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Cellular Signatures of Melanocortin Pathway Genes Across the Locus Coeruleus [Spatial Transcriptomics]

ABSTRACT: Obesity and Alzheimer’s disease (AD) are epidemiologically associated. The locus coeruleus (LC) – the brain’s primary and most significant source of norepinephrine – is one of the earliest sites of neurodegeneration in AD. The LC participates in feeding behavior through connections with the hypothalamus. The cellular composition of the LC has been characterized at single-cell resolution. However, the constituent cellular signatures of genes related to energy homeostasis – such as the melanocortin pathway genes – in the LC are unclear. We performed single-nucleus RNA sequencing and spatial transcriptomics (Visium) in the human LC, and HiPlex RNAscope in the LC of mice. The melanocortin pathway gene MRAP2 was expressed in the majority of DBH neurons across the LC. Mrap2 was also co-expressed with AD-associated genes such as App, Psen1, Psen2, and Sorl1. More than 20% of Dbh neurons in the LC were positive for Mrap2, App, Psen1, and Psen2. Mrap2 is expressed in the central nervous system and modulates the trafficking and signaling of all five G-protein coupled receptors (GPCRs) of the melanocortin receptor family: Mc1r, Mc2r, Mc3r, Mc4r, and Mc5r. In mice, among the melanocortin receptors, Mc5r showed the highest co-expression with Mrap2, accounting for 17.9% of Mrap2-positive cells, followed by Mc2r with 10.9% of Mrap2-positive cells. Mc1r, Mc3r, and Mc4r showed very limited co-expression with Mrap2. Our study reveals that many Mrap2-positive cells do not express any melanocortin receptor genes, warranting future studies into metabolically relevant GPCRs downstream of MRAP2 in the LC. In summary, our study characterizes melanocortin molecular substrates in the human and mouse LC and highlights MRAP2 as a potential link between pathways of energy homeostasis and neurodegeneration.

ORGANISM(S): Homo sapiens

PROVIDER: GSE327441 | GEO | 2026/04/20

REPOSITORIES: GEO

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Project description:Melanocortins mediate their biological functions via five different melanocortin receptors (MC1R - MC5R). MC1R is expressed in the skin and leukocytes and is thus involved in the regulation of skin pigmentation and inflammatory responses. MC1R is also present in the liver and white adipose tissue, but its functional role in these tissues is unclear. This study aimed at determining the regulatory role of MC1R in fatty acid metabolism. Recessive yellow (Mc1re/e) mice, a model of global MC1R deficiency, and hepatocyte-specific MC1R deficient mice (Mc1r LKO) were fed a chow or Western diet for 12 weeks. The mouse models were characterized for body weight and composition, adipose tissue mass, adipocyte size, glucose metabolism and lipid metabolism. Furthermore, qPCR and RNA sequencing analyses were used to investigate gene expression profiles in the liver and adipose tissue. HepG2 cells and primary mouse hepatocytes were to study the effects of pharmacological MC1R activation. Chow- and Western diet-fed Mc1re/e showed increased liver weight, white adipose tissue mass and plasma triglyceride (TG) concentration compared to wild type mice. This phenotype occurred without significant changes in food intake, body weight, physical activity or glucose metabolism. Mc1r LKO mice displayed a similar phenotype characterized by larger fat depots, increased adipocyte hypertrophy and enhanced accumulation of TGs in the liver and plasma. In terms of gene expression, markers of de novo lipogenesis, inflammation and apoptosis were upregulated in the liver of Mc1r LKO mice, while enzymes regulating lipolysis were downregulated in white adipose tissue of these mice. In cultured hepatocytes, selective activation of MC1R reduced ChREBP expression, which is a central transcription factor for lipogenesis. Hepatocyte-specific loss of MC1R disturbs fatty acid metabolism in the liver and leads to an obesity phenotype characterized by enhanced adipocyte hypertrophy and TG accumulation in the liver and circulation.

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Cellular Signatures of Melanocortin Pathway Genes Across the Locus Coeruleus [Spatial Transcriptomics]

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