Sinomenine pretreatment ameliorates septic acute lung injury through α7 nicotinic acetylcholine receptor-dependent inhibition of glycocalyx degradation and endothelial-to-mesenchymal transition.

Sepsis is an organ dysfunction syndrome driven by microbial invasion, characterized by endothelial barrier damage, microcirculatory failure, and hyper-inflammation. Sinomenine (SIN), an alkaloid from Sinomenium acutum, has been demonstrated to alleviate sepsis by suppressing inflammation and modulating metabolism. However, its effects on the endothelial barrier and its underlying mechanisms remain to be fully elucidated. This study explores the effects of SIN on the endothelial glycocalyx and endothelial-mesenchymal transition (EndMT) in septic acute lung injury (ALI) and elucidates the critical role of the cholinergic anti-inflammatory pathway (CAP). The sepsis model was induced via cecal ligation and puncture, and cellular inflammation was modeled in HUVECs and RAW264.7 cells with LPS. IHC, ELISA, and Evans blue assay were employed to assess pulmonary glycocalyx degradation and vascular permeability. Molecular docking and Cellular Thermal Shift Assay (CETSA) were performed to validate the interaction between SIN and α7 nicotinic acetylcholine receptor. WB and qRT-PCR were used to detect CAP, EndMT, and inflammation markers. These assays showed that SIN can directly bind to α7 nicotinic acetylcholine receptor in a manner analogous to acetylcholine (ACh), while exhibiting a more sustained anti-inflammatory effect. SIN pretreatment activates the CAP by upregulating CAP-related molecules to inhibit the inflammatory response, downregulates the glycocalyx-degrading enzymes HPSE and MMP9 to reduce glycocalyx degradation, and inhibits TGF-β/NOX4-mediated EndMT. However, AAV6-mediated specific knockdown of pulmonary Chrna7 significantly weakened these effects. Collectively, our findings demonstrate that SIN pretreatment alleviates ALI and endothelial barrier damage by inhibiting α7 nicotinic acetylcholine receptor-dependent glycocalyx degradation and EndMT.