VLDL Receptor mRNA Research Articles

Low Very low-Density Lipoprotein Cholesterol but High Very low-Density Lipoprotein Receptor mRNA Expression in Peripheral White Blood Cells: An Atherogenic Phenotype for Atherosclerosis in a Community-Based Population

Very low-density lipoprotein cholesterol (VLDL-C), via binding very low-density lipoprotein receptor (VLDLR), can induce the development of atherosclerosis. Besides monocytes, VLDLR expression is detected in various peripheral white blood cells (WBCs), yet its underlying role remains unclear. We thereby aimed to test the hypothesis that VLDLR in all types of peripheral WBCs may be involved in the association between VLDL-C and atherosclerosis. VLDLR mRNA expression in peripheral WBC and plasma VLDL-C levels were measured in 747 participants from a community-based study. Plaque prevalence and total plaque area (TPA) were used to evaluate the burden of carotid atherosclerosis. VLDL-C was positively associated with atherosclerosis risk, whereas this association was modified by VLDLR mRNA level. In participants with the lowest VLDL-C but the highest VLDLR mRNA expression, the risk for plaque prevalence unexpectedly was the highest. This association was also observed for TPA. Moreover, this association remained unchanged after adjusting for WBC or monocytes. Our findings described an atherogenic phenotype characterized by low VLDL-C but high VLDLR mRNA expression in peripheral WBCs, which suggested that VLDLR in all types of peripheral WBCs may be involved in lipid deposition, and VLDL-C and VLDLR may co-determine the development of atherosclerosis.

Use of Low‐Density Lipoprotein receptor and Very Low‐Density Lipoprotein Receptor as potential genetic markers to investigate the development of obesity in a non‐model fish species, Ictalurus punctarus

Dyslipidemia is a metabolic disorder that often develops in association with obesity. Most research regarding human metabolic disorders, including dyslipidemia, has been conducted using rodents. However, channel catfish selected for increased growth often develop obese‐like phenotype with increased fat accumulation in the abdomen, suggesting channel catfish can be useful in investigating the mechanism(s) associated with development of obesity in humans. Objectives of this experiment were to identify the genes encoding mRNA for two low density lipoprotein receptors (LDLrA and LDLrB) and examine their tissue distributions in channel catfish (Ictalurus punctarus). In addition, mRNA encoding very low density lipoprotein receptor (VLDLr) was identified and characterized. Channel catfish LDLrA, LDLrB, and VLDLr mRNA sequences were identified by screening the channel catfish genome database and their expression was examined in the brain, spleen, trunk kidney, liver, Bockmann body, and muscle. The PCR amplicon for respective mRNA was highly similar (>70%) with other species of fish. The sequences of LDLrA and LDLrB mRNA also shared a high degree of similarities (>65%) with rodents and humans. Expression of LDLrA and VLDLr mRNA sequences were detected at various levels in all tissues examined. LDLrB mRNA sequences were also detected at various levels in all tissues except in the brain. Currently, the changes in expression of the three mRNA expressions in relation to changes in food intake and development of obese‐like phenotype are being investigated.Support or Funding InformationThis research is supported by the Kansas Idea Network of Biomedical Research Excellence (P20GM103418).

Activation of PPAR-δ induces microRNA-100 and decreases the uptake of very low-density lipoprotein in endothelial cells.

Increased level of very low-density lipoprotein (VLDL) is a key feature of the metabolic syndrome and is associated with cardiovascular diseases. PPAR-δ agonists play a protective role in lipid metabolism and vascular function. In this study, we aimed to investigate the role of PPAR-δ in the uptake of VLDL in endothelial cells and its underlying mechanism(s). Uptake of VLDL in HUVECs was assessed by Dil-fluorescent labelling of VLDL. Levels of VLDL receptor mRNA and microRNA (miR-100) were detected by quantitative PCR. The target genes of miR-100 were predicted using bioinformatics analysis. 3'-Untranslated region (3'-UTR) luciferase reporter and Argonaute 1 pull-down assays were used to validate the target of miR-100. PPAR-δ agonist GW501516 decreased uptake of VLDL and expression of VLDL receptor at mRNA and protein levels. GW501516 inhibited the luciferase reporter activity of the 3'-UTR of VLDL receptor. VLDL receptor was a direct target of miR-100. miR-100 was significantly increased by GW501516 in HUVECs. Transfection of a miR-100 mimic decreased the mRNA and protein levels of VLDL receptor and uptake of VLDL. Furthermore, a miR-100 inhibitor abolished the inhibitory effect of PPAR-δ on VLDL receptor expression and VLDL uptake. In endothelial cells, activation of PPAR-δ decreased VLDL receptor expression and VLDL uptake via the induction of miR-100. These results provided a novel mechanism for the vascular protective effect of PPAR-δ agonists.

Energy replacement using glucose does not increase postprandial lipemia after moderate intensity exercise.

BackgroundAerobic exercise can decrease postprandial triglyceride (TG) concentrations but the relationship between exercise-induced energy deficits and postprandial lipemia is still unclear. The aim of the present study was to examine the effect of a single bout of aerobic exercise, with and without energy replacement, on postprandial lipemia and on peripheral blood mononuclear cell (PBMC) mRNA expression of very low density lipoprotein (VLDL) and low density lipoprotein (LDL) receptors and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR).MethodsNine healthy male humans completed three two-day trials in a random order. On day 1, volunteers rested (CON), completed 60 minutes of treadmill walking at 50% of VO2peak (EX) or completed the same bout of walking but with the energy replaced afterwards with a glucose solution (EXG). On day 2, volunteers rested and consumed a high fat test meal in the morning.ResultsTotal and incremental TG AUC were significantly lower on the EXG (P < 0.05) and EX (P < 0.05) trials than the CON trial with no difference between the two exercise trials. No significant difference was observed in VLDL or LDL receptor mRNA expression among the trials (P > 0.05).ConclusionsIn conclusion, energy replacement by glucose did not affect the decrease in postprandial TG concentrations observed after moderate intensity exercise and exercise does not affect changes in PBMC HMGCR, VLDL and LDL receptor mRNA expression.

Low density lipoprotein receptor–related protein 1 is upregulated in epicardial fat from type 2 diabetes mellitus patients and correlates with glucose and triglyceride plasma levels

Lipoprotein receptor expression plays a crucial role in the pathophysiology of adipose tissue in in vivo models of diabetes. However, there are no studies in diabetic patients. The aims of this study were to analyze (a) low-density lipoprotein receptor-related protein 1 (LRP1) and very low-density lipoprotein receptor (VLDLR) expression in epicardial and subcutaneous fat from type 2 diabetes mellitus compared with nondiabetic patients and (b) the possible correlation between the expression of these receptors and plasmatic parameters. Adipose tissue biopsy samples were obtained from diabetic (n = 54) and nondiabetic patients (n = 22) undergoing cardiac surgery before the initiation of cardiopulmonary bypass. Adipose LRP1 and VLDLR expression was analyzed at mRNA level by real-time PCR and at protein level by Western blot analysis. Adipose samples were also subjected to lipid extraction, and fat cholesterol ester, triglyceride, and free cholesterol contents were analyzed by thin-layer chromatography. LRP1 expression was higher in epicardial fat from diabetic compared with nondiabetic patients (mRNA 17.63 ± 11.37 versus 7.01 ± 4.86; P = 0.02; protein 11.23 ± 7.23 versus 6.75 ± 5.02, P = 0.04). VLDLR expression was also higher in epicardial fat from diabetic patients but only at mRNA level (231.25 ± 207.57 versus 56.64 ± 45.64, P = 0.02). No differences were found in the expression of LRP1 or VLDLR in the subcutaneous fat from diabetic compared with nondiabetic patients. Epicardial LRP1 and VLDLR mRNA overexpression positively correlated with plasma triglyceride levels (R(2) = 0.50, P = 0.01 and R(2) = 0.44, P = 0.03, respectively) and epicardial LRP1 also correlated with plasma glucose levels (R(2) = 0.33, P = 0.03). These results suggest that epicardial overexpression of certain lipoprotein receptors such as LRP1 and VLDLR expression may play a key role in the alterations of lipid metabolism associated with type 2 diabetes mellitus.

The Therapeutic Role of Very Low-Density Lipoprotein Receptor Gene in Hyperlipidemia in Type 2 Diabetic Rats

Hyperlipidemia is a common feature of type 2 diabetes and is related to cardiovascular disease. The very low-density lipoprotein receptor (VLDLR) binds to and internalizes triglyceride-rich lipoproteins with high specificity. In this study, we evaluated the role of VLDLR in hyperlipidemia in type 2 diabetic rats. Type 2 diabetes was induced in male Wistar rats by injection of low-dose streptozotocin coupled with a high-fat diet. Recombinant adeno-associated viral (rAAV) vectors encoding the human VLDLR gene (rAAV·VLDLR) were intravenously administered to diabetic rats. Results showed that in vivo, total VLDLR mRNA and protein levels were significantly decreased in skeletal muscle (type I VLDLR mainly reduced) and adipose tissue (type II VLDLR mainly reduced) but not in heart in hypercholesterolemic, hypertriglyceridemic diabetic rats compared with normal rats. And in vitro, in 3T3-L1 adipocytes, insulin-induced (1.0 mmol/liter) insulin resistance significantly decreased VLDLR mRNA expression. In rats, rAAV·VLDLR delivery resulted in a reduction in serum cholesterol and triglyceride that lasted for the duration of the study (12 weeks). Fasting blood insulin was significantly lower in the rAAV·VLDLR group versus untreated diabetic rats although fasting blood glucose levels were not significantly different in both groups at the end of the study. rAAV·VLDLR-treated animals had significantly increased lipoprotein lipase activity and reduced aortic atherosclerosis. Taken together, our data suggest that type 2 diabetes and related insulin resistance manifest decreased VLDLR with elevated serum cholesterol and triglyceride levels, and overexpression of VLDLR through a single injection of rAAV·VLDLR reversed these effects and consequentially attenuated aorta atherosclerotic plaque progression.

Peroxisome proliferator-activated receptor-γ regulates the expression and function of very-low-density lipoprotein receptor

Very-low-density lipoprotein receptor (VLDLR) is a member of the low-density receptor family, highly expressed in adipose tissue, heart, and skeletal muscle. It binds apolipoprotein E-triglyceride-rich lipoproteins and plays a significant role in triglyceride metabolism. PPARgamma is a primary regulator of lipid metabolism in adipocytes and controls the expression of an array of genes involved in lipid trafficking in adipocytes. However, it is not known whether VLDLR is also under the control of PPARgamma. In this study, we investigated the role of PPARgamma in the regulation of VLDLR expression and function in vivo and in vitro. During the differentiation of 3T3-L1 preadipocytes, the levels of VLDLR protein and mRNA increased in parallel with the induction of PPARgamma expression and reached maximum in mature adipocytes. Treatment of differentiated adipocytes with PPARgamma agonist pioglitazone upregulated VLDLR expression in dose- and time-dependent manners. In contrast, specific inhibition of PPARgamma significantly downregulated the protein level of VLDLR. Induction of VLDLR is also demonstrated in vivo in adipose tissue of wild-type (WT) mice treated with pioglitazone. In addition, pioglitazone increased plasma triglyceride-rich lipoprotein clearance and increased epididymal fat mass in WT mice but failed to induce similar effects in vldlr(-/-) mice. These results were further corroborated by the finding that pioglitazone treatment enhanced adipogenesis and lipid deposition in preadipocytes of WT mice, while its effect in VLDLR-null preadipocytes was significantly blunted. These findings provide direct evidence that VLDLR expression is regulated by PPARgamma and contributes in lipid uptake and adipogenesis.

Liver Carbohydrate and Lipid Metabolism of Insulin-Deficient Mice Is Altered by trans-10, cis-12 Conjugated Linoleic Acid ,

Feeding mice the trans-10, cis-12 (t10c12) conjugated linoleic acid (CLA) isomer is associated with lipodystrophy, insulin resistance, hyperinsulinemia, and liver steatosis. It has been hypothesized that CLA-induced liver steatosis is the result of increased hepatic lipogenesis stimulated by high insulin levels. We studied the effects of a 12-d t10c12CLA treatment (1 g/100 g diet) on liver carbohydrate and lipid metabolism in control and streptozotocin (STZ)-injected mice. STZ mice were characterized by insulin deficiency, hypertriglyceridemia, and depletion of liver triglyceride and glycogen. Remarkably, feeding t10c12CLA to diabetic mice (STZ-CLA) normalized these variables. Reconstitution of fat stores in the livers of STZ-CLA mice was associated with lower fatty acid (FA) oxidation rates and greater malonyl-CoA concentration than in STZ mice. FA translocase and VLDL receptor mRNA levels were greater in STZ-CLA than in STZ mice, suggesting that t10c12CLA increased liver lipid uptake. Phosphoenolpyruvate carboxykinase mRNA levels and AMP kinase phosphorylation were lower in STZ-CLA than in STZ mice, indicating that t10c12CLA may reduce glucogenic activity and promote glycogenesis in diabetic mice. Because glycemia and glucokinase expression were not modified by t10c12CLA treatment, we postulated that glycogen accumulation is likely not the result of an effect of t10c12CLA on plasma glucose utilization, but rather is due to the contribution of lactate, the concentration of which was higher in muscle of STZ-CLA mice. The results demonstrate that t10c12CLA stimulates liver lipid accumulation in the absence of insulin and, thus, suggest that t10c12CLA can improve liver carbohydrate and lipid metabolism in type I diabetic mice.

Overproduced interleukin 6 decreases blood lipid levels via upregulation of very-low-density lipoprotein receptor

BackgroundInterleukin 6 (IL6) blockade raises blood lipid levels in patients with rheumatoid arthritis.ObjectiveTo examine the influence of IL6 on lipid metabolism.MethodsVascular smooth muscle cells (VSMC) were cultured in the presence...

A neuronal VLDLR variant lacking the third complement-type repeat exhibits high capacity binding of apoE containing lipoproteins

Very-low-density lipoprotein receptor (VLDLR) is a multi ligand apolipoprotein E (apoE) receptor and is involved in brain development through Reelin signaling. Different forms of VLDLR can be generated by alternative splicing. VLDLR-I contains all exons. VLDLR-II lacks an O-linked sugar domain encoded by exon 16, while VLDLR-III lacks the third complement-type repeat in the ligand binding domain encoded by exon 4. We quantitatively compared lipoprotein binding to human VLDLR variants and analyzed their mRNA expression in both human cerebellum and mouse brain. VLDLR-III exhibited the highest capacity in binding to apoE enriched β-VLDL in vitro and was more effective in removing apoE containing lipoproteins from the circulation than other variants in vivo. In human cerebellum, the major species was VLDLR-II, while the second most abundant species was a newly identified VLDLR-IV which lacks both exon 4 and 16. VLDLR-I was present at low levels. In adult mice, exon 4 skipping varied between 30 and 47% in different brain regions, while exon 16 skipping ranged by 51–76%. Significantly higher levels of VLDLR proteins were found in mouse cerebellum and cerebral cortex than other regions. The deletions of exon 4 and exon 16 frequently occurred in primary neurons, indicating that newly identified variant VLDLR-IV is abundant in neurons. In contrast, VLDLR mRNA lacking exon 4 was not detectable in primary astrocytes. Such cell type-specific splicing patterns were found in both mouse cerebellum and cerebral cortex. These results suggest that a VLDLR variant lacking the third complement-type repeat is generated by neuron-specific alternative splicing. Such differential splicing may result in different lipid uptake in neurons and astrocytes.

Up-regulation of VLDL receptor expression and its signaling pathway induced by VLDL and β-VLDL

Very low density lipoprotein receptor (VLDLR) is thought to participate in the pathogenesis of atherosclerosis induced by VLDL and beta-VLDL. The present study was undertaken to elucidate the effects of VLDL and beta-VLDL on VLDLR expression and its signaling pathway. RAW264.7 cells were incubated with VLDL and beta-VLDL. The expression of VLDLR mRNA was detected by RT-PCR. The transcriptional activity of VLDLR gene was detected in recombinant plasmid pGL4.2VR-luciferase transfected RAW264.7. Western blot assay was used to detect the changes of phosphorylated ERK1/2 protein. Inhibitors or activators were used to observe the signal pathway involving VLDLR expression regulation. The results showed that VLDL and beta-VLDL stimulated ERK1/2 activity in a PKC-dependent manner. VLDL or beta-VLDL-induced VLDLR expression on macrophages was extremely abolished by inhibitors ERK1/2 or PKC. Our findings revealed that VLDL or beta-VLDL-induced VLDLR expression via PKC/ERK cascades and the effect was linked to the transcriptional activation of VLDLR gene promoter.

Adiponectin Reduces Plasma Triglyceride by Increasing VLDL Triglyceride Catabolism

OBJECTIVE—Adiponectin is an adipocyte-derived hormone that plays an important role in glucose and lipid metabolism. The main aims of this study are to investigate the effects of adiponectin on VLDL triglyceride (VLDL-TG) metabolism and the underlying mechanism.RESEARCH DESIGN AND METHODS—Adenoviruses were used to generate a mouse model with elevated circulating adiponectin. HepG2 and C2C12 cells were treated with recombinant human adiponectin.RESULTS—Three days after Ad-mACRP30 adenovirus injection, plasma adiponectin protein levels were increased 12-fold. All three main multimeric adiponectin molecules were proportionally elevated. Fasting plasma TG levels were significantly decreased (∼40%) in the mice with elevated adiponectin in circulation, as were the plasma levels of large and medium VLDL subclasses. Although apolipoprotein B mRNA levels were robustly suppressed in the livers of adiponectin-overexpressing mice and in cultured HepG2 cells treated with recombinant human adiponectin, hepatic VLDL-TG secretion rates were not altered by elevated plasma adiponectin. However, Ad-mACRP30–treated mice exhibited a significant increase of postheparin plasma lipoprotein lipase (LPL) activity compared with mice that received control viral vector. Skeletal muscle LPL activity and mRNA levels of LPL and VLDL receptor (VLDLr) were also increased in Ad-mACRP30–treated mice. Recombinant human adiponectin treatment increased LPL and VLDLr mRNA levels in differentiated C1C12 myotubes.CONCLUSIONS—These results suggest that adiponectin decreases plasma TG levels by increasing skeletal muscle LPL and VLDLr expression and consequently VLDL-TG catabolism.

Decreased expression of reelin receptor VLDLR in peripheral lymphocytes of drug-naive schizophrenic patients

Reelin, a secretory protease that plays major roles in neurodevelopment and synaptic plasticity, may also play a role in the pathogenesis of schizophrenia. The present study was undertaken to examine whether the expression of two receptors for reelin, very low-density lipoprotein receptor (VLDLR) and apolipoprotein E receptor type 2 (ApoER2), were abnormal in peripheral blood lymphocytes of schizophrenic patients. In this study, we measured the mRNA levels of VLDLR and ApoER2 in blood lymphocytes from patients with schizophrenia (drug-naive patients (n = 20) and medicated patients (n = 20)) and age-and gender-matched healthy controls (n = 40) using quantitative real-time RT-PCR. Furthermore, we examined the correlation between mRNA levels and clinical variables in patients. Levels of VLDLR mRNA in drug-naive, unmedicated patients with schizophrenia were significantly lower than those of controls. In contrast, levels of ApoER2 mRNA in drug-naive patients did not differ from those of controls, although the levels of ApoER2 mRNA in medicated patients were significantly lower than those of controls. Interestingly, levels of VLDLR mRNA in drug-naive patients showed significant increases with respect to baseline after six months of antipsychotic treatment, whereas levels of ApoER2 mRNA were significantly lower than baseline after six months of treatment. In all patients, there was a negative correlation between VLDLR mRNA levels and the severity of clinical symptoms. Our findings suggest that peripheral VLDLR mRNA levels may serve as a reliable peripheral biological marker of schizophrenia, and that the reelin-VLDLR/ApoER2 signaling pathway plays a role in the pathophysiology of schizophrenia.

LIPOPROTEIN SUPPORT OF STEROIDOGENESIS BY LUTEINIZING MACAQUE GRANULOSA CELLS: DIFFERENTIAL EFFECTS OF VLDL, LDL, AND HDL

Circulating lipoproteins are hypothesized to deliver cholesterol as substrate for ovarian steroidogenesis. The present study was designed to determine which of the 3 main lipoproteins (very low density [VLDL], low density [LDL], high density [HDL]) is the preferred source of cholesterol to support human chorionic gonadotropin (hCG)-stimulated progesterone (P) production by primate granulosa cells. Following the onset of menstruation, adult female rhesus monkeys were treated with recombinant human FSH (r-hFSH) for 7 days and non-luteinized granulosa cells were aspirated by an ultra-sound guided procedure. Some animals received FSH for 7 days followed by hCG for up to 24 hr to initiate periovulatory events before aspiration. Non-luteinized cells were cultured in serum-free media with hFSH (25 ng/ml) or hCG (20 IU/ml) + hFSH for up to 48 hrs. The expression of VLDL receptor mRNA decreased (p<0.05) within 3 hr of hCG administration in vivo, while LDL receptor mRNA increased (p<0.05) by 3–12 hr post-hCG and returned to pre-hCG levels at 24 hr. The expression of scavenger receptor-BI (SR-BI) mRNA increased by 6 hr and was maintained throughout 24 hr. Similar results were obtained from non-luteinized granulosa cells treated with FSH+hCG in vitro. VLDL, LDL, or HDL were added to cultures based either on molar concentration of lipoproteins (5, 25, 50 nM) or cholesterol content (1, 5, 10 microg/ml) for 24 hr (0–24 hr) in the presence of FSH or FSH+hCG. Alternatively, cells were cultured in the presence of only FSH or FSH+hCG for 24 hr to deplete stored cholesterol, and treated subsequently with lipoproteins for the next 24 hr (24–48 hr). During the initial 24 hr culture interval (0–24 hr), levels of P in lipoprotein-free media were significantly higher (p<0.05) in FSH+hCG treated cultures versus FSH only, suggesting the use of stored cholesterol. Molar equivalents of VLDL and LDL dose-dependently increased (p<0.05) hCG-stimulated P 0–24 hr, while HDL did not alter P synthesis. When lipoproteins were balanced to cholesterol content, similar results were obtained. In the absence of lipoproteins, P levels were not increased significantly by FSH+hCG vs FSH alone after 48 hr (24–48 hr), suggesting depletion of stored cholesterol esters between 24 and 48 hr after hCG treatment. The addition of VLDL and LDL during the 24–48 hr interval increased P levels in hCG-stimulated cells whether balanced to molar concentrations of lipoproteins or to cholesterol. Lipases involved in lipid metabolism (monoacylglycerol lipase [MGL]) and hydrolysis of estrified cholesterol (hormone sensitive lipase [HSL]) were examined to determine their role in P synthesis in vitro. Inhibitors of both MGL (0–100 microM) and HSL (0–400 mM) dose-dependently decreased (p<0.05) hCG-induced P synthesis after 6 hr. It is concluded that steroidogenesis by primate granulosa cells is supported primarily by stored cholesterol during the first 24 hr after an ovulatory stimulus, and thereafter by LDL and VLDL, but not HDL. The use of cholesterol stores during early luteinization is most likely mediated by hCG-activated lipases such as monoacylglycerol lipase and hormone sensitive lipase. The increased expression of LDL receptor and SR-BI after hCG suggest that either or both of these lipoprotein receptors mediate the use of LDL and VLDL during luteinization of primate granulosa cells. Supported in part by NIH HD043358 (CLC), RR13439 (CAV), RR00169 (CNPRC), HL075646 (AR). (poster)

Dietary Diacylglycerol Induces the Regression of Atherosclerosis in Rabbits ,2

Recent studies of the relation between serum triacylglycerol concentration and the risk for coronary artery disease suggest that inefficient clearance of postprandial triacylglycerols promotes atherogenesis. We recently demonstrated that dietary diacylglycerol (DAG), rich in the 1,3-species, suppresses the postprandial increase in serum triacylglycerol levels compared with dietary triacylglycerol (TAG). Here, we investigated the effects of dietary DAG on atherosclerosis in rabbits with cholesterol-induced atherosclerosis. New Zealand White rabbits (n = 20) were fed a diet containing 3% lard and 1.3% cholesterol for 50 d to induce atherosclerotic lesions. Thereafter, the rabbits were assigned to 2 groups and fed 90 g/d nonpurified diet and orally administered 5 g DAG or TAG for an additional 34 d. Reference rabbits (n = 5) were fed only the nonpurified diet throughout the 84-d study. The area of atherosclerotic lesions and aortic lipid concentrations were significantly lower in DAG-fed rabbits compared with TAG-fed rabbits. The VLDL receptor and macrophage antigen-1 mRNA expression levels were significantly lower in DAG-fed rabbits than in TAG-fed rabbits. In the liver of DAG-fed rabbits, the triacylglycerol concentration was lower and the carnitine palmitoyltransferase activity higher than in TAG-fed rabbits. Stimulation of hepatic lipid catabolism might be related to the reduced lipid accumulation in the liver and aorta by reducing the release of triacylglycerol into the circulation. Thus, long-term consumption of DAG, which reduces postprandial lipemia, might be useful for the regression of atherosclerosis by stimulating hepatic lipid catabolism and thereby modulating monocyte/macrophage migration and aortic lipid accumulation.

Localization of functional Reelin receptors as revealed by alkaline phosphatase–Reelin fusion protein

Reelin, a secretory protease that plays major roles in neurodevelopment and synaptic plasticity, may also play a role in the pathogenesis of schizophrenia. The present study was undertaken to examine whether the expression of two receptors for reelin, very low-density lipoprotein receptor (VLDLR) and apolipoprotein E receptor type 2 (ApoER2), were abnormal in peripheral blood lymphocytes of schizophrenic patients. In this study, we measured the mRNA levels of VLDLR and ApoER2 in blood lymphocytes from patients with schizophrenia (drug-naive patients (n = 20) and medicated patients (n = 20)) and age-and gender-matched healthy controls (n = 40) using quantitative real-time RT-PCR. Furthermore, we examined the correlation between mRNA levels and clinical variables in patients. Levels of VLDLR mRNA in drug-naive, unmedicated patients with schizophrenia were significantly lower than those of controls. In contrast, levels of ApoER2 mRNA in drug-naive patients did not differ from those of controls, although the levels of ApoER2 mRNA in medicated patients were significantly lower than those of controls. Interestingly, levels of VLDLR mRNA in drug-naive patients showed significant increases with respect to baseline after six months of antipsychotic treatment, whereas levels of ApoER2 mRNA were significantly lower than baseline after six months of treatment. In all patients, there was a negative correlation between VLDLR mRNA levels and the severity of clinical symptoms. Our findings suggest that peripheral VLDLR mRNA levels may serve as a reliable peripheral biological marker of schizophrenia, and that the reelin-VLDLR/ApoER2 signaling pathway plays a role in the pathophysiology of schizophrenia.

Deficiency of the Very Low-Density Lipoprotein (VLDL) Receptors in Streptozotocin-Induced Diabetic Rats: Insulin Dependency of the VLDL Receptor

Hyperlipidemia is a common feature of diabetes and is related to cardiovascular disease. The very low-density lipoprotein receptor (VLDL-R) is a member of the low-density lipoprotein receptor (LDL-R) family. It binds and internalizes triglyceride-rich lipoproteins with high specificity. We examined the etiology of hyperlipidemia in the insulin-deficient state. VLDL-R expression in heart and skeletal muscle were measured in rats with streptozotocin (STZ)-induced diabetes. STZ rats showed severe hyperlipidemia on d 21 and 28, with a dramatic decline in VLDL-R protein in skeletal muscle (>90%), heart (approximately 50%) and a loss of adipose tissues itself on d 28. The reduction of VLDL-R protein in skeletal muscle could not be explained simply by a decrease at the transcriptional level, because a dissociation between VLDL-R protein and mRNA expression was observed. The expression of LDL-R and LDL-R-related protein in liver showed no consistent changes. Furthermore, no effect on VLDL-triglyceride production in liver was observed in STZ rats. A decrease in postheparin plasma lipoprotein lipase activity started on d 7 and continued to d 28 at the 50% level even though severe hyperlipidemia was detected only on d 21 and 28. In rat myoblast cells, serum deprivation for 24 h induced a reduction in VLDL-R proteins. Insulin (10(-6) m), but not IGF-I (10 ng/ml), restored the decreased VLDL-R proteins by serum deprivation. These results suggest that the combination of VLDL-R deficiency and reduced plasma lipoprotein lipase activity may be responsible for severe hyperlipidemia in insulin-deficient diabetes.

Beta-VLDL induced VLDL-R's up-regulation via PKC-ERK1/2 signal pathway.

To explore the intracellular signal pathways for beta-VLDL induced very low density lipoprotein receptor (VLDL-R) transcription up-regulation and their effects on lipid accumulation in macrophages, Western Blot was used to examine phosphorylated ERK1/2 protein and regulated effects by different singal kinase inhibitants. It was found that beta-VLDL induced an increase in ERK1/2 activity in a protein kinase C (PKC)-dependent manner in murine RAW264.7 macrophages. By using different protein kinases inhibitors or activators, it was observed that the effect of beta-VLDL induced VLDL receptor transcription, which was monitored by RT-PCR analysis of VLDL receptor mRNA, was not affected by the inhibitor of p38 kinase and cAMP analog, but extremely abolished by pretreating cells with PD98059, an inhibitor of ERK and GF 109203X, an inhibitor of PKC. These results demonstrated that the PKC-ERK1/2 cascade is the essential signaling pathway by which beta-VLDL activated VLDL-R mRNA expression. Inhibition of the ERK1/2 signaling cascade resulted in suppression of the cellular lipid accumulation induced by beta-VLDL in macrophages.

Induction of very low density lipoprotein receptor (VLDLR) transcription by VLDL is mediated by the extracellular signal-regulated kinase signaling pathway.

To elucidate the intracellular signaling pathways for VLDL-induced VLDLR transcription, Western blot analysis was used to examine phosphorylated ERK1/2 protein. It was found that that VLDL induced an increase in ERK1/2 activity in a protein kinase C (PKC)-dependent manner in murine RAW264.7 macrophages. By using different protein kinases inhibitors or activators it was observed that the effect of VLDL-induced VLDL receptor transcription, which is monitored by RTPCR analysis of VLDL receptor mRNA, was not affected by the inhibitor of p38 kinase and cAMP analog, but completely abolished by pretreatment of the cells with PD 98059, an inhibitor of MEK and GF 109203X, an inhibitor of PKC. These results demonstrated that the PKC/ERK1/2 cascade is the essential signaling pathway by which VLDL activates VLDL receptor mRNA expression.

Dexamethasone stimulates very low density lipoprotein (VLDL) receptor gene expression in differentiating 3T3-L1 cells

To characterize endocrine mechanisms of very low density lipoprotein (VLDL) receptor regulation we studied mouse adipocytic 3T3-L1 cells. Lipid filled adipocyte-like cells are formed during a 5–7 day time course in the presence of insulin, dexamethasone and isobutylmethylxanthine (IBMX). The VLDL receptor protein, in the form of its ≈120 and ≈100 kDa type I and type II isoforms, as well as binding of 125I-β-VLDL, was induced several-fold during differentiation. Among the three different constituents added to the culture medium only dexamethasone (1 μM), but not insulin or IBMX, induced a time- and dose-dependent increase of VLDL receptor expression. Inclusion of RU-486 (10 μM) blocked the stimulatory effect of dexamethasone on VLDL receptor mRNA and protein levels. 3.6 kb of the 5′-untranslated region representing the VLDL receptor promoter were cloned and sequenced, and the transcriptional start site was determined by primer extension to be located 574 bases upstream from the initiating methionine. To investigate the functionality of the promoter, luciferase reporter gene constructs for the region −181 to −3726 bases were assembled and transfected into 3T3-L1 cells. An increased reporter gene activity was recorded when comparing preconfluent cells to fully differentiated cells. Between day 0 and day 2 (48 h after transfection) reporter gene activity was induced by dexamethasone, but not by insulin or IBMX. RU-486 inhibited this stimulatory effect for all constructs tested. No classical glucocorticoid receptor (GR) response element was found in the sequenced region of the VLDL receptor promoter. Thus, an indirect stimulatory effect mediated via GR on VLDL receptor gene transcription is the most likely mechanism of VLDL receptor gene activation in differentiating 3T3-L1 cells.