Interleukin-1β induces tumor necrosis factor-α secretion from rat hepatocytes

Aim Tumor necrosis factor‐α (TNF‐α) is a pleiotropic cytokine involved in various inflammatory diseases. The only production of TNF‐α in the liver is thought to be from hepatic macrophages known as Kupffer cells, predominantly in response to bacterial lipopolysaccharide (LPS). Methods Primary cultured rat hepatocytes were used to analyze TNF‐α expression in response to the pro‐inflammatory cytokine, interleukin‐1β (IL‐1β). Livers of rats subjected to LPS‐induced endotoxemia were analyzed. Results Immunocytochemistry and enzyme‐linked immunosorbent assays demonstrated that IL‐1β‐treated rat hepatocytes secreted TNF‐α, and RNA analyses indicated that TNF‐α mRNA was induced specifically by IL‐1β. Northern blot analysis showed that not only mRNA, but also a natural antisense transcript (asRNA), was transcribed from the rat Tnf gene in IL‐1β‐treated hepatocytes. TNF‐α was detected in the hepatocytes of LPS‐treated rats. Both TNF‐α mRNA and asRNA were expressed in the hepatocytes of LPS‐treated rats, human hepatocellular carcinoma and human monocyte/macrophage cells. To disrupt the interaction between TNF‐α asRNA and TNF‐α mRNA, sense oligonucleotides corresponding to TNF‐α mRNA were introduced into rat hepatocytes resulting in significantly increased levels of TNF‐α mRNA. One of these sense oligonucleotides increased a half‐life of TNF‐α mRNA, suggesting that the TNF‐α asRNA may reduce the stability of TNF‐α mRNA. Conclusion IL‐1β‐stimulated rat hepatocytes are a newly identified source of TNF‐α in the liver. TNF‐α mRNA and asRNA are expressed in rats and humans, and the TNF‐α asRNA reduces the stability of the TNF‐α mRNA. Hepatocytes and TNF‐α asRNA may be therapeutic targets to regulate levels of TNF‐α mRNA.