Deficiency of RAMP1 attenuates antigen-induced airway hyperresponsiveness in mice.

Manyu Li,Matthew F Krummel,Kathleen M Caron,Stephen L Tilley,Xiaoyang Hua,Sarah E Wetzel-Strong,Erin Oswald,Oliver Eickelberg

doi:10.1371/journal.pone.0102356

Abstract

Asthma is a chronic inflammatory disease affecting the lung, characterized by breathing difficulty during an attack following exposure to an environmental trigger. Calcitonin gene-related peptide (CGRP) is a neuropeptide that may have a pathological role in asthma. The CGRP receptor is comprised of two components, which include the G-protein coupled receptor, calcitonin receptor-like receptor (CLR), and receptor activity-modifying protein 1 (RAMP1). RAMPs, including RAMP1, mediate ligand specificity in addition to aiding in the localization of receptors to the cell surface. Since there has been some controversy regarding the effect of CGRP on asthma, we sought to determine the effect of CGRP signaling ablation in an animal model of asthma. Using gene-targeting techniques, we generated mice deficient for RAMP1 by excising exon 3. After determining that these mice are viable and overtly normal, we sensitized the animals to ovalbumin prior to assessing airway resistance and inflammation after methacholine challenge. We found that mice lacking RAMP1 had reduced airway resistance and inflammation compared to wildtype animals. Additionally, we found that a 50% reduction of CLR, the G-protein receptor component of the CGRP receptor, also ameliorated airway resistance and inflammation in this model of allergic asthma. Interestingly, the loss of CLR from the smooth muscle cells did not alter the airway resistance, indicating that CGRP does not act directly on the smooth muscle cells to drive airway hyperresponsiveness. Together, these data indicate that signaling through RAMP1 and CLR plays a role in mediating asthma pathology. Since RAMP1 and CLR interact to form a receptor for CGRP, our data indicate that aberrant CGRP signaling, perhaps on lung endothelial and inflammatory cells, contributes to asthma pathophysiology. Finally, since RAMP-receptor interfaces are pharmacologically tractable, it may be possible to develop compounds targeting the RAMP1/CLR interface to assist in the treatment of asthma.

Highlights

Asthma is a debilitating chronic disease affecting about 25 million people in the United States [1] that costs taxpayers over $56 billion per year in medical costs and lost productivity [2]
Since calcitonin gene-related peptide (CGRP) can signal via the Ramp1/Calcrl receptor, we were interested in determining whether a loss Ramp1 could result in an attenuation of airway hyperresponsiveness after sensitization to ovalbumin and a subsequent challenge period to reflect the findings of Aoki-Nagase et al we developed a global Ramp1 knockout mouse model, referred to as Ramp12/2 mice for the duration of this article
We have demonstrated that the loss of receptor activity-modifying protein 1 (RAMP1) in sensitized animals results in a reduction of the airway resistance compared to sensitized wildtype controls, indicating that RAMP1mediated signaling plays an important role in the hyperresponsiveness of the airways in this animal model of allergic asthma

Summary

Introduction

Asthma is a debilitating chronic disease affecting about 25 million people in the United States [1] that costs taxpayers over $56 billion per year in medical costs and lost productivity [2]. Individuals prone to asthma have chronic inflammation of the airways possibly caused by pre-sensitization of the immune system to substances that are normally innocuous [3]. When these immune cells become activated after recognition of a trigger, smooth muscle contraction, edema, and mucus hypersecretion are triggered, resulting in the appearance of symptoms. McLatchie et al determined that CGRP interacted with the calcitonin receptor-like receptor (Calcrl = gene; CLR = protein) in the presence of RAMP1, while the association of RAMP2 with CLR produced an AM receptor [7]. Compounds that block the RAMP1/CLR interface are currently undergoing clinical trials for the treatment of migraine pain mediated by CGRP signaling [13]

Methods

Results

Conclusion