Expression of CD14 by Hepatocytes: Upregulation by Cytokines during Endotoxemia

Abstract

Studies were undertaken to examine hepatocyte CD14 expression during endotoxemia. Our results show that lipopolysaccharide (LPS) treatment in vivo caused a marked upregulation in CD14 mRNA and protein levels in rat hepatocytes. Detectable increases in mRNA were seen as early as 1.5 h after LPS treatment; these increases peaked at 20-fold by 3 h and returned to baseline levels by 24 h. In situ hybridization localized the CD14 mRNA expression to hepatocytes both in vitro and in vivo. Increases in hepatic CD14 protein levels were detectable by 3 h and peaked at 12 h. Hepatocytes from LPS-treated animals expressed greater amounts of cell-associated CD14 protein, and more of the soluble CD14 was released by hepatocytes from LPS-treated rats in vitro. The increases in hepatocyte CD14 expression during endotoxemia occurred in parallel to increases of CD14 levels in plasma. To provide molecular identification of the hepatocyte CD14, we cloned the rat liver CD14 cDNA. The longest clone consists of a 1,591-bp insert containing a 1,116-bp open reading frame. The deduced amino acid sequence is 372 amino acids long, has 81.8 and 62.8% homology to the amino acid sequences of mouse and human CD14, respectively, and is identical to the rat macrophage CD14. The expressed CD14 protein from this clone was functional, as indicated by NF-κB activation in response to LPS and fluorescein isothiocyanate-LPS binding in CHO cells stably transfected with rat CD14. A nuclear run-on assay showed that CD14 transcription rates were significantly increased in hepatocytes from LPS-treated animals, indicating that the upregulation in CD14 mRNA levels observed in rat hepatocytes after LPS treatment is dependent, in part, on increased transcription. In vitro and in vivo experiments indicated that interleukin-1β and/or tumor necrosis factor α participate in the upregulation of CD14 mRNA levels in hepatocytes. Our data indicate that hepatocytes express CD14 and that hepatocyte CD14 mRNA and protein levels increase rapidly during endotoxemia. Our observations also support the idea that soluble CD14 is an acute-phase protein and that hepatocytes could be a source for soluble CD14 production.

CD14‐positive hepatic monocytes/macrophages increase in hereditary hemochromatosis

“…CD14 is recognized as a key component of the endotoxin receptor (18)(19)(20)(21)(22) since mice without CD14 have a dramatically blunted cytokine response to endotoxin (23). In the presence of endotoxin, CD14-positive macrophages are stimulated to release cytokines such as tumor necrosis factor-a, interleukin-1 (IL-1) and IL-6 (22,24,25). These pro-inflammatory cytokines may contribute to the activation state of hepatic stellate cells (25,26).…”

Endotoxin-stimulated macrophages decrease bile acid uptake in WIF-B cells, a rat hepatoma hybrid cell line

“…LPS may potentially affect hepatocellular integrity. [21][22][23] To exclude a direct effect of LPS on bile acid transport across the basolateral membrane, we investigated [ 3 H]TC uptake in WIF-B cells after 24 hours of exposure to LPS in the absence of exogenous cytokines (Fig. 3).…”

Chronic immune activation in common variable immunodeficiency (CVID) is associated with elevated serum levels of soluble CD14 and CD25 but not endotoxaemia

“…Plasma levels of sCD14, rather than LPS itself, predict disease progression independently in hepatitis B and C (HBV, HBC) in HIV-1 infection and in HIV-1/HCV co-infection [14,21,22]. However, alternative sources of sCD14 such as hepatocytes or activated neutrophils have been suggested [35][36][37][38][39][40][41]. Induction of sCD14 in conditions that are not associated with direct bacterial exposure, such as crystal-induced arthritis, Sjörgen's syndrome, Kawasaki disease and systemic lupus erythematosus, suggests that the production of sCD14 may be linked to inflammatory processes rather than endotoxaemia or bacteraemia [38,[42][43][44].…”