Nephron Research Articles

Role of the SLC22A17/lipocalin-2 receptor in renal endocytosis of proteins/metalloproteins: a focus on iron- and cadmium-binding proteins.

The transmembrane protein SLC22A17 [or the neutrophil gelatinase-associated lipocalin/lipocalin-2 (LCN2)/24p3 receptor] is an atypical member of the SLC22 family of organic anion and cation transporters: it does not carry typical substrates of SLC22 transporters but mediates receptor-mediated endocytosis (RME) of LCN2. One important task of the kidney is the prevention of urinary loss of proteins filtered by the glomerulus by bulk reabsorption of multiple ligands via megalin:cubilin:amnionless-mediated endocytosis in the proximal tubule (PT). Accordingly, overflow, glomerular, or PT damage, as in Fanconi syndrome, results in proteinuria. Strikingly, up to 20% of filtered proteins escape the PT under physiological conditions and are reabsorbed by the distal nephron. The renal distal tubule and collecting duct express SLC22A17, which mediates RME of filtered proteins that evade the PT but with limited capacity to prevent proteinuria under pathological conditions. The kidney also prevents excretion of filtered essential and nonessential transition metals, such as iron or cadmium, respectively, that are largely bound to proteins with high affinity, e.g., LCN2, transferrin, or metallothionein, or low affinity, e.g., microglobulins or albumin. Hence, increased uptake of transition metals may cause nephrotoxicity. Here, we assess the literature on SLC22A17 structure, topology, tissue distribution, regulation, and assumed functions, emphasizing renal SLC22A17, which has relevance for physiology, pathology, and nephrotoxicity due to the accumulation of proteins complexed with transition metals, e.g., cadmium or iron. Other putative renal functions of SLC22A17, such as its contribution to osmotic stress adaptation, protection against urinary tract infection, or renal carcinogenesis, are discussed.

Bartter Syndrome: A Case Report

Background: Bartter's syndrome refers to a group of genetic disorders that affect the renal tubular system, which is responsible for reabsorbing various substances such as sodium, potassium, and chloride from the urine into the blood. This study aimed to present a clinical case related to Bartter syndrome.
 Case presentation: A 52-year-old male patient in the internal medicine department of Dr. M. Djamil General Hospital Padang with the main complaint of weakness in both legs increasing since 1 day ago. On laboratory examination, the patient found potassium 1.7 mmol/L, indicating hypokalemia. Renal function examination showed normal kidney function. Examination of blood gas analysis showed results of metabolic alkalosis. Examination of urine potassium obtained potassium levels of 22 mmol/day, urine osmolarity of 140 mOsm/kgH2O at serum osmolarity of 274 mOsm/kgH2O, with TTKG (transtubular potassium gradient) = 28. The patient was diagnosed with Bartter syndrome. Treatment is carried out by administering KSR tablets 3x600 mg orally while monitoring electrolytes regularly.
 Conclusion: This patient has hypokalemia, metabolic alkalosis, normal magnesium and calcium, and hypercalciuria. This patient is diagnosed with Bartter syndrome.

Terabyte-scale supervised 3D training and benchmarking dataset of the mouse kidney

The performance of machine learning algorithms, when used for segmenting 3D biomedical images, does not reach the level expected based on results achieved with 2D photos. This may be explained by the comparative lack of high-volume, high-quality training datasets, which require state-of-the-art imaging facilities, domain experts for annotation and large computational and personal resources. The HR-Kidney dataset presented in this work bridges this gap by providing 1.7 TB of artefact-corrected synchrotron radiation-based X-ray phase-contrast microtomography images of whole mouse kidneys and validated segmentations of 33 729 glomeruli, which corresponds to a one to two orders of magnitude increase over currently available biomedical datasets. The image sets also contain the underlying raw data, threshold- and morphology-based semi-automatic segmentations of renal vasculature and uriniferous tubules, as well as true 3D manual annotations. We therewith provide a broad basis for the scientific community to build upon and expand in the fields of image processing, data augmentation and machine learning, in particular unsupervised and semi-supervised learning investigations, as well as transfer learning and generative adversarial networks.

The Integral Role of Chloride & With-No-Lysine Kinases in Cell Volume Regulation & Hypertension.

Chloride anions are the most abundant in humans. For many years, it has been believed that chloride is simply a counterion of all other cations, ensuring the electroneutrality of the extracellular space. Recent data suggests that chloride anions possess a broad spectrum of important activities that regulate vital cellular functions. It is now evident that, apart from its contribution to the electroneutrality of the extracellular space, it acts as an osmole and contributes to extracellular and intracellular volume regulation. Its anionic charge also contributes to the generation of cell membrane potential. The most interesting action of chloride anions is their ability to regulate the activity of with-no-lysine kinases, which in turn regulate the activity of sodium chloride and potassium chloride cotransporters and govern the reabsorption of salt and excretion of potassium by nephron epithelia. Chloride anions seem to play a crucial role in cell functions, such as cell volume regulation, sodium reabsorption in the distal nephron, potassium balance, and sodium sensitivity, which lead to hypertension. All of these functions are accomplished on a molecular level via complicated metabolic pathways, many of which remain poorly defined. We attempted to elucidate some of these pathways in light of recent advances in our knowledge, obtained mainly from experimental studies.

Dietary anions control potassium excretion: it is more than a poorly absorbable anion effect.

The urinary potassium (K+) excretion machinery is upregulated with increasing dietary K+, but the role of accompanying dietary anions remains inadequately characterized. Poorly absorbable anions, including [Formula: see text], are thought to increase K+ secretion through a transepithelial voltage effect. Here, we tested if they also influence the K+ secretion machinery. Wild-type mice, aldosterone synthase (AS) knockout (KO) mice, or pendrin KO mice were randomized to control, high-KCl, or high-KHCO3 diets. The K+ secretory capacity was assessed in balance experiments. Protein abundance, modification, and localization of K+-secretory transporters were evaluated by Western blot analysis and confocal microscopy. Feeding the high-KHCO3 diet increased urinary K+ excretion and the transtubular K+ gradient significantly more than the high-KCl diet, coincident with more pronounced upregulation of epithelial Na+ channels (ENaC) and renal outer medullary K+ (ROMK) channels and apical localization in the distal nephron. Experiments in AS KO mice revealed that the enhanced effects of [Formula: see text] were aldosterone independent. The high-KHCO3 diet also uniquely increased the large-conductance Ca2+-activated K+ (BK) channel β4-subunit, stabilizing BKα on the apical membrane, the Cl-/[Formula: see text] exchanger, pendrin, and the apical KCl cotransporter (KCC3a), all of which are expressed specifically in pendrin-positive intercalated cells. Experiments in pendrin KO mice revealed that pendrin was required to increase K+ excretion with the high-KHCO3 diet. In summary, [Formula: see text] stimulates K+ excretion beyond a poorly absorbable anion effect, upregulating ENaC and ROMK in principal cells and BK, pendrin, and KCC3a in pendrin-positive intercalated cells. The adaptive mechanism prevents hyperkalemia and alkalosis with the consumption of alkaline ash-rich diets but may drive K+ wasting and hypokalemia in alkalosis.NEW & NOTEWORTHY Dietary anions profoundly impact K+ homeostasis. Here, we found that a K+-rich diet, containing [Formula: see text] as the counteranion, enhances the electrogenic K+ excretory machinery, epithelial Na+ channels, and renal outer medullary K+ channels, much more than a high-KCl diet. It also uniquely induces KCC3a and pendrin, in B-intercalated cells, providing an electroneutral KHCO3 secretion pathway. These findings reveal new K+ balance mechanisms that drive adaption to alkaline and K+-rich foods, which should guide new treatment strategies for K+ disorders.

Similarities and Distinctions Between Acetazolamide and SGLT2 Inhibitors in Patients With Acute Heart Failure: Key Insights Into ADVOR and EMPULSE.

Both acetazolamide and sodium-glucose cotransporter 2 (SGLT2) inhibitors block sodium reabsorption in the proximal renal tubule primarily through inhibition of sodium hydrogen exchanger isoform 3 (NHE3), but neither SGLT2 inhibitors nor acetazolamide produce a sustained natriuresis due to compensatory upregulation of sodium reabsorption at distal nephron sites. Nevertheless, acetazolamide and SGLT2 inhibitors have been used as adjunctive therapy to loop diuretics in states where NHE3 is upregulated, e.g., acute heart failure. Two randomized controlled trials have been carried out with acetazolamide in acute heart failure (DIURESIS-CHF and ADVOR). In ADVOR, acetazolamide improved physical signs of fluid retention, but this finding could not be explained by the modest observed diuretic effect. Acetazolamide did not produce a natriuresis in the DIURESIS-CHF trial, and in ADVOR, immediate effects on symptoms and body weight were not reported, and the drug had no effect on morbidity or mortality after 90 days. Three randomized controlled trials have been carried out with empagliflozin (EMPAG-HF, EMPA-RESPONSE-AHF and EMPULSE in acute heart failure. The EMPULSE trial did not report effects on diuresis or in changes in physical signs of congestion during the first week of treatment, but in EMPAG-HF and EMPA-RESPONSE-AHF, empagliflozin had no effect of dyspnea, urinary sodium excretion or body weight during the first 4 days. In the EMPULSE trial, empagliflozin improved health status at 15 days and reduced the risk of worsening heart failure events at 90 days, but these effects are similar in magnitude and time course to the early statistical significance on the risk of heart failure hospitalizations achieved within 14-30 days in the major trials of SGLT2 inhibitors in patients with chronic heart failure. Neurohormonal inhibitors produce this early effect in the absence of a diuresis. Additionally, in numerous randomized controlled trials, in-hospital diuretic intensification has not reduced the risk of major heart failure events, even when treatment is sustained. These findings, taken collectively, suggest that any immediate diuretic effects of acetazolamide and SGLT2 inhibitors in acute heart failure are not likely to influence the short- or long-term clinical course of patients This article is protected by copyright. All rights reserved.

Evaluation of Renal Ischemia–Reperfusion Injury Using Optical Coherence Tomography Based on Fractal Dimension

Renal ischemia–reperfusion (IR) is inevitable in partial nephrectomy and kidney transplantation. Acute tubular necrosis (ATN) induced by renal IR causes the loss of functional units in the kidney, pathologically presenting as the nonhomogeneous distribution of normal uriniferous tubules and usually used to characterize kidney activity. Optical coherence tomography (OCT) has been proven to have the ability to image the kidney microstructure in vivo and in real time. However, a fast image analysis method is needed for clinical application purpose. In this work, a new method for assessing renal IR injury was developed using a fractal-dimension-based texture of the OCT kidney image. Thirty-five Wistar rats were divided into seven groups for renal ischemia–reperfusion: control and various ischemia-time groups. A time series of 3D OCT kidney images was obtained. We calculated the fractal dimension (FD) of OCT en face images and found that the value increased gradually and finally became stable after 90 min of reperfusion. The stable value in the long-ischemia-time group was smaller than that in the short-ischemia-time group. The FD value of the OCT kidney image was highly responsive to renal IR injury. The proposed method is promising for a fast diagnostic application.

Kir7.1 knockdown and inhibition alter renal electrolyte handling but not the development of hypertension in Dahl salt-sensitive rats.

High K+ supplementation is correlated with a lower risk of the composite of death, major cardiovascular events, and ameliorated blood pressure, but the exact mechanisms have not been established. Inwardly rectifying K+ (Kir) channels expressed in the basolateral membrane of the distal nephron play an essential role in maintaining electrolyte homeostasis. Mutations in this channel family have been shown to result in strong disturbances in electrolyte homeostasis, among other symptoms. Kir7.1 is a member of the ATP-regulated subfamily of Kir channels. However, its role in renal ion transport and its effect on blood pressure have yet to be established. Our results indicate the localization of Kir7.1 to the basolateral membrane of aldosterone-sensitive distal nephron cells. To examine the physiological implications of Kir7.1, we generated a knockout of Kir7.1 (Kcnj13) in Dahl salt-sensitive (SS) rats and deployed chronic infusion of a specific Kir7.1 inhibitor, ML418, in the wild-type Dahl SS strain. Knockout of Kcnj13 (Kcnj13-/-) resulted in embryonic lethality. Heterozygous Kcnj13+/- rats revealed an increase in K+ excretion on a normal-salt diet but did not exhibit a difference in blood pressure development or plasma electrolytes after 3 wk of a high-salt diet. Wild-type Dahl SS rats exhibited increased renal Kir7.1 expression when dietary K+ was increased. K+ supplementation also demonstrated that Kcnj13+/- rats excreted more K+ on normal salt. The development of hypertension was not different when rats were challenged with high salt for 3 wk, although Kcnj13+/- rats excrete less Na+. Interestingly, chronic infusion of ML418 significantly increased Na+ and Cl- excretion after 14 days of high salt but did not alter salt-induced hypertension development. Here, we found that reduction of Kir7.1 function, either through genetic ablation or pharmacological inhibition, can influence renal electrolyte excretion but not to a sufficient degree to impact the development of SS hypertension.NEW & NOTEWORTHY To investigate the role of the Kir7.1 channel in salt-sensitive hypertension, its function was examined using complementary genetic and pharmacological approaches. The results revealed that although reducing Kir7.1 expression had some impact on maintaining K+ and Na+ balance, it did not lead to a significant change in the development or magnitude of salt-induced hypertension. Hence, it is probable that Kir7.1 works in conjunction with other basolateral K+ channels to fine-tune membrane potential.

#4157 A NOVEL STRATEGY TO TARGET V2R IN RENAL CARCINOMA

Abstract Background and Aims The vasopressin V2 receptor (V2R) is a G-protein Coupled Receptor (GPCR) selectively expressed in the kidney. V2R is located at basolateral membrane of principal cells of the distal nephron and thick ascending limb cells and in response to circulating levels of vasopressin (AVP), promotes sodium and water reabsorption. Ectopic expression of V2R plays a role in clear cell renal carcinoma (ccRCC). A recent study shows that tolvaptan, a V2R-antagonist, inhibits cancer growth in an experimental model of ccRCC. However, polyuria remains a serious side effect, limiting the repositioning of this drug in clinical practise. Recent evidences demonstrate that ccRCC have also an up regulation of the transferrin receptor 1 (TfR1). Based on this, we developed Transferrin-conjugated liposomes (Tf-LPs) encapsulating tolvaptan to allow a site-specific delivery to the tumor site, in the attempt to reduce drug side effects. We performed in vitro studies to evaluate the effect of Tf-LPs on cell proliferation and the immunoblotting of cyclin A2, an essential regulator of the cell cycle that participates in the regulation of S phase as well as mitotic entry. Method Liposome formulation and characterization. Liposomes composed of DPPC/DSPEPEG2000/DSPEPEG-MAL were mixed with tolvaptan and prepared by hydration of a thin lipid film, followed by extrusion. Transferrin was conjugated to liposomes at room temperature, overnight. The resulting liposomes were then purified by ultracentrifuge (80000 rpm, 40 min, 4°C). Liposomes were characterized in terms of colloidal dimensions, polydispersity index and surface charge by using dynamic light scattering (DLS) (Zetasizer Nano Z, Malvern, UK). The encapsulation efficiency of Tolvaptan was measured by spectrophotometer (Epoch, Biotek) at the wavelength of 266 nm. In vitro studies. CAKI-1 cells were cultured until the exponentially growing phase. Cells were then incubated with Tf-LPs with or without tolvaptan in growth medium with 0.2%FBS for 24h. Cell viability was assessed by measuring the mitochondrial activity by the 3[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay quantified by spectrophotometry at 570nm. Cell lysate were immunoblotted and Cyclin A2 primary antibody tested as a marker of cell proliferation. Results The liposomes we have generated have an average diameter of about 100 nm, a low polydispersity index (<0.2) and a 50% encapsulation efficiency. MTT assay showed that, compared with control, cells treated with Tf-LPs encapsulating tolvaptan have a reduction in cell proliferation. Interestingly, this reduction starts at lower concentrations and timescales than in a previous study performed with free drug. To further confirm the previous result, we also performed immunoblotting of cyclin A2 which is usually linked to cell proliferation and as such is often found expressed at a high level in human cancers. The expression level of this protein is significantly reduced when cells are treated with Tf-LPs+TOLV while it remains the same in the treatment with Tf-LPs. Conclusion In this study we developed and tested Tf-LPs encapsulating tolvaptan with cytotoxic activity on tumor cells. The preliminary results of this study will be confirmed by subsequent in vivo studies to demonstrate the advantages of this system: site-specific delivery to the tumor site and reduction of drug side effects.

#4851 MOLECULAR FEATURES OF CIRCULATORY B CELLS AND RENAL CELLS AT THE SINGLE-CELL LEVEL IN AUTOANTIBODY-NEGATIVE PRIMARY MEMBRANOUS NEPHROPATHY PATIENTS

Abstract Background and Aims Primary membranous nephropathy (PMN) is an organ-specific autoimmune disease that is the most common cause of idiopathic nephrotic syndrome in adults. Furthermore, the incidence of PMN is increasing, especially in young adults and children. The landmark discovery of nephritogenic autoantibodies against podocyte antigens such as M-type phospholipase A2 receptor (PLA2R) and thrombospondin type-1 domain-containing protein 7A (THSD7A) has provided a paradigm shift in diagnosis and treatment of PMN. However, there are still few patients with negative serum and renal tissue autoantibodies. This study aims to explore the molecular features of antibody-negative PMN. Method We sorted CD19+ cells from the peripheral blood of a pediatric patient with seven nephritogenic autoantibodies-negative PMN (NEG) by flow cytometry and performed single-cell transcriptome sequencing (scRNA-seq) and single-cell B cell receptor sequencing (scBCR-seq). Meanwhile, scRNA-seq was performed on renal biopsy tissues from the same patient. In addition, we included the scRNA-seq data of renal from anti-PLA2R antibody positive patients (POS) and healthy controls (CTRL), and the scBCR-seq data of B cell from CTRL for integrative analysis. Results The NEG patient showed typical nephrotic syndrome and was diagnosed as stage Ⅲ membranous nephropathy by renal biopsy. There was no evidence of anti-PLA2R or anti-THSD7A antibodies in peripheral blood and seven nephritogenic autoantibodies such as anti-PLA2R antibodies in renal tissue. After excluding secondary factors, the patient was diagnosed with PMN. Through scRNA-seq of CD19+ cells, we found that the number, characteristic gene, function and clonotype of naÏve B cells and memory B cells in NEG were significantly changed. Expanded CD38+ naÏve B cells in NEG had the molecular characteristics of CD19+CD24+CD27-CD38+, defined as transitional B cells. This group of cells had distinct function features of cell activation, and its up-regulated genes were involved in multiple aspects of the BCR signaling pathway. Pseudotime trajectory analysis suggested CD38+ naÏve B cells were highly enriched in the beginning of B cell differentiation. There was a preference in the use of VJ gene segments of B cells between NEG and CTRL, especially an increase of the IGHV3-23 and IGLV2-14 in NEG. The stronger pairing frequencies, IGLV2-14/IGLJ3 and IGKV2D-29/IGKJ2, were indicated in NEG. We identified 14 distinct kidney cell types by marker genes. Through re-clustering of glomerular parietal epithelial cells (PECs), the patients were clearly distinct from their control counterparts, indicating a major shift in gene expression for this cell type. PECs in NEG showed significant up-regulation of cellular communication network factor-related genes (CCN1, CCN2), phospholipase A and acyltransferase-related genes (PLAAT4, PLAAT3), and septin protein-related genes (SEPTIN2, SEPTIN7), accompanied by significant down-regulation of podocyte-related genes. In addition, there are clearly distinct cellular functions and pseudotime trajectory in PECs from NEG and POS, and genes such as CCN2, PLAAT4, SEPTIN2 might drive the special trajectory of PECs in NEG. For the podocytes, the genes related with extracellular matrix and cell adhesion were significantly enhanced in NEG, which consistented with the functional enrichment analysis of the differentially expressed genes and gene set-based scores. We calculated the gene set-based scores including genes encoding lumen-to-blood sodium transporters. Results indicated the enhanced expression of sodium transporters in distal nephrons of MN patients. More surprisingly, a group of proximal tubule epithelial cells showed significantly higher expression levels of sodium transporters. Among them, the expression of SLC5A12 encoding SMCT2 increased significantly. Conclusion We have systematic revealed the cell-type specific molecular features of PMN patients from circulation to renal tissue. Our research provides valuable evidence for the molecular diagnosis of PMN in children and insights into pathogenic mechanism of classical nephritogenic autoantibody-negative PMN.

Localization of Diacylglycerol Kinase ζ in the Kidney of Adult Rats: Its Dominant Expression in Collecting Tubules and its Selective Lack in Proximal Tubules

Localization of Diacylglycerol Kinase ζ in the Kidney of Adult Rats: Its Dominant Expression in Collecting Tubules and its Selective Lack in Proximal Tubules

The AE4 transporter mediates kidney acid-base sensing

The kidney plays a key role in the correction of systemic acid-base imbalances. Central for this regulation are the intercalated cells in the distal nephron, which secrete acid or base into the urine. How these cells sense acid-base disturbances is a long-standing question. Intercalated cells exclusively express the Na+-dependent Cl−/HCO3− exchanger AE4 (Slc4a9). Here we show that AE4-deficient mice exhibit a major dysregulation of acid-base balance. By combining molecular, imaging, biochemical and integrative approaches, we demonstrate that AE4-deficient mice are unable to sense and appropriately correct metabolic alkalosis and acidosis. Mechanistically, a lack of adaptive base secretion via the Cl−/HCO3− exchanger pendrin (Slc26a4) is the key cellular cause of this derailment. Our findings identify AE4 as an essential part of the renal sensing mechanism for changes in acid-base status.

Defining corticosteroid-regulated sodium transport within the distal nephron

The aldosterone (ALDO)-sensitive distal nephron is typically defined as: the late distal convoluted tubule (DCT2), connecting tubule (CNT) and cortical collecting duct (CCD). ALDO-sensitivity is defined by 11βHSD2 (11β) activity (which inactivates corticosterone, CORT); mineralocorticoid (MR) rather than glucocorticoid receptor (GR) expression; and the target epithelial sodium channel (ENaC). Recent studies have reported ALDO-insensitive, but MR-dependent ENaC activity in DCT2/CNT and that CORT-stimulated ENaC may be relevant in MR antagonism as 4th line anti-hypertensive therapy. Whilst functional evidence of ALDO-insensitive ENaC activity is compelling, corticosteroid-regulated Na + transport along the distal nephron is not fully defined. AIM: to determine 11βHSD2, MR and GR expression alongside Na + transporter localisation in murine distal nephron and assess the endogenous receptor(s) underpinning steroid-stimulated ENaC activity.Male C57BL/6 mouse kidney sections were subject to multiplex immunofluorescence (11β, MR and GR) and immunohistochemical labelling (NCC, TRPV5, γ-ENaC and AQP2). Images were co-registered, annotated and analysed using Halo® software. Steroid-induced ENaC-mediated currents were measured in mCCD cl1 and primary CD cells. Carbenoxolone (CBX), mifepristone (MF) or PF-03882845 (PF) were used to inhibit 11β, GR and MR, respectively.Distal nephron segments were defined as: DCT - NCC; DCT/CNT - NCC and TRPV5; CNT - TRPV5; CNT/CCD - TRPV5 and γ-ENaC/AQP2; CCD - γ-ENaC/AQP2. We did not detect NCC and γ-ENaC co-localisation. Average cells/section, DCT: 874±39; DCT/CNT: 238±31; CNT: 198±63; CNT/CCD: 831±282; CCD: 2262±231 ( n=3). Negligible numbers of cells expressed both MR and GR.DCT was predominantly 11β- (~90%) and GR dominant (GR:MR ratio ~7:1). In 11β+ cells (~10%), GR was also dominant (GR:MR ratio ~4:1). DCT/CNT and CNT were mainly 11β- (~85 and ~75%, respectively), where MR and GR were similar. In 11β+ cells, MR and GR were similar in DCT/CNT but MR was greater in CNT (MR:GR ratio ~4:1). CNT/CCD contained a near equal split of 11β- (~52%) and 11β+ (~48%) cells. MR and GR were similar in 11β- cells, but 11β+ cells were almost exclusively MR (MR:GR ratio ~37:1). In CCD, ~35% of cells were 11β-, MR and GR were similar, and ~65% cells were 11β+, these were predominantly MR (MR:GR ratio ~30:1).In mCCD cl1 ( n=8-11) and primary CD cells ( n=6), ALDO-induced ENaC activity was inhibited by MR ( p<0.001) but not GR antagonists. DEX-induced ENaC activity was inhibited by GR ( p<0.001) but not MR antagonists. CORT-induced ENaC activity was modestly inhibited by MR ( p<0.05) but not by GR antagonists.Our data suggest that the DCT is a glucocorticoid-responsive segment, with 11β+ cells becoming progressively more dominant from CNT to CCD. The appearance of ENaC in the late CNT and particularly CCD, alongside 11β and MR, suggest these segments reflect the mineralocorticoid-responsive, and thus aldosterone-sensitive distal nephron. Kidney Research UK, The Royal Society 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.

Aberrant adaptation of the inner medullary collecting ducts results in sodium retention and hypernatremia in a thick ascending limb specific Myh9 and Myh10 conditional knockout mouse model

Sodium reabsorption in the thick ascending limb (TAL) epithelium is essential to generate and sustain the interstitial osmotic gradient, which facilitates water reabsorption in the adjacent collecting duct system. Impaired TAL function can compromise this gradient and lead to electrolyte imbalance. Our previous work demonstrated that pan renal tubular conditional genetic inactivation of nonmuscle myosin II genes Myh9&10 in adult mice results in progressive kidney disease of TAL origin with aberrant regulation of TAL proteins U MOD and NKCC2 (Otterpohl et al; 2020). To confirm the cell-autonomous role for NM2 proteins in adult TAL epithelial cells, we generated a TAL-specific conditional knockout mouse model of Myh9&10 using the UMOD->CreERT2 mouse line (cKO). Genetic inactivation of Myh9&10 in the TAL was induced at 5 weeks of age with tamoxifen injections. Age matched control and cKO littermates were part of every cohort. Mice underwent metabolic, histologic, immunohistochemical, and biochemical analyses at varying time points until moribund. Development of progressive kidney disease in cKO mice was indicated by increasing levels of blood urea nitrogen, serum creatinine, and the tubular injury marker NGAL. Our results show that cKO females experience significant loss of weight at 12 weeks of age and are moribund between 13 – 14 weeks, while cKO males survive up to 25 weeks. Interestingly, female cKO mice exhibit hypernatremia at 12 weeks of age and male cKO mice between 16 - 20 weeks of age. We analyzed NKCC2 protein levels in whole kidney lysates and a drastic reduction was evident in both female and male cKO mice by 9 weeks of age, therefore hypernatremia was unexpected. We examined if the hypernatremia in TAL-Myh9&10 cKO mice is due to tubular adaptation in the distal nephron and/or the collecting duct segments. Systematic analysis of sodium cotransporters and channels in the distal nephron and collecting duct segments revealed an increase in NCC/pNCC levels in males and a decrease in females when compared with age matched control littermates. No apparent volume loss (increased urine output) has been observed in the female mice. Additionally, immunostaining experiments showed aberrant increase in expression of ENaC gamma in the inner medullary collecting duct cells in female and not male mice by 9-weeks of age. ENaC expression is limited to cortical collecting duct and the connecting segment under normal conditions in the mouse kidney. Consistent with this, our control mice do not have ENaC gamma expression in the inner medullary collecting ducts. Further experiments are underway to determine the cellular state/identity of these ENaC expressing inner medullary collect duct cells. These experiments confirm the critical role for Myh9&10 proteins in TAL tubule NKCC2 transport, and reveal novel, sex specific, adaptive mechanisms in distal nephron and collecting ducts in response to compromised NKCC2 transport within the TAL. NIDDK RO1 DK131020-01A1 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.

Differential effects of the clock protein BMAL1, diet, and sex on purinergic receptor expression in the distal nephron

The circadian clock protein BMAL1 is a core component of the intrinsic molecular clock mechanism that governs circadian rhythms. We use a kidney-specific Bmal1 knockout mouse model (KS-BMAL1KO) with loss of BMAL1 expression in the distal segments of the kidney. When placed on a potassium-deficient, high salt diet (0K+HS), male KS-BMAL1KO mice do not show an elevation in blood pressure compared to their littermate controls (CNTL), suggesting a protective effect due to loss of BMAL1 in the distal nephron. A low K+ diet predisposes to salt-sensitive hypertension by a high salt diet, in part due to increased sodium retention. Our lab has previously shown that inappropriately high ENaC activity in mice on a high salt diet is due in part to impaired purinergic signaling. The purinergic signaling pathway regulates water and electrolytes in the kidney via purinergic receptors (P2) and our gene expression data show their oscillation in a circadian manner in the kidney. We hypothesized that BMAL1 in distal segments contributes to the regulation of P2 receptor expression. Kidneys from male and female KS-BMAL1KO and CNTL mice were harvested at zeitgeber time (ZT) 0 or ZT12 from mice on a normal or a 0K+HS diet for 10 days. RNA was isolated from the renal medulla and prepared for RNA sequencing (5-9 pooled samples for males, 4-8 for females). Expression levels of P2X and P2Y receptor transcripts were examined. Loss of BMAL1 in distal segments modified P2 receptor expression, as KS-BMAL1KO mice exhibited lower P2Y14 gene expression than CNTL after 0K+HS in both males (78 ± 0, n=7 vs. 49.5 ± 0.7 CPM, n=7, P<.05) and females (85.5 ± 3.5 n=4 vs. 46 ± 8.5 CPM, n=4, P<.05). 0K+HS diet increased P2X7 in CNTL mice compared to normal diet in both males (88.5 ± 9.2, n=5 vs. 189.50 ± 33.2 CPM 114.1, n=7, P<.05) and females (79.5 ± 3.5, n=5 vs. 130.50 ± 3.5 CPM, n=4, P<.05) with no difference in genotype (P=NS). Sex differences were also apparent, as P2Y2 also increased following 0K+HS, but only in male CNTL (327.5 ± 27.6, n=5 vs. 499 ± 24 CPM, n=7, P<.05) and KS-BMAL1KO mice (264 ± 41, n=6 vs. 510 ± 11.3 CPM n=7, P<.05), without a genotype difference. These results support our hypothesis that BMAL1 in distal segments of the nephron contributes to the regulation of selective P2 receptors in the renal medulla, potentially modulating P2 receptor expression through interactions with circadian clock-, dietary- and sex-dependent factors. Our work is supported by the NIH, NIDDK, ASN, and AHA. 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.

Furosemide rescues hypercalciuria in familial hypomagnesaemia with hypercalciuria and nephrocalcinosis model

Aim: Impaired calcium homeostasis limits life expectancy and quality in familial hypomagnesaemia with hypercalciuria and nephrocalcinosis (FHHNC). This rare disease is caused by loss-of-function mutations in CLDN16 or CLDN19 genes leading to impaired paracellular reabsorption of divalent cations along the cortical thick ascending limb (cTAL). The ensuing late distal nephron and collecting duct system partially compensate for the defect in cTAL by increased transcellular Ca 2+ reabsorption via the luminal transient receptor potential channel V5 (TRPV5), as well as basolateral plasma membrane calcium ATPase (PMCA) and sodium-potassium exchanger (NCX1). The loop diuretic furosemide induces compensatory activation in these distal segments due to blockade of NaCl and divalent cation reabsorption in the preceeding TAL. Although furosemide enhances urinary calcium excretion via inhibition of the aforementioned cTAL in general population, this effect is not expected in FHHNC patients with already severely impaired Ca 2+ transport in the cTAL. The present study follows the hypothesis that furosemide may alleviate hypercalciuria in this disease by activation of the distal transcellular Ca 2+ transport proteins. Methods: Cldn16-deficient mice (Cldn16-/- ) served as a FHHNC model. Wild-type (WT) and Cldn16-/- mice were treated with furosemide (7 days of 40 mg/kg bw) or vehicle. We assessed renal electrolyte handling (metabolic cages) and key divalent transport proteins. Results: Cldn16-/- mice show increased Ca 2+ excretion than WT and compensatory stimulation of Cldn2 in the proximal tubule, as well as of TRPV5, and NCX1 in the distal nephron at baseline. Furosemide reduced hypercalciuria in Cldn16-/- mice and enhanced TRPV5 and PMCA levels in Cldn16-/- but not in WT mice. Conclusions: Furosemide alleviated hypercalciuria in a mouse FHHNC model, likely via stimulation of transcellular luminal and basolateral Ca 2+ transport systems in the distal nephron and collecting duct. These results may have a clinical implication in FHHNC patients. No conflict of interests 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.

Role of paraoxonase 3 (PON3) in regulating ENaC-mediated sodium transport in distal nephron

PON3 is expressed in the aldosterone-sensitive distal nephron, where ENaC plays an essential role in maintaining Na+/K+ homeostasis in the kidney. The aims of our study were to determine the physiological roles of PON3 in renal Na+ and K+ handling. We hypothesize that PON3 functions as a molecular chaperone to regulate ENaC expressionand Na+ reabsorption in the kidney. We have obtained a Pon3 global knockout mouse model and examined the effect of PON3 on ENaC functional expression using several approaches, including biochemistry, immunohistochemistry, electrophysiology, and whole animal metabolic cage studies. Pon3 KO mice have normal kidney histology without evidence of inflammation or injury. At baseline, Pon3 KO mice have a significantly lower blood [K+] and higher blood [Na+] when compared to WT littermates. Amiloride-induced natriuresis was significantly greater in the KO mice, reflecting, in part, an upregulation in ENaC-dependent Na+reabsorption in the absence of the PON3. Immunoblotting of whole kidney lysates indicated that the total abundance of ENaC subunits was not altered in KO mice. Single channel recordings of ENaC in split-open tubules freshly isolated from WT or Pon3 KO mice kidneys demonstrated that open probability ( P O) was similar between the two groups of animals. However, the number of active channels per patch ( N) was significantly higher in Pon3 KO mice, resulting in a higher ENaC activity ( NP O) in the distal nephron segments of Pon3 KO mice. Consistent this notion, we found that ENaC γ subunit surface abundance was increased in mCCD cells when PON3 expression was knocked down by siRNA.Together, our data suggest that Pon3 KO mice have upregulated Na+ reabsorption and K+ secretion, likely a result of increased ENaC functional expression in the absence of PON3. This study was funded by NIH grants R01 DK130901 (to SS), R01 DK111380 (to SS), R01 HL128053 (to TRK and SS), R01 HL147818 (to TRK), and P30 DK079307 (the Pittsburgh Center for Kidney Research). SMM was supported by T32 DK061296, T32 DK007052, and a grant from Relypsa. 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.

Analysis of distal convoluted tubule (DCT) cell de-differentiation due to COP9 signalosome (CSN) dysfunction via enriched DCT single-nucleus RNA-sequencing

Cullin-RING-ligases (CRLs) are a group of E3 ubiquitin ligases that mediate the regulated degradation of proteins. All CRLs are regulated by the COP9 signalosome (CSN), which interacts with the CRL and turns off ubiquitin ligase activity. To investigate the role of impaired CSN dysfunction in the kidney, we inactivated the CSN by deleting Jab1 (the key CSN catalytic subunit) along the entire nephron. Even though the CSN is expressed all along the nephron, these mice showed remodeling only along the distal nephron, with shortening of the distal convoluted tubule (DCT) and a large reduction in DCT-specific proteins. The DCT is known to remodel due to changes in dietary salt intaked, drug administration, and human disease. Yet, the cellular and molecular basis for this plasticity is unclear. We hypothesized that CSN dysfunction causes de-differentiation of DCT cells leading to DCT remodeling. To test our hypothesis, inducible DCT-specific NCC-Cre-ERT2 mice were bred to INTACT (Isolation of Nuclei TAgged in specific Cell Types, which fluorescently labels nuclei) and Jab1 floxed mice to generate DCT-INTACT- Jab1 -/- mice. One adult male DCT-INTACT- Jab1 -/- mouse and one DCT-INTACT control mouse were treated with tamoxifen to induce nuclear GFP expression and to induce deletion of Jab1 only in DCT cells. Six-weeks post treatment, nuclei from one kidney cortex was isolated and the DCT was enriched using Fluorescence-Activated Nuclei Sorting (FANS). GFP-positive nuclei were used for single-nucleus RNA-sequencing (NovaSeq). Initial results showed that unbiased clustering and UMAP visualization revealed 7 clusters with most cells from the DCT (99.0% for control and 97.6% for Jab1 -/- mice), indicating that the enrichment process was highly successful. Both the control and Jab1 -/- mouse had similar proportions of DCT1 and DCT2 cells; however, we identified two specialized cell types (dDCT1 and dDCT2) which comprised a much larger proportion of the cells in the Jab1 -/- mouse (dDCT1: 2.9% in control vs 41.1% in Jab1 -/- ; dDCT2: 2.0% in control vs 13.9% in Jab1 -/- ). These cells were highly de-differentiated with lower expression of the canonical DCT identifier genes such as Egf and Umod for DCT1, Calb1 and S100g for DCT2, as well as Slc12a3. Both dDCT1 and dDCT2 cell populations had induced expression of the disease- or carcinoma-related genes Ano3, Nrg1, and Pvt1. In conclusion, Jab1 deletion causes de-differentiation of a population of DCT cells. Further examination of CSN dysfunction via DCT-enriched single-nucleus RNA-sequencing could lead to a better understanding of the molecular mechanisms involved in DCT remodeling. NIH K01DK120790, NIH R01DK51496, Foundation LeDucq: Transatlantic Network of Excellence 17CVD05 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.

Chronic aldosterone administration alters aquaporin expression and localization in the murine kidney

The steroid hormone aldosterone is an important regulator of fluid balance and electrolyte homeostasis. While acute aldosterone signaling is canonically associated with fluid retention due to its role in promoting sodium reabsorption through ENaC in the distal nephron, chronic aldosterone exposure has been shown to exacerbate urine production in a rat model of diabetes insipidus through its actions on aquaporin 2 (AQP2) localization and expression. In our studies, we aimed to characterize not only the effect of chronic aldosterone administration on AQP2 expression and localization, but also its effect on the basolateral water channels, AQP3 and AQP4. Given the large urinary output we observed in our animals following chronic aldosterone treatments, we hypothesized all three of these channels would show reduced expression.Aldosterone was administered to male C57Bl/6 mice at a dose of 200 μg/kg/day for 28 days via subcutaneous minipumps. Aldosterone treatment caused a significant diuresis as compared to control animals by day 15 (Ctl 4.8 ± 1.6 ml; Aldo 8.4 ± 2.4 ml), and this difference persisted for the remainder of the experiment. Mice given aldosterone also consumed more water as compared to their control counterparts (Ctl 4.0 ± 1.2 ml; Aldo 9.6 ± 2.3 ml). Urine osmolality was measured by freeze-point depression, with a significant decrease in urinary concentration being noted during the daytime by day 4 (Ctl 1219.8 ± 473.4 mOsm/kg; Aldo 638.8 ± 143.8 mOsm/kg) and during the night by day 17 (Ctl 905.3 ± 175.1 mOsm/kg; Aldo 522.2 ± 127.3 mOsm/kg). At the end of the 28 days of aldosterone administration, mice receiving aldosterone had a higher whole blood [Na + ] (Ctl 146 ± 1.9mmol/l; Aldo 152 ± 1.3mmol/l) and lower whole blood [K+] (Ctl 4.8 ± 0.56mmol/l; Aldo 3.0 ± 0.34mmol/l) as measured by iSTAT cartridge with terminal cardiac blood draw.Kidneys were examined by Western blot and immunofluorescent staining for expression and localization of the three AQPs. AQP2 expression decreased after both 14 and 28 days of aldosterone administration, with line scan analysis showing a decreased signal present at the apical membrane. AQP3 expression was decreased in the basolateral membranes of principal cells within the cortex of the kidney but increased in cells within the inner medulla after 28 days of aldosterone. AQP4 levels were significantly increased in AQP2-positive cells of the inner stripe of the outer medulla and the inner medulla, suggesting that this channel may be upregulated to compensate for changes in the other two aquaporins. Potassium supplementation to separate the effects of aldosterone administration from hypokalemia did not rescue the expression of these channels.Overall, our studies reveal that chronic aldosterone administration in healthy mice leads to polyuria and polydipsia, with decreased apical expression of AQP2 and variable changes in AQP3 and AQP4 dependent on location within in the kidney. This study was funded by NIH grants R01 DK130901 (to SS), R01 HL147818 and R01 DK129285 (to TRK), and P30 DK079307 (the Pittsburgh Center for Kidney Research). SMM was supported by T32 DK061296, T32 DK007052, and a grant from Relypsa. 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.