UCLA

Calcification, fibrosis, and chronic inflammation are the predominant features of calcific aortic valve disease, a life-threatening condition. Drugs that induce serotonin (5-hydroxytryptamine [5-HT]) are known to damage valves, and activated platelets, which carry peripheral serotonin, are known to promote calcific aortic valve stenosis. However, the role of 5-HT in valve leaflet pathology is not known. We tested whether serotonin mediates inflammation-induced matrix mineralization in valve cells. Real-time reverse transcription-polymerase chain reaction analysis showed that murine aortic valve interstitial cells (VICs) expressed both serotonin receptor types 2A and 2B (Htr2a and Htr2b). Although Htr2a expression was greater at baseline, Htr2b expression was induced several-fold more than Htr2a in response to the pro-calcific tumor necrosis factor-α (TNF-α) treatment. 5-HT also augmented TNF-α-induced osteoblastic differentiation and matrix mineralization of VIC, but 5-HT alone had no effects. Inhibition of serotonin receptor type 2B, using specific inhibitors or lentiviral knockdown in VIC, attenuated 5-HT effects on TNF-α-induced osteoblastic differentiation and mineralization. 5-HT treatment also augmented TNF-α-induced matrix metalloproteinase-3 expression, which was also attenuated by Htr2b knockdown. Htr2b expression in aortic roots and serum levels of peripheral 5-HT were also greater in the hyperlipidemic Apoe-/- mice than in control normolipemic mice. These findings suggest a new role for serotonin signaling in inflammation-induced calcific valvulopathy.