UCLA

Paraoxonase 2 (PON2) is a ubiquitously expressed antioxidant, anti-inflammatory protein localized in the inner mitochondrial membrane, where it protects against mitochondrial dysfunction and oxidative stress, among other protective properties. Human PON2 polymorphisms, particularly human PON2 Ser311Cys, has been implicated in the development of coronary artery disease, including myocardial infarction and ischemic stroke. Therefore, in this thesis, I explored the cardioprotective capacity of PON2 against myocardial infarction, specifically acute myocardial ischemia-reperfusion injury (IRI). My hypothesis is that PON2 protects against myocardial IRI in cardiomyocytes by modulating mitochondrial dysfunction and oxidative stress, particularly mitigating mitochondrial lipotoxicity (lipid peroxidation). I employed in vitro (rat ventricular cardiomyocyte cell line, H9c2 cells), ex vivo (cardiomyocytes derived from PON2-deficient mice hearts), and in vivo (PON2-deficient mice) models, subjecting them to cardiac IRI, to test my hypothesis. I determined that PON2 protects against myocardial IRI in cardiomyocytes by reducing mitochondrial dysfunction (stabilizing mitochondrial membrane potential and improving calcium retention capacity) and oxidative stress (reducing mitochondrial reactive oxygen species) via the reperfusion injury salvage kinase pathway (increasing phosphorylated glycogen synthase kinase-3β). Furthermore, there is an increase in mitochondrial lipid peroxidation in PON2-deficient mice subjected to myocardial IRI, with an increase in oxidized phosphatidylcholine species and eicosanoids (12, 15- hydroxyeicosatetraeonic acid), and a decrease in prostanoid production. These injuries are rescued by PON2 overexpression. Also, I observe an increase in cytoplasmic phospholipase A2 in the hearts of PON2-def mice subjected to myocardial IRI, serving as a potential mechanism by which PON2 modulates the increase in unesterified eicosanoid production. In order to further examine whether PON2 deficiency, exclusively in cardiomyocytes, is sufficient to induce increased myocardial IRI, I generated cardiomyocyte-specific PON2-KO mice. Lastly, I investigated the protective role of a novel drug, HSG4112, against cardiovascular risk factor, diet-induced obesity. I found that HSG4112 protects against diet-induced obesity by enhancing lactonase/arylesterase activity, reducing body weight and fat mass, and increasing lean (muscle) mass. Nevertheless, the protective effects of HSG4112 are significantly reduced in PON2-def mice, suggesting that PON2 is at least partly involved as a mode of action for HSG4112’s protective capacity.