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The glucagon-like peptide 1 receptor (GLP1R) is a major drug target with several agonists being prescribed in patients with type 2 diabetes (T2D) and obesity. The impact of genetic variability of the GLP1R gene on receptor function and its association with metabolic traits are unclear. Here, functional profiling of 59 rare and one common GLP1R variant across four signaling pathways reveals an unexpected diversity of phenotypes ranging from defective cell surface expression to complete or pathway-specific gain- and loss-of-functions. Defective insulin secretion of loss-of-function GLP1R variants was rescued by allosteric GLP1R ligands or high exendin-4 concentrations in INS-1 823/3 cells. Genetic association studies in 200K participants from UK Biobank show that impaired GLP1R cell surface expression contributes to impaired glucose control and increased adiposity with increased HbA1c, BMI and diastolic blood pressure. This study defines impaired GLP-1R cell surface expression as a risk factor for T2D- and obesity-associated traits.

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.

Abnormally high serum homocysteine levels have been associated with several disorders, including obesity, cardiovascular diseases or neurological diseases. Leptin is an anti-obesity protein and its action is mainly mediated by the activation of its Ob-R receptor in neuronal cells. The inability of leptin to induce activation of its specific signaling pathways, especially under endoplasmic reticulum stress, leads to the leptin resistance observed in obesity. The present study examined the effect of homocysteine on leptin signaling in SH-SY5Y neuroblastoma cells expressing the leptin receptor Ob-Rb. Phosphorylation of the signal transducer and activator of transcription (STAT3) and leptin-induced STAT3 transcriptional activity were significantly inhibited by homocysteine treatment. These effects may be specific to homocysteine and to the leptin pathway, as other homocysteine-related compounds, namely methionine and cysteine, have weak effect on leptin-induced inhibition of STAT3 phosphorylation, and homocysteine has no impact on IL-6-induced activation of STAT3. The direct effect of homocysteine on leptin-induced Ob-R activation, analyzed by Ob-R BRET biosensor to monitor Ob-R oligomerization and conformational change, suggested that homocysteine treatment does not affect early events of leptin-induced Ob-R activation. Instead, we found that, unlike methionine or cysteine, homocysteine increases the expression of the endoplasmic reticulum (ER) stress response gene, a homocysteine-sensitive ER resident protein. These results suggest that homocysteine may induce neuronal resistance to leptin by suppressing STAT3 phosphorylation downstream of the leptin receptor via ER stress.

Intracellular accumulation of tau protein is a hallmark of Alzheimer’s Disease and Progressive Supranuclear Palsy, as well as other neurodegenerative disorders collectively known as tauopathies. Despite our increasing understanding of the mechanisms leading to the initiation and progression of tau pathology, the field still lacks appropriate disease models to facilitate drug discovery. Here, we established a novel and modulatable seeding-based neuronal model of full-length 4R tau accumulation using humanized mouse cortical neurons and seeds from P301S human tau transgenic animals. The model shows specific and consistent formation of intraneuronal insoluble full-length 4R tau inclusions, which are positive for known markers of tau pathology (AT8, PHF-1, MC-1), and creates seeding competent tau. The formation of new inclusions can be prevented by treatment with tau siRNA, providing a robust internal control for use in qualifying the assessment of potential therapeutic candidates aimed at reducing the intracellular pool of tau. In addition, the experimental set up and data analysis techniques used provide consistent results in larger-scale designs that required multiple rounds of independent experiments, making this is a versatile and valuable cellular model for fundamental and early pre-clinical research of tau-targeted therapies.

Introduction: Metabolic dysfunction is now recognized as a pivotal component of Alzheimer’s disease (AD), the most common dementia worldwide. However, the precise molecular mechanisms linking metabolic dysfunction to AD remain elusive. Objective: Here, we investigated the direct impact of soluble oligomeric amyloid beta (Aβ) peptides, the main molecular hallmark of AD, on the leptin system, a major component of central energy metabolism regulation. Methods: We developed a new time-resolved fluorescence resonance energy transfer-based Aβ binding assay for the leptin receptor (LepR) and studied the effect of Aβ on LepR function in several in vitro assays. The in vivo effect of Aβ on LepR function was studied in an Aβ-specific AD mouse model and in pro-opiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus. Results: We revealed specific and high-affinity (Ki = 0.1 nM) binding of Aβ to LepR. Pharmacological characterization of this interaction showed that Aβ binds allosterically to the extracellular domain of LepR and negatively affects receptor function. Negative allosteric modulation of LepR by Aβ was detected at the level of signaling pathways (STAT-3, AKT, and ERK) in vitroand in vivo. Importantly, the leptin-induced response of POMC neurons, key players in the regulation of metabolic function, was completely abolished in the presence of Aβ. Conclusion: Our data indicate that Aβ is a negative allosteric modulator of LepR, resulting in impaired leptin action, and qualify LepR as a new and direct target of Aβ oligomers. Preventing the interaction of Aβ with LepR might improve both the metabolic and cognitive dysfunctions in AD condition.

International audience; COVID-19 is a complex disease with short- and long-term respiratory, inflammatory and neurological symptoms that are triggered by the infection with SARS-CoV-2. Invasion of the brain by SARS-CoV-2 has been observed in humans and is postulated to be involved in post-COVID state. Brain infection is particularly pronounced in the K18-hACE2 mouse model of COVID-19. Prevention of brain infection in the acute phase of the disease might thus be of therapeutic relevance to prevent long-lasting symptoms of COVID-19. We previously showed that melatonin or two prescribed structural analogs, agomelatine and ramelteon delay the onset of severe clinical symptoms and improve survival of SARS-CoV-2-infected K18-hACE2 mice. Here, we show that treatment of K18-hACE2 mice with melatonin and two melatonin-derived marketed drugs, agomelatine and ramelteon, prevents SARS-CoV-2 entry in the brain, thereby reducing virus-induced damage of small cerebral vessels, immune cell infiltration and brain inflammation. Molecular modeling analyses complemented by experimental studies in cells showed that SARS-CoV-2 entry in endothelial cells is prevented by melatonin binding to an allosteric-binding site on human angiotensin-converting enzyme 2 (ACE2), thus interfering with ACE2 function as an entry receptor for SARS-CoV-2. Our findings open new perspectives for the repurposing of melatonergic drugs and its clinically used analogs in the prevention of brain infection by SARS-CoV-2 and COVID-19-related long-term neurological symptoms

Aggregates of the tau protein are a well-known hallmark of several neurodegenerative diseases, collectively referred as tauopathies, including frontal temporal dementia and Alzheimer’s disease (AD). Monitoring the transformation process of tau from physiological monomers into pathological oligomers or aggregates in a high-throughput, quantitative manner and in a cellular context is still a major challenge in the field. Identifying molecules able to interfere with those processes is of high therapeutic interest. Here, we developed a series of inter- and intramolecular tau biosensors based on the highly sensitive Nanoluciferase (Nluc) binary technology (NanoBiT) able to monitor the pathological conformational change and self-interaction of tau in living cells. Our repertoire of tau biosensors reliably reporti.molecular proximity of physiological full-length tau at microtubules;ii.changes in tau conformation and self-interaction associated with tau phosphorylation, as well asiii.tau interaction induced by seeds of recombinant tau or from mouse brain lysates of a mouse model of tau pathology. By comparing biosensors comprising different tau forms (i.e.full-length or short fragments, wild-type or the disease-associated tau(P301L) variant) further insights in the tau transformation process are obtained. Proof-of-concept data for the high-throughput suitability and identification of molecules interfering with the pathological tau transformation processes are presented. This novel repertoire of tau biosensors is aimed to boost the disclosure of molecular mechanisms underlying pathological tau transformation in living cells and to discover new drug candidates for tau-related neurodegenerative diseases.

Neuroinvasion by SARS-CoV-2 is now accepted. To investigate whether low testosterone levels observed in men with severe COVID-19 could be of central origin, we retrospectively analyzed blood samples from 60 male intensive-care patients and explored SARS-CoV-2 brain entry using animal and cellular models as well as adult COVID-19 patient and fetal human brains. Most hypotestosteronemic patients displayed hypogonadotropic hypogonadism or abnormal hypothalamic-pituitary-gonadal axis regulation. Neurons producing gonadotropin-releasing hormone (GnRH), the master molecule controlling fertility, expressed angiotensin-converting enzyme 2 and neuropilin-1, two host-cell factors mediating infection, and were infected and dying in all COVID-19 patient brains. Tanycytes - hypothalamic glia that regulate GnRH secretion - were also infected. Additionally, human fetal olfactory and vomeronasal epithelia, from which GnRH neurons arise, richly expressed both the above host-cell susceptibility factors and formyl peptide receptor 2, a putative vomeronasal receptor that also appeared involved in SARS-CoV-2 pathogenesis in humans and mice. Finally, a fetal human GnRH cell line expressing all these receptors could be infected by a SARS-CoV-2-like pseudovirus. Together, our findings suggest that GnRH neurons, which may be implicated in brain development and aging in addition to reproduction, are particularly vulnerable to SARS-CoV-2 in both adults and fetuses/newborns, with potentially devastating long-term consequences.

Targeting the interaction between the SARS-CoV-2 spike protein and human ACE2, its primary cell membrane receptor, is a promising therapeutic strategy to prevent viral entry. Recent in vitro studies revealed that the receptor binding domain (RBD) of the spike protein plays a prominent role in ACE2 binding, yet a simple and quantitative assay for monitoring this interaction in a cellular environment is lacking. Here, we developed an RBD-ACE2 binding assay that is based on time-resolved FRET, which reliably monitors the interaction in a physiologically relevant and cellular context. Because it is modular, the assay can monitor the impact of different cellular components, such as heparan sulfate, lipids, and membrane proteins on the RBD-ACE2 interaction and it can be extended to the full-length spike protein. The assay is HTS compatible and can detect small-molecule competitive and allosteric modulators of the RBD-ACE2 interaction with high relevance for SARS-CoV-2 therapeutics., Graphical abstract, Cecon et al. describe a quantitative, time-resolved FRET assay capable of detecting SARS-CoV-2 spike interactions with ACE2 in living cells. The assay monitors the interaction in a physiologically relevant cellular environment and is suitable for diverse applications, including mechanistic studies, drug screening, and characterization of neutralizing antibodies or vaccine efficacy.

β-Arrestins are critical regulators of G protein-coupled receptors (GPCRs) that desensitize G protein signaling, promote receptor internalization, and initiate signaling on their own. Recent structural findings indicate that β-arrestins adopt different conformations upon interaction with agonist-activated GPCRs. Here, we established a β-arrestin-2 conformational bioluminescence resonance energy transfer (BRET) sensor composed of the bright Nanoluc BRET donor and the red-shifted CyOFP1 BRET acceptor. The sensor monitors early intramolecular conformational changes of β-arrestin-2 in complex with a wide panel of different class A and class B GPCRs upon agonist activation and with orphan GPCRs known to spontaneously recruit β-arrestin-2. The introduction of the R170E mutant in the β-arrestin-2 sensor allowed the detection of a partially active β-arrestin-2 conformation, which is not dependent on receptor phosphorylation, while the deletion of the β-arrestin-2 finger-loop region detected the "tail-conformation" corresponding to the interaction of β-arrestin with the carboxyl-terminal domain of GPCRs. The new sensors combine the advantages of the BRET technique in terms of sensitivity, robustness, and suitability for real-time measurements with a high responsiveness toward early conformational changes to help to elucidate the different conformational states of β-arrestins associated with GPCR activation in living cells.

Les récepteurs sont les pièces maîtresses véhiculant l’information apportée par l’hormone de l’environnement extracellulaire vers le milieu intracellulaire. Par ce fait, la fraction de récepteur à la surface de la cellule peut déterminer la force du signal. La régulation du trafic du récepteur vers la surface de la cellule ainsi que les processus de rétention du récepteur dans les compartiments intracellulaires constituent des mécanismes clés pour l’activité du récepteur de la leptine (ObR). Une altération de ces mécanismes conduit au développement de l’obésité. Par ailleurs, la part du mécanisme classique d’activation des récepteurs à la membrane plasmique est mise en question, depuis la découverte d’une activité de signalisation propre à ces récepteurs intracellulaires. Ceux-ci peuvent déclencher une signalisation régulant une fonction particulière, différente de la signalisation des récepteurs de surface, ou en continuité avec ces derniers. Nous aborderons à la fois ces deux aspects en nous intéressant particulièrement au cas du récepteur de la leptine, c’est à dire i) la régulation de son niveau d’exposition à la surface cellulaire et ses répercussions sur le développement de l’obésité, et ii) la découverte de sa localisation et de sa signalisation dans certains compartiments intracellulaires.

Greenhouse gas emission data from the mineralisation process in Sludge Treatment Reed Bed systems (STRB) are scarce. The aim of this study was to quantify the emission rates of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) and to investigate seasonal variations in order to estimate the annual greenhouse gas emission rate of the mineralisation process. The full-scale STRB at Helsinge wastewater treatment plant (WWTP) in Denmark was chosen as the study site. Gas emission rates were measured using static surface flux chambers. The measurements were carried out in October/November 2014, March/April 2015, June/July 2015 and January/February 2016. We found that the emission rates of all included gas species were significantly affected by season. For CO 2 and CH 4 , the highest emission rates were recorded in summer, being138 and 5.2 g m −2 d −1 , respectively, while the lowest rates were recorded in winter, being 442 and 0.7 g m −2 d −1 , respectively. For N 2 O, the highest and lowest rates were recorded in autumn and spring, being 0.47 and 0.31 g m −2 d −1 , respectively. Emissions of CO 2 and CH 4 appeared to be affected by changes in temperature, while N 2 O appeared to be affected not only by temperature, but also by the amount of precipitation. An annual greenhouse gas emission rate (given in CO 2 equivalents) of the mineralisation process was calculated for two scenarios based on the assumptions; 1) gas emission rates are not affected by the amount of sludge accumulated in the STRB and 2) gas emission rates are affected by the amount of sludge accumulated in the STRB. The results revealed that the annual global warming potential is to be found in a range between 7 and 13.4 kg CO 2 -eq·PE −1 y −1 .

Transmission of extracellular signals by G protein-coupled receptors typically relies on a cascade of intracellular events initiated by the activation of heterotrimeric G proteins or β-arrestins followed by effector activation/inhibition. Here, we report an alternative signal transduction mode used by the orphan GPR50 that relies on the nuclear translocation of its carboxyl-terminal domain (CTD). Activation of the calcium-dependent calpain protease cleaves off the CTD from the transmembrane-bound GPR50 core domain between Phe-408 and Ser-409 as determined by MALDI-TOF-mass spectrometry. The cytosolic CTD then translocates into the nucleus assisted by its 'DPD' motif, where it interacts with the general transcription factor TFII-I to regulate c-fos gene transcription. RNA-Seq analysis indicates a broad role of the CTD in modulating gene transcription with ~ 8000 differentially expressed genes. Our study describes a non-canonical, direct signaling mode of GPCRs to the nucleus with similarities to other receptor families such as the NOTCH receptor.

Background and purpose Progressive dysfunction of cholinergic transmission is a well-known characteristic of Alzheimer's disease (AD). Amyloid β (Aβ) peptide oligomers are known to play a central role in AD and are suggested to impair the function of the cholinergic nicotinic ACh receptor α7 (α7nAChR). However, the mechanism underlying the effect of Aβ on α7nAChR function is not fully understood, limiting the therapeutic exploration of this observation in AD. Here, we aimed to detect and characterize Aβ binding to α7nAChR, including the possibility of interfering with this interaction for therapeutic purposes. Experimental approach We developed a specific and quantitative time-resolved FRET (TR-FRET)-based binding assay for Aβ to α7nAChR and pharmacologically characterized this interaction. Key results We demonstrated specific and high-affinity (low nanomolar) binding of Aβ to the orthosteric binding site of α7nAChR. Aβ binding was prevented and reversed by the well-characterized orthosteric ligands of α7nAChR (epibatidine, α-bungarotoxin, methylylcaconitine, PNU-282987, S24795, and EVP6124) and by the type II positive allosteric modulator (PAM) PNU-120596 but not by the type I PAM NS1738. Conclusions and implications Our TR-FRET Aβ binding assay demonstrates for the first time the specific binding of Aβ to α7nAChR, which will be a crucial tool for the development, testing, and selection of a novel generation of AD drug candidates targeting Aβ/α7nAChR complexes with high specificity and fewer side effects compared to currently approved α7nAChR drugs. Linked articles This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Leptin links body energy stores to high energy demanding processes like reproduction and immunity. Based on leptin's role in autoimmune diseases and cancer, several leptin and leptin receptor (LR) antagonists have been developed, but these intrinsically lead to unwanted weight gain. Here, we report on the uncoupling of leptin's metabolic and immune functions based on the cross talk with the epidermal growth factor receptor (EGFR). We show that both receptors spontaneously interact and, remarkably, that this complex can partially overrule the lack of LR activation by a leptin antagonistic mutein. Moreover, this leptin mutant induces EGFR phosphorylation comparable to wild-type leptin. Exploiting this non-canonical leptin signalling pathway, we identified a camelid single-domain antibody that selectively inhibits this LR-EGFR cross talk without interfering with homotypic LR signalling. Administration in vivo showed that this single-domain antibody did not interfere with leptin's metabolic functions, but could reverse the leptin-driven protection against starvation-induced thymic and splenic atrophy. These findings offer new opportunities for the design and clinical application of selective leptin and LR antagonists that avoid unwanted metabolic side effects.

Receptors are the master regulators conveying the information provided by the hormone from the extracellular environment to the intracellular milieu. As a result, the level of receptors at the cell surface can determine the signaling strength. Regulation of receptor trafficking to the cell surface or receptor retention processes in intracellular compartments are key mechanisms for leptin receptor (ObR) activity. An alteration of these mechanisms leads to the development of obesity. However, the canonical mechanism of plasma membrane receptors activation is challenged by the discovery that intracellular receptors also have their own signaling activity inside specific intracellular compartments. These intracellular receptors can trigger signaling that regulates a particular function, different from, or in continuity with, surface receptor signaling. We will address both these aspects by focusing particularly on the case of the leptin receptor (ObR), i.e., i) the regulation of its level of exposure to the cell surface and its impact on the development of obesity, and ii) the discovery of its location and signaling in some intracellular compartments.

Neuroplin 1 (NRP1), a transmembrane protein interacting with Vascular Endothelial Growth Factor VEGF-A165 (called here VEGF165) and the tyrosine kinase Receptor 2 (VEGFR2) promote angiogenesis and vascular homeostasis. In a pathophysiological context, several studies suggested that VEGFR2 and NRP1 mediate tumor development and progression. Given the involvement of the VEGF165 network in promoting tumor angiogenesis, NRP1, VEGFR2 and VEGF165 have been identified as targets for anti-angiogenic therapy. No binding assay exists to monitor specifically the binding of VEGF165 to the VEGFR2/NRP1 complex in intact cells. We established a binding assay based on the homogenous time-resolved fluorescence (HTRF®) technology. This unique binding assay enables to assess the interaction of VEGF165 with VEGFR2 or NRP1 within the VEGFR2/NRP1 complex. Ligand binding saturation experiments revealed that VEGF165 binds the VEGFR2/NRP1 complex at the cell surface with a ten to twenty-fold higher affinity compared to SNAP-VEGFR2 or SNAP-NRP1 receptors alone not engaged in the heteromeric complex. The assay allows characterizing the impact of NRP1 ligands on VEGF165 to the complex. It shows high specificity, reproducibility and robustness, making it compatible with high throughput screening (HTS) applications for identifying new VEGF165 antagonists selective for NRP1 or the VEGFR2/NRP1 complex.

In Denmark, the conventional method for treating sewage sludge is mechanical dewatering and subsequent storage. However, sludge treatment reed bed systems, which are holistic sludge treatment facilities combining the dewatering, mineralisation and storage of sludge, have been more common during the last three decades. Treatment of sludge in a sludge treatment reed bed system can be combined with post-treatment (further dewatering and mineralisation) on a stockpile area. This study aimed to compare the environmental performances of a mechanical sludge treatment method with the sludge treatment reed bed system strategy, using the life cycle assessment approach and a life cycle inventory based on newly generated data obtained from Danish reference facilities. The scenarios based on the different treatment methods were initiated by sludge entering the sludge treatment reed bed system or the centrifuge and terminated by land application of the final sludge product. The environmental impacts caused by the sludge treatment reed bed system strategy were comparable to or lower than those caused by the mechanical sludge treatment method. The impacts on climate change were the same for all the treatment scenarios; however, the conversion of organic carbon and nitrogen into gas species was more efficient in the sludge treatment reed bed system compared to mechanical treatment. Thus, mechanically treated sludge contained more nitrogen, causing higher nitrogen emissions (nitrous oxide, nitrate and ammonia) when applied on land. Furthermore, the impact of resource depletion was higher for mechanical dewatering due to a larger fossil fuel demand related to daily operation and longer transportation distances in this scenario. According to the results of the life cycle assessment, there were no considerable environmental gains made by combining the treatment of sludge in a sludge treatment reed bed system with post-treatment on a stockpile area. However, some practical aspects, which are not expressed in a life cycle assessment, should also be taken into consideration when evaluating the performances of sludge treatment scenarios.

The hypothalamic arcuate nucleus (ARC) is a major integration center for energy and glucose homeostasis that responds to leptin. Resistance to leptin in the ARC is an important component of the development of obesity and type 2 diabetes. Recently, we showed that Endospanin1 (Endo1) is a negative regulator of the leptin receptor (OBR) that interacts with OBR and retains the receptor inside the cell, leading to a decreased activation of the anorectic STAT3 pathway. Endo1 is up-regulated in the ARC of high fat diet (HFD)-fed mice, and its silencing in the ARC of lean and obese mice prevents and reverses the development of obesity. Objective Herein we investigated whether decreased Endo1 expression in the hypothalamic ARC, associated with reduced obesity, could also ameliorate glucose homeostasis accordingly. Methods We studied glucose homeostasis in lean or obese mice silenced for Endo1 in the ARC via stereotactic injection of shRNA-expressing lentiviral vectors. Results We observed that despite being leaner, Endo1-silenced mice showed impaired glucose homeostasis on HFD. Mechanistically, we show that Endo1 interacts with p85, the regulatory subunit of PI3K, and mediates leptin-induced PI3K activation. Conclusions Our results thus define Endo1 as an important hypothalamic integrator of leptin signaling, and its silencing differentially regulates the OBR-dependent functions., Highlights • Endospanin1 interacts with p85, the regulatory subunit of PI3K. • Endospanin1 silencing increases STAT3 but decreases AKT activation mediated by leptin. • Endospanin1 dissociates leptin-regulated body weight and glucose homeostasis. • Endospanin1 differentially regulates leptin signaling and biological functions.

Spildevandsslam er restproduktet dannet ved rensning af spildevand fra husstande. Siden implementeringen af strengere krav til rensning af spildevand i den Europæiske Union i 2005 er produktionen af slam steget markant, hvilket øger efterspørgslen for mere effektiv behandling og genanvendelse af slam.I Danmark er en af de mest anvendte genanvendelsesstrategier for spildevandsslam ud-bringning på landbrugsjord, da dette giver mulighed for at recirkulere næringsstoffer og mikroelementer, og derved erstatter brugen af handelsgødning. I Danmark behandles spil-devandsslam konventionelt via mekanisk afvanding. I slutningen af 1980'erne blev der imidlertid indført en alternativ slambehandlingsmetode, biologiske slamanlæg (BSA). I 2016 var der i Danmark mere end 100 BSA i drift. Behandling af slam i BSA betragtes ofte som mere miljøvenlig i forhold til konventionelle slambehandlingsmetoder. Der er imidlertid kun udført få undersøgelser med formål at vurdere de miljømæssige effekter ved brug af BSA ift. andre slambehandlingsmetoder. Grundet et sparsomt datagrundlag for BSA er resultaterne af allerede udførte miljøvurderinger desuden behæftet med væsentlig usikkerhed.Formålet med projektet var at udføre en miljøvurdering af behandling af spildevandsslam i BSA, og at sammenligne denne med mekanisk behandling på centrifuge og efterfølgende oplagring. Projektet fulgte Erhvervs Ph.d. Programmet, udbudt af Innovationsfonden, og foregik som et samarbejde mellem Danmarks Tekniske Universitet (DTU) og den danske miljøingeniørvirksomhed Orbicon A/S. Resultatet af projektet var et metodespecifikt datasæt for BSA til brug i livscyklusvurderinger, og en livscyklusvurdering af BSA og mekanisk behandling, baseret på danske forhold.For at opnå pålidelige resultater var målet at generere nye data repræsentative for behandling af slam i BSA. Tre fokusområder blev valgt: Kvantificering af biologiske gasemissioner fra selve behandlingsprocessen i BSA, kortlægning af massestrømme gennem behand-lingsprocessen og en undersøgelse af dynamikken i omdannelse og udvaskning af kulstof- og nitrogenforbindelser i det færdigbehandlede slamprodukt i forbindelse med udbringning på landbrugsjord. For at gøre vurderingen af de to behandlingsmetoder så præcis som muligt, blev der for de samme fokusområder også indsamlet data repræsentative for mekanisk behandling af slam. Felt- og laboratoriearbejde udgjorde en væsentlig del af arbejdsprocessen. Data blev ind-samlet fra tre danske BSA kendt for at være veldrevne og for at levere et færdigt slamprodukt af god kvalitet. Endvidere blev data, repræsentative for mekanisk behandling af slam og for de samme fokusområder, også indsamlet. For at gøre data for de to behandlingsteknologier så sammenlignelige som muligt, blev størstedelen af data indsamlet på et renseanlæg, som anvender både BSA og mekanisk afvanding på centrifuge.Livscyklusvurderingen inkluderede 14 miljøpåvirkningskategorier. De miljømæssige bidrag blev normaliserede til at repræsentere de miljømæssige påvirkninger som følge af behandling af 1000 kg slam (vådvægt). Livscyklusvurdering fulgte de internationale standarder for livscyklusvurderingsprincippet. En attributionel tilgang til vurderingen blev valgt, hvilket betyder at sammenligningen tager udgangspunkt i teknologiernes aktuelle formåen. For alle påvirkningskategorier blev bidragene normaliserede til personækvivalenter (PE), hvor én PE repræsenterer det årlige bidrag produceret af én gennemsnitlig person. Tre scenarier for slambehandling blev opstillet: 1) mekanisk behandling, efterfulgt af oplagring udbringning på landbrugsjord (S-CEN), 2) behandling i BSA efterfulgt af udbringning på landbrugsjord (S-STRB) og 2) behandling i BSA efterfulgt af efterbehandling på omlasteplads og udbringning på landbrugsjord (S-SPA).Målsætningen om at producere et datasæt for BSA brugbart i livscyklusvurderinger, samt et datasæt, repræsentativt for mekanisk behandlet slam, blev nået. Biologiske slamanlæg viste sig at klare sig tilsvarende eller bedre end mekanisk slambehandling. Miljøpåvirkningen forårsaget af de to scenarier baseret på BSA (S-STRB og S-SPA) var stort set ens. I forhold til toksikologiske effekter var miljøpåvirkningen den samme for alle tre scenarier, svarende til 2.010-2 PE for påvirkningskategorierne Human Toksicitet – Ikke-kræftfremkaldende stoffer og Økotoksicitet, og 5.0 10-4 PE for kategorien Human Toksicitet – Kræftfremkaldende stoffer. Toksikologiske effekter blev primært forårsaget af metaller, hvilke for alle tre scenarier blev opkoncentreret i det færdigbehandlede slam, og derved ultimativt udbragt på landbrugsjord. Emissionsrater for CO2, CH4 og N2O fra biologiske processer i slam under behandling i BSA, blev målt for alle fire årstider. Resultaterne viste, at årstidsvariationer giver anledning til væsentlige udsving i emissionerne af de nævnte gasarter, og derfor bør inddrages, når gennemsnitlige årsrater beregnes. For mekanisk behandlet og efterfølgende oplagret slam var emissionsraten af CO2 meget lavere end for BSA, hvilket afspejler mindre biologisk aktivitet i mekanisk behandlet slam. Den procentvise andel af kulstof og nitrogen omdannet til de potente klimagasser CH4 og N2O var derimod lavere for BSA, hvilket betød at de miljømæssige bidrag til påvirkningskategorien Klimaforandringer var lige store for BSA (S-STRB og S-SPA) og mekanisk behandling (S-CEN), begge 9.0 10-4 PE, på trods af højere biologisk aktivitet i BSA.Som følge af den lavere biologiske aktivitet i oplagret, mekanisk behandlet slam viste mas-sestrømsanalysen at koncentrationerne af kulstof- og nitrogenforbindelser i det færdigbe-handlede slamprodukt, produceret af denne teknologi, var højere end i det færdigbehandlede slamprodukt fra BSA. Derfor var bidragene til påvirkningskategorier relateret til eutrofiering og forsuring højere fra mekanisk behandlet slam, især for kategorien Marin Eutrofiering, hvor det samlede bidrag fra mekanisk behandlet slam (S-CEN) udgjorde 8.0 10-4 PE, mens det for slam, behandlet i BSA (S-STRB og S-SPA), udgjorde 3.0 10-4 PE.Behandlingsprocessen knyttet til BSA havde et lavere forbrug af abiotiske ressourcer, ho-vedsageligt på grund af at den mekaniske behandlingsproces kræver et input af polymer-masse, hvilket BSA ikke gør. Desuden giver mekanisk behandlet slam ofte anledning til lugtgener, mens slam, behandlet i et velfungerende BSA, er uden lugt. Dette betyder, at slam behandlet i BSA typisk hurtigt bliver afsat til landbrug i lokalområdet, mens mekanisk afvandet slam må transporteres over længere afstande til landbrug, der er villige til modtage det, hvilket resulterer i et højere forbrug af brændstof i forbindelse med transport.I fremtiden vil det være relevant at bruge de nygenererede data for BSA til at udføre livs-cyklusvurderinger, der sammenligner teknologien med andre ofte anvendte slambehand-lingsmetoder. Det vil desuden være relevant at skabe lignende datasæt for BSA beliggende i andre klimazoner, og at udvide datasættende med detaljer om de økonomiske aspekter af behandlingsprocessen. Sewage sludge is generated from the treatment of domestic wastewaters at wastewater treatment plants. Since the implementation of stricter requirements for wastewater treatment in the European Union in 2005, the amount of sludge produced has increased, creating the demand for more effective treatment and recycling. In Denmark, the application of sludge on agricultural land is an often-used recycling strategy, as it returns nutrients and microelements to the soil, which can substitute for commercial fertilisers. Conventionally, sludge produced in Denmark is dewatered with mechanical devices; however, in the late 1980s, sludge treatment reed bed (STRB) systems were intro-duced in Denmark and in 2016, more than 100 STRB systems were operating in the country. Sludge treatment in STRB systems is often considered more environmentally friendly compared to mechanical sludge treatment technologies, albeit only a few life cycle assess-ments (LCAs) comparing the environmental performances of sludge treatment technologies include STRB systems. Furthermore, as data on the STRB system technology suitable for LCA are scarce, the results of these LCAs are unreliable.The project aimed at generating data on the STRB system technology that would be useable for LCA. Based on identified knowledge gaps, research focused on three areas; quantification of gas emissions directly related to treatment, establishment of substance flows through the technology and the fate of carbon and nitrogen-based compounds in treated sludge when applied to the land. The overall goal of the project was to perform an LCA comparing the environmental performance of the STRB system technology with a conventional technology based on mechanical dewatering of sludge on a decanter centrifuge and subsequent storage. Geographically, the project focused on Denmark, and was carried out as a collaborative effort between the Technical University of Denmark (DTU) and the Danish environmental consultancy Orbicon A/S. The outcome of the project was a dataset on the STRB system technology usable for LCA, and an LCA comparing the environmental profiles of the STRB system technology and a mechanical treatment technology, constituting a basis for decision-making in relation to choice of technology.A major part of the project involved performance of fieldwork and laboratory work. Data were collected at three Danish, well-operated STRB systems; furthermore, data required to represent the mechanical treatment technology were collected alongside data on STRB sys-tems. Most of the data collection was undertaken at a wastewater treatment plant housing both technologies, thereby making it possible to make the two datasets as comparable as possible.Fourteen environmental impact categories were included in the LCA, and the environmental loadings and saving provided by the sludge treatment technologies normalised to represent the treatment of 1000 kg wet weight of sludge. The life cycle inventory and the choices underlying the life cycle impact assessment were based on international acknowledged standards and recommendations. An attributional LCA approach was chosen, and the loadings and savings for all impact categories were normalised to people equivalents (PE) (the annual loadings and savings provided by one average person). Three sludge treatment scenarios were defined: 1) mechanical treatment on centrifuge, followed by storage and finally land application, 2) treatment in an STRB system and finally land application (S-STRB), and 3) treatment in an STRB system, followed by post-treatment on a stockpile area (SPA) and finally application (S-SPA).The project succeeded in generating data on STRB systems, which could form the basis for a LCA, and comparable data related to mechanical sludge treatment. The results of the LCA revealed that STRB systems performed comparable to or better than mechanical treatment. The two scenarios based on the STRB system technology (S-STRB and S-SPA) performed comparable which only minor differences.According to toxic impact categories, which for both technologies were mainly impacted by metals contained by treated sludge applied on land, the three scenarios performed com-parable. Indeed, the substance flow analyses revealed that the metals held by sludge subjected to treatment for all scenarios were accumulated in the final sludge product. For all scenarios, the net-loadings for the impact categories Human Toxicity – Non-Carcinogenic and Ecotoxicity corresponded to 2.010-2 PE, and for Human Toxicity – Carcinogenic to 5.0 10-4 PE.Emission rates of CO2, CH4 and N2O related to biological processes in sludge subjected to treatment in STRB systems were measured during all four seasons of the year. The results revealed that seasonal variations were considerable, and should be taken into account when calculating annual, average emission rates. The emission rate of CO2 measured from external storage of mechanically treated sludge was much lower compared to those measured for STRB systems, reflecting a lower microbial activity in the mechanical dewatered sludge. As the emission rates of the potent greenhouse gasses CH4 and N2O were larger for mechanical dewatered sludge, the net environmental loadings provided to the impact category Climate Change by this technology (S-CEN) and the STRB system technology (S-STRB and S-SPA) ended up being equally sized (9.010-4 PE), despite of higher biological activity in the STRB systems.As a consequence of the lower microbial activity in mechanically treated sludge, the con-centration of carbon and nitrogen-based compounds in the final sludge product produced by this treatment technology was higher compared to the final sludge product produced by treatment in STRB systems. Hence, the loadings affecting impact categories related to eu-trophication and acidification were higher for the mechanical treatment technology, espe-cially in relation to the category Marine Eutrophication, the net-loadings to this category being 8.0 10-4 PE for mechanical treatment (S-CEN) and 3.0 10-4 PE for STRB systems (S-STRB and S-SPA).The STRB system technology consumed fewer abiotic resources, due mainly to the fact that the mechanical treatment process requires an input of polymer coagulant, while a STRB system does not require this contribution. Furthermore, as mechanically treated sludge often have a stronger odour compared to sludge treated in STRB systems, the latter is often claimed by the local land application sites, while mechanically treated sludge often must be transported longer distances to land application sites willing to apply it. Hence, the STRB system technology required a lower input of fuel for transportation.In the future, it would be relevant to use the obtained data on STRB systems to compare the technology with other sludge treatment technologies commonly used. Furthermore, it would be relevant to generate a comparable dataset on representing the performance of the technology in other climate zones, and to expand the data set with more data related to economics, making it possible to make more detailed economical assessments.

Sludge treatment reed beds (STRB) are considered as eco-friendly and sustainable alternatives to conventional sludge treatment methods, although little is known about greenhouse gas emissions from such systems. We measured CO2 and CH4 emissions and substrate characteristics in a STRB, an occasionally loaded sludge depot (SD) and a natural reed wetland (NW). The aim was to compare (i) emissions among the sites in relation to substrate characteristics and to compare (ii) emissions before and after sludge loading in the STRB. The STRB emitted twice as much CO2 (1200 mg m-2 h-1) as the SD, whereas the SD emitted four times more CH4 (2 mg m-2 h-1) than the STRB. The NW had the lowest emissions of both gases. The differences in gas emissions among the sites were primarily explained by differences in the availability of oxygen in the substrate. As a consequence of overloading and poor management, the SD had no vegetation and a poor dewatering capacity, which resulted in anaerobic conditions favoring CH4 emission. In contrast, the well-managed STRB had more aerobic conditions in the sludge residue resulting in low CH4 emission rates. We conclude that well-designed and well-managed STRBs have a low climate impact relative to conventional treatment alternatives, but that overloading and poor sludge management enhances the emissions of CH4. Sludge treatment reed beds (STRB) are considered as eco-friendly and sustainable alternatives to conventional sludge treatment methods, although little is known about greenhouse gas emissions from such systems. We measured CO2 and CH4 emissions and substrate characteristics in a STRB, an occasionally loaded sludge depot (SD) and a natural reed wetland (NW). The aim was to compare (i) emissions among the sites in relation to substrate characteristics and (ii) emissions before and after sludge loading in the STRB. The STRB emitted twice as much CO2 (1200 mg m(-2) h(-1)) as the SD, whereas the SD emitted four times more CH4 (2 mg m(-2) h(-1)) than the STRB. The NW had the lowest emissions of both gases. The differences in gas emissions among the sites were primarily explained by differences in the availability of oxygen in the substrate. As a consequence of overloading and poor management, the SD had no vegetation and a poor dewatering capacity, which resulted in anaerobic conditions favoring CH4 emission. In contrast, the well-managed STRB had more aerobic conditions in the sludge residue resulting in low CH4 emission rates. We conclude that well-designed and well-managed STRBs have a low climate impact relative to conventional treatment alternatives, but that overloading and poor sludge management enhances the emissions of CH4.

Leptin targets specific receptors (OB-R) expressed in the hypothalamus to regulate energy balance. Leptin decreases food intake in normal weight individuals, but this effect is blunted in obese subjects who are characterized by a state of leptin resistance. The prevention of leptin resistance is one of the major goals of obesity research. Recently, we identified endospanin 1 as a negative regulator of OB-R, which by interacting with OB-R retains the receptor inside the cell. We show here that in obese mice endospanin 1 is upregulated in the hypothalamic arcuate nucleus (ARC), the major brain structure involved in body weight regulation, suggesting that endospanin 1 is implicated in obesity development and/or the installation of leptin resistance. In contrast, silencing of endospanin 1 with lentiviral vectors in the ARC of obese mice fully restores leptin responsiveness when combined with a switch to ad libitum fed chow diet. The recovery of central leptin sensitivity is accompanied by sustained body weight loss and amelioration of blood lipid parameters and steatosis. Collectively, our results define endospanin 1 as a novel therapeutic target against obesity.

International audience; Leptin secreted by adipocytes acts on the brain to reduce food intake by regulating neuronal activity in the mediobasal hypothalamus (MBH). Obesity is associated with resistance to high circulating leptin levels. Here, we demonstrate that peripherally administered leptin activates its receptor (LepR) in median eminence tanycytes followed by MBH neurons, a process requiring tanycytic ERK signaling and the passage of leptin through the cerebrospinal fluid. In mice lacking the signal-transducing LepRb isoform or with diet-induced obesity, leptin taken up by tanycytes accumulates in the median eminence and fails to reach the MBH. Triggering ERK signaling in tanycytes with EGF reestablishes leptin transport, elicits MBH neuron activation and energy expenditure in obese animals, and accelerates the restoration of leptin sensitivity upon the return to a normal-fat diet. ERK-dependent leptin transport by tanycytes could thus play a critical role in the pathophysiology of leptin resistance, and holds therapeutic potential for treating obesity.

A sludge treatment reed bed system (STRB) is a technology used for dewatering and stabilising sewage sludge via assisted biological mineralisation, which creates a sludge residue suitable for use as fertiliser on agricultural land. We evaluated the effect of sludge residue storage time (stabilisation time) for three STRBs on soil N mineralisation and CO 2 and N 2 O emissions in soil. The experiment revealed that the N mineralisation rate and emissions of CO 2 and N 2 O decreased as a function of treatment time in the STRBs. Mixed sludge residue (sludge residue subjected to different treatment times) for the three STRBs resulted in N mineralisation rates similar to the sludge residue subjected to a shorter treatment time but lower N 2 O emissions similar to the values of the older sludge residue. This finding reveals that combining fresh and more stabilised sludge residue ensures high N availability and reduces N 2 O emissions when applied to land.

The pleiotropic cytokine hormone leptin, by activating its receptor OB-R, plays a major role in many biological processes, including energy homeostasis, immune function, and cell survival and proliferation. Abnormal leptin action is associated with obesity, autoimmune diseases, and cancer. The pharmacological characterization of OB-R and the development of synthetic OB-R ligands are still in their infancy because currently available binding assays are not compatible with ligand saturation binding experiments and high-throughput screening (HTS) approaches. We have developed here a novel homogeneous time-resolved fluorescence-based binding assay that overcomes these limitations. In this assay, fluorescently labeled leptin or leptin antagonist binds to the SNAP-tagged OB-R covalently labeled with terbium cryptate (Tb). Successful binding is monitored by measuring the energy transfer between the Tb energy donor and the fluorescently labeled leptin energy acceptor. Ligand binding saturation experiments revealed high-affinity dissociation constants in the subnanomolar range with an excellent signal-to-noise ratio. The assay performed in a 384-well format shows high specificity and reproducibility, making it perfectly compatible with HTS applications to identify new OB-R agonists or antagonists. In addition, fluorescently labeled leptin and SNAP-tagged OB-R will be valuable tools for monitoring leptin and OB-R trafficking in cells and tissues.

Sludge treatment reed bed (STRB) systems have been used for dewatering and mineralisation of sludge in Europe since 1988. STRB systems provide substantial environmental, economic, and operational benefits compared to mechanical sludge dewatering solutions such as belt presses and centrifuges. They require less energy, no chemicals, reduce the sludge volume and produce bio solids with dry solid contents up to 20–40% under Danish climate conditions, depending on the sludge quality. Experience has shown that sludge treated in STRBs represents a high quality product with a low content of pathogens and hazardous organic compounds, qualities that make it suitable for recycling on agricultural land. The upfront capital cost for STRBs are often higher compared to mechanical dewatering devices. However, the operational expenses (OPEX) (including energy, chemicals, bio solid handling) are significantly lower compared to conventional mechanical dewatering devices, delivering an economic break-even of about 3–5 years. This paper provides an overview of the operation and maintenance costs and environmental benefits of a typical STRB based on the experiences gained from the operation of a large number of STRBs with yearly treatment capacities between 100 and 3,000 tonnes of dry solid up to approximately 250,000 PE in Denmark and Europe.

International audience; CONTEXT: The genomic organization of the LEPR gene is complex and generates three independent transcripts whose respective functions are still poorly understood. METHODS/RESULTS: We describe here a 7-year old patient with a homozygous 80kb deletion in the chromosomal 1p31.3 region with early onset obesity, mental retardation and epilepsy. The deleted region comprises the proximal promoter and exons 1 and 2 of the LEPR gene and exons 5 to 19 of the DNAJC6 gene. The deletion leads to the deficiency of all canonical OB-R isoforms but maintains the B219 OB-R short isoforms controlled by the preserved second LEPR promoter. The DNAJC6 gene encodes auxilin-1, a protein required for clathrin-dependent recycling of synaptic vesicles in neurons that is possibly at the origin of the mental retardation and epilepsy phenotype. The obese phenotype and the absence of signaling-competent OB-R are consistent with previously reported individuals with OB-R deficiency. The deletion eliminates an additional transcript of the LEPR gene that encodes endospanin-1, a protein that has been genetically and biochemically linked to OB-R function. CONCLUSIONS: Our study confirms the phenotype of individuals with OB-R deficiency and postulates the effects of auxilin-1 deficiency (mental retardation/epilepsy) and endospanin-1 deficiency (OB-R specific functions) in humans.

Recent genetic studies have highlighted the potential involvement of melatonin receptor 1 (MT(1)) and melatonin receptor 2 (MT(2)) in the pathogenesis of type 2 diabetes. Here we report that mice lacking MT(1) (MT(1) KO) tend to accumulate more fat mass than WT mice and exhibit marked systemic insulin resistance. Additional experiments revealed that the main insulin signaling pathway affected by the loss of MT(1) was the activation of phosphatidylinositol-3-kinase (PI3K). Transcripts of both catalytic and regulatory subunits of PI3K were strongly down-regulated within MT(1) KO mice. Moreover, the suppression of nocturnal melatonin levels within WT mice, by exposing mice to constant light, resulted in impaired PI3K activity and insulin resistance during the day, similar to what was observed in MT(1) KO mice. Inversely, administration of melatonin to WT mice exposed to constant light, was sufficient and necessary to restore insulin mediated PI3K activity and insulin sensitivity. Hence our data demonstrate that the activation of MT(1) signaling at night modulates insulin sensitivity during the day via the regulation of the PI3K transcription and activity. Lastly we provide evidence that decreased expression of MTNR1A (MT(1)) in the liver of diabetic individuals is associated with poorly controlled diabetes.

Produite par le tissu adipeux, la leptine regule positivement le comportement alimentaire et la depense energetique. Cependant, les personnes obeses, chez qui le taux de leptine est anormalement eleve, sont incapables de repondre a l’hormone et se trouvent dans un etat de resistance. La leptine declenche la reponse biologique en activant ses recepteurs (OB-R), et leur quantite exposee a la surface de la cellule est un des facteurs determinants de la sensibilite d’une cellule a la leptine. Notre equipe a identifie OB-RGRP, qui est issu du meme gene que celui codant pour OB-R, comme un nouveau regulateur de ce dernier. OB-RGRP est une proteine a quatre domaines transmembranaires qui interagit avec OB-R et le retient dans les compartiments intracellulaires, regulant ainsi son expression de surface. L’extinction ciblee du gene OB-RGRP au niveau du noyau arque (ARC) de l’hypothalamus, site principal d’action de la leptine et important pour la regulation de l’homeostasie energetique, est capable de prevenir l’obesite des souris soumises a un regime gras. Dans cet article, nous discutons de cette decouverte originale.

Recent evidence has highlighted the role of histamine in inflammation. Since this monoamine has also been strongly implicated in the pathogenesis of type-1 diabetes, we assessed its effect in the nonobese diabetic (NOD) mouse model. To this end, we used mice (inactivated) knocked out for the gene encoding histidine decarboxylase, the unique histamine-forming enzyme, backcrossed on a NOD genetic background. We found that the lack of endogenous histamine in NOD HDC−/−mice decreased the incidence of diabetes in relation to their wild-type counterpart. Whereas the proportion of regulatory T and myeloid-derived suppressive cells was similar in both strains, histamine deficiency was associated with increased levels of immature macrophages, as compared with wild-type NOD mice. Concerning the cytokine pattern, we found a decrease in circulating IL-12 and IFN-γin HDC−/−mice, while IL-6 or leptin remained unchanged, suggesting that histamine primarily modulates the inflammatory environment. Paradoxically, exogenous histamine given to NOD HDC−/−mice provided also protection against T1D. Our study supports the notion that histamine is involved in the pathogenesis of diabetes, thus providing additional evidence for its role in the regulation of the immune response.

G-protein-coupled receptors (GPCRs) are important drug targets and are involved in virtually every biological process. However, there are still more than 140 orphan GPCRs, and deciphering their function remains a priority for fundamental and clinical research. Research on orphan GPCRs has concentrated mainly on the identification of their natural ligands, whereas recent data suggest additional ligand-independent functions for these receptors. This emerging concept is connected with the observation that orphan GPCRs can heterodimerize with GPCRs that have identified ligands, and by so doing regulate the function of the latter. Pairing orphan GPCRs with their potential heterodimerization partners will have a major impact on our understanding of the extraordinary diversity offered by GPCR heterodimerization and, in addition, will constitute a novel strategy to elucidate the function of orphan receptors that needs to be added to the repertoire of 'deorphanization' strategies.

One-third of the approximately 400 nonodorant G protein-coupled receptors (GPCRs) are still orphans. Although a considerable number of these receptors are likely to transduce cellular signals in response to ligands that remain to be identified, they may also have ligand-independent functions. Several members of the GPCR family have been shown to modulate the function of other receptors through heterodimerization. We show that GPR50, an orphan GPCR, heterodimerizes constitutively and specifically with MT(1) and MT(2) melatonin receptors, using biochemical and biophysical approaches in intact cells. Whereas the association between GPR50 and MT(2) did not modify MT(2) function, GPR50 abolished high-affinity agonist binding and G protein coupling to the MT(1) protomer engaged in the heterodimer. Deletion of the large C-terminal tail of GPR50 suppressed the inhibitory effect of GPR50 on MT(1) without affecting heterodimerization, indicating that this domain regulates the interaction of regulatory proteins to MT(1). Pairing orphan GPCRs to potential heterodimerization partners might be of clinical importance and may become a general strategy to better understand the function of orphan GPCRs.

The function of leptin, initially confined to its role in energy homeostasis and obesity, has now expanded to the regulation of reproduction, glucose homeostasis, bone formation, wound healing and the immune system. Both stimulation and inhibition of the molecular target of leptin, the leptin receptor (LR), might find applications in disease treatment. Recent advances in the understanding of LR activation mechanisms have led to the design of LR antagonists. Several assays have been developed for the screening and evaluation of LR ligands. Both the extracellular and the intracellular domains of the LR are potential drug targets. The bioluminescence resonance energy transfer technique can be used to screen for compounds that target the extracellular part of the LR, and we propose that the novel reverse mammalian protein-protein interaction trap technique can be used to screen compounds that affect intracellular aspects of LR signalling. These assays can be easily adapted to other pharmacologically relevant receptors.

Interacting proteins in rapid association equilibrium exhibit coupled migration under the influence of an external force. In sedimentation, two-component systems can exhibit bimodal boundaries, consisting of the undisturbed sedimentation of a fraction of the population of one component, and the coupled sedimentation of a mixture of both free and complex species in the reaction boundary. For the theoretical limit of diffusion-free sedimentation after infinite time, the shapes of the reaction boundaries and the sedimentation velocity gradients have been predicted by Gilbert and Jenkins. We compare these asymptotic gradients with sedimentation coefficient distributions, c(s), extracted from experimental sedimentation profiles by direct modeling with superpositions of Lamm equation solutions. The overall shapes are qualitatively consistent and the amplitudes and weight-average s-values of the different boundary components are quantitatively in good agreement. We propose that the concentration dependence of the area and weight-average s-value of the c(s) peaks can be modeled by isotherms based on Gilbert-Jenkins theory, providing a robust approach to exploit the bimodal structure of the reaction boundary for the analysis of experimental data. This can significantly improve the estimates for the determination of binding constants and hydrodynamic parameters of the complexes.

The phenotypic exploration of obesity mutant mice in the 1950s was the starting point of a long scientific journey, which climaxed more than 40 years later with the identification of leptin and its receptor LepR. This was rapidly followed by the discovery of rare congenital leptin deficiency and mutations in LEPR in subjects with strikingly similar early-onset and massive obesity phenotypes as in obese mutant mice. In this chapter, we describe several genetic abnormalities found in human LEPR and their dramatic clinical consequences. We address the question of the difficult management of patients with LEPR mutation. Additionally, a wealth of information on LEPR structure and mechanism of action has been produced through molecular, biochemical, and modeling studies. However, as discussed in the first part of this chapter, deciphering the molecular mechanisms underlying resistance to leptin, which occur in the vast majority of obese subjects, remains a challenge.

International audience; After its discovery in 1994, leptin became the great hope as an anti-obesity treatment based on its ability to reduce food intake and increase energy expenditure. However, treat-ing obese people with exogenous leptin was unsuccessful in most cases since most of them present already high circulating leptin levels to which they do not respond anymore defining the so-called state of "leptin resistance." Indeed, leptin therapy is unsuccessful to lower body weight in commonly obese people but effective in people with rare single gene mutations of the leptin gene. Consequently, treatment of obese people with leptin was given less attention and the focus of obesity research shifted toward the prevention and reversal of the state of leptin resistance. Many of these new promising approaches aim to restore or sensitize the impaired function of the leptin receptor by pharmacological means. The current review will focus on the different emerging therapeutic strategies in obesity research that are related to leptin and its receptor.

The effect of mutations on the interactions between dimers in R67 dihydrofolate reductase (R67 DHFR), a tetrameric enzyme conferring resistance to trimethoprim, was investigated by site-directed mutagenesis combined with phenotypic, enzymatic, and biochemical analysis. Some 14 mutants at two positions involved in a hydrogen bond between dimers were constructed. All were shown to be dimers. However, complementation between pairs of dimeric mutated proteins resulted in the restoration of the enzymatic activity and heterotetramer formation. A combinatorial approach was set up to create efficiently such heterotetramers and identify the complementing pairs of mutations. A dozen of such pairs were found. An accurate method was set up to measure the association of the complementing dimers in a “quasi-isologous” heterotetramer and used to study the effects of mutations and pH on the association. Thus, the pair of proteins bearing respectively the S59A and H62L mutations was shown to form heterotetramers with catalytic properties close to those of the wild-type protein. Its association was as strong as that of the wild-type protein at cytoplasmic pH (6.5), and was more stable at lower pH values. A double-mutant protein bearing simultaneously the S59A and H62L mutations was produced and analyzed. Its association was weakened by 1.2 kcal/mol as compared to the wild-type enzyme at pH 6.5 but was insensitive to pH. Comparing the energy of association between dimers in the wild-type protein, the heterotetramer and the double mutant allowed us to dissect the effects of the pH and of the molecular context on a subset of interactions between the R67 DHFR subunits.

The leptin receptor, OBR, is involved in the regulation of whole-body energy homeostasis. Most obese people are resistant to leptin and do not respond to the hormone. The prevention and reversal of leptin resistance is one of the major current goals of obesity research. We showed previously that increased OBR cell surface expression concomitantly increases cellular leptin signaling and prevents obesity development in mice. Improvement of OBR cell surface expression can thus be considered as an interesting anti-obesity therapeutic strategy. To identify compounds that increase the surface expression of OBR, we developed a cell-based, phenotypic assay to perform a high-content screen (HCS) against a library of 50,000 chemical compounds. We identified 67 compounds that increased OBR cell surface expression with AC50 values in the low micromolar range and no effect on total OBR expression and cellular toxicity. Compounds were classified into 16 chemical clusters, of which 4 potentiated leptin-promoted signaling through the JAK2/STAT3 pathway. In conclusion, development of a robust phenotypic screening approach resulted in the discovery of four new scaffolds that demonstrate the desired biological activity and could constitute an original therapeutic solution against obesity and associated disorders.

During calorie restriction in mice, increased expression of FGF21 causes growth attenuation and growth hormone (GH) insensitivity. Previous evidence also indicates that fasting-associated increased expression of leptin receptor overlapping transcript (LEPROT) and LEPROT-like 1 (LEPROTL1) (two proteins that regulate intracellular protein trafficking) reduces GH receptor cell-surface expression in the liver. Thus, we hypothesized that FGF21 causes GH insensitivity through regulation of LEPROT and/or LEPROTL1 expression. After 4 weeks of food restriction, LEPROT and LEPROTL1 mRNA expression in the liver and in the tibial growth plate of wild-type (WT) mice was increased compared with WT mice fed ad libitum. In Fgf21 knock-out (KO) mice, LEPROT and LEPROTL1 mRNA expression in food-restricted and fed ad libitum was similar, with the exception of a subgroup of food-restricted Fgf21 KO mice treated with recombinant human (rh) FGF21 that experienced increased LEPROT and LEPROTL1 mRNA expression compared with untreated food-restricted Fgf21 KO mice. In cultured growth plate chondrocytes, FGF21 stimulated LEPROT and LEPROTL1 mRNA expression, with such effect being prevented in chondrocytes transfected with FGFR1 siRNA or ERK1 siRNA. In cells transfected with control siRNA, GH increased [3H]thymidine incorporation, collagen X, and IGF-1 mRNA expression, with all effects being prevented by rhFGF21. In addition, rhFGF21 decreased 125I-GH binding. In LEPROT siRNA- and/or LEPROTL1 siRNA-transfected cells, rhFGF21 did not prevent the GH stimulatory effects on thymidine incorporation, collagen X, and IGF-1 expression; furthermore, rhFGF21 did not prevent 125I-GH binding. Consistent with the effects of rhFGF21, LEPROT overexpression in chondrocytes resulted in the inhibition of GH action. Our findings indicate that the increased expression of FGF21 during chronic undernutrition inhibits GH action on chondrocytes by activating LEPROT and LEPROTL1. Background: FGF21 causes GH insensitivity. Results: Increased FGF21 expression induces LEPROT and LEPROTL1 expression. Inhibition of LEPROT or LEPROTL1 in growth plate chondrocytes prevents the FGF21-mediated inhibition of the GH stimulatory effects on chondrocyte function and IGF-1 expression. Conclusion: FGF21 prevents the GH effects on chondrocytes by activating LEPROT and LEPROTL1. Significance: LEPROT and LEPROTL1 mediate the FGF21 inhibition of GH action.

The structure of the natural cytotoxicity receptor NKp44, described in this issue of Structure, adds to our rapidly expanding knowledge of the structure of natural killer cell receptors, which play a key role in the elimination of virally infected and tumor cells during innate immune responses.

The ability of mammals to maintain a constant body temperature has proven to be a profound evolutionary advantage, allowing members of this class to thrive in most environments on earth. Intriguingly, some mammals employ bouts of deep hypothermia (torpor) to cope with reduced food supply and harsh climates [1, 2]. During torpor, physiological processes such as respiration, cardiac function, and metabolic rate are severely depressed, yet the neural mechanisms that regulate torpor remain unclear [3]. Hypothalamic responses to energy signals, such as leptin, influence the expression of torpor [4-7]. We show that the orphan receptor GPR50 plays an important role in adaptive thermogenesis and torpor. Unlike wild-type mice, Gpr50 -/- mice readily enter torpor in response to fasting and 2-deoxyglucose administration. Decreased thermogenesis in Gpr50 -/- mice is not due to a deficit in brown adipose tissue, the principal site of nonshivering thermogenesis in mice [8]. GPR50 is highly expressed in the hypothalamus of several species, including man [9, 10]. In line with this, altered thermoregulation in Gpr50 -/- mice is associated with attenuated responses to leptin and a suppression of thyrotropin-releasing hormone. Thus, our findings identify hypothalamic circuits involved in torpor and reveal GPR50 to be a novel component of adaptive thermogenesis in mammals. © 2012 Elsevier Ltd.

Endospanin-1 is a negative regulator of the cell surface expression of leptin receptor (OB-R), and endospanin-2 is a homologue of unknown function. We investigated the mechanism for endospanin-1 action in regulating OB-R cell surface expression. Here we show that endospanin-1 and -2 are small integral membrane proteins that localize in endosomes and the trans-Golgi network. Antibody uptake experiments showed that both endospanins are transported to the plasma membrane and then internalized into early endosomes but do not recycle back to the trans-Golgi network. Overexpression of endospanin-1 or endospanin-2 led to a decrease of OB-R cell surface expression, whereas shRNA-mediated depletion of each protein increased OB-R cell surface expression. This increased cell surface expression was not observed with OB-Ra mutants defective in endocytosis or with transferrin and EGF receptors. Endospanin-1 or endospanin-2 depletion did not change the internalization rate of OB-Ra but slowed down its lysosomal degradation. Thus, both endospanins are regulators of postinternalization membrane traffic of the endocytic pathway of OB-R.