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The role of CX3CR1, also known as fractalkine receptor, in hypertension is unknown. The present study determined the role of the fractalkine receptor CX3CR1 in hypertensive renal and cardiac injury. Expression of CX3CR1 was determined using CX3CR1GFP/+ mice that express a green fluorescent protein (GFP) reporter in CX3CR1+ cells. FACS analysis of leukocytes isolated from the kidney showed that 34% of CD45+ cells expressed CX3CR1. Dendritic cells were the majority of positive cells (67%) followed by macrophages (10%), NK cells (6%), and T cells (10%). With the use of confocal microscopy, the receptor was detected in the kidney only on infiltrating cells but not on resident renal cells. To evaluate the role of CX3CR1 in hypertensive end-organ injury, an aggravated model of hypertension was used. Unilateral nephrectomy was performed followed by infusion of angiotensin II (ANG II, 1.5 ng·g−1·min−1) and a high-salt diet in wild-type ( n = 15) and CX3CR1-deficient mice ( n = 18). CX3CR1 deficiency reduced the number of renal dendritic cells and increased the numbers of renal CD11b/F4/80+ macrophages and CD11b/Ly6G+ neutrophils in ANG II-infused mice. Surprisingly, CX3CR1-deficient mice exhibited increased albuminuria, glomerular injury, and reduced podocyte density in spite of similar levels of arterial hypertension. In contrast, cardiac damage as assessed by increased heart weight, cardiac fibrosis, and expression of fetal genes, and matrix components were not different between both genotypes. Our findings suggest that CX3CR1 exerts protective properties by modulating the invasion of inflammatory cells in hypertensive renal injury. CX3CR1 inhibition should be avoided in hypertension because it may promote hypertensive renal injury.

Adaptive and innate immune responses contribute to hypertension and hypertensive end-organ damage. Here, we determined the role of anaphylatoxin C5a, a major inflammatory effector of the innate immune system that is generated in response to complement activation, in hypertensive end-organ damage. For this purpose, we assessed the phenotype of C5a receptor 1 (C5aR1)-deficient mice in ANG II-induced renal and cardiac injury. Expression of C5aR1 on infiltrating and resident renal as well as cardiac cells was determined using a green fluorescent protein (GFP)-C5aR1 reporter knockin mouse. Flow cytometric analysis of leukocytes isolated from the kidney of GFP-C5aR1 reporter mice showed that 28% of CD45-positive cells expressed C5aR1. Dendritic cells were identified as the major C5aR1-expressing population (88.5%) followed by macrophages and neutrophils. Using confocal microscopy, we detected C5aR1 in the kidney mainly on infiltrating cells. In the heart, only infiltrating cells stained C5aR1 positive. To evaluate the role of C5aR1 deficiency in hypertensive injury, an aggravated model of hypertension was used. Unilateral nephrectomy was performed followed by infusion of ANG II (1.5 ng·g−1·min−1) and salt in wild-type ( n = 34) and C5aR1-deficient mice ( n = 32). C5aR1-deficient mice exhibited less renal injury, as evidenced by significantly reduced albuminuria. In contrast, cardiac injury was accelerated with significantly increased cardiac fibrosis and heart weight in C5aR1-deficient mice after ANG II infusion. No effect was found on blood pressure. In summary, the C5a:C5aR1 axis drives end-organ damage in the kidney but protects from the development of cardiac fibrosis and hypertrophy in experimental ANG II-induced hypertension.

Myeloperoxidase (MPO) is an enzyme expressed in neutrophils and monocytes/macrophages. Beside its well-defined role in innate immune defence, it may also be responsible for tissue damage. To identify the role of MPO in the progression of chronic kidney disease (CKD), we investigated CKD in a model of renal ablation in MPO knockout and wild-type mice. CKD was induced by 5/6 nephrectomy. Mice were followed for 10 wk to evaluate the impact of MPO deficiency on renal morbidity. Renal ablation induced CKD in wild-type mice with increased plasma levels of MPO compared with controls. No difference was found between MPO-deficient and wild-type mice regarding albuminuria 1 wk after renal ablation, indicating similar acute responses to renal ablation. Over the next 10 wk, however, MPO-deficient mice developed significantly less albuminuria and glomerular injury than wild-type mice. This was accompanied by a significantly lower renal mRNA expression of the fibrosis marker genes plasminogen activator inhibitor-I, collagen type III, and collagen type IV as well as matrix metalloproteinase-2 and matrix metalloproteinase-9. MPO-deficient mice also developed less renal inflammation after renal ablation, as indicated by a lower infiltration of CD3-positive T cells and F4/80-positive monocytes/macrophages compared with wild-type mice. In vitro chemotaxis of monocyte/macrophages isolated from MPO-deficient mice was impaired compared with wild-type mice. No significant differences were observed for mortality and blood pressure after renal ablation. In conclusion, these results demonstrate that MPO deficiency ameliorates renal injury in the renal ablation model of CKD in mice.

Fraune C, Lange S, Krebs C, Holzel A, Baucke J, Divac N, Schwedhelm E, Streichert T, Velden J, Garrelds IM, Danser AH, Frenay A, van Goor H, Jankowski V, Stahl R, Nguyen G, Wenzel UO. AT(1) antagonism and renin inhibition in mice: pivotal role of targeting angiotensin II in chronic kidney disease. Am J Physiol Renal Physiol 303: F1037-F1048, 2012. First published July 11, 2012; doi:10.1152/ajprenal.00672.2011.-The role of the renin-angiotensin system in chronic kidney disease involves multiple peptides and receptors. Exerting antipodal pathophysiological mechanisms, renin inhibition and AT1 antagonism ameliorate renal damage. However, it is unclear which mechanism exerts better nephroprotection. We compared the renin inhibitor aliskiren with the AT1 antagonist losartan in mice with chronic kidney disease due to renal ablation. Doses were adjusted to equipotent inhibition of the renin-angiotensin system, determined via a dose-response quantifying plasma and renal renin expression. Six-week treatment with either 500 mg/l drinking water losartan or 50 mg.kg(-1).day(-1) aliskiren significantly decreased albuminuria, glomerular damage, and transcription rates of renal injury markers to a similar extent. An array analysis comparing renal gene expression of losartan- and aliskiren-treated mice evaluating > 34,000 transcripts demonstrated regulation for 14 genes only, with small differences. No superior nephroprotection was found by combining losartan and aliskiren. Compared with plasma concentrations, aliskiren accumulated similar to 7- to 29-fold in the heart, liver, lung, and spleen and similar to 156-fold in the kidney. After withdrawal, plasma concentrations dropped to zero within 24 h, whereas renal tissue concentrations declined slowly over days. Withdrawal of aliskiren in mice with chronic kidney disease revealed a significantly delayed re-increase in albuminuria compared with withdrawal of losartan. This study demonstrates equieffective nephroprotection of renin inhibition and AT1 antagonism in mice with chronic kidney disease without additional benefit of combination therapy. These observations underscore the pivotal role of targeting ANG II to reduce renal injury.

Rho kinase signaling regulates inflammatory cell migration and chemokine production. We therefore investigated the mechanisms of Rho-kinase-dependent inflammation in lipopolysaccharide (LPS)-induced renal failure. C57/BL6 mice received intraperitoneal LPS with or without daily treatment with specific Rho kinase inhibitors (Y-27632 or HA-1077; 5 mg/kg). Rho kinase inhibitors were applied in a preventive (12 or 1 h before LPS) or a therapeutic (6 h after LPS) scheme. Both protected renal function and decreased tubular injury in LPS-treated mice. Enhanced Rho kinase activity was inhibited by HA-1077 in capillary endothelial cells, inflammatory cells, and tubuli by analysis of Rho kinase substrate phosphorylation. Early neutrophil influx was reduced by HA-1077 without reduction of the proinflammatory cytokine TNFalpha. In contrast, HA-1077 decreased the influx of monocytes/macrophages coinciding with reduced expression of the NF-kappaB-regulated chemokines CCL5 and CCL2. We therefore examined NF-kappaB signal transduction and found that NF-kappaB p65 phosphorylation and nuclear translocation were reduced by Rho kinase inhibition. IkappaBalpha degradation was not altered during the first 6 h but was reduced by HA-1077 at later time points. NF-kappaB p50-deficient mice were similarly protected from renal injury by Rho kinase inhibition further supporting the prominent role for p65 in Rho kinase inhibition. Together, these data suggest that Rho kinase inhibition by preventive or therapeutic treatment effectively reduced endotoxic kidney injury in part by attenuation of NF-kappaB p65 activation.