NHE3 Protein Expression Research Articles

NHE1 regulation in NAFLD in vitro contributes to hepatocyte injury and HSC crosstalk.

Non-alcoholic fatty liver disease (NAFLD) is the fastest growing cause of liver-associated death globally. Whole-body knockout (KO) of Na+/H+ exchanger 1 (NHE1, SLC9A1) was previously proposed to protect against high fat diet-induced liver damage, however, mechanistic insight was lacking. The aim of the present work was to address this question in vitro to determine how NHE1 specifically in hepatocytes impacts lipid overload-induced inflammation, fibrosis, and hepatocyte- hepatic stellate cell (HSC) crosstalk. We induced palmitate (PA)-based steatosis in AML12 and HepG2 hepatocytes, manipulated NHE1 activity pharmacologically and by CRISPR-Cas knockout (KO) and -overexpression, and measured intracellular pH (pHi), steatosis-associated inflammatory and fibrotic mediators and cell death. PA treatment increased NHE1 mRNA levels but modestly reduced NHE1 protein expression and hepatocyte pHi. NHE1 KO in hepatocytes did not alter lipid droplet accumulation but reduced inflammatory signaling (p38 MAPK activity), lipotoxicity (4-HNE accumulation) and apoptosis (PARP cleavage). Conditioned medium from PA-treated hepatocytes increased expression of NHE1 and of the fibrosis regulator tissue inhibitor of matrix metalloproteases-2 (TIMP2) in LX-2 HSCs, in a manner abolished by NHE1 KO in hepatocytes. We conclude that NHE1 is regulated in NAFLD in vitro and contributes to the ensuing damage by aggravating hepatocyte injury and stimulating hepatocyte-HSC crosstalk.

Myeloid Ptpn2 Deficiency in Mice Causes Functional Iron Deficiency

Background: Anemia is the most prevalent extraintestinal complication of inflammatory bowel disease (IBD) and is associated with the manifestation of Crohn’s disease. Anemia significantly reduces the quality of life, increases hospitalization visits, and increases medical care expenses of IBD patients. Iron deficiency is the leading cause of anemia in IBD; however, the physiological mechanisms involved are still poorly understood. Macrophages significantly contribute to iron homeostasis by mechanisms including iron recycling by phagocytosing senescent erythrocytes and damaged cells, and nurturing erythropoiesis in the bone marrow. In this study, we investigated the role of the IBD candidate gene, protein tyrosine phosphatase non-receptor type 2 ( PTPN2), in regulating macrophage iron homeostasis. Methods: Myeloid cell-specific knockout mice ( Ptpn2LysMCre) and control littermates ( Ptpn2fl/fl) were analyzed for serum iron content and liver and spleen non-heme iron. Duodenal epithelial cell (DEC) proteins were assayed by Western blotting. Localization of the brush border ferrous iron transporter, DMT1, and the coupled ferrous iron absorption driver, NHE3, in duodenal tissue was determined by immunohistochemistry (IHC). Gene expression profiles of macrophages were analyzed by Nanostring. Results: Ptpn2LysMCre mice had reduced serum iron ( p<0.0001; n=12) and reduced spleen non-heme iron (p=0.0017; n=6), whereas liver non-heme iron was unaltered (n=6), indicating iron deficiency in select tissues. DMT1 (n=8) and NHE3 (n=5) protein expression in DECs was unaltered and IHC confirmed the unaltered localization of DMT1 and NHE3 (n=6) in the duodenal epithelium of Ptpn2LysMCre mice, suggesting the reduction in serum iron was not due to an impairment in intestinal non-heme iron uptake. Nanostring analyses revealed that the gene expression of the iron transporter Dmt1, iron exporter Fpn, and iron importer Tfr1 were significantly downregulated (p<0.05; n=5) in macrophages from Ptpn2LysMCre mice, indicating an iron sequestering phenotype. Conclusions: Loss of myeloid Ptpn2 in mice causes functional iron deficiency. These findings indicate a major role of myeloid PTPN2 in regulating systemic iron homeostasis. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Porcine delta coronavirus inhibits NHE3 activity of porcine intestinal epithelial cells through miR-361–3p/NHE3 regulatory axis

Porcine deltacoronavirus (PDCoV) infection in piglets can cause small intestinal epithelial necrosis and atrophic enteritis, which leads to severe damages to host cells, and result in diarrhea. In this study, we investigated the relationship between miR-361, SLC9A3(Solute carrier family 9, subfamily A, member 3), and NHE3(sodium-hydrogen exchanger member 3) in in porcine intestinal epithelial cells (IPI-2I) cells after PDCoV infection. Our results showed that the ssc-miR-361–3p expression inhibits the mRNA level of SLC9A3 gene which lead to the descending of NHE3 protein expression, and the NHE3 activity was suppressed. NHE3 activity was suppressed via down-regulation expression of SLC9A3 mRNA by transfection with siRNA. Ssc-miR-361–3p mimics and inhibitors were used to change the expression of ssc-miR-361–3p in IPI-2I cells. Ssc-miR-361–3p overexpression reduced the mRNA level of SLC9A3 gene, the level of NHE3 protein expression and NHE3 activity in IPI-2I cells, while ssc-miR-361–3p inhibits NHE3. Furthermore, luciferase reporter assay showed that SLC9A3 gene was a direct target of ssc-miR-361–3p. Ssc-miR-361–3p inhibition restored NHE3 activity in PDCoV infected IPI-2I cells by up-regulating SLC9A3 mRNA expression and NHE3 protein expression. These results demonstrate that the PDCoV infection can inhibit NHE3 activity through miR-361–3p/SLC9A3 regulatory axis. The relevant research is reported for the first time in PDCoV, which has significance in exploring the pathogenic mechanism of PDCoV and can provide a theoretical basis for its prevention and control. suggesting that NHE3 and ssc-miR-361–3p may be potential therapeutic targets for diarrhea in infected piglets.

Rimeporide, a first in class Na/H exchanger-1 inhibitor, ameliorates right ventricular dysfunction and pulmonary arterial hypertension in a SuHx model

Abstract Background Pulmonary arterial hypertension (PAH) is characterized by pulmonary vasoconstriction and vascular remodeling leading to right ventricular (RV) failure. Although RV function is the major prognostic factor in PAH, no RV-specific therapies exist. The Na+/H+ exchanger type 1 (NHE1) regulates the intra- and extracellular pH balance mainly through the 1:1 exchange of intracellular H+ with extracellular Na+. Increased NHE-1 activity is involved in several diseases, including hypoxic PAH. Inhibition of NHE-1 activity attenuates pulmonary vascular remodeling in rodents exposed to hypoxia but its potential direct contribution in RV remodeling remains unclear. Aim In the current study, we aimed to investigate the effect of NHE-1 inhibition by Rimeporide a preclinical hypoxic models of PH: Sugen5416/hypoxia. Methods Sugen/hypoxia model: PAH was induced in adult Sprague-Dawley rats with a single injection of SU5416 (20 mg/kg) followed by 3 weeks of hypoxia (10% O2; Sugen/Hypoxia model: SuHx) and then return to normoxia. Control rats were injected with equal volume of vehicle. At week 5 post-injection, control and SuHx rats were treated with rimeporide (100 mg/Kg daily in drinking water, n=10/group) or placebo (n=11/group) for 3 weeks. Echocardiography and blood sampling were performed. RV phenotype was monitored by echocardiography and hemodynamic analysis. Lung and heart were collected for histological and protein expression analysis, such as NHE-1 (target of Rimeporide). Results SuHx caused severe PAH and RV dysfunction. RV dysfunction was accompanied by an increase in RV hypertrophy and RV fibrosis and PA remodeling (increase in the arteriolar wall thickness and fibrosis). A marked increase in macrophages was found in lung and RV tissues but not in LV. Moreover, Western blot analysis showed that RV protein levels of NHE-1 was higher in SuHx rats than Normoxia rats. Treatment with Rimeporide reversed SuHx-induced PAH as well as RV dysfunction and blunted pulmonary and RV inflammation, RV NHE-1 protein expression. Conclusion Our results indicate that NHE-1 levels are increased in RV tissues from SuHx-induced PAH rats. Rimeporide, through NHE-1 inhibition, might be a potential new target for treatment of RV dysfunction and PAH.

Abstract P383: The Renal Mechanisms Involved In The Response To Salt Intake Are Sex Related In Mice.

Dopamine receptor D2 (Drd2) plays an important role in maintaining normal blood pressure (BP) by regulating renal Na + transport. Knockdown of Drd2 in renal proximal tubule cells (RPTCs) may affect BP and Na + transport differently between male and female mice. We studied the effects of Drd2 in RPTCs of the mouse kidney by generating Drd2 fl/fl , P SGLT2 ::Cre + mice (D2R PT-/- ) that lack D2R only in RPTC and Drd2 fl/fl , P SGLT2 ::Cre - (D2R PT+/+ ) mice that do not have the deletion. The study was performed in male and female mice on normal (0.8% NaCl, NS) and low (0.025-0.05% NaCl; LS) salt diets. On NS diet mean arterial pressures (MAPs, mm Hg), measured under pentobarbital anesthesia, were similar in male D2R PT+/+ (86.38±2.20, n=13) and D2R PT-/- (91.58±1.63, n=19) and female D2R PT+/+ (82.57±2.33, n=14) and D2R PT-/- (85.17±6.09, n=12) mice . By contrast, in D2R PT-/- mice, LS diet similarly increased MAP in male (108.11±7.04 (n=10) and female (103.00±9.98 (n=5) mice. The renal NHE3 protein expression (%) was higher in male than female mice (D2R PT+/+ : 100±4 (male) vs 30±15 (female); n=8/group; P<0.0001; D2R PT-/- 117±10 (male) vs 44±16 (female); n=8/group; P<0.02 ). However, NKCC expression (%) was higher in female than male D2R PT+/+ (788±10 (female) vs 100±4 (male), n=8/group; P<0.01); there was no difference between D2R PT-/- male and female mice. The expressions of Na + -K + /ATPase, NCC, SGLT2, and ENaC were similar in males and females of the two genotypes. These findings suggest that on LS diet D2R knockdown in the RPTC increases BP in both male and female mice but the changes in NHE3 and NKCC expressions are different between male and female mice. These results suggests that the MAP response to salt intake is not affected by sex but the renal mechanisms involved are sex-related.

Intestinal Cckbr-specific knockout mouse as a novel model of salt-sensitive hypertension via sodium over-absorption.

To investigate the value of CCKBRfl/fl villin-Cre mice as a mouse model of salt-sensitive hypertension (SSH). In the first part, 2-month-old CCKBRfl/fl villin-Cre mice (CKO) and control CCKBRfl/fl mice (WT) were fed with normal diet (0.4% NaCl) or high salt diet (4% NaCl), separately for 6 weeks. In the rescue study, one week of hydrochlorothiazide or saline injection were treated with the CKO mice fed high salt diet. The blood pressure, biochemical indexes, and the expression of small intestinal sodium transporters (NHE3, NKCC1, eNaC) was detected. The organ injury markers (MMP2/MMP9) and the histopathological changes of kidneys were observed, whereas the changes of duodenal sodium absorption were detected by small intestinal perfusion in vivo. The CCKBRfl/fl villin-Cre mice with high salt intake exhibited high blood pressure, increased duodenal sodium absorption and urinary sodium excretion, and with renal injury. The protein expression of NHE3, NKCC1 and eNaC were also significant increase in the intestine of CKO-HS mice. Treatment with hydrochlorothiazide remarkably attenuated the elevated blood pressure by high salt absorption in the CCKBRfl/fl villin-Cre mice, but no significant histopathological changes were observed. These results support a crucial role of intestinal Cckbr deficiency on SSH development and the diuretic antihypertension effect in CCKBRfl/fl villin-Cre mice. The CCKBRfl/fl villin-Cre mice with the high salt intake may serve as a stable model of salt-sensitive hypertensive induced by sodium overloading.

High dietary K+ intake inhibits proximal tubule transport.

The impact of chronic dietary K+ loading on proximal tubule (PT) function was measured using free-flow micropuncture along with measurements of overall kidney function, including urine volume, glomerular filtration rate, and absolute and fractional Na+ and K+ excretion in the rat. Feeding animals a diet with 5% KCl [high K+ (HK)] for 7 days reduced glomerular filtration rate by 29%, increased urine volume by 77%, and increased absolute K+ excretion by 202% compared with rats on a 1% KCl [control K+ (CK)] diet. HK did not change absolute Na+ excretion but significantly increased fraction excretion of Na+ (1.40% vs. 0.64%), indicating that fractional Na+ absorption is reduced by HK. PT reabsorption was assessed using free-flow micropuncture in anesthetized animals. At 80% of the accessible length of the PT, measurements of inulin concentration indicated volume reabsorption of 73% and 54% in CK and HK, respectively. At the same site, fractional PT Na+ reabsorption was 66% in CK animals and 37% in HK animals. Fractional PT K+ reabsorption was 66% in CK and 37% in HK. To assess the role of Na+/H+ exchanger isoform 3 (NHE3) in mediating these changes, we measured NHE3 protein expression in total kidney microsomes as well as surface membranes using Western blots. We found no significant changes in protein in either cell fraction. Expression of the Ser552 phosphorylated form of NHE3 was also similar in CK and HK animals. Reduction in PT transport may facilitate K+ excretion and help balance Na+ excretion by shifting Na+ reabsorption from K+-reabsorbing to K+-secreting nephron segments.NEW & NOTEWORTHY In rats fed a diet rich in K+, proximal tubules reabsorbed less fluid, Na+, and K+ compared with those in animals on a control diet. Glomerular filtration rates also decreased, probably due to glomerulotubular feedback. These reductions may help to maintain balance of the two ions simultaneously by shifting Na+ reabsorption to K+-secreting nephron segments.

Constitutive Loss of Ptpn2 in Mice Causes Features of Anemia Including Iron Deficiency

Background: Anemia is the most frequent extraintestinal manifestation of inflammatory bowel disease (IBD) and is associated with the risk of Crohn’s disease. Anemia significantly impairs quality of life, increases hospitalization rates, and increases medical care costs of IBD patients. Iron deficiency is the most frequent cause of anemia in IBD; however, the mechanisms involved are still poorly understood. Here, we investigated the role of the IBD risk gene, protein tyrosine phosphatase non-receptor type 2 ( PTPN2), in regulating iron homeostasis. Methods: Constitutive Ptpn2 wild type (WT), heterozygous (Het), and knockout (KO) 3-week-old mice were analyzed for serum iron content, complete blood count parameters, and intestinal and extraintestinal non-heme iron. Protein and RNA from duodenal epithelial cells (DECs) were assayed by western blotting and qPCR. Localization of the brush border ferrous iron transporter, DMT1, and the ferrous iron absorption driver, NHE3, in duodenal tissue was determined by immunohistochemistry (IHC). Results: Ptpn2-KO mice had reduced i) serum iron ( p=0.0007; n=10); ii) serum iron carrier transferrin saturation ( p=0.0077; n=8); iii) hemoglobin ( p=0.0002; n=5); iv) hematocrit ( p=0.0023; n=5); v) intestinal non-heme iron: duodenum ( p=0.0128; n=10) and jejunum ( p=0.0006; n=8); and vi) extraintestinal tissue non-heme iron: liver ( p=0.0014; n=10), spleen ( p=0.04; n=10), kidney ( p=0.0004; n=7), and gastrocnemius muscle ( p=0.0436; n=9) vs. Ptpn2-WT and Het mice. This indicated that loss of Ptpn2 causes characteristics of anemia including decreased serum iron and tissue iron storage and impaired intestinal iron homeostasis. DEC gene expression of the intracellular iron storage molecule ferritin ( Fth1) was reduced ( p=0.048; n=4) while the basolateral cellular iron importer transferrin receptor 1 ( Tfrc1) was significantly increased ( p=0.0048; n=5) in Ptpn2-KO mice. Reduced FTH1 protein expression ( p=0.007; n=12) and increased TFRC1 protein expression ( p=0.0021; n=8) in DECs of Ptpn2-KO mice was confirmed by western blot, indicating cellular iron deficiency. DMT1 (n=6) and NHE3 (n=8) protein expression in DECs was unaltered, whereas IHC showed reduced apical membrane DMT1 and NHE3 in the duodenal epithelium of Ptpn2-KO mice (n=6), suggesting a possible mechanism of impaired intestinal non-heme iron uptake. Conclusions: Loss of Ptpn2 in mice causes features of anemia including iron deficiency associated with mislocalization of DMT1 and reduced apical membrane expression of NHE3. These findings identify a critical role for PTPN2 in regulating systemic iron homeostasis. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Renal NHE1 is required for regulation of intracellular pH in principal cells and type B intercalated cells

The sodium-hydrogen exchanger isoform 1 (NHE1) is a plasma membrane transporter with roles in transepithelial Na+/H+ transport, intracellular pH (pHi) and cell volume regulation. Within the kidney, NHE1 is previously documented to be expressed in all nephron segments. However, recent transcriptomic and proteomic analyses, and our staining results in mice, consistently find no expression of NHE1 in the proximal tubule or thick ascending limb, but in the distal nephron, including distal convoluted tubule, connecting tubule, and collecting duct (principal and intercalated cells, PC and IC, respectively). We hypothesized that basolateral NHE1 in IC (co-labelling with H+-ATPase B1 subunit, labeling all 3 types of IC: type A, B, and non-A-non-B) plays an important role in acid-base homeostasis. Due to lack of a suitable animal model, we generated kidney-specific NHE1 knockout (NHE1KS-KO) mice. NHE1KS-KO mice completely lack renal NHE1 protein expression compared to their control littermates (n=6 male mice/genotype). No differences were observed in body weight, food and water intake (determined in their home cages) or concentrations of blood Na+, K+, Ca2+, pH or HCO3-. Urine analysis showed no significant differences in electrolytes, minerals of pH. To mechanistically determine the role of NHE1 for pHi regulation in IC and PC we used confocal microscopy of acutely-split open cortical collecting ducts. This method allows for the analysis of a vast number of PC/IC simultaneously. To study the role of NHE1 we employed a NH4Cl pre-pulse (40 mM) and measured pHi recovery after switching back to a physiological solution. Intracellular pH recovery in PC (n=171) was significantly slower (~50%) in NHE1KS-KO mice compared to controls (n=85). Similar to PC, pHi recovery in type B IC of NHE1KS-KO mice (n=38) was significantly slower (~35%) compared to controls (n=40). No differences in type A IC were observed between NHE1KS-KO mice (n=35) and controls (n=29). Inhibition of ClC-K2 via NPPB (Cl-channel blocker) was used to confirm cell types: PC did not respond with a change in pHi but NPPB increased pHi in type A and decreased pHi in type B ICs. In summary, our results identify for the first time an important role of NHE1 for pHi regulation particularly in PCs and type B ICs. Funding to Dr. Rieg was provided by the NIDDK grant 1R01DK110621, VA Merit Review Award IBX004968A, AHA Transformational Research Award 19TPA34850116, and NIDDK Diabetic Complications Consortium grants DK076169 and DK115255. DK095029 and DK117865 (both to O. Pochynyuk). Dr. Thomas was supported by an AHA postdoctoral grant (828731), V. Tomilin by an AHA Career Development Award 19CDA34660148. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Empagliflozin and Renal Sodium-Hydrogen Exchange in Healthy Subjects.

Sodium glucose co-transporter-2 inhibitors exert clinically relevant cardiorenal protection. Among several mechanisms, inhibition of sodium-hydrogen exchanger-3 (NHE3) in proximal renal tubules has been proposed in rodents. Demonstration of this mechanism with the associated electrolyte and metabolic changes in humans is lacking. The present proof-of-concept study was designed to explore the involvement of NHE3 in modulating the response to sodium glucose co-transporter-2 inhibitors in humans. Twenty healthy male volunteers received 2 tablets of empagliflozin 25 mg during a standardized hydration scheme; freshly voided urines and blood samples were collected at timed intervals for 8 hours. Protein expression of relevant transporters was examined in exfoliated tubular cells. Urine pH levels increased after empagliflozin (from 5.81 ± 0.5 to 6.16 ± 0.6 at 6 hours, P = .008) as did urinary output (from median, 1.7; interquartile range [IQR, 0.6; 2.5] to 2.5 [IQR, 1.7; 3.5] mL/min-1, P = .008) and glucose (from median, 0.03 [IQR, 0.02; 0.04] to 34.8 [IQR, 31.6; 40.2] %, P < .0001), and sodium fractional excretion rates (from median, 0.48 [IQR, 0.34; 0.65] to 0.71 [IQR, 0.55; 0.85] %, P = .0001), whereas plasma glucose and insulin concentrations decreased and plasma and urinary ketones increased. Nonsignificant changes in NHE3, phosphorylated NHE3, and membrane-associated protein 17 protein expression were detected in urinary exfoliated tubular cells. In a time-control study in 6 participants, neither urine pH nor plasma and urinary parameters changed. In healthy young volunteers, empagliflozin acutely increases urinary pH while inducing a substrate shift toward lipid utilization and ketogenesis, without significant changes in renal NHE3 protein expression.

Downregulation of NHE-3 (SLC9A3) expression by MicroRNAs in intestinal epithelial cells.

Na+/H+ exchanger-3 (NHE-3) is the major apical membrane transporter involved in vectorial Na+ absorption in the intestine. Dysregulation of NHE-3 expression and/or function has been implicated in pathophysiology of diarrhea associated with gut inflammation and infections. Therefore, it is critical to understand the mechanisms involved in the regulation of NHE-3 expression. MicroRNAs (miRNAs) are highly conserved small RNAs that can regulate gene expression at the posttranscriptional level. To date, however, very little is known about the regulation of NHE-3 expression by microRNAs. Therefore, current studies were undertaken to examine the potential miRNA candidates that can regulate the expression of NHE-3 in intestinal epithelial cells. In silico analysis, using different algorithms, predicted several miRNAs that target NHE-3. MicroRNAs with highest context and target score, miR-326, miR-744-5p, and miR-330-5p, were selected for the current study. Human NHE-3 gene 3' untranslated region [3'UTR; 160 base pair (bp)] was cloned into pmirGLO vector upstream of luciferase reporter and transiently transfected with mimics of miR-326, miR-744-5p, and miR-330-5p into Caco-2, HT-29, and SK-CO15 cells. Cotransfection of NHE-3 3' UTR with miR-326 and -miR-330-5p mimics resulted in a significant decrease in relative luciferase activity. Transfection of miR-326 and -330-5p mimics into SK-CO15 cells significantly decreased the NHE-3 protein expression, with no change in NHE-3 messenger ribonucleic acid (mRNA) levels. Our findings demonstrate a novel mechanism for posttranscriptional regulation of NHE-3 by miR-326 and -330-5p by translational repression. We speculate that miR-326 and -330-5p dependent pathways may be involved in modulating NHE-3 expression under physiological and pathophysiological conditions.

Role of Dipeptidyl Peptidase 4 and Effects of a Western Diet in Renal Sodium Transport and Tubular Injury

The protein dipeptidyl peptidase 4 (DPP4) is a target in the management of Type 2 diabetes mellitus (T2DM) and inhibition decreases albuminuria in humans with high cardiovascular risk such as subjects with T2DM, obesity/insulin resistance and hypertension. Our laboratory and others have shown that inhibition or genetic deletion of DPP4 has nephroprotective effects not only in rodent models of DM/insulin resistance but also obesity and hypertension. In addition, all three conditions with high cardiovascular risk are characterized by sodium retention. Recent data shows that DPP4 may affect sodium transport within the kidney via binding to sodium/hydrogen exchanger 3 (NHE3) and translocating to the villi in the brush border of the tubules. We have observed increased tubular damage and sodium uptake in a high fat/high sugar diet (Western diet) model of obesity in the setting of increased DPP4 activity. Therefore, we hypothesized that reduction/suppression of DPP4 expression/signaling and/or activity may lead to decreased sodium retention in the kidney in the obese mice.MethodsProximal tubule specific DPP4fl/fl;SGLT2Cre+ (PT DPP4KO) and DPP4fl/fl;SGLT2Cre‐ (PT DPP4WT) mice were fed a WD and control chow (CD) till sacrifice (18 to 27 mths). 24 hour urine collection and measurement of sodium excretion was done in these mice while on the diets. Gene and protein expression of transporters (sodium and water) was quantitated. Whole body DPP4‐/‐ (DPP4KO) and DPP4+/+ (DPP4WT) were on control chow diet and placed in metabolic cages for sodium balance studies. On days 3 and 4, mice were given 1% NaCl in drinking water. Daily mice weight, food and water consumption and urinary excretion of sodium and potassium and creatinine were measured.ResultsThe PT DPP4WT mice showed a much reduced 24 hour excretion of sodium compared to the PT DPP4KO mice (p&lt;0.05) which was consistent with data from DPP4WT and DPP4KO mice on WD (unpublished) as well as data from DPP4 inhibitor treated mice (Nistala et al, Endocrinology 2014 Jun;155(6):2266‐76). Urinary sodium excretion was increased in both DPP4WT and DPP4KO mice on 1% NaCl in drinking water but the excretion was significantly increased in DPP4KO mice compared to DPP4WT mice. Excretion of glucose and other electrolytes reached a peak on the 3rd day and tapered off slightly on the 4th day. The increased excretion of sodium and water as well as slight reduction in food intake, led to gradual decrease in weight of the animals (~1gm) which was not significant between the WT and KO groups. The gene expression of many sodium and water transporters increased including NHE3, ENaCγ and AQP1/2 in the PT DPP4WT mice, while expression was reduced in the PT DPP4KO mice fed a Western Diet. The protein expression of NHE3 increased in WT mice and was suppressed in KO mice.ConclusionDPP4 expression was increased in PT DPP4WT mice fed a Western diet and reduced in the KO mice and this correlated with increased expression of NHE3 in the WT and reduction in KO mice. In the whole body DPP4KO mice, lack of DPP4 led to greater increase in sodium and water excretion. Taken together, proximal tubule DPP4 may be involved in regulating sodium and water homeostasis in CD and WD‐fed mice. Sodium excretion under conditions of low salt diet will help establish DPP4's role in sodium homeostasis.

Reduced activity of intestinal surface Na+/H+ exchanger NHE3 is a key factor for induction of diarrhea after PEDV infection in neonatal piglets

Porcine epidemic diarrhea virus (PEDV; family Coronaviridae, genus Alphacoronavirus) causes acute diarrhea and vomiting, dehydration, and high mortality in neonatal piglets. Despite extensive research focusing on the pathogenesis of PEDV infection, the molecular pathogenesis of PEDV-induced diarrhea in piglets remains unclear. Na+/H+ exchanger 3 (NHE3), the main exchanger of electroneutral sodium in intestinal epithelial cells, is closely associated with the occurrence of diarrhea. To date, there is no study on whether diarrhea caused by PEDV infection is related to the activity of NHE3. In the present study, it was found that the expression level of cell membrane protein NHE3 significantly decreased after PEDV infection, whereas the total level of protein expression was not significantly changed. The Na+/H+ transport rate and the mRNA abundance of NHE3 decreased; the NHE3 activity decreased gradually with increasing infection time. In vivo, after PEDV infection of newborn piglets, rupture of intestinal villi and interstitial degeneration of intestinal epithelial cells in different intestinal segments were observed by hematoxylin–eosin staining. Immunohistochemical and immunofluorescence methods were used to observe the decreased expression of NHE3 protein on the membrane of intestinal epithelial cells in the jejunum and ileum. Taken together, these data indicate that PEDV infection reduces NHE3 activity in intestinal epithelial cells, hindering Na+ transport and thus causing diarrhea.

Acid-base transporters and pH dynamics in human breast carcinomas predict proliferative activity, metastasis, and survival.

Breast cancer heterogeneity in histology and molecular subtype influences metabolic and proliferative activity and hence the acid load on cancer cells. We hypothesized that acid-base transporters and intracellular pH (pHi) dynamics contribute inter-individual variability in breast cancer aggressiveness and prognosis. We show that Na+,HCO3- cotransport and Na+/H+ exchange dominate cellular net acid extrusion in human breast carcinomas. Na+/H+ exchange elevates pHi preferentially in estrogen receptor-negative breast carcinomas, whereas Na+,HCO3- cotransport raises pHi more in invasive lobular than ductal breast carcinomas and in higher malignancy grade breast cancer. HER2-positive breast carcinomas have elevated protein expression of Na+/H+ exchanger NHE1/SLC9A1 and Na+,HCO3- cotransporter NBCn1/SLC4A7. Increased dependency on Na+,HCO3- cotransport associates with severe breast cancer: enlarged CO2/HCO3--dependent rises in pHi predict accelerated cell proliferation, whereas enhanced CO2/HCO3--dependent net acid extrusion, elevated NBCn1 protein expression, and reduced NHE1 protein expression predict lymph node metastasis. Accordingly, we observe reduced survival for patients suffering from luminal A or basal-like/triple-negative breast cancer with high SLC4A7 and/or low SLC9A1 mRNA expression. We conclude that the molecular mechanisms of acid-base regulation depend on clinicopathological characteristics of breast cancer patients. NBCn1 expression and dependency on Na+,HCO3- cotransport for pHi regulation, measured in biopsies of human primary breast carcinomas, independently predict proliferative activity, lymph node metastasis, and patient survival.

Unique Regulation of Coupled NaCl Absorption by Inducible Nitric Oxide in a Spontaneous SAMP1/YitFc Mouse Model of Chronic Intestinal Inflammation.

In the small intestine, Na:H (NHE3) and Cl:HCO3 (DRA or PAT1) exchangers present in the brush border membrane (BBM) of absorptive villus cells are primarily responsible for the coupled absorption of NaCl, the malabsorption of which causes diarrhea, a common symptom of inflammatory bowel disease (IBD). Inducible nitric oxide (iNO), a known mediator of inflammation, is increased in the mucosa of the chronically inflamed IBD intestine. An SAMP1/YitFc (SAMP1) mouse, a spontaneous model of chronic ileitis very similar to human IBD, was used to study alterations in NaCl absorption. The SAMP1 and control AKR mice were treated with I-N(6)-(1-Iminoethyl)-lysine (L-NIL) to inhibit iNO production, and DRA/PAT1 and NHE3 activities and protein expression were studied. Though Na:H exchange activity was unaffected, Cl:HCO3 activity was significantly decreased in SAMP1 mice due to a reduction in its affinity for Cl, which was reversed by L-NIL treatment. Though DRA and PAT1 expressions were unchanged in all experimental conditions, phosphorylation studies indicated that DRA, not PAT1, is affected in SAMP1. Moreover, the altered phosphorylation levels of DRA was restored by L-NIL treatment. Inducible NO mediates the inhibition of coupled NaCl absorption by decreasing Cl:HCO3 but not Na:H exchange. Specifically, Cl:HCO3 exchanger DRA but not PAT1 is regulated at the level of its phosphorylation by iNO in the chronically inflamed intestine.

Interaction of NHE1 and TRPA1 Activity in DRG Neurons Isolated from Adult Rats and its Role in Inflammatory Nociception

Transient receptor potential ankyrin 1 (TRPA1) channel is expressed in a subset of nociceptive neurons. This channel integrates several nociceptive signals. Particularly, it is modulated by intracellular pH (pHi). Na+/H+ exchanger 1 (NHE1) contributes to the maintenance of pHi in nociceptors. However, it is currently unknown whether the interaction between TRPA1 and NHE1 contributes to the nociceptive processing. Thus, the purpose of this study was to assess the functional interaction between NHE1 and TRPA1 in small dorsal root ganglion (DRG) neurons from primary culture obtained from adult rats. Moreover, we also evaluated their possible interaction in acute and inflammatory pain. Zoniporide (selective NHE1 inhibitor) reduced pHi and increased intracellular calcium in a concentration-dependent fashion in DRG neurons. Zoniporide and allyl isothiocyanate (AITC, TRPA1 agonist) increased calcium transients in the same DRG neuron, whereas that A-967079 (TRPA1 antagonist) prevented the effect of zoniporide in DRG neurons. Repeated AITC induced TRPA1 desensitization and this effect was prevented by zoniporide. Both NHE1 and TRPA1 were localized at the membrane surface of DRG neurons in culture. Local peripheral zoniporide enhanced AITC-induced pronociception and this effect was prevented by A-967079. Likewise, zoniporide potentiated Complete Freund’s Adjuvant (CFA)-induced hypersensitivity, effect which was prevented by A-967079 in vivo. CFA paw injection increased TRPA1 and decresed NHE1 protein expression in DRG. These results suggest a functional interaction between NHE1 and TRPA1 in DRG neurons in vitro. Moreover, data suggest that this interaction participates in acute and inflamatory pain conditions in vivo.

Selective Renal Silencing of the Calcineurin Homologous Protein‐1 Decreases Blood Pressure in Balb/cJ Mice

Hypertension has high incidence and health care cost. Its treatments are often ineffective; therefore, we are in need of new strategies to prevent, limit or reverse hypertension. Long-term regulation of blood pressure (BP) has fundamental renal components; in particular, the causes of impaired renal Na+ handling and possible strategies to overcome disturbances in renal Na+ balance in hypertension are not well defined. Recently, we have shown that a Ca2+-binding protein, the Calcineurin Homologous Protein-1 (CHP1), is a regulatory binding partner of a key player in the control of Na+ homeostasis, the epithelial brush-border Na+/H+ exchanger-3 (NHE3). Here, we proposed that CHP1 expression controls BP as a regulatory co-factor of NHE3 transport. Indeed, selective renal silencing of Chp1 via renal subcapsular infusion of Chp1 siRNA in Balb/cJ mice significantly reduced NHE3 protein expression (-50%). Importantly, Chp1 siRNA treated mice had a reduced systolic blood pressure compared to scrambled siRNA treated mice (-30%) measured in anesthetized mice from the aorta and femoral artery, and in conscious mice using noninvasive tail-cuff method. Chp1 siRNA treated mice also had markedly reduced serum Na+ and increased urinary Na+ excretion compared to scrambled siRNA treated mice. Serum K+ and Cl- did not change while urinary K+ and Cl- excretion were increased in Chp1 siRNA treated mice. Glomerular Filtration Rate estimated by creatinine clearance was reduced in Chp1 treated mice possibly as consequence of tubuloglomerular feedback. This is the first animal model in mammals where the effect of a reduction in CHP1 protein expression in the kidney was studied. Our findings provide new insights into the action of CHP1 on renal tubular Na+ transport and propose CHP1 protein expression as a novel tool to significantly control blood pressure.

Long-Term Angiotensin II Infusion Induces Oxidative and Endoplasmic Reticulum Stress and Modulates Na+ Transporters Through the Nephron.

High plasma angiotensin II (Ang II) levels are related to many diseases, including hypertension, and chronic kidney diseases (CKDs). Here, we investigated the relationship among prolonged Ang II infusion/AT1 receptor (AT1R) activation, oxidative stress, and endoplasmic reticulum (ER) stress in kidney tissue. In addition, we explored the chronic effects of Ang II on tubular Na+ transport mechanisms. Male Wistar rats were subjected to sham surgery as a control or prolonged Ang II treatment (200 ng⋅kg–1⋅min–1, 42 days) with or without losartan (10 mg⋅kg–1⋅day–1) for 14 days. Ang II/AT1R induced hypertension with a systolic blood pressure of 173.0 ± 20 mmHg (mmHg, n = 9) compared with 108.0 ± 7 mmHg (mmHg, n = 7) in sham animals. Under these conditions, gene and protein expression levels were evaluated. Prolonged Ang II administration/AT1R activation induced oxidative stress and ER stress with increased Nox2, Nox4, Cyba and Ncf1 mRNA expression, phosphorylated PERK and eIF2α protein expression as well as Atf4 mRNA expression. Ang II/AT1R also raised Il1b, Nfkb1 and Acta2 mRNA expression, suggesting proinflammatory, and profibrotic effects. Regarding Na+ tubular handling, Ang II/AT1R enhanced cortical non-phosphorylated and phospho/S552/NHE3, NHE1, ENaC β, NKCC2, and NCC protein expression. Our results also highlight the therapeutic potential of losartan, which goes beyond the antihypertensive effect, playing an important role in kidney tissue. This treatment reduced oxidative stress and ER stress signals and recovered relevant parameters of the maintenance of renal function, preventing the progression of Ang II-induced CKD.

Abstract P761: Reducing Reactive Astrocytes Improves Cognitive Function in a Mouse Model of Vascular Cognitive Impairment and Dementia

Inflammation and reactive astrocytes are pathologic features in vascular cognitive impairment and dementia (VCID). However, there are no effective therapies to reduce chronic hypoperfusion-induced reactive astrocytes and neuroinflammation and cognitive deficits in VCID. Activation of Na + /H + exchanger 1 (NHE1) in astrocytes mediates Na + influx in exchange of H + efflux, causing hypertrophy and swelling of reactive astrocytes after acute brain injury. Whether pharmacological blockade of NHE1 protein can reduce reactive astrocytes and improve cognitive deficits remains untested. Bilateral carotid artery stenosis (BCAS) with microcoils as a murine VCID model was induced in adult male C57BL/6 mice. BCAS procedures led to sustained reduction (30-40%) in cerebral blood flow (CBF) and deficits in special working memory by 30 days post-surgery (p &lt; 0.05). Compared with sham control mice, BCAS mice displayed demyelination in corpus callosum (CC) and external capsule (EC) at 30 days post-surgery (p &lt; 0.05). There were significantly increased GFAP + astrocytes and Iba1 + microglia in CC, EC and hippocampus in BCAS brain at 30 days post-surgery (p &lt; 0.05). Interestingly, those GFAP + astrocytes and Iba1 + microglia exhibited elevated NHE1 protein expression in these brain regions (p &lt; 0.05). These results suggest that NHE1 protein may play a role in chronic hypoperfusion-induced reactive astrocyte transformation and microglia activation. We administered saline vehicle (Veh) or NHE1 inhibitor HOE642 during 30 days post-BCAS (via either i.p. or osmotic mini-pump). The Veh- and HOE642-treated BCAS mice caused similar reduction in CBF. Compared to the Veh controls, both HOE642 treatment regimens significantly improved cognitive performance at 30 days post-surgery (p &lt; 0.05). Causative relationship between blockade of NHE1 protein activation and reducing glia-mediated inflammation and demyelination are under investigation by immunostaining assessments and ex-vivo MRI DTI analysis. Taken together, our study suggests that elevation of NHE1 protein activity plays a role in glial activation in the murine VCID model. Pharmacological blockade of NHE1 protein shows efficacy in reducing cerebral hypoperfusion-induced chronic brain injury and cognitive impairment.

Abstract 16216: Increases in Renal Nkcc2 and Ncc Preceded the Elevation of Blood Pressure in Mice Treated With Clozapine

One of major side effects of clozapine, a common antipsychotic drug, is hypertension. In order to explore the pathogenesis of the drug-induced hypertension, we examined the renal sodium transport proteins and BP in the C57Bl6/J male mice treated with clozapine at different doses for 1 week. Clozapine at 20mg/kg/day via osmotic mini-pump increased SBP ( 110±0.6,mmHg, femoral artery, under anesthesia) and DBP (76.7±1) relative to vehicle (97.6±1.2/71.2±2.7) while the renal protein expression of NKCC2 (180±21, % of vehicle) and NCC (171±22), and ENaC-α (140±7), β(166±21) and γ(130±7) was increased without changes in NHE3 and α1-NKA (n=5/group). Clozapine at lower doses (5&amp;10mg/kg/day,IP) did not change the conscious SBP and DBP monitored daily by tail-cuff, even on day 7 in 5 mg/kg group (115.61±1.6/90.1±1.3) and in 10mg/kg group (116.8±2/89.0±1.6) relative to vehicle (111.9±1.5/86.9±1.4) (n=4/group). Urinary excretion of Na + &amp; K + and serum concentrations of Na + , K + , Cl - , creatinine were similar in all groups. However, renal protein expression of NKCC2 was increased in 5mg/kg (360±80, % of vehicle) and 10mg/kg (247±50) groups; NCC was increased at 5 mg/kg (175±9); α1-NKA was increased in 5mg/kg (216±5) and 10mg/kg (163±2) groups. No increases were found in the protein expression of NHE3 and ENaCs. Those increases in renal NKCC2 &amp;NCC at 5 &amp; 10 mg/kg were consistent with those at 20 mg/kg. AT1R was increased at 5 (221±20) &amp;10mg/kg (255±21) while renin (186±15) and ACE1 (186±5), not ACE2, were increased at 5 mg/kg suggesting an activation of RAAS in kidney. NOX4, not NOX2, was increased at 5 mg/kg (453±69) while NOS3, not NOS1&amp;2, was decreased at 5 (60±21) and 10mg/kg (64±5) groups. TNFα, not IL-6 was increased at 5 (222±18) &amp;10 mg/kg (321±26). In cultured mouse distal convoluted tubule cells, clozapine also increased NCC and α1-NKA at 1nM (169±4;156±7) and 10nm(175±23;183±15) respectively ( 24h,n=4/group). Those changes in kidney, including increases in sodium transport proteins, RAAS components, ROS generation enzymes, inflammation factors and decrease in NO synthase, preceded the elevation of BP suggesting that direct or indirect regulations of clozapine on those proteins may play an important role in the pathogenesis of the drug-induced hypertension.