Kidney Proximal Tubule Cells Research Articles

The renal antioxidative effect of losartan involves heat shock protein 70 in proximal tubule cells.

Angiotensin II exerts a cardinal role in the pathogenesis of hypertension and renal injury via action of angiotensin II type 1 (AT1) receptors. Local renin-angiotensin system (RAS) activity is essential for the mechanisms mediating pathophysiological functions. Proximal tubular angiotensinogen and tubular AT1 receptors are augmented by intrarenal angiotensin II. Caveolin 1 plays an important role as a regulatory molecule for the compartmentalization of redox signaling events through angiotensin II-induced NADPH oxidase activation in the kidney. A role for the renin-angiotensin system in the development and/or maintenance of hypertension has been demonstrated in spontaneously hypertensive rats (SHRs). Many effects of angiotensin II are dependent on the AT1 stimulation of reactive oxygen species (ROS) production by NADPH oxidase. Angiotensin II upregulation stimulates oxidative stress in proximal tubules from SHR. The NADPH oxidase 4 (Nox4) is abundantly expressed in kidney proximal tubule cells. Induction of the stress response includes synthesis of heat shock protein 70, a molecular chaperone that has a critical role in the recovery of cells from stress and in cytoprotection, guarding cells from subsequent insults. HSP70 chaperones function in part by driving the molecular triage decision, which determines whether proteins enter the productive folding pathway or result in client substrate ubiquitination and proteasomal degradation. This review examines regulation of losartan-mediated antioxidative stress responses by the chaperone HSP70 in proximal tubule cells of spontaneously hypertensive rats.

Acute Kidney Injury in SARS-CoV-2 Infection: Direct Effect of Virus on Kidney Proximal Tubule Cells.

Coronaviruses (CoVs), including Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and the novel coronavirus disease-2 (SARS-CoV-2) are a group of enveloped RNA viruses that cause a severe respiratory infection which is associated with a high mortality [...].

Protein Kinase C-δ Mediates Kidney Tubular Injury in Cold Storage-Associated Kidney Transplantation.

Kidney injury associated with cold storage is a determinant of delayed graft function and the long-term outcome of transplanted kidneys, but the underlying mechanism remains elusive. We previously reported a role of protein kinase C-δ (PKCδ) in renal tubular injury during cisplatin nephrotoxicity and albumin-associated kidney injury, but whether PKCδ is involved in ischemic or transplantation-associated kidney injury is unknown. To investigate PKCδ's potential role in injury during cold storage-associated transplantation, we incubated rat kidney proximal tubule cells in University of Wisconsin (UW) solution at 4°C for cold storage, returning them to normal culture medium at 37°C for rewarming. We also stored kidneys from donor mice in cold UW solution for various durations, followed by transplantation into syngeneic recipient mice. We observed PKCδ activation in both in vitro and in vivo models of cold-storage rewarming or transplantation. In the mouse model, PKCδ was activated and accumulated in mitochondria, where it mediated phosphorylation of a mitochondrial fission protein, dynamin-related protein 1 (Drp1), at serine 616. Drp1 activation resulted in mitochondrial fission or fragmentation, accompanied by mitochondrial damage and tubular cell death. Deficiency of PKCδ in donor kidney ameliorated Drp1 phosphorylation, mitochondrial damage, tubular cell death, and kidney injury during cold storage-associated transplantation. PKCδ deficiency also improved the repair and function of the renal graft as a life-supporting kidney. An inhibitor of PKCδ, δV1-1, protected kidneys against cold storage-associated transplantation injury. These results indicate that PKCδ is a key mediator of mitochondrial damage and renal tubular injury in cold storage-associated transplantation and may be an effective therapeutic target for improving renal transplant outcomes.

Immunotoxin SS1P is rapidly removed by proximal tubule cells of kidney, whose damage contributes to albumin loss in urine

Recombinant immunotoxins (RITs) are chimeric proteins composed of an Fv and a protein toxin being developed for cancer treatment. The Fv brings the toxin to the cancer cell, but most of the RITs do not reach the tumor and are removed by other organs. To identify cells responsible for RIT removal, and the pathway by which RITs reach these cells, we studied SS1P, a 63-kDa RIT that targets mesothelin-expressing tumors and has a short serum half-life. The major organs that remove RIT were identified by live mouse imaging of RIT labeled with FNIR-Z-759. Cells responsible for SS1P removal were identified by immunohistochemistry and intravital two-photon microscopy of kidneys of rats. The primary organ of SS1P removal is kidney followed by liver. In the kidney, SS1P passes through the glomerulus, is taken up by proximal tubular cells, and transferred to lysosomes. In the liver, macrophages are involved in removal. The short half-life of SS1P is due to its very rapid filtration by the kidney followed by degradation in proximal tubular cells of the kidney. In mice treated with SS1P, proximal tubular cells are damaged and albumin in the urine is increased. SS1P uptake by kidney is reduced by coadministration of l-lysine. Our data suggests that l-lysine administration to humans might prevent SS1P-mediated kidney damage, reduce albumin loss in urine, and alleviate capillary leak syndrome.

Differential kidney proximal tubule cell responses to protein overload by albumin and its ligands.

Albuminuria is frequently associated with proximal tubule (PT) cytotoxicity that can feed back to cause glomerular damage and exacerbate kidney disease. PT cells express megalin and cubilin receptors that bind to and internalize albumin over a broad concentration range. How the exposure to high concentrations of albumin leads to PT cytotoxicity remains unclear. Fatty acids and other ligands bound to albumin are known to trigger production of reactive oxygen species (ROS) that impair PT function. Alternatively or in addition, uptake of high concentrations of albumin may overload the endocytic pathway and elicit downstream responses. Here, we used a well-differentiated PT cell culture model with high endocytic capacity to dissect the effects of albumin versus its ligands on endocytic uptake and degradation of albumin, production of ROS, and cell viability. Cellular responses differed dramatically, depending on the preparation of albumin tested. Knockdown of megalin or cubilin failed to prevent ROS production mediated by albumin ligands, suggesting that receptor-mediated internalization of albumin was not necessary to trigger cellular responses to albumin ligands. Moreover, albumin induced cytotoxic responses when added to the basolateral surface of PT cells. Whereas overnight incubation with high concentrations of fatty acid-free albumin had no overt effects on cell function or viability, lysosomal degradation kinetics were slowed upon longer exposure, consistent with overload of the PT endocytic/degradative pathway. Together, the results of our study demonstrate that the PT responds independently to albumin and to its ligands and suggest that the consequences of albumin overload in vivo may be dependent on metabolic state.

Localization of Cell Receptor-Related Genes of SARS-CoV-2 in the Kidney through Single-Cell Transcriptome Analysis

Background: The new coronavirus (SARS-CoV-2), which has been responsible for the recent coronavirus disease 2019 (COVID-19) pandemic, uses the cell receptor angiotensin converting enzyme-2 (ACE2) for entry and the serine protease TMPRSS2 for spike (S) protein priming. Meanwhile, the presence of B⁰AT1 (SLC6A19) may prevent TMPRSS2 from accessing the cutting position on ACE2. Identifying the expression of these cell receptor-related genes of SARS-CoV-2 is critical for understanding the pathogenesis of SARS-CoV-2 in various tissues, especially in the kidney. Methods: The single-cell transcription datasets of the human cell landscape (HCL) and other relevant single-cell transcription databases were used to analyze the expression of ACE2, TMPRSS2, and SLC6A19 in various organs and tissues, but mainly in the kidney. Results: ACE2 was significantly expressed in the S1, S2, and S3 segments of proximal tubule (PT) cells. TMPRSS2 was widely expressed in several renal tubule populations extending from the PT cells to the collection system cell type, of which intercalated cells and the distal convoluted tubule cells showed more significant expression than PT cells. Unexpectedly, although expressed on various renal tubule populations, SLC6A19 was mainly enriched in PT cells, in line with ACE2 expression. Although alveolar-type (AT) 2 cells of the lung and intestinal epithelial cells expressed ACE2 as well as PT cells, AT 2 cells significantly expressed TMPRSS2 but not SLC6A19, while all 3 genes were significantly expressed in intestinal epithelial cells. Conclusions: ACE2 was widely expressed in specific cell subgroups of various human tissues, especially in intestinal epithelial cells, kidney PT cells, and also AT 2 cells of the lung. These 3 types of cells demonstrated significant differences in the distribution of the cell receptor-related genes of SARS-CoV-2, which may indicate the diversity of cell surface structures and differences in the affinity between SARS-CoV-2 and cells.

Systemic Analysis of Tissue Cells Potentially Vulnerable to Sars-Cov-2 Infection by the Protein-Proofed Single-Cell Rna Profiling of Ace2, Tmprss2 and Furin Proteases

Single-cell RNA profiling of ACE2, the SARS-CoV-2 receptor, had proposed multiple tissue cells as the potential targets of SARS-CoV-2, the novel coronavirus causing the COVID-19 pandemic. However, most were not echoed by the patients’ clinical manifestations, largely due to the lack of protein expression information of ACE2 and co-factors. Here, we incorporated the protein information to analyse the expression of ACE2, together with TMPRSS2 and Furin, two proteases assisting SARS-CoV-2 infection, at single cell level in situ, which we called protein-proofed single-cell RNA (pscRNA) profiling. Systemic analysis across 36 tissues revealed a rank list of candidate cells potentially vulnerable to SARS-CoV-2. The top targets are lung AT2 cells and macrophages, then cardiomyocytes and adrenal gland stromal cells, followed by stromal cells in testis, ovary and thyroid. Whereas, the polarized kidney proximal tubule cells, liver cholangiocytes and intestinal enterocytes are less likely to be the primary SARS-CoV-2 targets as ACE2 localizes at the apical region of cells, where the viruses may not readily reach. These findings are in concert with the clinical characteristics of prominent lung symptoms, frequent heart injury, and uncommon intestinal symptoms and acute kidney injury. Together, we provide a comprehensive view on the potential SARS-CoV-2 targets by pscRNA profiling, and propose that, in addition to acute respiratory distress syndrome, attentions should also be paid to the potential injuries in cardiovascular, endocrine and reproductive systems during the treatment of COVID-19 patients.

The ethyl acetate fraction of Moringa oleifera leaves effects on endothelial stress in rat sepsis model

Background: Sepsis is a life-threatening organ dysfunction caused by the dysregulation of the host response to infection, facilitated by inflammation and endothelial stress. Moringa oleifera leaves fractioned with ethyl acetate (MO-EA fraction) is proposed to have the ability to suppress inflammation and oxidative stress through the control of NF-kB. This study aims to investigate the effect of the MO-EA fraction in a rat sepsis model.Material and Methods: The study is a laboratory experimental study. The research was conducted on a total of 30 rats, equally divided into five groups. One group did not receive lipopolysaccharide (LPS) induction as negative control group, but the others received LPS induction and received variable doses of MO-EA fraction (0, 10, 20, and 40 mg/kg of bodyweight). The measured outcome were serum concentration of of heparanase, CRP, malondialdehyde (MDA), and immunohistologic expression of e-selectin, NF-kB in cells, and histopathological necrosis in the aorta and kidney.Results: MO-EA fraction significantly decrease the serum levels of HPA, MDA on day 3 and 7, and lower the CRP serum level on day 7 (p<0.05). Other variables of interest did not show significant differences.Conclusion: The administration of MO-EA fraction of any dose significantly lower the serum level of HPA and MDA in mice sepsis models on day 3 and 7, and lower CRP on day 3 but not on day 7. However, examnationa of NF-kB and e-selectin expressions, and necrosis in kidney proximal tubule and aortic endothelial cells did not show the benefit of MO-EA fraction in preventing cell damage.

Empagliflozin reduces high glucose-induced oxidative stress and miR-21-dependent TRAF3IP2 induction and RECK suppression, and inhibits human renal proximal tubular epithelial cell migration and epithelial-to-mesenchymal transition

Proximal tubular epithelial cells (PTEC) in the S1 segment of the kidney abundantly express sodium-glucose co-transporters (SGLT) that play a critical role in whole body glucose homeostasis. We recently reported suppression of RECK (Reversion Inducing Cysteine Rich Protein with Kazal Motifs), a membrane anchored endogenous MMP inhibitor and anti-fibrotic mediator, in the kidneys of db/db mice, a model of diabetic kidney disease (DKD), as well as in high glucose (HG) treated human kidney proximal tubule cells (HK−2). We further demonstrated that empagliflozin (EMPA), an SGLT2 inhibitor, reversed these effects. Little is known regarding the mechanisms underlying RECK suppression under hyperglycemic conditions, and its rescue by EMPA. Consistent with our previous studies, HG (25 mM) suppressed RECK expression in HK-2 cells. Further mechanistic investigations revealed that HG induced superoxide and hydrogen peroxide generation, oxidative stress-dependent TRAF3IP2 upregulation, NF-κB and p38 MAPK activation, inflammatory cytokine expression (IL-1β, IL-6, TNF-α, and MCP-1), miR-21 induction, MMP2 activation, and RECK suppression. Moreover, RECK gain-of-function inhibited HG-induced MMP2 activation and HK-2 cell migration. Similar to HG, advanced glycation end products (AGE) induced TRAF3IP2 and suppressed RECK, effects that were inhibited by EMPA. Importantly, EMPA treatment ameliorated all of these deleterious effects, and inhibited epithelial-to-mesenchymal transition (EMT) and HK-2 cell migration. Collectively, these findings indicate that hyperglycemia and associated AGE suppress RECK expression via oxidative stress/TRAF3IP2/NF-κB and p38 MAPK/miR-21 induction. Furthermore, these results suggest that interventions aimed at restoring RECK or inhibiting SGLT2 have the potential to treat kidney inflammatory response/fibrosis and nephropathy under chronic hyperglycemic conditions, such as DKD.

Regenerating re-absorption function of proximal convoluted tubule using microfluidics for kidney-on-chip applications

Human kidney is a sophisticated organ with 1 Million nephrons arranged in subtle form. Kidney has the most failure cases in the world compared to the rest of the body organs. Kidney failure is a severe problem, where cardiac blood output is not filtered. Dialysis is one available substitute for kidney failure, which seems to help the patient incompletely. There is a great necessity for a device (artificial kidney) that can be implanted into the body to resume the kidney function. In replicating kidney function there are many potential challenges, which must be addressed for faithful regeneration. This paper primarily focuses on regenerating the proximal convoluted tubule (PCT) size dependent re-absorption, mimicking this function using microfluidics is not reported earlier. Different structural changes in the design have been adopted and the accomplishments are discussed. It is observed that the total flow (the total of flow through all 1000 channels) in straight is 0.4 × 10−16 m3/s, in the diagonal channel is 0.4 × 10−16 m3/s, in step is 0.32 × 10−16 m3/s and in serpentine is 0.38 × 10−16 m3/s. The size-dependent re-absorption of solutes, proteins, and urea with the help of array of channels has been achieved. The dimensions of the main tubule and channel are selected to replicate cell–cell interactions. The re-absorption rate obtained is around 48%, which is closely reaching the PCT re-absorption rate. The increase in the number of channels shows increase in re-absorption rate. The novelty of reported work lies in regenerating the human kidney proximal tubule cell function of size and shape dependent re-absorption using microfluidics technology. The proposed device performance proves its prevalence in kidney-on-chip applications.

In vitro toxicological assessment of free 3-MCPD and select 3-MCPD esters on human proximal tubule HK-2 cells.

Chloropropanols are chemical contaminants that can be formed during industrial processing of foods, such as lipids used in commercially available infant and toddler formula in the USA. Many researchers have studied the most common chloropropanol contaminant, 3-monochloropropane-1,2-diol (3-MCPD), as well as its lipid ester derivatives. A plethora of toxicological outcomes have been described in vivo, including effects on the heart, nervous system, reproductive organs, and kidneys. To better understand the concordance of some of these effects to in vitro outcomes, we focused our research on using an in vitro cellular model to investigate whether the proximal tubule cells of the kidney would be vulnerable to the effects of free 3-MCPD and nine of its common esters in commercial formula. Using the established human kidney proximal tubule cell line, HK-2, we performed 24-h treatments using 3-MCPD and nine mono- or di-esters derived from palmitate, oleate, and linoleate. By directly exposing HK-2 cells at treatment doses ranging from 0 to 100 μM, we could evaluate their effects on cell viability, mitochondrial health, reactive oxygen species (ROS) production, and other endpoints of toxicity. Since chloropropanols reportedly inhibit cellular metabolism through interference with glycolysis, we also tested the extent of this mechanism. Overall, we found mild but statistically significant evidence of cytotoxicity at the highest tested treatment concentrations, which were also associated with mitochondrial dysfunction and transient perturbations in cellular metabolism. Based on these findings, further studies will be required to better understand the effects of these compounds under conditions that are more physiologically relevant to human infant and toddler proximal tubules in order to mimic their exposure to chloropropanol-containing foods.

6-Shogaol protects against ischemic acute kidney injury by modulating NF-κB and heme oxygenase-1 pathways.

Acute kidney injury (AKI) due to renal ischemia-reperfusion (I/R) is a major clinical problem without effective therapy. Ginger is one of the most widely consumed spices in the world, and 6-shogaol, a major ginger metabolite, has anti-inflammatory effects in neuronal and epithelial cells. Here, we demonstrate our novel findings that 6-shogaol treatment protected against renal I/R injury with decreased plasma creatinine, blood urea nitrogen, and kidney neutrophil gelatinase-associated lipocalin mRNA synthesis compared with vehicle-treated mice subjected to renal I/R. Additionally, 6-shogaol treatment reduced kidney inflammation (decreased proinflammatory cytokine and chemokine synthesis as well as neutrophil infiltration) and apoptosis (decreased TUNEL-positive renal tubular cells) compared with vehicle-treated mice subjected to renal I/R. In cultured human and mouse kidney proximal tubule cells, 6-shogaol significantly attenuated TNF-α-induced inflammatory cytokine and chemokine mRNA synthesis. Mechanistically, 6-shogaol significantly attenuated TNF-α-induced NF-κB activation in human renal proximal tubule cells by reducing IKKαβ/IκBα phosphorylation. Furthermore, 6-shogaol induced a cytoprotective chaperone heme oxygenase (HO)-1 via p38 MAPK activation in vitro and in vivo. Consistent with these findings, pretreatment with the HO-1 inhibitor zinc protoporphyrin IX completely prevented 6-shogaol-mediated protection against ischemic AKI in mice. Taken together, our study showed that 6-shogaol protects against ischemic AKI by attenuating NF-κB activation and inducing HO-1 expression. 6-Shogaol may provide a potential therapy for ischemic AKI during the perioperative period.

Toxicoproteomic Analysis of Poly(ADP-Ribose)-Associated Proteins Induced by Oxidative Stress in Human Proximal Tubule Cells.

2,3,5-Tris-(glutathion-S-yl)hydroquinone (TGHQ) is a nephrotoxic and nephrocarcinogenic metabolite of hydroquinone. TGHQ generates reactive oxygen species (ROS), causing DNA-strand breaks, hyperactivation of PARP-1, increases in intracellular calcium ([Ca2+]i), and cell death. PARP-1 catalyzes the attachment of ADP-ribose polymers (PAR) to target proteins. In human kidney proximal tubule cells, ROS-mediated PARP-1 hyperactivation and elevations in [Ca2+]i are reciprocally coupled. The molecular mechanism of this interaction is unclear. The aim of the present study was to identify ROS-induced PAR-associated proteins to further understand their potential role in cell death. PAR-associated proteins were enriched by immunoprecipitation, identified by LC-MS/MS, and relative abundance was obtained by spectral counting. A total of 356 proteins were PAR-modified following TGHQ treatment. A total of 13 proteins exhibited gene ontology annotations related to calcium. Among these proteins, the general transcription factor II-I (TFII-I) is directly involved in the modulation of [Ca2+]i. TFII-I binding to phospholipase C (PLC) leads to calcium influx via the TRPC3 channel. However, inhibition of TRPC3 or PLC had no effect on TGHQ-mediated cell death, suggesting that their loss of function may be necessary but insufficient to cause cell death. Nevertheless, TGHQ promoted a time-dependent translocation of TFII-I from the nucleus to the cytosol concomitant with a decrease in tyrosine phosphorylation in α/β-TFII-I. Therefore it is likely that ROS have an important impact on the function of TFII-I, such as regulation of transcription, and DNA translesion synthesis. Our data also shed light on PAR-mediated signaling during oxidative stress, and contributes to the development of strategies to prevent PAR-dependent cell death.

Bariatric Surgery Modulates Urinary Levels of MicroRNAs Involved in the Regulation of Renal Function

Background: Obesity and diabetes cause chronic kidney disease with a common pathophysiology that is characterized by the accumulation of collagen in the extracellular matrix. Recent evidence has implicated the epithelial-to-mesenchymal transition (EMT) as a key step in this pathology with regulation by microRNAs. Weight loss leads to improvements in renal function; therefore, this study hypothesized that bariatric-surgery aided weight loss would lead to changes in urinary microRNAs involved in the regulation of renal function.Materials and methods: Twenty-four bariatric patients undergoing Roux-en-Y gastric bypass and sleeve gastrectomy donated urine pre-operatively and at 2–6 months and 1–2 years post-operatively. Urine samples were also obtained from 10 healthy weight and 7 morbidly obese non-surgical controls. Expression levels of kidney microRNAs were assessed in urine and the function of microRNAs was assessed through the in vitro transfection of HK-2 cells, a kidney proximal tubule cell line.Results: Levels of miR 192, miR 200a, and miR 200b were upregulated in urine following bariatric surgery. This increase was consistent across surgical type and diabetes status and was maintained and enhanced with time. Bariatric surgery alters urinary miR 192 expression from levels seen in morbidly obese patients to levels seen in healthy weight control patients. In mechanistic studies, the transfection of miR 192 in HK-2 cells increased miR 200a expression and decreased ZEB2, a key transcriptional promoter of kidney fibrosis.Conclusions: Bariatric surgery increased miR 192 and miR 200 urinary levels, key anti-fibrotic microRNAs that could contribute to a renal-protective mechanism and may be of value as urinary biomarkers following surgery. These findings suggest that urinary microRNAs may represent potential novel biomarkers for obesity-associated renal function.

Shear stress and oxygen availability drive differential changes in opossum kidney proximal tubule cell metabolism and endocytosis.

Kidney proximal tubule (PT) cells have high-metabolic demands to drive the extraordinary ion and solute transport, water reabsorption, and endocytic uptake that occur in this nephron segment. Increases in renal blood flow alter glomerular filtration rate and lead to rapid mechanosensitive adaptations in PT transport, impacting metabolic demand. Although the PT reabsorbs essentially all of the filtered glucose, PT cells rely primarily on oxidative metabolism rather than glycolysis to meet their energy demands. We lack an understanding of how PT functions are impacted by changes in O2 availability via cortical capillaries and mechanosensitive signaling in response to alterations in luminal flow. Previously, we found that opossum kidney (OK) cells recapitulate key features of PT cells in vivo, including enhanced endocytic uptake and ion transport, when exposed to mechanical stimulation by culture on an orbital shaker. We hypothesized that increased oxygenation resulting from orbital shaking also contributes to this more physiologic phenotype. RNA seq of OK cells maintained under static conditions or exposed to orbital shaking for up to 96 hours showed significant time- and culture-dependent changes in gene expression. Transcriptional and metabolomics data were consistent with a decrease in glycolytic flux and with an increased utilization of aerobic metabolic pathways in cells exposed to orbital shaking. Moreover, we found spatial differences in the pattern of mitogenesis vs development of ion transport and endocytic capacities in our culture system that highlight the complexity of O2 -dependent and mechanosensitive crosstalk to regulate PT cell function.

In Vitro Evaluation of Cimetidine Reno‐protective Effects on Cisplatin‐Induced Kidney Injury

ObjectivesCisplatin (CIS), a platinum‐based drug, is one of the most efficacious anti‐cancer agents prescribed for a variety of solid tumors. However, CIS‐induced kidney injury (CIKI) remains a clinical challenge. The Organic Cation Transporter 2 (OCT2) is an uptake transporter predominantly expressed in the kidney proximal tubule cells. OCT2 is responsible for the cellular uptake of CIS by kidney cells. Our study aims to evaluate and quantify the in vitro renotoxicity effect of CIS and the reno‐protective effect of cimetidine (CIM), an OCT2 inhibitor, against CIKI.MethodsHuman renal proximal tubular epithelial cells, SA7K, were exposed for 72 hours to a range of concentrations of CIS (1–100 μM), CIM (0.1–2 mM), or to at least 12 different combinations of the two drugs. The inhibition of cellular viability was measured at 0, 12, 24, 48, and 72 hours using a CCK‐8 cellular viability kit. CIKI was captured with CIS stimulation of apoptosis in SA7K cells. CIM action on SA7K cells was fixed to the control (no treatment) baseline value. The combination of CIM with CIS was characterized with a competitive antagonism model using the Gaddum equation. Mathematical modeling was performed using Monolix (2016R1). All estimated parameters were determined as mean±SE.ResultsA dose‐dependent pattern in CIS toxicity on SA7K cells and CIM protection from CIKI is observed. The first‐order rate constant for SA7K cells death was estimated at 0.0047±0.00024 h−1. The maximal effect of CIS on CIKI (Smax) was determined at 0.07±0.0064 h−1, while CIS concentration inducing 50% of Smax was estimated at 70.3±10.5 μM. The concentration of CIM leading to 50% of Smax was determined at 486.3±69.8 μM. All time course profiles of cell viability responses to the single agents and combinations of CIS with CIM were described with our developed models.ConclusionsThe combination of CIM with CIS was successfully evaluated in vitro. The competitive antagonism model adequately captured the reno‐protective effects of CIM against CIKI. Further studies are in progress to investigate the molecular mechanisms underlying the beneficial effects of CIM on CIKI.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Metabolism of Glycolate to Oxalate in Kidney Proximal Tubule Cells

BackgroundExcessive synthesis of oxalate is a hallmark of the inherited kidney stones disease primary hyperoxaluria. Evidence indicates that the liver is the main site of oxalate synthesis but that other tissues may also contribute up to 20%. Glycolate is one of the precursors of oxalate and both plasma and urine glycolate are elevated alongside oxalate in primary hyperoxaluria type 1, the most frequent and severe of PH types. New therapeutic strategies in PH1 further increase glycolate levels by inhibiting a liver‐specific enzyme, hydroxyacid oxidase 1 (HAO1), which catalyzes the oxidation of glycolate to glyoxylate, a precursor of oxalate. To examine whether kidneys contribute to oxalate synthesis, the metabolism of glycolate was studied in human and mouse kidney cell lines and tissue.MethodsTissue culture cells derived from human proximal tubule (HK2 cells) and mouse collecting duct (mIMCD cells) lineages were incubated with 13C2‐labeled glycolate (0 – 10mM) for up to 24 hours. Kidney tissue incubations with 13C2‐glycolate were performed on mouse kidneys and human surgical kidney remnants, by isolating and digesting cortical and medullary tissue fragments. The amount of 13C2‐labeled oxalate synthesized by the cells (and released in the media) was measured by ion chromatography coupled with mass spectrometry and normalized to total cell protein.ResultsMetabolism of glycolate to oxalate was observed in proximal tubule cells (HK2) in as little a time as 3 hours and with concentrations as low as 500 uM in contrast to cells isolated from the medulla and collecting duct (mIMCD). The synthesis of oxalate was also observed in human and mouse kidney cortical tissue but not medullary tissue. The involvement of the intermediate metabolite glyoxylate was suggested by the higher oxalate synthesis observed in the glyoxylate reductase knock‐out mouse model of PH type 2.ConclusionRenal cells, in particular proximal tubule cells, are equipped to metabolize glycolate to glyoxylate and oxalate. The time and dose dependence of glycolate to oxalate metabolism is compatible with an enzymatic pathway. The role of the candidate enzyme hydroxyacid oxidase 2, an isoenzyme of HAO1 and which is expressed in the proximal tubule, is currently being investigated.Support or Funding InformationNIH NIDDK K01DK114332This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Orbital shaking drives differential changes in OK proximal tubule cell metabolism and endocytosis

Kidney proximal tubule (PT) cells have high metabolic demands to drive the extraordinary ion and solute transport, water reabsorption, and endocytic uptake that occur in this nephron segment. Increases in renal blood flow alter glomerular filtration rate (GFR) and lead to rapid mechanosensitive adaptations in PT transport, impacting metabolic demand. Although the PT reabsorbs essentially all of the filtered glucose, PT cells rely primarily on oxidative metabolism rather than glycolysis to meet their energy demands. We lack an understanding of how PT metabolism is impacted by changes in O2 availability via cortical capillaries and mechanosensitive signaling in response to alterations in luminal flow. Previously, we found that opossum kidney (OK) cells recapitulate key features of PT cells in vivo, including enhanced endocytic uptake and ion transport, when exposed to mechanical stimulation by culture on an orbital shaker. We hypothesized that increased oxygenation resulting from orbital shaking also contributes to this more physiologic phenotype. RNA Seq of OK cells maintained under static conditions or exposed to orbital shaking for up to 96h revealed significant time‐ and culture‐dependent changes in gene expression. Transcriptional and metabolomics data were consistent with a decrease in glycolytic flux and with an increased utilization of aerobic metabolic pathways in cells exposed to orbital shaking. Moreover, we found spatial differences in the pattern of mitogenesis and endocytic capacity in our culture system that highlight the complexity of O2‐dependent and mechanosensitive crosstalk to regulate PT cell function.Support or Funding InformationTsinghua MD Scholars ProgramNIH R01 DK101484NIH P30 DK079307This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Reduced expression of pyruvate kinase in kidney proximal tubule cells is a potential mechanism of pravastatin altered glucose metabolism

Recent studies have reported that statins are associated with increased incidence of diabetes. Although several mechanisms have been proposed, the role of the kidney’s glucose metabolism upon statin treatment is still unclear. Thus, we investigated the role of pravastatin in gluconeogenesis and glycolysis. HK-2 and HepG2 cells were treated with pravastatin and cultured under either high- or normal-cholesterol conditions. In HK-2 cells treated with pravastatin under both high- and normal-cholesterol conditions, the protein expression of only pyruvate kinase isozymes L/R (PKLR) decreased in a dose-dependent manner, while the protein expression of other glucose metabolism related enzymes remained unchanged. Within the in vivo experiment, male C57BL/6 mice were fed either pravastatin-treated normal-fat diets for 2 or 4 weeks or pravastatin-treated high-fat diets for 16 weeks. Protein expression of PKLR in the kidneys from mice that consumed pravastatin-treated high-fat diets decreased significantly compared to the controls. Upon the treatments of pravastatin, only the PKLR expression decreased in lean mice. Furthermore, PKLR activity decreased significantly in the kidney after pravastatin treatments. However, there was no change in enzyme activity in the liver, suggesting that pravastatin decreased PKLR activity only in the kidney. This change may be associated with the hyperglycemic effect of statins.

The effect of loss of SETD2 on mitochondrial dysfunction in clear cell renal cell carcinoma.

567 Background: SET domain-containing protein 2 ( SETD2) is among the most commonly mutated genes in clear cell renal cell carcinoma (ccRCC). Classically, SETD2 modulates chromatin structure via the methylation of lysine 36 on histone H3. However, histone-independent functions of SETD2 are emerging. We sought to discover novel SETD2-dependent changes to the cellular lysine methylation landscape during kidney cancer tumorigenesis. Methods: In this study, we used HKC human proximal tubule kidney cell lines, the likely nephrogenic region of origin for ccRCC. The proteomes of wild type (WT) and SETD2-knock out (KO) cells were labeled using stable isotope labeling by amino acids in cell culture (SILAC). Proteins were trypsinized and lysine-methylated peptides were immunoprecipitated. Relative abundance of lysine-methylated peptides and total peptides were calculated in the WT and SETD2-KO using nano-liquid chromatography/tandem mass spectrometry (LC/MS-MS). Results: > 30,000 peptides were quantified, including > 50 lysine methylated peptides. We observed decreased lysine methylation of eukaryotic elongation factor 1A1 (eEF1A1), including K165 trimethylation (K165me3) and K318 monomethylation (K318me1). eEF1A1 is classically known for delivery of aminoacyl-tRNA to the ribosome, and its function is modulated via the lysine methyltranferases eEF1AKMT1-4. eEF1AKMT3 is responsible for trimethylation of K165, and expression of this enzyme was decreased in SETD2-KO cells. In addition, we observed significant decrease in expression in proteins of the electron transport chain (ETC) complex 1 in SETD2-KO cells yet normal gene expression, suggesting a translational defect. Functionally, SETD2-KO cells are characterized by decreased cellular oxygen consumption rate and increased mitochondrial mass, suggestive of ETC dysfunction. Conclusions: We observe decreased expression of eEF1AKMT3 in SETD2-KO cells, resulting in decreased K165me3 of eEFA1A, decreased translation of ETC proteins, and mitochondrial dysfunction. As mitochondrial dysfunction is commonly observed in RCC, we expect this represents a novel mechanism of SETD2-mediated tumorigenesis.