APO B 3' HVR polymorphism in healthy population: relationships to serum lipid levels

Insights from human congenital disorders of intestinal lipid metabolism

The intestine must challenge the profuse daily flux of dietary fat that serves as a vital source of energy and as an essential component of cell membranes. The fat absorption process takes place in a series of orderly and interrelated steps, including the uptake and translocation of lipolytic products from the brush border membrane to the endoplasmic reticulum, lipid esterification, Apo synthesis, and ultimately the packaging of lipid and Apo components into chylomicrons (CMs). Deciphering inherited disorders of intracellular CM elaboration afforded new insight into the key functions of crucial intracellular proteins, such as Apo B, microsomal TG transfer protein, and Sar1b GTPase, the defects of which lead to hypobetalipoproteinemia, abetalipoproteinemia, and CM retention disease, respectively. These "experiments of nature" are characterized by fat malabsorption, steatorrhea, failure to thrive, low plasma levels of TGs and cholesterol, and deficiency of liposoluble vitamins and essential FAs. After summarizing and discussing the functions and regulation of these proteins for reader's comprehension, the current review focuses on their specific roles in malabsorptions and dyslipidemia-related intestinal fat hyperabsorption while dissecting the spectrum of clinical manifestations and managements. The influence of newly discovered proteins (proprotein convertase subtilisin/kexin type 9 and angiopoietin-like 3 protein) on fat absorption has also been provided. Finally, it is stressed how the overexpression or polymorphism status of the critical intracellular proteins promotes dyslipidemia and cardiometabolic disorders.

Effect of the 3'APOB-VNTR polymorphism on the lipid profiles in the Guangxi Hei Yi Zhuang and Han populations

BACKGROUND

Apolipoprotein (Apo) B is the major component of low-density lipoprotein (LDL), very low-density lipoprotein (VLDL) and chylomicrons. Many genetic polymorphisms of the Apo B have been described, associated with variation of lipid levels. However, very few studies have evaluated the effect of the variable number of tandem repeats region 3' of the Apo B gene (3'APOB-VNTR) polymorphism on the lipid profiles in the special minority subgroups in China. Thus, the present study was undertaken to study the effect of the 3'APOB-VNTR polymorphism on the serum lipid levels in the Guangxi Hei Yi Zhuang and Han populations.

METHODS

A total of 548 people of Hei Yi Zhuang were surveyed by a stratified randomized cluster sampling. The epidemiological survey was performed using internationally standardized methods. Serum lipid and apolipoprotein levels were measured. The 3'APOB-VNTR alleles were determined by polymerase chain reaction (PCR) followed by electrophoresis in polyacrylamide gels, and classified according to the number of repeats of a 15-bp hypervariable elements (HVE). The sequence of the most common allele was determined using the PCR and direct sequencing. The possible association between alleles of the 3'APOB-VNTR and lipid variables was examined. The results were compared with those in 496 people of Han who also live in that district.

RESULTS

Nineteen alleles ranging from 24 to 64 repeats were detected in both Hei Yi Zhuang and Han. HVE56 and HVE58 were not be detected in Hei Yi Zhuang whereas HVE48 and HVE62 were totally absent in Han. The frequencies of HVE26, HVE30, HVE46, heterozygote, and short alleles (< 38 repeats) were higher in Hei Yi Zhuang than in Han. But the frequencies of HVE34, HVE38, HVE40, homozygote, and long alleles (> or = 38 repeats) were lower in Hei Yi Zhuang than in Han (P < 0.05-0.01). The levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and Apo B in Hei Yi Zhuang but not in Han were higher in VNTR-LS (carrier of one long and one short alleles) than in VNTR-LL (the individual carrying two long alleles) genotypes. The levels of TC, triglycerides (TG), LDL cholesterol, and Apo B in Hei Yi Zhuang were higher in both HVE34 and HVE36 alleles than in HVE32 allele. The levels of TC, TG, HDL-C and Apo B in Hei Yi Zhuang were also higher in homozygotes than in heterozygotes. There were no significant differences in the detected lipid parameters between the VNTR-SS (carrier of two short alleles) and VNTR-LS or VNTR-LL genotypes in both ethnic groups.

CONCLUSION

There were significant differences of the 3'APOB-VNTR polymorphism between the Hei Yi Zhuang and Han populations. An association between the 3'APOB-VNTR polymorphism and serum lipid levels was observed in the Hei Yi Zhuang but not in the Han populations.

Apolipoprotein B gene 3'VNTR polymorphism: association with plasma lipids and coronary heart disease in Han Chinese

BACKGROUND

Studies that considered polymorphisms within the apolipoprotein B (APOB) gene as risk factors for coronary heart disease (CHD) have reported conflicting results.

METHODS

The phenotypic effects of the 3'VNTR polymorphism of the APOB gene on the susceptibility to CHD were investigated in 120 unrelated healthy individuals and 137 CHD patients. The internal structure of APOB gene 3'VNTR alleles was also analyzed by the methods of SspI restriction mapping and DNA sequencing of the allele fragments.

RESULTS

In total, 14 segregating alleles and 32 genotypes of APOB gene 3'VNTR were characterized in the pooled total of 257 subjects. The frequency of 3'VNTR-B alleles [hypervariable element (HVE) > or =38)] in the CHD cases was higher than that of the controls (10.95% vs. 5.00%, p<0.05). 3'VNTR-B allele was dependently related to total cholesterol levels (p<0.05). Compared with SS homozygotes, 3'VNTR-B allele carriers were associated with an increased risk of CHD (OR=2.137, 95% CI=1.055-4.328, p=0.0349). No significant differences in the internal structure and sequences of APOB gene 3'VNTR alleles were found between cases and controls.

CONCLUSIONS

APOB gene 3'VNTR polymorphism exerts an impact on lipid metabolism and may contribute to the susceptibility to the development of CHD in Han Chinese.

A study of the average effect of the 3'APOB-VNTR polymorphism on lipidemic parameters could explain why the short alleles (<35 repeats) are rare in centenarians

Background

In studies on the genetics of human aging, we observed an age-related variation of the 3'APOB-VNTR genotypic pool (alleles: Short, S, <35 repeats; Medium, M, 35–39 repeats; Long, L, >39 repeats) with the homozygous SS genotype showing a convex frequency trajectory in a healthy aging population. This genotype was rare in centenarians, thus indicating that the S alleles are unfavorable to longevity, while common in adults, thus indicating a protective role at middle age. This apparent paradox could be due to possible effects exerted by the above polymorphism on lipidemic parameters. Aim of the work was to get insights into these puzzling findings

Methods

We followed a double strategy. Firstly, we analyzed the average effects of S (α_S), M (α_M), and L (α_L) alleles on lipidemic parameters in a sample of healthy people (409 subjects aged 20–102 years) recruited in Calabria (southern Italy). The (α_S), (α_M), and (α_L) values were estimated by relating 3'APOB-VNTR genotypes to lipidemic parameters, after adjustment for age, sex and body mass index (multiple regression). Then, we analyzed the S alleles as susceptibility factors of Cardiovascular Atherosclerotic Disease (CD) in CD patients characterized either by low serum HDL-Cholesterol or by high serum LDL-Cholesterol (CD-H and CD-L patients, 40 and 40 subjects respectively). The Odds Ratios (OR) were computed for carriers of S alleles in CD-H and CD-L patients matched for origin, sex and age with controls extracted from the sample of healthy subjects.

Results

By the analysis of the healthy sample group we found that the S alleles lower the average values of serum Total Cholesterol (α_S = -5.98 mg/dL with [-11.62 ÷ -0.74] 95% confidence interval) and LDL-Cholesterol (α_S = -4.41 mg/dL with [-8.93 ÷ -0.20] 95% confidence interval) while the alleles M and L have no significant effect on the lipidemic phenotype. In line with these findings, the analysis of CD patients showed that the S alleles are protective as for CD-L (O.R. = 0.55 with [0.21 ÷ 0.98] 95% confidence interval) while neutral as for CD-H (O.R. = 0.75 with [0.32 ÷ 1.60] 95% confidence interval).

Conclusion

On the whole, the S alleles would be advantageous in adults (by protecting from CD-L) while dangerous in the elderly, probably by lowering serum cholesterol below a critical threshold. This could explain the convex frequency trajectory of SS genotypes previously observed in a healthy aging population.