Enhanced mitochondrial buffering prevents Ca2+ overload in naked mole‐rat brain

Abstract

AbstractDeleterious Ca2+ accumulation is central to hypoxic cell death in the brain of most mammals. Conversely, hypoxia‐mediated increases in cytosolic Ca2+ are retarded in hypoxia‐tolerant naked mole‐rat brain. We hypothesized that naked mole‐rat brain mitochondria have an enhanced capacity to buffer exogenous Ca2+ and examined Ca2+ handling in naked mole‐rat cortical tissue. We report that naked mole‐rat brain mitochondria buffer >2‐fold more exogenous Ca2+ than mouse brain mitochondria, and that the half‐maximal inhibitory concentration (IC50) at which Ca2+ inhibits aerobic oxidative phosphorylation is >2‐fold higher in naked mole‐rat brain. The primary driving force of Ca2+ uptake is the mitochondrial membrane potential (Δψm), and the IC50 at which Ca2+ decreases Δψm is ∼4‐fold higher in naked mole‐rat than mouse brain. The ability of naked mole‐rat brain mitochondria to safely retain large volumes of Ca2+ may be due to ultrastructural differences that support the uptake and physical storage of Ca2+ in mitochondria. Specifically, and relative to mouse brain, naked mole‐rat brain mitochondria are larger and have higher crista density and increased physical interactions between adjacent mitochondrial membranes, all of which are associated with improved energetic homeostasis and Ca2+ management. We propose that excessive Ca2+ influx into naked mole‐rat brain is buffered by physical storage in large mitochondria, which would reduce deleterious Ca2+ overload and may thus contribute to the hypoxia and ischaemia‐tolerance of naked mole‐rat brain. imageKey points Unregulated Ca2+ influx is a hallmark of hypoxic brain death; however, hypoxia‐mediated Ca2+ influx into naked mole‐rat brain is markedly reduced relative to mice. This is important because naked mole‐rat brain is robustly tolerant against in vitro hypoxia, and because Ca2+ is a key driver of hypoxic cell death in brain. We show that in hypoxic naked mole‐rat brain, oxidative capacity and mitochondrial membrane integrity are better preserved following exogenous Ca2+ stress. This is due to mitochondrial buffering of exogenous Ca2+ and is driven by a mitochondrial membrane potential‐dependant mechanism. The unique ultrastructure of naked mole‐rat brain mitochondria, as a large physical storage space, may support increased Ca2+ buffering and thus hypoxia‐tolerance.