Mice that gorged during dietary restriction increased foraging related behaviors and differed in their macronutrient preference when released from restriction

Longitudinal study of energy, neurosensory and eating responses durinG pregnancY (ENERGY cohort): A study protocol

BACKGROUND AND AIMS

Physiological changes that occur during pregnancy can have long-term impacts on metabolism and neurosensory responses to food, which can impact nutrition and health outcomes. The ENERGY cohort is a longitudinal study that aims to capitalizes on pregnancy as a natural model of metabolic reprogramming in order to understand the neurosensory mechanisms underpinning links between metabolism and dietary behaviour. The study objectives are to test for multi-sensory shifts during pregnancy, and the effect of sensory changes on dietary choices and bodyweights, and to identify neurosensory mechanisms that determine macronutrient selection before and after pregnancy.

METHODS

A longitudinal cohort study involving 130 pregravid women planning to conceive with the next 12-months and 65 pregravid women with no short-term plans to conceive. Participants will be recruited from Dunedin and Auckland, New Zealand. The study will test for changes in diet, neurosensory outcomes, and metabolism across the reproductive cycle, from pre-pregnancy to 1-year post-pregnancy. Data will be collected at six timepoint throughout the pregnancy which will occur approximately every 3 months. The primary response variables will be changes in supra-threshold sensitivity across modalities, dietary intake, and metabolism between pre-pregnancy and post-pregnancy. Longitudinal data analysis will use linear mixed models to assess changes in the response outcomes over time adjusted for age, ethnicity, and socioeconomic status.

DISCUSSION

Understanding the relationship between metabolism, sensory processing, and macronutrient preferences will provide crucial insights into diet-related health issues, including obesity. This study will lead to the formation of a prospective research cohort that is unique to Aotearoa New Zealand, and will develop multidisciplinary skills that are increasingly necessary to addressing the obesity epidemic.

Studying food entrainment: Models, methods, and musings

The ability to tell time relative to predictable feeding opportunities has a long history of research, going back more than 100 years with behavioral observations of honeybees and rats. Animals that have access to food at a particular time of day exhibit “food anticipatory activity” (FAA), which is a preprandial increase in activity and arousal thought to be driven by food entrained circadian oscillator(s). However, the mechanisms behind adaptation of behavior to timed feeding continue to elude our grasp. Methods used to study circadian entrainment by food vary depending on the model system and the laboratory conducting the experiments. Most studies have relied on rodent model systems due to neuroanatomical tools and genetic tractability, but even among studies of laboratory mice, methods vary considerably. A lack of consistency within the field in experimental design, reporting, and definition of food entrainment, or even FAA, makes it difficult to compare results across studies or even within the same mutant mouse strain, hindering interpretation of replication studies. Here we examine the conditions used to study food as a time cue and make recommendations for study design and reporting.

Robustness analysis of metabolic predictions in algal microbial communities based on different annotation pipelines

Animals, plants, and algae rely on symbiotic microorganisms for their development and functioning. Genome sequencing and genomic analyses of these microorganisms provide opportunities to construct metabolic networks and to analyze the metabolism of the symbiotic communities they constitute. Genome-scale metabolic network reconstructions rest on information gained from genome annotation. As there are multiple annotation pipelines available, the question arises to what extent differences in annotation pipelines impact outcomes of these analyses. Here, we compare five commonly used pipelines (Prokka, MaGe, IMG, DFAST, RAST) from predicted annotation features (coding sequences, Enzyme Commission numbers, hypothetical proteins) to the metabolic network-based analysis of symbiotic communities (biochemical reactions, producible compounds, and selection of minimal complementary bacterial communities). While Prokka and IMG produced the most extensive networks, RAST and DFAST networks produced the fewest false positives and the most connected networks with the fewest dead-end metabolites. Our results underline differences between the outputs of the tested pipelines at all examined levels, with small differences in the draft metabolic networks resulting in the selection of different microbial consortia to expand the metabolic capabilities of the algal host. However, the consortia generated yielded similar predicted producible compounds and could therefore be considered functionally interchangeable. This contrast between selected communities and community functions depending on the annotation pipeline needs to be taken into consideration when interpreting the results of metabolic complementarity analyses. In the future, experimental validation of bioinformatic predictions will likely be crucial to both evaluate and refine the pipelines and needs to be coupled with increased efforts to expand and improve annotations in reference databases.

Extent of food restriction affects probability but not delay-based decision-making

Rodent studies on decision-making often use food rewards and food-restrict subjects in order to motivate performance. However, food restriction has widespread effects on brain and behavior, which depend on factors including extent of restriction and feeding schedule. These factors are well recognized for their effects on motivation, but may also cause effects on decision-making independent of motivation. We examined how the degree of weight-based food restriction in rats influenced decision-making on the probability and delay discounting tasks. Additionally, we examined how the method of food restriction (consistent amount vs. time constrained feeding schedule) influenced decision-making. Our results showed that the degree of weight-based food restriction significantly altered probability, but not delay discounting, and that these effects were not entirely explainable by differences in motivation. Additionally, the method of food restriction did not significantly influence discounting when animals were within the same range of weight-based restriction. Together, our findings suggest that the degree of food restriction may modulate the neural circuitry responsible for selective aspects of decision-making related to probability. Further, these data support the need for tight control and reporting of weight and feeding in studies relying on food restriction, and suggest that the effects of food restriction may be broader than previously considered.

Limits to sustained energy intake. XXX. Constraint or restraint? Manipulations of food supply show peak food intake in lactation is constrained

Lactating mice increase food intake 4- to 5-fold, reaching an asymptote in late lactation. A key question is whether this asymptote reflects a physiological constraint, or a maternal investment strategy (a 'restraint'). We exposed lactating mice to periods of food restriction, hypothesizing that if the limit reflected restraint, they would compensate by breaching the asymptote when refeeding. In contrast, if it was a constraint, they would by definition be unable to increase their intake on refeeding days. Using isotope methods, we found that during food restriction, the females shut down milk production, impacting offspring growth. During refeeding, food intake and milk production rose again, but not significantly above unrestricted controls. These data provide strong evidence that asymptotic intake in lactation reflects a physiological/physical constraint, rather than restraint. Because hypothalamic neuropeptide Y (Npy) was upregulated under both states of restriction, this suggests the constraint is not imposed by limits in the capacity to upregulate hunger signalling (the saturated neural capacity hypothesis). Understanding the genetic basis of the constraint will be a key future goal and will provide us additional information on the nature of the constraining factors on reproductive output, and their potential links to life history strategies.

Calorie restriction induces reversible lymphopenia and lymphoid organ atrophy due to cell redistribution

Calorie restriction (CR) without malnutrition increases life span and health span in multiple model organisms. In non-human and human primates, CR causes changes that protect against several age-related pathologies, reduces inflammation, and preserves or improves cell-mediated immunity. However, CR has also been shown to exhibit adverse effects on certain organs and systems, including the immune system, and to impact genetically different organisms of the same species differentially. Alternately, short periods of fasting followed by refeeding may result in the proliferation of bone marrow stem cells, suggesting a potential rejuvenation effect that could impact the hematopoietic compartment. However, the global consequences of CR followed by refeeding on the immune system have not been carefully investigated. Here, we show that individuals practicing long-term CR with adequate nutrition have markedly lower circulating levels of total leukocytes, neutrophils, lymphocytes, and monocytes. In 10-month-old mice, short-term CR lowered lymphocyte cellularity in multiple lymphoid tissues, but not in bone marrow, which appears to be a site of influx, or a "safe haven" for B, NK, and T cells during CR. Cellular loss and redistribution was reversed within the first week of refeeding. Based on BrdU incorporation and Ki67 expression assays, repopulating T cells exhibited high proliferation in the refeeding group following CR. Finally, we demonstrated that the thymus was not essential for T cell repopulation following refeeding. These findings are of potential relevance to strategies to rejuvenate the immune system in mammals and warrant further investigation.

A history of obesity leaves an inflammatory fingerprint in liver and adipose tissue

BACKGROUND/OBJECTIVES

Dieting is a popular yet often ineffective way to lower body weight, as the majority of people regain most of their pre-dieting weights in a relatively short time. The underlying molecular mechanisms driving weight regain and the increased risk for metabolic disease are still incompletely understood. Here we investigate the molecular alterations inherited from a history of obesity.

METHODS

In our model, male high-fat diet (HFD)-fed obese C57BL/6J mice were switched to a low caloric chow diet, resulting in a decline of body weight to that of lean mice. We measured body composition, as well as metrics of glucose, insulin and lipid homeostasis. This was accompanied by histological and gene expression analysis of adipose tissue and liver to assess adipose tissue inflammation and hepatosteatosis. Moreover, acute hypothalamic response to (re-) exposure to HFD was assessed by qPCR.

RESULTS & CONCLUSIONS

Within 7 weeks after diet switch, most obesity-associated phenotypes, such as body mass, glucose intolerance and blood metabolite levels were reversed. However, hepatic inflammation, hepatic steatosis as well as hypertrophy and inflammation of perigonadal, but not subcutaneous, adipocytes persisted in formerly obese mice. Transcriptional profiling of liver and perigonadal fat revealed an upregulation of pathways associated with immune function and cellularity. Thus, we show that weight reduction leaves signs of inflammation in liver and perigonadal fat, indicating that persisting proinflammatory signals in liver and adipose tissue could contribute to an increased risk of formerly obese subjects to develop the metabolic syndrome upon recurring weight gain.

The effects of graded levels of calorie restriction: VIII. Impact of short term calorie and protein restriction on basal metabolic rate in the C57BL/6 mouse

Under calorie restriction (CR) animals need to lower energy demands. Whether this involves a reduction in cellular metabolism is an issue of contention. We exposed C57BL/6 mice to graded CR for 3 months, measured BMR and dissected out 20 body compartments. From a separate age-matched group (n=57), we built 7 predictive models for BMR. Unadjusted BMR declined with severity of restriction. Comparison of measured and predicted BMR from the simple models suggested suppression occurred. The extent of 'suppression' was greater with increased CR severity. However, when models based on individual organ sizes as predictors were used, the discrepancy between the prediction and the observed BMR disappeared. This suggested 'metabolic suppression' was an artefact of not having a detailed enough model to predict the expected changes in metabolism. Our data have wide implications because they indicate that inferred 'metabolic' impacts of genetic and other manipulations may reflect effects on organ morphology.

Effect of calorie restriction on spontaneous physical activity and body mass in mice divergently selected for basal metabolic rate (BMR)

Spontaneous physical activity (SPA) represents an important component of daily energy expenditures in animals and humans. Intra-specific variation in SPA may be related to the susceptibility to metabolic disease or obesity. In particular, reduced SPA under conditions of limited food availability may conserve energy and prevent loss of body and fat mass ('thrifty genotype hypothesis'). However, both SPA and its changes during food restriction show wide inter-individual variations. We studied the effect of 30% caloric restriction (CR) on SPA in laboratory mice divergently selected for high (H-BMR) and low (L-BMR) basal metabolic rate. Selection increased SPA in the H-BMR line but did not change it in the L-BMR mice. This effect reflected changes in SPA intensity but not SPA duration. CR increased SPA intensity more strongly in the L-BMR line than in the H-BMR line and significantly modified the temporal variation of SPA. However, the initial between-line differences in SPA were not affected by CR. Loss of body mass during CR did not differ between both lines. Our results show that the H-BMR mice can maintain their genetically determined high SPA under conditions of reduced food intake without sacrificing their body mass. We hypothesize that this pattern may reflect the higher flexibility in the energy budget in the H-BMR line, as we showed previously that mice from this line reduced their BMR during CR. These energy savings may allow for the maintenance of elevated SPA in spite of reduced food intake. We conclude that the effect of CR on SPA is in large part determined by the initial level of BMR, whose variation may account for the lack of universal pattern of behavioural responses to CR.

Mice that are resistant to diet-induced weight loss have greater food anticipatory activity and altered melanocortin-3 receptor (MC3R) and dopamine receptor 2 (D2) gene expression

Diet-induced weight loss varies considerably between individuals, but the mechanisms driving these individual differences remain largely unknown. Here we investigated whether key neuropeptides involved in the regulation of energy balance or reward systems were differentially expressed in mice that were prone or resistant to caloric restriction (CR) induced weight loss. Mice (n=30 males and n=34 females) were fed 70% of their own baseline ad libitum intake for 25days, after which their brains were collected and expression of various neuropeptides were investigated and compared between the 10 male and 10 female mice that showed the greatest (high weight loss, HWL) or lowest weight loss (LWL) (n=40 in total). HWL mice showed a differential neuropeptide profile to LWL in both sexes, characterised by increased expression of neuropeptide Y (NPY), agouti-related peptide (AgRP), leptin receptor (ObRb), and melanocortin 3 receptor (MC3R) in the arcuate nucleus. No changes in the expression of fat mass and obesity related gene (FTO) or suppressor of cytokine signalling 3 (Socs3) were observed. Levels of dopamine D2 receptor were decreased in the nucleus accumbens in HWL compared to LWL mice. HWL mice showed a stronger increase in food anticipatory activity (FAA) in response to CR than LWL mice. These results indicate that the mice prone to diet-induced weight loss experienced greater hunger, potentially driving their elevated FAA.