Pulmonary hypertension (PH) is a severe disease leading to right heart failure and death. We have previously shown that blockade of the nerve growth factor NGF may be of therapeutic interest in PH, since NGF contributes to various pathophysiological aspects of this disease [1Freund-Michel V., Cardoso Dos Santos M., Guignabert C., et al. Role of nerve growth factor in development and persistence of experimental pulmonary hypertension Am J Respir Crit Care Med 2015 ;  192 : 342-355 [cross-ref]

Cliquez ici pour aller à la section Références]. Interleukin-1β (IL-1β) is a pro-inflammatory cytokine whose levels are increased in PH [2Humbert M., Monti G., Brenot F., et al. Increased interleukin-1 and interleukin-6 serum concentrations in severe primary pulmonary hypertension Am J Respir Crit Care Med 1995 ;  151 : 1628-1631 [cross-ref]

Cliquez ici pour aller à la section Références]. Our previous experiments have shown that NGF can enhance IL-1β secretion from both pulmonary arterial structural cells and inflammatory cells, i.e. monocytes. In the present study, we have investigated whether IL-1β may play a role in NGF-dependent pulmonary arterial (PA) alterations in PH.

In vitro, control human PA smooth muscle (hPASMC) or endothelial cells (hPAEC) were treated with IL-1β (10 or 100ng/mL, 24h). Cell proliferation (counting, Ki67 staining), migration (transwell assay), apoptosis (caspase 3,7 activities) and interleukin-6 (IL-6) secretion (ELISA) were then assessed. In hPAEC, expression of endothelial nitric oxide synthase (eNOS) and intercellular adhesion molecule-1 (ICAM-1) were also assessed by Western Blotting. Signalling pathways activated by IL-1β to induce IL-6 secretion were investigated by using PDTC (pyrrolidine dithiocarbamate, an NF-κB inhibitor, 50μM) or SP60025 (an inhibitor of Activator protein 1 [AP-1], 10μM). In vivo, PH was induced in rats by monocrotaline (MCT, 60mg/kg, intraperitoneal injection), and IL-1β plasmatic and pulmonary levels were then determined. Expression of inflammasome components (NLRP3/pro- and active caspase-1/pro-IL-1β) and of CD11b (marker of monocytes/macrophages infiltration) was also assessed in lung and PA homogenates by Western Blotting.

In vitro, IL-1β increased hPASMC and hPAEC proliferation and migration, as well as IL-6 secretion through activation of both NF-κB and AP-1. IL-1β also increased hPASMC resistance to apoptosis, and increased ICAM-1 expression whereas decreased eNOS expression in hPAEC. In vivo, IL-1β plasmatic and pulmonary levels as well as expression of inflammasome components and of CD11b were all increased in PH rats compared to controls.

In conclusion, our results suggest that IL-1β-induced stimulation of both hPASMC and hPAEC may play a role in PA remodelling, inflammation and altered endothelial function. Since NGF participates in IL-1β increased levels in PH, IL-1β may therefore contribute to NGF-dependent PA alterations in this disease.