A manganese superoxide dismutase (SOD2)-mediated adaptive response

Area of Science:

• Radiobiology
• Cellular and Molecular Biology
• Immunology

Background:

• Low doses of ionizing radiation can induce adaptive responses, enhancing cell survival and reducing DNA damage.
• Tumor Necrosis Factor (TNF) signaling plays a role in cellular stress responses.
• Manganese Superoxide Dismutase (SOD2) is a key enzyme in antioxidant defense.

Purpose of the Study:

• To investigate the role of TNF signaling in radiation-induced adaptive responses.
• To compare the mechanisms of adaptive response induction by low-dose radiation and amifostine.
• To elucidate the involvement of SOD2 in these adaptive responses.

Main Methods:

• Utilized RKO colon carcinoma cells, mouse embryo fibroblasts (MEF) wild-type and TNFR1(-)R2(-) knockout cells, and C57BL/6 and TNFR1(-)R2(-) knockout mice.
• Assessed cell survival and micronuclei formation as endpoints for adaptive responses.
• Measured manganese superoxide dismutase (SOD2) activity and expression.
• Employed SOD2 siRNA to investigate its role.
• Confirmed findings in vivo using micronucleus assays and N-Ethyl-N-nitrosourea (ENU) challenge.

Main Results:

• Intact TNF signaling is essential for low-dose radiation (5-100 mGy) to induce elevated SOD2 activity and adaptive responses against a later 2 Gy challenge.
• Amifostine's active metabolite WR1065 directly activates NF-κB, leading to elevated SOD2 activity and adaptive responses in both TNF receptor-competent and deficient cells.
• SOD2 knockdown using siRNA abolished both SOD2 activity elevation and adaptive responses.
• In vivo studies confirmed that TNF signaling is required for radiation-induced adaptive responses but not for amifostine-induced adaptive responses.

Conclusions:

• TNF signaling is a critical mediator for adaptive responses induced by very low doses of ionizing radiation, dependent on SOD2.
• Amifostine confers radio-protection through a TNF-independent pathway involving NF-κB and SOD2 activation.
• These findings highlight distinct molecular mechanisms underlying adaptive responses to radiation and radioprotective agents.