Influence of FADS2 expression on cardiovascular risk: role of mitochondrial arachidonic acid

2020 Fall.Includes bibliographical references.Long-chain polyunsaturated fatty acids (LC-PUFA) are widely believed to influence cardiovascular health and disease in humans and can be supplied through the diet or endogenously synthesized from the essential PUFAs linoleic acid (LA; n6) and alpha-linolenic acid (ALA; n3). Redistribution of PUFAs in serum and tissue phospholipids has been associated with various pathologies, manifesting primarily as a proportional loss of the essential PUFA LA paralleled by reciprocal increases in its long-chain product arachidonic acid (AA; n6). Epidemiological studies have linked greater AA/LA ratios in serum phospholipids to multiple parameters of cardiometabolic disease (CMD), such as obesity, insulin resistance, hypertension, atherosclerosis, and coronary artery disease. Single nucleotide polymorphisms in the FADS2 gene are associated with haplotypes of greater expression of FADS2, which may increase the production of AA from LA and increase serum AA/LA ratios. FADS2 encodes delta-6 desaturase, the rate-limiting enzyme in endogenous LC-PUFA biosynthesis, which is believed to participate in the development of CMD by interacting with the high dietary LA content found in the modern Western diet to disproportionally produce AA over other LC-PUFAs. The overarching hypothesis of this dissertation is that greater expression of FADS2 promotes the development of cardiovascular risk parameters. To investigate this, we generated mice with global (CMV promoter) transgenic overexpression of Fads2 (Fads2TG); these mice exhibit classic serum shifts in PUFA distribution characteristic of human FADS2 polymorphisms. A series of three projects were undertaken: 1) Investigate the interaction between dietary essential fatty acid intakes and Fads2 expression on cardiovascular risk; 2) Establish methodology for simultaneous measurement of mitochondrial respiration and ROS release in vitro; 3) Investigate effects of Fads2 expression on cardiac mitochondrial responses to Ca++-overload. These studies discovered that greater Fads2 expression is sufficient to increase several aspects of cardiovascular risk that were independent of the dietary ratio of n6:n3 essential PUFAs. Further investigation demonstrated that cardiac cardiolipin AA content predicted ischemia-reperfusion (IR) injury, suggesting a mechanistic role of mitochondria in this phenotype. Gain- and loss-of-function approaches in mice established that greater Fads2 expression lowers mitochondrial tolerance to Ca++-overload demonstrated by loss of OXPHOS-linked respiration, greater mitochondrial ROS release, and increased mitochondrial permeability transition. Furthermore, mitochondrial permeability transition by Ca++-overload could be attenuated by inhibition of AA release or metabolism. Collectively, the significance of these studies establish the influence of Fads2 on serum and tissue PUFA composition and the pathogenesis of IR injury through modulation of mitochondria membrane composition, thereby demonstrating Fads2 expression as an independent factor for cardiovascular risk