INTERSTITIAL INFLAMMATION AND FIBROSIS IN RATS WITH DIET-INDUCED HYPERCHOLESTEROLEMIA

Abnormalities in lipid metabolism appear to play a pathogenic role in progressive renal disease. To elucidate the cellular and molecular bas is of renal interstitial fibrosis in uninephrectomized rats with diet- induced hypercholesterolemia, we fed experimental rats with standard r at chow supplemented with 4% cholesterol and 1% cholic acid. Control r ats were fed an isocaloric diet. Groups of 7 control and 7 experimenta l rats were killed after 4, 8, and 12 weeks. Hypercholesterolemic rats developed albuminuria; serum creatinine was elevated at 12 weeks. By 12 weeks numerous oil red O-positive cells were present throughout the interstitium and to a lesser extent in tubules. Total renal lipid-per oxidation products were significantly increased (172 +/- 15, 198 +/- 2 8, and 197 +/- 13 mmol malondialdehyde/kidney at 4, 8, and 12 weeks vs . 123 +/- 17, 144 +/- 6, and 125 +/- 10 mmol in controls). Immunostain ing revealed oxidatively modified lipoproteins within tubular and inte rstitial cells. The interstitial disease was characterized by an inter stitial infiltrate of monocytes. Significant increases were detected i n renal cortical mRNA levels for monocyte chemoattractant protein-1 (M CP-1), osteopontin, and vascular cell adhesion molecule-1 (VCAM-1), as sociated with changes in the pattern of immunostaining for each encode d proteins. Total kidney collagen was significantly increased at 12 we eks (9.8 +/- 0.9 mg/kidney vs. 7.8 +/- 0.9 mg in controls). At 12 week s there was a significant increase in interstitial immunostaining for collagen I, collagen III, collagen IV, fibronectin and tenascin. A sig nificant threefold increase in renal cortical mRNA levels for transfor ming growth factor beta-1 (TGF-beta 1) at 4 and 12 weeks was associate d with the appearance of TGF-beta-positive interstitial cells. Renal m atrix protein mRNA levels were measured at 4, 8, and 12 weeks. The onl y statistically significant elevations were procollagen alpha 1(I) and procollagen alpha 1(III) at weeks 8 and 12. In contrast, renal cortic al mRNA levels for the tissue inhibitor of metalloproteinases-l (TIMP- 1) were significantly increased at 4, 8 and 12 weeks (1.4 +/- 0.5, 2.7 +/- 0.9 and 2.7 +/- 1.4 arbitrary densitometric units, respectively, vs. 1.0 +/- 0.4, 1.0 +/- 0.5 and 1.0 +/- 0.4 units for controls), and urokinase-type plasminogen activator (mu PA) mRNA levels were signific antly decreased at 4, 8, and 12 weeks (0.4 +/- 0.1 arbitrary densitome tric units for all three experimental groups vs. 1.0 +/- 0.4, 1.0 +/- 0.3, and 1.0 +/- 0.4 units for the control groups). In summary, rats w ith diet-induced hypercholesterolemia develop renal interstitial fibro sis over several weeks. Following the accumulation of lipids within tu bulointerstitial cells, interstitial nephritis develops. The fibrotic phase is characterized by modest changes in matrix protein mRNA levels , up-regulated TIMP-1, and down-regulated mu PA levels, suggesting tha t altered matrix degradation plays a role in the interstitial fibrogen esis in this model.