C-ter100 peptide derived from Vibrio vEP-45 protease acts as a pathogen-associated molecular pattern to induce inflammation and innate immunity.

The bacterium Vibrio vulnificus causes fatal septicemia in humans. Previously, we reported that an extracellular metalloprotease, vEP-45, secreted by V. vulnificus, undergoes self-proteolysis to generate a 34 kDa protease (vEP-34) by losing its C-terminal domain to produce the C-ter100 peptide. Moreover, we revealed that vEP-45 and vEP-34 proteases induce blood coagulation and activate the kallikrein/kinin system. However, the role of the C-ter100 peptide fragment released from vEP-45 in inducing inflammation is still unclear. Here, we elucidate, for the first time, the effects of C-ter100 on inducing inflammation and activating host innate immunity. Our results showed that C-ter100 could activate NF-κB by binding to the receptor TLR4, thereby promoting the secretion of inflammatory cytokines and molecules, such as TNF-α and nitric oxide (NO). Furthermore, C-ter100 could prime and activate the NLRP3 inflammasome (NLRP3, ASC, and caspase 1), causing IL-1β secretion. In mice, C-ter100 induced the recruitment of immune cells, such as neutrophils and monocytes, along with histamine release into the plasma. Furthermore, the inflammatory response induced by C-ter100 could be effectively neutralized by an anti-C-ter100 monoclonal antibody (C-ter100Mab). These results demonstrate that C-ter100 can be a pathogen-associated molecular pattern (PAMP) that activates an innate immune response during Vibrio infection and could be a target for the development of antibiotics. Author summary: This study focused on the specific molecules associated with the pathogenic Vibrio vulnificus that play a role in the initiation of the innate immune responses during infection. The C-domain of vEP-45 and the C-ter100 derived from vEP-45 act as the first signals (as PAMP) to prime the formation of NLRP3 inflammasome, during which they bind to TLR4, thereby activating it (as PRR), leading to the activation of NF-κB signaling pathway to produce a variety of inflammatory cytokines and regulators such as TNF-α and NO, accompanied with the expression of NLRP3 (Fig 1). The formation and activation of NLRP3 inflammasome are triggered by ATP, serving as the second signal and resulting in production of active caspase-1 (Casp 1), which converts pro-IL-1β into IL-1β. Anti-C-ter100 monoclonal antibody (C-ter100Mab) can relieve the inflammatory response by neutralizing both vEP-45 and C-ter100 (Fig 1). Conclusively, C-ter100 functioned as a novel pathogen-associated molecular pattern, potentiating the innate immune system, and thus constituting a new target for the development of antibiotics. We believe that our study makes a significant contribution to the literature because it confirmed the binding between TLR4 and C-ter100 that initiates the innate immune response against Vibrio infection and determined that blocking this binding with C-ter100Mab effectively inhibited vibriosis. These results are important because they further elucidated Vibrio pathogenesis and helped in the designing new treatments and therapies that could control vibriosis. [ABSTRACT FROM AUTHOR]