Relaxin receptor signalling and anti-fibrotic effects.
Biased activation of RXFP1 to promote matrix breakdown and vascular protection.
Relaxin is a hormone best known from pregnancy, where it contributes to remodelling of connective tissue and to systemic vasodilation and increased renal blood flow. Its principal receptor, relaxin family peptide receptor 1, is a G-protein-coupled receptor found in heart, kidney, lung, liver, and vasculature. Classical activation raises intracellular cyclic AMP, but the receptor also couples to other cascades including extracellular signal-regulated kinase signalling and nitric oxide production. The reason this receptor attracts interest is fibrosis. Fibrosis is the pathological accumulation of extracellular matrix, principally collagen, that stiffens organs and degrades their function, and it is a common endpoint in chronic heart, kidney, liver, and lung disease with very few effective treatments. Relaxin signalling opposes it from both directions: it suppresses the activation of fibroblasts into collagen-producing myofibroblasts, and it increases the activity of matrix metalloproteinases that degrade collagen already deposited. Combined with vasodilation and improved tissue perfusion, this makes RXFP1 an attractive anti-fibrotic and cardioprotective target. Native relaxin is a two-chain molecule held together by disulfide bonds, structurally similar to insulin. That architecture makes it expensive and difficult to manufacture at scale, which has been a real obstacle to developing it as a medicine. The compound in this group is a single-chain peptide designed to engage RXFP1 without that manufacturing burden. It is also described as functionally selective, or biased. Rather than strongly activating the cyclic AMP pathway as native relaxin does, it preferentially signals through the ERK pathway at the same receptor. Signalling bias means a ligand can trigger some of a receptor's downstream cascades while leaving others comparatively quiet. Here the proposal is that the ERK-biased profile retains the anti-fibrotic actions, including increased matrix metalloproteinase activity, while avoiding effects tied to the broader relaxin signalling profile. Preclinical work has reported vasoprotective and cardioprotective actions consistent with relaxin biology. On clinical relevance, caution is warranted. The receptor and the anti-fibrotic biology are legitimate and well studied, but full-length relaxin itself has been through large human trials in acute heart failure without confirming clinical benefit, which is a sobering precedent for the whole target. This single-chain compound has not been through human trials, is not approved anywhere, and its evidence base is entirely preclinical.
Peptides acting through this pathway.
FAQ.
What does relaxin receptor signalling and anti-fibrotic effects do?
Relaxin is a hormone best known from pregnancy, where it contributes to remodelling of connective tissue and to systemic vasodilation and increased renal blood flow. Its principal receptor, relaxin family peptide receptor 1, is a G-protein-coupled receptor found in heart, kidney, lung, liver, and vasculature. Classical activation raises intracellular cyclic AMP, but the receptor also couples to other cascades including extracellular signal-regulated kinase signalling and nitric oxide production. The reason this receptor attracts interest is fibrosis. Fibrosis is the pathological accumulation of extracellular matrix, principally collagen, that stiffens organs and degrades their function, and it is a common endpoint in chronic heart, kidney, liver, and lung disease with very few effective treatments. Relaxin signalling opposes it from both directions: it suppresses the activation of fibroblasts into collagen-producing myofibroblasts, and it increases the activity of matrix metalloproteinases that degrade collagen already deposited. Combined with vasodilation and improved tissue perfusion, this makes RXFP1 an attractive anti-fibrotic and cardioprotective target. Native relaxin is a two-chain molecule held together by disulfide bonds, structurally similar to insulin. That architecture makes it expensive and difficult to manufacture at scale, which has been a real obstacle to developing it as a medicine. The compound in this group is a single-chain peptide designed to engage RXFP1 without that manufacturing burden. It is also described as functionally selective, or biased. Rather than strongly activating the cyclic AMP pathway as native relaxin does, it preferentially signals through the ERK pathway at the same receptor. Signalling bias means a ligand can trigger some of a receptor's downstream cascades while leaving others comparatively quiet. Here the proposal is that the ERK-biased profile retains the anti-fibrotic actions, including increased matrix metalloproteinase activity, while avoiding effects tied to the broader relaxin signalling profile. Preclinical work has reported vasoprotective and cardioprotective actions consistent with relaxin biology. On clinical relevance, caution is warranted. The receptor and the anti-fibrotic biology are legitimate and well studied, but full-length relaxin itself has been through large human trials in acute heart failure without confirming clinical benefit, which is a sobering precedent for the whole target. This single-chain compound has not been through human trials, is not approved anywhere, and its evidence base is entirely preclinical.
Which peptides act through relaxin receptor signalling and anti-fibrotic effects?
B7-33. They share this pathway but differ in evidence, approval, and safety.
Does this mechanism prove a peptide works?
No. Mechanistic plausibility is not proof of clinical benefit. A plausible pathway is a reason to study a compound, not evidence that it works in humans.