Low levels of physical activity increase metabolic responsiveness to cold in a rat (Rattus fuscipes)

Effects of aquatic versus land-based exercise on irisin and fibroblast growth factor 21 expression and triiodothyronine and free fatty acid levels in elderly women

BACKGROUND

This study investigated the impacts of exercise on irisin and fibroblast growth factor 21 (FGF-21) expression, as well as triiodothyronine (T3 ) and free fatty acid (FFA) levels in elderly women.

METHODS

Thirty women aged 65 to 70 years (10 per group) were randomly assigned to aquatic exercise, land exercise, and control groups. The aquatic and land groups engaged in 3 exercise sessions per week (60 min/session) for 16 weeks. The intensity was progressively increased every 4 weeks.

RESULTS

Irisin and FGF-21 levels significantly increased in the aquatic exercise group. In the posttest, the aquatic exercise group had the highest irisin levels. Significant findings were observed for irisin and FGF-21 for the main effect between aquatic and band exercise groups (p<0.05 for both), the main effect between measurement times (p<0.01 and p<0.001, respectively), and the interaction effect (p<0.05 and p<0.001, respectively). The irisin level was significantly higher in the aquatic than in the land group 30 minutes after the last session (p<0.05). In both exercise groups, T3 levels were significantly higher 30 minutes after the final session (p<0.05) than before the program. The FFA level was significantly higher in the aquatic exercise group than the others. In the aquatic group, FFA levels were significantly higher 30 minutes after both the first (p<0.01) and the last (p<0.001) session compared to pre-program values.

CONCLUSION

Differences in exercise type and environment can promote fat metabolism by stimulating hormonal changes that induce brown fat activity and browning.

Biofabrication of vascularized adipose tissues and their biomedical applications

Recent advances in adipose tissue engineering and cell biology have led to the development of innovative therapeutic strategies in regenerative medicine for adipose tissue reconstruction. To date, the many in vitro and in vivo models developed for vascularized adipose tissue engineering cover a wide range of research areas, including studies with cells of various origins and types, polymeric scaffolds of natural and synthetic derivation, models presented using decellularized tissues, and scaffold-free approaches. In this review, studies on adipose tissue types with different functions, characteristics and body locations have been summarized with 3D in vitro fabrication approaches. The reason for the particular focus on vascularized adipose tissue models is that current liposuction and fat transplantation methods are unsuitable for adipose tissue reconstruction as the lack of blood vessels results in inadequate nutrient and oxygen delivery, leading to necrosis in situ. In the first part of this paper, current studies and applications of white and brown adipose tissues are presented according to the polymeric materials used, focusing on the studies which could show vasculature in vitro and after in vivo implantation, and then the research on adipose tissue fabrication and applications are explained.

Swimming in cold water upregulates genes involved in thermogenesis and the browning of white adipose tissues

The purpose of this study was to investigate whether there is an interacting effect of six weeks of swimming in cold water on the gene expression of browning markers in adipose tissue in rodents. Twenty male Wistar rats were randomly divided into four groups: Control (C, 25 °C), Cold Exposure (CE, 4 °C), Swimming in tepid Water (STW, 30 °C), and Swimming in Cold Water (SCW, 15 °C). The swimming included 2-3 min intervals, 1 min rest, until exhaustion, three days a week for six weeks, with 3 to 6% of bodyweight overload. Rats from CE were exposed to cold for 2 h per day, five days per week. After the experimental protocol, interscapular brown (BAT) and inguinal subcutaneous white (WAT) fat tissues were excised, weighed, and processed for beiging and mitochondrial biogenesis markers gene expression. The experimental protocols resulted in an apparent increase in the number of brown adipocytes (per mm²) in the adipose deposits compared to the C group; substantial changes were observed in the SCW group. Compared to other groups, cold exposure alone increased significantly serum norepinephrine, and also β₂-adrenergic receptor expression was upregulated in the adipocytes compared to the C group. The STW group increased the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ) coactivator-1 alpha (PGC-1α), β₂-adrenergic receptor, and CCAAT/enhancer-binding proteins-α(c/EBP-α) in WAT in comparison with the C group(p < 0.05). In both adipocytes, the SCW intervention significantly upregulated the expression of PGC-1α, PPAR-γ, and c/EBP-α genes in comparison with the C and CE groups. In addition, the expression of TFAM and UCP1 was upregulated substantially in the SCW group compared to other groups. Our data demonstrate that swim training and cold exposure present additive effects in the expression of genes involved in the beiging process and mitochondrial biogenesis markers in BAT and WAT. In addition, it seems that the upregulation of these genes is related to the activation of β₂-adrenergic receptors.

No Mitochondrial Related Transcriptional Changes in Human Skeletal Muscle after Local Heat Application

The purpose of the study is to determine the impact of local heating on skeletal muscle transcriptional response related to mitochondrial biogenesis and mitophagy. Twelve healthy subjects (height, 176.0 ± 11.9 cm; weight, 83.6 ± 18.3 kg; and body composition, 19.0 ± 7.7% body fat) rested in a semi-reclined position for 4 h with a heated thermal wrap (HOT) around one thigh and a wrap without temperature regulation (CON) around the other (randomized). Skin temperature, blood flow, intramuscular temperature, and a skeletal muscle biopsy from the vastus lateralis were obtained after the 4 h intervention. Skin temperature via infrared thermometer and thermal camera was higher after HOT (37.3 ± 0.7 and 36.7 ± 1.0 °C, respectively) than CON (34.8 ± 0.7, 35.2 ± 0.8 °C, respectively, p < 0.001). Intramuscular temperature was higher in HOT (36.3 ± 0.4 °C) than CON (35.2 ± 0.8 °C, p < 0.001). Femoral artery blood flow was higher in HOT (304.5 ± 12.5 mL‧min^-1) than CON (272.3 ± 14.3 mL‧min^-1, p = 0.003). Mean femoral shear rate was higher in HOT (455.8 ± 25.1 s^-1) than CON (405.2 ± 15.8 s^-1, p = 0.019). However, there were no differences in any of the investigated genes related to mitochondrial biogenesis (PGC-1α, NRF1, GAPBA, ERRα, TFAM, VEGF) or mitophagy (PINK-1, PARK-2, BNIP-3, BNIP-3L) in response to heat (p > 0.05). These data indicate that heat application alone does not impact the transcriptional response related to mitochondrial homeostasis, suggesting that other factors, in combination with skeletal muscle temperature, are involved with previous observations of altered exercise induced gene expression with heat.

Melatonin Potentiates Exercise-Induced Increases in Skeletal Muscle PGC-1α and Optimizes Glycogen Replenishment

Compelling evidence has demonstrated the effect of melatonin on exhaustive exercise tolerance and its modulatory role in muscle energy substrates at the end of exercise. In line with this, PGC-1α and NRF-1 also seem to act on physical exercise tolerance and metabolic recovery after exercise. However, the literature still lacks reports on these proteins after exercise until exhaustion for animals treated with melatonin. Thus, the aim of the current study was to determine the effects of acute melatonin administration on muscle PGC-1α and NRF-1, and its modulatory role in glycogen and triglyceride contents in rats subjected to exhaustive swimming exercise at an intensity corresponding to the anaerobic lactacidemic threshold (iLAn). In a randomized controlled trial design, thirty-nine Wistar rats were allocated into four groups: control (CG = 10), rats treated with melatonin (MG = 9), rats submitted to exercise (EXG = 10), and rats treated with melatonin and submitted to exercise (MEXG = 10). Forty-eight hours after the graded exercise test, the animals received melatonin (10 mg/kg) or vehicles 30 min prior to time to exhaustion test in the iLAn (tlim). Three hours after tlim the animals were euthanized, followed by muscle collection for specific analyses: soleus muscles for immunofluorescence, gluteus maximus, red and white gastrocnemius for the assessment of glycogen and triglyceride contents, and liver for the measurement of glycogen content. Student t-test for independent samples, two-way ANOVA, and Newman keuls post hoc test were used. MEXG swam 120.3% more than animals treated with vehicle (EXG; p < 0.01). PGC-1α and NRF-1 were higher in MEXG with respect to the CG (p < 0.05); however, only PGC-1α was higher for MEXG when compared to EXG. Melatonin reduced the triglyceride content in gluteus maximus, red and white gastrocnemius (F = 6.66, F = 4.51, and F = 6.02, p < 0.05). The glycogen content in red gastrocnemius was higher in MEXG than in CG (p = 0.01), but not in EXG (p > 0.05). In conclusion, melatonin was found to enhance exercise tolerance, potentiate exercise-mediated increases in PGC-1α, decrease muscle triglyceride content and increase muscle glycogen 3 h after exhaustive exercise, rapidly providing a better cellular metabolic environment for future efforts.

Effect of local heat application during exercise on gene expression related to mitochondrial homeostasis

The aim of this study was to determine the impact of local muscle heating during endurance exercise on human skeletal muscle mitochondrial-related gene expression. Twelve subjects (25 ± 6 yr, 177 ± 8 cm, 78 ± 16 kg, and peak aerobic capacity 45 ± 8 mL·kg-1·min-1) cycled with one leg heated (HOT) and the other serving as a control (CON). Skin and intramuscular temperatures were taken before temperature intervention (Pre), after 30 minutes (Pre30), after exercise (Post) and four hours after exercise (4Post). Muscle biopsies were taken from each leg at Pre and 4Post. Intramuscular temperature increased within HOT (34.4 ± 0.7 °C to 36.1 ± 0.5 °C, p < 0.001) and was higher than CON at Pre30 (34.0 ± 0.7 °C, p < 0.001). However, temperatures at POST were similar (HOT 38.4 ± 0.7 °C, CON 38.3 ± 0.5 °C, p = 0.661). Skin temperature was higher than CON at Post30 (30.3 ± 1.0 °C, p < 0.001) and Post (HOT 34.6 ± 0.9 °C, CON 32.3 ± 1.6 °C, p < 0.001). PGC-1α, VEGF and NRF2 mRNA increased with exercise (p < 0.05) but was not altered with heating (p > 0.05). TFAM increased after exercise with heat application (HOT, p = 0.019) but not with exercise alone (CON, p = 0.422). There was no difference in NRF1, ESRRα, or any of the mitophagy related genes in response to exercise or temperature (p > 0.05). In conclusion, TFAM is enhanced by local heat application during endurance exercise, whereas other genes related to mitochondrial homeostasis are unaffected. Novelty: The main finding of this study is that localized heating increased TFAM mRNA expression. The normal exercise-induced increased PGC-1α gene expression was unaltered by local muscle heating.

Survivable hypothermia or torpor in a wild-living rat: rare insights broaden our understanding of endothermic physiology

Maintaining a high and stable body temperature as observed in endothermic mammals and birds is energetically costly. Thus, it is not surprising that we discover more and more heterothermic species that can reduce their energetic needs during energetic bottlenecks through the use of torpor. However, not all heterothermic animals use torpor on a regular basis. Torpor may also be important to an individual’s probability of survival, and hence fitness, when used infrequently. We here report the observation of a single, ~ 5.5 h long hypothermic bout with a decrease in body temperature by 12 °C in the native Australian bush rat (Rattus fuscipes). Our data suggest that bush rats are able to rewarm from a body temperature of 24 °C, albeit with a rewarming rate lower than that expected on the basis of their body mass. Heterothermy, i.e. the ability to withstand and overcome periods of reduced body temperature, is assumed to be an evolutionarily ancestral (plesiomorphic) trait. We thus argue that such rare hypothermic events in species that otherwise appear to be strictly homeothermic could be heterothermic rudiments, i.e. a less derived form of torpor with limited capacity for rewarming. Importantly, observations of rare and extreme thermoregulatory responses by wild animals are more likely to be discovered with long-term data sets and may not only provide valuable insight about the physiological capability of a population, but can also help us to understand the constraints and evolutionary pathways of different phenologies.

New Insights into Molecular Mechanisms Mediating Adaptation to Exercise; A Review Focusing on Mitochondrial Biogenesis, Mitochondrial Function, Mitophagy and Autophagy

Exercise itself is fundamental for good health, and when practiced regularly confers a myriad of metabolic benefits in a range of tissues. These benefits are mediated by a range of adaptive responses in a coordinated, multi-organ manner. The continued understanding of the molecular mechanisms of action which confer beneficial effects of exercise on the body will identify more specific pathways which can be manipulated by therapeutic intervention in order to prevent or treat various metabolism-associated diseases. This is particularly important as exercise is not an available option to all and so novel methods must be identified to confer the beneficial effects of exercise in a therapeutic manner. This review will focus on key emerging molecular mechanisms of mitochondrial biogenesis, autophagy and mitophagy in selected, highly metabolic tissues, describing their regulation and contribution to beneficial adaptations to exercise.

Postnatal exercise protects offspring from high-fat diet-induced reductions in subcutaneous adipocyte beiging in C57Bl6/J mice

Maternal low-protein and postnatal high-fat (HF) diets program offspring obesity and type 2 diabetes mellitus (T2DM) risk by epigenetically reducing beige adipocytes (BAs) via increased G9a protein expression (Histone3 Lysine9 dimethyl transferase), an inhibitor of the BA marker fibroblast growth factor 21 (FGF21). Conversely, offspring exercise reduces fat mass and white adipocytes, but the mechanisms are not yet understood. This work investigated whether exercise reduces offspring obesity and T2DM risk caused by a maternal HF diet via regulation of G9a and FGF21 expression that would convert white to BA. Two-month-old female C57Bl/6J mice (F0) were fed a 16% (normal fat; NF) or a 45% HF diet for 3 months prior to breeding, and subsequent gestation and lactation. Male offspring (F1) were fed the same NF and HF diets and further divided into either sedentary (S) or voluntary wheel running (Ex) groups for an additional 3 months yielding eight groups: NF (maternal treatment condition)-NF-S (postweaning treatment conditions), NF-HF-S, NF-NF-Ex, NF-HF-Ex, HF-NF-S, HF-HF-S, HF-NF-Ex, and HF-HF-Ex. Subcutaneous adipose tissue was collected for protein and mRNA analysis of FGF21, peroxisome proliferator-activated receptor-gamma coactivator (PGC-1 alpha, inducer of FGF21), G9a, E4BP4 (G9a coactivator), and protein expression of H3K9 demethylases (KDM4C). Postnatal HF diet decreased FGF21 positive BA numbers regardless of maternal diets and postnatal exercise. Under sedentary conditions, postnatal HF diet increased protein expression of FGF21 transcription inhibitors G9a and E4BP4 compared to NF diet resulting in decreased FGF21 expression. In contrast, postnatal HF diet and exercise decreased G9a and E4BP4 protein expression while decreasing FGF21 expression compared to NF diet. Under exercised condition, postnatal HF diet-induced KDM4C protein expression while no changes in KDM4C protein expression were induced by postnatal HF diet under sedentary conditions. These findings suggest that the postnatal diet exerts a greater impact on offspring adiposity and BA numbers than maternal diets. These data also suggest that offspring exercise induces KDM4C to counter the increase in G9a that was triggered by maternal and postnatal HF diets. Future studies need to determine whether KDM4C induces methylation status of G9a to alter thermogenic function of BA.

Effect of local cold application during exercise on gene expression related to mitochondrial homeostasis

Exercise training increases mitochondrial content in active skeletal muscle. Previous work suggests that mitochondrial-related genes respond favorably to exercise in cold environments. However, the impact of localized tissue cooling is unknown. The purpose of this study was to determine the impact of local muscle cooling during endurance exercise on human skeletal muscle mitochondrial-related gene expression. Twelve subjects (age, 28 ± 6 years) cycled at 65% peak power output. One leg was cooled (C) for 30 min before and during exercise with a thermal wrap while the other leg was wrapped but not cooled, room temperature (RT). Muscle biopsies were taken from each vastus lateralis before and 4 h after exercise for the analysis of gene expression. Muscle temperature was lower in the C (29.2 ± 0.7 °C) than the RT (34.1 ± 0.3 °C) condition after pre-cooling for 30 min before exercise (p < 0.001) and remained lower after exercise in the C (36.9 ± 0.5) than the RT (38.4 ± 0.2, p < 0.001) condition. PGC-1α and NRF1 mRNA expression were lower in the C (p = 0.012 and p = 0.045, respectively) than the RT condition at 4 h after exercise. There were no temperature-related differences in other genes (p > 0.05). These data suggest that local cooling has an inhibitory effect on exercise-induced PGC-1α and NRF1 expression in human skeletal muscle. Those considering using local cooling during exercise should consider other systemic cooling options. Novelty: Local cooling has an inhibitory effect on exercise-induced PGC-1α and NRF1 expression in human skeletal muscle. Local cooling may lead to a less robust exercise stimulus compared with standard conditions.

In Vivo Detection of Human Brown Adipose Tissue During Cold and Exercise by PET/CT

The role of brown adipose tissue (BAT) in non-shivering thermogenesis is well established in animals. BAT is activated following cold exposure, resulting in non-shivering thermogenesis, to ensure a constant body temperature. In mitochondria of brown adipocytes, glucose and fatty acids are used as substrate for uncoupling resulting in heat production. Activated BAT functions as a sink for glucose and fatty acids and this hallmark has designated BAT a target in the fight against metabolic diseases like type 2 diabetes mellitus and obesity. In order to make valid claims regarding BAT activity in humans, BAT activity needs to be quantified. The combination of positron emission tomography (PET) and computer tomography (CT) analysis is currently the most frequently used imaging technique to determine BAT activity in humans. Here, we will discuss the history of PET/CT and radioisotopes used to determine BAT activity in humans. Moreover, we will assess how PET/CT is used to determine BAT activity following cold and exercise.

The Influence of Post-Exercise Cold-Water Immersion on Adaptive Responses to Exercise: A Review of the Literature

Post-exercise cold-water immersion (CWI) is used extensively in exercise training as a means to minimise fatigue and expedite recovery between sessions. However, debate exists around its merit in long-term training regimens. While an improvement in recovery following a single session of exercise may improve subsequent training quality and stimulus, reports have emerged suggesting CWI may attenuate long-term adaptations to exercise training. Recent developments in the understanding of the molecular mechanisms governing the adaptive response to exercise in human skeletal muscle have provided potential mechanistic insight into the effects of CWI on training adaptations. Preliminary evidence suggests that CWI may blunt resistance signalling pathways following a single exercise session, as well as attenuate key long-term resistance training adaptations such as strength and muscle mass. Conversely, CWI may augment endurance signalling pathways and the expression of genes key to mitochondrial biogenesis following a single endurance exercise session, but have little to no effect on the content of proteins key to mitochondrial biogenesis following long-term endurance training. This review explores current evidence regarding the underlying molecular mechanisms by which CWI may alter cellular signalling and the long-term adaptive response to exercise in human skeletal muscle.

The genomic basis of environmental adaptation in house mice

House mice (Mus musculus) arrived in the Americas only recently in association with European colonization (~400-600 generations), but have spread rapidly and show evidence of local adaptation. Here, we take advantage of this genetic model system to investigate the genomic basis of environmental adaptation in house mice. First, we documented clinal patterns of phenotypic variation in 50 wild-caught mice from a latitudinal transect in Eastern North America. Next, we found that progeny of mice from different latitudes, raised in a common laboratory environment, displayed differences in a number of complex traits related to fitness. Consistent with Bergmann's rule, mice from higher latitudes were larger and fatter than mice from lower latitudes. They also built bigger nests and differed in aspects of blood chemistry related to metabolism. Then, combining exomic, genomic, and transcriptomic data, we identified specific candidate genes underlying adaptive variation. In particular, we defined a short list of genes with cis-eQTL that were identified as candidates in exomic and genomic analyses, all of which have known ties to phenotypes that vary among the studied populations. Thus, wild mice and the newly developed strains represent a valuable resource for future study of the links between genetic variation, phenotypic variation, and climate.

Prior exercise training improves cold tolerance independent of indices associated with non-shivering thermogenesis

KEY POINTS

Mammals defend against cold-induced reductions in body temperature through both shivering and non-shivering thermogenesis. The activation of non-shivering thermogenesis is primarily driven by uncoupling protein-1 in brown adipose tissue and to a lesser degree by the browning of white adipose tissue. Endurance exercise has also been shown to increase markers of white adipose tissue browning. This study aimed to determine whether prior exercise training would alter the response to a cold challenge and if this would be associated with differences in indices of non-shivering thermogenesis. It is shown that exercise training protects against cold-induced weight loss by increasing food intake. Exercise-trained mice were better able to maintain their core temperature, independent of differences in markers of non-shivering thermogenesis.

ABSTRACT

Shivering is one of the first defences against cold, and as skeletal muscle fatigues there is an increased reliance on non-shivering thermogenesis. Brown and beige adipose tissues are the primary thermogenic tissues regulating this process. Exercise has also been shown to increase the thermogenic capacity of subcutaneous white adipose tissue. Whether exercise has an effect on the adaptations to cold stress within adipose tissue and skeletal muscle remains to be shown. Male C57BL/6 mice were either subjected to voluntary wheel running or remained sedentary for 12 days. Exercise led to decreased body weight and increased glucose tolerance. Mice were then divided into groups kept at 25°C room temperature or a cold challenge of 4°C for 48 h. Exercised mice were protected against cold-induced reductions in weight and in parallel with increased food intake. Providing exercised mice with the same amount of food as sedentary mice eliminated the protection against cold-induced weight loss. Cold exposure led to greater reductions in rectal temperature in sedentary compared to exercised mice. This protective effect was not explained by differences in the browning of white adipose tissue or brown adipose tissue mass. Similarly, the ability of the β₃ -adrenergic agonist CL 316,243 to increase energy expenditure was attenuated in previously exercised mice, suggesting that the activation of uncoupling protein-1 in brown and/or beige adipocytes is not the source of protective effects. We speculate that the protection against cold-induced reductions in rectal temperature could potentially be linked to exercise-induced alterations in skeletal muscle.

Effects of exercise in a cold environment on transcriptional control of PGC-1α

Peroxisome proliferator-activated receptor-α coactivator-1α (PGC-1α) mRNA is increased with both exercise and exposure to cold temperature. However, transcriptional control has yet to be examined during exercise in the cold. Additionally, the need for environmental cold exposure after exercise may not be a practical recovery modality. The purpose of this study was to determine mitochondrial-related gene expression and transcriptional control of PGC-1α following exercise in a cold compared with room temperature environment. Eleven recreationally trained males completed two 1-h cycling bouts in a cold (7°C) or room temperature (20°C) environment, followed by 3 h of supine recovery in standard room conditions. Muscle biopsies were taken from the vastus lateralis preexercise, postexercise, and after a 3-h recovery. Gene expression and transcription factor binding to the PGC-1α promoter were analyzed. PGC-1α mRNA increased from preexercise to 3 h of recovery, but there was no difference between trials. Estrogen-related receptor-α (ERRα), myocyte enhancer factor-2 (MEF2A), and nuclear respiratory factor-1 (NRF-1) mRNA were lower in cold than at room temperature. Forkhead box class-O (FOXO1) and cAMP response element-binding protein (CREB) binding to the PGC-1α promoter were increased postexercise and at 3 h of recovery. MEF2A binding increased postexercise, and activating transcription factor 2 (ATF2) binding increased at 3 h of recovery. These data indicate no difference in PGC-1α mRNA or transcriptional control after exercise in cold versus room temperature and 3 h of recovery. However, the observed reductions in the mRNA of select transcription factors downstream of PGC-1α indicate a potential influence of exercise in the cold on the transcriptional response related to mitochondrial biogenesis.

Local muscle cooling does not impact expression of mitochondrial-related genes

Recovery that takes place in a cold environment after endurance exercise elevates PGC-1α mRNA whereas ERRα and NRF2 mRNA expression are inhibited. However, the effect of local skeletal muscle cooling on mitochondrial-related gene expression is unknown.

PURPOSE

To determine the impact of local skeletal muscle cooling during recovery from an acute bout of exercise on mitochondrial-related gene expression.

METHODS

Recreationally-trained male cyclists (n=8, age 25±3 y, height 181±6cm, weight 79±8kg, 12.8±3.6% body fat, VO_2peak 4.52±0.88L·min^-1 protocol) completed a 90-min variable intensity cycling protocol followed by 4h of recovery. During recovery, ice was applied intermittently to one leg (ICE) while the other leg served as a control (CON). Intramuscular temperature was recorded continuously. Muscle biopsies were taken from each vastus lateralis at 4h post-exercise for the analysis of mitochondrial-related gene expression.

RESULTS

Intramuscular temperature was colder in ICE (26.7±1.1°C) than CON (35.5±0.1°C) throughout the 4h recovery period (p<0.001). There were no differences in expression of PGC-1α, TFAM, NRF1, NRF2, or ERRα mRNA between ICE and CON after the 4h recovery period.

CONCLUSION

Local muscle cooling after exercise does not impact the expression of mitochondrial biogenesis-related genes compared to recovery from exercise in control conditions. When these data are considered with previous research, the stimuli for cold-induced gene expression alterations may be related to factors other than local muscle temperature. Additionally, different intramuscular temperatures should be examined to determine dose-response of mitochondrial-related gene expression.

Exercise-induced effects on UCP1 expression in classical brown adipose tissue: a systematic review

Understanding the impact of regular exercise training on uncoupling protein 1 (UCP1) activity in classical brown adipose tissue (CBAT) is vital to our knowledge of whole-body thermogenic activity. The purpose of this systematic review was to evaluate the available experimental evidence on the effect of regular exercise training on UCP1 expression in CBAT. We performed a literature search using PubMed (1966-2016), Scopus, and EMBASE (1974-2016). Studies in any language that examined the effect of regular exercise training on UCP1 expression in CBAT, and not white adipose tissue (WAT), were eligible. Reviews, editorials, and conference proceedings were excluded. Nine studies fulfilled the set criteria. Risk of bias was assessed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) tool. The quality of reporting the results in the included studies was assessed using the 38-item checklist of the Animal Research Reporting of In Vivo Experiments (ARRIVE). Based on the evidence available and a comprehensive analysis of different confounding factors, we conclude that regular exercise training does not represent a major stimulus of UCP1 expression in CBAT. However, regular exercise training may induce adaptive responses to CBAT thermogenic activity in cases where: (i) animals consume a high-fat diet, (ii) exercise is combined with cold exposure, and (iii) animals show endogenously low UCP1 levels. Finally, it is important to note an inconsistency in the results from the analysed studies, which may be attributed to a number of confounding factors, increased risk of bias, as well as low quality of reporting the results.

Impact of hot and cold exposure on human skeletal muscle gene expression

Many human diseases lead to a loss of skeletal muscle metabolic function and mass. Local and environmental temperature can modulate the exercise-stimulated response of several genes involved in mitochondrial biogenesis and skeletal muscle function in a human model. However, the impact of environmental temperature, independent of exercise, has not been addressed in a human model. Thus, the purpose of this study was to compare the effects of exposure to hot, cold, and room temperature conditions on skeletal muscle gene expression related to mitochondrial biogenesis and muscle mass. Recreationally trained male subjects (n = 12) had muscle biopsies taken from the vastus lateralis before and after 3 h of exposure to hot (33 °C), cold (7 °C), or room temperature (20 °C) conditions. Temperature had no effect on most of the genes related to mitochondrial biogenesis, myogenesis, or proteolysis (p > 0.05). Core temperature was significantly higher in hot and cold environments compared with room temperature (37.2 ± 0.1 °C, p = 0.001; 37.1 ± 0.1 °C, p = 0.013; 36.9 ± 0.1 °C, respectively). Whole-body oxygen consumption was also significantly higher in hot and cold compared with room temperature (0.38 ± 0.01 L·min^-1, p < 0.001; 0.52 ± 0.03 L·min^-1, p < 0.001; 0.35 ± 0.01 L·min^-1, respectively). In conclusion, these data show that acute temperature exposure alone does not elicit significant changes in skeletal muscle gene expression. When considered in conjunction with previous research, exercise appears to be a necessary component to observe gene expression alterations between different environmental temperatures in humans.

Can Resistance Exercise Alter Irisin Levels and Expression Profiles of FNDC5 and UCP1 in Rats?

Background

Irisin is a new myokine secreted from the skeletal muscle and appears to affect the metabolism of adipose tissue.

Objectives

The mechanisms of cellular and molecular identification by which exercise training exerts its benefits remain unclear and are under investigation.

Methods

We examined the effect of 8-week resistance exercise on plasma irisin levels and expression profiles of muscle FNDC5 and subcutaneous adipose tissue UCP1 in male rats. Sixteen adult male rats were divided into two groups, control (n = 8) and exercise training (n = 8) groups. The training group received exercise for 3 days/week on a specific ladder (120 cm height) with a carrying load of 50% of body weight, which was attached to their tails.

Results

The weight of the load was gradually increased during the training sessions, ultimately reaching 200% of the body weight of rats in the final week. There were three sets of five repetitions with a 3-min rest between each set of exercise sessions and 1 minute between repetitions. Plasma irisin levels and relative mRNA expression of the genes UCP1 and FNDC5 were assessed. The results demonstrated a significant increase in the irisin levels after 8 weeks of resistance exercise (P < 0.001, t = 4.48). The relative expression of FNDC5 (P < 0.001, t = 6.18) and UCP1 genes (P < 0.001, t = 13.91) was also significantly increased.

Conclusions

Therefore, we can conclude from this study that resistance exercise may improve body composition possibly through increased thermogenesis in white adipose tissue through the secretion of irisin.

Changes in Brown Adipose Tissue and Muscle Development during Infancy

OBJECTIVE

To examine the relationship between brown adipose tissue (BAT) and muscle development, two tissues that derive from a common cell lineage, during the first 6 months of postnatal life.

STUDY DESIGN

Thirty healthy term infants (15 males and females) underwent whole-body magnetic resonance imaging examinations. Measurements of BAT in the supraclavicular area as well as measures of trunk musculature and subcutaneous adiposity were obtained at birth and at 6 months of age.

RESULTS

Paraspinous musculature and subcutaneous white adipose tissue (WAT) increased, and the proportion of BAT in the supraclavicular area decreased during infancy. Although measures of BAT did not correlate with paraspinous musculature through the first 6 months of life (r = -0.35; P = .09), BAT was a significant predictor of paraspinous musculature after adjusting for weight, body length, and WAT (P = .002); infants with the smallest decreases in BAT had the greatest gains in musculature. In contrast, changes in BAT did not predict increases in subcutaneous WAT (P = .25) during infancy, which were primarily determined by body weight.

CONCLUSIONS

Changes in BAT are associated with muscle development but not WAT accumulation in healthy infants. Studies are needed to determine the mechanism(s) by which BAT could facilitate muscle growth, and the degree to which decreased muscle mass, such as in preterm and low birth weight infants, is related to a deficiency of BAT.

Motives for adult participation in physical activity: type of activity, age, and gender

Background

In recent years, there has been a decline in physical activity among adults. Motivation has been shown to be a crucial factor in maintaining physical activity. The purpose of this study was to examine whether motives for participation could accurately discriminate gender, age, and type of physical activity.

Methods

A quantitative, cross-sectional descriptive research design was employed. The Physical Activity and Leisure Motivation Scale (PALMS) was used to assess motives for physical activity in 1,360 adults (703 males, 657 females) who had been exercising regularly for at least six months. The PALMS consists of 40 items that constitute eight sub-scales (mastery, enjoyment, psychological condition, physical condition, appearance, others’ expectations, affiliation, competition/ego). Respondents were divided into two age groups (young adults aged 20 to 40 years and middle-aged adults 41 to 64 years) and five types of activity (individual racing sports plus bowls, team sports, racquet sports, martial arts, and exercise).

Results

The group discriminant function analyses revealed significant canonical functions correctly classifying the cases into gender (82%), age group (83%), team sport players 76%, individual racing sport plus bowls players 91%, racquet sport players 90%, exercisers 84%, and martial art players 91%. The competition/ego, appearance, physical condition, and mastery sub-scales contributed most to gender differences. Five sub-scales (mastery, psychological condition, others’ expectations, affiliation, and enjoyment) contributed most to the discriminant function for age. For type of activity, different sub-scales were the strongest contributors to the discriminant function for each type of PA.

Conclusion

The findings in this study suggest that strong and important motives for participation in physical activity are different across type of activity, age, and gender in adults. Understanding the motives that influence physical activity participation is critical for developing interventions to promote higher levels of involvement.

Validating the Physical Activity and Leisure Motivation Scale (PALMS)

Background

Although there is abundant evidence to recommend a physically active lifestyle, adult physical activity (PA) levels have declined over the past two decades. In order to understand why this happens, numerous studies have been conducted to uncover the reasons for people’s participation in PA. Often, the measures used were not broad enough to reflect all the reasons for participation in PA. The Physical Activity and Leisure Motivation Scale (PALMS) was created to be a comprehensive tool measuring motives for participating in PA. This 40-item scale related to participation in sport and PA is designed for adolescents and adults. Five items constitute each of the eight sub-scales (mastery, enjoyment, psychological condition, physical condition, appearance, other’s expectations, affiliation, competition/ego) reflecting motives for participation in PA that can be categorized as features of intrinsic and extrinsic motivation based on self-determination theory. The aim of the current study was to validate the PALMS in the cultural context of Malaysia, including to assess how well the PALMS captures the same information as the Recreational Exercise Motivation Measure (REMM).

Method

To do so, 502 Malaysian volunteer participants, aged 18 to 67 years (mean ± SD; 31.55 ± 11.87 years), from a variety of PA categories, including individual sports, team sports, martial arts and exercise, completed the study.

Results

The hypothesized 8-factor model demonstrated a good fit with the data (CMIN/DF = 2.820, NFI = 0.90, CFI = 0.91, RMSEA = 0.06). Cronbach’s alpha coefficient (α = 0.79) indicated good internal consistency for the overall measure. Internal consistency for the PALMS subscales was sound, ranging from 0.78 to 0.82. The correlations between each PALMS sub-scale and the corresponding sub-scale on the validated REMM (the 73-item questionnaire from which the PALMS was developed) were also high and varied from 0.79 to 0.95. Also, test-retest reliability for the questionnaire sub-scales was between 0.78 and 0.94 over a 4-week period.

Conclusions

In this sample, the PALMS demonstrated acceptable factor structure, internal consistency, test-retest reliability, and criterion validity. It was applicable to diverse physical activity contexts.

Voluntary exercise adapts the hypothalamus-pituitary-thyroid axis in male rats

The hypothalamic-pituitary thyroid (HPT) axis modulates energy homeostasis. Its activity decreases in conditions of negative energy balance but the effects of chronic exercise on the axis are controversial and unknown at hypothalamic level. Wistar male rats were exposed for up to 14 days to voluntary wheel running (WR), or pair-feeding (PF; 18% food restriction), or to repeated restraint (RR), a mild stressor. WR and RR diminished food intake; body weight gain decreased in the 3 experimental groups, but WAT mass and serum leptin more intensely in the WR group. WR, but not RR, produced a delayed inhibition of central markers of HPT axis activity. At day 14, in WR rats paraventricular nucleus-pro-TRH mRNA and serum TSH levels decreased, anterior pituitary TRH-receptor 1 mRNA levels increased, but serum thyroid hormone levels were unaltered, which is consistent with decreased secretion of TRH and clearance of thyroid hormones. A similar pattern was observed if WR animals were euthanized during their activity phase. In contrast, in PF animals the profound drop of HPT axis activity included decreased serum T3 levels and hepatic deiodinase 1 activity; these changes were correlated with an intense increase in serum corticosterone levels. WR effects on HPT axis were not associated with changes in the activity of the hypothalamic-pituitary adrenal axis, but correlated positively with serum leptin levels. These data demonstrate that voluntary WR adapts the status of the HPT axis, through pathways that are distinct from those observed during food restriction or repeated stress.

Energy dissipation in brown adipose tissue: from mice to men

In rodents, brown adipose tissue (BAT) is a metabolic organ that produces heat in response to cold and dietary intake through mitochondrial uncoupling. For long time, BAT was considered to be solely important in small mammals and infants, however recent studies have shown that BAT is also functional in adult humans. Interestingly, the presence and/or functionality of this thermogenic tissue is diminished in obese people, suggesting a link between human BAT and body weight regulation. In the last years, evidence has also emerged for the existence of adipocytes that may have an intermediate thermogenic phenotype between white and brown adipocytes, so called brite or beige adipocytes. Together, these findings have resulted in a renewed interested in (human) brown adipose tissue and pathways to increase the activity and recruitment of these thermogenic cells. Stimulating BAT hypertrophy and hyperplasia in humans could be a potential strategy to target obesity. Here we will review suggested pathways leading to BAT activation in humans, and discuss novel putative BAT activators in rodents into human perspective.

Regulatory role of PGC-1α/PPAR signaling in skeletal muscle metabolic recruitment during cold acclimation

This study examined the molecular basis of energy-related regulatory mechanisms underlying metabolic recruitment of skeletal muscle during cold acclimation and possible involvement of the l-arginine/nitric oxide-producing pathway. Rats exposed to cold (4±1°C) for periods of 1, 3, 7, 12, 21 and 45 days were divided into three groups: untreated, l-arginine treated and N(ω)-nitro-l-arginine methyl ester (l-NAME) treated. Compared with controls (22±1°C), there was an initial increase in the protein level of 5'-AMP-activated protein kinase α (day 1), followed by an increase in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and peroxisome proliferator-activated receptors (PPARs): PPARα and PPARγ from day 1 and PPARδ from day 7 of cold acclimation. Activation of the PGC-1α/PPAR transcription program was accompanied by increased protein expression of the key metabolic enzymes in β-oxidation, the tricarboxylic acid cycle and oxidative phosphorylation, with the exceptions in complex I (no changes) and ATP synthase (decreased at day 1). Cold did not affect hexokinase and GAPDH protein levels, but increased lactate dehydrogenase activity compared with controls (1-45 days). l-arginine sustained, accelerated and/or intensified cold-induced molecular remodeling throughout cold acclimation. l-NAME exerted phase-dependent effects: similar to l-arginine in early cold acclimation and opposite after prolonged cold exposure (from day 21). It seems that upregulation of the PGC-1α/PPAR transcription program early during cold acclimation triggers the molecular recruitment of skeletal muscle underlying the shift to more oxidative metabolism during prolonged cold acclimation. Our results suggest that nitric oxide has a role in maintaining the skeletal muscle oxidative phenotype in late cold acclimation but question its role early in cold acclimation.

Truncated Product Methods for Panel Unit Root Tests

This paper proposes two new panel unit root tests based on Zaykin et al. (2002)'s truncated product method. The first one assumes constant correlation between p-values and the second one uses sieve bootstrap to allow for general forms of cross-section dependence in the panel units. Monte Carlo simulation shows that both tests have reasonably good size and are powerful in cases of some very large p-values. The proposed tests are applied to a panel of real GDP and inflation density forecasts, resulting in evidence that professional forecasters may not update their forecast precision in an optimal Bayesian way.

Effects of post-exercise recovery in a cold environment on muscle glycogen, PGC-1α, and downstream transcription factors

PURPOSE

The purpose of this investigation was to determine the impact of post-exercise environmental cold exposure on muscle glycogen, PGC-1α, and downstream transcription factors.

METHODS

Eight males cycled for 1h and recovered in either 7 °C (cold) or 20 °C (room temp) environment for 4h. Muscle biopsies were obtained pre, post, and 4h post exercise for the analysis of muscle glycogen and mRNA. During recovery participants consumed 1.8 g kg⁻¹ of body weight of an oral dextrose solution immediately following the post biopsy and 2h into recovery. Blood samples were obtained post exercise and at 30, 60, 120, 150, 180, and 240 min post exercise for the analysis of serum glucose and insulin AUC.

RESULTS

Oxygen uptake was lower during room temp than during cold recovery (0.40 ± 0.05 L x min⁻¹ vs. 0.80 ± 0.12 L x min⁻¹; p<0.01). There was no effect of temperature on muscle glycogen recovery or glucose AUC. However, insulin AUC was greater during the room temp trial compared to the cold trial (5139 ± 1412 vs. 4318 ± 1272, respectively; p=0.025). PGC-1α gene expression was higher (p=0.029), but ERRα and NRF2 were lower (p=0.019 and p=0.046, respectively) after recovery in the cold. There were no differences in NRF1 (p=.173) or TFAM (p=0.694).

CONCLUSIONS

This investigation shows no effect of a cold recovery environment on glycogen re-synthesis but does demonstrate reduced ERRα and NRF2 mRNA despite elevations in PGC-1α mRNA when recovery post-exercise takes place in a cold environment.

Searching for ways to switch on brown fat: are we getting warmer?

Obesity rates are increasing alongside those of its co-morbidities, placing a huge strain on health systems across the globe. Evidence points to inappropriate levels of ectopic lipid accumulation outside of adipose tissue being a major factor in the progression of many of these diseases. Brown adipose tissue (BAT) has a huge capacity to remove lipids from the circulatory system to fuel thermogenesis. Multiple studies have now confirmed the existence of active BAT in adult humans, making strategies aimed at activating it a potential therapeutic option in obese subjects. In recent years, researchers working in murine models have found a wide range of endogenous molecules with specific roles regulating BAT. These findings place BAT firmly within the wider network of physiological regulation covering global metabolism. They also highlight the possibility of targeting thermogenesis in a safe and specific manner to remove potentially harmful lipids released from stressed or failing white adipose tissue in obese states.

Differences in locomotor performance between individuals: importance of parvalbumin, calcium handling and metabolism

Locomotor performance is linked to fitness and health of animals and is expected to be under strong selection. However, interindividual variation in locomotor performance is pronounced in many species. It was our aim to investigate the relative importance of energy metabolism and calcium handling in determining sprint and sustained locomotion in the zebrafish (Danio rerio). Sprint and sustained performance (Ucrit) varied independently from each other. Using in vivo electroporation, we found that increased parvalbumin protein concentration improved both sprint and sustained locomotion. This is the first demonstration that parvalbumin plays a role in determining whole-animal performance. High sprint performance fish had greater mRNA concentrations of the metabolic regulators PPARδ and PGC1β compared with fish with poor sprint performance. High sustained performance fish, in contrast, had greater concentrations of PGC-1α and PGC-1β. The increased expression of these metabolic regulators indicates an enhancement of the metabolic machinery in high performance animals. Sprint performance is also enhanced by creatine kinase activity, which may be associated with increased PPARδ mRNA concentration. Ryanodine receptor (RyR) and sarcoplasmic reticulum Ca2+-ATPase 1 (SERCA1) mRNA concentrations were significantly increased in high sustained performance fish, while parvalbumin 2, dihydropyridine (DHPR) receptor and SERCA2 mRNA levels were increased in fish with high sprint velocities. Sustained performance was more sensitive to experimentally induced decreases in RyR and DHPR activity than sprint performance. We provide mechanistic explanations of why locomotor performance differs between individuals, which is important for understanding ecological and sporting success, disease and the evolutionary processes underlying selection.

In vivo cardiac anatomical and functional effects of wheel running in mice by magnetic resonance imaging

Physical activity is frequently used as a strategy to decrease pathogenesis and improve outcomes in chronic pathologies such as metabolic or cardiac diseases. In mice, it has been shown that voluntary wheel running (VWR) could induce an aerobic training effect and may provide a means of exploring the relationship between physical activity and the progression of pathology, or the effect of a drug on locomotor activity. To the best of our knowledge, in vivo magnetic resonance imaging (MRI) and other non-invasive methods had not been investigated for training evaluation in mice; therefore, it was proposed to test an MRI method coupled with a cardiorespiratory gating system on C57Bl/6 mice for in vivo heart anatomical and functional characterization in both trained and untrained animals. Twenty mice were either assigned to a 12-week VWR program or to a control group (CON - no wheel in the cage). At week 12, MRI scans showed an increase in the left ventricular (LV) wall mass in the VWR group compared with the CON group. The ex vivo measurements also found an increase in the heart and LV weight, as well as an increase in oxidative enzyme activities (i.e. cytochrome c oxidase [COx] in the soleus). In addition, correlations have been observed between ex vivo LV/body weight ratio, COx activity in the soleus and in vivo MRI LV wall mass/body weight. In conclusion, mouse cardiac MRI methods coupled with a cardio-respiratory gating system are sufficiently effective and feasible for non-invasive, training-induced heart hypertrophy characterization, and may be used for longitudinal training level follow-up in mouse models of cardiovascular and metabolic diseases.