Yin and Yang of mitochondrial ROS in Drosophila

Abstract

In this study, we test the hypothesis that Drosophila larvae producing mildly elevated levels of endogenous mitochondrial reactive oxygen species (ROS) benefit in stressful environmental conditions due to the priming of antioxidant responses. Reactive oxygen species (ROS) are produced as a by-product of oxidative phosphorylation and may be elevated when mutations decrease the efficiency of ATP production. In moderation, ROS are necessary for cell signaling and organismal health, but in excess can damage DNA, proteins, and lipids. We utilize two Drosophila melanogaster strains (Dahomey and Alstonville) that share the same nuclear genetic background but differ in their mitochondrial DNA haplotypes. Previously, we reported that Dahomey larvae harboring the V161L ND4 mtDNA mutation have reduced proton pumping and higher levels of mitochondrial ROS than Alstonville larvae when they are fed a 1:2 protein: carbohydrate (P:C) diet. Here, we explore the potential for mitochondrial ROS to provide resistance to dietary stressors by feeding larvae 1:2 P:C food supplemented with ethanol or hydrogen peroxide (H₂O₂). When fed a diet supplemented with ethanol or H₂O₂, Dahomey develop more quickly than Alstonville into larger pupae, while Alstonville developed faster on the control. Dahomey larvae displayed higher antioxidant capacity than Alstonville on all diets, with mitochondrial H₂O₂ levels unchanged after the addition of stressors. Addition of stressors to the diet did not affect the mitochondrial functions of Dahomey larvae as measured by mitochondrial membrane potential, respiratory control ratio, or larval survival after bacterial challenge. In contrast, Alstonville larvae developed slower, had lower pupal weight, higher cytosolic H₂O₂, and had reduced mitochondrial functions. Further, Alstonville larvae fed the ethanol treated diet had lower survival after bacterial infection than those fed the control diet. Surprisingly, they had greater survival when fed diet with H₂O₂ indicating a mitotype by stressor interaction that influences the immune response. Overall, these data suggest that elevated mitochondrial ROS in Dahomey can result in greater antioxidant capacity that prevents oxidative damage from exogenous stressors and may be a conserved response to high ethanol found in rotting fruit.

Keywords: Beneficial mutation; Dietary stressors; Drosophila, mitochondrial DNA; Reactive oxygen species.