Regulation of TREM expression in hepatic macrophages and endothelial cells during acute endotoxemia

Exp Mol Pathol. 2008 Apr;84(2):145-55. doi: 10.1016/j.yexmp.2007.11.004. Epub 2007 Dec 3.

Abstract

Triggering receptor expressed on myeloid cells (TREM) regulates inflammatory responses to lipopolysaccharide (LPS). In these studies, we analyzed the expression of TREM in hepatic macrophages and endothelial cells which play a central role in LPS clearance. LPS administration to C3H/HeOuJ mice resulted in a rapid induction of TREM-1 and TREM-3, but a decrease in TREM-2 in liver macrophages and endothelial cells. The observation that TREM family members are detectable in endothelial cells is novel and demonstrates that their expression is not limited to myeloid cells. LPS-induced alterations in TREM expression were not evident in cells from C3H/HeJ TLR-4 mutant mice, indicating that the response is dependent on TLR-4. IL-1beta and TNFalpha upregulated TREM-1 and TREM-3 expression and suppressed TREM-2 expression in macrophages and endothelial cells. This activity involved PI3-kinase and p38 MAP kinase signaling. Interestingly, no significant differences were noted in TREM expression between wild-type and TNFR1-/- mice treated with LPS. Treatment of macrophages and endothelial cells with LPS upregulated expression of nitric oxide synthase-2 (NOS-2). This was blocked by TREM-1 Fc/fusion protein, indicating that TREM-1 mediates LPS-induced NOS-2 expression. These results suggest that TREM proteins are important in the inflammatory response of hepatic macrophages and endothelial cells to acute endotoxemia.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Endothelial Cells / metabolism*
  • Endotoxemia / etiology
  • Endotoxemia / genetics
  • Endotoxemia / metabolism*
  • Escherichia coli
  • Gene Expression Regulation / drug effects
  • Gene Silencing
  • Kupffer Cells / metabolism*
  • Lipopolysaccharides / pharmacology
  • Liver / blood supply
  • Male
  • Membrane Glycoproteins / genetics
  • Membrane Glycoproteins / metabolism*
  • Mice
  • Mice, Inbred C3H
  • Mice, Inbred C57BL
  • Mice, Knockout
  • RNA, Messenger / metabolism
  • Receptors, Immunologic / genetics
  • Receptors, Immunologic / metabolism*
  • Recombinant Fusion Proteins / pharmacology
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / metabolism
  • Triggering Receptor Expressed on Myeloid Cells-1
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Lipopolysaccharides
  • Membrane Glycoproteins
  • RNA, Messenger
  • Receptors, Immunologic
  • Recombinant Fusion Proteins
  • TREM1 protein, mouse
  • Tlr4 protein, mouse
  • Toll-Like Receptor 4
  • Trem2 protein, mouse
  • Trem3 protein, mouse
  • Triggering Receptor Expressed on Myeloid Cells-1
  • Tumor Necrosis Factor-alpha

Grant support