Metabolic Preconditioning of Mammalian Cells: Approaches for Increasing Biostability after Desiccation

Abstract

Selected species in nature are able to tolerate prolonged periods of severe water stress. Survival of cellular desiccation in these anhydrobiotic organisms is conferred by a number of mechanisms including accumulation of stabilizing solutes, such as trehalose, and expression of Late Embryogenesis Abundant (LEA) proteins. An additional feature shared by some anhydrobiotic animals is the capacity to suppress mitochondrial oxidative phosphorylation in preparation for desiccation. These mechanisms improve the physiological robustness of cells to stress. The primary aim of this dissertation is to evaluate forms of metabolic preconditioning and to test the most propitious as a means to improve desiccation tolerance of mammalian cells. Several chemical agents, termed hypoxia mimetics, were evaluated in this study for utility in metabolic preconditioning. My results demonstrate that although each treatment increased Hypoxia Inducible Factor-1α (HIF-α) to varying degrees, none of them emulated every aspect of the hypoxia response in mammalian cells. A key aspect of the cellular hypoxia response is the phosphorylation and inhibition of pyruvate dehydrogenase (PDH). CoCl2 unexpectedly and strikingly decreased the phosphorylation of PDH. Neither desferrioxamine nor the prolyl-hydroxylase inhibitor FG-4592 caused an increase in PDH phosphorylation. Although dimethyloxalolglycine (DMOG) increased PDH phosphorylation, further examination of mitochondrial respiration showed that routine respiration was not reestablished 24 h after the treatment was removed. Based on these results hypoxia preconditioning was determined to be the most promising avenue for metabolic preconditioning. The effects of hypoxia preconditioning on desiccation tolerance were investigated with HepG2 cells that had been modified to accumulate trehalose and express AfrLEA2 from the brine shrimp Artemia franciscana. Spin-drying was used to quickly dehydrate the cells to a residual water content of 0.225 g H2O/g dry mass. Cells were then immediately rehydrated. The growth profiles of cells that received hypoxic preconditioning, with and without the nitric oxide donor MitoSNO, were compared to the growth of control cells without preconditioning. Results indicated that hypoxia preconditioning significantly increased cell proliferation compared to controls, and proliferation was further bolstered by the addition of MitoSNO. These findings support the concept that metabolic preconditioning can improve the biostability of mammalian cells after desiccation.