Effects of apolipoprotein A-IV genotype on glucose and plasma lipoprotein levels.

The effects of apolipoprotein (apo) A-IV genotype on serum glucose, total cholesterol, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, triglyceride and glucose concentrations were ascertained in a population of 373 men and 361 women with a mean age of about 57 years. Subjects were evaluated at entry into a lifestyle intervention program. Apolipoprotein A-IV genotype variations at residues 347 and 360 were examined, as these mutations affect the sequence of apo A-IV, a major protein constituent of intestinal triglyceride-rich lipoprotein and HDL. With regard to the apo A-IV 360 mutation, 16.4% of the females and 13.4% of the males carried the apo A-IV 2-allele, almost entirely in the heterozygous state. No effect of the apo A-IV 1/2 genotype was observed in either men or women on total cholesterol, LDL cholesterol, HDL cholesterol, triglyceride, the total cholesterol (TC)/HDL ratio, or on A-I, A-IV and apo B levels. This was also the case for the apo A-IV 347 mutation. However, women with the apo A-IV 360 1/2 genotype had significantly (p < 0.005) higher glucose levels (105.5 mg/dl) compared with the 1/1 wild-type (94.0 mg/dl). All analyses were also adjusted for age, body mass index, medications, alcohol use and cigarette smoking. The prevalence of the 347 mutation was somewhat higher than the 360 mutation, with 29% of the females and 32.0% of the males being heterozygous for this mutation, and 3.9% of the females and 5.4% of the males being homozygous for this mutation. These data are consistent with the concept that the apo A-IV 360 and 347 genotypes have no significant effect on apo A-IV levels and other lipid parameters in either gender. However, apo A-IV 360 1/2 genotype did have a significant effect on serum glucose levels in women.

Effects of apolipoprotein A-I genetic variations on plasma apolipoprotein, serum lipoprotein and glucose levels.

The present authors investigated the individual and combined associations of the apolipoprotein (apo) A-I -75 bp and +83 bp polymorphisms with plasma lipid, lipoprotein and apolipoprotein levels in 734 Caucasian men and women. The frequency of the A allele at position -75 bp (G-->A) was 0.14 in women and 0.17 in men. The frequencies for the rare M2 allele at position +83 bp and/or 84 bp (C-->T and G-->A, respectively) were 0.04 and 0.05 in women and men, respectively. In women, the A allele was associated with significantly higher levels of apo B (P = 0.016), total cholesterol (TC) (P = 0.005), low-density lipoprotein cholesterol (LDL-C) (P = 0.018) and TC:high-density lipoprotein (HDL) ratio (P = 0.026) compared to the G/G subjects. In men, no significant associations were detected between the -75 bp polymorphism and any lipid trait examined. The M2 allele for the +83 bp polymorphism was significantly associated in men with higher levels of apo A-I (P = 0.002) and TC (P = 0.046). In women, a significant effect was observed for TC (P = 0.036), with M2+/- subjects having lower levels than M2+/+ subjects. Significant linkage disequilibrium (P = 0.037) between the apo A-I -75 bp and +83 bp polymorphisms was detected. Women carrying both rare alleles (G/A M2+/-) had significantly higher TC:HDL ratios (P = 0.031) compared to the other haplotypes. In men, significant differences were observed for apo A-I (P = 0.021) and TC (P = 0.044), with carriers of the G/G M2+/- haplotype having the highest values compared to other genotype combinations. In conclusion, the -75 bp (G/A) polymorphism appears to have a significant effect on levels of apo B, plasma TC and LDL-C in women, while the +83 bp polymorphism seems to affect the apo A-I levels in men, and the plasma cholesterol levels in both genders.

Cholesterol efflux from normal and Tangier disease fibroblasts into normal, high-density lipoprotein-deficient, and apolipoprotein E-deficient plasmas.

Tangier disease (TD) fibroblasts have defective cholesterol release in the presence of lipid-free apolipoproteins. We compared normolipidemic probands and patients with apolipoprotein A-I (apoA-I) deficiency, apoE deficiency, or TD in terms of the plasma capacity to induce the efflux of [3H]-cholesterol from normal and TD fibroblasts and to esterify this cell-derived cholesterol. Compared with normal fibroblasts, TD fibroblasts released a significantly smaller fraction of [3H]-cholesterol into normal, high-density lipoprotein (HDL)-deficient, and apoE-deficient plasmas. Supplementation of apoE-deficient plasma with exogenous apoE normalized the cholesterol efflux from normal cells but did not fully restore the reduced cholesterol efflux from TD fibroblasts. Compared with control plasma, HDL- and apoE-deficient plasmas had a significantly reduced activity to esterify cell-derived cholesterol. Cholesterol derived from TD fibroblasts was less available for esterification in either patient or normal plasmas than cholesterol derived from normal cells. The esterification defect of TD cell-derived cholesterol was more pronounced in patient plasmas than in control plasma. We conclude that (1) apoA-I and, to a lesser degree, apoE are important determinants of the cholesterol efflux and esterification capacity of plasma, (2) TD fibroblasts have a reduced capacity to release cholesterol into the plasma, and (3) TD cell-derived cholesterol is less available for esterification in plasma than cholesterol from normal fibroblasts. The absence of distinct apoA-I- or apoE-containing subclasses aggravates the defective efflux and esterification of cholesterol derived from TD cells.

Association of apolipoprotein (Apo)E genotype with plasma apo E levels.

The purpose of this study was to investigate the effects of apolipoprotein (apo) E genotype on plasma apo E levels as well as serum total, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, triglyceride, and glucose values in 734 middle-aged and elderly, female and male subjects. Apo E allele frequencies were similar to those reported in other Caucasian populations. After adjustment for medications, alcohol use, smoking, age, and body mass index, apo E genotype was noted to have significant effects on apo E, total cholesterol, LDL cholesterol, and glucose levels in females, and on apo E, LDL cholesterol, and HDL cholesterol levels, as well as the total cholesterol (TC)/HDL cholesterol ratio in males. Female and male subjects with the apo E4 allele had significantly (P<0.05) lower plasma apo E (25 and 15%) and higher LDL cholesterol levels (5 and 2%), while those with the apo E2 allele had significantly (P<0.05) higher apo E (32 and 27%) and lower LDL cholesterol levels (10 and 10%) than the apo E3/3 group. Moreover, female apo E4 carriers had significantly (P<0.05) lower glucose values (11%) than the apo E3/3 group. These data are consistent with the concept that, in addition to the well known effects of apo E genotype on LDL-C values, this locus plays a very significant role in modulating plasma apo E levels.

Quantitation of apolipoprotein epsilon gene expression by competitive polymerase chain reaction in a patient with familial apolipoprotein E deficiency.

A simple method of obtaining semiquantitative and reliable data on apolipoprotein (apo) sigma gene expression is described. We detected apo sigma specific sequences by reverse transcription (rT)-PCR. For quantitative measurement, an apo sigma DNA standard was produced allowing the development of a competitive PCR-method. The efficiency of RNA extraction and cDNA synthesis was controlled by quantitation of a housekeeping gene (glyceraldehyde-3-phosphatedehydrogenase, G3PDH) in separate reactions. To imitate a defined induction of apo sigma gene expression, serial twofold dilutions of total RNA were reversely transcribed and the respective cDNAs used to perform a competitive apo sigma and G3PDH PCR. The change in apo sigma cDNA and G3PDH cDNA was 1.7-2.3-fold with an expected value of 2.0-fold. Standard deviations in three independently performed experiments were within a range of < 15% of the mean, indicating low intra-assay variation and high reproducibility. To illustrate this method, apo sigma gene expression was measured in a patient with complete lack of functional active apo E in comparison to healthy controls. The method presented here might be valuable in assessment of apo sigma gene expression in human disease.

Molecular basis of type III hyperlipoproteinemia in Germany.

Type III hyperlipoproteinemia (HLP) is usually associated with homozygosity for apolipoprotein (apo) E2 (Arg112 --> Cys, Arg158 --> Cys). This common apo E isoform is defective in its binding to lipoprotein receptors. However, other rare mutations in the apo epsilon gene may also, in part dominantly, predispose to the disease. In order to assess the prevalence of rare apo E variants and mutations in the apo epsilon gene in Germany, we examined apo epsilon genotypes by restriction isotyping (RI) and apo E phenotypes by isoelectric focusing (IEF) in 107 German patients with type III HLP. Concordance between apo epsilon genotype and apo E phenotype was observed in 101 subjects (94.4%). Six individuals (5.6%) had genotypes and phenotypes other than E2/2. One subject was apparently homozygous for apo E2 by IEF, but heterozygous for epsilon3/2 by RI. Sequencing of the apo epsilon gene disclosed a hitherto undescribed point mutation (TGG --> TGA) at the third position of the codon for amino acid 20 (Trp), introducing a premature termination codon. This is the first study demonstrating that in the German population type III HLP is mainly associated with homozygosity for apo E2 (Arg112 --> Cys, Arg158 --> Cys) and that discrepancies between apo epsilon genotype and apo E phenotype are rare in this genetic condition.

A competitive reverse transcription-PCR to study apolipoprotein epsilon gene expression.

We developed a rapid and simple competitive reverse transcription-polymerase chain reaction for the quantification of apo epsilon mRNA in human monocyte-derived macrophages. The method was applied, and its reliability was shown in patients with the familial lipoprotein disorder, type III hyperlipoproteinemia. Type III hyperlipoproteinemic patients express markedly higher concentrations of apo epsilon mRNA when compared with healthy controls. Patients with this disease are usually (>90%) homozygous for a receptor binding-defective isoform of apolipoprotein apo E (apo E2). The higher expression of apo epsilon mRNA in the patients could, therefore, be a physiological mechanism to compensate for functionally defective apo E. The developed procedure might be valuable in assessment of apo epsilon gene expression in human disease.

Apolipoprotein E2 (Arg136 --> Cys) mutation in the receptor binding domain of apoE is not associated with dominant type III hyperlipoproteinemia.

Using apoE phenotyping by immunoblotting and apoE genotyping we identified four heterozygous carriers of a rare apolipoprotein (apo) E2 variant, apoE2 (Arg136 --> Cys). ApoE2 (Arg136 --> Cys) was not distinct from apoE2 (Arg158 --> Cys) by phenotyping, but produced a unique pattern of bands on CfoI restriction typing of a 244 bp apoE gene fragment. Two of the four apoE2 (Arg136 --> Cys)/3 heterozygotes had elevated triglycerides, two were normolipidemic. The composition of very low density lipoproteins (VLDL) was normal in each of the four apoE2 (Arg136 --> Cys) carriers, regardless of the triglyceride concentrations. None of the apoE2 (Arg136 --> Cys) carriers displayed a broad beta-band and none revealed beta-migrating particles in the VLDL. The two hypertriglyceridemic carriers of apoE2 (Arg136 --> Cys) were, therefore, classified as having type IV rather than type III hyperlipoproteinemia. LDL receptor binding activities were studied using recombinant apoE loaded to dimyristoylphosphatidylcholine (DMPC) vesicles and to VLDL and from an apoE-deficient individual. LDL receptor binding of apoE2 (Arg136 --> Cys) was 14% of apoE3 and was thus higher than that of apoE2 (Arg158 --> Cys). Both apoE2 (Arg136 --> Cys) and apoE2 (Arg158 --> Cys) displayed substantial heparin binding (61 and 53% of apoE3, respectively). As the dominant apoE variants known so far are characterized by more pronounced reductions of heparin binding, we suggest that apoE2 (Arg136 --> Cys) is not associated with dominant expression of type III hyperlipoproteinemia. These findings lend support to the concept that apoE variants predisposing to dominant type III hyperlipoproteinemia differ from recessive mutations by a more severe defect in heparin binding.

Comparative effects of bezafibrate and micronised fenofibrate in patients with type III hyperlipoproteinemia.

Type III hyperlipoproteinemia (HLP) is characterized by elevated concentrations of plasma cholesterol and triglycerides due to an increase in atherogenic beta-very low density lipoproteins (beta-VLDL). As a consequence, affected individuals develop premature and accelerated atherosclerosis. Fibrates have been shown to be most effective in treatment of the dyslipidemia in type III HLP. However, comparative data on the efficacy of different fibrates in this disorder are very limited; to assess this further we have compared in a prospective study the hypolipidemic effects of bezafibrate (400 mg once daily) and micronised fenofibrate (200 mg once daily) in 23 patients with well-characterized type III HLP. Baseline values were obtained after 4 weeks on diet and treatment values were obtained after 12 weeks of treatment with each drug. Treatment with bezafibrate and micronised fenofibrate both resulted in significant reductions in the serum concentrations of total cholesterol (26.0% and 38.7%), VLDL cholesterol (41.5% and 54.1%) and total triglycerides (27.5% and 39.1%), as well as a significant increase in high density lipoprotein (HDL) cholesterol (15.0% and 27. 8%). Micronised fenofibrate was, however, significantly (P < 0.05) more effective in reducing serum concentrations of total cholesterol and VLDL cholesterol and increasing HDL cholesterol than was bezafibrate in the same patients.

Genetics of type III hyperlipoproteinemia.

One hundred forty-seven relatives of 43 patients with "classical" type III hyperlipoproteinemia (HLP) having the apolipoprotein (apo) E2/2 phenotype were studied to determine the occurrence of hyperlipidemia and the presence of further possible genes for lipoprotein disorders in these families. In 12 pedigrees primary dyslipidemia was prevalent among patients and respective blood-relatives. In these kindreds the coexistent presence of genes for familial combined hyperlipidemia (n = 6), familial hypertriglyceridemia (n = 5), and familial hypercholesterolemia (n = 1), respectively, was supposed. Our results, therefore, confirm and extend previous data on the multifactorial genesis of the diseases. Besides homozygosity for a receptor binding-defective isoform of apo E (apo E2), additional genes for familial lipoprotein disorders might operate in the pathogenesis of type III HLP. This is the largest family study performed so far in this primary lipoprotein disorder.

Severe xanthomatosis associated with familial apolipoprotein E deficiency.

AIM: To present the clinical, dermatological, and histological features of a patient with generalised xanthomatosis, familial apolipoprotein (apo) E deficiency, and unusual type III hyperlipoproteinaemia (HLP). METHODS: The underlying molecular defect was disclosed using molecular biological techniques. The unusual xanthomas were histologically analysed and the morphology of the abnormal lipoprotein particles examined using electron microscopy. RESULTS: A 10 base pair deletion in exon 4 of the proband's apo epsilon gene (base pairs 4037-4046 coding for amino acids 209-212 of the mature protein) was identified. This is predictive for a reading frameshift encoding a premature stop (TGA) in codon 229. The mutation is responsible for delayed catabolism of atherogenic lipoprotein remnants, lipid storage in monocyte/macrophages, and phenotypic expression of xanthomatosis early in life. CONCLUSIONS: Familial apo E deficiency is a rare genetic disease which offers the unique opportunity to study the impact of apo E on lipoprotein metabolism and development of atherosclerosis in humans.

Unusual xanthomas in a young patient with heterozygous familial hypercholesterolemia and type III hyperlipoproteinemia.

We report on a 20-year-old man with the combination of two independent familial lipoprotein disorders: heterozygous familial hypercholesterolemia (FH) and type III hyperlipoproteinemia (HLP). Familial hypercholesterolemia was diagnosed by elevated total and low density lipoprotein cholesterol levels and family history. By denaturing gradient gel electrophoresis, DNA sequencing and restriction fragment length polymorphism analysis, a G --> A splice donor mutation in intron 3 of the proband's low density lipoprotein receptor gene was identified as the underlying molecular defect. This mutation was described previously as a receptor-negative founder mutation in Norway (FH-Elverum) and subsequently in 6 unrelated heterozygous English patients, creating a severe phenotype of familial hypercholesterolemia. Type III HLP was confirmed by homozygosity for apolipoprotein (apo) E2 and an elevated ratio of very low density lipoprotein cholesterol to serum triglycerides (0.40; normal ratio about 0.20). The patient has unusual flat xanthomas in the interdigital webs of the hands which are normally not found in either disease. These dermatological findings might therefore be indicative of the rare combination of both disorders of lipoprotein metabolism in one individual.

Three-dimensional structure of the LDL receptor-binding domain of the human apolipoprotein E2 (Arg136-->Cys) variant.

The familial lipoprotein disorder type III hyperlipoproteinemia (HLP) is usually inherited as a recessive trait. Indeed, more than 90% of affected individuals are homozygous for a receptor binding-defective isoform of apolipoprotein (apo) E, apo E2. However, some rare apo E variants have been described that dominantly (thus in a single dose) predispose to the disease. Amino acid substitutions, which are accompanied with the loss of positive charges within the proposed apo E binding-region to lipoprotein receptors, seem to be responsible in most of these cases for the dominance with respect to the expression of type III HLP. So far available data in the literature on the naturally occurring human apo E2 (Arg136-->Cys) variant are not conclusive about its recessive or dominant character. We recently identified a subject heterozygous for this mutation, presenting the typical clinical and biochemical characteristics of type III HLP. In the present study we performed further analysis of the mutation on apo E structure and function based on computer modeling. Our combined data point to a dominant influence of the apo E2 (Arg136-->Cys) variant with respect to the transmission of the disease.

Apolipoprotein E5 (Glu212-->Lys): increased binding to cell surface proteoglycans but decreased uptake and lysosomal degradation in cultured fibroblasts.

A new apolipoprotein (apo) E variant, apoE5 (Glu212-->Lys) was identified in a Turkish family. The variant was due to a point mutation (CAG-->AAG) at the first nucleotide position of the codon encoding amino acid residue 212 of the mature apoE. The 23-year-old index patient was heterozygous for the mutation. Examination of the proband's kindred revealed six heterozygous and two homozygous mutation carriers. Compared to non-carriers, carriers of the mutation had slightly higher triglycerides (1.25 versus 1.11 g/l) and lower HDL cholesterol (0.36 versus 0.41 g/l). Very low density lipoproteins (VLDL) from an apoE5 (Glu212-->Lys) homozygote displayed enhanced binding (+17%, P < 0.05), but decreased uptake (-35%, P < 0.0001) and degradation (-51%, P < 0.0001) in cultured fibroblasts, compared to E3/3-VLDL. The region of the apoE molecule surrounding residue 212 contains a heparin binding domain. Consistently, the enhanced cell surface binding of E5/5-VLDL was observed in "wild-type" Chinese hamster ovary cells (+19%, P < 0.05), but not in proteoglycan-deficient cells. The binding of E5/5-VLDL to heparin was increased (+22%, P < 0.05). As the endocytosis of apoE-containing particles involves the transfer of proteoglycan-bound ligands to lipoprotein receptors, the stronger binding of apoE5 (Glu212-->Lys) to proteoglycans could reduce the rate at which the mutant is finally delivered to endocytotic pathways. These data may provide evidence for a functionally important heparin binding site around amino acid residue 212 of the apoE molecule in vivo.

A 10-bp deletion in the apolipoprotein epsilon gene causing apolipoprotein E deficiency and severe type III hyperlipoproteinemia.

Type III hyperlipoproteinemia (HLP) is usually associated with homozygosity for apolipoprotein (apo) E2. We identified a 30-year-old male German of Hungarian ancestry with severe type III HLP and apo E deficiency. The disease was expressed in an extreme phenotype with multiple cutaneous xanthomas. Apo E was detectable only in trace amounts in plasma but not in the different lipoprotein fractions. Direct sequencing of PCR-amplified segments of the apo epsilon gene identified a 10-bp deletion in exon 4 (bp 4037-4046 coding for amino acids 209-212 of the mature protein). The mutation is predictive for a reading frameshift introducing a premature stop codon (TGA) at amino acid 229. By western blot analysis, we found small amounts of a truncated apo E in the patient's plasma. Family analysis revealed that the proband was homozygous--and 10 of 24 relatives were heterozygous--for the mutation. Heterozygotes had, as compared to unaffected family members, significantly higher triglycerides (TG), very low-density lipoprotein (VLDL) cholesterol and a significantly higher VLDL cholesterol-to-serum TG ratio, which is indicative of a delayed remnant catabolism. We propose that the absence of a functionally active apo E is the cause of the severe type III HLP in the patient and that the mutation, even in a single dose in heterozygotes, predisposes in variable severity to the phenotypic expression of the disease.

Apolipoprotein E2 (Arg-136-->Cys), a variant of apolipoprotein E associated with late-onset dominance of type III hyperlipoproteinaemia.

Type III hyperlipoproteinaemia (HLP) is usually associated with homozygosity for apolipoprotein (apo) E2 (arg-158-->Cys). We identified a 46-year-old white female with severe hyperlipidaemia and the heterozygous apo E3/2* phenotype. Typical clinical characteristics of type III HLP, i.e. palmar xanthomas (orange-yellowish discolorations of the palmar creases) and tuberoeruptive xanthomas, were present in the patient. Without therapy the patient's serum triglycerides (1.098 mg dL(-1)), cholesterol (546 mg dL(-1)), very low-density lipoprotein (VLDL) cholesterol (372 mg dL(-1)) and the apo E concentration (25.0 mg dL(-1)) were distinctly elevated as well as her VLDL cholesterol to serum triglyceride (TG) ratio at 0.34 (normal ratio about 0.2). Direct sequencing of polymerase chain reaction (PCR)-amplified segments of the apo epsilon gene identified a thymine for cytosine (C-->T) exchange in the first base of codon 136 that is predictive for a Cys (TGC) for Arg (CGC) substitution in the encoded amino acid sequence. Two children, an 18-year-old female with the heterozygous apo E4/2* phenotype, a 25-year-old female with the heterozygous apo E3/2* phenotype and the 73-year-old father of the proband with the heterozygous apo E3/2* phenotype are also carriers of the rare mutant. The father has severe atherosclerosis and lipid values compatible with the diagnosis of type III HLP. The affected children have hyper/dyslipidaemia but as yet no clinical expression of the disease. We propose that in the analysed family this rare apo E2 (Arg-136-->Cys) variant is associated with late-onset dominance of type III HLP.

Prevalence and association of atherosclerosis at three different arterial sites in patients with type III hyperlipoproteinemia.

We have examined the prevalence of clinically significant atherosclerosis in 78 patients with type III hyperlipoproteinemia (HLP) and homozygosity for apolipoprotein (apo) E2. Forty-six of these individuals (59%) had no atherosclerosis, 32 patients (41%) had atherosclerosis, i.e., atherosclerosis of the extracranial carotid arteries (CAA), coronary arteries (CAD) or/and peripheral arteries of the legs (PVD), either singly or in combination. No association could be shown with respect to the co-prevalence of atherosclerotic lesions at these different arterial sites, except for the high predictive value (pv = 0.88, P = 0.006) of CAA for the presence of PVD. Hence, documentation of atherosclerosis under clinical aspects at one of these exposed arterial territories does not allow a reliable prediction of generalised atherosclerosis or local atherosclerosis at other sites of the arterial tree in individuals with this familial lipoprotein disorder. Therefore, assessment of the extent of clinically significant atherosclerosis in type III HLP patients should include careful and thorough examination of the extracranial carotid arteries, the coronary arteries, and the peripheral arteries of the legs.

Interaction of the lipoprotein lipase asparagine 291-->serine mutation with body mass index determines elevated plasma triacylglycerol concentrations: a study in hyperlipidemic subjects, myocardial infarction survivors, and healthy adults.

A mutation in the lipoprotein lipase (LPL) gene, resulting in the substitution of asparagine by serine at residue 291 (LPL-S291), was found to occur in young survivors of a myocardial infarction from Sweden, combined hyperlipidemic subjects from the United Kingdom, and type III hyperlipidemic subjects from Germany at allelic carrier frequencies no different from those found in companion healthy control subjects (3.63 vs. 3.37; 1.85 vs. 1.60; and 2.00 vs. 1.56%, respectively). In a group of 620 healthy middle-aged men from the United Kingdom with baseline and three subsequent annual lipid measurements, mean plasma triacylglycerol (TG), (but not plasma cholesterol) concentrations in carriers of the mutation were significantly elevated over non-carriers (1.95 vs. 1.61 mmol/l, P = 0.05, and 5.83 vs. 5.65 mmol/l, P = 0.29, respectively). When these healthy control subjects were divided according to tertiles of body mass index (BMI), as expected, non-carriers whose BMI was in the upper two tertiles (BMI > or = 25.0 kg/m2) had higher plasma TG concentrations than those in the lowest tertile (1.90 vs. 1.54 mmol/l), but this difference was much greater in LPL-S291 carriers (2.33 vs. 1.36 mmol/l, P = 0.01, BMI x genotype interaction, P = 0.02). To confirm this effect, a second group of 319 healthy subjects from the United Kingdom was screened for LPL-S291. The allelic frequency of the mutation was found to be 1.88% and the effect on plasma lipid concentrations was very similar to that observed in the first control group (plasma TG, 2.31 vs. 1.27 mmol/l, P < 0.001 for LPL-S291 carriers vs. non-carriers, respectively). As before, those carriers whose BMI was in the top two tertiles for this sample (BMI > or = 23.3 kg/m2) had higher plasma TG concentrations than non-carriers (2.31 vs. 1.42 mmol/l). Thus, the LPL-S291 variant may predispose individuals to elevated plasma TG concentrations under conditions such as increased BMI.

Regulation of beta 2-adrenergic receptor mRNA and gene transcription in rat C6 glioma cells: effects of agonist, forskolin, and protein synthesis inhibition.

Incubation of rat C6 glioma cells with beta-adrenergic receptor (beta AR) agonist or with agents that increase cAMP levels results in down-regulation of the beta 2AR, as measured by the loss of radioligand binding sites. In the present study, the role of beta 2AR mRNA expression and stability in the down-regulation of beta 2AR sites in C6 cells was examined. Isoproterenol or forskolin treatment decreased beta 2AR mRNA levels in a time-dependent manner, with maximal loss of approximately 50% being observed after 2 hr. Pretreatment of the cells with a potent protein synthesis inhibitor, Pseudomonas exotoxin A, completely blocked isoproterenol- and forskolin-mediated down-regulation of beta 2AR mRNA. Exposure to agonist did not significantly influence the half-life of beta 2AR mRNA, which was approximately 60 min. In contrast, isoproterenol treatment for 2 hr significantly decreased the rate of beta 2AR gene transcription, as determined by nuclear run-on analysis. Based on these results, we propose that agonist regulation of beta 2AR mRNA in C6 cells is mediated by activation of the cAMP system and occurs at the level of beta 2AR gene transcription, not mRNA stability. In addition, the observed requirement for protein synthesis indicates that down-regulation of beta 2AR mRNA may be mediated by expression of a repressor of beta 2AR gene transcription.