PD-L1 Regulates Inflammation in LPS-Induced Lung Epithelial Cells and Vascular Endothelial Cells by Interacting with the HIF-1α Signaling Pathway

Sepsis-induced lung injury was the most common cause of death in patients. This study aimed to investigate whether PD-L1 regulates the inflammation in LPS-induced lung epithelial cells and vascular endothelial cells by interacting with the HIF-1α signaling pathway. Sepsis-induced lung injury mice were constructed by cecal ligation and puncture (CLP) procedure, and lipopolysaccharide (LPS)-induced lung epithelial cells and vascular endothelial cells simulate the sepsis-induced lung injury model in vitro. Hematoxylin-eosin (HE) staining detected the morphological changes of the lung tissues, and immunohistochemistry (IHC) detected the PD-L1 expression in lung tissues. Bicinchoninic acid (BCA) assay determined the protein concentration in bronchial alveolar lavage fluid (BALF). The number of PD-1 (+) cells in blood was detected by flow cytometry. The apoptosis in lung tissues and LPS-induced cells was analyzed by TUNEL assay. The inflammatory factor levels and HIF-1α in lung tissues and LPS-induced cells were analyzed by ELISA. The transfection effects of KD-PDL1 or KD-HIF1A in lung epithelial cells and vascular endothelial cells were confirmed by qRT-PCR analysis. The protein expression related to the PD-L1- and HIF-1α-related pathway was determined by Western blot analysis. As a result, LMT-28, as an IL-6 inhibitor, alleviated lung injury and suppressed the apoptosis and inflammation in lung tissues in BALF and the number of PD-1 (+) cells in blood. Sepsis-induced lung injury activated the PD-L1- and HIF-1α-related pathway, while LMT-28 could not completely inhibit the pathway. In addition, downregulation of PD-L1 or downregulation of HIF-1α suppressed the apoptosis and alleviated the inflammation in LPS-induced lung epithelial cells and vascular endothelial cells. Downregulation of PD-L1 had significant effects on lung epithelial cells but had greater effects on vascular endothelial cells. Downregulation of HIF-1α could decrease PD-L1 expression, and downregulation of PD-L1 could also suppress the protein expression of HIF-1α and related pathways. In conclusion, downregulation of PD-L1 alleviated the inflammation in LPS-induced lung epithelial cells and vascular endothelial cells by suppressing the HIF-1α signaling pathway.