Voluntary Running Attenuates Metabolic Dysfunction in Ovariectomized Low-Fit Rats

Higher mitochondrial oxidative capacity is the primary molecular differentiator in muscle of rats with high and low intrinsic cardiorespiratory fitness

OBJECTIVE

Cardiorespiratory fitness (CRF) is tightly linked with health and longevity and is implicated in metabolic flexibility and substrate metabolism. The high capacity runner (HCR) and low capacity runner (LCR) rat lines are a genetically heterogeneous rat model selected and bred for CRF that reflect CRF in humans by exhibiting differences in nutrient handling. This study aims to differentiate the intrinsic substrate preference of the HCR compared to LCR rats to better understand the intersection of mitochondrial respiration and intrinsic CRF.

METHODS

We performed bulk skeletal muscle RNA-Sequencing on male and female HCR and LCR rats and assessed the effect of rat line on mitochondrial gene expression pathways using the MitoCarta3.0 database. In a separate cohort of rats, mitochondria were isolated from skeletal and cardiac muscle and maximal oxidation rates were measured using an Oroboros O2k when provided either pyruvate or fatty acid substrates.

RESULTS

The expression of mitochondrial genes are significantly upregulated in HCR skeletal muscle in both male and female rats. In respirometry experiments, fatty acid oxidative capacities were greater in HCR compared to LCR, and male compared to female rats, as a function of both mitochondrial quality and mitochondrial density. This effect was greater in the skeletal muscle than in the heart. Pyruvate oxidation did not differ significantly between lines.

CONCLUSIONS

The capacity for increased fatty acid oxidation in the HCR rat is a result of selection for running capacity and is likely a key contributor to the healthy metabolic phenotype of individuals with high CRF.

Conserved multi-tissue transcriptomic adaptations to exercise training in humans and mice

Physical activity is associated with beneficial adaptations in human and rodent metabolism. We studied over 50 complex traits before and after exercise intervention in middle-aged men and a panel of 100 diverse strains of female mice. Candidate gene analyses in three brain regions, muscle, liver, heart, and adipose tissue of mice indicate genetic drivers of clinically relevant traits, including volitional exercise volume, muscle metabolism, adiposity, and hepatic lipids. Although ∼33% of genes differentially expressed in skeletal muscle following the exercise intervention are similar in mice and humans independent of BMI, responsiveness of adipose tissue to exercise-stimulated weight loss appears controlled by species and underlying genotype. We leveraged genetic diversity to generate prediction models of metabolic trait responsiveness to volitional activity offering a framework for advancing personalized exercise prescription. The human and mouse data are publicly available via a user-friendly Web-based application to enhance data mining and hypothesis development.

Effects of Endurance Training on Metabolic Enzyme Activity and Transporter Proteins in Skeletal Muscle of Ovariectomized Mice

PURPOSE

Estrogen deficiency or insufficiency can occur under several conditions, leading to negative health outcomes. To establish an effective countermeasure against estrogen loss, we investigated the effects of endurance training on ovariectomy (OVX)-induced metabolic disturbances.

METHODS

Female Institute of Cancer Research mice underwent OVX or sham operations. On day 7 of recovery, the mice were randomized to remain either sedentary or undergo 5 wk of treadmill running (15-20 m·min -1 , 60 min, 5 d·wk -1 ). During week 5 of the training, all animals performed a treadmill running test (15 m·min -1 , 60 min).

RESULTS

After the experimental period, OVX resulted in greater gains in body mass, fat mass, and triglyceride content in the gastrocnemius muscle. OVX enhanced phosphofructokinase activity in the plantaris muscle and decreased lactate dehydrogenase activity in the plantaris and soleus muscles. OVX decreased the protein content of NDUFB8, a mitochondrial respiratory chain subunit, but did not decrease other mitochondrial proteins or enzyme activities. Endurance training significantly enhanced mitochondrial enzyme activity and protein content in the skeletal muscles. Although OVX increased the respiratory exchange ratio during the treadmill running test, and postexercise blood lactate levels, endurance training normalized these parameters.

CONCLUSIONS

The present findings suggest that endurance training is a viable strategy to counteract the negative metabolic consequences in hypoestrogenism.

The bidirectional relationship between AMPK pathway activation and myokine secretion in skeletal muscle: How it affects energy metabolism

Myokines are peptides and proteins secreted by skeletal muscle cells, into the interstitium, or in the blood. Their regulation may be dependent or independent of muscle contraction to induce a variety of metabolic effects. Numerous myokines have been implicated in influencing energy metabolism via AMP-activated protein kinase (AMPK) signalling. As AMPK is centrally involved in glucose and lipid metabolism, it is important to understand how myokines influence its signalling, and vice versa. Such insight will better elucidate the mechanism of metabolic regulation during exercise and at rest. This review encompasses the latest research conducted on the relationship between AMPK signalling and myokines within skeletal muscles via autocrine or paracrine signalling.

Physical exercise improves mitochondrial function in ovariectomized rats

Estrogen deficiency causes metabolic disorders in humans and rodents, including in part due to changes in energy expenditure. We have shown previously that skeletal muscle mitochondrial function is compromised in ovariectomized (Ovx) rats. Since physical exercise is a powerful strategy to improve skeletal muscle mitochondrial content and function, we hypothesize that exercise training would counteract the deficiency-induced skeletal muscle mitochondrial dysfunction in Ovx rats. We report that exercised Ovx rats, at 60-65% of maximal exercise capacity for 8 weeks, exhibited less fat accumulation and body weight gain compared with sedentary controls. Treadmill exercise training decreased muscle lactate production, indicating a shift to mitochondrial oxidative metabolism. Furthermore, reduced soleus muscle mitochondrial oxygen consumption confirmed that estrogen deficiency is detrimental to mitochondrial function. However, exercise restored mitochondrial oxygen consumption in Ovx rats, achieving similar levels as in exercised control rats. Exercise-induced skeletal muscle peroxisome proliferator-activated receptor-γ coactivator-1α expression was similar in both groups. Therefore, the mechanisms by which exercise improves mitochondrial oxygen consumption appears to be different in Ovx-exercised and sham-exercised rats. While there was an increase in mitochondrial content in sham-exercised rats, demonstrated by a greater citrate synthase activity, no induction was observed in Ovx-exercised rats. Normalizing mitochondrial respiratory capacity by citrate synthase activity indicates a better oxidative phosphorylation efficiency in the Ovx-exercised group. In conclusion, physical exercise sustains mitochondrial function in ovarian hormone-deficient rats through a non-conventional mitochondrial content-independent manner.

Multiple Applications of Different Exercise Modalities with Rodents

A large proportion of chronic diseases can be derived from a sedentary lifestyle. Raising physical activity awareness is indispensable, as lack of exercise is the fourth most common cause of death worldwide. Animal models in different research fields serve as important tools in the study of acute or chronic noncommunicable disorders. With the help of animal-based exercise research, exercise-mediated complex antioxidant and inflammatory pathways can be explored, which knowledge can be transferred to human studies. Whereas sustained physical activity has an enormous number of beneficial effects on many organ systems, these animal models are easily applicable in several research areas. This review is aimed at providing an overall picture of scientific research studies using animal models with a focus on different training modalities. Without wishing to be exhaustive, the most commonly used forms of exercise are presented.

Early life stress reduces voluntary exercise and its prevention of diet-induced obesity and metabolic dysfunction in mice

The development of obesity-related metabolic syndrome (MetS) involves a complex interaction of genetic and environmental factors. One environmental factor found to be significantly associated with MetS is early life stress (ELS). We have previously reported on our mouse model of ELS, induced by neonatal maternal separation (NMS), that displays altered regulation of the hypothalamic-pituitary-adrenal (HPA) axis and increased sensitivity in the urogenital organs, which was attenuated by voluntary wheel running. Here, we are using our NMS model to determine if ELS-induced changes in the HPA axis also influence weight gain and MetS. Naïve (non-stressed) and NMS male mice were given free access to a running wheel and a low-fat control diet at 4-weeks of age. At 16-weeks of age, half of the mice were transitioned to a high fat/sucrose (HFS) diet to investigate if NMS influences the effectiveness of voluntary exercise to prevent diet-induced obesity and MetS. Overall, we observed a greater impact of voluntary exercise on prevention of HFS diet-induced outcomes in naïve mice, compared to NMS mice. Although body weight and fat mass were still significantly higher, exercise attenuated fasting insulin levels and mRNA levels of inflammatory markers in epididymal adipose tissue in HFS diet-fed naïve mice. Only moderate changes were observed in exercised NMS mice on a HFS diet, although this could partially be explained by reduced running distance within this group. Interestingly, sedentary NMS mice on a control diet displayed impaired glucose homeostasis and moderately increased pro-inflammatory mRNA levels in epididymal adipose, suggesting that early life stress alone impairs metabolic function and negatively impacts the therapeutic effect of voluntary exercise.

Running wheel access fails to resolve impaired sustainable health in mice feeding a high fat sucrose diet

Diet and physical activity are thought to affect sustainable metabolic health and survival. To improve understanding, we studied survival of mice feeding a low-fat (LF) or high-saturated fat/high sugar (HFS) diet, each with or without free running wheel (RW) access. Additionally several endocrine and metabolic health indices were assessed at 6, 12, 18 and 24 months of age. As expected, HFS feeding left-shifted survival curve of mice compared to LF feeding, and this was associated with increased energy intake and increased (visceral/total) adiposity, liver triglycerides, and increased plasma cholesterol, corticosterone, HOMA-IR, and lowered adiponectin levels. Several of these health parameters improved (transiently) by RW access in HFS and LF fed mice (i.e., HOMA-IR, plasma corticosterone), others however deteriorated (transiently) by RW access only in HFS-fed mice (i.e., body adiposity, plasma resistin, and free cholesterol levels). Apart from these multiple and sometimes diverging health effects of RW access, RW access did not affect survival curves. Important to note, voluntary RW activity declined with age, but this effect was most pronounced in the HFS fed mice. These results thus challenge the hypothesis that voluntary wheel running can counteract HFS-induced deterioration of survival and metabolic health.

Overproduction of endothelin-1 impairs glucose tolerance but does not promote visceral adipose tissue inflammation or limit metabolic adaptations to exercise

Endothelin-1 (ET-1) is a potent vasoconstrictor and proinflammatory peptide that is upregulated in obesity. Herein, we tested the hypothesis that ET-1 signaling promotes visceral adipose tissue (AT) inflammation and disrupts glucose homeostasis. We also tested if reduced ET-1 is a required mechanism by which exercise ameliorates AT inflammation and improves glycemic control in obesity. We found that 1) diet-induced obesity, AT inflammation, and glycemic dysregulation were not accompanied by significantly increased levels of ET-1 in AT or circulation in wild-type mice and that endothelial overexpression of ET-1 and consequently increased ET-1 levels did not cause AT inflammation yet impaired glucose tolerance; 2) reduced AT inflammation and improved glucose tolerance with voluntary wheel running was not associated with decreased levels of ET-1 in AT or circulation in obese mice nor did endothelial overexpression of ET-1 impede such exercise-induced metabolic adaptations; 3) chronic pharmacological blockade of ET-1 receptors did not suppress AT inflammation in obese mice but improved glucose tolerance; and 4) in a cohort of human subjects with a wide range of body mass indexes, ET-1 levels in AT, or circulation were not correlated with markers of inflammation in AT. In aggregate, we conclude that ET-1 signaling is not implicated in the development of visceral AT inflammation but promotes glucose intolerance, thus representing an important therapeutic target for glycemic dysregulation in conditions characterized by hyperendothelinemia. Furthermore, we show that the salutary effects of exercise on AT and systemic metabolic function are not contingent on the suppression of ET-1 signaling.

Opposing effects of S-equol supplementation on metabolic and behavioral parameters in mice fed a high-fat diet

Phytoestrogens, such as daidzein and genistein, may be used to treat various hormone-dependent disorders. Daidzein can be metabolized by intestinal microbes to S-equol. However, not all individuals possess bacteria producing this metabolite, resulting in categorization of equol vs nonequol producers. Past human and rodent studies have suggested that supplementation of this compound might yield beneficial metabolic and behavioral effects. We hypothesized that administration of S-equol to diet-induced obese male and female mice would mitigate potential diet-induced metabolic and comorbid neurobehavioral disorders. To test this possibility, we placed 5-week-old C57 mice on a high-fat diet (HFD) to mimic the diet currently consumed by many Western adults. Animals were randomly assigned to S-equol supplementation (10 mg/kg body weight) or vehicle control group. After 4 weeks on HFD with or without S-equol supplementation, metabolic and behavioral phenotyping was performed. Although the initial hypothesis proposed that S-equol treatment would improve metabolic and neurobehavioral outcomes, this supplementation instead exacerbated aspects of HFD-induced metabolic disease, as indicated by suppressed physical activity in treated individuals, reduced energy expenditure in treated males, and serum chemistry changes (hyperglycemia in treated individuals; hyperinsulinemia and hypoleptinemia in treated males). Conversely, S-equol individuals exhibited less anxiety-like and depressive-like behaviors, as evidenced by increased exploratory time in the elevated plus maze by treated males and increased time spent mobile in the tail suspension test for treated individuals. In summary, S-equol may be beneficial in mitigating depression and anxiety disorders in individuals, but for indeterminate reasons, supplementation may worsen facets of metabolic disorders in obese individuals.

Fibroblast growth factor 21 increases hepatic oxidative capacity but not physical activity or energy expenditure in hepatic peroxisome proliferator-activated receptor γ coactivator-1α-deficient mice

NEW FINDINGS

What is the central question of this study? Does a reduction in hepatic peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), which has been observed in an insulin-resistant obese state, impair the ability of fibroblast growth factor 21 (FGF21) to modulate metabolism? What is the main finding and its importance? A deficit in hepatic PGC-1α does not compromise the ability of FGF21 to increase hepatic fatty acid oxidation; however, the effects of FGF21 to regulate whole-body metabolism (i.e. total and resting energy expenditure), as well as ambulatory activity, were altered when hepatic PGC-1α was reduced.

ABSTRACT

Fibroblast growth factor 21 (FGF21) treatment drives metabolic improvements, including increased metabolic flux and reduced hepatic steatosis, but the mechanisms responsible for these effects remain to be elucidated fully. We tested whether a targeted reduction in hepatic peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), which has been shown to occur with obesity, had a negative impact on the metabolic effects of FGF21. We infused FGF21 (1 mg kg^-1  day^-1 ) or saline in chow-fed wild-type (WT) and liver-specific PGC-1α heterozygous (LPGC-1α) mice for 4 weeks. Administration of FGF21 lowered serum insulin and cholesterol (P ≤ 0.05) and tended to lower free fatty acids (P = 0.057). The LPGC-1α mice exhibited reduced complete hepatic fatty acid oxidation (FAO; LPGC-1α, 1788 ± 165 nmol g^-1  h^-1 compared with WT, 2572 ± 437 nmol g^-1  h^-1 ; P < 0.001), which was normalized by FGF21 treatment (2788 ± 519 nmol g^-1  h^-1 ; P < 0.001). FGF21 also increased hepatic incomplete FAO by 12% in both groups and extramitochondrial FAO by 89 and 56% in WT and LPGC-1α mice, respectfully (P = 0.001), and lowered hepatic triacylglycerol by 30-40% (P < 0.001). Chronic treatment with FGF21 lowered body weight and fat mass (P < 0.05), while increasing food consumption (P < 0.05), total energy expenditure [7.3 ± 0.60 versus 6.6 ± 0.39 kcal (12 h)^-1 in WT mice; P = 0.009] and resting energy expenditure [5.4 ± 0.89 versus 4.6 ± 0.21 kcal (12 h)^-1 in WT mice; P = 0.005]. Interestingly, FGF21 only increased ambulatory activity in the WT mice (P = 0.03), without a concomitant increase in non-resting energy expenditure. In conclusion, although reduced hepatic PGC-1α expression was not necessary for FGF21 to increase FAO, it does appear to mediate FGF21-induced changes in total and resting energy expenditure and ambulatory activity in lean mice.

Voluntary exercise training restores anticontractile effect of NO in coronary arteries of adult rats with antenatal/early postnatal hypothyroidism

INTRODUCTION

Our recent study showed that NO-mediated anticontractile effect of endothelium is absent in coronary arteries of adult rats, which suffered from antenatal/early postnatal hypothyroidism. This study tested the hypothesis that exercise training would improve such detrimental consequences of early thyroid deficiency.

DESIGN AND METHODS

Wistar dams received propylthiouracil (PTU, 7 ppm) in drinking water during gestation and two weeks postpartum; control dams received tap water. Six-week-old male offspring of control (CON) and PTU dams was divided into sedentary (CON-Sed, n = 12; PTU-Sed, n = 10) and trained (CON-Tr, n = 12; PTU-Tr, n = 10) groups; the latter had 24-h access to running wheels. Eight weeks later coronary arteries were studied by wire myography. Anticontractile effect of NO was assessed by the effects of NOS inhibitor L-NNA on the basal tone and contractile response to U46619. Oxidative phosphorylation complexes and eNOS were estimated by Western blotting.

RESULTS

T₃/T₄ and TSH levels (ELISA) were normalized in the progeny of PTU-treated dams at the age of 6 weeks and were not affected by training. Total running distance did not differ between CON-Tr and PTU-Tr. The contents of oxidative phosphorylation complexes were increased post-training in triceps brachii muscle from CON-Tr and PTU-Tr and in heart from PTU-Tr. Coronary arteries of PTU-Sed compared to CON-Sed demonstrated higher basal tone and contractile response to U46619, which were not further increased by L-NNA. The effects of L-NNA on the basal tone and contractile response to U46619 did not differ in CON-Tr and PTU-Tr groups, but were elevated in PTU-Tr compared to PTU-Sed group. PTU-Tr rats in comparison to PTU-Sed group had higher eNOS content in heart. Responses of coronary arteries to DEA/NO did not differ among all experimental groups.

CONCLUSIONS

Long-lasting coronary endothelial dysfunction resulted from transient thyroid deficiency during the antenatal/early postnatal period can be corrected by voluntary exercise training.

Voluntary wheel running improves adipose tissue immunometabolism in ovariectomized low-fit rats

Loss of ovarian hormones is associated with increased adiposity, white adipose tissue (WAT) inflammation, and insulin resistance (IR). Previous work demonstrated ovariectomized (OVX) rats bred for high aerobic fitness (HCR) are protected against weight gain and IR compared to rats bred for low aerobic fitness (LCR) yet wheel running prevents OVX-induced IR in LCR rats. The purpose of this study was to determine whether adipose tissue immunometabolic characteristics from female HCR and LCR rats differs before or after OVX, and whether wheel running mitigates OVX-induced adipose tissue immunometabolic changes in LCR rats. Female OVX HCR and LCR rats were all fed a high fat diet (HFD) (n = 7-8/group) and randomized to either a running wheel or remain sedentary for 11 weeks. Ovary-intact rats (n = 7-12/group) were fed a standard chow diet with no wheel. Ovary-intact LCR rats had a greater visceral WAT inflammatory profile compared to HCR. Following OVX, sedentary LCR rats had greater serum leptin (p<0.001) and WAT inflammation (p<0.05) than sedentary HCR. Wheel running normalized the elevated serum leptin and reduced both visceral (p<0.05) and subcutaneous (p<0.03) WAT inflammatory markers in the LCR rats. Paradoxically, wheel running increased some markers of WAT inflammation in OVX HCR rats (p<0.05), which correlated with observed weight gain. Taken together, HCR rats appear to have a healthier WAT immune and metabolic profile compared to LCR, even following OVX. Wheel running improves WAT health in previously sedentary LCR rats. On the other hand, increased WAT inflammation is associated with adiposity gain despite a high volume of wheel running in HCR rats.