Date Published: February 25, 2015
Publisher: Public Library of Science
Author(s): Martin Heisig, Sarah Mattessich, Alison Rembisz, Ali Acar, Martin Shapiro, Carmen J. Booth, Girish Neelakanta, Erol Fikrig, Andreas Bergmann.
Ectotherms in northern latitudes are seasonally exposed to cold temperatures. To improve survival under cold stress, they use diverse mechanisms to increase temperature resistance and prevent tissue damage. The accumulation of anti-freeze proteins that improve cold hardiness occurs in diverse species including plants, arthropods, fish, and amphibians. We previously identified an Ixodes scapularis anti-freeze glycoprotein, named IAFGP, and demonstrated its cold protective function in the natural tick host and in a transgenic Drosophila model. Here we show, in a transgenic mouse model expressing an anti-freeze glycoprotein, that IAFGP protects mammalian cells and mice from cold shock and frostbite respectively. Transgenic skin samples showed reduced cell death upon cold storage ex vivo and transgenic mice demonstrated increased resistance to frostbite injury in vivo. IAFGP actively protects mammalian tissue from freezing, suggesting its application for the prevention of frostbite, and other diseases associated with cold exposure.
Ectotherms in cold environments have evolved molecular mechanisms to withstand extreme temperatures [1–5]. Very few organisms tolerate freezing solid and most avoid freezing by the accumulation of protective compounds [6,7]. Anti-freeze proteins (AFPs) contribute to cold hardiness by reducing cold-induced damage in a non-colligative manner, binding directly to the surface of ice crystals [8,9]. This interaction inhibits the addition of water molecules to the developing ice lattice and impedes crystal growth [10–12]. In turn, this prevents the formation of sharp ice needles that inflict tissue damage. These, and other adaptions, allow diverse forms of life to inhabit extreme niches, including arctic waters or glaciers, and they also contribute a survival advantage to organisms experiencing seasonal cold periods in temperate climate zones [1–5].
The exposure of ectotherms to cold temperatures causes molecular adaptions that aim to prevent permanent damage and improve survival. Mammals, maintaining a fairly constant body core temperature, do not have a similar adaptive system for protection against the cold. They rely on body insulation and blood flow management to control peripheral temperatures and prevent the detrimental effects of temperature extremes. Once these measures fail, such as during extended exposure to extreme cold, local tissue damage manifests as frostbite while systemic hypothermia can lead to death .
Mammals maintain their body temperature, under diverse environmental conditions, within a small thermal range. Local contact with extreme temperatures causes burn wounds or frostbite, and systemic exposure to extreme cold or heat can lead to death . Organisms without intrinsic temperature control have adapted to thrive within a wide range of body temperatures using various mechanisms to prevent harmful effects [1–5]. One strategy to survive cold temperatures, the expression of AFPs, prevents cold damage by modifying ice formation. These proteins bind to the surface of small ice nuclei and alter ice crystal growth, shape or size. AFPs are abundant in diverse organisms encountering cold or freezing environments, including fish, arthropods, and plants. One subgroup of the structurally diverse family of antifreeze proteins, the antifreeze glycoproteins (AFGP), is still poorly understood, in part because of its challenging molecular properties, which have complicated effective recombinant protein expression and purification . Highly repetitive primary DNA and amino acid sequences, pronounced glycosylation, and the proposed degradation into functional peptides thwart the application of standard techniques.