Elk1 enhances inflammatory cell infiltration and exacerbates acute lung injury/acute respiratory distress syndrome by suppressing Fcgr2b transcription

Abstract

LPS-induced ARDS rats and PMVECs have low Fcgr2b level and high Elk1 level; Fcgr2b overexpression mitigates LPS-induced ALI/ARDS in rats and PMVECs; Elk1 knockdown mitigates LPS-induced ALI/ARDS in rats and PMVECs; Elk1 represses Fcgr2b transcription by recruiting H3K9me3; Elk1/Fcgr2b axis aggravates LPS-induced ALI/ARDS in rats and PMVECs. Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are associated with significant mortality rates. The role of Fcgr2b in the pathogenesis of ALI/ARDS is not fully elucidated. This study aimed to investigate the functions of Fcgr2b in ALI/ARDS and explore its underlying mechanisms. Methods: In this study, rat models of ARDS and pulmonary microvascular endothelial cell (PMVEC) injury models were established through the administration of lipopolysaccharide (LPS). The expression levels of Fcgr2b and Elk1 were quantified in both LPS-induced ARDS rats and PMVECs. Subsequent gain- and loss-of-function experiments were conducted, followed by comprehensive assessments of lung tissue for pathomorphological changes, edema, glycogen storage, fibrosis, and infiltration of inflammatory cells. Additionally, bronchoalveolar lavage fluid was analyzed for T-helper 17 (Th17) cell infiltration, inflammatory response, and microvascular permeability to evaluate lung injury severity in ARDS models. Furthermore, the activity, cytotoxicity, apoptosis, and angiogenic potential of PMVECs were assessed to gauge cell injury. The interaction between Elk1 and Fcgr2b was also examined to confirm their regulatory relationship. In the context of LPS-induced ARDS and PMVEC injury, Fcgr2b expression was markedly reduced, whereas Elk1 expression was elevated. Overexpression of Fcgr2b led to a decrease in Th17 cell infiltration and mitigated lung tissue damage in ARDS models, in addition to reducing LPS-induced injury in PMVECs. Elk1 was found to suppress Fcgr2b transcription through the recruitment of histone 3 lysine 9 trimethylation (H3K9me3). Knockdown of Elk1 diminished Th17 cell infiltration and lung tissue damage in ARDS models, and alleviated LPS-induced injury in PMVECs, effects that were reversed upon Fcgr2b upregulation. Elk1 negatively regulates Fcgr2b transcription, thereby augmenting the inflammatory response and exacerbating lung injury in LPS-induced ALI/ARDS.