Jean-Louis Nahon

Variations in circulating inflammatory factors are related to changes in calorie and carbohydrate intakes early in the course of surgery-induced weight reduction.

BACKGROUNDnObesity is considered a low-grade inflammatory state that improves with weight loss. In addition to acute-phase proteins, other cytokines might contribute to systemic inflammation.nnnOBJECTIVEnOur objective was to compare serum concentrations of a large panel of inflammation-related factors in obese and normal-weight subjects and to determine kinetic changes induced by caloric restriction.nnnDESIGNnThe cohort comprised 14 normal-weight women and 51 obese women who were followed over 2 y after Roux-en-Y gastric bypass. Multiplexed proteomics were used to simultaneously assay 27 cytokines and growth factors in serum.nnnRESULTSnConcentrations of interleukin (IL)-9, IL-1-receptor antagonist, IL-10, interferon-γ-inducible protein 10, macrophage inflammatory protein 1β, monocyte chemoattractant protein 1, IL-8, RANTES (regulated upon activation, normal T cell expressed and secreted), monokine induced by interferon-γ, and vascular endothelial growth factor were found to be elevated in obesity. IL-10 was further elevated in diabetic obese patients, whereas eotaxin was found to be higher only in diabetic subjects. After surgery, many factors showed a biphasic pattern of variation, decreasing sharply at month 3 before rising back to presurgical values at month 6; these changes closely tracked similar kinetic changes in calorie and carbohydrate intake. After 1 y, an overall reduction in cytokines accompanied the reduction in body mass index and an amelioration in metabolic status.nnnCONCLUSIONSnObesity is associated with elevated circulating concentrations of a large panel of cytokines. Coordinated kinetic changes during weight loss suggest an early influence of calorie and carbohydrate intakes, whereas a longer-term reduction in corpulence might prevail in regulating circulating cytokine concentrations. This trial is registered at clincaltrials.gov as NCT00476658.

Pro-melanin concentrating hormone messenger ribonucleic acid and peptides expression in peripheral tissues of the rat.

Melanin-concentrating hormone (MCH) is a cyclic peptide which is predominantly synthetized in the hypothalamus of fish and mammalian brains. In the present paper we examined the expression of MCH mRNA and pro-MCH-derived peptides, i.e. MCH and neuropeptide-(N)-glutamic acid (E) isoleucine (I) amide (NEI), in peripheral tissues of adult rodents. By means of polymerase chain reaction (PCR) of reverse-transcribed RNA, low levels of MCH gene transcripts were detected reliably in testis, stomach, and intestine of Sprague-Dawley and Wistar rats, whereas strong expression was found in hypothalamus. Subsequent sequence analysis of the PCR products verified the authenticity of MCH mRNA found in hypothalamus and stomach. The length of MCH RNA species was measured by Northern blot and multiple MCH RNA species were detected in both rat species. Shortest polyadenylated tails were found in MCH RNAs isolated from the peripheral organs by comparison with hypothalamus MCH RNAs of Wistar rats. In order to localize MCH expression in gastrointestinal and genital tracts of Wistar rats we performed in situ hybridization with specific 33P-labeled oligoprobes joined to immunocytochemical studies with rat MCH or NEI antisera. In testis, the MCH transcripts and pro-MCH-derived peptide immunoreactivities were found at the periphery of the seminiferous tubules, suggesting expression in Sertoli cells. Studies with MCH oligoprobes and antisera directed towards MCH, NEI and alpha A-inhibin revealed similar pattern of expression in isolated Sertoli cells from Swiss mice, indicating that MCH RNA species were actually synthesized and translated in these cells. In the gastrointestinal (GI) tract, the cells expressing MCH RNA species and pro-MCH-derived peptides were predominantly expressed in the antral portion of the stomach and duodenum. Strikingly, distinct oligoprobes, recognizing antisense MCH transcript, revealed a pattern of hybridization in the GI tract similar to this observed with oligoprobes revealing the mature MCH mRNA. Furthermore, total RNA from the pyloric junction, duodenum, jejunum, ileum and hypothalamus as well appeared to contain RNA complementary to MCH mRNA suggesting therefore that antisense MCH RNA species may play a general role in regulation of MCH synthesis. Taken together, our present and previous data indicate that authentic MCH RNA species and translational products are expressed in various rodent tissues at the periphery. The cellular location suggests that MCH and associated peptides may play a role in spermatogenesis and in digestive processes.

Glucose Inhibition Persists in Hypothalamic Neurons Lacking Tandem-Pore K+ Channels

Glucose sensing by hypothalamic neurons triggers adaptive metabolic and behavioral responses. In orexin neurons, extracellular glucose activates a leak K+ current promoting electrical activity inhibition. Sensitivity to external acidification and halothane, and resistance to ruthenium red designated the tandem-pore K+ (K2P) channel subunit TASK3 as part of the glucose-induced channel. Here, we show that glucose inhibition and its pH sensitivity persist in mice lacking TASK3 or TASK1, or both subunits. We also tested the implication of another class of K2P channels activated by halothane. In the corresponding TREK1/2/TRAAK triple knock-out mice, glucose inhibition persisted in hypothalamic neurons ruling out a major contribution of these subunits to the glucose-activated K+ conductance. Finally, block of this glucose-induced hyperpolarizing current by low Ba2+ concentrations was consistent with the conclusion that K2P channels are not required for glucosensing in hypothalamic neurons.

Melanin-concentrating hormone regulates beat frequency of ependymal cilia and ventricular volume

Ependymal cell cilia help move cerebrospinal fluid through the cerebral ventricles, but the regulation of their beat frequency remains unclear. Using in vitro, high-speed video microscopy and in vivo magnetic resonance imaging in mice, we found that the metabolic peptide melanin-concentrating hormone (MCH) positively controlled cilia beat frequency, specifically in the ventral third ventricle, whereas a lack of MCH receptor provoked a ventricular size increase.

Lithium increases melanin-concentrating hormone mRNA stability and inhibits tyrosine hydroxylase gene expression in PC12 cells

Melanin-concentrating hormone (MCH) is a cyclic peptide involved in the regulation of food-intake behaviour and stress response in mammals. Expression of the MCH gene predominates in hypothalamic neurons. Mechanisms governing the regulation of expression of MCH gene in established cell lines were not explored yet. Here, we analysed the actions of nerve growth factor (NGF), dexamethasone, forskolin and lithium on MCH mRNA levels in the PC12 pheochromocytoma cell line. We compared them with those observed on tyrosine hydroxylase (TH) mRNA, constitutively expressed in PC12 cells, and neurotensin (NT) mRNA, taken as a control. In untreated cells, MCH RNA species of high molecular weight were found. Exposure of cells at a combination of NGF and lithium resulted in decreased expression of these MCH RNAs and in the transient production of mature MCH mRNA. Strikingly, after short exposure of PC12 cells to NGF, lithium per se elicited a marked increase in MCH mRNA levels whilst it exerted a potent inhibitory action on TH mRNA expression. Detailed investigations revealed that lithium enhanced MCH mRNA expression through post-transcriptional mechanisms whereas it regulated TH gene expression mainly at the level of transcription. These results demonstrate that lithium, an agent widely used for treatment of manic depressive illness, can exert an opposite effect on MCH and TH mRNA production in PC12 cells. The MCH gene system in NGF-treated PC12 cells provides a good opportunity for studying the effect of lithium on gene expression at post-transcriptional levels in a neuron-like cellular model.

Baclofen and Other GABAB Receptor Agents Are Allosteric Modulators of the CXCL12 Chemokine Receptor CXCR4

CXCR4, a receptor for the chemokine CXCL12 (stromal-cell derived factor-1α), is a G-protein-coupled receptor (GPCR), expressed in the immune and CNS and integrally involved in various neurological disorders. The GABAB receptor is also a GPCR that mediates metabotropic action of the inhibitory neurotransmitter GABA and is located on neurons and immune cells as well. Using diverse approaches, we report novel interaction between GABAB receptor agents and CXCR4 and demonstrate allosteric binding of these agents to CXCR4. First, both GABAB antagonists and agonists block CXCL12-elicited chemotaxis in human breast cancer cells. Second, a GABAB antagonist blocks the potentiation by CXCL12 of high-threshold Ca2+ channels in rat neurons. Third, electrophysiology in Xenopus oocytes and human embryonic kidney cell line 293 cells in which we coexpressed rat CXCR4 and the G-protein inward rectifier K+ (GIRK) channel showed that GABAB antagonist and agonist modified CXCL12-evoked activation of GIRK channels. To investigate whether GABAB ligands bind to CXCR4, we expressed this receptor in heterologous systems lacking GABAB receptors and performed competition binding experiments. Our fluorescent resonance energy transfer experiments suggest that GABAB ligands do not bind CXCR4 at the CXCL12 binding pocket suggesting allosteric modulation, in accordance with our electrophysiology experiments. Finally, using backscattering interferometry and lipoparticles containing only the CXCR4 receptor, we quantified the binding affinity for the GABAB ligands, confirming a direct interaction with the CXCR4 receptor. The effect of GABAergic agents on CXCR4 suggests new therapeutic potentials for neurological and immune diseases.

Differential neuronal expression and projections of melanin-concentrating hormone (MCH) and MCH-gene-overprinted-polypeptide (MGOP) in the rat brain

The rat melanin‐concentrating hormone (MCH) gene may produce, through alternative splicing, either the precursor of MCH and neuropeptide EI, two neuropeptides coexpressed in the zona incerta (ZI) and lateral hypothalamus (LHA), or a putative protein we named previously MCH‐gene‐overprinted‐polypeptide (MGOP). First, we investigated the distribution and relative expression of MCH and MGOP mRNA in the rat brain by Northern blotting, RT‐PCR and in situ hybridization. MGOP gene transcripts were detected mainly in the hypothalamus only by RT‐PCR. Second, different antisera were raised toward the C‐terminus of MGOP and used to identify the translational products. In the rat brain, no MGOP‐processed peptide could be detected based on RP‐HPLC coupled to specific RIA. A polypeptide of 14u2003kDa was found in the secretory pathway of transfected monkey COS7 cells expressing recombinant MGOP. In the rat hypothalamus, a specific protein of 12u2003kDa was identified by Western blot analysis. Finally, distribution of MGOP‐immunoreactivity (IR) was investigated in the rat brain. Colocalization studies demonstrated that 98% of the MGOP‐expressing perikarya in ZI/LHA also synthesized MCH. In addition, numerous, strongly stained MGOP‐containing neurons were encountered in the hypothalamic periventricular nucleus. Perikarya labelled with MGOP antiserum were also found scattered in the cortex, caudate putamen, amygdala and lateral septal nucleus. MCH was not detected in these MGOP‐containing neurons. Strikingly, dense staining of terminals was observed with MGOP antiserum but not with MCH antibodies in the suprachiasmatic, ventromedial and arcuate nuclei, and also in the external layer of the median eminence. These results demonstrated that MGOP and MCH‐IR overlapped in LHA/ZI but displayed a differential distribution in other areas. Based on this cerebral distribution, MGOP may act as a new secreted protein in regulating many neuroendocrine functions, such as nursing, feeding and growth control in associated behavioural components.

Comparative analysis of melanin-concentrating hormone structure and activity in fishes and mammals.

A comparative analysis of the structure of the melanin-concentrating hormone (MCH) precursor reveals that this sequence has been subjected to a higher selection pressure in mammals than in teleosts, suggesting that the structural constraints have not been the same throughout the vertebrate lineage. In contrast, the MCH peptide sequence has been very well conserved in all species. A sensitive and reproducible eel skin assay was developed and allowed us to define the structural features needed for a full MCH bioactivity. It was shown that the minimal structure carrying the critical residues was the same in fishes and in mammals. A pharmacological approach confirmed that MCH receptor activation decreased the cAMP levels in the fish skin, but this effect appeared to be independent from a Galphai protein. We propose that one of the intracellular signaling pathways of the MCH receptor in fish skin is the activation of one or several cellular phosphodiesterases.

Control of Ventricular Ciliary Beating by the Melanin Concentrating Hormone-Expressing Neurons of the Lateral Hypothalamus: A Functional Imaging Survey

The cyclic peptide Melanin Concentrating Hormone (MCH) is known to control a large number of brain functions in mammals such as food intake and metabolism, stress response, anxiety, sleep/wake cycle, memory, and reward. Based on neuro-anatomical and electrophysiological studies these functions were attributed to neuronal circuits expressing MCHR1, the single MCH receptor in rodents. In complement to our recently published work (1) we provided here new data regarding the action of MCH on ependymocytes in the mouse brain. First, we establish that MCHR1 mRNA is expressed in the ependymal cells of the third ventricle epithelium. Second, we demonstrated a tonic control of MCH-expressing neurons on ependymal cilia beat frequency using in vitro optogenics. Finally, we performed in vivo measurements of CSF flow using fluorescent micro-beads in wild-type and MCHR1-knockout mice. Collectively, our results demonstrated that MCH-expressing neurons modulate ciliary beating of ependymal cells at the third ventricle and could contribute to maintain cerebro-spinal fluid homeostasis.

Effect of ppMCH derived peptides on PBMC proliferation and cytokine expression

The mRNA encoding prepro-Melanin concentrating hormone (ppMCH) is mainly expressed in the central nervous system but has also been detected at lower amount in many peripheral tissues including spleen and thymus. At the peptide level however, several forms of the precursor can be detected in these tissues and are sometimes expressed at similar levels compared to brain. In the present work, we have studied the in vitro action of a wide range of concentration (1 nM to 1 microM) of the different peptides encoded by ppMCH i.e. neuropeptide glycine-glutamic acid (NGE), neuropeptide glutamic acid-isoleucine (NEI), Melanin concentrating hormone (MCH) and the dipeptide NEI-MCH on peripheral blood mononuclear cells (PBMC) proliferation and cytokine production following anti-CD3 stimulation. Among them only MCH decreased PBMC proliferation with a maximal effect of 35% at 100 nM. Moreover as demonstrated by using ELISA, MCH significantly decreases IL-2 production by 25% but not IL-4, INF-gamma or TNF-alpha expression. Interestingly, exogenous IL-2 decreases significantly MCH-mediated inhibition, suggesting that it is an important downstream mediator of MCH action. Finally, we showed that after 7 to 9 days of incubation, MCH also inhibits proliferation of non-stimulated PBMC. Altogether, these data demonstrate that fully mature MCH modulates proliferation of anti-CD3 stimulated PBMC partially through regulation of IL-2 production.