Morin,
P., Ni, Z., McMullen, D.C. and Storey, K.B. 2008. Expression of Nrf2 and its downstream gene
targets in hibernating thirteen-lined ground squirrels, Spermophilus
tridecemlineatus. Mol. Cell. Biochem. 312, 121-129. DOI:10.1007/s11010-008-9727-3
Expression of Nrf2 and its Downstream Gene Targets in Hibernating
Thirteen-lined Ground Squirrels, Spermophilus
tridecemlineatus
Pier
Morin, Zhouli Ni, David C. McMullen and
Kenneth B. Storey
Abstract
Mammalian hibernation is associated with wide variation in heart rate,
blood flow and oxygen delivery to tissues and is used as a model of natural
ischemia/reperfusion. In non-hibernators, ischemia/reperfusion is typically
associated with oxidative stress but hibernators seem to deal with potential
oxidative damage by enhancing antioxidant defenses in an anticipatory manner. The
present study assesses the role of the Nrf2 transcription factor in the regulation
of antioxidant defenses during hibernation. Nrf2 mRNA and protein expression
were enhanced in selected organs of thirteen-lined ground squirrels, Spermophilus tridecemlineatus during hibernation. Furthermore, Nrf2 protein in heart was elevated by
1.4-1.5 fold at multiple stages over a torpor/arousal bout including during
entry, long term torpor, and early arousal. Levels returned to euthermic values when squirrels were fully aroused in interbout. Protein levels of selected downstream target
genes under Nrf2 control were also measured via immunoblotting
over the torpor/arousal cycle in heart. Cu/Zn superoxide dismutase and aflatoxin aldehyde
reductase levels increased significantly during entry
into torpor and then gradually declined falling to control levels or below in
fully aroused animals. Heme oxygenase-1 also showed the same trend. This suggests a role
for Nrf2 in regulating the antioxidant defenses needed for hibernation success.
Heart nrf2 was amplified by PCR and
sequenced. The deduced amino acid sequence showed high identity with the
sequence from other mammals but with selected unique substitutions (e.g. proline residues at positions 111
and 230) that might be important for
conformational stability of the protein at near 0°C body temperatures in
the torpid state.