Essential role of neutrophils in the monocrotaline-induced pulmonary arterial hypertension in rats

Abstract

The lack of understanding of the inflammatory mechanism in pulmonary arterial hypertension (PAH) hinders the development of treatment protocols. This study aims to uncover the role of neutrophils, the essential players in innate immunity and inflammation, in the progression of PAH from early to late stages. PAH was induced in 108 rats by subcutaneous injection of monocrotaline (MCT). A comprehensive study of the morphological, functional and redox properties of neutrophils and the expression levels of molecular markers was performed. Significant alterations in neutrophil morphology and functions occur in time-dependent manner throughout PAH progression (8 weeks, 8 w) and more likely explain lung tissue remodeling. In the early stage (2 w), neutrophil functions are modified, resulting in decreased ROS generation and mitochondrial membrane potential, increased secretory degranulation. After PAH induction in 4 w, 6 w, and 8 w rat groups, an upregulation of granulopoiesis and priming to NETosis occur. In the late phase of PAH progression (8 w), neutrophil ROS production increases, cell membrane and cytoskeleton modify, myeloperoxidase (MPO) secretion increases causing hypochlorous acid overproduction and plasma thiol content decrease. Time-dependent increase in the release and halogenating activity of MPO results from significant priming of neutrophils for NETosis, indicating its decisive role in PAH progression. This study has established a substantial link between neutrophil-mediated halogenating stress related to neutrophil priming for NETosis and PAH progression, as well as the molecular mechanisms underlying PAH pathogenesis in vivo. Our results suggest a great potential of neutrophil-associated components as a target for the treatment of PAH.

Keywords: Hypochlorous acid; Monocrotaline; Myeloperoxidase; NETs; Neutrophil; Neutrophil extracellular traps; Pulmonary arterial hypertension.