STUDIES ON THE EFFECT OF AGEING ON PROTEIN TURNOVER IN CAENORHABDITIS ELEGANS USING STABLE ISOTOPE TECHNIQUES

Abstract

Protein turnover studies were executed post-reproductively in nematodes by feeding 15N-labelled diet followed by mass spectrometric analysis. Proteins reached a ‘plateau’ in isotopic enrichment ranging from 17% to 85%. The protein fraction that evaded turnover was unrelated to protein half-life. This challenges the paradigm of molecular ageing which assumes that mainly long-living proteins risk damage accumulation. Isotopic data from three cohorts of nematodes were analysed by kinetic modelling after exposure to 15N-labelled feed at different ages. The derived model was tested further by 15N-tracing in nematodes reared at different temperatures to alter lifespan. Age dependent changes in protein turnover were described mathematically for the first-time. Slowdown of turnover can be described as a function of nematode age Tw by a linear equation for the rate constant of turnover k=-mTw+c with m and c being protein-specific constants. Turnover was found to scale with median lifespan. Extrapolation of lines to k=0 yielded Ts whereby turnover shuts down, theoretically, which correlated with nematode median lifespans. The derived equation’s form describes ageing either by a slowdown of protein turnover with age, as suggested previously, or as a growing fraction of protein evading renewal at a constant turnover rate over life-time as an alternative mechanism.