Apelin/APJ system in inflammation.

Apelin, an endogenous ligand for the G protein-coupled receptor (APJ), is widely distributed within the central nervous system and diverse organs in human and animals. Recent studies indicate that the apelin/APJ system plays an important role in physiological and pathophysiological situations. Apelin/APJ could inhibit inflammatory response by down-regulation of the nuclear factor-κB (NF-κB) pathway and by up-regulation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway etc. Basic and preliminary research demonstrated that apelin/APJ system was involved in multiple diseases such as cardiovascular system diseases, liver and kidney diseases, neurological diseases, inflammatory intestinal diseases, pancreatitis, lung injury, aging, and obesity. Further, deficiency or overabundance of apelin can aggravate disease states in that inflammation is not only an important physiologic defense mechanism but also a potential mediator of organ damage. In this review, we summarize recent apelin/APJ system research progress with emphasis on the influence of the system on inflammation. Further, the mechanistic basis by which apelin regulates various inflammation-related diseases is analyzed. Finally, apelin and APJ might be presented as potential therapeutic targets for treatment of diseases mediated or exacerbated by inflammation.