A screen of small molecule and genetic modulators of life span in female Drosophila identifies etomoxir, RH5849 and unanticipated temperature effects

Abstract

Mifepristone increases life span in female Drosophila melanogaster , and its molecular target(s) remain unclear. Here small molecule and genetic interventions were tested for ability to mimic mifepristone, or to decrease life span in a way that can be rescued by mifepristone. Etomoxir inhibits lipid metabolism, and significantly increased life span in virgin and mated females, but not males, at 50 µM concentration. Pioglitazone is reported to activate both mammalian PPARγ and its Drosophila homolog Eip75B. Pioglitazone produced minor and inconsistent benefits for female Drosophila life span, and only at the lowest concentrations tested. Ecdysone is a Drosophila steroid hormone reported to regulate responses to mating, and RH5849 is a potent mimic of ecdysone. RH5849 reduced virgin female life span, and this was partly rescued by mifepristone. Mifepristone did not compete with RH5849 for activation of an ecdysone receptor (EcR)-responsive transgenic reporter, indicating that the relevant target for mifepristone is not EcR. The conditional GAL4/GAL80ts system was used in attempt to test the effect of an Eip75B RNAi construct on female life span. However, the 29°C temperature used for induction reduced or eliminated mating-induced midgut hypertrophy, the negative life span effects of mating, and the positive life span effects of mifepristone. Even when applied after mating was complete, a shift to 29°C temperature reduced mating-induced midgut hypertrophy by half, and the life span effects of mating by 4.8-fold. Taken together, these results identify promising small molecules for further analysis, and inform the design of experiments involving the GAL4/GAL80ts system.

Dhr96[1] mutation and maternal tudor[1] mutation increase life span and reduce the beneficial effects of mifepristone in mated female Drosophila

“…This difference may be due to the more intensive mating protocol employed here, where newly-eclosed females were mated to young, mature w[1118] strain males for 48 hours. Consistent with this conclusion, our previous studies indicated that 48 hours mating reduced female life span to a greater extent than did 24 hours mating [ 39 ], and that the more intensive mating protocol yields shorter mated female life spans and greater increases in life span upon mifepristone treatment [ 19 ].…”

“…Midgut diameter was assayed in flies at 14 days of age, which corresponds to 12 days of treatment +/- mifepristone. This time point was selected because this is the age where life span curves of mated females treated +/- mifepristone typically begin to diverge, and this time point has previously been found to show robust mating-induced midgut hypertrophy that is reversed by mifepristone treatment [ 21 , 39 ]. In the w[1118] control strain, mating caused increased midgut diameter, and this was significantly decreased by mifepristone treatment, consistent with previous assays of the w[1118] strain and other strains [ 21 ].…”

“…RH5849 is a potent mimic of ecdysone [ 11 , 43 ]. Our previous studies showed that 1000μg/ml RH5849 dramatically shortens life span in virgin females, and that this effect could be partially rescued by mifepristone [ 39 ]. This concentration of RH5849 was chosen because it was able to give a greater activation of an ecdysone-receptor-responsive transgenic reporter than was achieved with dietary ecdysone [ 39 ].…”

“…Our previous studies showed that 1000μg/ml RH5849 dramatically shortens life span in virgin females, and that this effect could be partially rescued by mifepristone [ 39 ]. This concentration of RH5849 was chosen because it was able to give a greater activation of an ecdysone-receptor-responsive transgenic reporter than was achieved with dietary ecdysone [ 39 ]. The previous study also showed that RH5849 significantly reduced food intake, and that mifepristone had no significant effect on food intake in the presence or absence of RH5849 [ 39 ].…”

“…This concentration of RH5849 was chosen because it was able to give a greater activation of an ecdysone-receptor-responsive transgenic reporter than was achieved with dietary ecdysone [ 39 ]. The previous study also showed that RH5849 significantly reduced food intake, and that mifepristone had no significant effect on food intake in the presence or absence of RH5849 [ 39 ]. Here the effects of RH5849 on life span were assayed, and found to be similar in the control and germ-line ablated females.…”