Title of the presentation:

Analysis of Protein Interactomes of Mutant Apolipoproteins Associated with Disease.

Biography:

Dr Yao is a lipid biochemist studying the metabolism of lipids and lipoproteins in disease. He is the Chair of the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa.

Short summary of research interests:

Research in the Yao laboratory focuses on the lipid and protein factors that regulate the biosynthesis of low and high density lipoproteins (LDL and HDL) yielding insights into the molecular mechanisms responsible for various diseases, including familial defective apoB (that causes high blood concentration of LDL), familial hypobetalipoproteinemia and familial abetalipoproteinemia (both have abnormally low blood concentration of LDL), and familial combined hyperlipidemia (caused by overproduction of disease-causing lipoproteins).

Abstract:

Overproduction of hepatic triacylglycerol (TAG)-rich lipoproteins, such as VLDL, is the main cause of dyslipidemia and associated with various metabolic abnormalities including type II diabetes. Mutations within the APOB gene often cause impaired secretion of the mutant apoB proteins, a structural component of VLDL, and a favorable low plasma TAG-rich lipoproteins (termed hypobetalipoproteinemia or FHBL). Moreover, heterozygote FHBL subjects do not develop overt hepatosteatosis. We have characterized intracellular itinerary of the mutant FHBL apoB proteins and the status of lipid homeostasis in hepatic cells expressing the mutant proteins. Subcellular fractionation in conjunction with immunocytochemistry and kinetic studies suggested intracellular degradation of the mutant proteins through a mechanism resembling autophagy. LC-MS/MS analysis of protein interactomes showed that >20 proteins had significant increase and ~10 proteins had significant decrease in binding to the apoB mutant. Proteins with increased binding to the apoB mutant included those that involved in protein folding (e.g. prolyl 3-hydroxylase 1, peptidyl-prolyl cis-trans isomerase B, and protein disulfide-isomerase), acted as molecular chaperones within the ER (e.g. DnaJ homolog subfamily members and calreticulin), ER quality control and ER-associated degradation (e.g. ARMET protein and sel-1 homolog 1), and chondroitin sulfate proteoglycan. Proteins with decreased binding to the A31P mutant included those required for N-linked glycosylation (e.g. ribophorin I), clotting factors (e.g. fibrinogen gamma chain, fibronectin isoform 4 and complement C1r), and the LDL receptor. These results suggest that (i) chaperone-mediated autophagy of mutant apoB, and (ii) the requirement of N-linked glycosylation and LDL receptor binding for ER-to-Golgi trafficking of apoB. Additional analysis of total cell proteome revealed that cells expressing the mutant proteins exhibited increased glycolysis and fermentation, reduced entry into the TCA cycle, and enhanced fatty acid beta-oxidation. Thus, hepatic cells may adopt a compensatory mechanism, by activating fermentation and beta-oxidation, to offset the impaired secretion of TAG-rich lipoproteins and maintain normal lipid homeostasis in FHBL liver.