Abstract 097: Knockout of Matrix Metalloproteinase 9 Protects Against Hypertension-induced Renal Disease in Hypertensive Dahl S Rats

Matrix metalloproteinase 9 (MMP9) is a member of gelatinase family of enzymes with potentially opposing actions on tissue fibrosis (i.e. the degradation of extracellular matrix). Our previous study showed that two nonselective MMP inhibitors, XL081 and XL784, which inhibit MMP2, 9, 13 and Adam10 could delay and even reverse the development of renal fibrosis in hypertensive Dahl Salt sensitive (SS) rats. However, the specific role of MMP9 to the development of hypertensive nephropathy in MMP9 knockout (KO) rat models is unknown. In the present study, MMP9 KO rats were created on the SS genetic background using a CRISPR/Cas 9 system and the effect of KO was verified in this model. The systolic pressure, diastolic pressure and mean blood pressure (MAP) were similar in 12 weeks old MMP9 KO (n=6) and SS rats (n=9) fed a low salt diet (145 ± 3 vs. 148 ± 2mmHg; 111 ± 2 vs. 107 ± 2mmHg; 128 ± 2 vs. 126 ± 2mmHg). MAP increased to 180 ± 4 vs. 154 ± 3mmHg in SS rats versus MMP9 KO rats fed 8% high salt (HS) diet for 3 weeks. Proteinuria increased from 196 ± 18 mg/day to 718 ± 61mg/day in HS treated SS rats (n=9). It was significantly reduced in HS treated MMP9 KO rats (211 ± 30mg/day, n=6). The degree of glomerular injury (2.88 ± 0.08 vs. 3.52 ± 0.02), interstitial fibrosis (4.57 ± 0.35% vs. 10.45 ± 0.55%), vascular wall-to-lumen ratio (0.63 ± 0.04 vs. 1.22 ± 0.08) and protein cast area (6.40 ± 0.07% vs. 20.27 ± 2.65%) were all significantly reduced in MMP9 KO rats (n=6) versus the corresponding values in SS rats (n=6) fed 8% HS diet for 3 weeks. Autoregulation of renal blood flow (RBF) to elevations in perfusion was impaired in SS rats prior to the development of hypertension, for RBF rose by 20.6 ± 3.6% (n=8) when MAP was increased from 110 to 150 mmHg. Autoregulation of RBF was restored in MMP9 KO rats and only increased by 7% when pressure was increased over the same range. In contrast, there was no difference in the fall in RBF in SS versus MMP9 KO rats when pressure was reduced from 110 to 50 mmHg. These findings suggest that knockout of MMP9 in SS rats restores autoregulation of RBF and opposes the development of hypertension, proteinuria, glomerular injury and renal interstitial fibrosis.