Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Physiology and Pharmacology

Supervisor

Koschinsky, Marlys L.

Affiliation

Robarts Research Institute

Abstract

Elevated plasma lipoprotein(a) (Lp(a)) is the most prevalent heritable risk factor in the development of cardiovascular disease. The apolipoprotein(a) (apo(a)) component of Lp(a) is strongly implicated in the pathogenicity of Lp(a). It is hypothesized that the inflammatory potential of Lp(a)/apo(a) is mediated by the lysine binding ability of the apo(a) kringle IV10 (KIV10) domain, along with its covalently bound oxidized phospholipid (oxPL). Using targeted mutagenesis, two novel null alleles for the LPA gene that generate non-secretable apo(a) species have been identified, resulting from amino acid substitutions in the KIV10 domain. A potential mechanism by which KIV10 oxPL modification is enriched was identified. Finally, RNA-Seq was utilized to demonstrate gene regulation in macrophage-like cells in response to the lysine binding function and covalent oxPL of the KIV10 domain. It was determined that the lysine binding ability and covalent oxPL of apo(a) KIV10 are both implicated in vascular cell inflammation and atherosclerosis.

Summary for Lay Audience

In humans, fats and cholesterol are transported in the blood stream as components of particles called lipoproteins. A high level of one lipoprotein variety, lipoprotein(a) (Lp(a)), has been determined to be the single most prevalent heritable risk factor for developing cardiovascular diseases by contributing to the build-up of plaques within the arteries, or “atherosclerosis”. Lp(a) is very similar to the more commonly known low-density lipoprotein (LDL), which is typically considered the “bad” cholesterol (in comparison to high density lipoprotein (HDL), which is typically considered the “good” cholesterol). Lp(a) contains a protein component called apolipoprotein(a) (apo(a)), which distinguishes Lp(a) from LDL, and is thought to be responsible for the increased pathogenicity of Lp(a) in comparison to LDL. Apo(a) contains many sub-sections, or “domains”, that contribute in different ways to its characteristics. One domain, kringle IV sub-type 10 (KIV10), is thought to be particularly important for the harmful effects of Lp(a) in the blood stream. Here, we investigated the implications of the functions of the KIV10 domain, and the potential roles this domain may have in the development of atherosclerosis. The KIV10 domain is able to bind lysine, which allows apo(a) or Lp(a) to associate closely with cell surface proteins and other ligands. Additionally, the KIV10 domain is modified covalently with an oxidized phospholipid (oxPL). The lysine binding ability of KIV10 has been determined to have atherosclerosis-related effects in certain vascular cell types, as have oxPLs. Together, this suggests that the KIV10 domain may represent an important factor in mediating the harmful effects of Lp(a) in the blood stream. We have determined that either of two independent amino acid substitutions in KIV10 can prevent the secretion of apo(a) entirely, and that a different substitution can change the amount of oxPL added to this domain. Beyond that, we have determined that the lysine binding ability and covalent oxPL of the KIV10 domain are implicated in many gene-regulatory processes that can potentially facilitate the development of atherosclerosis in humans.

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