The NLRP3 inflammasome plays an important role in liver fibrosis development. However, the mechanisms involved in NLRP3-induced fibrosis are unclear. Our aim was to test the hypothesis that the NLRP3 inflammasome in hepatic stellate cells (HSC) can directly regulate their activation and contribute to liver fibrosis. Primary HSC isolated from WT, Nlrp3-/- , or Nlrp3L351PneoR knock-in crossed to inducible (estrogen receptor Cre - CreT) mice were incubated with LPS and ATP, or 4OH-tamoxifen, respectively. HSC-specific Nlrp3L351P -knock-in mice were generated by crossing transgenic mice expressing lecithin retinol acyltransferase (Lrat)-driven Cre and maintained on standard rodent chow for 6 months. Mice were then sacrificed; liver tissue and serum were harvested. Nlrp3 inflammasome activation along with HSC phenotype and fibrosis were assessed by RT-PCR, Western blot, FACS, ELISA, immunofluorescence and immunohistochemistry. Stimulated WT HSC displayed increased levels of NLRP3 inflammasome-induced ROS production and Cathepsin B activity, accompanied by an upregulation of mRNA and protein levels of fibrotic makers, an effect abrogated in Nlrp3-/- HSC. Nlrp3L351P CreT HSC also showed elevated mRNA and protein expression of fibrotic markers 24h after inflammasome activation induced with 4OH-tamoxifen. Protein and mRNA expression levels of fibrotic markers were also found to be increased in isolated HSC and whole liver tissue from Nlrp3L351P Lrat Cre mice compared to WT. Liver sections from 24 week-old NlrpL351P Lrat Cre mice showed fibrotic changes with increased αSMA and desmin positive cells and collagen deposition, independent of inflammatory infiltrates; these changes were also observed after LPS challenge in 8 week-old NlrpL351P Lrat Cre mice. Conclusion Our results highlight a direct role for the NLRP3 inflammasome in the activation of HSC directly triggering liver fibrosis. This article is protected by copyright. All rights reserved.