Receptor component protein, an endogenous allosteric modulator of family B G protein coupled receptors

Biased Signaling in G Protein-Coupled Receptors: Understanding the Biological Relevance and Tools for Probing Functionally Selective Ligands

Biased signaling has transformed pharmacology by revealing that receptors, particularly G protein-coupled receptors (GPCRs), can activate specific intracellular pathways selectively rather than uniformly. This discovery enables the development of targeted therapeutics that minimize side effects by precisely modulating receptor activity. Functionally selective ligands, which preferentially activate distinct signaling branches, have become essential tools for exploring receptor mechanisms and uncovering the complexities of GPCR signaling. These ligands help clarify receptor function in various physiological and pathological contexts, offering profound implications for therapeutic innovation. GPCRs, which mediate a wide range of cellular responses through coupling to G proteins and arrestins, are key pharmacological targets, with nearly a third of FDA-approved drugs acting on them. Recent advancements in biosensor development, multiplex assay platforms, and deep mutational scanning methods are improving our ability to define GPCR signaling, allowing for a better understanding of biased signaling pathways.

Loss of Calcitonin Gene Related Receptor component protein (RCP) in nervous system can bias "gepant" antagonism

We examined calcitonin gene-related peptide (CGRP)'s effects on behavioral surrogates for motion-induced nausea and static imbalance in the nestinRCP (-/-), a novel mouse model that loses expression of receptor component protein (RCP) in the nervous system after tamoxifen induction. The assays used were the motion-induced thermoregulation and center of pressure (CoP) assays. Findings suggest CGRP's affects behavioral measures in the nestinRCP (-/-) similarly to littermate controls, since CGRP was observed to increase female sway and diminishes tail vasodilations to provocative motion in both sexes. However, the CGRP-receptor antagonist olcegepant did not antagonize CGRP's effects in the nestinRCP (-/-), whereas it was effective in littermate controls. Findings suggest RCP loss may change the sensitivity of the CGRP receptor and affect the efficacy of receptor antagonists.

Significance Statement

Research in calcitonin gene-related peptide (CGRP) has primarily focused on ligand- receptor interactions at the calcitonin-like receptor (CLR) and receptor activity-modifying unit 1 (RAMP1) subunits. However, the role of receptor component protein (RCP), which mediates signaling via the Gα-stimulatory pathway, is less understood. A novel tamoxifen-inducible mouse model, nestinRCP (-/-), was generated to study loss of RCP in CGRP signaling in the nervous system, and behavioral changes to motion-induced nausea and postural sway were studied after systemic injections of CGRP or CGRP co-delivered with migraine drugs. Findings from this study suggest the loss of CGRP-RCP can bias "gepant" antagonists like olcegepant, and may promote development of therapies to inhibit the RCP-CLR interactions.

Inhibition of CGRP signaling impairs fracture healing in mice

Calcitonin gene-related peptide (CGRP) is a neuropeptide produced by sensory nerves and functions as a pain sensor. It acts by binding to the calcitonin-like receptor (CLR, protein; Calcrl, gene). CGRP inhibition has been recently introduced as therapeutic treatment of migraine-associated pain. Previous studies have shown that CGRP stimulates bone formation. The aim of our study is to determine whether the inhibition of CGRP signaling negatively impacted fracture healing. Using α-smooth muscle actin (αSMA) Cre animals crossed with Ai9 reporter mice, we showed that CGRP-expressing nerves are near αSMA + cells in the periosteum. In vitro experiments revealed that periosteal cells express Calcrl and receptor activity modifying protein 1; and CGRP stimulation increased periosteal cell proliferation. Using a tamoxifen-inducible model αSMACre/CLRfl/fl , we targeted the deletion of CLR to periosteal progenitor cells and examined fracture healing. Microcomputed tomography of fractured femurs showed a reduction in bone mass in αSMACre+/CLRfl/fl female mice relative to controls and callus volume in males. Pharmacological CGRP-CLR inhibition was achieved by subcutaneous delivery of customized pellets with small molecule inhibitor olcegepant (BIBN-4096) at a dose of 10 μg/day. BIBN-4096-treated C57BL/6J mice had a higher latency toward thermal nociception than placebo-treated mice, indicating impaired sensory function through CGRP inhibition. CGRP inhibition also resulted in reduced callus volume, bone mass, and bone strength compared to placebo controls. These results indicate that inhibiting CGRP by deleting CLR or by using BIBN-4096, contributes to delayed bone healing.

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

Elucidating the Interactome of G Protein-Coupled Receptors and Receptor Activity-Modifying Proteins

G protein-coupled receptors (GPCRs) are known to interact with several other classes of integral membrane proteins that modulate their biology and pharmacology. However, the extent of these interactions and the mechanisms of their effects are not well understood. For example, one class of GPCR-interacting proteins, receptor activity-modifying proteins (RAMPs), comprise three related and ubiquitously expressed single-transmembrane span proteins. The RAMP family was discovered more than two decades ago, and since then GPCR-RAMP interactions and their functional consequences on receptor trafficking and ligand selectivity have been documented for several secretin (class B) GPCRs, most notably the calcitonin receptor-like receptor. Recent bioinformatics and multiplexed experimental studies suggest that GPCR-RAMP interactions might be much more widespread than previously anticipated. Recently, cryo-electron microscopy has provided high-resolution structures of GPCR-RAMP-ligand complexes, and drugs have been developed that target GPCR-RAMP complexes. In this review, we provide a summary of recent advances in techniques that allow the discovery of GPCR-RAMP interactions and their functional consequences and highlight prospects for future advances. We also provide an up-to-date list of reported GPCR-RAMP interactions based on a review of the current literature. SIGNIFICANCE STATEMENT: Receptor activity-modifying proteins (RAMPs) have emerged as modulators of many aspects of G protein-coupled receptor (GPCR)biology and pharmacology. The application of new methodologies to study membrane protein-protein interactions suggests that RAMPs interact with many more GPCRs than had been previously known. These findings, especially when combined with structural studies of membrane protein complexes, have significant implications for advancing GPCR-targeted drug discovery and the understanding of GPCR pharmacology, biology, and regulation.

Alpha-Calcitonin Gene Related Peptide: New Therapeutic Strategies for the Treatment and Prevention of Cardiovascular Disease and Migraine

Alpha-calcitonin gene-related peptide (α-CGRP) is a vasodilator neuropeptide of the calcitonin gene family. Pharmacological and gene knock-out studies have established a significant role of α-CGRP in normal and pathophysiological states, particularly in cardiovascular disease and migraines. α-CGRP knock-out mice with transverse aortic constriction (TAC)-induced pressure-overload heart failure have higher mortality rates and exhibit higher levels of cardiac fibrosis, inflammation, oxidative stress, and cell death compared to the wild-type TAC-mice. However, administration of α-CGRP, either in its native- or modified-form, improves cardiac function at the pathophysiological level, and significantly protects the heart from the adverse effects of heart failure and hypertension. Similar cardioprotective effects of the peptide were demonstrated in pressure-overload heart failure mice when α-CGRP was delivered using an alginate microcapsules-based drug delivery system. In contrast to cardiovascular disease, an elevated level of α-CGRP causes migraine-related headaches, thus the use of α-CGRP antagonists that block the interaction of the peptide to its receptor are beneficial in reducing chronic and episodic migraine headaches. Currently, several α-CGRP antagonists are being used as migraine treatments or in clinical trials for migraine pain management. Overall, agonists and antagonists of α-CGRP are clinically relevant to treat and prevent cardiovascular disease and migraine pain, respectively. This review focuses on the pharmacological and therapeutic significance of α-CGRP-agonists and -antagonists in various diseases, particularly in cardiac diseases and migraine pain.

Vasoactive neuropeptides and Alzheimer's disease: a systematic review focusing on calcitonin gene-related peptide

Vasoactive peptides constitute a heterogenous family of mediators exerting various physiological functions, mostly studied for their vasotropic effects and role as peripheral neurotransmitters/neuromodulators, mainly involved in nociceptive transmission modulation. They have been divided into vasodilatory or vasoconstrictive peptides, according to their predominant effects on vascular tone. Recent research has shown in the Central Nervous System effects as transmitters and "growth factor-like" signals. Therefore, deregulation of their signaling systems has been thought to play a role in neural cell death and in the pathogenesis of neurodegenerative disorders, including Alzheimer's disease, since these peptides can regulate neuronal stress signaling, survival cascades, synaptic plasticity. This review considers evidence about the implication of neuropeptide systems in Alzheimer's disease while focusing mainly on calcitonin gene-related peptide-alpha. In vitro and in vivo studies have shown potential implications in its pathogenesis. It has been possibly proposed as a neuroprotective agent, considering not only its pleiotropic actions on blood vessels, neurovascular coupling, energy metabolism, but also its potential actions on neuronal, glial, and immune system stress signaling, which might also derive from its structural homology to amylin. Amylin signaling is thought to be disrupted in Alzheimer's disease, and amylin itself takes part in the composition of senile plaques. Calcitonin gene-related peptide-containing systems seem more closely related to Alzheimer's disease pathogenesis than other neuropeptidergic systems, and their regulation might represent an interesting mechanism in developing novel therapeutic approaches.

Allosteric Modulator Leads Hiding in Plain Site: Developing Peptide and Peptidomimetics as GPCR Allosteric Modulators

Allosteric modulators (AMs) of G-protein coupled receptors (GPCRs) are desirable drug targets because they can produce fewer on-target side effects, improved selectivity, and better biological specificity (e.g., biased signaling or probe dependence) than orthosteric drugs. An underappreciated source for identifying AM leads are peptides and proteins-many of which were evolutionarily selected as AMs-derived from endogenous protein-protein interactions (e.g., transducer/accessory proteins), intramolecular receptor contacts (e.g., pepducins or extracellular domains), endogenous peptides, and exogenous libraries (e.g., nanobodies or conotoxins). Peptides offer distinct advantages over small molecules, including high affinity, good tolerability, and good bioactivity, and specific disadvantages, including relatively poor metabolic stability and bioavailability. Peptidomimetics are molecules that combine the advantages of both peptides and small molecules by mimicking the peptide's chemical features responsible for bioactivity while improving its druggability. This review 1) discusses sources and strategies to identify peptide/peptidomimetic AMs, 2) overviews strategies to convert a peptide lead into more drug-like "peptidomimetic," and 3) critically analyzes the advantages, disadvantages, and future directions of peptidomimetic AMs. While small molecules will and should play a vital role in AM drug discovery, peptidomimetics can complement and even exceed the advantages of small molecules, depending on the target, site, lead, and associated factors.

CGRP, adrenomedullin and adrenomedullin 2 display endogenous GPCR agonist bias in primary human cardiovascular cells

Agonist bias occurs when different ligands produce distinct signalling outputs when acting at the same receptor. However, its physiological relevance is not always clear. Using primary human cells and gene editing techniques, we demonstrate endogenous agonist bias with physiological consequences for the calcitonin receptor-like receptor, CLR. By switching the receptor-activity modifying protein (RAMP) associated with CLR we can “re-route” the physiological pathways activated by endogenous agonists calcitonin gene-related peptide (CGRP), adrenomedullin (AM) and adrenomedullin 2 (AM2). AM2 promotes calcium-mediated nitric oxide signalling whereas CGRP and AM show pro-proliferative effects in cardiovascular cells, thus providing a rationale for the expression of the three peptides. CLR-based agonist bias occurs naturally in human cells and has a fundamental purpose for its existence. We anticipate this will be a starting point for more studies into RAMP function in native environments and their importance in endogenous GPCR signalling.

Clark et al. explore the ability of ligands to activate the calcitonin-like receptor (CLR) in primary endothelial cells, and the influence of co-expressed receptor-activity modifying proteins (RAMPs). Their study reveals that GPCR agonist bias occurs naturally in human cells and plays a fundamental role in providing unique functions to endogenous agonists.