Compartmentalization of redox reactions is essential to all life forms. Protein activity can respond to changes in the local redox environment through the reversible oxidation of cysteine thiols. For the majority of cysteines in the proteome, this interaction takes place through equilibration with the glutathione pool; this raises the question whether this redox pool acts as a buffer, or instead as a sensitive media, transducing information from a local physiological state into protein function.
To pursue this question, we measured the spatio-temporal distribution of redox potential of the cytosolic glutathione pool, EGSH, in the nematode C. elegans. We used a genetically encoded redox sensor to quantify EGSH using ratiometric fluorescence microscopy. We found the redox potential in muscle, intestine and neurons to be far from glutathione's buffering regime; instead, these values are located in the highly sensitive regime. This suggests that the glutathione pool acts as a responsive physiological variable, rather than as a buffering system to prevent thiol oxidation.
We found that the cytosolic redox environment is spatially structured: in the pharynx, muscles segments show discrete redox environments. This occurs despite the physical coupling of their cytosols. The spatial pattern persists upon oxidative stress, with muscles exhibiting unique EGSH response dynamics. We identified a mechanism controlling redox potential as well as this spatial distribution: insulin signaling promotes an oxidizing effect in cytosol, and the FOXO/DAF-16 transcription factor contributes to the spatial patterning of EGSH in feeding muscle.
Insulin signaling also modulates EGSH in other tissues, and it does so in a tissue-specific manner. The link between redox potential and insulin signaling—a major determinant of lifespan—prompted us to investigate the effects of aging on the redox pattern. We discovered that during aging, the spatial differentiation of the cytosolic redox potential undergoes structured changes. Notably, while the absolute level of EGSH is uncorrelated with lifespan, we do find a correlation between spatial differences in redox potential and the animal's remaining lifespan. This shows that spatial patterning in the redox environment of the pharynx is linked to the aging process.
|Advisor:||Fontana, Walter, Mitchison, Timothy|
|Commitee:||DePace, Angela, Mitchison, Timothy, Needleman, Daniel|
|School Location:||United States -- Massachusetts|
|Source:||DAI-B 75/02(E), Dissertation Abstracts International|
|Subjects:||Molecular biology, Genetics, Cellular biology|
|Keywords:||Aging, Caenorhabditis elegans, Insulin signaling, Oxidation reduction of proteins, Redox potential of glutathione (GSH), Spatial patterning|
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