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Factors predisposing to the phenotypic features of hypertriglyceridemia have not been clearly defined. Here we report an association between a missense coding region polymorphism Asn985Tyr in the retinitis pigmentosa 1 gene ( RP1) and plasma triglyceride (TG) levels in 332 adult individuals from an east-central area of Japan. Age and gender-adjusted levels of LDL-cholesterol, TG, and HDL-cholesterol were analyzed. When we separate the subjects into two genotypic groups regarding this amino acid variation, those who lack the 985-Asn allele (asparagine at residue 985) had significantly higher plasma TG levels than the others who had at least one 985-Asn allele (mean: 175.8 mg/dl vs 123.3 mg/dl; P=0.0006, Mann-Whitney test). Similarly, the former subjects had significantly lower HDL-cholesterol levels than the latter (mean: 48.0 mg/dl vs 53.8 mg/dl; P=0.038). Of the 280 individuals without a 985-Asn allele, approximately half of the individuals presented with hypertriglyceridemia, whereas only a quarter were hypertriglyceridemic among 52 individuals with the 985-Asn allele ( P=0.04). Although this SNP marker may itself be in linkage disequilibrium with other unexamined functional variants within this locus, our data suggest that genetic variation at the RP1 locus is one of the likely candidate determinants for plasma triglyceride and HDL-cholesterol metabolisms.

Factors predisposing to the phenotypic features of higher total cholesterol (TC) have not been clearly defined. Here we report an association between a promoter SNP (-1323T>C) in G-substrate gene (GSBS) and TC levels in 368 adult individuals from an east-central area of Japan. Age and gender-adjusted levels of LDL-cholesterol, TG, TC, and HDL-cholesterol were analyzed. When we separate the subjects into two genotypic groups regarding T allele, those who bear the T allele had significantly higher plasma TC levels than the others who lack the T allele (mean; 239.6 mg/dl vs. 210.6 mg/dl; p=0.003; Mann-Whitney test). Of the 341 individuals with the T allele, approximately 80% individuals presented with hypercholesterolemia, whereas only 44% were hypercholesterolemic among the 27 individuals without the T allele (p=0.0001). These results indicate a significant elevating effect of plasma TC levels by a SNP in the putative regulatory region of the G-substrate gene in our studied population. These data suggest that genetic variation at the G-substrate gene may be one of the determinants for plasma lipoprotein levels.

To clarify the mechanism of smooth muscle cell (SMC)-derived foam cell formation, we investigated beta-very low density lipoprotein (beta-VLDL) cholesterol metabolism in vascular medial SMCs (M-SMCs) from normal rabbits compared with intimal SMCs (I-SMCs) from normal rabbits fed a high-cholesterol diet and LDL receptor-deficient rabbits. For both types of I-SMCs, uptake of [3H]cholesteryl oleate labeled beta-VLDL increased 1.6 times and release of [3H]cholesterol decreased 40% compared with M-SMCs. M-SMCs took up part of the beta-VLDL through the LDL receptor but I-SMCs did not. mRNAs for the VLDL receptor and the LDL receptor relative with 11 ligand binding repeats were expressed at similar levels in all SMCs. M-SMCs expressed more LDL receptor-related protein than I-SMCs. Ligand blotting analysis revealed greater 125I-beta-VLDL binding to a 700-kDa protein in I-SMCs compared with M-SMCs. I-SMCs had higher activities of acid cholesterol esterase and acyl-CoA:cholesterol acyltransferase, and lower activity of neutral cholesterol esterase than M-SMCs in both the absence and the presence of beta-VLDL. These results indicate that I-SMCs accumulate more cholesteryl ester than M-SMCs by taking up more beta-VLDL and by effluxing less cholesterol.

Platelet-derived growth factor (PDGF) stimulates expression of matrix metalloproteinases (MMPs), including stromelysin-1 (MMP-3). Induction of these expressions is known to occur during the course of atherosclerosis, tumor invasion, and metastasis. We investigated PDGF-alpha receptor (alphaR)- and beta receptor (betaR)-mediated signaling pathways for the expression of MMP-3 and invasion activity using porcine aortic endothelial (PAE) cells with stable expression of normal or mutated PDGF receptors. RT-PCR and Western blot analyses revealed that PDGF-BB induces MMP-3 expression in PAE cells that exclusively express either the PDGF-alphaR or the -betaR, but not in non-transfected control cells. To identify the signals necessary for PDGF receptor-mediated induction of MMP-3 expression, several lines of PAE cells expressing mutant PDGF receptors were further analyzed. Cells expressing mutant PDGF receptors unable to associate with Src or PLCgamma, retained the ability to induce MMP-3 expression as a result of PDGF-BB stimulation. However, incubation with PDGF-BB did not induce MMP-3 expression in cells expressing a mutant PDGF-betaR unable to associate with phosphatidylinositol 3(')-kinase (PI3K). LY294002, a PI3K inhibitor, reduced PDGF-BB-stimulated MMP-3 expression in PAE cells expressing wild-type PDGF receptors. In contrast, PDGF-BB induced MMP-3 expression in the presence of U-73122, a PLCgamma inhibitor. Moreover, PDGF-BB enhanced the invasiveness of cells expressing wild type PDGF-beta receptors, but not of cells expressing mutant PDGF-betaRs impaired in their ability to associate with PI3K. In light of these results, it appears that PDGF-BB is capable of inducing MMP-3 expression through both the PDGF-alphaR and the -betaR, and the effects are contributed by the PI3K-mediated transduction pathways., ((c) 2002 Elsevier Science (USA).)

We have previously reported a potent and specific cholesteryl ester transfer protein (CETP) inhibitor JTT-705 was a potentially anti-atherogenic compound (Nature 406 (2000) 203). In the present study, we investigated in vitro how this compound affects properties of high density lipoprotein (HDL) in Japanese white (JW) rabbits in terms of reverse cholesterol transport in J774 macrophages. Plasma HDL-cholesterol (C) level was significantly higher in the rabbits administered JTT-705 than in control rabbits on days 3 and 7. Both HDL(2) and HDL(3)-C levels were also significantly higher in JTT-705-administered rabbits than in control rabbits. During this period, plasma CETP activity was kept lower in JTT-705-administered rabbits than in controls. To determine how this compound affects the property of HDL particles, we investigated the C efflux induced by HDL from JTT-705-administered and control rabbits in J774 macrophages. Cholesterol ester (CE) concentration in J774 macrophages was reduced in proportion with increasing concentration of the added HDL to the culture media for J774 macrophages in both groups, suggesting that the HDL from JTT-705-administered rabbits was able to reduce CE concentration in J774 macrophages as efficiently as that from control rabbits. This result, together with the finding that the absolute HDL concentration increased in JW rabbits administered this CETP inhibitor, suggests that treatment with this new compound causes a beneficial effect on lipid metabolism in terms of anti-atherogenicity.

Background: LR11, a member of the LDL receptor family, is highly expressed in vascular smooth muscle cells (SMCs) of the hyperplastic intima but not media. To further clarify the involvement of LR11 in the process of atherosclerosis, we have characterized the migration and invasion activities of LR11-overexpressing SMCs., Methods and Results: LR11 cDNA was transfected into the rat SMC line A7r5. Compared with mock cells (C-1), in the presence of platelet-derived growth factor-BB, the transfected cells (R-1 and R-2) showed 3.5- to 4.0-fold higher expression of LR11 protein, 1.7- to 1.8-fold increased migration, and 2.0- to 2.2-fold elevated invasion activities, respectively. The increases were essentially abolished by the addition of receptor-associated protein, anti-LR11 antibodies, or apolipoprotein E. Immunological analyses showed that urokinase-type plasminogen activator receptor (uPAR) levels were increased in LR11-overexpressing cells. Anti-urokinase-type plasminogen activator (uPA) and anti-uPAR antibodies reduced the migration and invasion activities of R-1 and R-2 cells to baseline levels. Receptor-associated protein, anti-LR11 antibodies, and apolipoprotein E decreased uPAR expression in the LR11-overexpressing cells by approximately 50%. Cellular catabolism of uPAR was significantly decreased in R-1 and R-2 cells compared with control. Cultured SMCs isolated from intima of atherosclerotic rabbit aortas showed increased expression levels of LR11 and uPAR and enhanced migration and invasion compared with SMCs from medial layers., Conclusions: Overexpression of LR11 induces enhanced migration and invasion activities of intimal SMCs in vitro, probably through its regulation of the uPA/uPAR system.

Recent establishment of a sensitive ELISA system using antibodies against malondialdehyde-modified low density lipoprotein (MDA-LDL) made it possible to determine the circulating oxidized lipoprotein levels. Here, we investigated the serum levels of MDA-LDL in 62 patients with coronary artery disease (CAD) compared with the levels in 42 patients without CAD [groups CAD(+) and CAD(-), respectively], which are adjusted for age, serum total cholesterol, LDL and high density lipoprotein cholesterol, and triglyceride levels. Serum MDA-LDL levels were 113.4+/-49.1 IU/L in CAD(+), which were significantly higher than the levels in CAD(-) (85.2+/-22.5 IU/L, P<0.0005). The ratio of MDA-LDL/LDL cholesterol was 0.95+/-0.32 in CAD(+), indicating a significant increase compared with the ratio in CAD(-) (0.68+/-0.19, P<0.0005). The positive correlation of MDA-LDL level and the ratio of MDA-LDL/LDL cholesterol with intima-media thickness in carotid arteries was observed. Age was not clearly associated with the MDA-LDL level (P=0.865). The serum MDA level was positively correlated with LDL cholesterol (P<0.0001) and with triglycerides (P<0.001) and negatively correlated with high density lipoprotein cholesterol (P<0.05). Furthermore, the MDA-LDL level was negatively correlated with the peak size of the LDL particle (P<0.01). The LDL subclasses that were identified by using the sera collected from the subjects by sequential ultracentrifugation showed that the ratios of MDA-LDL/apolipoprotein B in LDL3 and LDL4 were nearly 3-fold higher than those in LDL1 and LDL2 for CAD(+) and CAD(-). These results indicate that the circulating MDA-LDL level is increased in CAD(+), independent of the serum LDL cholesterol level but in association with the peak size of LDL particles. The measurement of serum MDA-LDL level may be useful for the identification of patients with advanced atherosclerosis.

Patients with heterozygous familial hypercholesterolemia (FH) were examined with B-mode ultrasound in order to determine intima-media thickness (IMT) in the common carotid artery, and to uncover potential risk factors responsible for the development of IMT. Ninety seven FH subjects and 132 non FH type IIa hyperlipidemic subjects were involved in the present study. Age was found to correlate positively with IMT in both FH and non FH groups. FH individuals showed a higher IMT, along with elevated low density lipoprotein (LDL) cholesterol levels, compared with age-matched non FH individuals. To clarify potential factors contributing to the formation and development of carotid atherosclerosis, we divided the FH subjects into two subgroups, namely FH with high IMT group (HIG), and those with low IMT group (LIG). We investigated those two subgroups on the presence of angiographically documented coronary heart disease (CHD), of family history of CHD and of 'midband lipoproteins' by polyacrylamide gel electrophoresis (PAGE) analysis, by matching for age and LDL-cholesterol (LDL-C) level. Fifty percent of FH men in HIG was found to have CHD, whereas only 14% of those in LIG had CHD (P<0.05). Thirty-three percent of FH women in HIG was found to have CHD, whereas only 12% of those in LIG had CHD (P<0.05). Fifty percent of FH men in HIG was found to have 'midband lipoproteins', whereas only 7% of those in LIG had 'midband lipoproteins' (P<0.01). Seventy-three percent of FH women in HIG had 'midband lipoproteins', whereas only 21% of those in LIG had 'midband lipoproteins' (P<0.0005). Fifty-five percent of FH men in HIG was had positive family history for CHD, whereas only 14% of those in LIG had positive family history for CHD (P<0.05). Sixty-three percent of FH women in HIG was found to have positive family history for CHD, whereas only 29% of those in LIG had positive family history for CHD (P<0.05). Based on these findings, we propose that, besides age and elevated levels of LDL-C, positive family history for CHD and 'midband lipoproteins' are important determinants for the development of carotid atherosclerosis in FH individuals in Japanese population.

We report a 43-year-old Japanese man with hypobetalipoproteinemia likely due to apolipoprotein (apo) B-76, a new truncation of apo B, and with homozygosity for the apo E2 isoform. He had no history suggestive of fat malabsorption and no sign of neurological disorder. His fasting baseline serum low-density lipoprotein (LDL) cholesterol and apo B levels were approximately half of normal. His plasma apo E level was elevated and its phenotype showed the E2/E2 homozygote. SDS-polyacrylamide gel electrophoresis of delipidated LDL fraction revealed a new truncated apo B, designated as apo B-76 according to the centile system of nomenclature. The postprandial lipid metabolism of the patient showed an almost normal response after fat loading.

Since the molecular identification of the low density lipoprotein receptor (LDLR), an ever increasing number of related proteins have been discovered. These receptors belonging to the LDLR family are thought to play key roles in lipoprotein metabolism in a variety of tissues, including the arterial wall. We have discovered that the expression of a 250-kDa mosaic LDLR-related protein, which we termed LR11 for the presence of 11 LDLR ligand-binding repeats, is markedly induced in smooth muscle cells in the hyperplastic intima of animal models used for the study of atherosclerosis. Here, we demonstrate that the human LR11, when overexpressed in hamster cells, binds and internalizes 39-kDa receptor-associated protein (RAP), an in vitro ligand for all receptors belonging to the LDLR family. Furthermore, LR11 binds the apolipoprotein E (apoE)-rich lipoproteins, beta-very low density lipoproteins (VLDLs), with a high affinity similar to that of other members, such as the LDLR and VLDL receptor. RAP and beta-VLDL compete with each other; however, other serum lipoproteins are not able to inhibit their binding. LR11 shows specific binding of apoE-enriched HDL prepared from human cerebrospinal fluid as well as of beta-VLDL, suggesting that the apoE content of lipoproteins is most likely important for mediating the high-affinity binding to the receptor. LR11-overexpressing cells are able to internalize and degrade the bound beta-VLDL; these cells also show increased accumulation of cholesteryl esters when incubated with beta-VLDL. Incubation for 48 hours with beta-VLDL of LR11-overexpressing cells, but not of control cells, promotes the appearance of numerous intracellular lipid droplets. Taken together, LR11, a mosaic LDLR family member whose expression in smooth muscle cells is markedly induced in atheroma, has all the properties of a receptor for the endocytosis of lipoproteins, particularly for the incorporation of apoE-rich lipoproteins.

The authors investigated the binding of human plasma 125I-labelled chylomicrons to Chinese hamster ovary (CHO) cells, i.e. native CHO cells are mutant ldl-A7 cells lacking the low-density lipoproteins receptor, in the absence and presence of exogenous bovine milk lipoprotein lipase (LPL) in the culture medium. Only a small amount of binding to either cell was observed in the absence of added LPL. Exogenously added LPL increased the specific binding of chylomicrons to ldl-A7 cells, as well as to native CHO cells. The enhanced binding of chylomicrons to ldl-A7 cells or native CHO cells by LPL was inhibited by heparinase and a monoclonal antibody against LPL (5D2) which recognizes the carboxyl terminal of LPL. However, the enhanced binding was not inhibited by 1 M NaCl, which abolishes the enzymatic activity of LPL in either ldl-A7 cell or native CHO cells. These results suggest that LPL enhances the binding of chylomicrons to heparan sulphate proteoglycans of CHO cells, and that it is the carboxyl terminal of LPL but not the enzymatic activity of LPL that is essential for LPL to mediate the binding of chylomicrons to CHO cells.

High density lipoprotein-cholesterol (HDL-C) levels are inversely related to the incidence of coronary artery disease. We studied the influence of a G(-75)-->A transition in the promoter of the apolipoprotein (apo) A-I gene, a major protein component of HDL, on serum HDL-C levels in hyperlipidemic subjects. Seventy three hyperlipidemic subjects with serum levels of high HDL-C (HDL-C > or = 70 mg/dl, Group H) were compared with hyperlipidemic subjects with levels of HDL-C between 40 and 70 mg/dl (Group N) and those with HDL-C < 40 mg/dl (Group L). Group H showed a higher incidence (45.2%) of low plasma cholesteryl ester transfer protein (CETP) activity than Groups N (9.1%) and L (5.3%) (p < 0.001). Group H had a higher incidence of the G(-75)-->A transition (0.275) than Groups N (0.117, p < 0.05) and L (0.056, p < 0.01), among subjects with normal CETP activities. The HDL-C levels in subjects with the transition (84 +/- 16 mg/dl) were higher than those in subjects without the transition (56 +/- 12 mg/dl) (p < 0.05). These data suggest that a G(-75)-->A transition of the apo A-I gene promoter, in addition to the common mutation of CETP gene, contributes to high HDL-C levels among hyperlipidemic patients in Japan.

Postprandial hyperlipidemia is frequently accompanied with intra-abdominal visceral accumulation in human subjects. We have found that the decreased lipoprotein lipase (LPL) mass and activity is negatively associated with the amount of visceral fat accumulation. Here, we studied the postprandial hyperlipidemia using the OLETF rat, a model with visceral obesity, in order to clarify the molecular mechanism causing postprandial hyperlipidemia accompanied with visceral obesity. At the same age of 32 weeks, the OLETF rats showed obviously higher plasma leptin, total cholesterol, triglyceride, and HDL-cholesterol levels than the control LETO rats, although the plasma glucose level was not significantly different. Fat-loading test revealed the delayed metabolism of exogenous fat in the OLETF rats compared to the LETO rats, similar to human subjects with visceral obesity. In the obese rats, plasma levels of LPL mass and activities were 60 and 49% of control rats. The expression of LPL gene was decreased in subcutaneous adipose tissues and skeletal muscle of OLETF rats to 40 and 52% compared to those of LETO rats. In OLETF rats, plasma tumor necrosis factor-alpha (TNF-alpha) and insulin levels were increased to 2.0- and 2.3-folds compared to those in control rats. Furthermore, plasma insulin and TNF-alpha levels in OLETF rats were negatively correlated with the expression levels of LPL gene in subcutaneous fat and muscle. These results indicate that decreased LPL mass and activity in the animal model with visceral obesity is possibly caused by decreased expression of LPL gene in tissues mediated by the increased levels of insulin and TNF-alpha. The different expression of LPL gene in tissues associated with the increased levels of insulin and TNF-alpha possibly elucidate the underlying mechanisms involving the postprandial hyperlipidemia observed in visceral obesity., (Copyright 2000 Academic Press.)

In this study, we analyzed plasma lipid and lipoprotein levels before and after treatment with 1-desamino-8-D-arginine vasopressin (DDAVP) in subjects with partial and complete central diabetes insipidus (DI) in order to determine how a shortage and supplement of this hormone affect plasma lipid metabolism. The subjects consisted of 6 patients with partial and 6 with complete central DI. After treatment with DDAVP through nasal cavity, plasma total cholesterol (TC) level did not decrease either in complete or partial form. Plasma triglyceride (TG) levels decreased from 306+/-175 mg/dl to 198+/-91 (35% decrease, p=0.027) in complete form, while TG did not change significantly in partial form. A detailed investigation of plasma lipoprotein metabolism during treatment with DDAVP was carried out in 3 of the 6 subjects with complete form of DI. Lipoprotein lipase activity and mass in post-heparin plasma from those three subjects tended to increase after treatment with DDAVP, along with the complete disappearance of an unusual lipoprotein between low density lipoprotein (LDL) and very low density lipoprotein (VLDL) as analyzed by polyacrylamide gel electrophoresis. These results suggest that the DDAVP treatment has a favorable effect on lipid and lipoprotein metabolism, especially triglyceride-rich lipoproteins, either directly or through modifying factors contributing to lipid metabolism.

A 61-year-old Japanese woman with heterozygous familial hypercholesterolemia (FH), type 2 diabetes mellitus and coronary artery disease underwent coronary artery bypass grafting (CABG) utilizing a saphenous vein graft at the age of 46, in June 1984, 6 months before low density lipoprotein (LDL) apheresis was started. She had received LDL apheresis every two weeks, along with combined drug treatment since the age of 47 (December 1984). She had bilateral xanthelasma and Achilles tendon xanthomas. Her fasting baseline serum total cholesterol and triglyceride level were 464 mg/dl and 57 mg/dl, respectively at the age of 47 when she visited our hospital for the first time. Analysis of the genomic DNA from the patient revealed heterozygous amino acid substitution of Leu for Pro664 in the LDL receptor gene. She was diagnosed as type 2 diabetes mellitus at the age of 53. Combined treatment in the steady state yielded a pretreatment LDL cholesterol level of 230+/-14 mg/dl and a posttreatment level of 57+/-7.6. All grafts were widely patent after as long as 14 years since CABG, suggesting that LDL apheresis combined with drug therapy is highly effective in preventing the occlusion of bypass grafts in a patient with heterozygous FH and type 2 diabetes mellitus.

An involvement of the low density lipoprotein receptor (LDLR) gene family in both intracellular signal pathways for neural organization and metabolic pathways for lipoprotein homeostasis is now well established. The discovery of LR11, a mosaic LDLR family member offers the opportunity to gain new insights into receptor multifunctionality. Here, we studied the proliferation-dependent expression of LR11 mRNA and protein using two cultured cell lines, IMR32 neuroblastoma and PC12 pheochromocytoma. Within 24 h, the LR11 protein rose 1.9-fold in proliferating IMR32 cells, and increased further to 5.3-fold at 72 h. This conformed with a transcript level increase of 4.7-fold at 72 h in the proliferating cells. On the other hand, under differentiation conditions, a 2.9-fold increase was observed within 24 h, but at 72 h thereafter the protein levels decreased to 60% of control. The transcript also increased to 1. 8-fold within 24 h, and then decreased to 1.1-fold at 72 h. In order to assess the transcriptional activities of the LR11 gene, we identified the 5'-flanking region of the murine LR11 gene. Transfection of IMR32 and PC12 cells with plasmids containing the whole or deleted fragments of 5'-flanking region showed that element(s) responsible for the above described different transcriptional activities are located in the upstream sequence between -861 and -396. Thus, the transcription of LR11 in these two cell systems is regulated differently during proliferation and differentiation, suggesting that the multifunctionality of LR11, as well as other LDLR family members, for rapid cell growth in malignant cells and neural outgrowth in cultured neurons, respectively. The possible involvement of LR11 in cellular proliferation and differentiation sheds new light on its functions in neurons, malignant, and vascular cells., (Copyright 2000 Academic Press.)

Leptin exerts its effects by interacting with specific membrane receptors (Ob-R). We studied the exact localization of long intracellular domain form (Ob-Rb) in human brain. In addition, we analyzed the regulatory features of Ob-Rb expression in two neuroblastoma cell lines. The Ob-Rb mRNAs were abundant in putamen, frontal lobe, medulla, cerebral cortex, cerebellum, thalamus, hippocampus, corpus callosum, caudate nucleus, and amygdala, indicating that Ob-Rb transcripts are expressed differently from that of other Ob-R isoforms. In SK-N-MC cells, the expression of Ob-Rb mRNA was induced by increasing doses of insulin, and the maximum amount of mRNA expression was 9.4-fold higher in the presence of insulin (100 nM for 24 h), compared to the absence of insulin. In IMR32 cells, the transcripts were increased 4.0-fold when cells were incubated with 1 nM of insulin for 48 h. In contrast, Ob-Rb expression in IMR32 cells decreased to 18% of control following a 24-h incubation period with 50 ng/mL of leptin, compared to incubation in the absence of leptin. These results indicate that expression of Ob-Rb is differentially regulated by inhibitory signals of energy balance in neuroblastoma cells. The identification of the novel regulatory mechanisms involving the Ob-Rb isoform by insulin and leptin now makes it possible to elucidate the underlying mechanisms involving increased food intake and uncontrolled energy balance associated with leptin resistance in obese individuals., (Copyright 2000 Academic Press.)

Intimal hyperplasia following arterial endothelial denudation results in large part from the proliferation of vascular smooth muscle cells (SMCs) and matrix accumulation. Procollagen COOH-terminal proteinase enhancer (PCPE) binds procollagen COOH-propeptides and potentiates procollagen COOH-proteinase activity to cleave COOH-propeptides of procollagens I-III. Here we report the enhanced expression of PCPE in cultured SMCs and in intimal thickening induced by arterial injury. The levels of PCPE mRNA in parallel with the level of p21(Cip1) mRNA, as a negative regulator of cellular proliferation, increased under serum deprivation or reduced cellular proliferation in cultured SMCs. In contrast, rapidly proliferating cells show the decreased levels of PCPE mRNA. In vivo, the marked induction of PCPE in injured rat arteries occurred at 14 days after endothelial denudation. The induced expression levels of PCPE as well as p21(Cip1) were maintained until 42 days, although cyclin E expression declined. Furthermore, transforming growth factor beta1 (TGF-beta1), an important regulator of cellular proliferation in atheroma, increased the levels of the PCPE mRNA in cultured SMCs. Thus, the regulatory expression of PCPE dependent on cellular proliferation, and particularly contact inhibition, may play a key role in the proliferation of SMCs and matrix production during the process of atheroma formation., (Copyright 2000 Academic Press.)

Receptors belonging to the low density lipoprotein receptor (LDLR) superfamily play important biological roles in addition to mediating the lipoprotein metabolism. The recent discovery of a novel mosaic LDLR family member by us (Yamazaki H, Bujo H, Kusunoki J, Seimiya K, Kanaki T, Morisaki N, Schneider WJ, and Saito Y J Biol Chem 271: 24761-24768, 1996) and others, which we termed LR11, offers the opportunity to gain new insights into receptor multifunctionality. The expression of a 250-kDa mosaic LDLR family member, which we termed LR11 due to the presence of 11 ligand binding repeats, is markedly induced during the process of atherogenesis in two animal models. The highest induction of LR11 occurs in the intimal smooth muscle cells (SMCs) of atheromatous lesions. In agreement with the correlation of LR11 induction during increased cell proliferation in vivo, cultured SMCs showed a marked increase in LR11 expression in the proliferative phase. Furthermore, such proliferation-dependent expression of LR11 could be observed in a cultured neuroblastoma cell line, which was established to be a suitable in vitro model for proliferation and differentiation. Possible involvement of LR11 in the cellular proliferation sheds new light on the recently proposed novel functions of the LDL receptor gene family in atherosclerosis.

The LDL receptor family is known to bind and internalize apoE-rich lipoproteins, and thought to play a role in lipoprotein metabolism. The recently identified new members showed the structural heterogeneity in the family, and molecular biological approach using animal models revealed the essential biological function in neural development. These increasing novel findings suggest that the LDL receptor family is a cluster of multifunctional receptors for intracellular signal transduction, neuron migration and vascular smooth muscle cell proliferation, as well as lipoprotein incorporation.

Receptors belonging to the LDL receptor (LDLR) family are thought to play key roles in lipoprotein metabolism in a variety of tissues, including the arterial wall. Here, we report that the expression of a 250-kDa mosaic LDLR family member, which we called LR11 for the presence of 11 ligand-binding repeats, is markedly induced during the process of atherogenesis in 2 animal models. Analysis by reverse transcription-polymerase chain reaction and RNase protection assays revealed that LR11 transcript levels rise in rabbit aortas displaying atheromatous lesions after the rabbits have been fed a high-cholesterol diet. Immunohistochemistry demonstrated that the highest induction of LR11 occurs in intimal smooth muscle cells (SMCs), followed by medial SMCs close to the intimal border of the atheromatous lesions. Experimental intimal hyperplasia by endothelial denudation showed that LR11 mRNA levels were also increased in the arteries after balloon injury, with the transcripts localized primarily in the hyperplastic intimal layer. In agreement with the correlation of LR11 induction during increased cell proliferation, cultured SMCs showed an increase in LR11 expression in the proliferative phase. Furthermore, Northern and Western blot analyses showed that medium conditioned by the monocyte-macrophage cell line THP-1 enhanced LR11 expression in cultured SMCs. These findings suggest that upregulation of LR11 might be contributing to the pathological roles of intimal and medial SMCs during arteriosclerotic lesion development and provide the first insight into the as yet unknown functional significance of this intriguing LDLR family member.

Aims: To clarify how troglitazone, an insulin-sensitizing agent, affects lipid metabolism and postheparin plasma lipoprotein lipase (LPL)., Methods: Fifteen patients (3 male, 12 female) (the average age 62+/-7 years; the mean body mass index (BMI) 25+/-3 kg/m2 ) were recruited for this study. The serum lipids and postheparin plasma lipoprotein lipase (LPL) mass before and 4 weeks after oral administration of troglitazone (200 mg day-1 ) were measured. A mouse preadipocyte cell line, 3T3-L1, was incubated with troglitazone and LPL enzyme protein mass in the culture media was measured by an enzyme linked immunosorbent assay. A reverse transcription polymerase chain reaction (RT-PCR) using primers specific for the carboxyl terminal 135 amino acid of mouse LPL cDNA was used to evaluate the effect of troglitazone on expression of LPL and Northern blot analysis carried out to determine expression of LPL., Results: The average levels before treatment of fasting serum total cholesterol, triglycerides, high density lipoprotein cholesterol, plasma glucose and glycohaemoglobin A1c were 5.6+/-0.9, 1.8+/-1.0, 1.5+/-0.5, 8.1+/-1.7 mmol l-1 and 7.8+/-1.6% respectively. Four weeks after treatment, those levels were 5.4+/-0.9, 1.2+/-0.3 (P=0.004), 1.6+/-0.5 (P=0.02) mmol l-1, 7.7+/-2.3 mmol l-1 and 7. 3+/-0.6% (P=0.01), respectively. The postheparin plasma LPL mass increased from 226+/-39 to 257+/-68 ng ml-1 (P=0.03) during that period. The LPL mass in the media of 3T3 L1 cells cultured in the presence of 10, 20 or 30 microm of this compound increased in a dose dependent manner. RT-PCR revealed that the area of the bands of the RT-PCR products on 1.5% agarose gel analyzed with NIH image from the cell extracts cultured in the presence of 10 microm troglitazone was significantly larger (P=0.0069) than that in the absence of this compound. Northern blot analysis revealed that in the cultured 3T3-L1 cells, the expression of LPL was enhanced in the presence of 10 microm troglitazone., Conclusions: Troglitazone improves plasma triglyceride-rich lipoproteins metabolism by enhancing the expression of LPL in adipocytes.

Receptors belonging to the low density lipoprotein receptor (LDLR) superfamily play important biological roles in addition to mediating lipoprotein metabolism. The recent discovery of a novel mosaic LDLR family member by us (Yamazaki H., Bujo, H., Kusunoki, J., Seimiya, K., Kanaki, T., Morisaki, N., Schneider, W.J., and Saito, Y. (1996) J. Biol. Chem. 271, 24761-24768) and others, which we termed LR11, offers the opportunity to gain new insights into receptor multifunctionality. The predominant expression of LR11 in brain and the presence of elements found in neural adhesion molecules suggested a function(s) in the central nervous system (CNS). In order to gain information about this complex receptor in an accessible system, we have molecularly characterized the murine LR11 and report on its detailed localization and developmental expression pattern. The primary sequence of the murine protein further establishes that LRlls are among the closest relatives within the LDLR family and that brain is the predominant site of expression. In situ hybridization showed that neuronal bodies such as Purkinje cells in the cerebellum and other neurons in the hippocampal formations and the cerebral cortex are particularly rich in LR11 transcripts. The developmental pattern of LR11 expression in brain, which peaks at 2 weeks, is in contrast to those of two other LDLR family members, the very low density lipoprotein receptor and the LDLR. During early development, murine LR11 expression levels are highly dependent on neural cell types. These findings are compatible with function(s) of LR11 in neural organization and, possibly, pathogenesis of degenerative brain diseases. In addition, detailed knowledge of LR11 biology will help to elucidate the roles of other mosaic proteins that share with LR11 elements whose function is not yet known.

The list of LDL receptor superfamily relatives is still growing. The two most recently discovered family branches are (1) a set of receptors characterized by expression in brain and a very close relationship to the LDL and VLDL receptors, and (2) highly cross-species (man, mouse, rabbit, chicken) conserved complex mosaic receptors which contain structural domains so far not found in the superfamily. At present, we know very little about the physiological function(s) of these molecules. They can be safely assumed, based on the presence of seven, eight or 11 clustered LDL receptor ligand binding repeats, to recognize mammalian apolipoprotein E but, based on the absence of apolipoprotein E in birds, they may exhibit interactions quite different from and/or in addition to typical lipoprotein receptors in vivo.

Certain receptors belonging to the LDL receptor (LDLR) gene family appear to constitute a newly identified branch whose members are expressed in brain, in addition to other tissues. In support of this concept, we have now discovered the expression and delineated the molecular structures of a representative of this emerging branch from two such diverse species as human and chicken. This membrane receptor, called LR11 and thus far only known to exist in the rabbit, is a complex seven-domain mosaic protein containing, among other structural elements, a cluster of 11 LDLR ligand-binding repeats and a domain with homology to VPS10, a yeast receptor for vacuolar protein sorting. Cytoplasmic signature sequences define the receptor as competent for endocytosis. The most striking properties of LR11s are their (1) high degree of structural conservation (>80% identity among mammals and birds), with 100% identity in the membrane-spanning and cytoplasmic domains of rabbit and human; (2) lack of regulation by cholesterol and estrogen; and (3) expression in brain. The features of LR11 suggest important roles in intercellular and intracellular ligand transport processes, some of which it may share with other brain-specific LDLR family members.

Yolk represents the last growth stage of a single cell, the oocyte, which contains, besides bona fide cytoplasm, endocytosed serum-derived lipoproteins and minor components essential for normal embryo development. Transport of bulk lipoproteins, micronutrients, and morphogens to oocytes in parallel with maintenance of somatic homeostasis is achieved by ligand targeting via cell-specific expression of receptors and subtle differences in ligand structure. Lipoprotein metabolism is the prime example of these regulatory principles, in which receptors belonging to the low density lipoprotein receptor gene family play key roles. Here, we present the laying hen's features that make it an attractive model system to dissect macromolecular transport processes at the molecular level. In addition to the characterization of a family of yolk precursor receptors, studies on systemic vs. oocyte-directed transport have uncovered new aspects of the biological rationale for simultaneous expression of closely related genes in a single organism.

Members of the low-density lipoprotein receptor (LDLR) supergene family interact with a large number of diverse ligands. One of the relevant receptors is the recently characterized LDLR relative with eight ligand-binding repeats, termed LR8, which exists in two splice variant forms. The gonads, relying on receptor-mediated lipoprotein supply for steroidogenesis, and on interplay of germ cells with somatic cells, provide a particularly attractive setting to study details of the expression of LR8. Here we show by polymerase chain reactions and Northern analysis, as well as by in situ hybridization, that the longer of the two splice variants (LR8+), containing an additional region defining an O-linked sugar domain, is produced in the somatic cells of chicken testis, whereas the shorter form lacking this domain (LR8-) is expressed in the male germ cells. Interestingly, as shown by transcript analysis and at the functional level by ligand blotting, LR8- expression in the spermatoids increases with germ cell maturation, but is absent from ejaculated sperm. This constitutes a scenario reminiscent of the situation in growing vitellogenic oocytes, which express very high levels of LR8-, but lack the receptor following ovulation. Thus, the cell-specific expression of different LR8 splice variants may relate to the requirements of extensive communication and cooperation between germ cells and somatic cells in the gonads.

We now have discovered and characterized a novel multi-domain protein and classified it as a member of the LDL receptor gene family. The approximately 250 kDa membrane protein, termed LR11, highly conserved in man, rabbit and chicken, contains a cluster of 11 LDL receptor ligand binding repeats, a group of 5 LDL receptor "YWTD" repeats, a large hexarepeat domain of structural elements found in neural cell adhesion molecules, and a domain with similarity to a yeast receptor for vacuolar protein sorting, VPS10. The cytoplasmic domain exhibits features typical of endocytosis-competent coated pit receptors. The mosaic, and presumably multifunctional, receptor is expressed abundantly in brain, liver and adrenal glands. Ligand blotting of LR11-transfected cells demonstrated that LR11 binds apolipoproteinE-containing lipoproteins, as well as other members of LDL receptor gene family. In contrast to the LDL receptor, the mRNA levels in rabbit liver is unaffected by hyperlipidemia. The features of this highly conserved and complex mosaic protein suggest the importance of the ever expanding LDL receptor gene family in the evolution and proposed multifunctionality.

Most of the LDL receptor family members recognize apolipoprotein E. The structures of the VLDL receptor, and recently identified apolipoprotein E receptor 2, closely resemble the LDL receptor. Recent studies have demonstrated that the VLDL receptor is responsible for the reproduction of premammalian species by mediating oogenesis. Despite the importance of the VLDL receptor in premammalian species, the biological role of the mammalian VLDL receptor is still unclear. Apolipoprotein E receptor 2 is structurally most closely related to the LDL receptor and expressed predominantly in brain. This newly identified receptor may play a role in the uptake of cholesterol in the central nervous system.

The VLDL receptor is made up of five functional domains that resemble the LDL receptor. In mammals, the receptor is highly expressed in muscle and fat cells, while in chicken, it is abundant in oocytes. The extremely high degree of amino acid conservation of the VLDL receptor during the evolution suggests that the receptor plays an essential role in vertebrates. Recent studies on the chicken VLDL receptor revealed that the receptor plays a key role in the uptake of yolk precursors in oocytes and mediates the growth of oocytes. The VLDL receptor is an essential receptor in avian species and the receptor-deficient mutant hens are sterile and exhibit severe hyperlipidemia with aortic atherosclerosis.

The so-called very low density lipoprotein receptors (VLDLRs) are related to the LDLR gene family. So far, naturally occurring mutations have only been described for the prototype LDLR; in humans, they cause familial hypercholesterolemia. Here we describe a naturally occurring mutation in a VLDLR that causes a dramatic abnormal phenotype. Hens of the mutant restricted-ovulator chicken strain carry a single mutation, lack functional oocyte receptors, are sterile, and display severe hyperlipidemia with associated premature atherosclerosis. The mutation converts a cysteine residue into a serine, resulting in an unpaired cysteine and greatly reduced expression of the mutant avian VLDLR on the oocyte surface. Extraoocytic cells in the mutant produce higher than normal amounts of a differentially spliced form of the receptor that is characteristic for somatic cells but absent from germ cells.

An abundant 95-kDa protein belonging to the low density lipoprotein receptor supergene family is essential for chicken oocyte growth by mediating the uptake of multiple plasma-borne yolk precursors. This receptor harbors at the amino terminus a cluster of eight tandemly arranged repeats typical of the ligand binding domains of members of this family and is designated low density lipoprotein receptor relative with 8 repeats (LR8). Here, we demonstrate by reverse transcriptase-polymerase chain reaction, Northern, and Western blot analyses that the chicken expresses two forms of LR8, which are generated by differential splicing of an exon encoding a serine- and threonine-rich region characteristic of LRs, termed O-linked sugar domain. The female germ cell of the chicken expresses extremely high levels of the short form of LR8 (LR8-), i.e. the 95-kDa protein; in contrast, somatic cells express lower but detectable levels of the form containing the O-linked sugar domain (LR8+). The main sites of LR8+ expression in the chicken are the heart and skeletal muscle, i.e. the same tissues were LR8 mRNAs predominate in mammals; in addition, in situ hybridization demonstrates that a significant amount of LR8+ is produced in the hen's ovarian follicular granulosa cells. We found no apparent functional difference between the two receptor forms; however, cell type-specific targeting of the multiple ligands of these receptors possibly relates to their respective expression on the cell surface.

Receptor-associated protein (RAP) was originally described as a 39-kDa intracellular protein copurifying with mammalian low density lipoprotein (LDL) receptor-related protein/alpha 2-macroglobulin receptor (LRP/alpha 2MR). RAP has a high affinity for LRP/alpha 2MR and interferes with the receptor's ability to bind a variety of ligands. The laying hen expresses, in a tissue-specific manner, at least four different proteins which belong to the same family of receptors as LRP/alpha 2MR. Here we show that the chicken also produces RAP, so far thought to be expressed only in mammals. Studies on the interaction of recombinant human RAP with the LDL receptor family in the chicken revealed that RAP binds with high affinity to the abundant oocyte receptor for yolk precursors (OVR) as well as to the somatic cell-specific LRP/alpha 2MR. Significantly, RAP interacts with a lower affinity with the LDL receptor, but does not bind to the oocyte-specific form of LRP. Binding of RAP to OVR inhibits the interaction of the receptor with all known physiological ligands, i.e. the yolk precursors very low density lipoprotein, vitellogenin, and alpha 2-macroglobulin. In COS cells transfected with OVR, RAP is internalized and degraded in a concentration-dependent and saturable manner. Lactoferrin, another protein with a high affinity for mammalian LRP/alpha 2MR, also binds to OVR and abolishes its interaction with yolk precursors. Cross-competition experiments show that RAP and lactoferrin recognize sites different from those involved in yolk precursor binding. The availability of pure OVR and LDLR enable us to determine kinetic parameters for the binding of RAP and lactoferrin to these receptors by surface plasmon resonance. Taken together, our results strongly suggest that chicken OVR, which is easily accessible and highly abundant in growing oocytes, represents a superior system for studying mechanistic and structural aspects of the interaction of ligands and modulating proteins with members of the LDL receptor gene family.

Lecithin: cholesterol acyltransferase (LCAT) is the enzyme that catalyze the esterification of free cholesterol in plasma proteins. The functional abnormalities of LCAT are known to cause two diseases characterized by severe corneal opacity; familial LCAT deficiency that is accompanied with anemia and frequently, though not invariably, renal failure, and fish eye disease (FED) without any other severe symptoms. Notably, it has been shown that the clinical symptoms and biochemical features are highly variable in each patient with the diseases. Recent genetic studies on the cases of LCAT deficiency or FED revealed both diseases to be caused by respective mutations of the LCAT gene. These findings suggest the abnormal or defective LCAT by each gene mutation underlies the heterogeneity in the biochemical and, possibly, clinical characteristics observed in LCAT deficiency and FED.

Deposition of the yolk mass components of chicken oocytes, very low density lipoprotein (VLDL) and vitellogenin (VTG), is mediated by a 95 kDa plasma membrane protein, termed VLDL/VTG receptor (VLDL/VTGR). Molecular characterization of the VLDL/VTGR revealed that it is a member of the LDLR gene superfamily, and harbours eight complement-type, cysteine-rich ligand binding repeats at the N-terminus. This ligand binding domain structure is the hallmark of the recently discovered mammalian so-called VLDLRs, whose true physiological function remains to be elucidated. Northern blot analysis revealed that this receptor is expressed almost exclusively in oocytes, with very much lower levels of hybridizing transcripts present in heart and skeletal muscle. Heterologous expression of the cloned receptor demonstrated its ability to bind both VLDL and VTG. The receptor gene is located on the avian sex chromosome Z, in agreement with the sex linkage of a single-gene defect in animals that fail to reproduce because of the lack of expression of functional VLDL/VTGR. In situ hybridization analysis of oocytes suggested that VLDL/VTGR mRNA may relocalize during oocyte growth. Thus, the current study has identified and characterized the first non-mammalian VLDLR. Its key role in avian reproduction and extremely high evolutionary conservation shed new light on VLDLR function in mammals, which also express the gene in ovaries.

Plasma HDL are a negative risk factor for atherosclerosis. Cholesteryl ester transfer protein (CETP; 476 amino acids) transfers cholesteryl ester from HDL to other lipoproteins. Subjects with homozygous CETP deficiency caused by a gene splicing defect have markedly elevated HDL; however, heterozygotes have only mild increases in HDL. We describe two probands with a CETP missense mutation (442 D:G). Although heterozygous, they have threefold increases in HDL concentration and markedly decreased plasma CETP mass and activity, suggesting that the mutation has dominant effects on CETP and HDL in vivo. Cellular expression of mutant cDNA results in secretion of only 30% of wild type CETP activity. Moreover, coexpression of wild type and mutant cDNAs leads to inhibition of wild type secretion and activity. The dominant effects of the CETP missense mutation during cellular expression probably explains why the probands have markedly increased HDL in the heterozygous state, and suggests that the active molecular species of CETP may be multimeric.

Lecithin: cholesterol acyltransferase (LCAT) is the enzyme that catalyzes the esterification of free cholesterol in plasma lipoproteins. Familial LCAT deficiency, which is a rare hereditary disorder of lipid metabolism, inherited as an autosomal recessive trait, is characterized by corneal opacity, anemia and frequently, though not invariably, renal failure. Recently, LCAT cDNA and gene have been cloned. Studies on DNA samples from unrelated patients with familial LCAT deficiency and fish eye disease, which is characterized by severe corneal opacity alone, revealed both diseases to be caused by respective mutations of the LCAT gene. It is suspected that defect or functional abnormality of LCAT, caused by these genetic defects, underlie the various clinical and biochemical characteristics observed in LCAT deficiency or fish eye disease.

Familial lecithin:cholesterol acyltransferase (LCAT) deficiency is a hereditary disorder with clinical manifestations including corneal opacity, premature atherosclerosis and renal failure. In this study, we analyzed the molecular base underlying a case of Japanese LCAT deficiency, in which both LCAT mass and activity of the proband were nearly absent. DNA blot hybridization analysis showed no gross rearrangement in the LCAT gene of the proband. The nucleotide sequence analysis of the cloned LCAT gene demonstrated only an extra nucleotide "C" insertion at the first exon, when compared to the sequence of wild type. This single base insertion caused a shift of the following reading frame, probably resulting in a truncated abnormal LCAT polypeptide that consist of only 16 amino acids. The direct sequence analysis of PCR-amplified DNA showed only the same insertion, indicating that the LCAT-deficient proband is a homozygote for the mutant allele. These results indicate that the clinical and biochemical feature of the patient is mainly caused by a complete deficiency of the enzyme based on a homozygous abnormality of LCAT gene.

The complete amino acid sequences of two mouse glutamate receptor subunits (GluR1 and GluR2) have been deduced by cloning and sequencing the cDNAs. Xenopus oocytes injected with mRNA derived from the GluR1 cDNA exhibit current responses both to kainate and to quisqualate as well as to glutamate, whereas oocytes injected with mRNA derived from the GluR2 cDNA show little response. Injection of oocytes with both the mRNAs produces current responses larger than those induced by the GluR1-specific mRNA and the dose-response relations indicate a positively cooperative interaction between the two subunits. These results suggest that kainate and quisqualate can activate a common glutamate receptor subtype and that glutamate-gated ionic channels are hetero-oligomers of different subunits.

The structure-function relationship of the nicotinic acetylcholine receptor (AChR) has been effectively studied by the combination of complementary DNA manipulation and single-channel current analysis. Previous work with chimaeras between the Torpedo californica and bovine AChR delta-subunits has shown that the region comprising the hydrophobic segment M2 and its vicinity contains an important determinant of the rate of ion transport through the AChR channel. It has also been suggested that this region is responsible for the reduction in channel conductance caused by divalent cations and that segment M2 contributes to the binding site of noncompetitive antagonists. To identify those amino acid residues that interact with permeating ions, we have introduced various point mutations into the Torpedo AChR subunit cDNAs to alter the net charge of the charged or glutamine residues around the proposed transmembrane segments. The single-channel conductance properties of these AChR mutants expressed in Xenopus laevis oocytes indicate that three clusters of negatively charged and glutamine residues neighbouring segment M2 of the alpha-, beta-, gamma- and delta-subunits, probably forming three anionic rings, are major determinants of the rate of ion transport.

The combination of complementary DNA expression and single-channel current analysis provides a powerful tool for studying the structure-function relationship of the nicotinic acetylcholine receptor (AChR) (refs 1-5). We have previously shown that AChR channels consisting of subunits from different species, expressed in the surface membrane of Xenopus oocytes, can be used to relate functional properties to individual subunits. Here we report that, in extracellular solution of low divalent cation concentration, the bovine AChR channel has a smaller conductance than the Torpedo AChR channel. Replacement of the delta-subunit of the Torpedo AChR by the bovine delta-subunit makes the channel conductance similar to that of the bovine AChR channel. To locate the region in the delta-subunit responsible for this difference, we have constructed chimaeric delta-subunit cDNAs with different combinations of the Torpedo and bovine counterparts. The conductances of AChR channels containing chimaeric delta-subunits suggest that a region comprising the putative transmembrane segment M2 and the adjacent bend portion between segments M2 and M3 is involved in determining the rate of ion transport through the open channel.