Drosophila Model of Oxalate Nephrolithiasis Project

  • MicroCT detects CaOx crystals in Drosophila

    (A) CaOx crystals ("stones") are detected in Oxalate-fed Drosophila (Ox-fed) but not controls (Ctl). (B) Surface rendering of microCT image for fly #3. The lower images include the density extremes: low density (air sacs, green) and high density (CaOx, grey).

MicroCT detects CaOx crystals in Drosophila

Principal investigator:
Michael F. Romero, Ph.D.

Researchers in the O'Brien Urology Research Center at Mayo Clinic have developed a drosophila model of oxalate nephrolithiasis. This model is useful because formation of stones can occur in minutes (in drosophila flies) versus months or years (in humans). Dr. Romero's research team is using this drosophila model to test genes involved in calcium oxalate (CaOx) stone formation and to test potential therapeutics.

Using a genome-wide association study (GWAS) analysis of a canine CaOx model, Eva Furrow, V.M.D., Ph.D., at the University of Minnesota, identified a critical region of dog chromosome 37. This region contains 18 genes (orthologs on human chromosome 2), of which 12 genes have drosophila homologs and available RNAi lines.

The project takes a multipronged approach, drawing on the strengths of our collaborators in the research group of Julian A.T. Dow, D.Sc., Ph.D., at the University of Glasgow. By combining resources and expertise, we can screen genes and compounds in multiple ways, taking advantage of the small size of flies and the quick phenotypic manifestation of CaOx microliths.

Preliminary experiments demonstrated that urine crystallization inhibitors (thiosulfate and tannic acid) can interact with the oxalate transporter as well as inhibit CaOx crystal formation in tubule assays.

The Drosophila Model of Oxalate Nephrolithiasis Project screens larval and adult flies using gene knockdown, birefringence and microCT projection densities. The aims of the project are to:

  • Use RNAi lines of the 12 dog homologs to determine which of these genes, when interrupted, alter CaOx crystal formation
  • Screen compounds known to change CaOx supersaturation
  • Investigate "compound hits" with more detailed analysis of dose dependence, mode of inhibition and effect on oxalate transporter biophysics

These experiments will identify lead compounds for further therapeutic development to prevent or lessen CaOx crystal formation (kidney stones).

Significance to patient care

Kidney stones are common (occurring in 10 percent of adults in the U.S), painful and expensive. They can cause renal complications, such as acute kidney injury, and contribute to end-stage renal disease. CaOx stones are the most common type of stone, seen in roughly 70 to 80 percent of cases.

In 2012, the U.S. spent approximately $10 billion — one-third of the entire NIH annual budget — on treatment of kidney stones and related kidney injuries and complications. Current therapies, which only slow recurrence and may not be effective, are limited to options such as altering diet, increasing fluid intake and surgically removing stones.

However, gut oxalate transport and excess urinary oxalate excretion are important pathogenic factors producing CaOx stones, especially in hyperoxaluria. Slc26a6 is a Cl-/ox2- exchanger involved in both intestinal and renal oxalate excretion. Both gut and renal transport of oxalate are maintained in our drosophila model of oxalate nephrolithiasis.

Because the drosophila CaOx crystals form fast (30 minutes in flies versus months to years in humans), we can use drosophila to understand the transport of oxalate. More importantly, this fly model is used as a tool for screening therapeutics that prevent the formation of CaOx crystals — that is, drugs to prevent kidney stones.