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The suprachiasmatic nucleus (SCN) synchronizes physiology with the individual's environment to optimize bodily functions. A new study reveals that tanycytes follow the tempo set by the SCN to effect circadian changes in both brain entry of blood glucose and glycemia.

Metabolic health depends on the brain’s ability to control food intake and nutrient use versus storage, processes that require peripheral signals such as the adipocyte-derived hormone, leptin, to cross brain barriers and mobilize regulatory circuits. We have previously shown that hypothalamic tanycytes shuttle leptin into the brain to reach target neurons. Here, using multiple complementary models, we show that tanycytes express functional leptin receptor (LepR), respond to leptin by triggering Ca2+ waves and target protein phosphorylation, and that their transcytotic transport of leptin requires the activation of a LepR–EGFR complex by leptin and EGF sequentially. Selective deletion of LepR in tanycytes blocks leptin entry into the brain, inducing not only increased food intake and lipogenesis but also glucose intolerance through attenuated insulin secretion by pancreatic β-cells, possibly via altered sympathetic nervous tone. Tanycytic LepRb–EGFR-mediated transport of leptin could thus be crucial to the pathophysiology of diabetes in addition to obesity, with therapeutic implications. Duquenne et al. show that tanycyte leptin receptor expression is required for leptin to enter the brain and regulate peripheral lipogenesis and pancreatic β-cell function.

International audience; At the present time, no viable treatment exists for cognitive and olfactory deficits in Down syndrome (DS). We show in a DS model (Ts65Dn mice) that these progressive nonreproductive neurological symptoms closely parallel a postpubertal decrease in hypothalamic as well as extrahypothalamic expression of a master molecule that controls reproduction—gonadotropin-releasing hormone (GnRH)—and appear related to an imbalance in a microRNA-gene network known to regulate GnRH neuron maturation together with altered hippocampal synaptic transmission. Epigenetic, cellular, chemogenetic, and pharmacological interventions that restore physiological GnRH levels abolish olfactory and cognitive defects in Ts65Dn mice, whereas pulsatile GnRH therapy improves cognition and brain connectivity in adult DS patients. GnRH thus plays a crucial role in olfaction and cognition, and pulsatile GnRH therapy holds promise to improve cognitive deficits in DS.

Therapies based on glucagon-like peptide-1 (GLP-1) long-acting analogs and insulin are often used in the treatment of metabolic diseases. Both insulin and GLP-1 receptors are expressed in metabolically relevant brain regions, suggesting a cooperative action. However, the mechanisms underlying the synergistic actions of insulin and GLP-1R agonists remain elusive. In this study, we show that insulin-induced hypoglycemia enhances GLP-1R agonists entry in hypothalamic and area, leading to enhanced whole-body fat oxidation. Mechanistically, this phenomenon relies on the release of tanycyctic vascular endothelial growth factor A, which is selectively impaired after calorie-rich diet exposure. In humans, low blood glucose also correlates with enhanced blood-to-brain passage of insulin, suggesting that blood glucose gates the passage other energy-related signals in the brain. This study implies that the preventing hyperglycemia is important to harnessing the full benefit of GLP-1R agonist entry in the brain and action onto lipid mobilization and body weight loss.

Ghrelin is a peptide hormone mainly secreted from gastrointestinal tract that acts via the growth hormone secretagogue receptor (GHSR), which is highly expressed in the brain. Strikingly, the accessibility of ghrelin to the brain seems to be limited and restricted to few brain areas. Previous studies in mice have shown that ghrelin can access the brain via the blood-cerebrospinal fluid (CSF) barrier, an interface constituted by the choroid plexus and the hypothalamic tanycytes. Here, we performed a variety of in vivo and in vitro studies to test the hypothesis that the transport of ghrelin across the blood-CSF barrier occurs in a GHSR-dependent manner. In vivo, we found that the uptake of systemically administered fluorescent ghrelin in the choroid plexus epithelial (CPE) cells and in hypothalamic tanycytes depends on the presence of GHSR. Also, we detected lower levels of CSF ghrelin after a systemic ghrelin injection in GHSR-deficient mice, as compared to WT mice. In vitro, the internalization of fluorescent ghrelin was reduced in explants of choroid plexus from GHSR-deficient mice, and unaffected in primary cultures of hypothalamic tanycytes derived from GHSR-deficient mice. Finally, we found that the GHSR mRNA is detected in a pool of CPE cells, but is nearly undetectable in hypothalamic tanycytes with current approaches. Thus, our results suggest that circulating ghrelin crosses the blood-CSF barrier mainly by a mechanism that involves the GHSR, and also possibly via a GHSR-independent mechanism.

Most patients with COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), display neurological symptoms, and respiratory failure in certain cases could be of extra-pulmonary origin. Hypothalamic neural circuits play key roles in sex differences, diabetes, hypertension, obesity and aging, all risk factors for severe COVID-19, besides being connected to olfactory/gustative and brainstem cardiorespiratory centers. Here, human brain gene-expression analyses and immunohistochemistry reveal that the hypothalamus and associated regions express angiotensin-converting enzyme 2 and transmembrane proteinase, serine 2, which mediate SARS-CoV-2 cellular entry, in correlation with genes or pathways involved in physiological functions or viral pathogenesis. A post-mortem patient brain shows viral invasion and replication in both the olfactory bulb and the hypothalamus, while animal studies indicate that sex hormones and metabolic diseases influence this susceptibility.

Summary Appropriate cristae remodeling is a determinant of mitochondrial function and bioenergetics and thus represents a crucial process for cellular metabolic adaptations. Here, we show that mitochondrial cristae architecture and expression of the master cristae-remodeling protein OPA1 in proopiomelanocortin (POMC) neurons, which are key metabolic sensors implicated in energy balance control, is affected by fluctuations in nutrient availability. Genetic inactivation of OPA1 in POMC neurons causes dramatic alterations in cristae topology, mitochondrial Ca2+ handling, reduction in alpha-melanocyte stimulating hormone (α-MSH) in target areas, hyperphagia, and attenuated white adipose tissue (WAT) lipolysis resulting in obesity. Pharmacological blockade of mitochondrial Ca2+ influx restores α-MSH and the lipolytic program, while improving the metabolic defects of mutant mice. Chemogenetic manipulation of POMC neurons confirms a role in lipolysis control. Our results unveil a novel axis that connects OPA1 in POMC neurons with mitochondrial cristae, Ca2+ homeostasis, and WAT lipolysis in the regulation of energy balance., Graphical abstract, Highlights • Nutritional state shapes mitochondrial cristae and OPA1 expression in POMC neurons • OPA1 deletion in POMC neurons alters mitochondrial Ca2+ handling and α-MSH release • POMC OPA1-deficient mice show impaired fat lipolysis and metabolic health • Pharmacological restoration of Ca2+ recovered molecular and metabolic alterations, Gómez-Valadés et al. report that mitochondrial cristae dynamically reshape in POMC neurons in response to nutritional state. With genetic targeting, they reveal that the cristae-remodeling protein OPA1 is essential to sustain cristae structure and mitochondrial Ca2+ homeostasis in POMC neurons, ensuring appropriate modulation of α-MSH release, the lipolytic program in adipose tissue and metabolic health.

International audience; Liraglutide, an anti-diabetic drug and agonist of the glucagon-like peptide one receptor (GLP1R), has recentlybeen approved to treat obesity in individuals with or without type 2 diabetes. Despite its extensive metabolicbenefits, the mechanism and site of action of liraglutide remain unclear. Here, we demonstrate that liraglutideis shuttled to target cells in the mouse hypothalamus by specialized ependymoglial cells called tanycytes,bypassing the blood-brain barrier. Selectively silencing GLP1R in tanycytes or inhibiting tanycytic transcytosisby botulinum neurotoxin expression not only hampers liraglutide transport into the brain and its activationof target hypothalamic neurons, but also blocks its anti-obesity effects on food intake, body weight and fatmass, and fatty acid oxidation. Collectively, these striking data indicate that the liraglutide-induced activationof hypothalamic neurons and its downstream metabolic effects are mediated by its tanycytic transport intothe mediobasal hypothalamus, strengthening the notion of tanycytes as key regulators of metabolic homeostasis.

The control of body weight and glucose homeostasis are the bedrock of type 2 diabetes medication. Therapies based on co-administration of glucagon-like peptide-1 (GLP-1) long-acting analogues and insulin are becoming popular in the treatment of T2D. Both insulin and GLP-1 receptors (InsR and GLP1-R, respectively) are expressed in brain regions critically involved in the regulation of energy homeostasis, suggesting a possible cooperative action. However, the mechanisms underlying the synergistic action of insulin and GLP-1R agonists on body weight loss and glucose homeostasis remain largely under-investigated. In this study, we provide evidence that peripheral insulin administration modulates the action of GLP-1R agonists onto fatty acids oxidation. Taking advantage of fluorescently labeled insulin and GLP-1R agonists, we found that glucoprivic condition, either achieved by insulin or by 2-deoxyglucose (2-DG), acts as a permissive signal on the blood-brain barrier (BBB) at circumventricular organs, including the median eminence (ME) and the area postrema (AP), enhancing the passage and action of GLP-1-R agonists. Mechanistically, this phenomenon relied on the release of tanycyctic vascular endothelial growth factor A (VEGF-A) and it was selectively impaired after calorie-rich diet exposure. Finally, we found that in human subjects, low blood glucose also correlates with enhanced blood-to-brain passage of insulin suggesting that changes in glycaemia also affect passage of peptide hormones into the brain in humans.In conclusion, we describe a yet unappreciated mechanism by which acute variations of glycaemia gate the entry and action of circulating energy-related signals in the brain. This phenomenon has physiological and clinical relevance implying that glycemic control is critical to harnessing the full benefit of GLP-1R agonist co-treatment in body weight loss therapy.

Melanin-Concentrating Hormone (MCH) is one of the most relevant orexigenic factors specifically located in the lateral hypothalamic area (LHA), with its physiological relevance demonstrated in studies using several genetically manipulated mice models. However, the central mechanisms controlling MCH-induced hyperphagia remain largely uncharacterized. Here, we show that central injection of MCH in mice deficient for kappa opoid receptor (k-OR) failed to stimulate feeding. To determine the hypothalamic area responsible for this MCH/k-OR interaction, we performed virogenetic studies and found that downregulation of k-OR by adeno-associated viruses (shOprk1-AAV) in LHA, but not in other hypothalamic nuclei, was sufficient to block MCH-induced food intake. Next, we sought to investigate the molecular signaling pathway within the LHA that mediates acute central MCH stimulation of food intake. We found that MCH activates k-OR and that increased levels of phosphorylated extracellular signal regulated kinase (ERK) are associated with downregulation of phospho-S6 Ribosomal Protein. This effect was prevented when a pharmacological inhibitor of k-OR was co-administered with MCH. Finally, the specific activation of the direct upstream regulator of S6 (p70S6K) in the LHA attenuated MCH-stimulated food consumption. Our results reveal that lateral hypothalamic k-OR system modulates the orexigenic action of MCH via the p70S6K/S6 pathway. This work has been supported by grants from Ministerio de Economia y Competitividad (CD: BFU2014-55871; RN: BFU2015-70664-R; ML: SAF2015-71026-R), Xunta de Galicia (ML: 2015- CP079; RN: 2015-CP080 and PIE13/00024); Fundacion SEEN (RN); Helse Vest RHF (JF); Fundación AstraZeneca (RN: 2016-PO031); Centro de Investigacion Biomédica en Red (CIBER) de Fisiopatología de la Obesidad y Nutricion (CIBERobn). CIBERobn is an initiative of the Instituto de Salud Carlos III (ISCIII) of Spain which is supported by FEDER funds. The research leading to these results has also received funding from the European Community's Seventh Framework Programme under the following grant: RN: ERC StG281408

Altres ajuts: Horizon 2020 Marie Sklodowska-Curie actions - European Research Fellowship (H2020-MSCA-IF-2017). Support of COST Action CM1306 is kindly acknowledged. LAC thanks Generalitat de Catalunya for her Ph.D. grant. LM thanks the 'Talent 2017' program from the Universitat Autònoma de Barcelona. Congenital hypogonadotropic hypogonadism (CHH) is a condition characterized by absent puberty and infertility due to gonadotropin releasing hormone (GnRH) deficiency, which is often associated with anosmia (Kallmann syndrome, KS). We identified loss-of-function heterozygous mutations in anti-Müllerian hormone (AMH) and its receptor, AMHR2, in 3% of CHH probands using whole-exome sequencing. We showed that during embryonic development, AMH is expressed in migratory GnRH neurons in both mouse and human fetuses and unconvered a novel function of AMH as a pro-motility factor for GnRH neurons. Pathohistological analysis of Amhr2- deficient mice showed abnormal development of the peripheral olfactory system and defective embryonic migration of the neuroendocrine GnRH cells to the basal forebrain, which results in reduced fertility in adults. Our findings highlight a novel role for AMH in the development and function of GnRH neurons and indicate that AMH signaling insufficiency contributes to the pathogenesis of CHH in humans

The opioid system is widely known to modulate the brain reward system and thus affect the behavior of humans and other animals, including feeding. We hypothesized that the hypothalamic opioid system might also control energy metabolism in peripheral tissues. Mice lacking the kappa opioid receptor (κOR) and adenoviral vectors overexpressing or silencing κOR were stereotaxically delivered in the lateral hypothalamic area (LHA) of rats. Vagal denervation was performed to assess its effect on liver metabolism. Endoplasmic reticulum (ER) stress was inhibited by pharmacological (tauroursodeoxycholic acid) and genetic (overexpression of the chaperone glucose-regulated protein 78 kDa) approaches. The peripheral effects on lipid metabolism were assessed by histological techniques and western blot. We show that in the LHA κOR directly controls hepatic lipid metabolism through the parasympathetic nervous system, independent of changes in food intake and body weight. κOR colocalizes with melanin concentrating hormone receptor 1 (MCH-R1) in the LHA, and genetic disruption of κOR reduced melanin concentrating hormone–induced liver steatosis. The functional relevance of these findings was given by the fact that silencing of κOR in the LHA attenuated both methionine choline–deficient, diet-induced and choline-deficient, high-fat diet–induced ER stress, inflammation, steatohepatitis, and fibrosis, whereas overexpression of κOR in this area promoted liver steatosis. Overexpression of glucose-regulated protein 78 kDa in the liver abolished hypothalamic κOR-induced steatosis by reducing hepatic ER stress. Conclusions: This study reveals a novel hypothalamic–parasympathetic circuit modulating hepatic function through inflammation and ER stress independent of changes in food intake or body weight; these findings might have implications for the clinical use of opioid receptor antagonists. (Hepatology 2016;64:1086-1104)

International audience; Melanin-concentrating hormone (MCH) is an important regulator of food intake, glucose metabolism, and adiposity. However, the mechanisms mediating these actions remain largely unknown. We used pharmacological and genetic approaches to show that the sirtuin 1 (SIRT1)/FoxO1 signaling pathway in the hypothalamic arcuate nucleus (ARC) mediates MCH-induced feeding, adiposity, and glucose intolerance. MCH reduces proopiomelanocortin (POMC) neuronal activity, and the SIRT1/FoxO1 pathway regulates the inhibitory effect of MCH on POMC expression. Remarkably, the metabolic actions of MCH are compromised in mice lacking SIRT1 specifically in POMC neurons. Of note, the actions of MCH are independent of agouti-related peptide (AgRP) neurons because inhibition of γ-aminobutyric acid receptor in the ARC did not prevent the orexigenic action of MCH, and the hypophagic effect of MCH silencing was maintained after chemogenetic stimulation of AgRP neurons. Central SIRT1 is required for MCH-induced weight gain through its actions on the sympathetic nervous system. The central MCH knockdown causes hypophagia and weight loss in diet-induced obese wild-type mice; however, these effects were abolished in mice overexpressing SIRT1 fed a high-fat diet. These data reveal the neuronal basis for the effects of MCH on food intake, body weight, and glucose metabolism and highlight the relevance of SIRT1/FoxO1 pathway in obesity.

p53 family members control several metabolic and cellular functions. The p53 ortholog p63 modulates cellular adaptations to stress and has a major role in cell maintenance and proliferation. Here we show that p63 regulates hepatic lipid metabolism. Mice with liver-specific p53 deletion develop steatosis and show increased levels of p63. Down-regulation of p63 attenuates liver steatosis in p53 knockout mice and in diet-induced obese mice, whereas the activation of p63 induces lipid accumulation. Hepatic overexpression of N-terminal transactivation domain TAp63 induces liver steatosis through IKKβ activation and the induction of ER stress, the inhibition of which rescues the liver functions. Expression of TAp63, IKKβ and XBP1s is also increased in livers of obese patients with NAFLD. In cultured human hepatocytes, TAp63 inhibition protects against oleic acid-induced lipid accumulation, whereas TAp63 overexpression promotes lipid storage, an effect reversible by IKKβ silencing. Our findings indicate an unexpected role of the p63/IKKβ/ER stress pathway in lipid metabolism and liver disease., p53 regulates lipid metabolism and fatty acid oxidation, and its inactivation promotes diet-induced liver steatosis. Here Porteiro et al. show that p53 deficiency leads to compensatory p63 upregulation, which, in turn, triggers endoplasmic reticulum stress through IKKβ activation, fatty acid synthesis and lipid accumulation.

p53 family members control several metabolic and cellular functions. The p53 ortholog p63 modulates cellular adaptations to stress and has a major role in cell maintenance and proliferation. Here we show that p63 regulates hepatic lipid metabolism. Mice with liver-specific p53 deletion develop steatosis and show increased levels of p63. Down-regulation of p63 attenuates liver steatosis in p53 knockout mice and in diet-induced obese mice, whereas the activation of p63 induces lipid accumulation. Hepatic overexpression of N-terminal transactivation domain TAp63 induces liver steatosis through IKK beta activation and the induction of ER stress, the inhibition of which rescues the liver functions. Expression of TAp63, IKK beta and XBP1s is also increased in livers of obese patients with NAFLD. In cultured human hepatocytes, TAp63 inhibition protects against oleic acid-induced lipid accumulation, whereas TAp63 overexpression promotes lipid storage, an effect reversible by IKK beta silencing. Our findings indicate an unexpected role of the p63/IKK beta/ER stress pathway in lipid metabolism and liver disease. We deeply thank Dr Manuel Serrano (Spanish National Cancer Research Center, CNIO, Spain) for kindly providing p53 null mice and critically reading the article. This work has been supported by grants from Ministerio de Economia y Competitividad (C.D.: BFU2014-55,871; R.N.: BFU2015-70,664-R; M.M.M.: BFU2013-44229-R; A.C.: SAF2016-79381-R, FEDER/UE; GS: SAF2013-43506-R; M.L.M.-C.: SAF2014-54658-R; M.L.: SAF2015-71026-R; P.A.: SAF2015-64352-R; B.G.-T.: FPI Severo Ochoa CNIC program SVP-2013-067639), Xunta de Galicia (M.L.: 2015-CP079; R.N.: 2015-CP080 and PIE13/00024), Comunidad de Madrid (G.S.: S2010/BMD-2326); Fondo de Investigaciones Sanitarias (M.M.: PI10/01692), Fundacion SEEN (R.N.), GV-Departamento de Salud-2013111114 (to M.L.M.-C.), ISCIII: PIE14/00031 (to M.L.M.-C.), Junta Provincial de Bizkaia-AECC (to M.L.M.-C.), AECC (T.C.D.); Basque Department of Industry, Tourism and Trade (Etortek) (A.C.), the BBVA foundation (A.C.), Fundacion AstraZeneca (R.N.) Centro de Investigacion Biomedica en Red (CIBER) de Fisiopatologia de la Obesidad y Nutricion (CIBERobn). CIBERobn is an initiative of the Instituto de Salud Carlos III (ISCIII) of Spain, which is supported by FEDER funds. The participation of A.C. and A.Z.-L. as part of CIBERONC was co-funded with FEDER funds. The research leading to these results has also received funding from the European Community's Seventh Framework Programme under the following grant: A.C.: ERC StG-336343; R.N.: ERC StG-281408 and G.S.: ERC StG-260464. Sí

The G protein-coupled receptor GPR55 has been proposed as a new cannabinoid receptor associated with obesity in humans. We have investigated the regulation of GPR55 in rat white adipose tissue (WAT) in different physiological and pathophysiological settings involved in energy balance. We compared GPR55 expression with Cannabinoid Receptor type 1 (CB1), which mediates the metabolic actions of endocannabinoids, by real time PCR and western blotting. Circulating levels of lysophosphatidylinositol (LPI), the endogenous ligand of GPR55, were measured by liquid chromatography-mass spectrometry. Both WAT CB1 and GPR55 levels were increased after fasting and recovered after leptin treatment. Their expression was decreased during gestation and increased throughout lifespan. Orchidectomy diminished WAT CB1 and GPR55 expression whereas ovariectomized rats showed increased GPR55 but decreased CB1 levels. Alterations in pituitary functions also modified WAT CB1 and GPR55 levels. Serum LPI levels were inversely regulated by fasting and gonadectomy in comparison to WAT GPR55. Our findings indicate that GPR55 and LPI are regulated by different physiological and pathophysiological settings known to be associated with marked alterations in energy status.

GPR55 is a G-protein-coupled receptor (GPCR) that has been identified as a new cannabinoid receptor. Given the wide localization of GPR55 in brain and peripheral tissues, this receptor has emerged as a regulator of multiple biological actions. Lysophosphatidylinositol (LPI) is generally accepted as the endogenous ligand of GPR55. In this review, we will focus on the role of GPR55 in energy balance and glucose metabolism. We will summarize its actions on feeding, nutrient partitioning, gastrointestinal motility and insulin secretion in preclinical models and the scarce data available in humans. The potential of GPR55 to become a new pharmaceutical target to treat obesity and type 2 diabetes, as well as the foreseeing difficulties are also discussed.

Proopiomelanocortin (POMC) neurons are critical sensors of nutrient availability implicated in energy balance and glucose metabolism control. However, the precise mechanisms underlying nutrient sensing in POMC neurons remain incompletely understood. We show that mitochondrial dynamics mediated by Mitofusin 1 (MFN1) in POMC neurons couple nutrient sensing with systemic glucose metabolism. Mice lacking MFN1 in POMC neurons exhibited defective mitochondrial architecture remodeling and attenuated hypothalamic gene expression programs during the fast-to-fed transition. This loss of mitochondrial flexibility in POMC neurons bidirectionally altered glucose sensing, causing abnormal glucose homeostasis due to defective insulin secretion by pancreatic β cells. Fed mice lacking MFN1 in POMC neurons displayed enhanced hypothalamic mitochondrial oxygen flux and reactive oxygen species generation. Central delivery of antioxidants was able to normalize the phenotype. Collectively, our data posit MFN1-mediated mitochondrial dynamics in POMC neurons as an intrinsic nutrient-sensing mechanism and unveil an unrecognized link between this subset of neurons and insulin release.

The cannabinoid CB1 receptor is a well-known player in energy homeostasis and its specific antagonism has been used in clinical practice for the treatment of obesity. The G protein-coupled receptor GPR55 has been recently proposed as a new cannabinoid receptor and, by contrast, its pharmacology is still enigmatic and its physiological role is largely unexplored, with no reports investigating its putative role in metabolism. Thus, we aim to investigate in rats the presence, distribution and putative physiological role of GPR55 in a key metabolic tissue, the endocrine pancreas. We found high Gpr55 mRNA content in pancreatic islets and considerable protein distribution in insulin-secreting β-cells. Activation of GPR55 by the agonist O-1602 increased calcium transients (PPGpr55 KO mice suggesting that O-1602 is acting, at least in part, through GPR55. Indeed, acute in vivo experiments showed that GPR55 activation increases glucose tolerance (PPin vivo physiological relevance of GPR55 systemic stimulation. Taken together, these results reveal the expression of GPR55 receptors in the endocrine pancreas as well as its function at stimulus-secretion coupling of insulin secretion, suggesting a role in glucose homeostasis. In this context, it may also represent a new target for consideration in the management of type 2 diabetes and related diseases.

Nature Communications 8: Article number:15111 (2017); Published: 8 May 2017; Updated: 16 June 2017 The affiliation details for Paula Iruzubieta and Javier Crespo are incorrect in this Article. The correct affiliation details for these authors are given below: Department of Gastroenterology and Hepatology, Marqués de Valdecilla University Hospital, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd).

Krüppel-like factor 4 (KLF4) is a zinc-finger-type transcription factor expressed in a range of tissues that plays multiple functions. We report that hypothalamic KLF4 represents a new transcription factor specifically modulating agouti-related protein (AgRP) expression in vivo. Hypothalamic KLF4 colocalizes with AgRP neurons and is modulated by nutritional status and leptin. Over-expression of KLF4 in the hypothalamic arcuate nucleus (ARC) induces food intake and increases body weight through the specific stimulation of AgRP, as well as blunting leptin sensitivity in lean rats independent of forkhead box protein 01 (FoxO1). Down-regulation of KLF4 in the ARC inhibits fasting-induced food intake in both lean and diet-induced obese (DIO) rats. Silencing KLF4, however, does not, on its own, enhance peripheral leptin sensitivity in DIO rats., Graphical abstract

GLP-1 receptor (GLP-1R) is widely located throughout the brain, but the precise molecular mechanisms mediating the actions of GLP-1 and its long-acting analogs on adipose tissue as well as the brain areas responsible for these interactions remain largely unknown. We found that central injection of a clinically used GLP-1R agonist, liraglutide, in mice stimulates brown adipose tissue (BAT) thermogenesis and adipocyte browning independent of nutrient intake. The mechanism controlling these actions is located in the hypothalamic ventromedial nucleus (VMH), and the activation of AMPK in this area is sufficient to blunt both central liraglutide-induced thermogenesis and adipocyte browning. The decreased body weight caused by the central injection of liraglutide in other hypothalamic sites was sufficiently explained by the suppression of food intake. In a longitudinal study involving obese type 2 diabetic patients treated for 1 year with GLP-1R agonists, both exenatide and liraglutide increased energy expenditure. Although the results do not exclude the possibility that extrahypothalamic areas are also modulating the effects of GLP-1R agonists, the data indicate that long-acting GLP-1R agonists influence body weight by regulating either food intake or energy expenditure through various hypothalamic sites and that these mechanisms might be clinically relevant.

Mitofusin 2 (MFN2) plays critical roles in both mitochondrial fusion and the establishment of mitochondria-endoplasmic reticulum (ER) interactions. Hypothalamic ER stress has emerged as a causative factor for the development of leptin resistance, but the underlying mechanisms are largely unknown. Here, we show that mitochondria-ER contacts in anorexigenic pro-opiomelanocortin (POMC) neurons in the hypothalamus are decreased in diet-induced obesity. POMC-specific ablation of Mfn2 resulted in loss of mitochondria-ER contacts, defective POMC processing, ER stress-induced leptin resistance, hyperphagia, reduced energy expenditure, and obesity. Pharmacological relieve of hypothalamic ER stress reversed these metabolic alterations. Our data establish MFN2 in POMC neurons as an essential regulator of systemic energy balance by fine-tuning the mitochondrial-ER axis homeostasis and function. This previously unrecognized role for MFN2 argues for a crucial involvement in mediating ER stress-induced leptin resistance. © 2013 Elsevier Inc., This work has been supported by: RecerCaixa Grant 2010ACUP_00275 (M.C.); EFSD/Lilly Fellowship Award (M.C.); Ministerio de Ciencia e Innovación (MICINN), Instituto de Salud Carlos III (ISCIII) Grant PI10/01074 (M.C.); MICINN Grant SAF2010-19527 (R.G.); Ministerio de Economia y Competitividad (MINECO) Grant BFU2012-35255 (RN); Xunta de Galicia Grant EM2012/039 and 2012-CP069 (R.N.); CIBERobn (R.N.); European Community’s Seventh Framework Programme Grant ERC-2011-StG-OBESITY53-281408 (R.N.); MINECO Grant SAF2008-03803 (A.Z.); Generalitat de Catalunya Grant 2009SGR915 (A.Z.); CIBERDEM (A.Z.); INTERREG IV-B-SUDOE-FEDER (DIOMED, SOE1/P1/E178) (A.Z.); European Commission Seventh Framework Programme (FP7), MITIN Grant HEALTH-F4-2008-223450 (A.Z.); MICINN Grant BFU2011- 24679 (P.M.G.-R.); ISCIII Grant PI10/00290 (A.B.). T.L.H. and M.O.D. are supported by NIH (DP1DK006850, R01AG040236, P01NS062686), American Diabetes Association, Helmholtz society (ICEMED) and by Conselho Nacional de Desenvolvimento Científico e Tecnológico (401476/2012-0, Brazil). M.S. is a recipient of an undergraduate grant from the University of Barcelona. M.C. is a recipient of a Miguel Servet contract (CP09/00233) from MICINN-ISCIII. P.M.G.-R. is a recipient of a Ramon y Cajal contract (RYC-2009-05158) from MICINN. Some of these grants are cofinanced by the European Regional Development Fund “A way to build Europe.” This work was carried out in part at the Esther Koplowitz Centre, Barcelona.

Colorectal cancer is characterized by a low survival rate even though the basis for colon cancer development, which involves the evolution of adenomas to carcinoma, is known. Moreover, the mortality rates continue to rise in economically transitioning countries although there is the opportunity to intervene in the natural history of the adenoma-cancer sequence through risk factors, screening, and treatment. Screening in particular accounted for most of the decline in colorectal cancer mortality achieved in the USA during the period 1975-2000. Patients show a better prognosis when the neoplasm is diagnosed early. Among the variety of screening strategies, the methods range from invasive and costly procedures such as colonoscopy to more low-cost and non-invasive tests such as the fecal occult blood test (guaiac and immunochemical). As a non-invasive biological serum marker would be of great benefit because of the performance of the test, several biomarkers, including cytologic assays, DNA and mRNA, and soluble proteins, have been studied. We found that the soluble CD26 (sCD26) concentration is diminished in serum of colorectal cancer patients compared to healthy donors, suggesting the potential utility of a sCD26 immunochemical detection test for early diagnosis. sCD26 originates from plasma membrane CD26 lacking its transmembrane and cytoplasmic domains. Some 90%-95% of sCD26 has been associated with serum dipeptidyl peptidase IV (DPP-IV) activity. DPP-IV, assigned to the CD26 cluster, is a pleiotropic enzyme expressed mainly on epithelial cells and lymphocytes. Our studies intended to validate this test for population screening to detect colorectal cancer and advanced adenomas are reviewed here.

BACKGROUND & AIMS:: Specific neuronal circuits modulate autonomic outflow to liver and white adipose tissue. Melanin-concentrating hormone (MCH) deficient mice are hypophagic, lean and do not develop hepatosteatosis when fed on high fat diet. Herein, we sought to investigate the role of melanin-concentrating hormone (MCH), an orexigenic neuropeptide specifically expressed in the lateral hypothalamic area (LHA), on hepatic and adipocyte metabolism. METHODS:: Chronic central administration of MCH and adenoviral vectors increasing MCH signalling were performed in rats and mice. Vagal dennervation was done to assess its effect on liver metabolism. The peripheral effects on lipid metabolism were assessed by real-time PCR and western blot. RESULTS:: We demonstrate that the activation of MCH receptors (MCH-R) promotes nonalcoholic fatty liver disease (NAFLD) through the parasympathetic nervous system (PSNS), whereas it increases fat deposition in WAT via the suppression of sympathetic traffic. These metabolic actions are independent of parallel changes in food intake and energy expenditure. In the liver, MCH triggers lipid accumulation and lipid uptake, being c-Jun N-terminal kinase (JNK1) an essential player, while in adipocytes MCH induces metabolic pathways that promote lipid storage and decreases lipid mobilization. Genetic activation of MCH-R or infusion of MCH specifically in the LHA modulated hepatic lipid metabolism, whereas the specific activation of this receptor in the arcuate nucleus (ARC) affected adipocyte metabolism. CONCLUSIONS:: Our findings reveal that central MCH directly controls hepatic and adipocyte metabolism through different pathways.

International audience; Hypothalamic glucose sensing enables an organism to match energy expenditure and food intake to circulating levels of glucose, the main energy source of the brain. Here, we established that tanycytes of the hypothalamic arcuate nucleus, specialized glia that line the wall of the third ventricle, convert brain glucose supplies into lactate that they transmit through monocarboxylate transporters to arcuate proopiomelanocortin neurons, which integrate this signal to drive their activity and to adapt the metabolic response to meet physiological demands. Furthermore, this transmission required the formation of extensive Connexin-43 gap-junction-mediated metabolic networks by arcuate tanycytes. Selectively suppressing either tanycytic monocarboxylate transporters or gap junctions resulted in altered feeding behavior and energy metabolism. Tanycytic intercellular communication and lactate production are thus integral to the mechanism by which hypothalamic neurons that regulate energy and glucose homeostasis efficiently perceive alterations in systemic glucose levels as a function of the physiological state of the organism.