Program of the 2001 International Worm Meeting - Sternberg Lab ...

338
338. Caloric restriction activates
stress resistance and confers life
extension
Koen Houthoofd, Bart Braeckman,
Annemie De Vreese, Isabelle
Malcorps, Kristel Brys, Sylvie Van
Eygen, Jacques R. Vanfleteren
Department of Biology, Ghent University, K.L.
Ledeganckstraat 35, B-9000 Ghent, BELGIUM
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.
339. Molecular mechanisms
underlying the effects of caloric
restriction on aging in C. elegans
Nektarios Tavernarakis, Monica
Driscoll
Dept. of Molecular Biology and Biochemistry,
Rutgers Univ., 604 Allison Rd, Piscataway NJ
08855.
339
Although low caloric intake (caloric restriction,
CR) has been documented to significantly
lengthen lifespan in a wide variety of organisms,
very little is known about the molecular
mechanisms that are responsible for this effect.
In C. elegans, lowering food intake by reducing
its availability in the environment prolongs
animal lifespan, indicating that a CR-related
mechanism of extending lifespan exists in the
worm (Johnson et al., 1984). In addition,
genetically reducing feeding efficiency by
means of mutations that compromise the
animals ability to ingest food has a similar effect
on longevity (Lakowski and Hekimi, 1998).
Gene expression profiling studies in mice
subjected to CR highlight several genes
involved in protein turnover (synthesis and
degradation), which have significantly altered
expression levels (Lee et al. 1999). These
findings suggest that a shift towards higher
protein turnover rates is associated with CR.
Increased protein turnover might consequently
be one of the major causes of lifespan extension
under CR, by facilitating the maintenance of a
fresher pool of proteins with less accumulated
damage. We are currently testing this hypothesis
by overexpressing wild type and mutant variants
of the eukaryotic elongation factor 2 (eEF-2), in
C. elegans. eEF-2 is a key translation factor that
is required for the translocation step of peptide
chain elongation, which involves movement of
the ribosome one codon at a time along the
mRNA. When phosphorylated at threonine 56
and 58 this factor is rendered inactive and
translation is blocked. Our preliminary work
suggests that overexpression of wild type and
non-phosporylatable eEF-2 variants can prolong
lifespan. We hypothesize that this effect could
reflect a postulated higher protein synthesis rate
in the overexpressing lines. We will extend this
study to include eEF-2 mutants that mimic its
phosphorylated form and are expected to have
the opposite effect on protein synthesis.