Fruit Flies and Kidney Stones

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Developing accurate animal models of human diseases is a well-established research goal but a recent paper reporting a new animal model of nephrolithiasis caught my attention. Kidney stones are an important cause of morbidity and dealing with them is estimated to cost more than $5 billion yearly in the US alone. The majority of cases are due to calcium oxalate stones which variously results from increased urinary calcium excretion or increased urinary oxalate (which may be due to increased production or gut absorption of oxalate).

A group in the Mayo clinic and Glasgow have developed a fruit fly model of calcium oxalate nephrolithiasis. Fruit flies have a single transparent kidney tubule and feeding the larvae a diet high in oxalate for just two days leads to the formation of visible calcium oxalate kidney stones.

The upper panel of the image above shows a renal tubule dissected out from a fruit fly fed with oxalate compared with one fed with a normal diet. The second panel is a high power view of the tubule along with a nice picture of some calcium oxalate crystals. The lower 3 panels are a series of pictures of a tubule kept in a bath high in oxalate where you can see the crystals forming over a period of hours - the authors helpfully included a video if this happening in the supplemental data of the manuscript. There are also some micro-CT images of the fruit flies with the stones in situ. The rapid formation of stones in these flies makes it an excellent model for the study of nephrolithiasis.

Also, it's really cool.