- Hypertension, Renal
- Kidney Stones
Honors & Awards
Phi Beta Kappa, Stanford University (1994)
John S. Miller Award, University of Texas Southwestern Medical Center (2001)
SPARK Scholar, Stanford University (2010)
Fellowship: UCSF Dept of Nephrology (2006) CA
Residency: University of Texas Southwestern Medical Center (2001) TX
M.D., Washington University, Medicine (1998)
B.S., Stanford University, Biological Sciences (1994)
Current Research and Scholarly Interests
We are interested in how the kidneys control salt, water, and electrolyte homeostasis in the body. We use cultured kidney cells, transgenic mice, and human samples to study hormonal and signal transduction pathways that control epithelial ion transport. Clinical implications of our work include a better understanding of the pathogenesis of salt-sensitive hypertension and kidney stone formation and growth.
Graduate and Fellowship Programs
Osteoporosis, Fractures, and Bone Mineral Density Screening in Veterans With Kidney Stone Disease.
Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research
Whether a link exists between kidney stone disease and osteoporosis or fractures remains an open question. In this retrospective cohort study, we sought to determine the prevalence of osteoporosis and fractures and rate of bone mineral density screening by dual-energy X-ray absorptiometry (DXA) in patients with kidney stone disease. We examined nationwide data from the Veterans Health Administration and identified 531,431 patients with kidney stone disease between 2007 and 2015. Nearly 1 in 4 patients (23.6%, 95% confidence interval [CI] 23.5-23.7) with kidney stone disease had a prevalent diagnosis of osteoporosis or fracture. In patients with no prior history of osteoporosis or bone mineral density assessment before a kidney stone diagnosis, 9.1% were screened with DXA after their kidney stone diagnosis, of whom 20% were subsequently diagnosed with osteoporosis. Our findings provide support for wider use of bone mineral density screening in patients with kidney stone disease, including middle-aged and older men, a group less well recognized as at risk for osteoporosis or fractures. © 2021 American Society for Bone and Mineral Research (ASBMR).
View details for DOI 10.1002/jbmr.4260
View details for PubMedID 33655611
Evaluation of Patient Treatment Preferences for 15-20mm Kidney Stones: A Conjoint Analysis.
Journal of endourology
INTRODUCTION AND OBJECTIVE: Ureteroscopy (URS) and percutaneous nephrolithotomy (PCNL) are standard surgical treatments for intermediate-size (15-20mm) kidney stones but differ in their postoperative recovery, stone-free rates, and complication risks. We aimed to evaluate what affects patient treatment preferences.METHODS: Patients with urinary stone disease completed a choice-based conjoint analysis exercise assessing four treatment attributes associated with URS and PCNL. A sensitivity analysis using a market simulator was performed and the relative importance of each attribute was calculated. Differences in treatment preferences by demographic subgroup were assessed.RESULTS: A total of 58 patients completed the conjoint analysis exercise. Stone-free rate was the most important treatment attribute while length of hospital stay and cosmesis were less important. Overall, sensitivity analysis based on market simulation scenarios predicted almost equal preference for URS (52.4%) compared to PCNL (47.6%) for treatment of an intermediate-size stone. Older patients (>65 yo) expressed stronger preferences for lower infection rates and shorter hospital stays, and were more likely to prefer URS (67.2%, 95% CI: 52 - 82.5%) compared to younger patients (20-34 yo) (20.3%, 95% CI: 0 - 41.5%) who preferred higher procedure success rates and fewer repeat procedures.CONCLUSION: Conjoint analysis predicts nearly equal patient preference for URS or PCNL for the treatment of intermediate-size kidney stones. Older patients prefer the lower UTI risk and shorter hospital stay associated with URS, while younger patients prefer higher stone-free rates associated with PCNL. These results can help guide urologists in counseling patients and improve the shared decision-making process.
View details for DOI 10.1089/end.2020.0370
View details for PubMedID 32867549
Analysis of Primary Hyperparathyroidism Screening Among US Veterans With Kidney Stones.
Importance: Approximately 3% to 5% of patients with kidney stones have primary hyperparathyroidism (PHPT), a treatable cause of recurrent stones. However, the rate of screening for PHPT in patients with kidney stones remains unknown.Objectives: To estimate the prevalence of parathyroid hormone (PTH) testing in veterans with kidney stones and hypercalcemia and to identify the demographic, geographic, and clinical characteristics of veterans who were more or less likely to receive PTH testing.Design, Setting, and Participants: This cohort study obtained Veterans Health Administration (VHA) health records from the Corporate Data Warehouse for veterans who received care in 1 of the 130 VHA facilities across the United States from January 1, 2008, through December 31, 2013. Historical encounters, medical codes, and laboratory data were assessed. Included patients had diagnostic or procedural codes for kidney or ureteral stones, and excluded patients were those with a previous serum PTH level measurement. Data were collected from January 1, 2006, to December 31, 2014. Data analysis was conducted from June 1, 2019, to January 31, 2020.Exposures: Elevated serum calcium concentration measurement between 6 months before and 6 months after kidney stone diagnosis.Main Outcomes and Measures: Proportion of patients with a serum PTH level measurement and proportion of patients with biochemical evidence of PHPT who underwent parathyroidectomy.Results: The final cohort comprised 7561 patients with kidney stones and hypercalcemia and a mean (SD) age of 64.3 (12.3) years. Of these patients, 7139 were men (94.4%) and 5673 were white individuals (75.0%). The proportion of patients who completed a serum PTH level measurement was 24.8% (1873 of 7561). Across the 130 VHA facilities included in the study, testing rates ranged from 4% to 57%. The factors associated with PTH testing included the magnitude of calcium concentration elevation (odds ratio [OR], 1.07 per 0.1 mg/dL >10.5 mg/dL; 95% CI, 1.05-1.08) and the number of elevated serum calcium concentration measurements (OR, 1.08 per measurement >10.5 mg/dL; 95% CI, 1.06-1.10) as well as visits to both a nephrologist and a urologist (OR, 6.57; 95% CI, 5.33-8.10) or an endocrinologist (OR, 4.93; 95% CI, 4.11-5.93). Of the 717 patients with biochemical evidence of PHPT, 189 (26.4%) underwent parathyroidectomy within 2 years of a stone diagnosis.Conclusions and Relevance: This cohort study found that only 1 in 4 patients with kidney stones and hypercalcemia were tested for PHPT in VHA facilities and that testing rates varied widely across these facilities. These findings suggest that raising clinician awareness to PHPT screening indications may improve evaluation for parathyroidectomy, increase the rates of detection and treatment of PHPT, and decrease recurrent kidney stone disease.
View details for DOI 10.1001/jamasurg.2020.2423
View details for PubMedID 32725208
- Role of AVP in the Pathology of Liddle's Syndrome WILEY. 2020
The Urine Albumin-Creatinine Ratio and Kidney Function after Nephrectomy.
The Journal of urology
BACKGROUND: Patients with kidney cancer are at risk of developing chronic kidney disease (CKD) after radical and partial nephrectomy. We sought to determine if the urine albumin-creatinine ratio (UACR) is independently associated with progressive CKD after nephrectomy.METHODS: We performed a cohort study based within a large, integrated health care system. We identified patients who underwent radical or partial nephrectomy from 2004 to 2014 with UACR measured in the 12 months prior to surgery. We fit multivariable models to determine if the UACR was associated with the time to CKD progression (defined as reaching stage 4 or 5 CKD, eGFR <30 mL/min/1.73m2). We performed a parallel analysis measuring the time to stage 3b, 4 or 5 CKD (eGFR <45 mL/min/1.73m2) among patients with normal or near-normal preoperative kidney function (eGFR ≥60 mL/min/1.73 m2). We also examined the association between UACR and survival.RESULTS: 1930 patients underwent radical or partial nephrectomy and had preoperative UACR and pre- and post-operative eGFR. Of these, 658 (34%) and 157 (8%) had moderate (UACR 30-300mg/g) or severe albuminuria (UACR > 300mg/g), respectively. Albuminuria severity was independently associated with progressive CKD after radical (moderate albuminuria HR 1.7, 95%CI 1.4-2.2; severe albuminuria HR 2.3, 95%CI 1.7-3.1) and partial nephrectomy (moderate albuminuria HR 1.8, 95%CI 1.2-2.7; severe albuminuria HR 4.3, 95%CI 2.7-7.0). Albuminuria was also associated with survival following radical and partial nephrectomy.CONCLUSIONS: In patients undergoing radical or partial nephrectomy, the severity of albuminuria can stratify risk of progressive CKD.
View details for DOI 10.1097/JU.0000000000001005
View details for PubMedID 32125227
SLIPS-LAB-A bioinspired bioanalysis system for metabolic evaluation of urinary stone disease.
2020; 6 (21)
Urinary stone disease is among the most common medical conditions. Standard evaluation of urinary stone disease involves a metabolic workup of stone formers based on measurement of minerals and solutes excreted in 24-hour urine samples. Nevertheless, 24-hour urine testing is slow, expensive, and inconvenient for patients, which has hindered widespread adoption in clinical practice. Here, we demonstrate SLIPS-LAB (Slippery Liquid-Infused Porous Surface Laboratory), a droplet-based bioanalysis system, for rapid measurement of urinary stone-associated analytes. The ultra-repellent and antifouling properties of SLIPS, which is a biologically inspired surface technology, allow autonomous liquid handling and manipulation of physiological samples without complicated sample preparation procedures and supporting equipment. We pilot a study that examines key urinary analytes in clinical samples from patients with urinary stone. The simplicity and speed of SLIPS-LAB hold the potential to provide actionable diagnostic information for patients with urinary stone disease and rapid feedback for responses to dietary and pharmacologic treatments.
View details for DOI 10.1126/sciadv.aba8535
View details for PubMedID 32937323
Urinary Stone Disease in Pregnancy: Current Management Practices in a Large National Cohort.
To define current national practice patterns of imaging modalities and urologic procedures in pregnant women with urinary stone disease.Using the IBM® MarketScan® national insurance claims database, we identified pregnant women with urinary stone disease and their corresponding gestational age between 2011-2016 using administrative claims data. We then assessed each encounter for urinary stone disease or stone-related urologic procedure during their pregnancy. We abstracted demographic information as well as codes for stone procedures and imaging.We identified 14,298 pregnant women with urinary stone disease during the study period. Of the 12,315 undergoing abdominal imaging (86.1%), magnetic resonance imaging (MRI) in 2.8%, x-ray in 9%, and ultrasound in 74.3%. Computed tomography was not used as a diagnostic modality during pregnancy. Procedural intervention was performed in 749 women (5.2%): 476 (3.3%) ureteral stent placement without definitive stone treatment, 93 (0.6%) percutaneous nephrostomy placement, and 180 (1.3%) ureteroscopy (URS) for definitive stone treatment. URS was most commonly performed before 34 weeks gestation with only 27 cases (15%) performed after.This large national cohort reveals the current imaging and procedural practice patterns for urinary stone disease during pregnancy and provides a critical baseline as these practice patterns evolve in the future.
View details for DOI 10.1016/j.urology.2020.03.050
View details for PubMedID 32311447
Urinary Stone Disease in Pregnancy: A Claims-Based Analysis of 1.4 Million Patients.
The Journal of urology
PURPOSE: Urinary stone disease during pregnancy is poorly understood but is thought to be associated with increased maternal and fetal morbidity. We sought to determine the prevalence of urinary stone disease in pregnancy and whether urinary stone disease during pregnancy is associated with adverse pregnancy outcomes.MATERIALS AND METHODS: We identified all pregnant women from 2003 through 2017 in the Optum national insurance claims database. We used diagnosis claims to identify urinary stone disease and assess medical comorbidity. We established the prevalence of urinary stone disease during pregnancy, stratified by week of pregnancy. We further evaluated associations among urinary stone disease and maternal complications and pregnancy outcomes in both univariable and multivariable analyses.RESULTS: Urinary stone disease affects 8/1000 pregnancies and is more common in white women and women with more comorbid conditions. In fully adjusted models, pregnancies complicated by urinary stone disease had higher rates of adverse fetal outcomes, including prematurity and spontaneous abortions. This analysis is limited by its retrospective administrative claims design.CONCLUSIONS: The rate of urinary stone disease during pregnancy is higher than previously reported. Urinary stone disease is associated with adverse pregnancy outcomes.
View details for DOI 10.1097/JU.0000000000000657
View details for PubMedID 31738114
Ultra-low-dose CT: An Effective Follow-up Imaging Modality for Ureterolithiasis.
Journal of endourology
BACKGROUND AND PURPOSE: Classically, abdominal X-ray (KUB), ultrasound or a combination of both have been routinely used for ureteral stone surveillance after initial diagnosis. More recently, ultra-low-dose CT (ULD CT) has emerged as a CT technique that reduces radiation dose while maintaining high sensitivity and specificity for urinary stone detection. We aim to evaluate our initial experience with ULD CT for patients with ureterolithiasis, measuring real-world radiation doses and stone detection performance.METHODS: We reviewed all ULD CT scans performed at the Veterans Affairs Palo Alto Health Care System between 2016 and 2018. We included patients with ureteral stones and calculated the mean effective radiation dose per scan. We determined stone location and size, if the stone was visible on the associated KUB or CT scout film, and if hydronephrosis was present. We performed logistic regression to identify variables associated with visibility on KUB or CT scout film and hydronephrosis.RESULTS: One-hundred and eighteen ULD scans were reviewed, of which 50 detected ureteral stones. The mean effective radiation dose was 1.04 ± 0.41 mSv. Of the ULD CTs that detected ureterolithiasis, 38% lacked visibility on KUB/CT scout film and had no associated hydronephrosis, suggesting they would be missed with a combination of KUB and ultrasound. Larger stones (OR: 1.40, 95% CI: 1.08-1.96 for every 1mm increase in stone size) were more likely to be detected by KUB/CT scout or ultrasound, while stones in the distal ureter (OR: 0.18, 95% CI: 0.03-0.81) were more likely to be missed by KUB/CT scout or hydronephrosis.CONCLUSION: Based on our institutions' initial experience with ULD CT, ULD CT detects small and distal ureteral stones that would likely be missed by KUB or ultrasound, while maintaining a low effective radiation dose. An ULD CT protocol should be considered when re-imaging for ureteral stones is necessary.
View details for DOI 10.1089/end.2019.0574
View details for PubMedID 31663371
Prevalence of twenty-four hour urine testing in Veterans with urinary stone disease.
2019; 14 (8): e0220768
The American Urological Association guidelines recommend 24-hour urine testing in patients with urinary stone disease to decrease the risk of stone recurrence; however, national practice patterns for 24-hour urine testing are not well characterized. Our objective is to determine the prevalence of 24-hour urine testing in patients with urinary stone disease in the Veterans Health Administration and examine patient-specific and facility-level factors associated with 24-hour urine testing. Identifying variations in clinical practice can inform future quality improvement efforts in the management of urinary stone disease in integrated healthcare systems.We accessed national Veterans Health Administration data through the Corporate Data Warehouse (CDW), hosted by the Veterans Affairs Informatics and Computing Infrastructure (VINCI), to identify patients with urinary stone disease. We defined stone formers as Veterans with one inpatient ICD-9 code for kidney or ureteral stones, two or more outpatient ICD-9 codes for kidney or ureteral stones, or one or more CPT codes for kidney or ureteral stone procedures from 2007 through 2013. We defined a 24-hour urine test as a 24-hour collection for calcium, oxalate, citrate or sulfate. We used multivariable regression to assess demographic, geographic, and selected clinical factors associated with 24-hour urine testing.We identified 130,489 Veterans with urinary stone disease; 19,288 (14.8%) underwent 24-hour urine testing. Patients who completed 24-hour urine testing were younger, had fewer comorbidities, and were more likely to be White. Utilization of 24-hour urine testing varied widely by geography and facility, the latter ranging from 1 to 40%.Fewer than one in six patients with urinary stone disease complete 24-hour urine testing in the Veterans Health Administration. In addition, utilization of 24-hour urine testing varies widely by facility identifying a target area for improvement in the care of patients with urinary stone disease. Future efforts to increase utilization of 24-hour urine testing and improve clinician awareness of targeted approaches to stone prevention may be warranted to reduce the morbidity and cost of urinary stone disease.
View details for DOI 10.1371/journal.pone.0220768
View details for PubMedID 31393935
- Spironolactone plus patiromer: proceed with caution. Lancet (London, England) 2019; 394 (10208): 1486–88
Twenty-Four Hour Urine Testing and Prescriptions for Urinary Stone Disease-Related Medications in Veterans.
Clinical journal of the American Society of Nephrology : CJASN
Current guidelines recommend 24-hour urine testing in the evaluation and treatment of persons with high-risk urinary stone disease. However, how much clinicians use information from 24-hour urine testing to guide secondary prevention strategies is unknown. We sought to determine the degree to which clinicians initiate or continue stone disease-related medications in response to 24-hour urine testing.We examined a national cohort of 130,489 patients with incident urinary stone disease in the Veterans Health Administration between 2007 and 2013 to determine whether prescription patterns for thiazide diuretics, alkali therapy, and allopurinol changed in response to 24-hour urine testing.Stone formers who completed 24-hour urine testing (n=17,303; 13%) were significantly more likely to be prescribed thiazide diuretics, alkali therapy, and allopurinol compared with those who did not complete a 24-hour urine test (n=113,186; 87%). Prescription of thiazide diuretics increased in patients with hypercalciuria (9% absolute increase if urine calcium 201-400 mg/d; 21% absolute increase if urine calcium >400 mg/d, P<0.001). Prescription of alkali therapy increased in patients with hypocitraturia (24% absolute increase if urine citrate 201-400 mg/d; 34% absolute increase if urine citrate ≤200 mg/d, P<0.001). Prescription of allopurinol increased in patients with hyperuricosuria (18% absolute increase if urine uric acid >800 mg/d, P<0.001). Patients who had visited both a urologist and a nephrologist within 6 months of 24-hour urine testing were more likely to have been prescribed stone-related medications than patients who visited one, the other, or neither.Clinicians adjust their treatment regimens in response to 24-hour urine testing by increasing the prescription of medications thought to reduce risk for urinary stone disease. Most patients who might benefit from targeted medications remain untreated.
View details for DOI 10.2215/CJN.03580319
View details for PubMedID 31712387
- Payer Type, Race/Ethnicity, and the Timing of Surgical Management of Urinary Stone Disease JOURNAL OF ENDOUROLOGY 2019; 33 (2): 152–58
PREOPERATIVE KIDNEY FUNCTION TRENDS: IMPROVING ESTIMATES OF BASELINE KIDNEY FUNCTION PRIOR TO KIDNEY CANCER SURGERY
ELSEVIER SCIENCE INC. 2018: E362
View details for Web of Science ID 000429166601066
Unplanned Emergency Department Visits and Hospital Admissions Following Ureteroscopy: Do Ureteral Stents Make a Difference?
The comparative effectiveness of ureteral stents placed during ureteroscopy for urinary stone disease is widely debated. We sought to evaluate unplanned medical visits within the early post-operative period after ureteroscopy in patients with and without ureteral stent placement.We identified all ureteroscopic procedures for urinary stone disease in the California Office of Statewide Health Planning and Development (OSHPD) database from 2010-2012. The primary outcome was any emergency department visit or inpatient hospital admission in the first 7 days following ureteroscopy. Patients were sub-categorized by type of ureteroscopy (i.e. laser lithotripsy versus basket retrieval) and analyzed for significant differences between stented and unstented patients. Multivariable logistic regression was performed to determine if ureteral stent placement was independently associated with unplanned visits.Our analytic cohort included 16,060 patients undergoing 17,716 ureteroscopy procedures. A ureteral stent was placed in 86.2% of patients undergoing laser lithotripsy, and 70.5% of patients receiving basket retrieval. In the 7 days following ureteroscopy, 6.6% of patients were seen in the emergency department and 2.2% of patients were admitted to a hospital. In a fully adjusted model, the utilization of a ureteral stent was not associated with emergency department visits or inpatient admissions.Ureteral stent placement during ureteroscopy is not associated with an increased odds of emergency department visits and inpatient admissions in the early post-operative period.
View details for PubMedID 29601836
Redefining the Stone Belt: Precipitation is Associated with Increased Risk of Urinary Stone Disease.
Journal of endourology
Objectives The American Southeast has been labeled the "Stone Belt" due to its relatively high burden of urinary stone disease, presumed to be related to its higher temperatures. However, other regions with high temperatures (e.g. the Southwest) do not have the same disease prevalence as the southeast. We seek to explore the association of stone disease to other climate-associated factors beyond temperature including precipitation and temperature variation.We identified all patients who underwent a surgical procedure for urinary stone disease from the California Office of Statewide Health Planning and Development (OSHPD) databases (2010-2012). Climate data obtained from the National Oceanic and Atmospheric Administration was compared to population adjusted county operative stone burden, controlling for patient and county demographic data as potential confounders.A total of 63,994 unique patients underwent stone procedures in California between 2010-2012. Multivariate modeling revealed higher precipitation (0.019 average increase in surgeries per 1000 persons per inch, p<0.01) and higher mean temperature (0.029 average increase in surgeries per 1000 persons per degree, p<0.01) were both independently associated with an increased operative stone disease burden. Controlling for county level patient factors did not change these observed effects. Conclusion In the state of California, higher precipitation and higher mean temperature are associated with increased rates of stone surgery. Our results appear to agree with the larger trends seen throughout the United States where the areas of highest stone prevalence have warm wet climates, and not warm arid, climates.
View details for PubMedID 28830242
Crescentic Glomerulonephritis With Immunoglobulin G4-Related Disease.
The American journal of the medical sciences
2017; 354 (3): 236–39
Immunoglobulin G4 (IgG4)-related disease is an uncommon autoimmune disease that affects multiple organ systems. Renal involvement typically presents as tubulointerstitial nephritis and less commonly as membranous glomerulonephritis. In this case report, we discuss a 68-year-old patient who presented with rapidly progressive glomerulonephritis. His renal biopsy revealed a membranoproliferative pattern of injury with fibrocellular crescents and extensive infiltration of the tubulointerstitium with IgG4-positive plasma cells. We treated the patient with both corticosteroids and rituximab because of the aggressive nature of crescentic glomerulonephritis. The patient demonstrated a partial improvement in kidney function after 2 cycles of rituximab with a decrease in serum creatinine levels from 6.9-4.7mg/dL after 6 months from presentation. This case illustrates the importance of considering IgG4-related disease in cases of rapidly progressive glomerulonephritis and the need for effective treatments for more aggressive forms of this recently recognized disease entity.
View details for PubMedID 28918828
An experimentum crucis in salt sensitivity.
American journal of physiology. Renal physiology
2017; 312 (1): F190–F191
View details for PubMedID 27654894
SGK1 regulation by miR-466g in cortical collecting duct cells
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2016; 310 (11): F1251-F1257
MicroRNAs (miRNAs) are non-coding RNAs that bind target mRNA transcripts and modulate gene expression. In the cortical collecting duct (CCD), aldosterone stimulates the expression of genes that increase activity of the epithelial sodium channel (ENaC); in the early phase of aldosterone induction, one such gene is serum and glucocorticoid regulated kinase 1 (SGK1). We hypothesized that aldosterone regulates the expression of miRNAs in the early phase of induction to control the expression of target genes that stimulate ENaC activity. We treated mpkCCDc14 cells with aldosterone or vehicle for 1 hour and used a miRNA microarray to analyze differential miRNA expression. We identified miR-466g as a miRNA that was decreased by 57% after 1 hour of aldosterone treatment. Moreover, we identified a putative miR-466g binding site in the 3'-UTR of SGK1. We constructed an SGK1 3'-UTR luciferase reporter and found that co-transfection of miR-466g suppressed luciferase activity in HEK293 cells in a dose dependent manner. Deletion or introduction of point mutations that disrupt the miR-466g target site attenuated miR-466g-directed suppression of luciferase activity. Finally, we generated stably transduced mpkCCDc14 cell lines over-expressing miR-466g. Cells over-expressing miR-466g demonstrated 12.9 fold lower level of SGK1 mRNA compared to control cells after 6 hours of aldosterone induction; moreover, cells over-expressing miR-466g exhibited 25% decrease in amiloride-sensitive current after 6 hours of aldosterone induction and complete loss of amiloride-sensitive current after 24 hours of aldosterone induction. Our findings implicate miR-466g as a novel aldosterone responsive miRNA that regulates SGK1 and ENaC in CCD cells.
View details for DOI 10.1152/ajprenal.00024.2016
View details for PubMedID 26911843
Serum- and glucocorticoid-inducible kinase SGK2 regulates human organic anion transporters 4 via ubiquitin ligase Nedd4-2.
2016; 102: 120-129
Human organic anion transporter 4 (hOAT4) belongs to a family of organic anion transporters that play critical roles in the body disposition of clinically important drugs, including anti-viral therapeutics, anti-cancer drugs, antibiotics, antihypertensives, and anti-inflammatories. hOAT4 is abundantly expressed in the kidney and placenta. In the current study, we examined the regulation of hOAT4 by serum- and glucocorticoid-inducible kinase 2 (sgk2) in the kidney COS-7 cells. We showed that sgk2 stimulated hOAT4 transport activity. Such stimulation mainly resulted from an increased cell surface expression of the transporter, kinetically revealed as an increased maximal transport velocity Vmax without significant change in substrate-binding affinity Km. We further showed that regulation of hOAT4 activity by sgk2 was mediated by ubiquitin ligase Nedd4-2. Overexpression of Nedd4-2 enhanced hOAT4 ubiquitination, and inhibited hOAT4 transport activity, whereas overexpression of ubiquitin ligase-dead mutant Nedd4-2/C821A or siRNA knockdown of endogenous Nedd4-2 had opposite effects on hOAT4. Our co-immunoprecipitation experiment revealed that sgk2 weakened the association between hOAT4 and Nedd4-2. In conclusion, our study demonstrated for the first time that sgk2 stimulated hOAT4 transport activity by abrogating the inhibitory effect of Nedd4-2 on the transporter.
View details for DOI 10.1016/j.bcp.2015.11.024
View details for PubMedID 26740304
- There and back again: insulin, ENaC, and the cortical collecting duct. Physiological reports 2016; 4 (10)
Harvest and primary culture of the murine aldosterone-sensitive distal nephron.
American journal of physiology. Renal physiology
2015; 308 (11): F1306-15
The aldosterone-sensitive distal nephron (ASDN) exhibits axial heterogeneity in structure and function from the distal convoluted tubule to the medullary collecting duct. Ion and water transport is primarily divided between the cortex and medulla of the ASDN, respectively. Transcellular transport in this segment is highly regulated in health and disease and is integrated across different cell types. We currently lack an inexpensive, high-yield, and tractable technique to harvest and culture cells for the study of gene expression and physiologic properties of mouse cortical ASDN. To address this need, we harvested tubules bound to Dolichos biflorus agglutinin (DBA) lectin-coated magnetic beads from kidney cortex and characterized these cell preparations. We determined that these cells are enriched for markers of distal convoluted tubule, connecting tubule, and cortical collecting duct, including principal and intercalated cells. In primary culture these cells develop polarized monolayers with high-resistance (1000-1500 Ω*cm(2)), and maintain expression and activity of key channels. These cells demonstrate an amiloride-sensitive short-circuit current that can be enhanced with aldosterone and maintain measurable potassium and anion secretion. Our method can be easily adopted to study the biology of the ASDN and to investigate phenotypic differences between wild-type and transgenic mouse models.
View details for DOI 10.1152/ajprenal.00668.2014
View details for PubMedID 25810438
Activation of ENaC by AVP contributes to the urinary concentrating mechanism and dilution of plasma.
American journal of physiology. Renal physiology
2015; 308 (3): F237-43
Vasopressin (AVP) activates the epithelial Na+ channel (ENaC). The physiological significance of this activation is unknown. The current studies test if activation of ENaC contributes to AVP-sensitive urinary concentration. Consumption of a 3% NaCl solution induced hypernatremia and plasma hypertonicity in mice. Plasma [AVP] and urine osmolality increased in hypernatremic mice in an attempt to compensate for increases in plasma tonicity. ENaC activity was elevated in mice consuming 3% NaCl solution compared to mice consuming a diet enriched in Na+ with ad libitum tap water. The latter diet does not cause hypernatremia. To determine whether the increase in ENaC activity in mice consuming 3% NaCl solution served to compensate for hypernatremia, mice were treated with the ENaC inhibitor benzamil. Co-administration of benzamil with 3% NaCl solution decreased urinary osmolality and increased urine flow so that urinary Na+ excretion increased with no effect on urinary [Na+]. This decrease in urinary concentration further increased plasma [Na+], osmolality, and [AVP] in these already hypernatremic mice. Benzamil similarly compromised urinary concentration in water deprived mice and in mice treated with desmopressin. These results demonstrate that stimulation of ENaC by AVP plays a critical role in water homeostasis by facilitating urinary concentration, which can compensate for hypernatremia or exacerbate hyponatremia. The current findings are consistent with ENaC in addition to serving as a final effector of the renin-angiotensin-aldosterone system and blood pressure homeostasis, also playing a key role in water homeostasis by regulating urine concentration and dilution of plasma.
View details for DOI 10.1152/ajprenal.00246.2014
View details for PubMedID 25391898
- Urine electrolyte composition and diuretic therapy in heart failure: back to the future? Circulation. Heart failure 2014; 7 (5): 697-698
Update on the Guytonian view of hypertension.
Current opinion in nephrology and hypertension
2014; 23 (4): 391-398
Dr Arthur Guyton hypothesized that the capacity of the kidney to excrete sodium ultimately dictates long-term changes in blood pressure. This model has had a profound influence on our understanding of blood pressure regulation. The goal of this article is to review a selection of classic studies and highlight more recent molecular studies supporting or refuting the Guyton model of blood pressure regulation.Molecular characterizations of human disorders of sodium homeostasis and blood pressure, and phenotypic analysis of transgenic mouse models, strongly support the Guytonian view that the kidney plays a central role in blood pressure control. However, recent studies also support the view that primary changes in the vasculature and nervous system significantly contribute to long-term changes in blood pressure.The findings from provocative studies, particularly those that demonstrate how primary changes in the vasculature alter blood pressure without affecting renal sodium handling, challenge the Guyton model and need to be reconciled with the basic tenets of this model. Future characterization of these exceptions to the Guyton model will be critical in gaining a more complete understanding of the physiology of blood pressure regulation. This path of discovery will undoubtedly lead to new approaches for the diagnosis and treatment of hypertension.
View details for DOI 10.1097/01.mnh.0000450777.17698.8e
View details for PubMedID 24901409
Prostaglandin E2 induces chloride secretion through crosstalk between cAMP and calcium signaling in mouse inner medullary collecting duct cells.
American journal of physiology. Cell physiology
2014; 306 (3): C263-78
Under conditions of high dietary salt intake, prostaglandin E2 (PGE2) production is increased in the collecting duct and promotes urinary sodium chloride (NaCl) excretion; however, the molecular mechanisms by which PGE2 increases NaCl excretion in this context have not been clearly defined. We used the mIMCD-K2 cell line to characterize mechanisms underlying PGE2-regulated NaCl transport. When epithelial Na(+) channels were inhibited, PGE2 exclusively stimulated basolateral EP4 receptors to increase short-circuit current (Isc(PGE2)). We found that Isc(PGE2) was sensitive to inhibition by H-89 and CFTR-172, indicating that EP4 receptors signal through protein kinase A to induce Cl- secretion via Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Unexpectedly, we also found that IscPGE2 was sensitive to inhibition by BAPTA-AM (Ca(2+) chelator), 2-APB (IP3 receptor blocker), and FFA (Ca(2+) activated Cl(-) channel (CACC) inhibitor), suggesting that EP4 receptors also signal through Ca(2+) to induce Cl(-) secretion via CACC. Additionally, we observed that PGE2 stimulated an increase in Isc through crosstalk between cAMP and Ca(2+) signaling: BAPTA-AM or 2-APB inhibited a component of Isc(PGE2) that was sensitive to CFTR-172 inhibition; H-89 inhibited a component of Isc(PGE2) that was sensitive to FFA inhibition. Together, our findings indicate that PGE2 activates basolateral EP4 receptors and signals through both cAMP and Ca(2+) to stimulate Cl(-) secretion in IMCD-K2 cells. We propose that these signaling pathways, and the crosstalk between them, may provide a concerted mechanism for enhancing urinary NaCl excretion under conditions of high dietary NaCl intake.
View details for DOI 10.1152/ajpcell.00381.2012
View details for PubMedID 24284792
Fulvene-5 inhibition of Nadph oxidases attenuates activation of epithelial sodium channels in A6 distal nephron cells
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2013; 305 (7): F995-F1005
Nadph oxidase 4 is an important cellular source of reactive oxygen species (ROS) generation in the kidney. Novel antioxidant drugs, such as Nox4 inhibitor compounds, are being developed. There is, however, very little experimental evidence for the biological role and regulation of Nadph oxidase isoforms in the kidney. Herein, we show that Fulvene-5 is an effective inhibitor of Nox-generated ROS and report the role of Nox isoforms in activating epithelial sodium channels (ENaC) in A6 distal nephron cells via oxidant signaling and cell stretch activation. Using single-channel patch-clamp analysis, we report that Fulvene-5 blocked the increase in ENaC activity that is typically observed with H2O2 treatment of A6 cells: average ENaC NPo values decreased from a baseline level of 1.04 ± 0.18 (means ± SE) to 0.25 ± 0.08 following Fulvene-5 treatment. H2O2 treatment failed to increase ENaC activity in the presence of Fulvene-5. Moreover, Fulvene-5 treatment of A6 cells blocked the osmotic cell stretch response of A6 cells, indicating that stretch activation of Nox-derived ROS plays an important role in ENaC regulation. Together, these findings indicate that Fulvene-5, and perhaps other classes of antioxidant inhibitors, may represent a novel class of compounds useful for the treatment of pathological disorders stemming from inappropriate ion channel activity, such as hypertension.
View details for DOI 10.1152/ajprenal.00098.2013
View details for Web of Science ID 000325353900010
View details for PubMedID 23863470
Novel diuretic targets
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2013; 305 (7): F931-F942
As the molecular revolution continues to inform a deeper understanding of disease mechanisms and pathways, there exist unprecedented opportunities for translating discoveries at the bench into novel therapies for improving human health. Despite the availability of several different classes of antihypertensive medications, only about half of the 67 million Americans with hypertension manage their blood pressure appropriately. A broader selection of structurally diverse antihypertensive drugs acting through different mechanisms would provide clinicians with greater flexibility in developing effective treatment regimens for an increasingly diverse and aging patient population. An emerging body of physiological, genetic, and pharmacological evidence has implicated several renal ion-transport proteins, or regulators thereof, as novel, yet clinically unexploited, diuretic targets. These include the renal outer medullary potassium channel, ROMK (Kir1.1), Kir4.1/5.1 potassium channels, ClC-Ka/b chloride channels, UTA/B urea transporters, the chloride/bicarbonate exchanger pendrin, and the STE20/SPS1-related proline/alanine-rich kinase (SPAK). The molecular pharmacology of these putative targets is poorly developed or lacking altogether; however, recent efforts by a few academic and pharmaceutical laboratories have begun to lessen this critical barrier. Here, we review the evidence in support of the aforementioned proteins as novel diuretic targets and highlight examples where progress toward developing small-molecule pharmacology has been made.
View details for DOI 10.1152/ajprenal.00230.2013
View details for Web of Science ID 000325353900001
View details for PubMedID 23863472
View details for PubMedCentralID PMC3798746
- Landscape of ENaC regulation in the kidney AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY 2012; 303 (9): F1287-F1288
Prostaglandin E-2 mediates proliferation and chloride secretion in ADPKD cystic renal epithelia
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2012; 303 (10): F1425-F1434
Prostaglandin E(2) (PGE(2)) contributes to cystogenesis in genetically nonorthologous models of autosomal dominant polycystic kidney disease (ADPKD). However, it remains unknown whether PGE(2) induces the classic features of cystic epithelia in genetically orthologous models of ADPKD. We hypothesized that, in ADPKD epithelia, PGE(2) induces proliferation and chloride (Cl(-)) secretion, two archetypal phenotypic features of ADPKD. To test this hypothesis, proliferation and Cl(-) secretion were measured in renal epithelial cells deficient in polycystin-1 (PC-1). PC-1-deficient cells increased in cell number (proliferated) faster than PC-1-replete cells, and this proliferative advantage was abrogated by cyclooxygenase inhibition, indicating a role for PGE(2) in cell proliferation. Exogenous administration of PGE(2) increased proliferation of PC-1-deficient cells by 38.8 ± 5.2% (P < 0.05) but inhibited the growth of PC-1-replete control cells by 49.4 ± 1.9% (P < 0.05). Next, we tested whether PGE(2)-specific E prostanoid (EP) receptor agonists induce intracellular cAMP and downstream β-catenin activation. PGE(2) and EP4 receptor agonism (TCS 2510) increased intracellular cAMP concentration and the abundance of active β-catenin in PC-1-deficient cells, suggesting a mechanism for PGE(2)-mediated proliferation. Consistent with this hypothesis, antagonizing EP4 receptors reverted the growth advantage of PC-1-deficient cells, implicating a central role for the EP4 receptor in proliferation. To test whether PGE(2)-dependent Cl(-) secretion is also enhanced in PC-1-deficient cells, we used an Ussing chamber to measure short-circuit current (I(sc)). Addition of PGE(2) induced a fivefold higher increase in I(sc) in PC-1-deficient cells compared with PC-1-replete cells. This PGE(2)-induced increase in I(sc) in PC-1-deficient cells was blocked by CFTR-172 and flufenamic acid, indicating that PGE(2) activates CFTR and calcium-activated Cl(-) channels. In conclusion, PGE(2) activates aberrant signaling pathways in PC-1-deficient epithelia that contribute to the proliferative and secretory phenotype characteristic of ADPKD and suggests a therapeutic role for PGE(2) inhibition and EP4 receptor antagonism.
View details for DOI 10.1152/ajprenal.00010.2012
View details for Web of Science ID 000311208200004
View details for PubMedID 22933297
View details for PubMedCentralID PMC3517629
SGK regulation of renal sodium transport
CURRENT OPINION IN NEPHROLOGY AND HYPERTENSION
2012; 21 (5): 534-540
The serum and glucocorticoid regulated kinase (SGK) family of protein kinases shares similar biochemical and hormonal signaling properties; however, the SGK kinases also exhibit distinct differences in regulating renal sodium (Na(+)) transport. This review will highlight recent advances in our understanding of the specificity of SGK kinase signaling and regulation of renal Na(+) transport.Differential expression of SGK kinases at the cellular and subcellular levels contributes to signaling specificity. New evidence indicates that SGK1 associates with the apical cell membrane of cortical collecting duct cells to regulate open probability of the epithelial Na(+) channel (ENaC). Scaffold proteins can also recruit SGK1 to multiprotein complexes for regulation of ENaC expression in the apical membrane. Recent SGK1 knockout models have implicated the NaCl co-transporter (NCC) as another target of SGK1 regulation. Less is known about the function of SGK2 or SGK3, but both kinases can regulate Na(+)/H(+) exchanger 3 (NHE3) activity.The SGK kinases assume distinct roles in regulating Na transport in both proximal and distal elements of the kidney tubule. Future examination of the molecular mechanisms by which the SGK kinases regulate specific substrates will inform our understanding of how these kinases contribute to the physiology of renal Na(+) transport.
View details for DOI 10.1097/MNH.0b013e32835571be
View details for Web of Science ID 000307649300012
View details for PubMedID 22691875
Differential effects of extracellular ATP on chloride transport in cortical collecting duct cells
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2012; 303 (4): F483-F491
Extracellular ATP in the cortical collecting duct can inhibit epithelial sodium channels (ENaC) but also stimulate calcium-activated chloride channels (CACC). The relationship between ATP-mediated regulation of ENaC and CACC activity in cortical collecting duct cells has not been clearly defined. We used the mpkCCD(c14) cortical collecting duct cell line to determine effects of ATP on sodium (Na(+)) and chloride (Cl(-)) transport with an Ussing chamber system. ATP, at a concentration of 10(-6) M or less, did not inhibit ENaC-mediated short-circuit current (I(sc)) but instead stimulated a transient increase in I(sc). The macroscopic current-voltage relationship for ATP-inducible current demonstrated that the direction of this ATP response changes from positive to negative when transepithelial voltage (V(te)) is clamped to less than -10 mV. We hypothesized that this negative V(te) might be found under conditions of aldosterone stimulation. We next stimulated mpkCCD(c14) cells with aldosterone (10(-6) M) and then clamped the V(te) to -50 mV, the V(te) of aldosterone-stimulated cells under open-circuit conditions. ATP (10(-6) M) induced a transient increase in negative clamp current, which could be inhibited by flufenamic acid (CACC inhibitor) and BAPTA-AM (calcium chelator), suggesting that ATP stimulates Cl(-) absorption through CACC. Together, our findings suggest that the status of ENaC activity, by controlling V(te), may dictate the direction of ATP-stimulated Cl(-) transport. This interplay between aldosterone and purinergic signaling pathways may be relevant for regulating NaCl transport in cortical collecting duct cells under different states of extracellular fluid volume.
View details for DOI 10.1152/ajprenal.00062.2012
View details for Web of Science ID 000307791200001
View details for PubMedID 22647633
Metabolic syndrome, insulin resistance and kidney function in non-diabetic individuals
NEPHROLOGY DIALYSIS TRANSPLANTATION
2012; 27 (4): 1410-1415
Metabolic syndrome has been recently identified as a risk factor for chronic kidney disease (CKD). Since the five individual components of the metabolic syndrome have also been identified as risk factors for CKD, the metabolic syndrome diagnosis may represent an aggregate of CKD risk factors. On the other hand, the components of the metabolic syndrome are also associated with insulin resistance, which may directly mediate the increased CKD risk.This study was a cross-sectional evaluation of the relationship between metabolic syndrome, insulin resistance and estimated glomerular filtration rate (eGFR) in 574 non-diabetic individuals. Insulin resistance was directly quantified using the insulin suppression test, and the metabolic syndrome components were measured. eGFR was calculated using the three validated estimation equations: the Chronic Kidney Disease Epidemiology Collaboration equation, the Mayo quadratic equation and the Modification of Diet in Renal Disease study equation.While CKD prevalence was higher and mean eGFR was lower in individuals who met the metabolic syndrome criteria compared with those who did not, we did not observe a significant relationship between insulin resistance and eGFR. Of all of the components of the metabolic syndrome, only hypertension was significantly associated with CKD prevalence [odds ratio (95% confidence interval), 3.5 (1.2-10.1), P=0.02].Although CKD is more common among individuals with the metabolic syndrome, insulin resistance is not a common factor.
View details for DOI 10.1093/ndt/gfr498
View details for Web of Science ID 000302310700022
View details for PubMedID 21908415
View details for PubMedCentralID PMC3315670
- ßPix is a New Player in Renal Physiology. Frontiers in physiology 2012; 3: 268-?
Epithelial Sodium Channel Regulation by Cell Surface-associated Serum- and Glucocorticoid-regulated Kinase 1
JOURNAL OF BIOLOGICAL CHEMISTRY
2011; 286 (37): 32074-32085
Serum- and glucocorticoid-regulated kinase 1 (sgk1) participates in diverse biological processes, including cell growth, apoptosis, and sodium homeostasis. In the cortical collecting duct of the kidney, sgk1 regulates sodium transport by stimulating the epithelial sodium channel (ENaC). Control of subcellular localization of sgk1 may be an important mechanism for modulating specificity of sgk1 function; however, which subcellular locations are required for sgk1-regulated ENaC activity in collecting duct cells has yet to be established. Using cell surface biotinylation studies, we detected endogenous sgk1 at the apical cell membrane of aldosterone-stimulated mpkCCD(c14) collecting duct cells. The association of sgk1 with the cell membrane was enhanced when ENaC was co-transfected with sgk1 in kidney cells, suggesting that ENaC brings sgk1 to the cell surface. Furthermore, association of endogenous sgk1 with the apical cell membrane of mpkCCD(c14) cells could be modulated by treatments that increase or decrease ENaC expression at the apical membrane; forskolin increased the association of sgk1 with the apical surface, whereas methyl-β-cyclodextrin decreased the association of sgk1 with the apical surface. Single channel recordings of excised inside-out patches from the apical membrane of aldosterone-stimulated A6 collecting duct cells revealed that the open probability of ENaC was sensitive to the sgk1 inhibitor GSK650394, indicating that endogenous sgk1 is functionally active at the apical cell membrane. We propose that the association of sgk1 with the apical cell membrane, where it interacts with ENaC, is a novel means by which sgk1 specifically enhances ENaC activity in aldosterone-stimulated collecting duct cells.
View details for DOI 10.1074/jbc.M111.278283
View details for PubMedID 21784856
Activation of P2Y(1) and P2Y(2) receptors induces chloride secretion via calcium-activated chloride channels in kidney inner medullary collecting duct cells
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2011; 301 (3): F544-F553
Dysregulation of urinary sodium chloride (NaCl) excretion can result in extracellular fluid (ECF) volume expansion and hypertension. Recent studies demonstrated that urinary nucleotide excretion increases in mice ingesting a high-salt diet and that these increases in extracellular nucleotides can signal through P2Y(2) receptors in the kidney collecting duct to inhibit epithelial Na(+) channels (ENaC). However, under conditions of ECF volume expansion brought about by high-dietary salt intake, ENaC activity should already be suppressed. We hypothesized that alternative pathways exist by which extracellular nucleotides control renal NaCl excretion. We used an inner medullary collecting duct (mIMCD-K2) cell line in an Ussing chamber system as a model to study additional ion transport pathways that are regulated by extracellular nucleotides. When ENaC was inhibited, the addition of adenosine triphosphate (ATP) to the basal side of cell sheets activated both P2Y(1) and P2Y(2) receptors, inducing a transient increase in short-circuit current (I(sc)); addition of ATP to the apical side activated only P2Y(2) receptors, inducing first a transient and then a sustained increase in I(sc). The ATP-induced increases in I(sc) were blocked by pretreatment with a phospholipase C (PLC) inhibitor, a calcium (Ca(2+)) chelator, or Ca(2+)-activated Cl(-) channel (CACC) inhibitors, suggesting that ATP signals through both PLC and intracellular Ca(2+) to activate CACC. We propose that P2Y(1) and P2Y(2) receptors operate in tandem in IMCD cells to provide an adaptive mechanism for enhancing urinary NaCl excretion in the setting of high-dietary NaCl intake.
View details for DOI 10.1152/ajprenal.00709.2010
View details for Web of Science ID 000294551400011
View details for PubMedID 21653634
The natriuretic mechanism of Gamma-Melanocyte-Stimulating Hormone
2011; 32 (5): 1068-1072
Gamma-Melanocyte Stimulating Hormone (Gamma-MSH) regulates sodium (Na(+)) balance and blood pressure through activation of the melanocortin receptor 3 (MC3-R). The mechanism of the natriuretic effect is proposed to involve binding of MC3-R either in the kidney to directly inhibit tubular Na(+) transport or in the brain to inhibit central neural pathways that control renal tubular Na(+) absorption. This study aimed to clarify the mechanism involved in the natriuretic effect of Gamma-MSH on MC3-R in kidney cells. In Ussing chamber studies, we observed no effects of Gamma-MSH on NaCl transport in the mouse inner medullary collecting duct cell line (mIMCD-K2). We also found that neither MC3-R protein nor mRNA was expressed in mouse kidney, suggesting that renal Gamma-MSH action may not be mediated through direct effects on tubular Na(+) transport but rather through effects on central neural pathways that innervate the kidney.
View details for DOI 10.1016/j.peptides.2011.02.006
View details for Web of Science ID 000291286200032
View details for PubMedID 21335042
View details for PubMedCentralID PMC3112371
Expression and role of serum and glucocorticoid-regulated kinase 2 in the regulation of Na+/H+ exchanger 3 in the mammalian kidney
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2010; 299 (6): F1496-F1506
Serum and glucocorticoid-regulated kinase 2 (sgk2) is 80% identical to the kinase domain of sgk1, an important mediator of mineralocorticoid-regulated sodium (Na(+)) transport in the distal nephron of the kidney. The expression pattern and role in renal function of sgk2 are virtually uncharacterized. In situ hybridization and immunohistochemistry of rodent kidney coupled with real-time RT-PCR of microdissected rat kidney tubules showed robust sgk2 expression in the proximal straight tubule and thick ascending limb of the loop of Henle. Sgk2 expression was minimal in distal tubule cells with aquaporin-2 immunostaining but significant in proximal tubule cells with Na(+)/H(+) exchanger 3 (NHE3) immunostaining. To ascertain whether mineralocorticoids regulate expression of sgk2 in a manner similar to sgk1, we examined sgk2 mRNA expression in the kidneys of adrenalectomized rats treated with physiological doses of aldosterone together with the glucocorticoid receptor antagonist RU486. Northern blot analysis and in situ hybridization showed that, unlike sgk1, sgk2 expression in the kidney was not altered by aldosterone treatment. Based on the observation that sgk2 is expressed in proximal tubule cells that also express NHE3, we asked whether sgk2 regulates NHE3 activity. We heterologously expressed sgk2 in opossum kidney (OKP) cells and measured Na(+)/H(+) exchange activity by Na(+)-dependent cell pH recovery. Constitutively active sgk2, but not sgk1, stimulated Na(+)/H(+) exchange activity by >30%. Moreover, the sgk2-mediated increase in Na(+)/H(+) exchange activity correlated with an increase in cell surface expression of NHE3. Together, these results suggest that the pattern of expression, regulation, and role of sgk2 within the mammalian kidney are distinct from sgk1 and that sgk2 may play a previously unrecognized role in the control of transtubular Na(+) transport through NHE3 in the proximal tubule.
View details for DOI 10.1152/ajprenal.00075.2010
View details for Web of Science ID 000285084700030
View details for PubMedID 20926631
View details for PubMedCentralID PMC3006302
Adenosine Activates A2b Receptors and Enhances Chloride Secretion in Kidney Inner Medullary Collecting Duct Cells
2010; 55 (5): 1123-U89
In the kidney, defects in the regulation of urine salt excretion can result in extracellular fluid volume expansion, leading to salt-sensitive hypertension. Previous studies have demonstrated that, when rats are maintained on a high sodium chloride (NaCl) diet, adenosine production increases in the renal medulla with parallel changes in adenosine receptor expression. These studies suggest that adenosine signaling in the kidney can respond to high NaCl loading; however, the functional consequences of these changes in adenosine signaling are not clear. We used the immortalized cell line mIMCD-K2, a murine model system for the renal inner medullary collecting duct, to study the direct effects of adenosine on NaCl transport across the inner medullary collecting duct epithelium with an Ussing chamber system. When epithelial Na(+) channels were inhibited, the addition of adenosine to the apical side of mIMCD-K2 cell sheets stimulated short-circuit current in a dose-dependent manner. This increase in short-circuit current was inhibited by a cystic fibrosis transmembrane conductance regulator Cl(-) channel inhibitor. Pharmacological studies with a panel of adenosine receptor agonists and antagonists demonstrated that adenosine activates apical A2b adenosine receptors to enhance the short-circuit current. Furthermore, adenosine application to mIMCD-K2 cell sheets increased intracellular cAMP, whereas inhibition of protein kinase A completely blocked the adenosine response. Together, our findings indicate that adenosine stimulates Cl(-) secretion through the cystic fibrosis transmembrane conductance regulator in mIMCD-K2 cells by activating apical A2b receptors and signaling through cAMP/protein kinase A. We propose that this adenosine receptor pathway may provide one mechanism for enhancing urine NaCl excretion in the setting of high dietary NaCl intake.
View details for DOI 10.1161/HYPERTENSIONAHA.109.10404
View details for Web of Science ID 000276672500013
View details for PubMedID 20308611
View details for PubMedCentralID PMC2885947
Melamine nephrotoxicity: an emerging epidemic in an era of globalization
2009; 75 (8): 774-779
Recent outbreaks of nephrolithiasis and acute kidney injury among children in China have been linked to ingestion of milk-based infant formula contaminated with melamine. These cases provide evidence in humans for the nephrotoxicity of melamine, which previously had been described only in animals. The consequences of this outbreak are already severe and will likely continue to worsen. Herein we summarize the global impact of the melamine milk contamination, the reemergence of melamine-tainted animal feed, and potential mechanisms of melamine nephrotoxicity. Large-scale epidemiologic studies are necessary to further characterize this disease and to assess its potential long-term sequelae. This epidemic of environmental kidney disease highlights the morbidity associated with adulterated food products available in today's global marketplace and reminds us of the unique vulnerability of the kidney to environmental insults. Melamine is the latest in a growing list of diverse potentially toxic compounds about which nephrologists and other health-care providers responsible for the diagnosis and management of kidney disease must now be aware.
View details for DOI 10.1038/ki.2009.16
View details for PubMedID 19212415
NH2 terminus of serum and glucocorticoid-regulated kinase 1 binds to phosphoinositides and is essential for isoform-specific physiological functions
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2007; 292 (6): F1741-F1750
Serum and glucocorticoid regulated kinase 1 (SGK1) has been identified as a key regulatory protein that controls a diverse set of cellular processes including sodium (Na(+)) homeostasis, osmoregulation, cell survival, and cell proliferation. Two other SGK isoforms, SGK2 and SGK3, have been identified, which differ most markedly from SGK1 in their NH(2)-terminal domains. We found that SGK1 and SGK3 are potent stimulators of epithelial Na(+) channel (ENaC)-dependent Na(+) transport, while SGK2, which has a short NH(2) terminus, is a weak stimulator of ENaC. Further characterization of the role of the SGK1 NH(2) terminus revealed that its deletion does not affect in vitro kinase activity but profoundly limits the ability of SGK1 either to stimulate ENaC-dependent Na(+) transport or inhibit Forkhead-dependent gene transcription. The NH(2) terminus of SGK1, which shares sequence homology with the phosphoinositide 3-phosphate [PI(3)P] binding domain of SGK3, binds phosphoinositides in protein lipid overlay assays, interacting specifically with PI(3)P, PI(4)P, and PI(5)P, but not with PI(3,4,5)P(3). Moreover, a point mutation that reduces phosphoinositide binding to the NH(2) terminus also reduces SGK1 effects on Na(+) transport and Forkhead activity. These data suggest that the NH(2) terminus, although not required for PI 3-kinase-dependent modulation of SGK1 catalytic activity, is required for multiple SGK1 functions, including stimulation of ENaC and inhibition of the proapoptotic Forkhead transcription factor. Together, these observations support the idea that the NH(2)-terminal domain acts downstream of PI 3-kinase-dependent activation to target the kinase to specific cellular compartments and/or substrates, possibly through its interactions with a subset of phosphoinositides.
View details for DOI 10.1152/ajprenal.00027.2007
View details for Web of Science ID 000247942000010
View details for PubMedID 17356130
Disinhibitory pathways for control of sodium transport: regulation of ENaC by SGK1 and GILZ
AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY
2006; 291 (4): F714-F721
Regulation of ENaC occurs at several levels. The principal hormonal regulator of ENaC, aldosterone, acts through the mineralocorticoid receptor to modulate ENaC-mediated sodium transport, and considerable attention has focused on defining the components of the early phase of this response. Two genes, SGK1 and GILZ, have now been implicated in this regulation. While the functional significance of SGK1 in mediating aldosterone effects is well established, new evidence has enhanced our understanding of the mechanisms of SGK1 action. In addition, recent work demonstrates a novel role for GILZ in the stimulation of ENaC-mediated sodium transport. Interestingly, both SGK1 and GILZ appear to negatively regulate tonic inhibition of ENaC and thus use disinhibition to propagate the rapid effects of aldosterone to increase sodium reabsorption in tight epithelia.
View details for DOI 10.1152/ajprenal.00061.2006
View details for Web of Science ID 000240313000002
View details for PubMedID 16720863
Serum- and glucocorticoid-regulated kinase 1 regulates ubiquitin ligase neural precursor cell-expressed, developmentally down-regulated protein 4-2 by inducing interaction with 14-3-3
2005; 19 (12): 3073-3084
Serum- and glucocorticoid-regulated kinase 1 (SGK1) is an aldosterone-regulated early response gene product that regulates the activity of several ion transport proteins, most notably that of the epithelial sodium channel (ENaC). Recent evidence has established that SGK1 phosphorylates and inhibits Nedd4-2 (neural precursor cell-expressed, developmentally down-regulated protein 4-2), a ubiquitin ligase that decreases cell surface expression of the channel and possibly stimulates its degradation. The mechanistic basis for this SGK1-induced Nedd4-2 inhibition is currently unknown. In this study we show that SGK1-mediated phosphorylation of Nedd4-2 induces its interaction with members of the 14-3-3 family of regulatory proteins. Through functional characterization of Nedd4-2-mutant proteins, we demonstrate that this interaction is required for SGK1-mediated inhibition of Nedd4-2. The concerted action of SGK1 and 14-3-3 appears to disrupt Nedd4-2-mediated ubiquitination of ENaC, thus providing a mechanism by which SGK1 modulates the ENaC-mediated Na(+) current. Finally, the expression pattern of 14-3-3 is also consistent with a functional role in distal nephron Na(+) transport. These results demonstrate a novel, physiologically significant role for 14-3-3 proteins in modulating ubiquitin ligase-dependent pathways in the control of epithelial ion transport.
View details for DOI 10.1210/me.2005-0193
View details for Web of Science ID 000233460500015
View details for PubMedID 16099816
SGK1: A rapid aldosterone-induced regulator of renal sodium reabsorption
2005; 20: 134-139
Recently, substantial progress has been made in understanding the mechanisms by which aldosterone rapidly stimulates sodium transport in the distal nephron and other tight epithelia. Serum- and glucocorticoid-regulated kinase 1 (SGK1) has been identified as an important mediator of this process. Its physiological relevance has been revealed through heterologous expression in cultured cells and generation of SGK1 knockout mice.
View details for DOI 10.1152/physiol.00053.2004
View details for Web of Science ID 000227958500008
View details for PubMedID 15772302