Biology subjects

Gribble, F.

Publications and source records attributed to Gribble, F..

7 recordsLinked to original sources

bioRxiv2024

GLP1R agonists activate human POMC neurons

Drugs like semaglutide (a.k.a. Ozempic/Wegovy) that activate the glucagon-like peptide-1 receptor (GLP-1R) are a promising therapy for obesity and type 2 diabetes (T2D). Animal studies suggest that these drugs likely function by stimulating GLP-1R on appetite-suppressing neuron populations in the brain, but it is still unclear how they act to reduce food intake in humans. We therefore generated appetite-regulatory hypothalamic neurons from human pluripotent stem cells (hPSCs) to study their responses to GLP-1R agonists by calcium imaging and electrophysiology. We found that hPSC-derived proopiomelanocortin (POMC) and other hypothalamic neuron subtypes expressed GLP1R mRNA, and many of these neurons robustly responded to GLP-1R agonists by membrane depolarization, increased action potential firing, and extracellular calcium influx that persisted long after agonist withdrawal. The observed GLP-1R-induced response was likely mediated by the activation of PKA and L-type calcium channels, and led to significant changes in gene expression. These findings provide mechanistic insight into how GLP-1R agonists may suppress appetite in humans.

neuroscience↗

bioRxiv2023

Fetally-encoded GDF15 and maternal GDF15 sensitivity are major determinants of nausea and vomiting in human pregnancy

Human pregnancy is frequently accompanied by nausea and vomiting that may become severe and life-threatening, as in hyperemesis gravidarum (HG), the cause of which is unknown. Growth Differentiation Factor-15 (GDF15), a hormone known to act on the hindbrain to cause emesis, is highly expressed in the placenta and its levels in maternal blood rise rapidly in pregnancy. Variants in the maternal GDF15 gene are associated with HG. Here we report that fetal production of GDF15, and maternal sensitivity to it, both contribute substantially to the risk of HG. We found that the great majority of GDF15 in maternal circulation is derived from the feto-placental unit and that higher GDF15 levels in maternal blood are associated with vomiting and are further elevated in patients with HG. Conversely, we found that lower levels of GDF15 in the non-pregnant state predispose women to HG. A rare C211G variant in GDF15 which strongly predisposes mothers to HG, particularly when the fetus is wild-type, was found to markedly impair cellular secretion of GDF15 and associate with low circulating levels of GDF15 in the non-pregnant state. Consistent with this, two common GDF15 haplotypes which predispose to HG were associated with lower circulating levels outside pregnancy. The administration of a long-acting form of GDF15 to wild-type mice markedly reduced subsequent responses to an acute dose, establishing that desensitisation is a feature of this system. GDF15 levels are known to be highly and chronically elevated in patients with beta thalassemia. In women with this disorder, reports of symptoms of nausea or vomiting in pregnancy were strikingly diminished. Our findings support a causal role for fetal derived GDF15 in the nausea and vomiting of human pregnancy, with maternal sensitivity, at least partly determined by pre-pregnancy exposure to GDF15, being a major influence on its severity. They also suggest mechanism-based approaches to the treatment and prevention of HG.

genetics↗

bioRxiv2020

Central and peripheral GLP-1 systems independently and additively suppress eating

The anorexigenic peptide glucagon-like peptide-1 (GLP-1) is secreted from gut enteroendocrine cells and brain preproglucagon (PPG) neurons, which respectively define the peripheral and central GLP-1 systems. As peripheral satiation signals are integrated in the nucleus tractus solitarius (NTS), PPGNTS neurons are assumed to link the peripheral and central GLP-1 systems, forming a unified GLP-1 gut-brain satiation circuit. This hypothesis, however, remains unsubstantiated. We report that PPGNTS neurons encode satiation in mice, consistent with vagal gastrointestinal distension signalling. However, PPGNTS neurons predominantly receive vagal input from oxytocin receptor-expressing vagal neurons, rather than those expressing GLP-1 receptors. Furthermore, PPGNTS neurons are not necessary for eating suppression induced by the GLP-1 receptor agonists liraglutide or semaglutide, and semaglutide and PPGNTS neuron activation additively suppress eating. Central and peripheral GLP-1 systems thus suppress eating via independent gut-brain circuits, hence PPGNTS neurons represent a rational pharmacological target for anti-obesity combination therapy with GLP-1 receptor agonists. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/234427v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@1c7643aorg.highwire.dtl.DTLVardef@18520daorg.highwire.dtl.DTLVardef@12fc8fdorg.highwire.dtl.DTLVardef@34809b_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract: C_FIG

neuroscience↗

bioRxiv2020

Unbiased placental secretome characterization identifies candidates for pregnancy complications

Pregnancy requires adaptation of maternal physiology to enable normal fetal development. These adaptations are driven, in part, by the production of placental hormones. Failures in maternal adaptation and placental function lead to pregnancy complications including abnormal birthweight and gestational diabetes. However, we lack information on the full identity of hormones secreted by the placenta that mediate changes in maternal physiology. This study used an unbiased approach to characterise the secretory output of mouse placental endocrine cells and examined whether these data could identify placental hormones that are important for determining pregnancy outcome in humans. Secretome and cell peptidome analyses were performed using mass spectrometry on cultured primary trophoblast and fluorescence-activated sorted endocrine cells from pregnant mouse dams, and a placenta secretome map containing 319 proteins was generated. Gene ontology analyses showed that a high proportion of placental secretome proteins are involved in metabolic and immune modulation, signalling and growth. The majority of proteins identified are also expressed by human placenta and several have been reported to be dysregulated in pregnancy complications. Moreover, in proof of concept studies, we found that the relative abundance of secreted placental proteins (sFLT1/MIF and ANGPT2/MIF ratios) was increased in women at 12 weeks of pregnancy, prior to diagnosis of gestational diabetes. Finally, we identified several transcription factors that may be important for controlling hormone production by the placenta and associate with pregnancy outcome. Thus, our observations suggest that analysis of the placental secretome could lead to the identification of new placental biomarkers of pregnancy complications.

physiology↗

bioRxiv2019

Secretin release after Roux-en-Y Gastric Bypass reveals a population of glucose-sensitive S-cells in distal small intestine

ObjectiveGastrointestinal hormones contribute to the beneficial effects of Roux-en-Y gastric bypass surgery (RYGB) on glycemic control. Secretin is secreted from duodenal S-cells in response to low luminal pH, but it is unknown whether its secretion is altered after RYGB and if secretin contributes to the post-operative improvement in glycemic control. We hypothesized that secretin secretion increases after RYGB as a result of the diversion of nutrients to more distal parts of the small intestine, and thereby affects islet hormone release.\n\nMethodsA specific secretin radioimmunoassay was developed, evaluated biochemically, and used to quantify plasma concentrations of secretin in 13 obese individuals before, 1 week after and 3 months after RYGB. Distribution of secretin and its receptor was assessed by RNA-sequencing, mass-spectrometry and in situ hybridization in human and rat tissues. Isolated, perfused rat intestine and pancreas were used to explore the molecular mechanism underlying glucose-induced secretin secretion and to study direct effects of secretin on glucagon, insulin and somatostatin secretion. Secretin was administered alone or in combination with GLP-1 to non-sedated rats to evaluate effects on glucose regulation.\n\nResultsPlasma postprandial secretin was more than doubled in humans after RYGB (P<0.001). The distal small intestine harbored secretin expressing cells in both rats and humans. Glucose increased secretion of secretin in a sodium-glucose co-transporter dependent manner when administered to the distal part but not into the proximal part of the rat small intestine. Secretin stimulated somatostatin secretion (fold change: 1.59, P<0.05) from the perfused rat pancreas but affected neither insulin (P=0.2) nor glucagon (P=0.97) secretion. When administered to rats in vivo, insulin secretion was attenuated and glucagon secretion increased (P=0.04), while blood glucose peak time was delayed (from 15 min to 45 min) and gastric emptying time prolonged (P=0.004).\n\nConclusionGlucose-sensing secretin cells located in the distal part of the small intestine may contribute to increased plasma concentrations observed after RYGB. The metabolic role of the distal S-cells warrants further studies.

physiology↗

bioRxiv2018

Human POMC processing in vitro and in vivo revealed by quantitative peptidomics

Human obesity can result from the aberrant production or processing of proopiomelanocortin (POMC) in hypothalamic neurons, but it is unclear which human POMC-derived peptides are most relevant to body weight regulation. To address this question, we analysed both hypothalamic neurons derived from human pluripotent stem cells (hPSCs) and primary human hypothalamic tissue using quantitative liquid chromatography tandem mass spectroscopy (LC-MS/MS). In both in vitro- and in vivo-derived samples, we found that POMC was processed into {beta}-melanocyte stimulating hormone ({beta}-MSH), whose existence in the human brain has been controversial. {beta}-MSH and desacetyl -MSH (d--MSH) were produced at roughly equimolar concentrations and in vast excess to acetylated -MSH (5-to 200-fold), suggesting that the importance of both d--MSH and {beta}-MSH to human obesity has been underestimated. Since body weight is sensitive to changes in MSH concentration, we asked whether hPSC-derived hypothalamic neurons could provide mechanistic insights into the processing and secretion of MSH peptides. We found that cultured human hypothalamic neurons appropriately trafficked POMC and its derivatives, and robustly (P<0.0001) secreted them when depolarised. Furthermore, the adipocyte-derived hormone leptin significantly (P<0.01) promoted their production of both d--MSH and {beta}-MSH. These results establish hPSC-derived hypothalamic neurons as a model system for studying human-specific aspects of POMC processing that might be therapeutically harnessed to treat obesity.

neuroscience↗

bioRxiv2018

Rapid sensing of L-leucine by human and murine hypothalamic neurons: neurochemical and mechanistic insights

ObjectiveDietary proteins are sensed by hypothalamic neurons and strongly influence multiple aspects of metabolic health, including appetite, weight gain and adiposity. However, little is known about the mechanisms by which hypothalamic neural circuits controlling behavior and metabolism sense protein availability. The aim of this study is to characterize how neurons from the mediobasal hypothalamus respond to a signal of protein availability: the amino acid L-leucine.\n\nMethodsWe used primary cultures of post-weaning murine mediobasal hypothalamic neurons, hypothalamic neurons derived from human induced pluripotent stem cells, and calcium imaging to characterize rapid neuronal responses to physiological changes in extracellular L-Leucine concentration.\n\nResultsA neurochemically diverse subset of both mouse and human hypothalamic neurons responded rapidly to L-leucine. Consistent with L-leucines anorexigenic role, we found that 25% of mouse MBH POMC neurons were activated by L-leucine. 10% MBH NPY neurons were inhibited by L-leucine, and leucine rapidly reduced AGRP secretion, providing a mechanism for the rapid leucine-induced inhibition of foraging behaviour in rodents. Surprisingly, none of the candidate mechanisms previously implicated in hypothalamic leucine sensing (KATP channels, mTORC1 signaling, amino-acid decarboxylation) were involved in the acute activity changes produced by L-leucine. Instead, our data indicate that leucine-induced neuronal activation involves a plasma membrane Ca2+ channel, whereas leucine-induced neuronal inhibition is mediated by inhibition of a store-operated Ca2+ current.\n\nConclusionsA subset of neurons in the mediobasal hypothalamus rapidly respond to physiological changes in extracellular leucine concentration. Leucine can produce both increases and decreases in neuronal Ca2+ concentrations in a neurochemically-diverse group of neurons, including some POMC and NPY/AGRP neurons. Our data reveal that leucine can signal through novel mechanisms to rapidly affect neuronal activity.\n\nHighlights- A neurochemically diverse group of mouse and human hypothalamic neurons rapidly sense and respond to L-leucine\n- Leucine can produce neuronal activation or neuronal inhibition via distinct and novel Ca2+ signaling mechanisms.\n- Leucine activates 25% ARH POMC neurons\n- Leucine inhibits 10% ARH NPY/AGRP neurons and reduces AGRP secretion from fasted mediobasal hypothalamic slices

neuroscience↗