Extremeophiles and Extreme Environments

Antioxidant Defense in the Toughest Animals on the Earth: Its Contribution to the Extreme Resistance of Tardigrades

By Keith Cowing
Status Report
Int J Mol Sci via PubMed
September 23, 2024
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Antioxidant Defense in the Toughest Animals on the Earth: Its Contribution to the Extreme Resistance of Tardigrades
Tardigrade Hypsibius exemplaris. — Int J Mol Sci.

Tardigrades are unique among animals in their resistance to dehydration, mainly due to anhydrobiosis and tun formation. They are also very resistant to high-energy radiation, low and high temperatures, low and high pressure, and various chemical agents, Interestingly, they are resistant to ionizing radiation both in the hydrated and dehydrated states to a similar extent. They are able to survive in the cosmic space.

Apparently, many mechanisms contribute to the resistance of tardigrades to harmful factors, including the presence of trehalose (though not common to all tardigrades), heat shock proteins, late embryogenesis-abundant proteins, tardigrade-unique proteins, DNA repair proteins, proteins directly protecting DNA (Dsup and TDR1), and efficient antioxidant system. Antioxidant enzymes and small-molecular-weight antioxidants are an important element in the tardigrade resistance.

The levels and activities of many antioxidant proteins is elevated by anhydrobiosis and UV radiation; one explanation for their induction during dehydration is provided by the theory of “preparation for oxidative stress”, which occurs during rehydration. Genes coding for some antioxidant proteins are expanded in tardigrades; some genes (especially those coding for catalases) were hypothesized to be of bacterial origin, acquired by horizontal gene transfer. An interesting antioxidant protein found in tardigrades is the new Mn-dependent peroxidase.

Scheme of the mechanism of action of various environmental factors and main protective mechanisms in tardigrades. All these factors inflict damage on DNA and proteins and oxidative stress (increased generation of reactive oxygen species (ROS)). ROS themselves can damage DNA and proteins. Protective mechanisms are shown in green. TDPs, tardigrade disordered proteins; Dsup, damage suppressor protein.– Int J Mol Sci.

Antioxidant Defense in the Toughest Animals on the Earth: Its Contribution to the Extreme Resistance of Tardigrades, Int J Mol Sci. 2024 Aug; 25(15): 8393. Published online 2024 Aug 1. doi: 10.3390/ijms25158393 (open access), via PubMed

Astrobiology

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