HMGB1 and pulmonary arterial hypertension: The expression of high mobility group box-1 (HMGB1) and toll-like receptor 4 (TLR4) was significantly increased in the lungs of PAH patients, and HMGB1 promoted PAH through activation of TLR4 (Ranchoux et al., 2017; Goldenberg et al., 2019).