Abstract
Hepatic sterol carrier protein-2 (SCP2) and sterol carrier protein-X (SCPx) levels in normal and in mutant Niemann-Pick Type C mice were determined by immunoblotting with antiserum against rat SCP2. A 14-kDa protein (SCP2) was detected in the cytosol fraction and a 58-kDa protein (SCPx) was found in both cytosolic and organellar fractions. Expression of hepatic SCPx protein was developmentally regulated in a sex-specific pattern. The amounts of organelle-associated SCPx increased 4-fold during sexual development of normal males but decreased dramatically during development of normal females. Levels of hepatic SCP2 increased much less dramatically during sexual maturation of normal males and females. Adult Niemann-Pick Type C mice were deficient in both hepatic SCPx and SCP2. The deficit in SCPx in affected males reflected a failure to increase hepatic SCPx levels during sexual maturation. In affected males SCPx remained at levels found in immature mice. Affected male and female mice were also unable to maintain levels of hepatic SCP2. The level of SCP2 was near normal in affected immature males and subnormal in affected immature females. During sexual maturation hepatic SCP2 declined in affected animals.
Highlights
Hepatic sterol carrier protein-2 (SCP2) and sterol carrier protein-X (SCP,) levels in normal and in mutant Niemann-Pick Type C mice were determined by immunoblotting with antiserum against rat SCP2
Immunoreactive Sterol Carrier Proteins in Liver of Normal Mature Mice-Hepatic extracts from 60-day-old normal male mice contained two polypeptides of -58 and -14 kDa that were detected with anti-rat SCP, (Fig. lA, lanes 1 and 2)
Fractions isolated from 1 g of liver from 60-day-old normal and affected male mice were assayed for SCP, and SCP2 by immunoblotting and for catalase activity as described in the Sigmacatalogue
Summary
When SCP2was coexpressedwith steroidogenic enzymes progestin synthesis was enhanced over levels in cells not hyperexpressing SCP, [12] These observations suggest a role for SCP, in vivo that mimics the in vitro stimulation of cholesterol movement and utilization by mitochondria. SCtearrPorlrioetreins in Niemann-Pick Type C Mice associated with uptake of exogenous cholesterol was shown to be partially affected in fibroblasts obtained from obligate human and mouse NPC heterozygotes [34,35], suggesting the possible involvement of a cholesterol transport protein whose activity is rate limiting for intracellular movement of exogenously derived cholesterol. Because of the suggested participation of SCP, in cellular cholesterol transport wehavecompared the relative abundance of sterol carrier proteins in liver of normal and NPC mice
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