Published online before print January 17, 2008

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Copyright © 2008 American Society for Investigative Pathology
American Journal of Pathology, doi:10.2353/ajpath.2008.070358

Accepted for publication November 21, 2007.

Article

Role of a Serotonin Precursor in Development of Gut Microvilli

Kazuhiro Nakamura^*, Taku Sato, Akiko Ohashi, Hiromichi Tsurui^*, and Hiroyuki Hasegawa^@

From the Department of Pathology,* Juntendo University School of Medicine, Tokyo; and the Department of Biosciences, Teikyo University of Science and Technology, Uenohara, Japan

^@ To whom correspondence should be addressed. E-mail: hasegawa{at}ntu.ac.jp.

	Abstract

Monoamines exert diverse functions in various cells in peripheral organs as well as in the central nervous system. 5-Hydroxy-L-tryptophan (5-HTP) has been simply regarded as a precursor of serotonin, and it is believed that the biological significance of 5-HTP is essentially ascribable to the production of serotonin. Systemic treatment with 5-HTP is often applied to patients with low serotonin levels in the brain. Here we show that endogenous and exogenous 5-HTP but not serotonin induced the development of microvilli in the gut villi epithelium. In contrast, serotonin but not 5-HTP regulated phagocytosis by macrophages. 5-HTP specifically induced actin remodeling and decreased phosphorylation of extracellular signal-regulated kinase (ERK) in the gut, whereas serotonin stimulated actin remodeling and increased ERK phosphorylation in macrophages. Functionally, inhibition of ERK activity promoted the development of microvilli in the gut and ameliorated phagocytosis by macrophages. Thus, 5-HTP and serotonin contribute to distinct cell-type-specific functions via common mediators. Our study might create an opportunity to explore the effects of exogenously applied 5-HTP in humans.