Renal Mitochondrial Response to Low Temperature in Non-Hibernating and Hibernating Species

Significance: Therapeutic hypothermia is commonly applied to limit ischemic injury in organ transplantation, during cardiac and brain surgery and after cardiopulmonary resuscitation. In these procedures, the kidneys are particularly at risk for ischemia/reperfusion injury (IRI), likely due to their high rate of metabolism. Although hypothermia mitigates ischemic kidney injury, it is not a panacea. Residual mitochondrial failure is believed to be a key event triggering loss of cellular homeostasis, and potentially cell death. Subsequent rewarming generates large amounts of reactive oxygen species that aggravate organ injury. Recent Advances: Hibernators are able to withstand periods of profoundly reduced metabolism and body temperature ("torpor"), interspersed by brief periods of rewarming ("arousal") without signs of organ injury. Specific adaptations allow maintenance of mitochondrial homeostasis, limit oxidative stress, and protect against cell death. These adaptations consist of active suppression of mitochondrial function and upregulation of anti-oxidant enzymes and anti-apoptotic pathways.

Critical issues: Unraveling the precise molecular mechanisms that allow hibernators to cycle through torpor and arousal without precipitating organ injury may translate into novel pharmacological approaches to limit IRI in patients.

Future directions: Although the precise signaling routes involved in natural hibernation are not yet fully understood, torpor-like hypothermic states with increased resistance to ischemia/reperfusion can be induced pharmacologically by 5'-adenosine monophosphate (5'-AMP), adenosine, and hydrogen sulfide (H₂S) in non-hibernators. In this review, we compare the molecular effects of hypothermia in non-hibernators with natural and pharmacologically induced torpor, to delineate how safe and reversible metabolic suppression may provide resistance to renal IRI. Antioxid. Redox Signal. 27, 599-617.