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)) levels are a causal risk factor for cardiovascular disease (CVD), but development of specific Lp(a) lowering therapeutics has been hindered by insufficient understanding of Lp(a) biology. For example, the location of the noncovalent interaction that precedes the extracellular disulfide linkage between apolipoprotein(a) (apo(a)) and apolipoprotein B-100 (apoB-100) in Lp(a) biosynthesis is unclear. In this study we modulated known intracellular regulators of apoB-100 production and then assessed apo(a) secretion from human HepG2 cells expressing 17-kringle (17K) apo(a) isoform variants using pulse-chase analysis. Treating 17K-expressing HepG2 cells withproprotein convertase subtilisin-kexin type 9(PCSK9) significantly increased apo(a) secretion. Treating the same cell line with Lomitapide, a microsomal triglyceride transfer protein (MTP) inhibitor, significantly decreased apo(a) secretion. Overexpression of human sortilin variants (F404Y and K302E) significantly increased apo(a) secretion relative to wild-type. Our findings suggest a role for sortilin, PCSK9, and MTP in modulating Lp(a) levels through effects on apo(a) secretion, possibly through impacting the intracellular bioavailability of apoB-100.

Summary for Lay Audience

Lipoprotein(a) (Lp(a)) is a circulating lipoprotein that contributes to the development of cardiovascular disease. The structure of lipoprotein(a) consists of a low-density lipoprotein-like core that is covalently attached to apolipoprotein(a). Unfortunately, no pharmacological therapies designed to specifically lower Lp(a) currently exist, which reflects a lack of fundamental understanding of the mechanisms regulating Lp(a) production and catabolism. In this study, we modulated known regulators of apoB-100 secretion and subsequently analyzed apo(a) secretion to determine if a non-covalent interaction exists between apo(a) and apoB-100 in Lp(a) production.

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