Matrix Metalloprotease Activity in Vascular Lesions of Malignant Hypertensive Rats

Background: In malignant hypertension (MH), far more severe kidney injury occurs than in the “benign” form (NMH) of the disease. In a previously reported RNA-Seq analysis of renal cortical tissue from a rat model of MH, we observed an altered expression of several matrix metalloproteases (MMP). We now investigated gelatinase activity localized to the characteristic vascular lesions of MH. Methods: Renovascular hypertension in rats was induced by placing a 0.2 mm clip on the left renal artery (2K1C), controls were sham operated. To distinguish MH from NMH, we considered weight loss and typical vascular lesions (onion-skin and fibrinoid necroses). The expression of MMPs was measured by RT-PCR; immunohistochemistry was performed for MMP-2 and 9. In-situ zymography was performed to localize gelatinase activity. Results: Mean blood pressure measured intra-arterially was elevated to a similar degree in MH (220±7 mmHg) and NMH (192±6 mmHg), compared to controls (119±2 mmHg, p<0.05). MMP-2, -7, -8, -10, -12, -16 and -19 expression were all elevated in NMH and significantly higher increased in MH. The only exception was MMP-9 mRNA which barely changed in NMH but decreased by 0.2-fold in MH (p<0.05). In situ zymography revealed gelatinase activity predominantly in preglomerular vascular lesions of MH (52.8 ± 7.2 versus 20.5 ± 6.1 per medium power field in NMH, p<0.05) in right kidneys exposed to high blood pressure. The number of these gelatinase activity lesions correlated with the glomerulosclerosis score (r=0.75, p<0.0001). There was no gelatinase activity in sham operated animals, or in left (post-stenotic) kidneys of MH or NMH. MMP-2 staining was detected in, or closely surrounding, vascular lesions (3.46 ± 0.9 MMP-2 positive lesions per 10 high power fields in MH versus 0.22 ± 0.09 in NMH and 0 in sham, p<0.05). MMP-9 staining was observed in proximal tubules, individual interstitial cells, and intact or hypertrophic preglomerular vessels but absent from malignant vascular lesions. Conclusion: In malignant hypertension of 2K1C rats, most MMPs are upregulated, broadly consistent with enhanced tissue injury. However, the gelatinases MMP-2 and MMP-9 exhibited a strikingly divergent regulation, with MMP-2 clearly localized to malignant vascular lesions with gelatinase activity. Funding: Government Support – Non-U.S.