Exposure to bacterial cell wall products triggers an inflammatory phenotype in hepatic stellate cells

Abstract

Brun, Paola, Ignazio Castagliuolo, Massimo Pinzani, Giorgio Palù , and Diego Martines. Exposure to bacterial cell wall products triggers an inflammatory phenotype in hepatic stellate cells. Activated hepatic stellate cells (HSCs) secrete extracellular matrix components during hepatic fibrosis, but recent studies have shown that HSCs can also release a variety of proinflammatory cytokines. Moreover, bacterial endotoxemia is not only associated with systemic complications in the late stages of liver failure but is also a direct cause of liver damage, activating resident inflammatory cells. In this study, we investigated whether HSCs can respond directly to bacterial cell wall products acquiring a new phenotype. RT-PCR and immunocytochemistry assays were used to show that murine HSCs expressed specific mRNA transcripts and proteins for LPS and lipoteichoic acid (LTA) receptor systems and peptidoglycan recognition proteins. Exposing HSCs to bacterial endotoxins led to phosphorylation of mitogenactivated protein kinase ERK1 and the development of a proinflammatory phenotype. After exposure to LPS, LTA, or N-acetyl muramyl peptide, transforming growth factor-␤1, IL-6, and monocyte chemoattractant protein-1 (MCP-1) mRNA specific transcripts and proteins increased significantly in HSCs, as assayed by quantitative real-time RT-PCR and ELISA. These LPS-mediated effects in HSCs were receptor dependent, because LPS-induced ERK1 phosphorylation, IL-6, and MCP-1 mRNA and protein level upregulation were significantly less pronounced in HSCs isolated from C3H/HeJ mice lacking Toll-like receptor 4. In conclusion, our results show that murine HSCs express functional receptors for bacterial endotoxins, and HSCs exposed to bacterial products develop a strong proinflammatory phenotype. We speculate that high levels of bacterial endotoxins in the portal vein may directly induce a proinflammatory phenotype in HSCs that contributes to liver damage.

Alcohol, intestinal bacterial growth, intestinal permeability to endotoxin, and medical consequences: Summary of a symposium

“…Culture-activated human HSCs expressed LPS receptors CD-14 and TLR-4, and stimulation of these cells with LPS induced NF-kB activation and up-regulated gene expression of chemokines -interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) -and adhesion molecules (intercellular adhesion molecules and vascular cellular adhesion molecules -1) (Paik et al, 2003). Activated mouse HSCs expressed TLR-4 and CD-14 and responded to LPS with an up regulation of extracellular signal-regulated kinase phosphorylation and IL-6, transforming growth factor-β1, and MCP-1 secretion (Brun et al, 2005). In quiescent rat hepatic stellate cells, LPS stimulated the synthesis of proinflammatory cytokines TNF-α, IL-6, and IL-1 (Thirunavukkarasu et al, 2005).…”

Hepatic stellate cells primed with cytokines upregulate inflammation in response to peptidoglycan or lipoteichoic acid

“…In addition, Brun et al 18 recently reported that lipoteichoic acid and N-acetyl muramyl peptide induced TGF-b, IL-6, and MCP-1 in murine HSCs, suggesting the substantial role of gram-positive bacterial products in hepatic inflammation and fibrosis. However, the molecular mechanisms involved in the gram-positive bacterial product induction of inflammatory signaling in human HSCs are still unknown.…”

Hepatic stellate cells (HSC) cell line (LX-2) and Toll-like receptors – phenotypic/mRNA expression and in vitro functional studies

“…Exposure of murine HSC to ligands of Toll-like receptors (TLRs) such as LPS or lipoteichoic acid, triggered the release a variety of proinflammatory cytokines apparently involved in the liver damage [9].…”