A Salt-Induced Reno-Cerebral Reflex Activates Renin-Angiotensin Systems and Promotes CKD Progression

High salt diet impairs cerebral blood flow regulation via salt-induced angiotensin II suppression

OBJECTIVES

This study sought to determine whether salt-induced ANG II suppression contributes to impaired CBF autoregulation.

METHODS

Cerebral autoregulation was evaluated with LDF during graded reductions of blood pressure. Autoregulatory responses in rats fed HS (4% NaCl) diet vs LS (0.4% NaCl) diet were analyzed using linear regression analysis, model-free analysis, and a mechanistic theoretical model of blood flow through cerebral arterioles.

RESULTS

Autoregulation was intact in LS-fed animals as MAP was reduced via graded hemorrhage to approximately 50 mm Hg. Short-term (3 days) and chronic (4 weeks) HS diet impaired CBF autoregulation, as evidenced by progressive reductions of laser Doppler flux with arterial pressure reduction. Chronic low dose ANG II infusion (5 mg/kg/min, i.v.) restored CBF autoregulation between the pre-hemorrhage MAP and 50 mm Hg in rats fed short-term HS diet. Mechanistic-based model analysis showed a reduced myogenic response and reduced baseline VSM tone with short-term HS diet, which was restored by ANG II infusion.

CONCLUSIONS

Short-term and chronic HS diet lead to impaired autoregulation in the cerebral circulation, with salt-induced ANG II suppression as a major factor in the initiation of impaired CBF regulation.

Targeted Ablation of Distal Cerebrospinal Fluid-Contacting Nucleus Alleviates Renal Fibrosis in Chronic Kidney Disease

The potential function of distal cerebrospinal fluid-contacting nucleus (dCSF-CNs) in chronic kidney disease (CKD) development is poorly understood. We hypothesized that dCSF-CNs might affect the renin-angiotensin system (RAS) in kidney injury progression, with dCSF-CNs ablation potentially alleviating local RAS and renal fibrosis in rats after five-sixths nephrectomy (5/6Nx). Part of rats were randomly administered artificial cerebrospinal fluid (aCSF) intracerebroventricularly (icv), followed by 5/6Nx or sham operation; and other part of rats were administered Cholera toxin B subunit conjugated with saporin (CB-SAP) for dCSF-CNs lesion before 5/6Nx. The effect of CB-SAP on dCSF-CNs ablation was confirmed by double immunofluorescence staining. RAS component, NOX₂ and c-fos levels in the subfornical organ (SFO), hypothalamic paraventricular nucleus (PVN) and hippocampus, as well as tyrosine hydroxylase (TH) and c-fos positive cells in rostral ventrolateral medulla (RVLM) were assessed. Next, the levels of RAS components (angiotensinogen [AGT], angiotensin-converting enzyme [ACE], Ang II type 1 receptor [AT1R], angiotensin-converting enzyme 2 [ACE2], and Mas receptor), NADPH oxidases (NOX₂ and catalase), inflammatory cytokines (monocyte chemotactic protein 1 [MCP-1] and IL-6), and fibrotic factors (fibronectin and collagen I) were assessed. Less CB-labeled neurons were found in dCSF-CNs of CB-SAP-treated rats compared with 5/6Nx animals. Meanwhile, CB-SAP downregulated AGT, Ang II, AT1R, NOX₂, catalase, MCP-1, IL-6, fibronectin, and collagen I, and upregulated ACE2 and Mas receptor, compared with CKD rats. More TH and c-fos positive cells were found in RVLM of 5/6Nx rats but the number decreased after dCSF-CNs ablation. Targeted dCSF-CNs ablation could alleviate renal inflammation and fibrosis in chronic kidney injury by inhibiting cerebral and renal RAS/NADPH oxidase.

A renal-cerebral-peripheral sympathetic reflex mediates insulin resistance in chronic kidney disease

Background

Insulin resistance (IR) complicates chronic kidney disease (CKD). We tested the hypothesis that CKD activates a broad reflex response from the kidneys and the white adipose tissue to impair peripheral glucose uptake and investigated the role of salt intake in this process.

Methods

5/6-nephrectomized rats were administered normal- or high-salt for 3 weeks. Conclusions were tested in 100 non-diabetic patients with stage 3–5 CKD.

Findings

High-salt in 5/6-nephrectomized rats decreased insulin-stimulated 2-deoxyglucose uptake >25% via a sympathetic nervous system (SNS) reflex that linked the IR to reactive oxygen species (ROS) and the renin-angiotensin system (RAS) in brain and peripheral tissues. Salt-loading in CKD enhanced inflammation in adipose tissue and skeletal muscle, and enhanced the impairment of insulin signaling and Glut4 trafficking. Denervation of the kidneys or adipose tissue or deafferentation of adipose tissue improved IR >40%. In patients with non-diabetic CKD, IR was positively correlated with salt intake after controlling for cofounders (r = 0.334, P = 0.001) and was linked to activation of the RAS/SNS and to impaired glucose uptake in adipose tissue and skeletal muscle, all of which depended on salt intake.

Interpretation

CKD engages a renal/adipose-cerebral-peripheral sympathetic reflex that activates the RAS/ROS axes to promote IR via local inflammation and impaired Glut4 trafficking that are enhanced by high-salt intake. The findings point to a role for blockade of RAS or α-and-β-adrenergic receptors to reduce IR in patients with CKD.

Fund

National Natural Science Foundation of China.

High Salt Enhances Reactive Oxygen Species and Angiotensin II Contractions of Glomerular Afferent Arterioles From Mice With Reduced Renal Mass

High salt, Ang II (angiotensin II), and reactive oxygen species enhance progression of chronic kidney disease. We tested the hypothesis that a high salt intake generates specific reactive oxygen species to enhance Ang II contractions of afferent arterioles from mice with reduced renal mass (RRM). C57BL/6 mice were subjected to surgical RRM or sham operations and received 6% or 0.4% NaCl salt diet for 3 months. Ang II contractions were measured in perfused afferent arterioles and superoxide (O2-) and hydrogen peroxide (H2O2) by fluorescence microscopy. RRM enhanced the afferent arteriolar gene expression for p47phox and neutrophil oxidase (NOX) 2 and high salt intake in RRM mice enhanced gene expression for angiotensin type 1 receptors, POLDIP2 and NOX4 and reduced catalase. High salt in mice with RRM enhanced arteriolar O2- and H2O2 generation and maximal contractions to Ang II (10-6 mol/L) that were dependent on O2- because they were prevented by gene deletion of p47phox and on H2O2 because they were prevented by transgenic smooth muscle cell expression of catalase (tgCAT-SMC) and POLDIP2 gene deletion. Three months of tempol normalized arteriolar reactive oxygen species and Ang II contractions. However, arteriolar contractions to lower concentrations of Ang II (10-8 to 10-11 mol/L) were paradoxically inhibited by H2O2 and POLDIP2. In conclusion, both O2- from p47phox/NOX2 and H2O2 from NOX4/POLDIP2 enhance maximal arteriolar Ang II contractions from RRM mice during high salt, but H2O2 and NOX4/POLDIP2 reduce the sensitivity to lower concentrations of Ang II by >100-fold. Tempol prevents all of these changes in function.

Urinary angiotensinogen predicts progressive chronic kidney disease after an episode of experimental acute kidney injury

One of the major obstacles to prevent AKI-CKD transition is the lack of effective methods to follow and predict the ongoing kidney injury after an AKI episode. In the present study, we test the utility of urinary angiotensinogen (UAGT) for dynamically evaluating renal structural changes and predicting AKI-CKD progression by using both mild and severe bilateral renal ischemia/reperfusion injury mice. UAGT returns to pre-ischemic levels 14 days after mild AKI followed by kidney architecture restoration, whereas sustained increase in UAGT accompanies by ongoing renal fibrosis after severe AKI. UAGT at day 14-42 correlates with renal fibrosis 84 days after AKI. For predicting fibrosis at day 84, the area under receiver operating characteristics curve of UAGT at day 14 is 0.81. Persistent elevation in UAGT correlates with sustained activation of intrarenal renin-angiotensin system (RAS) during AKI-CKD transition. Abrogating RAS activation post AKI markedly reduced renal fibrosis, with early RAS intervention (from 14 days after IRI) more beneficial than late intervention (from 42 days after IRI) in alleviating fibrosis. Importantly, UAGT decreases after RAS intervention, and its level at day 14-28 correlates with the extent of renal fibrosis at day 42 post RAS blockade. A pilot study conducted in patients with acute tubular necrosis finds that compared with those recovered, patients with AKI-CKD progression exhibits elevated UAGT during the 3-month follow-up after biopsy. Our study suggests that UAGT enables the dynamical monitoring of renal structural recovery after an AKI episode and may serve as an early predictor for AKI-CKD progression and treatment response.

Cross-talks between the kidneys and the central nervous system in multiple sclerosis

Multiple sclerosis (MS) is an inflammatory demyelinating disease, which is considered as a common autoimmune disorder in young adults. A growing number of evidences indicated that the impairment in non-neural tissues plays a significant role in pathology of MS disease. There are bidirectional relationship, metabolic activities and functional similarity between central nervous system (CNS) and kidneys which suggest that kidney tissue may exert remarkable effects on some aspects of MS disorder and CNS impairment in these patients compels the kidney to respond to central inflammation. Recently, it has been well documented that hormonal secretion possesses the important role on CNS abnormalities. In this regard, due to the functional similarity and significant hormonal and non-hormonal relationship between CNS and kidneys, we hypothesized that kidneys exert significant effect on initiation, progression or amelioration of MS disease which might be regarded as potential therapeutic approach in the treatment of MS patients in the future.

Effect of Salt Intervention on Serum Levels of Fibroblast Growth Factor 23 (FGF23) in Chinese Adults: An Intervention Study

Background

Fibroblast growth factor 23 (FGF23), a prominent regulator of phosphate and calcium metabolism, regulates sodium excretion in distal tubules through sodium-chloride cotransporter. This effect regulates blood pressure. Salt intake exerts effects on serum levels of FGF23 in mice. The aim of this study was to explore whether salt intervention affects serum concentrations of FGF23 in Chinese adults.

Material/Methods

We enrolled 44 participants from Lantian, a rural community of Shaanxi, China. All participants were maintained on a three-day normal diet, which was sequentially followed by a seven-day low-Na⁺ diet and seven-day high-Na⁺ diet. Serum FGF23 concentrations were assessed by ELISA.

Results

Serum FGF23 concentrations elevated during low-salt diet compared with levels at baseline (66.20±44.21 pg/mL versus 86.77±53.74 pg/mL, p<0.05) and remarkably decreased when changed from low to high salt intake (86.77±53.74 pg/mL versus 49.26±42.67 pg/mL, p<0.001). Responses of FGF23 to salt intervention were more prominent in normotensive, older than 60 years, BMI <24 kg/m² and salt-resistant individuals. Furthermore, a significant inverse correlation was observed between 24-hour urinary sodium and serum concentrations of FGF23 after adjusting age, sex, BMI and hypertension status.

Conclusions

Dietary salt intervention significantly affects serum FGF23 in Chinese adults.

Maternal high-salt diet alters redox state and mitochondrial function in newborn rat offspring's brain

Excessive salt intake is a common feature of Western dietary patterns, and has been associated with important metabolic changes including cerebral redox state imbalance. Considering that little is known about the effect on progeny of excessive salt intake during pregnancy, the present study investigated the effect of a high-salt diet during pregnancy and lactation on mitochondrial parameters and the redox state of the brains of resulting offspring. Adult female Wistar rats were divided into two dietary groups (n 20 rats/group): control standard chow (0·675 % NaCl) or high-salt chow (7·2 % NaCl), received throughout pregnancy and for 7 d after delivery. On postnatal day 7, the pups were euthanised and their cerebellum, hypothalamus, hippocampus, prefrontal and parietal cortices were dissected. Maternal high-salt diet reduced cerebellar mitochondrial mass and membrane potential, promoted an increase in reactive oxygen species allied to superoxide dismutase activation and decreased offspring cerebellar nitric oxide levels. A significant increase in hypothalamic nitric oxide levels and mitochondrial superoxide in the hippocampus and prefrontal cortex was observed in the maternal high-salt group. Antioxidant enzymes were differentially modulated by oxidant increases in each brain area studied. Taken together, our results suggest that a maternal high-salt diet during pregnancy and lactation programmes the brain metabolism of offspring, favouring impaired mitochondrial function and promoting an oxidative environment; this highlights the adverse effect of high-salt intake in the health state of the offspring.

Myeloid CD11c+ Antigen-Presenting Cells Ablation Prevents Hypertension in Response to Angiotensin II Plus High-Salt Diet

Increasing evidence shows that antigen-presenting cells (APCs) are involved in the development of inflammation associated to hypertension. However, the potential role of APCs in the modulation of renal sodium transport has not been addressed. We hypothesized that APCs participate in renal sodium transport and, thus, development of high blood pressure in response to angiotensin II plus a high-salt diet. Using transgenic mice that allow the ablation of CD11c^high APCs, we studied renal sodium transport, the intrarenal renin-angiotensin system components, blood pressure, and cardiac/renal tissue damage in response to angiotensin II plus a high-salt diet. Strikingly, we found that APCs are required for the development of hypertension and that the ablation/restitution of APCs produces rapid changes in the blood pressure in mice with angiotensin II plus a high-salt diet. Moreover, APCs were necessary for the induction of intrarenal renin-angiotensin system components and affected the modulation of natriuresis and tubular sodium transporters. Consistent with the prevention of hypertension, the ablation of APCs also prevented cardiac hypertrophy and the induction of several indicators of renal and cardiac damage. Thus, our findings indicate a prominent role of APCs as modulators of blood pressure by mechanisms including renal sodium handling, with kinetics that suggest the involvement of tubular cell functions in addition to the modulation of inflammation and adaptive immune response.

Contrast-Enhanced Ultrasound for Assessing Renal Perfusion Impairment and Predicting Acute Kidney Injury to Chronic Kidney Disease Progression

AIMS

Acute kidney injury (AKI) is increasingly recognized as a major risk factor leading to progression to chronic kidney disease (CKD). However, the diagnostic tools for predicting AKI to CKD progression are particularly lacking. Here, we tested the utility of contrast-enhanced ultrasound (CEUS) for predicting progression to CKD after AKI by using both mild (20-min) and severe (45-min) bilateral renal ischemia-reperfusion injury mice.

RESULTS

Renal perfusion measured by CEUS reduced to 25% ± 7% and 14% ± 6% of the pre-ischemic levels in mild and severe AKI 1 h after ischemia (p < 0.05). Renal perfusion returned to pre-ischemic levels 1 day after mild AKI followed by restoration of kidney function. However, severe AKI caused persistent renal perfusion impairment (60% ± 9% of baseline levels) accompanied by progressive renal fibrosis and sustained decrease in renal function. Renal perfusion at days 1-21 significantly correlated with tubulointerstitial fibrosis 42 days after AKI. For predicting renal fibrosis at day 42, the area under the receiver operating characteristics curve of renal perfusion impairment at day 1 was 0.84. Similar changes in the renal image of CEUS were observed in patients with AKI-CKD progression.

INNOVATION

This study demonstrates that CEUS enables dynamic and noninvasive detection of renal perfusion impairment after ischemic AKI and the perfusion abnormalities shown by CEUS can early predict the progression to CKD after AKI.

CONCLUSIONS

These results indicate that CEUS enables the evaluation of renal perfusion impairment associated with CKD after ischemic AKI and may serve as a noninvasive technique for assessing AKI-CKD progression. Antioxid. Redox Signal. 27, 1397-1411.

Melatonin ameliorates intrarenal renin-angiotensin system in a 5/6 nephrectomy rat model

BACKGROUND

Activation of the intrarenal renin-angiotensin system (RAS) plays a critical role in the pathophysiology of chronic kidney disease (CKD) and hypertension. It has been reported that reactive oxygen species (ROS) are important components of intrarenal RAS activation. Melatonin is recognized as a powerful antioxidant, and we recently reported that impaired nighttime melatonin secretion correlates negatively with urinary angiotensinogen excretion, the surrogate marker of intrarenal RAS activity in patients with CKD. However, whether melatonin supplementation ameliorates the augmentation of intrarenal RAS in CKD has remained unknown. We aimed to clarify whether exogenous melatonin ameliorates intrarenal RAS activation via the reduction of ROS production.

METHODS

5/6 Nephrectomized (Nx) rats were used as a chronic progressive CKD model and compared with sham-operated control rats. The Nx rats were divided into untreated Nx rats and melatonin-treated Nx rats. The levels of intrarenal RAS, ROS components, and renal injury were evaluated after 4 weeks of treatment.

RESULTS

Compared with the control rats, the untreated Nx rats exhibited significant increases in intrarenal angiotensinogen, angiotensin II (AngII) type 1 receptors, and AngII, accompanied by elevated blood pressure, higher oxidative stress (8-hydroxy-2'-deoxyguanosine), lower antioxidant (superoxide dismutase) activity, and increased markers of interstitial fibrosis (α-smooth muscle actin, Snail, and type I collagen) in the remnant kidneys. Treatment with melatonin significantly reversed these abnormalities.

CONCLUSION

Antioxidant treatment with melatonin was shown to ameliorate intrarenal RAS activation and renal injury in a 5/6 Nx rat model.

MYH9 E1841K Mutation Augments Proteinuria and Podocyte Injury and Migration

Intronic variants of the MYH9 gene that encodes the nonmuscle myosin heavy chain IIA are associated with diabetic nephropathy in European Americans and with sickle cell disease-associated nephropathy. However, the causal functional variants of MYH9 have remained elusive. Rare missense mutations in MYH9 cause macrothrombocytopenia and are occasionally associated with development of nephropathy. The E1841K mutation is among the common MYH9 missense mutations and has been associated with nephropathy in some carriers. To determine the contribution of the E1841K mutation in kidney disease, we studied the effects of the E1841K mutation in mice subjected to high salt or angiotensin II (Ang II) as models of hypertension and in mice subjected to renal mass reduction as a model of CKD. Despite similar levels of BP among wild-type (MYH9^+/+ ) mice and mice heterozygous (MYH9^+/E1841K ) and homozygous (MYH9^{E1841K/E1841K} ) for the mutation in each model, MYH9^{E1841K/E1841K} mice exhibited mildly increased albuminuria in response to high salt; severe albuminuria, nephrinuria, FSGS, and podocyte foot effacement in Ang II-induced hypertension; and early mortality in the renal mass reduction model. Treatment with candesartan during Ang II-induced hypertension attenuated kidney disease development in MYH9^{E1841K/E1841K} mice. In vitro, isolated primary podocytes from MYH9^{E1841K/E1841K} mice exhibited increased lamellipodia formation and reorganization of F-actin stress fibers. Wound healing assays revealed that MYH9^+/+ podocytes had the lowest migration rate, followed by MYH9^+/E1841K then MYH9^{E1841K/E1841K} podocytes. In conclusion, the MYH9 E1841K variant alters podocyte cytoskeletal structure and renders podocytes more susceptible to injury after a damaging stimulus.

Biomarkers for Chronic Kidney Disease Associated with High Salt Intake

High salt intake has been related to the development to chronic kidney disease (CKD) as well as hypertension. In its early stages, symptoms of CKD are usually not apparent, especially those that are induced in a “silent” manner in normotensive individuals, thereby providing a need for some kind of urinary biomarker to detect injury at an early stage. Because traditional renal biomarkers such as serum creatinine are insensitive, it is difficult to detect kidney injury induced by a high-salt diet, especially in normotensive individuals. Recently, several new biomarkers for damage of renal tubular epithelia such as neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (Kim-1) have been identified. Previously, we found a novel renal biomarker, urinary vanin-1, in several animal models with renal tubular injury. However, there are few studies about early biomarkers of the progression to CKD associated with a high-salt diet. This review presents some new insights about these novel biomarkers for CKD in normotensives and hypertensives under a high salt intake. Interestingly, our recent reports using spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) fed a high-salt diet revealed that urinary vanin-1 and NGAL are earlier biomarkers of renal tubular damage in SHR and WKY, whereas urinary Kim-1 is only useful as a biomarker of salt-induced renal injury in SHR. Clinical studies will be needed to clarify these findings.

Reno-Cerebral Reflex Activates the Renin-Angiotensin System, Promoting Oxidative Stress and Renal Damage After Ischemia-Reperfusion Injury

AIMS

A kidney-brain interaction has been described in acute kidney injury, but the mechanisms are uncertain. Since we recently described a reno-cerebral reflex, we tested the hypothesis that renal ischemia-reperfusion injury (IRI) activates a sympathetic reflex that interlinks the renal and cerebral renin-angiotensin axis to promote oxidative stress and progression of the injury.

RESULTS

Bilateral ischemia-reperfusion activated the intrarenal and cerebral, but not the circulating, renin-angiotensin system (RAS), increased sympathetic activity in the kidney and the cerebral sympathetic regulatory regions, and induced brain inflammation and kidney injury. Selective renal afferent denervation with capsaicin or renal denervation significantly attenuated IRI-induced activation of central RAS and brain inflammation. Central blockade of RAS or oxidative stress by intracerebroventricular (ICV) losartan or tempol reduced the renal ischemic injury score by 65% or 58%, respectively, and selective renal afferent denervation or reduction of sympathetic tone by ICV clonidine decreased the score by 42% or 52%, respectively (all p < 0.05). Ischemia-reperfusion-induced renal damage and dysfunction persisted after controlling blood pressure with hydralazine.

INNOVATION

This study uncovered a novel reflex pathway between ischemic kidney and the brain that sustains renal oxidative stress and local RAS activation to promote ongoing renal damage.

CONCLUSIONS

These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral sympathetic reflex that is activated by ischemia-reperfusion, which contributes to ischemia-reperfusion-induced brain inflammation and worsening of the acute renal injury. Antioxid. Redox Signal. 27, 415-432.

Potential predictors of susceptibility to occupational stress in Japanese novice nurses - a pilot study

Background

Occupational stress is a known factor behind employee resignations; thus, early identification of individuals prone to such stress is important. Accordingly, in this pilot study we evaluated potential predictors of susceptibility to occupational stress in Japanese novice nurses.

Methods

Forty-two female novice nurses at Kagoshima University Hospital were recruited for the study population. Each underwent physical health and urinary examinations, and completed a lifestyle questionnaire at the time of job entry. Each also completed a Brief Job Stress Questionnaire (BJSQ), related to mental health status, at job entry and 5 months post-entry. Psychological stress, somatic symptoms, and combined BJSQ scores were determined for each time point.

Results

All three stress condition scores had significantly decreased at 5 months post-entry, suggesting occupational stress. Systolic blood pressure (r = −0.324, p < 0.05) and urinary sodium (r = −0.313, p < 0.05) were significantly negatively correlated with combined BJSQ score at 5 months post-entry. Post-entry stress condition scores were significantly low in subjects reporting substantial 1-year body weight change (≤ ± 3 kg) and short times between dinner and bedtimes (≤2 h), though baseline stress condition scores were not. Urinary sodium concentration, 1-year body weight change, and pre-sleep evening meals were then targeted for multivariate analysis, and confirmed as independent explanatory variables for post-entry stress condition scores.

Conclusions

One-year body weight change, times between dinner and bedtimes, and urinary sodium concentration are promising potential predictors of susceptibility to occupational stress, and should be further investigated in future research.

Trial registration

ISRCTN ISRCTN17516023. Retrospectively registered 7 December 2016.

High-salt diet induces outward remodelling of efferent arterioles in mice with reduced renal mass

AIM

The glomerular filtration rate (GFR) falls progressively in chronic kidney disease (CKD) which is caused by a reduction in the number of functional nephrons. The dysfunctional nephron exhibits a lower glomerular capillary pressure that is induced by an unbalance between afferent and efferent arteriole. Therefore, we tested the hypothesis that oxidative stress induced by CKD differentially impairs the structure or function of efferent vs. afferent arterioles.

METHODS

C57BL/6 mice received sham operations (sham) or 5/6 nephrectomy (RRM) and three months of normal- or high-salt diet or tempol. GFR was assessed from the plasma inulin clearance, arteriolar remodelling from media/lumen area ratio, myogenic responses from changes in luminal diameter with increases in perfusion pressure and passive wall compliance from the wall stress/strain relationships.

RESULTS

Mice with RRM fed a high salt (vs. sham) had a lower GFR (553 ± 25 vs. 758 ± 36 μL min^-1  g^-1 kidney, P < 0.01) and a larger efferent arteriolar diameter (9.6 ± 0.8 vs. 7.4 ± 0.7 μm, P < 0.05) resulting in a lower media/lumen area ratio (1.4 ± 0.1 vs. 2.4 ± 0.2, P < 0.01). These alterations were corrected by tempol. The myogenic responses of efferent arterioles were about one-half that of afferent arterioles and were unaffected by RRM or salt. Passive wall compliance was reduced by high salt in both afferent and efferent arterioles.

CONCLUSION

A reduction in renal mass with a high-salt diet induces oxidative stress that leads to an outward eutrophic remodelling in efferent arterioles and reduced wall compliance in both afferent and efferent arterioles. This may contribute to the lower GFR in this model of CKD.

Increased Apoptosis in the Paraventricular Nucleus Mediated by AT1R/Ras/ERK1/2 Signaling Results in Sympathetic Hyperactivity and Renovascular Hypertension in Rats after Kidney Injury

Background: The central nervous system plays a vital role in the development of hypertension, but the molecular regulatory mechanisms are not fully understood. This study aimed to explore signaling in the paraventricular nucleus (PVN) which might contribute to renal hypertension.

Methods: Renal hypertension model was established by five-sixth nephrectomy operation (5/6Nx) in male Sprague Dawley rats. Ten weeks afterwards, they were random assigned to no treatment, or intracerebroventricular injection (ICV) with artificial cerebrospinal fluid, losartan [angiotensin II receptor type 1 (AT1R) antagonist], farnesylthiosalicylic acid (Ras inhibitor), PD98059 (MEK inhibitor), or SB203580 (p38 inhibitor) and Z-DEVD-FMK (caspase-3 inhibitor). Before and after treatment, physiological and biochemical indices were measured. Immunohistochemistry, western blot and RT-PCR were applied to quantify key components of renin-angiotensin system, apoptosis-related proteins, Ras-GTP, and MAPKs in the PVN samples. TUNEL assay was used to measure the situ apoptosis in PVN.

Results: The 5/6Nx rats showed significantly elevated systolic blood pressure, urinary protein excretion, serum creatinine, and plasma norepinephrine (p < 0.05) compared to sham rats. The expression of angiotensinogen, Ang II, AT1R, p-ERK1/2, or apoptosis-promoting protein Bax were 1.08-, 2.10-, 0.74-, 0.82-, 0.83-fold higher in the PVN of 5/6Nx rats, than that of sham rats, as indicated by immunohistochemistry. Western blot confirmed the increased levels of AT1R, p-ERK1/2 and Bax; meanwhile, Ras-GTP and p-p38 were also found higher in the PVN of 5/6Nx rats, as well as the apoptosis marker cleaved caspase-3 and TUNEL staining. In 5/6Nx rats, ICV infusion of AT1R antagonist, Ras inhibitor, MEK inhibitor or caspase-3 inhibitor could lower systolic blood pressure (20.8-, 20.8-, 18.9-, 14.3%-fold) together with plasma norepinephrine (53.9-, 57.8-,63.3-, 52.3%-fold). Western blot revealed that blocking the signaling of AT1R, Ras, or MEK/ERK1/2 would significantly reduce PVN apoptosis as indicated by changes of apoptosis-related proteins (p < 0.05). AT1R inhibition would cause reduction in Ras-GTP and p-ERK1/2, but not vice versa; such intervention with corresponding inhibitors also suggested the unidirectional regulation of Ras to ERK1/2.

Conclusion: These findings demonstrated that the activation of renin-angiotensin system in PVN could induce apoptosis through Ras/ERK1/2 pathway, which then led to increased sympathetic nerve activity and renal hypertension in 5/6Nx rats.

Wnt/β-catenin signaling and renin-angiotensin system in chronic kidney disease

PURPOSE OF REVIEW

Intrarenal activation of the renin-angiotensin system (RAS) plays an essential role in the pathogenesis of hypertension and chronic kidney diseases (CKD). However, how RAS genes are regulated in vivo was poorly understood until recently. This review focuses on recent findings of the transcriptional regulation of RAS components, as well as their implication in developing novel strategies to treat the patients with CKD.

RECENT FINDINGS

Bioinformatics analyses have uncovered the presence of putative binding sites for T-cell factor/β-catenin in the promoter region of all RAS genes. Both in-vitro and in-vivo studies confirm that Wnt/β-catenin is the master upstream regulator that controls the expression of all RAS components tested, such as angiotensinogen, renin, angiotensin converting enzyme and the angiotensin II type I receptor in the kidney. Targeted inhibition of Wnt/β-catenin, by either small molecule ICG-001 or endogenous Wnt antagonist Klotho, represses RAS activation and ameliorates proteinuria and kidney injury. Blockade of Wnt/β-catenin signaling also normalizes blood pressure in a mouse model of CKD.

SUMMARY

These recent studies identify Wnt/β-catenin as the master regulator that controls multiple RAS genes, and suggest that targeting this upstream signaling could be an effective strategy for the treatment of patients with hypertension and CKD.

Proteomic and phosphoproteomic analysis of renal cortex in a salt-load rat model of advanced kidney damage

Salt plays an essential role in the progression of chronic kidney disease and hypertension. However, the mechanisms underlying pathogenesis of salt-induced kidney damage remain largely unknown. Here, Sprague-Dawley rats, that underwent 5/6 nephrectomy (5/6Nx, a model of advanced kidney damage) or sham operation, were treated for 2 weeks with a normal or high-salt diet. We employed aTiO₂ enrichment, iTRAQ labeling and liquid-chromatography tandem mass spectrometry strategy for proteomic and phosphoproteomic profiling of the renal cortex. We found 318 proteins differentially expressed in 5/6Nx group relative to sham group, and 310 proteins significantly changed in response to salt load in 5/6Nx animals. Totally, 1810 unique phosphopeptides corresponding to 550 phosphoproteins were identified. We identified 113 upregulated and 84 downregulated phosphopeptides in 5/6Nx animals relative to sham animals. Salt load induced 78 upregulated and 91 downregulated phosphopeptides in 5/6Nx rats. The differentially expressed phospholproteins are important transporters, structural molecules, and receptors. Protein-protein interaction analysis revealed that the differentially phosphorylated proteins in 5/6Nx group, Polr2a, Srrm1, Gsta2 and Pxn were the most linked. Salt-induced differential phosphoproteins, Myh6, Lmna and Des were the most linked. Altered phosphorylation levels of lamin A and phospholamban were validated. This study will provide new insight into pathogenetic mechanisms of chronic kidney disease and salt sensitivity.

Stroke and Risks of Development and Progression of Kidney Diseases and End-Stage Renal Disease: A Nationwide Population-Based Cohort Study

BACKGROUND

There is little information about the association between stroke and kidney diseases. We aimed to investigate the impact of stroke on long-term renal outcomes.

METHODS

In this large population-based retrospective cohort study, we identified 100,353 subjects registered in the National Health Insurance Research Database of Taiwan from January 1, 2000, through December 31, 2012, including 33,451 stroke patients and 66,902 age-, sex- and Charlson's comorbidity index score-matched controls.

RESULTS

The incidence rate of chronic kidney disease (CKD) was higher in the stroke than in the control cohort (17.5 vs. 9.06 per 1000 person-years). After multivariate adjustment, the risk of developing CKD was significantly higher in patients with stroke (adjusted hazard ratio [aHR] 1.43, 95% confidence interval [CI] 1.36-1.50, P<0.001). Subgroup analysis showed that stroke patients <50 years (aHR 1.61, P<0.001) and those with concomitant diabetes mellitus (aHR 2.12, P<0.001), hyperlipidemia (aHR 1.53, P<0.001) or gout (aHR 1.84, P<0.001) were at higher risk of incident CKD. Additionally, the risks of progression to advanced CKD and end-stage renal disease (ESRD) were significantly higher for stroke patients (aHRs, 1.22 and 1.30; P = 0.04 and P = 0.008, respectively), independent of age, sex, comorbidities and long-term medications.

CONCLUSIONS

Stroke is associated with higher risks for incident CKD, decline in renal function and ESRD. Younger stroke patients, as well as those with concomitant diabetes mellitus, hyperlipidemia or gout are at greater risk for kidney diseases.

Augmented circadian rhythm of the intrarenal renin-angiotensin systems in anti-thymocyte serum nephritis rats

We report that disturbance to the circadian rhythm of urinary angiotensinogen (AGT) excretion may lead to renal damage, hypertension and diurnal blood pressure (BP) variations. We aim to clarify the circadian rhythm of the intrarenal renin-angiotensin system (RAS) and its contribution to renal damage, hypertension and BP variations, and to evaluate whether the administration of RAS blockers influences the circadian rhythms of intrarenal RAS components. Anti-thymocyte serum (ATS) nephritis rats were used as a chronic progressive glomerulonephritis model (group A) and compared with control rats (group C). Other rats with ATS nephritis received olmesartan medoxomil (an angiotensin II (AngII) type 1 receptor (AT1R) blocker; group AO) or hydralazine (a vasodilator; group AH). The levels of intrarenal RAS components were evaluated every 6 h. The expression levels of intrarenal AGT, AngII and AT1R were increased in group A and peaked at the same time as BP and urinary protein excretion during the rest phase. The amplitude of the circadian fluctuation of these proteins was more increased in group A than in group C. The circadian fluctuation of these proteins was reduced in groups AO and AH. However, renal function, proteinuria and augmentation of intrarenal RAS components were reduced only in group AO. Intrarenal RAS components, such as AGT, AngII and AT1R proteins, were increased and the amplitude of the oscillations of these proteins was augmented in ATS nephritis rats. Interestingly, renal damage may be linked to the activation of the intrarenal RAS independent of the amplitude of its oscillations and BP.

High-Salt Enhances the Inflammatory Response by Retina Pigment Epithelium Cells following Lipopolysaccharide Stimulation

High-salt has been shown to play a role in the pathogenesis of autoimmune disease. In this study, we investigated the effect of high-salt on the production of inflammatory mediators by ARPE-19 cells and the possible mechanisms involved. ARPE-19 cells were cultured with LPS in DMEM to which extra NaCl had been added (20 mM and 40 mM). NaCl had no influence on the apoptosis and proliferation of ARPE-19. Addition of 40 mM NaCl significantly induced IL-6 and MCP-1 production but had no effect on IL-8 secretion. High mannitol, as an osmotic stress control, did not affect the secretion of inflammatory mediators by ARPE-19 cells indicating that the effect was not mediated by osmolarity. Coculture of ARPE-19 cells with NaCl resulted in significant increases in the phosphorylation of p38 MAPK, Akt, and NF-κB and an upregulation of the transcription factors NFAT5 and SGK1. High-salt significantly promotes IL-6 and MCP-1 production by ARPE-19 cells and is associated with activation of the p38 MAPK, Akt, and NF-κB pathway and NFAT-SGK1 pathways.