Transdifferentiation of distal but not proximal tubular epithelial cells from human kidney in culture

Assessing kidney development and disease using kidney organoids and CRISPR engineering

The differentiation of human pluripotent stem cells (hPSCs) towards organoids is one of the biggest scientific advances in regenerative medicine. Kidney organoids have not only laid the groundwork for various organ-like tissue systems but also provided insights into kidney embryonic development. Thus, several protocols for the differentiation of renal progenitors or mature cell types have been established. Insights into the interplay of developmental pathways in nephrogenesis and determination of different cell fates have enabled the in vitro recapitulation of nephrogenesis. Here we first provide an overview of kidney morphogenesis and patterning in the mouse model in order to dissect signalling pathways that are key to define culture conditions sustaining renal differentiation from hPSCs. Secondly, we also highlight how genome editing approaches have provided insights on the specific role of different genes and molecular pathways during renal differentiation from hPSCs. Based on this knowledge we further review how CRISPR/Cas9 technology has enabled the recapitulation and correction of cellular phenotypes associated with human renal disease. Last, we also revise how the field has positively benefited from emerging technologies as single cell RNA sequencing and discuss current limitations on kidney organoid technology that will take advantage from bioengineering solutions to help standardizing the use of this model systems to study kidney development and disease.

Tissue Culture Models of AKI: From Tubule Cells to Human Kidney Organoids

AKI affects approximately 13.3 million people around the world each year, causing CKD and/or mortality. The mammalian kidney cannot generate new nephrons after postnatal renal damage and regenerative therapies for AKI are not available. Human kidney tissue culture systems can complement animal models of AKI and/or address some of their limitations. Donor-derived somatic cells, such as renal tubule epithelial cells or cell lines (RPTEC/hTERT, ciPTEC, HK-2, Nki-2, and CIHP-1), have been used for decades to permit drug toxicity screening and studies into potential AKI mechanisms. However, tubule cell lines do not fully recapitulate tubular epithelial cell properties in situ when grown under classic tissue culture conditions. Improving tissue culture models of AKI would increase our understanding of the mechanisms, leading to new therapeutics. Human pluripotent stem cells (hPSCs) can be differentiated into kidney organoids and various renal cell types. Injury to human kidney organoids results in renal cell-type crosstalk and upregulation of kidney injury biomarkers that are difficult to induce in primary tubule cell cultures. However, current protocols produce kidney organoids that are not mature and contain off-target cell types. Promising bioengineering techniques, such as bioprinting and "kidney-on-a-chip" methods, as applied to kidney nephrotoxicity modeling advantages and limitations are discussed. This review explores the mechanisms and detection of AKI in tissue culture, with an emphasis on bioengineered approaches such as human kidney organoid models.

Clear cell clusters in the kidney: a rare finding that should not be misdiagnosed as renal cell carcinoma

Clear cytoplasm is a major characteristic feature of most malignant renal neoplasms. Benign clear cells in the renal parenchyma, usually histiocytes, can occasionally be found, but they are infrequently of an epithelial nature. We report histological, immunohistochemical, ultrastructural, and cytogenomic features of clear epithelial cell clusters incidentally found in four kidney specimens. Multiple microscopic clear cell clusters were present in the cortex, often in subcapsular location. They were composed of large epithelial cells with strikingly clear cytoplasm, without nuclear atypia, arranged in solid nests, and some tubules with narrow lumina. Immunohistochemically, they were positive for AE1AE3, PAX 8, EMA, kidney-specific cadherin, cytokeratin 7, E cadherin, and CD117, with focal immunoreactivity for CD10. Carbonic anhydrase IX, vimentin, and markers related to apoptosis and proliferation were negative. Ultrastructurally, the cytoplasms were enlarged and poor in organelles, showing ballooning degeneration. Array comparative genomic hybridization showed no chromosomal gains or losses. Clear cell clusters constitute a rare finding in the kidney and must be differentiated from benign lesions (ectopic adrenal tissue, osmotic tubulopathy, histiocytic clusters, renal adenomas) and renal cell carcinomas. Clear cell clusters appear to be generated from "endocrine-type" atrophic tubules whose cells are enlarged due to intracellular oedema. Immunohistochemistry shows a distal nephron phenotype with a limited expression of a proximal marker, CD10. Coexisting chronic renal disease or ischemic conditions seem to be related to the development of clear cell clusters. Pathological, ultrastructural, and cytogenomic features do not support a preneoplastic nature of this lesion, at least in the cases studied here.

Differentiating Induced Pluripotent Stem Cells into Renal Cells: A New Approach to Treat Kidney Diseases

Renal disease is a major issue for global public health. Despite some progress in supportive care, the mortality rates among patients with this condition remain alarmingly high. Studies in pursuit of innovative strategies to treat renal diseases, especially stimulating kidney regeneration, have been developed. In this field, stem cell-based therapy has been a promising area. Induced pluripotent stem cell-derived renal cells (iPSC-RCs) represent an interesting source of cells for treating kidney diseases. Advances in regenerative medicine using iPSC-RCs and their application to the kidney are discussed in this review. Furthermore, the way differentiation protocols of induced pluripotent stem cells into renal cells may also be applied for the generation of kidney organoids is also described, contributing to studies in renal development, kidney diseases, and drug toxicity tests. The translation of the differentiation methodologies into animal model studies and the safety and feasibility of renal differentiated cells as a treatment for kidney injury are also highlighted. Although only few studies were published in this field, the results seem promising and support the use of iPSC-RCs as a potential therapy in the future.

A Simple Bioreactor-Based Method to Generate Kidney Organoids from Pluripotent Stem Cells

Kidney organoids made from pluripotent stem cells have the potential to revolutionize how kidney development, disease, and injury are studied. Current protocols are technically complex, suffer from poor reproducibility, and have high reagent costs that restrict scalability. To overcome some of these issues, we have established a simple, inexpensive, and robust method to grow kidney organoids in bulk from human induced pluripotent stem cells. Our organoids develop tubular structures by day 8 and show optimal tissue morphology at day 14. A comparison with fetal human kidneys suggests that day-14 organoid tissue most closely resembles late capillary loop stage nephrons. We show that deletion of HNF1B, a transcription factor linked to congenital kidney defects, interferes with tubulogenesis, validating our experimental system for studying renal developmental biology. Taken together, our protocol provides a fast, efficient, and cost-effective method for generating large quantities of human fetal kidney tissue, enabling the study of normal and aberrant kidney development.

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Technically simple and cost-efficient protocol for kidney organoid generation

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Tubular organoids are obtained rapidly, with high efficiency, yield, and robustness

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Organoids contain nephrons that correspond to human fetal nephrons

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The applicability to model congenital kidney defects is presented

The Fibrin Cleavage Product Bβ15-42 Channels Endothelial and Tubular Regeneration in the Post-acute Course During Murine Renal Ischemia Reperfusion Injury

Early and adequate restoration of endothelial and tubular renal function is a substantial step during regeneration after ischemia reperfusion (IR) injury, occurring, e.g., in kidney transplantation, renal surgery, and sepsis. While tubular epithelial cell injury has long been of central importance, recent perception includes the renal vascular endothelium. In this regard, the fibrin cleavage product fibrinopeptide Bβ_15-42 mitigate IR injury by stabilizing interendothelial junctions through its affinity to VE-cadherin. Therefore, this study focused on the effect of Bβ_15-42 on post-acute physiological renal regeneration. For this, adult male C57BL/6 mice were exposed to a 30 min bilateral renal ischemia and reperfusion for 24 h or 48 h. Animals were randomized in a non-operative control group, two operative groups each treated with i.v. administration of either saline or Bβ_15-42 (2.4 mg/kg) immediately prior to reperfusion. Endothelial activation and inflammatory response was attenuated in renal tissue homogenates by single application of Bβ_15-42. Meanwhile, Bβ_15-42 did not affect acute kidney injury markers. Regarding the angiogenetic players VEGF-A, Angiopoietin-1, Angiopoietin-2, however, we observed significant higher expressions at mRNA and trend to higher protein level in Bβ_15-42 treated mice, compared to saline treated mice after 48 h of IR, thus pointing toward an increased angiogenetic activity. Similar dynamics were observed for the intermediate filament vimentin, the cytoprotective protein klotho, stathmin and the proliferation cellular nuclear antigen, which were significantly up-regulated at the same points in time. These results suggest a beneficial effect of anatomical contiguously located endothelial cells on tubular regeneration through stabilization of endothelial integrity. Therefore, it seems that Bβ_15-42 represents a novel pharmacological approach in the targeted therapy of acute renal failure in everyday clinical practice.

Lithium induces mesenchymal-epithelial differentiation during human kidney development by activation of the Wnt signalling system

Kidney function is directly linked to the number of nephrons which are generated until 32–36 weeks gestation in humans. Failure to make nephrons during development leads to congenital renal malformations, whilst nephron loss in adulthood occurs in progressive renal disease. Therefore, an understanding of the molecular processes which underlie human nephron development may help design new treatments for renal disease. Mesenchyme to epithelial transition (MET) is critical for forming nephrons, and molecular pathways which control rodent MET have been identified. However, we do not know whether they are relevant in human kidney development. In this study, we isolated mesenchymal cell lines derived from human first trimester kidneys in monolayer culture and investigated their differentiation potential. We found that the mesenchymal cells could convert into osteogenic, but not adipogenic or endothelial lineages. Furthermore, addition of lithium chloride led to MET which was accompanied by increases in epithelial (CDH1) and tubular (ENPEP) markers and downregulation of renal progenitor (SIX2, EYA1, CD133) and mesenchymal markers (HGF, CD24). Prior to phenotypic changes, lithium chloride altered Wnt signalling with elevations in AXIN2, GSK3β phosphorylation and β-catenin. Collectively, these studies provide the first evidence that lithium-induced Wnt activation causes MET in human kidneys. Therapies targeting Wnts may be critical in the quest to regenerate nephrons for human renal diseases.

Engineering kidney cells: reprogramming and directed differentiation to renal tissues

Growing knowledge of how cell identity is determined at the molecular level has enabled the generation of diverse tissue types, including renal cells from pluripotent or somatic cells. Recently, several in vitro protocols involving either directed differentiation or transcription-factor-based reprogramming to kidney cells have been established. Embryonic stem cells or induced pluripotent stem cells can be guided towards a kidney fate by exposing them to combinations of growth factors or small molecules. Here, renal development is recapitulated in vitro resulting in kidney cells or organoids that show striking similarities to mammalian embryonic nephrons. In addition, culture conditions are also defined that allow the expansion of renal progenitor cells in vitro. Another route towards the generation of kidney cells is direct reprogramming. Key transcription factors are used to directly impose renal cell identity on somatic cells, thus circumventing the pluripotent stage. This complementary approach to stem-cell-based differentiation has been demonstrated to generate renal tubule cells and nephron progenitors. In-vitro-generated renal cells offer new opportunities for modelling inherited and acquired renal diseases on a patient-specific genetic background. These cells represent a potential source for developing novel models for kidney diseases, drug screening and nephrotoxicity testing and might represent the first steps towards kidney cell replacement therapies. In this review, we summarize current approaches for the generation of renal cells in vitro and discuss the advantages of each approach and their potential applications.

A novel model of surgical injury in adult rat kidney: a "pouch model"

Regenerative mechanisms after surgical injury have been studied in many organs but not in the kidney. Studying surgical injury may provide new insights into mechanisms of kidney regeneration. In rodent models, extrarenal tissues adhere to surgical kidney wound and interfere with healing. We hypothesized that this can be prevented by wrapping injured kidney in a plastic pouch. Adult rats tolerated 5/6 nephrectomy with pouch application well. Histological analysis demonstrates that application of the pouch effectively prevented formation of adhesions and induced characteristic wound healing manifested by formation of granulation tissue. Additionally, selected tubules of the wounded kidney extended into the granulation tissue forming branching tubular epithelial outgrowths (TEOs) without terminal differentiation. Tubular regeneration outside of renal parenchyma was not previously observed, and suggests previously unrecognized capacity for regeneration. Our model provides a novel approach to study kidney wound healing.

Isolation and characterization of a primary proximal tubular epithelial cell model from human kidney by CD10/CD13 double labeling

Renal proximal tubular epithelial cells play a central role in renal physiology and are among the cell types most sensitive to ischemia and xenobiotic nephrotoxicity. In order to investigate the molecular and cellular mechanisms underlying the pathophysiology of kidney injuries, a stable and well-characterized primary culture model of proximal tubular cells is required. An existing model of proximal tubular cells is hampered by the cellular heterogeneity of kidney; a method based on cell sorting for specific markers must therefore be developed. In this study, we present a primary culture model based on the mechanical and enzymatic dissociation of healthy tissue obtained from nephrectomy specimens. Renal epithelial cells were sorted using co-labeling for CD10 and CD13, two renal proximal tubular epithelial markers, by flow cytometry. Their purity, phenotypic stability and functional properties were evaluated over several passages. Our results demonstrate that CD10/CD13 double-positive cells constitute a pure, functional and stable proximal tubular epithelial cell population that displays proximal tubule markers and epithelial characteristics over the long term, whereas cells positive for either CD10 or CD13 alone appear to be heterogeneous. In conclusion, this study describes a method for establishing a robust renal proximal tubular epithelial cell model suitable for further experimentation.

Explanting is an ex vivo model of renal epithelial-mesenchymal transition

Recognised by their de novo expression of alpha-smooth muscle actin (SMA), recruitment of myofibroblasts is key to the pathogenesis of fibrosis in chronic kidney disease. Increasingly, we realise that epithelial-mesenchymal transition (EMT) may be an important source of these cells. In this study we describe a novel model of renal EMT. Rat kidney explants were finely diced on gelatin-coated Petri dishes and cultured in serum-supplemented media. Morphology and immunocytochemistry were used to identify mesenchymal (vimentin+, α-smooth muscle actin (SMA)+, desmin+), epithelial (cytokeratin+), and endothelial (RECA+) cells at various time points. Cell outgrowths were all epithelial in origin (cytokeratin+) at day 3. By day 10, 50 ± 12% (mean ± SE) of cytokeratin+ cells double-labelled for SMA, indicating EMT. Lectin staining established a proximal tubule origin. By day 17, cultures consisted only of myofibroblasts (SMA+/cytokeratin−). Explanting is a reproducible ex vivo model of EMT. The ability to modify this change in phenotype provides a useful tool to study the regulation and mechanisms of renal tubulointerstitial fibrosis.

Cyclophilin B interacts with sodium-potassium ATPase and is required for pump activity in proximal tubule cells of the kidney

Cyclophilins (Cyps), the intracellular receptors for Cyclosporine A (CsA), are responsible for peptidyl-prolyl cis-trans isomerisation and for chaperoning several membrane proteins. Those functions are inhibited upon CsA binding. Albeit its great benefits as immunosuppressant, the use of CsA has been limited by undesirable nephrotoxic effects, including sodium retention, hypertension, hyperkalemia, interstial fibrosis and progressive renal failure in transplant recipients. In this report, we focused on the identification of novel CypB-interacting proteins to understand the role of CypB in kidney function and, in turn, to gain further insight into the molecular mechanisms of CsA-induced toxicity. By means of yeast two-hybrid screens with human kidney cDNA, we discovered a novel interaction between CypB and the membrane Na/K-ATPase β1 subunit protein (Na/K-β1) that was confirmed by pull-down, co-immunoprecipitation and confocal microscopy, in proximal tubule-derived HK-2 cells. The Na/K-ATPase pump, a key plasma membrane transporter, is responsible for maintenance of electrical Na+ and K+ gradients across the membrane. We showed that CypB silencing produced similar effects on Na/K-ATPase activity than CsA treatment in HK-2 cells. It was also observed an enrichment of both alpha and beta subunits in the ER, what suggested a possible failure on the maturation and routing of the pump from this compartment towards the plasma membrane. These data indicate that CypB through its interaction with Na/K-β1 might regulate maturation and trafficking of the pump through the secretory pathway, offering new insights into the relationship between cyclophilins and the nephrotoxic effects of CsA.

Human renal cells from the thick ascending limb and early distal tubule: characterization of primary isolated and cultured cells by reverse transcription polymerase chain reaction

AIM

Human renal tubular cells of well-defined nephron origin are an important basis in the research of various physiological and pathophysiological mechanisms in the kidney. Whereas an exceeding amount of data has been obtained on proximal tubular cells, only limited data of cells of the human thick ascending limb and the early distal tubule (TALDC) are available.

METHODS

TALDC have been isolated immunomagnetically according to their specific antigen expression of Tamm-Horsfall glycoprotein (THG). Cells were either directly processed for analysis or cultured under normal cell culture conditions. Differentiation of primary isolates and cultured cells was assessed by reverse transcription polymerase chain reaction using characteristic markers. As controls, we used RNA from whole human kidney and cultured HK-2 cells. Additional characterizations were made by morphological analysis and western blotting.

RESULTS

Primary isolated TALDC express the characteristic markers epidermal growth factor receptor, Na-K-2Cl transporter 2, epithelial calcium canal, and THG but were negative for Pax-2, aquaporin-2 and -3. Cultured TALDC were positive for epidermal growth factor receptor and Na-K-2Cl transporter 2 but have lost their epithelial calcium canal and THG expression and started to express Pax-2. All probes were positive for the specific markers kidney-specific cadherin and cytokeratin-8. Furthermore, differentiation of cultured TALDC was shown by cell morphology and their characteristic protein expression pattern.

CONCLUSION

Our results highlight the purity of primary isolates and the differentiation of cultured TALDC, and show that they can be used as an in vitro system studies of the human thick ascending limb of Henle's loop and early distal tubule.

Glucagon-like peptide 1 receptor expression in primary porcine proximal tubular cells

BACKGROUND

GLP-1 is secreted into the circulation after food intake. The main biological effects of GLP-1 include stimulation of glucose dependent insulin secretion and induction of satiety feelings. Recently, it was demonstrated in rats and humans that GLP-1 can stimulate renal excretion of sodium. Based on these data, the existence of a renal GLP-1 receptor (GLP-1R) was postulated. However, the exact localization of the GLP-1R and the mechanism of this GLP-1 action have not yet been investigated.

METHODS

Primary porcine proximal tubular cells were isolated from porcine kidneys. Expression of GLP-1R was measured at the mRNA level by quantitative RT-PCR. Protein expression of GLP-1R was verified with immunocytochemistry, immunohistochemistry and Western blot analysis. Functional studies included transport assessments of sodium and glucose using three different GLP-1 concentrations (200 pM, 2 nM and 20 nM), 200 pM exendin-4 (GLP-1 analogue) and an inhibitor of the dipeptidylpeptidase IV (DPPIV) enzyme (P32/98 at 10 microM). Finally, the expression of NHE3, the predominant Na(+)/H(+) exchanger in proximal tubular cells, was also investigated.

RESULTS

GLP-1R, NHE3 and DPPIV were expressed at the mRNA level in porcine proximal tubular kidney cells. GLP-1R expression was confirmed at the protein level. Staining of human and pig kidney cortex revealed that GLP-1R was predominantly expressed in proximal tubular cells. Functional assays demonstrated an inhibition of sodium re-absorption with GLP-1 after 3 h of incubation. Exendin-4 and GLP-1 in combination with P32/98 co-administration had no clear influence on glucose and sodium uptake and transport.

CONCLUSION

GLP-1R is functionally expressed in porcine proximal tubular kidney cells. Addition of GLP-1 to these cells resulted in a reduced sodium re-absorption. GLP-1 had no effect on glucose re-absorption. We conclude that GLP-1 modulates sodium homeostasis in the kidney most likely through a direct action via its GLP-1R in proximal tubular cells.

Differentiation Status of Human Renal Proximal and Distal Tubular Epithelial Cells in vitro: Differential Expression of Characteristic Markers

BACKGROUND

The culture of human renal tubular cells of well-defined nephron origin is an important basis in the research of various physiological and pathophysiological mechanisms in the kidney. In vitro differentiation of cultured cells is affected by cell isolation and culture conditions. Our study describes in vitro differentiation of cultured human renal proximal and distal (thick ascending limb and early distal) tubular epithelial cells.

METHODS

Proximal tubular cells (PTC) and early distal tubular cells (DTC) were isolated immunomagnetically and cultured. In vitro differentiation was assessed by Western blot analysis and reverse transcriptase polymerase chain reaction using characteristic markers. Morphologic characterization was shown by fluorescence and scanning electron microscopy.

RESULTS

E-cadherin was highly expressed in DTC, whereas expression was low in PTC. In contrast to DTC, in PTC, intercellular adhesion molecule 1 and aquaporin 1 were constitutively expressed at high levels. Both cell types expressed cytokeratin 18 and Na-K-ATPase but not alpha-smooth muscle actin. Morphological analysis showed that PTC develop long microvilli, whereas DTC formed short microvilli in culture, and both express the tight junction protein zona occludens protein 1.

CONCLUSIONS

We demonstrate differential expression of E-cadherin, intercellular adhesion molecule 1 and aquaporin 1 in cultured PTC and DTC as described for the renal tubule in vivo. We could show the in vitro differentiation of the cells, and thus, their usefulness as an in vitro model of the human proximal and early distal tubule.

Different Effects of Growth Factors on Human Renal Early Distal Tubular Cells in vitro

BACKGROUND

In the kidney, recovery from tubular damage requires regenerative mechanisms leading to re-epithelialization of the injured tubules. Current evidence supports the para- or autocrine role of growth factors in repair and regeneration of ischemic or nephrotoxic experimental acute renal failure.

METHODS

We evaluated the effects of EGF, HGF, IGF-1, and bFGF on human renal thick ascending limb and distal convoluted cells (TALDC) in vitro. TALDC were isolated by immunomagnetic separation and cultured. Signal transduction of the growth factors was evaluated by Western blot of ERK1/2 MAP-K phosphorylation. Cell proliferation was measured by MTT assay and a fluorometric assay.

RESULTS

A significant, dose- and time-dependent phosphorylation of ERK1/2 could be detected exclusively after stimulation with EGF. No other growth factor induced a significant MAPK phosphorylation. In the same manner, proliferation assays showed a significant growth-promoting effect of EGF. Neither HGF, nor IGF-1 or bFGF showed a stimulative effect on TALDC proliferation.

CONCLUSION

The present study highlights the effects of growth factors on cultured TALDC and supports the hypothesis that in vivo EGF plays a para- or autocrine role during renal repair mechanisms.

TGFbeta1 induces epithelial-mesenchymal transition, but not myofibroblast transdifferentiation of human kidney tubular epithelial cells in primary culture

The origin and fate of renal interstitial myofibroblasts (MFs), the effector cells of renal fibrosis, are still debated. Experimental evidence suggests that renal MFs derive from tubular epithelial cells throughout the epithelial-mesenchymal transition (EMT) process. Primary human tubular epithelial cells (HUTECs) were cultured for 4 and 6 days on plastic or type I collagen-coated plates with 1, 5, 10 and 50 ng/ml of transforming growth factor beta1 (TGFbeta1). The EMT process was monitored by morphology and immunophenotyping for alphaSMA, cytokeratin 8-18, E-cadherin, vimentin and collagen III. Quantitative comparative RT/PCR and real-time PCR were used to evaluate the expression of collagen III and IV, fibronectin, tenascin, MMP-2, CTGF, E-cadherin and cadherin 11 genes, as well as those of the Smad signalling pathway. TGFbeta1 was found capable of reactivating the mesenchymal programme switched off during tubulogenesis, but it induced no de novo expression of alphaSMA gene or myofibroblast phenotype. We demonstrate that the EMT process is conditioned by the extracellular matrix and characterized by TGFbeta1-driven Smad3 downregulation. Our study results suggest that TGFbeta1 could function as a classic embryonal inducer, initiating a cascade of de-differentiating events that might be further controlled by other factors in the cellular environment.

Glucose transporters in human renal proximal tubular cells isolated from the urine of patients with non-insulin-dependent diabetes

The bulk of glucose that is filtered by the renal glomerulus is reabsorbed by the glucose transporters of the proximal convoluted tubular epithelium. However, it has been difficult to investigate this in diseases such as type 2 diabetes because of the inability to isolate primary renal cells from patients without a renal biopsy. We report here a method for the immunomagnetic isolation and novel primary culture of human exfoliated proximal tubular epithelial cells (HEPTECs) from fresh urine. The primary isolates are highly enriched and differentiated and express characteristic proximal tubular phenotypic markers. They continue to express the proximal tubular markers CD13/aminopeptidase-N, sodium glucose cotransporter (SGLT) 2, and alkaline phosphatase through up to six subsequent subcultures in a similar way to human proximal cells isolated from renal biopsies. In a hyperglycemic environment, HEPTECs isolated from patients with type 2 diabetes expressed significantly more SGLT2 and the facilitative glucose transporter GLUT2 than cells from healthy individuals. We also demonstrated a markedly increased renal glucose uptake in HEPTECs isolated from patients with type 2 diabetes compared with healthy control subjects. Our findings indicate for the first time in a human cellular model that increased renal glucose transporter expression and activity is associated with type 2 diabetes.

Isolation of renal progenitor cells from adult human kidney

We describe here isolation and characterization of CD133+ cells derived from normal adult human kidney. These cells lacked the expression of hematopoietic markers and expressed PAX-2, an embryonic renal marker, suggesting their renal origin. Renal tissue-derived CD133+ cells and clones of individual cells were capable of expansion and limited self-renewal and differentiated in vitro into epithelial or endothelial cells. On subcutaneous implantation in SCID mice, the undifferentiated cells formed tubular structures expressing renal epithelial markers. At variance, when differentiated in endothelial cells, these cells formed functional vessels. On intravenous injection in SCID mice with glycerol-induced tubulonecrosis, the in vitro expanded renal-derived CD133+ cells homed into the injured kidney and integrated in tubules. We propose that CD133+ cells from kidney represent a multipotent adult resident stem cell population that may contribute to the repair of renal injury.

Effects of mycophenolic acid on IL-6 expression of human renal proximal and distal tubular cells in vitro

BACKGROUND

Interleukin-6 (IL-6) is a multifunctional cytokine which regulates immune responses and host defence mechanisms. IL-6 has been found to be increased in certain inflammatory conditions of the kidney, in which tubular epithelial cells play a pivotal role. Human renal tubular cells express IL-6. Until now no data about the effect of the immunosuppressant drug mycophenolic acid (MPA) on IL-6 expression were available.

METHODS

Proximal and distal tubular epithelial cells (PTC/DTC) have been isolated immunomagnetically. Confluent monolayers were stimulated with interleukin-1beta (IL-1beta; 25 U/ml), IL-1beta+ MPA (0.25-50 micro M) or MPA alone for 48 h. Release of IL-6 protein into the supernatant was evaluated with an enzyme immunoassay, IL-6 mRNA expression was evaluated using the Quantikine mRNA kit.

RESULTS

After IL-1beta stimulation, a highly significant 2.6- (PTC) and 3.8-fold (DTC) upregulation of IL-6 expression was detectable. IL-6 mRNA was upregulated by IL-1beta [1.57- (PTC) and 2.03-fold (DTC)]. MPA inhibited this cytokine-induced IL-6 expression in a dose-dependent manner. Incubation with the lowest MPA concentration had no effect on the stimulated upregulation, whereas all higher doses significantly decreased IL-6 expression. Dexamethasone significantly inhibited the cytokine-induced IL-6 protein release in PTC, but not in DTC.

CONCLUSIONS

In this study we demonstrated for the first time an inhibitory effect of MPA on the stimulated IL-6 expression of renal tubular epithelial cells. In contrast to older data, which showed a synergistic upregulation of the expression of a CC-chemokine by a combination of cytokines and MPA, in the present study we could demonstrate an immunosuppressive effect of MPA on the expression of an important cytokine.

Differential effects of DNA tumor virus genes on the expression profiles, differentiation, and morphogenetic reprogramming potential of epithelial cells

The availability of cell lines that retain their differentiation programs is important for the study of differentiated cell types and the development of cell therapies. DNA tumor virus genes are often used to establish cell lines from primary culture for the analysis of cell-specific functions. To ascertain whether viral immortalizing or transforming genes differed in their effects on cellular differentiation programs, the E1A 12S (WT12S) gene of adenovirus and the large T antigen (LT) gene of SV40 were used to derive stable cell lines from primary kidney. The resultant cell types exhibited very different morphologies, growth and behavior patterns, differentiation states, and plasticities. Renal cells immortalized by LT exhibited branching tubulogenesis in response to Matrigel. This was in contrast to their behavior under normal culture conditions, wherein they were less differentiated, very nonadhesive, very rapidly growing, and transformed. These cells coexpressed adult epithelial (keratin) and embryonic mesenchymal (vimentin, osteopontin, FSP1, PAX-2, and WT1) genes. WT12S-immortalized cells grown on or in Matrigel formed cysts or tubules, consistent with their expression profiles, which consisted of both epithelial and adult kidney markers (E-cadherin, alpha-catenin, circumferential actin filaments (CAF), alkaline phosphatase, aminopeptidase M, BMP7, or podocalyxin), but not embryonic/mesenchymal markers (PAX-2 or WT1). The WT12S-expressing cells were well differentiated, adhesive, slow growing, and nontransformed. Thus, cells expressing WT12S maintained their original differentiation status and were less sensitive to reprogramming, while cells expressing LT were dedifferentiated, but had the potential for reprogramming by exogenous factors.

Failure of BCL-2 up-regulation in proximal tubular epithelial cells of donor kidney biopsy specimens is associated with apoptosis and delayed graft function

SUMMARY

In renal transplantation, postischemic acute renal failure (ARF) develops in more than 20% of patients. We investigated whether tubular epithelial cells obtained from donor kidneys without subsequent ARF express a different pattern of survival genes, compared with cells from kidneys exhibiting ARF. Donor kidney biopsy specimens were obtained before transplantation from eight recipients of cadaveric kidneys with primary graft function (CAD-PF), eight patients with biopsy-proven ARF without rejection (CAD-ARF), and eight recipients of living donor kidneys with primary graft function (LIV). One thousand proximal tubular epithelial cells per biopsy specimen were isolated by laser capture microdissection. Quantitative analysis of apoptosis and the apoptosis regulatory genes Bcl-2, Bcl-xL, and Bax were performed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick-end labeling staining and real-time PCR, respectively. Primary cultures of human proximal tubular epithelial cells served as calibrator. The number of apoptotic cells was significantly higher in CAD-ARF compared with LIV and CAD-PF (1.5 +/- 1.1% [p < 0.05] vs. 0.3 +/- 0.2% vs. 0.4 +/- 0.2%; mean +/- SD). The apoptosis inhibitors Bcl-2 and Bcl-xL were significantly up-regulated in renal tubular cells of recipients without ARF compared with CAD-ARF. The ratios of Bcl-2/GAPDH normalized to calibrator were as follows: LIV 48 +/- 30, CAD-PF 38 +/- 55, and CAD-ARF 5 +/- 7 (p < 0.05). The corresponding ratios for Bcl-xL were as follows: LIV 6 +/- 6, CAD-PF 5 +/- 3, and CAD-ARF 1 +/- 1 (p < 0.05). No difference in the expression of the proapoptotic Bax could be observed. These data suggest that failure of proximal tubular cells to respond to injury by up-regulation of survival factors from the Bcl-2 family contributes to postischemic ARF in patients after cadaveric renal transplantation.

Effects of mycophenolic acid on human renal proximal and distal tubular cells in vitro

BACKGROUND

Mycophenolic acid has been shown to be effective for the prevention and treatment of renal allograft rejection. Rejection episodes were found to be associated with an infiltration of lymphocytes and macrophages/monocytes into the diseased kidney. Expression of RANTES, HLA-DR and ICAM-1 may be important for the pathogenesis of this leukocyte infiltration. Therefore the aim of this study was to evaluate the effect of the antiproliferative and immunosuppressive agent mycophenolic acid (MPA) on cell growth and cytokine-induced expression of RANTES, HLA-DR and ICAM-1 of highly purified proximal (PTC) and distal tubular cells (DTC) from human kidney.

METHODS

Human PTC and DTC were cultured in the presence of different concentrations of MPA (0.25-50 microM) or MPA plus guanosine (100 microM). Total cell number (DNA content) was determined after 4 days of cell culture by a non-radioactive fluorescence assay. Cells were stimulated by a combination of cytokines (IL1beta+gammaIFN+TNFalpha=cytomix) or cytomix plus MPA. Secretion of RANTES protein was evaluated with an enzyme-linked-immunosorbent assay. Cell surface expression of HLA-DR and ICAM-1 was assessed by flow cytometric analysis.

RESULTS

MPA inhibited cell growth of PTC and DTC in a dose-dependent manner. This effect was totally abolished by the addition of guanosine. Cytokine-induced RANTES expression was synergistically increased in the presence of MPA, an effect that was partially prevented by the addition of guanosine. Cytokine stimulation resulted in de novo expression of HLA-DR and a marked increase of ICAM-1 expression, which was partially inhibited by dexamethasone. Addition of MPA did not influence this stimulated expression.

CONCLUSIONS

We demonstrate that MPA has an effect on cell growth and chemokine release of tubular epithelial cells, and that these effects are dependent on the inhibition of cellular guanosine production. The clinical consequences of this possible pro-inflammatory effect of MPA on RANTES release may be abolished by a concomitant treatment with steroids.