Mifepristone Increases Life Span in Female Drosophila Without Detectable Antibacterial Activity

Mifepristone and rapamycin have non-additive benefits for life span in mated female Drosophila

The drugs mifepristone and rapamycin were compared for their relative ability to increase the life span of mated female Drosophila melanogaster. Titration of rapamycin indicated an optimal concentration of approximately 50 μM, which increased median life span here by average +81%. Meta-analysis of previous mifepristone titrations indicated an optimal concentration of approximately 466 μM, which increased median life span here by average +114%. Combining mifepristone with various concentrations of rapamycin did not produce further increases in life span, and instead reduced life span relative to either drug alone. Assay of maximum midgut diameter indicated that rapamycin was equally efficacious as mifepristone in reducing mating-induced midgut hypertrophy. The mito-QC mitophagy reporter is a previously described green fluorescent protein (GFP)-mCherry fusion protein targeted to the outer mitochondrial membrane. Inhibition of GFP fluorescence by the acidic environment of the autophagolysosome yields an increased red/green fluorescence ratio indicative of increased mitophagy. Creation of a multi-copy mito-QC reporter strain facilitated assay in live adult flies, as well as in dissected midgut tissue. Mifepristone was equally efficacious as rapamycin in activating the mito-QC mitophagy reporter in the adult female fat-body and midgut. The data suggest that mifepristone and rapamycin act through a common pathway to increase mated female Drosophila life span, and implicate increased mitophagy and decreased midgut hypertrophy in that pathway.

Metabolic pathways that mediate the effects of food deprivation on reproductive behavior in female Drosophila melanogaster

In most species studied, energy deficits inhibit female reproductive behavior, but the location and nature of energy sensors and how they affect behavior are unknown. Progress has been facilitated by using Drosophila melanogaster, a species in which reproduction and food availability are closely linked. Adult males and females were either fed or food deprived (FD) and then tested in an arena with a fed, opposite-sex conspecific with no food in the testing arena. Only FD females (not FD males) significantly decreased their copulation rate and increased their copulation latency, and the effects of FD were prevented in females fed either yeast alone or glucose alone, but not sucralose alone, cholesterol alone, or amino acids alone. It is well-known that high-fat diets inhibit copulation rate in this species, and the effects of FD on copulation rate were mimicked by treatment with an inhibitor of glucose but not free fatty acid oxidation. The availability of oxidizable glucose was a necessary condition for copulation rate in females fed either yeast alone or fed a nutritive fly medium, which suggests that the critical component of yeast for female copulation rate is oxidizable glucose. Thus, female copulation rate in D. melanogaster is sensitive to the availability of oxidizable metabolic fuels, particularly the availability of oxidizable glucose or substrates/byproducts of glycolysis.NEW & NOTEWORTHY Copulation rate was decreased in food-deprived female but not in male adults when tested without food in the testing arena. Copulation rate was 1) maintained by feeding glucose alone, yeast alone, nutritive medium lacking yeast, but not sucralose, amino acids, or cholesterol alone; 2) decreased by inhibition of glycolysis in females fed either nutritive medium or yeast alone; and 3) not affected by inhibition of fatty acid oxidation. Thus, female copulation rate was linked to glycolytic status.

Conditional Inhibition of Eip75B Eliminates the Effects of Mating and Mifepristone on Lifespan in Female Drosophila

Mating in female Drosophila melanogaster causes midgut hypertrophy and reduced lifespan, and these effects are blocked by the drug mifepristone. Eip75B is a transcription factor previously reported to have pleiotropic effects on Drosophila lifespan. Because Eip75B null mutations are lethal, conditional systems and/or partial knock-down are needed to study Eip75B effects in adults. Previous studies showed that Eip75B is required for adult midgut cell proliferation in response to mating. To test the possible role of Eip75B in mediating the lifespan effects of mating and mifepristone, a tripartite FLP-recombinase-based conditional system was employed that provides controls for genetic background. Expression of a Hsp70-FLP transgene was induced in third instar larvae by a brief heat pulse. The FLP recombinase catalyzed the recombination and activation of an Actin5C-GAL4 transgene. The GAL4 transcription factor in turn activated expression of a UAS-Eip75B-RNAi transgene. Inhibition of Eip75B activity was confirmed by loss of midgut hypertrophy upon mating, and the lifespan effects of both mating and mifepristone were eliminated. In addition, the negative effects of mifepristone on egg production were eliminated. The data indicate that Eip75B mediates the effects of mating and mifepristone on female midgut hypertrophy, egg production, and lifespan.

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

Mating and receipt of male Sex Peptide hormone cause increased egg laying, increased midgut size and decreased life span in female Drosophila. Feeding mated females with the synthetic steroid mifepristone decreases egg production, reduces midgut size, and increases life span. Here, several gene mutations were assayed to investigate possible mechanisms for mifepristone action. Drosophila Dhr96 is a hormone receptor, and a key positive regulator of midgut lipid uptake and metabolism. Dhr96[1] null mutation increased female life span, and reduced the effects of mifepristone on life span, suggesting that Dhr96[1] mutation and mifepristone may act in part through the same mechanism. Consistent with this idea, lipidomics analysis revealed that mating increases whole-body levels of triglycerides and fatty-acids in triglycerides, and these changes are reversed by mifepristone. Maternal tudor[1] mutation results in females that lack the germ-line and produce no eggs. Maternal tudor[1] mutation increased mated female life span, and reduced but did not eliminate the effects of mating and mifepristone on life span. This indicates that decreased egg production may be related to the life span benefits of mifepristone, but is not essential. Mifepristone increases life span in w[1118] mutant mated females, but did not increase life span in w[1118] mutant virgin females. Mifepristone decreased egg production in w[1118] mutant virgin females, indicating that decreased egg production is not sufficient for mifepristone to increase life span. Mifepristone increases life span in virgin females of some, but not all, white[+] and mini-white[+] strains. Backcrossing of mini-white[+] transgenes into the w[1118] background was not sufficient to confer a life span response to mifepristone in virgin females. Taken together, the data support the hypothesis that mechanisms for mifepristone life span increase involve reduced lipid uptake and/or metabolism, and suggest that mifepristone may increase life span in mated females and virgin females through partly different mechanisms.

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

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.