FXYD2 and Na,K-ATPase Expression in Isolated Human Proximal Tubular Cells: Disturbed Upregulation on Renal Hypomagnesemia?

Autosomal dominant renal hypomagnesemia (OMIM 154020), associated with hypocalciuria, has been linked to a 121G to A mutation in the FXYD2 gene. To gain insight into the molecular mechanisms linking this mutation to the clinical phenotype, we studied isolated proximal tubular cells from urine of a patient and a healthy subject. Cells were immortalized and used to assess the effects of hypertonicity-induced overexpression of FXYD2 on amount, activity and apparent affinities for Na+, K+ and ATP of Na,K-ATPase. Both cell lines expressed mRNA for FXYD2a and FXYD2b, and patient cells contained both the wild-type and mutated codons. FXYD2 protein expression was lower in patient cells and could be increased in both cell lines upon culturing in hyperosmotic medium but to a lesser extent in patient cells. Similarly, hyperosmotic culturing increased Na,K-ATPase protein expression and ATP hydrolyzing activity but, again, to a lesser extent in patient cells. Apparent affinities of Na,K-ATPase for Na+, K+ and ATP did not differ between patient and control cells or after hyperosmotic induction. We conclude that human proximal tubular cells respond to a hyperosmotic challenge with an increase in FXYD2 and Na,K-ATPase protein expression, though to a smaller absolute extent in patient cells

Novel conditionally immortalized human proximal tubule cell line expressing functional influx and efflux transporters

Reabsorption of filtered solutes from the glomerular filtrate and excretion of waste products and xenobiotics are the main functions of the renal proximal tubular (PT) epithelium. A human PT cell line expressing a range of functional transporters would help to augment current knowledge in renal physiology and pharmacology. We have established and characterized a conditionally immortalized PT epithelial cell line (ciPTEC) obtained by transfecting and subcloning cells exfoliated in the urine of a healthy volunteer. The PT origin of this line has been confirmed morphologically and by the expression of aminopeptidase N, zona occludens 1, aquaporin 1, dipeptidyl peptidase IV and multidrug resistance protein 4 together with alkaline phosphatase activity. ciPTEC assembles in a tight monolayer with limited diffusion of inulin-fluorescein-isothiocyanate. Concentration and time-dependent reabsorption of albumin via endocytosis has been demonstrated, together with sodium-dependent phosphate uptake. The expression and activity of apical efflux transporter p-glycoprotein and of baso-lateral influx transporter organic cation transporter 2 have been shown in ciPTEC. This established human ciPTEC expressing multiple endogenous organic ion transporters mimicking renal reabsorption and excretion represents a powerful tool for future in vitro transport studies in pharmacology and physiology

Cystinosis: practical tools for diagnosis and treatment

Cystinosis is the major cause of inherited Fanconi syndrome, and should be suspected in young children with failure to thrive and signs of renal proximal tubular damage. The diagnosis can be missed in infants, because not all signs of renal Fanconi syndrome are present during the first months of life. In older patients cystinosis can mimic idiopathic nephrotic syndrome due to focal and segmental glomerulosclerosis. Measuring elevated white blood cell cystine content is the corner stone for the diagnosis. The diagnosis is confirmed by molecular analysis of the cystinosin gene. Corneal cystine crystals are invariably present in all patients with cystinosis after the age of 1 year. Treatment with the cystine depleting drug cysteamine should be initiated as soon as possible and continued lifelong to prolong renal function survival and protect extra-renal organs. This educational feature provides practical tools for the diagnosis and treatment of cystinosis

Fluorescence-Based Transport Assays Revisited in a Human Renal Proximal Tubule Cell Line

Apical transport is key in renal function, and the activity of efflux transporters and receptor-mediated endocytosis is pivotal in this process. The conditionally immortalized proximal tubule epithelial cell line (ciPTEC) endogenously expresses these systems. Here, we used ciPTEC to investigate the activity of three major efflux transporters, viz. breast cancer resistance protein (BCRP), multidrug resistance protein 4 (MRP4) and P-glycoprotein (P-gp), as well as protein uptake through receptor-mediated endocytosis using a fluorescence-based setup for transport assays. To this end, cells were exposed to Hoechst33342, chloromethylfluorescein-diacetate (CMFDA) and calcein-AM in presence or absence of model inhibitors for BCRP (KO143), P-gp (PSC833) or MRP's (MK571). Overexpression cell lines MDCKII-BCRP and MDCKII-P-gp were used as positive controls and membrane vesicles over-expressing one transporter were used to determine substrate and inhibitor specificities. Receptor-mediated endocytosis was investigated by determining the intracellular accumulation of fluorescently labeled receptor associated protein (RAP-GST). In ciPTEC, BCRP and P-gp showed similar expressions and activities while MRP4 was more abundantly expressed. Hoechst33342, GS-MF and calcein are retained in the presence of KO143, MK571 and PSC833, showing clearly redundancy between the transporters. Noteworthy is the fact that both KO143 and MK571 can block BCRP, P-gp and MRP's, while PSC833 appears a potent inhibitor for BCRP and P-gp, but not the MRP's. Furthermore, ciPTEC accumulate RAP-GST in intracellular vesicles in a dose and time dependent manner, which was reduced in megalin-deficient cells. In conclusion, fluorescent probe-based assays are fast and reproducible in determining apical transport mechanisms, in vitro. We demonstrate that typical substrates and inhibitors are not specific for the designated transporters, reflecting the complex interactions that can take place in vivo. The set of tools we describe are also compatible with innovative kidney culture models, and allows studying transport mechanisms that are central to drug absorption, disposition and detoxification

Recellularized native kidney scaffolds as a novel tool in nephrotoxicity screening

Drug-induced kidney injury (DIKI) in medicinal compound development accounts for over 20% of clinical trials failure and involves damage to different nephron segments, mostly the proximal tubule. Yet, currently applied cell models fail to reliably predict nephrotoxicity nor are easy to establish. Here, we developed a novel three-dimensional (3D) nephrotoxicity platform based on decellularized rat kidneys scaffolds (DS) recellularized with conditionally immortalized human renal proximal tubule epithelial cells overexpressing the organic anion transporter 1 (ciPTEC-OAT1). A 5-days sodium dodecyl sulfate (SDS)-based decellularization protocol was used to generate DS , of which 100 um slices were cut and used for cell seeding. After 8 days of culturing, recellularized scaffolds (RS) demonstrated 3D tubules formation along with tubular epithelial characteristics, including drug transporter funcion. Exposure of RS to cisplatin (CDDP), tenofovir (TFV) or cyclosporin A (CsA) as prototypical nephrotoxic drugs, revealed concentration-dependent reduction in cell viability, as assessed by PrestoBlue and Live/Dead staining assays. CDDP, TFV and CsA TC50-values were 108 ± 1 and 12 ± 1, 212 ± 1 and 97 ± 1, 129 ± 2 and 294 ± 2 μM in 2D and 3D cultures, respectively. This was most likely due to specific uptake of CDDP by the organic cation transporter 2 (OCT2), TFV through organic anion transporter 1 (OAT1) and CsA competing for P-glycoprotein-mediated efflux. As compared to 2D cultures, RS showed an increased sensitivity to cisplatin and tenofovir toxicity after 24h exposure (9 and 2.2 fold, respectively). In conclusion, we developed a physiologically-relevant 3D nephrotoxicity screening platform that could potentially be suitable as a novel alternative in drug development

Recellularized native kidney scaffolds as a novel tool in nephrotoxicity screening

Drug-induced kidney injury (DIKI) in medicinal compound development accounts for over 20% of clinical trials failure and involves damage to different nephron segments, mostly the proximal tubule. Yet, currently applied cell models fail to reliably predict nephrotoxicity nor are easy to establish. Here, we developed a novel three-dimensional (3D) nephrotoxicity platform based on decellularized rat kidneys scaffolds (DS) recellularized with conditionally immortalized human renal proximal tubule epithelial cells overexpressing the organic anion transporter 1 (ciPTEC-OAT1). A 5-days sodium dodecyl sulfate (SDS)-based decellularization protocol was used to generate DS , of which 100 um slices were cut and used for cell seeding. After 8 days of culturing, recellularized scaffolds (RS) demonstrated 3D tubules formation along with tubular epithelial characteristics, including drug transporter funcion. Exposure of RS to cisplatin (CDDP), tenofovir (TFV) or cyclosporin A (CsA) as prototypical nephrotoxic drugs, revealed concentration-dependent reduction in cell viability, as assessed by PrestoBlue and Live/Dead staining assays. CDDP, TFV and CsA TC50-values were 108 ± 1 and 12 ± 1, 212 ± 1 and 97 ± 1, 129 ± 2 and 294 ± 2 μM in 2D and 3D cultures, respectively. This was most likely due to specific uptake of CDDP by the organic cation transporter 2 (OCT2), TFV through organic anion transporter 1 (OAT1) and CsA competing for P-glycoprotein-mediated efflux. As compared to 2D cultures, RS showed an increased sensitivity to cisplatin and tenofovir toxicity after 24h exposure (9 and 2.2 fold, respectively). In conclusion, we developed a physiologically-relevant 3D nephrotoxicity screening platform that could potentially be suitable as a novel alternative in drug development

Flow stimulates drug transport in a human kidney proximal tubule-on-a-chip independent of primary cilia

BACKGROUND: Kidney disease modeling and assessment of drug-induced kidney injury can be advanced using three-dimensional (3D) microfluidic models that recapitulate in vivo characteristics. Fluid shear stress (FSS) has been depicted as main modulator improving in vitro physiology in proximal tubule epithelial cells (PTECs). We aimed to elucidate the role of FSS and primary cilia on transport activity and morphology in PTECs. METHODS: Human conditionally immortalized PTEC (ciPTEC-parent) was cultured in a microfluidic 3D device, the OrganoPlate, under a physiological peak FSS of 2.0 dyne/cm2 or low peak FSS of 0.5 dyne/cm2. Upon a 9-day exposure to FSS, albumin-FITC uptake, activity of P-glycoprotein (P-gp) and multidrug resistance-associated proteins 2/4 (MRP2/4), cytotoxicity and cell morphology were determined. RESULTS: A primary cilium knock-out cell model, ciPTEC-KIF3α-/-, was successfully established via CRISPR-Cas9 genome editing. Under physiological peak FSS, albumin-FITC uptake (p = .04) and P-gp efflux (p = .002) were increased as compared to low FSS. Remarkably, a higher albumin-FITC uptake (p = .03) and similar trends in activity of P-gp and MRP2/4 were observed in ciPTEC-KIF3α-/-. FSS induced cell elongation corresponding with the direction of flow in both cell models, but had no effect on cyclosporine A-induced cytotoxicity. CONCLUSIONS: FSS increased albumin uptake, P-gp efflux and cell elongation, but this was not attributed to a mechanosensitive mechanism related to primary cilia in PTECs, but likely to microvilli present at the apical membrane. GENERAL SIGNIFICANCE: FSS-induced improvements in biological characteristics and activity in PTECs was not mediated through a primary cilium-related mechanism

Flow stimulates drug transport in a human kidney proximal tubule-on-a-chip independent of primary cilia

BACKGROUND: Kidney disease modeling and assessment of drug-induced kidney injury can be advanced using three-dimensional (3D) microfluidic models that recapitulate in vivo characteristics. Fluid shear stress (FSS) has been depicted as main modulator improving in vitro physiology in proximal tubule epithelial cells (PTECs). We aimed to elucidate the role of FSS and primary cilia on transport activity and morphology in PTECs. METHODS: Human conditionally immortalized PTEC (ciPTEC-parent) was cultured in a microfluidic 3D device, the OrganoPlate, under a physiological peak FSS of 2.0 dyne/cm2 or low peak FSS of 0.5 dyne/cm2. Upon a 9-day exposure to FSS, albumin-FITC uptake, activity of P-glycoprotein (P-gp) and multidrug resistance-associated proteins 2/4 (MRP2/4), cytotoxicity and cell morphology were determined. RESULTS: A primary cilium knock-out cell model, ciPTEC-KIF3α-/-, was successfully established via CRISPR-Cas9 genome editing. Under physiological peak FSS, albumin-FITC uptake (p = .04) and P-gp efflux (p = .002) were increased as compared to low FSS. Remarkably, a higher albumin-FITC uptake (p = .03) and similar trends in activity of P-gp and MRP2/4 were observed in ciPTEC-KIF3α-/-. FSS induced cell elongation corresponding with the direction of flow in both cell models, but had no effect on cyclosporine A-induced cytotoxicity. CONCLUSIONS: FSS increased albumin uptake, P-gp efflux and cell elongation, but this was not attributed to a mechanosensitive mechanism related to primary cilia in PTECs, but likely to microvilli present at the apical membrane. GENERAL SIGNIFICANCE: FSS-induced improvements in biological characteristics and activity in PTECs was not mediated through a primary cilium-related mechanism

Layered argumentation for fuzzy automation controllers

We develop a layered argumentation system (LAS) for efficient implementation of Fuzzy automation controllers. LAS extends a logic based proposal of argumentation with subsumption concept and varying degree of confidences in beliefs. We show that this argumentation system can be used to model Fuzzy automation controllers. The argumentation system is based on a nonmonotonic logic, the computational complexity of which is known to be linear to the size of the knowledge base. LAS theories can also be mapped into RTL-VHDL (Register Transfer Level-VLSI Hardware Description Language) or RTL Verilog for very efficient hardware implementation of Fuzzy automation controllers