Amylin receptor components and the leptin receptor are co‐expressed in single rat area postrema neurons

Abstract

Amylin is a pancreatic -cell hormone that acts as a satiating signal to inhibit food intake by binding to amylin receptors (AMYs) and activating a specific neuronal population in the area postrema (AP). AMYs are heterodimers that include a calcitonin receptor (CTR) subunit [CTR isoform a or b (CTRa or CTRb)] and a member of the receptor activity-modifying proteins (RAMPs). Here, we used single-cell quantitative polymerase chain reaction to assess co-expression of AMY subunits in AP neurons from rats that were injected with amylin or vehicle. Because amylin interacts synergistically with the adipokine leptin to reduce body weight, we also assessed the co-expression of AMY and the leptin receptor isoform b (LepRb) in amylin-activated AP neurons. Single cells were collected from Wistar rats and from transgenic Fos-GFP rats that express green fluorescent protein (GFP) under the control of the Fos promoter. We found that the mRNAs of CTRa, RAMP1, RAMP2 and RAMP3 were all co-expressed in single AP neurons. Moreover, most of the CTRa+ cells co-expressed more than one of the RAMPs. Amylin down-regulated RAMP1 and RAMP3 but not CTR mRNAs in AMY+ neurons, suggesting a possible negative feedback mechanism of amylin at its own primary receptors. Interestingly, amylin upregulated RAMP2 mRNA. We also found that a high percentage of single cells that co-expressed all components of a functional AMY expressed LepRb mRNA. Thus, single AP cells expressed both AMY and LepRb, which formed a population of first-order neurons that presumably can be directly activated by amylin and, at least in part, also by leptin. Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/ejn.13163 This article is protected by copyright. All rights reserved. Accepted ArticleThis article is protected by copyright. All rights reserved. Accepted ArticleThis article is protected by copyright. All rights reserved. feedback mechanism of amylin at its own primary receptors. Interestingly, amylin upregulated RAMP2 mRNA. We also found that a high percentage of single cells that coexpressed all components of a functional AMY expressed LepRb mRNA. Thus, single APcells express both AMY and LepRb that form a population of first-order neurons and that presumably can be directly activated by amylin and at least in part also by leptin.

Glial Endozepines Inhibit Feeding-Related Autonomic Functions by Acting at the Brainstem Level

“…In addition, we reported a labeling in AP-surrounding regions i.e., the funiculus separens and the subpostremal/commissural NTS. From a functional point of view, the AP constitute a circumventricular organ of the brainstem necessary to relay the anorexic effects of circulating compounds such as amylin or leptin (Lutz et al, 2001; Liberini et al, 2016; Smith et al, 2016; Levin and Lutz, 2017). Furthermore, a subpopulation of AP neurons project heavily onto the immediately subjacent NTS i.e., subpostremal and commissural subnuclei (Shapiro and Miselis, 1985).…”

From sensory circumventricular organs to cerebral cortex: Neural pathways controlling thirst and hunger

“…106 It is this effect that has lead to GLP-1 agonists being adopted as frontline treatments for type 2 diabetes and, more recently, as a result of their anorexigenic properties, as anti-obesity pharmacotherapies. 106,107 Alternatively, higher levels of circulating GLP-1 or analogues with longer halflives may saturate the available DPP-IV, an enzyme in the walls of capillaries that would normally degrade the peptide, and, as such, increase the availability of GLP-1 in the circulation to enable its actions directly in the CNS 108,113 or at CVOs including the subfornical organ and area postrema. 106,107 Alternatively, higher levels of circulating GLP-1 or analogues with longer halflives may saturate the available DPP-IV, an enzyme in the walls of capillaries that would normally degrade the peptide, and, as such, increase the availability of GLP-1 in the circulation to enable its actions directly in the CNS 108,113 or at CVOs including the subfornical organ and area postrema.…”

“…106 The latter effects may be mediated by local actions of GLP-1 on vagal afferent neurones within the intestinal mucosa. 106,107 Alternatively, higher levels of circulating GLP-1 or analogues with longer halflives may saturate the available DPP-IV, an enzyme in the walls of capillaries that would normally degrade the peptide, and, as such, increase the availability of GLP-1 in the circulation to enable its actions directly in the CNS 108,113 or at CVOs including the subfornical organ and area postrema. 114,115 There is evidence that GLP-1 receptors are present at high density in the area postrema 116 and that peripheral infusion of GLP-1 analogues activates neurones in the area postrema 117 projecting to sites implicated in the control of energy balance, including the parabrachial nucleus and NTS.…”

Amylin-mediated control of glycemia, energy balance, and cognition

“…Leptin receptors are not highly expressed in the AP [176-178], and the ability of amylin to enhance leptin-induced pSTAT3 signaling in the AP is inconsistent [165, 169]. However, recent single-cell PCR data indicate that some cells in the AP express mRNA for the components of the amylin receptor as well as the leptin receptor [179]. Co-expression of the receptors at the protein level remains to be evaluated, but certainly, this novel finding invites the question of whether a subset of AP neurons may indeed support an interaction between amylin and leptin.…”