| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
GROWTH, DIFFERENTIATION, AND APOPTOSIS
Institute of Anatomy, University of Zurich, Zurich, Switzerland
Submitted 31 May 2006 ; accepted in final form 13 September 2006
 |
ABSTRACT |
|---|
 TOP ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
immunohistochemistry; cell cycle; proliferation; renal stem cells; proximal tubule; renal epithelial cells
By definition, stem cells are self-renewing, slow-cycling, undifferentiated cells, with the potential to produce more than one type of differentiated cell. A division of a stem cell produces one stem cell (self-renewal) and one transit-amplifying (TA) cell (1). TA cells are rapidly cycling progenitors, which means that there is no phase of quiescence between successive cell cycles (1). In various epithelial cell types, the cycling time of TA cells does not exceed 72 h in vivo (12).
After a few divisions of TA cells, the progeny become quiescent and differentiated. Such systems have been described in some epithelia (12, 21).
In a previous study we examined cell proliferation in the healthy kidney of young rats (26). Compared with models of tubular necrosis, this approach has the advantage that tubular cells display their normal, well-known phenotype. We reasoned that if cell proliferation is based on stem cells, then the dividing progenitors, i.e., the stem cells and the TA cells, should be less differentiated than the bulk of tubular cells. However, cycling cells did not display a lower degree of differentiation than their noncycling neighbors. This finding does not rule out the presence of a stem cell system. Indeed, stem cells might have been overlooked because of their low incidence and TA cells might already reach a substantial level of differentiation in the first generation.
In the present study we searched for evidence of a tubular stem cell system by examining the level of differentiation of slow-cycling cells and by attempting to detect rapidly cycling tubular cells. Growing rats were investigated because they display much higher rates of cell proliferation than grown-up rats. The focus was on the S3 segment of the proximal tubule, since in preliminary studies it showed the highest rate of proliferation in the healthy kidney and since it is particularly susceptible to acute tubular necrosis. We could not detect a population of rapidly cycling cells. In addition, slow-cycling cells were differentiated. Thus, in the S3 segment of the proximal tubule, the pattern of cell proliferation fails to display characteristic features of a stem cell system.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
Experimental Protocol
Experiment 1: Continuous infusion of BrdU for 1 wk. See the schematic in Fig. 1. Osmotic pumps (type 2ML1; Alzet, Cupertino, CA) loaded with 2 ml of 10 mg/ml 5-bromo-2'-deoxyuridine (BrdU) (Sigma, St. Louis, MO) in 0.9% NaCl were implanted into 7 rats under light diethyl ether anesthesia between 2:00 PM and 2:30 PM. The osmotic pumps release 10 µl of the solution per hour over 1 wk. One week after implantation, the rats were perfusion-fixed between 9 AM and 11 AM, while the pumps were still operating.
|
Experiment 3: Sequential administration of single doses of CldU and IdU. See the schematic in Fig. 1. The thymidine analogs 5-chloro-2'-deoxyuridine (CldU) and 5-iodo-2'-deoxyuridine (IdU) can be detected separately in the chromatin by immunofluorescence (see below). Eight rats received 25 mg/kg CldU (Sigma) subcutaneously in isotonic saline. They were then divided into 4 pairs which received 25 mg/kg IdU (Sigma) 15, 20, 26 or 32 h after injection of CldU. All rats were perfusion-fixed 2 h after IdU administration, between 1 PM and 4:30 PM.
Experiment 4: Administration of BrdU on days 1 and 2, perfusion on days 4, 6, 8, and 14. Twelve rats were injected subcutaneously with 10 mg/kg body weight of BrdU on days 1 and 2 at 7 AM and 7 PM Between 9 AM and 11 AM on days 4, 6, 8, and 14, three rats were perfusion-fixed.
Experiment 5: Lead(II)-acetate treatment. We used 7-wk-old rats (210–230 g body wt). 190 mg of C4H6O4Pb·3 H2O (Merck, Darmstadt, Germany) was dissolved in 20 ml distilled H2O and administered intravenously to 3 animals at 3.8 mg/100 g body weight. Three control animals received the corresponding volume of isotonic saline. The rats were perfusion-fixed between 9 AM and 11 AM, 36 h after administration of treatments.
Fixation and Tissue Treatment
The rats were anesthetized by an intraperitoneal injection of pentobarbital (100 mg/kg body wt) and fixed by vascular perfusion (5). The fixative contained 3% paraformaldehyde (PFA), 0.01% glutardialdehyde (GA), and 0.5% picric acid, dissolved in a 3:2 mixture of 0.1 M cacodylate buffer (pH 7.4, added with sucrose, final osmolality 300 mosmol/kgH2O) and 4% hydroxyl ethyl starch (HES; Fresenius Kabi, Bad Homburg, Germany) in 0.9% NaCl. The kidneys were fixed for 5 min, and then rinsed by vascular perfusion with 0.1 M cacodylate buffer for 5 min.
Antibodies
The following antibodies were rabbit polyclonals: anti-proliferating cell nuclear antigen (PCNA) (Delta Biolabs, Campbell, CA); anti-Ki67 (Novocastra Laboratories, Newcastle, UK); anti-XT2 [orphan transporter localized in the brush-border (22)] (gift from Dr. F. Verrey, Institute of Physiology, University of Zurich). Anti-cyclin D1 was a rabbit monoclonal antibody (clone SP4; NeoMarkers, Fremont, CA).
The following antibodies were mouse monoclonals: anti-BrdU (clone 3D4; BD Biosciences Pharmingen, San Diego, CA), anti-BrdU (clone B44; BD Biosciences), anti-Na+-K+-ATPase (clone C464.6; Upstate Biotechnology, Lake Placid, NY).
The anti-BrdU clone BU1/75 (ICR1) (ab6326; Abcam, Cambridge, UK) was a rat monoclonal.
Immunofluorescence
Two-millimeter-thick slices of fixed kidney were frozen in liquid propane cooled down to the temperature of liquid nitrogen and cut into 4-µm-thick cryostat sections. Sections were thawed on slides and microwaved for 10 min in 0.01 M citrate buffer at pH 6.0. After pretreatment for 1 h in 5% normal goat serum in phosphate-buffered saline (PBS), the sections were incubated overnight in a humidified chamber at 4°C with the primary antibodies, diluted in PBS supplemented with 1% bovine serum albumin.
To visualize consecutive divisions, the thymidine analogs CldU and IdU were injected one after the other at various time intervals. For the independent detection of CldU and IdU, a procedure was adapted from a published protocol (2). The rat antibody BU1/75 binds to CldU but not to IdU, whereas the mouse antibody B44 binds strongly to IdU but only weakly to CldU. Sections were first incubated overnight with both antibodies (rat anti-BrdU, 1:1,000; mouse anti-BrdU, 1:200). They were then washed twice for 10 min in 36 mM Tris buffer, pH 8, containing 0.5 M NaCl and 0.5% Tween-20 at room temperature to displace the mouse anti-BrdU antibody from CldU. After 10 min wash in PBS, the sections were re-incubated with rat anti-BrdU for 1 h at room temperature to label CldU.
Binding sites of the primary antibodies were revealed with Cy3-conjugated, goat anti-rabbit IgG (red), a fluorescein isothiocyanate (FITC)-conjugated, goat anti-rat IgG and FITC (green)- or Cy5-conjugated goat anti-mouse IgG (blue). Antibodies with minimal cross-reactivity to other secondary antibody species were employed (Jackson ImmunoResearch Laboratories, West Grove, PA). For nuclear staining, 4',6-diamidino-2-phenylindole (DAPI; Sigma) was added to the working dilution of the secondary antibodies. Multiple labeling was performed using cocktails of primary antibodies and the respective secondary antibodies. Controls without primary antibodies were negative. The sections were coverslipped using DAKO-Glycergel (Dakopatts), to which 2.5% 1,4-diazabicyclo[2,2,2]octane (DABCO; Sigma) was added as fading retardant.
Fluorescent-labeled specimens were examined using a confocal laser-scanning microscope (CLSM SP2; Leica, Mannheim, Germany) or a Polyvar microscope (Reichert Jung, Vienna, Austria).
Quantitative Evaluation of Nuclear Labeling
By using the nuclear DNA labeling of DAPI, the outer stripe was located, and micrographs were made randomly using the x40 magnification of the laser-scanning microscope. The surface area of tissue on each micrograph was 375 µm2. The proximal tubule was identified by the brush border, detectable in background fluorescence.
Nuclei of proximal epithelial cells positive for BrdU, CldU, IdU, PCNA, or Ki67 were counted on the whole micrographs. Because of the large numbers of DAPI- and of cyclin D1-positive cells, these were evaluated in a uniform random systematic sample (10% sampling fraction) of the area of the micrograph.
Statistical analysis of the data was performed with the GraphPad Prism software (GraphPad Software, San Diego, CA). Differences were considered significant if P was less than 0.05 in Student's t-test for unpaired samples. All data are given as means ± SD.
|
RESULTS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
With experiment 1 we wanted to assess DNA synthesis, as an indicator for cell proliferation, in the healthy kidney of young rats. We used the thymidine analog BrdU as a tool for detection of DNA synthesis. BrdU is incorporated into DNA during S phase of the cell cycle and is detectable in the cell nuclei by immunofluorescence. Thus all cells that had gone through S phase during the treatment period are revealed by nuclear BrdU staining.
We applied BrdU continuously for 7 days up to perfusion-fixation of the kidneys. The incidence of BrdU-positive nuclei was much higher in the medullary rays of the cortex and in the outer stripe of the medulla than in other zones (Fig. 2). The majority of BrdU-positive cells were found in the S3 segment of the proximal tubule, in which 46.1 ± 6.3% (n = 7) of the cells were labeled.
|
Slow-Cycling Cells are Differentiated
The aim of experiment 2 was to detect slow-cycling cells and to determine their level of differentiation. According to the classical paradigm of adult stem cells, dividing cells are either slowly cycling stem cells or rapidly cycling TA cells. By definition the former are undifferentiated and they become transiently cycle arrested after a division, whereas the latter undergo several successive cycles (1). In our previous study on the morphology of dividing cells in the S3 segment of the proximal tubule, we did not attempt to discriminate between these two populations (26). Therefore, we may have examined mainly TA cells and may have missed slow cycling cells.
The experimental protocol was similar to that used in experiment 1, with the continuous BrdU application period being extended to 14 days. The rationale was as follows: with assumed cycling times ranging from 1–3 days in different epithelia (13), the rapidly cycling TA cells should all have gone through the cell cycle at least once during 14 days, and therefore, they should all be labeled with BrdU. In contrast, cells that did not pass the S phase during this period should be BrdU-negative. A BrdU-negative cell expressing the proliferation marker Ki67 (24) would necessarily be a slowly cycling cell.
After 14 days of continuous BrdU infusion, 64.6 ± 1.9% (n = 3) of cells in S3 were BrdU-positive. Since BrdU was applied up to the time of perfusion, the Ki67-positive cells in the S, G2, or M phase were necessarily BrdU-positive. All Ki67-positive/BrdU-negative cells displayed a low immunoreactivity for Ki67. This suggests that they were in the late G1, when upregulation of Ki67 is starting. We examined the Ki67-positive/BrdU-negative cells for the presence of Na+-K+-ATPase and XT2 by simultaneous labeling of the four antigens. Fifty-eight Ki67-positive/BrdU-negative slow cycling cells were found in S3. All of them showed Na+-K+-ATPase in their basolateral membranes and XT2 in their brush border (Fig. 3). Both transport proteins were similarly abundant in Ki67-positive/BrdU-negative cells as in neighboring tubular cells. We also examined the proximal tubule in the cortical labyrinth, which contains the segments S1 and S2. Fifteen Ki67-positive/BrdU-negative cells were found, all displaying immunoreactivity for Na+-K+-ATPase and XT2 (data not shown). Therefore, slow-cycling cells in the proximal tubule are differentiated.
|
Next we wanted to assess whether the bulk of dividing proximal tubule cells are rapidly cycling cells, as predicted in a stem cell system (1). In experiment 3, the animals were injected once with the thymidine analog CldU and at given time intervals with a second analog, IdU. Two hours after the IdU injection, the animals were perfusion-fixed. Both thymidine analogs can be detected separately using immunofluorescence. As an endogenous marker for the S phase we used PCNA, which is highly expressed at the end of G1 and in the S phase. If a cell was in the S phase at the time of CldU application and its daughter cells in the S phase at the time of IdU application, then the latter would be double-positive for CldU and IdU and also for CldU and PCNA.
Eight rats received CldU. After 15, 20, 26, and 32 h, two rats were injected with IdU respectively, and perfusion-fixed 2 h later (17, 22, 28, and 34 h after CldU injection). Triple immunofluorescence for CldU, IdU, and PCNA, and DNA staining with DAPI was performed. With that protocol it should be possible to obtain an approximation of the cycling time in S3, provided that it does not exceed 40 h (34 h plus one S phase). A preliminary experiment in which the two thymidine analogs were injected separately in different rats revealed the specificity of detection of the analogs. There was no immunoreactivity for CldU in kidneys of rats that received IdU, and conversely, there was no immunoreactivity for IdU in rats that received CldU. Micrographs were evaluated until at least 40 PCNA-positive cells per rat in the S3 segment were collected. In a total of 25,830 cells (DAPI) in the eight rats 518 PCNA-positive cells (2.1 ± 0.6%), 867 CldU-positive cells (3.3 ± 0.9%), and 455 IdU-positive cells (1.8 ± 0.9%) cells were encountered. Of the 867 CldU-positive cells, none showed immunoreactivity for PCNA or IdU (Fig. 4). Because the CldU labeled cells did not enter a second S phase during the observation frame, the cycling time in the segment S3 is longer than 40 h.
|
Since we did not detect consecutive S phases in the previous experiment we broadened the time frame of observation (experiment 4). BrdU was applied on days 1 and 2 and the kidneys were perfused on days 4, 6, 8 and 14. The aim of this experiment was to compare the proliferation rate in the population of cells that had been in the S phase at any time during days 1 and 2 (BrdU-positive) with the proliferation rate in the remaining cells (BrdU-negative). Because it was found in the previous experiment that PCNA reliably labeled cells in the S phase, we omitted the injection of a second thymidine analog before perfusion. The BrdU-positive cells in the S3 segment ranged from 5.7 ± 0.9% to 8.4 ± 0.9% with no statistically significant difference of incidence between time points. Micrographs were evaluated until at least 40 PCNA-positive cells per rat were sampled. On days 4, 6, and 8, i.e., about 1.5, 3.5, and 5.5 days after the last injection of BrdU, the incidence of PCNA-positive cells was significantly higher (P < 0.05) in the BrdU-negative population than in the BrdU-positive population. At least 180 BrdU-positive cells per rat were counted and only one BrdU/PCNA double positive cell was found in one of the three rats at each of these time points, indicating a very low rate of repetitive divisions during the first 8 days. On day 14 a substantial number of BrdU-positive cells expressed PCNA, with no statistically significant difference in the incidence of PCNA-positive cells in the BrdU-positive and BrdU-negative cell populations (Fig. 5A).
|
Cells Become Cycle-Arrested after Division
To test if the absence of rapidly cycling cells is due to a very slow progression through G1 or to cycle arrest after mitosis, we examined the immunoreactivity for cyclin D1, which is not expressed in cycle-arrested cells. Rats at days 4 and 14 in experiment 4 were evaluated for cyclin D1 and BrdU. At least 600 cyclin D1-positive and 150 BrdU-positive cells per animal and time point were evaluated. At day 4, 94.7 ± 4% of BrdU-positive cells were negative for cyclin D1, suggesting cycle arrest (Fig. 6). This is significantly higher than the 68.5 ± 3.4% cyclin D1-negative cells in the BrdU-negative population. The level of immunofluorescence for cyclin D1 was distinctly lower in BrdU-positive cells than in the average population, suggesting that BrdU-positive/cyclin D1-positive cells were at an early stage of G1. Analogously to PCNA (Fig. 5A), the frequency of cyclin D1 in the BrdU-positive and -negative populations converged on day 14 (Fig. 5B).
|
Half of the Cells in S3 Enter the Cell Cycle after a Strong Mitotic Stimulus
Since data collected in physiological growth were not suggestive of a stem cell system, we decided to investigate cycling under a potent proliferation stimulus. Lead salts induce the proliferation of proximal tubular cells without inducing tubular necrosis (4), possibly via activation of the mitogen-activated protein kinase pathway (14). Lead acetate was administered to three rats (experiment 5). Thirty-six hours after injection, 52.6 ± 15.9% of cells in the S3 segment were Ki67-positive, compared with 2.7 ± 1.1% in control animals. Thus roughly half of the tubular cells in S3 are able to enter the cell cycle within 36 h of stimulation. Mitotic figures were frequently observed in the treated rats (Fig. 7), whereas they were scarce in the controls.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
BrdU was applied continuously for 14 days to identify slow-cycling cells, and thus putative stem cells, in the S3 segment of the proximal tubule. In various epithelia in healthy adult rodents, the duration of a cycle in the TA cell population varies between 18 h and 72 h (12). Therefore, at the end of the BrdU application period of 14 days, all rapidly cycling cells should be BrdU-positive, and consequently BrdU-negative cycling cells (Ki67-positive) are slow-cycling. Since Ki67-positive/BrdU-negative cells expressed Na+-K+-ATPase and the brush border transporter XT2 they were differentiated. Therefore, they can hardly represent stem cells.
To test for the presence of rapidly cycling cells and thus of a TA cell population, we labeled cells in the S phase with a thymidine analog. If cell proliferation in S3 relied on rapidly cycling cells, then the labeled cell population should display a much higher rate of cycling (expression of PCNA) during the few days after application of the analog compared with the unlabeled cell population. The inverse pattern was found. Indeed, during a period of at least one week after application of the thymidine analog, the labeled cells displayed a markedly lower rate of cycling than the nonlabeled cells. While these data do not allow an evaluation of the cycling time, they suggest that cell proliferation in the S3 segment does not involve a population of rapidly cycling cells.
Data with cyclin D1 further support the conclusion that dividing cells in the S3 segment are not rapidly cycling. Indeed, on the fourth day after the start of BrdU application, cyclin D1 was detected in 41.5% of all cells in S3 but only in about 5.3% of the BrdU-positive cells, and here at conspicuously low levels of immunoreactivity. Absence of cyclin D1 is a characteristic feature of cycle arrest (25). In rapidly cycling cells, cyclin D1 is expressed throughout G2, M, and G1 and it is undetectable only in the S phase. In contrast, in slow-cycling cells cyclin D1 is undetectable in S, G2, and M and in the period of cycle arrest (G0). Upregulation occurs when the cell resumes progression in G1. Cells in S3 do not remain indefinitely quiescent after one division, since 14 days after injection of BrdU the incidence of PCNA-positive cells and of cyclin D1-positive cells was similar in the BrdU-positive population as in the BrdU-negative population.
The failure to detect a rapidly cycling TA cell population does not definitively exclude the presence of stem cells. Indeed, in the healthy tubule the division of a stem cell might directly yield a quiescent differentiated cell, and TA cells might be produced only when an accelerated rate of generation of new cells is needed. If so, the 46% BrdU-positive cells after 1 wk of continuous application of BrdU in experiment 1 would be daughters of stem cells, suggesting that more than 20% of cells in S3 are stem cells. Likewise, the data of experiment 5 are explainable in the context of a stem cell system only if an extremely large fraction of cells were stem cells. Thirty-six hours after injection of lead acetate, mitotic figures were widespread in S3, and 52.6% of the cells in this segment expressed Ki67. These data suggest that the proliferation potential in S3 is not limited to a small population of stem cells.
The data in the present study suggest the following model. In the S3 segment of the proximal tubule, all tubular cells have an equal potential to enter the cell cycle. After mitosis daughter cells are cycle-arrested for a period of about 1 wk on average, after which they can again progress in the G1 phase. The presence of a large fraction of cells progressing in G1 might allow, when required, a very rapid increase in cell division.
|
GRANTS |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
|
REFERENCES |
|---|
|
TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONGRANTSREFERENCES |
|---|
2. Aten JA, Bakker PJ, Stap J, Boschman GA, Veenhof CH. DNA double labelling with IdUrd and CldUrd for spatial and temporal analysis of cell proliferation and DNA replication. Histochem J 24: 251–259, 1992.[CrossRef][Web of Science][Medline]
3. Bonventre JV. Dedifferentiation and proliferation of surviving epithelial cells in acute renal failure. J Am Soc Nephrol 14: S55–S61, 2003.
4. Choie DD, Richter GW. Cell proliferation in mouse kidney induced by lead. I. Synthesis of deoxyribonucleic acid. Lab Invest 30: 647–651, 1974.[Web of Science]
5. Dawson TP, Gandhi R, Le Hir M, Kaissling B. Ecto 5'-nucleotidase: localization in rat kidney by light microscopic histochemical and immunohistochemical methods. J Histochem Cytochem 37: 39–47, 1989.[Abstract]
6. Duffield JS, Park KM, Hsiao LL, Kelley VR, Scadden DT, Ichimura T, Bonventre JV. Restoration of tubular epithelial cells during repair of the postischemic kidney occurs independently of bone marrow-derived stem cells. J Clin Invest 115: 1743–1755, 2005.[CrossRef][Web of Science][Medline]
7. Fang TC, Alison MR, Cook HT, Jeffery R, Wright NA, Poulsom R. Proliferation of bone marrow-derived cells contributes to regeneration after folic acid-induced acute tubular injury. J Am Soc Nephrol 6: 6, 2005.
8. Gupta S, Verfaillie C, Chmielewski D, Kim Y, Rosenberg ME. A role for extrarenal cells in the regeneration following acute renal failure. Kidney Int 62: 1285–1290, 2002.[CrossRef][Web of Science][Medline]
9. Ichimura T, Hung CC, Yang SA, Stevens JL, Bonventre JV. Kidney injury molecule-1: a tissue and urinary biomarker for nephrotoxicant-induced renal injury. Am J Physiol Renal Physiol 286: F552–F563, 2004.
10. Imgrund M, Grone E, Grone HJ, Kretzler M, Holzman L, Schlondorff D, Rothenpieler UW. Re-expression of the developmental gene Pax-2 during experimental acute tubular necrosis in mice 1. Kidney Int 56: 1423–1431, 1999.[CrossRef][Web of Science][Medline]
11. Kale S, Karihaloo A, Clark PR, Kashgarian M, Krause DS, Cantley LG. Bone marrow stem cells contribute to repair of the ischemically injured renal tubule. J Clin Invest 112: 42–49, 2003.[CrossRef][Web of Science][Medline]
12. Lehrer MS, Sun TT, Lavker RM. Strategies of epithelial repair: modulation of stem cell and transit amplifying cell proliferation. J Cell Sci 111: 2867–2875, 1998.[Abstract]
13. Lin F, Moran A, Igarashi P. Intrarenal cells, not bone marrow-derived cells, are the major source for regeneration in postischemic kidney. J Clin Invest 115: 1756–1764, 2005.[CrossRef][Web of Science][Medline]
14. Lu H, Guizzetti M, Costa LG. Inorganic lead activates the mitogen-activated protein kinase kinase-mitogen-activated protein kinase-p90(RSK) signaling pathway in human astrocytoma cells via a protein kinase C-dependent mechanism. J Pharmacol Exp Ther 300: 818–823, 2002.
15. Maeshima A, Yamashita S, Nojima Y. Identification of renal progenitor-like tubular cells that participate in the regeneration processes of the kidney. J Am Soc Nephrol 14: 3138–3146, 2003.
16. Megyesi J, Andrade L, Vieira JM Jr, Safirstein RL, Price PM. Coordination of the cell cycle is an important determinant of the syndrome of acute renal failure. Am J Physiol Renal Physiol 283: F810–F816, 2002.
17. Megyesi J, Safirstein RL, Price PM. Induction of p21WAF1/CIP1/SDI1 in kidney tubule cells affects the course of cisplatin-induced acute renal failure. J Clin Invest 101: 777–782, 1998.[Web of Science][Medline]
18. Mengel M, Jonigk D, Wilkens L, Radermacher J, von Wasielewski R, Lehmann U, Haller H, Mihatsch M, Kreipe H. Chimerism of metanephric adenoma but not of carcinoma in kidney transplants. Am J Pathol 165: 2079–2085, 2004.
19. Morigi M, Imberti B, Zoja C, Corna D, Tomasoni S, Abbate M, Rottoli D, Angioletti S, Benigni A, Perico N, Alison M, Remuzzi G. Mesenchymal stem cells are renotropic, helping to repair the kidney and improve function in acute renal failure. J Am Soc Nephrol 15: 1794–1804, 2004.
20. Oliver JA, Maarouf O, Cheema FH, Martens TP, Al-Awqati Q. The renal papilla is a niche for adult kidney stem cells. J Clin Invest 114: 795–804, 2004.[CrossRef][Web of Science][Medline]
21. Pinto D, Clevers H. Wnt control of stem cells and differentiation in the intestinal epithelium. Exp Cell Res 306: 357–363, 2005.[CrossRef][Web of Science][Medline]
22. Romeo E, Dave MH, Bacic D, Ristic Z, Camargo SM, Loffing J, Wagner CA, Verrey F. Luminal kidney and intestine SLC6 amino acid transporters of B0AT-cluster and their tissue distribution in Mus musculus. Am J Physiol Renal Physiol 290: F376–F383, 2006.
23. Rookmaaker MB, Verhaar MC, van Zonneveld AJ, Rabelink TJ. Progenitor cells in the kidney: biology and therapeutic perspectives. Kidney Int 66: 518–522, 2004.[CrossRef][Web of Science][Medline]
24. Scholzen T, Gerdes J. The Ki-67 protein: from the known and the unknown. J Cell Physiol 182: 311–322, 2000.[CrossRef][Web of Science][Medline]
25. Stacey DW. Cyclin D1 serves as a cell cycle regulatory switch in actively proliferating cells. Curr Opin Cell Biol 15: 158–163, 2003.[CrossRef][Web of Science][Medline]
26. Vogetseder A, Karadeniz A, Kaissling B, Le Hir M. Tubular cell proliferation in the healthy rat kidney. Histochem Cell Biol 124: 97–104, 2005.[CrossRef][Web of Science][Medline]
27. Witzgall R, Brown D, Schwarz C, Bonventre JV. Localization of proliferating cell nuclear antigen, vimentin, c-Fos, and clusterin in the postischemic kidney. Evidence for a heterogenous genetic response among nephron segments, and a large pool of mitotically active and dedifferentiated cells. J Clin Invest 93: 2175–2188, 1994.[Web of Science][Medline]
This article has been cited by other articles:
|
|
 |
|
  Y. Fujigaki, M. Sakakima, Y. Sun, T. Fujikura, T. Tsuji, H. Yasuda, and A. Hishida Cell division and phenotypic regression of proximal tubular cells in response to uranyl acetate insult in rats Nephrol. Dial. Transplant., April 25, 2009; (2009) gfp199v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H. Geng, R. Lan, G. Wang, A. R. Siddiqi, M. C. Naski, A. I. Brooks, J. L. Barnes, P. Saikumar, J. M. Weinberg, and M. A. Venkatachalam Inhibition of Autoregulated TGF{beta} Signaling Simultaneously Enhances Proliferation and Differentiation of Kidney Epithelium and Promotes Repair Following Renal Ischemia Am. J. Pathol., April 1, 2009; 174(4): 1291 - 1308. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Witzgall Are renal proximal tubular epithelial cells constantly prepared for an emergency? Focus on "The proliferation capacity of the renal proximal tubule involves the bulk of differentiated epithelial cells" Am J Physiol Cell Physiol, January 1, 2008; 294(1): C1 - C3. [Full Text] [PDF]
|
|
|
|
|
|
A. Vogetseder, N. Picard, A. Gaspert, M. Walch, B. Kaissling, and M. Le Hir Proliferation capacity of the renal proximal tubule involves the bulk of differentiated epithelial cells Am J Physiol Cell Physiol, January 1, 2008; 294(1): C22 - C28. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Lechner, N. A. Malloth, P. Jennings, D. Heckl, W. Pfaller, and T. Seppi Opposing roles of EGF in IFN-{alpha}-induced epithelial barrier destabilization and tissue repair Am J Physiol Cell Physiol, December 1, 2007; 293(6): C1843 - C1850. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
