Dahl Salt-sensitive Hypertensive Rats Research Articles

Cordyceps militaris improves the survival of Dahl salt-sensitive hypertensive rats possibly via influences of mitochondria and autophagy functions

The genus Cordyceps and its specific ingredient, cordycepin, have attracted much attention for multiple health benefits and expectations for lifespan extension. We analyzed whether Cordyceps militaris (CM), which contains large amounts of cordycepin, can extend the survival of Dahl salt-sensitive rats, whose survival was reduced to ∼3 months via a high-salt diet. The survival of these life-shortened rats was extended significantly when supplemented with CM, possibly due to a minimization of the effects of stroke. Next, we analyzed the effect of CM on hypertension-sensitive organs, the central nervous systems (CNS), heart, kidney and liver of these rats. We attempted to ascertain how the organs were improved by CM, and we paid particular attention to mitochondria and autophagy functions. The following results were from CM-treated rats in comparison with control rats. Microscopically, CNS neurons, cardiomyocytes, glomerular podocytes, renal epithelial cells, and hepatocytes all were improved. However, immunoblot and immunohistochemical analysis showed that the expressions of mitochondria-related proteins, ATP synthase β subunit, SIRT3 and SOD2, and autophagy-related proteins, LC3-II/LC3-I ratio and cathepsin D all were reduced significantly in the CNS neurons, but increased significantly in the cells of the other three organs, although p62 was decreased in its expression in all the organs tested. Activity of Akt and mTOR was enhanced but that of AMPK was reduced in the CNS, while such kinase activity was completely the opposite in the other organs. Together, the influence of CM may differ between mitochondria and autophagy functioned between the two organ groups, as mitochondria and autophagy seemed to be repressed and promoted, respectively, in the CNS, while both mitochondria and autophagy were activated in the others. This could possibly be related to the steady or improved cellular activity in both the organs, which might result in the life extension of these rats.

Sustained Activation of Guanylate Cyclase-A with TDT, a Natriuretic Peptide Derivative, Exhibits Cardiorenal Protection in Dahl Salt-Sensitive Hypertensive Rats.

Heart failure often presents with prognosis-relevant impaired renal function. To investigate whether the chronic activation of guanylate cyclase-A (GC-A) protects both heart and kidney, we examined the effects of TDT, a neprilysin (NEP)-resistant natriuretic peptide (NP) derivative, on cardiac and renal dysfunction in Dahl salt-sensitive hypertensive (DS) rats. Pretreatment with NEP or NEP inhibitor did not influence GC-A activation by TDT both in vitro and in vivo, resulting in a long-acting profile of TDT compared with native human atrial NP (hANP). The repeated administration of TDT to DS rats suppressed the progress of cardiac hypertrophy, systolic/diastolic dysfunction, and proteinuria in a dose-dependent manner. Compared with vehicle and hANP, salt diet-induced podocyte injury was reduced by TDT, as analyzed by urinary podocalyxin concentration, renal expression of nephrin mRNA, and glomerular expression of desmin protein. Since glomerular TRPC6 plays detrimental roles in podocyte homeostasis, we examined the renal expression of TRPC6 in DS rats and found that salt diet upregulated the expression of TRPC6. Importantly, TRPC6 induction was significantly decreased in TDT-treated rats, compared with vehicle and hANP. Consistently, in primary-culture podocytes from DS rats, TDT inhibited ATP-induced calcium influx, similar to TRPC inhibitor SKF96365. Finally, TDT-mediated protection of podocytes was abolished by protein kinase G inhibitor KT5823. In conclusion, TDT treatment attenuated heart and kidney dysfunction, accompanied by podocyte protection through inhibition of TRPC6. Thus, long-acting NPs could be a new avenue for treatment of heart failure.

O23-3 - Role of Xanthine Oxidase in Hypertensive Heart Failure in Dahl Salt-sensitive Rats

Aims: Xanthine oxidase (XO) is one of the sources of superoxide production in cardiac myocytes. However, pathophysiological role of XO in hypertensive heart failure has not been clear. Thus, the present study examined impact of high salt intake and XO inhibition on cardiac hypertrophy and fibrosis in hypertensive Dahl salt-sensitive (Dahl-S) rats. Metods: 8-week old, male Dahl-S rats were fed a normal salt diet or a high salt diet for 8 weeks. A part of rats fed the HS diet were treated simultaneously with a XO inhibitor, febuxostat. Results: HS intake increased blood pressure and heart weight, and Fx diminished them. HS intake caused cardiomyocyte hypertrophy and interstitial fibrosis in left ventricle (LV), and FX ameliorated them. HS increased XO activity 4.7 fold and NADPH oxidase activity 1.5 fold, and Fx suppressed XO activity completely and NADPH oxidase activity by 80%. HS increased protein expression of XO, p47phox, angiotensin-converting enzyme, angiotensin II type 1 receptor, transforming growth factor-β1 and activation of extracellular signal-regulated kinase in LV, and Fx reduced them except XO. Conclusion: HS intake induces hypertension, LV hypertrophy and fibrosis with activation of XO, NADPH oxidase and renin-angiotensin (RA) system in Dahl-S rats. Fx inhibits not only XO but also NADPH oxidase and RA system, suggesting that XO inhibition may be an effective therapy for hypertensive heart failure.

Abstract P278: Identification of Differentially Expressed Aortic Genes in Brown Norway Introgressed Chromosome 2 Segments into Hypertensive Dahl Salt Sensitive Rats

Background: Rat chromosome (RNO) 2 introgression from normotensive Brown Norway (BN) rats into hypertensive Dahl salt sensitive (SS) background (consomic SB2) reduced vascular inflammation. We hypothesized that the BN-RNO2 contains genes that reduce vascular inflammation, which could be identified using microRNA (miRNA) and total RNA expression profiling in aorta of congenic rats containing different portions of BN-RNO2 on the SS background. Methods and Results: Twelve-to-13-week-old male SS rats and congenic rats containing the distal portion of BN-RNO2 (SB2a), the middle segment (SB2b) and the proximal segment (SB2e) on the SS background, fed a normal-salt diet, were studied. Systolic blood pressure (SBP) was measured by telemetry. SBP was lower in SB2a and SB2b but not SB2e compared to SS (125±3, 127±6, 138±4 vs 146±2 mm Hg, P <0.05). Total RNA was extracted from aorta and used to construct libraries for small and total RNA sequencing using Illumina HiSeq-2500. The bioinformatics pipeline included: FastQC for quality control, STAR for genome alignment to Rattus norvegicus release-86, mirdeep2 for miRNA annotation and counting, Htseq-count for mRNA and long non-coding RNA annotation and counting; R for differential expression analysis. Differentially expressed miRNAs and genes (mRNA and non-coding RNA) were identified in SB2a vs SS (miRNAs: 3 up and 2 down, genes: 1 up and 3 down), SB2b vs SS (miRNAs: 2 up and 3 down, genes: 67 up and 112 down) and SB2e vs SS (miRNAs: 29 up and 25 down, genes: 12 up and 35 down), with FDR<0.05. Differentially expressed genes encoded within different BN-RNO2 congenic portions were identified in SB2a vs SS (2 down), SB2b vs SS (14 up and 18 down) and SB2e vs SS (1 down). Conclusions and Perspectives: Differentially expressed BN-RNO2 encoded genes were identified in aorta of congenic SB2a, SB2b and SB2e rats. Whether these genes play a role in inflammation or vascular injury remains to be determined.

Abstract P281: Urinary Metabolites Associated With Blood Pressure on a Low- or High-sodium Diet

Dietary salt intake has significant effects on arterial blood pressure and the development of hypertension. Mechanisms underlying salt-dependent changes in blood pressure remain poorly understood. The goal of the present study was to utilize urine samples from the Dietary Approaches to Stop Hypertension (DASH)-Sodium trial and a targeted metabolomic approach to identify associations of urinary metabolites with blood pressure phenotypes on low- or high-sodium intake. We examined urinary levels of metabolites in 103 participants of the DASH-Sodium trial after 30 days on a defined diet containing high sodium (targeting 150 mmol sodium intake per day) or low sodium (50 mmol sodium per day). Systolic or diastolic pressure was 10 or more mmHg higher on the high-sodium intake in 51 of the 103 participants. Targeted chromatography/mass spectrometry analysis was performed in 24-h urine samples for 10 metabolites related to the tricarboxylic acid cycle and 47 amino metabolites. Urinary metabolite levels improved the prediction of classification of blood pressure salt-sensitivity based on race, age and sex. Random forest and generalized linear mixed model analyses identified significant (false discovery rate <0.05) associations between 24 h excretions of β-aminoisobutyric acid, cystine, citrulline, homocysteine and lysine and systolic blood pressure and between cystine and diastolic blood pressure. The differences of 24 h excretion of homocysteine between low- and high-sodium intakes were significantly associated with the differences in diastolic blood pressure. These associations were significant with or without considering demographic factors. Treatment with β-aminoisobutyric acid significantly attenuated high-salt-induced hypertension in Dahl salt-sensitive rats. These findings support the presence of new mechanisms of blood pressure regulation involving metabolic intermediaries.

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.

Abstract P285: Hydralazine Attenuates the Development of Hypertension in the Female Dahl Salt-sensitive Rat in a T Cell-independent Manner

Introduction: Several studies in Dahl salt-sensitive ( DS ) rats suggest that T cells play a role in salt-sensitive hypertension. To further investigate the role of T cells, we compared T cell profiles in hypertensive DS and normotensive Dahl salt-resistant ( DR ) rats as well as in DS rats treated with hydralazine ( HYD ) to attenuate the development of hypertension. Methods: Mean arterial pressure ( MAP ) was measured by telemetry in DS rats (n=13) from 1 to 4.5 months ( mo ) of age. At 1.5 mo, all of the DR (n=8) and half of the DS rats were treated with vehicle (VEH, n=7). The other half of the DS rats (n=6) received HYD (25 mg/kg/day) in the drinking water. At 4.5 mo, renal T helper ( Th ) and cytotoxic ( Tc ) cells were assessed by multicolor flow cytometry. Results: In the DS kidney, the frequency of CD4 + Th cells [(%): DS-VEH, 76±1.2* vs. DR-VEH, 55±0.7; *p<0.0001; n=7-8/group] was higher while the frequency of CD8 + Tc cells [(%): DS-VEH, 14±1.2* vs. DR-VEH, 35±1; *p<0.0001; n=7-8/group] was lower compared to DR rats. 10 weeks of HYD treatment attenuated the age-associated increase in MAP observed in DS rats [p<0.0001, Two-Way ANOVA (time, treatment); MAP (mmHg): DS-VEH, 157±4 vs. DS-HYD, 133±3; *p<0.0004; n=6-7/group]. HYD had no effect on the frequency of CD4 + [(%):77±1.5] or CD8 + [(%):15.5±0.9] T cells in the kidney of DS rats [(CD4 + ): DS-VEH vs. DS-HYD, p=0.83; (CD8 + ): DS-VEH vs. DS-HYD, p=0.5; n=7-8/group]. In summary, the ratio of Th (CD4 + ) to Tc (CD8 + ) cells is higher in the kidney of DS compared to DR rats and HYD had no effect on the T cell profile in the DS rat kidney under conditions in which the MAP was attenuated by 20 mm Hg. Conclusions: These findings indicate the DS rat has more active Th cells in the kidney compared to the DR rat. Our study also suggests that vasodilators can attenuate the development of hypertension in the DS rat in a Th- and Tc-independent manner.

Preventive and therapeutic effect of brozopine on stroke in Dahl Salt-sensitive hypertensive rats

Our aim was to explore the preventive and therapeutic effects of sodium (±)-5-bromo-2-(α-hydroxypentyl) benzoate (brand name: brozopine, BZP) on stroke in Dahl Salt-sensitive (Dahl-SS) hypertensive rats. Dahl-SS rats were fed a high-salt diet to observe the effect of BZP on blood pressure, and brain, heart, and kidney tissues. Additionally, the incidence of stroke was recorded according to the neurological score. The relative mechanisms investigated included anti-oxidative effects and anti-platelet aggregation. BZP reduced the incidence of stroke, neuronal necrosis in the brain, and cell swelling and inflammatory infiltration in the kidney. Its mechanisms were related to the increased activities of gluthatione peroxidase and catalase and the decreased level of plasma nitric oxide. BZP inhibited arachidonic acid (AA) – induced platelet aggregation (IC50: 12µM) rather than that of adenosine diphosphate (ADP) – and/or thrombin-induced platelet aggregation in vitro. Interestingly, BZP inhibited ADP-, thrombin-, or AA-induced platelet aggregation and elevated the level of AMP-activated protein kinase, cyclic guanosine monophosphate, and vasodilator-stimulated-phosphoprotein, and attenuated ATP contents and mitogen-activated protein kinase levels in platelet and inhibited thrombus formation in a carotid artery thrombosis model, dose-dependently, in Dahl-SS hypertensive-induced stroke rats. In conclusion, BZP can have therapeutic and preventive effects on stroke in Dahl-SS hypertensive rats, the mechanisms of which may be related to anti-oxidant, anti-platelet aggregation and anti-thrombus formation.

Dietary salt blunts vasodilation by stimulating epithelial sodium channels in endothelial cells from salt-sensitive Dahl rats.

Our recent studies show that the reduced activity of epithelial sodium channels (ENaC) in endothelial cells accounts for the adaptation of vasculature to salt in Sprague-Dawley rats. The present study examines a hypothesis that enhanced ENaC activity mediates the loss of vasorelaxation in Dahl salt-sensitive (SS) rats. We used the cell-attached patch-clamp technique to record ENaC activity in split-open mesenteric arteries. Western blot and immunofluorescence staining were used to evaluate the levels of aldosterone, ENaC, eNOS and NO. Blood pressure was measured with the tail-cuff method and the artery relaxation was measured with the wire myograph assay. High-salt (HS) diet significantly increased plasma aldosterone and ENaC activity in the endothelial cells of Dahl SS rats. The endothelium-dependent artery relaxation was blunted by HS challenge in these rats. Amiloride, a potent blocker of ENaC, increased both phosphorylated eNOS and NO and therefore prevented the HS-induced loss of vasorelaxation. As, in SS rats, endogenous aldosterone was already elevated by HS challenge, exogenous aldosterone did not further elevate ENaC activity in the rats fed with HS. Eplerenone, a mineralocorticoid receptor antagonist, attenuated the effects of HS on both ENaC activity and artery relaxation. These data suggest that HS diet blunts artery relaxation and causes hypertension via a pathway associated with aldosterone-dependent activation of ENaC in endothelial cells. This pathway provides one of the mechanisms by which HS causes hypertension in Dahl SS rats. This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Lack of Effects of Metformin and AICAR Chronic Infusion on the Development of Hypertension in Dahl Salt-Sensitive Rats.

In the kidney, reabsorption via the epithelial sodium channel (ENaC) is involved in long-term blood pressure control. Previously we demonstrated that ENaC hyperactivity is associated with development of salt-sensitive (SS) hypertension in Dahl SS rats. AMP-activated kinase (AMPK), playing a role in cellular energy homeostasis, has been shown to decrease ENaC activity. Here, we tested whether metformin and AICAR, two drugs that activate AMPK, affect the development of salt-induced hypertension. High salt diet significantly increased mean arterial pressure (MAP) in Dahl SS rats. Blood pressure elevation was accompanied by a short-term decline of heart rate and increased circadian arterial pressure dipping. Metformin and AICAR were delivered intravenously at doses of 200 and 20 mg/kg/day, respectively. However, both control and drug-treated groups had similar development of high blood pressure within 3 weeks of 8% NaCl dietary salt intake. In the metformin-treated animals MAP reached 164.9 ± 9.1 mmHg, which was not significantly different from the control group (171.8 ± 5.6 mmHg). Patch clamp analysis revealed that the metformin-treated rats had no difference in the activity of ENaC. AICAR treatment also did not affect the development of hypertension and kidney injury. MAP reached 182.8 ± 4.8 and 178.0 ± 2.8 mmHg in AICAR and vehicle treated groups, respectively. Of note, we found that high-salt diet activated AMPK in the Dahl SS rats, and treatment with these AMPK activators had no significant further effect on AMPK activity. We conclude that AMPK activators, at least under these conditions, do not affect development of hypertension during high-salt diet in the Dahl SS rat model.

Knockout of matrix metalloproteinase‐9 rescues the development of cognitive impairments in hypertensive Dahl salt sensitive rats

MMP‐9 is a member of the matrix metalloproteinases family of enzymes that degrade collagen and fibronectin. It regulates neutrophil migration cross the basement membrane, and plays an important role in angiogenesis and extracellular matrix remodeling associated with various physiological or pathological processes. Recent studies indicated that the expression of MMP‐9 is elevated after cerebral ischemia and is involved in accelerating matrix degradation and disrupting the blood‐brain barrier. MMP9 has a diverse effect in Alzheimer's disease (AD), it is neurotoxic by indirectly facilitating tau aggregation, but evidence also suggested that it may contribute to clearance of amyloid‐beta plaques by degrading the fibrils. However, very little is known about whether MMP9 modulates the progression of stroke, cognitive impairments or AD, and whether the mechanisms are involved in the regulation of cerebral vascular function. The present study examined the role of MMP9 in the development of hypertension‐induced cognitive impairments using a MMP9 knockout (KO) rat in the Dahl salt sensitive (SS) genetic background that we created. Baseline mean arterial pressure measured by telemetry was similar in 12‐week old MMP9 KO (n = 8) and SS rats (n = 49) fed a low salt diet, and averaged 125± 2 vs. 119 ± 2 mmHg, respectively. Proteinuria was significantly lower in MMP9 KO rats than in SS rats fed a low salt diet (60 ± 5 mg/day, n = 22 versus 101 ± 8 mg/day, n = 19). Protein excretion remained significantly lower in MMP9 KO than SS rats fed a 8% NaCl diet for 3 weeks (248 ± 26 mg/day, n=11 vs. 437 ± 39 mmHg, n = 17). The diameter of the isolated perfused middle cerebral artery (MCA) decreased to 78 ± 7 % in MMP9 KO rats when pressure was increased from 40 to 140 mmHg. In contrast, the myogenic response of the MCA isolated from SS rats did not constrict. CBF increased by 27 ± 2% (n = 8) in MMP9 KO than in SS rats (64 ± 4%, n = 10), respectively, when MAP was increased from 100 to 180 mmHg. CBF fell by 30 ± 3% (n = 9) in hypertensive MMP9 KO rats vs. 51 ± 2% (n = 10) in hypertensive SS rats when MAP was decreased from 100 to 40 mmHg. The MMP9 KO rats were 2 times as fast in escaping from an eight‐arm water maze in comparison with SS rats after induction of hypertension with a high salt diet for 3 weeks, suggesting the learning and memory deficits in hypertensive SS rats were rescued. These findings indicate that knockout of MMP9 protects against the development of proteinuria, enhances the myogenic response and autoregulation of cerebral blood flow and rescues the progression of cognitive dysfunction in hypertensive SS rats. Our studies suggest that the role of MMP9 in cognitive impairments may be involved in the regulation of cerebral vascular function. Further research is needed to understand the mechanism of MMP9 to design specific drugs and devise therapeutic strategies for dementia.Support or Funding InformationThis study was supported by grants HL36279 (RJR) and DK104184 (RJR), AG050049 (FF), P20GM104357 (RJR and FF) from the National Institutes of Health; 16GRNT31200036 (FF) from the American Heart Association. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

High fat diet increases salt sensitivity and promotes metabolic disorder‐independent hypertension in Dahl salt sensitive rats

Salt sensitivity of blood pressure is common in obesity associated hypertension and may have a neurogenic basis. We and others have previously reported that high fat (HF) diet promotes hypertension in Dahl salt sensitive (SS) male rats ingesting a “normal” salt diet (0.33% NaCl). It is unclear if a low salt intake would reduce blood pressure in this model of obesity‐associated hypertension. Therefore in the current study Dahl SS rats were fed a normal fat (NF, 10% kcal from fat) and HF (60% kcal from fat) diet with different salt contents for 24–26 weeks after weaning (3 weeks of age). In rats fed a diet containing 0.24–0.33% NaCl (the normal salt content (NS) in rodent diets), HFNS (n=9) rats had a much higher MAP than NFNS rats (n=10) at the end of the study (158±1 mmHg versus 130±1 mmHg, P<0.05), confirming our previous findings. However, in low salt fed rats (LS, 0.1% NaCl), MAP at the end of the study was only slightly higher in HFLS (n=4) than NFLS (n=5) rats (131±1 mmHg vs 121±3 mmHg, P<0.05). Body weight was not significantly greater, but visceral adipose accumulation was higher, in HFNS and HFLS rats compared to NFNS and NFLS fed rats, respectively. HF fed rats did not show significant alterations in plasma levels of fasting glucose, insulin, leptin, aldosterone and serum creatinine compared to NF rats. Only HFNS rats showed hyperlipidemia and only NFLS rats showed lower plasma urea BUN levels than the other groups of rats. HFNS rats had a larger depressor response to ganglion blockade than did NFNS rats, but this was not observed in HFLS rats compared to NFLS animals. HF diet did not affect the mesenteric arterial (MA) contractile responses to neurotransmitters (norepinephrine and ATP), but MA from HFNS rats exhibited significantly increased wall‐thickness (and cardiac hypertrophy) compared to NFNS rats. Morphological studies did not reveal greater fibrosis in adventitia of mesenteric, intrarenal or coronary arteries in HF rats, suggesting arterial hyperplasia accounted for arterial remodeling in HFNS rats. Our studies suggested that obesity‐associated hypertension in Dahl SS rats is salt‐sensitive and neurogenic, but not associated with obvious metabolic disorders.Support or Funding InformationSupported by NIH2P01HL070687‐11A1

Up-Regulation of the Voltage-Gated KV2.1 K+ Channel in the Renal Arterial Myocytes of Dahl Salt-Sensitive Hypertensive Rats.

Salt-sensitive hypertension induces renal injury via decreased blood flow in the renal artery (RA), and ion channel dysfunction in RA myocytes (RAMs) may be involved in the higher renal vascular resistance. We examined the effects of several voltage-gated K+ (KV) channel blockers on the resting tension in endothelium-denuded RA strips and delayed-rectifier K+ currents in RAMs of Dahl salt-sensitive hypertensive rats (Dahl-S) fed with low- (Dahl-LS) and high-salt diets (Dahl-HS). The tetraethylammonium (TEA)-induced contraction in RA strips were significantly larger in Dahl-HS than Dahl-LS. Correspondingly, TEA-sensitive KV currents were significantly larger in the RAMs of Dahl-HS than Dahl-LS. Among the TEA-sensitive KV channel subtypes, the expression levels of KV2.1 transcript and protein were significantly higher in the RA of Dahl-HS than Dahl-LS, while those of KV1.5, KV7.1, and KV7.4 transcripts was comparable in two groups. KV2.1 currents detected as the guangxitoxin-1E-sensitive component were larger in the RAMs of Dahl-HS than Dahl-LS. These suggest that the up-regulation of the KV2.1 channel in RAMs may be involved in the compensatory mechanisms against decreased renal blood flow in salt-sensitive hypertension.

Endoplasmic reticulum stress inhibition limits the progression of chronic kidney disease in the Dahl salt-sensitive rat.

Proteinuria is one of the primary risk factors for the progression of chronic kidney disease (CKD) and has been implicated in the induction of endoplasmic reticulum (ER) stress. We hypothesized that the suppression of ER stress with a low molecular weight chemical chaperone, 4-phenylbutyric acid (4-PBA), would reduce the severity of CKD and proteinuria in the Dahl salt-sensitive (SS) hypertensive rat. To induce hypertension and CKD, 12-wk-old male rats were placed on a high-salt (HS) diet for 4 wk with or without 4-PBA treatment. We assessed blood pressure and markers of CKD, including proteinuria, albuminuria, and renal pathology. Furthermore, we determined if HS feeding resulted in an impaired myogenic response, subsequent to ER stress. 4-PBA treatment reduced salt-induced hypertension, proteinuria, and albuminuria and preserved myogenic constriction. Furthermore, renal pathology was reduced with 4-PBA treatment, as indicated by lowered expression of profibrotic markers and fewer intratubular protein casts. In addition, ER stress in the glomerulus was reduced, and the integrity of the glomerular filtration barrier was preserved. These results suggest that 4-PBA treatment protects against proteinuria in the SS rat by preserving the myogenic response and by preventing ER stress, which led to a breakdown in the glomerular filtration barrier. As such, alleviating ER stress serves as a viable therapeutic strategy to preserve kidney function and to delay the progression of CKD in the animal model under study.

Abstract P291: High Fat Diet Promotes Hypertension and Vascular Remodeling but Not Vascular Fibrosis or Altered Contractility in Dahl Salt Sensitive Rats

Obesity associated hypertension in rodent models is commonly associated with altered vascular reactivity to sympathetic neurotransmitters and inflammation-induced vascular remodeling/fibrosis. Dahl salt-sensitive (SS) rats exhibit elevated sympathetic activity and vascular remodeling. We hypothesized that diet-induced obesity in Dahl SS rats would promote hypertension, vascular dysfunction and remodeling/fibrosis. Male Dahl SS rats were placed on high fat diet (HFD, 60% kcal from fat with final concentrations of 0.33% NaCl and 1% K + , n=5) or normal-fat diet (NFD; 10% kcal from fat, 0.24% NaCl, 0.36% K + , n=5) for 24-26 weeks after weaning (3 weeks of age). Compared with NFD rats, HFD rats displayed severe hypertension (MAP, 165±4 mmHg vs 133±6 mmHg, P<0.05), higher body-weight (470±6g vs 433±7g, P<0.05), and hyperlipidemia (cholesterol, 211±22 mg/dl vs 138±23 mg/dl, P=0.05). HFD rats did not show significant changes in plasma levels of fasting glucose (85±5 mg/dl vs 75±5 mg/dl), insulin (2.6±0.8 ng/ml vs 2.2±1.1 ng/ml), leptin (0.77±0.18 ng/ml vs 0.44±0.06 ng/ml), or aldosterone (249±3 pg/ml vs 234±3 pg/ml) (all P>0.05). HFD did not affect pressurized mesenteric arterial (~300 μm inner diameter, 60 mmHg) reactivity to norepinephrine or ATP in vitro . Pressurized mesenteric arteries from HFD rats displayed thicker walls (Ca 2+ free buffer, 40±1 μm vs 36±1 μm, P<0.05), but showed slightly increased distensibility. Morphological studies did not reveal greater fibrosis in adventitia of mesenteric, intrarenal and coronary arteries from HFD rats. However, HFD induced inflammation in mesenteric perivascular adipose tissue, as shown by increased CD3 positive cell infiltration and histological evidence of fibrosis and angiogenesis. Our studies indicate that HFD in male Dahl SS rats promotes hypertension, perivascular adipose tissue inflammation and vascular remodeling, but not vascular fibrosis. Alteration of vascular contractility to sympathetic neurotransmitters, however, is not required for obesity associated hypertension in Dahl SS rats.

Abstract 051: A Panel of CRISPR/Cas9 Genome Edited Rat Models Define Quantitative Trait Nucleotides within a Novel Rat Long Non-coding RNA Implicated in Cardiovascular Disease

This study is focused on a GWAS locus for cardiovascular disease (QT-interval) on human chromosome 17. The homologous genomic segment of this human locus was previously mapped with high resolution to <42.5 kb on rat chromosome 10. The locus in rats regulates both QT-interval and blood pressure and contains a novel long non-coding RNA (lncRNA), with a large 19bp deletion/insertion polymorphism observed between the strains used to map the locus. Characterization of this novel lncRNA using rapid amplification of cDNA ends (RACE) provided evidence for the presence of more than a single isoform of the lncRNA. To further assess the role of this locus, a panel of CRISPR/Cas9 based gene-edited ‘knockout’ models of the lncRNA was developed. The lncRNA targeted rats were developed on the genomic background of the hypertensive Dahl salt-sensitive rats and harbored varied disruptions around the critical 19bp region. The rat strains with the disrupted lncRNA sequences had a significantly elevated blood pressure compared with the controls. QT-interval is currently being examined. Overall, this is the first demonstration of a CRISPR/Cas9 based targeted gene-editing approach applied to identify a novel lncRNA as a Blood Pressure Quantitative Trait Locus.

Retinoblastoma-associated protein 140 as a candidate for a novel etiological gene to hypertension

ABSTRACTGene discovery in animal models may lead to the revelation of therapeutic targets for essential hypertension as well as mechanistic insights into blood pressure (BP) regulation. Our aim was to identify a disease-causing gene for a component of polygenic hypertension contrasting inbred hypertensive Dahl salt-sensitive (DSS) and normotensive Lewis rats. The chromosome segment harboring a quantitative trait locus (QTL), C16QTL, was first isolated from the rat genome via congenic strains. A candidate gene responsible for C16QTL causing a BP difference between DSS and Lewis rats was then identified using molecular analyses combining our independently-conducted total genome and gene-specific sequencings. The retinoblastoma-associated protein 140 (Rap140)/family with sequence similarity 208 member A (Fam208a) is the only candidate gene supported to be C16QTL among three genes in genome block 1 present in the C16QTL-residing interval. A mode of its actions could be to influence the expressions of genes that are downstream in a pathway potentially leading to BP regulation such as that encoding the solute carrier family 7 (cationic amino acid transporter, y+ system) member 12 (Slc7a12), which is specifically expressed in kidneys. Thus, Rap140/Fam208a probably encoding a transcription factor is the strongest candidate for a novel BP QTL that acts via a putative Rap140/Fam208a–Slc7a12-BP pathway. These data implicate a premier physiological role for Rap140/Fam208 beyond development and a first biological function for the Slc7a12 protein in any organism.

Aberrant Glycosylation in the Left Ventricle and Plasma of Rats with Cardiac Hypertrophy and Heart Failure.

Targeted proteomics focusing on post-translational modifications, including glycosylation, is a useful strategy for discovering novel biomarkers. To apply this strategy effectively to cardiac hypertrophy and resultant heart failure, we aimed to characterize glycosylation profiles in the left ventricle and plasma of rats with cardiac hypertrophy. Dahl salt-sensitive hypertensive rats, a model of hypertension-induced cardiac hypertrophy, were fed a high-salt (8% NaCl) diet starting at 6 weeks. As a result, they exhibited cardiac hypertrophy at 12 weeks and partially impaired cardiac function at 16 weeks compared with control rats fed a low-salt (0.3% NaCl) diet. Gene expression analysis revealed significant changes in the expression of genes encoding glycosyltransferases and glycosidases. Glycoproteome profiling using lectin microarrays indicated upregulation of mucin-type O-glycosylation, especially disialyl-T, and downregulation of core fucosylation on N-glycans, detected by specific interactions with Amaranthus caudatus and Aspergillus oryzae lectins, respectively. Upregulation of plasma α-l-fucosidase activity was identified as a biomarker candidate for cardiac hypertrophy, which is expected to support the existing marker, atrial natriuretic peptide and its related peptides. Proteomic analysis identified cysteine and glycine-rich protein 3, a master regulator of cardiac muscle function, as an O-glycosylated protein with altered glycosylation in the rats with cardiac hypertrophy, suggesting that alternations in O-glycosylation affect its oligomerization and function. In conclusion, our data provide evidence of significant changes in glycosylation pattern, specifically mucin-type O-glycosylation and core defucosylation, in the pathogenesis of cardiac hypertrophy and heart failure, suggesting that they are potential biomarkers for these diseases.

Role of Nox4 and p67phox subunit of Nox2 in ROS production in response to increased tubular flow in the mTAL of Dahl salt-sensitive rats.

Nox4 and Nox2 are the most abundant NADPH oxidases (Nox) in the kidney and have been shown to contribute to hypertension, renal oxidative stress, and injury in Dahl salt-sensitive (SS) hypertensive rats. The present study focused on the role of Nox4 and p67phox/Nox2 in the generation of H2O2 and O2 (·-) in the renal medullary thick ascending limb of Henle (mTAL) of SS rats in response to increasing luminal flow (from 5 to 20 nl/min). Nox4 and p67phox/Nox2 genes were found to be expressed in the mTAL of SS rats. Responses of SS rats were compared with those of SS rats with knockout of Nox4 (SS(Nox4-/-)) or functional mutation of p67phox (SS(p67phox-/-)). Nox4 was the dominant source of increased intracellular H2O2 production in response to increased luminal flow as determined using the fluorescent dye peroxyfluor 6-AM (PF6-AM). The rate of mitochondrial H2O2 production [as determined by mitochondria peroxy yellow 1 (mitoPY1)] was also significantly reduced in SS(Nox4-/-) compared with SS rats, but not in SS(p67phox-/-) rats. In contrast, intracellular superoxide (O2 (·-)) production (the ratio of ethidium to dihydroethidium) in the mTAL of SS(Nox4-/-) rats was nearly identical to that of SS rats in response to luminal flow, indicating that Nox4 made no measurable contribution. mTAL O2 (·-) production was reduced in SS(p67phox-/-) compared with SS rats at the lower luminal flow of 5 nl/min and progressively increased when perfusion was changed to 20 nl/min. We conclude that increased mTAL luminal flow results in increases in intracellular and mitochondrial H2O2, which are dependent on the presence of Nox4, and that p67phox/Nox2 accounts solely for increases in O2 (·-) production.

Glucose-independent renoprotective mechanisms of the tissue dipeptidyl peptidase-4 inhibitor, saxagliptin, in Dahl salt-sensitive hypertensive rats

Although previous studies have shown an important role of renal dipeptidyl peptidase-4 (DPP-4) inhibition in ameliorating kidney injury in hypertensive rats, the renal distribution of DPP-4 and mechanisms of renoprotective action of DPP-4 inhibition remain unclear. In this study, we examined the effects of the DPP-4 inhibitor saxagliptin on DPP-4 activity in renal cells (using in situ DPP-4 staining) and on renal gene expression related to inflammation and fibrosis in the renal injury in hypertensive Dahl salt-sensitive (Dahl-S) rats. Male rats fed a high-salt (8% NaCl) diet received vehicle (water) or saxagliptin (12.7mg/kg/day) for 4 weeks. Blood pressure (BP), serum glucose and 24-h urinary albumin and sodium excretions were measured, and renal histopathology was performed. High salt-diet increased BP and urinary albumin excretion, consequently resulting in glomerular sclerosis and tubulointerstitial fibrosis. Although saxagliptin did not affect BP and blood glucose levels, it significantly ameliorated urinary albumin excretion. In situ staining showed DPP-4 activity in glomerular and tubular cells. Saxagliptin significantly suppressed DPP-4 activity in renal tissue extracts and in glomerular and tubular cells. Saxagliptin also significantly attenuated the increase in inflammation and fibrosis-related gene expressions in the kidney. Our results demonstrate that saxagliptin inhibited the development of renal injury independent of its glucose-lowering effect. Glomerular and tubular DPP-4 inhibition by saxagliptin was associated with improvements in albuminuria and the suppression of inflammation and fibrosis-related genes. Thus, local glomerular and tubular DPP-4 inhibition by saxagliptin may play an important role in its renoprotective effects in Dahl-S rats.