Chen Yan, Cai Shasha, Qiao Xue, Wu Mali, Guo Zhilai, Wang Renping, Kuang Yi-Qun, Yu Haining, Wang Yipeng
Department of Pharmaceutical Sciences, College of Pharmaceutical Sciences, Soochow University, Suzhou, Jiangsu 215123, China.
Department of Bioscience and Biotechnology, Dalian University of Technology, Dalian, Liaoning 116023, China.
Biochem J. 2017 Aug 10;474(16):2861-2885. doi: 10.1042/BCJ20170334.
Crocodilians are regarded as possessing a powerful immune system. However, the composition and action of the crocodilian immune system have remained unclear until now. Cathelicidins, the principal family of host defense peptides, play pivotal roles in vertebrate immune defense against microbial invasions. However, cathelicidins from crocodilians have not been extensively studied to date. In the present study, six novel cathelicidins (As-CATH1-6) were identified and characterized from the endangered Chinese alligator (). As-CATH1-6 exhibit no sequence similarity with any of the known cathelicidins. Structure analysis indicated that As-CATH1-3 adopt a random coil secondary conformation, whereas As-CATH4-6 were predicted to mainly adopt an amphipathic α-helix conformation. Among them, As-CATH4-6 exhibited potent, broad-spectrum and rapid antimicrobial activity by inducing the disruption of cell membrane integrity. They also exhibited strong ability to prevent the formation of bacterial biofilms and eradicate preformed biofilms. Furthermore, As-CATH4-6 exhibited potent anti-inflammatory activity by inhibiting the lipopolysaccharide (LPS)-induced production of nitric oxide (NO) and pro-inflammatory cytokines in mouse peritoneal macrophages. They directly neutralized LPS toxicity and therefore inhibited the binding of LPS to the TLR4 receptor and the subsequent activation of inflammatory response pathways. In a peritonitis mice model, As-CATH2-6 provided effective protection against bacterial infection through enhanced immune cell recruitment. In the host Chinese alligator, As-CATH1-6 are mainly expressed in immune organs and epithelial tissues. Bacterial infection significantly enhances their expression, which implies an important role in host anti-infective response. Taken together, the diversity and multiple functions of As-CATH1-6 partially reveal the powerful immune system of the Chinese alligator.
鳄鱼被认为拥有强大的免疫系统。然而，迄今为止，鳄鱼免疫系统的组成和作用仍不清楚。宿主防御肽的主要家族——cathelicidins，在脊椎动物抵御微生物入侵的免疫防御中发挥着关键作用。然而，迄今为止，来自鳄鱼的cathelicidins尚未得到广泛研究。在本研究中，从濒危的中国短吻鳄中鉴定并表征了六种新型cathelicidins（As-CATH1-6）。As-CATH1-6与任何已知的cathelicidins均无序列相似性。结构分析表明，As-CATH1-3呈现无规卷曲二级构象，而As-CATH4-6预计主要呈现两亲性α-螺旋构象。其中，As-CATH4-6通过诱导细胞膜完整性破坏表现出强大、广谱和快速的抗菌活性。它们还表现出强大的能力来防止细菌生物膜的形成并根除预先形成的生物膜。此外，As-CATH4-6通过抑制小鼠腹腔巨噬细胞中脂多糖（LPS）诱导的一氧化氮（NO）和促炎细胞因子的产生表现出强大的抗炎活性。它们直接中和LPS毒性，因此抑制LPS与TLR4受体的结合以及随后炎症反应途径的激活。在腹膜炎小鼠模型中，As-CATH2-6通过增强免疫细胞募集为细菌感染提供了有效的保护。在宿主中国短吻鳄中，As-CATH1-6主要在免疫器官和上皮组织中表达。细菌感染显著增强它们的表达，这暗示了其在宿主抗感染反应中的重要作用。综上所述，As-CATH1-6的多样性和多种功能部分揭示了中国短吻鳄强大的免疫系统。
