Mitochondria, metabolic control and microRNA: Advances in understanding amphibian freeze tolerance

Abstract

Winter survival for many animal species depends freeze tolerance, a capacity to endure the conversion of as much as 65–70% of total body water into extracellular ice while reorganizing metabolism to provide cells with cryoprotection against insults that include prolonged ischemia and hyperosmotic stress. Natural freeze tolerance involves not just de novo preservation mechanisms such as synthesis of high levels of cryoprotectants or novel proteins that manage ice formation, but also requires attention to and co‐ordination of many cellular processes. The present review examines recent studies of the freeze‐tolerant wood frog (Rana sylvatica) that probed previously unexplored areas of metabolic adaptation for freezing survival, with a particular emphasis on mitochondria. Post‐translational controls on enzyme function play a prominent role in resculpting metabolic responses of the wood frog to freezing including reversible phosphorylation control over fuel processing at the pyruvate dehydrogenase locus and modulation of antioxidant defense enzymes (Mn‐SOD, catalase). Enzymes involved in mitochondrial nitrogen metabolism (glutamate dehydrogenase, carbamoyl phosphate synthetase) are also differentially regulated during freezing but by different post‐translational modifications including ADP‐ribosylation, lysine acetylation or glutarylation. The action of microRNAs in mediating post‐translational controls on gene expression aid the suppression of energy‐expensive (cell cycle) or destructive (apoptosis) processes in the frozen state while also providing storage of transcripts that will be immediately available for repair or reactivation of metabolic processes after thawing. The effects of low temperature in strengthening mRNA–microRNA interactions can also provide a passive mechanism of metabolic suppression in the frozen state.

Metabolic responses of plasma to extreme environments in overwintering Tibetan frogs Nanorana parkeri: a metabolome integrated analysis

“…Hence, amphibians that successfully hibernate underwater face challenges of hypoxia but freezing only rarely [ 1 ]. In general, there are two paramount physiological mechanisms that allow amphibians to survive the winter underwater: one is protecting themselves against cold and/or hypoxia injury and the other is maintaining long-term metabolic homeostasis [ 8 , 10 – 13 ].…”

“…Protective mechanisms against winter cold have been widely explored in a number of overwintering amphibians. Among freeze tolerant terrestrially hibernating species these mechanisms include accumulation of low molecular mass cryoprotectants (e.g., glucose, urea, glycerol) and production of ice-binding proteins that can trigger and regulate where ice forms [ 8 , 13 , 14 ]. Given that preserving membrane structure and function plays a significant role in living in extremely cold environments [ 15 ], membrane adaptation (e.g., altering membrane lipid composition) is also essential for winter survival [ 16 ].…”

Multiple omic investigations of freeze tolerance adaptation in the aquatic ectothermic vertebrate, the Amur sleeper

“…Most natural freeze tolerance refers to ice formation in extracellular spaces while resisting intercellular freezing to avoid damage of subcellular compartments and the cytoskeleton (Costanzo and Lee 2013; Storey and Storey 2017). Ice crystals exclude solutes greatly elevates the osmolality of extracellular fluids, producing a hyperosmotic stress that draws water out of cells causing them to shrink (Storey and Storey 2020). Besides physical and osmotic damage, freezing causes important consequences including hypoxia/anoxia, ischemia, dehydration and hypometabolism etc (Storey and Storey 2017; Toxopeus and Sinclair 2018).…”

Cryopreservation of Animals and Cryonics: Current Technical Progress, Difficulties and Possible Research Directions

“…These principles include: (A) Hypothermia can reduce or pause metabolism and other biochemical reactions while offering protection against ischemic injury. This is a natural occurrence for the northern wood frog ( Rana sylvatica ), which adapts to subzero temperatures (−3 to −6°C) for prolonged durations by transitioning into a semi-frozen phase devoid of cardiac function ( 3 ). Clinically, cryopreservation technology is applied extensively to extend the survival time of different cells, tissues and organs which would naturally lose viability if left unpreserved.…”