EXTRACELLULAR-MATRIX ACCUMULATION IN IMMUNE-MEDIATED TUBULOINTERSTITIAL INJURY

The accumulation of excessive extracellular matrix (ECM) following tub ular injury likely represents an imbalance between ECM production and degradation. We assessed the temporal relationship between the accumul ation of ECM, cell adhesion molecules, matrix degrading proteinases, a nd their inhibitors in a rat model of anti-tubular basement membrane ( TBM) antibody-associated tubulointerstitial nephritis (TIN) by the RNa se protection assay and immunohistochemistry. There was an increase in the steady state expression of fibronectin (FN) and alpha(2)(IV) coll agen mRNAs beginning on day 7 with the onset of neutrophil infiltratio n. An increase in alpha(1)(III) collagen and alpha(1)-integrin did not occur until days 9 and 10, respectively, at which time mononuclear le ukocytes were the predominant infiltrating cell. Increased levels of F N, alpha(1)(III), alpha(2)(IV) and alpha(1)-integrin mRNAs occurred th rough day 14. By immunohistochemistry, increased accumulation of colla gen IV, heparan sulfate proteoglycan, and laminin were detected along the thickened TBM; collagens I and III were immunolocalized within the tubulointerstitium, while FN was present in both the TBM and intersti tium in rats with TIN on day 14. The increase in matrix accumulation w as associated with little or no increase in proteinases. u-PA transcri pts fell beginning on day 8, with recovery to control values by day 12 . Transin mRNA was found at low levels only on days 8 and 9, and the p rotein could not be detected by Western blotting. In contrast, these c hanges were associated with an increase in proteinase inhibitors, so t hat TIMP and PAI-1 mRNAs increased beginning on day 7 and persisted th rough day 14. PAI-1 mRNA correlated with biologic activity, while TIMP was immunolocalized within the peritubular endothelium and infiltrati ng leukocytes. These data demonstrate a temporal association between E CM accumulation, a minimal change in proteinase, and an increase in pr oteinase inhibitors.