5-Hydroxytryptamine Limits Pulmonary Arterial Hypertension Progression by Regulating Th17/Treg Balance

Pulmonary arterial hypertension (PAH) is a progressive disorder that lacks a validated and effective therapy. Thus, further investigation of the pathogenesis of PAH will help explore novel treatments. The increase in T helper 17 (Th17) cell-mediated pro-inflammatory response and reduction of regulatory T (Treg) cell-mediated anti-inflammatory effect exacerbates PAH progression. Increasing evidence indicates that 5-hydroxytryptamine (5-HT) is closely related to Th17 and Treg polarization. Here, a decrease of 5-HT was found in hypoxia-induced CD4 + T cells. Hypoxia also resulted in a reduction in Treg cells and an increase in Th17 cells, but the addition of 5-HT rescued Th17/Treg balance, confirming that hypoxia destroyed Th17/Treg balance by inducing a 5-HT decrease. Furthermore, we found that 5-HT-restored Th17/Treg balance mitigated primary pulmonary artery smooth muscle cell (PASMC) proliferation, migration, and contraction, which are important factors in vascular remodeling in PAH. In summary, our findings demonstrate that hypoxia-induced 5-HT decline interferes with the balance of Th17/Treg, which affects the biofunction of PASMCs, thus accelerating PAH development. 5-HT-mediated Th17/Treg balance is expected to act as a novel immunotherapy for PAH treatment.