A non-bactericidal antimicrobial peptide provides protective effect against bacterial sepsis via regulation of antimicrobial immunity and vascular endothelial functions.

摘要

The anti-infective properties of bactericidal antimicrobial peptides (AMPs) have been extensively studied, yet the functions and mechanisms of non-bactericidal AMPs in sepsis remain poorly understood. In this study, a novel β-sheet cathelicidin peptide, named Og-CATH, was identified from the skin of Odorrana grahami. Although Og-CATH showed no detectable direct antimicrobial activity in vitro, it provided both prophylactic and therapeutic protection in mouse models of sepsis induced by Staphylococcus aureus, Escherichia coli, or cecal ligation and puncture. This protection depended on neutrophils and monocytes/macrophages, but not T or B lymphocytes. Og-CATH did not directly chemoattract phagocytes. Instead, it stimulated P2X7 receptor-dependent chemokine release from macrophages, thereby promoting macrophage and neutrophil trafficking to sites of infection. Og-CATH also enhanced oxygen-independent bacterial clearance by increasing phagocytosis and neutrophil degranulation. In parallel, Og-CATH suppressed tissue factor production, a major trigger of the extrinsic coagulation cascade, and increased activated protein C expression in endothelial cells and mice, thereby reducing pulmonary fibrin deposition and thrombosis. Mechanistically, Og-CATH targeted myeloid differentiation protein 2 (MD2) and inhibited lipopolysaccharide (LPS)-induced recruitment of MyD88 to TLR4 in endothelial cells, thus preserving endothelial barrier integrity during sepsis. These findings identify Og-CATH as a non-bactericidal AMP that protects against sepsis by coordinating phagocyte recruitment, antibacterial effector activity, coagulation control, and endothelial stabilization. Og-CATH therefore represents a promising immunomodulatory candidate for further therapeutic development against sepsis. 抗菌肽的抗感染特性已被广泛研究，但非杀菌性抗菌肽在脓毒症中的作用及机制尚未完全明确。本研究从无指盘臭蛙中鉴定出一种新型cathelicidin抗菌肽，其二级结构为β-折叠，命名为Og-CATH。体外实验表明Og-CATH无直接抗菌活性，但有趣的是，在金黄色葡萄球菌、大肠杆菌感染及盲肠结扎穿孔（CLP）诱导的脓毒症小鼠模型中，该肽均展现出显著的预防与治疗效果。进一步的研究发现，Og-CATH的保护作用依赖于中性粒细胞和单核/巨噬细胞，而非T/B淋巴细胞。尽管Og-CATH无法直接趋化吞噬细胞，但可通过P2X7受体促进巨噬细胞分泌趋化因子，进而间接介导巨噬细胞与中性粒细胞向感染部位迁移。此外，Og-CATH还能通过增强中性粒细胞的吞噬作用与脱颗粒功能，提升其非氧依赖型杀菌活性。更重要的是，本研究证实Og-CATH可抑制内皮细胞及小鼠体内组织因子（外源性凝血级联反应的关键启动子）的产生，同时上调生理性抗凝物质活化蛋白C（APC）的表达，减少小鼠肺部纤维蛋白沉积及体内血栓形成。机制上，Og-CATH靶向髓样分化蛋白2（MD2），抑制脂多糖诱导的内皮细胞中MyD88向TLR4受体的募集，进而缓解内皮屏障功能障碍。综上，本研究表明Og-CATH主要通过调控吞噬细胞与内皮细胞功能发挥脓毒症保护作用。这些发现不仅丰富了我们对非杀菌性抗菌肽抗感染机制的认识，也证明了Og-CATH是脓毒症治疗药物开发的优良候选分子。.