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Biomedical subjects

M E Gåfvels

Publications and source records attributed to M E Gåfvels.

9 recordsLinked to original sources
PubMed1996

Expression of very low density lipoprotein receptor in the vascular wall. Analysis of human tissues by in situ hybridization and immunohistochemistry.

The recently cloned very low density lipoprotein (VLDL) receptor binds triglyceride-rich, apolipoprotein-E-containing lipoproteins with high affinity. The observation that VLDL receptor mRNA is abundantly expressed in extracts of tissues such as skeletal muscle and heart, but not liver, has led to the hypothesis that this receptor may facilitate the peripheral uptake of triglyceride-rich lipoproteins. However, little information is available concerning the types of cells that express this receptor in vivo. As expression of the VLDL receptor in the vascular wall might have important implications for the uptake and transport of triglyceride-rich lipoproteins, and perhaps facilitate the development of atherosclerosis in hypertriglyceridemic individuals, we used in situ hybridization and immunohistochemistry to determine whether VLDL receptor mRNA and protein was expressed in human vascular tissue. We observed expression of the receptor by both endothelial and smooth muscle cells within normal arteries and veins, as well as within atherosclerotic plaques. In the latter, the VLDL receptor was also expressed by macrophage-derived foam cells. The widespread distribution of the VLDL receptor in vascular tissue suggests a potentially important role for this receptor in normal and pathophysiological vascular processes.

Arteriosclerosis↗
PubMed1995

Localization and regulation of the human very low density lipoprotein/apolipoprotein-E receptor: trophoblast expression predicts a role for the receptor in placental lipid transport.

The very low density lipoprotein/apolipoprotein-E receptor (VLDLR) is the newest member of the low density lipoprotein receptor (LDLR) family. Very little is known about VLDLR localization and regulation. Immunohistochemical analysis of human placenta with a specific polyclonal antibody detected VLDLR in syncytiotrophoblast and intermediate trophoblast cells. VLDLR transcripts were also localized in these cells by in situ hybridization histochemistry. In addition, VLDLR messenger RNA (mRNA) was detected in villous core endothelial cells and cells appearing to be Hofbauer cells. Northern blot analysis of placenta revealed a 2.6-fold increase in VLDLR mRNA at term compared to that in the first trimester. The regulation of VLDLR expression was studied in JEG-3 and BeWo choriocarcinoma cells, two trophoblast-derived cell lines. Treatment of these cells with 8-bromo-cAMP caused a profound suppression of VLDLR message, whereas LDLR transcripts were increased. Incubation of JEG-3 cells with 25-hydroxycholesterol did not lead to sterol negative feedback on VLDLR gene expression, unlike LDLR mRNA, which declined markedly. Insulin (200 mg/L) up-regulated VLDLR message in JEG-3 cells 2-fold, as did the fibrate hypolipidemic drug, clofibric acid. We conclude that 1) VLDLR is expressed in human placental trophoblast cells in a pattern consistent with a role in placental lipid transport; 2) VLDLR expression is high at term relative to that in the first trimester; and 3) the trophoblast VLDLR is subject to down-regulation by cAMP and up-regulation by insulin and fibrate hypolipidemic drugs.

Apolipoproteins↗
PubMed1994

The 39-kDa receptor-associated protein regulates ligand binding by the very low density lipoprotein receptor.

A 39-kDa receptor associated protein (RAP) binds and inhibits ligand binding by two members of the low density lipoprotein (LDL) receptor family, gp330 and low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor. To determine if additional members of the LDL receptor family may interact with RAP, Chinese hamster ovary cells were transfected with plasmids directing expression of the very low density lipoprotein (VLDL) receptor cDNA or the LDL receptor cDNA. Detergent-soluble extracts from these and normal Chinese hamster ovary cells were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, after which the proteins were transferred to nitrocellulose membranes and incubated with RAP. When detergent extracts from normal cells were incubated with RAP, several polypeptides, including a 130-kDa protein, were observed to bind RAP. In cells transfected with the VLDL receptor cDNA, a substantial increase in RAP binding to the 130-kDa polypeptide was noted. This protein was identified as the VLDL receptor by immunoblotting. The VLDL receptor present in detergent extracts from transfected cells bound to RAP-Sepharose, and a KD of 0.7 nM for the interaction between RAP and the purified VLDL receptor was determined using enzyme-linked immunosorbent assay. The purified VLDL receptor bound 125I-labeled VLDL, but not 125I-labeled LDL, and the binding of 125I-labeled VLDL was completely inhibited by RAP. Further, RAP inhibited the uptake and degradation of 125I-VLDL by cells overexpressing the VLDL receptor. Thus the VLDL receptor represents the third member of the LDL receptor family whose ligand binding properties are antagonized by RAP. This suggests a common functional role for RAP in modulating ligand binding by members of the LDL receptor family.

Amino Acid Sequence↗
PubMed1994

Cloning of a complementary deoxyribonucleic acid encoding the murine homolog of the very low density lipoprotein/apolipoprotein-E receptor: expression pattern and assignment of the gene to mouse chromosome 19.

We report the cloning of a complementary DNA for the mouse homolog of the very low density lipoprotein (VLDL)/apolipoprotein-E receptor (VLDLR), the deduced amino acid sequence of the protein, and the mapping of the gene encoding the receptor to mouse chromosome 19. Northern hybridization revealed that the VLDLR messenger RNA (mRNA) is most abundant in skeletal muscle, heart, kidney, and brain. It was also detected in lung and in low levels in liver, but it was not found in spleen or testes. Levels of VLDLR mRNA in mouse placenta increased from days 8-18 of gestation. The VLDLR mRNA was induced in 3T3-L1 cells undergoing differentiation into adipocytes. The increase in VLDLR mRNA paralleled the rise in lipoprotein lipase and hormone-sensitive lipase mRNAs. However, VLDLR and low density lipoprotein receptor-related protein were increased in the presence of retinoic acid, whereas the induction of lipoprotein lipase and hormone-sensitive lipase mRNAs was inhibited. Our observations demonstrate regulated expression of the VLDLR gene in placenta and adipocytes, where the receptor protein may play roles in the uptake of triglyceride-rich particles for storage of lipid (adipocytes) or for lipid transport to the fetus (placenta). The availability of a murine complementary DNA probe and the knowledge of the map position of the VLDLR gene in the mouse genome will facilitate studies on the function and regulation of this protein.

3T3 Cells↗
PubMed1994

Expression of alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein and the 39-kd receptor-associated protein in human trophoblasts.

The alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR/LRP) and its 39-kd receptor-associated protein (RAP) were identified by indirect immunofluorescence in human extravillous and villous trophoblast cells at different stages of pregnancy. The alpha 2MR/LRP was detected in invading trophoblast cells and in some instances these invading cells did not express RAP. In chorionic villi of first and second trimester placenta, alpha 2MR/LRP and RAP were found in cytotrophoblast and syncytiotrophoblast. With advancing pregnancy alpha 2MR/LRP became primarily localized to the apical surface of the syncytiotrophoblast, while RAP was present in the cytoplasm. Villous cytotrophoblast cells lost both proteins by the third trimester. Isolated cytotrophoblast cells that undergo spontaneous differentiation into syncytiotrophoblast in culture increased expression of both alpha 2MR/LRP and RAP. With syncytium formation, alpha 2MR/LRP became localized to the plasma membrane in cup-like structures. Changes in the mRNAs for alpha 2MR/LRP and RAP paralleled the changes in relative abundance of the proteins assessed by immunofluorescence. cAMP treatment suppressed both alpha 2MR/LRP and RAP in the cultured trophoblasts, but alpha 2MR/LRP was reduced to a greater extent than RAP. We conclude that alpha 2MR/LRP and RAP are developmentally regulated in human trophoblast cells, that the temporal and spatial patterns of expression of these proteins can be dissociated, and that cAMP modulates both alpha 2MR/LRP and RAP in human trophoblast. The patterns of alpha 2MR/LRP and RAP expression in trophoblast cells are consistent with roles for the receptor in trophoblast invasion and transport of molecules across the syncytiotrophoblast.

Carrier Proteins↗
PubMed1993

Cloning of a cDNA encoding a putative human very low density lipoprotein/apolipoprotein E receptor and assignment of the gene to chromosome 9pter-p23.

We report the cloning of a 3656-bp cDNA encoding a putative human very low density lipoprotein (VLDL)/apolipoprotein E (ApoE) receptor. The gene encoding this protein was mapped to chromosome 9pter-p23. Northern analysis of human RNA identified cognate mRNAs of 6.0 and 3.8 kb with most abundant expression in heart and skeletal muscle, followed by kidney, placenta, pancreas, and brain. The pattern of expression generally paralleled that of lipoprotein lipase mRNA but differed from that of the low density lipoprotein (LDL) receptor and the low density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor (LRP), which are members of the same gene family. VLDL/ApoE receptor message was not detected in liver, whereas mRNAs for both LDL receptor and LRP were found in hepatic tissue. In mouse 3T3-L1 cells, VLDL/ApoE receptor mRNA was induced during the transformation of the cells into adipocytes. Expression was also detected in human choriocarcinoma cells, suggesting that at least part of the expression observed in placenta may be in trophoblasts, cells which would be exposed to maternal blood. Expression in brain may be related to high levels of ApoE expression in that organ, an observation of potential relevance to the recently hypothesized role for ApoE in late onset Alzheimer disease. Our results suggest that the putative VLDL/ApoE receptor could play a role in the uptake of triglyceride-rich lipoprotein particles by specific organs including striated and cardiac muscle and adipose tissue and in the transport of maternal lipids across the placenta. The findings presented here, together with recent observations from other laboratories, bring up the possibility that a single gene, the VLDL/ApoE receptor, may play a role in the pathogenesis of certain forms of atherosclerosis, Alzheimer disease, and obesity.

3T3 Cells↗
PubMed1992

Regulated expression of the trophoblast alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein. Differentiation and cAMP modulate protein and mRNA levels.

The alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein (alpha 2MR/LRP) has several ligands including activated alpha 2-macroglobulin, pregnancy zone protein, and very low density lipoproteins enriched with apolipoprotein E. The diversity of ligands suggests a role for the alpha 2MR/LRP in a variety of processes including tissue remodeling and lipoprotein metabolism. We examined alpha 2MR/LRP in placental trophoblasts, invasive cells that also function in lipid transport and cholesterol metabolism. alpha 2MR/LRP protein was localized by immunohistochemistry in the syncytiotrophoblast of term placenta. Cytotrophoblasts did not stain prominently. alpha 2MR/LRP (protein and message) in primary cultures of human trophoblast cells increased as cytotrophoblasts differentiated into syncytiotrophoblast. 8-Bromo-cAMP prevented this increase and suppressed alpha 2MR/LRP expression. The cyclic nucleotide had similar suppressive effects on alpha 2MR/LRP in BeWo choriocarcinoma cells. In contrast, low density lipoprotein receptor gene expression was increased. We conclude that: 1) there is a differentiation-dependent pattern of alpha 2MR/LRP expression in the human trophoblast; 2) cAMP negatively regulates alpha 2MR/LRP; 3) there is an inverse relationship between alpha 2MR/LRP and low density lipoprotein receptor gene expression in trophoblast cells.

Base Sequence↗