The Role of Macrophages and the NLRP3 Inflammasome In Right Ventricular Failure in Pulmonary Arterial Hypertension

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Al-Qazazi, Ruaa
Pulmonary Arterial Hypertension , Right Ventricular Failure , Macrophages , NLRP3 inflammasome
Background: Pulmonary arterial hypertension (PAH) is an obliterative pulmonary vasculopathy that results in right ventricular failure (RVF). We speculate that RVF results from inflammation due to the influx of inflammatory cells into the RV. Macrophages may contribute to PAH-RVF by activating pyrin domain-containing protein 3 (NLRP3) inflammasome, triggering cytokine release. Currently, there are no approved medications targeting PAH-RV inflammation. This work aims to assess the role of macrophages and the NLRP3 inflammasome in RVF and find effective therapeutic strategies in preclinical rat models of PAH. Methods & Results: We studied PAH-RV inflammation in a monocrotaline (MCT) rat model, characterized by RVF and inflammation, and compared it to the pulmonary artery banded (PAB) rat model that has similar RV pressure overload and hypertrophy (RVH), but which lacks RVF. Macrophages and NLRP3 were examined in control, PAB and MCT-RV using super-resolution confocal microscopy. MCT-RV macrophages were significantly increased compared to their control; whereas, PAB-RV macrophages were not increased compared to sham. Flow cytometry was used to identify macrophages, endothelial cells and fibroblasts, and measure RV cell-specific NLRP3 expression. MCT-RV and lung macrophages were significantly increased in number compared to control, with a shift favouring M2 phenotype in the lungs. Macrophages were the main source of NLRP3 inflammasome. RV-NLRP3, caspase 1 and IL-1b content were significantly higher in MCT-RV than control. Fibrosis was significantly increased in MCT and PAB-RVs, but more severe in MCT-RV, as assessed by picrosirius stain. Cultured MCT-monocytes (±MCC950, an NLRP3 inhibitor) revealed a significant increase of NLRP3:ASC interaction, reflecting inflammasome activation, at 10-minutes post-nigericin (an NLRP3 activator). Treating MCT-rats with intraperitoneal gp130 antagonist (an inhibitor of the gp130 subunit of the interleukin-6 receptor) significantly reduced the RV macrophage count and NLRP3 inflammasome content and improved RV function without altering pulmonary vascular remodelling. Conclusion: RV inflammation mediated by the NLRP3 inflammasome in macrophages contributes to RVF. There is greater macrophage infiltration and NLRP3 inflammasome expression and activation in MCT-RV versus PAB-RV. Blocking gp130 signalling in vivo, a mechanism critical to interleukin-6 signalling and macrophage recruitment prevents RV-macrophage accumulation and improves RV function, suggesting a new therapeutic paradigm for PAH.
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