In nearly every organism studied, reduced caloric intake extends life span. In yeast, life span extension from dietary restriction is mediated by the highly conserved, nutrient-responsive target of rapamycin (TOR), protein kinase A (PKA), and Sch9 (S-6) kinases. These kinases coordinately regulate various cellular processes including stress responses, protein turnover, cell growth, and riibosome biogenesis and translation. We have begun to examine similar processes in C.elegans during life-extension protocols.
As in yeast, bacterial food deprivation (BD) of C. Elegans extends the lifespan in C. Elegans dramatically (see below). One of the downstream targets of BD is the protein synthesis apparatus. Deletions of the protein synthesis initiation factor IFG-1 or the S-6 kinase RSKS-1 also lengthen lifespan. I have collaborated with Vivian Mckay in a project to examine the genes whose translation is altered during during BD and specifically downstream of decreased protein synthesis by utilizing polysome gradient profiles of Fed and BD worms. BD decreases dcreases the average size of polysomes in the gradient profiles.
Even 3 hours of BD reduces polysome sizes in gradients (see Figure 1) and longer BD periods induce a more severe decrease in average polysome size. A dramatic reduction in of polysome size is seen in worms lacking proper S-6 kinase activity (RSKS-1) as expected. These worms encode a defective putative r ibosomal protein S6 kinase activity that is required additively with IFG-1 for normally high levels of protein synthesis, and for normally short lifespan; RSKS-1's effect on lifespan is independent of DAF-16, ISP-1, and SIR-2.1 involved in other longevity pathways. Further analysis of the specific genes whose translation are down-regulated by BD are underway by array analysis of aliquots from different sized polysomes regions from the gradients.
Surprisingly, BD also strongly depletes free ubiquitin staining in Western analysis of the worms (see Figure 2). Sumoylation of proteins, a similar type of modifcation was unaffected indicating ubiquitin depletion isa rather specific alteration. Not all mutations that lengthen lifespan in C. Elegans
by Jenny Sager
Recently, BD has been found to increase lifespan through a combination of reduced food consumption and reduced bacterial sensing. My project is focused on elucidating the mechanisms by which chemosensation regulates lifespan in C. elegans. I am working to identify bacterial compounds and nematode sensory pathways that influence longevity.