Abstract
To evaluate the sources of high density lipoprotein (HDL) particles containing only apolipoprotein A-I (apoA-I), the synthesis of apoA-I and apolipoprotein A-II (apoA-II) was examined in human liver and small intestine as well as the human intestinally derived cell line, Caco-2. Human liver contained apoA-I, apoA-II as well as apolipoprotein B (apoB) mRNA. In contrast, human adult small intestine total and polyA+ RNA had little or no apoA-II despite the presence of apoA-I and apoB. Intestinal biopsies from normal individuals failed to show de novo apoA-II protein synthesis in the media of organ cultures during [35S]methionine pulse-chase labeling, whereas apoA-I could be readily detected. Caco-2 cells contained apoA-II mRNA and secreted apoA-II protein into the tissue culture media. These data indicate that the primary site of human apoA-II synthesis is in the liver and that the small intestine secretes apoA-I-containing high density lipoproteins.
Highlights
To evaluate the sources of high density lipoprotein (HDL) particles containing only apolipoprotein A-I, the synthesis of a p d - I and apolipoprotein A-I1 was examined in human liver and small intestine as well as the human intestinally derived cell line, Caco-2
Because of the discrepancies in the literature ascribed to the physiologic and pathophysiologic roles of HDL particles with different apolipoprotein A-I (apoA-I)/apoA-11compositions, possibly reflecting different synthetic sites, we have investigated the human liver and small intestine as sources for apoA-I and apolipoprotein A-11 (apoA-11)
Northern blot analysis revealed the presence of apoA-I mRNA (Fig. 1, panel A) and apolipoprotein B (apoB) mRNA (Fig. 1, panel B) in all of the samples analyzed
Summary
To evaluate the sources of high density lipoprotein (HDL) particles containing only apolipoprotein A-I ( a p d - I ) , the synthesis of a p d - I and apolipoprotein A-I1 (apoA-11) was examined in human liver and small intestine as well as the human intestinally derived cell line, Caco-2. Human liver contained apoA-I, apoA-I1 as well as apolipoprotein B (apoB) mRNA. Human adult small intestine total and polyA+ RNA had little or no apoA-I1 despite the presence of apoA-I and apoB. Caco-2 cells contained apoA-I1 mRNA and secreted apoA-I1 protein into the tissue culture media. M These data indicate that the primary site of human apoA-I1 synthesis is in the liver and that the small intestine secretes apd-I-containing high density lipoproteins.
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