The exceptional longevity of the naked mole‐rat may be explained by mitochondrial antioxidant defenses

Abstract

Naked mole‐rats (NMRs) are mouse‐sized mammals that exhibit an exceptionally long lifespan (>30 vs. <4 years for mice), and resist aging‐related pathologies such as cardiovascular and pulmonary diseases, cancer, and neurodegeneration. However, the mechanisms underlying this exceptional longevity and disease resistance remain poorly understood. The oxidative stress theory of aging posits that (a) senescence results from the accumulation of oxidative damage inflicted by reactive oxygen species (ROS) of mitochondrial origin, and (b) mitochondria of long‐lived species produce less ROS than do mitochondria of short‐lived species. However, comparative studies over the past 28 years have produced equivocal results supporting this latter prediction. We hypothesized that, rather than differences in ROS generation, the capacity of mitochondria to consume ROS might distinguish long‐lived species from short‐lived species. To test this hypothesis, we compared mitochondrial production and consumption of hydrogen peroxide (H2O2; as a proxy of overall ROS metabolism) between NMR and mouse skeletal muscle and heart. We found that the two species had comparable rates of mitochondrial H2O2 generation in both tissues; however, the capacity of mitochondria to consume ROS was markedly greater in NMRs. Specifically, maximal observed consumption rates were approximately two and fivefold greater in NMRs than in mice, for skeletal muscle and heart, respectively. Our results indicate that differences in matrix ROS detoxification capacity between species may contribute to their divergence in lifespan.

Comparative studies of mitochondrial reactive oxygen species in animal longevity: Technical pitfalls and possibilities

“…This raises the concern that past studies might have underestimated superoxide/H 2 O 2 formation rates of short‐lived species. In our case, rates of superoxide/H 2 O 2 formation were always lower for mice when a five minutes of equilibration period was observed before addition of succinate ( n = 3), whereas acquiring data immediately after addition of mitochondria to the chambers resulted in significantly higher rates for mice as compared to NMR (Munro et al, ).…”

“…This effect seems to primarily involve superoxide production at site I Q as it is observed in the presence of succinate as the sole respiratory substrate, but absent when rotenone is added (Treberg, Braun, Zacharias, & Kroeker, ). Preliminary tests for our recent study (Munro, Baldy, Pamenter, & Treberg, ) showed that the time spent (in the absence of substrates) by mice skeletal muscle mitochondria inside the chambers of the Oroboros, before addition of substrates, also leads to a pronounced decline in the capacity for superoxide/H 2 O 2 generation at site I Q (succinate alone, Figure ). This effect is however not seen in the presence of glutamate + malate and is also not observed in mitochondria of the long‐lived naked mole‐rat (NMR, not shown in Figure ).…”

“…In support of this conclusion, we observed an average 13% loss of respiration with malate and a 10% loss with glutamate + malate + succinate + ADP, when using 50 µM Amplex UltraRed during pilot tests with mice skeletal muscle mitochondria (data not shown). Preliminary tests with 10 µM Amplex UltraRed revealed that this concentration was sufficient to maintain the linearity of standard curves, and allowed us to avoid adverse effects on the energetics of isolated mitochondria (Munro et al, ).…”

“…The integrity of this complex suite of enzymatic and bioenergetics steps is lost along with the integrity of the inner membrane after freezing of the mitochondrial isolate. Instead, a very straightforward and much better proxy of the integrated capacity for the detoxification of H 2 O 2 in vivo is to challenge energized isolated mitochondria with a bolus of H 2 O 2 in a respiration medium, so as to follow the rate of H 2 O 2 decay over time (Munro et al, , ; Starkov et al, ; Treberg et al, ; Zoccarato et al, ). In this regard, we have shown for rat skeletal muscle mitochondria that malate is sufficient to spark full activity of both the GSH‐ and TRx‐dependent pathways while minimizing concomitant superoxide/H 2 O 2 formation, providing an interesting proxy of the maximal capacity of the mitochondrion to consume H 2 O 2 (Treberg et al, ).…”

“…One limitation of using CDNB and auranofin, however, is potential species‐specific off‐target effects (Treberg et al, ). For example, in our recent study (Munro et al, ), the protocols developed for rat skeletal muscle mitochondria required adaptation to work with murine mitochondria, which generally seem more fragile (Treberg et al, ). Specifically, the concentration of auranofin was reduced from 2 to 0.5 µM, and the duration of the CDNB pretreatment was reduced from five to four minutes reaction time at room temperature in order to respect our threshold of a 5% maximal effect on coupled respiration in convergent electron flow (glutamate + malate + succinate + ADP).…”