Date of this Version
Rose, Jordan. (2019). Xenobiotic Exposure Requires Mitochondrial Metabolism for REDOX Homeostasis and Survival in Astrocytes. Masters Dissertation, University of Nebraska-Lincoln.
Astrocytes are integral components of glutamatergic neurotransmission, providing essential metabolic processes for neuronal homeostasis and acting as the first line of defense against xenobiotics crossing the blood brain barrier. Arsenic is a xenobiotic with widespread natural and industrial prevalence, and has been linked to impaired neurodevelopment and neuronal death. Given the integrated metabolic nature of astrocytes and neurons, we sought to explore how arsenic impacts astrocyte metabolism in order to better understand the mechanisms of xenobiotic toxicity in the mammalian brain.
We demonstrate that astrocyte viability depends upon de novoglutathione (GSH) synthesis during arsenic exposure, and sub-lethal arsenic exposure (iAs
U-13C-glucose NMR-based metabolomics revealed that iAs induced an anaplerotic generation of glutamate via the tricarboxylic acid cycle and its extracellular release in astrocytes. Quantification of the extracellular glutamate indicated potentially excitotoxic concentrations were reached (Glu > 20µM), which were not significantly altered by γ-glutamyl transpeptidase (γGT) or MRP1 inhibition. Excitatory amino acid transporter 1 and 2 (EAAT1/2) inhibition significantly increased extracellular glutamate accumulation even in the absence of arsenic.
Mitotoxins rotenone (Rote), paraquat (PQ), or 1-methyl-4-phenylpyridinium (MPP+) sensitized the astrocytes to arsenic. Inhibition of mitochondrial carbon inputs by etomoxir (Eto) or UK5099 (UK), or of transamination by aminooxyacetic acid (AOAA), sensitized astrocytes to arsenic to a similar degree. Eto, UK, and AOAA increased arsenic accumulation in astrocytes but did not significantly alter extracellular glutamate accumulation.
This thesis illustrates that mitochondrial metabolism is essential to astrocytes survival during xenobiotic exposure. Further, the significant efflux of glutamate may create toxic conditions for neurons. Astrocytes previously have been shown to be glycolytic, resistant to mitochondrial toxins, and viable in vivo without functional electron transport chain. These results now demonstrate that mitochondria metabolism is essential for astrocytes survival under conditions of stress and require us to reassess the role of mitochondrial metabolism in astrocytes.
Advisor: Rodrigo Franco-Cruz