Tumor necrosis factor alpha (TNF-alpha), a crucial inflammatory cytokine, is involved in the pathogenesis of pulmonary arterial hypertension (PAH). TNF-alpha can induce claudin-1 (CLDN1) expression and CLDN1 has been reported to be associated with the regulation of cellular functions including cell proliferation, migration. Thus, we aimed to explore whether CLDN1 participated in the etiology of PAH. Our study showed that CLDN1 expression was markedly increased in the lungs of rats with monocrotaline(MCT)-induced PAH, especially in the pulmonary arterial smooth muscle sections. We also found that CLDN1 expression in primary human PASMCs was up-regulated by TNF-alpha, and the Nuclear factor-kappa B (NF-kappa B) inhibitor BAY 11-7082 suppressed CLDN1 up-regulation by TNF-alpha. CLDN1 overexpression by adenoviral transduction promoted PASMCs proliferation, while knockdown of CLDN1 by siRNA inhibited TNF-alpha- induced cell proliferation. Mechanistic studies revealed that CLDN1 regulated human PASMC proliferation through the activation of ERK1/2. Together, our findings indicate that up-regulation of CLDN1 promotes PASMC proliferation contributing to pulmonary arterial remodeling in PAH. (C) 2017 Elsevier Masson SAS. All rights reserved.