Resistance to the most common optic neuropathy is associated with systemic mitochondrial efficiency

Glaucomatous optic neuropathy, an important neurodegenerative condition and the commonest optic neuropathy in humans, is the leading cause of irreversible blindness worldwide. Its prevalence and incidence increase exponentially with ageing and raised intraocular pressure (IOP). Using glaucomatous optic neuropathy as an exemplar for neurodegeneration, this study investigates putative factors imparting resistance to neurodegeneration. Systemic mitochondrial function, oxidative stress and vascular parameters were compared from isolated lymphocytes, whole blood and urine samples between 30 patients who have not developed the neuropathy despite being exposed for many years to very high IOP ('resistant'), 30 fast deteriorating glaucoma patients despite having low IOP ('susceptible'), and 30 age-similar controls. We found that 'resistant' individuals showed significantly higher rates of ADP phosphorylation by mitochondrial respiratory complexes I, II and IV, hyperpolarised mitochondrial membrane potential, higher levels of mitochondrial DNA, and enhanced capacity to deal with cytosolic calcium overload and exogenous oxidative stress, as compared to both controls and glaucoma patients. While it has been known for some years that mitochondrial dysfunction is implicated in neurodegeneration, this study provides a fresh perspective to the field of neurodegeneration by providing, for the first time, evidence that systemic mitochondrial efficiency above normal healthy levels is associated with an enhanced ability to withstand optic nerve injury. These results demonstrate the importance of cellular bioenergetics in glaucomatous disease progression, with potential relevance for other neurodegenerative disorders, and raise the possibility for new therapeutic targets in the field of neurodegeneration.