Hepatic stellate cells play a quantitatively important role in hepatic retinoid metabolism and storage in rats maintained under normal nutritional conditions. Studies were conducted to further explore the biochemical characteristics of hepatic stellate cells. Stellate cells were isolated in high purity and yield from the livers of normal rats. The isolated cells had the morphology expected (on electron micrographs) for stellate cells, and were enriched in retinoids and in the intracellular retinoidbinding proteins. The composition of the stellate cell lipid droplets was examined. These lipid droplets were isolated in high purity and integrity from frozen and thawed stellate cell preparations by differential centrifugation. We estimate that the lipid composition of stellate cell lipid droplets consisted of approximately 42% retinyl ester, 28% triglyceride, 13% cholesterol (total) and 4% phospholipid. Thus, stellate cell lipid droplets contain substantial levels of both cholesterol and triglyceride, in addition to retinyl esters. Stellate cell homogenates were assayed for both retinol-binding protein and transthyretin by specific radioimmunoassays. Within the detection limits of these radioimmunoassays, we were unable to detect the presence of either retinolbinding protein (<9 ng per 10' cells) or transthyretin (el1 ng per lo6 cells) in the stellate cell preparations.
Total RNA, prepared from the isolated stellate cells, was examined by Northern blot analysis for retinol-binding protein mRNA and transthyretin mRNA, using cDNA probes for retinol-binding protein and transthyretin. Within the sensitivity of these assays, retinol-binding protein mRNA and transthyretin mRNA were not detected in stellate cells. These findings suggest that stellate cells do not synthesize or accumulate retinol-binding protein.
Two types of hepatic cells, parenchymal and stellate cells (also called fat-storing cells, lipocytes and It0 cells), play important roles in retinoid (vitamin A) metabolism in the liver. The large and abundant parenchymal cells