The Effect Of Chronic Lithium Treatment On The Aging Of Drosophila Melanogaster

1. Aim:This study aims to find out about the effect of chronic lithium treatment on the aging of the fly Drosophila melanogaster.2. Method:One to two days old newly eclosioned adult flies are collected and sorted according to gender after slight CO2 anesthesia. Cohorts of flies are then transferred into plastic rearing tubes containing different regimes of lithium,40 animals per tube, single-sexed. For each gender on each lithium regime, equal number of groups are adopted. The lifespan assay begins after the animals are transferred into their respective rearing tubes and ends when all animals are dead. Every 2-3 days during the lifespan assay, animals are checked and transferred into new rearing medium to avoid starvation. Numbers of animals that are dead are recorded during each time of transfer. Animals that have escaped during the transfer are recorded as censored data. GraphPrism is adapted to draw the survival curves and SPSS 16.0 is utilized to statistically analyze the data.3. Results:(1) We adopted Cox regression model to test if lithium dose, sex and dose-sex interaction affect the survival curves significantly. Treatment A/B is set as the stratum factor. The results show that lithium dose does not affect survival curves significantly (P=0.865). (2) Lithium chloride hurdles pre-eclosion development of flies. The number of offspring produced per female fly drops dramatically with the increase of lithium dose, and is near zero when lithium dose reaches to 20mM. However, in the 1mM and lOmM groups, the median survival time of offspring, whether exposed to lithium during pre-eclosion (treatment A) or not (treatment B), are not significantly different, indicating that lithium has a selective effect on developing flies. (3) Control females outlive control males for 26.37%. However, the female advantage dimishes with the increase of lithium dose. In the 1mM-B group, females outlive males for 11.28%, in the 10mM group, females outlive males only for 2.4%.4. Conclusions:In this study lithium chloride does not display a similar lifespan extending effect in Drosophila melanogaster to that in C. elegans. This phenomenon might be explained by the intrinsic physiological difference between the two species. We also discovered that lithium chloride negatively affects fly development, with a selective effect during the pre-eclosion stage. Plus, increasing dose of lithium dimishes the female advantage in lifespan in flies. This specific effect can be as significant as reducing a gender gap of more than 25% in control groups, to a gender gap of nearly zero in 20mM groups. Possible explanation of these effects of lithium may include a regulation in biological processes such as histone demethylation from a molecular biology point of view, or a living strategy selected by species under harsh environments from an evolutionary point of view. The ability of lithium to alter the sex dimorphism of fly aging is interesting, as it hints at a possible path into solving the mystery of the differential longevity of the sexes.