High-calorie diets uncouple hypothalamic oxytocin neurons from a gut-to-brain satiation pathway via κ-opioid signaling.

Oxytocin-expressing paraventricular hypothalamic neurons (PVNOT neurons) integrate afferent signals from the gut, including cholecystokinin (CCK), to adjust whole-body energy homeostasis. However, the molecular underpinnings by which PVNOT neurons orchestrate gut-to-brain feeding control remain unclear. Here, we show that mice undergoing selective ablation of PVNOT neurons fail to reduce food intake in response to CCK and develop hyperphagic obesity on a chow diet. Notably, exposing wild-type mice to a high-fat/high-sugar (HFHS) diet recapitulates this insensitivity toward CCK, which is linked to diet-induced transcriptional and electrophysiological aberrations specifically in PVNOT neurons. Restoring OT pathways in diet-induced obese (DIO) mice via chemogenetics or polypharmacology sufficiently re-establishes CCK's anorexigenic effects. Last, by single-cell profiling, we identify a specialized PVNOT neuronal subpopulation with increased κ-opioid signaling under an HFHS diet, which restrains their CCK-evoked activation. In sum, we document a (patho)mechanism by which PVNOT signaling uncouples a gut-brain satiation pathway under obesogenic conditions.

The obesity-linked human lncRNA AATBC stimulates mitochondrial function in adipocytes.

Adipocytes are critical regulators of metabolism and energy balance. While white adipocyte dysfunction is a hallmark of obesity-associated disorders, thermogenic adipocytes are linked to cardiometabolic health. As adipocytes dynamically adapt to environmental cues by functionally switching between white and thermogenic phenotypes, a molecular understanding of this plasticity could help improving metabolism. Here, we show that the lncRNA Apoptosis associated transcript in bladder cancer (AATBC) is a human-specific regulator of adipocyte plasticity. Comparing transcriptional profiles of human adipose tissues and cultured adipocytes we discovered that AATBC was enriched in thermogenic conditions. Using primary and immortalized human adipocytes we found that AATBC enhanced the thermogenic phenotype, which was linked to increased respiration and a more fragmented mitochondrial network. Expression of AATBC in adipose tissue of mice led to lower plasma leptin levels. Interestingly, this association was also present in human subjects, as AATBC in adipose tissue was inversely correlated with plasma leptin levels, BMI, and other measures of metabolic health. In conclusion, AATBC is a novel obesity-linked regulator of adipocyte plasticity and mitochondrial function in humans.

Estradiol regulates leptin sensitivity to control feeding via hypothalamic Cited1.

Until menopause, women have a lower propensity to develop metabolic diseases than men, suggestive of a protective role for sex hormones. Although a functional synergy between central actions of estrogens and leptin has been demonstrated to protect against metabolic disturbances, the underlying cellular and molecular mechanisms mediating this crosstalk have remained elusive. By using a series of embryonic, adult-onset, and tissue/cell-specific loss-of-function mouse models, we document an unprecedented role of hypothalamic Cbp/P300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 1 (Cited1) in mediating estradiol (E2)-dependent leptin actions that control feeding specifically in pro-opiomelanocortin (Pomc) neurons. We reveal that within arcuate Pomc neurons, Cited1 drives leptin's anorectic effects by acting as a co-factor converging E2 and leptin signaling via direct Cited1-ERα-Stat3 interactions. Together, these results provide new insights on how melanocortin neurons integrate endocrine inputs from gonadal and adipose axes via Cited1, thereby contributing to the sexual dimorphism in diet-induced obesity.

Diet triggers specific responses of hypothalamic astrocytes in time and region dependent manner.

Hypothalamic astrocytes are particularly affected by energy-dense food consumption. How the anatomical location of these glial cells and their spatial molecular distribution in the arcuate nucleus of the hypothalamus (ARC) determine the cellular response to a high caloric diet remains unclear. In this study, we investigated their distinctive molecular responses following exposure to a high-fat high-sugar (HFHS) diet, specifically in the ARC. Using RNA sequencing and proteomics, we showed that astrocytes have a distinct transcriptomic and proteomic profile dependent on their anatomical location, with a major proteomic reprogramming in hypothalamic astrocytes. By ARC single-cell sequencing, we observed that a HFHS diet dictates time- and cell- specific transcriptomic responses, revealing that astrocytes have the most distinct regulatory pattern compared to other cell types. Lastly, we topographically and molecularly characterized astrocytes expressing glial fibrillary acidic protein and/or aldehyde dehydrogenase 1 family member L1 in the ARC, of which the abundance was significantly increased, as well as the alteration in their spatial and molecular profiles, with a HFHS diet. Together, our results provide a detailed multi-omics view on the spatial and temporal changes of astrocytes particularly in the ARC during different time points of adaptation to a high calorie diet.

Exploring the Mechanisms of Recovery in Anorexia Nervosa through a Translational Approach: From Original Ecological Measurements in Human to Brain Tissue Analyses in Mice.

Anorexia nervosa (AN) is a severe eating disorder where caloric restriction, excessive physical activity and metabolic alterations lead to life-threatening situations. Despite weight restoration after treatment, a significant part of patients experience relapses. In this translational study, we combined clinical and preclinical approaches. We describe preliminary data about the effect of weight gain on the symptomatology of patients suffering from acute AN (n = 225) and partially recovered (n = 41). We measured more precisely physical activity with continuous cardiac monitoring in a sub-group (n = 68). Using a mouse model, we investigated whether a long-term food restriction followed by nutritional recovery associated or not with physical activity may differentially impact peripheral and central homeostatic regulation. We assessed the plasma concentration of acyl ghrelin, desacyl ghrelin and leptin and the mRNA expression of hypothalamic neuropeptides and their receptors. Our data show an effect of undernutrition history on the level of physical activity in AN. The preclinical model supports an important role of physical activity in the recovery process and points out the leptin system as one factor that can drive a reliable restoration of metabolic variables through the hypothalamic regulation of neuropeptides involved in feeding behavior.

Obesity-associated hyperleptinemia alters the gliovascular interface of the hypothalamus to promote hypertension.

Pathologies of the micro- and macrovascular systems are a hallmark of the metabolic syndrome, which can lead to chronically elevated blood pressure. However, the underlying pathomechanisms involved still need to be clarified. Here, we report that an obesity-associated increase in serum leptin triggers the select expansion of the micro-angioarchitecture in pre-autonomic brain centers that regulate hemodynamic homeostasis. By using a series of cell- and region-specific loss- and gain-of-function models, we show that this pathophysiological process depends on hypothalamic astroglial hypoxia-inducible factor 1α-vascular endothelial growth factor (HIF1α-VEGF) signaling downstream of leptin signaling. Importantly, several distinct models of HIF1α-VEGF pathway disruption in astrocytes are protected not only from obesity-induced hypothalamic angiopathy but also from sympathetic hyperactivity or arterial hypertension. These results suggest that hyperleptinemia promotes obesity-induced hypertension via a HIF1α-VEGF signaling cascade in hypothalamic astrocytes while establishing a novel mechanistic link that connects hypothalamic micro-angioarchitecture with control over systemic blood pressure.

Dietary fat exacerbates postprandial hypothalamic inflammation involving glial fibrillary acidic protein-positive cells and microglia in male mice.

In humans, obesity is associated with brain inflammation, glial reactivity, and immune cells infiltration. Studies in rodents have shown that glial reactivity occurs within 24 hr of high-fat diet (HFD) consumption, long before obesity development, and takes place mainly in the hypothalamus (HT), a crucial brain structure for controlling body weight. Here, we sought to characterize the postprandial HT inflammatory response to 1, 3, and 6 hr of exposure to either a standard diet (SD) or HFD. HFD exposure increased gene expression of astrocyte and microglial markers (glial fibrillary acidic protein [GFAP] and Iba1, respectively) compared to SD-treated mice and induced morphological modifications of microglial cells in HT. This remodeling was associated with higher expression of inflammatory genes and differential regulation of hypothalamic neuropeptides involved in energy balance regulation. DREADD and PLX5622 technologies, used to modulate GFAP-positive or microglial cells activity, respectively, showed that both glial cell types are involved in hypothalamic postprandial inflammation, with their own specific kinetics and reactiveness to ingested foods. Thus, recurrent exacerbated postprandial inflammation in the brain might promote obesity and needs to be characterized to address this worldwide crisis.

Functional identity of hypothalamic melanocortin neurons depends on Tbx3.

Heterogeneous populations of hypothalamic neurons orchestrate energy balance via the release of specific signatures of neuropeptides. However, how specific intracellular machinery controls peptidergic identities and function of individual hypothalamic neurons remains largely unknown. The transcription factor T-box 3 (Tbx3) is expressed in hypothalamic neurons sensing and governing energy status, whereas human TBX3 haploinsufficiency has been linked with obesity. Here, we demonstrate that loss of Tbx3 function in hypothalamic neurons causes weight gain and other metabolic disturbances by disrupting both the peptidergic identity and plasticity of Pomc/Cart and Agrp/Npy neurons. These alterations are observed after loss of Tbx3 in both immature hypothalamic neurons and terminally differentiated mouse neurons. We further establish the importance of Tbx3 for body weight regulation in Drosophila melanogaster and show that TBX3 is implicated in the differentiation of human embryonic stem cells into hypothalamic Pomc neurons. Our data indicate that Tbx3 directs the terminal specification of neurons as functional components of the melanocortin system and is required for maintaining their peptidergic identity. In summary, we report the discovery of a key mechanistic process underlying the functional heterogeneity of hypothalamic neurons governing body weight and systemic metabolism.

Hypothalamic Inflammation and Energy Balance Disruptions: Spotlight on Chemokines.

The hypothalamus is a key brain region in the regulation of energy balance as it controls food intake and both energy storage and expenditure through integration of humoral, neural, and nutrient-related signals and cues. Many years of research have focused on the regulation of energy balance by hypothalamic neurons, but the most recent findings suggest that neurons and glial cells, such as microglia and astrocytes, in the hypothalamus actually orchestrate together several metabolic functions. Because glial cells have been described as mediators of inflammatory processes in the brain, the existence of a causal link between hypothalamic inflammation and the deregulations of feeding behavior, leading to involuntary weight loss or obesity for example, has been suggested. Several inflammatory pathways that could impair the hypothalamic control of energy balance have been studied over the years such as, among others, toll-like receptors and canonical cytokines. Yet, less studied so far, chemokines also represent interesting candidates that could link the aforementioned pathways and the activity of hypothalamic neurons. Indeed, chemokines, in addition to their role in attracting immune cells to the inflamed site, have been suggested to be capable of neuromodulation. Thus, they could disrupt cellular activity together with synthesis and/or secretion of multiple neurotransmitters/mediators involved in the maintenance of energy balance. This review discusses the different inflammatory pathways that have been identified so far in the hypothalamus in the context of feeding behavior and body weight control impairments, with a particular focus on chemokines signaling that opens a new avenue in the understanding of the major role played by inflammation in obesity.

Long-Term Energy Deficit in Mice Causes Long-Lasting Hypothalamic Alterations after Recovery.

Although the short-term effects of fasting or energy deficit on hypothalamic neuropeptide circuitries are now better understood, the effects of long-term energy deficit and refeeding remain to be elucidated. We showed that after a long-term energy deficit, mice exhibited persistent hypoleptinemia following the refeeding period despite restoration of fat mass, ovarian activity, and feeding behavior. We aimed to examine the hypothalamic adaptations after 10 weeks of energy deficit and after 10 further weeks of nutritional recovery. To do so, we assessed the mRNA levels of the leptin receptor and the main orexigenic and anorexigenic peptides, and their receptors regulated by leptin. Markers of hypothalamic inflammation were assessed as leptin can also participate in this phenomenon. Long-term time-restricted feeding and separation induced significant increase in mRNA levels of hypothalamic orexigenic peptides, while both Y1 and Y5 receptor mRNAs were downregulated. No changes occurred in the mRNA levels of orexin (OX), melanin-concentrating hormone, pro-opiomelanocortin, 26RFa (26-amino acid RF-amide peptide), and their receptors despite an increase in the expression of melanocortin receptors (MC3-R and MC4-R) and OXR1 (OX receptor 1). The refeeding period induced an overexpression of leptin receptor mRNA in the hypothalamus. The other assessed mRNA levels were normalized except for Y2, Y5, MC3-R, and MC4-R, which remained upregulated. No convincing changes were observed in neuroinflammatory markers, even if interleukin-1ß mRNA levels were increased in parallel with those of Iba1 (ionized calcium-binding adaptor molecule 1), a marker of microglial activation. Normalization of leptin-regulated functions and hypothalamic gene expressions in refed mice with low plasma leptin levels could be sustained by recalibration of hypothalamic sensitivity to leptin.

Central CCL2 signaling onto MCH neurons mediates metabolic and behavioral adaptation to inflammation.

Sickness behavior defines the endocrine, autonomic, behavioral, and metabolic responses associated with infection. While inflammatory responses were suggested to be instrumental in the loss of appetite and body weight, the molecular underpinning remains unknown. Here, we show that systemic or central lipopolysaccharide (LPS) injection results in specific hypothalamic changes characterized by a precocious increase in the chemokine ligand 2 (CCL2) followed by an increase in pro-inflammatory cytokines and a decrease in the orexigenic neuropeptide melanin-concentrating hormone (MCH). We therefore hypothesized that CCL2 could be the central relay for the loss in body weight induced by the inflammatory signal LPS. We find that central delivery of CCL2 promotes neuroinflammation and the decrease in MCH and body weight. MCH neurons express CCL2 receptor and respond to CCL2 by decreasing both electrical activity and MCH release. Pharmacological or genetic inhibition of CCL2 signaling opposes the response to LPS at both molecular and physiologic levels. We conclude that CCL2 signaling onto MCH neurons represents a core mechanism that relays peripheral inflammation to sickness behavior.

Astrocytic Insulin Signaling Couples Brain Glucose Uptake with Nutrient Availability.

We report that astrocytic insulin signaling co-regulates hypothalamic glucose sensing and systemic glucose metabolism. Postnatal ablation of insulin receptors (IRs) in glial fibrillary acidic protein (GFAP)-expressing cells affects hypothalamic astrocyte morphology, mitochondrial function, and circuit connectivity. Accordingly, astrocytic IR ablation reduces glucose-induced activation of hypothalamic pro-opio-melanocortin (POMC) neurons and impairs physiological responses to changes in glucose availability. Hypothalamus-specific knockout of astrocytic IRs, as well as postnatal ablation by targeting glutamate aspartate transporter (GLAST)-expressing cells, replicates such alterations. A normal response to altering directly CNS glucose levels in mice lacking astrocytic IRs indicates a role in glucose transport across the blood-brain barrier (BBB). This was confirmed in vivo in GFAP-IR KO mice by using positron emission tomography and glucose monitoring in cerebral spinal fluid. We conclude that insulin signaling in hypothalamic astrocytes co-controls CNS glucose sensing and systemic glucose metabolism via regulation of glucose uptake across the BBB.

[Hypothalamic inflammation and energy balance deregulations: focus on chemokines.] / Inflammation hypothalamique et dérégulations de la balance énergétique : focus sur les chimiokines.

The hypothalamus is a key brain region in the regulation of energy balance. It especially controls food intake and both energy storage and expenditure through integration of humoral, neural and nutrient-related signals and cues. Hypothalamic neurons and glial cells act jointly to orchestrate, both spatially and temporally, regulated metabolic functions of the hypothalamus. Thus, the existence of a causal link between hypothalamic inflammation and deregulations of feeding behavior, such as involuntary weight-loss or obesity, has been suggested. Among the inflammatory mediators that could induce deregulations of hypothalamic control of the energy balance, chemokines represent interesting candidates. Indeed, chemokines, primarily known for their chemoattractant role of immune cells to the inflamed site, have also been suggested capable of neuromodulation. Thus, chemokines could disrupt cellular activity together with synthesis and/or secretion of multiple neurotransmitters/mediators that are involved in the maintenance of energy balance. Here, we relate, on one hand, recent results showing the primary role of the central chemokinergic signaling CCL2/CCR2 for metabolic and behavioral adaptation to high-grade inflammation, especially loss of appetite and weight, through its activity on hypothalamic neurons producing the orexigenic peptide Melanin-Concentrating Hormone (MCH) and, on the other hand, results that suggest that chemokines could also deregulate hypothalamic neuropeptidergic circuits to induce an opposite phenotype and eventually participate in the onset/development of obesity. In more details, we will emphasize a study recently showing, in a model of high-grade acute inflammation of LPS injection in mice, that central CCL2/CCR2 signaling is of primary importance for several aspects explaining weight loss associated with inflammation: after LPS injection, animals lose weight, reduce their food intake, increase their fat oxidation (thus energy consumption from fat storage)...These inflammation-induced metabolic and behavioral changes are reduced when central CCR2 signaling is disrupted either pharmacologically (by a specific inhibitor of CCR2) or genetically (in mice deficient for CCR2). This underlines the importance of this signaling in inflammation-related weight loss. We further determined that the LPS-induced and CCR2-mediated weight loss depends on the direct effect of CCR2 activation on MCH neurons activity. Indeed, the MCH neurons express CCR2, and the application of CCL2 on brain slices revealed that activation of CCR2 actually depolarizes MCH neurons and induces delays and/or failures of action potential emission. Furthermore, CCL2 is able to reduce KCl-evoked MCH secretion from hypothalamic explants. Taken together, these results demonstrate the role of the central CCL2/CCR2 signaling in metabolic and behavioral adaptation to inflammation. On the other hand, this first description of how the chemokinergic system can actually modulate the activity of the hypothalamic regulation of energy balance, but also some less advanced studies and some unpublished data, suggest that some other chemokines, such as CCL5, could participate in the development of the opposite phenotype, that is to say obesity.

The complex contribution of chemokines to neuroinflammation: switching from beneficial to detrimental effects.

Inflammation is an innate mechanism that defends organisms against harmful stimuli. Inflammation leads to the production and secretion of proinflammatory mediators that activate and recruit immune cells to damaged tissues, including the brain, to resolve the cause of inflammation. In the central nervous system, inflammation is referred to as neuroinflammation, which occurs in various pathological conditions of the brain. The primary role of neuroinflammation is to protect the brain. However, prolonged and/or inappropriate inflammation can be harmful for the brain, from individual cells to the whole tissue. This review focuses on a particular type of inflammatory mediator, chemokines, and describes their complex effects both under physiological and pathophysiological conditions of the brain. The clinical relevance of the multiple characters of chemokines is highlighted with respect to acute and chronic inflammation of the brain, including their actions in stroke and Alzheimer's disease, respectively.

Effects of sleeve gastrectomy in high fat diet-induced obese mice: respective role of reduced caloric intake, white adipose tissue inflammation and changes in adipose tissue and ectopic fat depots.

BACKGROUND: Sleeve gastrectomy (SG) has become a popular bariatric procedure. The mechanisms responsible for weight loss and improvement of metabolic disturbances have still not been completely elucidated. We investigated the effect of SG on body weight, adipose tissue depots, glucose tolerance, and liver steatosis independent of reduced caloric intake in high-fat-diet-induced obese mice. METHODS: C57BI/6 J mice fed a high fat diet (45 %) for 33 weeks were divided into three groups: sleeve gastrectomy (SG, 13 mice), sham-operated ad libitum fed (SALF, 13 mice) and sham-operated pair fed (PFS, 13 mice). The animals were humanely killed 23 days after surgery. RESULTS: In SG mice, food intake was reduced transiently, but weight loss was significant and persistent compared to controls (SG vs. PFS, P < 0.05; PFS vs. SALF, P < 0.05). SG mice showed improved glucose tolerance and lower levels of liver steatosis compared with controls (area under the curve, SG vs. PFS, P < 0.01; PFS vs. SALF, P < 0.05) (liver steatosis, SG vs. PFS, P < 0.05; PFS vs. SALF, P < 0.01). This was associated with a decrease in the ratios of the weight of pancreas, epididymal and inguinal adipose tissues to body weight, and an increase in the ratio of brown adipose tissue weight to body weight. Epididymal adipose tissue was also infiltrated by fewer activated T cells and by more anti-inflammatory regulatory T cells. Serum levels of fasting acyl ghrelin were still significantly decreased 3 weeks after surgery in SG mice compared to PFS mice (P < 0.05). CONCLUSIONS: Reduced white adipose tissue inflammation, modification of adipose tissue development (brown vs. white adipose tissue), and ectopic fat are potential mechanisms that may account for the reduced caloric intake independent effects of SG.

The ß-secretase-derived C-terminal fragment of ßAPP, C99, but not Aß, is a key contributor to early intraneuronal lesions in triple-transgenic mouse hippocampus.

Triple-transgenic mice (3xTgAD) overexpressing Swedish-mutated ß-amyloid precursor protein (ßAPP(swe)), P310L-Tau (Tau(P301L)), and physiological levels of M146V-presenilin-1 (PS1(M146V)) display extracellular amyloid-ß peptides (Aß) deposits and Tau tangles. More disputed is the observation that these mice accumulate intraneuronal Aß that has been linked to synaptic dysfunction and cognitive deficits. Here, we provide immunohistological, genetic, and pharmacological evidences for early, age-dependent, and hippocampus-specific accumulation of the ß-secretase-derived ßAPP fragment C99 that is observed from 3 months of age and enhanced by pharmacological blockade of γ-secretase. Notably, intracellular Aß is only detectable several months later and appears, as is the case of C99, in enlarged cathepsin B-positive structures, while extracellular Aß deposits are detected ~12 months of age and beyond. Early C99 production occurs mainly in the CA1/subicular interchange area of the hippocampus corresponding to the first region exhibiting plaques and tangles in old mice. Furthermore, the comparison of 3xTgAD mice with double-transgenic mice bearing the ßAPP(swe) and Tau(P301L) mutations but expressing endogenous PS1 (2xTgAD) demonstrate that C99 accumulation is not accounted for by a loss of function triggered by PS1 mutation that would have prevented C99 secondary cleavage by γ-secretase. Together, our work identifies C99 as the earliest ßAPP catabolite and main contributor to the intracellular ßAPP-related immunoreactivity in 3xTgAD mice, suggesting its implication as an initiator of the neurodegenerative process and cognitive alterations taking place in this mouse model.