Serotonin Increases Interleukin-6 Synthesis in Human Vascular Smooth Muscle Cells

Background—Interleukin-6 (IL-6) is a key molecule in chronic inflammation and has been implicated in the progression of atherosclerosis. Serotonin (5-hydroxytryptamine; 5-HT) causes vascular contraction and proliferation, but its role in atherogenesis has not been clarified. We investigated the effects of 5-HT on IL-6 synthesis in human vascular smooth muscle cells (VSMCs). Methods and Results—IL-6 levels in the culture medium of VSMCs were determined by ELISA. IL-6 mRNA accumulation was determined by use of a Quantikine mRNA colorimetric quantification kit. NF-kB activation was tested by gel retardation assay. 5-HT induced IL-6 production by VSMCs in a time- and dose-dependent manner, with increased IL-6 mRNA accumulation and nuclear factor-kB activation. The effect of 5-HT on IL-6 production was significantly inhibited by the 5-HT2 receptor antagonist ketanserin and the selective 5-HT2A receptor antagonist sarpogrelate. Conversely, the 5-HT2 receptor agonist a-methyl-5-HT increased IL-6 production. The protein kinase C (PKC) inhibitor calphostin C, but not the protein kinase A inhibitor KT5720, suppressed 5-HT–induced IL-6 production. The effect of 5-HT was also abolished in PKC-depleted VSMCs after pretreatment with phorbol 12-myristate 13-acetate for 24 hours. Conclusions—5-HT acts on 5-HT2A receptors and increases IL-6 synthesis in human VSMCs at least partially through a PKC-dependent pathway. These results suggested that 5-HT may contribute to inflammatory activation of the vessel