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Jeffrey T Billheimer - One of the best experts on this subject based on the ideXlab platform.
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Human sterol carrier protein x/sterol carrier protein 2 gene has two promoters.
Biochemistry, 1995Co-Authors: Takashi Ohba, Jeffrey T Billheimer, John A. Holt, Jerome F. StraussAbstract:The human sterol carrier protein x (SCPx)/sterol carrier protein 2 (SCP2) gene gives rise to two mRNAs: a 2.8 kb mRNA encoding SCPx, a peroxisome-associated thiolase, and a 1.5 kb mRNA encoding SCP2, which is thought to be an intracellular lipid transfer protein. The SCPx/SCP2 gene is highly expressed in organs involved in lipid metabolism, but the relative abundance of SCPx and SCP2 mRNAs varies. Here we report that the two transcripts are produced under the direction of two independent promoters. We determined the DNA sequence of 3.4 kb of the proximal promoter governing the transcription of SCPx sequences. The promoter governing the transcription of SCP2 sequences was identified 45 kb downstream from the SCPx promoter in intron XI. This promoter initiates transcription within exon XII. Both the SCPx and SCP2 promoters lack TATA boxes and initiate transcription at multiple sites. They share features that are found in the promoters of genes encoding other peroxisomal proteins. The basal activities of the two promoters were tested as fusion gene constructs in selected host cells, including BeWo choriocarcinoma cells, HepG2 hepatoblastoma cells, murine Y1 adrenocortical tumor cells, and Balb 3T3 fibroblasts. Cell host-specific patterns of promoter activity were observed. In addition, 8-Br-cAMP and phorbol myristate acetate were found to increase SCPx promoter activity in a host cell-specific manner. The SCP2 promoter was not significantly influenced by these agents.(ABSTRACT TRUNCATED AT 250 WORDS)
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Reduced hepatic sterol carrier protein-2 expression in the streptozotocin treated diabetic rat
Endocrine, 1995Co-Authors: M. P. Mclean, Keisuke Nanjo, K. J. Warden, Rosalyn B Irby, Jeffrey T BillheimerAbstract:While a strong relationship between the hypercholesterolemia of diabetes and premature atherosclerosis is established, the etiology for the elevation in serum cholesterol in this disease is unknown. To determine whether diabetic hypercholesterolemia may be related to alterations in hepatic cholesterol transport capacity, sterol carrier protein-2 (SCP2) expression was examined in rats treated with streptozotocin (SZT). Furthermore, this study examined whether 17β-estradiol and insulin confer a protective effect on liver cholesterol homeostasis by maintaining hepatic SCP2 levels. SCP2 protein and mRNA expression were examined 13 days following SZT-induced diabetes onset and in diabetic rats treated with estradiol (1 cm silastic implant) or insulin (12 units/day). Data indicate that SCP2 protein levels were significantly reduced in the diabetic animals and that SCP2 protein expression in the liver was inversely related to the level of serum cholesterol in the diabetic animals. In contrast, SCP2 mRNA levels examined by slot blot, ribonuclease protection assay, and Northern blot analysis were significantly elevated. Both insulin and estradiol were able to enhance the expression of SCP2 protein in the liver following SZT treatment. The results of this investigation clearly indicate that hepatic SCP2 protein levels are significantly altered in the diabetic state suggesting that cholesterol transport capacity is reduced in the SZT-treated diabetic rat. The inverse relationship between serum cholesterol and hepatic SCP2 protein content suggests that the reduction in this protein may be a contributing factor in diabetic hypercholesterolemia.
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Sterol carrier protein 2: a role in steroid hormone synthesis?
The Journal of Steroid Biochemistry and Molecular Biology, 1993Co-Authors: Samantha Pfeifer, Jeffrey T Billheimer, Takashi Ohba, Emma E. Furth, Yueh J. Chang, Hanna Rennert, Noriaki Sakuragi, Jerome F. StraussAbstract:Abstract The intracellular movement of cholesterol is an important regulated step in the process of steroidogenesis. However, the molecular mechanisms by which cholesterol is translocated to key organelles, including the mitochondria, remains poorly understood. Lipid transfer proteins may have an important function in this process. One candidate lipid transfer protein is sterol carrier protein 2 (SCP2). This 13.2 kDa protein enhances the movement of cholesterol between vesicles and isolated mitochondria. It also stimulates mitochondrial pregnenolone synthesis. When introduced into intact cells, anti-SCP2 antibodies reduce steroid secretion. Moreover, expression of SCP2 in COS cells engineered to produce progestins increases steroid formation. SCP2 is abundant in steroidogenic glands and the pattern of SCP2 gene expression is consistent with a role for the protein in hormone synthesis: SCP2 transcripts are more prominent in the most steroidogenic compartments of the ovary and tropic hormones that stimulate steroidogenesis increase SCP2 gene expression. Other evidence that suggests that SCP2 plays important roles in cellular function includes a remarkable conservation of primary structure across species. The mechanisms by which SCP2 promotes intracellular sterol movement have not been elucidated. The protein appears to bind sterols and is synthesized with a 20 amino acid N-terminal “pro-” sequence that may serve to target SCP2 to mitochondria. In addition, the C-terminus of SCP2 contains a peroxisome-targeting sequence. SCP2 is derived from a large gene that encodes transcripts that are translated into larger proteins of 30 and 58 kDa. The 58 kDa protein, which has some structural homologies with thiolases, seems to be specifically targeted to peroxisomes whereas SCP2 has a broader subcellular distribution. The significance of the peroxisome association of SCP2 and steroidogenesis has not been disclosed. However, diseases of peroxisome function, including adrenoleukodystrophy and Zellweger syndrome, have notable deficits in steroid and bile acid metabolism, thus linking peroxisomes and steroidogenesis. SCP2 is deficient in fibroblasts of patients with these diseases.
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Expression of the mature and the pro-form of human sterol carrier protein 2 in Escherichia coli alters bacterial lipids.
Biochemistry, 1993Co-Authors: Janet E. Matsuura, Jerome F. Strauss, Henry J. George, N. Ramachandran, Juan G. Alvarez, Jeffrey T BillheimerAbstract:Sterol carrier protein 2 (SCP2) is a protein that is believed to be involved in the intracellular transport of cholesterol and phospholipids. Expression in mammalian COS cells of a cDNA encoding SCP2 revealed that the mature protein is synthesized as a pro-form containing a 20-residue amino-terminal leader sequence. The function of this presequence is currently not known, and pro-SCP2 is generally not detected in tissues. In order to obtain large quantities of pro-SCP2 as well as the mature form of human SCP2, Escherichia coli expression plasmids were constructed. Both proteins were produced in high yield (10-30% of the total cell protein) and were found in the supernatant fraction after cell lysis. Recombinant human SCP2 and pro-SCP2 were purified to homogeneity by acid precipitation followed by ion-exchange chromatography. Both recombinant human SCP2 and pro-SCP2 had sterol exchange activity similar to that seen with SCP2 purified from rat liver. In addition, the lipid content of SCP2- and pro-SCP2-producing E. coli was analyzed. Acidic lipids were significantly increased in the transfected cells. Specifically, fatty acids were increased 2-3-fold, phosphatidylglycerol was increased 2-fold, and lipid A was increased 3-4-fold, while neutral lipids were decreased 2-3-fold as compared to control cells. This alteration of the lipid composition of E. coli expressing SCP2 or pro-SCP2 is consistent with the proposed role for SCP2 in intracellular lipid movement.
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Regulated expression of sterol carrier protein 2 in the ovary: a key role for cyclic AMP.
Biochemistry, 1991Co-Authors: Hanna Rennert, Jeffrey T Billheimer, Abraham Amsterdam, Jerome F. StraussAbstract:Sterol carrier protein 2 (SCP2) is believed to play an important role in the intracellular movement of cholesterol in steroidogenic cells. We examined the distribution of SCP2 gene expression in the rat ovary and the role of gonadotropins and cyclic AMP in the regulation of SCP2 mRNA levels. In situ hybridization revealed that the most steroidogenically active ovarian compartments (e.g., corpora lutea and theca cells) contain significant amounts of SCP2 mRNA whereas granulosa cells have modest levels. Gonadotropins, which promote follicular growth and luteinization, increased the ovarian content of SCP2 mRNA as assessed by Northern blotting along with increases in cytochrome P450scc mRNA. Using steroidogenic transformed rat granulosa cells (Grs-21), a cyclic AMP analogue (8-Br-cAMP) was found to increase SCP2 mRNA and protein levels within 24 h of treatment. P450scc mRNA was also induced whereas actin mRNA levels were not affected. The 8-Br-cAMP stimulation of SCP2 mRNA accumulation was completely inhibited by actinomycin D and cycloheximide. The cyclic AMP analogue also increased SCP2 mRNA levels in a non-steroid hormone producing transformed rat granulosa cell line Gs-8. We conclude that SCP2 gene expression in the ovary is correlated with the state of differentiation of granulosa cells. Gonadotropic hormones which stimulate luteinization of the cells increase SCP2 gene expression. These actions of gonadotropins appear to be mediated at least in part by cyclic AMP through a mechanism requiring ongoing RNA and protein synthesis. However, SCP2 gene expression is not obligatorily coupled to steroidogenic activity, as cyclic AMP analogues can increase SCP2 mRNA in a line of transformed ovarian granulosa cells incapable of synthesizing hormones.
Udo Seedorf - One of the best experts on this subject based on the ideXlab platform.
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disruption of the sterol carrier protein 2 gene in mice impairs biliary lipid and hepatic cholesterol metabolism
Journal of Biological Chemistry, 2001Co-Authors: Michael Fuchs, Frank Kannenberg, Andrea Hafer, Christian Munch, Sandra Teichmann, Jurgen Scheibner, Eduard F Stange, Udo SeedorfAbstract:Hepatic up-regulation of sterol carrier protein 2 (SCP2) in mice promotes hypersecretion of cholesterol into bile and gallstone formation in response to a lithogenic diet. We hypothesized that SCP2 deficiency may alter biliary lipid secretion and hepatic cholesterol metabolism. Male gallstone-susceptible C57BL/6 and C57BL/6(SCP2(-/-)) knockout mice were fed a standard chow or lithogenic diet. Hepatic biles were collected to determine biliary lipid secretion rates, bile flow, and bile salt pool size. Plasma lipoprotein distribution was investigated, and gene expression of cytosolic lipid-binding proteins, lipoprotein receptors, hepatic regulatory enzymes, and intestinal cholesterol absorption was measured. Compared with chow-fed wild-type animals, C57BL/6(SCP2(-/-)) mice had higher bile flow and lower bile salt secretion rates, decreased hepatic apolipoprotein expression, increased hepatic cholesterol synthesis, and up-regulation of liver fatty acid-binding protein. In addition, the bile salt pool size was reduced and intestinal cholesterol absorption was unaltered in C57BL/6(SCP2(-/-)) mice. When C57BL/6(SCP2(-/-)) mice were challenged with a lithogenic diet, a smaller increase of hepatic free cholesterol failed to suppress cholesterol synthesis and biliary cholesterol secretion increased to a much smaller extent than phospholipid and bile salt secretion. SCP2 deficiency did not prevent gallstone formation and may be compensated in part by hepatic up-regulation of liver fatty acid-binding protein. These results support a role of SCP2 in hepatic cholesterol metabolism, biliary lipid secretion, and intracellular cholesterol distribution.
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defective peroxisomal catabolism of branched fatty acyl coenzyme a in mice lacking the sterol carrier protein 2 sterol carrier protein x gene function
Genes & Development, 1998Co-Authors: Udo Seedorf, Peter Ellinghaus, Martin Raabe, Frank Kannenberg, Manfred Fobker, Thomas Engel, Simone Denis, Fred S Wouters, Karel W A WirtzAbstract:Gene targeting in mice was used to investigate the unknown function of SCP2, encoding sterol carrier protein-2 (SCP2; a peroxisomal lipid carrier) and sterol carrier protein-x (SCPx; a fusion protein between SCP2 and a peroxisomal thiolase). Complete deficiency of SCP2 and SCPx was associated with marked alterations in gene expression, peroxisome proliferation, hypolipidemia, impaired body weight control, and neuropathy. Along with these abnormalities, catabolism of methyl-branched fatty acyl CoAs was impaired. The defect became evident from up to 10-fold accumulation of the tetramethyl-branched fatty acid phytanic acid in SCP2(˛/˛) mice. Further characterization supported that the gene disruption led to inefficient import of phytanoyl-CoA into peroxisomes and to defective thiolytic cleavage of 3-ketopristanoyl-CoA. These results corresponded to high-affinity binding of phytanoyl-CoA to the recombinant rat SCP2 protein, as well as high 3-ketopristanoyl-CoA thiolase activity of the recombinant rat SCPx protein.
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Functional Analysis of Sterol Carrier Protein-2 (SCP2) in the SCP2 Knockout Mouse
Intracellular Cholesterol Trafficking, 1998Co-Authors: Udo SeedorfAbstract:Sterol carrier protein-2 (SCP2) and sterol carrier protein-x (SCPx, peroxisomal 3-ketoacyl-CoA thiolase with intrinsic non-specific lipid transfer activity) are expressed from a fused gene (designated SCP2) which is similarly organized in all vertebrates and could be traced back to Drosophila melanogaster. Numerous in vitro studies were performed over the past two decades. They have led to the concept that SCP2 functions intracellularly in cholesterol transport to diverse subcellular locations. On the other hand, apparent lack of transport specificity and the well established localization of SCP2 within peroxisomes has made it difficult to understand how the protein might carry out this function in the intact cell. This chapter summarizes phenotypic abnormalities, that were detected in a murine strain harboring a targeted SCP2 null mutation. Whereas the SCP2/SCPx-deficient strain revealed no major abnormality in cholesterol trafficking, profound effects were found with regard to the metabolism of several methyl-branched acyl-CoAs that are metabolized in peroxisomes. Along with the metabolic abnormalities, the gene disruption led to diet-dependent alterations in gene expression, peroxisome proliferation, hypolipidemia, impaired body weight control and neuropathy.
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Structure and chromosomal assignment of the murine sterol carrier protein 2 gene (SCP2) and two related pseudogenes by in situ hybridization
Cytogenetic and Genome Research, 1996Co-Authors: M. Raabe, Udo Seedorf, Peter Ellinghaus, H. Hameister, G. AssmannAbstract:The murine sterol carrier protein 2 gene ( SCP2 ) has been mapped to chromosome 4C5→D1 by in situ hybridization. This location is syntenic with the locus of SCP2 on human chromosome 1
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Intrinsic sterol- and phosphatidylcholine transfer activities of 17β-hydroxysteroid dehydrogenase type IV
The Journal of Steroid Biochemistry and Molecular Biology, 1995Co-Authors: Udo Seedorf, Thomas Engel, Gerd Assmann, F Leenders, J AdamskiAbstract:Previous studies have shown that the 80 kDa 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) type IV comprises distinct domains, including an N-terminal region related to the short chain alcohol dehydrogenase multigene family and a C-terminal part related to the lipid transfer protein sterol carrier protein 2 (SCP2). In this study, we have investigated whether the SCP2-related part of the 80 kDa protein leads to an intrinsic sterol and phospholipid transfer activity, as shown earlier for the 60 kDa SCP2-related peroxisomal 3-ketoacyl CoA thiolase with intrinsic sterol and phospholipid transfer activity called sterol carrier protein x (SCPx). Our results indicate that a fraction rich in the 80 kDa form of 17 beta-HSD type IV exhibits high transfer activities for 7-dehydrocholesterol and phosphatidylcholine. In addition, a purified recombinant peptide derived from the SCP2-related domain of the 17 beta-HSD type IV has about 30% of the transfer activities for 7-dehydrocholesterol and phosphatidylcholine seen with purified recombinant human SCP2. We conclude that the 80 kDa type IV 17 beta-HSD represents a potentially multifunctional protein with intrinsic in vitro sterol and phospholipid transfer activity in addition to its enzymatic activity.
Mario R. Ermácora - One of the best experts on this subject based on the ideXlab platform.
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The structure of unliganded sterol carrier protein 2 from Yarrowia lipolytica unveils a mechanism for binding site occlusion.
Journal of structural biology, 2020Co-Authors: Alejo R. Gianotti, Sebastián Klinke, Mario R. ErmácoraAbstract:Abstract Isolated or as a part of multidomain proteins, Sterol Carrier Protein 2 (SCP2) exhibits high affinity and broad specificity for different lipidic and hydrophobic compounds. A wealth of structural information on SCP2 domains in all forms of life is currently available; however, many aspects of its ligand binding activity are poorly understood. ylSCP2 is a well-characterized single domain SCP2 from the yeast Yarrowia lipolytica. Herein, we report the X-ray structure of unliganded ylSCP2 refined to 2.0 A resolution. Comparison with the previously solved liganded ylSCP2 structure unveiled a novel mechanism for binding site occlusion. The liganded ylSCP2 binding site is a large cavity with a volume of more than 800 A3. In unliganded ylSCP2 the binding site is reduced to about 140 A3. The obliteration is caused by a swing movement of the C-terminal α helix 5 and a subtle compaction of helices 2–4. Previous pairwise comparisons were between homologous SCP2 domains with a uncertain binding status. The reported unliganded ylSCP2 structure allows for the first time a fully controlled comparative analysis of the conformational effects of ligand occupation dispelling several doubts regarding the architecture of SCP2 binding site.
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Binding properties of sterol carrier protein 2 (SCP2) characterized using Laurdan.
Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2018Co-Authors: Alejo R. Gianotti, Raúl G. Ferreyra, Mario R. ErmácoraAbstract:Abstract Sterol carrier protein 2 (SCP2) binds lipids with high affinity and broad specificity. The overall hydrophobicity, fluidity, and dipolar dynamics of the binding site of SCP2 from Yarrowia lipolytica were characterized using the environmentally-sensitive fluorescent probe Laurdan. The study revealed a binding site with an overall polarity similar to that of dichloromethane and an internal phase comparable to that of phospholipid membranes with coexisting solid-ordered and liquid-crystalline states. The fluorescence properties of bound Laurdan also revealed that the binding site of SCP2 can accommodate competitively more than one ligand, with micro and nanomolar dissociation constants. The much higher affinity for the second than for the first ligand implies that the most prominent SCP2 species in the cellular context are those occupied by two ligands. Thus SCP2 may carry a highly populated lipid in the background and a second one, specific for the functional purpose of SCP2. Our findings are important for the characterization of SCP2 biological functions and the design of specific inhibitors.
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A structural appraisal of sterol carrier protein 2.
Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics, 2017Co-Authors: Noelia I. Burgardt, Alejo R. Gianotti, Raúl G. Ferreyra, Mario R. ErmácoraAbstract:Sterol Carrier Protein 2 (SCP2) has been associated with lipid binding and transfer activities. However, genomic, proteomic, and structural studies revealed that it is an ubiquitous domain of complex proteins with a variety functions in all forms of life. High-resolution structures of representative SCP2 domains are available, encouraging a comprehensive review of the structural basis for its success. Most SCP2 domains pertain to three major families and are frequently found as stand-alone or at the C-termini of lipid related peroxisomal enzymes, acetyltransferases causing bacterial resistance, and bacterial environmentally important sulfatases. We (1) analyzed the structural basis of the fold and the classification of SCP2 domains; (2) identified structure-determined sequence features; (3) compared the lipid binding cavity of SCP2 and other lipid binding proteins; (4) surveyed proposed mechanisms of SCP2 mediated lipid transfer between membranes; and (5) uncovered a possible new function of the SCP2 domain as a protein-protein recognition device.
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The crystal structure of sterol carrier protein 2 from Yarrowia lipolytica and the evolutionary conservation of a large, non-specific lipid-binding cavity
Journal of Structural and Functional Genomics, 2013Co-Authors: Federico Perez Berti, Noelia I. Burgardt, Raúl G. Ferreyra, Stefano Capaldi, Juan P. Acierno, Sebastián Klinke, Hugo L. Monaco, Mario R. ErmácoraAbstract:Sterol carrier protein 2 (SCP2), a small intracellular domain present in all forms of life, binds with high affinity a broad spectrum of lipids. Due to its involvement in the metabolism of long-chain fatty acids and cholesterol uptake, it has been the focus of intense research in mammals and insects; much less characterized are SCP2 from other eukaryotic cells and microorganisms. We report here the X-ray structure of Yarrowia lipolytica SCP2 (YLSCP2) at 2.2 Å resolution in complex with palmitic acid. This is the first fungal SCP2 structure solved, and it consists of the canonical five-stranded β-sheet covered on the internal face by a layer of five α-helices. The overall fold is conserved among the SCP2 family, however, YLSCP2 is most similar to the SCP2 domain of human MFE-2, a bifunctional enzyme acting on peroxisomal β-oxidation. We have identified the common structural elements defining the shape and volume of the large binding cavity in all species characterized. Moreover, we found that the cavity of the SCP2 domains is distinctly formed by carbon atoms, containing neither organized water nor rigid polar interactions with the ligand. These features are in contrast with those of fatty acid binding proteins, whose internal cavities are more polar and contain bound water. The results will help to design experiments to unveil the SCP2 function in very different cellular contexts and metabolic conditions.
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A yeast sterol carrier protein with fatty-acid and fatty-acyl-CoA binding activity.
Archives of Biochemistry and Biophysics, 2006Co-Authors: Raúl G. Ferreyra, Noelia I. Burgardt, Daniel Milikowski, Gustavo J. Melen, Alberto R. Kornblihtt, Esteban C. Dell’ Angelica, José A. Santomé, Mario R. ErmácoraAbstract:Abstract The 14-kDa sterol carrier protein 2 (SCP2) domain is present in Eukaria, Bacteria and Archaea, and has been implicated in the transport and metabolism of lipids. We report the cloning, expression, purification and physicochemical characterization of a SCP2 from the yeast Yarrowia lipolytica (YLSCP2). Analytical size-exclusion chromatography, circular dichroism and fluorescence spectra, indicate that recombinant YLSCP2 is a well-folded monomer. Thermal unfolding experiments show that SCP2 maximal stability is at pH 7.0–9.0. YLSCP2 binds cis-parinaric acid and palmitoyl-CoA with KD values of 81 ± 40 nM and 73 ± 33 nM, respectively, sustaining for the first time the binding of fatty acids and their CoA esters to a nonanimal SCP2. The role of yeast SCP2 and other lipid binding proteins in transport, storage and peroxisomal oxidation of fatty acids is discussed.
Mark P. Mclean - One of the best experts on this subject based on the ideXlab platform.
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Characterization of a steroidogenic factor-1-binding site found in promoter of sterol carrier protein-2 gene.
Endocrine, 2001Co-Authors: Dayami Lopez, Wendy Shea-eaton, Mark P. McleanAbstract:Sterol carrier protein-2 (SCP2) is thought to mediate intracellular cholesterol transport in steroidogenic tissues. To elucidate the mechanism underlying the expression of this gene, a 300-bp fragment of the SCP2 promoter was cloned and analyzed for regulatory motifs. This promoter region contained a SF-1 binding motif, three activator protein-1 elements, an insulin response element, and a peroxisomal proliferator response element. The putative SF-1 binding region reacted with recombinant SF-1 DNA-binding domain in a mobility shift assay. The SCP2 promoter fragment was linked to a luciferase reporter gene and cotransfected in the presence or absence of SF-1 into HTB-9 cells. The results indicated that SF-1 was able to increase SCP2 promoter activity, an effect that was enhanced by cAMP. Similar results were obtained when the SCP2 promoter construct was cotransfected into Y1 cells. Cotransfection studies carried out in Kin 8 cells, a Y1 cell line with a mutation that prevents cAMP activation of PKA, revealed that a functional PKA is required for cAMP induction of SCP2 gene transcription. These results demonstrated that SF-1 confers cAMP responsiveness to the SCP2 promoter suggesting that SF-1 activation may be critical in regulation of this cholesterol transport protein.
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Reduced hepatic LDL-receptor, 3-hydroxy-3-methylglutaryl coenzyme A reductase and sterol carrier protein-2 expression is associated with pregnancy loss in the diabetic rat
Endocrine, 1995Co-Authors: Mark P. Mclean, Zhihong Zhao, Gene C. NessAbstract:Hepatic low density lipoprotein receptor (LDLR), 3-hydroxy-3-methylglutaryl coenyzme A reductase (HMGR), cholesterol 7α-hydroxylase, and sterol carrier protein-2 are important proteins associated with the uptake, synthesis, degradation and transport of cellular cholesterol. Since cholesterol is critically important for steroid hormone synthesis and is an essential component in membrane biosynthesis, this study investigated whether these proteins are altered in the normal pregnant and streptozotocin (STZ)-induced diabetic pregnant rat. The goal of these experiments was to determine whether diabetic reproductive dysfunction is associated with a significant change in maternal cholesterol homeostasis. Diabetic animals were grouped based on their ability or inability to maintain pregnancy up to day 15 post-conception. LDLR and HMGR mRNA levels were significantly reduced in animals which did not maintain pregnancy whereas diabetic animals with fetuses had normal LDLR and HMGR mRNA levels. Hepatic LDLR, HMGR, and SCP2 protein levels were examined in normal pregnant and diabetic pregnant animals by Western blot analysis. SCP2 levels were reduced in all diabetic animals, particularly in the diabetic animals which lost their fetuses. The decline in SCP2 was associated with an increase in sterol carrier protein-X (SCPx), a protein related to SCP2. SCPx has been shown to have thiolytic activity and is thought to have a role in β-oxidation of fatty acids. HMGR was also significantly reduced in diabetic animals which lost their fetuses. Cholesterol 7α-hydroxylase mRNA was slightly, but not significantly, reduced in all diabetic animals. Serum very low density lipoprotein (VLDL) +LDL cholesterol increased significantly in the STZ-treated diabetic rats while the HDL cholesterol levels declined in these animals. Reduced hepatic LDLR and HMGR mRNA levels were consistently associated with reduced serum progesterone and an inability to maintain pregnancy. The results of this study suggest that the maintenance of maternal cholesterol metabolism is a critical factor directly associated with successful pregnancy outcome in the diabetic rat.
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DIFFERENTIAL EXPRESSION OF HEPATIC STEROL CARRIER PROTEINS IN THE STREPTOZOTOCIN-TREATED DIABETIC RAT
Endocrinology, 1995Co-Authors: Mark P. Mclean, K. J. Warden, J.t. Billheimer, Rosalyn B IrbyAbstract:Sterol carrier protein-2 (SCP2) is a 13.2-kilodalton protein that has been implicated in intracellular cholesterol transport, whereas a related sterol carrier protein, sterol carrier protein-X (SCPx; 58 kilodaltons) has been suggested to function also in the beta-oxidation of fatty acids. Although diabetes-related hyperlipidemia and altered cholesterol metabolism have been extensively studied, the intracellular cholesterol transport capacity during hyperglycemic states has not been examined. The fact that beta-oxidation is increased in diabetes whereas hepatic cholesterol metabolism is reduced suggests that differential expression of these sterol carrier proteins may accompany diabetic dyslipidemia. In this study, SCP2 protein levels were reduced by 60% in mildly hypercholesterolemic (cholesterol, > 130 and 150 mg/dl; P < 0.002) diabetic animals. In contrast, hepatic SCPx protein expression increased (3.5-fold) after diabetes induction with streptozotocin (STZ). The decline in SCP2 was inversely related to serum cholesterol levels. Hepatic SCP messenger RNA levels examined by ribonuclease protection assay demonstrated that hepatic SCP messenger RNA was increased 2-fold in diabetic animals. Northern blot analysis indicated that both the 0.8-kilobase SCP2-specific and the 2.1-kilobase SCPx-specific transcripts increased after STZ injection. SCPx protein induction preceded the decline in SCP2 by 4-5 days. Insulin treatment reversed the increase in SCPx and prevented the decline in SCP2. We conclude that SCP2 and SCPx are differentially expressed in the STZ-diabetic rat and suggest that this change in SCP expression should be considered a potential contributing mechanism through which cholesterol metabolism may be altered in diabetes.
Rosalyn B Irby - One of the best experts on this subject based on the ideXlab platform.
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Reduced hepatic sterol carrier protein-2 expression in the streptozotocin treated diabetic rat
Endocrine, 1995Co-Authors: M. P. Mclean, Keisuke Nanjo, K. J. Warden, Rosalyn B Irby, Jeffrey T BillheimerAbstract:While a strong relationship between the hypercholesterolemia of diabetes and premature atherosclerosis is established, the etiology for the elevation in serum cholesterol in this disease is unknown. To determine whether diabetic hypercholesterolemia may be related to alterations in hepatic cholesterol transport capacity, sterol carrier protein-2 (SCP2) expression was examined in rats treated with streptozotocin (SZT). Furthermore, this study examined whether 17β-estradiol and insulin confer a protective effect on liver cholesterol homeostasis by maintaining hepatic SCP2 levels. SCP2 protein and mRNA expression were examined 13 days following SZT-induced diabetes onset and in diabetic rats treated with estradiol (1 cm silastic implant) or insulin (12 units/day). Data indicate that SCP2 protein levels were significantly reduced in the diabetic animals and that SCP2 protein expression in the liver was inversely related to the level of serum cholesterol in the diabetic animals. In contrast, SCP2 mRNA levels examined by slot blot, ribonuclease protection assay, and Northern blot analysis were significantly elevated. Both insulin and estradiol were able to enhance the expression of SCP2 protein in the liver following SZT treatment. The results of this investigation clearly indicate that hepatic SCP2 protein levels are significantly altered in the diabetic state suggesting that cholesterol transport capacity is reduced in the SZT-treated diabetic rat. The inverse relationship between serum cholesterol and hepatic SCP2 protein content suggests that the reduction in this protein may be a contributing factor in diabetic hypercholesterolemia.
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DIFFERENTIAL EXPRESSION OF HEPATIC STEROL CARRIER PROTEINS IN THE STREPTOZOTOCIN-TREATED DIABETIC RAT
Endocrinology, 1995Co-Authors: Mark P. Mclean, K. J. Warden, J.t. Billheimer, Rosalyn B IrbyAbstract:Sterol carrier protein-2 (SCP2) is a 13.2-kilodalton protein that has been implicated in intracellular cholesterol transport, whereas a related sterol carrier protein, sterol carrier protein-X (SCPx; 58 kilodaltons) has been suggested to function also in the beta-oxidation of fatty acids. Although diabetes-related hyperlipidemia and altered cholesterol metabolism have been extensively studied, the intracellular cholesterol transport capacity during hyperglycemic states has not been examined. The fact that beta-oxidation is increased in diabetes whereas hepatic cholesterol metabolism is reduced suggests that differential expression of these sterol carrier proteins may accompany diabetic dyslipidemia. In this study, SCP2 protein levels were reduced by 60% in mildly hypercholesterolemic (cholesterol, > 130 and 150 mg/dl; P < 0.002) diabetic animals. In contrast, hepatic SCPx protein expression increased (3.5-fold) after diabetes induction with streptozotocin (STZ). The decline in SCP2 was inversely related to serum cholesterol levels. Hepatic SCP messenger RNA levels examined by ribonuclease protection assay demonstrated that hepatic SCP messenger RNA was increased 2-fold in diabetic animals. Northern blot analysis indicated that both the 0.8-kilobase SCP2-specific and the 2.1-kilobase SCPx-specific transcripts increased after STZ injection. SCPx protein induction preceded the decline in SCP2 by 4-5 days. Insulin treatment reversed the increase in SCPx and prevented the decline in SCP2. We conclude that SCP2 and SCPx are differentially expressed in the STZ-diabetic rat and suggest that this change in SCP expression should be considered a potential contributing mechanism through which cholesterol metabolism may be altered in diabetes.