Proteomic Identification and Biochemical Linkage of Isocitrate Dehydrogenase as a
Novel Mediator of Preconditioning
Stephanie L. H. Zeiger1,3, Jacquelynn E. Brown1,3, and BethAnn McLaughlin1,2,3
Departments of Neurology1 and Pharmacology2 and Vanderbilt Kennedy Center for
Research on Human Development3
A short, sublethal event can lead to subsequent neuronal resistance to an otherwise lethal
stimulus, a phenomenon referred to as preconditioning. In order to investigate the
cellular and molecular cues involved in this process, we have developed in vivo and in
vitro models in which forebrain neuronal cells can be rendered less sensitive to cell death
following a nontoxic ‘priming’ exposure. Using these models, we have previously found
that caspase activation and generation of reactive oxygen species elicit heat shock protein
70 (HSP70) induction.
HSP70 functions as a multi-chaperone complex and its activity can be altered by changes
within the cellular environment. Indeed, essential HSP70 cysteine residues which are
susceptible to redox stress alter its expression and function. Similarly, ATPase activity of
the complex is impacted by energetic tone. Thus, we believe that redox and energetic
stress converge on essential gatekeeping molecules to determine neuronal fate following
preconditioning.
In support of this hypothesis, we recently performed a proteomic analysis of in vivo
preconditioned tissue and found a significant loss of the NADH synthesizing enzyme
isocitrate dehydrogenase (ICDH). Western blot analysis also revealed a decrease in ICDH
expression in our in vitro model. This Krebs cycle enzyme has not previously been
linked to neuroprotection, yet it provides an essential means to balance aerobic and
anaerobic respiration.
Using a bioluminescent assay, we observed a very mild loss of ATP following
preconditioning in our in vitro model despite substantial aerobic respiratory challenge.
This data suggests the cells are undergoing bioenergetic adaptations to maintain ATP
levels. Thus, we hypothesize that decreased ICDH expression leads to a shift from
aerobic to anaerobic respiration to keep pace with metabolic demand and allows the
neuron to become energetically poised for surviving an otherwise lethal event.