Evidence for linkage of the apolipoprotein A-II locus to plasma apolipoprotein A-II and free fatty acid levels in mice and humans

Interaction between Apo A-II -265T>C polymorphism and dietary total antioxidant capacity on some anthropometric indices and serum lipid profile in patients with type 2 diabetes mellitus

The present study aimed to investigate the interaction of Apo A-II polymorphism and dietary total antioxidant capacity (DTAC) with lipid profile and anthropometric markers in patients with type 2 diabetes (T2DM) that are at risk for atherosclerosis. This cross-sectional study was conducted on 778 patients with T2DM (35–65 years). Dietary intakes were assessed by a 147-item food frequency questionnaire. DTAC was computed using international databases. Participants were categorised into two groups based on rs5082 genotypes. The gene–diet interaction was analysed by an ANCOVA multivariate interaction model. Total cholesterol, TC; triacylglycerol, TG; high- and low-density lipoprotein, HDL and LDL; TC–HDL ratio; waist circumference, WC and body mass index, BMI were obtained according to standard protocols. Overall, the frequency of CC homozygous was 12⋅1 % among study participants. We found that a significant interaction between rs5082 variants and DTAC on mean WC (P_TEAC = 0⋅044), TC concentration (P_FRAP = 0⋅049 and P_TEAC = 0⋅031) and TC/HDL (P_FRAP = 0⋅031 and P_TRAP = 0⋅040). Among patients whose DTAC was higher than the median intake, the mean of weight, WC and TC/HDL were significantly higher only in individuals with CC genotype. Also, the high DTAC was associated with a lower TC concentration only in T-allele carriers (P_FRAP = 0⋅042). We found that adherence to a diet with high total antioxidant capacity can improve the complications of diabetes and atherosclerosis in the T carrier genotype more effectively than the CC genotype. These results could indicate the anti-atherogenic properties of Apo A-II. However, further studies are needed to shed light on this issue.

Generation of Gene-Knockout Mongolian Gerbils via CRISPR/Cas9 System

The Mongolian gerbil (Meriones unguiculatus), a well-known "multifunctional" experimental animal, plays a crucial role in the research of hearing, cerebrovascular diseases and Helicobacter pylori infection. Although the whole-genome sequencing of Mongolian gerbils has been recently completed, lack of valid gene-editing systems for gerbils largely limited the further usage of Mongolian gerbils in biomedical research. Here, efficient targeted mutagenesis in Mongolian gerbils was successfully conducted by pronuclear injection with Cas9 protein and single-guide RNAs (sgRNAs) targeting Cystatin C (Cst3) or Apolipoprotein A-II (Apoa2). We found that 22 h after human chorionic gonadotropin (hCG) injection, zygote microinjection was conducted, and the injected zygotes were transferred into the pseudopregnant gerbils, which were induced by injecting equine chorionic gonadotropin (eCG) and hCG at a 70 h interval and being caged with ligated male gerbils. We successfully obtained Cst3 and Apoa2 gene knockout gerbils with the knockout efficiencies of 55 and 30.9%, respectively. No off-target effects were detected in all knockout gerbils and the mutations can be germline-transmitted. The absence of CST3 protein was observed in the tissues of homozygous Cst3 knockout (Cst3-KO) gerbils. Interestingly, we found that disruption of the Cst3 gene led to more severe brain damage and neurological deficits after unilateral carotid artery ligation, thereby indicating that the gene modifications happened at both genetic and functional levels. In conclusion, we successfully generated a CRISPR/Cas9 system based genome editing platform for Mongolian gerbils, which provided a foundation for obtaining other genetically modified gerbil models for biomedical research.

Gene-nutrient interactions and susceptibility to human obesity

A large number of genome-wide association studies, transferability studies, and candidate gene studies performed in diverse populations around the world have identified gene variants that are associated with common human obesity. The mounting evidence suggests that these obesity gene variants interact with multiple environmental factors and increase susceptibility to this complex metabolic disease. The objective of this review article is to provide concise and updated information on energy balance, heritability of body weight, origins of gene variants, and gene-nutrient interactions in relation to human obesity. It is proposed that knowledge of these related topics will provide valuable insight for future preventative lifestyle intervention using targeted nutritional and medicinal therapies.

C57BL/6J mouse apolipoprotein A2 gene is deterministic for apnea

RATIONALE

Brainstem apolipoprotein AII (apoa2) mRNA expression correlates with apnea in breathing present in the adult C57Bl/6J (B6) sleep apnea model.

OBJECTIVES

To test the hypothesis that the B6 apoa2 gene contributes to the trait, we performed plethysmographic testing in apoa2 knock out (KO: -/-) mice, an in situ brainstem-spinal cord preparation comparing KO to WT (+/+) mice, and B6xDBA recombinant inbred strains (RISs).

MEASUREMENTS AND MAIN RESULTS

Apoa2 WT do, but KO and heterozygote (+/-) mice do not exhibit apnea during post-hypoxic breathing, measured in vivo. In the in situ model, pauses and instability in fictive phrenic bursting are substantially reduced in KO vs. WT preparations. In 24 RISs, apnea number in vivo was higher in strains with B6 apoa2 than with DBA apoa2 alleles.

CONCLUSIONS

The B6 apoa2 polymorphism is directly involved in breath production, and its identification suggests a novel pathway influencing risk for adult sleep apnea.

Proteomic characterization of pediatric craniopharyngioma intracystic fluid by LC-MS top-down/bottom-up integrated approaches

The combination of top-down and bottom-up platforms was utilized for the LC-MS proteomic characterization of the intracystic fluid of adamantinomatous craniopharyngioma pediatric brain tumor disease. Proteins and peptides characterization was achieved by high-resolution LC-ESI-LTQ-Orbitrap-MS analysis while low-resolution LC-ESI-IT-MS was applied for the complete screening of the samples and the evaluation of the protein distribution within patients. Top-down analyses were applied to liquid/liquid extracted samples while bottom-up analyses were performed after trypsin digestion of both untreated and pretreated samples. The two proteomic approaches were complementary for the characterization of the proteome of craniopharyngioma intracystic fluid. Proteins and peptides involved in inflammation, mineralization processes and lipid transport were identified, in agreement with the calcium flecks, cholesterol granules and bone residues characteristic of this fluid. Apolipoprotein A-I, A-II, C-I and J, hemoglobin fragments, ubiquitin, α-2-HS-glycoprotein or fetuin A, α-1-antichymotrypsin, vitamin D binding protein, and α-1-acid glycoprotein were characterized. These data could be relevant for the comprehension of the processes involved in the pathogenesis of the disease and the development of the cyst and could contribute to the individuation of therapeutic targets for the reduction of the cyst volume delaying and/or avoiding invasive surgical treatments.

Genome-wide scans for candidate genes involved in the aquatic adaptation of dolphins

Since their divergence from the terrestrial artiodactyls, cetaceans have fully adapted to an aquatic lifestyle, which represents one of the most dramatic transformations in mammalian evolutionary history. Numerous morphological and physiological characters of cetaceans have been acquired in response to this drastic habitat transition, such as thickened blubber, echolocation, and ability to hold their breath for a long period of time. However, knowledge about the molecular basis underlying these adaptations is still limited. The sequence of the genome of Tursiops truncates provides an opportunity for a comparative genomic analyses to examine the molecular adaptation of this species. Here, we constructed 11,838 high-quality orthologous gene alignments culled from the dolphin and four other terrestrial mammalian genomes and screened for positive selection occurring in the dolphin lineage. In total, 368 (3.1%) of the genes were identified as having undergone positive selection by the branch-site model. Functional characterization of these genes showed that they are significantly enriched in the categories of lipid transport and localization, ATPase activity, sense perception of sound, and muscle contraction, areas that are potentially related to cetacean adaptations. In contrast, we did not find a similar pattern in the cow, a closely related species. We resequenced some of the positively selected sites (PSSs), within the positively selected genes, and showed that most of our identified PSSs (50/52) could be replicated. The results from this study should have important implications for our understanding of cetacean evolution and their adaptations to the aquatic environment.

Apolipoprotein A-II: evaluating its significance in dyslipidaemia, insulin resistance, and atherosclerosis

Reduced HDL cholesterol, commonly found in subjects with obesity and type 2 diabetes, is associated with increased risk of cardiovascular disease (CVD). ApoA-II, a constituent apolipoprotein of certain HDL particles, plays an important role in the regulation of cholesterol efflux, HDL remodelling, and cholesteryl ester uptake via its interactions with lipid transfer proteins, lipases, and cellular HDL receptors. Recent studies have linked apoA-II directly with triglyceride and glucose metabolism. Most of the data are, however, derived from cellular systems and transgenic animal models. Direct evidence from human studies is scarce. Clinical studies demonstrate that apoA-II is a strong predictor of risk for CVD. There is no evidence, however, that selective therapeutic modification of apoA-II impacts on atherosclerosis and clinical outcomes. More research is required to investigate further the significance of apoA-II in clinical medicine.

Gene-diet interactions in childhood obesity

Childhood overweight and obesity have reached epidemic proportions worldwide, and the increase in weight-associated co-morbidities including premature type 2 diabetes mellitus (T2DM) and atherosclerotic cardiovascular disease will soon become major healthcare and economic problems. A number of studies now indicate that the childhood obesity epidemic which has emerged during the past 30 years is a complex multi-factorial disease resulting from interaction of susceptibility genes with an obesogenic environment. This review will focus on gene-diet interactions suspected of having a prominent role in promoting childhood obesity. In particular, the specific genes that will be presented (FTO, MC4R, and NPC1) have recently been associated with childhood obesity through a genome-wide association study (GWAS) and were shown to interact with nutritional components to increase weight gain. Although a fourth gene (APOA2) has not yet been associated with childhood obesity, this review will also present information on what now represents the best characterized gene-diet interaction in promoting weight gain.

Apolipoprotein AII is a regulator of very low density lipoprotein metabolism and insulin resistance

Apolipoprotein AII (apoAII) transgenic (apoAIItg) mice exhibit several traits associated with the insulin resistance (IR) syndrome, including IR, obesity, and a marked hypertriglyceridemia. Because treatment of the apoAIItg mice with rosiglitazone ameliorated the IR and hypertriglyceridemia, we hypothesized that the hypertriglyceridemia was due largely to overproduction of very low density lipoprotein (VLDL) by the liver, a normal response to chronically elevated insulin and glucose. We now report in vivo and in vitro studies that indicate that hepatic fatty acid oxidation was reduced and lipogenesis increased, resulting in a 25% increase in triglyceride secretion in the apoAIItg mice. In addition, we observed that hydrolysis of triglycerides from both chylomicrons and VLDL was significantly reduced in the apoAIItg mice, further contributing to the hypertriglyceridemia. This is a direct, acute effect, because when mouse apoAII was injected into mice, plasma triglyceride concentrations were significantly increased within 4 h. VLDL from both control and apoAIItg mice contained significant amounts of apoAII, with approximately 4 times more apoAII on apoAIItg VLDL. ApoAII was shown to transfer spontaneously from high density lipoprotein (HDL) to VLDL in vitro, resulting in VLDL that was a poorer substrate for hydrolysis by lipoprotein lipase. These results indicate that one function of apoAII is to regulate the metabolism of triglyceride-rich lipoproteins, with HDL serving as a plasma reservoir of apoAII that is transferred to the triglyceride-rich lipoproteins in much the same way as VLDL and chylomicrons acquire most of their apoCs from HDL.

Apolipoprotein A-II Is Inversely Associated With Risk of Future Coronary Artery Disease

Background— Although the vasculoprotective effects of apolipoprotein A-I (apoA-I), the major protein associated with high-density lipoprotein, have been universally accepted, apoA-II has been suggested to have poor antiatherogenic or even proatherogenic properties. To study this suggestion more closely, we evaluated how serum levels of apoA-II and apoA-I relate to the risk of future coronary artery disease (CAD) in a large, prospective study.

Methods and Results— We performed a nested case-control study in the prospective EPIC-Norfolk (European Prospective Investigation into Cancer and Nutrition–Norfolk) cohort. Case subjects (n=912) were apparently healthy men and women aged 45 to 79 years who developed fatal or nonfatal CAD during a mean follow-up of 6 years. Control subjects (n=1635) were matched by age, gender, and enrollment time. Conditional logistic regression was used to quantify the relationship between serum apoA-II levels and risk of CAD. Serum apoA-II concentration was significantly lower in case subjects (34.5±6.3 mg/dL) than in control subjects (35.2±5.8 mg/dL) and was inversely associated with risk of CAD, such that patients in the upper quartile (>38.1 mg/dL) had an odds ratio of 0.59 (95% confidence interval 0.46 to 0.76) versus those in the lowest quartile (<31.1 mg/dL; P for linearity <0.0001). After adjustment for fasting time, alcohol use, and cardiovascular risk factors (systolic blood pressure, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, body mass index, smoking, diabetes mellitus, and C-reactive protein), the corresponding risk estimate was 0.48 (95% confidence interval 0.34 to 0.67, P for linearity <0.0001). Surprisingly, additional adjustment for serum apoA-I levels did not affect risk prediction of apoA-II for future CAD (odds ratio 0.49, 95% confidence interval 0.34 to 0.68, P for linearity <0.0001). Also, after adjustment for high-density lipoprotein particle number and size, apoA-II was still associated with the risk of future CAD (odds ratio 0.62, 95% confidence interval 0.43 to 0.90, P for linearity 0.02).

Conclusions— ApoA-II is associated with a decreased risk of future CAD in apparently healthy people. These findings imply that apoA-II itself exerts effects on specific antiatherogenic pathways. On the basis of these findings, discussion of the potential proatherogenic effects of apoA-II can cease.

An apolipoprotein A-II polymorphism (-265T/C, rs5082) regulates postprandial response to a saturated fat overload in healthy men

Apolipoprotein (Apo) A-II is an apolipoprotein with an unknown role in lipid metabolism. It has been suggested that the presence of the less frequent allele of a single nucleotide polymorphism (Apo A-II -265T/C, rs5082) reduces the transcription rate of Apo A-II and enhances VLDL postprandial clearance in middle-aged men. To further investigate the role of Apo A-II -265T/C on lipid metabolism, we studied 88 normolipidemic young men. The participants were given a fatty meal containing 1 g fat and 7 mg cholesterol/kg weight and capsules containing 60,000 IU vitamin A (retinyl palmitate, 15.15 mg RE) per square meter body surface area. Postprandial lipemia was assessed during the 11 h following the meal. Total cholesterol (Chol) and triacylglycerols (TG) in plasma and TG-rich lipoproteins (TRL) (large TRL and small TRL) were measured, as well as HDL, Apo A-I, Apo B, Apo B-48, and Apo B-100. Postprandial responses were higher in the TT group than in carriers of the minor allele (CC/TC) for total TG in plasma (21.37% of change of area under curve, P = 0.014), large TRL-TG (24.75% change, P = 0.017) and small TRL-Chol (26.63% change, P = 0.003). Our work shows that carriers of the minor allele for Apo A-II -265T/C (CC/TC) have a lower postprandial response compared with TT homozygotes. This finding may partially explain the role of Apo A-II in lipid metabolism and can identify a population with a decreased risk of cardiovascular disease, as corresponds to the lower level of postprandial hypertriglyceridemia.

The -256T>C polymorphism in the apolipoprotein A-II gene promoter is associated with body mass index and food intake in the genetics of lipid lowering drugs and diet network study

BACKGROUND

Apolipoprotein A-II (APOA2) plays an ambiguous role in lipid metabolism, obesity, and atherosclerosis.

METHODS

We studied the association between a functional APOA2 promoter polymorphism (-265T>C) and plasma lipids (fasting and postprandial), anthropometric variables, and food intake in 514 men and 564 women who participated in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) study. We obtained fasting and postprandial (after consuming a high-fat meal) measures. We measured lipoprotein particle concentrations by proton nuclear magnetic resonance spectroscopy and estimated dietary intake by use of a validated questionnaire.

RESULTS

We observed recessive effects for this polymorphism that were homogeneous by sex. Individuals homozygous for the -265C allele had statistically higher body mass index (BMI) than did carriers of the T allele. Consistently, after multivariate adjustment, the odds ratio for obesity in CC individuals compared with T allele carriers was 1.70 (95% CI 1.02-2.80, P = 0.039). Interestingly, total energy intake in CC individuals was statistically higher [mean (SE) 9371 (497) vs 8456 (413) kJ/d, P = 0.005] than in T allele carriers. Likewise, total fat and protein intakes (expressed in grams per day) were statistically higher in CC individuals (P = 0.002 and P = 0.005, respectively). After adjustment for energy, percentage of carbohydrate intake was statistically lower in CC individuals. These associations remained statistically significant even after adjustment for BMI. We found no associations with fasting lipids and only some associations with HDL subfraction distribution in the postprandial state.

CONCLUSIONS

The -265T>C polymorphism is consistently associated with food consumption and obesity, suggesting a new role for APOA2 in regulating dietary intake.

Identification of potential markers for the detection of pancreatic cancer through comparative serum protein expression profiling

OBJECTIVE

Early detection is the only promising approach to significantly improve the survival of patients with pancreatic cancer (PCa). Noninvasive tools for the diagnosis, prognosis, and monitoring of this disease are of urgent need. The purpose of this study was to identify and validate new biomarkers in PCa patient serum samples.

METHODS

Surface-enhanced laser desorption/ionization time-of-flight mass spectrometry has been applied to analyze serum protein alterations associated with PCa and to identify sets of potential biomarkers indicative for this disease. A cohort of 96 serum samples from patients undergoing PCa surgery was compared with sera from 96 healthy volunteers as controls. The sera were fractionated by anion exchange chromatography, and 3 of 6 fractions were analyzed onto 2 different chromatographic arrays.

RESULTS

Data analysis revealed 24 differentially expressed protein peaks (P < 0.001), of which 21 were downregulated in the PCa samples. The best single marker can predict 92% of the controls and 89% of the cancer samples correctly. In addition, multivariate pattern analysis was performed. The best pattern model using a set of 3 markers was obtained using fraction 6 on immobilized metal affinity capture, loaded with Cu-Cu arrays. With this pattern model, a sensitivity of 100% and a specificity of 98% for the training data set and a sensitivity of 83% and specificity of 77% for the test data set were achieved with the PCa group set as true positive. Several of protein peaks, including the best single marker at 17.27 kd and other proteins from the pattern models, were purified and identified by peptide mapping and postsource decay-matrix-assisted laser desorption ionization-time-of-flight mass spectrometry. Apolipoprotein A-II, transthyretin, and apolipoprotein A-I were identified as markers, and these identified proteins were decreased at least 2-fold in PCa serum when compared with the control group.

CONCLUSIONS

PCa is associated with a specific decrease of distinct serum proteins, which allows a reliable differentiation between pancreatic cancer and healthy controls.

Identification of Apolipoprotein A-II in Cerebrospinal Fluid of Pediatric Brain Tumor Patients by Protein Expression Profiling

Background: Our aim was to detect differences in protein expression profiles of cerebrospinal fluid (CSF) from pediatric patients with and without brain tumors.

Methods: We used surface-enhanced laser desorption/ionization time-of-flight (SELDI-TOF) mass spectrometry and Q10 ProteinChip arrays to compare protein expression profiles of CSF from 32 pediatric brain tumor patients and 70 pediatric control patients. A protein with high discriminatory power was isolated and identified by subsequent anion-exchange and reversed-phase fractionation, gel electrophoresis, and mass spectrometry. The identity of the protein was confirmed by Western blotting and immunohistochemistry.

Results: Of the 247 detected protein peak clusters, 123 were differentially expressed between brain tumor and control patients with a false discovery rate of 1%. Double-loop classification analysis gave a mean prediction accuracy of 88% in discriminating brain tumor patients from control patients. From the 123 clusters, a highly overexpressed protein peak cluster in CSF from brain tumor patients was selected for further analysis and identified as apolipoprotein A-II. Apolipoprotein A-II expression in CSF was correlated with the CSF albumin concentration, suggesting that the overexpression of apolipoprotein A-II is related to a disrupted blood–brain barrier.

Conclusions: SELDI-TOF mass spectrometry can be successfully used to find differentially expressed proteins in CSF of pediatric brain tumor and control patients. Apolipoprotein A-II is highly overexpressed in CSF of pediatric brain tumor patients, which most likely is related to a disrupted blood–brain barrier. Ongoing studies are aimed at finding subtype specific proteins in larger groups of pediatric brain tumor patients.

Trans-10, cis-12- and cis-9, trans-11-conjugated linoleic acid isomers selectively modify HDL-apolipoprotein composition in apolipoprotein E knockout mice

Trans-10, cis-12-conjugated linoleic acid (CLA)-enriched diets promote atherosclerosis in mice despite increasing blood concentrations of HDL cholesterol. This suggests that under these conditions, the HDL apolipoproteins (apo) produced are abnormal. To test this hypothesis, apoE-deficient mice were fed a Western-type diet enriched with linoleic acid (control), cis-9, trans-11-CLA or trans-10, cis-12-CLA (1.0% wt/wt) for 12 wk, and the effects on HDL metabolism and apoC-III levels recorded. Compared with the control and cis-9, trans-11-CLA mice, those fed the trans-10, cis-12-CLA diet had significantly higher HDL cholesterol concentrations, and had a higher incidence of hypertriglyceridemia and hepatic steatosis. Plasma apoA-I and paraoxonase concentrations were significantly lower in the trans-10, cis-12-CLA group than in the cis-9, trans-11-CLA group. These reductions were associated with decreased hepatic expression of these proteins and a shift toward lipid-poor apolipoprotein particles. The plasma apoA-II concentration increased with its corresponding mRNA concentration in the liver, and was preferentially bound to HDL in the trans-10, cis-12-CLA mice, thus explaining the increased HDL cholesterol concentrations in this group. Significant, positive associations were found between apoA-II and C-III (r=0.883, P<0.001) and between apoA-II and atherosclerosis (r=0.68, P<0.001). These results indicate that trans-10, cis-12-CLA intake modifies HDL to form a proatherogenic apoA-II containing particle and promotes phenotypic changes compatible with metabolic syndrome. Cis-9, trans-11-CLA does not promote this detrimental effect.

Integrating Genetic and Gene Expression Data to Study the Metabolic Syndrome and Diabetes in Mice

Increasingly, the mouse is becoming the standard model for mammalian physiology and disease. It can be genetically analyzed and manipulated with relative ease. Moreover, the endogenous genetic variation that exists among inbred mouse strains can be exploited to identify genetic control of complex physiologic processes involved in diabetes and the metabolic syndrome, among other conditions relevant to human disease. Recent advances in genetics and gene expression technology have greatly increased the knowledge to be derived from this approach when applied to traditional genetic studies.

Serum Levels of an Isoform of Apolipoprotein A-II as a Potential Marker for Prostate Cancer

Purpose: We recently showed that protein expression profiling of serum using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) has potential as a diagnostic approach for detection of prostate cancer. As a parallel effort, we have been pursuing the identification of the protein(s) comprising the individual discriminatory “peaks” and evaluating their utility as potential biomarkers for prostate disease.

Experimental Design: We employed liquid chromatography, gel electrophoresis and tandem mass spectroscopy to isolate and identify a protein that correlates with observed SELDI-TOF MS mass/charge (m/z) values. Immunodepletion, immunoassay, and Western analysis were used to verify that the identified protein generated the observed SELDI peak. Subsequent immunohistochemistry was used to examine the expression of the proteins in prostate tumors.

Results: An 8,946 m/z SELDI-TOF MS peak was found to retain discriminatory value in each of two separate data sets with an increased expression in the diseased state. Sequence identification by liquid chromatography-MS/MS and subsequent immunoassays verified that an isoform of apolipoprotein A-II (ApoA-II) is the observed 8,946 m/z SELDI peak. Immunohistochemistry revealed that ApoA-II is overexpressed in prostate tumors. SELDI-based immunoassay revealed that an 8.9-kDa isoform of ApoA-II is specifically overexpressed in serum from individuals with prostate cancer. ApoA-II was also overexpressed in the serum of individuals with prostate cancer who have normal prostate-specific antigen (0-4.0 ng/mL).

Conclusions: We have identified an isoform of ApoA-II giving rise to an 8.9K m/z SELDI “peak” that is specifically overexpressed in prostate disease. The ability of ApoA-II to detect disease in patients with normal prostate-specific antigen suggests potential utility of the marker in identifying indolent disease.

Genetics of atherosclerosis

Atherosclerosis, the primary cause of coronary artery disease (CAD) and stroke, is a disorder with multiple genetic and environmental contributions. Genetic-epidemiologic studies have identified a surprisingly long list of genetic and nongenetic risk factors for CAD. However, such studies indicate that family history is the most significant independent risk factor (15, 52, 77). Many Mendelian disorders associated with atherosclerosis, such as familial hypercholesterolemia (FH), have been characterized, but they explain only a small percentage of disease susceptibility (although a substantial fraction of early CAD). Most cases of myocardial infarction (MI) and stroke result from the interactions of multiple genetic and environmental factors, none of which can cause disease by itself. Successful discovery of these genetic factors will require using complementary approaches with animal models, large-scale human genetic studies, and functional experiments. This review emphasizes the common, complex forms of CAD.

An autosomal genomic scan for loci linked to type 2 diabetes in northern Han Chinese

We report the results of a genome-wide scan conducted in 219 individuals from 34 large multiplex nuclear pedigrees from the northern Han Chinese population at an average resolution of about 10 cM. Nonparametric two-point and multipoint linkage analyses were performed to detect evidence of linkage with type 2 diabetes in this study. On chromosome 1 four regions showed evidence of linkage with type 2 diabetes in northern Han Chinese. Of these regions a marker D1S193 (73 cM) showed evidence of linkage (two-point nonparametric linkage 2.409), and another region (around 190 cM) was a replication of several other studies performed in different ethnic populations. Evidences of linkage have been confirmed by typing additional markers (average distance 1-5 cM) flanking these two positive regions on chromosome 1. We also found indication of linkage with type 2 diabetes on chromosomes 2, 10, 12, 18, 20, and 22 by two-point linkage analyses.

Mechanisms mediating insulin resistance in transgenic mice overexpressing mouse apolipoprotein A-II

We previously demonstrated that transgenic mice overexpressing mouse apolipoprotein A-II (apoA-II) exhibit several traits associated with the insulin resistance (IR) syndrome, including increased atherosclerosis, hypertriglyceridemia, obesity, and IR. The skeletal muscle appeared to be the insulin-resistant tissue in the apoA-II transgenic mice. We now demonstrate a decrease in FA oxidation in skeletal muscle of apoA-II transgenic mice, consistent with reports that decreased skeletal muscle FA oxidation is associated with increased skeletal muscle triglyceride accumulation, skeletal muscle IR, and obesity. The decrease in FA oxidation is not due to decreased carnitine palmitoyltransferase 1 activity, because oxidation of palmitate and octanoate were similarly decreased. Quantitative RT-PCR analysis of gene expression demonstrated that the decrease in FA oxidation may be explained by a decrease in medium chain acyl-CoA dehydrogenase. We previously demonstrated that HDLs from apoA-II transgenic mice exhibit reduced binding to CD36, a scavenger receptor involved in FA metabolism. However, studies of combined apoA-II transgenic and CD36 knockout mice suggest that the major effects of apoA-II are independent of CD36. Rosiglitazone treatment significantly ameliorated IR in the apoA-II transgenic mice, suggesting that the underlying mechanisms of IR in this animal model may share common features with certain types of human IR.

Apolipoprotein A-II, genetic variation on chromosome 1q21-q24, and disease susceptibility

PURPOSE OF REVIEW

Apolipoprotein (apo) A-II is the second most abundant HDL apolipoprotein; however its function remains largely unknown. Owing to the lack of consequences of apoA-II deficiency in humans, it has long been considered an apolipoprotein of minor importance. Overexpression of apoA-II in transgenic mice, however, causes combined hyperlipidemia and, in some cases, insulin resistance. This, and the location of the apoA-II gene in chromosome 1q23, a hot region in the search for genes associated with familial combined hyperlipidemia, insulin resistance and type 2 diabetes mellitus, has greatly increased interest in this protein.

RECENT FINDINGS

ApoA-II is biochemically and genetically linked to familial combined hyperlipidemia. Given that the chromosome 1q21-q24 region is associated with insulin resistance or type 2 diabetes, this region is a now a focus of interest in the study of these complex, often overlapping diseases. However, no polymorphisms that increase apoA-II levels have been identified to date in humans. Other nonstructural loci may regulate apoA-II plasma concentration. Further, plasma apoA-II concentration is increased by saturated fat intake. Several reports have added to our understanding of the relationship between apoA-II mutations and amyloidosis both in humans and mice.

SUMMARY

An increased plasma concentration of apoA-II might contribute to familial combined hyperlipidemia or type 2 diabetes mellitus expression, which emphasizes the need to understand its function and metabolism. Genetic studies in well characterized patients and genomic and proteomic approaches in cell and mouse models may help to achieve this understanding.

Polymorphisms of mouse apolipoprotein A-II: seven alleles found among 41 inbred strains of mice

In mice, apolipoprotein A-II (apoA-II) associates to form amyloid fibrils in an age-associated manner. We determined the complete nucleotide sequences of the apoA-II gene (Apoa2) cDNA in 41 inbred strains of mice including Mus musculus domesticus (laboratory mouse), Mus musculus castaneus, Mus musculus molossinus, Mus musculus musculus and Mus spretus. Among these strains we identified 7 alleles (Apoa2a1, Apoa2a2, Apoa2b, Apoa2c, Apoa2d, Apoa2e and Apoa2f). Polymorphisms of nucleotides at 15 positions were detected and amino acid substitutions were found at 8 positions. Apoa2a1 was found in all mouse subspecies, but Apoa2b and Apoa2c were found only in Mus musculus domesticus. Two strains of Mus spretus have the unique alleles Apoa2e and Apoa2f which resemble Apoa2c. We confirmed that VICS in which we found severe amyloidosis here and other amyloidoneic strains in published reports have Apoa2c allele. We determined the plasma concentrations of total and HDL cholesterol in the strains of Mus musculus domesticus with the Apoa2a1, Apoa2b and Apoa2c alleles. Significantly higher concentrations of plasma cholesterol were observed in mouse strains with the Apoa2b allele. These findings provide fundamental data on mouse Apoa2 alleles. Furthermore, differences in these alleles likely have considerable influence on traits related to amyloidosis and lipid metabolism.

Biochemical and genetic association of plasma apolipoprotein A-II levels with familial combined hyperlipidemia

Apolipoprotein A-II (apoA-II) is a major protein on high-density lipoprotein (HDL) particles, and in mice, its levels are associated with triglyceride and glucose metabolism. In particular, transgenic mice overexpressing apoA-II exhibit hypertriglyceridemia, increased body fat, and insulin resistance, whereas apoA-II-null mice have decreased triglycerides and increased insulin sensitivity. Given the phenotypic overlap between familial combined hyperlipidemia (FCH) and apoA-II transgenic mice, we investigated the relationship of apoA-II to this disorder. Despite having lower HDL-cholesterol (HDL-C), FCH subjects had higher apoA-II levels compared with unaffected relatives (P<0.00016). Triglyceride and HDL-C levels were significant predictors of apoA-II, demonstrating that apoA-II variation is associated with several FCH-related traits. After adjustment for multiple covariates, there was evidence for the heritability of apoA-II levels (h2=0.15; P<0.02) in this sample. A genome scan for apoA-II levels identified significant evidence (LOD=3.1) for linkage to a locus on chromosome 1q41, coincident with a suggestive linkage for triglycerides (LOD score=1.4). Thus, this locus may have pleiotropic effects on apoA-II and FCH traits. Our results demonstrate that apoA-II is biochemically and genetically associated with FCH and may serve as a useful marker for understanding the mechanism by which FCH develops.

Apolipoprotein A-II: beyond genetic associations with lipid disorders and insulin resistance

PURPOSE OF REVIEW

Apolipoprotein A-II, the second major HDL apolipoprotein, was often considered of minor importance relatively to apolipoprotein A-I and its role was controversial. This picture is now rapidly changing, due to novel polymorphisms and mutations, to the outcome of clinical trials, and to studies with transgenic mice.

RECENT FINDINGS

The -265 T/C polymorphism supports a role for apolipoprotein A-II in postprandial very-low-density lipoprotein metabolism. Fibrates, which increase apolipoprotein A-II synthesis, significantly decrease the incidence of major coronary artery disease events, particularly in subjects with low HDL cholesterol, high plasma triglyceride, and high body weight. The comparison of transgenic mice overexpressing human or murine apolipoprotein A-II has highlighted major structural differences between the two proteins; they have opposite effects on HDL size, apolipoprotein A-I content, plasma concentration, and protection from oxidation. Human apolipoprotein A-II is more hydrophobic, displaces apolipoprotein A-I from HDL, accelerates apolipoprotein A-I catabolism, and its plasma concentration is decreased by fasting. Apolipoprotein A-II stimulates ATP binding cassette transporter 1-mediated cholesterol efflux. Human and murine apolipoprotein A-II differently affect glucose metabolism and insulin resistance. A novel beneficial role for apolipoprotein A-II in the pathogenesis of hepatitis C virus has been shown.

SUMMARY

The hydrophobicity of human apolipoprotein A-II is a key regulatory factor of HDL metabolism. Due to the lower plasma apolipoprotein A-II concentration during fasting, measurements of apolipoprotein A-II in fed subjects are more relevant. More clinical studies are necessary to clarify the role of apolipoprotein A-II in well-characterized subsets of patients and in the insulin resistance syndrome.

A candidate gene study in low HDL-cholesterol families provides evidence for the involvement of the APOA2 gene and the APOA1C3A4 gene cluster

In patients with premature coronary heart disease, the most common lipoprotein abnormality is high-density lipoprotein (HDL) deficiency. To assess the genetic background of the low HDL-cholesterol trait, we performed a candidate gene study in 25 families with low HDL, collected from the genetically isolated population of Finland. We studied 21 genes encoding essential proteins involved in the HDL metabolism by genotyping intragenic and flanking markers for these genes. We found suggestive evidence for linkage in two candidate regions: Marker D1S2844, in the apolipoprotein A-II (APOA2) region, yielded a LOD score of 2.14 and marker D11S939 flanking the apolipoprotein A-I/C-III/A-IV gene cluster (APOA1C3A4) produced a LOD score of 1.69. Interestingly, we identified potential shared haplotypes in these two regions in a subset of low HDL families. These families also contributed to the obtained positive LOD scores, whereas the rest of the families produced negative LOD scores. None of the remaining candidate regions provided any evidence for linkage. Since only a limited number of loci were tested in this candidate gene study, these LOD scores suggest significant involvement of the APOA2 gene and the APOA1C3A4 gene cluster, or loci in their immediate vicinity, in the pathogenesis of low HDL.

Significant impact of the highly informative (CA)n repeat polymorphism of the APOA-II gene on the plasma APOA-II concentrations and HDL subfractions: The ECTIM study

High density lipoproteins (HDL) are heterogeneous in their apolipoprotein composition and the role of apolipoprotein A-II (APOA-II) in HDL structure and metabolism is poorly understood. Yet, studies of naturally occurring variations of APOA-II in mice and experiments in transgenic mice overexpressing the APOA-II gene (APOA-II) have shown that APOA-II expression influences APOA-II plasma levels and HDL size and composition. In humans, two RFLPs (BstNI and MspI) have been described in the APOA-II gene. These RFLPs, however, have been inconstantly associated with variations in APOA-II plasma levels. In particular, the large multicentric ECTIM Study did not show any significant effect of the two RFLPs. Other polymorphisms consisting of repetitive sequences have been proposed as more informative markers than RFLPs. Thus, data from the ECTIM Study were reconsidered by integrating the additional information obtained from a highly informative multiallelic (CA)(n)-repeat polymorphism located in the second intron of the gene. The population study was composed of 763 non-treated male controls and 594 cases of myocardial infarction. In controls, the (CA)(19) allele was associated with significantly decreased APOA-II (P < 0.0009) and LpA-II:A-I (P < 0.02) plasma levels. Although the APOA-I plasma levels were not affected by the polymorphism, the (CA)(19) allele was associated with an increased LpA-I/LpA-II:A-I ratio (P < 0.004). No effect, however, could be detected on myocardial infarction. Study of the linkage disequilibrium and the estimation of haplotype frequencies indicated that the impact of the APOA-II locus could hardly be detected by using the BstNI and MspI RFLPs. These data revive interest in evaluating the role of the APOA-II locus in the control of APOA-II plasma levels and HDL composition.

Human evidence that the apolipoprotein a-II gene is implicated in visceral fat accumulation and metabolism of triglyceride-rich lipoproteins

BACKGROUND

Apolipoprotein (apo) A-II is a major structural protein of plasma HDLs, but little is known regarding its functions.

METHODS AND RESULTS

To investigate the physiological role of apoA-II in humans, we screened the promoter region of the apoA-II gene for a functional polymorphism and used this polymorphism as a tool in association studies. A common, functional polymorphism in the promoter region of the apoA-II gene, a T to C substitution at position -265, was found. Electrophoretic mobility shift assays demonstrated that the -265T/C polymorphism influences the binding of nuclear proteins, whereas transient transfection studies in human hepatoma cells showed a reduced basal rate of transcription of the -265C allele compared with the -265T allele. The -265C allele was associated with decreased plasma apoA-II concentration and decreased waist circumference in healthy 50-year-old men. In addition, oral fat tolerance tests provided evidence that the -265C allele enhances postprandial metabolism of large VLDLs.

CONCLUSIONS

ApoA-II appears to promote visceral fat accumulation and impair metabolism of large VLDLs.

Studies with apolipoprotein A-II transgenic mice indicate a role for HDLs in adiposity and insulin resistance

Apolipoprotein A-II (apoA-II) is the second most abundant protein in HDLs. Genetic studies in humans have provided evidence of linkage of the apoA-II gene locus to plasma free fatty acid (FFA) levels and to type 2 diabetes, and transgenic mice overexpressing mouse apoA-II have elevated levels of both FFA and triglycerides. We now show that apoA-II promotes insulin resistance and has diverse effects on fat homeostasis. ApoA-II transgenic mice have increased adipose mass and higher plasma leptin levels than C57BL/6J control mice. Fasting glucose levels were similar between apoA-II transgenic and control mice, but plasma insulin levels were elevated approximately twofold in the apoA-II transgenic mice. Compared with control mice, apoA-II transgenic mice exhibited a delay in plasma clearance of a glucose bolus. Adipose tissue isolated from fasted apoA-II transgenic mice exhibited a 50% decrease in triglyceride hydrolysis compared with adipose tissue from control mice. This is consistent with a normal response of adipose tissue to the increased insulin levels in the apoA-II transgenic mice and may partially explain the increased fat deposition. Skeletal muscle isolated from fasted apoA-II transgenic mice exhibited reduced uptake of 2-deoxyglucose compared with muscles isolated from control mice. Our observations indicate that a primary disturbance in lipoprotein metabolism can result in several traits associated with insulin resistance, consistent with the hypothesis that insulin resistance and type 2 diabetes can, under certain circumstances, be related primarily to altered lipid metabolism rather than glucose metabolism.

Increased production of very-low-density lipoproteins in transgenic mice overexpressing human apolipoprotein A-II and fed with a high-fat diet

We investigated the mechanisms that lead to combined hyperlipidemia in transgenic mice that overexpress human apolipoprotein (apo) A-II (line 11.1). The 11.1 transgenic mice develop pronounced hypertriglyceridemia, and a moderate increase in free fatty acid (FFA) and plasma cholesterol, especially when fed a high-fat/high-cholesterol diet. Post-heparin plasma lipoprotein lipase and hepatic lipase activities (using artificial or natural autologous substrates), the decay of plasma triglycerides with fasting, and the fractional catabolic rate of the radiolabeled VLDL-triglyceride (both fasting and postprandial) were similar in 11. 1 transgenic mice and in control mice. In contrast, a 2.5-fold increase in hepatic VLDL-triglyceride production was observed in 11. 1 transgenic mice in a period of 2 h in which blood lipolysis was inhibited. This increased synthesis of hepatic VLDL-triglyceride used preformed FFA rather than FFA of de novo hepatic synthesis. The 11.1 transgenic mice also presented reduced epididymal/parametrial white adipose tissue weight (1.5-fold), increased rate of epididymal/parametrial hormone-sensitive lipase-mediated lipolysis (1.2-fold) and an increase in cholesterol and, especially, in triglyceride liver content, suggesting an enhanced mobilization of fat as the source of preformed FFA reaching the liver. Increased plasma FFA was reverted by insulin, demonstrating that 11.1 transgenic mice are not insulin resistant. We conclude that the overexpression of human apoA-II in transgenic mice induces combined hyperlipidemia through an increase in VLDL production. These mice will be useful in the study of molecular mechanisms that regulate the overproduction of VLDL, a situation of major pathophysiological interest since it is the basic mechanism underlying familial combined hyperlipidemia.

Association between serum amyloid A proteins and coronary artery disease: evidence from two distinct arteriosclerotic processes

BACKGROUND

Serum amyloid A (SAA) proteins are a family of inflammatory apolipoproteins that may modify high-density lipoprotein structure and function. Elevations of SAA have been reported in unstable coronary syndromes, but the levels and types of SAA protein in humans with spontaneous or transplant-associated coronary artery disease are not known.

METHODS AND RESULTS

SAA levels were analyzed using an ELISA in 76 sera from 36 patients after cardiac transplantation and in 346 other individuals, 85 patients with atherosclerotic coronary disease plus 261 of their relatives. The mean SAA level was 5-fold higher in transplant patients (203+/-181 microg/mL [23 to 934 microg/mL]) compared with normal subjects without coronary disease (36+/-16 microg/mL [2.8 to 193 microg/mL], P<.005). The mean SAA level was significantly elevated in patients with transplant coronary disease (206+/-160 microg/mL, n=23) compared with those without (140+/-104 microg/mL, n=12, P=.02). Elevated SAA levels were associated with increased mortality after transplantation. On multiple regression analysis, SAA levels were predicted by corticosteroid dose, pretransplant diagnosis of atherosclerotic coronary artery disease, and the presence of transplant coronary disease. SAA levels were elevated in patients with spontaneous atherosclerotic coronary disease (49+/-31 microg/mL) compared with unaffected relatives (39+/-36 microg/mL, mean+/-SD, P=.02). There was no evidence for a genetic contribution to SAA levels. All inducible human SAA protein types were documented by immunoblotting in both spontaneous and transplant coronary disease.

CONCLUSIONS

Environmentally determined elevations in SAA levels in patients with both spontaneous and transplant coronary artery disease provide further evidence for a potential pathophysiological link between inflammation, lipoprotein metabolism, and the development of atherosclerosis.

The MspI polymorphism of the apolipoprotein A-II gene as a modulator of the dyslipidemic state found in visceral obesity

The aim of the present study was to examine the effect of variation at the apolipoprotein (apo) A-II gene locus on lipoprotein levels in visceral obesity. A total of 145 sedentary men, free from metabolic disorders requiring pharmacotherapy, were classified into two groups on the basis of their apo A-II-MspI genotype determined by the polymerase chain reaction: 1) 43 M1 carriers or M1M2, including two M1M1 homozygotes and 41 M1M2 heterozygotes, and 2) 102 M2M2 homozygotes for the presence of a MspI restriction site. The two genotypic groups did not differ for body mass index (BMI, expressed in kg/m2), body fat mass, visceral adipose tissue (AT) accumulation, as well as for insulin, glucose and free fatty acids levels measured in the fasting state and in response to an oral glucose tolerance test. In addition, 65 and 63% of M1 carriers had plasma HDL2 cholesterol levels and a HDL2/HDL3 cholesterol ratio below the 50th percentile of their distributions compared with 45%(P < 0.05) and 46%(P = 0.06), respectively, in M2M2 homozygotes. When subjects were further divided on the basis of visceral AT accumulation (below and above a value of 130 cm2), M1 carriers with low levels of visceral AT were characterized by high plasma HDL cholesterol and HDL2 cholesterol concentrations as well as by a higher HDL2/HDL3 ratio, compared with M1 carriers with high levels of visceral AT (> 130 cm2), or with M2M2 homozygotes with either a high or a low accumulation of visceral AT. Furthermore, M1 carriers with high levels of visceral AT showed a trend for lower plasma HDL2 cholesterol levels and were characterized by a significantly lower HDL2/HDL3 cholesterol ratio compared with the other three groups. No difference in HDL and HDL2 cholesterol levels and in the HDL2/HDL3 cholesterol ratio was noted when M2 homozygotes with lower versus higher levels of visceral AT were compared. The contribution of hyperinsulinemia was also examined by dividing subjects on the basis of the 50th percentile of the integrated insulin response to an oral glucose challenge. Significantly lower plasma HDL2 cholesterol levels and a reduced HDL2/HDL3 cholesterol ratio were noted among M1 carriers with high plasma insulin responses compared with M1 carriers with low insulin responses. Among M2M2 homozygotes, no difference was noted in plasma HDL cholesterol and in HDL2 cholesterol concentrations between men with low versus high insulin responses to the oral glucose load. These results suggest that the apo A-II-MspI polymorphism could modulate plasma HDL cholesterol levels among visceral obese, insulin-resistant men.

Dramatically decreased high density lipoprotein cholesterol, increased remnant clearance, and insulin hypersensitivity in apolipoprotein A-II knockout mice suggest a complex role for apolipoprotein A-II in atherosclerosis susceptibility

Apolipoprotein (apo) A-II is the second most abundant apolipoprotein in high density lipoprotein (HDL). To study its role in lipoprotein metabolism and atherosclerosis susceptibility, apo A-II knockout mice were created. Homozygous knockout mice had 67% and 52% reductions in HDL cholesterol levels in the fasted and fed states, respectively, and HDL particle size was reduced. Metabolic turnover studies revealed the HDL decrease to be due to both decreased HDL cholesterol ester and apo A-I transport rate and increased HDL cholesterol ester and apo A-I fractional catabolic rate. The apo A-II deficiency trait was bred onto the atherosclerosis-prone apo E-deficient background, which resulted in a surprising 66% decrease in cholesterol levels due primarily to decreased atherogenic lipoprotein remnant particles. Metabolic turnover studies indicated increased remnant clearance in the absence of apo A-II. Finally, apo A-II deficiency was associated with lower free fatty acid, glucose, and insulin levels, suggesting an insulin hypersensitivity state. In summary, apo A-II plays a complex role in lipoprotein metabolism, with some antiatherogenic properties such as the maintenance of a stable HDL pool, and other proatherogenic properties such as decreasing clearance of atherogenic lipoprotein remnants and promotion of insulin resistance.

Conformational studies of an amphipathic peptide corresponding to human apolipoprotein A-II residues 18-30 with a C-terminal lipid binding motif EWLNS

A peptide was designed and synthesized to enhance the lipid binding properties of a 13-residue fragment of apolipoprotein A-II. The peptide, VTDYGKDLMEKVKEWLNS [apoA-II(18-30)+], contains a five-residue amphipathic motif, EWLNS, at the C-terminus of apolipoprotein A-II residues 18-30. The lipid binding properties of apoA-II(18-30)+ were assessed using optical spectroscopy in the presence of sodium dodecyl sulfate (SDS), dodecylphosphocholine (DPC), tetradecyltrimethyl ammonium chloride (TMA) and dimyristoylphosphatidylcholine (DMPC). The fluorescence emission spectra and the circular dichroism data suggested that apoA-II(18-30)+ interacted most strongly with SDS and most weakly with DMPC. An ensemble of structures for apoA-II(18-30)+ in aqueous solution containing SDS was calculated using distance geometry/simulated annealing methods from 308 NOE-based distance restraints. The backbone (N-C-C = O) RMSD from the average structure of an ensemble of 15 out of 20 calculated structures was 0.54 +/- 0.16 A. Apart from some dynamic fraying at both termini, the distance geometry and simulated annealing calculations showed that apoA-II(18-30)+ adopted a well defined amphipathic helix with distinct hydrophobic and hydrophilic faces.

Functional lecithin:cholesterol acyltransferase deficiency and high density lipoprotein deficiency in transgenic mice overexpressing human apolipoprotein A-II

The concentration of high density lipoproteins (HDL) is inversely related to the risk of atherosclerosis. The two major protein components of HDL are apolipoprotein (apo) A-I and apoA-II. To study the role of apoA-II in lipoprotein metabolism and atherosclerosis, we have developed three lines of C57BL/6 transgenic mice expressing human apoA-II (lines 25.3, 21.5, and 11.1). Northern blot experiments showed that human apoA-II mRNA was present only in the liver of transgenic mice. SDS-polyacrylamide gel electrophoresis and Western blot analysis demonstrated a 17.4-kDa human apoA-II in the HDL fraction of the plasma of transgenic mice. After 3 months on a regular chow, the plasma concentrations of human apoA-II were 21 +/- 4 mg/dl in the 25.3 line, 51 +/- 6 mg/dl in the 21.5 line, and 74 +/- 4 mg/dl in the 11.1 line. The concentration of cholesterol in plasma was significantly lower in transgenic mice than in control mice because of a decrease in HDL cholesterol that was greatest in the line that expressed the most apoA-II (23 mg/dl in the 11.1 line versus 63 mg/dl in control mice). There was also a reduction in the plasma concentration of mouse apoA-I (32 +/- 2, 56 +/- 9, 91 +/- 7, and 111 +/- 2 mg/dl for lines 11.1, 21.5, 25.3, and control mice, respectively) that was inversely correlated with the amount of human apoA-II expressed. Additional changes in plasma lipid/lipoprotein profile noted in line 11.1 that expressed the highest level of human apoA-II include elevated triglyceride, increased proportion of total plasma, and HDL free cholesterol and a marked (>10-fold) reduction in mouse apoA-II. Total endogenous plasma lecithin:cholesterol acyltransferase (LCAT) activity was reduced to a level directly correlated with the degree of increased plasma human apoA-II in the transgenic lines. LCAT activity toward exogenous substrate was, however, only slightly decreased. The biochemical changes in the 11.1 line, which is markedly deficient in plasma apoA-I, an activator for LCAT, are reminiscent of those in patients with partial LCAT deficiency. Feeding the transgenic mice a high fat, high cholesterol diet maintained the mouse apoA-I concentration at a normal level (69 +/- 14 mg/dl in line 11.1 compared with 71 +/- 6 mg/dl in nontransgenic controls) and prevented the appearance of HDL deficiency. All this happened in the presence of a persistently high plasma human apoA-II (96 +/- 14 mg/dl). Paradoxical HDL elevation by high fat diets has been observed in humans and is reproduced in human apoA-II overexpressing transgenic mice but not in control mice. Finally, HDL size and morphology varied substantially in the three transgenic lines, indicating the importance of apoA-II concentration in the modulation of HDL formation. The LCAT and HDL deficiencies observed in this study indicate that apoA-II plays a dynamic role in the regulation of plasma HDL metabolism.

Multilocus genetic determinants of LDL particle size in coronary artery disease families

Recent interest in atherosclerosis has focused on the genetic determinants of low-density lipoprotein (LDL) particle size, because of (i) the association of small dense LDL particles with a three-fold increased risk for coronary artery disease (CAD) and (ii) the recent report of linkage of the trait to the LDL receptor (chromosome 19). By utilizing nonparametric quantitative sib-pair and relative-pair analysis methods in CAD families, we tested for linkage of a gene or genes controlling LDL particle sizes with the genetic loci for the major apolipoproteins and enzymes participating in lipoprotein metabolism. We confirmed evidence for linkage to the LDL receptor locus (P=.008). For six candidate gene loci, including apolipoprotein(apo)B, apoAII, apo(a), apoE-CI-CII, lipoprotein lipase, and high-density lipoprotein-binding protein, no evidence for linkage was observed by sib-pair linkage analyses (P values ranged from .24 to .81). However, in addition, we did find tentative evidence for linkage with the apoAI-CIII-AIV locus (chromosome 11) (P=.06) and significant evidence for linkage of the cholesteryl ester transfer protein locus (chromosome 16) (P=.01) and the manganese superoxide dismutase locus (chromosome 6) (P=.001), thus indicating multilocus determination of this atherogenic trait.