The orphan nuclear receptor, NOR-1, a target of beta-adrenergic signaling, regulates gene expression that controls oxidative metabolism in skeletal muscle

NR4A3 prevents diabetes induced atrial cardiomyopathy by maintaining mitochondrial energy metabolism and reducing oxidative stress

BACKGROUND

Atrial cardiomyopathy (ACM) is responsible for atrial fibrillation (AF) and thromboembolic events. Diabetes mellitus (DM) is an important risk factor for ACM. However, the potential mechanism between ACM and DM remains elusive.

METHODS

Atrial tissue samples were obtained from patients diagnosed with AF or sinus rhythm (SR) to assess alterations in NR4A3 expression, and then two distinct animal models were generated by subjecting Nr4a3-/- mice and WT mice to a high-fat diet (HFD) and Streptozotocin (STZ), while db/db mice were administered AAV9-Nr4a3 or AAV9-ctrl. Subsequently, in vivo and in vitro experiments were conducted to assess the impact of NR4A3 on diabetes-induced atrial remodeling through electrophysiological, biological, and histological analyses. RNA sequencing (RNA-seq) and metabolomics analysis were employed to unravel the downstream mechanisms.

FINDINGS

The expression of NR4A3 was significantly decreased in atrial tissues of both AF patients and diabetic mice compared to their respective control groups. NR4A3 deficiency exacerbated atrial hypertrophy and atrial fibrosis, and increased susceptibility to pacing-induced AF. Conversely, overexpression of NR4A3 alleviated atrial structural remodeling and reduced AF induction rate. Mechanistically, we confirmed that NR4A3 improves mitochondrial energy metabolism and reduces oxidative stress injury by preserving the transcriptional expression of Sdha, thereby exerting a protective influence on atrial remodeling induced by diabetes.

INTERPRETATION

Our data confirm that NR4A3 plays a protective role in atrial remodeling caused by diabetes, so it may be a new target for treating ACM.

FUNDING

This study was supported by the major research program of National Natural Science Foundation of China (NSFC) No: 82370316 (to Q-S. W.), No. 81974041 (to Y-P. W.), and No. 82270447 (to Y-P. W.) and Fundation of Shanghai Hospital Development Center (No. SHDC2022CRD044 to Q-S. W.).

Methylome-proteome integration after late-life voluntary exercise training reveals regulation and target information for improved skeletal muscle health

Exercise is a potent stimulus for combatting skeletal muscle ageing. To study the effects of exercise on muscle in a preclinical setting, we developed a combined endurance-resistance training stimulus for mice called progressive weighted wheel running (PoWeR). PoWeR improves molecular, biochemical, cellular and functional characteristics of skeletal muscle and promotes aspects of partial epigenetic reprogramming when performed late in life (22-24 months of age). In this investigation, we leveraged pan-mammalian DNA methylome arrays and tandem mass-spectrometry proteomics in skeletal muscle to provide detailed information on late-life PoWeR adaptations in female mice relative to age-matched sedentary controls (n = 7-10 per group). Differential CpG methylation at conserved promoter sites was related to transcriptional regulation genes as well as Nr4a3, Hes1 and Hox genes after PoWeR. Using a holistic method of -omics integration called binding and expression target analysis (BETA), methylome changes were associated with upregulated proteins related to global and mitochondrial translation after PoWeR (P = 0.03). Specifically, BETA implicated methylation control of ribosomal, mitoribosomal, and mitochondrial complex I protein abundance after training. DNA methylation may also influence LACTB, MIB1 and UBR4 protein induction with exercise - all are mechanistically linked to muscle health. Computational cistrome analysis predicted several transcription factors including MYC as regulators of the exercise trained methylome-proteome landscape, corroborating prior late-life PoWeR transcriptome data. Correlating the proteome to muscle mass and fatigue resistance revealed positive relationships with VPS13A and NPL levels, respectively. Our findings expose differential epigenetic and proteomic adaptations associated with translational regulation after PoWeR that could influence skeletal muscle mass and function in aged mice. KEY POINTS: Late-life combined endurance-resistance exercise training from 22-24 months of age in mice is shown to improve molecular, biochemical, cellular and in vivo functional characteristics of skeletal muscle and promote aspects of partial epigenetic reprogramming and epigenetic age mitigation. Integration of DNA CpG 36k methylation arrays using conserved sites (which also contain methylation ageing clock sites) with exploratory proteomics in skeletal muscle extends our prior work and reveals coordinated and widespread regulation of ribosomal, translation initiation, mitochondrial ribosomal (mitoribosomal) and complex I proteins after combined voluntary exercise training in a sizeable cohort of female mice (n = 7-10 per group and analysis). Multi-omics integration predicted epigenetic regulation of serine β-lactamase-like protein (LACTB - linked to tumour resistance in muscle), mind bomb 1 (MIB1 - linked to satellite cell and type 2 fibre maintenance) and ubiquitin protein ligase E3 component N-recognin 4 (UBR4 - linked to muscle protein quality control) after training. Computational cistrome analysis identified MYC as a regulator of the late-life training proteome, in agreement with prior transcriptional analyses. Vacuolar protein sorting 13 homolog A (VPS13A) was positively correlated to muscle mass, and the glycoprotein/glycolipid associated sialylation enzyme N-acetylneuraminate pyruvate lyase (NPL) was associated to in vivo muscle fatigue resistance.

Parallel expression patterns of NR4A nuclear receptor family genes in the pituitary gland of proestrus rats

The NR4A nuclear receptor family (NR4As), encompassing NR4A1, NR4A2, and NR4A3, exerts pivotal roles in cellular processes through intricate expression patterns and interactions. Despite the influence of some NR4As on anterior pituitary functions regulated by the hypothalamus, their physiological expression patterns remain unclear. In our prior work, we demonstrated the specific upregulation of NR4A3 in the rat anterior pituitary gland during the proestrus afternoon, coinciding with a gonadotropin surge. In this study, we investigated changes in pituitary Nr4a gene expression throughout the estrous cycle in rats and a gonadotropin surge-induced model. Nr4a1 and Nr4a2 gene expression significantly increased during proestrus, aligning with previous observations for Nr4a3. Furthermore, prolactin gene expression increased sequentially with rising Nr4a gene expression, while thyroid-stimulating hormone beta gene expression remained stable. Immunohistochemistry revealed a widespread and differential distribution of NR4A proteins in the anterior pituitary, with NR4A1 and NR4A3 being particularly abundant in thyrotrophs, and NR4A2 in gonadotrophs. In estrogen-treated ovariectomized rats, elevated luteinizing hormone secretion corresponded to markedly upregulated expression of Nr4a1, Nr4a2, and Nr4a3. In gonadotroph and somatomammotroph cell lines, gonadotropin- and thyrotropin-releasing hormones transiently and dose-dependently increased the expression of Nr4a genes. These findings suggest that hypothalamic hormone secretion during proestrus may induce the parallel expression of pituitary Nr4a genes, potentially influencing the pituitary gene expression program related to endocrine functions before and after ovulation.

β2-Adrenergic receptor agonists as a treatment for diabetic kidney disease

We have previously shown that the long-acting β2-adrenergic receptor (β2-AR) agonist formoterol induced recovery from acute kidney injury in mice. To determine whether formoterol protected against diabetic nephropathy, the most common cause of end-stage kidney disease (ESKD), we used a high-fat diet (HFD), a murine type 2 diabetes model, and streptozotocin, a murine type 1 diabetes model. Following formoterol treatment, there was a marked recovery from and reversal of diabetic nephropathy in HFD mice compared with those treated with vehicle alone at the ultrastructural, histological, and functional levels. Similar results were seen after formoterol treatment in mice receiving streptozotocin. To investigate effects in humans, we performed a competing risk regression analysis with death as a competing risk to examine the association between Veterans with chronic kidney disease (CKD) and chronic obstructive pulmonary disease (COPD), who use β2-AR agonists, and Veterans with CKD but no COPD, and progression to ESKD in a large national cohort of Veterans with stage 4 CKD between 2011 and 2013. Veterans were followed until 2016 or death. ESKD was defined as the initiation of dialysis and/or receipt of kidney transplant. We found that COPD was associated with a 25.6% reduction in progression from stage 4 CKD to ESKD compared with no COPD after adjusting for age, diabetes, sex, race-ethnicity, comorbidities, and medication use. Sensitivity analysis showed a 33.2% reduction in ESKD in Veterans with COPD taking long-acting formoterol and a 20.8% reduction in ESKD in Veterans taking other β2-AR agonists compared with those with no COPD. These data indicate that β2-AR agonists, especially formoterol, could be a treatment for diabetic nephropathy and perhaps other forms of CKD.NEW & NOTEWORTHY Diabetic nephropathy is the most common cause of ESKD. Formoterol, a long-acting β2-adrenergic receptor (β2-AR) agonist, reversed diabetic nephropathy in murine models of type 1 and 2 diabetes. In humans, there was an association with protection from progression of CKD in patients with COPD, by means of β2-AR agonist intake, compared with those without COPD. These data indicate that β2-AR agonists, especially formoterol, could be a new treatment for diabetic nephropathy and other forms of CKD.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Nuclear receptors as potential therapeutic targets in peripheral arterial disease and related myopathy

Peripheral arterial disease (PAD) is a prevalent cardiovascular complication of limb vascular insufficiency, causing ischemic injury, mitochondrial metabolic damage and functional impairment in the skeletal muscle, and ultimately leading to immobility and mortality. While potential therapies have been mostly focussed on revascularization, none of the currently available pharmacological treatments are fully effective in PAD, often leading to amputations, particularly in chronic metabolic diseases. One major limitation of focussed angiogenesis and revascularization as a therapeutic strategy is a limited effect on metabolic restoration and muscle regeneration in the affected limb. Therefore, additional preclinical investigations are needed to discover novel treatment options for PAD preferably targeting multiple aspects of muscle recovery. In this review, we propose nuclear receptors expressed in the skeletal muscle as potential candidates for ischemic muscle repair in PAD. We review classic steroid and orphan receptors that have been reported to be involved in the regulation of paracrine muscle angiogenesis, oxidative metabolism, mitochondrial biogenesis and muscle regeneration, and discuss how these receptors could be critical for recovery from ischemic muscle damage. Furthermore, we identify existing gaps in our understanding of nuclear receptor signalling in the skeletal muscle and propose future areas of research that could be instrumental in exploring nuclear receptors as therapeutic candidates for treating PAD.

Acute Effects of Single Versus Combined Inhaled β2-Agonists Salbutamol and Formoterol on Time Trial Performance, Lung Function, Metabolic and Endocrine Variables

BACKGROUND

High prevalence rates of β2-agonist use among athletes in competitive sports makes it tempting to speculate that illegitimate use of β2-agonists boosts performance. However, data regarding the potential performance-enhancing effects of inhaled β2-agonists and its underlying molecular basis are scarce.

METHODS

In total, 24 competitive endurance athletes (12f/12m) participated in a clinical double-blinded balanced four-way block cross-over trial to investigate single versus combined effects of β2-agonists salbutamol (SAL) and formoterol (FOR), to evaluate the potential performance enhancement of SAL (1200 µg, Cyclocaps, Pb Pharma GmbH), FOR (36 µg, Sandoz, HEXAL AG) and SAL + FOR (1200 µg + 36 µg) compared to placebo (PLA, Gelatine capsules containing lactose monohydrate, Pharmacy of the University Hospital Ulm). Measurements included skeletal muscle gene and protein expression, endocrine regulation, urinary/serum β2-agonist concentrations, cardiac markers, cardiopulmonary and lung function testing and the 10-min time trial (TT) performance on a bicycle ergometer as outcome variables. Blood and urine samples were collected pre-, post-, 3 h post- and 24 h post-TT.

RESULTS

Mean power output during TT was not different between study arms. Treatment effects regarding lung function (p < 0.001), echocardiographic (left ventricular end-systolic volume p = 0.037; endocardial global longitudinal strain p < 0.001) and metabolic variables (e.g. NR4A2 and ATF3 pathway) were observed without any influence on performance. In female athletes, total serum β2-agonist concentrations for SAL and FOR were higher. Microarray muscle gene analysis showed a treatment effect for target genes in energy metabolism with strongest effect by SAL + FOR (NR4A2; p = 0.001). Of endocrine variables, follicle-stimulating hormone (3 h Post-Post-TT), luteinizing hormone (3 h Post-Pre-TT) and insulin (Post-Pre-TT) concentrations showed a treatment effect (all p < 0.05).

CONCLUSIONS

No endurance performance-enhancing effect for SAL, FOR or SAL + FOR within the permitted dosages compared to PLA was found despite an acute effect on lung and cardiac function as well as endocrine and metabolic variables in healthy participants. The impact of combined β2-agonists on performance and sex-specific thresholds on the molecular and cardiac level and their potential long-term performance enhancing or health effects have still to be determined.

TRIAL REGISTRATION

Registered at Eudra CT with the number: 2015-005598-19 (09.12.2015) and DRKS with number DRKS00010574 (16.11.2021, retrospectively registered).

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.

Extraskeletal myxoid chondrosarcoma: A study of 17 cases focusing on the diagnostic utility of INSM1 expression and presenting rare morphological variants associated with non-EWSR1::NR4A3 fusions

Extraskeletal myxoid chondrosarcoma (EMC) is a rare sarcoma of uncertain lineage. Insulinoma-associated protein 1 (INSM1) has recently been described as a highly specific and sensitive immunohistochemical marker for EMC. The goal of this study was to evaluate the diagnostic significance of INSM1 immunohistochemistry in EMC. Furthermore, correlations between molecular and morphological findings were performed. Sixteen of 17 EMC cases were stained with the INSM1 antibody. Tumors with at least 5% INSM1-positive cells and any staining intensity were considered positive. Molecular testing was successfully performed in 12/17 cases. The immunohistochemical analysis detected 13 INSM1-positive (81%) and 3 INSM1-negative tumors (19%). The extent of the staining was classified as 1+ in 7 cases (44%), 2+ in 2 cases (13%), 3+ in 2 cases (13%) and 4+ in 2 cases (13%). Intensity of immunostaining was weak in 5 cases (31%), moderate in 2 cases (13%) and strong in 6 cases (38%). Molecular assays revealed 8 EWSR1::NR4A3 positive tumors (67%), 2 TAF15::NR4A3 positive tumors (17%), 1 TCF12::NR4A3 positive tumor (8%) and 1 NR4A3 positive tumor (8%) in which no other gene alteration was identified. Two of them, namely TCF12 positive and one TAF15 positive tumors, were highly cellular and partially associated with pseudopapillary architecture. Our study found that moderate/strong expression of INSM1 in more than 25% of tumor cells was present in only 31% of cases. Thus, the diagnostic utility of INSM1 is rather low. Two morphologically unique cases of non-EWSR1 rearranged EMC with an extremely rare pseudopapillary growth pattern are also reported.

Mechano-growth factor E-domain modulates cardiac contractile function through 14-3-3 protein interactomes

In the heart, alternative splicing of the igf-I gene produces two isoforms: IGF-IEa and IGF-IEc, (Mechano-growth factor, MGF). The sequence divergence between their E-domain regions suggests differential isoform function. To define the biological actions of MGF's E-domain, we performed in silico analysis of the unique C-terminal sequence and identified a phosphorylation consensus site residing within a putative 14-3-3 binding motif. To test the functional significance of Ser 18 phosphorylation, phospho-mimetic (S/E¹⁸) and phospho-null (S/A¹⁸) peptides were delivered to mice at different doses for 2 weeks. Cardiovascular function was measured using echocardiography and a pressure-volume catheter. At the lowest (2.25 mg/kg/day) and highest (9 mg/kg/day) doses, the peptides produced a depression in systolic and diastolic parameters. However, at 4.5 mg/kg/day the peptides produced opposing effects on cardiac function. Fractional shortening analysis also showed a similar trend, but with no significant change in cardiac geometry. Microarray analysis discovered 21 genes (FDR p < 0.01), that were expressed accordant with the opposing effects on contractile function at 4.5 mg/kg/day, with the nuclear receptor subfamily 4 group A member 2 (Nr4a2) identified as a potential target of peptide regulation. Testing the regulation of the Nr4a family, showed the E-domain peptides modulate Nr4a gene expression following membrane depolarization with KCl in vitro. To determine the potential role of 14-3-3 proteins, we examined 14-3-3 isoform expression and distribution. 14-3-3γ localized to the myofilaments in neonatal cardiac myocytes, the cardiac myocytes and myofilament extracts from the adult heart. Thermal shift analysis of recombinant 14-3-3γ protein showed the S/A¹⁸ peptide destabilized 14-3-3γ folding. Also, the S/A¹⁸ peptide significantly inhibited 14-3-3γ's ability to interact with myosin binding protein C (MYPC3) and phospholamban (PLN) in heart lysates from dobutamine injected mice. Conversely, the S/E¹⁸ peptide showed no effect on 14-3-3γ stability, did not inhibit 14-3-3γ's interaction with PLN but did inhibit the interaction with MYPC3. Replacing the glutamic acid with a phosphate group on Ser 18 (pSer¹⁸), significantly increased 14-3-3γ protein stability. We conclude that the state of Ser 18 phosphorylation within the 14-3-3 binding motif of MGF's E-domain, modulates protein-protein interactions within the 14-3-3γ interactome, which includes proteins involved in the regulation of contractile function.

Pharmaceutical Agents for Contractile-Metabolic Dysfunction After Volumetric Muscle Loss

Volumetric muscle loss (VML) injuries represent a majority of military service member casualties and are common in civilian populations following blunt and/or penetrating traumas. Characterized as a skeletal muscle injury with permanent functional impairments, there is currently no standard for rehabilitation, leading to lifelong disability. Toward developing rehabilitative strategies, previous research demonstrates that the remaining muscle after a VML injury lacks similar levels of plasticity or adaptability as healthy, uninjured skeletal muscle. This may be due, in part, to impaired innervation and vascularization of the remaining muscle, as well as disrupted molecular signaling cascades commonly associated with muscle adaptation. The primary objective of this study was to assess the ability of four pharmacological agents with a strong record of modulating muscle contractile and metabolic function to improve functional deficits in a murine model of VML injury. Male C57BL/6 mice underwent a 15% multimuscle VML injury of the posterior hindlimb and were randomized into drug treatment groups (formoterol [FOR], 5-aminoimidazole-4-carboxamide riboside [AICAR], pioglitazone [PIO], or sildenafil [SIL]) or untreated VML group. At the end of 60 days, the injury model was first validated by comparison to age-matched injury-naive mice. Untreated VML mice had 22% less gastrocnemius muscle mass, 36% less peak-isometric torque, and 27% less maximal mitochondrial oxygen consumption rate compared to uninjured mice (p < 0.01). Experimental drug groups were, then, compared to VML untreated, and there was minimal evidence of efficacy for AICAR, PIO, or SIL in improving contractile and metabolic functional outcomes. However, FOR-treated VML mice had 18% greater peak isometric torque (p < 0.01) and permeabilized muscle fibers had 36% greater State III mitochondrial oxygen consumption rate (p < 0.01) compared to VML untreated mice, suggesting an overall improvement in muscle condition. There was minimal evidence that these benefits came from greater mitochondrial biogenesis and/or mitochondrial complex protein content, but could be due to greater enzyme activity levels for complex I and complex II. These findings suggest that FOR treatment is candidate to pair with a rehabilitative approach to maximize functional improvements in VML-injured muscle. Impact statement Volumetric muscle loss (VML) injuries result in deficiencies in strength and mobility, which have a severe impact on patient quality of life. Despite breakthroughs in tissue engineering, there are currently no treatments available that can restore function to the affected limb. Our data show that treatment of VML injuries with clinically available and FDA-approved formoterol (FOR), a beta-agonist, significantly improves strength and metabolism of VML-injured muscle. FOR is therefore a promising candidate for combined therapeutic approaches (i.e., regenerative rehabilitation) such as pairing FOR with structured rehabilitation or cell-seeded biomaterials as it may provide greater functional improvements than either strategy alone.

Insight Into the Metabolic Adaptations of Electrically Pulse-Stimulated Human Myotubes Using Global Analysis of the Transcriptome and Proteome

Electrical pulse stimulation (EPS) has proven to be a useful tool to interrogate cell-specific responses to muscle contraction. In the present study, we aimed to uncover networks of signaling pathways and regulatory molecules responsible for the metabolic effects of exercise in human skeletal muscle cells exposed to chronic EPS. Differentiated myotubes from young male subjects were exposed to EPS protocol 1 (i.e. 2 ms, 10 V, and 0.1 Hz for 24 h), whereas myotubes from middle-aged women and men were exposed to protocol 2 (i.e. 2 ms, 30 V, and 1 Hz for 48 h). Fuel handling as well as the transcriptome, cellular proteome, and secreted proteins of EPS-treated myotubes from young male subjects were analyzed using a combination of high-throughput RNA sequencing, high-resolution liquid chromatography-tandem mass spectrometry, oxidation assay, and immunoblotting. The data showed that oxidative metabolism was enhanced in EPS-exposed myotubes from young male subjects. Moreover, a total of 81 differentially regulated proteins and 952 differentially expressed genes (DEGs) were observed in these cells after EPS protocol 1. We also found 61 overlapping genes while comparing the DEGs to mRNA expression in myotubes from the middle-aged group exposed to protocol 2, assessed by microarray. Gene ontology (GO) analysis indicated that significantly regulated proteins and genes were enriched in biological processes related to glycolytic pathways, positive regulation of fatty acid oxidation, and oxidative phosphorylation, as well as muscle contraction, autophagy/mitophagy, and oxidative stress. Additionally, proteomic identification of secreted proteins revealed extracellular levels of 137 proteins were changed in myotubes from young male subjects exposed to EPS protocol 1. Selected putative myokines were measured using ELISA or multiplex assay to validate the results. Collectively, our data provides new insight into the transcriptome, proteome and secreted proteins alterations following in vitro exercise and is a valuable resource for understanding the molecular mechanisms and regulatory molecules mediating the beneficial metabolic effects of exercise.

Slc12a8 in the lateral hypothalamus maintains energy metabolism and skeletal muscle functions during aging

Sarcopenia and frailty are urgent socio-economic problems worldwide. Here we demonstrate a functional connection between the lateral hypothalamus (LH) and skeletal muscle through Slc12a8, a recently identified nicotinamide mononucleotide transporter, and its relationship to sarcopenia and frailty. Slc12a8-expressing cells are mainly localized in the LH. LH-specific knockdown of Slc12a8 in young mice decreases activity-dependent energy and carbohydrate expenditure and skeletal muscle functions, including muscle mass, muscle force, intramuscular glycolysis, and protein synthesis. LH-specific Slc12a8 knockdown also decreases sympathetic nerve signals at neuromuscular junctions and β2-adrenergic receptors in skeletal muscle, indicating the importance of the LH-sympathetic nerve-β2-adrenergic receptor axis. LH-specific overexpression of Slc12a8 in aged mice significantly ameliorates age-associated decreases in energy expenditure and skeletal muscle functions. Our results highlight an important role of Slc12a8 in the LH for regulation of whole-body metabolism and skeletal muscle functions and provide insights into the pathogenesis of sarcopenia and frailty during aging.

The Impact of CB1 Receptor on Nuclear Receptors in Skeletal Muscle Cells

Cannabinoids are abundant signaling compounds; their influence predominantly arises via engagement with the principal two G-protein-coupled cannabinoid receptors, CB1 and CB2. One suggested theory is that cannabinoids regulate a variety of physiological processes within the cells of skeletal muscle. Earlier publications have indicated that expression of CB1 receptor mRNA and protein has been recognized within myotubes and tissues of skeletal muscle from both murines and humans, thus representing a potentially significant pathway which plays a role in the control of skeletal muscular activities. The part played by CB1 receptor activation or inhibition with respect to these functions and relevant to targets in the periphery, especially skeletal muscle, is not fully delineated. Thus, the aim of the current research was to explore the influence of CB1 receptor stimulation and inhibition on downstream signaling of the nuclear receptor, NR4A, which regulates the immediate impacts of arachidonyl-2′-chloroethylamide (ACEA) and/or rimonabant in the cells of skeletal muscle. Murine L6 skeletal muscle cells were used in order to clarify additional possible molecular signaling pathways which contribute to alterations in the CB1 receptor. Skeletal muscle cells have often been used; it is well-documented that they express cannabinoid receptors. Quantitative real-time probe-based polymerase chain reaction (qRT-PCR) assays are deployed in order to assess the gene expression characteristics of CB1 receptor signaling. In the current work, it is demonstrated that skeletal muscle cells exhibit functional expression of CB1 receptors. This can be deduced from the qRT-PCR assays; triggering CB1 receptors amplifies both NR4A1 and NR4A3 mRNA gene expression. The impact of ACEA is inhibited by the selective CB1 receptor antagonist, rimonabant. The present research demonstrated that 10 nM of ACEA notably amplified mRNA gene expression of NR4A1 and NR4A3; this effect was suppressed by the addition of 100 nM rimonabant. Furthermore, the CB1 receptor antagonist led to the downregulation of mRNA gene expression of NR4A1, NR4A2 and NR4A3. In conclusion, in skeletal muscle, CB1 receptors were recognized to be important moderators of NR4A1 and NR4A3 mRNA gene expression; these actions may have possible clinical benefits. Thus, in skeletal muscle cells, a possible physiological expression of CB1 receptors was identified. It is as yet unknown whether these CB1 receptors contribute to pathways underlying skeletal muscle biological function and disease processes. Further research is required to fully delineate their role(s).

2-Adrenergic receptor agonist induced hepatic steatosis in mice: modeling nonalcoholic fatty liver disease in hyperadrenergic states

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of disorders ranging from hepatic steatosis [excessive accumulation of triglycerides (TG)] to nonalcoholic steatohepatitis, which can progress to cirrhosis and hepatocellular carcinoma. The molecular pathogenesis of steatosis and progression to more severe NAFLD remains unclear. Obesity and aging, two principal risk factors for NAFLD, are associated with a hyperadrenergic state. β-Adrenergic responsiveness in liver increases in animal models of obesity and aging, and in both is linked to increased hepatic expression of β2-adrenergic receptors (β2-ARs). We previously showed that in aging rodents intracellular signaling from elevated hepatic levels of β2-ARs may contribute to liver steatosis. In this study we demonstrate that injection of formoterol, a highly selective β2-AR agonist, to mice acutely results in hepatic TG accumulation. Further, we have sought to define the intrahepatic mechanisms underlying β2-AR mediated steatosis by investigating changes in hepatic expression and cellular localization of enzymes, transcription factors, and coactivators involved in processes of lipid accrual and disposition-and also functional aspects thereof-in livers of formoterol-treated animals. Our results suggest that β2-AR activation by formoterol leads to increased hepatic TG synthesis and de novo lipogenesis, increased but incomplete β-oxidation of fatty acids with accumulation of potentially toxic long-chain acylcarnitine intermediates, and reduced TG secretion-all previously invoked as contributors to fatty liver disease. Experiments are ongoing to determine whether sustained activation of hepatic β2-AR signaling by formoterol might be utilized to model fatty liver changes occurring in hyperadrenergic states of obesity and aging, and thereby identify novel molecular targets for the prevention or treatment of NAFLD.NEW & NOTEWORTHY Results of our study suggest that β2-adrenergic receptor (β2-AR) activation by agonist formoterol leads to increased hepatic TG synthesis and de novo lipogenesis, incomplete β-oxidation of fatty acids with accumulation of long-chain acylcarnitine intermediates, and reduced TG secretion. These findings may, for the first time, implicate a role for β2-AR responsive dysregulation of hepatic lipid metabolism in the pathogenetic processes underlying NAFLD in hyperadrenergic states such as obesity and aging.

Effects of Exercise and a High-Fat, High-Sucrose Restriction Diet on Metabolic Indicators, Nr4a3, and Mitochondria-Associated Protein Expression in the Gastrocnemius Muscles of Mice with Diet-Induced Obesity

Background

Exercise and high fat, high sucrose restriction diets are well known treatments for obesity. The aim of this study was to measure the effects of those lifestyle interventions on molecular transducers of exercise, such as Nr4a3, mitochondria-associated proteins, and muscle function.

Methods

We conducted 8 weeks of treadmill exercise and sucrose or fat restriction diets in obese mice. The mice were divided into eight groups: the normal diet (CON) group, normal diet with exercise (CONEX) group, high fat, high sucrose diet (HFHS) group, HFHS with exercise (HFHSEX) group, sucrose restriction (SR) group, SR with exercise (SREX) group, high fat, high sucrose restriction (ND) group, and ND with exercise (NDEX) group.

Results

The 8 weeks of exercise reduced body weight, improved lipid profiles (total cholesterol, triglycerides), and increased hanging time. The combination of exercise and a fat and sucrose restriction diet improved glucose tolerance and increased grip strength. The 8 weeks of intervention did not significantly affect the Nr4a3 protein level. The sucrose and fat restriction diet increased the phosphorylated protein kinase B (pAkt)/Akt ratio, and its level was lower in the HFHS group. Exercise increased the protein expression level of PGC-1α in obese conditions. Moreover, SR led reduced the phosphorylated AMP-activated protein kinase (pAMPK)/AMPK ratio and PGC-1α to the control level.

Conclusion

The 8 weeks of exercise or a sucrose and fat restriction diet improved metabolic indicators and muscle function. SR reduced pAMPK/AMPK and PGC-1α to the control level. Nr4a3 protein expression was not significantly changed by either exercise or a fat and sucrose restriction diet.

The Role of the FOXO1/β2-AR/p-NF-κB p65 Pathway in the Development of Endometrial Stromal Cells in Pregnant Mice under Restraint Stress

Restraint stress causes various maternal diseases during pregnancy. β₂-Adrenergic receptor (β₂-AR) and Forkhead transcription factor class O 1 (FOXO1) are critical factors not only in stress, but also in reproduction. However, the role of FOXO1 in restraint stress, causing changes in the β₂-AR pathway in pregnant mice, has been unclear. The aim of this research was to investigate the β₂-AR pathway of restraint stress and its impact on the oxidative stress of the maternal uterus. In the study, maternal mice were treated with restraint stress by being restrained in a transparent and ventilated device before sacrifice on Pregnancy Day 5 (P5), Pregnancy Day 10 (P10), Pregnancy Day 15 (P15), and Pregnancy Day 20 (P20) as well as on Non-Pregnancy Day 5 (NP5). Restraint stress augmented blood corticosterone (CORT), norepinephrine (NE), and blood glucose levels, while oestradiol (E2) levels decreased. Moreover, restraint stress increased the mRNA levels of the FOXO family, β₂-AR, and even the protein levels of FOXO1 and β₂-AR in the uterus and ovaries. Furthermore, restraint stress increased uterine oxidative stress level. In vitro, the protein levels of FOXO1 were also obviously increased when β₂-AR was activated in endometrial stromal cells (ESCs). In addition, phosphorylated-nuclear factor kappa-B p65 (p-NF-κB p65) and its target genes decreased significantly when FOXO1 was inhibited. Overall, it can be said that the β₂-AR/FOXO1/p-NF-κB p65 pathway was activated when pregnant mice were under restraint stress. This study provides a scientific basis for the origin of psychological stress in pregnant women.

β-Catenin drives distinct transcriptional networks in proliferative and nonproliferative cardiomyocytes

The inability of the adult mammalian heart to regenerate represents a fundamental barrier in heart failure management. By contrast, the neonatal heart retains a transient regenerative capacity, but the underlying mechanisms for the developmental loss of cardiac regenerative capacity in mammals are not fully understood. Wnt/β-catenin signalling has been proposed as a key cardioregenerative pathway driving cardiomyocyte proliferation. Here, we show that Wnt/β-catenin signalling potentiates neonatal mouse cardiomyocyte proliferation in vivo and immature human pluripotent stem cell-derived cardiomyocyte (hPSC-CM) proliferation in vitro By contrast, Wnt/β-catenin signalling in adult mice is cardioprotective but fails to induce cardiomyocyte proliferation. Transcriptional profiling and chromatin immunoprecipitation sequencing of neonatal mouse and hPSC-CMs revealed a core Wnt/β-catenin-dependent transcriptional network governing cardiomyocyte proliferation. By contrast, β-catenin failed to re-engage this neonatal proliferative gene network in the adult heart despite partial transcriptional re-activation of a neonatal glycolytic gene programme. These findings suggest that β-catenin might be repurposed from regenerative to protective functions in the adult heart in a developmental process dependent on the metabolic status of cardiomyocytes.

Targeting Orphan Nuclear Receptors NR4As for Energy Homeostasis and Diabetes

Orphan nuclear receptors are important members of the nuclear receptor family and may regulate cell proliferation, metabolism, differentiation, and apoptosis. NR4As, a subfamily of orphan nuclear receptors, have been reported to play key roles in carbohydrate and lipid metabolism and energy homeostasis. Popularity of obesity has resulted in a series of metabolic diseases such as diabetes and its complications. While imbalance of energy intake and expenditure is the main cause of obesity, the concrete mechanism of obesity has not been fully understood. It has been reported that NR4As have significant regulatory effects on energy homeostasis and diabetes and are expected to become new targets for discovering drugs for metabolic syndrome. A number of studies have demonstrated that abnormalities in metabolism induced by altered levels of NR4As may contribute to numerous diseases, such as chronic inflammation, tumorigenesis, diabetes and its complications, atherosclerosis, and other cardiovascular diseases. However, systematic reviews focusing on the roles of NR4As in mediating energy homeostasis and diabetes remain limited. Therefore, this article reviews the structure and regulation of NR4As and their critical function in energy homeostasis and diabetes, as well as small molecules that may regulate NR4As. Our work is aimed at providing valuable support for the research and development of drugs targeting NR4As for the treatment of obesity and related metabolic diseases.

NR4A3 induces endothelial dysfunction through up-regulation of endothelial 1 expression in adipose tissue-derived stromal cells

Hypertension is one of the most prevalent diseases worldwide. Increased synthesis of the vasoconstrictor peptide endothelin 1 (encoded by EDN1) might be responsible for high blood pressure. The present study further confirmed the abnormal EDN1 upregulation within adipose tissue-derived stromal cells (ADSCs) derived from morbidly obese subjects. The overexpression of EDN1 in ADSCs derived from non-obese subjects significantly promoted the proliferation and migration of HUVECs and tube formation by human umbilical vein endothelial cell (HUVEC). Transcription factor NR4A3 was positively correlated with EDN1, binding to EDN1 promoter region to upregulate EDN1 expression. Similarly, the overexpression of NR4A3 in ADSCs derived from non-obese subjects significantly promoted the proliferation and migration of HUVECs and tube formation by HUVECs, as well as EDN1 protein levels in ADSCs. However, the effects of NR4A3 overexpression on EDN1 protein levels in ADSCs and the proliferation and migration of HUVECs and tube formation by HUVECs were significantly reversed by EDN1 silencing in ADSCs. In conclusion, NR4A3 is abnormally upregulated in ADSCs derived from morbidly obese subjects; NR4A3 could promote HUVEC angiogenesis through binding to EDN1 promoter and upregulating EDN1 expression.

The nuclear receptor 4A family members: mediators in human disease and autophagy

The Nuclear receptor 4A (NR4A) subfamily, which belongs to the nuclear receptor (NR) superfamily, has three members: NR4A1 (Nur77), NR4A2 (Nurr1) and NR4A3 (Nor1). They are gene regulators with broad involvement in various signaling pathways and human disease responses, including autophagy. Here, we provide a concise overview of the current understanding of the role of the NR4A subfamily members in human diseases and review the research into their regulation of cell autophagy. A deeper understanding of these mechanisms has potential to improve drug development processes and disease therapy.

Augmentation of Nr4a3 and Suppression of Fshb Expression in the Pituitary Gland of Female Annexin A5 Null Mouse

GnRH enhances the expression of annexin A5 (ANXA5) in pituitary gonadotropes, and ANXA5 enhances gonadotropin secretion. However, the impact of ANXA5 regulation on the expression of pituitary hormone genes remains unclear. Here, using quantitative PCR, we demonstrated that ANXA5 deficiency in female mice reduced the expression of Fshb and Gh in their pituitary glands. Transcriptome analysis confirmed a specific increase in Nr4a3 mRNA expression in addition to lower levels of Fshb expression in ANXA5-deficient female pituitary glands. This gene was then found to be a GnRH-inducible immediate early gene, and its increased expression caused protein to accumulate in the nucleus after administration of a GnRH agonist in LβT2 cells, which are an in vitro pituitary gonadotrope model. The increase in ANXA5 protein levels in LβT2 cells clearly suppressed Nr4a3 expression. siRNA-mediated inhibition of Nr4a3 expression increased Fshb expression. The results revealed that GnRH stimulates Nr4a3 and Anxa5 sequentially. NR4A3 suppression of Fshb may be necessary for later massive secretion of FSH by GnRH in gonadotropes, and Nr4a3 would be negatively regulated by ANXA5 to increase FSH secretion.

Metabolic reprogramming by tobacco-specific nitrosamines (TSNAs) in cancer

Metabolic reprogramming is a hallmark of cancer and the link between oncogenes activation, tumor supressors inactivation and bioenergetics modulation is well established. However, numerous carcinogenic environmental factors are responsible for early cancer initiation and their impact on metabolic reprogramming just starts to be deciphered. For instance, it was recently shown that UVB irradiation triggers metabolic reprogramming at the pre-cancer stage with implication for skin cancer detection and therapy. These observations foster the need to study the early changes in tissue metabolism following exposure to other carcinogenic events. According to the International Agency for Research on Cancer (IARC), tobacco smoke is a major class I-carcinogenic environmental factor that contains different carcinogens, but little is known on the impact of tobacco smoke on tissue metabolism and its participation to cancer initiation. In particular, tobacco-specific nitrosamines (TSNAs) play a central role in tobacco-smoke mediated cancer initiation. Here we describe the recent advances that have led to a new hypothesis regarding the link between nitrosamines signaling and metabolic reprogramming in cancer.

Function of Nr4a Orphan Nuclear Receptors in Proliferation, Apoptosis and Fuel Utilization Across Tissues

The Nr4a family of nuclear hormone receptors is composed of three members-Nr4a1/Nur77, Nr4a2/Nurr1 and Nr4a3/Nor1. While currently defined as ligandless, these transcription factors have been shown to regulate varied processes across a host of tissues. Of particular interest, the Nr4a family impinge, in a tissue dependent fashion, on cellular proliferation, apoptosis and fuel utilization. The regulation of these processes occurs through both nuclear and non-genomic pathways. The purpose of this review is to provide a balanced perspective of the tissue specific and Nr4a family member specific, effects on cellular proliferation, apoptosis and fuel utilization.

NURR1 activation in skeletal muscle controls systemic energy homeostasis

Skeletal muscle plays a central role in the control of metabolism and exercise tolerance. Analysis of muscle enhancers activated after exercise in mice revealed the orphan nuclear receptor NURR1/NR4A2 as a prominent component of exercise-responsive enhancers. We show that exercise enhances the expression of NURR1, and transgenic overexpression of NURR1 in skeletal muscle enhances physical performance in mice. NURR1 expression in skeletal muscle is also sufficient to prevent hyperglycemia and hepatic steatosis, by enhancing muscle glucose uptake and storage as glycogen. Furthermore, treatment of obese mice with putative NURR1 agonists increases energy expenditure, improves glucose tolerance, and confers a lean phenotype, mimicking the effects of exercise. These findings identify a key role for NURR1 in governance of skeletal muscle glucose metabolism, and reveal a transcriptional link between exercise and metabolism. Our findings also identify NURR1 agonists as possible exercise mimetics with the potential to ameliorate obesity and other metabolic abnormalities.

Skeletal muscle Nur77 and NOR1 insulin responsiveness is blunted in obesity and type 2 diabetes but improved after exercise training

Obesity and type 2 diabetes (T2DM) are characterized by a blunted metabolic response to insulin, and strongly manifests in skeletal muscle insulin resistance. The orphan nuclear receptors, Nur77 and NOR1, regulate insulin-stimulated nutrient metabolism where Nur77 and NOR1 gene expression is increased with acute aerobic exercise and acute insulin stimulation. Whether Nur77 or NOR1 are associated with the insulin-sensitizing effects of chronic aerobic exercise training has yet to be elucidated. Fourteen lean healthy controls (LHC), 12 obese (OB), and 10 T2DM individuals (T2DM) underwent hyperinsulinemic-euglycemic clamps with skeletal muscle biopsies. Muscle was analyzed for Nur77 and NOR1 gene and protein expression at basal and insulin-stimulated conditions. Furthermore, a subcohort of 18 participants (OB, n = 12; T2DM, n = 6) underwent a 12-week aerobic exercise intervention (85% HRmax , 60 min/day, 5 days/week). In response to insulin infusion, LHC increased protein expression of Nur77 (8.7 ± 3.2-fold) and NOR1 (3.6 ± 1.1-fold), whereas OB and T2DM remained unaffected. Clamp-derived glucose disposal rates correlated with Nur77 (r2  = 0.14) and NOR1 (r2  = 0.12) protein expression responses to insulin, whereas age (Nur77: r2  = 0.22; NOR1: r2  = 0.25) and BMI (Nur77: r2  = 0.22; NOR1: r2  = 0.42) showed inverse correlations, corroborating preclinical data. In the intervention cohort, exercise improved Nur77 protein expression in response to insulin (PRE: -1.2 ± 0.3%, POST: 6.2 ± 1.5%). Also, insulin treatment of primary human skeletal muscle cells increased Nur77 and NOR1 protein. These findings highlight the multifactorial nature of insulin resistance in human obesity and T2DM. Understanding the regulation of Nur77 and NOR1 in skeletal muscle and other insulin-sensitive tissues will create opportunities to advance therapies for T2DM.

Next-Generation Sequencing Identifies Polyunsaturated Fatty Acid Responsive Genes in the Juvenile Rat Cerebellum

Dietary n-3 polyunsaturated fatty acids (PUFA) influence postnatal brain growth and development. However, little data exist regarding the impacts of dietary n-3 PUFA in juvenile animals post weaning, which is a time of rapid growth. We tested the hypothesis that depleting dietary n-3 PUFA would result in modifications to the cerebellar transcriptome of juvenile rats. To test this hypothesis, three week old male rats (an age that roughly corresponds to an 11 month old child in brain development) were fed diets containing either soybean oil (SO) providing 1.1% energy from α-linolenic acid (ALA; 18:3n-3; ALA-sufficient) or corn oil (CO) providing 0.13% energy from ALA (ALA-deficient) for four weeks. Fatty acids (FAs) in the cerebellum were analyzed and revealed a 4-fold increase in n-6 docosapentaenoic acid (DPA; 22:5n-6), increases in arachidonic acid (AA; 20:4n-6) and docosatetraenoic acid (DTA; 22:4n-6), but no decrease in docosahexaenoic acid (DHA; 22:6n-3), in animals fed CO versus SO. Transcript abundance was then characterized to identify differentially expressed genes (DEGs) between the two diets. Upper quartile (UQ) scaling and transcripts per million (TPM) data normalization identified 100 and 107 DEGs, respectively. Comparison of DEGs from the two normalization methods identified 70 genes that overlapped, with 90% having abundance differences less than 2-fold. Nr4a3, a transcriptional activator that plays roles in neuroprotection and learning, was elevated over 2-fold from the CO diet. These data indicate that expression of Nr4a3 in the juvenile rat cerebellum is responsive to dietary n-3 PUFA, but additional studies are needed clarify the neurodevelopmental relationships between n-3 PUFA and Nr4a3 and the resulting impacts.

Anabolic and Pro-metabolic Functions of CREB-CRTC in Skeletal Muscle: Advantages and Obstacles for Type 2 Diabetes and Cancer Cachexia

cAMP is one of the earliest described mediators of hormone action in response to physiologic stress that allows acute stress responses and adaptation in every tissue. The classic role of cAMP signaling in metabolic tissues is to regulate nutrient partitioning. In response to acute stress, such as epinephrine released during strenuous exercise or fasting, intramuscular cAMP liberates glucose from glycogen and fatty acids from triglycerides. In the long-term, activation of Gs-coupled GPCRs stimulates muscle growth (hypertrophy) and metabolic adaptation through multiple pathways that culminate in a net increase of protein synthesis, mitochondrial biogenesis, and improved metabolic efficiency. This review focuses on regulation, function, and transcriptional targets of CREB (cAMP response element binding protein) and CRTCs (CREB regulated transcriptional coactivators) in skeletal muscle and the potential for targeting this pathway to sustain muscle mass and metabolic function in type 2 diabetes and cancer. Although the muscle-autonomous roles of these proteins might render them excellent targets for both conditions, pharmacologic targeting must be approached with caution. Gain of CREB-CRTC function is associated with excess liver glucose output in type 2 diabetes, and growing evidence implicates CREB-CRTC activation in proliferation and invasion of different types of cancer cells. We conclude that deeper investigation to identify skeletal muscle specific regulatory mechanisms that govern CREB-CRTC transcriptional activity is needed to safely take advantage of their potent effects to invigorate skeletal muscle to potentially improve health in people with type 2 diabetes and cancer.

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.

Genetic variant in the β2 -adrenergic receptor (Arg16Gly) influences fat-free mass, muscle strength and motor unit behaviour in young men

NEW FINDINGS

What is the central question of this study? Does a common genetic variant in the β₂ -adrenergic receptor (β₂ -AR) have effects on skeletal muscle function in young, healthy men? What is the main finding and its importance? This study provides preliminary evidence that β₂ -AR Arg16Gly genotype has a significant effect on fat-free mass, muscle strength and motor unit behaviour in recreationally trained men. These data might have important clinical and exercise-related implications. For example, β₂ -AR (rs1042713) genotype might influence the responsiveness of skeletal muscle to clinical or exercise-based interventions or β-AR agonist treatment.

ABSTRACT

This study explored whether the β₂ -adrenergic receptor (β₂ -AR) single nucleotide polymorphism at amino acid 16 (Arg16Gly) has functional effects on skeletal muscle mass, torque production and motor unit behaviour in young, healthy men. Twenty-eight recreationally active men (mean ± SD 23.1 ± 1.3 years of age) were genotyped for Arg16Gly polymorphisms of β₂ -AR as arginine homozygous (ArgArg; n = 5), glycine homozygous (GlyGly; n = 11) or arginine-glycine heterozygous (ArgGly; n = 12). The participants then completed body composition testing, assessments of leg extensor size and echo intensity, and evoked and voluntary isometric leg-extension muscle actions. During the evoked muscle actions, peak twitch torque, peak rate of torque development and peak relaxation rate were assessed. During the voluntary muscle actions, maximal voluntary isometric (MVIC) strength was assessed, and surface EMG signals were obtained during submaximal isometric muscle actions and later decomposed to examine motor unit firing behaviour. Fat-free mass and MVIC strength were greater (P = 0.004, d = 1.74 and P = 0.026, d = 1.10, respectively) in those expressing the GlyGly versus ArgArg allele. The slope of the mean firing rate versus recruitment threshold relationship was more negative in the GlyGly than the ArgArg allele carriers (P = 0.012, d = 1.68) at 50% MVIC, but was less negative in GlyGly and ArgGly versus ArgArg allele carriers (P = 0.013 and 0.016, respectively; d = 1.34 and 1.20, respectively) at 70% MVIC. These data provide preliminary evidence that β₂ -AR Arg16Gly genotype has a significant effect on fat-free mass, muscle strength and motor unit behaviour in humans.

Regulation of human trophoblast cell syncytialization by transcription factors STAT5B and NR4A3

In human trophoblast cells, cyclic AMP or its inducer forskolin (FSK) activates two downstream signaling molecules, protein kinase A (PKA) and exchange protein directly activated by cAMP (EPAC), both of which induce syncytialization, cell fusion, and the production of human chorionic gonadotropin (hCG) and progesterone. However, a transcription factor other than GCM1 and molecular mechanisms associated with these events have not been well characterized. To identify novel transcription factors involved in syncytialization of cAMP-stimulated human choriocarcinoma BeWo cells, the microarray analysis was performed with RNAs extracted from PKA- or EPAC-selective cAMP analog-stimulated BeWo cells, from which two up-regulated transcription factors, STAT5 and NR4A3, were found. The knockdown of STAT5B decreased FSK-induced cell fusion and the expression of syncytialization markers, CGB, syncytin1, syncytin2, GCM1, and OVOL1, but NR4A3 knockdown increased FSK-induced cell fusion and the expression of CGB and syncytin2. These findings indicated that cAMP-PKA up-regulated STAT5B, followed by increase in syncytin2 expression through GCM1 and OVOL1, resulting in cell fusion and hCG production, while cAMP-PKA-up-regulated NR4A3 could decrease syncytin2 expression, and suggested that both positive and negative effects of STAT5B and NR4A3, respectively, are required to control the degree of syncytialization in human trophoblast cells.

Control of Muscle Metabolism by the Mediator Complex

Exercise represents an energetic challenge to whole-body homeostasis. In skeletal muscle, exercise activates a variety of signaling pathways that culminate in the nucleus to regulate genes involved in metabolism and contractility; however, much remains to be learned about the transcriptional effectors of exercise. Mediator is a multiprotein complex that links signal-dependent transcription factors and other transcriptional regulators with the basal transcriptional machinery, thereby serving as a transcriptional "hub." In this article, we discuss recent studies highlighting the role of Mediator subunits in metabolic regulation and glucose metabolism, as well as exercise responsiveness. Elucidation of the roles of Mediator subunits in metabolic control has revealed new mechanisms and molecular targets for the modulation of metabolism and metabolic disorders.

A Single Bout of Electroacupuncture Remodels Epigenetic and Transcriptional Changes in Adipose Tissue in Polycystic Ovary Syndrome

A single bout of electroacupuncture results in muscle contractions and increased whole body glucose uptake in women with polycystic ovary syndrome (PCOS). Women with PCOS have transcriptional and epigenetic alterations in the adipose tissue and we hypothesized that electroacupuncture induces epigenetic and transcriptional changes to restore metabolic alterations. Twenty-one women with PCOS received a single bout of electroacupuncture, which increased the whole body glucose uptake. In subcutaneous adipose tissue biopsies, we identified treatment-induced expression changes of 2369 genes (Q < 0.05) and DNA methylation changes of 7055 individual genes (Q = 0.11). The largest increase in expression was observed for FOSB (2405%), and the largest decrease for LOC100128899 (54%). The most enriched pathways included Acute phase response signaling and LXR/RXR activation. The DNA methylation changes ranged from 1-16%, and 407 methylation sites correlated with gene expression. Among genes known to be differentially expressed in PCOS, electroacupuncture reversed the expression of 80 genes, including PPARγ and ADIPOR2. Changes in the expression of Nr4a2 and Junb are reversed by adrenergic blockers in rats demonstrating that changes in gene expression, in part, is due to activation of the sympathetic nervous system. In conclusion, low-frequency electroacupuncture with muscle contractions remodels epigenetic and transcriptional changes that elicit metabolic improvement.

NR4A1 and NR4A3 restrict HSC proliferation via reciprocal regulation of C/EBPα and inflammatory signaling

Members of the NR4A subfamily of nuclear receptors have complex, overlapping roles during hematopoietic cell development and also function as tumor suppressors of hematologic malignancies. We previously identified NR4A1 and NR4A3 (NR4A1/3) as functionally redundant suppressors of acute myeloid leukemia (AML) development. However, their role in hematopoietic stem cell (HSC) homeostasis remains to be disclosed. Using a conditional Nr4a1/Nr4a3 knockout mouse (CDKO), we show that codepletion of NR4A1/3 promotes acute changes in HSC homeostasis including loss of HSC quiescence, accumulation of oxidative stress, and DNA damage while maintaining stem cell regenerative and differentiation capacity. Molecular profiling of CDKO HSCs revealed widespread upregulation of genetic programs governing cell cycle and inflammation and an aberrant activation of the interferon and NF-κB signaling pathways in the absence of stimuli. Mechanistically, we demonstrate that NR4A1/3 restrict HSC proliferation in part through activation of a C/EBPα-driven antiproliferative network by directly binding to a hematopoietic-specific Cebpa enhancer and activating Cebpa transcription. In addition, NR4A1/3 occupy the regulatory regions of NF-κB-regulated inflammatory cytokines, antagonizing the activation of NF-κB signaling. Taken together, our results reveal a novel coordinate control of HSC quiescence by NR4A1/3 through direct activation of C/EBPα and suppression of activation of NF-κB-driven proliferative inflammatory responses.

AMPK in skeletal muscle function and metabolism

Skeletal muscle possesses a remarkable ability to adapt to various physiologic conditions. AMPK is a sensor of intracellular energy status that maintains energy stores by fine-tuning anabolic and catabolic pathways. AMPK’s role as an energy sensor is particularly critical in tissues displaying highly changeable energy turnover. Due to the drastic changes in energy demand that occur between the resting and exercising state, skeletal muscle is one such tissue. Here, we review the complex regulation of AMPK in skeletal muscle and its consequences on metabolism (e.g., substrate uptake, oxidation, and storage as well as mitochondrial function of skeletal muscle fibers). We focus on the role of AMPK in skeletal muscle during exercise and in exercise recovery. We also address adaptations to exercise training, including skeletal muscle plasticity, highlighting novel concepts and future perspectives that need to be investigated. Furthermore, we discuss the possible role of AMPK as a therapeutic target as well as different AMPK activators and their potential for future drug development.—Kjøbsted, R., Hingst, J. R., Fentz, J., Foretz, M., Sanz, M.-N., Pehmøller, C., Shum, M., Marette, A., Mounier, R., Treebak, J. T., Wojtaszewski, J. F. P., Viollet, B., Lantier, L. AMPK in skeletal muscle function and metabolism.

Personalized analysis of pathway aberrance induced by sevoflurane and propofol

Anesthetic agents are used in surgical operations to reversibly reduce consciousness and pain. Sevoflurane is an inhalational anesthetic. Propofol is a short-acting intravenous general anesthetic. The mechanism of anesthetic agents at pathway level on individual patients has not been reported to date. In the present study, pathway aberrance in the human atrial tissue in response to anesthetics was examined. Microarray data of anesthesia-treated samples were downloaded from the Array Express database. Pathway information was obtained from the Reactome Pathway Database. The individual pathway aberrance score (iPAS) was introduced to identify dysregulated pathways in individual patients. The present data demonstrated 157 dysregulated pathways in the sevoflurane group, and 44 pathways were identified with the least P-values. A subset of 49 differentially expressed genes (DEGs) that were shared between the expression profiling results and the dysregulated pathways results were constructed into a co-expression network. The top 5 ranked DEGs, nuclear receptor subfamily 4 group A member 3 (NR4A3), JUNB proto-oncogene, MYC proto-oncogene, tachykinin precursor 1 and nicotinamide phosphoribosyltransferase, were identified as important in the topology analysis. In the propofol group, 87 dysregulated pathways were identified and 44 pathways had the least P-values. In total 28 DEGs were constructed into a co-expression network, of which 5 DEGs were important in the topology analysis, NR4A3, suppressor of cytokine signaling 3, cyclin dependent kinase inhibitor 1A, C-C motif chemokine ligand 2 and C-X-C motif chemokine ligand 1. A total of 72 dysregulated pathways were identified in common in the two groups. In conclusion, the two types of anesthetics induced partially similar mechanisms. The pathways enriched by DEGs, particularly those that were unique to sevoflurane and propofol, may affect surgical outcomes and aid the prevention of complications from anesthetics.

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.

Phosphodiesterase 4 Inhibitors Attenuate the Asthma Phenotype Produced by β2-Adrenoceptor Agonists in Phenylethanolamine N-Methyltransferase-Knockout Mice

Mice lacking the endogenous β2-adrenoceptor (β2AR) agonist epinephrine (phenylethanolamine N-methyltransferase [PNMT]-knockout mice) are resistant to developing an "asthma-like" phenotype in an ovalbumin sensitization and challenge (Ova S/C) model, and chronic administration of β2AR agonists to PNMT-KO mice restores the phenotype. Based on these and other studies showing differential effects of various β2AR ligands on the asthma phenotype, we have speculated that the permissive effect of endogenous epinephrine and exogenous β2AR agonists on allergic lung inflammation can be explained by qualitative β2AR signaling. The β2AR can signal through at least two pathways: the canonical Gαs-cAMP pathway and a β-arrestin-dependent pathway. Previous studies suggest that β-arrestin-2 is required for allergic lung inflammation. On the other hand, cell-based assays suggest antiinflammatory effects of Gαs-cAMP signaling. This study was designed to test whether the in vitro antiinflammatory effects of phosphodiesterase 4 inhibitors, known to increase intracellular cAMP in multiple airway cell types, attenuate the asthma-like phenotype produced by the β2AR agonists formoterol and salmeterol in vivo in PNMT-KO mice, based on the hypothesis that skewing β2AR signaling toward Gαs-cAMP pathway is beneficial. Airway inflammatory cells, epithelial mucus production, and airway hyperresponsiveness were quantified. In Ova S/C PNMT-KO mice, formoterol and salmeterol restored the asthma-like phenotype comparable to Ova S/C wild-type mice. However, coadministration of either roflumilast or rolipram attenuated this formoterol- or salmeterol-driven phenotype in Ova S/C PNMT-KO. These findings suggest that amplification of β2AR-mediated cAMP by phosphodiesterase 4 inhibitors attenuates the asthma-like phenotype promoted by β-agonists.

Brain nuclear receptors and body weight regulation

Neural pathways, especially those in the hypothalamus, integrate multiple nutritional, hormonal, and neural signals, resulting in the coordinated control of body weight balance and glucose homeostasis. Nuclear receptors (NRs) sense changing levels of nutrients and hormones, and therefore play essential roles in the regulation of energy homeostasis. Understanding the role and the underlying mechanisms of NRs in the context of energy balance control may facilitate the identification of novel targets to treat obesity. Notably, NRs are abundantly expressed in the brain, and emerging evidence indicates that a number of these brain NRs regulate multiple aspects of energy balance, including feeding, energy expenditure and physical activity. In this Review we summarize some of the recent literature regarding effects of brain NRs on body weight regulation and discuss mechanisms underlying these effects.

Molecular determinants of the adrenal gland functioning related to stress-sensitive hypertension in ISIAH rats

Background

The adrenals are known as an important link in pathogenesis of arterial hypertensive disease. The study was directed to the adrenal transcriptome analysis in ISIAH rats with stress-sensitive arterial hypertension and predominant involvement in pathogenesis of the hypothalamic-pituitary-adrenal and sympathoadrenal systems.

Results

The RNA-Seq approach was used to perform the comparative adrenal transcriptome profiling in hypertensive ISIAH and normotensive WAG rats. Multiple differentially expressed genes (DEGs) related to different biological processes and metabolic pathways were detected.

The discussion of the results helped to prioritize the several DEGs as the promising candidates for further studies of the genetic background underlying the stress-sensitive hypertension development in the ISIAH rats. Two of these were transcription factor genes (Nr4a3 and Ppard), which may be related to the predominant activation of the sympathetic-adrenal medullary axis in ISIAH rats. The other genes are known as associated with hypertension and were defined in the current study as DEGs making the most significant contribution to the inter-strain differences. Four of them (Avpr1a, Hsd11b2, Agt, Ephx2) may provoke the hypertension development, and Mpo may contribute to insulin resistance and inflammation in the ISIAH rats.

Conclusions

The study strongly highlighted the complex nature of the pathogenesis of stress-sensitive hypertension. The data obtained may be useful for identifying the common molecular determinants in different animal models of arterial hypertension, which may be potentially used as therapeutic targets for pharmacological intervention.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3354-2) contains supplementary material, which is available to authorized users.

Epigenetic silencing of the NR4A3 tumor suppressor, by aberrant JAK/STAT signaling, predicts prognosis in gastric cancer

While aberrant JAK/STAT signaling is crucial to the development of gastric cancer (GC), its effects on epigenetic alterations of its transcriptional targets remains unclear. In this study, by expression microarrays coupled with bioinformatic analyses, we identified a putative STAT3 target gene, NR4A3 that was downregulated in MKN28 GC daughter cells overexpressing a constitutively activated STAT3 mutant (S16), as compared to an empty vector control (C9). Bisulphite pyrosequencing and demethylation treatment showed that NR4A3 was epigenetically silenced by promoter DNA methylation in S16 and other GC cell lines including AGS cells, showing constitutive activation of STAT3. Subsequent experiments revealed that NR4A3 promoter binding by STAT3 might repress its transcription. Long-term depletion of STAT3 derepressed NR4A3 expression, by promoter demethylation, in AGS GC cells. NR4A3 re-expression in GC cell lines sensitized the cells to cisplatin, and inhibited tumor growth in vitro and in vivo, in an animal model. Clinically, GC patients with high NR4A3 methylation, or lower NR4A3 protein expression, had significantly shorter overall survival. Intriguingly, STAT3 activation significantly associated only with NR4A3 methylation in low-stage patient samples. Taken together, aberrant JAK/STAT3 signaling epigenetically silences a potential tumor suppressor, NR4A3, in gastric cancer, plausibly representing a reliable biomarker for gastric cancer prognosis.

β-Cell deletion of Nr4a1 and Nr4a3 nuclear receptors impedes mitochondrial respiration and insulin secretion

β-Cell insulin secretion is dependent on proper mitochondrial function. Various studies have clearly shown that the Nr4a family of orphan nuclear receptors is essential for fuel utilization and mitochondrial function in liver, muscle, and adipose. Previously, we have demonstrated that overexpression of Nr4a1 or Nr4a3 is sufficient to induce proliferation of pancreatic β-cells. In this study, we examined whether Nr4a expression impacts pancreatic β-cell mitochondrial function. Here, we show that β-cell mitochondrial respiration is dependent on the nuclear receptors Nr4a1 and Nr4a3. Mitochondrial respiration in permeabilized cells was significantly decreased in β-cells lacking Nr4a1 or Nr4a3. Furthermore, respiration rates of intact cells deficient for Nr4a1 or Nr4a3 in the presence of 16 mM glucose resulted in decreased glucose mediated oxygen consumption. Consistent with this reduction in respiration, a significant decrease in glucose-stimulated insulin secretion rates is observed with deletion of Nr4a1 or Nr4a3. Interestingly, the changes in respiration and insulin secretion occur without a reduction in mitochondrial content, suggesting decreased mitochondrial function. We establish that knockdown of Nr4a1 and Nr4a3 results in decreased expression of the mitochondrial dehydrogenase subunits Idh3g and Sdhb. We demonstrate that loss of Nr4a1 and Nr4a3 impedes production of ATP and ultimately inhibits glucose-stimulated insulin secretion. These data demonstrate for the first time that the orphan nuclear receptors Nr4a1 and Nr4a3 are critical for β-cell mitochondrial function and insulin secretion.

The Nuclear Receptor, Nor-1, Induces the Physiological Responses Associated With Exercise

Skeletal muscle remodels metabolic capacity, contractile and exercise phenotype in response to physiological demands. This adaptive remodeling response to physical activity can ameliorate/prevent diseases associated with poor diet and lifestyle. Our previous work demonstrated that skeletal muscle-specific transgenic expression of the neuron-derived orphan nuclear receptor, Nor-1 drives muscle reprogramming, improves exercise endurance, and oxidative metabolism. The current manuscript investigates the association between exercise, Nor-1 expression and the role of Nor-1 in adaptive remodeling. We demonstrate that Nor-1 expression is induced by exercise and is dependent on calcium/calcineurin signaling (in vitro and in vivo). Analysis of fatigue-resistant transgenic mice that express Nor-1 in skeletal muscle revealed increased hypertrophy and vascularization of muscle tissue. Moreover, we demonstrate that transgenic Nor-1 expression is associated with increased intracellular recycling, ie, autophagy, involving 1) increased expression of light chain 3A or LC3A-II, autophagy protein 5, and autophagy protein 12 in quadriceps femoris muscle extracts from Tg-Nor-1 (relative to Wild-type (WT) littermates); 2) decreased p62 expression indicative of increased autophagolysosome assembly; and 3) decreased mammalian target of rapamycin complex 1 activity. Transfection of LC3A-GFP-RFP chimeric plasmid demonstrated that autophagolysosome formation was significantly increased by Nor-1 expression. Furthermore, we demonstrated a single bout of exercise induced LC3A-II expression in skeletal muscle from C57BL/6 WT mice. This study, when combined with our previous studies, demonstrates that Nor-1 expression drives multiple physiological changes/pathways that are critical to the beneficial responses of muscle to exercise and provides insights into potential pharmacological manipulation of muscle reprogramming for the treatment of lifestyle induced chronic diseases.

Nuclear receptor 4A (NR4A) family - orphans no more

The orphan nuclear receptors NR4A1, NR4A2 and NR4A3 are immediate early genes induced by multiple stressors, and the NR4A receptors play an important role in maintaining cellular homeostasis and disease. There is increasing evidence for the role of these receptors in metabolic, cardiovascular and neurological functions and also in inflammation and inflammatory diseases and in immune functions and cancer. Despite the similarities of NR4A1, NR4A2 and NR4A3 and their interactions with common cis-genomic elements, they exhibit unique activities and cell-/tissue-specific functions. Although endogenous ligands for NR4A receptors have not been identified, there is increasing evidence that structurally-diverse synthetic molecules can directly interact with the ligand binding domain of NR4A1 and act as agonists or antagonists, and ligands for NR4A2 and NR4A3 have also been identified. Since NR4A receptors are key factors in multiple diseases, there are opportunities for the future development of NR4A ligands for clinical applications in treating multiple health problems including metabolic, neurologic and cardiovascular diseases, other inflammatory conditions, and cancer.

Mitochondrial Quality Control as a Therapeutic Target

In addition to oxidative phosphorylation (OXPHOS), mitochondria perform other functions such as heme biosynthesis and oxygen sensing and mediate calcium homeostasis, cell growth, and cell death. They participate in cell communication and regulation of inflammation and are important considerations in aging, drug toxicity, and pathogenesis. The cell's capacity to maintain its mitochondria involves intramitochondrial processes, such as heme and protein turnover, and those involving entire organelles, such as fusion, fission, selective mitochondrial macroautophagy (mitophagy), and mitochondrial biogenesis. The integration of these processes exemplifies mitochondrial quality control (QC), which is also important in cellular disorders ranging from primary mitochondrial genetic diseases to those that involve mitochondria secondarily, such as neurodegenerative, cardiovascular, inflammatory, and metabolic syndromes. Consequently, mitochondrial biology represents a potentially useful, but relatively unexploited area of therapeutic innovation. In patients with genetic OXPHOS disorders, the largest group of inborn errors of metabolism, effective therapies, apart from symptomatic and nutritional measures, are largely lacking. Moreover, the genetic and biochemical heterogeneity of these states is remarkably similar to those of certain acquired diseases characterized by metabolic and oxidative stress and displaying wide variability. This biologic variability reflects cell-specific and repair processes that complicate rational pharmacological approaches to both primary and secondary mitochondrial disorders. However, emerging concepts of mitochondrial turnover and dynamics along with new mitochondrial disease models are providing opportunities to develop and evaluate mitochondrial QC-based therapies. The goals of such therapies extend beyond amelioration of energy insufficiency and tissue loss and entail cell repair, cell replacement, and the prevention of fibrosis. This review summarizes current concepts of mitochondria as disease elements and outlines novel strategies to address mitochondrial dysfunction through the stimulation of mitochondrial biogenesis and quality control.

Interaction of ApoA-IV with NR4A1 and NR1D1 Represses G6Pase and PEPCK Transcription: Nuclear Receptor-Mediated Downregulation of Hepatic Gluconeogenesis in Mice and a Human Hepatocyte Cell Line

We have previously shown that the nuclear receptor, NR1D1, is a cofactor in ApoA-IV-mediated downregulation of gluconeogenesis. Nuclear receptor, NR4A1, is involved in the transcriptional regulation of various genes involved in inflammation, apoptosis, and glucose metabolism. We investigated whether NR4A1 influences the effect of ApoA-IV on hepatic glucose metabolism. Our in situ proximity ligation assays and coimmunoprecipitation experiments indicated that ApoA-IV colocalized with NR4A1 in human liver (HepG2) and kidney (HEK-293) cell lines. The chromatin immunoprecipitation experiments and luciferase reporter assays indicated that the ApoA-IV and NR4A1 colocalized at the RORα response element of the human G6Pase promoter, reducing its transcriptional activity. Our RNA interference experiments showed that knocking down the expression of NR4A1 in primary mouse hepatocytes treated with ApoA-IV increased the expression of NR1D1, G6Pase, and PEPCK, and that knocking down NR1D1 expression increased the level of NR4A1. We also found that ApoA-IV induced the expression of endogenous NR4A1 in both cultured primary mouse hepatocytes and in the mouse liver, and decreased glucose production in primary mouse hepatocytes. Our findings showed that ApoA-IV colocalizes with NR4A1, which suppresses G6Pase and PEPCK gene expression at the transcriptional level, reducing hepatic glucose output and lowering blood glucose. The ApoA-IV-induced increase in NR4A1 expression in hepatocytes mediates further repression of gluconeogenesis. Our findings suggest that NR1D1 and NR4A1 serve similar or complementary functions in the ApoA-IV-mediated regulation of gluconeogenesis.