Elevated neuronal nitric oxide synthase expression during ageing and mitochondrial energy production

Abstract

This study evaluated the effect of ageing on brain mitochondrial function mediated through protein post-translational modifications. Neuronal nitric oxide synthase increased with age and this led to a discreet pattern of nitration of mitochondrial proteins. LC/MS/MS analyses identified the nitrated mitochondrial proteins as succinyl-CoA-transferase and F1-ATPase; the latter was nitrated at Tyr269, suggesting deficient ADP binding to the active site. Activities of succinyl-CoA-transferase, F1-ATPase and cytochrome oxidase decreased with age. The decreased activity of the latter cannot be ascribed to protein modifications and is most likely due to a decreased expression and assembly of complex IV. Mitochondrial protein post-translational modifications were associated with a moderately impaired mitochondrial function, as indicated by the decreased respiratory control ratios as a function of age and by the release of mitochondrial cytochrome c to the cytosol, thus supporting the amplification of apoptotic cascades.

Mechanisms of Altered Redox Regulation in Neurodegenerative Diseases—Focus on S-Glutathionylation

“…This important pathway provides an alternative source of energy in the brain during times of low glucose. In studies of aging rats, succinyl CoA transferase was nitrated and this was attributed to elevated nNOS (101). In isolated rat brain mitochondria, this enzyme also was shown to be glutathionylated, resulting in diminished enzyme activity (66).…”

“…Loss of activity would mean diminished levels of ATP for the brain cells. In addition to ATP synthase, studies of young and aged rats showed an increase in nNOS content with age as well as increased nitration of ATP synthase (101). Further studies need to be performed to determine whether inhibition of ATP synthase occurs in samples from patients with neurodegerative disease and contributes to neuronal cell death.…”

Regulation of Mitochondrial Glutathione Redox Status and Protein Glutathionylation by Respiratory Substrates

“…Interestingly, these two enzymes were also the two major proteins identified to be nitrated with age in brain (31), thus suggesting that ATPase and succinyl-CoA transferase can undergo several types of post-translational modifications under oxidative and nitrosative stress. Glutathionylation of these enzymes resulted in decreased activities, which may impair energy production in mitochondria.…”

“…ATP synthase activity was assayed in submitochondrial particles by coupling its activity to pyruvate kinase and lactate dehydrogenase and monitoring consumption of NADH (Ϫd[NADH]/dt) at 340 nm (31).…”

Nicotinamide Nucleotide Transhydrogenase (Nnt) Links the Substrate Requirement in Brain Mitochondria for Hydrogen Peroxide Removal to the Thioredoxin/Peroxiredoxin (Trx/Prx) System

“…Trx/Prx activity is critically important in mitochondria to maintain the delicate balance of ROS production for signaling activities versus catabolism to prevent detrimental oxidative stress. The Trx/Prx and GSH systems require NADPH, which can be generated through multiple pathways in neuronal cells (45)(46)(47), and therefore, it was important to determine the link between Nnt activity to mitochondrial function and antioxidant activity in intact ROS-sensitive dopaminergic cells. Previous work in cell and animal models suggests that Nnt inhibition by siRNA transfection results in a more oxidized NADP ϩ /NADPH ratio accompanied by a more oxidized GSH/GSSG ratio (20,22,48).…”