We located hepatic lipase in space of Disse and subendothelial space of heart and aorta. Hepatic lipase in the space of Disse was associated with the extracellular matrix at basal surfaces of sinusoidal epithelium and hepatocytes, and at surfaces of non-parenchymal cells and lipoprotein sized particles. Hepatic lipase was present in heart in extracellular matrix around capillaries and at surfaces of myocytes. A striking finding was the presence of hepatic lipase in aorta, beneath the endothelium and in the adventitia. Thus hepatic lipase was located in the space of Disse, where it could act on remnants prior to uptake by hepatocytes, and in subendothelial space, where it could act on lipoproteins transported across endothelium. Perilipin, a hormonally regulated phosphoprotein, was located intracellularly in cultured 3T3-L1 adipocytes, adipocytes isolated from rat epididymal fat pads and adipocytes within lactating rat mammary gland. In developing adipocytes and mature adipocytes, perilipin is localized on the monolayered surface of lipid droplets. Perilipin was not found in mammary alveolar cells which synthesize and secrete triacylglycerol lipid droplets as milk lipid. Immunofluorescent studies on cultured 3T3-L1 adipocytes incubated with cAMP analogues show, that cells decrease perilipin at the lipid droplet surface and disperse perilipin into the cytoplasm in response to cAMP kinase activation. Golgi compartments are involved in the intracellular trafficking of cholesterol derived from LDL. In normal fibroblasts both trans Golgi vacuoles and cis Golgi cisternae accumulate cholesterol in response to LDL uptake suggesting a route of transport for cholesterol from trans Golgi vacuoles to plasma membrane and cis Golgi to endoplasmic reticulum. In fibroblasts derived from patients with Niemann-Pick Type C disease cholesterol accumulates in trans Golgi cisternae suggesting impaired cholesterol transport through the Golgi. The ability of cells to process cholesterol rich lipoproteins could depend on modulation of cholesterol enriched membrane traffic through the Golgi to intracellular homeostatic sites. We found recently that normal fibroblasts, incubated with progesterone and LDL abnormally accumulate cholesterol in lysosomes. Upon progesterone removal, unesterified cholesterol leaves lysosomes and cholesterol ester is synthesized in these normal cells. However, monensin, a compound which inhibits Golgi membrane trafficking to the plasma membrane, retards cholesterol efflux from cholesterol laden lysosomes and increases cholesterol in Golgi. This rapidly reversible cholesterol lipidosis in normal cells provides an experimental opportunity to study mechanisms that regulate intracellular cholesterol transport.
