C. Elegans - Oxidative Stress and Aging
Reactive oxygen species (ROS) like superoxide (O2-) and hydrogen peroxide (H2O2) are continuously generated during cellular respiration. Tightly regulated anti-oxidant machineries prevent the accumulation of excess ROS, which can otherwise damage lipids, proteins and DNA and severely impair cell integrity and functionality. The free radical theory of aging has postulated that the accumulation of oxidative damage in macromolecules is cause for the observed age-related decline of cells and tissues. Excessive ROS are also thought to be involved in inflammatory processes such as atherosclerosis and rheumatoid arthritis, degenerative processes like Alzheimer’s and Parkinson’s disease as well as cardiovascular diseases, diabetes and cancer.
We have started to monitor and visualize the effects of oxidative stress treatment of C. elegans using 2D gel electrophoresis. This analysis revealed a number of proteins that show substantially increased levels of oxidative protein modifications. One of these proteins is the highly abundant PRDX-2, a 2-Cys Peroxiredoxin, which is responsible for the detoxification of peroxides. We found that short-term exposure of synchronized L4 larvae to sublethal concentrations of H2O2 leads to the rapid over-oxidation of PRDX-2’s catalytic cysteine. This reversible overoxidation leads to the inactivation of PRDX-2’s peroxidase activity and apparently turns PRDX-2 into a molecular chaperone. Prdx-2 knockout worms show substantial delays in oxidative stress recovery and reveal a significantly shortened lifespan at 15°C. To dissect the peroxidase function of PRDX-2 from its chaperone activity, we began to analyze the role of PRDX-2 in sestrin knockout worms. Sestrins are a class of proteins, which have recently been shown in human colon carcinoma (RKO) cells to selectively reduce the overoxidized form of 2-Cys peroxiredoxins. Preliminary evidence suggests that sestrin knockout worms accumulate PRDX-2 in the overoxidized form, indicating that sestrin might be the dedicated PRXD-2 sulfinic acid reductase in C. elegans. Interestingly, both prdx-2 and sestrin knockout worms reveal similar phenotypes, indicating that it is indeed the peroxidase activity of PRDX-2 that plays the major lifespan determining role in C. elegans.
Another interesting topic we work on is the role of superoxide in the aging process of our model system C. elegans. To understand how superoxide affects physiological processes and behavior in C. elegans and to identify the proteins that might be superoxide-sensitive, we treated synchronized L4 larvae with a short bolus of the superoxide generating herbicide paraquat. Then, we assayed progeny production, movement and life span of C. elegans. We discovered that short-term treatment with sublethal paraquat concentrations caused a substantially reduced progeny production within the first two days of their reproductive phase, after which slightly higher progeny production was observed in the paraquat treated animals as compared to the control group. Surprisingly, while the mobility of the animals was not immediately affected by the paraquat stress treatment, paraquat-treated worms began to show age-dependent movement defects at much earlier time points than non-treated animals. This shortened motility span coincided with a substantially shortened mean life span of paraquat-treated C. elegans. These results provide first evidence that a short-term exposure to severe superoxide stress at very early stages in the life time of an organism might be sufficient to significantly affect life quality and life span of the organism.