The relaxin receptor RXFP1 signals through a mechanism of autoinhibition

Biased agonism in peptide-GPCRs: A structural perspective

G protein-coupled receptors (GPCRs) are dynamic membrane receptors that transduce extracellular signals to the cell interior by forming a ligand-receptor-effector (ternary) complex that functions via allosterism. Peptides constitute an important class of ligands that interact with their cognate GPCRs (peptide-GPCRs) to form the ternary complex. "Biased agonism", a therapeutically relevant phenomenon exhibited by GPCRs owing to their allosteric nature, has also been observed in peptide-GPCRs, leading to the development of selective therapeutics with fewer side effects. In this review, we have focused on the structural basis of signalling bias at peptide-GPCRs of classes A and B, and reviewed the therapeutic relevance of bias at peptide-GPCRs, with the hope of contributing to the discovery of novel biased peptide drugs.

A novel long-acting relaxin-2 fusion, AZD3427, improves cardiac performance in non-human primates with cardiac dysfunction

AIM

Relaxin-2, a well-known human hormone primarily associated with pregnancy, has shown promising cardiovascular benefits in both preclinical models and clinical trials. However, its therapeutic potential has been limited due to the short half-life and the short duration of treatment. To address this, we developed AZD3427, a novel long-acting relaxin-2 analogue and assessed its efficacy during prolonged treatment in a large animal model with cardiac dysfunction.

METHODS AND RESULTS

Extensive protein engineering resulted in AZD3427, a novel fusion protein, which closely mimics the natural hormone's structure and consists of a single relaxin-2 and the Fc fragment of human IgG1 to extend its half-life. AZD3427 exhibits an improved pharmacokinetic profile, allowing for weekly or less frequent, subcutaneous dosing, and maintains the pharmacology profile of relaxin-2 with signalling via RXFP1 in cell systems. The effects of chronic RXFP1 agonism with AZD3427 were investigated in a non-human primate (NHP) model with systolic dysfunction and metabolic syndrome. Administration of AZD3427 over a twenty-one-week period led to significant improvements in cardiac function, as evidenced by increased ejection fraction (EF), cardiac output (CO) and stroke volume (SV), as well as reduced systemic vascular resistance (SVR). Importantly, no adverse events related to treatments were observed and there were no concomitant changes in heart rate (HR) or blood pressure (BP). During the eighteen-week washout period, the observed effects gradually disappeared.

CONCLUSIONS

Prolonged administration of AZD3427, a long-acting relaxin receptor RXFP1 agonist, resulted in remarkable improvement in cardiac function in a NHP model. Findings of this study are an important translational step to developing future therapies and support further clinical development of AZD3427 as a novel treatment for patients with heart failure (HF).

Biased activation of the vasopressin V2 receptor probed by molecular dynamics simulations, NMR and pharmacological studies

G protein-coupled receptors (GPCRs) control critical cell signaling. Their response to extracellular stimuli involves conformational changes to convey signals to intracellular effectors, among which the most important are G proteins and β-arrestins (βArrs). Biased activation of one pathway is a field of intense research in GPCR pharmacology. Combining NMR, site-directed mutagenesis, molecular pharmacology, and molecular dynamics (MD) simulations, we studied the conformational diversity of the vasopressin V2 receptor (V2R) bound to different types of ligands: the antagonist Tolvaptan, the endogenous unbiased agonist arginine-vasopressin, and MCF14, a partial Gs protein-biased agonist. A double-labeling NMR scheme was developed to study the receptor conformational changes and ligand binding: V2R was subjected to lysine 13CH3 methylation for complementary NMR studies, whereas the agonists were tagged with a paramagnetic probe. Paramagnetic relaxation enhancements and site-directed mutagenesis validated the ligand binding modes in the MD simulations. We found that the bias for the Gs protein over the βArr pathway involves interactions between the conserved NPxxY motif in the transmembrane helix 7 (TM7) and TM3, compacting helix 8 (H8) toward TM1 and likely inhibiting βArr signaling. A similar mechanism was elicited for the pathogenic mutation I130N, which constitutively activates the Gs proteins without concomitant βArr recruitment. The findings suggest common patterns of biased signaling in class A GPCRs, as well as a rationale for the design of G protein-biased V2R agonists.

Engineering and Characterization of a Long-Half-Life Relaxin Receptor RXFP1 Agonist

Relaxin-2 is a peptide hormone with important roles in human cardiovascular and reproductive biology. Its ability to activate cellular responses such as vasodilation, angiogenesis, and anti-inflammatory and antifibrotic effects has led to significant interest in using relaxin-2 as a therapeutic for heart failure and several fibrotic conditions. However, recombinant relaxin-2 has a very short serum half-life, limiting its clinical applications. Here, we present protein engineering efforts targeting the relaxin-2 hormone in order to increase its serum half-life while maintaining its ability to activate the G protein-coupled receptor RXFP1. To achieve this, we optimized a fusion between relaxin-2 and an antibody Fc fragment, generating a version of the hormone with a circulating half-life of around 3 to 5 days in mice while retaining potent agonist activity at the RXFP1 receptor both in vitro and in vivo.

Relaxin suppresses atrial fibrillation, reverses fibrosis and reduces inflammation in aged hearts

Healthy aging results in cardiac structural and electrical remodeling that increase susceptibility to cardiovascular diseases. Relaxin has shown broad cardioprotective effects including anti-fibrotic, anti-arrhythmic and anti-inflammatory outcomes in multiple models. This paper focuses on the cardioprotective effects of Relaxin in a rat model of aging. Sustained atrial or ventricular fibrillation are readily induced in the hearts of aged but not young control animals. Treatment with Relaxin suppressed this arrhythmogenic response by increasing conduction velocity, decreasing fibrosis and promoting substantial cardiac remodeling. Relaxin treatment resulted in a significant increase in the levels of: Nav1.5, Cx43, βcatenin and Wnt1 in rat hearts. In isolated cardiomyocytes, Relaxin increased Nav1.5 expression. These effects were mimicked by CHIR 99021, a pharmacological activator of canonical Wnt signaling, but blocked by the canonical Wnt inhibitor Dickkopf1. Relaxin prevented TGF-β-dependent differentiation of cardiac fibroblasts into myofibroblasts while increasing the expression of Wnt1; the effects of Relaxin on cardiac fibroblast differentiation were blocked by Dickkopf1. RNASeq studies demonstrated reduced expression of pro-inflammatory cytokines and an increase in the expression of α- and β-globin in Relaxin-treated aged males. Relaxin reduces arrhythmogenicity in the hearts of aged rats by reduction of fibrosis and increased conduction velocity. These changes are accompanied by substantial remodeling of the cardiac tissue and appear to be mediated by increased canonical Wnt signaling. Relaxin also exerts significant anti-inflammatory and anti-oxidant effects in the hearts of aged rodents. The mechanisms by which Relaxin increases the expression of Wnt ligands, promotes Wnt signaling and reprograms gene expression remain to be determined.

Conformational dynamics underlying atypical chemokine receptor 3 activation

Atypical Chemokine Receptor 3 (ACKR3) belongs to the G protein-coupled receptor family but it does not signal through G proteins. The structural properties that govern the functional selectivity and the conformational dynamics of ACKR3 activation are poorly understood. Here, we combined hydrogen/deuterium exchange mass spectrometry, site-directed mutagenesis, and molecular dynamics simulations to examine the binding mode and mechanism of action of ACKR3 ligands of different efficacies. Our results show that activation or inhibition of ACKR3 is governed by intracellular conformational changes of helix 6, intracellular loop 2, and helix 7, while the DRY motif becomes protected during both processes. Moreover, we identified the binding sites and the allosteric modulation of ACKR3 upon β-arrestin 1 binding. In summary, this study highlights the structure-function relationship of small ligands, the binding mode of β-arrestin 1, the activation dynamics, and the atypical dynamic features in ACKR3 that may contribute to its inability to activate G proteins.

Evolutionary genetics of pulmonary anatomical adaptations in deep-diving cetaceans

BACKGROUND

Cetaceans, having experienced prolonged adaptation to aquatic environments, have undergone evolutionary changes in their respiratory systems. This process of evolution has resulted in the emergence of distinctive phenotypic traits, notably the abundance of elastic fibers and thickened alveolar walls in their lungs, which may facilitate alveolar collapse during diving. This structure helps selective exchange of oxygen and carbon dioxide, while minimizing nitrogen exchange, thereby reducing the risk of DCS. Nevertheless, the scientific inquiry into the mechanisms through which these unique phenotypic characteristics govern the diving behavior of marine mammals, including cetaceans, remains unresolved.

RESULTS

This study entails an evolutionary analysis of 42 genes associated with pulmonary fibrosis across 45 mammalian species. Twenty-one genes in cetaceans exhibited accelerated evolution, featuring specific amino acid substitutions in 14 of them. Primarily linked to the development of the respiratory system and lung morphological construction, these genes play a crucial role. Moreover, among marine mammals, we identified eight genes undergoing positive selection, and the evolutionary rates of three genes significantly correlated with diving depth. Specifically, the SFTPC gene exhibited convergent amino acid substitutions. Through in vitro cellular experiments, we illustrated that convergent amino acid site mutations in SFTPC contribute positively to pulmonary fibrosis in marine mammals, and the presence of this phenotype can induce deep alveolar collapse during diving, thereby reducing the risk of DCS during diving.

CONCLUSIONS

The study unveils pivotal genetic signals in cetaceans and other marine mammals, arising through evolution. These genetic signals may influence lung characteristics in marine mammals and have been linked to a reduced risk of developing DCS. Moreover, the research serves as a valuable reference for delving deeper into human diving physiology.

Identification of Novel Series of Potent and Selective Relaxin Family Peptide Receptor 1 (RXFP1) Agonists

Relaxin H2 is a clinically relevant peptide agonist for relaxin family peptide receptor 1 (RXFP1), but a combination of this hormone's short plasma half-life and the need for injectable delivery limits its therapeutic potential. We sought to overcome these limitations through the development of a potent small molecule (SM) RXFP1 agonist. Although two large SM HTS campaigns failed in identifying suitable hit series, we uncovered novel chemical space starting from the only known SM RXFP1 agonist series, represented by ML290. Following a design-make-test-analyze strategy based on improving early dose to man ranking, we discovered compound 42 (AZ7976), a highly selective RXFP1 agonist with sub-nanomolar potency. We used AZ7976, its 10 000-fold less potent enantiomer 43 and recombinant relaxin H2 to evaluate in vivo pharmacology and demonstrate that AZ7976-mediated heart rate increase in rats was a result of RXFP1 agonism. As a result, AZ7976 was selected as lead for continued optimization.

The diverse influences of relaxin-like peptide family on tumor progression: Potential opportunities and emerging challenges

Relaxin-like peptide family exhibit differential expression patterns in various types of cancers and play a role in cancer development. This family participates in tumorigenic processes encompassing proliferation, migration, invasion, tumor microenvironment, immune microenvironment, and anti-cancer resistance, ultimately influencing patient prognosis. In this review, we explore the mechanisms underlying the interaction between the RLN-like peptide family and tumors and provide an overview of therapeutic approaches utilizing this interaction.

Intramolecular activity regulation of adhesion GPCRs in light of recent structural and evolutionary information

The class B2 of GPCRs known as adhesion G protein-coupled receptors (aGPCRs) has come under increasing academic and nonacademic research focus over the past decade due to their physiological importance as mechano-sensors in cell-cell and cell-matrix contexts. A major advance in understanding signal transduction of aGPCRs was achieved by the identification of the so-called Stachel sequence, which acts as an intramolecular agonist at the interface between the N terminus (Nt) and the seven-transmembrane helix domain (7TMD). Distinct extracellular signals received by the Nt are integrated at the Stachel into structural changes of the 7TMD towards an active state conformation. Until recently, little information was available on how the activation process of aGPCRs is realized at the molecular level. In the past three years several structures of the 7TMD plus the Stachel in complex with G proteins have been determined, which provide new insights into the architecture and molecular function of this receptor class. Herein, we review this structural information to extract common and distinct aGPCR features with particular focus on the Stachel binding site within the 7TMD. Our analysis extends the current view of aGPCR activation and exposes similarities and differences not only between diverse aGPCR members, but also compared to other GPCR classes.