CGRP receptor activity in mice with global expression of human receptor activity modifying protein 1

Abstract

BACKGROUND AND PURPOSECGRP is a potent vasodilator and nociceptive neuropeptide linked to migraine. CGRP receptors are heterodimers of receptor activity modifying protein 1 (RAMP1) and either calcitonin receptor-like receptor (CLR; forms canonical CGRP receptor) or calcitonin receptor (CT receptor; forms AMY 1 receptor). The goal of this study was to test whether transgenic mice globally expressing human RAMP1 have increased CGRP receptor activity and whether the receptors are sensitive to human selective antagonist telcagepant. EXPERIMENTAL APPROACHcAMP production was measured in primary cultures of aortic smooth muscle and trigeminal ganglia neurons from global hRAMP1 mice and non-transgenic littermates. Functional activity and inhibition were compared with clonal cell lines expressing combinations of CLR or CT receptors with RAMP1. KEY RESULTSCultured smooth muscle from global hRAMP1 mice had a 10-fold greater CGRP-induced cAMP maximal response (Rmax) than non-transgenic littermates, with similar EC 50 s. In contrast, cultured trigeminal ganglia from global hRAMP1 mice had a 40-fold leftward shift of the EC 50 , with similar Rmax values as littermates. In both hRAMP1 cultures, telcagepant blocked CGRP-induced cAMP production, but was not effective in non-transgenic cultures. IC 50 values were closer to those observed for CT receptor/hRAMP1 than CLR/hRAMP1 in clonal cell lines. CONCLUSIONS AND IMPLICATIONSOverexpression of hRAMP1 increases CGRP signalling by changing the maximal response or ligand sensitivity, depending on tissue type. Furthermore, telcagepant inhibited transgenic hRAMP1 CGRP receptors, but the degree of inhibition suggests that the transgenic mice are only partially humanized or both canonical CGRP and AMY 1 receptors are functional in trigeminal ganglia neurons and vascular smooth muscle.Abbreviations AMY 1 , amylin 1; CLR, calcitonin receptor-like receptor; CT receptor, calcitonin receptor; hRAMP1, human receptor activity modifying protein 1; K b , binding constant; NGF, nerve growth factor; Q-PCR, quantitative PCR; RAMP1, receptor activitymodifying protein-1; Rmax, maximal response; TG, trigeminal ganglia; VSMC, vascular smooth muscle cells

Cross-talk signaling in the trigeminal ganglion: role of neuropeptides and other mediators

“…Interestingly, the expression pattern of AMY1 receptor is suggestive of co-localization with CGRP, as discussed below, although this remains to be demonstrated. AMY1 receptors are also present in vascular smooth muscle based on immunostaining (Walker et al 2015) and suggested by functional data from cell culture studies (Bohn et al 2017). CGRP receptor expression in the trigeminal ganglion is possibly involved in signaling mechanisms that may be important for sensitizing mechanisms in facial pain and headache generation.…”

Targeted CGRP Small Molecule Antagonists for Acute Migraine Therapy

“…This is in agreement with clinical trial data in patients with stable coronary artery disease, whereby no significant drug-related cardiovascular adverse events were reported [ 85 ]. Additionally, when administered to trigeminal ganglion and smooth muscle cell cultures from human RAMP1 overexpressing mice, with increased CGRP, telcagepant significantly inhibited CGRP induced increases in cAMP production [ 86 ]. This effect was not observed in wild-type mice lacking the human RAMP1, further highlighting the limited preclinical utility of telcagepant.…”

CGRP in Animal Models of Migraine

“…Global overexpression of hRAMP1 in all tissues was achieved using mice expressing Cre recombinase under the control of the ubiquitous adenovirus EIIa promoter (Bohn et al 2017). Cultures obtained from vascular smooth muscle and trigeminal ganglia from those global mice showed an increased CGRP receptor activity that could be blocked by drugs such as CGRP receptor antagonists telcagepant and CGRP 8-37 (Bohn et al 2017).…”

“…Global overexpression of hRAMP1 in all tissues was achieved using mice expressing Cre recombinase under the control of the ubiquitous adenovirus EIIa promoter (Bohn et al 2017). Cultures obtained from vascular smooth muscle and trigeminal ganglia from those global mice showed an increased CGRP receptor activity that could be blocked by drugs such as CGRP receptor antagonists telcagepant and CGRP 8-37 (Bohn et al 2017). Mice with global hRAMP1 overexpression display increased vasodilation of the carotid and basilar arteries, and cerebral arterioles after CGRP application (Chrissobolis et al 2010), and decreased angiotensin II-induced hypertension (Sabharwal et al 2010).…”