RENAL EXPRESSION OF GENES THAT PROMOTE INTERSTITIAL INFLAMMATION AND FIBROSIS IN RATS WITH PROTEIN-OVERLOAD PROTEINURIA

Rats with significant proteinuria induced by daily injections of bovin e serum albumin develop interstitial inflammation and fibrosis. The pr esent study was designed to investigate the molecular basis of interst itial monocyte (M0) recruitment and early interstitial fibrosis. Group s of rats were sacrificed after one, two and three weeks. Despite an i ncrease in interstitial M0 at week 1, whole kidney mRNA levels were no t elevated for monocyte chemoattractant protein-1 (MCP-1), osteopontin or vascular cell adhesion molecule-1 (VCAM-1). Only osteopontin mRNA levels were significantly elevated in the renal cortex at four days. A t two and three weeks, MCP-1 and osteopontin mRNA levels were increase d and the proteins showed distinct tubular patterns of distribution. B y immunostaining increased expression of VCAM-1 and intercellular adhe sion molecule-1 (ICAM-1) was restricted to their presence or the surfa ce of the interstitial inflammatory cells. TGF-beta 1 mRNA levels were increased at weeks 1, 2 and 3 (2.1, 2.9, 3.6x); interstitial and occa sional cortical tubular cells expressed TGF-beta 1 mRNA and protein. T here was a progressive rise in the number of cortical interstitial fie lds with increased staining for collagen (col) 1 (18, 29, 44%), col II I (39, 61, 63%), col IV (7, 13, 29%), laminin (4, 10, 30%), fibronecti n (14, 28, 37%), tenascin (19, 22, 14%) and in total renal col measure d biochemically (1.1, 1.4, 2.0x) at weeks 1, 2 and 3, respectively. Re nal matrix protein mRNA levels were variable and not always predictive of fibrosis. Only col I and tenascin levels were increased at week 1; all matrix protein mRNA levels except col IV were increased at week 2 ; but only tenascin, laminin and col IV mRNA levels remained elevated at three weeks. Plasminogen activator inhibitor-1 (PAI-1) and tissue i nhibitor of metalloproteinases (TIMP)-1 mRNA levels were significantly increased at two weeks. During the three weeks there was no change in urokinase, stromelysin or TIMP-3 mRNA levels. These results suggest t hat both increased matrix protein synthesis and altered matrix remodel ing/degradation contribute to the final interstitial fibrogenic proces s in rats with protein-overload proteinuria. M0, one of the sources of TGF-beta 1, infiltrate the interstitium by complex recruitment mechan isms which may depend in part on osteopontin, ICAM-1 and VCAM-1 expres sion.