TNF-α mediates mitochondrial uncoupling and enhances ROS-dependent cell migration via NF-κB activation in liver cells

Development of hepatocellular carcinoma (HCC) is accompanied by a continuous increase in reactive oxygen species (ROS) levels. To investigate the primary source of ROS in liver cells, we used tumor necrosis factor-alpha (TNF-α) as stimulus. Applying inhibitors against the respiratory chain complexes, we identified mitochondria as primary source of ROS production. TNF-α altered mitochondrial integrity by mimicking a mild uncoupling effect in liver cells, as indicated by a 40% reduction in membrane potential and ATP depletion (35%). TNF-α-induced ROS production activated NF-κB 3.5-fold and subsequently enhanced migration up to 12.7-fold. This study identifies complex I and complex III of the mitochondrial respiratory chain as point of release of ROS upon TNF-α stimulation of liver cells, which enhances cell migration by activating NF-κB signalling.

Protective effects of lycopene against methylmercury-induced neurotoxicity in cultured rat cerebellar granule neurons

Methylmercury (MeHg) is a neurotoxin that induces neuronal degeneration in the central nervous system. Oxidative stress and mitochondrial dysfunction are widely accepted as central pathogenic mechanisms of MeHg-mediated neurotoxicity. Lycopene, a carotenoid compound, is a potent antioxidant with demonstrated neuroprotective properties in several experimental models of oxidative damage. The present study was designed to investigate whether lycopene could provide protective effects against MeHg-induced neurotoxicity in cultured rat cerebellar granule neurons (CGNs). The cultured CGNs were pretreated with different dose of lycopene for 2h, followed by the challenge with 500nM MeHg for 12h. It was found that MeHg exposure caused the loss of cell viability and the LDH release. Furthermore, we demonstrated that MeHg exposure significantly elevated intracellular reactive oxygen species generation and mitochondria-derived superoxide production, caused disruption of mitochondrial membrane potential and opening of mPTP, inhibited mitochondrial complex enzyme activities (complex III and complex IV), reduced ATP generation and decreased mtDNA copy numbers and mtDNA transcript levels. However, each of these oxidative damages was efficiently attenuated by lycopene pretreatment. Collectively, these results suggest that lycopene affords protection against MeHg-induced neurotoxicity in CGNs, and these beneficial effects of lycopene may be attributable to its roles in preventing mitochondrial dysfunction.

Repression of the mitochondrial peroxiredoxin antioxidant system does not shorten life span but causes reduced fitness in Caenorhabditis elegans

The mitochondrial free radical theory of aging proposes that aging is a consequence of progressive mitochondrial dysfunction caused by lifelong accumulation of oxidative damage. Aging is therefore expected to accelerate if the rate of this oxidative damage accumulation increases. Studies attempting to test this prediction through modulation of oxidative damage by altering antioxidant defenses have reported conflicting results. Here we investigated the effects of repressing prdx-3, responsible for the detoxification of mitochondrial hydrogen peroxide, in developmentally normal wild-type Caenorhabditis elegans. We report that life span and levels of oxidative protein damage were not altered when prdx-3 was repressed in adult nematodes. We further found evidence that mitochondrial uncoupling increased in response to repression of prdx-3. Nevertheless repression of prdx-3 led to reductions in steady-state levels of ATP, motility, and brood size, indicating the importance of this enzyme to normal life in C. elegans.