A comparative study on the effects of acute and chronic downhill running vs uphill running exercise on the RNA levels of the skeletal muscles PGC1-α, FNDC5 and the adipose UCP1 in BALB/c mice

High-intensity interval training ameliorates postnatal immune activation-induced mood disorders through KDM6B-regulated glial activation

Postnatal immune activation (PIA) induces persistent glial activation in the brain and causes various neuropathologies in adults. Exercise training improves stress-related mood disorders; however, the role of exercise in psychiatric disorders induced by early-life immune activation and the association between exercise training and glial activation remain unclear. We compared the effects of different exercise intensities on the PIA model, including high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT). Both HIIT and MICT in adolescent mice inhibited neuroinflammation, remodeled synaptic plasticity, and improved PIA-induced mood disorders in adulthood. Importantly, HIIT was superior to MICT in terms of reducing inflammation and increasing body weight. RNA-seq of prefrontal cortex (PFC) tissues revealed a gene expression pattern, confirming that HIIT was more effective than MICT in improving brain glial cell activation through epigenetic modifications of KDM6B. We investigated the role of KDM6B, a specific histone lysine demethylation enzyme - histone 3 lysine 27 demethylase, in inhibiting glial activation against PIA-induced depression and anxiety by regulating the expression of IL-4 and brain-derived neurotrophic factor (BDNF). Overall, our data support the idea that HIIT improves PIA-induced mood disorders by regulating KDM6B-mediated epigenetic mechanisms and indicate that HIIT might be superior to MICT in improving mood disorders with PIA in mice. Our findings provide new insights into the treatment of anxiety and depression disorders.

Eccentric Contraction Enhances Healing of the Bone-Tendon Interface After Rotator Cuff Repair in Mice

BACKGROUND

Various muscle contraction modalities have differing effects on the musculoskeletal system. To understand the magnitude of these effects, the authors investigated the effects of eccentric and concentric contractions on the bone-tendon interface after rotator cuff repair in mice.

HYPOTHESIS

Eccentric contraction promotes healing of the bone-tendon interface after rotator cuff repair in mice better than other muscle contraction patterns.

STUDY DESIGN

Controlled laboratory study.

METHODS

The authors performed acute supraspinatus tendon repair of the right shoulder in 104 C57BL/6 mice. Animals were randomized into 4 groups postoperatively: control group (Con group), horizontal running group (Horz group), +15° uphill running group (Up group), and -15° downhill running group (Down group), with 26 animals in each group. At 4 and 8 weeks postoperatively, the authors removed the eyeball, collected blood samples, and extracted the supraspinatus tendon-humerus complex for histological, immunological, bone morphological, and biomechanical tests.

RESULTS

At 4 and 8 weeks postoperatively, the Down group exhibited a better collagen cell arrangement and fibrocartilage layer than the other 3 groups. At 4 weeks postoperatively, anti-inflammatory macrophages (M2 macrophages) were observed at the repair site in all groups except for the Con group. At 8 weeks postoperatively, M2 macrophages were withdrawn from the tendon site in all groups. The transforming growth factor β1 concentration in the Down group was greater than that in the other 3 groups at 4 weeks postoperatively, and it was higher than that in the Con group at 8 weeks postoperatively. The bone volume fraction, number of trabeculae, and thickness of trabeculae at the repair site in the Down group, as well as the ultimate strength and failure load in the biomechanical tests, were greater than those in the other 3 groups at 8 weeks postoperatively.

CONCLUSION

Eccentric contraction promotes healing of the bone-tendon interface after rotator cuff repair in mice better than other muscle contraction patterns.

CLINICAL RELEVANCE

After clinical rotator cuff repair, patients can be rehabilitated by eccentric training to speed up the functional recovery of the shoulder joint.

ATF3 induction prevents precocious activation of skeletal muscle stem cell by regulating H2B expression

Skeletal muscle stem cells (also called satellite cells, SCs) are important for maintaining muscle tissue homeostasis and damage-induced regeneration. However, it remains poorly understood how SCs enter cell cycle to become activated upon injury. Here we report that AP-1 family member ATF3 (Activating Transcription Factor 3) prevents SC premature activation. Atf3 is rapidly and transiently induced in SCs upon activation. Short-term deletion of Atf3 in SCs accelerates acute injury-induced regeneration, however, its long-term deletion exhausts the SC pool and thus impairs muscle regeneration. The Atf3 loss also provokes SC activation during voluntary exercise and enhances the activation during endurance exercise. Mechanistically, ATF3 directly activates the transcription of Histone 2B genes, whose reduction accelerates nucleosome displacement and gene transcription required for SC activation. Finally, the ATF3-dependent H2B expression also prevents genome instability and replicative senescence in SCs. Therefore, this study has revealed a previously unknown mechanism for preserving the SC population by actively suppressing precocious activation, in which ATF3 is a key regulator.

Effects of exercise-induced metabolic and mechanical loading on skeletal muscle mitochondrial function in male rats

Over the last decades, a growing interest in eccentric (ECC) exercise has emerged, but mitochondrial adaptations to ECC training remain poorly documented. Using an approach for manipulating mechanical and metabolic exercise power, we positioned that for same metabolic power, training using concentric (CON) or ECC contractions would induce similar skeletal muscle mitochondrial adaptations. Sixty adult rats were randomly assigned to a control (CTRL) or three treadmill training groups running at 15m·min^-1 for 45min, 5days weekly for 8 weeks at targeted upward or downward slopes. Animals from the CON (+15%) and ECC30 (-30%) groups trained at iso-metabolic power while CON and ECC15 (-15%) exercised at iso-mechanical power. Assessments were made of Vastus Intermedius mitochondrial respiration (oxygraphy), enzymatic activities (spectrophotometry) and real-time qPCR for mRNA transcripts. Maximal rates of mitochondrial respiration was 14-15% higher in CON and ECC30 compared to CTRL and ECC15. Apparent K_m for ADP for trained groups was 40-66% higher than CTRL, with statistical significance reached for CON and ECC30. Complex I and citrate synthase activities were 1.6 (ECC15) to 1.8 (ECC30 and CON) times values of CTRL. Complex IV activity was higher than CTRL (p<0.05) only for CON and ECC30. mRNA transcripts analyses showed higher TFAM, SLC25A4, CKMT2 and PPID in the ECC30 compared to CTRL. Findings confirm that training-induced skeletal muscle mitochondrial function adaptations are governed by the extent of metabolic overload irrespective of exercise modality. The distinctive ECC30 mRNA transcript pattern may reflect a cytoskeleton damage-repair or ECC adaptive cycle that differs from that of biogenesis.

Progress and Challenges in the Biology of FNDC5 and Irisin

In 2002, a transmembrane protein-now known as FNDC5-was discovered and shown to be expressed in skeletal muscle, heart, and brain. It was virtually ignored for 10 years, until a study in 2012 proposed that, in response to exercise, the ectodomain of skeletal muscle FNDC5 was cleaved, traveled to white adipose tissue, and induced browning. The wasted energy of this browning raised the possibility that this myokine, named irisin, might mediate some beneficial effects of exercise. Since then, more than 1000 papers have been published exploring the roles of irisin. A major interest has been on adipose tissue and metabolism, following up the major proposal from 2012. Many studies correlating plasma irisin levels with physiological conditions have been questioned for using flawed assays for irisin concentration. However, experiments altering irisin levels by injecting recombinant irisin or by gene knockout are more promising. Recent discoveries have suggested potential roles of irisin in bone remodeling and in the brain, with effects potentially related to Alzheimer's disease. We discuss some discrepancies between research groups and the mechanisms that are yet to be determined. Some important questions raised in the initial discovery of irisin, such as the role of the mutant start codon of human FNDC5 and the mechanism of ectodomain cleavage, remain to be answered. Apart from these specific questions, a promising new tool has been developed-mice with a global or tissue-specific knockout of FNDC5. In this review, we critically examine the current knowledge and delineate potential solutions to resolve existing ambiguities.

Modulation of TRIB3 and Macrophage Phenotype to Attenuate Insulin Resistance After Downhill Running in Mice

Eccentric exercise training accompanied by a low-fat diet can prevent insulin resistance (IR) and is currently an effective method for the treatment of IR induced by high-fat diet (HFD)-associated obesity. However, the molecular mechanisms underlying this improvement of IR in adipose tissue are still not completely clear. In this study, 5–6-week-old male mice were randomly divided into a standard control diet (SCD) group (SC, n = 12) and a HFD group (HF, n = 72). After 12 weeks, 12 mice in each group were randomly sacrificed. The remaining mice in the HF group were randomly submitted to one of the following experimental protocols for 8 weeks: obesity-HFD-sedentary (OHF-Sed, n = 14), obesity-HFD-exercise (OHF-Ex, n = 16), obesity-SCD-sedentary (OSC-Sed, n = 14), and obesity-SCD-exercise (OSC-Ex, n = 16). All obese mice in the exercise group were subjected to downhill running. Half of the mice in each group received an insulin injection (0.75 U/kg) before sample collection. Epididymal fat was removed and weighed. Adipocyte size and inflammatory cell infiltration were observed by H&E staining. Both basal and insulin-stimulated GLUT4 fluorescence and protein contents were detected by immunofluorescence and Western blot. Levels of IL-1β and IL-10 were detected by ELISA. Protein contents of iNOS, Arg-1, TRIB3, p-AKT, and AKT were determined by Western blot. CD86 and CD206 fluorescence were determined by immunofluorescence. The results showed that a HFD for 12 weeks induced IR accompanied by adipose tissue macrophages M1 polarization (increased iNOS protein content and CD86 fluorescence) and TRIB3-AKT activation. Downhill running accompanied by a low-fat diet attenuated IR (p < 0.01), reduced inflammation levels (increased IL-10 protein content and decreased IL-1β protein content), inhibited adipose tissue macrophages M1 polarization (decreased iNOS protein content and CD86 fluorescence) and promoted M2 polarization (increased Arg-1 protein content and CD206 fluorescence), and suppressed TRIB3-AKT signaling. We concluded that downhill running accompanied by dietary fat regulation attenuates HFD-related IR in mice, which may be associated with reduced TRIB3-AKT signaling and activated M2 macrophages in adipose tissue.

Transcriptional Factors of Thermogenic Adipocyte Development and Generation of Brown and Beige Adipocytes From Stem Cells

Brown and beige adipocytes have been widely known for their potential to dissipate excessive energy into heat form, resulting in an alleviation of obesity and other overweight-related conditions. This review highlights the origins, characteristics, and functions of the various kinds of adipocytes, as well as their anatomic distribution inside the human body. This review mainly focuses on various essential transcriptional factors such as PRDM16, FGF21, PPARα, PPARγ and PGC-1α, which exert their effects on the development and activation of thermogenic adipocytes via important pathways such as JAK-STAT, cAMP-PKA and PI3K-AKT signaling pathways. Additionally, this review will underline promising strategies to generate an unexhausted source of thermogenic adipocytes differentiated from human stem cells. These exogenous thermogenic adipocytes offer therapeutic potential for improvement of metabolic disorders via application as single cell or whole tissue transplantation. Graphical abstract Caption is required. Please provide.

Beneficial Role of Exercise in the Modulation of mdx Muscle Plastic Remodeling and Oxidative Stress

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive lethal disorder caused by the lack of dystrophin, which determines myofibers mechanical instability, oxidative stress, inflammation, and susceptibility to contraction-induced injuries. Unfortunately, at present, there is no efficient therapy for DMD. Beyond several promising gene- and stem cells-based strategies under investigation, physical activity may represent a valid noninvasive therapeutic approach to slow down the progression of the pathology. However, ethical issues, the limited number of studies in humans and the lack of consistency of the investigated training interventions generate loss of consensus regarding their efficacy, leaving exercise prescription still questionable. By an accurate analysis of data about the effects of different protocol of exercise on muscles of mdx mice, the most widely-used pre-clinical model for DMD research, we found that low intensity exercise, especially in the form of low speed treadmill running, likely represents the most suitable exercise modality associated to beneficial effects on mdx muscle. This protocol of training reduces muscle oxidative stress, inflammation, and fibrosis process, and enhances muscle functionality, muscle regeneration, and hypertrophy. These conclusions can guide the design of appropriate studies on human, thereby providing new insights to translational therapeutic application of exercise to DMD patients.

Post-exercise Effects and Long-Term Training Adaptations of Hormone Sensitive Lipase Lipolysis Induced by High-Intensity Interval Training in Adipose Tissue of Mice

Although studies have proven that high-intensity interval training (HIIT) shows a comparable effect to moderate-intensity continuous training (MICT) on reducing body fat, especially visceral fat, the mechanism is still unclear. Since MICT consumes more fat during exercise, the mechanism of HIIT weight loss may be related to post-exercise effects, long-term adaptive changes, and hormone sensitive lipase (HSL). The objective of this study was to compare the post-effects of acute exercise, long-term adaptive changes on HSL activity, and catecholamine-induced lipolysis between HIIT and MICT. Following a 14-week high-fat diet (HFD), obese female C57Bl/6 mice were divided into acute exercise groups (one time training, sacrificed at rest and 0, 1, and 12 h after exercise, n = 49), -L groups (12-week long-term training, 12-h fasting, n = 21), and -C groups (12-week training, primary adipocytes were isolated and stimulated by catecholamine in vitro, n = 18). MICT or HIIT treadmill protocols (running distance matched) were carried out during training. Comparison of acute exercise effects by two-way ANOVA showed no time × group interaction effect, however, a significant increase in HSL-Ser563 (at 0 and 1 h) and Ser660 phosphorylation (at 0, 1, and 12 h) in inguinal (subcutaneous) fat was only observed in HIIT mice (p < 0.05 vs. rest), but not in MICT mice. The periuterine (visceral) fat HSL expression and phosphorylation of HIIT mice was similar to or lower than MICT mice. After long-term training, 12-h fasting significantly increased periuterine fat Ser563 phosphorylation in HIIT mice (p < 0.05), but there was no change in MICT mice. Under stimulation of catecholamine in vitro, isolated primary adipocytes from periuterine fat of long-term HIIT mice showed a higher Ser563 increase than that found in MICT mice (p < 0.05). The quantity of triglyceride (TG) lipid bonds (representing lipolysis level) was significantly lower after HIIT than MICT (p < 0.05). The results indicate that (1) acute HIIT can induce an increase of HSL phosphorylation in subcutaneous fat lasting at least 12 h, implying longer post-exercise lipolysis than MICT and (2) long-time HIIT has a better effect on improving catecholamine resistance of visceral adipocytes caused by a HFD, which allows fat to be mobilized more easily when stimulated.

Liver macrophages mediate effects of downhill running and caloric restriction on nonalcoholic fatty liver disease of high fat diet-fed mice

AIMS

The mechanism of physical activity and calorie restriction remedying non-alcoholic fatty liver disease (NAFLD) remains elusive. The purpose of this study is to explore the effects of eccentric exercise and dietary regulation allied or alone on high-fat diet (HFD) induced NAFLD and its potential mechanism.

MATERIALS AND METHODS

Mice were fed with HFD for 12 weeks and subsequently treated with chronic downhill running and caloric restriction for 8 weeks. Related biochemical index were examined both before and during intervention to evaluate the liver injury and dyslipidemia. Levels of MCP1, TNFα, IL-1β, IL-6 and IL-10 were detected by ELISA. Liver morphology was observed by H&E and oil red O staining. Protein contents of iNOS, Arg-1, IL-1β and IL-10 were determined by Western blot. CD86 and CD206 fluorescence were determined by Immunofluorescence. KEY FINDING: (1) 12 weeks' HFD induced hyperlipemia and hepatic steatosis by activating M1 macrophages phenotype and inhibiting M2 macrophages. (2) Chronic downhill running and caloric restriction promoted liver M2 macrophages phenotype, and inhibited M1 macrophages, to attenuate chronic inflammation and ameliorate hepatic steatosis. (3) The effects of downhill running and dietary regulation allied were more effective on improving NAFLD compared with downhill running or caloric restriction alone.

SIGNIFICANCE

Eccentric exercise accompanied by caloric restriction attenuates HFD-related NAFLD by promoting M2 macrophages phenotype and inhibiting M1 macrophages in liver. These findings may be help to designing better non-pharmacological intervention programs for NAFLD patients.

Eccentric exercise and dietary restriction inhibits M1 macrophage polarization activated by high-fat diet-induced obesity

AIMS

Obesity induce low-grade inflammation and elicit insulin resistance (IR), exercise training accompanied by a low-fat diet has been prescribed as part of the treatment for managing obesity and IR. The purpose of this study is to evaluate the effect of eccentric exercise accompanied by a low-fat diet on glycolipid metabolism, exercise capacity, and macrophage polarization in obesity-induced IR mice.

MATERIALS AND METHODS

Mice were fed with 60% high fat diet (HFD) for 12 weeks and subsequently treated with eccentric exercise or/and dietary restriction for 8 weeks. Related biochemical index were examined both before and during intervention to evaluate the ability of glycolipid metabolism. Exercise capacity was measured to verify the results of biochemical index. At 12 weeks and 12 + 8 weeks, infiltration was observed by H&E staining in adipose tissue, and macrophage polarization was detected by Immunofluorescence staining and ELISA.

KEY FINDING

1) obesity-induced IR model was established by HFD fed for 12 weeks accompanied by impaired exercise ability and increased M1 macrophage, 2) eccentric exercise accompanied by a low-fat diet markedly rescued obesity-induced IR and improved exercise capacity, 3) eccentric exercise accompanied by a low-fat diet markedly inhibited M1 macrophage polarization and activated M2 macrophage.

SIGNIFICANCE

Eccentric exercise accompanied by a low-fat diet rescued obesity-induced IR and improved exercise capacity, which were associated with the inhibition of M1 macrophage polarization and the activation of M2 macrophage. These indicate that macrophage polarization provides the potential target of intervention for inflammation and IR in obesity.

Cardiac adaptation to exercise training in health and disease

The heart is the primary pump that circulates blood through the entire cardiovascular system, serving many important functions in the body. Exercise training provides favorable anatomical and physiological changes that reduce the risk of heart disease and failure. Compared with pathological cardiac hypertrophy, exercise-induced physiological cardiac hypertrophy leads to an improvement in heart function. Exercise-induced cardiac remodeling is associated with gene regulatory mechanisms and cellular signaling pathways underlying cellular, molecular, and metabolic adaptations. Exercise training also promotes mitochondrial biogenesis and oxidative capacity leading to a decrease in cardiovascular disease. In this review, we summarized the exercise-induced adaptation in cardiac structure and function to understand cellular and molecular signaling pathways and mechanisms in preclinical and clinical trials.

FNDC5: A novel player in metabolism and metabolic syndrome

Half a decade ago, transmembrane protein fibronectin type III domain-containing protein 5 (FNDC5) was found to be cleaved as a novel myokine irisin, which burst into prominence for browning of white adipose tissue during exercise. However, FNDC5, the precursor of irisin, has been paid relatively little attention compared with irisin despite evidence that FNDC5 is associated with the metabolic syndrome, which accounts for one-fourth of the world's adult population and contributes to diabetes, cardiovascular disease and all-cause mortality. Besides N-terminal and C-terminal sequences, the FNDC5 protein contains an irisin domain and a short transmembrane region. FNDC5 has shown to be widely distribute in different tissues and is highly expressed in heart, brain, liver, and skeletal muscle. Clinical studies have demonstrated that FNDC5 is essential for maintaining metabolic homeostasis and dysregulation of FNDC5 will lead to systemic metabolism imbalance and the onset of metabolic disorders. Growing evidence has suggested that FNDC5 gene polymorphisms are related to health and disease in different human populations. Additionally, FNDC5 has been found relevant to the regulation of metabolism and metabolic syndrome through diverse upstream and downstream signaling pathways in experimental studies. The present review summarizes the characteristics, clinical significance, and molecular mechanisms of FNDC5 in metabolic syndrome and proposes a novel concept that FNDC5 is activated by forming a putative ligand-receptor complex. Knowledge about the role of FNDC5 may be translated into drug development and clinical applications for the treatment of metabolic disorders.