In mosquitoes, warmer temperature reverses the aging-dependent decrease in nitric oxide synthase activity, modifying the expression of oxidative stress and immune genes

In mosquitoes, reactive oxygen and nitrogen species (ROS and RNS) are immune effectors, byproducts of metabolism, and regulators of homeostasis. However, imbalances in ROS and RNS cause oxidative stress. Given that warmer temperature accelerates the aging-dependent weakening of immunity, we hypothesized that temperature and aging interactively modify the production of ROS/RNS like nitric oxide, and their effects. We tested this in Anopheles gambiae by rearing mosquitoes at 27C, 30C and 32C, and assessing phenotypes at 1, 5, 10 and 15 days of adulthood. Using NADPH diaphorase staining, we show that, in mosquitoes infected with bacteria, warmer temperature increases the activity of nitric oxide synthase (NOS; produces nitric oxide), while aging decreases NOS activity. Importantly, during late aging, warmer temperature reverses the aging-dependent decline in NOS activity. By mining an RNAseq dataset, we uncovered that warmer temperature and aging interact to increase the expression of both NOS and JNK, which are involved in immunity and oxidative stress. Additionally, warmer temperature and aging interact to downregulate expression of genes encoding antimicrobial effectors and superoxide detoxification enzymes, but upregulate expression of genes involved in hydrogen peroxide detoxification. Finally, manipulating nitric oxide production modifies the expression of immune genes in a temperature and age dependent manner. These findings suggest that heightened oxidative stress caused by warmer temperature accelerates senescence.