The apelin receptor APJ: journey from an orphan to a multifaceted regulator of homeostasis

    1. George R Pope
    1. Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, School of Clinical Sciences, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
    1. Correspondence should be addressed to A-M O'Carroll; Email: A.M.OCarroll{at}bristol.ac.uk

    Abstract

    The apelin receptor (APJ; gene symbol APLNR) is a member of the G protein-coupled receptor gene family. Neural gene expression patterns of APJ, and its cognate ligand apelin, in the brain implicate the apelinergic system in the regulation of a number of physiological processes. APJ and apelin are highly expressed in the hypothalamo–neurohypophysial system, which regulates fluid homeostasis, in the hypothalamic–pituitary–adrenal axis, which controls the neuroendocrine response to stress, and in the forebrain and lower brainstem regions, which are involved in cardiovascular function. Recently, apelin, synthesised and secreted by adipocytes, has been described as a beneficial adipokine related to obesity, and there is growing awareness of a potential role for apelin and APJ in glucose and energy metabolism. In this review we provide a comprehensive overview of the structure, expression pattern and regulation of apelin and its receptor, as well as the main second messengers and signalling proteins activated by apelin. We also highlight the physiological and pathological roles that support this system as a novel therapeutic target for pharmacological intervention in treating conditions related to altered water balance, stress-induced disorders such as anxiety and depression, and cardiovascular and metabolic disorders.

    Keywords
    • Received in final form 6 August 2013
    • Accepted 12 August 2013
    • Made available online as an Accepted Preprint 13 August 2013
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