Chronic TLR Stimulation Controls NLRP3 Inflammasome Activation through IL-10 Mediated Regulation of NLRP3 Expression and Caspase-8 Activation

Abstract

While the molecular mechanisms promoting activation of the Nod-like Receptor (NLR) family member NLRP3 inflammasome are beginning to be defined, little is known about the mechanisms that regulate the NLRP3 inflammasome. Acute (up to 4 hours) LPS stimulation, followed by ATP is frequently used to activate the NLRP3 inflammasome in macrophages. Interestingly, we observed that the ability of LPS to license NLRP3 is transient, as prolonged (12 to 24 hours) LPS exposure was a relatively ineffective priming stimulus. This suggests that relative to acute LPS, chronic LPS exposure triggers regulatory mechanisms to dampen NLRP3 activation. Transfer of culture supernatants from macrophages stimulated with LPS for 24 hours dramatically reduced ATP- and nigericin-induced NLRP3 inflammasome activation in naïve macrophages. We further identified IL-10 as the secreted inflammasome-tolerizing factor that acts in an autocrine manner to control activation of the NLRP3 inflammasome. Finally, we demonstrated that IL-10 dampens NLRP3 expression to control NLRP3 inflammasome activation and subsequent caspase-8 activation. In conclusion, we have uncovered a mechanism by which chronic, but not acute, LPS exposure induces IL-10 to dampen NLRP3 inflammasome activation to avoid overt inflammation.

Helicobacter pylori controls NLRP3 expression by regulating hsa-miR-223-3p and IL-10 in cultured and primary human immune cells

“…Gurung et al reported that reduced mature IL-1b secretion during classical NLRP3 inflammasome activation was more pronounced in the late time point, owing to the decreased NLRP3 expression. 52 Our findings of increased hsamiR-223-3p and gradually increasing IL-10 in these infected cell systems could be correlated with decreased expression of NLRP3 at the late time point of H. pylori infection (24 h). We also noted that H. pylori-infected THP-1 monocytes secreted very low levels of mature IL-1b secretion during the entire infection period (Figure 8b).…”

“…[50][51][52][53] H. pylori-infected macrophages secreted significantly more IL-10 than mock control; however, it was < 30 pg/ml, even after 24 h of infection. This low level of IL-10 was not enough to control NLRP3 expression in macrophages (Figure 5a, c).…”

“…[50][51][52][53] We analyzed this effect by measuring the levels of IL-10 secretion in LPS-primed and nigericin-induced THP-1 monocytes and human PBMCs in relation to secreted mature IL-1b. As expected, the results showed that IL-10 levels were gradually increased from 6 h of treatment to 24 h, and the secreted levels of mature IL-1b were significantly reduced (Figure 8a, b), which could be correlated with the abovementioned recent findings of the effect of IL-10 on NLRP3 expression and mature IL-1b secretion.…”

Interaction of Mycoplasma hominis PG21 with Human Dendritic Cells: Interleukin-23-Inducing Mycoplasmal Lipoproteins and Inflammasome Activation of the Cell

“…The NLRP7-encoding gene was not regulated in our model of coincubation, although (i) NLRP7 had been specifically identified as an intracellular sensor of mycoplasmal acylated lipoproteins and (ii) NLRP7 was reported to activate the inflammasome of the THP-1 cell line after exposure to A. laidlawii, to lipopeptides derived from mycoplasmas such as FSL-1 and MALP-2, and to the synthetic lipopeptides Pam 2 CSK4 and Pam 3 CSK4 (16). Notably, we observed a significant downregulation of the NLRP3-encoding gene and of the adaptor PYCARD-coding gene at 24 h. The ability of LPS to activate NLRP3 was described to be weak and transient, with a low capacity of NLRP3 activation after 24 h (29). Chronic LPS stimulation was also reported to trigger IL-10-dependent regulatory mechanisms.…”

Inflammasome Priming in Sterile Inflammatory Disease

“…The deubiquitinase responsible for NLRP3 inflammasome priming thus remains to be identified. In vivo, ubiquitination may be regulated in a tissue-specific manner, with mouse macrophages experiencing high levels of IL-10 that promote ubiquitinated-NLRP3 turnover, and, because the macrophages were obtained from colonic tissue, this pathway may have relevant implications for the pathogenesis of inflammatory bowel disease [68,69] .…”