Mechanism of matrix accumulation and glomerulosclerosis in spontaneously hypertensive rats

BACKGROUND: Renal interstitial fibrosis and thickening of the glomerular basement membrane are associated with hypertension. However, the mechanism of matrix accumulation is unclear. Spontaneously hypertensive rats (SHR) develop hypertension at between 2 and 6 weeks of age. METHODS: To test the hypothesis that increased matrix metalloproteinase (MMP) and tissue inhibitor of metalloproteinase (TIMP) contribute to the pathomechanisms of hypertensive nephropathy, the cortex and medulla of male SHR at 2 and 6 weeks were analyzed for MMP-2, MMP-7, and MMP-9 by gelatin and elastin gel zymography. The levels of TIMP-4 were measured by western blot analysis. The bands in blots were scanned and normalized with actin. To localize MMP-2 and TIMP-4 in situ, immuno-labeling was performed. To determine proteinuresis, urinary protein was measured by Bio-Rad dye binding assay. The mean arterial pressure (mmHg) was measured in Inactin-anesthetized rats by a PE-50 catheter in the femoral artery. Age-sex matched normotensive Wistar rats (NWR) were used as controls and grouped: (1). SHR, 2 weeks; (2). SHR, 6 weeks; (3). NWR, 2 weeks; and (4). NWR, 6 weeks (n = 6 in each group). RESULTS: Levels of cortex MMP-2 and MMP-9 were increased in 6 week SHR as compared with NWR. In the medulla, MMP-9 and MMP-7 were increased, but there was no change in MMP-2. The levels of cortex TIMP-4 tended to increase but insignificantly. In contrast, there were significant increases in the levels of TIMP-4 in the medulla of 6 week SHR as compared with 2 week SHR or NWR. In addition, there were substantial elastinolytic activity in the cortex of 6 week SHR. The in situ labeling suggested no TIMP-4 in the glomeruli. There was substantial TIMP-4 in the epithelial layer of tubules. The levels of fibrotic collagen were significantly higher in both the glomeruli and tubular interstitium. Urinary protein excretion was increased significantly in 6 week SHR when compared with other groups. The mean arterial pressure was 1.6-fold higher in 6 week SHR than in controls. CONCLUSION: These results suggest that increased MMP-2 and MMP-9 activity contributes to glomerular injury and hypertensive remodeling. The increased levels of TIMP-4 in the medulla may inhibit the collagenolytic activity of MMP but is unable to inhibit the elastinolytic activity. An important role of MMP-2, MMP-9, and TIMP-4 in hypertensive remodeling of the cortex and medulla in the SHR is demonstrated.