Functional modulation of mitochondrial cytochrome c oxidase underlies adaptation to high-altitude hypoxia in a Tibetan migratory locust

Mitochondria are crucial to the hypoxia response of aerobic organisms. However, mitochondrial mechanisms for hypoxia adaptation remain largely unknown. We conducted a comparative study on the mitochondrial hypoxia response and adaptation of the Tibetan Plateau and North China lowland populations of migratory locusts, Locusta migratoria. Compared with lowland locusts, Tibetan locusts presented significantly higher hypoxia tolerance and a better-maintained mitochondrial structure in flight muscles under oxygen partial pressure of 1.6 kPa. The hypoxic treatment inhibited the NADH-linked oxidative phosphorylation (OXPHOS) significantly in both locust populations, but to a less extent in Tibetan locusts. Among the critical components of OXPHOS, only cytochrome c oxidase (COX) exhibited significantly higher activity in Tibetan locusts under normoxia and hypoxia. Pharmacological interventions using NaN3 confirmed that COX activity inhibition reduced hypoxia tolerance by downregulating OXPHOS in both locust populations. The enhanced COX activity was caused not by protein content, but by elevated catalytic efficiency resulting from the increased ferrocytochrome c affinity of COX and the increased electron transport rate via catalytic redox centres. These findings reveal a novel mechanism that confers mitochondrial robustness against hypoxia by modulating the COX activity, which represents an adaptation to permanent hypoxia in the Tibetan Plateau.