Regulation of monocyte chemoattractant protein 1 by cytokines and oxygen free radicals in rat hepatic fat-storing cells

Background and Aims: Monocyte chemoattractant protein 1 (MCP-1) is a potent monocyte/macrophage chemoattractant expressed by fat-storing cells (FSCs) in rat models of liver injury. This study investigated the mechanism of this activation of hepatic MCP-1 expression. Methods: The regulation of MCP-1 messenger RNA (mRNA) expression and protein synthesis was examined in FSC lines derived from CCl₄-induced cirrhotic rat liver (cirrhotic FSCs) and normal rat liver (normal FSCs). Results: Northern blot hybridization analysis revealed low levels of MCP-1 mRNA in cultured cirrhotic FSCs that increased markedly after treatment with tumor necrosis factor α, interleukin 1α, or transforming growth factor β1. All three cytokines increased the synthesis and secretion of MCP-1 protein. Oxygen free radical production also increased MCP-1 mRNA levels. These increases in MCP-1 mRNA were blocked by dexamethasone. In normal FSCs, levels of MCP-1 mRNA and secreted protein were increased in response to cytokines or oxygen free radical production, but the magnitude and duration of this increase was less than in cirrhotic FSCs. Conclusions: In liver injury, monocyte/macrophage recruitment and activation from FSC production of MCP-1 may be stimulated by cytokines and oxygen free radicals. During chronic liver injury leading to cirrhosis, FSCs may become hypersensitive to these stimuli, further fueling the inflammatory response.