Neurochemical Characterization of Brainstem Pro-Opiomelanocortin Cells.

Teodora Georgescu,Luke K Burke,Alastair S Garfield,Brian Y H Lam,Barbora Doslikova,Giles S H Yeo,Lora K Heisler,David Lyons,Raffaella Chianese,Ana Paula Garcia,Oliver Marston,Justin J Rochford

doi:10.1210/endocr/bqaa032

Abstract

Genetic research has revealed pro-opiomelanocortin (POMC) to be a fundamental regulator of energy balance and body weight in mammals. Within the brain, POMC is primarily expressed in the arcuate nucleus of the hypothalamus (ARC), while a smaller population exists in the brainstem nucleus of the solitary tract (POMCNTS). We performed a neurochemical characterization of this understudied population of POMC cells using transgenic mice expressing green fluorescent protein (eGFP) under the control of a POMC promoter/enhancer (PomceGFP). Expression of endogenous Pomc mRNA in the nucleus of the solitary tract (NTS) PomceGFP cells was confirmed using fluorescence-activating cell sorting (FACS) followed by quantitative PCR. In situ hybridization histochemistry of endogenous Pomc mRNA and immunohistochemical analysis of eGFP revealed that POMC is primarily localized within the caudal NTS. Neurochemical analysis indicated that POMCNTS is not co-expressed with tyrosine hydroxylase (TH), glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), brain-derived neurotrophic factor (BDNF), nesfatin, nitric oxide synthase 1 (nNOS), seipin, or choline acetyltransferase (ChAT) cells, whereas 100% of POMCNTS is co-expressed with transcription factor paired-like homeobox2b (Phox2b). We observed that 20% of POMCNTS cells express receptors for adipocyte hormone leptin (LepRbs) using a PomceGFP:LepRbCre:tdTOM double-reporter line. Elevations in endogenous or exogenous leptin levels increased the in vivo activity (c-FOS) of a small subset of POMCNTS cells. Using ex vivo slice electrophysiology, we observed that this effect of leptin on POMCNTS cell activity is postsynaptic. These findings reveal that a subset of POMCNTS cells are responsive to both changes in energy status and the adipocyte hormone leptin, findings of relevance to the neurobiology of obesity.

Highlights

The rapid rise in the prevalence of obesity has emphasized the need for a greater understanding of the neurobiological mechanisms that underlie energy homeostasis and body weight
Using in situ hybridization with a 35S Pomc riboprobe, endogenous Pomc mRNA expression was visualized within the nucleus of the solitary tract (NTS) of wild-type male and female mice on a C56BL/6 background (n = 7) and PomceGFP mice (n = 7). 35S Pomc within the NTS was most abundant between -7.5 to -7.8 from bregma (Fig. 1A and 1B)
Obesity has emerged as a key challenge to human health, making it essential that the neurobiology underpinning energy homeostasis is clarified to foster the identification of new strategies to prevent and treat this condition

Summary

Introduction

The rapid rise in the prevalence of obesity has emphasized the need for a greater understanding of the neurobiological mechanisms that underlie energy homeostasis and body weight. Previous reports indicate that receptors (LepRbs) for the adipocyte hormone leptin are co-expressed with a subset of POMCNTS neurons using a PomcGFP mouse line [43, 45], though others have not found evidence for this using a PomcCRE line [46] In both mice and humans, the absence of LepRb/LEPRB leads to morbid obesity, hyperphagia, insulin resistance, and decreased energy expenditure, amongst other symptoms [47,48,49]. We aimed to clarify the distribution, neurochemical identify, and leptin responsiveness of POMCNTS

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