LPAR1 Promotes Activation of Pathways Alveolar Hypercoagulation and Fibrinolytic Inhibition in ARDS via NF-κB Signaling Pathway

Alveolar hypercoagulation and fibrinolytic inhibition are critical mechanisms contributing to refractory hypoxemia in acute respiratory distress syndrome (ARDS). The nuclear factor kappa-B (NF-κB) pathway is known to play a role in these processes. Lysophosphatidic acid receptor 1 (LPAR1) has been identified as being associated with the NF-κB pathway. We hypothesize that LPAR1 may regulate alveolar hypercoagulation and fibrinolytic inhibition in ARDS, potentially through modulation of the NF-κB pathway. The rat model of acute respiratory distress syndrome (ARDS) was induced via inhalation of lipopolysaccharide (LPS). In some rats, pulmonary tissue was subjected to either overexpression or knockdown of the LPAR1 gene using lentiviral-mediated transfection prior to LPS exposure. The impact of LPAR1 modulation on alveolar hypercoagulation, fibrinolytic inhibition, acute lung injury, and the NF-κB signaling pathway in the ARDS rat model was investigated. In vitro, the expression level of LPAR1 in LPS-stimulated type II alveolar epithelial cells (AECII) was monitored over time. Additionally, we assessed the influence of LPAR1 on the expression of tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1), as well as its role in the NF-κB signaling pathway within these cells. The potential influence of LPAR1 on the hypercoagulation and fibrinolytic inhibition in LPS-induced ARDS via the NF-κB signaling pathway was also examined. An increase in LPAR1 expression was observed in the lung tissue of rats with ARDS. Our findings indicated that overexpression of LPAR1 significantly intensified lung injury and the wet-to-dry (W/D) ratio, both of which are induced by LPS, while the knockdown of LPAR1 substantially reduced these effects. Inhalation of LPS resulted in elevated expression levels of TF, plasminogen activator inhibitor-1 (PAI-1), as well as increased activity of TF, PAI-1, and Thrombin in bronchoalveolar lavage fluid (BALF). These effects were exacerbated by LPAR1 overexpression but were notably diminished by LPAR1 knockdown. Overexpression of LPAR1 further activated the LPS-induced NF-κB signaling pathway, whereas reduced LPAR1 expression significantly dampened NF-κB activation. In cellular studies, LPAR1 levels began to rise 6 h post-LPS stimulation, peaked at 24 h, and subsequently declined. LPS stimulation also increased TF and PAI-1 expression and activated the NF-κB signaling pathway. The enhancements of TF and PAI-1 expressions observed in LPAR1-overexpressing conditions were markedly counteracted by LPAR1 knockdown. Rescue experiments validated that the inhibition of the NF-κB signaling pathway significantly reversed the upregulation of TF and PAI-1 caused by LPAR1 overexpression in LPS-stimulated RLE-6TN cells. The findings of our study provide evidence that LPAR1 exacerbates LPS-induced alveolar hypercoagulation and the inhibition of fibrinolysis in LPS-induced ARDS through the NF-κB signaling pathway. The LPAR1/NF-κB signaling axis may represent a promising target for further investigation into the molecular mechanisms underlying ARDS.

NF‐κB signaling pathway; acute respiratory distress syndrome; alveolar hypercoagulation; fibrinolytic inhibition; lysophosphatidic acid receptor 1.