Separate gut-brain circuits for fat and sugar reinforcement combine to promote overeating

Food is a powerful natural reinforcer that guides feeding decisions. The vagus nerve conveys internal sensory information from the gut to the brain about nutritional value; however, the cellular and molecular basis of macronutrient-specific reward circuits is poorly understood. Here, we monitor in vivo calcium dynamics to provide direct evidence of independent vagal sensing pathways for the detection of dietary fats and sugars. Using activity-dependent genetic capture of vagal neurons activated in response to gut infusions of nutrients, we demonstrate the existence of separate gut-brain circuits for fat and sugar sensing that are necessary and sufficient for nutrient-specific reinforcement. Even when controlling for calories, combined activation of fat and sugar circuits increases nigrostriatal dopamine release and overeating compared with fat or sugar alone. This work provides new insights into the complex sensory circuitry that mediates motivated behavior and suggests that a subconscious internal drive to consume obesogenic diets (e.g., those high in both fat and sugar) may impede conscious dieting efforts.

Hindbrain REV-ERB nuclear receptors regulate sensitivity to diet-induced obesity and brown adipose tissue pathophysiology

OBJECTIVE

The dorsal vagal complex (DVC) of the hindbrain is a major point of integration for central and peripheral signals that regulate a wide variety of metabolic functions to maintain energy balance. The REV-ERB nuclear receptors are important modulators of molecular metabolism, but their role in the DVC has yet to be established.

METHODS

Male REV-ERBα/β floxed mice received stereotaxic injections of a Cre expressing virus to the DVC to create the DVC REV-ERBα/β double knockout (DVC RDKO). Control littermates received stereotaxic injections to the DVC of a green fluorescent protein expressing virus. Animals were maintained on a normal chow diet or a 60% high-fat diet to observe the metabolic phenotype arising from DVC RDKO under healthy and metabolically stressed conditions.

RESULTS

DVC RDKO animals on high-fat diet exhibited increased weight gain compared to control animals maintained on the same diet. Increased weight gain in DVC RDKO animals was associated with decreased basal metabolic rate and dampened signature of brown adipose tissue activity. RDKO decreased gene expression of calcitonin receptor in the DVC and tyrosine hydroxylase in the brown adipose tissue.

CONCLUSIONS

These results suggest a previously unappreciated role of REV-ERB nuclear receptors in the DVC for maintaining energy balance and metabolic rate potentially through indirect sympathetic outflow to the brown adipose tissue.

Hepatic Vagal Afferents Convey Clock-Dependent Signals to Regulate Circadian Food Intake

Circadian desynchrony induced by shiftwork or jetlag is detrimental to metabolic health, but how synchronous/desynchronous signals are transmitted among tissues is unknown. Here we report that liver molecular clock dysfunction is signaled to the brain via the hepatic vagal afferent nerve (HVAN), leading to altered food intake patterns that are corrected by ablation of the HVAN. Hepatic branch vagotomy also prevents food intake disruptions induced by high-fat diet feeding and reduces body weight gain. Our findings reveal a previously unrecognized homeostatic feedback signal that relies on synchrony between the liver and the brain to control circadian food intake patterns. This identifies the hepatic vagus nerve as a therapeutic target for obesity in the setting of chrono-disruption.

One Sentence Summary

The hepatic vagal afferent nerve signals internal circadian desynchrony between the brain and liver to induce maladaptive food intake patterns.

Oleocanthal Ameliorates Metabolic and Behavioral Phenotypes in a Mouse Model of Alzheimer's Disease

Aging is a major risk factor for Alzheimer's disease (AD). AD mouse models are frequently used to assess pathology, behavior, and memory in AD research. While the pathological characteristics of AD are well established, our understanding of the changes in the metabolic phenotypes with age and pathology is limited. In this work, we used the Promethion cage systems^® to monitor changes in physiological metabolic and behavioral parameters with age and pathology in wild-type and 5xFAD mouse models. Then, we assessed whether these parameters could be altered by treatment with oleocanthal, a phenolic compound with neuroprotective properties. Findings demonstrated metabolic parameters such as body weight, food and water intake, energy expenditure, dehydration, and respiratory exchange rate, and the behavioral parameters of sleep patterns and anxiety-like behavior are altered by age and pathology. However, the effect of pathology on these parameters was significantly greater than normal aging, which could be linked to amyloid-β deposition and blood-brain barrier (BBB) disruption. In addition, and for the first time, our findings suggest an inverse correlation between sleep hours and BBB breakdown. Treatment with oleocanthal improved the assessed parameters and reduced anxiety-like behavior symptoms and sleep disturbances. In conclusion, aging and AD are associated with metabolism and behavior changes, with the changes being greater with the latter, which were rectified by oleocanthal. In addition, our findings suggest that monitoring changes in metabolic and behavioral phenotypes could provide a valuable tool to assess disease severity and treatment efficacy in AD mouse models.

Role of liquid fructose/sucrose in regulating the hepatic transcriptome in a high-fat Western diet model of NAFLD

Nonalcoholic fatty liver disease (NAFLD), which ranges from simple steatosis to nonalcoholic steatohepatitis (NASH), is the most common chronic liver disease. Yet, the molecular mechanisms for the progression of steatosis to NASH remain largely undiscovered. Thus, there is a need for identifying specific gene and pathway changes that drive the progression of NAFLD. This study uses high-fat Western diet (HFWD) together with liquid sugar [fructose and sucrose (F/S)] feeding for 12 weeks in mice to induce obesity and examine hepatic transcriptomic changes that occur in NAFLD progression. The combination of a HFWD+F/S in the drinking water exacerbated HFWD-induced obesity, hyperinsulinemia, hyperglycemia, hepatic steatosis, inflammation, and human and murine fibrosis gene set enrichment that is consistent with progression to NASH. RNAseq analysis revealed differentially expressed genes (DEGs) associated with HFWD and HFWD+F/S dietary treatments compared to Chow-fed mice. However, liquid sugar consumption resulted in a unique set of hepatic DEGs in HFWD+F/S-fed mice, which were enriched in the complement and coagulation cascades using network and biological analysis. Cluster analysis identified Orosomucoid (ORM) as a HFWD+F/S upregulated complement and coagulation cascades gene that was also upregulated in hepatocytes treated with TNFα or free fatty acids in combination with hypoxia. ORM expression was found to correlate with NAFLD parameters in obese mice. Taken together, this study examined key genes, biological processes, and pathway changes in the liver of HFWD+F/S mice in an effort to provide insight into the molecular basis for which the addition of liquid sugar promotes the progression of NAFLD.

REV-ERB nuclear receptors in the suprachiasmatic nucleus control circadian period and restrict diet-induced obesity

Circadian disruption, as occurs in shift work, is associated with metabolic diseases often attributed to a discordance between internal clocks and environmental timekeepers. REV-ERB nuclear receptors are key components of the molecular clock, but their specific role in the SCN master clock is unknown. We report here that mice lacking circadian REV-ERB nuclear receptors in the SCN maintain free-running locomotor and metabolic rhythms, but these rhythms are notably shortened by 3 hours. When housed under a 24-hour light:dark cycle and fed an obesogenic diet, these mice gained excess weight and accrued more liver fat than controls. These metabolic disturbances were corrected by matching environmental lighting to the shortened endogenous 21-hour clock period, which decreased food consumption. Thus, SCN REV-ERBs are not required for rhythmicity but determine the free-running period length. Moreover, these results support the concept that dissonance between environmental conditions and endogenous time periods causes metabolic disruption.

Integrative Longitudinal Analysis of Metabolic Phenotype and Microbiota Changes During the Development of Obesity

Obesity has increased at an alarming rate over the past two decades in the United States. In addition to increased body mass, obesity is often accompanied by comorbidities such as Type II Diabetes Mellitus and metabolic dysfunction-associated fatty liver disease, with serious impacts on public health. Our understanding of the role the intestinal microbiota in obesity has rapidly advanced in recent years, especially with respect to the bacterial constituents. However, we know little of when changes in these microbial populations occur as obesity develops. Further, we know little about how other domains of the microbiota, namely bacteriophage populations, are affected during the progression of obesity. Our goal in this study was to monitor changes in the intestinal microbiome and metabolic phenotype following western diet feeding. We accomplished this by collecting metabolic data and fecal samples for shotgun metagenomic sequencing in a mouse model of diet-induced obesity. We found that after two weeks of consuming a western diet (WD), the animals weighed significantly more and were less metabolically stable than their chow fed counterparts. The western diet induced rapid changes in the intestinal microbiome with the most pronounced dissimilarity at 12 weeks. Our study highlights the dynamic nature of microbiota composition following WD feeding and puts these events in the context of the metabolic status of the mammalian host.

Doxorubicin induces dysregulation of AMPA receptor and impairs hippocampal synaptic plasticity leading to learning and memory deficits

Doxorubicin (Dox) is a chemotherapeutic agent used widely to treat a variety of malignant cancers. However, Dox chemotherapy is associated with several adverse effects, including "chemobrain," the observation that cancer patients exhibit through learning and memory difficulties extending even beyond treatment. This study investigated the effect of Dox treatment on learning and memory as well as hippocampal synaptic plasticity. Dox-treated mice (5 mg/kg weekly x 5) demonstrated impaired performance in the Y-maze spatial memory task and a significant reduction in hippocampal long-term potentiation. The deficit in synaptic plasticity was mirrored by deficits in the functionality of synaptic `α-amino-3- hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) channels, including reduced probability of opening, decreased dwell open time, and increased closed times. Furthermore, a reduction in the AMPAR subunit GluA1 level, its downstream signaling molecule Ca2+/calmodulin-dependent protein kinase (CaMKII), and brain-derived neurotrophic factor (BDNF) were observed. This was also accompanied by an increase in extracellular signal regulated kinase (ERK) and protein kinase B (AKT) activation. Together these data suggest that Dox-induced cognitive impairments are at least partially due to alterations in the expression and functionality of the glutamatergic AMPAR system.

The Systemic and Cellular Metabolic Phenotype of Infection and Immune Response to Listeria monocytogenes

It is widely accepted that infection and immune response incur significant metabolic demands, yet the respective demands of specific immune responses to live pathogens have not been well delineated. It is also established that upon activation, metabolic pathways undergo shifts at the cellular level. However, most studies exploring these issues at the systemic or cellular level have utilized pathogen associated molecular patterns (PAMPs) that model sepsis, or model antigens at isolated time points. Thus, the dynamics of pathogenesis and immune response to a live infection remain largely undocumented. To better quantitate the metabolic demands induced by infection, we utilized a live pathogenic infection model. Mice infected with Listeria monocytogenes were monitored longitudinally over the course of infection through clearance. We measured systemic metabolic phenotype, bacterial load, innate and adaptive immune responses, and cellular metabolic pathways. To further delineate the role of adaptive immunity in the metabolic phenotype, we utilized two doses of bacteria, one that induced both sickness behavior and protective (T cell mediated) immunity, and the other protective immunity alone. We determined that the greatest impact to systemic metabolism occurred during the early immune response, which coincided with the greatest shift in innate cellular metabolism. In contrast, during the time of maximal T cell expansion, systemic metabolism returned to resting state. Taken together, our findings demonstrate that the timing of maximal metabolic demand overlaps with the innate immune response and that when the adaptive response is maximal, the host has returned to relative metabolic homeostasis.

Whole-slide image analysis outperforms micrograph acquisition for adipocyte size quantification

The distinction between biological processes of adipose tissue expansion is crucial to understanding metabolic derangements, but a robust method for quantifying adipocyte size has yet to be standardized. Here, we compared three methods for histological analysis in situ: one conventional approach using individual micrographs acquired by digital camera, and two with whole-slide image analysis pipelines involving proprietary (Visiopharm) and open-source software (QuPath with a novel ImageJ plugin). We found that micrograph analysis identified 10–40 times fewer adipocytes than whole-slide methods, and this small sample size resulted in high variances that could lead to statistical errors. The agreement of the micrograph method to measure adipocyte area with each of the two whole-slide methods was substantially less (R² of 0.6644 and 0.7125) than between the two whole-slide methods (R² of 0.9402). These inconsistencies were more pronounced in samples from high-fat diet fed mice. While the use of proprietary software resulted in the highest adipocyte count, the lower cost, ease of use, and minimal variances of the open-source software provided a distinct advantage for measuring the number and size of adipocytes. In conclusion, we recommend whole-slide image analysis methods to consistently measure adipocyte area and avoid unintentional errors due to small sample sizes.

Restricted feeding for 9h in the active period partially abrogates the detrimental metabolic effects of a Western diet with liquid sugar consumption in mice

BACKGROUND

Obesity is a major public health concern that can result from diets high in fat and sugar, including sugar sweetened beverages. A proposed treatment for dietary-induced obesity is time-restricted feeding (TRF), which restricts consumption of food to specific times of the 24-hour cycle. Although TRF shows great promise to prevent obesity and the development of chronic disease, the effects of TRF to reverse metabolic changes and the development of NAFLD in animal models of a Western diet with sugary water consumption is not known.

OBJECTIVE

The objective of the current study was to evaluate the role of TRF in the treatment of obesity and NAFLD through examination of changes in metabolic and histopathologic parameters.

METHODS

To better understand the role of TRF in the treatment of obesity and NAFLD, we investigated the metabolic phenotype and NAFLD parameters in a mouse model of NAFLD in which obesity and liver steatosis are induced by a Western Diet (WD): a high-fat diet of lard, milkfat and Crisco with sugary drinking water. Mice were subjected to a short-term (4-weeks) and long-term (10-weeks) TRF in which food was restricted to 9h at night.

RESULTS

Prior to TRF treatment, the WD mice had increased body mass, and exhibited less activity, and higher average daytime energy expenditure (EE) than chow fed mice. Approximately 4- and 10-weeks following TFR treatment, WD-TRF had moderate but not statistically significant weight loss compared to WD-ad libitum (WD-AL) mice. There was a modest but significant reduction in the inguinal adipose tissue weight in both WD-TRF groups compared to the WD-AL groups; however, there was no difference in epididymal and retroperitoneal adipose tissue mass or adipocyte size distribution. In contrast, the diet-induced increase in normalized liver tissue weight, hepatic triglyceride, and NAFLD score was partially abrogated in the 4-week WD-TRF mice, while systemic insulin resistance was partially abrogated and glucose intolerance was completely abrogated in the 10-week WD-TRF mice. Importantly, WD-induced metabolic dysfunction (substrate utilization, energy expenditure, and activity) was partially abrogated by 4- and 10-week TRF.

CONCLUSIONS

Our results support the hypothesis that TRF aids in reducing the detrimental metabolic effects of consuming a WD with sugary drinking water but does not ameliorate obesity.