Biochemical, functional, and morphological characterization of a primary culture of rabbit proximal tubule cells

Generation and characterization of iPSC-derived renal proximal tubule-like cells with extended stability

The renal proximal tubule is responsible for re-absorption of the majority of the glomerular filtrate and its proper function is necessary for whole-body homeostasis. Aging, certain diseases and chemical-induced toxicity are factors that contribute to proximal tubule injury and chronic kidney disease progression. To better understand these processes, it would be advantageous to generate renal tissues from human induced pluripotent stem cells (iPSC). Here, we report the differentiation and characterization of iPSC lines into proximal tubular-like cells (PTL). The protocol is a step wise exposure of small molecules and growth factors, including the GSK3 inhibitor (CHIR99021), the retinoic acid receptor activator (TTNPB), FGF9 and EGF, to drive iPSC to PTL via cell stages representing characteristics of early stages of renal development. Genome-wide RNA sequencing showed that PTL clustered within a kidney phenotype. PTL expressed proximal tubular-specific markers, including megalin (LRP2), showed a polarized phenotype, and were responsive to parathyroid hormone. PTL could take up albumin and exhibited ABCB1 transport activity. The phenotype was stable for up to 7 days and was maintained after passaging. This protocol will form the basis of an optimized strategy for molecular investigations using iPSC derived PTL.

The Use of the Epithelial Kidney OK Cell Line for Studying the Nephrotoxicity of Anticancer Platinum Coordination Complexes

Nephrotoxicity is one of the most important dose-limiting side-effects of cis-diaminedichloroplatinum (II) (cDDP) in humans. Quiescent OK cells grown in hormonally-defined, serum-free medium in the total absence of antibiotics were used to study the in vitro nephrotoxicity of three platinum complexes which produce different renal toxicity in vivo: cDDP, its stereoisomer trans-diaminedichloroplatinum (II) (tDDP), and cis-diamine-1,1-cyclobutane-dicarboxylateplatinUm (II) (CBDCA). The uptake and cytotoxicity of these compounds at concentrations of 3-l,600μM and their impact on DNA and protein synthesis, glucose uptake, Na+-K+-ATPase and succinate dehydrogenase activities, as well as intracellular total glutathione level, were measured. The results showed that the cytotoxicity ranking of these three compounds, assessed by the LDH release method, was not in agreement with their in vivo nephrotoxic potentials (tDDP > cDDP > CBDCA00 in OK cells versus cDDP > CBDCA > tDDP in vivo). cDDP and tDDP showed similar uptakes at all the concentrations studied, which demonstrated that their cytotoxic potential was not directly related to intracellular levels of platinum. At non-cytotoxic concentrations, both cDDP and CBDCA decreased DNA and protein synthesis and, to a lesser extent, Na+-K+-ATPase activity, whereas no effect on glucose uptake and succinate dehydrogenase activity (a mitochondrial marker enzyme) was observed. Nevertheless, 5–10 times greater concentrations of CBDCA were required to induce effects similar to those induced by cDDP. Our results did not show a rapid and early depletion of intracellular glutathione after exposure to cDDP or CBDCA. tDDP exhibited the characteristics of a non-specific cytotoxic chemical which was unable to markedly inhibit the biochemical and functional parameters studied at non-cytotoxic concentrations. These results underline the key role of the inhibition of synthetic activities in the pathogenesis of cDDP-induced and CBDCA-induced nephrotoxicity in OK cells.

The cat as a naturally occurring model of renal interstitial fibrosis: Characterisation of primary feline proximal tubular epithelial cells and comparative pro-fibrotic effects of TGF-β1

Chronic kidney disease (CKD) is common in both geriatric cats and aging humans, and is pathologically characterised by chronic tubulointerstitial inflammation and fibrosis in both species. Cats with CKD may represent a spontaneously occurring, non-rodent animal model of human disease, however little is known of feline renal cell biology. In other species, TGF-β1 signalling in the proximal tubular epithelium is thought to play a key role in the initiation and progression of renal fibrosis. In this study, we first aimed to isolate and characterise feline proximal tubular epithelial cells (FPTEC), comparing them to human primary renal epithelial cells (HREC) and the human proximal tubular cell line HK-2. Secondly, we aimed to examine and compare the effect of human recombinant TGF-β1 on cell proliferation, pro-apoptotic signalling and genes associated with epithelial-to-mesenchymal transition (EMT) in feline and human renal epithelial cells. FPTEC were successfully isolated from cadaverous feline renal tissue, and demonstrated a marker protein expression profile identical to that of HREC and HK-2. Exposure to TGF-β1 (0-10 ng/ml) induced a concentration-dependent loss of epithelial morphology and alterations in gene expression consistent with the occurrence of partial EMT in all cell types. This was associated with transcription of downstream pro-fibrotic mediators, growth arrest in FPTEC and HREC (but not HK-2), and increased apoptotic signalling at high concentrations of TGF- β1. These effects were inhibited by the ALK5 (TGF-β1RI) antagonist SB431542 (5 μM), suggesting they are mediated via the ALK5/TGF-β1RII receptor complex. Taken together, these results suggest that TGF-β1 may be involved in epithelial cell dedifferentiation, growth arrest and apoptosis in feline CKD as in human disease, and that cats may be a useful, naturally occurring model of human CKD.

pH-responsive, gluconeogenic renal epithelial LLC-PK1-FBPase+cells: a versatile in vitro model to study renal proximal tubule metabolism and function

Ammoniagenesis and gluconeogenesis are prominent metabolic features of the renal proximal convoluted tubule that contribute to maintenance of systemic acid-base homeostasis. Molecular analysis of the mechanisms that mediate the coordinate regulation of the two pathways required development of a cell line that recapitulates these features in vitro. By adapting porcine renal epithelial LLC-PK1 cells to essentially glucose-free medium, a gluconeogenic subline, termed LLC-PK1-FBPase(+) cells, was isolated. LLC-PK1-FBPase(+) cells grow in the absence of hexoses and pentoses and exhibit enhanced oxidative metabolism and increased levels of phosphate-dependent glutaminase. The cells also express significant levels of the key gluconeogenic enzymes, fructose-1,6-bisphosphatase (FBPase) and phosphoenolpyruvate carboxykinase (PEPCK). Thus the altered phenotype of LLC-PK1-FBPase(+) cells is pleiotropic. Most importantly, when transferred to medium that mimics a pronounced metabolic acidosis (9 mM HCO3 (-), pH 6.9), the LLC-PK1-FBPase(+) cells exhibit a gradual increase in NH4 (+) ion production, accompanied by increases in glutaminase and cytosolic PEPCK mRNA levels and proteins. Therefore, the LLC-PK1-FBPase(+) cells retained in culture many of the metabolic pathways and pH-responsive adaptations characteristic of renal proximal tubules. The molecular mechanisms that mediate enhanced expression of the glutaminase and PEPCK in LLC-PK1-FBPase(+) cells have been extensively reviewed. The present review describes novel properties of this unique cell line and summarizes the molecular mechanisms that have been defined more recently using LLC-PK1-FBPase(+) cells to model the renal proximal tubule. It also identifies future studies that could be performed using these cells.

hTERT alone immortalizes epithelial cells of renal proximal tubules without changing their functional characteristics

Telomere-dependent replicative senescence is one of the mechanisms that limit the number of population doublings of normal human cells. By overexpression of telomerase, cells of various origins have been successfully immortalized without changing the phenotype. While a limited number of telomerase-immortalized cells of epithelial origin are available, none of renal origin has been reported so far. Here we have established simple and safe conditions that allow serial passaging of renal proximal tubule epithelial cells (RPTECs) until entry into telomere-dependent replicative senescence. As reported for other cells, senescence of RPTECs is characterized by arrest in G1 phase, shortened telomeres, staining for senescence-associated beta-galactosidase, and accumulation of gamma-H2AX foci. Furthermore, ectopic expression of the catalytic subunit of telomerase (TERT) was sufficient to immortalize these cells. Characterization of immortalized RPTEC/TERT1 cells shows characteristic morphological and functional properties like formation of tight junctions and domes, expression of aminopeptidase N, cAMP induction by parathyroid hormone, sodium-dependent phosphate uptake, and the megalin/cubilin transport system. No genomic instability within up to 90 population doublings has been observed. Therefore, these cells are proposed as a valuable model system not only for cell biology but also for toxicology, drug screening, biogerontology, as well as tissue engineering approaches.

Regulatory mechanisms of Na(+)/glucose cotransporters in renal proximal tubule cells

Glucose is a key fuel and an important metabolic substrate in mammals. Renal proximal tubular cells (PTCs) not only reabsorb filtered glucose but are also believed to play a role in the glucotoxicity associated with renal pathogenesis, such as in diabetes. The proximal tubule environment is where 90% of the filtered glucose is reabsorbed by the low-affinity/high-capacity Na(+)/glucose cotransporter 2 (SGLT2) and facilitated diffusion glucose transporter 2 (GLUT2). Both active and facilitative glucose transporters have distinct distribution profiles along the proximal tubule related to their particular kinetic characteristics. A number of mechanisms contribute to the changes in the cellular functions, which occur in response to exposure to various endogenous factors. Hyperglycemia was reported to regulate the renal SGLT activities through the reactive oxygen species-nuclear factor-kappaB pathways, which suggests that the transcellular glucose uptake within the PTCs contribute to the development of diabetic-like nephropathy. Angiotensin II (ANG II) plays an important role in its development through epidermal growth factor receptor (EGFR) transactivation. Therefore, a combination of high glucose, ANG II, and EGF are involved in diabetic-like nephropathy by regulating the SGLT activity. In addition, endogenously enhanced SGLTs have a cytoprotective function. The renal proximal tubules play a major role in regulating the plasma glucose levels, and there is increasing interest in the renal glucose transporters on account of their potential implications in the treatment of various conditions including diabetes mellitus.

Renal nucleoside transporters: physiological and clinical implicationsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease

Renal handling of physiological and pharmacological nucleosides is a major determinant of their plasma levels and tissue availabilities. Additionally, the pharmacokinetics and normal tissue toxicities of nucleoside drugs are influenced by their handling in the kidney. Renal reabsorption or secretion of nucleosides is selective and dependent on integral membrane proteins, termed nucleoside transporters (NTs) present in renal epithelia. The 7 known human NTs (hNTs) exhibit varying permeant selectivities and are divided into 2 protein families: the solute carrier (SLC) 29 (SLC29A1, SLC29A2, SLC29A3, SLC29A4) and SLC28 (SLC28A1, SLC28A2, SLC28A3) proteins, otherwise known, respectively, as the human equilibrative NTs (hENTs, hENT1, hENT2, hENT3, hENT4) and human concentrative NTs (hCNTs, hCNT1, hCNT2, hCNT3). The well characterized hENTs (hENT1 and hENT2) are bidirectional facilitative diffusion transporters in plasma membranes; hENT3 and hENT4 are much less well known, although hENT3, found in lysosomal membranes, transports nucleosides and is pH dependent, whereas hENT4–PMAT is a H+-adenosine cotransporter as well as a monoamine–organic cation transporter. The 3 hCNTs are unidirectional secondary active Na+-nucleoside cotransporters. In renal epithelial cells, hCNT1, hCNT2, and hCNT3 at apical membranes, and hENT1 and hENT2 at basolateral membranes, apparently work in concert to mediate reabsorption of nucleosides from lumen to blood, driven by Na+ gradients. Secretion of some physiological nucleosides, therapeutic nucleoside analog drugs, and nucleotide metabolites of therapeutic nucleoside and nucleobase drugs likely occurs through various xenobiotic transporters in renal epithelia, including organic cation transporters, organic anion transporters, multidrug resistance related proteins, and multidrug resistance proteins. Mounting evidence suggests that hENT1 may have a presence at both apical and basolateral membranes of renal epithelia, and thus may participate in both selective secretory and reabsorptive fluxes of nucleosides. In this review, the renal handling of nucleosides is examined with respect to physiological and clinical implications for the regulation of human kidney NTs and adenosine signaling, intracellular nucleoside transport, and nephrotoxicities associated with some nucleoside drugs.

Changes in gene expression in human renal proximal tubule cells exposed to low concentrations of S-(1,2-dichlorovinyl)-l-cysteine, a metabolite of trichloroethylene

Epidemiology studies suggest that there may be a weak association between high level exposure to trichloroethylene (TCE) and renal tubule cell carcinoma. Laboratory animal studies have shown an increased incidence of renal tubule carcinoma in male rats but not mice. TCE can undergo metabolism via glutathione (GSH) conjugation to form metabolites that are known to be nephrotoxic. The GSH conjugate, S-(1,2-dichlorovinyl)glutathione (DCVG), is processed further to the cysteine conjugate, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), which is the penultimate nephrotoxic species. We have cultured human renal tubule cells (HRPTC) in serum-free medium under a variety of different culture conditions and observed growth, respiratory control and glucose transport over a 20 day period in medium containing low glucose. Cell death was time- and concentration-dependent, with the EC(50) for DCVG being about 3 microM and for DCVC about 7.5 microM over 10 days. Exposure of HRPTC to sub-cytotoxic doses of DCVC (0.1 microM and 1 microM for 10 days) led to a small number of changes in gene expression, as determined by transcript profiling with Affymetrix human genome chips. Using the criterion of a mean 2-fold change over control for the four samples examined, 3 genes at 0.1 microM DCVC increased, namely, adenosine kinase, zinc finger protein X-linked and an enzyme with lyase activity. At 1 microM DCVC, two genes showed a >2-fold decrease, N-acetyltransferase 8 and complement factor H. At a lower stringency (1.5-fold change), a total of 63 probe sets were altered at 0.1 microM DCVC and 45 at 1 microM DCVC. Genes associated with stress, apoptosis, cell proliferation and repair and DCVC metabolism were altered, as were a small number of genes that did not appear to be associated with the known mode of action of DCVC. Some of these genes may serve as molecular markers of TCE exposure and effects in the human kidney.

ATP stimulates Na+-glucose cotransporter activity via cAMP and p38 MAPK in renal proximal tubule cells

Extracellular ATP plays an important role in the regulation of renal function. However, the effect of ATP on the Na(+)-glucose cotransporters (SGLTs) has not been elucidated in proximal tubule cells (PTCs). Therefore, this study was performed to examine the action of ATP on SGLTs and their related signal pathways in primary cultured rabbit renal PTCs. ATP increased [(14)C]-alpha-methyl-d-glucopyranoside (alpha-MG) uptake in a time-dependent (>1 h) and dose-dependent (>10(-6) M) manner. ATP stimulated alpha-MG uptake by increasing in V(max) without affecting K(m). ATP-induced increase of alpha-MG uptake was correlated with the increase in both SGLT1 and SGLT2 protein expression levels. ATP-induced stimulation of alpha-MG uptake was blocked by suramin (nonspecific P2 receptor antagonist), RB-2 (P2Y receptor antagonist), and MRS-2179 (P2Y(1) receptor antagonist), suggesting a role for the P2Y receptor. ATP-induced stimulation of alpha-MG uptake was blocked by pertussis toxin (PTX, a G(i) protein inhibitor), SQ-22536 (an adenylate cyclase inhibitor), and PKA inhibitor amide 14-22 (PKI). ATP also increased cAMP formation, which was blocked by PTX and RB-2. However, pretreatment of adenosine deaminase did not block ATP-induced cAMP formation. In addition, ATP-induced stimulation of alpha-MG uptake was blocked by SB-203580 (p38 MAPK inhibitor), but not by PD-98059 (p44/42 MAPK inhibitor) or SP-600125 (JNK inhibitor). Indeed, ATP induced phosphorylation of p38 MAPK. In conclusion, ATP increases alpha-MG uptake via cAMP and p38 MAPK in renal PTCs.

Signaling cascade of ANG II-induced inhibition of alpha-MG uptake in renal proximal tubule cells

ANG II and Na+-glucose cotransporter have been reported to be associated with the onset of diverse renal diseases. However, the effect of ANG II on Na+-glucose cotransporter activity was not elucidated. The effects of ANG II on alpha-methyl-D-[14C]glucopyranoside (alpha-MG) uptake and its related signal pathways were examined in the primary cultured rabbit renal proximal tubule cells (PTCs). ANG II (>2 h; >10(-9) M) inhibited alpha-MG uptake in a time- and concentration-dependent manner and decreased the protein level of Na+-glucose cotransporters, the expression of which was abrogated by both actinomycin D and cycloheximide exposure. ANG II-induced inhibition of alpha-MG uptake was blocked by losartan, an ANG II type 1 (AT1) receptor blocker, but not by PD-123319, an ANG II type 2 receptor blocker. ANG II-induced inhibition of alpha-MG uptake was blocked by genistein, herbimycin A [tyrosine kinase (TK) inhibitors], mepacrine, and AACOCF3 (phospholipase A2 inhibitors), suggesting the role of TK phosphorylation and arachidonic acid (AA). Indeed, ANG II increased AA release, which was blocked by losartan or TK inhibitors. The effects of ANG II on AA release and alpha-MG uptake also were abolished by staurosporine and bisindolylmaleimide I (protein kinase C inhibitors) or PD-98059 (p44/42 MAPK inhibitor), but not SB-203580 (p38 MAPK inhibitor), respectively. Indeed, ANG II increased p44/42 MAPK activity. ANG II-induced activation of p44/42 MAPK was blocked by staurosporine. In conclusion, ANG II inhibited alpha-MG uptake via PKC-MAPK-cPLA2 signal cascade through the AT1 receptor in the PTCs.

Estrogen modulates ClC-2 chloride channel gene expression in rat kidney

ClC-2 is a CLC family member of chloride channels sensitive to changes in cell volume, pH and voltage. The ClC-2 is widely distributed along the nephron although in the kidney its role still not well understood. Aldosterone studies suggest that ClC-2 expression in the kidney may be hormonally regulated. To explore the possibility that estrogen control ClC-2 expression, we investigated whether its expression changed in the kidney of female Wistar rats subjected to ovariectomy with or without near-physiological or high doses of 17beta-estradiol benzoate treatment for 10 days. Total RNA isolated from rat kidney and dissected nephron segments was analyzed by ribonuclease protection assay and/or a semi-quantitative RT-PCR. The renal ClC-2 protein expression was analyzed by Western blot. The decreased renal expression of ClC-2 mRNA and protein observed in ovariectomized rats was restored to control levels after treatment with low doses of estradiol. Higher dose estradiol lead to an even greater increase in ClC-2 mRNA and protein expression. This change in overall expression was shown to be caused by the modulation of ClC-2 mRNA expression in the proximal tubule. These results suggest that ClC-2 may be involved in estrogen-induced Cl(-) transport in rat kidney.

Glucose-6-phosphatase mRNA levels in kidney isolated tubule suspensions are increased by dexamethasone and decreased by insulin

The strong induction of renal glucose-6-phosphatase (G6Pase) during starvation has been suggested to be responsible for the increased role of the kidney in glucose production during long-term fasting. To investigate whether this induction may be caused by a direct hormonal effect on the renal proximal tubular cell, we incubated rat renal tubule suspensions in the presence of glucocorticoids or insulin for 6 hours; normoxia was required, since hypoxic conditions were associated with markedly decreased G6Pase mRNA levels despite maintenance of adenosine triphosphate (ATP) levels. The G6Pase mRNA level was increased twofold to threefold by 10(-8) to 10(-5) mol/L dexamethasone (DXM), whereas the most effective concentration of insulin, 10(-9) mol/L, induced only a 40% decrease. These results suggest that the increased role of the kidney in glucose production during long-term starvation could be linked to a direct effect of glucocorticoids on renal G6Pase.

Characterization of a primary cell culture model of the avian renal proximal tubule

Methods have been developed for producing functional, transporting monolayers of avian proximal tubule (PT) cells. A highly homogenous fraction of PT fragments was prepared by enzymatic digestion (collagenase + Dispase) of chick (3- to 5-day-old) kidneys, followed by Percoll gradient centrifugation. The PT fraction was enriched in glucose-6-phosphatase, a proximal enzyme marker, and reduced in specific activity of hexokinase, a distal marker. PT fragments were grown to confluence in serum-free media on collagen-coated permeable filter supports. Electron microscopy of confluent monolayers revealed numerous microvilli and mitochondria, central cilia, and tight junctions, all characteristic of PT cells. gamma-Glutamyltranspeptidase, a proximal brush-border enzyme, showed threefold higher activity on apical than on basolateral sides of the monolayer. The electrophysiological characteristics of monolayers were investigated by voltage-clamp techniques. Monolayers displayed low transepithelial resistances (40-60 Omega . cm2), lumen-negative potentials, and baseline currents of 6-12 microA/cm2 (with or without 5 mM glucose). Both alpha-methyl-D-glucose (2 mM), a nonmetabolizable hexose, and phenylalanine (2 mM) significantly stimulated short-circuit current when added to the mucosal side of glucose-free monolayers. Phloridzin, a specific inhibitor of Na+-coupled glucose transport, significantly inhibited short-circuit current, as did 10(-5) M amiloride. Monolayers also expressed net secretory transport of urate. This cell culture preparation may provide a useful working model for the study of avian PT transport.

Morphological and biochemical characterization of primary culture of rabbit proximal kidney tubule cells grown on collagen-IV coated Millicell-CM

The aim of this study was to better characterize rabbit proximal kidney tubule cells cultured on collagen IV-coated porous inserts, as compared to the same cells seeded in standard plastic wells. Total protein contents in confluent monolayers on permeable membranes were about twofold higher than those measured in confluent cultures in plastic wells. Microscopy examinations suggested that such a difference was probably due to a higher cell density and to an impressive development of the apical brush-border membrane. Moreover, measurement of unidirectional transport of p-aminohippuric acid and tetraethylammonium bromide confirmed the high polarization level of cultures on porous inserts. Results of methyl(alpha-D-[U-14C]glyco)pyranoside uptake suggested that cell phenotype was probably influenced by culture conditions. Analysis of different markers as a function of time in culture showed decreases of alkaline phosphatase (AP), gamma-glutamyltranspeptidase (GGT), and Na(+)-K(+)-ATPase activities as well as increases in LDH, ATP, and glutathione levels, similar to those formerly reported for cells cultured in standard plastic plates. However, comparative data from 6-d-old monolayers have shown that AP, GGT, Na(+)-K(+)-ATPase, glutathione reductase (GRED), and selenium-dependent glutathione peroxidase (Se-GPX) activities were 2.8-, 2.6-, 1.6-, 1.2-, and 2.1-fold, respectively, better preserved on precoated permeable membranes. On the other hand, this paper reports for the first time in the literature that GRED and SE-GPX, two phase II detoxification enzymes, were well maintained in cultures of rabbit proximal kidney tubule cells. Our results show that culturing rabbit proximal kidney tubule cells on collagen IV-coated porous membranes was accompanied by an improvement of both morphological and biochemical properties of the cells.

Cell lines with extended in vitro growth potential from human renal proximal tubule: characterization, response to inducers, and comparison with established cell lines

Few model systems exist for the study of injury to human renal proximal tubule epithelium. Optimized differentiated human renal epithelial cell lines with extended in vitro growth potential would provide an alternative model system to primary culture or other available non-human mammalian kidney cell lines. For this purpose, human renal tubule epithelial cells were isolated from normal kidney cortex and exposed in culture to a hybrid immortalizing virus, adenovirus 12-SV40. Cell lines were developed by limiting dilution, and three selected cell lines were screened for growth pattern, production of immortalizing virus, tumorigenicity, and ploidy. Cell lines were also monitored for response to inducer agents and matrix factors and were screened for expression of biochemical properties and differentiation markers of renal epithelium. All three are nonproducers of the immortalizing virus and are nontumorigenic. They grow in monolayer, have intermediate growth kinetics, and express markers of renal proximal tubular epithelium by immunohistochemistry. They also express biochemical properties comparable to other widely used proximal tubular cell lines including LLC-RK1, OK, and HK-2 and comparable to human tubular cells in stable culture. Growth medium containing low levels of fetal calf serum, or epidermal growth factor combined with parathyroid hormone, produced optimal growth characteristics, brush border enzyme expression, biochemical properties, and glucose transport in a selected cell line. The addition of dimethyl sulfoxide allows maintenance in morphologically intact monolayers for prolonged periods. These cell lines should be useful model systems for the study of human renal proximal tubular injury or disease.

Normal rat kidney proximal tubule cells in primary and multiple subcultures

An in vitro model to establish primary and subcultures of rat kidney proximal tubule (RPT) cells is described. After excising the kidneys and separating the cortex, the cortical tissue is digested with the enzymes DNAse-collagenase (Type I) resulting in a high yield of viable RPT Cells. The isolated RPT cells are then seeded onto rat tail collagen-coated surfaces and grown to confluency in a serum-free, hormonally defined medium. The cell yield can be increased by transferring the conditioned medium on Day 1 to more rat tail collagen-coated surfaces. RPT cell attachment and morphology was better on rat tail collagen-coated surfaces than on bovine collagen Type I coated surfaces. The culture medium was a 1:1 mixture of Ham's F-12 and Dulbecco's modified Eagle's medium supplemented with bovine serum albumin, insulin, transferrin, selenium, hydrocortisone, triiodothyronine, epidermal growth factor, and glutamine. The RPT cells became confluent in 7-10 d, at which point they could be subcultured by trypsinizing and growth in the same medium. In some studies, 10 ng/ml cholera toxin was added to the culture medium. We could passage the RPT cells up to 14 times in the presence of cholera toxin. The cells were investigated for activity of several markers. The cells were histochemically positive for alkaline phosphatase and gamma-glutamyl transpeptidase activity and synthesized the intermediate filament pankeratin. The RPT cells displayed apically directed sodium-dependent active glucose transport in culture. Hence, the RPT cells retain structural and functional characteristics of transporting renal epithelia in culture. This rat cell culture model will be a valuable tool for substrate uptake and nephrotoxicity studies.

Impact of cephaloridine on glutathione and related enzymes: comparison of in vivo and in vitro rat models

The aim of this study was to investigate the early effects of cephaloridine (CPH) on glutathione-dependent phase II detoxification in the rat proximal tubular cell and to find an in vitro alternative to the in vivo model. The in vivo study was conducted in three groups of rats which received CPH at doses of 250, 500 or 750 mg/kg per day for 3 days, while another group received 500 mg/kg as a single dose. For the in vitro study, rat renal proximal tubular cultured cells were exposed to CPH at concentrations of 0.3, 0.6, 1, 1.7 mM for 24, 48 and 72 h. Glutathione-dependent detoxification was evaluated in vivo and in vitro on the basis of total intracellular glutathione (GSH), glutathione S-transferase (GST) and glutathione peroxidase (GPX). Glutathione reductase (GRED) and GST mRNA levels were also determined. Results of in vivo and in vitro models were comparable in terms of the early increase of GSH, GST and GRED. This increase had a bell-shaped dose-response with a maximum at 500 mg/kg in vivo and 1 mM in vitro. Beyond these doses, GSH and its dependent enzyme levels decreased, associated with cytotoxicity in vitro and renal insufficiency in vivo. The increased GST activity was associated with an increased level of GST7 in vivo and a markedly increased level of GST1-2 in vitro. We concluded that the in vitro model can be used as an alternative to animal experimentation to study glutathione-dependent detoxication. Low cytotoxic doses of CPH induced an early increase of glutathione phase II-dependent detoxification enzymes.

Susceptibility of primary cultures of proximal tubular and distal tubular cells from rat kidney to chemically induced toxicity

Isolated proximal tubular (PT) and distal tubular (DT) cells from rat kidney were cultured for up to 9 days under serum-free, hormonally-defined conditions on 35-mm polystyrene culture dishes. Several hormonal and growth factor supplements were assessed for their ability to promote growth (increased protein and DNA content) and stability of differentiated phenotype (high activities of gamma-glutamyltransferase and alkaline phosphatase as brush-border membrane markers in PT cells; maintenance of high activities of glutamate dehydrogenase as a mitochondrial marker in both PT and DT cells; maintenance of low and high activities of lactate dehydrogenase in PT and DT cells, respectively; expression of cytokeratins). Basal supplemented media (DMEM/F12, 1:1 v/v) contained insulin, hydrocortisone, epidermal growth factor, sodium selenite and transferrin as supplements. Additionally, triiodothyronine selectively promoted growth and stability of differentiated phenotype in PT cells and thyrocalcitonin selectively promoted growth and stability of differentiated phenotype in DT cells. On Day 3 of primary culture, PT and DT cells were incubated for up to 8 h with either tert-butyl hydroperoxide (tBH; 0.5-10 mM), methyl vinyl ketone (MVK; 1-10 mM), or p-aminophenol (PAP; 1-10 mM) and cellular injury, as assessed by cellular release of lactate dehydrogenase, was determined. DT cells were significantly more susceptible to injury from both tBH and MVK, but the two cell populations were equally susceptible to injury from PAP, which is the same susceptibility pattern seen in freshly isolated cells. These results suggest that primary cultures of rat renal PT and DT cells reflect similar biochemical properties as freshly isolated cells and are, therefore, useful models for study of chemically induced injury.

Cultured proximal cells derived from transgenic mouse provide a model to study drug toxicity

The effects of gentamicin on N-acetyl-beta-D-glucosaminidase (NAG) and acid phosphatase (AcP), two lysosomal enzymes present in proximal renal tubule cells, were studied in the PKSV-PCT cell line derived from proximal convoluted tubules from the kidney of a transgenic mouse carrying SV40 large T antigen under the control of the L-type pyruvate kinase gene. Gentamicin (400 micrograms/ml for 72 hr) did not alter cell viability, but significantly reduced cell growth and favored the formation of myeloid bodies. Gentamicin (50 to 800 micrograms/ml for 72 hr) decreased in a dose-dependent manner the cellular NAG in PKSV-PCT cells and stimulated its secretion by 20 to 60%. Chloroquine (50 to 100 microns) and ammonium chloride (NH4Cl, 30mM), two lysosomotropic amines known to stimulate the secretion of lysosomal enzymes in fibroblasts and macrophages, also stimulated secreted NAG in PKSV-PCT cells. However, the effect of chloroquine was less marked in PKSV-PCT cells than in cultured mouse 3T3 fibroblasts. Gentamicin induced lysosomal alkalinization but, in contrast to chloroquine and NH4Cl, the aminoside strongly stimulated the secretion of AcP. The secretion induced by gentamicin was nonpolarized, since the percentage of secreted NAG significantly increased from both the apical and basal sides of PKSV-PCT cells grown on permeable filters. Thus, these data suggest that gentamicin alters the secretion of NAG and AcP by a non-specific pathway and indicate that the PKSV-PCT cell line is a suitable system to examine the cellular action of drugs in kidney proximal tubule cells.

Expression and subcellular distribution of phosphoenolpyruvate carboxykinase in primary cultures of rabbit kidney proximal tubule cells: comparative study with renal and hepatic PEPCK in vivo

The behaviour of the phosphoenolpyruvate carboxykinase (PEPCK) in rabbit proximal tubule cells in primary culture was investigated and compared with renal and hepatic PEPCK in vivo. The enzyme activity decreased rapidly in rabbit proximal tubule cells developed in hormonally defined medium supplemented with glucose and insulin. In this condition, the cytosolic form disappears with time. Without glucose and insulin, the subcellular location of PEPCK is similar to the location observed in proximal tubule freshly isolated and in renal cortex, with approx. 50% of mitochondrial form and approx. 50% of cytosolic form. However, the levels of mRNA that encode the cytosolic PEPCK are not detectable in cell cultures, whatever the medium composition. Treatment with dibutyryl cAMP caused a 14-fold induction of PEPCK mRNA in 6 h. This result indicates that the transcription of cytosolic PEPCK can be induced in cell cultures. Lactate or pyruvate additions did not modify the levels of PEPCK mRNA whereas specific activity increased rapidly, suggesting an activation of an inactive form in cell cultures. Moreover, lactate induced increased specific activity of the sole mitochondrial form while pyruvate induced increased specific activities of both mitochondrial and cytosolic form. Thus, subcellular location of PEPCK in rabbit proximal tubule cells appears to be modulated by the available substrate in culture medium. This observation parallels the changes observed in vivo since a modification of subcellular location of this enzyme was seen between fed and fasted rabbit, when subcellular distribution remains similar between fed and starved rats. Moreover, in the fasted liver of rabbit, a decrease of the mitochondrial PEPCK specific activity is seen concomitant with an increase in cytosolic PEPCK activity. These results point out the relative contributions of the cytosolic and mitochondrial PEPCK to rabbit gluconeogenesis.

Modulation of sodium-coupled uptake and membrane fluidity by cisplatin in renal proximal tubular cells in primary culture and brush-border membrane vesicles

The proximal tubule appears to be the main target for the adverse effects of cis-diamminedichloroplatinum (II) (cDDP). We evaluated the early effects of cDDP at concentrations (3 to 67 microM) lower that those which alter cell viability, on three apical transport systems and on the physical state of the brush border membrane (BBM) in rabbit proximal tubule (RPT) cells in primary culture. The maximal effect, corresponding to a 30% decrease in Na(+)-coupled uptake of phosphate (Pi) and alpha-methylglucopyranoside (MGP) and a twofold increase in Na(+)-coupled alanine uptake, was obtained at 17 microM (5 micrograms/ml) cDDP and occurred through a modification of their affinity. At this concentration, cDDP increased BBM fluidity and decreased the BBM cholesterol content by 28%, without increasing the permeability of tight junctions. To clarify the role of cDDP-induced increase in BBM fluidity on alterations of Na(+)-coupled uptake, these parameters were also investigated in BBM vesicles isolated from rabbit renal cortex directly exposed to cDDP. cDDP induced a concentration-dependent inhibition of Na(+)-coupled uptake of MGP, Pi and alanine in BBM vesicles from the renal cortex, associated with a decrease in protein sulfhydryl content, without modifying BBM fluidity. Our findings strongly suggest that the cDDP-induced increase in BBM fluidity in RPT cells results from an indirect mechanism, possibly an alteration of cholesterol metabolism, and did not play a major role in the cDDP-induced inhibition of Na+/Pi and Na+/glucose cotransport systems that may be mainly mediated through a direct chemical interaction with essential sulfhydryl groups of the transporters.

Decreasing glycolysis increases sensitivity to mitochondrial inhibition in primary cultures of renal proximal tubule cells

We have previously shown that shaking the culture plates (SHAKE) of rabbit renal proximal tubule cells (RPTC) to maintain adequate aeration increased aerobic metabolism and decreased the induction of glycolysis compared to RPTC cultured under standard conditions (STILL). However, glycolysis in SHAKE RPTC remained elevated compared to glycolysis in proximal tubules in vivo. In the present study the contribution of culture medium sugar composition and concentration to glycolytic metabolism was assessed in RPTC. SHAKE and STILL RPTC cultured in 5 mM glucose contained lactate levels equivalent to the respective SHAKE and STILL RPTC cultured in standard culture medium which contains 17.5 mM glucose. Similarly, the activity of lactate dehydrogenase was unchanged by lowering the medium glucose concentration. Substituting 5 mM galactose for 5 mM glucose in the culture medium significantly reduced the lactate content of both SHAKE and STILL RPTC but had no effect on lactate dehydrogenase activity. Cell growth was equivalent under all culture conditions. Sensitivity to mitochondrial inhibition was determined for each culture condition by measuring cell death after exposure to the respiratory inhibitor antimycin A. The results showed a hierarchy of sensitivity to antimycin A (5 mM galactose SHAKE > 5 mM glucose SHAKE > 17.5 mM glucose SHAKE = 17.5 mM glucose STILL), which was generally inversely correlated with the level of glycolysis as measured by lactate content (17.5 mM glucose STILL > 17.5 mM glucose SHAKE = 5 mM glucose SHAKE > 5 mM galactose SHAKE).

HK-2: an immortalized proximal tubule epithelial cell line from normal adult human kidney

Studies assessing mechanisms of proximal tubular cell (PTC) physiology and pathophysiology increasingly utilize cell culture systems to avoid the complexity of whole organ/whole animal experiments. However, no well-differentiated PTC line derived from adult human kidney currently exists. Therefore, the goal of this research was to establish such a line by transduction with human papilloma virus (HPV 16) E6/E7 genes. A primary PTC culture from normal adult human renal cortex was exposed to a recombinant retrovirus containing the HPV 16 E6/E7 genes, resulting in a cell line designated HK-2 (human kidney-2) which has grown continuously in serum free media for more than one year. HK-2 cell growth is epidermal growth factor dependent and the cells retain a phenotype indicative of well-differentiated PTCs (positive for alkaline phosphatase, gamma glutamyltranspeptidase, leucine aminopeptidase, acid phosphatase, cytokeratin, alpha 3 beta 1 integrin, fibronectin; negative for factor VIII-related antigen, 6.19 antigen and CALLA endopeptidase). Furthermore, HK-2 cells retain functional characteristics of proximal tubular epithelium (Na+ dependent/phlorizin sensitive sugar transport; adenylate cyclase responsiveness to parathyroid, but not to antidiuretic, hormone). The E6/E7 genes are present in the HK-2 genome, as determined by PCR. To assess its potential usefulness as a tool for studying injury and repair, HK-2 cells were exposed to a toxic concentration of H2O2 +/- iron chelation (deferoxamine) or hydroxyl radical scavenger (Na benzoate) therapy. Only the former blocked H2O2 cytotoxicity, reproducing results previously obtained with freshly isolated rat proximal tubular segments. In conclusion, an immortalized adult human PTC line has been established by transduction with HPV 16 E6/E7 genes. It appears to be well-differentiated on the basis of its histochemical, immune cytochemical, and functional characteristics, and it can reproduce experimental results obtained with freshly isolated PTCs. Thus, this new PTC line could have substantial research application.

Isolation and Culture of Proximal Tubular Cells from Porcine Kidney

Porcine proximal tubular cells (PPTC) were isolated from kidneys obtained from slaughterhouse pigs. After disruption of the connective tissue by collagenase, purification was achieved by filtration and centrifugation on a discontinuous density gradient. Single cells and clusters of 10–40 cells were obtained, having a viability of 93–99%. More than 81% of the single cells showed γ-glutamyltranspeptidase (GGT) activity and more than 95% showed non-specific esterase (NE) activity, marker enzymes for proximal tubule cells. One kidney yielded 1 x 107single cells and 3x107cells in clusters. Cells were kept in primary culture on plastic or collagen-coated dishes. In the presence of 10% serum, confluency was reached within four days. The monolayers could be kept in culture for four days after confluency, in serum-free conditions. When seeded in serum-free conditions, PPTC did not reach confluency, but the cells could be kept in culture for at least 16 days. The cells displayed epithelial morphology, i.e. cobblestone shape, dome formation, microvilli, basal infoldings and abundant mitochondria. PPTC in primary culture still displayed NE activity, while 80% of the cells showed GGT activity. In conclusion, the isolated cells are of proximal tubular origin, reach confluency in 3–4 days in the presence of 10% serum, and can be kept as monolayers in serum-free conditions for four additional days and may provide a suitable in vitro model for long-term nephrotoxicity studies.

The role of short chain fatty acid substrates in aerobic and glycolytic metabolism in primary cultures of renal proximal tubule cells

This study examined the role of odd and even short-chain fatty acid substrates on aerobic and glycolytic metabolism in well-aerated primary cultures of rabbit renal proximal tubule cells (RPTC). Increasing oxygen delivery to primary cultures of RPTC by shaking the dishes (SHAKE) reduced total lactate levels and lactate dehydrogenase (LDH) activity and reduced net glucose consumption compared to RPTC cultured under standard conditions (STILL). The addition of butyrate, valerate, heptanoate, or octanoate to SHAKE RPTC produced variable effects on glycolytic metabolism. Although butyrate and heptanoate further reduced total lactate levels and net glucose consumption during short-term culture (< 24 h), no fatty acid tested further reduced total lactate levels, net glucose consumption, or LDH activity during long-term culture (7 days). During the first 12 h of culture, maintenance of aerobic metabolism in SHAKE RPTC was dependent on medium supplementation with fatty acid substrates (2 mM). However, by 24 h, SHAKE RPTC did not require fatty acid substrates to maintain levels of aerobic metabolism equivalent to freshly isolated proximal tubules and greater than STILL RPTC. This suggests that SHAKE RPTC undergo adaptive changes between 12 and 24 h of culture, which give RPTC the ability to utilize other substrates for mitochondrial oxidation, therefore allowing greater expression of mitochondrial oxidative potential in SHAKE RPTC than in STILL RPTC.

Effect of glucose and insulin deprivation on differentiation and carbohydrate metabolism of rabbit proximal tubular cells in primary culture

Rabbit proximal tubule cells in primary culture revert from gluconeogenesis to glycolysis. To determine whether glucose and insulin deprivation of the culture medium could prevent this metabolic conversion without a loss of differentiation, rabbit proximal tubule cells were cultured in hormonally defined medium free of glucose and insulin and compared to rabbit proximal tubule cells cultured in medium supplemented with 17.5 mM glucose and 5 micrograms/ml insulin. In the two culture conditions, RPT cells grew at a similar rate and reached confluency within 4-5 days. Patterns of enzyme activity, including brush-border hydrolases, N-acetyl-beta-D-glucosaminidase and glutathione-S-transferases as a function of culture time were comparable in the two media. During the growth phase in glucose- and insulin-free medium, cells showed higher sodium-dependent glucose uptake. Scanning electron microscopy revealed a high density of microvilli at confluency regardless of the culture conditions. In both the presence and absence of glucose and insulin, the activities of gluconeogenic enzymes, phosphoenolpyruvate carboxykinase and fructose-1,6-bisphosphatase, as well as basal and pyruvate-stimulated glucose production fell markedly as a function of time. By contrast, glucose and insulin deprivation greatly reduced both the lactate production rate and the activities of glycolytic enzymes, pyruvate kinase, hexokinase and lactate dehydrogenase.

Platinum complex-induced dysfunction of cultured renal proximal tubule cells. A comparative study of carboplatin and transplatin with cisplatin

Platinum coordination complexes (PtCx) are potent against several types of cancer but are often nephrotoxic. With a view to developing a PtCx nephrotoxicity model, the toxicity of cisplatin (cDDP), transplatin (tDDP) and carboplatin (CBDCA) was studied in primary cultures of rabbit proximal tubule (RPT) cells and in the renal epithelial OK cell line. The cytotoxicity of these PtCx (10-3000 microM) was assessed after 24 h exposure of confluent monolayers in terms of LDH release; their effects at non-cytotoxic concentrations (1-1000 microM) on DNA and protein synthesis, glucose transport, marker enzymes and the total glutathione concentration were also determined, together with cellular platinum uptakes. The cytotoxicity ranking of the studied compounds differed for OK and RPT cells (cDDP > tDDP; cDDP > CBDCA and tDDP > cDDP; cDDP > CBDCA, respectively). Only results which were obtained in RPT cells corresponded to reported nephrotoxicity in vivo, making OK cells inappropriate for the study of PtCx nephrotoxicity in vitro. cDDP was about 10 times less cytotoxic for OK cells than for RPT cells because of lower cellular uptake. tDDP was unable markedly to inhibit biochemical and functional parameters in RPT cells below cytotoxic concentrations. At non-cytotoxic concentrations, cDDP and CBDCA depressed synthetic activity (mainly DNA) and, to a lesser extent, Na(+)-K(+)-ATPase activity and glucose transport in RPT cells. Total glutathione levels in RPT cells steadily increased during exposure to cDDP, tDDP and CBDCA, before the onset of cell death, arguing against an early role of glutathione depletion in PtCx toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of L-type Ca2+ channel blockers on anoxia-induced increases in intracellular Ca2+ concentration in rabbit proximal tubule cells in primary culture

Ca2+ channel blockers (CCB) have been shown to be protective against ischaemic damage of the kidney, suggesting an important role for intracellular Ca2+ ([Ca2+]i) in generating cell damage. To delineate the mechanism behind this protective effect, we studied [Ca2+]i in cultured proximal tubule (PT) cells during anoxia in the absence of glycolysis and the effect of methoxyverapamil (D 600) and felodipine on [Ca2+]i during anoxia. A method was developed whereby [Ca2+]i in cultured PT cells could be measured continuously with a fura-2 imaging technique during anoxic periods up to 60 min. Complete absence of O2 was realised by inclusion of a mixture of oxygenases in an anoxic chamber. [Ca2+]i in PT cells started to rise after 10 min of anoxia and reached maximal levels at 30 min, which remained stable up to 60 min. The onset of this increase and the maximal levels reached varied markedly among individual cells. The mean values for normoxic and anoxic [Ca2+]i were 118 +/- 2 (n = 98) and 662 +/- 22 (n = 160) nM, respectively. D 600 (1 microM), but not felodipine (10 microM), significantly reduced basal [Ca2+]i in normoxic incubations. During anoxia 1 microM and 100 microM D 600 significantly decreased anoxic [Ca2+]i levels by 22 and 63% respectively. Felodipine at 10 microM was as effective as 1 microM D 600. Removal of extracellular Ca2+ and addition of 0.1 mM La3+ completely abolished anoxia-induced increases in [Ca2+]i. We conclude that anoxia induces increases in [Ca2+]i in rabbit PT cells in primary culture, which results from Ca2+ influx. Since this Ca2+ influx is partially inhibited by low doses of CCBs, L-type Ca2+ channels may be involved.

Characterization of gentamicin-induced dysfunctions in vitro: the use of optimized primary cultures of rabbit proximal tubule cells

Compared to prior studies which frequently pinpoint the impairment of one parameter or function, this paper reports for the first time an extensive characterization of the toxic effects of gentamicin in a single model of primary cultured rabbit proximal tubule cells developed without insulin and glucose. Biochemical, functional and morphological approaches were used. Cellular response pattern was examined after a 72-h exposure during either the exponential growth phase or the stationary confluency phase of the culture to 0.2, 1, and 2.5 mM gentamicin. The biochemical study after gentamicin exposure showed increased activities for N-acetyl-beta-D-glucosaminidase and alkaline phosphatase, decreased activities for sphingomyelinase, cathepsin B, Na+/K(+)-ATPase, lactate dehydrogenase and NADPH cytochrome C reductase. Functional evaluation revealed decreased protein synthesis and alpha-methylglucose transport after gentamicin exposure. Morphometric study made it possible to show that the density of lysosomes, the cell fractional volume of the lysosomal compartment, and the mean size of the lysosomal profiles are increased in the cells. Intracellular accumulation of gentamicin in proximal tubular cells was dose dependent and reached high levels in cultured cells. In conclusion, this model compared to others in the literature allowed us to demonstrate in vitro a close response pattern to the in vivo situation after gentamicin exposure.

Development and characterization of rabbit proximal tubular epithelial cell lines

We have isolated rabbit kidney proximal tubular epithelial cell lines. The selection was based on their ability to form confluent monolayers on porous supports and to maintain receptor-mediated signal transduction and ion transport, characteristic of the proximal tubule. The isolation method consisted of several steps: (1) superficial cortical proximal tubule segments were microdissected and cultured on a matrix-coated porous support until cells formed a confluent monolayer; (2) primary cultures showing hormone-regulated ion transport typical for the proximal tubule were selected and co-cultured with irradiated fibroblasts; and (3) the epithelial cells surviving after several passages were expanded and passaged on porous substrates. Most of the cell lines developed in this manner were obtained by co-culture with irradiated fibroblasts producing a recombinant retrovirus encoding SV40 large T antigen and G418 resistance. However, SV40 T antigen expression was not essential for immortalization, since neither T antigen nor G418 resistance was detected in the isolated cell lines and co-culture with non-producing 3T3 cells gave similar results. One cell line (vEPT) has been characterized in some detail with respect to morphological, biochemical, and ion transport properties. This line forms confluent monolayers with apical microvilli, tight junctions, and convolutions of the basolateral plasma membrane. Once confluent, monolayers maintain conductances of 25 to 32 mS/cm2 for several weeks in culture and possess phlorizin-sensitive short-circuit current (Isc) in glucose containing media, indicative of apical Na(+)-glucose co-transport. vEPT cells also retain receptor and signaling mechanisms for angiotensin II (Ang II). Apical and basal Ang II and 5,6-epoxy-eicosatrienoic acid (5,6-EET) modulate the Isc in a manner similar to primary cultures. The cell lines share with primary cultures expression of the cytokeratins K8, K10/K11, and K19 ("nomenclature" [21]). They also retain several receptor and signal transduction mechanisms. For example, Ang II, arachidonate, bradykinin, 5,6-EET, parathyroid hormone (residues 1 through 34), and purine nucleotides increase cytosolic Ca2+, PTH elevates cAMP levels, and Ang II enhances proximal tubule-specific arachidonic acid metabolism.

α-Fetoprotein expression in fetal kidney cells does not require enhancers

Expression of the alpha-fetoprotein (AFP) and albumin genes was examined in fetal mouse kidney by analysis of tissue mRNA pool sizes during development and transient expression assays in primary kidney tissue culture cells. AFP is expressed at a much lower level in kidney than in liver but transcription of the gene is activated early during development and repressed after birth with a time-course similar to liver. However, albumin mRNA was not detected in fetal or new born mouse kidney. Transient expression assays using AFP- and albumin-CAT (chloramphenicol acetyl transferase) vectors were employed to characterize cis-acting elements active in the regulation of AFP expression in kidney. Primary fetal liver and kidney cells in culture were used for these assays. The AFP promoter is active in kidney cells and the information necessary for tissue specific expression and developmental repression are contained within the first 1.0 kb of 5' flanking sequences of the AFP gene. In addition, the AFP upstream enhancer elements are inactive in primary kidney cells. The mouse albumin promoter is shown to be inactive in kidney cells. The results obtained using transient expression assays are consistent with the observed low level of AFP expression, developmental repression of AFP, and the absence of expression of albumin in the mouse kidney.

Renal proximal tubule cell cultures for studying drug-induced nephrotoxicity and modulation of phenotype expression by medium components

The characteristics of two established renal cell lines (LLC-PKI and OK) and of primary cultures of rabbit and human proximal tubule cells are described by summarizing the literature about specific properties retained by these cells in culture. Furthermore, comparative biochemical and functional properties are presented including both specific marker enzymes and transport properties of these cells grown in various media. The impact of culture medium composition on the expressed cellular phenotype is discussed and its consequences on the profile of toxic response due to aminoglycoside antibiotics is analyzed. The in vitro nephrotoxicity of three platinum-containing coordination complexes which exhibited different in vivo nephrotoxic potentials is studied by another technique in a model of rabbit proximal tubule cells in primary cultures in order to correlate results to in vivo data and to define reliable and sensitive parameters for the assessment of platinum-derivative-induced nephrotoxicity. Although animal cell lines have been established in serum-supplemented medium, LLC-PK1 and OK cells as well as primary cultures of proximal tubules are successfully grown in hormonally defined medium, the standardization of which is better controlled for nephrotoxicity studies.

vHNF1 is expressed in epithelial cells of distinct embryonic origin during development and precedes HNF1 expression

HNF1 (Hepatic Nuclear Factor 1) and vHNF1 are transcriptional regulators containing a highly divergent homeodomain. The first was initially found in liver nuclear extracts and is crucial for the transcription of albumin and many other hepatocyte specific genes, while the second was found in dedifferentiated hepatoma cells. Both recognize the same DNA binding site and can form homo and heterodimers in vitro and in vivo. In situ hybridization analyses have been performed to delineate the spatial and temporal pattern of expression of vHNF1 relative to HNF1 during mouse embryogenesis. The results show that accumulation of vHNF1 mRNAs expression is detected in several tissues of the embryo of both endodermal and mesodermal origin. Expression occurs in the yolk sac, the primitive gut, the liver primordium, and at different stages of kidney development in polarized epithelial structures and usually precedes that of HNF1. vHNF1 expression seems particularly prevalent with morphogenetic events in the kidney and may be a marker for certain polarized epithelium.