Published online May 7, 2014. doi: 10.3748/wjg.v20.i17.4963
Revised: December 25, 2013
Accepted: March 5, 2014
Published online: May 7, 2014
AIM: To investigate whether naofen is involved in tumor necrosis factor (TNF)-α-mediated apoptosis of hepatocytes induced by lipopolysaccharide (LPS).
METHODS: In vivo, rats were treated with LPS or anti-TNF-α antibody, whereas in vitro, primary hepatocytes and Kupffer cells (KCs) were separately isolated from rat livers using collagenase perfusion, and primary hepatocytes were cultured in medium containing LPS or TNF-α, or in conditioned medium from LPS-treated KCs (KC-CM)/KC-CM + anti-TNF-α antibody. Naofen and TNF-α mRNA expression was examined by real-time reverse transcription-polymerase chain reaction. Immunoblotting was used to measure protein expression. Hepatocyte apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay.
RESULTS: LPS significantly induced both naofen expression and caspase-3 activity in the rat liver, which coincided with an increase in the number of TUNEL-positive hepatocytes. The increase of TNF-α expression induced by LPS was preceded by increases in naofen and caspase-3 activity. Elevation of naofen expression and caspase-3 activity was abrogated by pretreatment with anti-TNF-α antibody. In KCs, LPS caused an increase in TNF-α that was almost consistent with that in the liver of LPS-treated rats. In hepatocytes, neither LPS nor TNF-α alone affected either naofen expression or caspase-3 activation. The incubation of hepatocytes with KC-CM significantly enhanced both naofen expression and caspase-3 activity. Moreover, the effects of the KC-CM-induced increase in naofen expression and caspase-3 activity were blocked by anti-TNF-α antibody.
CONCLUSION: TNF-α released from KCs treated with LPS may induce hepatic naofen expression, which then stimulates hepatocellular apoptosis through activation of caspase-3.
Core tip: Naofen, a WD40-repeat protein, is increased in the liver but not in the kidneys, thymus or spleen of rats injected with lipopolysaccharide (LPS). Increased naofen expression is blocked by pretreatment with anti-tumor necrosis factor (TNF)-α antibody. TNF-α has no effect on naofen expression or caspase-3 activation in primary hepatocytes, but conditioned medium from LPS-treated Kupffer cells (KC-CM) significantly enhances both. KC-CM-induced increase in naofen expression and caspase-3 activity is blocked by anti-TNF-α antibody. LPS in the liver may enhance release of TNF-α from KCs, and induce hepatocyte apoptosis, for which naofen promotes caspase-3 activity through the mitochondrial pathway.