DNA sequence variation in human apolipoprotein C4 gene and its effect on plasma lipid profile

The brain-heart axis: Integrative analysis of the shared genetic etiology between neuropsychiatric disorders and cardiovascular disease

BACKGROUND

Multiple observational studies have reported substantial comorbidity between neuropsychiatric disorders and cardiovascular disease (CVD), but the underlying mechanisms remain largely unknown.

METHODS

Using GWAS summary datasets of 8 neuropsychiatric disorders and 6 cardiovascular diseases, an integrative analysis incorporating linkage-disequilibrium-score-regression (LDSC), Mendelian randomization (MR), functional mapping and annotation (FUMA), and functional enrichment analysis, was conducted to investigate shared genetic etiology of the brain-heart axis from the whole genome level, single-nucleotide polymorphism (SNP) level, gene level, and biological pathway level.

RESULTS

In LDSC analysis, 18 pairwise traits between neuropsychiatric disorders and CVD were identified with significant genetic overlaps, revealing extensive genome-wide genetic correlations. In bidirectional MR analysis, 19 pairwise traits were identified with significant causal relationships. Genetic liabilities to neuropsychiatric disorders, particularly attention-deficit hyperactivity disorder and major depressive disorder, conferred extensive significant causal effects on the risk of CVD, while hypertension seemed to be a risk factor for multiple neuropsychiatric disorders, with no significant heterogeneity or pleiotropy. In FUMA analysis, 13 shared independent significant SNPs and 887 overlapping protein-coding genes were detected between neuropsychiatric disorders and CVD. With GO and KEEG functional enrichment analysis, biological pathways of the brain-heart axis were highly concentrated in neurotransmitter synaptic transmission, lipid metabolism, aldosterone synthesis and secretion, glutathione metabolism, and MAPK signaling pathway.

CONCLUSION

Extensive genetic correlations and genetic overlaps between neuropsychiatric disorders and CVD were identified in this study, which might provide some new insights into the brain-heart axis and the therapeutic targets in clinical practice.

Quartet of APOCs and the Different Roles They Play in Diabetes

APOA1 and APOB are the structural proteins of high-density lipoprotein and APOB-containing lipoproteins, such as low-density lipoprotein and very low-density lipoprotein, respectively. The 4 smaller APOCs (APOC1, APOC2, APOC3, and APOC4) are exchangeable apolipoproteins; they are readily transferred among high-density lipoproteins and APOB-containing lipoproteins. The APOCs regulate plasma triglyceride and cholesterol levels by modulating substrate availability and activities of enzymes interacting with lipoproteins and by interfering with APOB-containing lipoprotein uptake through hepatic receptors. Of the 4 APOCs, APOC3 has been best studied in relation to diabetes. Elevated serum APOC3 levels predict incident cardiovascular disease and progression of kidney disease in people with type 1 diabetes. Insulin suppresses APOC3 levels, and accordingly, elevated APOC3 levels associate with insulin deficiency and insulin resistance. Mechanistic studies in a mouse model of type 1 diabetes have demonstrated that APOC3 acts in the causal pathway of diabetes-accelerated atherosclerosis. The mechanism is likely due to the ability of APOC3 to slow the clearance of triglyceride-rich lipoproteins and their remnants, thereby causing an increased accumulation of atherogenic lipoprotein remnants in lesions of atherosclerosis. Less is known about the roles of APOC1, APOC2, and APOC4 in diabetes.

Differential proteomic of plasma provides a new perspective on scientific diagnosis and drug screening for dampness heat diarrhea in calves

Dampness heat diarrhea (DHD) is one of the most common syndromes of calf diarrhea. Its complex etiology and lack of objective diagnostic criteria bring great challenges to the diagnosis and treatment of this disease. This study aims to screen some prospective diagnostic biomarkers or therapeutic targets for calves with DHD by investigating the differential protein profiles of plasma between DHD calves and clinically healthy calves by mass spectrometry-based proteomic. A total of 120 DHD calves and 90 clinically healthy calves were divided into two groups randomly, 30 DHD calves and 30 clinically healthy calves in the test group, and 90 DHD calves and 60 clinically healthy calves in the validation group. In the test group, a total of 52 proteins were differentially expressed between calves with DHD and clinically healthy calves, 13 proteins were significantly increased and 39 proteins were significantly decreased. The differentially expressed proteins were associated with the intestinal immune network of IgA production, caffeine metabolism, purine metabolism, and PI3K signaling pathway. In the validation group, 13 proteins were selected from 52 differential expression proteins for parallel reaction monitoring validation to verify their associations with DHD calves. The targeted proteomic results showed that fibronectin precursor (FN1) and apolipoprotein C-IV precursor (APOC4) were significantly associated with DHD in calves, and they were downregulated in sick calves. In conclusion, the differential expression of plasma proteins was associated with DHD pathogenesis in calves, and the FN1 and APOC4 might be the potential clinical biomarkers for diagnosis of DHD in calves, and the intestinal immune network of IgA production, caffeine metabolism, purine metabolism, and PI3K signaling pathway are the candidate targets to treat DHD in calves. Our finding provides a reference for further investigating the pathogenesis, developing techniques of diagnosis, and screening treatment drugs for DHD in calves.

Genetic Variants at the APOE Locus Predict Cardiometabolic Traits and Metabolic Syndrome: A Taiwan Biobank Study

Several apolipoprotein genes are located at the APOE locus on chromosome 19q13.32. This study explored the genetic determinants of cardiometabolic traits and metabolic syndrome at the APOE locus in a Taiwanese population. A total of 81,387 Taiwan Biobank (TWB) participants were enrolled to undergo genotype−phenotype analysis using data from the Axiom Genome-Wide CHB arrays. Regional association analysis with conditional analysis revealed lead single-nucleotide variations (SNVs) at the APOE locus: APOE rs7412 and rs429358 for total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol levels; CLPTM1 rs3786505 and rs11672748 for LDL and HDL cholesterol levels; and APOC1 rs438811 and APOE-APOC1 rs439401 for serum triglyceride levels. Genotype−phenotype association analysis revealed a significant association of rs429358 and rs438811 with metabolic syndrome and of rs7412, rs438811, and rs439401 with serum albumin levels (p < 0.0015). Stepwise regression analysis indicated that CLPTM1 variants were independently associated with LDL and HDL cholesterol levels (p = 3.10 × 10−15 for rs3786505 and p = 1.48 × 10−15 for rs11672748, respectively). APOE rs429358 and APOC1 rs438811 were also independently associated with metabolic syndrome (p = 2.29 × 10−14) and serum albumin levels (p = 3.80 × 10−6), respectively. In conclusion, in addition to APOE variants, CLPTM1 is a novel candidate locus for LDL and HDL cholesterol levels at the APOE gene region in Taiwan. Our data also indicated that APOE and APOC1 variants were independently associated with metabolic syndrome and serum albumin levels, respectively. These results revealed the crucial role of genetic variants at the APOE locus in predicting cardiometabolic traits and metabolic syndrome.

Plasma proteomics reveals crosstalk between lipid metabolism and immunity in dairy cows receiving essential fatty acids and conjugated linoleic acid

Essential fatty acids (EFA) and conjugated linoleic acids (CLA) are unsaturated fatty acids with immune-modulatory effects, yet their synergistic effect is poorly understood in dairy cows. This study aimed at identifying differentially abundant proteins (DAP) and their associated pathways in dairy cows supplied with a combination of EFA and CLA during the transition from antepartum (AP) to early postpartum (PP). Sixteen Holstein cows were abomasally infused with coconut oil as a control (CTRL) or a mixture of EFA (linseed + safflower oil) and CLA (Lutalin, BASF) (EFA + CLA) from − 63 to + 63 days relative to parturition. Label-free quantitative proteomics was performed on plasma samples collected at days − 21, + 1, + 28, and + 63. During the transition time, DAP, consisting of a cluster of apolipoproteins (APO), including APOE, APOH, and APOB, along with a cluster of immune-related proteins, were related to complement and coagulation cascades, inflammatory response, and cholesterol metabolism. In response to EFA + CLA, specific APO comprising APOC3, APOA1, APOA4, and APOC4 were increased in a time-dependent manner; they were linked to triglyceride-enriched lipoprotein metabolisms and immune function. Altogether, these results provide new insights into metabolic and immune adaptation and crosstalk between them in transition dairy cows divergent in EFA + CLA status.

Huang-Qi San improves glucose and lipid metabolism and exerts protective effects against hepatic steatosis in high fat diet-fed rats

Numerous researches supported that non-alcoholic fatty liver disease (NAFLD) was an emerging problem associated with increased visceral adiposity (obesity), diabetes and related metabolic disorders. Huang-Qi San (HQS) is composed of three traditional Chinese medicines (Astragali Radix, Pueraria Radix and Cortex Mori Radicis) with a weight ratio of 1:2:1. HQS has been reported to be effective in improving glucose-lipid metabolism, but its underlying mechanism on NAFLD has not been fully understood. The purpose of the present study was to assess the protective effects of HQS on obesity-induced hepatic steatosis in rats fed with high fat diet (HFD). Our data revealed that administration of HQS (1.2 and 2.4 g/kg body weight) resulted in significant reduction in body weight (BW) and organs coefficients of visceral fat. The full-Body CT scan demonstrated that HQS reduced liver fat ratio, visceral and subcutaneous fat mass in a dose-dependent manner. Additionally, HQS decreased plasma TC, TG, FFA and FABP4 levels, normalized glucose and insulin levels, and improved the glucose tolerance. Pathological examination showed that HQS alleviated hepatic steatosis and reduced the cell size of epididymal visceral adipose tissue. Hepatic lipid accumulation was also reduced by HQS treatment compared with HFD fed rats. RNA-Seq analysis combining with qPCR demonstrated that the mRNA expression of some important glucose and lipid metabolism-related genes including Acat2, Apoc4, Bhmt, Cyp3a62, Cyp51, Egln3 (Phd3), Fads1, Fads2, Gnmt, Hmgcs1 and Pemt, were significantly changed by HQS treatment. Taken together, these results suggested that HQS had beneficial effects on glucose-lipid metabolism and hepatic steatosis, and its mechanism might be related to the functions of the genes in regulating glucose and lipid metabolism.

Genetic determinants of inherited susceptibility to hypercholesterolemia - a comprehensive literature review

Hypercholesterolemia is a strong determinant of mortality and morbidity associated with cardiovascular diseases and a major contributor to the global disease burden. Mutations in four genes (LDLR, APOB, PCSK9 and LDLRAP1) account for the majority of cases with familial hypercholesterolemia. However, a substantial proportion of adults with hypercholesterolemia do not have a mutation in any of these four genes. This indicates the probability of having other genes with a causative or contributory role in the pathogenesis of hypercholesterolemia and suggests a polygenic inheritance of this condition. Here in, we review the recent evidence of association of the genetic variants with hypercholesterolemia and the three lipid traits; total cholesterol (TC), HDL-cholesterol (HDL-C) and LDL-cholesterol (LDL-C), their biological pathways and the associated pathogenetic mechanisms. Nearly 80 genes involved in lipid metabolism (encoding structural components of lipoproteins, lipoprotein receptors and related proteins, enzymes, lipid transporters, lipid transfer proteins, and activators or inhibitors of protein function and gene transcription) with single nucleotide variants (SNVs) that are recognized to be associated with hypercholesterolemia and serum lipid traits in genome-wide association studies and candidate gene studies were identified. In addition, genome-wide association studies in different populations have identified SNVs associated with TC, HDL-C and LDL-C in nearly 120 genes within or in the vicinity of the genes that are not known to be involved in lipid metabolism. Over 90% of the SNVs in both these groups are located outside the coding regions of the genes. These findings indicates that there might be a considerable number of unrecognized processes and mechanisms of lipid homeostasis, which when disrupted, would lead to hypercholesterolemia. Knowledge of these molecular pathways will enable the discovery of novel treatment and preventive methods as well as identify the biochemical and molecular markers for the risk prediction and early detection of this common, yet potentially debilitating condition.

The association of APOC4 polymorphisms with premature coronary artery disease in a Chinese Han population

Background

Hypercholesterolemia arising from abnormal lipid metabolism is one of the critical risk factors for coronary artery disease (CAD), however the roles of genetic variants in lipid metabolism-related genes on premature CAD (≤60 years old) development still require further investigation. We herein genotyped four single nucleotide polymorphisms (SNPs) in lipid metabolism-related genes (rs1132899 and rs5167 in APOC4, rs1801693 and rs7765781 in LPA), aimed to shed light on the influence of these SNPs on individual susceptibility to early-onset CAD.

Methods

Genotyping of the four SNPs (rs1132899, rs5167, rs1801693 and rs7765781) was performed in 224 premature CAD cases and 297 control subjects (≤60 years old) using polymerase chain reaction-ligation detection reaction (PCR–LDR) method. The association of these SNPs with premature CAD was performed with SPSS software.

Results

Multivariate logistic regression analysis showed that C allele (OR = 1.50, P = 0.027) and CC genotype (OR = 2.84, P = 0.022) of APOC4 rs1132899 were associated with increased premature CAD risk, while the other three SNPs had no significant effect. Further stratified analysis uncovered a more evident association with the risk of premature CAD among male subjects (C allele, OR = 1.65, and CC genotype, OR = 3.33).

Conclusions

Our data provides the first evidence that APOC4 rs1132899 polymorphism was associated with an increased risk of premature CAD in Chinese subjects, and the association was more significant among male subjects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-015-0065-7) contains supplementary material, which is available to authorized users.

A novel estrogen-regulated avian apolipoprotein

In search for yet uncharacterized proteins involved in lipid metabolism of the chicken, we have isolated a hitherto unknown protein from the serum lipoprotein fraction with a buoyant density of ≤1.063 g/ml. Data obtained by protein microsequencing and molecular cloning of cDNA defined a 537 bp cDNA encoding a precursor molecule of 178 residues. As determined by SDS-PAGE, the major circulating form of the protein, which we designate apolipoprotein-VLDL-IV (Apo-IV), has an apparent M_r of approximately 17 kDa. Northern Blot analysis of different tissues of laying hens revealed Apo-IV expression mainly in the liver and small intestine, compatible with an involvement of the protein in lipoprotein metabolism. To further investigate the biology of Apo-IV, we raised an antibody against a GST-Apo-IV fusion protein, which allowed the detection of the 17-kDa protein in rooster plasma, whereas in laying hens it was detectable only in the isolated ≤1.063 g/ml density lipoprotein fraction. Interestingly, estrogen treatment of roosters caused a reduction of Apo-IV in the liver and in the circulation to levels similar to those in mature hens. Furthermore, the antibody crossreacted with a 17-kDa protein in quail plasma, indicating conservation of Apo-IV in avian species. In search for mammalian counterparts of Apo-IV, alignment of the sequence of the novel chicken protein with those of different mammalian apolipoproteins revealed stretches with limited similarity to regions of ApoC-IV and possibly with ApoE from various mammalian species. These data suggest that Apo-IV is a newly identified avian apolipoprotein.

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Apo-VLDL-IV (Apo-IV) is a newly identified avian apolipoprotein.

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Apo-IV expression is suppressed by estrogen.

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Apo-IV containing VLDL particles are excluded from uptake into yolk.

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Apo-IV has limited similarity to mammalian ApoC-IV.

Large-scale gene-centric meta-analysis across 32 studies identifies multiple lipid loci

Genome-wide association studies (GWASs) have identified many SNPs underlying variations in plasma-lipid levels. We explore whether additional loci associated with plasma-lipid phenotypes, such as high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), and triglycerides (TGs), can be identified by a dense gene-centric approach. Our meta-analysis of 32 studies in 66,240 individuals of European ancestry was based on the custom ∼50,000 SNP genotyping array (the ITMAT-Broad-CARe array) covering ∼2,000 candidate genes. SNP-lipid associations were replicated either in a cohort comprising an additional 24,736 samples or within the Global Lipid Genetic Consortium. We identified four, six, ten, and four unreported SNPs in established lipid genes for HDL-C, LDL-C, TC, and TGs, respectively. We also identified several lipid-related SNPs in previously unreported genes: DGAT2, HCAR2, GPIHBP1, PPARG, and FTO for HDL-C; SOCS3, APOH, SPTY2D1, BRCA2, and VLDLR for LDL-C; SOCS3, UGT1A1, BRCA2, UBE3B, FCGR2A, CHUK, and INSIG2 for TC; and SERPINF2, C4B, GCK, GATA4, INSR, and LPAL2 for TGs. The proportion of explained phenotypic variance in the subset of studies providing individual-level data was 9.9% for HDL-C, 9.5% for LDL-C, 10.3% for TC, and 8.0% for TGs. This large meta-analysis of lipid phenotypes with the use of a dense gene-centric approach identified multiple SNPs not previously described in established lipid genes and several previously unknown loci. The explained phenotypic variance from this approach was comparable to that from a meta-analysis of GWAS data, suggesting that a focused genotyping approach can further increase the understanding of heritability of plasma lipids.

Apolipoprotein E/C1/C4/C2 gene cluster diversity in two native Andean populations: Aymaras and Quechuas

The APOE/C1/C4/C2 gene cluster presents high relevance in lipid metabolism and, therefore, has important epidemiological implications. Here, we study for the first time the variation patterns of 25 polymorphisms (10 short tandem repeats, STRs, and 15 single nucleotide polymorphismas, SNPs) in two native Andean samples from Bolivia (45 Aymaras and 45 Quechuas) as well as one European sample (n = 41) as external reference. We estimated diversity parameters, linkage disequilibrium patterns, population structure, and possible selective effects. In general, diversity was low and could be partly attributed to selection (probably due to its physiological importance), since the APOE/C1/C4/C2 region was highly conserved compared to the flanking genes in both Bolivians and Europeans. Moreover, the lower gene diversity in Bolivians compared to Europeans for some markers might indicate different demographic histories. Regarding the APOE isoforms, in addition to ɛ3 (94%) and ɛ4 (5%), isoform ɛ2 (1%) was also detected in Bolivians. In relation to previous hypotheses, our results support that genetic drift or founder effects rather than selection for increased cholesterol absorption are the main factors that have shaped the distribution of APOE isoforms observed in South America.

APOE/C1/C4/C2 gene cluster genotypes, haplotypes and lipid levels in prospective coronary heart disease risk among UK healthy men

The role of common APOE variants on plasma lipids, particularly low density lipoprotein (LDL) levels, and coronary heart disease (CHD) risk is well known; the influence of variation in the other nearby apolipoprotein genes APOC1, APOC4 and APOC2 is unclear. This study examines the association between APOE/C1/C4/C2 gene cluster variation using tagging SNPs and plasma lipid concentration along with risk of CHD in a prospective cohort. Genotypes for 11 common APOE/C1/C4/C2 SNPs were determined in 2,767 middle-aged (49 to 64 years) men from the Second Northwick Park Heart Study, with 275 CHD events over a 15-year follow-up period. Seven SNPs showed significant associations with one or more lipid trait in univariate analysis. Multivariate and haplotype analysis showed that the APOE genotypes are most strongly associated with effects on LDL-C and apoB concentration (explaining 3.4% of the LDL-C variance) while the other SNPs in this gene cluster explained an additional 1.2%. Haplotypes in APOC2 and APOC4 were associated with modest effects on HDL-C and apoAI (explaining respectively 1.4% and 1.2%). Carriers of the APOE ɛ2 SNP had a significantly lower risk of CHD hazard ratio (HR) of 0.63 (95% confidence interval [CI]: 0.42-0.95), as did carriers of the APOC2 SNP rs5127 (HR = 0.72, 95% CI: 0.56-0.93), while carriers of APOC1 SNP rs4803770 had higher risk of CHD (HR = 1.36, 95% CI: 1.04-1.78) compared with noncarriers. While the common APOE polymorphism explains the majority of the locus genetic determinants of plasma lipid levels, additional SNPs in the APOC1/C2 region may contribute to CHD risk, but these effects require confirmation.

APOE/C1/C4/C2 gene cluster genotypes, haplotypes and lipid levels in prospective coronary heart disease risk among UK healthy men

The role of common APOE variants on plasma lipids, particularly low density lipoprotein (LDL) levels, and coronary heart disease (CHD) risk is well known; the influence of variation in the other nearby apolipoprotein genes APOC1, APOC4 and APOC2 is unclear. This study examines the association between APOE/C1/C4/C2 gene cluster variation using tagging SNPs and plasma lipid concentration along with risk of CHD in a prospective cohort. Genotypes for 11 common APOE/C1/C4/C2 SNPs were determined in 2,767 middle-aged (49 to 64 years) men from the Second Northwick Park Heart Study, with 275 CHD events over a 15-year follow-up period. Seven SNPs showed significant associations with one or more lipid trait in univariate analysis. Multivariate and haplotype analysis showed that the APOE genotypes are most strongly associated with effects on LDL-C and apoB concentration (explaining 3.4% of the LDL-C variance) while the other SNPs in this gene cluster explained an additional 1.2%. Haplotypes in APOC2 and APOC4 were associated with modest effects on HDL-C and apoAI (explaining respectively 1.4% and 1.2%). Carriers of the APOE ɛ2 SNP had a significantly lower risk of CHD hazard ratio (HR) of 0.63 (95% confidence interval [CI]: 0.42-0.95), as did carriers of the APOC2 SNP rs5127 (HR = 0.72, 95% CI: 0.56-0.93), while carriers of APOC1 SNP rs4803770 had higher risk of CHD (HR = 1.36, 95% CI: 1.04-1.78) compared with noncarriers. While the common APOE polymorphism explains the majority of the locus genetic determinants of plasma lipid levels, additional SNPs in the APOC1/C2 region may contribute to CHD risk, but these effects require confirmation.

A microarray analysis of the temporal response of liver to methylprednisolone: a comparative analysis of two dosing regimens

Microarray analyses were performed on livers from adrenalectomized male Wistar rats chronically infused with methylprednisolone (MPL) (0.3 mg/kg.h) using Alzet mini-osmotic pumps for periods ranging from 6 h to 7 d. Four control and 40 drug-treated animals were killed at 10 different times during drug infusion. Total RNA preparations from the livers of these animals were hybridized to 44 individual Affymetrix REA230A gene chips, generating data for 15,967 different probe sets for each chip. A series of three filters were applied sequentially. These filters were designed to eliminate probe sets that were not expressed in the tissue, were not regulated by the drug, or did not meet defined quality control standards. These filters eliminated 13,978 probe sets (87.5%) leaving a remainder of 1989 probe sets for further consideration. We previously described a similar dataset obtained from animals after administration of a single dose of MPL (50 mg/kg given iv). That study involved 16 time points over a 72-h period. A similar filtering schema applied to the single-bolus-dose dataset identified 1519 probe sets as being regulated by MPL. A comparison of datasets from the two different dosing regimens identified 358 genes that were regulated by MPL in response to both dosing regimens. Regulated genes were grouped into 13 categories, mainly on gene product function. The temporal profiles of these common genes were subjected to detailed scrutiny. Examination of temporal profiles demonstrates that current perspectives on the mechanism of glucocorticoid action cannot entirely explain the temporal profiles of these regulated genes.

Proteomic analysis of human very low-density lipoprotein by two-dimensional gel electrophoresis and MALDI-TOF/TOF

Biochemical studies of lipoproteins have shed light on their composition, highly contributing to the comprehension of their function. Due to the complexity of their structure, however, an in-depth structural analysis, in terms of components and PTMs, may still unravel important players in physiological and pathological processes of lipid metabolism. In this study, we performed a protein map of very low-density lipoprotein (VLDL) using a 2-DE MALDI-TOF/TOF proteomic approach. Several VLDL-associated apolipoproteins were identified, including five isoforms of apoE, three isoforms of apoC-IV, and one isoform each of apoC-III, apoM, apoA-I, and apoA-IV. Notably, we also identified seven isoforms of apoL-I and two isoforms of prenylcysteine lyase as new VLDL-associated proteins. Furthermore, we were able to identify PTM of apoE, which was found to be differently O-glycosylated at Thr212 residue, and PTM of apoL-I which we described, for the first time, to be phosphorylated at Ser296. While the physiological relevance of our finding remains to be assessed, we believe that our results will be useful as reference for future studies of VLDL structure in specific physiopathological conditions.

Linkage analysis of LDL cholesterol in American Indian populations: the Strong Heart Family Study

Previous studies have demonstrated that low density lipoprotein cholesterol (LDL-C) concentration is influenced by both genes and environment. Although rare genetic variants associated with Mendelian causes of increased LDL-C are known, only one common genetic variant has been identified, the apolipoprotein E gene (APOE). In an attempt to localize quantitative trait loci (QTLs) influencing LDL-C, we conducted a genome-wide linkage scan of LDL-C in participants of the Strong Heart Family Study (SHFS). Nine hundred eighty men and women, age 18 years or older, in 32 extended families at three centers (in Arizona, Oklahoma, and North and South Dakota) were phenotyped for LDL-C concentration and other risk factors. Using a variance component approach and the program SOLAR, and after accounting for the effects of covariates, we detected a QTL influencing LDL-C on chromosome 19, nearest marker D19S888 at 19q13.41 [logarithm of odds (LOD) = 4.3] in the sample from the Dakotas. This region on chromosome 19 includes many possible candidate genes, including the APOE/C1/C4/C2 gene cluster. In follow-up association analyses, no significant evidence for an association was detected with the APOE*2 and APOE*4 alleles (P = 0.76 and P = 0.53, respectively). Suggestive evidence of linkage to LDL-C was detected on chromosomes 3q, 4q, 7p, 9q, 10p, 14q, and 17q. These linkage signals overlap positive findings for lipid-related traits and harbor plausible candidate genes for LDL-C.

Single nucleotide polymorphisms in the coding region of the apolipoprotein H (beta2-glycoprotein I) gene and their correlation with the protein polymorphism, anti-beta2glycoprotein I antibodies and cardiolipin binding: description of novel haplotypes and their evolution

Apolipoprotein H (APOH), also known as beta2-glycoprotein I, is a major autoantigen for the production of antiphospholipid antibodies (APA) in autoimmune diseases. APA is also recognized by a cryptic epitope generated following the interaction of APOH with anionic phospholipids (PL). The prevalence of APA in the general U.S. white population is about 10%, but it ranges from 30-70% in patients with lupus and antiphospholipid syndrome. Since the structural characterization of APOH from different mammalian species is important to identify the evolutionary conserved regions that may be critical for its function, we have previously determined the chimpanzee APOH gene structure and the prevalence of APA. There are only two amino acid differences between the chimpanzee and human wild type APOH proteins. Chimpanzees have an unusually high prevalence (64%) of APA. There is a common protein polymorphism in the human APOH gene, with the occurrence of four alleles APOH*1, APOH*2, APOH*3 and APOH*4, the latter being present only in blacks. Based on its differential reactivity with an APOH monoclonal antibody, the APOH*3 allele is further divided into APOH*3(W) (present only in whites) and APOH*3(B) (present only in blacks). In this study we have screened a large African population (n = 755) to determine the prevalence of APA and the molecular basis of the protein polymorphism. Almost 50% of the Africans were found to be positive for APA. The APOH*3(B) allele was found to be identical to the chimpanzee's wild type APOH. Novel two-site or three-site haplotypes, encoded in the third domain of APOH, explained the molecular basis of the APOH*3(B), APOH*3(W) and APOH*4 alleles. Based on the comparison of the human and chimpanzee APOH DNA sequences, we suggest that the APOH*3(W) and APOH*4 alleles arose on the ancestral APOH*3(B) haplotype after the split of human races. We also found that these haplotypes are associated with the occurrence of APA. Recombinant APOH haplotypes, expressed in COS-1 cells, showed that these mutations also affect the binding of APOH to anionic PL.

Evidence for a QTL on chromosome 19 influencing LDL cholesterol levels in the general population

The genetic basis of cardiovascular disease (CVD) with its complex etiology is still largely elusive. Plasma levels of lipids and apolipoproteins are among the major quantitative risk factors for CVD and are well-established intermediate traits that may be more accessible to genetic dissection than clinical CVD end points. Chromosome 19 harbors multiple genes that have been suggested to play a role in lipid metabolism and previous studies indicated the presence of a quantitative trait locus (QTL) for cholesterol levels in genetic isolates. To establish the relevance of genetic variation at chromosome 19 for plasma levels of lipids and apolipoproteins in the general, out-bred Caucasian population, we performed a linkage study in four independent samples, including adolescent Dutch twins and adult Dutch, Swedish and Australian twins totaling 493 dizygotic twin pairs. The average spacing of short-tandem-repeat markers was 6-8 cM. In the three adult twin samples, we found consistent evidence for linkage of chromosome 19 with LDL cholesterol levels (maximum LOD scores of 4.5, 1.7 and 2.1 in the Dutch, Swedish and Australian sample, respectively); no indication for linkage was observed in the adolescent Dutch twin sample. The QTL effects in the three adult samples were not significantly different and a simultaneous analysis of the samples increased the maximum LOD score to 5.7 at 60 cM pter. Bivariate analyses indicated that the putative LDL-C QTL also contributed to the variance in ApoB levels, consistent with the high genetic correlation between these phenotypes. Our study provides strong evidence for the presence of a QTL on chromosome 19 with a major effect on LDL-C plasma levels in outbred Caucasian populations.

Common gene polymorphisms and nutrition: emerging links with pathogenesis of multifactorial chronic diseases (review)

Rapid progress in human genome decoding has accelerated search for the role of gene polymorphisms in the pathogenesis of complex multifactorial diseases. This review summarizes the results of recent studies on the associations of common gene variants with multifactorial chronic conditions strongly affected by nutritional factors. Three main individual sections discuss genes related to energy homeostasis regulation and obesity, cardiovascular disease (CVD), and cancer. It is evident that several major chronic diseases are closely related (often through obesity) to deregulation of energy homeostasis. Multiple polymorphic genes encoding central and peripheral determinants of energy intake and expenditure have been revealed over the past decade. Food intake control may be affected by polymorphisms in the genes encoding taste receptors and a number of peripheral signaling peptides such as insulin, leptin, ghrelin, cholecystokinin, and corresponding receptors. Polymorphic central regulators of energy intake include hypothalamic neuropeptide Y, agouti-related protein, melanocortin pathway factors, CART (cocaine- and amphetamine-regulated transcript), some other neuropeptides, and receptors for these molecules. Potentially important polymorphisms in the genes encoding energy expenditure modulators (alpha- and beta- adrenoceptors, uncoupling proteins, and regulators of adipocyte growth and differentiation) are also discussed. CVD-related gene polymorphisms comprising those involved in the pathogenesis of atherosclerosis, blood pressure regulation, hemostasis control, and homocysteine metabolism are considered in a separate section with emphasis on multiple polymorphisms affecting lipid transport and metabolism and their interactions with diet. Cancer-associated polymorphisms are discussed for groups of genes encoding enzymes of xenobiotic metabolism, DNA repair enzymes, factors involved in the cell cycle control, hormonal regulation-associated proteins, enzymes related to DNA methylation through folate metabolism, and angiogenesis-related factors. There is an apparent progress in the field with hundreds of new gene polymorphisms discovered and characterized, however firm evidence consistently linking them with pathogenesis of complex chronic diseases is still limited. Ways of improving the efficiency of candidate gene approach-based studies are discussed in a short separate section. Successful unraveling of interaction between dietary factors, polymorphisms, and pathogenesis of several multifactorial diseases is exemplified by studies of folate metabolism in relation to CVD and cancer. It appears that several new directions emerge as targets of research on the role of genetic variation in relation to diet and complex chronic diseases. Regulation of energy homeostasis is a fundamental problem insufficiently investigated in this context so far. Impacts of genetic variation on systems controlling angiogenesis, inflammatory reactions, and cell growth and differentiation (comprising regulation of the cell cycle, DNA repair, and DNA methylation) are also largely unknown and need thorough analysis. These goals can be achieved by complex simultaneous analysis of multiple polymorphic genes controlling carefully defined and selected elements of relevant metabolic and regulatory pathways in meticulously designed large-scale studies.

Human apoC-IV: isolation, characterization, and immunochemical quantification in plasma and plasma lipoproteins

Apolipoprotein C-IV (apoC-IV), the newest member of the low-molecular-weight apoC group, has been characterized in blood plasma of rabbits, in which it is a major proline-rich apoC component (Zhang, L-H., L. Kotite, and R. J. Havel. 1996. Identification, characterization, cloning, and expression of apoC-IV, a novel sialoglycoprotein of rabbit plasma lipoproteins. J. Biol. Chem. 271: 1776-1783). Although the decoded sequence of mouse and human apoC-IV is known, apoC-IV has not been identified in blood plasma from these or other species. Rabbit apoC-IV exists in several sialoforms, and the asialoform has an acidic isoelectric point. We show that apoC-IV is a basic protein in human, monkey, and mouse plasma, present as a minor apoC component of VLDL. Human apoC-IV, isolated from apo VLDL by DEAE-cellulose chromatography and two-dimensional electrophoresis, was identified by microsequencing four tryptic peptides. The protein exhibits two major isoforms; one is N-glycosylated, and both are variably sialylated. In normolipidemic plasma, greater than 80% of the protein is in VLDL (0.7% of total apo VLDL), with most of the remainder in HDL. The concentration of apoC-IV in the plasma and lipoproteins of rho < 1.21 g/ml is closely related to plasma triglyceride concentration up to 1,770 mg/dl, varying from 0.1-1.9 mg/dl. Neither the human nor rabbit apoC-IV gene contains a typical TATA box in the 5'-flanking region, but the 5'-untranslated region of the rabbit gene contains a unique purine-rich sequence, GGGACAG(G/A), repeated nine times in tandem, with an additional two within the 5'-flanking sequence. This sequence, functioning as a GAGA box that has been implicated in the transcription of a number of genes, may explain the higher level of expression of apoC-IV in rabbits.