoption of the myogenic phenotype. Subsequently, TFs within the myogenic transcriptional program participate in entrainment of biological rhythms. These findings reveal a role for topological features of genome architecture in the initiation of transcriptional programs during TF-mediated human cellular reprogramming.

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4D Nucleome analysis of direct human fibroblast to muscle reprogramming

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A space-time bifurcation marks transit to a new cell identity

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Chromatin reorganization precedes significant transcriptional changes

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Myogenic master regulators have a role in entraining biological rhythms

The nuclear receptor NOR-1/NR4A3 regulates the multifunctional glycoprotein vitronectin in human vascular smooth muscle cells

The nuclear receptor NOR-1 (NR4A3) has recently been involved in the regulation of extracellular matrix (ECM) proteins associated with neointimal thickening and the vascular control of hemostasis. We sought to find as-yet unidentified NOR-1 target genes in human vascular smooth muscle cells (VSMCs). An in silico analysis identified putative NOR-1 response elements in the proximal promoter region of several genes encoding for ECM proteins, including vitronectin (VTN). Lentiviral overexpression of NOR-1 strongly increased VTN mRNA and protein levels, whereas NOR-1 silencing significantly reduced VTN expression. Deletion and site-directed mutagenesis studies, as well as EMSA and chromatin immunoprecipitation, identified the NBRE(-202/-195) site in the VTN promoter as an essential element for NOR-1 responsiveness. Furthermore, NOR-1 and VTN colocalized in VSMCs in human atherosclerotic lesions. VTN levels were increased in cell supernatants from VSMCs that overexpress NOR-1. Cell supernatants from VSMCs overexpressing NOR-1 induced cell migration to a greater extent than supernatants from control cells, and this effect was attenuated when cell supernatants were preincubated with anti-VTN blocking antibodies or VTN was silenced in supernatant-generating cells. These results indicate that VTN is a target of NOR-1 and suggest that this multifunctional glycoprotein may participate in vascular responses mediated by this nuclear receptor.-Martí-Pàmies, I., Cañes, L., Alonso, J., Rodríguez, C., Martínez-González, J. The nuclear receptor NOR-1/NR4A3 regulates the multifunctional glycoprotein vitronectin in human vascular smooth muscle cells.

NOR-1/NR4A3 regulates the cellular inhibitor of apoptosis 2 (cIAP2) in vascular cells: role in the survival response to hypoxic stress

Vascular cell survival is compromised under pathological conditions such as abdominal aortic aneurysm (AAA). We have previously shown that the nuclear receptor NOR-1 is involved in the survival response of vascular cells to hypoxia. Here, we identify the anti-apoptotic protein cIAP2 as a downstream effector of NOR-1. NOR-1 and cIAP2 were up-regulated in human AAA samples, colocalizing in vascular smooth muscle cells (VSMC). While NOR-1 silencing reduced cIAP2 expression in vascular cells, lentiviral over-expression of this receptor increased cIAP2 mRNA and protein levels. The transcriptional regulation of the human cIAP2 promoter was analyzed in cells over-expressing NOR-1 by luciferase reporter assays, electrophoretic mobility shift analysis and chromatin immunoprecipitation, identifying a NGFI-B site (NBRE-358/-351) essential for NOR-1 responsiveness. NOR-1 and cIAP2 were up-regulated by hypoxia and by a hypoxia mimetic showing a similar time-dependent pattern. Deletion and site-directed mutagenesis studies show that NOR-1 mediates the hypoxia-induced cIAP2 expression. While NOR-1 over-expression up-regulated cIAP2 and limited VSMC apoptosis induced by hypoxic stress, cIAP2 silencing partially prevented this NOR-1 pro-survival effect. These results indicate that cIAP2 is a target of NOR-1, and suggest that this anti-apoptotic protein is involved in the survival response to hypoxic stress mediated by NOR-1 in vascular cells.