SCAP/SREBP2-Mediated Cholesterol Biosynthetic Pathway Suppresses Particulate Matter-Induced Macrophage Activation and Airway Inflammation.

Objective: To investigate the role and mechanism of the SREBP cleavage activating protein/Sterol-regulatory element binding proteins 2(SCAP/SREBP2)-mediated cholesterol synthesis pathway in particulate matter (PM)-induced airway inflammation in macrophages. Methods: Bone marrow-derived macrophages (BMDMs) were cultured in vitro, and after intervention with PM, the macrophage phagocytic activity and expression of related inflammatory factors were assessed. RNA sequencing (RNA-seq) was performed on BMDMs before and after PM exposure to identify significantly altered pathways. The change of these pathways was validated. In vitro, the SCAP/SREBP2-mediated cholesterol synthesis pathway in macrophages was inhibited using LysMCre-Scapf/f mice, inhibitors, and siRNAs, and the effects on PM-induced macrophage activation were detected. The specific mechanism was further explored. In vivo, PM-induced airway inflammation models were established using LysMCre-Scapf/f mice and their littermate controls (Scapf/f ) to examine the role of the SCAP/SREBP2-mediated cholesterol synthesis pathway in PM-induced airway inflammation. Results: Macrophages were able to phagocytose PM, which led to the expression of inflammatory factors. After phagocytosis of PM, the cholesterol levels in macrophages decreased, which in turn triggered the maturation of SREBP2 and activated the cholesterol synthesis pathway. Both LysMCre-Scapf/f mice and siRNA-mediated knockdown of SREBP2 exhibited an enhanced expression of inflammatory factors after PM exposure. Further studies revealed that inhibition of cholesterol biosynthesis also promoted the expression of inflammatory factors induced by PM, while cholesterol supplementation suppressed the PM-induced inflammatory response. Additionally, myeloid-specific knockout of SCAP exacerbated PM-induced airway inflammation and mucus secretion. Conclusion: The SCAP/SREBP2-mediated cholesterol synthesis pathway inhibits macrophage activation and airway inflammation induced by PM through the production of cholesterol.