Mechanisms of renal immune cell infiltration in salt-sensitive hypertension

PROJECT SUMMARY Salt-sensitive hypertension is a significant health problem; there is a need to understand the underlying mechanisms to enable more effective treatments. The proposed studies are based on a strong scientific foundation with experiments performed in our laboratories in Dahl salt-sensitive (SS) rats demonstrating that both renal H2O2 production and inflammation play key roles in the initiation and progression of salt-sensitive hypertension, but the connection between these two has thus far not been elucidated. Based on prior work and exciting preliminary data, we hypothesize that renal inflammation in SS rats fed high salt is driven by an initial rise of arterial pressure with elevated Nox4-derived H2O2 production. This, in turn, results in leukocyte adhesion and infiltration into the kidney via activation of matrix metalloproteinase (MMP)-2 and -9 and the NLRP3 inflammasome. The infiltrated immune cells produce additional MMP-2 and H2O2 (and superoxide [O2-]) from Nox2 which facilitates the transition from a pre-hypertensive state to accelerated malignant hypertension and end-stage renal injury. Several unique methodologies enable us to address this overall hypothesis. First, we have developed an SS rat containing a null mutation in Nox4 (SSNox4-/-), a unique model of reduced H2O2 production with reduced salt-sensitive hypertension. Second, we have also developed novel SS rat strains with null mutations in MMP-2, MMP-9, and NLRP3 (SSMMP2-/-, SSMMP9-/-, and SSNLRP3-/-) enabling us to determine their involvement in salt-sensitive hypertension. Third, a custom-designed servo-control system which is unique to our laboratory enables the precise chronic control of renal perfusion pressure (RPP) to the left kidney of SS rats thereby allowing us to separate the effects of renal H2O2 production from those of differing RPPs. Moreover, given the profound effect of RPP on renal immune cell infiltration, this system enables us to perform pressure-matching studies to isolate the effects of genetic mutation of NLRP3, MMP-2 and MMP-9 on renal inflammation from the confounding effects of different RPP in the models. Finally, sophisticated bone marrow transfer studies, which utilize our genetically modified SS strains (SSp67phox-/- and SSMMP2-/-), will enable us to determine the relative contributions of parenchymal- and hematopoietic-derived H2O2/reactive oxygen species and MMP-2 to salt-sensitive hypertension and renal injury. This proposal has three Specific Aims: 1) will test the hypothesis that an initial rise of BP accompanied by elevated Nox4-derived H2O2 mediates immune cell infiltration into the kidney of hypertensive rats fed high salt; 2) will test the hypothesis that upregulation of MMP-2, MMP-9 and the NLRP3 inflammasome mediates renal immune cell infiltration in SS rats and participates in the progression of salt-induced hypertension; and 3) will test the hypothesis that T-cells that infiltrate into the kidney enhance H2O2 production via Nox2 and serve as a source of MMP-2 which further amplify immune cell infiltration and hypertension (i.e. creates a vicious cycle). Our unique ability to perform these studies will provide important insight into our fundamental understanding of salt-sensitive hypertension.