Serotonergic regulation of energy metabolism in peripheral tissues

Serotonin is a biogenic amine synthesized from the essential amino acid tryptophan. Because serotonin cannot cross the blood-brain barrier, it functions differently in neuronal and non-neuronal tissues. In the CNS, serotonin regulates mood, behavior, appetite, and energy expenditure. Although most serotonin in the body is synthesized at the periphery, its biological roles have not been well elucidated. Older studies using chemical agonists and antagonists yielded conflicting results, because the complexity of serotonin receptors and the low selectivity of agonists and antagonists were not known. Several recent studies using specific knock-out of serotonin receptors have been performed to assess the role of peripheral serotonin in regulating energy metabolism. This review discusses (1) the tissue-specific roles of peripheral serotonin in regulating energy metabolism, (2) the mechanism by which dysfunctional peripheral serotonin signaling can progress to metabolic diseases, and (3) how peripheral serotonin signaling could be a therapeutic target for metabolic diseases.