Bridging the phenotypic gap: real-time assessment of mitochondrial function and metabolism of the nematode Caenorhabditis elegans

Background
The ATP levels of an organism are an important physiological parameter that is affected by genetic make up, ageing, stress and disease.

Results
We have generated luminescent C. elegans through ubiquitous, constitutive expression of firefly luciferase, widely used for in vitro ATP determination. We hypothesise that whole animal luminescence reflects its intracellular ATP levels in vivo. To test this, we characterised the bioluminescence response of C. elegans during sublethal exposure to, and recovery from azide, a treatment that inhibits mitochondrial respiration reversibly, and causes ATP depletion. Consistent with our expectations, in vivo luminescence decreased with increasing sublethal azide levels, and recovered fully when worms were removed from azide. Firefly luciferase expression levels, stability and activity did not influence the final luminescence. Bioluminescence also reflected the lowered activity of the electron transport chain achieved with RNA interference (RNAi) of genes encoding respiratory chain components.

Conclusion
Results indicated that C. elegans luminescence reports on ATP levels in real-time. For the first time, we are able to directly assess the metabolism of a whole, living, multicellular organism by determination of the relative ATP levels. This will enable genetic analysis based on a readily quantifiable metabolic phenotype and will provide novel insights into mechanisms of fitness and disease that are likely to be of relevance for other organisms, as well as the worm.