Matrix metalloproteinases and their inhibitions in experimental renal scarring

Renal fibrosis is characterised by an excessive accumulation of extracellular matrix (ECM) proteins. Evidence suggests that this results from both increased ECM synthesis and a reduced degradation. Here, we determine changes in the matrix metalloproteinases (MMP) and their tissue inhibitors (TIMP) in relation to ECM production and the progression of renal fibrosis in subtotally nephrectomized (SNx) rats. Groups of 4-6 SNx or sham-operated male Wistar rats were sacrificed between days 7 and 120 following surgery. Total RNA was analysed by Northern blotting. Messenger RNA for collagens I (+710%), III (+674%), and IV (+358%) were significantly (p < 0.05) raised by day 7 and remained elevated over the 120 days. Significant (p < 0.05) increase in fibronectin, laminin and heparan sulfate proteoglycan mRNAs occurred latter at days 60 (+224%), 120 (+210%), and 120 (+256%), respectively. Increases (p < 0.05) in mRNA for MMP-1 (+360%) and MMP-2 (+239%) occurred from day 7 with MMP-1 reaching +881% by day 120. MMP-3 and -9 showed no change. Zymography on day 90 remnant kidneys showed mRNA changes were translated into active MMP-1 (+1,700%) and MMP-2 (+440%), p < 0.05. TIMP-1 mRNA was also raised (+548%, p < 0.05) by day 7 and remained elevated, while TIMP-2 mRNA levels only reached significance by day 120 (+165%). In contrast, TIMP-3 mRNA was decreased by day 30 (p > 0.05) and dropped to 27% of control by day 120. However, Western blot analysis of TIMPs 1 and 3 at day 90 showed a 5- and 4-fold increase respectively, while TIMP-2 levels were not significantly altered. Measurements of overall collagenase activities in remnant kidney homogenates were reduced. Using collagen I and IV substrates, proteolytic activity in remnant kidneys dropped to 40 and 27% of controls (p < 0.01), respectively. This data suggests that reduced MMP activity may contribute towards renal scarring, however this is not a result of reduced MMP transcription or activation, but likely to be due to the inhibition by TIMPs.