Ghrelin: friend or foe for neuroinflammation

Ghrelin is a recently identified gastric hormone that displays strong growth hormone (GH) releasing activity mediated by the GH secretagogue receptor (GHS-R). While this unique endogenous peptide participates in the regulation of energy homeostasis, increases food intake, and decreases energy expenditure, its ability to modulate immune regulation is another important feature. Here we discuss the effect of ghrelin on the immune system. Ghrelin was initially reported as an immune enhancing factor. More recently, however, the immunosuppressive effects of ghrelin have been found in several animal models including bowel disease, arthritis, and sepsis and endotoxemia. We recently demonstrated that exogenous administration of ghrelin suppressed experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis in association with the reduction of pro-inflammatory cytokines in microglia. These results shed light on the new role of ghrelin in the regulation of disorders that pro-inflammatory cytokines contribute to the pathogenesis such as neuroinflammatory and mental diseases.