TGF-β1 modulates LPS-induced NLRP3 inflammasome activity

The NLRP3 inflammasome is a multi-protein complex that, upon activation by a large range of stimuli, activates Caspase-1 that in turn mediates the maturation of the pro-inflammatory cytokines IL-1β and IL-18. In a previous study we have shown that LPS stimulation induces a clear time- and concentration-dependent induction of inflammasome-associated genes in the immortalized hepatic stellate cell line CFSC-2G [1]. Although there are actually many unclear and inconsistent data for TGF-β1, it was suggested that TGF-β expression is stimulated by the activity of the different inflammasome branches in hepatic stellate cells [2] and renal tubular epithelium [3].

By stimulation CFSC-2G cells with different concentrations and combinations of lipopolysaccharides (LPS) and TGF-β in short and long term, we now demonstrate that TGF-β1 slightly increases the expression of IL-1β and reduces expression of NLRP3 and inflammatory associated genes (e.g. IL-18, and TNF-α). In addition, by using quantitative real time PCR, Western Blot and TGF-β activity assay (CAGA- and mNLRP3-Luc-reporters) we demonstrate that TGF-β1 suppresses the NLRP3 inflammasome expression and activity. Furthermore, we observed that long term stimulation as well as higher concentrations of TGF-β1 abolished NLRP3 and TNF-α gene expression, while the expression of IL-18 was only marginal affected. The strongest stimulation of pNFκB p65 phosphorylation and IL-1β gene expression in short term (30 min) was found when both TGF-β and LPS were co-applied suggesting a co-stimulatory effect of both triggers.

References cited:

[1] Boaru SG, Borkham-Kamphorst E, Tihaa L, Haas U, Weiskirchen R. Expression analysis of inflammasome components in experimental models of inflammatory and fibrotic liver disease. J Inflamm 2012;9(1):48.

[2] Watanabe A, Sohail MA, Gomes DA, Hashmi A, Nagata J, Sutterwala FS, Mahmood S, Jhandier MN, Shi Y, Flavell RA, Mehal WZ. Inflammasome-mediated regulation of hepatic stellate cells. J Physiol Gastrointest Liver Physiol 2009;296:G1248 – 57.

[3] Wang W, Wang X, Chun J, Vilaysane A, Clark S, French G, Bracey NA, Trpkov K, Bonni S, Duff HJ, Beck PL, Muruve DA. Inflammasome-independent NLRP3 augments TGF-β signaling in kidney epithelium. J. Immunol. 2013;190:1239 – 49.