Phenotype and function of macrophage polarization in monocrotaline-induced pulmonary arterial hypertension rat model

Pulmonary arterial hypertension (PAH) isa fatal disease characterized by vascular remodeling and chronic inflammation. Macrophages are the key orchestrators of inflammatory and repair responses, and have been demonstrated to be vital in the pathogenesis of PAH. However, specific phenotype of macrophage polarization (M1 & M2 macrophage) in the development of PAH and the underlying mechanisms how they work are still largely unclear. A rat model of monocrotaline (MCT) induced PAH was used. Hemodynamic analysis and histopathological experiments were conducted at day 3, 7, 14, 21 and 28, respectively. In PAH rat lung tissue, confocal microscopic images showed that CD68+NOS2+ M1-like macrophages were remarkably infiltrated on early stage, but dramatically decreased in mid-late stage. Meanwhile, CD68+CD206+ M2-like macrophages in lung tissue accumulated gradually since day 7 to day 28, and the relative ratio of M2/M1 macrophage increased over time. Results detected by western blot and immunohistochemistry were consistent. Further vitro functional studies revealed the possible mechanism involved in this pathophysiological process. By using Transwell co-culture system, it was found that M1 macrophages inducedendothelial cellapoptosis, while M2 macrophages significantly promoted proliferation of both endothelial cell and smooth muscle cell.These data preliminarily demonstrated a temporal dynamic change of macrophage M1/M2 polarization status in the development of experimental PAH. M1 macrophages participated in the initial stage of inflammation by accelerating apoptosis of endothelial cell, while M2 macrophages predominated in the reparative stage of inflammation and the followed stage of aberrant tissue remodeling.