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Lipoprotein(a), atherosclerosis, and apolipoprotein(a) gene polymorphism
Insights
High lipoprotein(a) [Lp(a)] levels are a risk factor for heart disease. Apo(a) gene variations, like kringle-4 repeats and TTTTA(n) sequences, influence Lp(a) levels and may be regulated by liver-specific factors.
Area of Science:
- Genetics
- Cardiovascular Disease
- Molecular Biology
Background:
- High plasma lipoprotein(a) [Lp(a)] levels are an independent risk factor for coronary artery disease across diverse ethnic populations.
- Apolipoprotein(a) [Apo(a)], derived from a duplicated plasminogen gene, drives Lp(a) accumulation in artery walls, promoting atherosclerosis via extracellular matrix binding and smooth muscle cell proliferation.
Purpose of the Study:
- To investigate the influence of apolipoprotein(a) [Apo(a)] gene polymorphisms on lipoprotein(a) [Lp(a)] concentration.
- To explore the relationship between Apo(a) size polymorphism (kringle-4 VNTR) and pentanucleotide repeat (PNR) sequences in Lp(a) regulation.
- To propose a model for individual-specific Apo(a) gene regulation involving liver-specific transcriptional factors.
Main Methods:
- Analysis of Apo(a) genetic size polymorphism, specifically the variable number of transcribed kringle-4 repeats (k-4 VNTR).
- Examination of pentanucleotide TTTTA(n) repeat (PNR) sequences in the regulatory region of the Apo(a) gene.
- Assessment of linkage disequilibrium between PNR number and k-4 VNTR in different ethnic groups.
Main Results:
- An inverse relationship between Lp(a) levels and Apo(a) allele sizes (k-4 VNTR) is observed across populations.
- A negative correlation between PNR number and Lp(a) levels is found in Caucasians and Indians, but not African Americans.
- Significant linkage disequilibrium exists between PNR number and k-4 VNTR, suggesting coordinated regulation.
Conclusions:
- Apo(a) gene polymorphisms, including k-4 VNTR and PNR sequences, significantly contribute to Lp(a) level variability.
- Ethnic variations in Apo(a) allele size distribution and PNR correlation highlight population-specific genetic influences.
- Liver-specific transcriptional activators and repressors are proposed to mediate individual-specific differential expression of the Apo(a) gene.
Abstract:
High plasma lipoprotein(a) [Lp(a)] levels have been implicated as an independent risk factor for coronary artery disease in Caucasians, Chinese, Africans, and Indians. Apo(a) that evolved from a duplicated plasminogen gene during recent primate evolution is responsible for the concentration of Lp(a) in the artery wall leading to atherosclerosis, by virtue of its ability to bind to the extracellular matrix and its role in stimulating the proliferation and migration of human smooth muscle cells. Several types of polymorphisms, size as well as sequence changes both in the coding and regulatory sequences, have been reported to influence the variability of Lp(a) concentration. Apo(a) exhibits genetic size polymorphism varying between 300 and 800 kDa that could be attributed to the number of k-4 VNTR (variable number of transcribed kringle-4 repeats). An inverse relationship between Lp(a) level and apo(a) allele sizes is a general trend in all ethnic populations although apo(a) allele size distribution could be significantly variable in ethnic types. A negative correlation between the number of pentanucleotide TTTTA(n) repeat (PNR) sequences in the regulatory region of the apo(a) gene and Lp(a) level has also been observed in Caucasians and Indians, but not in African Americans. However, a significant linkage disequilibrium was noted between the PNR number and k-4 VNTR. In order to correlate the role of apo(a) gene polymorphisms to apo(a) gene regulation, we have proposed that liver-specific transcriptional activators and repressors might contribute to the differential expression of apo(a) gene, in an individual-specific manner.