The pck rat: a new model that resembles human autosomal dominant polycystic kidney and liver disease.

BACKGROUND: The pck rat is a recently identified model of polycystic kidney disease (PKD) and liver disease (PLD) that developed spontaneously in the rat strain Crj:CD/SD. Its pattern of inheritance is autosomal recessive.

METHODS: To characterize this new model, we studied pck rats derived from F9 breeding pairs from Charles River Japan and control Sprague-Dawley rats. Blood and tissues (kidneys, liver, and pancreas), obtained from these rats at 1, 7, 21, 70, and 182 days of age, were used for biochemical determinations, light and electron microscopy, and immunohistochemistry.

RESULTS: The pck rats develop progressive cystic enlargement of the kidneys after the first week of age, and liver cysts are evident by day 1. The renal cysts developed as a focal process from thick ascending loops of Henle, distal tubules, and collecting ducts in the corticomedullary region and outer medulla. Flat and polypoid epithelial hyperplasia were common in dilated tubules and cysts. Apoptosis was common and affected normal, as well as dilated tubules, but less frequently cysts lined by flat epithelium. The basement membranes of the cyst walls exhibited a variety of alterations, including thinning, lamellation, and thickening. Focal interstitial fibrosis and inflammation were evident by 70 days of age. Segmental glomerulosclerosis and segmental thickening of the basement membrane with associated effacement of the podocyte foot processes were noted in some rats at 70 days of age. The PKD was more severe in male than in female pck rats, as reflected by the higher kidney weights, while there was no gender difference in the severity of the PLD. Mild bile duct dilation was present as early as one day of age. With age, it became more severe, and the livers became markedly enlarged. Even then, however, there was only a mild increase in portal fibrosis, without formation of fibrous septae. Slight elevations of plasma blood urea nitrogen levels were detected at 70 and 182 days of age.

CONCLUSIONS: The pck rat is a new inherited model of PKD and PLD with a natural history and renal and hepatic histologic abnormalities that resemble human autosomal dominant PKD. This model may be useful for studying the pathogenesis and evaluating the potential therapies for PKD and PLD. The identification of the pck gene may provide further insight into the pathogenesis of autosomal dominant PKD.