Loss of HNRNPU in Skeletal Muscle Increases Intramuscular Infiltration of Ly6C Positive Cells, leading to Muscle Atrophy through Activation of NF-κB Signaling

Heterogeneous nuclear ribonucleoprotein U (hnRNPU) is known to play multiple biological roles by regulating transcriptional expression, RNA splicing, RNA stability, and chromatin structure in a tissue-dependent manner. The role of hnRNPU in skeletal muscle development and maintenance has not been previously evaluated. In this study, skeletal muscle specific hnRNPU knock out mice is utilized and evaluated skeletal muscle mass and immune cell infiltration through development. By 4 weeks, muscle-specific hnRNPU knockout mice revealed Ly6C+ monocyte infiltration into skeletal muscle, which preceded muscle atrophy. Canonical NF-kB signaling is activated in a myofiber-autonomous manner with hnRNPU repression. Inducible hnRNPU skeletal muscle knockout mice further demonstrated that deletion of hnRNPU in adulthood is sufficient to cause muscle atrophy, suggesting that hnRNPU's role in muscle maintenance is not during development alone. Treatment with salirasib, to inhibit proliferation of immune cells, prevents muscle atrophy in muscle-specific hnRNPU knock out mice, indicating that immune cell infiltration plays causal role in muscle atrophy of hnRNPU knock out mice. Overall, the findings suggest that loss of hnRNPU triggers muscle inflammation and activates NF-κB signaling in a cell-autonomous manner, culminating in muscle atrophy.

Endothelin-1 impairs skeletal muscle myogenesis and development via ETB receptors and p38 MAPK signaling pathway

Myopenia is a condition marked by progressive decline of muscle mass and strength and is associated with aging or obesity. It poses the risk of falling, with potential bone fractures, thereby also increasing the burden on family and society. Skeletal muscle wasting is characterized by a reduced number of myoblasts, impaired muscle regeneration and increased muscle atrophy markers (Atrogin-1, MuRF-1). Endothelin-1 (ET-1) is a potent vasoconstrictor peptide. Increased circulating levels of ET-1 is noted with aging and is associated with muscular fibrosis and decline of strength. However, the regulatory mechanism controlling its effect on myogenesis and atrophy remains unknown. In the present study, the effects of ET-1 on myoblast proliferation, differentiation and development were investigated in C2C12 cells and in ET-1-infused mice. The results show that ET-1, acting via ETB receptors, reduced insulin-stimulated cell proliferation, and also reduced MyoD, MyoG and MyHC expression in the differentiation processes of C2C12 myoblasts. ET-1 inhibited myoblast differentiation through ETB receptors and the p38 mitogen-activated protein kinase (MAPK)-dependent pathway. Additionally, ET-1 decreased MyHC expression in differentiated myotubes. Inhibition of proteasome activity by MG132 ameliorated the ET-1-stimulated protein degradation in differentiated C2C12 myotubes. Furthermore, chronic ET-1 infusion caused skeletal muscle atrophy and impaired exercise performance in mice. In conclusion, ET-1 inhibits insulin-induced cell proliferation, impairs myogenesis and induces muscle atrophy via ETB receptors and the p38 MAPK-dependent pathway.

Daily Eicosapentaenoic Acid Infusion in IUGR Fetal Lambs Reduced Systemic Inflammation, Increased Muscle ADRβ2 Content, and Improved Myoblast Function and Muscle Growth

Intrauterine growth-restricted (IUGR) fetuses exhibit systemic inflammation that contributes to programmed deficits in myoblast function and muscle growth. Thus, we sought to determine if targeting fetal inflammation improves muscle growth outcomes. Heat stress-induced IUGR fetal lambs were infused with eicosapentaenoic acid (IUGR+EPA; n = 9) or saline (IUGR; n = 8) for 5 days during late gestation and compared to saline-infused controls (n = 11). Circulating eicosapentaenoic acid was 42% less (p < 0.05) for IUGR fetuses but was recovered in IUGR+EPA fetuses. The infusion did not improve placental function or fetal O2 but resolved the 67% greater (p < 0.05) circulating TNFα observed in IUGR fetuses. This improved myoblast function and muscle growth, as the 23% reduction (p < 0.05) in the ex vivo differentiation of IUGR myoblasts was resolved in IUGR+EPA myoblasts. Semitendinosus, longissimus dorsi, and flexor digitorum superficialis muscles were 24-39% lighter (p < 0.05) for IUGR but not for IUGR+EPA fetuses. Elevated (p < 0.05) IL6R and reduced (p < 0.05) β2 adrenoceptor content in IUGR muscle indicated enhanced inflammatory sensitivity and diminished β2 adrenergic sensitivity. Although IL6R remained elevated, β2 adrenoceptor deficits were resolved in IUGR+EPA muscle, demonstrating a unique underlying mechanism for muscle dysregulation. These findings show that fetal inflammation contributes to IUGR muscle growth deficits and thus may be an effective target for intervention.

Pathological roles of bone marrow adipocyte-derived monocyte chemotactic protein-1 in type 2 diabetic mice

Type 2 diabetes mellitus (T2DM) has become a prevalent public health concern, with beta-cell dysfunction involved in its pathogenesis. Bone marrow adipose tissue (BMAT) increases in both the quantity and area in individuals with T2DM along with heightened monocyte chemotactic protein-1 (MCP-1) secretion. This study aims to investigate the influence and underlying mechanisms of MCP-1 originating from bone marrow adipocytes (BMAs) on systemic glucose homeostasis in T2DM. Initially, a substantial decrease in the proliferation and glucose-stimulated insulin secretion (GSIS) of islet cells was observed. Moreover, a comparative analysis between the control (Ctrl) group and db/db mice revealed significant alterations in the gene expression profiles of whole bone marrow cells, with a noteworthy upregulation of Mcp-1. And the primary enriched pathways included chemokine signaling pathway and AGE-RAGE signaling pathway in diabetic complications. In addition, the level of MCP-1 was distinctly elevated in BMA-derived conditional media (CM), leading to a substantial inhibition of proliferation, GSIS and the protein level of phosphorylated Akt (p-Akt) in Min6 cells. After blocking MCP-1 pathway, we observed a restoration of p-Akt and the proliferation of islet cells, resulting in a marked improvement in disordered glucose homeostasis. In summary, there is an accumulation of BMAs in T2DM, which secrete excessive MCP-1, exacerbating the abnormal accumulation of BMAs in the bone marrow cavity through paracrine signaling. The upregulated MCP-1, in turn, worsens glucose metabolism disorder by inhibiting the proliferation and insulin secretion of islet cells through an endocrine pathway. Inhibiting MCP-1 signaling can partially restore the proliferation and insulin secretion of islet cells, ultimately ameliorating glucose metabolism disorder. It's worth noting that to delve deeper into the impact of MCP-1 derived from BMAs on islet cells and its potential mechanisms, it is imperative to develop genetically engineered mice with conditional Mcp-1 knockout from BMAs.

Identification of State Markers in Anorexia Nervosa: Replication and Extension of Inflammation Associated Biomarkers Using Multiplex Profiling in Anorexia Nervosa and Atypical Anorexia Nervosa

Proteomics provides an opportunity for detection and monitoring of anorexia nervosa (AN) and its related variant, atypical-AN (atyp-AN). However, research to date has been limited by the small number of proteins explored, exclusive focus on adults with AN, and lack of replication across studies. This study performed Olink Proseek Multiplex profiling of 92 proteins involved in inflammation among females with AN and atyp-AN (N = 64), all < 90% of expected body weight, and age-matched healthy controls (HC; N=44). After correction for multiple testing, nine proteins differed significantly in the AN/atyp-AN group relative to HC group ( lower levels: CXCL1, HGF, IL-18R1, TNFSF14, TRANCE; higher levels: CCL23, Flt3L, LIF-R, MMP-1). The expression levels of three proteins ( lower IL-18R1, TRANCE; higher LIF-R) were uniquely disrupted in females with AN. No unique expression levels emerged for atyp-AN. Across the whole sample, twenty-one proteins correlated positively with BMI (ADA, AXIN1, CD5, CD244, CD40, CD6, CXCL1, FGF-21, HGF, IL-10RB, IL-12B, IL18, IL-18R1, IL6, LAP TGF-beta-1, SIRT2, STAMBP, TNFRSF9, TNFSF14, TRAIL, TRANCE) and six (CCL11, CCL23, FGF-19, IL8, LIF-R, OPG) were negatively correlated with BMI. Overall, our results replicate the prior study demonstrating a dysregulated inflammatory status in AN, and extend these results to atyp-AN (AN/atyp-AN all < 90% of expected body weight). Of the 27 proteins correlated with BMI, 18 were replicated from a prior study using similar methods, highlighting the promise of inflammatory protein expression levels as biomarkers of disease monitoring. Additional studies of individuals across the entire weight spectrum are needed to understand the role of inflammation in atyp-AN.

Signaling pathways and intervention for therapy of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents one of the fastest growing epidemic metabolic disorders worldwide and is a strong contributor for a broad range of comorbidities, including vascular, visual, neurological, kidney, and liver diseases. Moreover, recent data suggest a mutual interplay between T2DM and Corona Virus Disease 2019 (COVID-19). T2DM is characterized by insulin resistance (IR) and pancreatic β cell dysfunction. Pioneering discoveries throughout the past few decades have established notable links between signaling pathways and T2DM pathogenesis and therapy. Importantly, a number of signaling pathways substantially control the advancement of core pathological changes in T2DM, including IR and β cell dysfunction, as well as additional pathogenic disturbances. Accordingly, an improved understanding of these signaling pathways sheds light on tractable targets and strategies for developing and repurposing critical therapies to treat T2DM and its complications. In this review, we provide a brief overview of the history of T2DM and signaling pathways, and offer a systematic update on the role and mechanism of key signaling pathways underlying the onset, development, and progression of T2DM. In this content, we also summarize current therapeutic drugs/agents associated with signaling pathways for the treatment of T2DM and its complications, and discuss some implications and directions to the future of this field.

Elevated branched-chain amino acid promotes atherosclerosis progression by enhancing mitochondrial-to-nuclear H2O2-disulfide HMGB1 in macrophages

As the essential amino acids, branched-chain amino acid (BCAA) from diets is indispensable for health. BCAA supplementation is often recommended for patients with consumptive diseases or healthy people who exercise regularly. Latest studies and ours reported that elevated BCAA level was positively correlated with metabolic syndrome, diabetes, thrombosis and heart failure. However, the adverse effect of BCAA in atherosclerosis (AS) and its underlying mechanism remain unknown. Here, we found elevated plasma BCAA level was an independent risk factor for CHD patients by a human cohort study. By employing the HCD-fed ApoE^-/- mice of AS model, ingestion of BCAA significantly increased plaque volume, instability and inflammation in AS. Elevated BCAA due to high dietary BCAA intake or BCAA catabolic defects promoted AS progression. Furthermore, BCAA catabolic defects were found in the monocytes of patients with CHD and abdominal macrophages in AS mice. Improvement of BCAA catabolism in macrophages alleviated AS burden in mice. The protein screening assay revealed HMGB1 as a potential molecular target of BCAA in activating proinflammatory macrophages. Excessive BCAA induced the formation and secretion of disulfide HMGB1 as well as subsequent inflammatory cascade of macrophages in a mitochondrial-nuclear H₂O₂ dependent manner. Scavenging nuclear H₂O₂ by overexpression of nucleus-targeting catalase (nCAT) effectively inhibited BCAA-induced inflammation in macrophages. All of the results above illustrate that elevated BCAA promotes AS progression by inducing redox-regulated HMGB1 translocation and further proinflammatory macrophage activation. Our findings provide novel insights into the role of animo acids as the daily dietary nutrients in AS development, and also suggest that restricting excessive dietary BCAA consuming and promoting BCAA catabolism may serve as promising strategies to alleviate and prevent AS and its subsequent CHD.

Metformin-chlorogenic acid combination reduces skeletal muscle inflammation in c57BL/6 mice on high-fat diets

BACKGROUND

Inflammation at the low-grade level has been found to contribute to obesity-induced insulin resistance in the skeletal muscle (SM). This study investigated the anti-inflammatory potential of metformin (MET) combined with chlorogenic acid (CGA) in SM of mice fed a high-fat diet (HFD).

MATERIALS AND METHODS

The C57BL/6 mice were divided into five groups of ten each, normal diet, HFD, HFD + MET, HFD + CGA and HFD + MET + CGA.

RESULTS

The results revealed that MET and CGA, alone or in combination, have a reducing effect on weight gain, plasma triglyceride, glucose and insulin levels. MET in combination with CGA led to attenuation of SM inflammation, an effect that was associated with decreasing macrophages infiltration rate. Combined treatment of MET and CGA also resulted in switching macrophages from M1 to M2 phenotype, presented by the higher expression levels of arginase and CD206 (M2 markers) and lower expression levels of iNOS and cd11c markers (M1). In addition, combination treatment was more effective in increasing the anti-inflammatory cytokines expression (IL-10) and decreasing the expression of pro-inflammatory mediators (TNF-α, IL-1β, MCP-1 and IL-6).

CONCLUSION

These findings suggest that the combination treatment of MET and CGA is likely to be a promising approach to control SM inflammation in the HFD-fed model.

Inflammatory Mediation of Heat Stress-Induced Growth Deficits in Livestock and Its Potential Role as a Target for Nutritional Interventions: A Review

Simple Summary

Heat stress is a persistent challenge for livestock producers. Molecular changes throughout the body that result from sustained heat stress slow muscle growth and thus are detrimental to carcass yield and value. Feedlot animals are at particularly high risk for heat stress because their confinement limits their ability to pursue shade and other natural cooling behaviors. Changes in infrastructure to reduce the impact of heat stress are often cost-prohibitive, but recent studies have revealed that anti-inflammatory therapies may help to improve growth deficits in heat-stressed animals. This review describes the conditions that cause heat stress and explains the role of inflammation in muscle growth impairment. Additionally, it discusses the potential for several natural anti-inflammatory dietary additives to improve muscle growth outcomes in heat-stressed livestock.

Abstract

Heat stress is detrimental to well-being and growth performance in livestock, and systemic inflammation arising during chronic heat stress contributes to these poor outcomes. Sustained exposure of muscle and other tissues to inflammation can impair the cellular processes that facilitate muscle growth and intramuscular fat deposition, thus reducing carcass quality and yield. Climate change is expected to produce more frequent extreme heat events, increasing the potential impact of heat stress on sustainable livestock production. Feedlot animals are at particularly high risk for heat stress, as confinement limits their ability to seek cooling from the shade, water, or breeze. Economically practical options to circumvent heat stress in feedlot animals are limited, but understanding the mechanistic role of inflammation in heat stress outcomes may provide the basis for treatment strategies to improve well-being and performance. Feedlot animals receive formulated diets daily, which provides an opportunity to administer oral nutraceuticals and other bioactive products to mitigate heat stress-induced inflammation. In this review, we examine the complex associations between heat stress, systemic inflammation, and dysregulated muscle growth in meat animals. We also present evidence for potential nutraceutical and dietary moderators of inflammation and how they might improve the unique pathophysiology of heat stress.

Capmatinib improves insulin sensitivity and inflammation in palmitate-treated C2C12 myocytes through the PPARδ/p38-dependent pathway

Capmatinib (CAP) has been used to treat metastatic non-small lung cancer (NSCL) and suppress inflammation. It causes hypoglycemia in NSCL patients. Therefore, it is expected that CAP improves inflammation-mediated insulin resistance due to its anti-inflammatory effect. However, the impacts of CAP on insulin signaling in skeletal muscle cells have not yet been fully elucidated. Herein, we investigated the effect of CAP on insulin resistance in palmitate-treated C2C12 myocytes and explored the related molecular mechanisms. We found that treatment of C2C12 myocytes with CAP reversed palmitate-induced impairment of insulin signaling and glucose uptake. CAP treatment ameliorated phosphorylation of inflammatory markers, including NFκB and IκB, in palmitate-treated C2C12 myocytes. Further, it augmented PPARδ expression and suppressed palmitate-induced p38 phosphorylation in a dose-dependent manner. siRNA-mediated suppression of PPARδ abolished the effects of CAP on palmitate-induced insulin resistance and inflammation as well as p38 phosphorylation. Therefore, it has been shown that CAP treatment ameliorates insulin resistance in palmitate-treated C2C12 myocytes via PPARδ/p38 signaling-mediated suppression of inflammation. These results may represent a novel therapeutic approach that could halt insulin resistance and type 2 diabetes.

Visceral adipose tissue imparts peripheral macrophage influx into the hypothalamus

BACKGROUND

Obesity is characterized by a systemic inflammation and hypothalamic neuroinflammation. Systemic inflammation is caused by macrophages that infiltrate obese adipose tissues. We previously demonstrated that high-fat diet (HFD)-fed male mice exhibited peripheral macrophage infiltration into the hypothalamus, in addition to activation of resident microglia. Since this infiltration contributes to neuroinflammation and neuronal impairment, herein we characterize the phenotype and origin of these hypothalamic macrophages in HFD mice.

METHODS

C57BL/6J mice were fed HFD (60% kcal from fat) or control diet with matching sucrose levels, for 12-16 weeks. Males and females were analyzed separately to determine sex-specific responses to HFD. Differences in hypothalamic gene expression in HFD-fed male and female mice, compared to their lean controls, in two different areas of the hypothalamus, were determined using the NanoString neuroinflammation panel. Phenotypic changes in macrophages that infiltrated the hypothalamus in HFD-fed mice were determined by analyzing cell surface markers using flow cytometry and compared to changes in macrophages from the adipose tissue and peritoneal cavity. Adipose tissue transplantation was performed to determine the source of hypothalamic macrophages.

RESULTS

We determined that hypothalamic gene expression profiles demonstrate sex-specific and region-specific diet-induced changes. Sex-specific changes included larger changes in males, while region-specific changes included larger changes in the area surrounding the median eminence. Several genes were identified that may provide partial protection to female mice. We also identified diet-induced changes in macrophage migration into the hypothalamus, adipose tissue, and peritoneal cavity, specifically in males. Further, we determined that hypothalamus-infiltrating macrophages express pro-inflammatory markers and markers of metabolically activated macrophages that were identical to markers of adipose tissue macrophages in HFD-fed mice. Employing adipose tissue transplant, we demonstrate that hypothalamic macrophages can originate from the visceral adipose tissue.

CONCLUSION

HFD-fed males experience higher neuroinflammation than females, likely because they accumulate more visceral fat, which provides a source of pro-inflammatory macrophages that migrate to other tissues, including the hypothalamus. Our findings may explain the male bias for neuroinflammation and the metabolic syndrome. Together, our results demonstrate a new connection between the adipose tissue and the hypothalamus in obesity that contributes to neuroinflammation and hypothalamic pathologies.

Myotendinous Junction Components of Different Skeletal Muscles Present Morphological Changes in Obese Rats

Obesity is characterized by excess adipose tissue and chronic inflammation and promotes extensive changes that can compromise skeletal muscles’ structural and functional integrity. Obesity can seriously impact the force transmission region between the muscle and the tendon, the myotendinous junction (MTJ). The present study aimed to investigate the plasticity of muscle fibers and MTJ regions in high-fat diet-induced obesity in rat tibialis anterior (TA) and soleus (SO) muscles. Wistar rats were divided into control and obese groups (induced by a high-fat diet). The samples of TA and SO muscles were prepared for histochemical and ultrastructural analysis (sarcomeres and MTJ projection). In the muscle fiber, similar adaptations were observed between the muscles of the smaller fiber (types I and IIa) in the obesity results. The MTJ region demonstrated different adaptations between the analyzed muscles. The TA–MTJ region has shorter ultrastructures, while in the SO–MTJ region, the ultrastructures were larger. We conclude that obesity induced by a high-fat diet promotes similar adaptation in the muscle fibers; however, in the MTJ region, the sarcoplasmatic projections and adjacent sarcomere demonstrate different adaptations according to distinct muscle phenotypes.

Sex Differences in Macrophage Responses to Obesity-Mediated Changes Determine Migratory and Inflammatory Traits

The mechanisms whereby obesity differentially affects males and females are unclear. Because macrophages are functionally the most important cells in obesity-induced inflammation, we sought to determine reasons for male-specific propensity in macrophage migration. We previously determined that male mice fed a high-fat diet exhibit macrophage infiltration into the hypothalamus, whereas females were protected irrespective of ovarian estrogen, in this study, we show that males accumulate more macrophages in adipose tissues that are also more inflammatory. Using bone marrow cells or macrophages differentiated in vitro from male and female mice fed control or high-fat diet, we demonstrated that macrophages derived from male mice are intrinsically more migratory. We determined that males have higher levels of leptin in serum and adipose tissue. Serum CCL2 levels, however, are the same in males and females, although they are increased in obese mice compared with lean mice of both sexes. Leptin receptor and free fatty acid (FFA) receptor, GPR120, are upregulated only in macrophages derived from male mice when cultured in the presence of FFA to mimic hyperlipidemia of obesity. Unless previously stimulated with LPS, CCL2 did not cause migration of macrophages. Leptin, however, elicited migration of macrophages from both sexes. Macrophages from male mice maintained migratory capacity when cultured with FFA, whereas female macrophages failed to migrate. Therefore, both hyperlipidemia and hyperleptinemia contribute to male macrophage-specific migration because increased FFA induce leptin receptors, whereas higher leptin causes migration. Our results may explain sex differences in obesity-mediated disorders caused by macrophage infiltration.

Impact of Conventional and Atypical MAPKs on the Development of Metabolic Diseases

The family of mitogen-activated protein kinases (MAPKs) consists of fourteen members and has been implicated in regulation of virtually all cellular processes. MAPKs are divided into two groups, conventional and atypical MAPKs. Conventional MAPKs are further classified into four sub-families: extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK1, 2 and 3), p38 (α, β, γ, δ), and extracellular signal-regulated kinase 5 (ERK5). Four kinases, extracellular signal-regulated kinase 3, 4, and 7 (ERK3, 4 and 7) as well as Nemo-like kinase (NLK) build a group of atypical MAPKs, which are activated by different upstream mechanisms than conventional MAPKs. Early studies identified JNK1/2 and ERK1/2 as well as p38α as a central mediators of inflammation-evoked insulin resistance. These kinases have been also implicated in the development of obesity and diabetes. Recently, other members of conventional MAPKs emerged as important mediators of liver, skeletal muscle, adipose tissue, and pancreatic β-cell metabolism. Moreover, latest studies indicate that atypical members of MAPK family play a central role in the regulation of adipose tissue function. In this review, we summarize early studies on conventional MAPKs as well as recent findings implicating previously ignored members of the MAPK family. Finally, we discuss the therapeutic potential of drugs targeting specific members of the MAPK family.

Optimization of extraction parameters of Pleurotus eryngii polysaccharides and evaluation of the hypolipidemic effect

The hot water extraction of polysaccharides from the fruiting body of Pleurotus eryngii was studied. In this paper, according to single-factor experiments, a response surface methodology and the Box–Behnken design were applied to optimize the extraction parameters of Pleurotus eryngii polysaccharides (PEP). The optimal extraction conditions were as follows: a temperature of 79 °C, a time of 3.11 h, a ratio of water to fruiting bodies of 52.6 mL g⁻¹. Under these parameters, the yield of PEP was 7.53%. When mice with hyperlipidemia were administered low, medium or high doses of PEP, their body weight was reduced compared with the model group, and the degree of weight loss was proportional to the dose. At the 16th week of PEP treatment, blood lipid biochemical parameters such as total cholesterol, triglycerides, low-density lipoprotein-cholesterol, aspartate aminotransferase, and alanine aminotransferase levels were all decreased. However, high-density lipoprotein-cholesterol levels increased after PEP treatment. Histopathological examination of the liver showed that low, medium and high doses of PEP had a certain liver protective effect. High-dose PEP treatment had the best effect in regard to lipid-lowering and liver protection. In addition, the metabolome of the mice was analyzed by LC-MS, and the results indicated that C16 sphinganine can be used as a potential biomarker, which displayed significant differences among the six groups. In conclusion, the possible metabolic mechanism of the PEP on lipid-lowering was closely related to sphingolipid metabolism.

The hot water extraction of polysaccharides from the fruiting body of Pleurotus eryngii was studied.

Heat stress ameliorates tenotomy-induced inflammation in muscle-specific response via regulation of macrophage subtypes

During disuse-induced muscle atrophy, macrophages play a significant role in inflammatory responses that occur with muscle degeneration and repair. Heat treatment has been shown to alleviate muscle atrophy; however, the effect of heat on inflammatory responses following tenotomy has not been evaluated. This study examined the effects of heat stress on proinflammatory (M1-like) and anti-inflammatory (M2-like) macrophage populations. Also, cytokine protein expression in oxidative soleus and glycolytic plantaris muscles following Achilles tendon transection (tenotomy) was analyzed. Male Wistar rats were assigned into control, control plus heat stress, tenotomy, and tenotomy plus heat stress groups. Tenotomy was performed for 8 (TEN8) and 14 (TEN14) days to induce muscle inflammation. Heat treatments, 30 min at 40.5–41.5°C, were given 24 h before and 1–6 consecutive days after tenotomy (TEN8 group) or every other day (TEN14 group). Tenotomy induced muscle necrosis, extensive infiltration of M1- (CD68+), and M2- (CD163+) like macrophages and increased tumor necrosis factor-α (TNFα) but not interleukin-10 (IL-10) protein expression. Heat stress caused a reduction in necrotic fibers, M1-like macrophage invasion, and TNFα protein expression in tenotomized soleus muscle. Additionally, heat stress enhanced M2-like macrophage accumulation during the 14 days following tenotomy in soleus muscle but did not affect IL-10 protein level. Our results indicate that heat stress can limit tenotomy-induced inflammatory responses through modulation of macrophage subtypes and TNFα protein expression, preferentially in oxidative muscle. These findings shed light on the ability of heat stress as a therapeutic strategy to manipulate macrophages for optimal inflammation during muscle atrophy.

NEW & NOTEWORTHY We investigated differential effects of heat stress on modulating inflammation following 8 and 14 days of tenotomy in soleus and plantaris muscles. Heat exposure could reduce necrosis, suppress pro-inflammatory macrophage infiltration, and diminish TNFα protein expression in tenotomized muscle, which preferentially occurred in soleus muscle. Additionally, heat stress enhanced anti-inflammatory macrophages in soleus muscle in the 14-day study period. Neither tenotomy nor heat stress had an impact on IL-10 protein expression in either muscle examined.

Roles of leptin in the recovery of muscle and bone by reloading after mechanical unloading in high fat diet-fed obese mice

Muscle and bone masses are elevated by the increased mechanical stress associated with body weight gain in obesity. However, the mechanisms by which obesity affects muscle and bone remain unclear. We herein investigated the roles of obesity and humoral factors from adipose tissue in the recovery phase after reloading from disuse-induced muscle wasting and bone loss using normal diet (ND)- or high fat diet (HFD)-fed mice with hindlimb unloading (HU) and subsequent reloading. Obesity did not affect decreases in trabecular bone mineral density (BMD), muscle mass in the lower leg, or grip strength in HU mice. Obesity significantly increased trabecular BMD, muscle mass in the lower leg, and grip strength in reloading mice over those in reloading mice fed ND. Among the humoral factors in epididymal and subcutaneous adipose tissue, leptin mRNA levels were significantly higher in reloading mice fed HFD than in mice fed ND. Moreover, circulating leptin levels were significantly higher in reloading mice fed HFD than in mice fed ND. Leptin mRNA levels in epididymal adipose tissue or serum leptin levels positively correlated with the increases in trabecular BMD, total muscle mass, and grip strength in reloading mice fed ND and HFD. The present study is the first to demonstrate that obesity enhances the recovery of bone and muscle masses as well as strength decreased by disuse after reloading in mice. Leptin may contribute to the recovery of muscle and bone enhanced by obesity in mice.

TGF-β1 alleviates HgCl2 induced apoptosis via P38 MAPK signaling pathway in human trophoblast cells

It is well known that embryonic development can be perturbed by environmental factors such as heavy metals. Mercury is one of the most significant threats to the environment and human health. Mercury can damage many parts of the human body, including lungs, kidneys, nerves and fetus. However, the effect of mercury on human embryo remains unknown. Here, we showed that HgCl₂ treatment resulted in a significant increase in apoptosis in HTR-8/SVneo cells. However, the effect of HgCl₂ on apoptosis was partially reduced by the combination treatment with TGF-β1 and HgCl₂ in HTR-8/SVneo cells. Moreover, HgCl₂ treatment gradually decreased the expression of TGF-β1 in a dose dependent manner. Furthermore, a P38 MAPK inhibitor, SB202190, decreased the cell apoptosis and caspase activation induced by HgCl₂ in trophoblast cells. In addition, TGF-β1 alleviated HgCl₂ induced apoptosis of HTR-8/SVneo cells via p38 MAPK signaling pathway, which was involved in the TAK1 expression. These results might provide a theoretical basis for mercury induced trophoblast associated embryo damage and a potential avenue of intervention.

Markers of adipose tissue inflammation are transiently elevated during intermittent fasting in women who are overweight or obese

OBJECTIVE

This study compared the effects of daily calorie restriction (DR) versus intermittent fasting (IF) on markers of inflammation and extracellular matrix deposition in adipose tissue and skeletal muscle in a controlled feeding trial in women with overweight or obesity.

METHODS

Women (N = 76) were randomised to one of three diets and provided with all foods at 100% (IF100) or 70% (IF70 and DR70) of calculated energy requirements for 8 weeks. IF groups ate breakfast prior to fasting for 24-h on 3 non-consecutive days/week. Weight, body composition, serum non-esterified fatty acids (NEFA), tumour necrosis factor-alpha (TNFα), interleukin-6 (IL-6), interleukin-10 (IL-10), M1- and M2-macrophage markers by qPCR and immunohistochemistry in adipose tissue and skeletal muscle were measured following a 12-h overnight fast (fed day, all groups) and a 24-h fast (IF groups only).

RESULTS

IF70 resulted in greater weight and fat losses and reductions in serum NEFA versus DR70 and IF100 (P < 0.05) after fed days. Markers of inflammation in serum (TNFα, IL6 and IL10), subcutaneous adipose tissue and skeletal muscle (CD68, CD40 and CD163) were unchanged by DR or IF after fed days. After fasting, NEFA, M1-macrophages (CD40⁺) in adipose tissue, and M2-macrophages (CD163⁺) in muscle were increased in IF70 and IF100 (all P < 0.05) and the changes in NEFA and mRNA of pan-macrophage marker CD68 in adipose tissue were positively correlated (r = 0.56, P = 0.002).

CONCLUSIONS

Unlike caloric restriction, IF transiently elevated markers of macrophage infiltration in adipose tissue and skeletal muscle, possibly in response to marked increases in adipose tissue lipolysis.

AMPK/FOXO1 signaling pathway is indispensable in visfatin-regulated myosin heavy chain expression in C2C12 myotubes

OBJECTIVE

Few studies have addressed the effects of visfatin on skeletal muscle remodeling. The aim of the study was to investigate the effects of visfatin on the expressions of myosin heavy chain (MHC) and its isoforms, the major indicator of fiber types and contractile properties of skeletal muscle.

MATERIALS AND METHODS

Levels of MHC, MHC I, MHC IIa, MHC IIb, adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), p-AMPK and forkhead box protein O1 (FOXO1) were tested in visfatin-treated C2C12 myotubes. C2C12 myotubes were treated with visfatin combined with AMPK inhibitor or AMPK activator to investigate the role of AMPK in visfatin-mediated MHC expression. FOXO1 was overexpressed or knocked down in C2C12 myotubes to explore the role of FOXO1 in visfatin-mediated MHC expression.

RESULTS

Compared with the vehicle group, treatment with 5 μg/ml visfatin increased the levels of total MHC and its isoforms, MHC I, MHC IIa and MHC IIb, by 1.93, 1.84, 1.80, and 1.92 folds, respectively (all p = 0,001). Visfatin suppressed AMPK phosphorylation and decreased FOXO1 expression in C2C12 myotubes. The effects of visfatin on MHC I and MHC IIa expression were canceled by AMPK activator AICAR. FOXO1 overexpression minimized the visfatin-induced upregulation of MHC I, MHC IIa and MHC IIb. The effect of AMPK activator AICAR on MHC and its isoforms expression was minimized by knockdown of FOXO1.

CONCLUSIONS

The findings revealed that visfatin promoted expressions of MHC and its isoforms in C2C12 myotubes via suppressing AMPK/FOXO1 signaling pathway.