Elevated plasma concentration of Lp(a) is one of the major inherited risk factors for atherosclerosis, and may account for roughly one-fourth of the heart attacks suffered by men under 60. Lp(a) resembles the cholesterol- rich low density lipoprotein (LDL), but is distinguished by the presence of an additional protein known as apolipoprotein(a), [apo(a)]. Apo(a) closely resembles plasminogen, providing a possible link between thrombosis and atherosclerosis. The plasma levels of apo(a) vary one thousand-fold in the population, yet for a given individual change little during lifetime. Apo(a) level is genetically determined with relatively little environmental influence. Since the level of apo(a) is linked to atherosclerosis, understanding of the regulation of gene expression and the molecular determinants for the variation between individuals is clearly important. We propose to clone human apo(a) genomic DNA, characterize its promoter region and study the transcriptional regulation of its expression. The 5' flanking region of the highly similar apo(a) and plasminogen genes will be compared. We will examine the apo(a) gene sequence variation between representative individuals with varied plasma apo(a) levels and attempt to establish a correlation between these parameters. We propose that variations in regulatory elements in the promoter region are responsible for the differences in apo(a) expression levels. This will be tested by transient expression studies using reporter gene approaches, by in vitro transcription and by site directed mutagenesis. The in vivo effect of sequence variations will be tested by hybridization and PCR analysis of family members. In the second part of this proposal, we will produce transgenic animals expressing human apo(a), to directly test its proposed role in the development of atherosclerosis and thrombosis. Arterial injury animal models will also be employed to study the ways in which elevated apo(a) may lead to accelerated restenosis, as implied by human epidemiologic studies.
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