Hypertension-induced Renal Disease Research Articles

The adducin saga: pleiotropic genomic targets for precision medicine in human hypertension-vascular, renal, and cognitive diseases.

Hypertension is a leading risk factor for stroke, heart disease, chronic kidney disease, vascular cognitive impairment, and Alzheimer's disease. Previous genetic studies have nominated hundreds of genes linked to hypertension, and renal and cognitive diseases. Some have been advanced as candidate genes by showing that they can alter blood pressure or renal and cerebral vascular function in knockout animals; however, final validation of the causal variants and underlying mechanisms has remained elusive. This review chronicles 40 years of work, from the initial identification of adducin (ADD) as an ACTIN-binding protein suggested to increase blood pressure in Milan hypertensive rats, to the discovery of a mutation in ADD1 as a candidate gene for hypertension in rats that were subsequently linked to hypertension in man. More recently, a recessive K572Q mutation in ADD3 was identified in Fawn-Hooded Hypertensive (FHH) and Milan Normotensive (MNS) rats that develop renal disease, which is absent in resistant strains. ADD3 dimerizes with ADD1 to form functional ADD protein. The mutation in ADD3 disrupts a critical ACTIN-binding site necessary for its interactions with actin and spectrin to regulate the cytoskeleton. Studies using Add3 KO and transgenic strains, as well as a genetic complementation study in FHH and MNS rats, confirmed that the K572Q mutation in ADD3 plays a causal role in altering the myogenic response and autoregulation of renal and cerebral blood flow, resulting in increased susceptibility to hypertension-induced renal disease and cerebral vascular and cognitive dysfunction.

Knockout of γ-Adducin Promotes NG-Nitro-L-Arginine-Methyl-Ester-Induced Hypertensive Renal Injury.

Previous studies identified a region on chromosome 1 associated with NG-nitro-L-arginine methyl ester (L-NAME) hypertension-induced renal disease in fawn-hooded hypertensive (FHH) rats. This region contains a mutant γ-adducin (Add3) gene that impairs renal blood flow (RBF) autoregulation, but its contribution to renal injury is unknown. The present study evaluated the hypothesis that knockout (KO) of Add3 impairs the renal vasoconstrictor response to the blockade of nitric oxide synthase and enhances hypertension-induced renal injury after chronic administration of L-NAME plus a high-salt diet. The acute hemodynamic effect of L-NAME and its chronic effects on hypertension and renal injury were compared in FHH 1Brown Norway (FHH 1BN) congenic rats (WT) expressing wild-type Add3 gene versus FHH 1BN Add3 KO rats. RBF was well autoregulated in WT rats but impaired in Add3 KO rats. Acute administration of L-NAME (10 mg/kg) raised mean arterial pressure (MAP) similarly in both strains, but RBF and glomerular filtration rate (GFR) fell by 38% in WT versus 15% in Add3 KO rats. MAP increased similarly in both strains after chronic administration of L-NAME and a high-salt diet; however, proteinuria and renal injury were greater in Add3 KO rats than in WT rats. Surprisingly, RBF, GFR, and glomerular capillary pressure were 41%, 82%, and 13% higher in L-NAME-treated Add3 KO rats than in WT rats. Hypertensive Add3 KO rats exhibited greater loss of podocytes and glomerular nephrin expression and increased interstitial fibrosis than in WT rats. These findings indicate that loss of ADD3 promotes L-NAME-induced renal injury by altering renal hemodynamics and enhancing the transmission of pressure to glomeruli. SIGNIFICANCE STATEMENT: A mutation in the γ-adducin (Add3) gene in fawn-hooded hypertensive rats that impairs autoregulation of renal blood flow is in a region of rat chromosome 1 homologous to a locus on human chromosome 10 associated with diabetic nephropathy. The present results indicate that loss of ADD3 enhanced NG-nitro-L-arginine methyl ester-induced hypertensive renal injury by altering the transmission of pressure to the glomerulus.

Abstract MP46: Knockout Of Add3 Impairs Autoregulation Of Renal Blood Flow And Promotes Hypertension-induced Renal Injury By Increasing Glomerular Capillary Pressure And Podocyte Loss

Recently, we reported that a mutation in γ-Adducin (ADD3) alters the actin cytoskeleton and is associated with an impaired myogenic response of the afferent arteriole and enhanced hypertension-induced renal disease. However, it remains to be determined whether the loss of ADD3 function promotes renal injury by increasing glomerular capillary pressure (Pgc) and podocyte loss or other mechanisms. The present study compared the time course of changes in renal hemodynamics and the progression of renal injury during the development of DOCA-salt hypertension in FHH 1 BN rats (WT) with an intact myogenic response vs. FHH 1 BN Add3KO rats (Add3KO) in which the myogenic response is impaired. When transmural pressure rose from 40 to 100 mmHg, the inner diameter of the preglomerular artery constricted by 19% (47.7 ± 4.3 to 38.4 ± 3.4 μm, n = 5) in WT, but it dilated by 28% (53.0 ± 2.2 to 67.9 ± 4.3 μm, n = 7) in Add3KO. Pgc was similar (50.1 ± 0.4 vs. 51.2 ± 0.8 mmHg, n = 6) at 100 mmHg, but rose by 6 and 14 mmHg in WT vs. Add3KO when perfusion pressure rose to 150 mmHg. Mean arterial pressure increased similarly and reached 177.7 ± 3.5 vs. 182.6 ± 2.3 mmHg (n = 9) after 3 weeks of DOCA-salt hypertension in WT vs. Add3KO. After 1 week of DOCA-salt hypertension, glomerular filtration rate (GFR) increased by 38% (1.2 ± 0.1 to 1.6 ± 0.1 ml/min/kidney, n = 6) and glomerular nephrin expression decreased by 20% (165.4 ± 4.5 to 131.614 ± 5.2 RFU, n = 7) in Add3KO. Both were unaltered in WT. Proteinuria increased 2 folds in WT (56.9 ± 4.7 to 168.6 ± 26.7 mg/day, n = 12) in the first week of hypertension vs. a 6-fold increase in Add3KO (64.6 ± 4.1 to 446.0 ± 41.9 mg/day, n = 9). After 3 weeks of hypertension, the degree of glomerulosclerosis (3.4 ± 0.1 vs. 2.4 ± 0.1 glomerular injury score, n = 9~12), protein cast formation (9.0% ± 0.8% vs. 4.8% ± 0.4% of area, n = 6), epithelial-mesenchymal transition, interstitial fibrosis (17.9% ± 0.8% vs. 9.5% ± 0.3% of area, n = 6), and inflammation was significantly greater in Add3KO vs. WT. GFR and Pgc were 28% and 19% lower in Add3KO than WT. These results indicate that the impaired myogenic response increases the transmission of pressure to the glomerulus to induce the loss of podocytes, which accelerates the progression of renal injury during the development of hypertension in Add3KO.

Abstract 067: Genetic Complementation Establishes That a K572Q Mutation in Gamma-adducin Plays a Causal Role in Renal Microvascular Dysfunction in FHH and MNS Rats

The Fawn-Hooded hypertensive (FHH) rat is a genetic model of hypertension-induced renal disease. However, the causal genes and pathways involved are unclear. We previously reported that the transfer of a small region in Chr. 1 of Brown-Norway (BN) rats which contains 15 genes, including gamma-Adducin (Add3), into the FHH background restores renal microvascular function and attenuates the development of proteinuria in FHH rats. Our further work identified a K572Q mutation in Add3 in FHH rats as a potential candidate variant in the pathogenesis of renal disease. The present study examined the role of Add3 in the impaired myogenic response of the afferent artery (Af-art) and autoregulation of renal blood flow (RBF) using transgenic and KO rats. RBF increased by 21.5 ± 3.0% in SD. Add3 KO rats (n=7) when mean arterial pressure (MAP) was increased from 100 to 150 mmHg. In contrast, RBF only increased by 3.5 ± 0.9% in wildtype SD rats (n=13). The diameters of the renal Af-art decreased by 12.9 ± 0.8% in SD rats when perfusion pressure was increased from 60 to 120 mmHg, but it increased in SD.Add3 KO rats. The myogenic response of the Af-art in FHH rats was markedly impaired and increased by 8 ± 1.2% when the pressure was increased by from 60 to120 mmHg. The myogenic response was restored, and the diameters of the Af-art decreased by 12 ± 0.7% and 7 ± 1.0% in FHH. 1 BN congenic rats (n=27) and FHH.Add3 transgenic rats that express wt-Add3. RBF increased by 35.1 ± 3.0% when MAP was increased from 100 to 150 mmHg in FHH rats (n=15) versus 7.5 ± 1.7% and 6.0+ 1.3% in FHH.1 BN or a F1 cross of FHH and FHH.1 BN rats (n=8) and FHH.Add3 transgenic rats. The myogenic response of Af-art and autoregulation of RBF were also impaired in MNS rats (n=6) that carry the same K572Q mutation in Add3 as FHH rats. These phenotypes were complemented in a F1 cross of FHH and MNS rats (n=7), but the myogenic response and autoregulation of RBF were restored in an F1 cross of FHH and FHH.1 BN rats with one copy of wt-Add3. These results indicate that the recessive K572Q mutation of Add3 in FHH and MNS rats plays a causal role in renal microvascular dysfunction, which may contribute to the development of chronic kidney disease induced by hypertension in these models.

Hemodynamic basis for the limited renal injury in rats with angiotensin II-induced hypertension.

ANG II is thought to increase the susceptibility to hypertension-induced renal disease (HIRD) via blood pressure (BP)-dependent and BP-independent pathways; however, the quantitative relationships between BP and HIRD have not been examined in ANG II-infused hypertensive rats. We compared the relationship between radiotelemetrically measured BP and HIRD in Sprague-Dawley rats (Harlan) chronically administered ANG II (300-500 ng·kg(-1)·min(-1), n = 19) for 4 wk versus another commonly employed pharmacological model of hypertension induced by the chronic administration of N(ω)-nitro-l-arginine methyl ester (l-NAME, 50 mg·kg(-1)·day(-1), n = 23). [DOSAGE ERROR CORRECTED]. Despite the significantly higher average systolic BP associated with ANG II (191.1 ± 3.2 mmHg) versus l-NAME (179.9 ± 2.5 mmHg) administration, the level of HIRD was very modest in the ANG II versus l-NAME model as evidenced by significantly less glomerular injury (6.6 ± 1.3% vs. 11.3 ± 1.5%, respectively), tubulointerstitial injury (0.3 ± 0.1 vs. 0.7 ± 0.1 injury score, respectively), proteinuria (66.3 ± 10.0 vs. 117.5 ± 10.1 mg/day, respectively), and serum creatinine levels (0.5 ± 0.04 vs. 0.9 ± 0.07 mg/dl, respectively). Given that HIRD severity is expected to be a function of renal microvascular BP transmission, BP-renal blood flow (RBF) relationships were examined in additional conscious rats administered ANG II (n = 7) or l-NAME (n = 8). Greater renal vasoconstriction was observed during ANG II versus l-NAME administration (41% vs. 23% decrease in RBF from baseline). Moreover, administration of ANG II, but not l-NAME, led to a unique BP-RBF pattern in which the most substantial decreases in RBF were observed during spontaneous increases in BP. We conclude that the hemodynamic effects of ANG II may mediate the strikingly low susceptibility to HIRD in the ANG II-infused model of hypertension in rats.

The RenTg Mice: A Powerful Tool to Study Renin-Dependent Chronic Kidney Disease

BackgroundSeveral studies have shown that activation of the renin-angiotensin system may lead to hypertension, a major risk factor for the development of chronic kidney disease (CKD). The existing hypertension-induced CDK mouse models are quite fast and consequently away from the human pathology. Thus, there is an urgent need for a mouse model that can be used to delineate the pathogenic process leading to progressive renal disease. The objective of this study was dual: to investigate whether mice overexpressing renin could mimic the kinetics and the physiopathological characteristics of hypertension-induced renal disease and to identify cellular and/or molecular events characterizing the different steps of the progression of CKD.Methodology/Principal FindingsWe used a novel transgenic strain, the RenTg mice harboring a genetically clamped renin transgene. At 3 months, heterozygous mice are hypertensive and slightly albuminuric. The expression of adhesion markers such as vascular cell adhesion molecule-1 and platelet endothelial cell adhesion molecule-1 are increased in the renal vasculature indicating initiation of endothelial dysfunction. At 5 months, perivascular and periglomerular infiltrations of macrophages are observed. These early renal vascular events are followed at 8 months by leukocyte invasion, decreased expression of nephrin, increased expression of KIM-1, a typical protein of tubular cell stress, and of several pro-fibrotic agents of the TGFβ family. At 12 months, mice display characteristic structural alterations of hypertensive renal disease such as glomerular ischemia, glomerulo- and nephroangio-sclerosis, mesangial expansion and tubular dilation.Conclusions/SignificanceThe RenTg strain develops CKD progressively. In this model, endothelial dysfunction is an early event preceding the structural and fibrotic alterations which ultimately lead to the development of CKD. This model can provide new insights into the mechanisms of chronic renal failure and help to identify new targets for arresting and/or reversing the development of the disease.

Abstract 493: Impact of Renal Vasoconstriction on the Relationship Between Blood Pressure and Renal Injury in Angiotensin II-induced Hypertensive Rats

Ang II is thought to play a prominent role in the development of hypertension-induced renal disease via BP dependent and independent pathways; however the quantitative relationships between BP and renal injury have not been rigorously examined in Ang II-induced hypertension. The major goals of the present study were to assess: 1) the relationship between BP and renal injury in rats with hypertension induced by Ang II vs. renal mass reduction (RMR) and 2) the pressure-flow relationships in conscious Ang II-infused rats. One group of male Sprague-Dawley rats (Charles River) were implanted with a BP radiotransmitter and 10 days later administered Ang II (n=12; 500 ng/kg/min via osmotic minipump) or subjected to 3/4 RMR via right uninephrectomy + infarction of ∼ 1/2 of the left kidney (RKI, n=5). BP was measured continuously and kidneys were perfused fixed at 6 weeks for the assessment of renal injury. In a separate experiment, MAP and RBF (Transonic) were measured in conscious chronically instrumented rats. After recovery from surgery (∼7 days), baseline MAP and RBF were assessed (∼4 hours @ 200 Hz) on 2 consecutive days. Subsequently, rats were administered Ang II (n=6; 500 ng/kg/min) or saline (n=7; sham) via osmotic minipump and MAP and RBF were again assessed every 2-3 days for 10 days. Despite a higher average systolic BP over 6 weeks in Ang II (174±3 mmHg) vs. RKI (165±6 mmHg) rats, glomerulosclerosis (GS) was higher (p<0.05) in RKI (15±7% out of 100 glomeruli) vs. Ang II (6±1% out of 100 glomeruli) rats. Moreover, the slope of the relationship between BP and %GS (Δ%GS/ΔmmHg) was greater in RKI vs. Ang II rats. Both MAP (98±2 vs. 99±3 mmHg) and RBF (8.1±1vs. 8.2±1 ml/min) were similar at baseline in Ang II and sham rats, respectively. MAP was elevated by day 3 (123±6 mmHg) and further increased to 157±5 mmHg by day 10 in Ang II rats. Conversely, RBF was decreased at day 3 (6.6±0.6 ml/min) and the vasoconstriction persisted over the experimental protocol as RBF further decreased to 5.6±0.7 ml/min at day 10 in Ang II rats. In conclusion, Ang II-induced hypertension is associated with a diminished susceptibility to renal injury as compared to rats with RMR likely due, in part, to the AngII-induced vasoconstriction, which reduces BP transmission to the renal microvasculature.

Transfer of the CYP4A region of chromosome 5 from Lewis to Dahl S rats attenuates renal injury

This study examined the effect of transfer of overlapping regions of chromosome 5 that includes (4A(+)) or excludes (4A(-)) the cytochrome P-450 4A (CYP4A) genes from the Lewis rat on the renal production of 20-hydroxyeicosatetraenoic acid (20-HETE) and the development of hypertension-induced renal disease in congenic strains of Dahl salt-sensitive (Dahl S) rats. The production of 20-HETE was higher in the outer medulla of 4A(+) than in Dahl S or 4A(-) rats. Mean arterial pressure (MAP) rose to 190 +/- 7 and 185 +/- 3 mmHg in Dahl S and 4A(-) rats fed a high-salt (HS) diet for 21 days but only to 150 +/- 5 mmHg in the 4A(+) strain. Protein excretion increased to 423 +/- 40 and 481 +/- 37 mg/day in Dahl S and 4A(-) rats vs. 125 +/- 15 mg/day in the 4A(+) strain. Baseline glomerular capillary pressure (Pgc) was lower in 4A(+) rats (38 +/- 1 mmHg) than in Dahl S rats (42 +/- 1 mmHg). Pgc increased to 50 +/- 1 mmHg in Dahl S rats fed a HS diet, whereas it remained unaltered in 4A(+) rats (39 +/- 1 mmHg). Baseline glomerular permeability to albumin (P(alb)) was lower in 4A(+) rats (0.19 +/- 0.05) than in Dahl S or 4A(-) rats (0.39 +/- 0.02). P(alb) rose to approximately 0.61 +/- 0.03 in 4A(-) and Dahl S rats fed a HS diet for 7 days, but it remained unaltered in the 4A(+) rats. The expression of transforming growth factor-beta2 was higher in glomeruli of Dahl S rats than in 4A(+) rats fed either a low-salt (LS) or HS diet. Chronic administration of a 20-HETE synthesis inhibitor (HET0016; 10 mg.kg(-1).day(-1) sc) reversed the fall in MAP and renoprotection seen in 4A(+) rats. These results indicate that the introgression of the CYP4A genes from Lewis rats into the Dahl S rats increases the renal formation of 20-HETE and attenuates the development of hypertension and renal disease.

Discoidin Domain Receptor 1 Null Mice Are Protected against Hypertension-Induced Renal Disease

A frequent complication of hypertension is the development of chronic renal failure. This pathology usually is initiated by inflammatory events and is characterized by the abnormal accumulation of collagens within the renal tissue. The purpose of this study was to investigate the role of discoidin domain receptor 1 (DDR1), a nonintegrin collagen receptor that displays tyrosine-kinase activity, in the development of renal fibrosis. To this end, hypertension was induced with angiotensin in mice that were genetically deficient of DDR1 and in wild-type controls. After 4 or 6 wk of angiotensin II administration, wild-type mice developed hypertension that was associated with perivascular inflammation, glomerular sclerosis, and proteinuria. Systolic pressure increase was similar in the DDR1-deficient mice, but the histologic lesions of glomerular fibrosis and inflammation were significantly blunted and proteinuria was markedly prevented. Immunostaining for lymphocytes, macrophages, and collagens I and IV was prominent in the renal cortex of wild-type mice but substantially reduced in DDR1 null mice. In separate experiments, renal cortical slices of DDR1 null mice showed a blunted response of chemokines to LPS that was accompanied by a considerable protection against the LPS-induced mortality. These results indicate the importance of DDR1 in mediating inflammation and fibrosis. Use of DDR1 inhibitors could provide a completely novel therapeutic approach against diseases that have these combined pathologies.