Serotonin transporter downregulation is associated with aortic stenosis, and early profibrotic remodeling is mitigated by pharmacological inhibition of HTR2B receptor

Background: Aortic Stenosis (AS) is a highly prevalent disease involving physiological and structural remodeling of aortic valve, yet lacks effective medical therapy to halt its progression. Serotonin (5HT) signaling has been implicated in valvular disease. We hypothesized that AS is associated with impaired 5HT clearance due to reduced serotonin receptor (SERT) expression and increased 5HT receptor (HTR) activity. Methods: Sixty-six patients with severe AS undergoing aortic valve (AV) replacement were enrolled in the study, and samples from their explanted AV were harvested. Anatomically normal control AVs were obtained from transplant donors. Explanted AVs were collected for gene expression analysis and 5-HTTLPR genotyping. Gene expression was assessed by RT2-profiler gene array. In vivo, 8-week-old mice received 28-day Angiotensin-II (AngII) infusions ± HTR2B antagonist (LY272015) through subcutaneous Alzet osmotic-pump implants. AV structure and function were assessed via echocardiography, histology, and RNA sequencing. Human aortic valve interstitial cells (AVICs) were treated with either H2O2 or AngII ± SERT siRNAs to assess 5HT signaling and fibrotic/osteogenic markers. Results: AS patients exhibited reduced SERT and increased HTR expression. Oxidative stress in cultured human AVICs suppressed SERT and induced HTR2B expression. AngII ± SERT siRNA promoted VIC osteogenic marker expression. In mice, AngII caused AV thickening, increased velocities and gradients, and activation of fibrosis and calcification-related gene sets, including serotonin, TGFβ, Wnt/β-catenin, PI3K/Akt, and Notch pathways. Pharmacological inhibition of HTR2B preserved AV structure, normalized transvalvular velocities and pressure gradients, and reversed AngII-induced transcriptional changes. Conclusions: In human and mouse AVs, reduced SERT and elevated HTR2B signaling contribute to early-onset fibro-calcific remodeling. HTR2B inhibition by LY272015 reverses these effects, suggesting it as a potential therapeutic strategy for AS.