Condition-dependent effects of knockdown of autophagy on C. elegans longevity

Abstract

Autophagy is proposed to protect against aging by clearing damaged cellular constituents. In line with this several life-extending interventions in model organisms show some degree of autophagy dependence. In C. elegans, inhibiting autophagy can shorten, lengthen or have no effect on lifespan. Differences between published findings likely reflect variability in experimental conditions. Here we investigate the condition dependence of effects on lifespan of RNA-mediated interference (RNAi) knockdown of autophagy pathway components. Effects on interventions causing a strong Age (increased lifespan) phenotype were examined: mainly mutation of daf-2 (insulin/IGF-1 receptor), but also suppression of germline development by mutation of glp-1. Factors varied included daf-2 mutant allele class, atg gene, temperature and presence of 5-fluoro-2-deoxyuridine (FUDR). Effects on lifespan of atg RNAi proved to be highly condition dependent. Notably, for most atg genes tested lifespan was not usually reduced more in the long-lived mutant than in the wild-type control. Greater suppression was seen at 20{degrees}C for certain atg genes with daf-2(e1368) but not daf-2(e1370). At 25{degrees}C, little reduction in lifespan was seen. However, atg-18 knockdown behaved differently, suppressing daf-2 Age under all conditions, suggesting possible pleiotropic action. In wild-type C. elegans, FUDR at a high concentration caused knockdown of several atg genes to increase lifespan. Thus, depending on experimental conditions, atg knockdown can increase, decrease or have no effect on daf-2 Age. Condition dependent effects were also seen with respect to glp-1 Age. The lack of suppression of daf-2 Age by atg RNAi under most conditions questions the importance of autophagy for this phenotype. Moreover, condition dependence of effects creates a risk of possible condition selection bias.