Exercise Increases and Browns Muscle Lipid in High-Fat Diet-Fed Mice

Exercise attenuates high-fat diet-induced PVAT dysfunction through improved inflammatory response and BMP4-regulated adipose tissue browning

Background

Perivascular adipose tissue (PVAT) dysfunction impairs vascular homeostasis. Impaired inflammation and bone morphogenetic protein-4 (BMP4) signaling are involved in thoracic PVAT dysfunction by regulating adipokine secretion and adipocyte phenotype transformation. We investigated whether aerobic exercise training could ameliorate high-fat diet (HFD)-induced PVAT dysfunction via improved inflammatory response and BMP4-mediated signaling pathways.

Methods

Sprague-Dawley rats (n = 24) were divided into three groups, namely control, high-fat diet (HFD), and HFD plus exercise (HEx). After a 6-week intervention, PVAT functional efficiency and changes in inflammatory biomarkers (circulating concentrations in blood and mRNA expressions in thoracic PVAT) were assessed.

Results

Chronic HFD feeding caused obesity and dyslipidemia in rats. HFD decreased the relaxation response of PVAT-containing vascular rings and impaired PVAT-regulated vasodilatation. However, exercise training effectively reversed these diet-induced pathological changes to PVAT. This was accompanied by significantly (p < 0.05) restoring the morphological structure and the decreased lipid droplet size in PVAT. Furthermore, HFD-induced impaired inflammatory response (both in circulation and PVAT) was notably ameliorated by exercise training (p < 0.05). Specifically, exercise training substantially reversed HFD-induced WAT-like characteristics to BAT-like characteristics as evidenced by increased UCP1 and decreased FABP4 protein levels in PVAT against HFD. Exercise training promoted transcriptional activation of BMP4 and associated signaling molecules (p38/MAPK, ATF2, PGC1α, and Smad5) that are involved in browning of adipose tissue. In conjunction with gene expressions, exercise training increased BMP4 protein content and activated downstream cascades, represented by upregulated p38/MAPK and PGC1α proteins in PVAT.

Conclusion

Regular exercise training can reverse HFD-induced obesity, dyslipidemia, and thoracic PVAT dysfunction in rats. The browning of adipose tissue through exercise appears to be modulated through improved inflammatory response and/or BMP4-mediated signaling cascades in obese rats.

Early Movement Restriction Affects FNDC5/Irisin and BDNF Levels in Rat Muscle and Brain

Interaction with the environment appears necessary for the maturation of sensorimotor and cognitive functions in early life. In rats, a model of sensorimotor restriction (SMR) from postnatal day 1 (P1) to P28 has shown that low and atypical sensorimotor activities induced the perturbation of motor behavior due to muscle weakness and the functional disorganization of the primary somatosensory and motor cortices. In the present study, our objective was to understand how SMR affects the muscle-brain dialogue. We focused on irisin, a myokine secreted by skeletal muscles in response to exercise. FNDC5/irisin expression was determined in hindlimb muscles and brain structures by Western blotting, and irisin expression in blood and cerebrospinal fluid was determined using an ELISA assay at P8, P15, P21 and P28. Since irisin is known to regulate its expression, Brain-Derived Neurotrophic Factor (BDNF) levels were also measured in the same brain structures. We demonstrated that SMR increases FNDC5/irisin levels specifically in the soleus muscle (from P21) and also affects this protein expression in several brain structures (as early as P15). The BDNF level was increased in the hippocampus at P8. To conclude, SMR affects FNDC5/irisin levels in a postural muscle and in several brain regions and has limited effects on BDNF expression in the brain.

The association of serum irisin with anthropometric, metabolic, and bone parameters in obese children and adolescents

Background

Irisin is an adipomyokine secreted by muscle and adipose cells, and it plays a role in glucose, fat, and bone metabolism. This study aimed to determine the correlation of serum irisin levels with anthropometric, metabolic, and bone parameters in obese children and adolescents.

Methods

This single-center study included 103 Korean children and adolescents: 54 (52.4%) obese participants with a body mass index (BMI) ≥95th percentile and 49 (47.6%) healthy controls with BMI within the 15th to 85th percentile. Various parameters were measured, including fasting blood glucose, fasting insulin, homeostasis model assessment of insulin resistance (HOMA-IR), triglyceride and glucose (TyG) index, lipid profile, alkaline phosphatase (ALP), osteocalcin, and 25(OH)-Vitamin D levels. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry (DEXA) in 33 healthy subjects.

Results

Serum irisin was significantly higher in the obese group than in the control group (mean 18.1 ± 3.5 vs. 16.2 ± 2.0 ng/mL; p = 0.001). Serum irisin level was positively correlated with chronological age (r = 0.28; p = 0.004), height SDS (r = 0.24; p = 0.02), BMI SDS (r = 0.37; p < 0. 001), fasting glucose (r = 0.27; p = 0.007), fasting insulin (r = 0.23; p = 0.03), HOMA-IR (r = 0.21; p = 0.04), osteocalcin (r = 0.27; p = 0.006) and negatively correlated with HDL cholesterol (r = -0.29; p = 0.005). All these correlations were evident in obese subjects but not in healthy subjects. ALP and 25(OH)-Vitamin D were unrelated to irisin levels. Among 33 healthy subjects, total body-less head (TBLH) BMD Z-score was positively correlated with serum irisin (r = 0.39; p = 0.03), osteocalcin (r = 0.40; p = 0.02), fasting insulin (r = 0.39; p = 0.04), and HOMA-IR (r = 0.38; p = 0.047).

Conclusion

This study demonstrated an association between irisin levels and glucose, lipid, and bone parameters in children and adolescents. Our findings suggest that irisin has a potential role in metabolic disorders and bone health in obese children and adolescents.

Diet-Stimulated Marrow Adiposity Fails to Worsen Early, Age-Related Bone Loss

INTRODUCTION

Longitudinal effect of diet-induced obesity on bone is uncertain. Prior work showed both no effect and a decrement in bone density or quality when obesity begins prior to skeletal maturity. We aimed to quantify long-term effects of obesity on bone and bone marrow adipose tissue (BMAT) in adulthood.

METHODS

Skeletally mature, female C57BL/6 mice (n = 70) aged 12 weeks were randomly allocated to low-fat diet (LFD; 10% kcal fat; n = 30) or high-fat diet (HFD; 60% kcal fat; n = 30), with analyses at 12, 15, 18, and 24 weeks (n = 10/group). Tibial microarchitecture was analyzed by µCT, and volumetric BMAT was quantified via 9.4T MRI/advanced image analysis. Histomorphometry of adipocytes and osteoclasts, and qPCR were performed.

RESULTS

Body weight and visceral white adipose tissue accumulated in response to HFD started in adulthood. Trabecular bone parameters declined with advancing experimental age. BV/TV declined 22% in LFD (p = 0.0001) and 17% in HFD (p = 0.0022) by 24 weeks. HFD failed to appreciably alter BV/TV and had negligible impact on other microarchitecture parameters. Both dietary intervention and age accounted for variance in BMAT, with regional differences: distal femoral BMAT was more responsive to diet, while proximal femoral BMAT was more attenuated by age. BMAT increased 60% in the distal metaphysis in HFD at 18 and 24 weeks (p = 0.0011). BMAT in the proximal femoral diaphysis, unchanged by diet, decreased 45% due to age (p = 0.0002). Marrow adipocyte size via histomorphometry supported MRI quantification. Osteoclast number did not differ between groups. Tibial qPCR showed attenuation of some adipose, metabolism, and bone genes. A regulator of fatty acid β-oxidation, cytochrome C (CYCS), was 500% more abundant in HFD bone (p < 0.0001; diet effect). CYCS also increased due to age, but to a lesser extent. HFD mildly increased OCN, TRAP, and SOST.

CONCLUSIONS

Long-term high fat feeding after skeletal maturity, despite upregulation of visceral adiposity, body weight, and BMAT, failed to attenuate bone microarchitecture. In adulthood, we found aging to be a more potent regulator of microarchitecture than diet-induced obesity.

Resistance and Aerobic Training Were Effective in Activating Different Markers of the Browning Process in Obesity

Lifestyle changes regarding diet composition and exercise training have been widely used as a non-pharmacological clinical strategy in the treatment of obesity, a complex and difficult-to-control disease. Taking the potential of exercise in the browning process and in increasing thermogenesis into account, the aim of this paper was to evaluate the effect of resistance, aerobic, and combination training on markers of browning of white adipose tissue from rats with obesity who were switched to a balanced diet with normal calorie intake. Different types of training groups promote a reduction in the adipose tissue and delta mass compared to the sedentary high-fat diet group (HS). Interestingly, irisin in adipose tissues was higher in the resistance exercise (RE) and aerobic exercise (AE) groups compared to control groups. Moreover, in adipose tissue, the fibroblast growth factor 21 (FGF21), coactivator 1 α (PGC1α), and peroxisome proliferator-activated receptor gamma (PPARγ) were higher in response to resistance training RE compared with the control groups, respectively. Additionally, uncoupling protein 1 (UCP1) showed higher levels in response to group AE compared to the HS group. In conclusion, the browning process in white adipose tissue responds differently toward different training exercise protocols, with resistance and aerobic training efficient in activating different biomarkers of the browning process, upregulating irisin, FGF21, PGC1α, PPARγ, and UCP1 in WAT, which together may suggest an improvement in the thermogenic process in the adipose tissue. Considering the experimental conditions of the present investigation, we suggest future research to pave new avenues to be applied in clinical practices to combat obesity.

RIPK3 dampens mitochondrial bioenergetics and lipid droplet dynamics in metabolic liver disease

BACKGROUND AND AIMS

Receptor-interacting protein kinase 3 (RIPK3) mediates NAFLD progression, but its metabolic function is unclear. Here, we aimed to investigate the role of RIPK3 in modulating mitochondria function, coupled with lipid droplet (LD) architecture in NAFLD.

APPROACH AND RESULTS

Functional studies evaluating mitochondria and LD biology were performed in wild-type (WT) and Ripk3-/- mice fed a choline-deficient, amino acid-defined (CDAA) diet for 32 and 66 weeks and in CRISPR-Cas9 Ripk3 -null fat-loaded immortalized hepatocytes. The association between hepatic perilipin (PLIN) 1 and 5, RIPK3, and disease severity was also addressed in a cohort of patients with NAFLD and in PLIN1 -associated familial partial lipodystrophy. Ripk3 deficiency rescued impairment in mitochondrial biogenesis, bioenergetics, and function in CDAA diet-fed mice and fat-loaded hepatocytes. Ripk3 deficiency was accompanied by a strong upregulation of antioxidant systems, leading to diminished oxidative stress upon fat loading both in vivo and in vitro. Strikingly, Ripk3-/- hepatocytes displayed smaller size LD in higher numbers than WT cells after incubation with free fatty acids. Ripk3 deficiency upregulated adipocyte and hepatic levels of LD-associated proteins PLIN1 and PLIN5. PLIN1 upregulation controlled LD structure and diminished mitochondrial stress upon free fatty acid overload in Ripk3-/- hepatocytes and was associated with diminished human NAFLD severity. Conversely, a pathogenic PLIN1 frameshift variant was associated with NAFLD and fibrosis, as well as with increased hepatic RIPK3 levels in familial partial lipodystrophy.

CONCLUSIONS

Ripk3 deficiency restores mitochondria bioenergetics and impacts LD dynamics. RIPK3 inhibition is promising in ameliorating NAFLD.

Distinct subcellular localisation of intramyocellular lipids and reduced PKCε/PKCθ activity preserve muscle insulin sensitivity in exercise-trained mice

AIMS/HYPOTHESIS

Athletes exhibit increased muscle insulin sensitivity, despite increased intramuscular triacylglycerol content. This phenomenon has been coined the 'athlete's paradox' and is poorly understood. Recent findings suggest that the subcellular distribution of sn-1,2-diacylglycerols (DAGs) in the plasma membrane leading to activation of novel protein kinase Cs (PKCs) is a crucial pathway to inducing insulin resistance. Here, we hypothesised that regular aerobic exercise would preserve muscle insulin sensitivity by preventing increases in plasma membrane sn-1,2-DAGs and activation of PKCε and PKCθ despite promoting increases in muscle triacylglycerol content.

METHODS

C57BL/6J mice were allocated to three groups (regular chow feeding [RC]; high-fat diet feeding [HFD]; RC feeding and running wheel exercise [RC-EXE]). We used a novel LC-MS/MS/cellular fractionation method to assess DAG stereoisomers in five subcellular compartments (plasma membrane [PM], endoplasmic reticulum, mitochondria, lipid droplets and cytosol) in the skeletal muscle.

RESULTS

We found that the HFD group had a greater content of sn-DAGs and ceramides in multiple subcellular compartments compared with the RC mice, which was associated with an increase in PKCε and PKCθ translocation. However, the RC-EXE mice showed, of particular note, a reduction in PM sn-1,2-DAG and ceramide content when compared with HFD mice. Consistent with the PM sn-1,2-DAG-novel PKC hypothesis, we observed an increase in phosphorylation of threonine1150 on the insulin receptor kinase (IRKT1150), and reductions in insulin-stimulated IRKY1162 phosphorylation and IRS-1-associated phosphoinositide 3-kinase activity in HFD compared with RC and RC-EXE mice, which are sites of PKCε and PKCθ action, respectively.

CONCLUSIONS/INTERPRETATION

These results demonstrate that lower PKCθ/PKCε activity and sn-1,2-DAG content, especially in the PM compartment, can explain the preserved muscle insulin sensitivity in RC-EXE mice.

Transcriptomic profiling of the telomerase transformed Mesenchymal stromal cells derived adipocytes in response to rosiglitazone

Background

Differentiation of Immortalized Human Bone Marrow Mesenchymal Stromal Cells - hTERT (iMSC3) into adipocytes is in vitro model of obesity. In our earlier study, rosiglitazone enhanced adipogenesis particularly the brown adipogenesis of iMSC3. In this study, the transcriptomic profiles of iMSC3 derived adipocytes with and without rosiglitazone were analyzed through mRNA sequencing.

Results

A total of 1508 genes were differentially expressed between iMSC3 and the derived adipocytes without rosiglitazone treatment. GO and KEGG enrichment analyses revealed that rosiglitazone regulates PPAR and PI3K-Akt pathways. The constant rosiglitazone treatment enhanced the expression of Fatty Acid Binding Protein 4 (FABP4) which enriched GO terms such as fatty acid binding, lipid droplet, as well as white and brown fat cell differentiation. Moreover, the constant treatment upregulated several lipid droplets (LDs) associated proteins such as PLIN1. Rosiglitazone also activated the receptor complex PTK2B that has essential roles in beige adipocytes thermogenic program. Several uniquely expressed novel regulators of brown adipogenesis were also expressed in adipocytes derived with rosiglitazone: PRDM16, ZBTB16, HOXA4, and KLF15 in addition to other uniquely expressed genes.

Conclusions

Rosiglitazone regulated several differentially regulated genes and non-coding RNAs that warrant further investigation about their roles in adipogenesis particularly brown adipogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-022-01027-z.

Exercise to Mend Aged-tissue Crosstalk in Bone Targeting Osteoporosis & Osteoarthritis

Aging induces alterations in bone structure and strength through a multitude of processes, exacerbating common aging- related diseases like osteoporosis and osteoarthritis. Cellular hallmarks of aging are examined, as related to bone and the marrow microenvironment, and ways in which these might contribute to a variety of age-related perturbations in osteoblasts, osteocytes, marrow adipocytes, chondrocytes, osteoclasts, and their respective progenitors. Cellular senescence, stem cell exhaustion, mitochondrial dysfunction, epigenetic and intracellular communication changes are central pathways and recognized as associated and potentially causal in aging. We focus on these in musculoskeletal system and highlight knowledge gaps in the literature regarding cellular and tissue crosstalk in bone, cartilage, and the bone marrow niche. While senolytics have been utilized to target aging pathways, here we propose non-pharmacologic, exercise-based interventions as prospective "senolytics" against aging effects on the skeleton. Increased bone mass and delayed onset or progression of osteoporosis and osteoarthritis are some of the recognized benefits of regular exercise across the lifespan. Further investigation is needed to delineate how cellular indicators of aging manifest in bone and the marrow niche and how altered cellular and tissue crosstalk impact disease progression, as well as consideration of exercise as a therapeutic modality, as a means to enhance discovery of bone-targeted therapies.

Irisin in atherosclerosis

Irisin, a novel exercise-induced myokine, has been shown to play important roles in increasing white adipose tissue browning, regulating energy metabolism and improving insulin resistance. Growing evidence suggests a direct role for irisin in preventing atherosclerosis (AS) by inhibiting oxidative stress, improving dyslipidemia, facilitating anti-inflammation, reducing cellular damage and recovering endothelial function. In addition, some studies have noted that serum irisin levels play an essential role in cardiovascular diseases (CVDs) risk prediction, highlighting that irisin has the potential to be a useful predictive marker and therapeutic target of AS, especially in monitoring therapeutic efficacy. This review summarizes the understanding of irisin-mediated regulation in essential biological pathways and functions in atherosclerosis and prompts further exploitation of the biological properties of irisin in the pathogenesis of atherosclerosis.

[Myokines and adipomyokines: inflammatory mediators or unique molecules of targeted therapy for obesity?]

Skeletal muscles make up about 25% of the total mass in children and more than 40% in adults. Studies of the last twenty years have shown that along with the main functions, muscle tissue has hormonal activity. It was found that myocytes are able to release signaling molecules-myokines. They act auto-and paracrine within the muscle, and at a high level-through the systemic circulation, carrying out interactions between skeletal muscles and various organs and tissues, such as the liver, bone and adipose tissue, the brain. It is proved that the key factor in the expression of myokines is physical activity, and their level largely depends on physical fitness, the amount of skeletal muscle mass and its composition (the ratio of fast and slow fibers), on the intensity and duration of physical activity. Myokines have a wide range of physiological effects: myostatin suppresses the growth and differentiation of muscle tissue, and decorin, acting as its antagonist, promotes muscle hypertrophy. Interleukin 6 provides an energy substrate for contracting muscle fibers, fibroblast growth factor 21 activates the mechanisms of energy production during fasting and improves tissue sensitivity to insulin; irisin stimulates thermogenesis, glucose uptake by myocytes, and also contributes to an increase in bone mineral density. The study of myokines is one of the key links in understanding the mechanisms underlying obesity and metabolic complications, the consequences of a sedentary lifestyle, as well as the implementation of the action of physical activity. Taking into account the physiological effects of myokines in the body, in the future they can become therapeutic targets for the treatment of these conditions.

Exercise Increases Bone in SEIPIN Deficient Lipodystrophy, Despite Low Marrow Adiposity

Exercise, typically beneficial for skeletal health, has not yet been studied in lipodystrophy, a condition characterized by paucity of white adipose tissue, with eventual diabetes, and steatosis. We applied a mouse model of global deficiency of Bscl2 (SEIPIN), required for lipid droplet formation. Male twelve-week-old B6 knockouts (KO) and wild type (WT) littermates were assigned six-weeks of voluntary, running exercise (E) versus non-exercise (N=5-8). KO weighed 14% less than WT (p=0.01) and exhibited an absence of epididymal adipose tissue; KO liver Plin1 via qPCR was 9-fold that of WT (p=0.04), consistent with steatosis. Bone marrow adipose tissue (BMAT), unlike white adipose, was measurable, although 40.5% lower in KO vs WT (p=0.0003) via 9.4T MRI/advanced image analysis. SEIPIN ablation's most notable effect marrow adiposity was in the proximal femoral diaphysis (-56% KO vs WT, p=0.005), with relative preservation in KO-distal-femur. Bone via μCT was preserved in SEIPIN KO, though some quality parameters were attenuated. Running distance, speed, and time were comparable in KO and WT. Exercise reduced weight (-24% WT-E vs WT p<0.001) but not in KO. Notably, exercise increased trabecular BV/TV in both (+31%, KO-E vs KO, p=0.004; +14%, WT-E vs WT, p=0.006). The presence and distribution of BMAT in SEIPIN KO, though lower than WT, is unexpected and points to a uniqueness of this depot. That trabecular bone increases were achievable in both KO and WT, despite a difference in BMAT quantity/distribution, points to potential metabolic flexibility during exercise-induced skeletal anabolism.

The Effect of Irisin as a Metabolic Regulator and Its Therapeutic Potential for Obesity

Obesity is a worldwide health problem due to the imbalance of energy intake and energy expenditure. Irisin, a newly identified exercise-responsive myokine, which is produced by the proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5), has emerged as a promising therapeutic strategy to combat obesity and obesity-related complications. Various studies in mice have shown that irisin could respond to systematic exercise training and promote white-to-brown fat transdifferentiation, but the role and function of irisin in humans are controversial. In this review, we systematically introduced and analyzed the factors that may contribute to these inconsistent results. Furthermore, we also described the potential anti-inflammatory properties of irisin under a variety of inflammatory conditions. Finally, the review discussed the existing unresolved issues and controversies about irisin, including the transcription of the irisin precursor FNDC5 gene in humans, the cleavage site of the yet unknown proteolytic enzyme that cleaves irisin from FNDC5, and the reliability of irisin levels measured with available detection methods.

Impacts of rat hindlimb Fndc5/irisin overexpression on muscle and adipose tissue metabolism

Myokines, such as irisin, have been purported to exert physiological effects on skeletal muscle in an autocrine/paracrine fashion. In this study, we aimed to investigate the mechanistic role of in vivo fibronectin type III domain-containing 5 (Fndc5)/irisin upregulation in muscle. Overexpression (OE) of Fndc5 in rat hindlimb muscle was achieved by in vivo electrotransfer, i.e., bilateral injections of Fndc5 harboring vectors for OE rats (n = 8) and empty vector for control rats (n = 8). Seven days later, a bolus of D₂O (7.2 mL/kg) was administered via oral gavage to quantify muscle protein synthesis. After an overnight fast, on day 9, 2-deoxy-d-glucose-6-phosphate (2-DG6P; 6 mg/kg) was provided during an intraperitoneal glucose tolerance test (2 g/kg) to assess glucose handling. Animals were euthanized, musculus tibialis cranialis muscles and subcutaneous fat (inguinal) were harvested, and metabolic and molecular effects were evaluated. Muscle Fndc5 mRNA increased with OE (~2-fold; P = 0.014), leading to increased circulating irisin (1.5 ± 0.9 to 3.5 ± 1.2 ng/mL; P = 0.049). OE had no effect on protein anabolism or mitochondrial biogenesis; however, muscle glycogen was increased, along with glycogen synthase 1 gene expression (P = 0.04 and 0.02, respectively). In addition to an increase in glycogen synthase activation in OE (P = 0.03), there was a tendency toward increased glucose transporter 4 protein (P = 0.09). However, glucose uptake (accumulation of 2-DG6P) was identical. Irisin elicited no endocrine effect on mitochondrial biogenesis or uncoupling proteins in white adipose tissue. Hindlimb overexpression led to physiological increases in Fndc5/irisin. However, our data indicate limited short-term impacts of irisin in relation to muscle anabolism, mitochondrial biogenesis, glucose uptake, or adipose remodeling.

Auricular acupuncture induces FNDC5/irisin and attenuates obese inflammation in mice

OBJECTIVE

To investigate whether auricular acupuncture (AA) attenuates bodyweight and obese inflammation through the release of irisin from muscle tissue in mice.

METHODS

Sixty 4-week-old mice were fed a high fat diet (HFD) for 4 weeks. These animals were divided into six groups that remained untreated (HFD) or underwent electrical AA (HFD+EAA), sham EAA (HFD+SEAA), adrenalectomy (HFD+AD), adrenalectomy and EAA (HFD+AD+EAA), or adrenalectomy and injection of recombinant lentivirus expressing fibronectin type III domain-containing protein 5 (rFNDC) (HFD+AD+rFNDC) in the ninth week. The EAA and SEAA were performed at two traditional auricular acupuncture points daily for 4 weeks. An additional 10 mice fed a control diet were included as a normal control (NC) group. At the end of the study, norepinephrine (NE) in the serum, tumour necrosis factor α (TNFα) and interleukin 1β (IL-1β) in the serum and white adipose tissue, irisin in the serum and muscle, uncoupling protein-1 (UCP-1) in the brown adipose tissue (BAT), and FNDC5 in the muscle, were analysed.

RESULTS

The AD+EAA group exhibited better control of bodyweight and inflammation compared with the AD+SEAA and untreated HFD model groups (P<0.05), especially regarding the increased expression of NE, FNDC5, irisin and UCP-1 (P<0.05). After adrenalectomy, mice receiving EAA had less NE, FNDC5, irisin and UCP-1 as well as greater expression of inflammatory cytokines and bodyweight. However, lentiviral overexpression of rFNDC successfully reversed this situation in the AD mice and mimicked the effects of EAA on bodyweight, inflammation and expression of FNDC5, irisin and UCP-1, although it did not impact NE.

CONCLUSIONS

EAA promoted NE release from the adrenal gland leading to further expression of FNDC5, irisin and UCP-1, which contributed to weight management and inflammatory inhibition.

Effect of post-implant exercise on tumour growth rate, perfusion and hypoxia in mice

Preclinical studies have shown a larger inhibition of tumour growth when exercise begins prior to tumour implant (preventative setting) than when training begins after tumour implant (therapeutic setting). However, post-implantation exercise may alter the tumour microenvironment to make it more vulnerable to treatment by increasing tumour perfusion while reducing hypoxia. This has been shown most convincingly in breast and prostate cancer models to date and it is unclear whether other tumour types respond in a similar way. We aimed to determine whether tumour perfusion and hypoxia are altered with exercise in a melanoma model, and compared this with a breast cancer model. We hypothesised that post-implantation exercise would reduce tumour hypoxia and increase perfusion in these two models. Female, 6-10 week old C57BL/6 mice were inoculated with EO771 breast or B16-F10 melanoma tumour cells before randomisation to either exercise or non-exercising control. Exercising mice received a running wheel with a revolution counter. Mice were euthanised when tumours reached maximum ethical size and the tumours assessed for perfusion, hypoxia, blood vessel density and proliferation. We saw an increase in heart to body weight ratio in exercising compared with non-exercising mice (p = 0.0008), indicating that physiological changes occurred with this form of physical activity. However, exercise did not affect vascularity, perfusion, hypoxia or tumour growth rate in either tumour type. In addition, EO771 tumours had a more aggressive phenotype than B16-F10 tumours, as inferred from a higher rate of proliferation (p<0.0001), a higher level of tumour hypoxia (p = 0.0063) and a higher number of CD31+ vessels (p = 0.0005). Our results show that although a physiological training effect was seen with exercise, it did not affect tumour hypoxia, perfusion or growth rate. We suggest that exercise monotherapy is minimally effective and that future preclinical work should focus on the combination of exercise with standard cancer therapies.

Exercise Degrades Bone in Caloric Restriction, Despite Suppression of Marrow Adipose Tissue (MAT)

Marrow adipose tissue (MAT) and its relevance to skeletal health during caloric restriction (CR) is unknown: It remains unclear whether exercise, which is anabolic to bone in a calorie-replete state, alters bone or MAT in CR. We hypothesized that response of bone and MAT to exercise in CR differs from the calorie-replete state. Ten-week-old female B6 mice fed a regular diet (RD) or 30% CR diet were allocated to sedentary (RD, CR, n = 10/group) or running exercise (RD-E, CR-E, n = 7/group). After 6 weeks, CR mice weighed 20% less than RD, p < 0.001; exercise did not affect weight. Femoral bone volume (BV) via 3D MRI was 20% lower in CR versus RD (p < 0.0001). CR was associated with decreased bone by μCT: Tb.Th was 16% less in CR versus RD, p < 0.003, Ct.Th was 5% less, p < 0.07. In CR-E, Tb.Th was 40% less than RD-E, p < 0.0001. Exercise increased Tb.Th in RD (+23% RD-E versus RD, p < 0.003) but failed to do so in CR. Cortical porosity increased after exercise in CR (+28%, p = 0.04), suggesting exercise during CR is deleterious to bone. In terms of bone fat, metaphyseal MAT/ BV rose 159% in CR versus RD, p = 0.003 via 3D MRI. Exercise decreased MAT/BV by 52% in RD, p < 0.05, and also suppressed MAT in CR (-121%, p = 0.047). Histomorphometric analysis of adipocyte area correlated with MAT by MRI (R2 = 0.6233, p < 0.0001). With respect to bone, TRAP and Sost mRNA were reduced in CR. Intriguingly, the repressed Sost in CR rose with exercise and may underlie the failure of CR-bone quantity to increase in response to exercise. Notably, CD36, a marker of fatty acid uptake, rose 4088% in CR (p < 0.01 versus RD), suggesting that basal increases in MAT during calorie restriction serve to supply local energy needs and are depleted during exercise with a negative impact on bone. © 2019 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Metabolic implications of organelle-mitochondria communication

Cellular organelles are not static but show dynamism-a property that is likely relevant for their function. In addition, they interact with other organelles in a highly dynamic manner. In this review, we analyze the proteins involved in the interaction between mitochondria and other cellular organelles, especially the endoplasmic reticulum, lipid droplets, and lysosomes. Recent results indicate that, on one hand, metabolic alterations perturb the interaction between mitochondria and other organelles, and, on the other hand, that deficiency in proteins involved in the tethering between mitochondria and the ER or in specific functions of the interaction leads to metabolic alterations in a variety of tissues. The interaction between organelles is an emerging field that will permit to identify key proteins, to delineate novel modulation pathways, and to elucidate their implications in human disease.

New opportunities: Drosophila as a model system for exercise research

Because of the growing rates of obesity in much of the world, exercise as a treatment option for obesity and as part of a healthy lifestyle is of great interest to the general public, health policy makers, and scientists alike. Despite the long history of exercise promotion and exercise research, there are still significant gaps in our understanding of how exercise impacts individuals and what role genetics plays in determining an individual’s response to exercise. Model organisms are positioned uniquely to help address these questions because of the challenges associated with carrying out large-scale, well-controlled studies in humans. The fruit fly model system, Drosophila melanogaster, has joined the models used for exercise research only recently but already has made significant contributions to the field. In this review, we highlight the opportunities for exercise research in Drosophila. We review the resources available to researchers interested in using Drosophila for exercise research, focusing on the existing systems to induce exercise in Drosophila, to measure the amount of exercise performed, and to assess physical fitness. We illustrate the potential of the Drosophila system by drawing attention to pioneering studies in Drosophila exercise research and emphasize the unique opportunities this model system represents.

High Fat With High Sucrose Diet Leads to Obesity and Induces Myodegeneration

Skeletal muscle utilizes both free fatty acids (FFAs) and glucose that circulate in the blood stream. When blood glucose levels acutely increase, insulin stimulates muscle glucose uptake, oxidation, and glycogen synthesis. Under these conditions, skeletal muscle preferentially oxidizes glucose while the oxidation of fatty acids (FAs) oxidation is reciprocally decreased. In metabolic disorders associated with insulin resistance, such as diabetes and obesity, both glucose uptake, and utilization muscle are significantly reduced causing FA oxidation to provide the majority of ATP for metabolic processes and contraction. Although the causes of this metabolic inflexibility or disrupted "glucose-fatty acid cycle" are largely unknown, a diet high in fat and sugar (HFS) may be a contributing factor. This metabolic inflexibility observed in models of obesity or with HFS feeding is detrimental because high rates of FA oxidation in skeletal muscle can lead to the buildup of toxic metabolites of fat metabolism and the accumulation of pro-inflammatory cytokines, which further exacerbate the insulin resistance. Further, HFS leads to skeletal muscle atrophy with a decrease in myofibrillar proteins and phenotypically characterized by loss of muscle mass and strength. Overactivation of ubiquitin proteasome pathway, oxidative stress, myonuclear apoptosis, and mitochondrial dysfunction are some of the mechanisms involved in muscle atrophy induced by obesity or in mice fed with HFS. In this review, we will discuss how HFS diet negatively impacts the various physiological and metabolic mechanisms in skeletal muscle.

Comparative studies on the effects of high-fat diet, endurance training and obesity on Ucp1 expression in male C57BL/6 mice

BACKGROUND

Obesity triggers a variety of severe conditions, therefore deteriorates metabolism rate of adipose tissues and muscles. Uncoupling proteins which are highly stimulated by fatty acids are potential targets for anti-obesity agents through breaking the electron gradient in the mitochondrial matrix and creating imbalances in the electron transport chain, thereby increasing the amount of substrate used to produce energy. Therefore, the aim of present study is assessment of exercise and high fat diet on expression level of Ucp1 subcutaneous white and brown adipose tissues (scWAT & BAT) respectively.

METHODS

To perform experiments, 48 male C57BL/6 mice were divided to two major groups and fed with high fat diet (HFD) or low fat diet (LFD) during a period of 12 weeks. After the first intervention, each groups was divided into four groups randomly as (HF-EX), (HF-SED), (LF-EX), (LF-SED) [EX: exercise; SED: sedentary] in form of treadmill running for 45 min/day, 5 days/week during 8 weeks. One day after the last practice session, mice were sacrificed and Ucp1 expression was assessed on scWAT & BAT.

RESULTS

Data indicated a down-regulation in scWAT Ucp1 in obese mice similar to what observed for the expression of Pgc1α. Both, BAT Ucp1 and Pgc1α mRNA decreased significantly in response to obesity and physical activity. Moreover, exercise caused significant decrease in scWAT mitochondrial proteins contradictory to BAT.

CONCLUSION

Taken together, exercise exerted controversial effects compared with HFD and obesity on expression of Ucp1 and Pgc1α in scWAT dissimilar to BAT tissues, concluding that obesity may cause a resistance to exercise in terms of metabolic demands for scWAT tissue.

An update on the role of irisin in the regulation of endocrine and metabolic functions

Irisin is a novel myokine and adipokine that has gained much attention recently due to its mechanisms of action. Irisin is secreted following proteolytic cleavage of its precursor fibronectin type III domain containing 5 (FNDC5). Following its release, irisin exerts its major action by increasing the expression of mitochondrial uncoupling protein 1 (UCP 1), which facilitates the conversion of white adipose tissue (WAT) into beige adipose tissue. Irisin is distributed in various body tissues and several actions have been attributed to its presence in those tissues. It has been suggested that it plays a role in metabolic diseases, ageing, inflammation and neurogenesis. However, the circulating levels of irisin are modulated by several factors such as diet, obesity, exercise, pharmacological agents and different pathological conditions. In this review, we have discussed the mechanisms by which irisin influences the functions of different body systems and how external factors in turn affect the circulating level of irisin. In conclusion, modification of circulating irisin level may help in the management of a variety of endocrine and metabolic disorders.

Is irisin the new player in exercise-induced adaptations or not? A 2017 update

Irisin is produced by a proteolytic cleavage of fibronectin type III domain-containing protein 5 (FNDC5) and has emerged as a potential mediator of exercise-induced energy metabolism. The purpose of this study was to review the results of studies that investigated irisin responses to acute and chronic exercise and provide an update. A comprehensive search in the databases of MEDLINE was performed (74 exercise studies). The focus of the analysis was on data concerning FNDC5 mRNA expression in skeletal muscle and circulating irisin concentration relatively to exercise mode, intensity, frequency and duration and the characteristics of the sample used. Circulating irisin levels may either not relate to FNDC5 transcription or expression of the later precedes irisin rise in the blood. Acute speed/strength and endurance exercise protocols represent potent stimuli for irisin release if they are characterized by adequate intensity and/or duration. There are no reports regarding irisin responses to field sport activities. Although animal studies suggest that irisin may also respond to systematic exercise training, the majority of human studies has produced contradictory results. Certain methodological issues need to be considered here such as the analytical assays used to measure irisin concentration in the circulation. Results may also be affected by subjects’ age, conditioning status and exercise intensity. The role of irisin as a moderator of energy metabolism during exercise remains to be seen.

Antiobesity effects of resveratrol: which tissues are involved?

The prevalence of obesity has been increasing in recent decades and is reaching epidemic proportions. The current options for overweight and obesity management are energy restriction and physical activity. However, compliance with these treatments is frequently poor and less successful than expected. Therefore, the scientific community is interested in active biomolecules, which may be useful in body weight management. Among them, resveratrol (3,5,4'-trihydroxy-trans-stilbene) has generated great interest as an antiobesity agent. The focus of this report is the mechanisms of action of resveratrol on several tissues (i.e., white and brown adipose tissues, liver, and skeletal muscle). Resveratrol blunts fat accumulation through decreasing adipogenesis and/or de novo lipogenesis in white adipose tissue. The effects on lipolysis are controversial. Regarding brown adipose tissue, resveratrol increases the capacity for adaptive thermogenesis. As far as liver and skeletal muscle is concerned, resveratrol increases lipid oxidation in both tissues. Therefore, in rodents, there is a general consensus concerning the effect of resveratrol on reducing body fat accumulation. By contrast, in humans, the studies are scarce, and no clear antiobesity action has been revealed so far.

Acute exercise elicits differential expression of insulin resistance genes in the skeletal muscle of patients with polycystic ovary syndrome

OBJECTIVE

This study aimed to explore the role of acute exercise on skeletal muscle gene expression related to insulin resistance in patients with polycystic ovary syndrome (PCOS) and controls.

METHODS

Four obese women with PCOS and four body mass index (BMI)-matched controls (CTRL) participated in this study. After an overnight fast, the subjects underwent a single 40-min bout of aerobic exercise. Muscle samples were obtained from vastus lateralis at baseline and 60 min after exercise. The expression of a panel of insulin resistance genes was evaluated by a quantitative PCR array system. Network-based analyses were performed to interpret transcriptional changes occurring before and after the exercise challenge.

RESULTS

Overall, differentially expressed genes associated with mitochondria function and peroxisome proliferator-activated receptor signalling were identified. At baseline, there was a significant upregulation of six genes exclusively in PCOS (i.e. NFKBIA, MAPK3, PPARGC1A, GAPDH, ACTB and PPARA). Twelve genes were upregulated in CTRL after a single bout of aerobic exercise (i.e. LEPR, CXCR4, CCR5, IL-18R1, CRLF2, ACACA, CEBPA, PPARGC1A, UCP1, TNFRSF1B, TLR4 and IKBKB). After the exercise session, three genes were upregulated in PCOS (i.e. SOCS3, NAMPT and IL-8), whilst IL-6 was upregulated in both groups after exercise.

CONCLUSIONS

This study provides novel evidence on the effects of acute exercise on insulin resistance genes in skeletal muscle of PCOS. The differentially expressed genes reported herein could be further investigated as targets for therapeutic interventions aimed at improving insulin resistance in this syndrome.

Physical activity prevents alterations in mitochondrial ultrastructure and glucometabolic parameters in a high-sugar diet model

Endurance exercise is a remarkable intervention for the treatment of many diseases. Mitochondrial changes on skeletal muscle are likely important for many of the benefits provided by exercise. In this study, we aimed to evaluate the effects that a regular physical activity (swimming without workload) has on mitochondrial morphological alterations and glucometabolic parameters induced by a high-sugar diet (HSD). Weaned male Wistar rats fed with a standard diet or a HSD (68% carbohydrate) were subjected to 60 minutes of regular physical activity by swimming (without workload) for four- (20 sessions) or eight-week (40 sessions) periods. After training, animals were euthanized and the sera, adipose tissues, and skeletal muscles were collected for further analysis. The HSD increased body weight after an 8-week period; it also increased the fat pads and the adipose index, resulting in glucose intolerance and insulin resistance (IR). Transmission electron microscopy showed an increase in alterations of mitochondrial ultrastructure in the gastrocnemius muscle, as well as a decrease in superoxide dismutase (SOD) activity, and an increase in protein carbonylation. Regular physical activity partially reverted these alterations in rats fed a HSD, preventing mitochondrial morphological alterations and IR. Moreover, we observed a decrease in Pgc1α expression (qPCR analysis) in STD-EXE group and a less pronounced reduction in HSD-EXE group after an 8-week period. Thus, regular physical activity (swimming without workload) in rats fed a HSD can prevent mitochondrial dysfunction and IR, highlighting the crucial role for physical activity on metabolic homeostasis.

Novel Browning Agents, Mechanisms, and Therapeutic Potentials of Brown Adipose Tissue

Nonshivering thermogenesis is the process of biological heat production in mammals and is primarily mediated by brown adipose tissue (BAT). Through ubiquitous expression of uncoupling protein 1 (Ucp1) on the mitochondrial inner membrane, BAT displays uncoupling of fuel combustion and ATP production in order to dissipate energy as heat. Because of its crucial role in regulating energy homeostasis, ongoing exploration of BAT has emphasized its therapeutic potential in addressing the global epidemics of obesity and diabetes. The recent appreciation that adult humans possess functional BAT strengthens this prospect. Furthermore, it has been identified that there are both classical brown adipocytes residing in dedicated BAT depots and "beige" adipocytes residing in white adipose tissue depots that can acquire BAT-like characteristics in response to environmental cues. This review aims to provide a brief overview of BAT research and summarize recent findings concerning the physiological, cellular, and developmental characteristics of brown adipocytes. In addition, some key genetic, molecular, and pharmacologic targets of BAT/Beige cells that have been reported to have therapeutic potential to combat obesity will be discussed.

Effects of physical exercise on myokines expression and brown adipose-like phenotype modulation in rats fed a high-fat diet

AIMS

Exercise-stimulated myokine secretion into circulation may be related with browning in white adipose tissue (WAT), representing a positive metabolic effect on whole-body fat mass. However, limited information is yet available regarding the impact of exercise on myokine-related modulation of adipocyte phenotype in WAT from obese rats.

MAIN METHODS

Sprague-Dawley rats (n=60) were divided into sedentary and voluntary physical activity (VPA) groups and fed with standard (35kcal% fat) or high-fat (HFD, 71kcal% fat)-isoenergetic diets. The VPA-groups had unrestricted access to wheel running throughout the protocol. After-9weeks, half of sedentary standard (SS) and sedentary HFD (HS)-fed animals were exercised on treadmill (endurance training, ET) for 8-weeks while maintaining the dietary treatments.

KEY FINDINGS

The adipocyte hypertrophy induced by HFD were attenuated by VPA and ET. HFD decreased 5' AMP-activated protein kinase (AMPK) activity in muscle as well as peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) and uncoupling protein 1 (UCP1) proteins in eWAT, while not affecting circulating irisin. VPA increased eWAT Tmem26 mRNA levels in the standard diet-fed group, whereas ET increased AMPK, interleukin 6 (IL-6) and fibronectin type III domain-containing protein 5 (FNDC5) protein expression in muscle, but had no impact on circulating irisin protein content. In eWAT, ET increased bone morphogenetic protein 7 (Bmp7), Cidea and PGC-1α in both diet-fed animals, whereas BMP7, Prdm16, UCP1 and FNDC5 only in standard diet-fed group.

SIGNIFICANCE

Data suggest that ET-induced myokine production seems to contribute, at least in part, to the "brown-like" phenotype in WAT from rats fed a HFD.