TY - JOUR

T1 - Small-Molecule Mn Antioxidants in Caenorhabditis elegans and Deinococcus radiodurans Supplant MnSOD Enzymes during Aging and Irradiation

AU - Gaidamakova, Elena K.

AU - Sharma, Ajay

AU - Matrosova, Vera Y.

AU - Grichenko, Olga

AU - Volpe, Robert P.

AU - Tkavc, Rok

AU - Conze, Isabel H.

AU - Klimenkova, Polina

AU - Balygina, Irina

AU - Horne, William H.

AU - Gostincar, Cene

AU - Chen, Xiao

AU - Makarova, Kira S.

AU - Shuryak, Igor

AU - Srinivasan, Chandra

AU - Jackson-Thompson, Belinda

AU - Hoffman, Brian M.

AU - Daly, Michael J.

N1 - Funding Information: Establishment and maintenance of C. elegans colonies on NGM agar plates. Colonies of the following C. elegans strains were established and maintained on nematode growth medium (NGM) agar and fed OP50 E. coli. Strain Bristol N2 (WT) (a gift from David Eisenmann, UMBC, Baltimore, MD) and SOD mutants (see above, “Nematodes”) were provided by the CGC, funded by the NIH Office of Research Infrastructure Programs (P40OD010440). Briefly, ;1,000 worms were maintained at ambient temperature on a 100-mm petri dish containing NGM medium (1.7% agar [wt/vol], 50 mM NaCl, 0.25% peptone [wt/vol], 1 mM CaCl2, 5 µg/mL cholesterol, 25 mM KH2PO4, and 1 mM MgSO4) and seeded with a lawn of E. coli OP50 as the food source. As the OP50 lawns were depleted, an ;1-cm2 section of agar (containing worms) was incised from the agar plate and inverted onto a fresh lawn of OP50, thus giving the worms sufficient nutrients to continue developing and reproducing. Funding Information: This study was supported by NIH grant GM111097 (to B.M.H.) and by funds received from the Defense Threat Reduction Agency (DTRA) grant HDTRA1620354 (to M.J.D.) and from the USU Intramural Program to the Deinococcus Group. C.G. acknowledges the financial support from the state budget of the Slovenian Research Agency (grants J4-2549, P1-0198, and BI-US/18-20-032), and C.S. acknowledges the financial support from NIH grant 1 R15 GM090169-01. K.S.M.’s research is supported by the NIH Intramural Research Program at the National Library of Medicine. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The opinions expressed here are those of the authors and are not necessarily representative of those of the USUHS, HJF, DTRA, or NIH. Publisher Copyright: © 2022 American Society for Microbiology. All rights reserved.

PY - 2022/2/1

Y1 - 2022/2/1

N2 - Denham Harman’s oxidative damage theory identifies superoxide (O22) radicals as central agents of aging and radiation injury, with Mn21-dependent superoxide dismutase (MnSOD) as the principal O22-scavenger. However, in the radiation-resistant nematode Caenorhabditis elegans, the mitochondrial antioxidant enzyme MnSOD is dispensable for longevity, and in the model bacterium Deinococcus radiodurans, it is dispensable for radiation resistance. Many radiation-resistant organisms accumulate small-molecule Mn21-antioxidant complexes well-known for their catalytic ability to scavenge O22, along with MnSOD, as exemplified by D. radiodurans. Here, we report experiments that relate the MnSOD and Mn-antioxidant content to aging and oxidative stress resistances and which indicate that C. elegans, like D. radiodurans, may rely on Mn-antioxidant complexes as the primary defense against reactive oxygen species (ROS). Wild-type and DMnSOD D. radiodurans and C. elegans were monitored for gamma radiation sensitivities over their life spans while gauging Mn21-antioxidant content by electron paramagnetic resonance (EPR) spectroscopy, a powerful new approach to determining the in vivo Mn-antioxidant content of cells as they age. As with D. radiodurans, MnSOD is dispensable for radiation survivability in C. elegans, which hyperaccumulates Mn-antioxidants exceptionally protective of proteins. Unexpectedly, DMnSOD mutants of both the nematodes and bacteria exhibited increased gamma radiation survival compared to the wild-type. In contrast, the loss of MnSOD renders radiation-resistant bacteria sensitive to atmospheric oxygen during desiccation. Our results support the concept that the disparate responses to oxidative stress are explained by the accumulation of Mn-antioxidant complexes which protect, complement, and can even supplant MnSOD. IMPORTANCE The current theory of cellular defense against oxidative damage identifies antioxidant enzymes as primary defenders against ROS, with MnSOD being the preeminent superoxide (O22) scavenger. However, MnSOD is shown to be dispensable both for radiation resistance and longevity in model organisms, the bacterium Deinococcus radiodurans and the nematode Caenorhabditis elegans. Measured by electron paramagnetic resonance (EPR) spectroscopy, small-molecule Mn-antioxidant content was shown to decline in unison with age-related decreases in cell proliferation and radioresistance, which again are independent of MnSOD presence. Most notably, the Mn-antioxidant content of C. elegans drops precipitously in the last third of its life span, which links with reports that the steady-state level of oxidized proteins increases exponentially during the last third of the life span in animals. This leads us to propose that global responses to oxidative stress must be understood through an extended theory that includes small-molecule Mn-antioxidants as potent O22-scavengers that complement, and can even supplant, MnSOD.

AB - Denham Harman’s oxidative damage theory identifies superoxide (O22) radicals as central agents of aging and radiation injury, with Mn21-dependent superoxide dismutase (MnSOD) as the principal O22-scavenger. However, in the radiation-resistant nematode Caenorhabditis elegans, the mitochondrial antioxidant enzyme MnSOD is dispensable for longevity, and in the model bacterium Deinococcus radiodurans, it is dispensable for radiation resistance. Many radiation-resistant organisms accumulate small-molecule Mn21-antioxidant complexes well-known for their catalytic ability to scavenge O22, along with MnSOD, as exemplified by D. radiodurans. Here, we report experiments that relate the MnSOD and Mn-antioxidant content to aging and oxidative stress resistances and which indicate that C. elegans, like D. radiodurans, may rely on Mn-antioxidant complexes as the primary defense against reactive oxygen species (ROS). Wild-type and DMnSOD D. radiodurans and C. elegans were monitored for gamma radiation sensitivities over their life spans while gauging Mn21-antioxidant content by electron paramagnetic resonance (EPR) spectroscopy, a powerful new approach to determining the in vivo Mn-antioxidant content of cells as they age. As with D. radiodurans, MnSOD is dispensable for radiation survivability in C. elegans, which hyperaccumulates Mn-antioxidants exceptionally protective of proteins. Unexpectedly, DMnSOD mutants of both the nematodes and bacteria exhibited increased gamma radiation survival compared to the wild-type. In contrast, the loss of MnSOD renders radiation-resistant bacteria sensitive to atmospheric oxygen during desiccation. Our results support the concept that the disparate responses to oxidative stress are explained by the accumulation of Mn-antioxidant complexes which protect, complement, and can even supplant MnSOD. IMPORTANCE The current theory of cellular defense against oxidative damage identifies antioxidant enzymes as primary defenders against ROS, with MnSOD being the preeminent superoxide (O22) scavenger. However, MnSOD is shown to be dispensable both for radiation resistance and longevity in model organisms, the bacterium Deinococcus radiodurans and the nematode Caenorhabditis elegans. Measured by electron paramagnetic resonance (EPR) spectroscopy, small-molecule Mn-antioxidant content was shown to decline in unison with age-related decreases in cell proliferation and radioresistance, which again are independent of MnSOD presence. Most notably, the Mn-antioxidant content of C. elegans drops precipitously in the last third of its life span, which links with reports that the steady-state level of oxidized proteins increases exponentially during the last third of the life span in animals. This leads us to propose that global responses to oxidative stress must be understood through an extended theory that includes small-molecule Mn-antioxidants as potent O22-scavengers that complement, and can even supplant, MnSOD.

KW - Aging

KW - Caenorhabditis

KW - Deinococcus

KW - Desiccation

KW - EPR

KW - Ionizing radiation

KW - Lactobacillus

KW - Mn antioxidants

KW - MnSOD

KW - Reactive oxygen species

KW - ROS

KW - Superoxide dismutase

KW - Deinococcus/metabolism

KW - Reactive Oxygen Species/metabolism

KW - Manganese/metabolism

KW - Caenorhabditis elegans/metabolism

KW - Animals

KW - Superoxides/metabolism

KW - Antioxidants/metabolism

KW - Superoxide Dismutase/metabolism

UR - http://www.scopus.com/inward/record.url?scp=85125922454&partnerID=8YFLogxK

U2 - 10.1128/MBIO.03394-21

DO - 10.1128/MBIO.03394-21

M3 - Article

C2 - 35012337

AN - SCOPUS:85125922454

VL - 13

JO - mBio

JF - mBio

SN - 2161-2129

IS - 1

M1 - e03394

ER -