Adrenomedullin (ADM or AM) is a vasodilator peptide hormone of uncertain significance in human health and disease. It was initially isolated in 1993 from a pheochromocytoma, a tumor of the adrenal medulla: hence the name. [5]
In humans ADM is encoded by the ADM gene. ADM is a peptide expressed by all tissues, and found in the circulation. A similar peptide named adreomedullin2 was reported in rats in 2004 which exhibits a similar function. [6]
Adrenomedullin may function as a hormone in the circulation control because it is found in blood in a considerable concentration. It was initially identified as a vasodilator, and some argued that it is the most potent endogenous vasodilatory peptide found in the body. Differences in opinion regarding the ability of AM to relax vascular tone may arise from the differences in the model system used. [7]
Adrenomedullin consists of 52 amino acids, has 1 intramolecular disulfide bond, and shows a slight homology with the calcitonin gene-related peptide (CGRP). The precursor, called preproadrenomedullin, consists of 185 amino acids and can be cleaved by plasma kallikrein at the Lys-Arg and Arg-Arg sites. [8] By RNA-blot analysis, human adrenomedullin mRNA was found to be expressed in all tissues, and most highly expressed in the placenta, fat cells, lung, pancreatic islets, smooth muscle, and skin. [9]
The human AM gene is localized to a single locus on Chromosome 11 with 4 exons and 3 introns. The AM gene initially codes for a 185-amino acid precursor peptide, that can be differentially excised to form a number of peptides, including an inactive 53-amino acid AM, e PAMP, adrenotensin and AM95-146. Mature human AM is activated to form a 52 amino acid, 6-amino acid ring, that shares moderate structural similarity to the calcitonin family of regulatory peptides (calcitonin, CGRP and amylin). Circulating AM consists of both amidated active form (15%) and the glycated inactive form (85%). It has a plasma half-life of 22min, mean clearance rate of 27.4 mL/kg/min, and apparent volume of distribution of 880 ± 150 mL/kg. [10]
Adrenomedullin (AM) exerts its actions through combinations of the calcitonin receptor like receptor (CALCRL) or CLR; and either (Receptor activity-modifying protein) 2 (RAMP2) or RAMP3, (known as AM1 and AM2 receptors respectively). Both transduce the hormone binding to intracellular signaling via second messenger cascades. The AM2 receptor has a low affinity for CGRP, but this is of no physiological relevance. Unlike the classical one ligand-one receptor notion of receptor signalling, the interaction of both CALCRL and RAMP at the membrane is required for AM to mediate its action: neither can bind the hormone (and therefore transduce a signal) alone. Stimulation by AM of its receptor increases production of both cyclic AMP (cAMP) and nitric oxide. [11] [12]
Before the discovery of the RAMPs and the identification of heteromeric receptors for the calcitonin family of peptides, a single G Protein coupled Adrenomedullin receptor was identified, [13] but more recent reports have cast doubts as to its importance in the major effects of adrenomedullin. In more recent research, the roles of the AM1 and AM2 receptors have been clarified through studies in genetically manipulated mice. The adrenomedullin knockout is an embryonic lethal phenotype and dies mid gestation from a condition known as hydrops fetalis. The CALCRL or CLR KO mouse recapitulates the same phenotype, as it lacks both the AM1 and AM2 receptors (incidentally confirming the lack of physiological significance for the earlier single protein AM receptor discovered by Kapas). RAMP2 KO mice also recapitulates the same phenotype showing that major physiological effects of AM are transduced by the AM1 receptor. Even the heterozygote RAMP 2 mice have disturbed physiology with unusual bone and mammary gland defects, and very aberrant endocrinology, leading to poor fertility and lactation problems. [14] What is very surprising is that the effect of deletion of RAMP3 has no deleterious effects and seems to confer advantages due to higher than normal bone mass, and reduced weight gain in older age. [15]
Parathyroid hormone (PTH), also called parathormone or parathyrin, is a peptide hormone secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine.
Calcitonin is a 32 amino acid peptide hormone secreted by parafollicular cells (also known as C cells) of the thyroid (or endostyle) in humans and other chordates in the ultimopharyngeal body. It acts to reduce blood calcium (Ca2+), opposing the effects of parathyroid hormone (PTH).
Amylin, or islet amyloid polypeptide (IAPP), is a 37-residue peptide hormone. It is co-secreted with insulin from the pancreatic β-cells in the ratio of approximately 100:1 (insulin:amylin). Amylin plays a role in glycemic regulation by slowing gastric emptying and promoting satiety, thereby preventing post-prandial spikes in blood glucose levels.
Calcitonin gene-related peptide (CGRP) is a member of the calcitonin family of peptides consisting of calcitonin, amylin, adrenomedullin, adrenomedullin 2 (intermedin) and calcitonin‑receptor‑stimulating peptide. Calcitonin is mainly produced by thyroid C cells whilst CGRP is secreted and stored in the nervous system. This peptide, in humans, exists in two forms: CGRP alpha, and CGRP beta. α-CGRP is a 37-amino acid neuropeptide and is formed by alternative splicing of the calcitonin/CGRP gene located on chromosome 11. β-CGRP is less studied. In humans, β-CGRP differs from α-CGRP by three amino acids and is encoded in a separate, nearby gene. The CGRP family includes calcitonin (CT), adrenomedullin (AM), and amylin (AMY).
The calcitonin receptor (CT) is a G protein-coupled receptor that binds the peptide hormone calcitonin and is involved in maintenance of calcium homeostasis, particularly with respect to bone formation and metabolism.
The gastric inhibitory polypeptide receptor (GIP-R), also known as the glucose-dependent insulinotropic polypeptide receptor, is a protein that in humans is encoded by the GIPR gene.
Receptor activity-modifying proteins (RAMPs) are a class of protein that interact with and modulate the activities of several Class B G protein-coupled receptors including the receptors for secretin, calcitonin (CT), glucagon, and vasoactive intestinal peptide (VIP). There are three distinct types of RAMPs in mammals, designated RAMP1, RAMP2, and RAMP3, each encoded by a separate gene.
Receptor activity modifying protein 1 is a protein that in humans is encoded by the RAMP1 gene.
Receptor activity modifying protein 2, also known as RAMP2, is a protein which in humans is encoded by the RAMP2 gene.
Receptor activity modifying protein 3, also known as RAMP3, is a human gene.
Calcitonin receptor-like (CALCRL), also known as the calcitonin receptor-like receptor (CRLR), is a human protein; it is a receptor for calcitonin gene-related peptide.
Corticotropin-releasing hormone receptor 2 (CRHR2) is a protein, also known by the IUPHAR-recommended name CRF2, that is encoded by the CRHR2 gene and occurs on the surfaces of some mammalian cells. CRF2 receptors are type 2 G protein-coupled receptors for corticotropin-releasing hormone (CRH) that are resident in the plasma membranes of hormone-sensitive cells. CRH, a peptide of 41 amino acids synthesized in the hypothalamus, is the principal neuroregulator of the hypothalamic-pituitary-adrenal axis, signaling via guanine nucleotide-binding proteins (G proteins) and downstream effectors such as adenylate cyclase. The CRF2 receptor is a multi-pass membrane protein with a transmembrane domain composed of seven helices arranged in a V-shape. CRF2 receptors are activated by two structurally similar peptides, urocortin II, and urocortin III, as well as CRH.
Pyroglutamylated RFamide peptide receptor also known as orexigenic neuropeptide QRFP receptor or G-protein coupled receptor 103 (GPR103) is a protein that in humans is encoded by the QRFPR gene.
G protein-coupled receptor family C group 6 member A (GPRC6A) is a protein that in humans is encoded by the GPRC6A gene. This protein functions as a receptor of L-α-amino acids, cations, osteocalcin, and steroids. It is a membrane androgen receptor.
DNA-directed RNA polymerase III subunit RPC9 is an enzyme that in humans is encoded by the CRCP gene.
ADM2 is a protein that in humans is encoded by the ADM2 gene.
GPR182 is a human gene which is an orphan G-protein coupled receptor.
Fibronectin type III domain-containing protein 5, the precursor of irisin, is a type I transmembrane glycoprotein that is encoded by the FNDC5 gene. Irisin is a cleaved version of FNDC5, named after the Greek messenger goddess Iris.
In molecular biology, the amylin protein family or calcitonin/CGRP/IAPP protein family is a family of proteins, which includes the precursors of calcitonin/calcitonin gene-related peptide (CGRP), islet amyloid polypeptide (IAPP) and adrenomedullin.
Zucapsaicin (Civanex) is a medication used to treat osteoarthritis of the knee and other neuropathic pain. Zucapsaicin is a member of phenols and a member of methoxybenzenes. It is a modulator of transient receptor potential cation channel subfamily V member 1 (TRPV-1), also known as the vanilloid or capsaicin receptor 1 that reduces pain, and improves articular functions. It is the cis-isomer of capsaicin. Civamide, manufactured by Winston Pharmaceuticals, is produced in formulations for oral, nasal, and topical use.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.
