Fasted/fed states regulate postsynaptic hub protein DYNLL2 and glutamatergic transmission in oxytocin neurons in the hypothalamic paraventricular nucleus

Dimerization of hub protein DYNLL1 and bZIP transcription factor CREB3L1 enhances transcriptional activation of CREB3L1 target genes like arginine vasopressin

bZIP transcription factors can function as homodimers or heterodimers through interactions with their disordered coiled-coil domain. Such dimer assemblies are known to influence DNA-binding specificity and/or the recruitment of binding partners, which can cause a functional switch of a transcription factor from being an activator to a repressor. We recently identified the genomic targets of a bZIP transcription factor called CREB3L1 in rat hypothalamic supraoptic nucleus by ChIP-seq. The objective of this study was to investigate the CREB3L1 protein-to-protein interactome of which little is known. For this approach, we created and screened a rat supraoptic nucleus yeast two-hybrid prey library with the bZIP region of rat CREB3L1 as the bait. Our yeast two-hybrid approach captured five putative CREB3L1 interacting prey proteins in the supraoptic nucleus. One interactor was selected by bioinformatic analyses for more detailed investigation by co-immunoprecipitation, immunofluorescent cellular localisation, and reporter assays in vitro. Here we identify dimerisation hub protein Dynein Light Chain LC8-Type 1 as a CREB3L1 interacting protein that in vitro enhances CREB3L1 activation of target genes.

The effects of Phycocyanobilin on experimental arthritis involve the reduction in nociception and synovial neutrophil infiltration, inhibition of cytokine production, and modulation of the neuronal proteome

Introduction

The antinociceptive and pharmacological activities of C-Phycocyanin (C-PC) and Phycocyanobilin (PCB) in the context of inflammatory arthritis remain unexplored so far. In the present study, we aimed to assess the protective actions of these compounds in an experimental mice model that replicates key aspects of human rheumatoid arthritis.

Methods

Antigen-induced arthritis (AIA) was established by intradermal injection of methylated bovine serum albumin in C57BL/6 mice, and one hour before the antigen challenge, either C-PC (2, 4, or 8 mg/kg) or PCB (0.1 or 1 mg/kg) were administered intraperitoneally. Proteome profiling was also conducted on glutamate-exposed SH-SY5Y neuronal cells to evaluate the PCB impact on this key signaling pathway associated with nociceptive neuronal sensitization.

Results and discussion

C-PC and PCB notably ameliorated hypernociception, synovial neutrophil infiltration, myeloperoxidase activity, and the periarticular cytokine concentration of IFN-γ, TNF-α, IL-17A, and IL-4 dose-dependently in AIA mice. In addition, 1 mg/kg PCB downregulated the gene expression for T-bet, RORγ, and IFN-γ in the popliteal lymph nodes, accompanied by a significant reduction in the pathological arthritic index of AIA mice. Noteworthy, neuronal proteome analysis revealed that PCB modulated biological processes such as pain, inflammation, and glutamatergic transmission, all of which are involved in arthritic pathology.

Conclusions

These findings demonstrate the remarkable efficacy of PCB in alleviating the nociception and inflammation in the AIA mice model and shed new light on mechanisms underlying the PCB modulation of the neuronal proteome. This research work opens a new avenue to explore the translational potential of PCB in developing a therapeutic strategy for inflammation and pain in rheumatoid arthritis.

Fasting inhibits excitatory synaptic input on paraventricular oxytocin neurons via neuropeptide Y and Y1 receptor, inducing rebound hyperphagia, and weight gain

Fasting with varying intensities is used to treat obesity-related diseases. Re-feeding after fasting exhibits hyperphagia and often rebound weight gain. However, the mechanisms underlying the hyperphagia and rebound remain elusive. Here we show that 24 h food restriction (24 h FR) and milder 50% FR, both depress synaptic transmission in the hypothalamic paraventricular nucleus (PVN) and induce acute hyperphagia in rats. 24 h FR is followed by weight rebound but 50% FR is not. Orexigenic neuropeptide Y (NPY) via the Y1 receptor (Y1R) inhibited the miniature excitatory postsynaptic current (mEPSC) on anorexigenic oxytocin neurons in the PVN. 24 h FR and 50% FR activated this neuronal pathway to induce acute hyperphagia on Days 1-3 and Days 1-2 after FR, respectively. 24 h FR induced large mEPSC depression, recurrent hyperphagia on Days 9-12 and rebound weight gain on Days 12-17, whereas 50% FR induced moderate mEPSC depression and sustained weight reduction. Transverse data analysis on Day 1 after 24 h FR and 50% FR demonstrated saturation kinetics for the mEPSC depression-hyperphagiacurve, implying hysteresis. The results reveal FR-driven synaptic plasticity in the NPY-Y1R-oxytocin neurocircuit that drives acute hyperphagia. FR with the intensity that regulates the synapse-feeding relay without hysteresis is the key for successful dieting.

Oxytocin in the dorsal raphe nucleus antagonizes the inhibition of maternal care induced by food deprivation

Lactation is indispensable for the pup's survival, but is considered a survival burden in dams under negative energy conditions. In the present study, we tested our hypothesis that oxytocin may facilitate energy investment to pups through behavioral control as well as milk ejection. Maternal care was observed in dams at 3 h but not 8 h after food deprivation. We investigated whether oxytocin in the dorsal raphe nucleus (DRN), which is involved in energy state-dependent regulation of maternal care, regulates maternal care. For this purpose, 2-pmol L368899, an oxytocin receptor antagonist, was injected into the DRN; after treatment, maternal care was inhibited in the dams with 3-h fasting, but not in the fed dams. In contrast, recovery of maternal care was observed in the dams with 8-h fasting who underwent 100-pmol oxytocin injection at the DRN. These results indicate that oxytocin in the DRN is required for displaying maternal behavior under fasting conditions, but not under fed conditions. Next, we investigated the site of oxytocin release. Presentation of pups decreased the oxytocin immunoreactivity at the paraventricular nucleus (PVN) of the hypothalamus in the 3-h-fasted dams, but not in the fed or 8-h-fasted dams. No change of the serum oxytocin level was observed. Few oxytocin-positive neurons projecting from the PVN to the DRN were detected through labeling with the retrograde tracer fluorogold. Oxytocin secreted at the PVN, which reaches the DRN, but not released as a hormone or neurotransmitter may mediate maternal care under food-restricted conditions.

The relationship between oxytocin, dietary intake and feeding: A systematic review and meta-analysis of studies in mice and rats

The neuropeptide oxytocin has been associated with food intake and feeding behaviour. This systematic review aimed to investigate the impact of oxytocin on dietary intake and feeding behaviour in rodent studies. Six electronic databases were searched to identify published studies to April 2018. Preclinical studies in mice and rats were included if they reported: (1) a dietary measure (i.e. food or nutrient and/or behaviour (2) an oxytocin measure, and (3) relationship between the two measures. A total of 75 articles (n = 246 experiments) were included, and study quality appraised. The majority of studies were carried out in males (87%). The top three oxytocin outcomes assessed were: exogenous oxytocin administration (n = 126), oxytocin-receptor antagonist administration (n = 46) and oxytocin gene deletion (n = 29). Meta-analysis of exogenous studies in mice (3 studies, n = 43 comparisons) and rats (n = 8 studies, n = 82 comparisons) showed an overall decrease in food intake with maximum effect shown at 2 h post-administration.

Brain-Derived Neurotrophic Factor and Oxytocin Signaling in Association With Clinical Symptoms in Adolescent Inpatients With Anorexia Nervosa-A Longitudinal Study

INTRODUCTION

Brain-derived neurotrophic factor (BDNF), as well as oxytocin (OXY), are centrally secreted neuropeptides regulating a range of physiological processes, including food intake and metabolism. Moreover, numerous reports suggest their role in affective and cognitive symptoms of various psychiatric disorders. Thus, the study aimed to measure the serum level of BDNF and its receptor-tropomyosin-related kinase B (TrkB) and OXY in the malnourished anorexia nervosa patients and following partial weight-recovery. The correlations between levels of these proteins with the primary symptoms of the anorexia nervosa (AN) were also analyzed.

METHODOLOGY

Eighty-four adolescent AN patients were recruited into the study, but only forty-two AN patients completed it. The control group comprises of thirty age- and height-matched girls (CG). Serum BDNF, TrkB, and OXY levels were measured in AN group in two time-points-at the beginning of the hospitalization in malnourished patients (AN-T1) and again after partial weight normalization, on the day of discharge (AN-T2). The severity of eating disorders, as well as depressive and obsessive-compulsive symptoms, were assessed at the same two-time points.

RESULTS

Body mass index (BMI) differed significantly between the AN-T1, AN-T2, and CG. BDNF levels for the AN-T2 increased significantly in comparison to the AN-T1, but at two-time points were significantly lower than in the CG. The OXY level did not change with weight gain and in both groups AN-T1 and AN-T2 were statistically significantly higher than in the CG. Statistically significant negative correlations between BDNF and the severity of eating disorders symptoms were found. Depressive and obsessive-compulsive symptoms did not show significant correlations with levels of studied proteins for either malnourished or partially weight recovered AN patients.

CONCLUSIONS

BDNF serum levels were decreased in the malnourished AN patients and tended to normalize with partial weight recovery. OXY serum levels were found to be increased in the malnourished AN patients and did not normalize with partial weight recovery, confirming previous reports about its role in the etiopathogenesis of AN. BDNF can be related to aberrant eating behaviors occurring in AN. Our results do not support the role of serum levels of BDNF, TrkB, or OXY in the modulation of depressive or obsessive-compulsive symptoms.

Oxytocin and Eating Disorders: A Narrative Review on Emerging Findings and Perspectives

BACKGROUND

The hypothalamic neuropeptide oxytocin regulates reproductive behavior and mother-infant interaction, and conclusive studies in humans indicate that oxytocin is also a potent modulator of psychosocial function. Pilot experiments have yielded first evidence that this neuropeptide moreover influences eating behavior.

METHODS

We briefly summarize currently available studies on the involvement of the oxytocin system in the pathophysiology of eating disorders, as well as on the effects of oxytocin administration in patients with these disorders.

RESULTS

Brain administration of oxytocin in animals with normal weight, but also with diet-induced or genetically induced obesity, attenuates food intake and reduces body weight. In normal-weight and obese individuals, acute intranasal oxytocin delivery curbs calorie intake from main dishes and snacks. Such effects might converge with the poignant social and cognitive impact of oxytocin to also improve dysfunctional eating behavior in the therapeutic context. This assumption has received support in first studies showing that oxytocin might play a role in the disease process of anorexia nervosa. In contrast, respective experiments in patients with bulimia nervosa and binge eating disorder are still scarce.

CONCLUSIONS

We propose a framework of oxytocin's role and its therapeutic potential in eating disorders that aims at integrating social and metabolic aspects of its pharmacological profile, and ponder perspectives and limitations of oxytocin use in the clinical setting.

Impact of external pneumatic compression target inflation pressure on transcriptome-wide RNA expression in skeletal muscle

Next‐generation RNA sequencing was employed to determine the acute and subchronic impact of peristaltic pulse external pneumatic compression (PEPC) of different target inflation pressures on global gene expression in human vastus lateralis skeletal muscle biopsy samples. Eighteen (N = 18) male participants were randomly assigned to one of the three groups: (1) sham (n = 6), 2) EPC at 30–40 mmHg (LP‐EPC; n = 6), and 3) EPC at 70–80 mmHg (MP‐EPC; n = 6). One hour treatment with sham/EPC occurred for seven consecutive days. Vastus lateralis skeletal muscle biopsies were performed at baseline (before first treatment; PRE), 1 h following the first treatment (POST1), and 24 h following the last (7th) treatment (POST2). Changes from PRE in gene expression were analyzed via paired comparisons within each group. Genes were filtered to include only those that had an RPKM ≥ 1.0, a fold‐change of ≥1.5 and a paired t‐test value of <0.01. For the sham condition, two genes at POST1 and one gene at POST2 were significantly altered. For the LP‐EPC condition, nine genes were up‐regulated and 0 genes were down‐regulated at POST1 while 39 genes were up‐regulated and one gene down‐regulated at POST2. For the MP‐EPC condition, two genes were significantly up‐regulated and 21 genes were down‐regulated at POST1 and 0 genes were altered at POST2. Both LP‐EPC and MP‐EPC acutely alter skeletal muscle gene expression, though only LP‐EPC appeared to affect gene expression with subchronic application. Moreover, the transcriptome response to EPC demonstrated marked heterogeneity (i.e., genes and directionality) with different target inflation pressures.

Adiponectin at physiological level glucose-independently enhances inhibitory postsynaptic current onto NPY neurons in the hypothalamic arcuate nucleus

Adiponectin regulates glucose and lipid metabolism, acting against atherosclerosis and metabolic syndrome. Accumulating evidences suggest that adiponectin acts on the brain including the arcuate nucleus of hypothalamus (ARC). The ARC contains orexigenic neuropeptide Y (NPY)/agouti related peptide (AgRP) neurons and anorexigenic proopiomelanocortin (POMC) neurons, the first order neurons for feeding regulation. We recently reported that intracerebroventricular injection of adiponectin at low glucose level suppressed food intake, while at elevated glucose level it promoted food intake, exhibiting glucose-dependent reciprocal effects. As an underlying neuronal mechanism, physiological level of adiponectin at low glucose activated ARC POMC neurons and at high glucose inactivated them. Now, whether physiological level of adiponectin also affects NPY/AgRP neurons is essential for fully understanding the adiponectin action, but it remains to be clarified. We here report that a physiological dose of adiponectin, in both high and low glucose conditions, attenuated action potential firing without altering resting membrane potential in ARC NPY neurons. This adiponectin effect was abolished by GABA_A receptor blockade. Adiponectin enhanced amplitude but not frequency of inhibitory postsynaptic current (IPSC) onto NPY neurons. These results demonstrate that adiponectin enhances IPSC onto NPY neurons to attenuate action potential firing in NPY neurons in a glucose-independent manner, being contrasted to its glucose-dependent effect on POMC neurons.

Plasticity of calcium-permeable AMPA glutamate receptors in Pro-opiomelanocortin neurons

POMC neurons integrate metabolic signals from the periphery. Here, we show in mice that food deprivation induces a linear current-voltage relationship of AMPAR-mediated excitatory postsynaptic currents (EPSCs) in POMC neurons. Inhibition of EPSCs by IEM-1460, an antagonist of calcium-permeable (Cp) AMPARs, diminished EPSC amplitude in the fed but not in the fasted state, suggesting entry of GluR2 subunits into the AMPA receptor complex during food deprivation. Accordingly, removal of extracellular calcium from ACSF decreased the amplitude of mEPSCs in the fed but not the fasted state. Ten days of high-fat diet exposure, which was accompanied by elevated leptin levels and increased POMC neuronal activity, resulted in increased expression of Cp-AMPARs on POMC neurons. Altogether, our results show that entry of calcium via Cp-AMPARs is inherent to activation of POMC neurons, which may underlie a vulnerability of these neurons to calcium overload while activated in a sustained manner during over-nutrition.

DOI:http://dx.doi.org/10.7554/eLife.25755.001

Age-dependent alterations to paraventricular nucleus insulin-like growth factor 1 receptor as a possible link between sympathoexcitation and inflammation

Modifications to neural circuits of the paraventricular hypothalamic nucleus (PVN) have been implicated in sympathoexcitation and systemic cardiovascular dysfunction. However, to date, the role of insulin-like growth factor 1 receptor (IGF-1R) expression on PVN pathophysiology is unknown. Using confocal immunofluorescence quantification and electrophysiological recordings from acute PVN slices, we investigated the mechanism through which age-dependent IGF-1R depletion contributes to the progression of inflammation and sympathoexcitation in the PVN of spontaneously hypertensive rats (SHR). Four and twenty weeks old SHR and Wistar Kyoto (WKY) rats were used for this study. Our data showed that angiotensin I/II and pro-inflammatory high mobility box group protein 1 (HMGB1) exhibited increased expression in the PVN of SHR versus WKY at 4 weeks (p < 0.01), and were even more highly expressed with age in SHR (p < 0.001). This correlated with a significant decrease in IGF-1R expression, with age, in the PVN of SHR when compared with WKY (p < 0.001) and were accompanied by related changes in astrocytes and microglia. In subsequent analyses, we found an age-dependent change in the expression of proteins associated with IGF-1R signaling pathways involved in inflammatory responses and synaptic function in the PVN. MAPK/ErK was more highly expressed in the PVN of SHR by the fourth week (p < 0.001; vs. WKY), while expression of neuronal nitric oxide synthase (p < 0.001) and calcium-calmodulin-dependent kinase II alpha (CamKIIα; p < 0.001) were significantly decreased by the 4th and 20th week, respectively. Age-dependent changes in MAPK/ErK expression in the PVN correlated with an increase in the expression of vesicular glutamate transporter (p < 0.001 vs. WKY), while decreased levels of CamKIIα was associated with a decreased expression of tyrosine hydroxylase (p < 0.001) by the 20th week. In addition, reduced labeling for ϒ-aminobutyric acid in the PVN of SHR (p < 0.001) correlated with a decrease in neuronal nitric oxide synthase labeling (p < 0.001) when compared with the WKY by the 20th week. Electrophysiological recordings from neurons in acute slice preparations of the PVN of 4 weeks old SHR revealed spontaneous post-synaptic currents of higher frequency when compared with neurons from WKY PNV slices of the same age (p < 0.001; n = 14 cells). This also correlated with an increase in PSD-95 in the PVN of SHR when compared with the WKY (p < 0.001). Overall, we found an age-dependent reduction of IGF-1R, and related altered expression of associated downstream signaling molecules that may represent a link between the concurrent progression of synaptic dysfunction and inflammation in the PVN of SHR.

Glucose level determines excitatory or inhibitory effects of adiponectin on arcuate POMC neuron activity and feeding

Adiponectin regulates glucose and lipid metabolism, acting against metabolic syndrome and atherosclerosis. Accumulating evidence suggest that adiponectin acts on the brain including hypothalamic arcuate nucleus (ARC), where proopiomelanocortin (POMC) neurons play key roles in feeding regulation. Several studies have examined intracerebroventricular (ICV) injection of adiponectin and reported opposite effects, increase or decrease of food intake. These reports used different nutritional states. The present study aimed to clarify whether adiponectin exerts distinct effects on food intake and ARC POMC neurons depending on the glucose concentration. Adiponectin was ICV injected with or without glucose for feeding experiments and administered to ARC slices with high or low glucose for patch clamp experiments. We found that adiponectin at high glucose inhibited POMC neurons and increased food intake while at low glucose it exerted opposite effects. The results demonstrate that glucose level determines excitatory or inhibitory effects of adiponectin on arcuate POMC neuron activity and feeding.

Optogenetic activation of leptin- and glucose-regulated GABAergic neurons in dorsomedial hypothalamus promotes food intake via inhibitory synaptic transmission to paraventricular nucleus of hypothalamus

OBJECTIVE

The dorsomedial hypothalamus (DMH) has been considered an orexigenic nucleus, since the DMH lesion reduced food intake and body weight and induced resistance to diet-induced obesity. The DMH expresses feeding regulatory neuropeptides and receptors including neuropeptide Y (NPY), cocaine- and amphetamine-regulated transcript (CART), cholecystokinin (CCK), leptin receptor, and melanocortin 3/4 receptors. However, the principal neurons generating the orexigenic function in the DMH remain to be defined. This study aimed to clarify the role of the DMH GABAergic neurons in feeding regulation by using optogenetics and electrophysiological techniques.

METHODS

We generated the mice expressing ChRFR-C167A, a bistable chimeric channelrhodopsin, selectively in GABAergic neurons of DMH via locally injected adeno-associated virus 2. Food intake after optogenetic activation of DMH GABAergic neurons was measured. Electrophysiological properties of DMH GABAergic neurons were measured using slice patch clamp.

RESULTS

Optogenetic activation of DMH GABAergic neurons promoted food intake. Leptin hyperpolarized and lowering glucose depolarized half of DMH GABAergic neurons, suggesting their orexigenic property. Optical activation of axonal terminals of DMH GABAergic neurons at the paraventricular nucleus of hypothalamus (PVN), where anorexigenic neurons are localized, increased inhibitory postsynaptic currents on PVN neurons and promoted food intake.

CONCLUSION

DMH GABAergic neurons are regulated by metabolic signals leptin and glucose and, once activated, promote food intake via inhibitory synaptic transmission to PVN.