Biological relevance of Granzymes A and K during E. coli sepsis

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[Aims]: Recent in vitro findings suggest that the serine protease Granzyme K (GzmK) may act as a proinflammatory mediator. However, its role in sepsis is unknown. Here we aim to understand the role of GzmK in a mouse model of bacterial sepsis and compare it to the biological relevance of Granzyme A (GzmA).
[Methods]: Sepsis was induced in WT, GzmA-/- and GzmK-/- mice by an intraperitoneal injection of 2x108 CFU from E. coli. Mouse survival was monitored during 5 days. Levels of IL-1α, IL-1β, TNFα and IL-6 in plasma were measured and bacterial load in blood, liver and spleen was analyzed. Finally, profile of cellular expression of GzmA and GzmK was analyzed by FACS.
[Results]: GzmA and GzmK are not involved in the control of bacterial infection. However, GzmA and GzmK deficient mice showed a lower sepsis score in comparison with WT mice, although only GzmA deficient mice exhibited increased survival. GzmA deficient mice also showed reduced expression of some proinflammatory cytokines like IL1-α, IL-β and IL-6. A similar result was found when extracellular GzmA was therapeutically inhibited in WT mice using serpinb6b, which improved survival and reduced IL-6 expression. Mechanistically, active extracellular GzmA induces the production of IL-6 in macrophages by a mechanism dependent on TLR4 and MyD88.
[Conclusions]: These results suggest that although both proteases contribute to the clinical signs of E. coli-induced sepsis, inhibition of GzmA is sufficient to reduce inflammation and improve survival irrespectively of the presence of other inflammatory granzymes, like GzmK.
This work was supported by grant SAF2017-83120-C2-1-R and PID2020-113963RBI00 from the Ministry of Science, Innovation and Universities and FEDER (Group B29_17R, Aragon Government). IU-M , MG-T and CP were supported by a PhD fellowships from Aragon Government, Ministry of Science, Innovation and Universities (FPI) and Asociacion Española contra el Cancer (AECC). MA and LS were supported by a post-doctoral fellowship “Juan de la Cierva-formación” (MA, LS) and "Juan de la Cierva-incorporacion" (MA) from the Ministry of Science, Innovation and Universities. JP was supported by ARAID Foundation.