Role of lysosomal cathepsins and NLRP3 activation in the immunostimulatory proprieties of flagellin

• Grant number: 13/22770-2
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: February 18, 2014
• End date: July 17, 2014
• Field of knowledge: Biological Sciences - Immunology - Cellular Immunology
• Principal Investigator: Karina Ramalho Bortoluci
• Grantee: Silvia Lucena Lage
• Supervisor: Franklin Alan Sher
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: National Institutes of Health, Bethesda (NIH), United States
• Associated to the scholarship: 11/08502-0 - Cell death processes involvement in the flagellin adjuvant properties, BP.DR

Abstract

Flagellin is an agonist of TLR and NLR receptors that has been extensively investigated as an adjuvant. Innate immune recognition of flagellin is shared by transmembranic TLR5 and cytosolic Naip5/NLRC4 inflammasome complex. We have demonstrated a process of necrotic cell death induced by cytosolic flagellin that does not require NLRC4, ASC or caspase-1/11 but it is regulated by lysosomal cathepsins, with cathepsins B and D playing a major role. Moreover, cathepsin B seems to regulate the inflammasome-induced IL-1b and pyroptosis in response to cytosolic flagellin, suggesting a cooperation between inflammasome and the lysosomal pathways in response to flagellin. Thus, our data demonstrate that flagellin, besides being an inflammasome-activating factor that can be directly sensed by Naip5 molecules, is also a lysosome-disrupting agent by a mechanism yet not elucidated. Interestingly, lysosome damage accompanied by loss of lysosomal cathepsins is an event so far associated with the NLRP3 inflammasome activation in response to several particulate stimuli. Thus, these data open new perspectives regarding to the involvement of the lysosomal pathway and NLRP3 inflammasome activation in the immunomodulatory properties of flagellin. Therefore, we have established a collaboration with the group of Dr Alan Sher, to gain benefits from the expertise of this group and the facilities of the NIH institute to deeply investigate the molecular link between the lysosomal pathway (i.e activated cathepsins into cell cytosol) and NLRC4 and NLRP3 inflammasome activation induced by flagellin and the relevance of these process to its adjuvant properties. (AU)