Prior Endurance Training Enhances Beta-Adrenergic Signaling in Epidydimal Adipose from Mice Fed a High-Fat Diet

Sclerostin Influences Exercise-Induced Adaptations in Body Composition and White Adipose Tissue Morphology in Male Mice

Sclerostin is an inhibitor of the osteogenic Wnt/β-catenin signaling pathway that also has an endocrine role in regulating adipocyte differentiation and metabolism. Additionally, subcutaneous white adipose tissue (scWAT) sclerostin content decreases following exercise training (EXT). Therefore, we hypothesized that EXT-induced reductions in adipose tissue sclerostin may play a role in regulating adaptations in body composition and whole-body metabolism. To test this hypothesis, 10-week-old male C57BL/6J mice were either sedentary (SED) or performing 1 hour of treadmill running at ~65% to 70% maximum oxygen consumption (VO_2max ) 5 day/week (EXT) for 4 weeks and had subcutaneous injections of either saline (C) or recombinant sclerostin (S) (0.1 mg/kg body mass) 5 day/week; thus, making four groups (SED-C, EXT-C, SED-S, and EXT-S; n = 12/group). No differences in body mass were observed between experimental groups, whereas food intake was higher in EXT (p = 0.03) and S (p = 0.08) groups. There was a higher resting energy expenditure in all groups compared to SED-C. EXT-C had increased lean mass and decreased fat mass percentage compared to SED-C and SED-S. No differences in body composition were observed in either the SED-S or EXT-S groups. Lower scWAT (inguinal), epididymal white adipose tissue (eWAT) (visceral epididymal) mass, and scWAT adipocyte cell size and increased percentage of multilocular cells in scWAT were observed in the EXT-C group compared to SED-C, whereas lower eWAT was only observed in the EXT-S group. EXT mice had increased scWAT low-density lipoprotein receptor-related protein 4 (Lrp4) and mitochondrial content and sclerostin treatment only inhibited increased Lrp4 content with EXT. Together, these results provide evidence that reductions in resting sclerostin with exercise training may influence associated alterations in energy metabolism and body composition, particularly in scWAT. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

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

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

Effects of electrical stimulation-induced resistance exercise training on white and brown adipose tissues and plasma meteorin-like concentration in rats

Chronic endurance exercise training induces morphological and metabolic alterations including mitochondrial biogenesis in white adipose tissue (WAT) and brown adipose tissue (BAT) in rodents. A myokine called meteorin-like (Metrnl) is associated with morphological and metabolic adaptation and increased in blood after acute resistance exercise. However, the effects of chronic resistance exercise training (RT), which aims to increase muscle mass and strength, on WAT and BAT are unclear. Therefore, we aimed to clarify the effects of RT on morphological and metabolic parameters in WAT and BAT and on plasma Metrnl concentrations. We applied electrical stimulation to both legs of rats as RT three times a week for 4 weeks. RT reduced adipocyte size in subcutaneous WAT but induced no changes in mitochondrial and thermogenesis proteins. In BAT, peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) protein levels and mitochondrial content markers were significantly higher in the RT group compared with the control group. A significant positive correlation was found between the expression of PGC-1α in BAT and plasma Metrnl concentrations. These results suggest that plasma Metrnl is associated with PGC-1α and mitochondrial biogenesis in BAT. This study describes a potential role of RT in preventing metabolic diseases via altering WAT and BAT and increasing plasma Mertnl concentrations.

Sex differences in the peripubertal response to a short-term, high-fat diet intake

Obesity is one of the most important health problems facing developed countries because being overweight is associated with a higher incidence of type 2 diabetes, cardiovascular disease and cancer, as well as other comorbidities. Although increased weight gain results from a combination of poor dietary habits and decreased energy expenditure, not all individuals have equal propensities to gain weight or to develop secondary complications of obesity. This is partially a result not only of genetics, including sex, but also the time during which an individual is exposed to an obesogenic environment. In the present study, we have compared the response of male and female mice to short-term exposure to a high-fat diet (HFD) or a low-fat diet during the peripubertal period (starting at 42 days of age) because this is a stage of dramatic hormonal and metabolic modifications. After 1 week on a HFD, there was no significant increase in body weight, although females significantly increased their energy intake. Serum leptin levels increased in both sexes, even though no change in fat mass was detected. Glyceamia and homeostasis model assessment increased in males, suggesting a rapid change in glucose metabolism. Hypothalamic pro-opiomelanocortin mRNA levels were significantly higher in females on a HFD compared to all other groups, which may be an attempt to reduce their increased energy intake. Hypothalamic inflammation and gliosis have been implicated in the development of secondary complications of obesity; however, no indication of activation of inflammatory processes or gliosis was found in response to 1 week of HFD in the hypothalamus, hippocampus or cerebellum of these young mice. These results indicate that there are both sex and age effects in the response to poor dietary intake because peripubertal male and female mice respond differently to short-term dietary changes and this response is different from that reported in adult rodents.