Extension of lifespan in C. elegans by naphthoquinones that act through stress hormesis mechanisms

Hormesis occurs when a low level stress elicits adaptive beneficial responses that protect against subsequent exposure to severe stress. Recent findings suggest that mild oxidative and thermal stress can extend lifespan by hormetic mechanisms. Here we show that the botanical pesticide plumbagin, while toxic to C. elegans nematodes at high doses, extends lifespan at low doses. Because plumbagin is a naphthoquinone that generates free radicals in vivo, we investigated whether it extends lifespan by activating an adaptive cellular stress response pathway. Mammalian NF-E2-related factor 2 (Nrf2) and its C. elegans ortholog SKN-1, mediate protective responses to oxidative stress by promoting target gene expression via antioxidant response elements (ARE). Genetic analyses showed that skn-1 mediates plumbagin’s lifespan-extending effect in C. elegans. Further screening of a series of plumbagin analogs identified three additional naphthoquinones that could induce SKN-1 targets in C. elegans. Naphthazarin showed skn-1-dependent lifespan extension, over an extended dose range compared to plumbagin, while the other naphthoquinones, oxoline and menadione, had differing effects on C. elegans survival and failed to activate ARE reporter expression in cultured mammalian cells. Our findings reveal the potential for low doses of naturally occurring naphthoquinones to extend lifespan by engaging a specific adaptive cellular stress response pathway. Approximately 1,000 age-synchronized young adults were treated for two days with either 100 µM plumbagin or DMSO as a vehicle control and then washed three times in M9 and flash frozen with dry ice. RNA was isolated with the Absolutely RNA Miniprep Kit (Agilent Technologies, USA). RNA concentration and quality was assessed using an Agilent Bioanalyzer 2100 (Agilent Technologies, USA). Microarray hybridizations were performed with the C. elegans 4x44K Oligo Microarray (Agilent Technologies, USA). Raw microarray hybridization intensity data from four separate experiments were log-transformed and normalized to generate z-scores and subsequent z-ratios (Cheadle et al. 2003).