Quantitation of apolipoprotein E mRNA in the liver and peripheral tissues of nonhuman primates

A sensitive DNA-excess solution hybridization assay was used to quantitate apo-E mRNA in the liver and peripheral tissues of two nonhuman primates, Macaca fascicularis and Cercopithecus aethiops. When expressed on the basis of total RNA, apo-E mRNA values for M. fascicularis adrenal, brain, testis, and spleen ranged from 17-52% of the liver value. Apo-E mRNA values for mesenteric lymph node, kidney, thymus, and skeletal muscle were 1-5% of the liver value. When expressed on a cellular basis, apo-E mRNA was most abundant in the liver at approximately 1200 molecules/cell. Peripheral tissues showed a continuous range of apo-E mRNA from 1.5 molecules/cell in the thymus up to 350 molecules/cell in the brain. Similar results were obtained with peripheral tissues from C. aethiops in which case apo-E mRNA also was found in skin, lung, skeletal muscle, small intestine, and vascular tissues such as heart, aorta, and brachial artery. Calculation of the total apo-E mRNA/organ showed that most of the apo-E mRNA was present in the liver. However, summation of apo-E mRNA in peripheral tissues indicated that 20-40% of total body apo-E mRNA was extrahepatic. This results indicates that apo-E made in peripheral tissues may play a quantitatively important role in cholesterol metabolism since peripheral tissues have the potential to contribute a significant fraction of plasma apo-E.