Biology subjects

Dowsett, G.

Publications and source records attributed to Dowsett, G..

5 recordsLinked to original sources

bioRxiv2024

The MRAP2 accessory protein directly interacts with melanocortin-3 receptor to enhance signaling

The central melanocortin system links nutrition to energy expenditure, with melanocortin-4 receptor (MC4R) controlling appetite and food intake, and MC3R regulating timing of sexual maturation, rate of linear growth and lean mass accumulation. Melanocortin-2 receptor accessory protein-2 (MRAP2) is a single transmembrane protein that interacts with MC4R to potentiate its signalling, and human mutations in MRAP2 cause obesity. Previous studies have been unable to consistently show whether MRAP2 affects MC3R activity. Here we used single-molecule pull-down (SiMPull) to confirm that MC3R and MRAP2 interact in HEK293 cells. Analysis of fluorescent photobleaching steps showed that MC3R and MRAP2 readily form heterodimers most commonly with a 1:1 stoichiometry. Human single-nucleus and spatial transcriptomics show MRAP2 is co-expressed with MC3R in hypothalamic neurons with important roles in energy homeostasis and appetite control. Functional analyses showed MRAP2 enhances MC3R cAMP signalling, impairs {beta}-arrestin recruitment, and reduces internalization in HEK293 cells. Structural homology models revealed putative interactions between the two proteins and alanine mutagenesis of five MRAP2 and three MC3R transmembrane residues significantly reduced MRAP2 effects on MC3R signalling. Finally, we showed genetic variants in MRAP2 that have been identified in individuals that are overweight or obese prevent MRAP2s enhancement of MC3R-driven signalling. Thus, these studies reveal MRAP2 as an important regulator of MC3R function and provide further evidence for the crucial role of MRAP2 in energy homeostasis.

molecular biology↗

bioRxiv2024

Adult oligodendrogenesis gates arcuate neuronal glucose sensing through remodelling of the blood-hypothalamus barrier via ADAMTS4

Brain glucose sensing is critical for survival during hypoglycaemia and tunes the level of defended blood glucose, which goes up in diabetes. Neuronal glucose sensing neurons and mechanisms have been identified, but how these neurons access blood concentrations of glucose to adjust their output and maintain glucose homeostasis is unclear. Here, we demonstrate that adult oligodendrogenesis in the median eminence (ME) is modulated by changes in circulating glucose levels and rapidly upregulated by hypoglycaemia. We show that genetic blockade of new OL production in adult mice impairs the regulation of glucose homeostasis, the integrity of the ME blood-hypothalamus barrier, and neuronal glucose sensing in the arcuate nucleus of the hypothalamus (ARH). Unexpectedly, functional integrity of adult-formed myelin is not required for the maintenance of glucose homeostasis. Instead, newly formed OLs exert their glucoregulatory actions via the synthesis of A disintegrin and metallopeptidase with thrombospondin motifs 4 (ADAMTS4), a metallopeptidase expressed exclusively by OLs and dependent on adult OL genesis to maintain its expression in the ME. Both lack of Adamts4 and ADAMTS4 gain-of-function are associated with impaired glucose homeostasis and remodelling of the blood-hypothalamus barrier, indicating that optimal ADAMTS4 expression is required for the integrity of vascular permeability and normal glycaemic control. Finally, we show that ME ADAMTS4 expression is regulated by changes in peripheral glycaemia and is dysregulated in diabetes, providing a mechanism by which ME OLs contribute to the regulation of glucose homeostasis.

neuroscience↗

bioRxiv2023

Human HYPOMAP: A comprehensive spatio-cellular map of the human hypothalamus

The hypothalamus is a brain region that plays a key role in coordinating fundamental biological functions. However, our understanding of the underlying cellular components and circuitry, have, until recently, emerged primarily from rodent studies. Here, we combine a single-nucleus sequencing database of 433,369 human hypothalamic cells, with spatial transcriptomics, to present a comprehensive spatio-cellular transcriptional map of the human hypothalamus, the HYPOMAP. Analysing hypothalamic leptin melanocortin pathway neuronal populations that play a role in appetite control, we identify spatially distinct populations of arcuate nucleus POMC and AGRP neurons, and their receptors MC3R and MC4R. Next, we map the cells expressing incretin receptors, targets of the new generation of anti-obesity medications, and uncover transcriptionally distinct GLP1R and GIPR-expressing cellular populations. Finally, out of the 458 hypothalamic cell types in HYPOMAP, we find 182 neuronal clusters are significantly enriched in expression of BMI GWAS genes. This enrichment is driven by 375 effector genes, with rare deleterious variants in 6 of these; MC4R, PCSK1, POMC, CALCR, BSN and CORO1A, the last of which has previously not been linked to obesity; being significantly associated with changes in BMI at the population level. Thus, the HYPOMAP provides a detailed atlas of the human hypothalamus in a spatial context, and serves as an important resource to identify novel druggable targets for treating a wide range of conditions, including reproductive, circadian, and metabolic disorders.

neuroscience↗

bioRxiv2022

Obesity medication lorcaserin requires brainstem GLP-1 neurons to reduce food intake in mice

Overweight and obesity are rapidly becoming the "new normal" in developed countries, which promotes a widespread negative impact on human health. Amongst recently developed obesity medications are the serotonin 2C receptor (5-HT2CR) agonist lorcaserin and glucagon-like peptide-1 receptor (GLP-1R) agonists, but the brain circuits employed by these medications to produce their therapeutic effects remain to be fully defined. 5-HT2CRs and GLP-1Rs are widely distributed in the brain, including in the key homeostatic region the nucleus of the solitary tract (NTS) where GLP-1 is produced by preproglucagon (PPGNTS) neurons. PPGNTS cells were profiled using histochemistry and single nucleus RNA sequencing (Nuc-Seq) of mouse brainstem. Transcriptomic analyses revealed 5-HT2CR expression was widespread in PPGNTS clusters. Demonstrating the functional significance of this co-expression, lorcaserin required PPGNTS to reduce food intake. Analysis of second order neurons revealed that local GLP1-R neurons within the NTS are necessary for 5-HT2CRNTS food intake suppression. In contrast, GLP-1RNTS were not required for GLP-1R agonist liraglutide and exendin-4s short term feeding reduction, suggesting scope for lorcaserin and GLP1-R agonist combination therapy. In support of this, lorcaserin+liraglutide and lorcaserin+exendin-4 produced greater reductions in food intake when administered in combination as compared to monotherapies. These data provide insight into the therapeutic mechanisms of lorcaserin and identify a combination strategy to improve the therapeutic profile of lorcaserin and GLP1-R agonists.

neuroscience↗

bioRxiv2021

The neural cell adhesion molecule NrCAM regulates development of hypothalamic tanycytes

Hypothalamic tanycytes are neural stem and progenitor cells, but little is known of how they are regulated. Here we provide evidence that the cell adhesion molecule, NrCAM, regulates tanycytes in the adult niche. NrCAM is strongly expressed in adult mouse tanycytes. Immunohistochemical and in situ hybridization analysis revealed that NrCAM loss of function leads to both a reduced number of tanycytes and reduced expression of tanycyte-specific cell markers, along with a small reduction in tyrosine hydroxylase-positive arcuate neurons. Similar analyses of NrCAM mutants at E16 identify few changes in gene expression or cell composition, indicating that NrCAM regulates tanycytes, rather than early embryonic hypothalamic development. Neurosphere and organotypic assays support the idea that NrCAM governs cellular homeostasis. Single-cell RNA sequencing (scRNA-Seq) shows that tanycyte-specific genes, including a number that are implicated in thyroid hormone metabolism, show reduced expression in the mutant mouse. However, the mild tanycyte depletion and loss of markers observed in NrCAM-deficient mice were associated with only a subtle metabolic phenotype.

neuroscience↗