Apolipoprotein B plasma levels, hepatic synthesis and secretion, andmRNA abundance and editing in copper-deficient rats.
AuthorReaves, Scott Kenneth.
Committee ChairLei, David K.Y.
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PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThe effects of dietary copper deficiency on plasma apoB levels and hepatic apolipoprotein (apo) B synthesis, secretion and intracellular degradation were examined in rats. In addition, hepatic apoB mRNA abundance as well as editing in the liver and intestine were also determined. Male weanling Sprague-Dawley rats were assigned to copper-deficient (9.0 μmol Cu/kg diet) or copper-adequate (102 μmol Cu/kg diet) dietary treatments, for six weeks. In vitro hepatic apoB synthesis, secretion, and degradation were determined by pulse-chase studies using freshly isolated rat liver parenchymal cells. Two x 10⁸ cells were pulsed for 20 minutes in minimum essential medium (MEM) with [³H]phenylalanine and chased for 10, 20, 30 and 45 min in MEM with 0.1 mM PRE. Triton X-IOO and Na deoxycholate were added to cell and medium samples and apoB in the detergent soluble fractions was immunoprecipitated with monospecific polyclonal antibody. Proteins were resolved by SDS-PAGE and radioactivities associated with apoB-48 or apoB-IOO were counted. In vitro apoB-48 and apoB-loo synthesis was not altered, secretion was increased twofold and intracellular degradation of total apoB was significantly reduced in cells derived from copper-deficient rats. Plasma levels of apoB-48 and apoB-IOO were determined by resolving delipidated LDL and VLDL fractions by SDS-PAGE. Apolipoprotein bands were identified and quantitated by loading various amounts of purified apoB-48 and apoB-l 00 on each gel. Plasma apoB-48 and apoB-l 00 levels were increased by copper deficiency but only the apoB-48 increase was found to be significant, thereby, indicating a preferential increase in plasma apoB-48. ApoB mRNA editing activity was determined by using the PCR cloning-colony hybridization technique. Hepatic apoB mRNA editing, expressed as a ratio of apoB-48 mRNNapoB-48 plus apoB-loo mRNA, was significantly increased from 60.8% in copper-adequate to 70.2% in copper-deficient rats. Moreover, hepatic apoB mRNA abundance, as determined by dot blot hybridization with a specific [³²P]-labelled rat apoB cDNA probe, was not significantly increased by copper-deficiency. Thus, the increased amount of nascent apoB-48 secreted into the medium as well as the enhanced apoB mRNA editing may have contributed to the differential increase in plasma apoB-48 over apoB-1 00 level in copper-deficient rats.
Degree ProgramNutritional Sciences