title: Serotonin acts as an up-regulator of acyl-coenzyme A:cholesterol acyltransferase-1 in human monocyte-macrophages.
abstract: Acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) converts intracellular free cholesterol into cholesterol ester for storage in lipid droplets and plays an important role in the formation of macrophage-derived foam cells in atherosclerotic lesions. Serotonin (5-HT), a potent vasoconstrictor that is released from activated platelets, increases uptake of oxidized low-density lipoprotein (LDL) by macrophages, leading to foam cell formation, and contributes to the development of atherosclerotic plaque. However, it is not yet known whether 5-HT affects ACAT-1 expression in human monocyte-macrophages as the molecular mechanism of enhanced foam cell formation by 5-HT remains unclear. We examined the effects of 5-HT on ACAT-1 expression during differentiation of cultured human monocytes into macrophages. Expression of ACAT-1 protein but not 5-HT2A receptor increased in a time-dependent manner. 5-HT increased ACAT activity in a concentration-dependent manner after 7 days in primary monocyte culture. Immunoblotting analysis showed that 5-HT at 10 microM increased ACAT-1 protein expression level by two-fold, and this effect was abolished completely by a 5-HT2A receptor antagonist (sarpogrelate), its major metabolite (M-1), a G protein inactivator (GDP-beta-S), a protein kinase C (PKC) inhibitor (rottlerin), a Src family inhibitor (PP2), or a mitogen-activated protein kinase (MAPK) kinase inhibitor (PD98059). Northern blotting analysis indicated that among the four ACAT-1 mRNA transcripts (2.8-, 3.6-, 4.3-, and 7.0-kb), the levels of the 2.8- and 3.6-kb transcripts were selectively up-regulated by approximately 1.7-fold by 5-HT (10 microM). The results of the present study suggested that 5-HT may play a crucial role in macrophage-derived foam cell formation by up-regulating ACAT-1 expression via the 5-HT2A receptor/G protein/c-Src/PKC/MAPK pathway, contributing to the progression of atherosclerotic plaque.
authors.affiliation: First Department of Internal Medicine, Showa University School of Medicine, Tokyo 142-8666, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Suguro
authors.forename: Takuya
authors.initials: T
authors.lastname: Watanabe
authors.forename: Tomoko
authors.initials: T
authors.lastname: Kanome
authors.forename: Syuusuke
authors.initials: S
authors.lastname: Kodate
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Hirano
authors.forename: Akira
authors.initials: A
authors.lastname: Miyazaki
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Adachi
mesh_terms: D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000201:enzymology / Q000378:metabolism; D008264:Macrophages / Q000201:enzymology* / Q000378:metabolism; D009000:Monocytes / Q000201:enzymology* / Q000378:metabolism; D012701:Serotonin / Q000502:physiology*; D002785:Sterol O-Acyltransferase / Q000096:biosynthesis* / Q000235:genetics; D015854:Up-Regulation / Q000235:genetics / Q000502:physiology*
chemical_list: D012701:Serotonin; D002785:Sterol O-Acyltransferase; C493492:sterol O-acyltransferase 1