Integrative transcriptomic and metabolic analyses of the mammalian hibernating brain identifies a key role for succinate dehydrogenase in ischemic tolerance
Ischemic stroke results in a loss of tissue homeostasis and integrity, the underlying pathobiology of which stems primarily from the depletion of cellular energy stores and perturbation of available metabolites1. Hibernation in thirteen-lined ground squirrels (TLGS), Ictidomys tridecemlineatus, provides a natural model of ischemic tolerance as these mammals undergo prolonged periods of critically low cerebral blood flow without evidence of central nervous system (CNS) damage2. Studying the complex interplay of genes and metabolites that unfolds during hibernation may provide novel insights into key regulators of cellular homeostasis during brain ischemia. Herein, we interrogated the molecular profiles of TLGS brains at different time points within the hibernation cycle via RNA sequencing coupled with a untargeted metabolomics. We demonstrated that hibernation leads to major changes in the expression of genes involved in oxidative phosphorylation coupled with an accumulation of the tricarboxylic acid (TCA) cycle intermediates citrate, cis-aconitate, and a-ketoglutarate-aKG. Integration of the gene expression and metabolomics datasets identified succinate dehydrogenase (SDH) as the most critical enzymes during hibernation, suggesting a break in the TCA cycle at that level. Accordingly, the SDH inhibitor dimethyl malonate (DMM) was able to rescue the effects of hypoxia on human neuronal cells in vitro and in mice subjected to permanent ischemic stroke in vivo. Our findings indicate that studying the regulation of the controlled metabolic depression that occurs in hibernating mammals may lead to novel therapeutic targets to increase ischemic tolerance in the CNS.