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Role of NLRP3 and lysosomal cathepsins in NLRC4 inflammasome activation

Grant number: 17/21814-7
Support type:Scholarships abroad - Research Internship - Doctorate (Direct)
Effective date (Start): February 19, 2018
Effective date (End): February 18, 2019
Field of knowledge:Biological Sciences - Immunology
Principal Investigator:Karina Ramalho Bortoluci
Grantee:Laura Migliari Branco
Supervisor abroad: Bernardo Simoes Franklin
Home Institution: Centro de Terapia Celular e Molecular. Universidade Federal de São Paulo (UNIFESP). Campus São Paulo. São Paulo , SP, Brazil
Local de pesquisa : Universität Bonn, Germany  
Associated to the scholarship:15/09029-7 - Interaction between NLRP3 and NLRC4 inflamassomes in macrophages activation, BP.DD

Abstract

Inflammasomes are molecular complexes that detect sterile or infectious stimuli and trigger caspase-1 activation, leading to the release of IL-1² and IL-18 and cell death by pyroptosis. NLRP3 is assembled in response to pathogenic microorganisms and sterile signals, while NAIP/NLRC4 is classically activated by bacterial protein that reaches the cytosol, such as flagellin. In different contexts, NLRP3 and NLRC4 cooperate and interact, generating a more robust response. In macrophages transfected with flagellin, or infected with Salmonella thyphimurium, NLRP3 contributes to increase IL-1² production. Also, our group demonstrated that cytosolic flagellin activates a lysosomal pathway leading to cathepsin B-dependent IL-1² release, indicating a crosstalk between inflammasomes and lysosomes. However, the molecular mechanism mediated by cathepsins to regulate NLRP3 and, especially NLRC4 inflammasomes activation remains to be elucidated. During my PhD, we obtained data indicating that cathepsins and NLRP3 recruitment are non-redundant pathways required to optimize flagellin-induced NAIP/NLRC4 activation. Moreover, we observed that cathepsins seem to act during the effector phase of inflammasome formation rather than at the priming phase, since the pharmacological inhibition of these proteases had no effect in the induction of pro-IL-1² and pro-caspase-1, but inhibited their cleavage into active forms. Since ASC oligomerization into specks is crucial for IL-1² cleavage and release, we hypothesized that cathepsins could interfere in this step of NLRC4/NLRP3 assembly and activation. In order to address this issue, we have established a collaboration with Dr. Bernardo Franklin's group. He has pioneered the research on extracellular ASC functions, having a great expertise in inflammasomes regulation and function in infectious and sterile contexts. His laboratory has established different techniques to visualize and analyze ASC aggregation, offering all the required tools to elucidate the molecular mechanisms mediated by cathepsins during inflammasome activation. Therefore, we believe that the results to be reached during the BEPE internship will allow us to unravel the signals involved in the regulation of inflammasome formation, a central question of the field and also to open up new avenues for the study of these platforms under physiological and pathological conditions.