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Stimulation of inducible nitric oxide synthase in rat liver by hyaluronan fragments
Author(s) -
Rockey Don C.,
Chung John J.,
McKee Charlotte M.,
Noble Paul W.
Publication year - 1998
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.510270115
Subject(s) - nitric oxide synthase , hepatic stellate cell , microbiology and biotechnology , nitric oxide , messenger rna , stimulation , kupffer cell , signal transduction , lipopolysaccharide , biology , liver cytology , gene expression , chemistry , biochemistry , endocrinology , immunology , gene , liver metabolism
Hepatic injury and chronic wounding are characterized by increased synthesis of extracellular matrix proteins including hyaluronan (HA). Recently, it has been recognized that low‐molecular‐weight fragments of HA, but not native HA (e.g., high‐molecular‐weight HA), induce inflammatory gene expression, and activate the transcriptional regulator, nuclear factor κB (NF‐κB). The inducible isoform of nitric oxide synthase (iNOS) is induced by cytokines and/or lipopolysaccharide (LPS) through the NF‐κB signal transduction pathway. Because of this association, we hypothesized that HA fragments might also stimulate iNOS gene transcription. The aims of this study were therefore to determine whether HA or HA fragments induced iNOS in hepatic cells, and to characterize the signaling pathway. HA fragments (100 μg/mL) markedly stimulated iNOS messenger RNA (mRNA) in endothelial and Kupffer cells, but minimally induced this mRNA in hepatocytes and stellate cells. High‐molecular‐weight HA (200 μg/mL) had no effect on iNOS mRNA in any cell type. The addition of interferon gamma (IFN‐γ) to HA fragments resulted in stimulation of iNOS mRNA 2‐, 3‐, 4‐, and 10‐fold above that for HA fragments alone in hepatocytes, endothelial, Kupffer, and stellate cells, respectively. The combination of HA fragments and LPS did not result in an incremental increase in iNOS mRNA induction. iNOS protein and nitrite levels (used as a measure of NO production and NOS enzymatic activity) paralleled closely iNOS mRNA expression and increased proportionally to HA fragment concentration in a dose‐dependent fashion. At 1 hour following stimulation, NF‐κB DNA binding activity was detected in extracts from Kupffer cells stimulated with HA fragments, but not in those exposed to media alone or to high‐molecular‐weight HA. Finally, inhibitors of NF‐κB blocked HA fragment–dependent iNOS mRNA induction in Kupffer and sinusoidal endothelial cells. The data indicate that HA fragments, but not high‐molecular‐weight HA, induce iNOS in liver, having the greatest effects on endothelial and Kupffer cells. We speculate that HA fragments may be an important stimulus for NO production in various forms of liver disease, particularly as a cofactor with inflammatory cytokines.