Abstract

Acyl-CoA oxidase (Aox) is an enzyme that carries out the first step of Ý-oxidation of free fatty acids in peroxisomes. Here I describe a novel role for Aox in peroxisome biogenesis. I found that the peroxisome becomes competent for division only after it acquires the complete set of matrix proteins involved in lipid metabolism. Overloading the peroxisome with matrix proteins promotes the relocation of Aox from the matrix to the membrane. The binding of Aox to Pex16p, a membrane-associated peroxin required for peroxisome biogenesis, initiates the biosynthesis of phosphatidic acid and diacylglycerol (DAG) in the membrane. The formation of these two lipids and the subsequent transbilayer movement of DAG initiate the assembly of a complex between the peroxins Pex10p and Pex19p, the dynamin-like GTPase Vps1p, and several actin cytoskeletal proteins on the peroxisomal surface. This protein team promotes membrane fission, thereby executing the terminal step of peroxisome division. One of my objectives was to understand what role (if any) Aox and other peroxisomal enzymes of fatty acid oxidation may play in regulating yeast longevity. I found that Aox is an essential component of the protein network controlling the chronological lifespan of yeast placed on a low-calorie diet called calorie restriction (CR). My findings lead to the conlusion that fatty acid oxidation in peroxisomes controls longevity by modulating the rate of ATP synthesis in mitochondria, but not by generating the ROS hydrogen peroxide. Recent studies in Dr. Titorenko's laboratory identified novel small molecules that greatly increase the chronological lifespan of yeast. My experiments with one of these novel anti-aging drugs, a commercially available compound further referred to as "LA", revealed that it extends yeast longevity under CR conditions. My studies aimed at elucidating the molecular mechanisms by which LA increases yeast lifespan revealed that . lack of Aox or any other enzyme of peroxisomal fatty acid oxidation does not impair the anti-aging effect of LA. My findings demonstrated that LA extends yeast longevity by: (1) reducing the damaging effect of ROS on cellular macromolecules; and (2) amplifying the so-called "hormetic" effect of ROS through the activation of stress-protecting and other anti-aging proteins.