Contradictory roles ofPorphyromonas gingivalisgingipains in caspase-1 activation

Abstract

Porphyromonas gingivalis utilizes its major proteases, Arg gingipains (RgpA and RgpB) and Lys gingipain (Kgp), for dysregulation of host immune systems. The aim of this study was to investigate the roles of gingipains in caspase-1 activation and its sequelae in P. gingivalis-infected macrophages. Infection with P. gingivalis at low multiplicity of infections (MOIs), but not at high MOIs, resulted in low levels of interleukin-1β and lactate dehydrogenase without detectable active caspase-1 in the culture supernatants. The proteins released from caspase-1-activated cells were rapidly degraded by gingipains. However, P. gingivalis with gingipains induced higher intracellular caspase-1 activity in the infected cells than the gingipain-null mutant, which was associated with ATP release from the infected cells. In addition, growing the gingipain-null mutant with gingipains enhanced caspase-1 activation by the mutant. In contrast, inhibition of the protease activity of Kgp or Rgps increased the caspase-1-activating potential of wild-type P. gingivalis, indicating an inhibitory effect of the collaborative action of Kgp and Rgps. These results illuminate the contradictory roles of gingipains in the manipulation of host defence systems by P. gingivalis, as they act by both stimulating and inhibiting innate immune responses.

Porphyromonas gingivalis triggers NLRP3‐mediated inflammasome activation in macrophages in a bacterial gingipains‐independent manner

“…The detection levels of the cytoplasmic proIL‐1β, procaspase‐1, or β‐actin, were not affected by bacterial infection. These data are consistent with those of a previous study . In the early stage (3 h post‐infection) infection with WT bacteria, mature IL‐1β was detected on immunoblot as well as on ELISA (Fig.…”

“…Basically, in exploring inflammasome activation, analysis of the cleavage of caspase‐1 and IL‐1β by immunoblot analysis and ELISA assay, respectively, is to detect the final readouts after inflammasome activation. In this context, previous papers have reported gingipains‐mediated proteolysis of extracellular proteins, however, it has not been clearly elucidated whether gingipains degrade the final products of inflammasome activation, or actually inhibit inflammasome activation itself. We examined other parameters for inflammasome activation, such as speck formation of the adaptor protein ASC, by immunostaining, and oligomerization of ASC by immunoblotting.…”

“…On the other hand, reports have also suggested an inhibitory effect of WT P. gingivalis on inflammasome activation by other stimulators . A recent study showed that gingipains apparently have reciprocal activities, namely, to enhance caspase‐1 activation, on the other hand, to cause proteolytic depletion of caspase‐1 and IL‐1β that are released into the supernatants . The discrepant results obtained from in vitro studies may be related to differences in the experimental designs and procedures, differences in the prepared materials, such as the bacterial strains, and/or differences in the activation status of the isolated macrophages.…”

Metabolic Remodeling, Inflammasome Activation, and Pyroptosis in Macrophages Stimulated by Porphyromonas gingivalis and Its Outer Membrane Vesicles

“…There is conflicting evidence as to whether P. gingivalis can activate the inflammasome in macrophages, which in large part seems to be due to differences in cell populations studied (Taxman et al, 2006 , 2012 ; Slocum et al, 2014 ). Another complication has been the gingipain-mediated degradation of the major readouts used to determine inflammasome activation and pyroptosis (Jung et al, 2015 ). P. gingivalis evasion of inflammasome activation would provide an intracellular niche for the pathogen to survive and disseminate to distant sites.…”

Involvement of NLRP10 in IL-1α induction of oral epithelial cells by periodontal pathogens

“…NLRP3 inflammasome activation by P. gingivalis, T. denticola and Aggregatibacter actinomycetemcomitans induced IL-1b secretion in monocytes and macrophages. [15][16][17][18] Porphyromonas gingivalis in subgingival biofilm downregulated NLRP3 expression and IL-1b secretion, which prolonged the survival and persistence of biofilm species during the host immune response. 19 Fusobacterium nucleatum induced IL-1b secretion via NLRP3 activation in gingival epithelial cells.…”