Role of liver extracellular matrix in transcriptional and post-transcriptional regulation of apolipoprotein A-I by hepatocytes

Abstract

Apolipoprotein A-I, a protein produced mainly by hepatocytes, is of major importance in prevention of atherosclerosis. Its serum level varies according to the degree of liver fibrosis and the mechanism of this regulation is unknown. The aim of this study was to investigate the role of extracellular matrix in the regulation of apolipoprotein A-I by the liver. Primary mouse hepatocytes were cultured on different extracellular matrix components. The apolipoprotein A-I mRNA level was quantified in these different culture conditions by a sensitive quantitative RT-PCR procedure and compared according to the extracellular matrix component used as substrate. A significant decrease in the apolipoprotein A-I mRNA level was observed when cells were plated on fibronectin by comparison with cells cultured on all other components. Potential binding of apolipoprotein A-I to the different matrix components was also studied in vitro. We demonstrated that apolipoprotein A-I significantly bound to fibronectin in a concentration-dependent, saturable and specific manner. Thus, fibronectin, a major liver extracellular matrix component, can interact with apolipoprotein A-I both by downregulating its mRNA level in liver cells and by binding this molecule after its secretion in the extracellular space. Since fibronectin is the first matrix component to be produced in excess and deposited in liver fibrosis, it could be involved in the decrease in serum apolipoprotein A-I in alcoholic patients with liver fibrosis and cirrhosis.