IL18 induces p38 MAP kinase activation and adhesion capacities in BMPRII knocked down human lung microvascular endothelial cells

Abstract

Mutations in the bone morphogenetic protein receptor 2 ( BMPR2 ) gene are associated with heritable pulmonary arterial hypertension (PAH). In addition, BMPRII signalling is impaired in idiopathic PAH. Since BMPR2 mutation carriers do not all develop PAH, inflammatory mediators could trigger the disease in BMPR2 mutation carriers. Since circulating levels and pulmonary tissue expression of interleukin-18 (IL18) are elevated in PAH, we hypothesized that IL18 could contribute to PAH pathogenesis, in addition to impaired BMPRII signalling. Lentiviral vectors encoding microRNA 30-based knockdown hairpins derived from BMPR2 siRNAs were generated and transduced in human lung microvascular endothelial cells (HLMVEC) to mimic impaired BMPR2 signalling in vitro. Effects of IL-18 on i) adhesion of HLMVEC to human monocytic cell line THP-1, endothelial integrity, adhesion molecule expression and activation of p38 MAP kinase and SMAD proteins were investigated. Knockdown of BMPR2 in HLMVEC resulted in decreased activation of SMAD proteins, increased activation of p38 MAP kinase and endothelium permeability. In BMPR2 knocked-down HLMVEC, IL18 and TNFα increased adhesion to monocytes by 35% and 77%, respectively and activated p38 MAP kinase. Interestingly, TNFα induced mRNA IL18 receptor expression in BMPR2 knocked-down HLMVEC. To conclude, in BMPR2 knocked-down HLMVEC, IL18 induced adhesion and p38 MAP kinase activation, suggesting that IL-18 could trigger PAH pathogenesis, in addition to BMPR2 impaired signalling.