Freshwater turtles survive prolonged
anoxia and reoxygenation without overt brain damage by well-described physiological processes, but little work has been done to investigate the molecular changes associated with anoxic survival. We examined
stress proteins and apoptotic regulators in the turtle during early (1 h) and long-term
anoxia (4, 24 h) and reoxygenation. Western blot analyses showed changes within the first hour of
anoxia; multiple
stress proteins (Hsp72,
Grp94, Hsp60, Hsp27, and HO-1) increased while apoptotic regulators (Bcl-2 and Bax) decreased. Levels of the ER
stress protein Grp78 were unchanged.
Stress proteins remained elevated in long-term
anoxia while the Bcl-2/Bax ratio was unaltered. No changes in cleaved
caspase 3 levels were observed during
anoxia while
apoptosis inducing factor increased significantly. Furthermore, we found no evidence for the anoxic translocation of Bax from the cytosol to mitochondria, nor movement of
apoptosis inducing factor between the mitochondria and nucleus. Reoxygenation did not lead to further increases in
stress proteins or apoptotic regulators except for HO-1. The apparent protection against cell damage was corroborated with immunohistochemistry, which indicated no overt damage in the turtle brain subjected to
anoxia and reoxygenation. The results suggest that molecular adaptations enhance pro-survival mechanisms and suppress apoptotic pathways to confer
anoxia tolerance in freshwater turtles.