Kidney Homeostasis Research Articles

Melatonin attenuates arsenic induced nephropathy via the regulation of oxidative stress and inflammatory signaling cascades in mice

Arsenic is a potent inducer of several acute and chronic nephrotoxic disorders. It promotes deleterious phenomenon like oxidative stress, inflammation, cell death and altered glucose uptake leading to distorted kidney homeostasis that end up in chronic kidney disease. This study investigated the possible protective role of melatonin; a natural antioxidant produced by the pineal gland, against arsenic induced nephrotoxicity. Melatonin successfully ameliorated arsenic induced renal toxicity both in in vitro and in vivo models. Elevated BUN, creatinine, urine glucose and protein levels and altered renal histopathological conditions were observed in arsenic intoxicated mice. Significant oxidative stress induced damage of biomolecules along with downregulation in antioxidant enzymes and thiols were also detected in the kidney tissues of arsenic-intoxicated mice. These alterations along with mitochondrial dysfunction ultimately triggered TNFα mediated inflammatory and cell death cascades. Interestingly arsenic also led to disruption of glucose uptake in the kidney. These findings suggest that melatonin protects the kidney against toxic effect of arsenic, presumably through its antioxidant, anti-inflammatory and antidiabetic properties by inhibiting inflammatory outburst, apoptosis, necroptosis and stimulating glucose uptake. As melatonin is a natural antioxidant molecule, detailed pharmacokinetic and pharmacodynamic studies are expected to establish it as an effective nephro-protective agent in future.

The impact of preserved Klotho gene expression on antioxidative stress activity in healthy kidney.

Klotho, which was originally identified as an antiaging gene, forms a complex with fibroblast growth factor 23 receptor in the kidney, with subsequent signaling that regulates mineral metabolism. Other biological activities of Klotho, including antiaging effects such as protection from various types of cellular stress, have been shown; however, the precise mechanism of these effects of Klotho gene in the healthy human kidney is not well understood. In this study, we examined the relationships of Klotho and antioxidative stress gene expression levels in zero-hour biopsy specimens from 44 donors in kidney transplantation and verified them in animal models whose Klotho gene expression levels were varied. The nitrotyrosine expression level in the kidney was evaluated in these animal models. Expression levels of Klotho gene were positively correlated with the p53 gene and antioxidant enzyme genes such as catalase, superoxide dismutase 1 (SOD1), SOD2, peroxiredoxin 3 (PRDX3), and glutathione peroxidase 1 (GPX1) but not clinical parameters such as age and renal function or pathological features such as glomerulosclerosis and interstitial fibrosis tubular atrophy. The expression levels of all genes were significantly higher in mice with Klotho overexpression than in wild-type mice, and those except for catalase, PRDX3, and GPX1 were significantly lower in Klotho-deficient mice than in wild-type littermate mice. Nitrotyrosine-positive bands of various sizes were observed in kidney from Klotho-deficient mice only. The preservation of Klotho gene expression might induce the antioxidative stress mechanism for homeostasis of healthy human kidney independently of its general condition, including age, renal function, and histological findings.

Nutritional Considerations for Dialysis Vegetarian Patients, Part Two

Nutritional Considerations for Dialysis Vegetarian Patients, Part Two

Kidney-Derived c-Kit+ Cells Possess Regenerative Potential.

SummaryKidney‐derived c‐Kit+ cells exhibit progenitor/stem cell properties in vitro (self‐renewal capacity, clonogenicity, and multipotentiality). These cells can regenerate epithelial tubular cells following ischemia‐reperfusion injury and accelerate foot processes effacement reversal in a model of acute proteinuria in rats. Several mechanisms are involved in kidney regeneration by kidney‐derived c‐Kit+ cells, including cell engraftment and differentiation into renal‐like structures, such as tubules, vessels, and podocytes. Moreover, paracrine mechanisms could also account for kidney regeneration, either by stimulating proliferation of surviving cells or modulating autophagy and podocyte cytoskeleton rearrangement through mTOR‐Raptor and ‐Rictor signaling, which ultimately lead to morphological and functional improvement. To gain insights into the functional properties of c‐Kit+ cells during kidney development, homeostasis, and disease, studies on lineage tracing using transgenic mice will unveil their fate. The results obtained from these studies will set the basis for establishing further investigation on the therapeutic potential of c‐Kit+ cells for treatment of kidney disease in preclinical and clinical studies. stem cells translational medicine 2018;7:317–324

Grain Amaranth Is Associated with Improved Hepatic and Renal Calcium Metabolism in Type 2 Diabetes Mellitus of Male Wistar Rats.

Background Dysregulation of calcium signaling is a hallmark of diabetes mellitus (DM) and grain amaranth (AG) has antidiabetic properties. Information on the mechanism of action of AG on blood, renal, and hepatic tissues is sparse, although it continues to be an important alternative medicinal plant in several developing countries. The objective of the study was to determine key changes in calcium levels and s100a1 protein levels and antioxidant and histopathologic changes in blood, renal, and hepatic tissues of male diabetic Wistar rats. Materials and Methods This was an experimental study in which 30 male Wistar rats were kept for 5 weeks (6 groups, N =5). Groups 1-IV had T2DM induced using Nicotinamide and Streptozotocin: Group I, Mixtard®; group II, positive control; group III, 25% AG; group IV, 50% AG. Furthermore, group V consisted of normal rats given 50% GA and group VI was negative control. Blood, renal, and hepatic tissues were collected and analyzed for calcium, s100a1 protein levels, and antioxidant and histopathological changes. Results and Discussion In blood, renal, and hepatic tissue, calcium and s100a1 levels were low during T2DM and these increased following AG supplementation. This was important for improved metabolic processes, thus leading to the low malondialdehyde (MDA) and glutathione peroxidase (GPx) activity in the tissues. Efficient antioxidant status was important for improved calcium signaling mechanisms, thus leading to improved tissue function and protection demonstrating the importance of AG as an alternative medicinal source through the calcium signaling pathway. Conclusion Grain amaranth exerts its antidiabetic properties through improved calcium homeostasis in blood, kidney, and liver.

The Role of Vasodilator Receptors of Renin-angiotensin System on Nitric Oxide Formation and Kidney Circulation after Angiotensin II Infusion in Renal Ischemia/Reperfusion Rats.

Background:Nitric oxide (NO) as a vasodilator factor has renoprotective effect against renal ischemia. The balance between angiotensin II (Ang II) and NO can affect kidney homeostasis. The aim of this study was to determine NO alteration in response to renin–Ang system vasodilator receptors antagonists (PD123319; Ang II type 2 receptor antagonist and A779; Mas receptor antagonist) in renal ischemia/reperfusion injury (IRI) in rats.Materials and Methods:Sixty-three Wistar male and female rats were used. Animals from each gender were divided into four groups received saline, Ang II, PD123319 + Ang II, and A779 + Ang II after renal IRI. Renal IRI induced with an adjustable hook. Blood pressure and renal blood flow (RBF) measured continuously. The nitrite levels were measured in serum, kidney, and urine samples.Results:In female rats, the serum and kidney nitrite levels increased significantly by Ang II (P < 0.05) and decreased significantly (P < 0.05) when PD123319 was accompanied with Ang II. Such observation was not seen in male. Ang II decreased RBF significantly in all groups (P < 0.05), while PD + Ang II group showed significant decrease in RBF in comparison with the other groups in female rats (P < 0.05).Conclusion:Males show more sensibility to Ang II infusion; in fact, it is suggested that there is gender dimorphism in the Ang II and NO production associated with vasodilator receptors.

Unraveling the Mechanistic Complexity of the Glomerulocystic Phenotype in Dicer Conditional KO Mice by 2D Gel Electrophoresis Coupled Mass Spectrometry.

Dicer, an RNase III type endonuclease, is a key enzyme involved in miRNA biogenesis. It has been shown that this enzyme is essential for several aspects of postnatal kidney functions and homeostasis. In this study, we have examined conditional knockout (cKO) mice for Dicer in Pax8 (Paired-box gene 8) expressing cells to investigate the kidney protein profile. This specific model develops a glomerulocystic phenotype coupled with urinary concentration impairment, proteinuria, and severe renal failure. Proteomic analysis was performed on kidney tissue extracts from cKO and control (Ctr) mice by 2D Gel Electrophoresis coupled with mass spectrometry. The analysis highlighted 120 protein spots differentially expressed in Dicer cKO tissue compared with control; some of these proteins were validated by Western blotting. Ingenuity Pathway Analysis led to the identification of some interesting networks; among them, the one having ERK as a central hub may explain, through the modulation of the expression of a number of identified protein targets, the metabolic and structural alterations occurring during kidney cyst development in Dicer cKO mouse model. Our results contribute to gain new insights into molecular mechanisms through which Dicer endonuclease controls kidney development and physiological functions.

Transcription factor activity rhythms and tissue-specific chromatin interactions explain circadian gene expression across organs.

Temporal control of physiology requires the interplay between gene networks involved in daily timekeeping and tissue function across different organs. How the circadian clock interweaves with tissue-specific transcriptional programs is poorly understood. Here, we dissected temporal and tissue-specific regulation at multiple gene regulatory layers by examining mouse tissues with an intact or disrupted clock over time. Integrated analysis uncovered two distinct regulatory modes underlying tissue-specific rhythms: tissue-specific oscillations in transcription factor (TF) activity, which were linked to feeding-fasting cycles in liver and sodium homeostasis in kidney; and colocalized binding of clock and tissue-specific transcription factors at distal enhancers. Chromosome conformation capture (4C-seq) in liver and kidney identified liver-specific chromatin loops that recruited clock-bound enhancers to promoters to regulate liver-specific transcriptional rhythms. Furthermore, this looping was remarkably promoter-specific on the scale of less than 10 kilobases (kb). Enhancers can contact a rhythmic promoter while looping out nearby nonrhythmic alternative promoters, confining rhythmic enhancer activity to specific promoters. These findings suggest that chromatin folding enables the clock to regulate rhythmic transcription of specific promoters to output temporal transcriptional programs tailored to different tissues.

Troy/TNFRSF19 marks epithelial progenitor cells during mouse kidney development that continue to contribute to turnover in adult kidney

During kidney development, progressively committed progenitor cells give rise to the distinct segments of the nephron, the functional unit of the kidney. Similar segment-committed progenitor cells are thought to be involved in the homeostasis of adult kidney. However, markers for most segment-committed progenitor cells remain to be identified. Here, we evaluate Troy/TNFRSF19 as a segment-committed nephron progenitor cell marker. Troy is expressed in the ureteric bud during embryonic development. During postnatal nephrogenesis, Troy+ cells are present in the cortex and papilla and display an immature tubular phenotype. Tracing of Troy+ cells during nephrogenesis demonstrates that Troy+ cells clonally give rise to tubular structures that persist for up to 2 y after induction. Troy+ cells have a 40-fold higher capacity than Troy- cells to form organoids, which is considered a stem cell property in vitro. In the adult kidney, Troy+ cells are present in the papilla and these cells continue to contribute to collecting duct formation during homeostasis. The number of Troy-derived cells increases after folic acid-induced injury. Our data show that Troy marks a renal stem/progenitor cell population in the developing kidney that in adult kidney contributes to homeostasis, predominantly of the collecting duct, and regeneration.

Chromatin Conformation Links Distal Target Genes to CKD Loci.

Genome-wide association studies (GWASs) have identified many genetic risk factors for CKD. However, linking common variants to genes that are causal for CKD etiology remains challenging. By adapting self-transcribing active regulatory region sequencing, we evaluated the effect of genetic variation on DNA regulatory elements (DREs). Variants in linkage with the CKD-associated single-nucleotide polymorphism rs11959928 were shown to affect DRE function, illustrating that genes regulated by DREs colocalizing with CKD-associated variation can be dysregulated and therefore, considered as CKD candidate genes. To identify target genes of these DREs, we used circular chromosome conformation capture (4C) sequencing on glomerular endothelial cells and renal tubular epithelial cells. Our 4C analyses revealed interactions of CKD-associated susceptibility regions with the transcriptional start sites of 304 target genes. Overlap with multiple databases confirmed that many of these target genes are involved in kidney homeostasis. Expression quantitative trait loci analysis revealed that mRNA levels of many target genes are genotype dependent. Pathway analyses showed that target genes were enriched in processes crucial for renal function, identifying dysregulated geranylgeranyl diphosphate biosynthesis as a potential disease mechanism. Overall, our data annotated multiple genes to previously reported CKD-associated single-nucleotide polymorphisms and provided evidence for interaction between these loci and target genes. This pipeline provides a novel technique for hypothesis generation and complements classic GWAS interpretation. Future studies are required to specify the implications of our dataset and further reveal the complex roles that common variants have in complex diseases, such as CKD.

MDM2 Contributes to High Glucose-Induced Glomerular Mesangial Cell Proliferation and Extracellular Matrix Accumulation via Notch1

Murine double minute 2 (MDM2) is an E3-ubiquitin ligase critical for various biological functions. Previous data have revealed an indispensable role of MDM2 in kidney homeostasis. However, its role in glomerular mesangial cell (GMC) proliferation and extracellular matrix (ECM) accumulation during hyperglycemia condition remains unclear. In our present study, we found that MDM2 protein level was significantly upregulated in high glucose-treated GMCs, while knocking down MDM2 by siRNA could attenuate high glucose-induced ECM accumulation and GMCs proliferation. Unexpectedly, Nutlin-3a, a MDM2-p53 interaction blocker, had no benefit in protecting diabetic mice from renal impairment in vivo and in alleviating high glucose-induced ECM accumulation in vitro. Intriguingly, we found that Notch1 signaling activation was obviously attenuated by MDM2 depletion in GMCs with high glucose exposure. However, Numb, a substrate of MDM2 which suppresses Notch1 signaling, was found not to be involved in the MDM2 and Notch1 association. Moreover, our findings demonstrated that MDM2 interacted with Notch1 intracellular domain (NICD1) independent of Numb and regulated the ubiquitination status of NICD1. Collectively, our data propose a pivotal role of MDM2 in high glucose-induced GMC proliferation and ECM accumulation, via modulating the activation of Notch1 signaling pathway in an ubiquitination-dependent way.

The Calcium/Phosphorus Homeostasis in Chronic Kidney Disease: From Clinical Epidemiology to Pathophysiology.

A simple data filtering process together with some basic concepts of control theory applied to electronically storedclinical data were used to identify some of the pathophysiological mechanisms underlying the perturbations of the calcium/phosphorushomeostasis in chronic kidney disease. Retrospective data (a set per patient of serum single value concentrations of creatinine, calcium, phosphorus,parathormone, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D) from 2507 patients with stable chronic kidney disease not on renalreplacement therapy were studied. The variables were paired and subjected sequentially to a moving average and partioned intofrequency classes. The plots were interpreted using the concept of a feedback loop comprising two branches of opposite sign and ofset point of the loop. The set point for each pair of variables is displaced in the course of the disease and this displacement indicateswhich of the two factors involved (the serum concentrations of calcium or parathormone, for example) is primarily affected. This analysis showed that in the course of the development of chronic kidney disease the relationships between the observedvariables progressed following a monotonous, a biphasic or a triphasic pattern. As chronic kidney disease progresses, calcium/phosphorus metabolism regulation evolves through different phases. Later,there is a progressive loss of the parathyroid gland sensitivity to the control by the serum concentrations of calcium and phosphorus.The sensitivity to the inhibitory action of 1,25-dihydroxyvitamin D decreases monotonously but never releases the gland. The clinical data analysis used permits to illustrate the underlying pathophysiological mechanisms.

Transcription of immune related genes in Solea senegalensis vaccinated against Photobacterium damselae subsp. piscicida. Identification of surrogates of protection

Solea senegalensis is a flatfish with a great potential for aquaculture, but infectious diseases restrict its production, being this fish species highly susceptible to Photobacterium damselae subsp. piscicida (Phdp) infections. A better understanding of the mechanisms related to fish immune response is crucial for the development of effective approaches in disease management. In the present work, transcriptional changes of immune related genes have been evaluated in farmed S. senegalensis specimens vaccinated against Phdp by intraperitoneal injection (IP) and immersion (IM). IP fish showed higher antibody levels and increased transcription of genes encoding lysozyme C1, complement factors involved in the classical pathway and components involved in the opsonization and the limitation of free iron availability, all of them facilitating the faster elimination of the pathogen and promoting higher RPS after the infection with Phdp. The results of this study seem to support a different intensity of the specimens immune response in the head kidney. Analysis of the immune response in 15 day post-challenged fish showed up-regulation of genes involved in all stages of S. senegalensis immune response, but especially those genes encoding proteins related to the innate response such as complement, lysozyme and iron homeostasis in the head kidney. On the other hand, liver transcription was higher for genes related to inflammation, apoptosis and cell mediated cytotoxicity (CMC). Furthermore, comparison of the differential response of S. senegalensis genes in vaccinated and unvaccinated fish to Phdp infection allowed the identification of a potential biosignature, consisting in 10 genes, as a surrogate of protection and therefore, as indicator of vaccine success against fotobacteriosis after IP vaccination. These results provide important insights into the S. senegalensis protection against Phdp induced by vaccination.

The para isomer of dinitrobenzene disrupts redox homeostasis in liver and kidney of male wistar rats

BackgroundPara-Dinitrobenzene (p-DNB) is one of the isomers of dinitrobenzene which have been detected as environmental toxicants. Skin irritation and organ toxicities are likely for industrial workers exposed to p-DNB. This study evaluated the effect of sub-chronic exposure of rats to p-DNB on cellular redox balance, hepatic and renal integrity. MethodsForty eight male Wistar rats weighing 160–180g were administered 50, 75, 1000 and 2000mg/kg b.wt (body weight) of p-DNB or an equivalent volume of vehicle (control) orally and topically for 14 days. After the period of treatment, the activities of kidney and liver catalase (CAT), alkaline phosphatase (ALP) and superoxide dismutase (SOD) as well as extent of renal and hepatic lipid peroxidation (LPO) were determined. Serum ALP activity and plasma urea concentration were also evaluated. ResultsCompared with control animals, p-DNB -administered rats showed decrease in the body and relative kidney and liver weights as well as increased renal and hepatic hydrogen peroxide and lipid peroxidation levels accompanied by decreased superoxide dismutase and catalase activities. However, p-DNB caused a significant increase in plasma urea concentration and serum, liver and kidney ALP activities relative to control. In addition, p-DNB caused periportal infiltration, severe macro vesicular steatosis and hepatic necrosis in the liver. ConclusionsOur findings show that sub-chronic oral and sub-dermal administration of p-DNB may produce hepato-nephrotoxicity through oxidative stress.

Phosphodiesterase-5 inhibition preserves renal hemodynamics and function in mice with diabetic kidney disease by modulating miR-22 and BMP7

Diabetic Nephropathy (DN) is the leading cause of end-stage renal disease. Preclinical and experimental studies show that PDE5 inhibitors (PDE5is) exert protective effects in DN improving perivascular inflammation. Using a mouse model of diabetic kidney injury we investigated the protective proprieties of PDE5is on renal hemodynamics and the molecular mechanisms involved. PDE5i treatment prevented the development of DN-related hypertension (P < 0.001), the increase of urine albumin creatinine ratio (P < 0.01), the fall in glomerular filtration rate (P < 0.001), and improved renal resistive index (P < 0.001) and kidney microcirculation. Moreover PDE5i attenuated the rise of nephropathy biomarkers, soluble urokinase-type plasminogen activator receptor, suPAR and neutrophil gelatinase-associated lipocalin, NGAL. In treated animals, blood vessel perfusion was improved and vascular leakage reduced, suggesting preserved renal endothelium integrity, as confirmed by higher capillary density, number of CD31+ cells and pericyte coverage. Analysis of the mechanisms involved revealed the induction of bone morphogenetic protein-7 (BMP7) expression, a critical regulator of angiogenesis and kidney homeostasis, through a PDE5i-dependent downregulation of miR-22. In conclusion PDE5i slows the progression of DN in mice, improving hemodynamic parameters and vessel integrity. Regulation of miR-22/BMP7, an unknown mechanism of PDE5is in nephrovascular protection, might represent a novel therapeutic option for treatment of diabetic complications.

Connective Tissue Growth Factor Domain 4 Amplifies Fibrotic Kidney Disease through Activation of LDL Receptor-Related Protein 6.

Connective tissue growth factor (CTGF), a matrix-associated protein with four distinct cytokine binding domains, has roles in vasculogenesis, wound healing responses, and fibrogenesis and is upregulated in fibroblasts and myofibroblasts in disease. Here, we investigated the role of CTGF in fibrogenic cells. In mice, tissue-specific inducible overexpression of CTGF by kidney pericytes and fibroblasts had no bearing on nephrogenesis or kidney homeostasis but exacerbated inflammation and fibrosis after ureteral obstruction. These effects required the WNT receptor LDL receptor-related protein 6 (LRP6). Additionally, pericytes isolated from these mice became hypermigratory and hyperproliferative on overexpression of CTGF. CTGF is cleaved in vivo into distinct domains. Treatment with recombinant domain 1, 1+2 (N terminus), or 4 (C terminus) independently activated myofibroblast differentiation and wound healing responses in cultured pericytes, but domain 4 showed the broadest profibrotic activity. Domain 4 exhibited low-affinity binding to LRP6 in in vitro binding assays, and inhibition of LRP6 or critical signaling cascades downstream of LRP6, including JNK and WNT/β-catenin, inhibited the biologic activity of domain 4. Administration of blocking antibodies specifically against CTGF domain 4 or recombinant Dickkopf-related protein-1, an endogenous inhibitor of LRP6, effectively inhibited inflammation and fibrosis associated with ureteral obstruction in vivo Therefore, domain 4 of CTGF and the WNT signaling pathway are important new targets in fibrosis.

Aristolochic Acid-Induced Autophagy Promotes Epithelial-to-Myofibroblast Transition in Human Renal Proximal Tubule Epithelial Cells.

Autophagy plays an essential role in cellular homeostasis in kidney. Previous studies have found that aristolochic acid (AA) can induce autophagy of renal tubular epithelial cells and epithelial-to-myofibroblast transition (EMT). However, the relationship between AA-induced autophagy and EMT is unclear. Our results showed that, after AA stimulation, the appearance of autophagy preceded EMT. Autophagy of HKC cells began to increase gradually from the 3rd hour, reached the peak at 12th hour, and then weakened gradually until 36th hour; the EMT process of HKC continued to increase from 6th hour to 36th hour after AA stimulation. The enhancement of autophagy using autophagy inducers, rapamycin or serum-free medium, led to an aggravation of EMT and upregulated expression of fibronectin, a component of extracellular matrix, in AA-treated HKC cells. In contrast, the inhibition of autophagy by autophagy inhibitor, 3-methyladenine, or by knockdown of Beclin 1 led to an attenuation of EMT and downregulated expression of fibronectin in AA-treated HKC cells. Taken together, our study suggests that, after AA stimulation, two types of cell responses of HKC cells, autophagy and EMT, will successively appear, and autophagy can promote EMT of HKC.

The relationship between chronic kidney function and homeostasis model assessment of insulin resistance and beta cell function in Korean adults with or without type 2 diabetes mellitus.

The present study was conducted to assess the relationship between chronic kidney disease (CKD) and the homeostasis model assessment of insulin resistance (HOMA-IR) and beta cell function (HOMA-B) in Korean adults with or without type 2 diabetes mellitus (T2DM). This study included 5,188 adults aged 20 or older using the 2015 Korea National Health and Nutrition Examination Survey (KNHANES) data, which represents national data in Korea. A covariance test adjusted for covariates was performed for HOMA-IR and HOMA-B in relation to CKD. The present study has several key findings. First, in T2DM, HOMA-IR (p = 0.035) was higher in the CKD group than in the non-CKD group after adjusting for the related variables but HOMA-B (p = 0.141) was not significant. Second, in non-T2DM, HOMA-IR (p = 0.163) and HOMA-B (p = 0.658) were not associated with CKD after adjusting for the related variables (except age). However, when further adjusted for age, HOMA-IR (p = 0.020) and HOMA-B (p = 0.006) were higher in the CKD group than in the non-CKD group. In conclusion, insulin resistance was positively associated CKD with in Korean adults with or without T2DM. Beta cell function was positively associated CKD with in Korean adults without T2DM but not in Korean adults with T2DM.

Rhein reverses Klotho repression via promoter demethylation and protects against kidney and bone injuries in mice with chronic kidney disease

Rhein is an anthraquinone compound isolated from the medicinal plant rhubarb and mainly used in the clinical treatment of diabetic nephropathy. Rhein exhibits various renoprotective functions, but the underlying mechanisms are not fully determined. However, its renoprotective properties recapitulate the role of Klotho, a renal-specific antiaging protein critical for maintaining kidney homeostasis. Here we explored the connections between rhein renoprotection and Klotho in a mouse model of adenine-induced chronic kidney disease. In addition to being an impressive Klotho upregulator, rhein remarkably reversed renal Klotho deficiency in adenine-treated mice. This effect was associated with significant improvement in disturbed serum biochemistry, profibrogenic protein expression, and kidney and bone damage. Further investigation of the molecular basis of Klotho loss revealed that these kidneys displayed marked inductions of DNA methyltransferase DNMT1/DNMT3a and Klotho promoter hypermethylation, whereas rhein treatment effectively corrected these alterations. The renal protective effects of rhein were largely abolished when Klotho was knocked-down by RNA interferences, suggesting that rhein reversal of Klotho deficiency is essential for its renoprotective actions. Thus, our study clarifies how rhein regulation of Klotho expression contributes to its renoprotection and brings new insights into Klotho-targeted strategy for the treatment of kidney diseases of various etiologies.

The Renal Sodium Bicarbonate Cotransporter NBCe2: Is It a Major Contributor to Sodium and pH Homeostasis?

The sodium bicarbonate cotransporter (NBCe2, aka NBC4) was originally isolated from the human testis and heart (Pushkin et al. IUBMB Life 50:13-19, 2000). Subsequently, NBCe2 was found in diverse locations where it plays a role in regulating sodium and bicarbonate transport, influencing intracellular, extracellular, interstitial, and ultimately plasma pH (Boron et al. J Exp Biol. 212:1697-1706, 2009; Parker and Boron, Physiol Rev. 93:803-959, 2013; Romero et al. Mol Asp Med. 34:159-182, 2013). NBCe2 is located in human and rodent renal-collecting duct and proximal tubule. While much is known about the two electrogenic sodium bicarbonate cotransporters, NBCe1 and NBCe2, in the regulation of sodium homeostasis and pH balance in the rodent kidney, little is known about their roles in human renal physiology. NBCe2 is located in the proximal tubule Golgi apparatus under basal conditions and then disperses throughout the cell, but particularly into the apical membrane microvilli, during various maneuvers that increase intracellular sodium. This review will summarize our current understanding of the distribution and function of NBCe2 in the human kidney and how genetic variants of its gene, SLC4A5, contribute to salt sensitivity of blood pressure.