Bart P Braeckman et al. (2001) International C. elegans Meeting "No reduction of energy metabolism in Clk mutants."

Isabelle Malcorps, Kristel Brys, Jacques Vanfleteren, Annemie De Vreese, Bart P Braeckman, Koen Houthoofd

[International C. elegans Meeting, 2001]

The Clk genes clk-1 , clk-2 , clk-3 , and gro-1 , control the timing of a range of physiological processes in C. elegans . Mutation in these genes causes a mean increase of adult life span, cell cycle length, and a slowing down of development and behavioral activity (pharyngeal pumping, defecating, egg laying, and moving). Is a reduced energy metabolism responsible for both the Slow and Age phenotype of the Clk mutants, as the rate-of-living hypothesis would suggest? We determined metabolic rate by monitoring several physiological and biochemical parameters in synchronously ageing cohorts: oxygen consumption, heat generation, ATP levels, metabolic potential (lucigenin assay), reductase activity, and autofluorescence. All measurements were normalised to protein content. Surprisingly, oxygen consumption rate, heat output, ATP levels, metabolic potential, reductase activity, and oxidised flavin autofluorescence were generally higher in most Clk mutants compared to wild type. In contrast to the other Clk's, clk-2(qm37) showed a wild-type pattern for most parameters, but, at advanced ages, light production (lucigenin assay) was significantly lower than wild type. Autofluorescence of lipofuscin (and reduced nicotinamids as well) was slightly reduced in clk-1(e2519) and clk-2(qm37) mutants, whereas clk-3(qm38) and gro-1(e2400) showed wild type levels. Contrary to the above speculation, we found that several parameters of energy metabolism are upregulated in clk-1(e2519) , clk-3(qm38) , and gro-1(e2400) mutants. We conclude that energy production is not lower, rather higher, in the Clk mutants. The enhanced reductase activity may confer increased resistance to oxidative stress and prolonged life span. Unlike the other Clk's, clk-2(qm37) showed a wild-type like metabolism, but produced less superoxide in the lucigenin assay. Its low oxidised flavin autofluorescence may indicate an altered redox-balance.

Koen Houthoofd et al. (2001) International C. elegans Meeting "Caloric restriction activates stress resistance and confers life extension"

Sylvie Van Eygen, Bart Braeckman, Jacques R Vanfleteren, Isabelle Malcorps, Koen Houthoofd, Kristel Brys, Annemie De Vreese

[International C. elegans Meeting, 2001]

Caloric restriction increases life span of a wide range of animals including C elegans . The mechanisms underlying this effect are still unknown. We used axenic culture medium and eat-2 mutants to study the effect of dietary restriction on metabolism and stress resistance. All empirical data were normalised to protein content to account for differences in body mass. Stress resistance was assessed by assaying survival at elevated temperature. Wild-type worms grown in axenic culture medium consume more oxygen and produce more heat than worms grown on a bacterial diet and this effect is slightly higher in eat-2 mutants (at advanced ages). ATP levels decline steeply with age in worms grown on E. coli . A much milder decrease is seen in axenically cultured worms. However, the light production potential (a measure of maximum metabolic, mainly mitochondrial, performance) decreases similarly in worms grown in either nutritional regime. Axenically cultured worms have enhanced catalase activities. Wild-type worms acquire an Itt (increased thermotolerance) phenotype in axenic culture medium. eat-2 mutant worms are Itt, and this phenotype is strengthened in axenic medium. We conclude that axenic culture medium confers life span extension by eliciting enhanced stress resistance, rather than lowering metabolic rate.

Koen Houthoofd et al. (2001) International C. elegans Meeting "Dauers: what makes them long-lived?"

Jacques R Vanfleteren, Annemie De Vreese, Sylvie Van Eygen, Kristel Brys, Koen Houthoofd, Bart Braeckman, Isabelle Malcorps

[International C. elegans Meeting, 2001]

The dauer larva is a stress resistant and seemingly non-ageing alternative third stage larva. We have been performing a number of experimental approaches in an attempt to reveal mechanisms that underlie sustained life in dauers, and to examine whether the diapause stage has any effect on post dauer metabolism and life span. We have measured several parameters that reflect metabolic condition, including oxygen consumption rates, heat output, ATP levels, light production potential, XTT reducing capacity and autofluorescence intensities. The potential to resist oxidative stress was assessed by measuring catalase and superoxide dismutase activities. The experimental data were normalised to protein content to account for size differences. Dauers consume less oxygen and produce less heat than young adults, but unlike adults they can maintain fairly stable rates for several weeks. However, the light production potential declines almost as steeply with time in adults and dauers, suggesting increasing mitochondrial dysfunction in both developmental stages. This could be reflected by rapidly decreasing ATP levels in adults, but much milder decreases are observed in dauers. Reducing capacity is constantly high in dauers reflecting a potential for anabolic reactions. A strongly negative reduction potential would plausibly also protect against oxidative damage. Dauers also have greatly increased activity levels of superoxide dismutase and catalase to scavenge reactive oxygen species. Blue fluorescence due to lipofuscin and reduced nicotinamides increases rapidly with age in adults and more gradually in dauers. We conclude that the superior antioxidant capacity of the dauer metabolism plays a major role in the upregulation of longevity during diapause.