Uric acid builds up with both age and a nutrient-rich diet1-9. Elevated uric acid is associated with higher all-cause mortality risk and aging-related diseases such as hypertension, dyslipidemia, type-2 diabetes, cardiovascular disease, metabolic syndrome and gouty arthritis in clinical cohort studies. Elevated serum or urinary UA level in humans is a consequence of the loss of the enzyme uricase, during evolution, further augmented by the consumption of an enriched diet in humans, with hyperuricemia afflicting over 20% of the US population10,11. Despite being a risk factor for increased morbidity, the genetic and mechanistic causes of increasing uric acid levels are not well known. Tests of unknown genetic associations have previously been performed utilizing several human cohorts to find genes associated with either serum uric acid levels or gout, but in vivo tests have not been performed to validate these genes. This is primarily due to the lack of applicable animal models. Therefore, we established a Drosophila melanogaster model using Uricase knockdown, which increases UA levels. The inhibition of uricase led to both a diet-dependent shortening of lifespan and a buildup of UA concretions. Genetic and pharmacological inhibition of insulin-like signaling (ILS) pathway genes reduced UA load and concretion formation. Furthermore, a conserved role for the ILS in modulating UA was supported by data showing that SNPs in the ILS genes IGFR1, AKT2, and FOXO3 are associated with regulating serum UA levels or gout in humans. To identify other regulators of uric acid, I performed a Genome-Wide Association Study (GWAS) of uric acid and upstream purine pathway metabolites in ~150 different fly strains from the DGRP collection on two different diets. We validated 5 novel genes that modulate uric acid accumulation.
In Aim 1 I will examine the role of the ILS pathway which has been identified in human cohorts as a modulator of uric acid. ILS is a well-conserved signaling cascade that is activated when Drosophila is fed a high protein diet. I hypothesize that levels of uric acid are mediated through a multifaceted adjustment of purine homeostasis acting through FOXO and downstream effects on ROS production.
In Aim 2 I will characterize candidates from a genetic screen that has uncovered novel modulators of purine metabolism in the Drosophila Genetic Reference Panel (DGRP) collection of flies. I will characterize their role in hyperuricemia mediated concretion formation, healthspan, and lifespan in our fly model. I will also collaborate with the Giacomini lab to determine if human orthologs of candidate fly genes also modulate hyperuricemia in humans. My work will help better understand how ILS and purine metabolism influence uric acid levels and lifespan, identifying therapeutic targets to reduce human hyperuricemia-related pathologies.
Purine metabolism is known to have wide and significant effects on human health with age, though it is not known why purine dysregulation leads to these aging-related disorders. I propose to identify genetic variants that influence changes in purine metabolism using Drosophila melanogaster as a model organism. The identified genes will provide viable genetic candidate targets for more efficacious treatments for healthspan and age- related disorders.