The Impact of Long-term Physical Inactivity on Adipose Tissue Immunometabolism.

CONTEXT: Adipose tissue and physical inactivity both influence metabolic health and systemic inflammation, but how adipose tissue responds to chronic physical inactivity is unknown. OBJECTIVE: This work aimed to characterize the impact of chronic physical inactivity on adipose tissue in healthy, young males. METHODS: We collected subcutaneous adipose tissue from 20 healthy, young men before and after 60 days of complete bed rest with energy intake reduced to maintain energy balance and fat mass. We used RNA sequencing, flow cytometry, ex vivo tissue culture, and targeted protein analyses to examine adipose tissue phenotype. RESULTS: Our results indicate that the adipose tissue transcriptome, stromal cellular compartment, and insulin signaling protein abundance are largely unaffected by bed rest when fat mass is kept stable. However, there was an increase in the circulating concentration of several adipokines, including plasma leptin, which was associated with inactivity-induced increases in plasma insulin and absent from adipose tissue cultured ex vivo under standardized culture conditions. CONCLUSION: Physical inactivity-induced disturbances to adipokine concentrations such as leptin, without changes to fat mass, could have profound metabolic implications outside a clinical facility when energy intake is not tightly controlled.

Among- and within-individual correlations between basal and maximal metabolic rates in birds.

The aerobic capacity model proposes that endothermy is a by-product of selection favouring high maximal metabolic rates (MMR) and its mechanistic coupling with basal metabolic rate (BMR). Attempts to validate this model in birds are equivocal and restricted to phenotypic correlations (rP), thus failing to distinguish among- and within-individual correlations (rind and re). We examined 300 paired measurements of BMR and MMR from 60 house sparrows before and after two levels of experimental manipulation - testosterone implants and immune challenge. Overall, repeatability was significant in both BMR (R=0.25±0.06) and MMR (R=0.52±0.06). Only the testosterone treatment altered the rP between BMR and MMR, which resulted from contrasting effects on rind and re. While rind was high and significant (0.62±0.22) in sham-implanted birds, re was negative and marginally non-significant (-0.15±0.09) in testosterone-treated birds. Thus, the expected mechanistic link between BMR and MMR was apparent, but only in birds with low testosterone levels.

Juvenile nutritional stress affects growth rate, adult organ mass, and innate immune function in zebra finches (Taeniopygia guttata).

Developmental conditions may influence many aspects of adult phenotype, including growth and immune function. Whether poor developmental environments impair both growth and immune function or induce a trade-off between the two processes is inconclusive, and the impact of the timing of stress in determining this relationship has so far been overlooked. We tested the hypothesis that the long-term effects of nutritional stress on growth, body composition, and immune function in zebra finches (Taeniopygia guttata) are different depending on whether stress is experienced during an early or a juvenile phase (i.e., before or after nutritional independence, respectively). We raised birds on high (H) or low (L) food conditions until posthatch day (PHD) 35 and switched treatments for half of the birds in each of the H and L groups from PHD 36 to 61. We found that unfavorable juvenile conditions (PHD 36-61) increased somatic growth rates and liver mass, body fat, and some aspects of immune function. We also observed a positive relationship between growth and immune function, as individuals that grew faster as juveniles also had better innate immune responses as adults. There was no effect of treatment on basal metabolic rate. These findings demonstrate the importance of juvenile developmental conditions in shaping multiple aspects of the adult phenotype.

Chronic mild stress induces variations in locomotive behavior and metabolic rates in high fat fed rats

Chronic mild stress (CMS) has been often associated to the pathogenesis of manydiseases including obesity. Indeed, visceral obesity has been linked to the developmentof metabolic syndrome features and constitutes a serious risk factor for cardiovasculardiseases and diabetes. In order to study possible mechanistic relationshipsbetween stress and the onset of obesity, we developed during 11 weeks a model ofhigh-fat dietary intake (cafeteria diet) together with a CMS regimen in male Wistarrats. During the experimental period, basal metabolism by indirect calorimetry, rectaltemperature, food intake, and locomotive markers were specifically analyzed.After 77 days, animals were sacrificed and body, adiposity and plasma biochemicalprofiles were also examined. As expected, cafeteria diet in unstressed animals induceda significative increase in body weight, adiposity, and insulin resistance markers.Locomotive variables, specifically distance, rearing and meander, were significantlyincreased by CMS on the first weeks of stress. Moreover, this model of CMS in Wistarrats increased significantly energy expenditure, and apparently interplayed withthe dietary treatment on the muscle weight/fat weight ratio. In summary, this chronicstress model did not affected weight gain in control and high fat fed animals, butinduced an interaction concerning the metabolic muscle/fat repartitioning (AU)

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House sparrows (Passer domesticus) adjust their social status position to their physiological costs.

For group-living animals, the maintenance of a position in the social hierarchy may be associated with physiological costs such as increased stress and energy expenditure or suppressed immune functions. In this study, we experimentally manipulated the social status of house sparrows so that each bird experienced two social environments in random sequence: being dominant and subordinate. For 14 males, we investigated how corticosterone concentrations, energy expenditure and immune functions were affected by these changes in social status position. We found that the cost of maintaining a social status position differed between individuals and were related to individual body size. Birds with small body size had increased costs in terms of increased stress responses and reduced cell-mediated immune responses while being experimentally kept as dominants, while birds with large body size had increased costs while they were subordinates. We also found that birds with increased energetic and immunological costs as dominants obtained a low status position in the large group, while birds with increased costs as subordinates obtained a high status position in the large group. In summary, we found that the costs associated with the maintenance of social status position differed between individuals and was related to the individuals' body size. Furthermore, in a large group, individuals maintained a social status position that minimized energetic and immunological costs.