An introduction to Research | Current research funded by CLDF | Functional characterisation of fibrocystin in extrahepatic biliary atresia

Functional characterisation of fibrocystin in extrahepatic biliary atresia

Dr. Colin A. Johnson - Institute of Biomedical Research, The Medical School, University of Birmingham

The epithelial cells (lining cells) of many internal organs such as the tubules (collecting ducts) in the kidney and the bile ducts of the liver (biliary tree) are continuously exposed to mechanical forces, such as fluid flow shear stresses. These epithelial cells possess primary cilia, that are finger-like structures that project from the cell surface into the luminal space (or cavity), that can sense fluid flow. Previous studies have investigated the role the cilia of tubular epithelial cells in two childhood cystic kidney diseases; polycystic kidney disease (PKD) and nephronophthisis (NPHP). These studies have shown that key genes are mutated (abnormal) in these diseases. The mutated genes control the development of both kidney tubule and bile duct epithelial cells (lining cells) and encode proteins that are components of primary cilia. We have shown recently that severe mutations in a particular gene, the PKHD1 gene, which encodes the primary ciliary protein fibrocystin, are found in patients with extra-hepatic biliary atresia (EHBA) who develop renal cysts later in life. EHBA is the single most common cause of liver disease in infants, with progressive damage to the extrahepatic biliary tree leading to liver failure in the first two years of life, without treatment. It is the main indication for paediatric liver transplantation.
In this application, we wish to determine:

1) if mutations in PKHD1 are more widespread in other cases of EHBA that lack any renal cystic changes
2) if the biliary epithelia of EHBA patients have structural or functional defects in primary cilia
3) if the primary cilia of biliary epithelia cells sense fluid flow, and if a defect in this mechano-sensory function can prevent normal bile duct formation or function, with the subsequent development of EHBA.

The latter two aims will be addressed by using an in vitro model system of human biliary cells, with the new technique of RNA interference (RNAi) to “knock down” the expression of the PKHD1 gene. This work should provide highly significant and novel insights into the disease mechanism of EHBA.

Budget:

Project - October 2005, for 36 months