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Metamorphosis is a transition from growth to reproduction, through which an animal adopts adult behavior and metabolism. Yet the mechanisms underlying the switch is unclear. Here we report that neuronalE93, a transcription factor essential for metamorphosis, regulates the adult metabolism and circadian rhythm inDrosophila melanogaster. WhenE93is specifically knocked down in neurons, the flies become hyperphagic and obese with increased energy stores and disrupted circadian rhythms. A screen of Gal4 lines targeting subsets of neurons and endocrine cells identified neurons producing GABA and myoinhibitory peptide (MIP) as the main sites ofE93action. Knockdown of the ecdysone receptor specifically in MIP neurons partly phenocopies the MIP neuron-specific knockdown ofE93suggesting the steroid signal coordinates adult metabolism viaE93. The circadian disruption caused by neuronal knockdown ofE93is also observed whenE93is knockdown in GABA and MIP neurons. Based on these results we suggest that neuronalE93is a key switch for metabolic transition representing an intersectional node between metabolism and circadian biology.

Cannabinoid 1 receptor (CB1R) inverse agonists reduce body weight and improve several parameters of glucose homeostasis. However, these drugs have also been associated with deleterious side effects. CB1R expression is widespread in the brain and in peripheral tissues, but whether specific sites of expression can mediate the beneficial metabolic effects of CB1R drugs, while avoiding the untoward side effects, remains unclear. Evidence suggests inverse agonists may act on key sites within the central nervous system to improve metabolism. The ventromedial hypothalamus (VMH) is a critical node regulating energy balance and glucose homeostasis. To determine the contributions of CB1Rs expressed in VMH neurons in regulating metabolic homeostasis, we generated mice lacking CB1Rs in the VMH. We found that the deletion of CB1Rs in the VMH did not affect body weight in chow- and high-fat diet-fed male and female mice. We also found that deletion of CB1Rs in the VMH did not alter weight loss responses induced by the CB1R inverse agonist SR141716. However, we did find that CB1Rs of the VMH regulate parameters of glucose homeostasis independent of body weight in diet-induced obese male mice. NEW & NOTEWORTHY Cannabinoid 1 receptors (CB1Rs) regulate metabolic homeostasis, and CB1R inverse agonists reduce body weight and improve parameters of glucose metabolism. However, the cell populations expressing CB1Rs that regulate metabolic homeostasis remain unclear. CB1Rs are highly expressed in the ventromedial hypothalamic nucleus (VMH), which is a crucial node that regulates metabolism. With CRISPR/Cas9, we generated mice lacking CB1Rs specifically in VMH neurons and found that CB1Rs in VMH neurons are essential for the regulation of glucose metabolism independent of body weight regulation.

Visual Abstract, There has been a long-standing debate regarding the role of peripheral afferents in mediating rapid-onset anorexia among other responses elicited by peripheral inflammatory insults. Thus, the current study assessed the sufficiency of peripheral afferents expressing toll-like receptor 4 (TLR4) to the initiation of the anorexia caused by peripheral bacterial lipopolysaccharide (LPS). We generated a Tlr4 null (Tlr4LoxTB) mouse in which Tlr4 expression is globally disrupted by a loxP-flanked transcription blocking (TB) cassette. This novel mouse model allowed us to restore the endogenous TLR4 expression in specific cell types. Using Zp3-Cre and Nav1.8-Cre mice, we produced mice that express TLR4 in all cells (Tlr4LoxTB X Zp3-Cre) and in peripheral afferents (Tlr4LoxTB X Nav1.8-Cre), respectively. We validated the Tlr4LoxTB mice, which were phenotypically identical to previously reported global TLR4 knock-out mice. Contrary to our expectations, the administration of LPS did not cause rapid-onset anorexia in mice with Nav1.8-restricted TLR4. The later result prompted us to identify Tlr4-expressing vagal afferents using in situ hybridization (ISH). In vivo, we found that Tlr4 mRNA was primarily enriched in vagal Nav1.8 afferents located in the jugular ganglion that co-expressed calcitonin gene-related peptide (CGRP). In vitro, the application of LPS to cultured Nav1.8-restricted TLR4 afferents was sufficient to stimulate the release of CGRP. In summary, we demonstrated using a new mouse model that vagally-expressed TLR4 is selectively involved in stimulating the release of CGRP but not in causing anorexia.

Environmental light cycles entrain circadian feeding behaviors in animals that produce rhythms in exposure to foodborne bacteria. Here, we show that the intestinal microbiota generates diurnal rhythms in innate immunity that synchronize with feeding rhythms to anticipate microbial exposure. Rhythmic expression of antimicrobial proteins was driven by daily rhythms in epithelial attachment by segmented filamentous bacteria (SFB), members of the mouse intestinal microbiota. Rhythmic SFB attachment was driven by the circadian clock through control of feeding rhythms. Mechanistically, rhythmic SFB attachment activated an immunological circuit involving group 3 innate lymphoid cells. This circuit triggered oscillations in epithelial STAT3 expression and activation that produced rhythmic antimicrobial protein expression and caused resistance to Salmonella Typhimurium infection to vary across the day-night cycle. Thus, host feeding rhythms synchronize with the microbiota to promote rhythms in intestinal innate immunity that anticipate exogenous microbial exposure.

Atypical antipsychotics such as olanzapine often induce excessive weight gain and type 2 diabetes. However, the mechanisms underlying these drug-induced metabolic perturbations remain poorly understood. Here, we used an experimental model that reproduces olanzapine-induced hyperphagia and obesity in female C57BL/6 mice. We found that olanzapine treatment acutely increased food intake, impaired glucose tolerance, and altered physical activity and energy expenditure in mice. Furthermore, olanzapine-induced hyperphagia and weight gain were blunted in mice lacking the serotonin 2C receptor (HTR2C). Finally, we showed that treatment with the HTR2C-specific agonist lorcaserin suppressed olanzapine-induced hyperphagia and weight gain. Lorcaserin treatment also improved glucose tolerance in olanzapine-fed mice. Collectively, our studies suggest that olanzapine exerts some of its untoward metabolic effects via antagonism of HTR2C.

Objective The sympathetic nervous system (SNS) is a key regulator of the metabolic and endocrine functions of adipose tissue. Increased SNS outflow promotes fat mobilization, stimulates non-shivering thermogenesis, promotes browning, and inhibits leptin production. Most of these effects are attributed to norepinephrine activation of the Gs-coupled beta adrenergic receptors located on the surface of the adipocytes. Evidence suggests that other adrenergic receptor subtypes, including the Gi-coupled alpha 2 adrenergic receptors might also mediate the SNS effects on adipose tissue. However, the impact of acute stimulation of adipocyte Gs and Gi has never been reported. Methods We harness the power of chemogenetics to develop unique mouse models allowing the specific and spatiotemporal stimulation of adipose tissue Gi and Gs signaling. We evaluated the impact of chemogenetic stimulation of these pathways on glucose homeostasis, lipolysis, leptin production, and gene expression. Results Stimulation of Gs signaling in adipocytes induced rapid and sustained hypoglycemia. These hypoglycemic effects were secondary to increased insulin release, likely consequent to increased lipolysis. Notably, we also observed differences in gene regulation and ex vivo lipolysis in different adipose depots. In contrast, acute stimulation of Gi signaling in adipose tissue did not affect glucose metabolism or lipolysis, but regulated leptin production. Conclusion Our data highlight the significance of adipose Gs signaling in regulating systemic glucose homeostasis. We also found previously unappreciated heterogeneity across adipose depots following acute stimulation. Together, these results highlight the complex interactions of GPCR signaling in adipose tissue and demonstrate the usefulness of chemogenetic technology to better understand adipocyte function., Highlights • Chemogenetic stimulation of Gs signaling in adipose tissue potently induces hypoglycemia in mice. • The magnitude by which adipose Gs stimulation reduces blood glucose is similar to the hypoglycemic effects of insulin. • Chemogenetic stimulation of Gs signaling in adipose tissue ex vivo stimulates lipolysis. • Chemogenetic stimulation of adipose Gi signaling does not affect glycemia or lipolysis, but increases leptin levels. • Our data demonstrate the usefulness of chemogenetic technology to understand adipocytes functions.

Phosphoinositide 3-kinase (PI3K) signaling in hypothalamic neurons integrates peripheral metabolic cues, including leptin and insulin, to coordinate systemic glucose and energy homeostasis. PI3K is composed of different subunits, each of which has several unique isoforms. However, the role of the PI3K subunits and isoforms in the ventromedial hypothalamus (VMH), a prominent site for the regulation of glucose and energy homeostasis, is unclear. Here we investigated the role of subunit p110β in steroidogenic factor-1 (SF-1) neurons of the VMH in the regulation of metabolism. Our data demonstrate that the deletion of p110β in SF-1 neurons disrupts glucose metabolism, rendering the mice insulin resistant. In addition, the deletion of p110β in SF-1 neurons leads to the whitening of brown adipose tissues and increased susceptibility to diet-induced obesity due to blunted energy expenditure. These results highlight a critical role for p110β in the regulation of glucose and energy homeostasis via VMH neurons., Metabolism: Enzymatic subunit essential to brain’s glucose responses A particular subunit of a critical signaling enzyme is needed for neurons inside the brain’s hypothalamus to properly regulate energy metabolism. Ki Woo Kim from Yonsei University College of Dentistry, Seoul, South Korea, and colleagues explored the role that the PI3K enzyme plays in neurons of the ventromedial area toward the front of the hypothalamus, a region involved in regulating hunger and metabolism. Deleting a subunit of PI3K called p110β, which is needed for enzymatic function, made mice less responsive to insulin, the hormone that keeps blood sugar levels at healthy levels. As well as having abnormal glucose metabolism, the mice converted more brown fat, which burns energy, into white fat, which stores energy. They were also more susceptible to diet-induced obesity. The findings point toward p110β as a potential drug target for treating diabetes.

Sustained oliguria during fluid resuscitation represents a perplexing problem in patients undergoing therapy for septic acute kidney injury. Here, we tested whether lipopolysaccharide induces filtrate leakage from the proximal tubular lumen into the interstitium, thus disturbing the recovery of urine output during therapy, such as fluid resuscitation, aiming to restore the glomerular filtration rate. Intravital imaging of the tubular flow rate in the proximal tubules in mice showed that lipopolysaccharide did not change the inflow rate of proximal tubule filtrate, reflecting an unchanged glomerular filtration rate, but significantly reduced the outflow rate, resulting in oliguria. Lipopolysaccharide disrupted tight junctions in proximal tubules and induced both paracellular leakage of filtered molecules and interstitial accumulation of extracellular fluid. These changes were diminished by conditional knockout of Toll-like receptor 4 in the proximal tubules. Importantly, these conditional knockout mice showed increased sensitivity to fluid resuscitation and attenuated acute kidney injury. Thus, lipopolysaccharide induced paracellular leakage of filtrate into the interstitium via a Toll-like receptor 4-dependent mechanism in the proximal tubules of endotoxemic mice. Hence, this leakage might diminish the efficacy of fluid resuscitation aiming to maintain renal hemodynamics and glomerular filtration rate. publishedVersion

Leptin is critical for energy balance, glucose homeostasis, and for metabolic and neuroendocrine adaptations to starvation. A prevalent model predicts that leptin’s actions are mediated through pro-opiomelanocortin (POMC) neurons that express leptin receptors (LEPRs). However, previous studies have used prenatal genetic manipulations, which may be subject to developmental compensation. Here, we tested the direct contribution of POMC neurons expressing LEPRs in regulating energy balance, glucose homeostasis and leptin secretion during fasting using a spatiotemporally controlledLeprexpression mouse model. We report a dissociation between leptin’s effects on glucose homeostasis versus energy balance in POMC neurons. We show that these neurons are dispensable for regulating food intake, but are required for coordinating hepatic glucose production and for the fasting-induced fall in leptin levels, independent of changes in fat mass. We also identify a role for sympathetic nervous system regulation of the inhibitory adrenergic receptor (ADRA2A) in regulating leptin production. Collectively, our findings highlight a previously unrecognized role of POMC neurons in regulating leptin levels.

Interactions between the brain and distinct adipose depots have a key role in maintaining energy balance, thereby promoting survival in response to metabolic challenges such as cold exposure and starvation. Recently, there has been renewed interest in the specific central neuronal circuits that regulate adipose depots. Here, we review anatomical, genetic and pharmacological studies on the neural regulation of adipose function, including lipolysis, non-shivering thermogenesis, browning and leptin secretion. In particular, we emphasize the role of leptin-sensitive neurons and the sympathetic nervous system in modulating the activity of brown, white and beige adipose tissues. We provide an overview of advances in the understanding of the heterogeneity of the brain regulation of adipose tissues and offer a perspective on the challenges and paradoxes that the community is facing regarding the actions of leptin on this system.

Objective Recent studies have suggested a critical role for toll-like receptor 4 (TLR4) in the development of alcoholic liver disease. As TLR4 is widely expressed throughout the body, it is unclear which TLR4-expressing cell types contribute to alcohol-induced liver damage. Methods We selectively ablated TLR4 in hepatocytes and myeloid cells. Male mice were fed a liquid diet containing either 5% alcohol or pair-fed a control diet for 4 weeks to examine chronic alcohol intake-induced liver damage and inflammation. In addition, mice were administered a single oral gavage of alcohol to investigate acute alcohol drinking-associated liver injury. Results We found that selective hepatocyte TLR4 deletion protected mice from chronic alcohol-induced liver injury and fatty liver. This result was in part due to decreased expression of endogenous lipogenic genes and enhanced expression of genes involved in fatty acid oxidation. In addition, mice lacking hepatocyte TLR4 exhibited reduced mRNA expression of inflammatory genes in white adipose tissue. Furthermore, in an acute alcohol binge model, hepatocyte TLR4 deficient mice had significantly decreased plasma alanine transaminase (ALT) levels and attenuated hepatic triglyceride content compared to their alcohol-gavaged control mice. In contrast, deleting TLR4 in myeloid cells did not affect the development of chronic-alcohol induced fatty liver, despite the finding that mice lacking myeloid cell TLR4 had significantly reduced circulating ALT concentrations. Conclusions These findings suggest that hepatocyte TLR4 plays an important role in regulating alcohol-induced liver damage and fatty liver disease., Highlights • Hepatocyte TLR4 ablated mice were protected from both chronic and acute alcohol-induced hepatic triglyceride accumulation. • Hepatocyte TLR4 ablated mice showed attenuated inflammation in the fat pad and the circulation after chronic alcohol intake. • Loss of TLR4 in myeloid cells did not affect alcohol-induced development of fatty liver.

Our modern lifestyle is characterised by easy access to nutrient dense foods combined with limited physical activity. A sedentary lifestyle is one of several factors that have contributed to the global obesity epidemic and it also predisposes to chronic illnesses such as diabetes and cardiovascular disease. Although many studies have focused on the benefits of exercise in peripheral tissues, the contributions of the central nervous system to these exercise-induced metabolic adaptations are relatively unknown. The present review highlights the role of the ventromedial hypothalamus in regulating the metabolic response to exercise.

Objective and methods Metabolic viscera and their vasculature are richly innervated by peripheral sensory neurons. Here, we examined the metabolic and inflammatory profiles of mice with selective ablation of all Nav1.8-expressing primary afferent neurons. Results While mice lacking sensory neurons displayed no differences in body weight, food intake, energy expenditure, or body composition compared to controls on chow diet, ablated mice developed an exaggerated inflammatory response to high-fat feeding characterized by bouts of weight loss, splenomegaly, elevated circulating interleukin-6 and hepatic serum amyloid A expression. This phenotype appeared to be directly mediated by the ingestion of saturated lipids. Conclusions These data demonstrate that the Nav1.8-expressing afferent neurons are not essential for energy balance but are required for limiting the acute phase response caused by an obesogenic diet., Graphical abstract Image 1, Highlights • Peripheral afferents are dispensable to the regulation of energy balance. • Mice lacking peripheral afferents are intolerant to high-fat diet. • Saturated fat produces an exaggerated acute phase response in mice lacking peripheral afferents.

Steroidogenic factor 1 (SF-1) is a transcription factor expressed in the ventral medial nucleus of the hypothalamus that regulates energy homeostasis. However, the molecular mechanisms of SF-1 in the control of energy balance are largely unknown. Here, we show that nutritional conditions, such as the presence or absence of serum, affect SF-1 action. Serum starvation significantly decreased hypothalamic SF-1 levels by promoting ubiquitin-dependent degradation and sumoylation was required for this process. SF-1 transcriptional activity was also differentially regulated by nutritional status. Under normal conditions, the transcriptional activity of hypothalamic SF-1 was activated by SUMO, but this was attenuated during starvation. Taken together, these results indicate that sumoylation and ubiquitination play crucial roles in the regulation of SF-1 function and that these effects are dependent on nutritional conditions, further supporting the importance of SF-1 in the control of energy homeostasis.

Peroxisome proliferator-activated receptor gamma (PPARg) is a ligand-activated transcription factor that was originally identified as a regulator of peroxisome proliferation and adipocyte differentiation. Emerging evidence suggests that functional PPARg signaling also occurs within the hypothalamus. However, the exact distribution and identities of PPARg-expressing hypothalamic cells remains under debate. The present study systematically mapped PPARg mRNA expression in the adult mouse brain using in situ hybridization histochemistry. PPARg mRNA was found to be expressed at high levels outside the hypothalamus including the neocortex, the olfactory bulb, the organ of the vasculosum of the lamina terminalis, and the subfornical organ. Within the hypothalamus, PPARg was present at moderate levels in the suprachiasmatic nucleus and the ependymal of the 3rd ventricle. In all examined feeding-related hypothalamic nuclei, PPARg was expressed at very low levels that were close to the limit of detection. Using qPCR techniques, we demonstrated that PPARg mRNA expression was upregulated in the suprachiasmatic nucleus in response to fasting. Double in situ hybridization further demonstrated that PPARg was primarily expressed in neurons. Collectively, our observations provide a comprehensive map of PPARg distribution and regulation in the intact adult mouse hypothalamus.

Peripheral neural sensory mechanisms play a crucial role in metabolic regulation but less is known about the mechanisms underlying vagal sensing itself. Recently, we identified an enrichment of liver X receptor alpha and beta (LXRα/β) in the nodose ganglia of the vagus nerve. In this study, we show mice lacking LXRα/β in peripheral sensory neurons have increased energy expenditure and weight loss when fed a Western diet (WD). Our findings suggest that the ability to metabolize and sense cholesterol and/or fatty acids in peripheral neurons is an important requirement for physiological adaptations to WDs. DOI: http://dx.doi.org/10.7554/eLife.06667.001, eLife digest The vagus nerves run from the brainstem to the heart and the digestive system and help to control several processes including digestion and heart rate. Because of their role in regulating food intake, these nerves are attractive targets for scientists hoping to develop treatments for obesity. There are two types of fat tissue found in mammals: white fat, which is used as an energy store and makes up most of the extra fat seen in obese individuals; and brown fat, which can generate body heat. The vagus nerves monitor fat and cholesterol levels in the body via receptor proteins that respond to messages sent from the fat tissues and the liver. Previous research unexpectedly found that mice genetically engineered to lack these receptor proteins—called LXRα and LXRβ—do not become obese even when fed a high-fat, high-cholesterol diet that would make normal mice gain excessive weight. Mansuy-Aubert et al. have now investigated in more detail why mice without these receptor proteins are resistant to obesity. When fed a high-fat, high-cholesterol diet, mice that lacked the LXRα and LXRβ receptors in sensory neurons had higher cholesterol levels in their nerve cells than normal mice on the same diet. Mice lacking these receptors also burned more energy and gained less weight than normal mice. Next, Mansuy-Aubert et al. examined fat tissue from both types of mice. This revealed that the heat-generating brown fat was more active in mice lacking the LXRα and LXRβ receptors. Some of the white fat in these mice had also become more like brown fat, allowing the mice to burn more energy and so gain less weight. In many Western countries, many people also eat a diet that is high in fat and cholesterol. This raises the possibility that drugs that block the LXRα and LXRβ receptors in sensory neurons in humans could help to treat or prevent obesity, although further work will be needed to investigate this. DOI: http://dx.doi.org/10.7554/eLife.06667.002