The main aim of this investigation was to verify the effects of overtraining (OT) on the insulin and inflammatory signaling pathways in mice skeletal muscles. Rodents were divided into control (CT), overtrained by downhill running (OTR/down), overtrained by uphill running (OTR/up), and overtrained by running without inclination (OTR) groups. Rotarod, incremental load, exhaustive, and grip force tests were used to evaluate performance. Thirty-six hours after the grip force test, the extensor digitorum longus (EDL) and soleus were extracted for subsequent protein analyses. The three OT protocols led to similar responses of all performance evaluation tests. The phosphorylation of insulin receptor beta (pIRβ; Tyr), protein kinase B (pAkt; Ser473), and the protein levels of plasma membrane glucose transporter-4 (GLUT4) were lower in the EDL and soleus after the OTR/down protocol and in the soleus after the OTR/up and OTR protocols. While the pIRβ was lower after the OTR/up and OTR protocols, the pAkt was higher after the OTR/up in the EDL. The phosphorylation of IκB kinase alpha and beta (pIKKα/β; Ser180/181), stress-activated protein kinases/Jun amino-terminal kinases (pSAPK-JNK; Thr183/Tyr185), factor nuclear kappa B (pNFκB p65; Ser536), and insulin receptor substrate 1 (pIRS1; Ser307) were higher after the OTR/down protocol, but were not altered after the two other OT protocols. In summary, these data suggest that OT may lead to skeletal muscle insulin signaling pathway impairment, regardless of the predominance of eccentric contractions, although the insulin signal pathway impairment induced in OTR/up and OTR appeared to be muscle fiber-type specific.

In addition to the ascertained efficacy as antidiabetic drug, metformin is increasingly being used as weight-loss agent in obesity, and as insulin sensitizer in nonalcoholic fatty liver disease (NAFLD). However, the mechanisms underlying these effects are still incompletely understood. Emerging evidence suggest metformin as leptin sensitizer to mediate the weight-loss effect in the brain. In this study, we investigated effects of metformin on expression of leptin receptors in liver and kidney in mice. C57BL/6 mice were fed with chow diet (CD) or high-fat diet (HF) for 5months. Afterward, mice were treated with metformin (50mg/kg or 200mg/kg) for 15days. Metabolic parameters and hepatic gene expression were analyzed at the end of the treatment. We also tested the effects of metformin on plasma-soluble leptin receptor (sOB-R) levels in newly diagnosed type 2 diabetes mellitus (T2DM) patients, and assessed its effect on hepatosteatosis in mice. Results showed that metformin upregulates the expression of leptin receptors (OB-Ra, -Rb, -Rc, and -Rd) in liver but not kidney. The stimulation effect is dose-dependent in both chow and HF mice. Upregulation of OB-Rb, long signaling isoform, needs a relatively higher dose of metformin. This effect was paralleled by increased sOBR levels in mice and T2DM patients, and decreased hepatic triglyceride (TG) content and lipogenic gene expression, including sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthase (FAS) and acetyl-CoA carboxylase-1 (ACC-1). Taken together, these data identify hepatic leptin receptor as target gene being upregulated by metformin which may enhance leptin sensitivity in liver to alleviate steatosis.

The enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD) interconverts active glucocorticoids and their intrinsically inert 11-keto forms. The type 1 isozyme, 11β-HSD1, predominantly reactivates glucocorticoids in vivo and can also metabolise bile acids. 11β-HSD1-deficient mice show altered inflammatory responses and are protected against the adverse metabolic effects of a high-fat diet. However, the impact of 11β-HSD1 on the composition of the gut microbiome has not previously been investigated. We used high-throughput 16S rDNA amplicon sequencing to characterise the gut microbiome of 11β-HSD1-deficient and C57Bl/6 control mice, fed either a standard chow diet or a cholesterol- and fat-enriched ‘Western’ diet. 11β-HSD1 deficiency significantly altered the composition of the gut microbiome, and did so in a diet-specific manner. On a Western diet, 11β-HSD1 deficiency increased the relative abundance of the family Bacteroidaceae, and on a chow diet, it altered relative abundance of the family Prevotellaceae. Our results demonstrate that (i) genetic effects on host–microbiome interactions can depend upon diet and (ii) that alterations in the composition of the gut microbiome may contribute to the aspects of the metabolic and/or inflammatory phenotype observed with 11β-HSD1 deficiency.

IFN-γ is a pleotropic cytokine produced in the bone microenvironment. Although IFN-γ is known to play a critical role on bone remodeling, its function is not fully elucidated. Consistently, outcomes on the effects of IFN-γ recombinant protein on bone loss are contradictory among reports. In our work we explored, for the first time, the role of IFN-γ encoding plasmid (pIFN-γ) in a mouse model of osteopenia induced by ovariectomy and in the sham-operated counterpart to estimate its effects in skeletal homeostasis. Ovariectomy produced a dramatic decrease of bone mineral density (BMD). pINF-γ injected mice showed a pathologic bone and bone marrow phenotype; the disrupted cortical and trabecular bone microarchitecture was accompanied by an increased release of pro-inflammatory cytokine by bone marrow cells. Moreover, mesenchymal stem cells’ (MSCs) commitment to osteoblast was found impaired, as evidenced by the decline of osterix-positive (Osx⁺) cells within the mid-diaphyseal area of femurs. For instance, a reduction and redistribution of CXCL12 cells have been found, in accordance with bone marrow morphological alterations. As similar effects were observed both in sham-operated and in ovariectomized mice, our studies proved that an increased IFN-γ synthesis in bone marrow might be sufficient to induce inflammatory and catabolic responses even in the absence of pathologic predisposing substrates. In addition, the obtained data might raise questions about pIFN-γ’s safety when it is used as vaccine adjuvant.

The adverse metabolic effects of prescribed and endogenous glucocorticoid excess, ‘Cushing’s syndrome’, create a significant health burden. While skeletal muscle atrophy and resultant myopathy is a clinical feature, the molecular mechanisms underpinning these changes are not fully defined. We have characterized the impact of glucocorticoids upon key metabolic pathways and processes regulating muscle size and mass including: protein synthesis, protein degradation, and myoblast proliferation in both murine C2C12 and human primary myotube cultures. Furthermore, we have investigated the role of pre-receptor modulation of glucocorticoid availability by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in these processes. Corticosterone (CORT) decreased myotube area, decreased protein synthesis, and increased protein degradation in murine myotubes. This was supported by decreased mRNA expression of insulin-like growth factor (IGF1), decreased activating phosphorylation of mammalian target of rapamycin (mTOR), decreased phosphorylation of 4E binding protein 1 (4E-BP1), and increased mRNA expression of key atrophy markers including: atrogin-1, forkhead box O3a (FOXO3a), myostatin (MSTN), and muscle-ring finger protein-1 (MuRF1). These findings were endorsed in human primary myotubes, where cortisol also decreased protein synthesis and increased protein degradation. The effects of 11-dehydrocorticosterone (11DHC) (in murine myotubes) and cortisone (in human myotubes) on protein metabolism were indistinguishable from that of CORT/cortisol treatments. Selective 11β-HSD1 inhibition blocked the decrease in protein synthesis, increase in protein degradation, and reduction in myotube area induced by 11DHC/cortisone. Furthermore, CORT/cortisol, but not 11DHC/cortisone, decreased murine and human myoblast proliferative capacity. Glucocorticoids are potent regulators of skeletal muscle protein homeostasis and myoblast proliferation. Our data underscores the potential use of selective 11β-HSD1 inhibitors to ameliorate muscle-wasting effects associated with glucocorticoid excess.

This study tested the hypothesis that estrogen programs mechanisms within the primate fetus that promote insulin sensitivity and glucose homeostasis in offspring. Glucose tolerance tests were performed longitudinally in prepubertal offspring of baboons untreated or treated on days 100 to 165/175 of gestation (term is 184 days) with the aromatase inhibitor letrozole, which decreased fetal estradiol levels by 95%. Basal plasma insulin levels were over two-fold greater in offspring delivered to letrozole-treated than untreated animals. Moreover, the peak 1min, average of the 1, 3, and 5min, and area under the curve blood glucose and plasma insulin levels after an i.v. bolus of glucose were greater (P<0.05 and P<0.01, respectively) in offspring deprived of estrogen in utero than in untreated animals and partially or completely restored in letrozole plus estradiol-treated baboons. The value for the homeostasis model assessment of insulin resistance was 2.5-fold greater (P<0.02) and quantitative insulin sensitivity check index lower (P<0.01) in offspring of letrozole-treated versus untreated animals and returned to almost normal in letrozole plus estradiol-treated animals. The exaggerated rise in glucose and insulin levels after glucose challenge in baboon offspring deprived of estrogen in utero indicates that pancreatic beta cells had the capacity to secrete insulin, but that peripheral glucose uptake and/or metabolism were impaired, indicative of insulin resistance and glucose intolerance. We propose that estrogen normally programs mechanisms in utero within the developing primate fetus that lead to insulin sensitivity, normal glucose tolerance, and the capacity to metabolize glucose after birth.

Leptin, critical in regulation of energy metabolism, is also important for normal bone growth, maturation and turnover. Compared to wild type (WT) mice, bone mass is lower in leptin-deficient ob/ob mice. Osteopenia in growing ob/ob mice is due to decreased bone accrual, and is associated with reduced longitudinal bone growth, impaired cancellous bone maturation and increased marrow adipose tissue (MAT). However, leptin deficiency also results in gonadal dysfunction, disrupting production of gonadal hormones which regulate bone growth and turnover. The present study evaluated the role of increased estrogen in mediating the effects of leptin on bone in ob/ob mice. Three-month-old female ob/ob mice were randomized into one of the 3 groups: (1) ob/ob + vehicle (veh), (2) ob/ob + leptin (leptin) or (3) ob/ob + leptin and the potent estrogen receptor antagonist ICI 182,780 (leptin + ICI). Age-matched WT mice received vehicle. Leptin (40 µg/mouse, daily) and ICI (10 µg/mouse, 2×/week) were administered by subcutaneous injection for 1 month and bone analyzed by X-ray absorptiometry, microcomputed tomography and static and dynamic histomorphometry. Uterine weight did not differ between ob/ob mice and ob/ob mice receiving leptin + ICI, indicating that ICI successfully blocked the uterine response to leptin-induced increases in estrogen levels. Compared to leptin-treated ob/ob mice, ob/ob mice receiving leptin + ICI had lower uterine weight; did not differ in weight loss, MAT or bone formation rate; and had higher longitudinal bone growth rate and cancellous bone volume fraction. We conclude that increased estrogen signaling following leptin treatment is dispensable for the positive actions of leptin on bone and may attenuate leptin-induced bone growth.

Exosomes are endosomally derived vesicles that are secreted from cells and contain a suite of molecules, including proteins and nucleic acids. Recent studies suggest the possibility that exosomes in circulation may be affecting recipient target cell function, but the modes of action are unclear. Here, we tested the hypothesis that exosomes are in circulation in fish plasma and that these vesicles are enriched with heat shock protein 70 (Hsp70). Exosomes were isolated from rainbow trout (Oncorhynchus mykiss) plasma using differential centrifugation, and their presence was confirmed by transmission electron microscopy and the exosomal marker acetylcholinesterase. Plasma exosomes were enriched with Hsp70, and this stress protein was transiently elevated in trout plasma in response to a heat shock in vivo. Using trout hepatocytes in primary culture, we tested whether stress levels of cortisol, the principle corticosteroid in teleosts, regulates exosomal Hsp70 content. As expected, a 1-h heat shock (+15°C above ambient) increased Hsp70 expression in hepatocytes, and this led to higher Hsp70 enrichment in exosomes over a 24-h period. However, cortisol treatment significantly reduced the expression of Hsp70 in exosomes released from either unstressed or heat-shocked hepatocytes. This cortisol-mediated suppression was not specific to Hsp70 as beta-actin expression was also reduced in exosomes released from hepatocytes treated with the steroid. Our results suggest that circulating Hsp70 is released from target tissues via exosomes, and their release is modulated by stress and cortisol. Overall, we propose a novel role for extracellular vesicular transport of Hsp70 in the organismal stress response.

The 5α-reductase enzymes play an important role during male sexual differentiation, and in pregnant females, especially equine species where maintenance relies on 5α-reduced progesterone, 5α-dihydroprogesterone (DHP). Epididymis expresses 5α-reductases but was not studied elaborately in horses. Epididymis from younger and older postpubertal stallions was divided into caput, corpus and cauda and examined for 5α-reductase activity and expression of type 1 and 2 isoforms by quantitative real-time polymerase chain reaction (qPCR). Metabolism of progesterone and testosterone to DHP and dihydrotestosterone (DHT), respectively, by epididymal microsomal protein was examined by thin-layer chromatography and verified by liquid chromatography tandem mass spectrometry (LC-MS/MS). Relative inhibitory potencies of finasteride and dutasteride toward equine 5α-reductase activity were investigated. Pregnenolone was investigated as an additional potential substrate for 5α-reductase, suggested previously from in vivo studies in mares but never directly examined. No regional gradient of 5α-reductase expression was observed by either enzyme activity or transcript analysis. Results of PCR experiments suggested that type 1 isoform predominates in equine epididymis. Primers for the type 2 isoform were unable to amplify product from any samples examined. Progesterone and testosterone were readily reduced to DHP and DHT, and activity was effectively inhibited by both inhibitors. Using epididymis as an enzyme source, no experimental evidence was obtained supporting the notion that pregnenolone could be directly metabolized by equine 5α-reductases as has been suggested by previous investigators speculating on alternative metabolic pathways leading to DHP synthesis in placenta during equine pregnancies.

Transmembrane protein 18 (TMEM18) is an ill-described, obesity-related gene, but few studies have explored its molecular function. We found single-nucleotide polymorphism data, suggesting that TMEM18 may be involved in the regulation/physiology of metabolic syndrome based on associations with insulin, homeostatic model assessment-β (HOMAβ), triglycerides, and blood sugar. We then found an ortholog in the Drosophila genome, knocked down Drosophila Tmem18 specifically in insulin-producing cells, and tested for its effects on metabolic function. Our results suggest that TMEM18 affects substrate levels through insulin and glucagon signaling, and its downregulation induces a metabolic state resembling type 2 diabetes. This work is the first to experimentally describe the metabolic consequences of TMEM18 knockdown, and further supports its association with obesity.