Apelin-36, Human

Apelin-36 (human). The Apelin receptor, also known as APJ, APLNR, and AGTRL1, is a member of the class A family of G protein-coupled receptors (GPCRs). It has been identified in various species, including mouse, rat, cow, rhesus macaque, Xenopus laevis, and Danio rerio, and it shares structural similarities with the angiotensin II type l receptor (AT1). However, despite a 54% homology in transmembrane regions with AT1, it does not bind angiotensin II. Comprising 380 amino acid residues, APJ features the characteristic 7-transmembrane domain structure, typical of a class A GPCR. Nowadays, it is known that APLNR depicts physiological roles, including regulation of cardiovascular function, fluid homeostasis, the adipoinsular axis, gastrointestinal and immunomodulatory functions. Apelin isoforms: Apelin (APLN) endogenous APJ ligand, is a 36-amino acids peptide, initially discovered in bovine stomach extracts. It is expressed and released by cultured adipocytes from a 77-amino acids prepropeptide, whose sequence was identified in human and bovine tissues, with the last 23 residues of the C terminus being identical in mammals. Cleavage of this preproapelin at specific sites generates different isoforms, including apelin-36, apelin-17, apelin-13, and (Pyr1)apelin-13, which all act as agonists at the apelin receptor and equipotent mediators of vascular tone and cardiac contractility in human tissues in vitro. All of these predicted isoforms have been shown to be present in vivo, but the predominant isoforms in plasma are (Pyr1)apelin-13, apelin-13 and apelin-17, with (Pyr1)apelin-13 and apelin-13. Among these, (Pyr1)apelin-13 and apelin-13 are notably robust activators of apelin receptors in cell lines, while apelin-36 demonstrates remarkable efficacy as an inhibitor of HIV infection in vitro. Apelin-36 peptide exhibits distinct functions and binding affinities. While it is a less potent agonist compared to apelin-17 and apelin-13, apelin-36's high binding affinity to the apelin receptor underscores its role in cellular signaling. This versatile peptide drives internalization of the apelin receptor and plays a role in cardiac precursor cell movements during gastrulation and heart morphogenesis. It also exerts inhibitory effects on cytokine production in response to T-cell receptor/CD3 cross-linking, suggesting its potential role in modulating immune responses. Apelin-36's influence extends to early coronary blood vessel formation, myocardial contractility mediated through the ERK1/2 pathway, and central control of body fluid homeostasis by impacting vasopressin release and drinking behavior. Furthermore, apelin-36 exhibits remarkable inhibitory action against HIV infection by blocking HIV-1 and HIV-2 co-receptor APJ to avoid viral entry into NP-2/CD4 cells. Apelin-36 demonstrates potent anti-infective properties, supporting its potential therapeutic implications beyond its well-documented cardiovascular and metabolic roles.