Candida Infection Biology – fungal armoury, battlefields ... - FINSysB

Poster number: 34
Candida albicans Secreted Aspartic Proteases Cause
Inflammatory Response Irrespective of Their Proteolytic
Activity
Neelam Pandey 1 , Donatella Pietrella 1 , Lydia Schild 2 , Francesco Bistoni 1 ,
Bernhard Hube 2 and Anna Vecchiarelli 1
1 Department of Experimental Medicine and Biochemical Science, University of Perugia,
Perugia, Italy; 2 Department of Microbial Pathogenicity Mechanisms, Leibniz Institute for
Natural Product Research and Infection Biology, Hans Knoell Institute, Jena, Germany2;
Candida albicans normally inhabits humans as a commensal, but causes fatal infections
when the immune system of patients is suppressed. It has a strong armory of virulence
attributes which facilitates bypassing the immune system and causes mucosal, cutaneous
and systemic infections. These attributes are the ability to colonize, invade the host tissue
and secrete aspartic proteases. We here report that recombinant secreted aspartic
proteases (rSaps) including rSap1, rSap2, rSap3 and rSap6 induce inflammatory cytokine
production by human monocytes to different degrees. rSap1, rSap2 and rSap6 induced
the secretion of IL-1beta, TNF-alpha and IL-6 significantly, while rSap3 stimulated the
secretion of IL-1beta and TNF-alpha. All these rSaps induced Ca 2+ influx in monocytes.
Pepstatin A, a potential inhibitor of aspartic proteases, has no effect on the cytokine
secretion induced by these rSaps. This suggests that the inflammatory response due to
rSaps is not because of their proteolytic activity, a hypothesis further supported by the
observation that the ability of rSaps to induce inflammatory cytokine secretion was
independent of protease-activated receptor (PAR) activation, and of the optimal pH for
individual rSap activity. Moreover, rSaps stimulated Akt activation and thus induced IkBalpha
phosphorylation which mediated translocation of NFkB into the nucleus in human
monocytes. These findings give evidence that rSap1, rSap2 and rSap3 cause an
inflammatory response irrespective of their proteolytic activity and mediate the inflammatory
response via activation of Akt/NF-kB. The inflammatory response terminates with
inflammasome activation. This occurs through a process requiring Sap internalization via a
clathrin dependent mechanism, and caspase-1 activation, and it is mediated by K + efflux
and ROS production. By demonstrating that the recognized virulence factors of C. albicans
such as Sap2 and Sap6 are potent inducers of inflammasome activation, our results
represent a step forward in the comprehension of the close relationship between fungus
virulence and host response mechanisms.
We are extending our study by using an in vivo experimental model of murine candidiasis
to analyze the role of Sap2 and Sap6 in the inflammatory response in the vaginal candidiasis,
and to investigate whether specific mAbs are indeed able to affect this process.
This study was funded by the European Commission (FINSysB Marie Curie Initial Training Network grant PITN-
GA-2008-214004).
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