March 2004 - Researchers at UT Southwestern Medical Center at Dallas have uncovered a link between two cyst-forming diseases that affect the kidneys, a finding that could lead to treatments for both a rare form of diabetes and a common kidney disease.
"We discovered that the formation of kidney cysts in both maturity-onset diabetes of the young type 5 (MODY5) and autosomal recessive polycystic disease is related to the same gene abnormality. It was a surprise to find this link, as it was not suspected that these two diseases were linked together," said Dr. Peter Igarashi, chief of nephrology at UT Southwestern and senior author of the study, which appears in the March issue of The Journal of Clinical Investigation.
"This finding provides a framework for further investigation. The goal is to understand disease mechanisms, and any time you can find a link between two diseases, it provides an opportunity to better understand the mechanisms involved," Dr. Igarashi said.
MODY5 is a rare inherited form of diabetes caused by mutations of HNF-1�, a protein that regulates gene expression. The disease is associated with congenital abnormalities of the kidneys, a condition resulting in large, fluid-filled cysts that lead to kidney failure.
Since it is largely unknown what triggers these cysts to form, Dr. Igarashi and his colleagues used a mouse model to express a mutant form of HNF-1� similar to the form in humans with MODY5. These mice also developed kidney cysts and eventually experienced kidney failure.
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The researchers then looked for changes in the expression of other genes involved in cyst formation. Surprisingly, they found the expression of the PKHD1 gene was markedly decreased in the mutated mice. Mutations of PKHD1 cause autosomal recessive polycystic kidney disease, a common genetic cystic disease that affects between one in 10,000 to 40,000 babies and is often fatal in the first month of life. In addition, they found that the PKHD1 promoter was directly regulated by the HNF-1� protein.
"Mutations in HNF-1�, the cause of MODY5, interfere with the transcription of PKHD1, a gene known to be mutated in autosomal recessive polycystic kidney disease," said Dr. Thomas Hiesberger, assistant professor of internal medicine and the study's lead author. "This link may allow for similar future therapeutic approaches for both diseases."
At this point, little is known about how inhibition of PKHD1 causes cysts. That is the next step for the researchers and will provide new insight into how both MODY5 and the kidney disease develop.
Other UT Southwestern internal medicine contributors to the study were Dr. Xinli Shao, postdoctoral researcher; Yun Bai, senior research associate; Brian McNally, student research assistant; and Dr. Angus M. Sinclair, former assistant professor. Drs. Xin Tian and Stefan Somlo from Yale University School of Medicine also contributed.
Research was funded by grants from the National Institutes of Health and the Polycystic Kidney Disease Foundation.
Source: University of Texas Southwestern
