Methylprednisolone retards the progression of inherited polycystic kidney disease in rodents.

Polycystic kidney disease in adult laboratory animals and humans is associated with enlarged kidneys and a progressive decline of renal function, resulting in death from uremia. Interstitial inflammation and fibrosis typically are observed in association with the development of renal insufficiency. To determine whether amelioration of interstitial inflammation and fibrosis may diminish cyst expansion/kidney enlargement and stabilize renal function, we administered methylprednisolone, an anti-inflammatory drug with antifibrogenic effects, to mice and rats with hereditary polycystic kidney disease. The experiment was repeated once for each species. Mice were studied both in America and in Japan. Weanling male and female mice (DBA/FG pcy/pcy [cystic] and +/+ [normal], n = 87 and 20, respectively) and rats (Han:SPRD Cy/+ and +/+, n = 70 and 33, respectively) were administered methylprednisolone (1 to 2 mg/kg/d) in the drinking water for 100 days (mice) or 42 days (rats). Control animals drank distilled water. In normal DBA +/+ mice, methylprednisolone had no effect on serum urea nitrogen (SUN) levels, kidney weight, or kidney/body weight. Untreated male and female mice developed cystic kidneys and azotemia to an equal extent. Methylprednisolone administered in America to mice with renal cystic disease decreased kidney weight, kidney/body weight, SUN levels, volume density of cysts, and severity of interstitial fibrosis. In Japan, methylprednisolone decreased kidney weight and SUN levels of animals with cystic disease, but the effect on kidney/body weight did not reach statistical significance. In contrast to mice, male rats developed more severe renal cystic changes and were more azotemic than female rats. Methylprednisolone administered to male rats with cystic disease decreased SUN levels, kidney weight, kidney/body weight, volume density of cysts, and severity of interstitial fibrosis. Methylprednisolone had no effect on kidney/body weight or SUN levels in female rats with renal cystic disease. In normal Han:SPRD (+/+) rats of both sexes, kidney and body weight were decreased by methylprednisolone, but kidney/body weight and SUN levels were unchanged. On the basis of this study, we conclude that methylprednisolone decreased the extent of renal enlargement, reduced renal interstitial fibrosis, and preserved kidney function in mice and rats with relatively severe forms of inherited polycystic kidney disease.

Renal cysts in transgenic mice expressing transforming growth factor-alpha.

Transforming growth factor-alpha (TGF-alpha) is a member of the epidermal growth factor (EGF) family of proteins and, like EGF, elicits its cellular function by binding to the EGF receptor. EGF stimulation may have a role in several normal and pathologic processes in the kidney, and EGF has been implicated in the development of renal cysts in vitro and in human autosomal dominant polycystic kidney disease. We sought to determine whether renal expression of an EGF-like protein (TGF-alpha) could lead to the formation of renal cysts in vivo. We examined morphologic alterations to the normal kidney caused by renal expression of a TGF-alpha transgene linked to a mouse metallothionein promoter stably integrated into the genome of the CD1 mouse. TGF-alpha transgene expression was induced with exogenous zinc treatment starting at 4 weeks of age, and mice were killed at 8 weeks of age. The transgene was expressed at higher levels in female transgenic mice than in male transgenic mice. The augmented expression of the TGF-alpha transgene in females was associated with increased renal size and the development of renal epithelial cysts. Both male and female mice exhibited increases in glomerular size and mesangial volume density. These results provide evidence that stimulation by an endogenous EGF-like protein can lead to renal enlargement, glomerular mesangial expansion, and renal cyst formation.

Autosomal-dominant polycystic kidney disease in the rat.

Kaspareit-Rittinghausen described a rodent model of inherited polycystic kidney disease (PKD), the Han:SPRD rat [1, 2], in which heterozygotes develop renal cysts and renal failure (in males) over several months, whereas homozygous animals develop rapidly progressive renal enlargement that leads to death in a few weeks. In this study, we examined selected elements of the pathogenesis of this disease in heterozygotes and homozygotes from birth to advanced disease. Heterozygous male rats developed slowly progressive renal cystic disease with interstitial fibrosis and azotemia seen by six months of age. Female heterozygotes developed slowly progressive renal cystic disease, but did not develop interstitial fibrosis or azotemia. Epithelial cells lining cyst cavities showed various degrees of morphologic immaturity. Cyst walls also developed basement membrane thickening, especially in areas of cellular immaturity, suggesting an interrelationship between this basement membrane thickening and cellular dedifferentiation. Thickened basement membranes were associated with increased immunoreactivity for type IV collagen, laminin, and fibronectin. Homozygous rats developed massive renal enlargement, marked azotemia, and died near three weeks of age. Renal c-myc proto-oncogene expression was elevated in homozygous cystic infants and in adult heterozygotes. In situ hybridization showed high levels of c-myc mRNA in cyst epithelia, suggesting abnormal regulation of cellular proliferation in the cells lining cysts, as seen in other models of PKD. The Han:SPRD rat is the only well-documented animal model of inherited PKD with an autosomal-dominant inheritance pattern and appears to have several features which resemble human ADPKD.