Pathological protection and molecular regulation of cystatin B in Nile tilapia (Oreochromis niloticus) bacterial disease

Cystatin B (CSTB) is an endogenous cysteine protease inhibitor that plays a critical role in the modulation of numerous biological processes, involving immune responses, apoptosis, and inflammation in mammals. However, its immunological functions in teleost, particularly Nile tilapia (Oreochromis niloticus) remain unclear. In the present study, the CSTB was cloned and characterized from Nile tilapia (On-CSTB) and its role in bacterial infection was revealed. The On-CSTB open reading frame is 300 bp encoding 99 amino acids that contains a conserved cystatin domain. Multiple sequence alignment analysis revealed that On-CSTB share over 75% identity with fish lineages, and 45% identity with mammals. qPCR analysis showed that On-CSTB is widely expressed across various tissues and highly expressed in blood cells and intestines and can be significantly inducted by Streptococcus agalactiae (S. agalactiae) and Aeromonas hydrophila (A. hydrophila). In vivo experiments demonstrated that On-CSTB protein could suppress inflammation while participating in the MyD88/NF-κB signaling pathway and inflammasome activation, affecting apoptosis and pyroptosis processes. Moreover, On-CSTB contributed to enhanced tissue integrity and alleviated pathological damage. These findings collectively highlight On-CSTB as a crucial immunomodulator that contributes to host defense and tissue protection in fish. The present study offers novel perspectives on the immunomodulatory role of CSTB in tilapia, providing a basis for disease resistance strategies in aquaculture.

胱抑素B（Cystatin B, CSTB）是一种内源性半胱氨酸蛋白酶抑制剂，在哺乳动物体内可调控免疫应答、细胞凋亡与炎症反应等诸多生物学过程，发挥关键作用。然而，其在硬骨鱼（尤其是尼罗罗非鱼（Oreochromis niloticus））中的免疫功能仍有待阐明。
本研究从尼罗罗非鱼中克隆并鉴定了CSTB（命名为On-CSTB），并揭示了其在细菌感染中的作用机制。On-CSTB的开放阅读框长度为300 bp，编码99个氨基酸，包含一个保守的半胱氨酸蛋白酶抑制剂结构域。多序列比对分析结果显示，On-CSTB与鱼类类群的序列同源性超过75%，与哺乳动物的同源性达45%。
实时荧光定量PCR（qPCR）分析表明，On-CSTB在尼罗罗非鱼各组织中广泛表达，在血细胞与肠道中表达量较高，且可被无乳链球菌（Streptococcus agalactiae, S. agalactiae）和嗜水气单胞菌（Aeromonas hydrophila, A. hydrophila）显著诱导上调。
体内实验证实，On-CSTB蛋白可抑制炎症反应，同时参与MyD88/NF-κB信号通路与炎症小体活化过程，调控细胞凋亡及焦亡事件。此外，On-CSTB能够增强组织完整性，缓解病理损伤。
上述研究结果共同表明，On-CSTB是一种关键的免疫调节因子，在鱼类宿主防御与组织保护中发挥重要功能。本研究为尼罗罗非鱼CSTB的免疫调节功能提供了全新视角，为水产养殖中的抗病策略研发提供了理论基础。