Extreme longevity is associated with increased resistance to oxidative stress in Arctica islandica, the longest-living non-colonial animal

Abstract

We assess whether reactive oxygen species production and resistance to oxidative stress might be causally involved in the exceptional longevity exhibited by the ocean quahog Arctica islandica. We tested this hypothesis by comparing reactive oxygen species production, resistance to oxidative stress, antioxidant defenses, and protein damage elimination processes in long-lived A islandica with the shorter-lived hard clam, Mercenaria mercenaria. We compared baseline biochemical profiles, age-related changes, and responses to exposure to the oxidative stressor tert-butyl hydroperoxide (TBHP). Our data support the premise that extreme longevity in A islandica is associated with an attenuated cellular reactive oxygen species production. The observation of reduced protein carbonyl concentration in A islandica gill tissue compared with M mercenaria suggests that reduced reactive oxygen species production in long-living bivalves is associated with lower levels of accumulated macromolecular damage, suggesting cellular redox homeostasis may determine life span. Resistance to aging at the organismal level is often reflected in resistance to oxidative stressors at the cellular level. Following TBHP exposure, we observed not only an association between longevity and resistance to oxidative stress-induced mortality but also marked resistance to oxidative stress-induced cell death in the longer-living bivalves. Contrary to some expectations from the oxidative stress hypothesis, we observed that A islandica exhibited neither greater antioxidant capacities nor specific activities than in M mercenaria nor a more pronounced homeostatic antioxidant response following TBHP exposure. The study also failed to provide support for the exceptional longevity of A islandica being associated with enhanced protein recycling. Our findings demonstrate an association between longevity and resistance to oxidative stress-induced cell death in A islandica, consistent with the oxidative stress hypothesis of aging and provide justification for detailed evaluation of pathways involving repair of free radical-mediated macromolecular damage and regulation of apoptosis in the world's longest-living non-colonial animal.

Figure 1.

(A) Photographs of the marine bivalves Mercenaria mercenaria (left) and Arctica islandica (right). (B) Production of H₂O₂ in gill, muscle, and heart tissues isolated from M mercenaria and A islandica, as assessed by the Amplex Red/HRP assay. Data are mean ± SEM (n = 8 animals for each group). *p < .05 versus M mercenaria. (C and D) Representative images showing red nuclear dihydroethidium (DHE) fluorescence, representing cellular $O_2^{·-}$ production, in sections of the heart of M mercenaria (C) and A islandica (D). Original magnification: 20×. (E) Summary data for average nuclear DHE fluorescence intensities in sections of the gill and heart of M mercenaria and A islandica. Data are mean ± SEM (n = 5 animals for each group). *p < .05 versus M mercenaria. (F) Carbonyl content of cellular proteins isolated from M mercenaria and A islandica. Data are mean ± SEM (n = 8 animals for each group). *p < .05 versus M mercenaria.

Figure 2.

Production of H₂O₂ in the gill of young and aged Mercenaria mercenaria and Arctica islandica, as assessed by the Amplex Red/HRP assay (for the mean chronological ages of each group, see the Methods). Data are mean ± SEM (n = 3–8 animals for each group). *p < .05 versus respective young controls.

Figure 3.

(A and B) Survival analysis of Mercenaria mercenaria and Arctica islandica under exposure to 10⁻³ mol/L (A) or 6 × 10⁻³ mol/L (B) tert-butyl hydroperoxide (TBHP). (C) TBHP (10⁻⁴ mol/L, for 24 hours)-induced changes in caspase 3/7 activity in gills of M mercenaria and A islandica. Data are mean ± SEM (n = 8 for each group). *p < .05 versus untreated control, #p < .05 versus M mercenaria.

Figure 4.

Oxygen radical absorbance capacity (ORAC, A) and hydroxyl radical antioxidant capacity (HORAC, C) in homogenates of gill tissues from young Mercenaria mercenaria and Arctica islandica maintained under control conditions (“baseline”) or exposed to tert-butyl hydroperoxide (TBHP; 10⁻⁴ mol/L, for 24 hours). Data are mean ± SEM (n = 8 in each group). ORAC (B) and HORAC (D) were also compared in young and aged M mercenaria and A islandica (for the mean chronological ages of each group, see the Methods). Data are mean ± SEM (n = 3–8 animals for each group).

Figure 5.

Antioxidant enzyme activities in Mercenaria mercenaria and Arctica islandica. Catalase activity (A), superoxide dismutase (SOD) activity (C), and glutathione peroxidase (GPX) activity (E) were assessed in homogenates of gill tissues from M mercenaria and A islandica maintained under control conditions (“baseline”) or exposed to tert-butyl hydroperoxide (TBHP; 10⁻⁴ mol/L, for 24 hours). Data are mean ± SEM (n = 8 in each group). Catalase activity (B), SOD activity (D), and GPX activity (F) were also compared between young and aged M mercenaria and A islandica (for the mean chronological ages of each group, see the Methods). Data are mean ± SEM (n = 3–8 animals for each group).

Figure 6.

Proteasome activity in Mercenaria mercenaria and Arctica islandica. Trypsin-like activity (A), chymotrypsin-like activity (B), and caspase-like activity (C) were assessed in homogenates of gill tissues from M mercenaria and A islandica maintained under control conditions (“baseline”) or exposed to tert-butyl hydroperoxide (TBHP; 10⁻⁴ mol/L, for 24 hours). Data are mean ± SEM (n = 8 in each group).