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Investigators have for decades used mouse voiding patterns as end points for studying behavioral biology. It is only recently that mouse voiding patterns were adopted for study of lower urinary tract physiology. The spontaneous void spot assay (VSA), a popular micturition assessment tool, involves placing a mouse in an enclosure lined by filter paper and quantifying the resulting urine spot pattern. The VSA has advantages of being inexpensive and noninvasive, but some investigators challenge its ability to distinguish lower urinary tract function from behavioral voiding. A consensus group of investigators who regularly use the VSA was established by the National Institutes of Health in 2015 to address the strengths and weaknesses of the assay, determine whether it can be standardized across laboratories, and determine whether it can be used as a surrogate for evaluating urinary function. Here we leverage experience from the consensus group to review the history of the VSA and its uses, summarize experiments to optimize assay design for urinary physiology assessment, and make best practice recommendations for performing the assay and analyzing its results. [ABSTRACT FROM AUTHOR]

In the kidney, the thick ascending limb (TAL) of the loop of Henle plays a vital role in NaCl homeostasis and blood pressure regulation. In human and animal models of salt-sensitive hypertension, NaCl reabsorption via the apical Na+/K+/2Cl− cotransporter (NKCC2) is abnormally increased in the TAL. We showed that NaCl reabsorption is controlled by the presence of NKCC2 at the apical surface of TALs. However, the molecular mechanisms that maintain the steady-state levels of NKCC2 at the apical surface are not clearly understood. Here, we report that NKCC2 interacts with the F-actin cross-linking protein actinin-4 (ACTN4). We find that ACTN4 is expressed in TALs by Western blot and immunofluorescence microscopy. ACTN4 immunoprecipitated with NKCC2 and recombinant glutathione-S-transferase (GST)-ACTN4 pulled down NKCC2 from TAL lysates. ACTN4 is involved in endocytosis in other cells. Therefore, we hypothesized that ACTN4 binds apical NKCC2 and regulates its trafficking. To study the role of ACTN4 in NKCC2 surface expression, we silenced ACTN4 in vivo via shRNA or CRISPR/Cas9 system to decrease ACTN4 expression in TALs. We observed that silencing ACTN4 in vivo via shRNA or CRISPR/Cas9 system increased the amount of NKCC2 at the apical surface of TALs. Consistent with an increase in surface NKCC2, bumetanide-induced diuresis and natriuresis were enhanced by 35% after silencing of ACTN4 in vivo (AV-NKCC2-Cas9: 3,841 ± 709 vs. AAV-gRNA-ACTN4: 5,546 ± 622 µmol Na/8 h, n = 5, P < 0.05). We conclude that ACTN4 binds NKCC2 to regulate its surface expression. Selective depletion of ACTN4 in TALs using shRNA or CRISPR/Cas9 enhances surface NKCC2 and TAL-NaCl reabsorption, indicating that regulation of the ACTN4-NKCC2 interaction is important for renal NaCl reabsorption and could be related to hypertension. NEW & NOTEWORTHY: ACTN4 function and dysfunction in glomerular podocytes have been extensively studied. However, the function of ACTN4 in the nephron has not been studied. Our paper shows for the first time that ACTN4, in the nephron, regulates NaCl reabsorption in part by affecting NKCC2 surface expression. Protein-protein interactions between ACTN4 and NKCC2 seem to mediate NKCC2 endocytosis in TALs. When ACTN4 was silenced in the TAL in vivo using CRISPR/Cas9 or shRNAs, surface NKCC2 and NaCl reabsorption increased. [ABSTRACT FROM AUTHOR]

This article focuses on the role of the kidney in maintaining acid-base balance in the body with reference to two papers in renal physiology. The first one is by R.F. Pitts and R.S. Alexander and second one is by R.F. Pitts and W.D. Lotspeich. The kidney maintains acid-base balance by secreting acid at a rate equal to that of nonvolatile acid production and to reabsorb almost all of the filtered bicarbonate to prevent depletion of the body's alkali reserves. In these two paper, researchers provided the key data in support of the countercurrent multiplication mechanism as well as the essential transport properties of the ascending and descending limbs of the loop of Henle and the collecting duct.

This article presents information about the American Physiological Society (APS). The APS was founded in 1887 and since then the Society has grown to one of the most important scientific organizations in the world. The main reason for this growth is publication of various journals by the APS. These journals are the American Journal of Physiology, the Journal of Applied Physiology and the Journal of Neurophysiology . The APS also conceived and created a Legacy Project to increase awareness of and access to seminal papers in physiology. Over the past three years, the entire content of all the APS journals has been scanned into a searchable PDF format and deposited on the world wide web.

Dietary potassium deficiency causes stimulation of sodium reabsorption leading to an increased risk in blood pressure elevation. The distal convoluted tubule (DCT) is the main rheostat linking plasma K+ levels to the activity of the Na-Cl cotransporter (NCC). This occurs through basolateral membrane potential sensing by inwardly rectifying K+ channels (Kir4.1/5.1); decrease in intracellular Cl−; activation of WNK4 and interaction and phosphorylation of STE20/SPS1-related proline/alanine-rich kinase (SPAK); binding of calcium-binding protein 39 (cab39) adaptor protein to SPAK, leading to its trafficking to the apical membrane; and SPAK binding, phosphorylation, and activation of NCC. As kidney-specific with-no-lysine kinase 1 (WNK1) isoform (KS-WNK1) is another participant in this pathway, we examined its function in NCC regulation. We eliminated KS-WNK1 specifically in the DCT and demonstrated increased expression of WNK4 and long WNK1 (L-WNK1) and increased phosphorylation of NCC. As in other KS-WNK1 models, the mice were not hyperkalemic. Although wild-type mice under low-dietary K+ conditions demonstrated increased NCC phosphorylation, the phosphorylation levels of the transporter, already high in KS-WNK1, did not change under the low-K+ diet. Thus, in the absence of KS-WNK1, the transporter lost its sensitivity to low plasma K+. We also show that under low K+ conditions, in the absence of KS-WNK1, there was no formation of WNK bodies. These bodies were observed in adjacent segments, not affected by the targeting of KS-WNK1. As our data are overall consistent with those of the global KS-WNK1 knockout, they indicate that the DCT is the predominant segment affecting the salt transport regulated by KS-WNK1. NEW & NOTEWORTHY: In this paper, we show that KS-WNK1 is a critical component of the distal convoluted tubule (DCT) K+ switch pathway. Its deletion results in an inability of the DCT to sense changes in plasma potassium. Absence of KS-WNK1 leads to abnormally high levels of WNK4 and L-WNK1 in the DCT, resulting in increased Na-Cl phosphorylation and function. Our data are consistent with KS-WNK1 targeting WNK4 and L-WNK1 to degradation. [ABSTRACT FROM AUTHOR]

Mouse urinary behavior is quantifiable and is used to pinpoint mechanisms of voiding dysfunction and evaluate potential human therapies. Approaches to evaluate mouse urinary function vary widely among laboratories, however, complicating cross-study comparisons. Here, we describe development and multi-institutional validation of a new tool for objective, consistent, and rapid analysis of mouse void spot assay (VSA) data. Void Whizzard is a freely available software plugin for FIJI (a distribution of ImageJ) that facilitates VSA image batch processing and data extraction. We describe its features, demonstrate them by evaluating how specific VSA method parameters influence voiding behavior, and establish Void Whizzard as an expedited method for VSA analysis. This study includes control and obese diabetic mice as models of urinary dysfunction to increase rigor and ensure relevance across distinct voiding patterns. In particular, we show that Void Whizzard is an effective tool for quantifying nonconcentric overlapping void spots, which commonly confound analyses. We also show that mouse genetics are consistently more influential than assay design parameters when it comes to VSA outcomes. None of the following procedural modifications to reduce overlapping spots masked these genetic-related differences: reduction of VSA testing duration, water access during the assay period, placement of a wire mesh cage bottom on top of or elevated over the filter paper, treatment of mesh with a hydrophobic spray, and size of wire mesh opening. The Void Whizzard software and rigorous validation of VSA methodological parameters described here advance the goal of standardizing mouse urinary phenotyping for comprehensive urinary phenome analyses. [ABSTRACT FROM AUTHOR]

Chronic kidney disease is increasing at an alarming rate and correlates with the increase in diabetes, obesity, and hypertension that disproportionately impact socioeconomically disadvantaged communities. Iron plays essential roles in many biological processes including oxygen transport, mitochondrial function, cell proliferation, and regeneration. However, excess iron induces the generation and propagation of reactive oxygen species, which lead to oxidative stress, cellular damage, and ferroptosis. Iron homeostasis is regulated in part by the kidney through iron resorption from the glomerular filtrate and exports into the plasma by ferroportin (FPN). Yet, the impact of iron overload in the kidney has not been addressed. To test more directly whether excess iron accumulation is toxic to kidneys, we generated a kidney proximal tubule-specific knockout of FPN. Despite significant intracellular iron accumulation in FPN mutant tubules, basal kidney function was not measurably different from wild type kidneys. However, upon induction of acute kidney injury (AKI), FPN mutant kidneys exhibited significantly more damage and failed recovery, evidence for ferroptosis, and increased fibrosis. Thus, disruption of iron export in proximal tubules, leading to iron overload, can significantly impair recovery from AKI and can contribute to progressive renal damage indicative of chronic kidney disease. Understanding the mechanisms that regulate iron homeostasis in the kidney may provide new therapeutic strategies for progressive kidney disease and other ferroptosis-associated disorders. NEW & NOTEWORTHY Physiological iron homeostasis depends in part on renal resorption and export into the plasma. We show that specific deletion of iron exporters in the proximal tubules sensitizes cells to injury and inhibits recovery. This can promote a chronic kidney disease phenotype. Our paper demonstrates the need for iron balance in the proximal tubules to maintain and promote healthy recovery after acute kidney injury. [ABSTRACT FROM AUTHOR]

The voiding spot assay (VSA) on filter paper is an increasingly popular method for studying lower urinary tract physiology in mice. However, the ways VSAs are performed differ significantly between laboratories, and many variables are introduced compared with the mouse’s normal housing situation. Rodents are intelligent social animals, and it is increasingly understood that social and environmental stresses have significant effects on their physiology. Surprisingly, little is known about whether change of environment during VSA affects mouse voiding and what the best methodologies are for retaining “natural” micturition patterns. It is well known that stress-related neuropeptide corticotropin-releasing factor is significantly elevated and induces dramatic voiding changes when rodents encounter stresses. Therefore we hypothesized that changes in the environmental situation could potentially alter voiding during VSA. We have examined multiple factors to test whether they affect female mouse voiding patterns during VSA, including cage type, cage floor, water availability, water bottle location, single or group housing, and different handlers. Our results indicate that mice are surprisingly sensitive to changes in cage type and floor surface, water bottle location, and single/group housing, each of which induces significant changes in voiding patterns, indicative of a stress response. In contrast, neither changing handler nor 4 h of water deprivation affected voiding patterns. Our data indicate that VSA should be performed under conditions as close as possible to the mouse’s normal housing. Optimizing VSA methodology will be useful in uncovering voiding alterations in both genetic and disease models of lower urinary dysfunctions. [ABSTRACT FROM AUTHOR]

Competent statistical analysis is essential to maintain rigor and reproducibility in physiological research. Unfortunately, the benefits offered by statistics are often negated by misuse or inadequate reporting of statistical methods. To address the need for improved quality of statistical analysis in papers, the American Physiological Society released guidelines for reporting statistics in journals published by the society. The guidelines reinforce high standards for the presentation of statistical data in physiology but focus on the conceptual challenges and, thus, may be of limited use to an unprepared reader. Experimental scientists working in the renal field may benefit from putting the existing guidelines in a practical context. This paper discusses the application of widespread hypothesis tests in a confirmatory study. We simulated pharmacological experiments assessing intracellular calcium in cultured renal cells and kidney function at the systemic level to review best practices for data analysis, graphical presentation, and reporting. Such experiments are ubiquitously used in renal physiology and could be easily translated to other practical applications to fit the reader's specific needs. We provide step-by-step guidelines for using the most common types of t tests and ANOVA and discuss typical mistakes associated with them. We also briefly consider normality tests, exclusion criteria, and identification of technical and experimental replicates. This review is supposed to help the reader analyze, illustrate, and report the findings correctly and will hopefully serve as a gauge for a level of design complexity when it might be time to consult a biostatistician. [ABSTRACT FROM AUTHOR]

Technical advancements in research techniques in science are made in slow increments. Even so, large advances from insight and hard work of an individual with a single technique can have astonishing ramifications. Here, we examine the impact of Dr. Maurice B. Burg and the isolated perfused renal tubule technique and celebrate the 50th anniversary of the publication by Dr. Burg and his colleagues of their landmark paper in the American Journal of Physiology in 1966. In this study, we have taken a scientific visualization approach to study the scientific contributions of Dr. Burg and the isolated perfused tubule preparation as determining research impact by the number of research students, postdoctoral fellows, visiting scientists, and national and international collaborators. Additionally, we have examined the research collaborations (first and second generation scientists), established the migrational visualization of the first generation scientists who worked directly with Dr. Burg, quantified the metrics indices, identified and quantified the network of coauthorship of the first generation scientists with their second generation links, and determined the citations analyses of outputs of Dr. Burg and/or his first generation collaborators as coauthors. We also review the major advances in kidney physiology that have been made with the isolated perfused tubule technique. Finally, we are all waiting for the discoveries that the isolated perfused preparation technique will bring during the next 50 years. [ABSTRACT FROM AUTHOR]

Vasopressin controls water permeability in the renal collecting duct by regulating the water channel protein, aquaporin-2 (AQP2). Phosphoproteomic studies have identified multiple proteins that undergo phosphorylation changes in response to vasopressin. The kinases responsible for the phosphorylation of most of these sites have not been identified. Here, we use large-scale Bayesian data integration to predict the responsible kinases for 51 phosphoproteomically identified vasopressin-regulated phosphorylation sites in the renal collecting duct. To do this, we applied Bayes' rule to rank the 515 known mammalian protein kinases for each site. Bayes' rule was applied recursively to integrate each of the seven independent datasets, each time using the posterior probability vector of a given step as the prior probability vector of the next step. In total, 30 of the 33 phosphorylation sites that increase with vasopressin were predicted to be phosphorylated by protein kinase A (PKA) catalytic subunit-α, consistent with prior studies implicating PKA in vasopressin signaling. Eighteen of the vasopressin-regulated phosphorylation sites were decreased in response to vasopressin and all but three of these sites were predicted to be targets of extracellular signal-regulated kinases, ERK1 and ERK2. This result implies that ERK1 and ERK2 are inhibited in response to vasopressin V2 receptor occupation, secondary to PKA activation. The six phosphorylation sites not predicted to be phosphorylated by PKA or ERK1/2 are potential targets of other protein kinases previously implicated in aquaporin-2 regulation, including cyclin-dependent kinase 18 (CDK18), calmodulin-dependent kinase 2δ (CAMK2D), AMP-activated kinase catalytic subunit-α-1 (PRKAA1) and CDC42 binding protein kinase β (CDC42BPB). NEW & NOTEWORTHY: Vasopressin regulates water transport in the renal collecting duct in part through phosphorylation or dephosphorylation of proteins that regulate aquaporin-2. Prior studies have identified 51 vasopressin-regulated phosphorylation sites in 45 proteins. This study uses Bayesian data integration techniques to combine information from multiple prior proteomics and transcriptomics studies to predict the protein kinases that phosphorylate the 51 sites. Most of the regulated sites were predicted to be phosphorylated by protein kinase A or ERK1/ERK2. [ABSTRACT FROM AUTHOR]

Glycolytic overload in diabetes causes large accumulation of the highly reactive dicarbonyl compound methylglyoxal (MGO) and overproduction of advanced glycation end products (AGEs), which interact with their receptors (RAGE), leading to diabetes-associated macrovascular complications. The bladder is an organ that stays most in contact with dicarbonyl species, but little is known about the importance of the MGO-AGEs-RAGE pathway to diabetes-associated bladder dysfunction. Here, we aimed to investigate the role of the MGO-AGEs-RAGE pathway in bladder dysfunction of diabetic male and female ob/ ob mice compared with wild-type (WT) lean mice. Diabetic ob/ob mice were treated with the AGE breaker alagebrium (ALT711, 1 mg/kg) for 8 wk in drinking water. Compared with WT animals, male and female ob/ob mice showed marked hyperglycemia and insulin resistance, whereas fluid intake remained unaltered. Levels of total AGEs, MGO-derived hydroimidazolone 1, and RAGE in bladder tissues, as well as fluorescent AGEs in serum, were significantly elevated in ob/ob mice of either sex. Collagen content was also markedly elevated in the bladders of ob/ob mice. Void spot assays in filter paper in conscious mice revealed significant increases in total void volume and volume per void in ob/ob mice with no alterations of spot number. Treatment with ALT-711 significantly reduced the levels of MGO, AGEs, RAGE, and collagen content in ob/ob mice. In addition, ALT-711 treatment normalized the volume per void and increased the number of spots in ob/ob mice. Activation of AGEs-RAGE pathways by MGO in the bladder wall may contribute to the pathogenesis of diabetes-associated bladder dysfunction. NEW & NOTEWORTHY The involvement of methylglyoxal (MGO) and advanced glycation end products (AGEs) in bladder dysfunction of diabetic ob/ob mice treated with the AGE breaker ALT-711 was investigated here. Diabetic mice exhibited high levels of MGO, AGEs, receptor for AGEs (RAGE), and collagen in serum and/or bladder tissues along with increased volume per void, all of which were reduced by ALT-711. Activation of the MGO-AGEs-RAGE pathway in the bladder wall contributes to the pathogenesis of diabetes-associated bladder dysfunction. [ABSTRACT FROM AUTHOR]

Gut microbiome research has increased dramatically in the last decade, including in renal health and disease. The field is moving from experiments showing mere association to causation using both forward and reverse microbiome approaches, leveraging tools such as germ-free animals, treatment with antibiotics, and fecal microbiota transplantations. However, we are still seeing a gap between discovery and translation that needs to be addressed, so that patients can benefit from microbiome-based therapies. In this guideline paper, we discuss the key considerations that affect the gut microbiome of animals and clinical studies assessing renal function, many of which are often overlooked, resulting in false-positive results. For animal studies, these include suppliers, acclimatization, baseline microbiota and its normalization, littermates and cohort/cage effects, diet, sex differences, age, circadian differences, antibiotics and sweeteners, and models used. Clinical studies have some unique considerations, which include sampling, gut transit time, dietary records, medication, and renal phenotypes. We provide best-practice guidance on sampling, storage, DNA extraction, and methods for microbial DNA sequencing (both 16S rRNA and shotgun metagenome). Finally, we discuss follow-up analyses, including tools available, metrics, and their interpretation, and the key challenges ahead in the microbiome field. By standardizing study designs, methods, and reporting, we will accelerate the findings from discovery to translation and result in new microbiome-based therapies that may improve renal health. [ABSTRACT FROM AUTHOR]

The textbook account of whole body acid-base balance in terms of endogenous acid production, renal net acid excretion, and gastrointestinal alkali absorption, which is the only comprehensive model around, has never been applied in clinical practice or been formally validated. To improve understanding of acid-base modeling, we managed to write up this conventional model as an expression solely on urine chemistry. Renal net acid excretion and endogenous acid production were already formulated in terms of urine chemistry, and we could from the literature also see gastrointestinal alkali absorption in terms of urine excretions. With a few assumptions it was possible to see that this expression of net acid balance was arithmetically identical to minus urine charge, whereby under the development of acidosis, urine was predicted to acquire a net negative charge. The literature already mentions unexplained negative urine charges so we scrutinized a series of seminal papers and confirmed empirically the theoretical prediction that observed urine charge did acquire negative charge as acidosis developed. Hence, we can conclude that the conventional model is problematic since it predicts what is physiologically impossible. Therefore, we need a new model for whole body acid-base balance, which does not have impossible implications. Furthermore, new experimental studies are needed to account for charge imbalance in urine under development of acidosis. [ABSTRACT FROM AUTHOR]

Lower urinary tract (LUT) symptoms become prevalent with aging and affect millions; however, therapy is often ineffective because the etiology is unknown. Existing assays of LUT function in animal models are often invasive; however, a noninvasive assay is required to study symptom progression and determine genetic correlates. Here, we present a spontaneous voiding assay that is simple, reproducible, quantitative, and noninvasive. Young female mice from eight inbred mouse strains (129S1/SvImJ, A/J, C57BL/6J, NOD/ShiLtJ, NZO/H1LtJ, CAST/EiJ, PWK/PhJ, and WSB/EiJ) were tested for urination patterns on filter paper. Repeat testing at different times of the day showed minimal within-individual and within-strain variations, but all parameters (spot number, total volume, percent area in primary void, corner voiding, and center voiding) exhibited significant variations between strains. Calculation of the intraclass correlation coefficient, an estimate of broad-sense heritability, for each time of day and for each voiding parameter revealed highly significant heritability [spot number: 61%, percent urine in primary void: 90%, and total volume: 94% (afternoon data)]. Cystometrograms confirmed strong strain-specific urodynamic characteristics. Behavior-voiding correlation analysis showed no correlation with anxiety phenotypes. Diagnostically, the assay revealed LUT symptoms in several systems, including a demonstration of voiding abnormalities in older C57BL/6J mice (18-24 mo), in a model of protamine sulfate-induced urothelial damage and in a model of sucrose-induced diuresis. This assay may be used to derive pathophysiological LUT readouts from mouse models. Voiding characteristics are heritable traits, opening the way for genetic studies of LUT symptoms using outbred mouse populations. [ABSTRACT FROM AUTHOR]

While urothelial signals, including sonic hedgehog (Shh), drive bladder mesenchyme differentiation, it is unclear which pathways within the mesenchyme are critical for its development. Studies have shown that fibroblast growth factor receptor 2 (Fgfr2) is necessary for kidney and ureter mesenchymal development. Our objective was to determine the role of Fgfr2 in bladder mesenchyme. We used Tbx18cre mice to delete Fgfr2 in bladder mesenchyme (Fgfr2BM-/-). We performed three-dimensional reconstructions, quantitative real-time PCR, in situ hybridization, immunolabeling, ELISAs, immunoblotting, void stain on paper, ex vivo bladder sheet assays, and in vivo decerebrated cystometry. Compared with controls, embryonic (E) day 16.5 (E16.5) Fgfr2BM-/- bladders have thin muscle layers with reduced α-smooth muscle actin levels and thickened lamina propria with increased collagen expression that intrudes into muscle. From postnatal (P) day 1 (P1) to P30, Fgfr2BM-/- bladders demonstrate progressive muscle loss and increased collagen expression. Postnatal Fgfr2BM-/- bladder sheets exhibit decreased contractility and increased passive stretch tension compared with controls. In vivo cystometry revealed high baseline and threshold pressures and shortened intercontractile intervals in Fgfr2BM-/- bladders compared with controls. Mechanistically, while Shh expression appears normal, mRNA and protein readouts of hedgehog activity are increased in E16.5 Fgfr2BM-/- bladders compared with controls. Moreover, E16.5 Fgfr2BM-/- bladders exhibit higher levels of Cdo and Boc, hedgehog coreceptors that enhance sensitivity to Shh, than controls. Fgfr2 is critical for bladder mesenchyme patterning by virtue of its role in modulation of hedgehog signaling. [ABSTRACT FROM AUTHOR]

Autosomal dominant polycystic kidney disease (ADPKD) is the fourth most common cause of endstage renal disease. The disease course can be highly variable and treatment options are limited. To identify new therapeutic targets and prognostic biomarkers of disease, we conducted parallel discovery microarray profiling in normal and diseased human PKD1 cystic kidney cells. A total of 1,515 genes and 5 miRNA were differentially expressed by more than twofold in PKD1 cells. Functional enrichment analysis identified 30 dysregulated signaling pathways including the epidermal growth factor (EGF) receptor pathway. In this paper, we report that the EGF/ErbB family receptor ErbB4 is a major factor driving cyst growth in ADPKD. Expression of ErbB4 in vivo was increased in human ADPKD and Pkd1 cystic kidneys, both transcriptionally and posttranscriptionally by mir-193b-3p. Ligand-induced activation of ErbB4 drives cystic proliferation and expansion suggesting a pathogenic role in cystogenesis. Our results implicate ErbB4 activation as functionally relevant in ADPKD, both as a marker of disease activity and as a new therapeutic target in this major kidney disease. [ABSTRACT FROM AUTHOR]

The article examines R.J. Cross and J.V. Taggart's paper "Renal tubular transport: accumulation of p-aminohippurate by rabbit kidney slices." In the paper, Cross and Taggart examined the factors that influence the renal tubular transport of para-aminohippurate (PAH). The study showed that the transport of PAH into the cells was against an electrochemical gradient and required energy.

Concentrating models of the renal inner medulla can be classified according to external free-energy balance into passive models (positive values) and models that require an external energy source (negative values). Here we introduce an online computational tool that implements the equations of Stephenson and colleagues (Stephenson JL, Tewarson RP, Mejia R. Proc Natl Acad Sci USA 71: 1618-1622, 1974) to calculate external free-energy balance at steady state for the inner medulla (http://helixweb.nih.gov/ESBL/FreeEnergy). Here "external free-energy balance" means the sum of free-energy flows in all streams entering and leaving the inner medulla. The program first assures steady-state mass balance for all components and then tallies net external free-energy balance for the selected flow conditions. Its use is illustrated by calculating external free-energy balance for an example of the passive concentrating model taken from the original paper by Kokko and Rector (Kokko JP, Rector FC Jr. Kidney Int 2: 214-223, 1972). [ABSTRACT FROM AUTHOR]

An essay is presented regarding the six papers published in the "American Journal of Physiology" that is freely available online including "Micropuncture study of renal potassium excretion in the rat." The author mentions that the papers were made possible by the skills and imagination of Malnic, Giebisch, and Klose. He states that the papers showed that potassium is resorbed by the proximal tubule and the loop of Henle and that it offer insight into potassium transport's cellular mechanism.

Angiotensin II signaling plays a crucial role in many different diseases. Although it has been known for several decades that local angiotensin II signaling molecules are present in the bladder, the understanding of their functions there is still limited, especially compared with other organ systems such as cardiovascular and respiratory systems. This article reviews current literature regarding local angiotensin II signaling in the urinary bladder. By reviewing several decades of literature, the field has provided strong evidence to support the presence of local angiotensin II signaling in the bladder, including the expression of angiotensin type 1 receptor and angiotensin type 2 receptor in both human and animal tissues. In addition, evidence suggests a functional role of angiotensin type 1 receptor in mediating bladder contractions. In bladder disease models, angiotensin II signaling can be upregulated, and angiotensin type 1 receptor activity is associated with increases in inflammation, fibrosis, and oxidative stress. We also address the gaps in knowledge that remain in understanding local angiotensin II signaling in the bladder, including limitations on clinical translatability. Although there is a strong foundation regarding the local presence and role of angiotensin II signaling in the bladder, further research is needed to support translational applications. [ABSTRACT FROM AUTHOR]

Oxidative stress mediated by reactive oxygen species (ROS) contributes to apoptosis of tubular epithelial cells (TECs) and renal inflammation during acute kidney injury (AKI). Copper metabolism MURR1 domain-containing 5 [COMMD5/hypertension-related, calcium-regulated gene (HCaRG)] shows strong cytoprotective properties. COMMD5 is highly expressed in proximal tubules (PTs), where it controls cell differentiation. We assessed its role in cisplatin-induced AKI using transgenic mice in which COMMD5 is overexpressed in the PTs. Cisplatin caused the accumulation of damaged mitochondria and cellular waste in PTs, thus increasing the apoptosis of TECs. COMMD5 overexpression effectively protected TECs from cisplatin nephrotoxicity by decreasing intracellular ROS levels, mitochondrial dysfunction, and apoptosis through the preservation of tubular epithelial integrity, thus alleviating morphological and functional kidney damage. Excessive ROS production by hydrogen peroxide led to long-term autophagy activation through an increased burden on the autophagy/lysosome degradation system in TECs, and autophagic elimination of damaged mitochondria and cellular waste was compromised. COMMD5 attenuated oxidative injury by increasing autophagy flux, possibly due to a reduction of intracellular ROS levels through maintained tubular epithelial integrity, which decreased JNK/caspase-3-dependent apoptosis. Meanwhile, COMMD5 inhibition by siRNA reduced the resistance of TECs to cisplatin cytotoxicity, as shown by disrupted tubular epithelial integrity and cell viability. These data indicated that COMMD5 protects TECs from drug-induced oxidative stress and toxicity by maintaining tubular epithelial integrity and autophagy flux and ultimately decreases mitochondrial dysfunction and apoptosis. Increasing COMMD5 content in PTs is proposed as a new protective and therapeutic strategy against AKI. NEW & NOTEWORTHY: Oxidative stress overload by drug treatment causes the accumulation of damaged mitochondria that could contribute to tubulopathy. However, effective preventive treatment for drug-induced acute kidney injury remains incompletely understood. Our study showed that copper metabolism MURR1 domain-containing 5 (COMMD5) reduced mitochondrial dysfunction and increased autophagy flux by alleviating reactive oxygen species production through maintaining tubular epithelial integrity when tubular epithelial cells were under oxidative stress, thus ameliorating renal function in cisplatin-treated mice. These results uncover a novel renoprotective mechanism underlying tubular epithelial integrity and autophagy flux. [ABSTRACT FROM AUTHOR]

The long-term effects of a single episode of acute kidney injury (AKI) induced by bilateral ischemia-reperfusion injury (BIRI) on kidney lymphatic dynamics are not known. The purpose of this study was to determine if alterations in kidney lymphatics are sustained in the long term and how they relate to inflammation and injury. Mice underwent BIRI as a model of AKI and were followed up to 9 mo. Although kidney function markers normalized following initial injury, histological analysis revealed sustained tissue damage and inflammation for up to 9 mo. Transcriptional analysis showed both acute and late-stage lymphangiogenesis, supported by increased expression of lymphatic markers, with unique signatures at each phase. Expression of Ccl21a was distinctly upregulated during late-stage lymphangiogenesis. Three-dimensional tissue cytometry confirmed increased lymphatic vessel abundance, particularly in the renal cortex, at early and late timepoints postinjury. In addition, the study identified the formation of tertiary lymphoid structures composed of CCR7+ lymphocytes and observed changes in immune cell composition over time, suggesting a complex and dynamic response to AKI involving tissue remodeling and immune cell involvement. This study provides new insights into the role of lymphatics in the progression of AKI to chronic kidney disease. NEW & NOTEWORTHY: Here, we perform the first, comprehensive study of long-term lymphatic dynamics following a single acute kidney injury (AKI) event. Using improved three-dimensional image analysis and an expanded panel of transcriptional markers, we identify multiple stages of lymphatic responses with distinct transcriptional signatures, associations with the immune microenvironment, and collagen deposition. This research advances kidney lymphatic biology, emphasizing the significance of longitudinal studies in understanding AKI and the transition to chronic kidney disease. [ABSTRACT FROM AUTHOR]

As shown in our previous paper (Kriz W, Löwen J, Federico G, van den Born J, Gröne E, Gröne HJ. Am J Physiol Renal Physiol 312: F1101–F1111, 2017), mesangial matrix expansion in diabetic nephropathy (DN) results for a major part from the accumulation of worn-out undegraded glomerular basement membrane material. Here, based on the reevaluation of >900 biopsies of DN, we show that this process continues with the progression of the disease finally leading to the herniation of the matrix-overloaded tuft through the glomerular entrance to the outside. This leads to severe changes in the glomerular surroundings, including a dissociation of the juxtaglomerular apparatus with displacement of the macula densa. The herniation is associated with a prominent outgrowth of glomerular vessels from the tuft. Mostly, these aberrant vessels are an abnormal type of arteriole with frequent intramural insudations of plasma. They spread into glomerular surroundings extending in intertubular and periglomerular spaces. Their formation is associated with elevated mRNA levels of vascular endothelial growth factor-A, angiopoietins 1 and 2, and the corresponding receptors. Functionally, these processes seem to compromise tubuloglomerular feedback-related functions and may be one factor why Na+-glucose cotransporter-2 inhibitors are not effective in advanced stages of DN. [ABSTRACT FROM AUTHOR]

Biological information is growing at a rapid pace, making it difficult for individual investigators to be familiar with all information that is relevant to their own research. Computers are beginning to be used to extract and curate biological information; however, the complexity of human language used in research papers continues to be a critical barrier to full automation of knowledge extraction. Here, we report a manually curated knowledge base of vasopressin actions in renal epithelial cells that is designed to be readable either by humans or by computer programs using natural language processing algorithms. The knowledge base consists of three related databases accessible at https://helixweb.nih.gov/ESBL/TinyUrls/Vaso_portal.html. One of the component databases reports vasopressin actions on individual proteins expressed in renal epithelia, including effects on phosphorylation, protein abundances, protein translocation from one subcellular compartment to another, protein-protein binding interactions, etc. The second database reports vasopressin actions on physiological measures in renal epithelia, and the third reports specific mRNA species whose abundances change in response to vasopressin. We illustrate the application of the knowledge base by using it to generate a protein kinase network that connects vasopressin binding in collecting duct cells to physiological effects to regulate the water channel protein aquaporin-2. [ABSTRACT FROM AUTHOR]

This article focuses on a conceptual model of the countercurrent multiplication mechanism followed by the mammalian kidney to excrete concentrated urine. The concurrent model is discussed with reference to two papers by C.W. Gottschalk and M. Mylle and K.J. Ullrich. These researchers had analyzed micro-samples of interstitial fluid from the medulla and had shown that NaCl and urea were the primary contributors, in approximately equal proportion, to the medullary hypertonicity, and that concentrations of both solutes rose progressively from the corticomedullary junction to the tip of the papila.

Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS) is a chronic inflammatory disease without consistently effective treatment. We investigate the role of toll-like receptor 4 (TLR4) on voiding dysfunction and inflammation in the cyclophosphamide (CYP)-induced mouse cystitis. Male C57BL/6 [wild-type,(WT)] and/or TLR4 knockout (TLR4-/-) mice were treated with an injection of CYP (300 mg/kg, 24 h) or saline (10 ml/kg). The pharmacological blockade of the TLR4 by resatorvid (10 mg/kg) was also performed 1 h prior CYP-injection in WT mice. Urodynamic profiles were assessed by voiding stain on filter paper and filling cystometry. Contractile responses to carbachol were measured in isolated bladders. In CYP-exposed WT mice, mRNA for TLR4, myeloid differentiation primary response 88, and TIR-domain-containing adapter-inducing interferon-β increased by 45%, 72%, and 38%, respectively (P < 0.05). In free-moving mice, CYP-exposed mice exhibited a higher number of urinary spots and smaller urinary volumes. Increases of micturition frequency and nonvoiding contractions, concomitant with decreases of intercontraction intervals and capacity, were observed in the filling cystometry of WT mice (P < 0.05). Carbachol-induced bladder contractions were significantly reduced in the CYP group, which was paralleled by reduced mRNA for M2 and M3 muscarinic receptors. These functional and molecular alterations induced by CYP were prevented in TLR4-/- and resatorvid-treated mice. Additionally, the increased levels of inflammatory markers induced by CYP exposure, myeloperoxidase activity, interleukin-6, and tumor necrosis factor-alpha were significantly reduced by resatorvid treatment. Our findings reveal a central role for the TLR4 signaling pathway in initiating CYP-induced bladder dysfunction and inflammation and thus emphasize that TLR4 receptor blockade may have clinical value for IC/BPS treatment. [ABSTRACT FROM AUTHOR]

The prorenin receptor (PRR) was originally proposed to be a member of the renin-angiotensin system (RAS); however, recent work questioned their association. The present paper describes a functional link between the PRR and RAS in the renal juxtaglomerular apparatus (JGA), a classic anatomical site of the RAS. PRR expression was found in the sensory cells of the JGA, the macula densa (MD), and immunohistochemistry-localized PRR to the MD basolateral cell membrane in mouse, rat, and human kidneys. MD cell PRR activation led to MAP kinase ERK1/2 signaling and stimulation of PGE2 release, the classic pathway of MD-mediated renin release. Exogenous renin or prorenin added to the in vitro microperfused JGA-induced acute renin release, which was inhibited by removing the MD or by the administration of a PRR decoy peptide. To test the function of MD PRR in vivo, we established a new mouse model with inducible conditional knockout (cKO) of the PRR in MD cells based on neural nitric oxide synthase-driven Cre-lox recombination. Deletion of the MD PRR significantly reduced blood pressure and plasma renin. Challenging the RAS by low-salt diet + captopril treatment caused further significant reductions in blood pressure, renal renin, cyclooxygenase-2, and microsomal PGE synthase expression in cKO vs. wild-type mice. These results suggest that the MD PRR is essential in a novel JGA short-loop feedback mechanism, which is integrated within the classic MD mechanism to control renin synthesis and release and to maintain blood pressure. [ABSTRACT FROM AUTHOR]

Identifying effective drugs for focal segmental glomerulosclerosis (FSGS) treatment holds significant importance. Our high-content drug screening on zebrafish larvae relies on nitroreductase/metronidazole (NTR/MTZ)-induced podocyte ablation to generate FSGS-like injury. A crucial factor for successful drug screenings is minimizing variability in injury induction. For this, we introduce nifurpirinol (NFP) as a more reliable prodrug for targeted podocyte depletion. NFP showed a 2.3-fold increase in efficiency at concentrations 1,600-fold lower compared with MTZ-mediated injury induction. Integration into the screening workflow validated its suitability for the high-content drug screening. The presence of crucial FSGS hallmarks, such as podocyte foot process effacement, proteinuria, and activation of parietal epithelial cells, was observed. After the isolation of the glomeruli from the larvae, we identified essential pathways by proteomic analysis. This study shows that NFP serves as a highly effective prodrug to induce the FSGS-like disease in zebrafish larvae and is well-suited for a high-content drug screening to identify new candidates for the treatment of FSGS. NEW & NOTEWORTHY: This research investigated the use of nifurpirinol in nanomolar amounts as a prodrug to reliably induce focal segmental glomerulosclerosis (FSGS)-like damage in transgenic zebrafish larvae. Through proteomic analysis of isolated zebrafish glomeruli, we were further able to identify proteins that are significantly regulated after the manifestation of FSGS. These results are expected to expand our knowledge of the pathomechanism of FSGS. [ABSTRACT FROM AUTHOR]

Epithelial-to-mesenchymal transition (EMT) is considered as one of the senescence processes; reportedly, antisenescence therapies effectively reduce EMT. Some models have shown antisenescence effects with the use of sodium-glucose cotransporter 2 (SGLT2) inhibitor. Therefore, our study investigated the antisenescence effects of empagliflozin as an SGLT2 inhibitor in a peritoneal fibrosis model and their impact on EMT inhibition. For in vitro study, human peritoneal mesothelial cells (HPMCs) were isolated and grown in a 96-well plate. The cell media were exchanged with serum-free M199 medium with d -glucose, with or without empagliflozin. All animal experiments were carried out in male mice. Mice were randomly classified into three treatment groups based on peritoneal dialysis (PD) or empagliflozin. We evaluated changes in senescence and EMT markers in HPMCs and PD model. HPMCs treated with glucose transformed from cobblestone to spindle shape, resulting in EMT. Empagliflozin attenuated these morphological changes. Reactive oxygen species production, DNA damage, senescence, and EMT markers were increased by glucose treatment; however, cotreatment with glucose and empagliflozin attenuated these changes. For the mice with PD, an increase in thickness, collagen deposition, staining for senescence, or EMT markers of the parietal peritoneum was observed, which, however, was attenuated by cotreatment with empagliflozin. p53, p21, and p16 increased in mice with PD compared with those in the control group; however, these changes were decreased by empagliflozin. In conclusion, empagliflozin effectively attenuated glucose-induced EMT in HPMCs through a decrease in senescence. Cotreatment with empagliflozin improved peritoneal thickness and fibrosis in PD. NEW & NOTEWORTHY: Epithelial-to-mesenchymal transition (EMT) is considered one of the senescence processes. Antisenescence therapies may effectively reduce EMT in peritoneal dialysis models. Human peritoneal mesothelial cells treated with glucose show an increase in senescence and EMT markers; however, empagliflozin attenuates these changes. Mice undergoing peritoneal dialysis exhibit increased senescence and EMT markers, which are decreased by empagliflozin. These findings suggest that empagliflozin may emerge as a novel strategy for prevention or treatment of peritoneal fibrosis. [ABSTRACT FROM AUTHOR]

Chronic kidney disease (CKD) is characterized by inflammation and fibrosis in the kidney. Renal biopsies and estimated glomerular filtration rate (eGFR) remain the standard of care, but these endpoints have limitations in detecting the stage, progression, and spatial distribution of fibrotic pathology in the kidney. MRI diffusion tensor imaging (DTI) has emerged as a promising noninvasive technology to evaluate renal fibrosis in vivo both in clinical and preclinical studies. However, these imaging studies have not systematically identified fibrosis particularly deeper in the kidney where biopsy sampling is limited, or completed an extensive analysis of whole organ histology, blood biomarkers, and gene expression to evaluate the relative strengths and weaknesses of MRI for evaluating renal fibrosis. In this study, we performed DTI in the sodium oxalate mouse model of CKD. The DTI parameters fractional anisotropy, apparent diffusion coefficient, and axial diffusivity were compared between the control and oxalate groups with region of interest (ROI) analysis to determine changes in the cortex and medulla. In addition, voxel-based analysis (VBA) was implemented to systematically identify local regions of injury over the whole kidney. DTI parameters were found to be significantly different in the medulla by both ROI analysis and VBA, which also spatially matched with collagen III immunohistochemistry (IHC). The DTI parameters in this medullary region exhibited moderate to strong correlations with histology, blood biomarkers, hydroxyproline, and gene expression. Our results thus highlight the sensitivity of DTI to the heterogeneity of renal fibrosis and importance of whole kidney noninvasive imaging. NEW & NOTEWORTHY: Chronic kidney disease (CKD) can be characterized by inflammation and fibrosis of the kidney. Although standard of care methods have been limited in scope, safety, and spatial distribution, MRI diffusion tensor imaging (DTI) has emerged as a promising noninvasive technology to evaluate renal fibrosis in vivo. In this study, we performed DTI in an oxalate mouse model of CKD to systematically identify local kidney injury. DTI parameters strongly correlated with histology, blood biomarkers, hydroxyproline, and gene expression. [ABSTRACT FROM AUTHOR]

Ubiquitination influences the expression of the epithelial Na+ channel (ENaC). We assessed the mechanisms of selective ubiquitination of the mature, cleaved form of γENaC in both native rodent kidneys and Fisher rat thyroid (FRT) cells expressing the channel heterologously. In both models, singly cleaved and fully cleaved γENaCs were strongly ubiquitinated, implying that the second cleavage releasing an inhibitory peptide was not essential for the process. To see whether location of the protein in or near the apical membrane rather than cleavage per se influences ubiquitination, we studied mutants of γENaC in which cleavage sites are abolished. These subunits were ubiquitinated only when coexpressed with α- and βENaC, facilitating trafficking through the Golgi apparatus. To test whether reaching the apical surface is necessary we performed in situ surface biotinylation and measured ENaC ubiquitination in the apical membrane of rat kidney. Ubiquitination of cleaved γENaC was similar in whole kidney and surface fractions, implying that both apical and subapical channels could be modified. In FRT cells, inhibiting clathrin-mediated endocytosis with Dyngo-4a increased both total and ubiquitinated γENaC at the cell surface. Finally, we tested the idea that increased intracellular Na+ could stimulate ubiquitination. Administration of amiloride to block Na+ entry through the channels did not affect ubiquitination of γENaC in either FRT cells or the rat kidney. However, presumed large increases in cellular Na+ produced by monensin in FRT cells or acute Na+ repletion in rats increased ubiquitination and decreased overall ENaC expression. NEW & NOTEWORTHY: We have explored the mechanisms underlying the ubiquitination of the γ subunit of epithelial Na+ channel (ENaC), a process believed to control channel internalization and degradation. We previously reported that the mature, cleaved form of the subunit is selectively ubiquitinated. Here we show that this specificity arises not from the cleavage state of the protein but from its location in the cell. We also show that under some conditions, increased intracellular Na+ can stimulate ENaC ubiquitination. [ABSTRACT FROM AUTHOR]

This document is a corrigendum for an article titled "Podocytes from hypertensive and obese mice acquire an inflammatory, senescent, and aged phenotype" published in the American Journal of Physiology: Renal Physiology. The corrigendum adds Dr. Thomas Carroll as an author based on their contribution to the study. The author line and affiliation line have been updated accordingly. Additionally, the grants section of the article reflects additional funding received for the research. The corrigendum also includes copyright information and a link to access the article online. [Extracted from the article]

The exocyst and Ift88 are necessary for primary ciliogenesis. Overexpression of Exoc5 (OE), a central exocyst component, resulted in longer cilia and enhanced injury recovery. Mitochondria are involved in acute kidney injury (AKI). To investigate cilia and mitochondria, basal respiration and mitochondrial maximal and spare respiratory capacity were measured in Exoc5 OE, Exoc5 knockdown (KD), Exoc5 ciliary targeting sequence mutant (CTS-mut), control Madin-Darby canine kidney (MDCK), Ift88 knockout (KO), and Ift88 rescue cells. In Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells, these parameters were decreased. In Exoc5 OE and Ift88 rescue cells they were increased. Reactive oxygen species were higher in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells compared with Exoc5 OE, control, and Ift88 rescue cells. By electron microscopy, mitochondria appeared abnormal in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells. A metabolomics screen of control, Exoc5 KD, Exoc5 CTS-mut, Exoc5 OE, Ift88 KO, and Ift88 rescue cells showed a marked increase in tryptophan levels in Exoc5 CTS-mut (113-fold) and Exoc5 KD (58-fold) compared with control cells. A 21% increase was seen in Ift88 KO compared with rescue cells. In Exoc5 OE compared with control cells, tryptophan was decreased 59%. To determine the effects of ciliary loss on AKI, we generated proximal tubule-specific Exoc5 and Ift88 KO mice. These mice had loss of primary cilia, decreased mitochondrial ATP synthase, and increased tryptophan in proximal tubules with greater injury following ischemia-reperfusion. These data indicate that cilia-deficient renal tubule cells are primed for injury with mitochondrial defects in tryptophan metabolism. NEW & NOTEWORTHY Mitochondria are centrally involved in acute kidney injury (AKI). Here, we show that cilia-deficient renal tubule cells both in vitro in cell culture and in vivo in mice are primed for injury with mitochondrial defects and aberrant tryptophan metabolism. These data suggest therapeutic strategies such as enhancing ciliogenesis or improving mitochondrial function to protect patients at risk for AKI. [ABSTRACT FROM AUTHOR]

The lack of standardization in antibody validation remains a major contributor to irreproducibility of human research. To address this, we have applied a standardized approach to validate a panel of antibodies to identify 18 major cell types and 5 extracellular matrix compartments in the human kidney by immunofluorescence (IF) microscopy. We have used these to generate an organ mapping antibody panel for two-dimensional (2-D) and three-dimensional (3-D) cyclical IF (CyCIF) to provide a more detailed method for evaluating tissue segmentation and volumes using a larger panel of markers than would normally be possible using standard fluorescence microscopy. CyCIF also makes it possible to perform multiplexed IF microscopy of whole slide images, which is a distinct advantage over other multiplexed imaging technologies that are applicable to limited fields of view. This enables a broader view of cell distributions across larger anatomical regions, allowing a better chance to capture localized regions of dysfunction in diseased tissues. These methods are broadly accessible to any laboratory with a fluorescence microscope, enabling spatial cellular phenotyping in normal and disease states. We also provide a detailed solution for image alignment between CyCIF cycles that can be used by investigators to perform these studies without programming experience using opensourced software. This ability to perform multiplexed imaging without specialized instrumentation or computational skills opens the door to integration with more highly dimensional molecular imaging modalities such as spatial transcriptomics and imaging mass spectrometry, enabling the discovery of molecular markers of specific cell types, and how these are altered in disease. NEW & NOTEWORTHY We describe here validation criteria used to define on organ mapping panel of antibodies that can be used to define 18 cell types and five extracellular matrix compartments using cyclical immunofluorescence (CyCIF) microscopy. As CyCIF does not require specialized instrumentation, and image registration required to assemble CyCIF images can be performed by any laboratory without specialized computational skills, this technology is accessible to any laboratory with access to a fluorescence microscope and digital scanner. [ABSTRACT FROM AUTHOR]

Stretch-activated two-pore domain K+ (K2P) channels play important roles in many visceral organs, including the urinary bladder. The TWIK-related K+ channel TREK-1 is the predominantly expressed K2P channel in the urinary bladder of humans and rodents. Downregulation of TREK-1 channels was observed in the urinary bladder of patients with detrusor overactivity, suggesting their involvement in the pathogenesis of voiding dysfunction. This study aimed to characterize the long-term effects of TREK-1 on bladder function with global and smooth muscle-specific TREK-1 knockout (KO) mice. Bladder morphology, bladder smooth muscle (BSM) contractility, and voiding patterns were evaluated up to 12 mo of age. Both sexes were included in this study to probe the potential sex differences. Smooth muscle-specific TREK-1 KO mice were used to distinguish the effects of TREK-1 downregulation in BSM from the neural pathways involved in the control of bladder contraction and relaxation. TREK-1 KO mice developed enlarged urinary bladders (by 60.0% for males and by 45.1% for females at 6 mo; P < 0.001 compared with the age-matched control group) and had a significantly increased bladder capacity (by 137.7% at 12 mo; P < 0.0001) and compliance (by 73.4% at 12 mo; P < 0.0001). Bladder strips isolated from TREK-1 KO mice exhibited decreased contractility (peak force after KCl at 6 mo was 1.6 ± 0.7 N/g compared with 3.4 ± 2.0 N/g in the control group; P = 0.0005). The lack of TREK-1 channels exclusively in BSM did not replicate the bladder phenotype observed in TREK-1 KO mice, suggesting a strong neurogenic origin of TREK-1-related bladder dysfunction. NEW & NOTEWORTHY: This study compared voiding function and bladder phenotypes in global and smooth muscle-specific TREK-1 KO mice. We found significant age-related changes in bladder contractility, suggesting that the lack of TREK-1 channel activity might contribute to age-related changes in bladder smooth muscle physiology. [ABSTRACT FROM AUTHOR]

Conduit arterial disease in chronic kidney disease (CKD) is an important cause of cardiac complications. Cardiac function in CKD has not been studied in the absence of arterial disease. In an Alport syndrome model bred not to have conduit arterial disease, mice at 225 days of life (dol) had CKD equivalent to humans with CKD stage 4-5. Parathyroid hormone (PTH) and FGF23 levels were one log order elevated, circulating sclerostin was elevated, and renal activin A was strongly induced. Aortic Ca levels were not increased, and vascular smooth muscle cell (VSMC) transdifferentiation was absent. The CKD mice were not hypertensive, and cardiac hypertrophy was absent. Freshly excised cardiac tissue respirometry (Oroboros) showed that ADP-stimulated O2 flux was diminished from 52 to 22 pmol/mg (P = 0.022). RNA-Seq of cardiac tissue from CKD mice revealed significantly decreased levels of cardiac mitochondrial oxidative phosphorylation genes. To examine the effect of activin A signaling, some Alport mice were treated with a monoclonal Ab to activin A or an isotype-matched IgG beginning at 75 days of life until euthanasia. Treatment with the activin A antibody (Ab) did not affect cardiac oxidative phosphorylation. However, the activin A antibody was active in the skeleton, disrupting the effect of CKD to stimulate osteoclast number, eroded surfaces, and the stimulation of osteoclast-driven remodeling. The data reported here show that cardiac mitochondrial respiration is impaired in CKD in the absence of conduit arterial disease. This is the first report of the direct effect of CKD on cardiac respiration. [ABSTRACT FROM AUTHOR]

Men are likely at greater risk for heat-induced acute kidney injury compared with women, possibly due to differences in vascular control. We tested the hypothesis that the renal vasoconstrictor and vasodilator responses will be greater in younger women compared with men during passive heat stress. Twenty-five healthy adults [12 women (early follicular phase) and 13 men] completed two experimental visits, heat stress or normothermic time-control, assigned in a block-randomized crossover design. During heat stress, participants wore a water-perfused suit perfused with 50°C water. Core temperature was increased by ∼0.8°C in the first hour before commencing a 2-min cold pressor test (CPT). Core temperature remained clamped and at 1-h post-CPT, subjects ingested a whey protein shake (1.2 g of protein/kg body wt), and measurements were taken pre-, 75 min, and 150 min post-protein. Beat-to-beat blood pressure (Penaz method) was measured and segmental artery vascular resistance (VR, Doppler ultrasound) was calculated as segmental artery blood velocity ÷ mean arterial pressure. CPT-induced increases in segmental artery VR did not differ between trials (trial effect: P = 0.142) nor between men (heat stress: 1.5-±-1.0 mmHg/cm/s, normothermia: 1.4-±-1.0 mmHg/cm/s) and women (heat stress: 1.4-±-1.2 mmHg/cm/s, normothermia: 2.1-±-1.1 mmHg/cm/s) (group effect: P = 0.429). Reductions in segmental artery VR following oral protein loading did not differ between trials (trial effect: P = 0.080) nor between men (heat stress: −0.6-±-0.8 mmHg/cm/s, normothermia: −0.6-±-0.6 mmHg/cm/s) and women (heat stress: −0.5-±-0.5 mmHg/cm/s, normothermia: −1.1-±-0.6 mmHg/cm/s) (group effect: P = 0.204). Renal vasoconstrictor responses to the cold pressor test and vasodilator responses following an oral protein load during heat stress or normothermia do not differ between younger men and younger women in the early follicular phase of the menstrual cycle. [ABSTRACT FROM AUTHOR]

The article presents information on the editorial policy of the periodical.

The paracellular pathways in renal tubular epithelia such as the proximal tubules, which reabsorb the largest fraction of filtered solutes and water and are leaky epithelia, are important routes for transepithelial transport of solutes and water. Movement occurs passively via an extracellular route through the tight junction between cells. The characteristics of paracellular transport vary among different nephron segments with leaky or tighter epithelia. Claudins expressed at tight junctions form pores and barriers for paracellular transport. Claudins are from a multigene family, comprising at least 27 members in mammals. Multiple claudins are expressed at tight junctions of individual nephron segments in a nephron segment-specific manner. Over the last decade, there have been advances in our understanding of the structure and functions of claudins. This paper is a review of our current knowledge of claudins, with special emphasis on their physiological roles in proximal tubule paracellular solute and water transport. [ABSTRACT FROM AUTHOR]

The role of 5-HT1A receptors in regulating voiding functions remains unclear, particularly regarding the urine flow rate (UFR) during voiding. This study examined the effects of 5-HT1A receptors on regulating urethral functions in female rats and investigated underlying modulatory mechanisms. Intravesical pressure (IVP), external urethral sphincterelectromyography (EUS-EMG), and UFR were simultaneously recorded during continuous transvesical infusion to examine the effects of a 5-HT1A receptor agonist (8-OH-DPAT) and antagonist (WAY- 100635) on bladder and urethral functions. In addition, this study evaluated the independent roles of urethral striated and smooth muscles in the UFR in rats after a neuromuscular blockade (NMB) treatment and bilateral hypogastric nerve transection. Our results revealed that 8-OH-DPAT significantly increased the maximal UFR but reduced the mean UFR. This discrepancy may be because 8-OHDPAT markedly increased the maximal UFR during the initial segment of the flow duration and subsequently induced an approximately zero level of long oscillatory waves during the remaining flow duration. Thus the mean UFR was reduced because of the prolonged approximately zero level of the UFR. However, paralyzing the EUS with an NMB agent, 8-OH-DPAT, significantly increased the maximal and mean UFRs because the prolonged zero level of the oscillatory UFR did not continue. These results support the hypothesis that the increased UFR in female rats during voiding is due to the induction of urethral smooth muscle relaxation by 8-OH-DPAT. This paper provides a detailed understanding of the role of 5-HT1A receptors in controlling the UFR in female rats. [ABSTRACT FROM AUTHOR]

The availability of oxygen in renal tissue is determined by the complex interactions among a host of processes, including renal blood flow, glomerular filtration, arterial-to-venous oxygen shunting, medullary architecture, Na+ transport, and oxygen consumption. When this delicate balance is disrupted, the kidney may become susceptible to hypoxic injury. Indeed, renal hypoxia has been implicated as one of the major causes of acute kidney injury and chronic kidney diseases. This review highlights recent advances in our understanding of renal hypoxia; some of these studies were published in response to a recent Call for Papers of this journal: Renal Hypoxia. [ABSTRACT FROM AUTHOR]

The incidence and progression of kidney diseases are influenced by sex. The renin-angiotensin system (RAS) is an important regulator of cardiovascular and renal function. Sex differences in the renal response to RAS blockade have been demonstrated. Circulating and renal RAS has been shown to be altered in type 1 and type 2 diabetes; this enzymatic cascade plays a critical role in the development of diabetic nephropathy (DN). Angiotensin-converting enzyme (ACE) and ACE2 are differentially regulated depending on its localization within the diabetic kidney. Furthermore, clinical and experimental studies have shown that circulating levels of sex hormones are clearly modulated in the context of diabetes, suggesting that sex-dependent RAS regulation may also be affected in these individuals. The effect of sex hormones on circulating and renal RAS may be involved in the sex differences observed in DN progression. In this paper we will review the influence of sex hormones on RAS expression and its relation to diabetic kidney disease. A better understanding of the sex dimorphism on RAS might provide a new approach for diabetic kidney disease treatment. [ABSTRACT FROM AUTHOR]

Acute kidney injury (AKI) remains a significant clinical problem through its diverse etiologies, the challenges of robust measurements of injury and recovery, and its progression to chronic kidney disease (CKD). Bridging the gap in our knowledge of this disorder requires bringing together not only the technical resources for research but also the investigators currently endeavoring to expand our knowledge and those who might bring novel ideas and expertise to this important challenge. The University of Alabama at Birmingham-University of California-San Diego O'Brien Center for Acute Kidney Injury Research brings together technical expertise and programmatic and educational efforts to advance our knowledge in these diverse issues and the required infrastructure to develop areas of novel exploration. Since its inception in 2008, this O'Brien Center has grown its impact by providing state-of-the-art resources in clinical and preclinical modeling of AKI, a bioanalytical core that facilitates measurement of critical biomarkers, including serum creatinine via LC-MS/MS among others, and a biostatistical resource that assists from design to analysis. Through these core resources and with additional educational efforts, our center has grown its investigator base to include >200 members from 51 institutions. Importantly, this center has translated its pilot and catalyst funding program with a $37 return per dollar invested. Over 500 publications have resulted from the support provided with a relative citation ratio of 2.18 ± 0.12 (iCite). Through its efforts, this disease-centric O'Brien Center is providing the infrastructure and focus to help the development of the next generation of researchers in the basic and clinical science of AKI. This center creates the promise of the application at the bedside of the advances in AKI made by current and future investigators. [ABSTRACT FROM AUTHOR]