Normal distribution and medullary-to-cortical shift of Nestin-expressing cells in acute renal ischemia

Distribution, contribution and regulation of nestin+ cells

BACKGROUND

Nestin is an intermediate filament first reported in neuroepithelial stem cells. Nestin expression could be found in a variety of tissues throughout all systems of the body, especially during tissue development and tissue regeneration processes.

AIM OF REVIEW

This review aimed to summarize and discuss current studies on the distribution, contribution and regulation of nestin+ cells in different systems of the body, to discuss the feasibility ofusing nestin as a marker of multilineage stem/progenitor cells, and better understand the potential roles of nestin+ cells in tissue development, regeneration and pathological processes.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review highlights the potential of nestin as a marker of multilineage stem/progenitor cells, and as a key factor in tissue development and tissue regeneration. The article discussed the current findings, limitations, and potential clinical implications or applications of nestin+ cells. Additionally, it included the relationship of nestin+ cells to other cell populations. We propose potential future research directions to encourage further investigation in the field.

Impairment of muscular endothelial cell regeneration in dermatomyositis

Background and aim

Inflammatory myopathies are heterogeneous in terms of etiology, (immuno)pathology, and clinical findings. Endothelial cell injury, as it occurs in DM, is a common feature of numerous inflammatory and non-inflammatory vascular diseases. Vascular regeneration is mediated by both local and blood-derived mechanisms, such as the mobilization and activation of so-called proangiogenic cells (PACs) or early endothelial progenitor cells (eEPCs). The current study aimed to evaluate parameters of eEPC integrity in dermatomyositis (DM), compared to necrotizing myopathy (NM) and to non-myopathic controls.

Methods

Blood samples from DM and NM patients were compared to non-myositis controls and analyzed for the following parameters: circulating CD133⁺/VEGFR-2⁺ cells, number of colony-forming unit endothelial cells (CFU-ECs), concentrations of angiopoietin 1, vascular endothelial growth factor (VEGF), and CXCL-16. Muscle biopsies from DM and NM subjects underwent immunofluorescence analysis for CXCR6, nestin, and CD31 (PECAM-1). Finally, myotubes, derived from healthy donors, were stimulated with serum samples from DM and NM patients, subsequently followed by RT-PCR for the following candidates: IL-1β, IL-6, nestin, and CD31.

Results

Seventeen (17) DM patients, 7 NM patients, and 40 non-myositis controls were included. CD133⁺/VEGFR-2⁺ cells did not differ between the groups. Both DM and NM patients showed lower CFU-ECs than controls. In DM, intramuscular CD31 abundances were significantly reduced, which indicated vascular rarefaction. Muscular CXCR6 was elevated in both diseases. Circulating CXCL-16 was higher in DM and NM in contrast, compared to controls. Serum from patients with DM but not NM induced a profound upregulation of mRNS expression of CD31 and IL-6 in cultured myotubes.

Conclusion

Our study demonstrates the loss of intramuscular microvessels in DM, accompanied by endothelial activation in DM and NM. Vascular regeneration was impaired in DM and NM. The findings suggest a role for inflammation-associated vascular damage in the pathogenesis of DM.

Age-Associated Loss in Renal Nestin-Positive Progenitor Cells

The decrease in the number of resident progenitor cells with age was shown for several organs. Such a loss is associated with a decline in regenerative capacity and a greater vulnerability of organs to injury. However, experiments evaluating the number of progenitor cells in the kidney during aging have not been performed until recently. Our study tried to address the change in the number of renal progenitor cells with age. Experiments were carried out on young and old transgenic nestin-green fluorescent protein (GFP) reporter mice, since nestin is suggested to be one of the markers of progenitor cells. We found that nestin⁺ cells in kidney tissue were located in the putative niches of resident renal progenitor cells. Evaluation of the amount of nestin⁺ cells in the kidneys of different ages revealed a multifold decrease in the levels of nestin⁺ cells in old mice. In vitro experiments on primary cultures of renal tubular cells showed that all cells including nestin⁺ cells from old mice had a lower proliferation rate. Moreover, the resistance to damaging factors was reduced in cells obtained from old mice. Our data indicate the loss of resident progenitor cells in kidneys and a decrease in renal cells proliferative capacity with aging.

Targeting Strategies for Renal Cancer Stem Cell Therapy

Renal cell carcinoma (RCC) is an intractable genitourinary malignancy that accounts for approximately 4% of adult malignancies. Currently, there is no approved targeted therapy for RCC that has yielded durable remissions, and they remain palliative in intent. Emerging evidence has indicated that renal tumorigenesis and RCC treatment-resistance may originate from renal cancer stem cells (CSCs) with tumor-initiating capacity (CSC hypothesis). A better understanding of the mechanism underlying renal CSCs will help to dissect RCC heterogeneity and drug treatment efficiency, to promote more personalized and targeted therapies. In this review, we summarized the stem cell characteristics of renal CSCs. We outlined the targeting strategies and challenges associated with developing therapies that target renal CSCs angiogenesis, immunosuppression, signaling pathways, surface biomarkers, microRNAs and nanomedicine. In conclusion, CSCs are an important role in renal carcinogenesis and represent a valid target for treatment of RCC patients.

Transgenic models for investigating the nervous system: Currently available neurofluorescent reporters and potential neuronal markers

Recombinant DNA technologies have enabled the development of transgenic animal models for use in studying a myriad of diseases and biological states. By placing fluorescent reporters under the direct regulation of the promoter region of specific marker proteins, these models can localize and characterize very specific cell types. One important application of transgenic species is the study of the cytoarchitecture of the nervous system. Neurofluorescent reporters can be used to study the structural patterns of nerves in the central or peripheral nervous system in vivo, as well as phenomena involving embryologic or adult neurogenesis, injury, degeneration, and recovery. Furthermore, crucial molecular factors can also be screened via the transgenic approach, which may eventually play a major role in the development of therapeutic strategies against diseases like Alzheimer's or Parkinson's. This review describes currently available reporters and their uses in the literature as well as potential neural markers that can be leveraged to create additional, robust transgenic models for future studies.

Kidney Cells Regeneration: Dedifferentiation of Tubular Epithelium, Resident Stem Cells and Possible Niches for Renal Progenitors

A kidney is an organ with relatively low basal cellular regenerative potential. However, renal cells have a pronounced ability to proliferate after injury, which undermines that the kidney cells are able to regenerate under induced conditions. The majority of studies explain yielded regeneration either by the dedifferentiation of the mature tubular epithelium or by the presence of a resident pool of progenitor cells in the kidney tissue. Whether cells responsible for the regeneration of the kidney initially have progenitor properties or if they obtain a “progenitor phenotype” during dedifferentiation after an injury, still stays the open question. The major stumbling block in resolving the issue is the lack of specific methods for distinguishing between dedifferentiated cells and resident progenitor cells. Transgenic animals, single-cell transcriptomics, and other recent approaches could be powerful tools to solve this problem. This review examines the main mechanisms of kidney regeneration: dedifferentiation of epithelial cells and activation of progenitor cells with special attention to potential niches of kidney progenitor cells. We attempted to give a detailed description of the most controversial topics in this field and ways to resolve these issues.

A novel role of HIF-1α/PROX-1/LYVE-1 axis on tissue regeneration after renal ischaemia/reperfusion in mice

Context: Renal ischaemia reperfusion (I/R) is a common clinical condition with a high morbidity and mortality rate. To date, I/R-induced renal injury remains an ineffective treatment. Objective: We hypothesis that angiogenesis and lymphangiogenesis markers, prospero homeobox-1 (PROX-1) and lymphatic endothelial hyaluronan receptor-1 (LYVE-1), are critical during I/R. Material and methods: Kunming mice were subjected to I/R and observed for the following eight consecutive days. Pathology analysis and protein distribution were detected by H&E staining, immunohistochemistry and immunofluorescence confocal analysis. Results: After I/R treatment, renal pathology was changed. HIF-1α was induced in the early stage and colocalisation with PROX-1 mainly in the renal tubular region, whereas PROX-1 and LYVE-1 were colocalised in the glomerulus of the endothelial region. Conclusions: In this study, we revealed HIF-1α/PROX-1/LVYE-1 axis dynamic changes in different regions after I/R and demonstrated for the first time it activates during I/R repair.

Hypoxia-inducible Factor-1α directs renal regeneration induced by decellularized scaffolds

Although mammalian kidney regeneration has been reported to occur throughout life, mature kidneys in mammals are not thought to regenerate sufficiently, particularly glomeruli. In our previous work, we found that renal regeneration could be enhanced by decellularized renal scaffolds after partial nephrectomy. In this study, we verified that the enhanced renal regeneration mediated by decellularized scaffolds could be attributed to regenerated glomeruli, which were counted both indirectly and directly under a microscope. Using the isobaric tag for relative and absolute quantitation, we performed proteomics analysis and found that hypoxia-inducible factor (HIF)-1α may be a key factor involved in induced renal regeneration. Dimethyloxyallyl glycine (DMOG), a propyl hydroxylase inhibitor, was applied to stabilize constitutive expression of HIF-1α protein, and small interfering RNA was used to inhibit gene expression. Administration of DMOG to decellularized scaffold-grafted rats improved the induced renal regeneration, whereas siHif1α transfection decreased the regeneration capacity. These findings revealed the critical role of HIF-1α in renal regeneration and provided important insights into our understanding of kidney development and the treatment of various kidney diseases.

Comparing adult renal stem cell identification, characterization and applications

Despite growing interest and effort, a consensus has yet to be reached in regards to the identification of adult renal stem cells. Organ complexity and low turnover of renal cells has made stem cell identification difficult and lead to the investigation of multiple possible populations. In this review, we summarize the work that has been done toward finding and characterizing an adult renal stem cell population. In addition to giving a general overview of what has been done, we aim to highlight the variation in methods and outcomes. The methods used to locate potential stem cell populations can vary widely, but even within the relatively standard practice of BrdU labeling of slowly dividing cells, there are significant differences in protocols and results. Additional diversity exists in cell marker profiles and apparent differentiation potential seen in potential stem cell sources. Cataloging the variety of methods and outcomes seen so far may help to streamline future investigation and stear the field toward consensus. But even without firmly defined populations, the application of renal stem cells holds tantalizing potential. Populations of highly proliferative, multipotent cells of renal origin show the ability to engraft in injured kidneys, mitigate functional loss and occasionally show the ability to generate nephrons de novo. The progress toward regenerative medicine applications is also summarized.

Interstitial stromal progenitors during kidney development: here, there and everywhere

In recent years, the renal interstitium has been identified as the site of multiple cell types, giving rise to multiple contiguous cellular networks with multiple fundamental structural and functional roles. Few studies have been carried out on the morphological and functional properties of the stromal/interstitial renal cells during the intrauterine life. This work was aimed at reviewing the peculiar features of renal interstitial stem/progenitor cells involved in kidney development. The origin of the renal interstitial progenitor cells remains unknown. During kidney development, besides the Six2 + cells of the cap mesenchyme, a self-renewing progenitor population, characterized by the expression of Foxd1, represents the first actor of the non-nephrogenic lineage. Foxd1 + interstitial progenitors originate the cortical and the renal medullary interstitial progenitors. Here, the most important stromal/interstitial compartments present in the developing human kidney will be analyzed: capsular stromal cells, cortical interstitial cells, medullary interstitial cells, the interstitium inside the renal stem cell niche, Hilar interstitial cells and Ureteric interstitial cells. Data reported here indicate that the different interstitial compartments of the developing kidney are formed by different cell types that characterize the different renal areas. Further studies are needed to better characterize the different pools of renal interstitial progenitors and their role in human nephrogenesis.

Kinetics of Label Retaining Cells in the Developing Rat Kidneys

Background

The kidney is a specialized low-regenerative organ with several different types of cellular lineages. The BrdU label-retaining cell (LRCs) approach has been used as part of a strategy to identify tissue-specific stem cells in the kidney; however, because the complementary base pairing in double-stranded DNA blocks the access of the anti-BrdU antibody to BrdU subunits, the stem cell marker expression in BrdU-labeled cells are often difficult to detect. In this study, we introduced a new cell labeling and detection method in which BrdU was replaced with 5-ethynyl-2-deoxyuridine (EdU) and examined the time-dependent dynamic changes of EdU-labeled cells and potential stem/progenitor markers in the development of kidney.

Methods

Newborn rats were intraperitoneally injected with EdU, and their kidneys were harvested respectively at different time points at 1 day, 3 days, 1 week, 2 weeks, and 6 weeks post-injection. The kidney tissues were processed for EdU and cellular markers by immunofluorescence staining.

Results

At the early stage, LRCs labeled by EdU were 2176.0 ± 355.6 cells at day one in each renal tissue section, but dropped to 168 ± 48.4 cells by week 6. As time increased, the numbers of LRCs were differentially expressed in the renal cortex and papilla. At the postnatal day one, nearly twice as many cells in the cortex were EdU-labeled as compared to the papilla (28.6 ± 3.6% vs. 15.6 ± 3.4%, P<0.05), while there were more LRCs within the renal papilla since the postnatal week one, and at the postnatal week 6, one third as many cells in the cortex were EdU-labeled as compared to the papilla (2.5 ± 0.1% vs. 7.7 ± 2.7%, P<0.05). The long-term LRCs at 6-week time point were associated exclusively with the glomeruli in the cortex and the renal tubules in the papilla. At 6 weeks, the EdU-labeled LRCs combined with expression of CD34, RECA-1, Nestin, and Synaptopodin were discretely but widely distributed within the glomeruli; Stro-1 around the glomeruli; and α-smooth muscle actin (SMA) in arteries. Conversely, co-expression of CD34, RECA-1, and Nestin with the long term EdU-labeled LRCs was significantly lower in renal tubules (P<0.01), while Stro-1 and Synaptopodin were not detected.

Conclusion

Our data found that at 6-week time point, EdU-labeled LRCs existing in the glomeruli expressed undifferentiated podocyte and endothelial markers at high rates, while those in the renal tubules expressed Nestin and vascular markers at low rates. To understand the characterization and localization of these EdU-LRCs, further studies will be needed to test cell lineage tracing, clonogenicity and differentiation potency, and the contributions to the regeneration of the kidney in response to renal injury/repair.

Nicotine modulates neurogenesis in the central canal during experimental autoimmune encephalomyelitis

Nicotine has been shown to attenuate experimental autoimmune encephalomyelitis (EAE) through inhibiting inflammation in microglial populations during the disease course. In this study, we investigated whether nicotine modified the regenerative process in EAE by examining nestin-expressing neural stem cells (NSCs) in the spinal cord, which is the primary area of demyelination and inflammation in EAE. Our results show that the endogenous neurogenic responses in the spinal cord after EAE are limited and delayed: while nestin expression is increased, the proliferation of ependymal cells is inhibited compared to healthy animals. Nicotine application significantly reduced nestin expression and partially allowed for the proliferation of ependymal cells. We found that reduction of ependymal cell proliferation correlated with inflammation in the same area, which was relieved by the administration of nicotine. Further, increased numbers of oligodendrocytes (OLs) were observed after nicotine treatment. These findings give a new insight into the mechanism of how nicotine functions to attenuate EAE.

Nestin(+) kidney resident mesenchymal stem cells for the treatment of acute kidney ischemia injury

Renal resident mesenchymal stem cells (MSCs) are important regulators of kidney homeostasis, repair or regeneration. However, natural distribution and the starting population properties of these cells remain elusive because of the lack of specific markers. Here, we identified post-natal kidney derived Nestin(+) cells that fulfilled all of the criteria as a mesenchymal stem cell. These isolated Nestin(+) cells expressed the typical cell-surface marker of MSC, including Sca-1, CD44, CD106, NG2 and PDGFR-α. They were capable of self-renewal, possessed high clonogenic potential and extensive proliferation for more than 30 passages. Under appropriate differentiation conditions, these cells could differentiate into adipocytes, osteocytes, chondrocytes and podocytes. After intravenous injection into acute kidney injury mice, Nestin(+) cells contributed to functional improvement by significantly decreasing the peak level of serum creatinine and BUN, and reducing the damaged cell apoptosis. Furthermore, conditioned medium from Nestin(+) cells could protect against ischemic acute renal failure partially through paracrine factor VEGF. Taken together, our findings indicate that renal resident Nestin(+) MSCs can be derived, propagated, differentiated, and repair the acute kidney injury, which may shed new light on understanding MSCs biology and developing cell replacement therapies for kidney disease.

Regenerative medicine for the kidney: stem cell prospects & challenges

The kidney has key roles in maintaining human health. There is an escalating medical crisis in nephrology as growing numbers of patients suffer from kidney diseases that culminate in organ failure. While dialysis and transplantation provide life-saving treatments, these therapies are rife with limitations and place significant burdens on patients and healthcare systems. It has become imperative to find alternative ways to treat existing kidney conditions and preemptive means to stave off renal dysfunction. The creation of innovative medical approaches that utilize stem cells has received growing research attention. In this review, we discuss the regenerative and maladaptive cellular responses that occur during acute and chronic kidney disease, the emerging evidence about renal stem cells, and some of the issues that lie ahead in bridging the gap between basic stem cell biology and regenerative medicine for the kidney.

Kidney regeneration and repair after transplantation

PURPOSE OF REVIEW

To briefly show which are the mechanisms and cell types involved in kidney regeneration and describe some of the therapies currently under study in regenerative medicine for kidney transplantation.

RECENT FINDINGS

The kidney contains cell progenitors that under specific circumstances have the ability to regenerate specific structures. Apart from the knowledge gained in the self-regenerative properties of the kidney, new concepts in regenerative medicine such as organ engineering and the use of mesenchymal stem cell-based therapies are currently the focus of attention in the field.

SUMMARY

Overall, kidney regeneration is a reality and the knowledge on how to control it will be one of the main scopes in the present and future.

Upregulation of nestin in proximal tubules may participate in cell migration during renal repair

The characteristics of renal tubular progenitor/precursor cells and the role of renal tubule regeneration in the repair of remnant kidneys (RKs) after nephrectomy are not well known. In the present study of a murine model of subtotal nephrectomy, we used immunofluorescence (IF), immunoblot analysis, and in situ hybridization methods to demonstrate that nestin expression was transiently upregulated in tubule cells near the incision edges of RKs. The nestin-positive tubules were immature proximal tubules that colabeled with lotus tetragonolobus agglutinin but not with markers of mature tubules (aquaporin-1, Tamm-Horsfall protein, and aquaporin-2). In addition, many of the nestin-expressing tubule cells were actively proliferative cells, as indicated by colabeling with bromodeoxyuridine. Double-label IF and immunoblot analysis also showed that the upregulation of tubular nestin was associated with enhanced transforming growth factor-β1 (TGF-β1) expression in the incision edge of RKs but not α-smooth muscle actin, which is a marker of fibrosis. In cultured human kidney proximal tubule cells (HKC), immunoblot analysis indicated that TGF-β1 induced nestin expression and loss of E-cadherin expression, suggesting an association of nestin expression and cellular dedifferentiation. Knockdown of nestin expression by a short hairpin RNA-containing plasmid led to decreased migration of HKC cells that were induced by TGF-β1. Taken together, our results suggest that the tubule repair that occurs during the recovery process following nephrectomy may involve TGF-β1-induced nestin expression in immature renal proximal tubule cells and the promotion of renal cell migration.

Renal stem cells: fact or science fiction?

The kidney is widely regarded as an organ without regenerative abilities. However, in recent years this dogma has been challenged on the basis of observations of kidney recovery following acute injury, and the identification of renal populations that demonstrate stem cell characteristics in various species. It is currently speculated that the human kidney can regenerate in some contexts, but the mechanisms of renal regeneration remain poorly understood. Numerous controversies surround the potency, behaviour and origins of the cell types that are proposed to perform kidney regeneration. The present review explores the current understanding of renal stem cells and kidney regeneration events, and examines the future challenges in using these insights to create new clinical treatments for kidney disease.

Expression of Bcl-2 and Bax in mouse renal tubules during kidney development

Bcl-2 and Bax play an important role in apoptosis regulation, as well as in cell adhesion and migration during kidney morphogenesis, which is structurally and functionally related to mitochondria. In order to elucidate the role of Bcl-2 and Bax during kidney development, it is essential to establish the exact location of their expression in the kidney. The present study localized their expression during kidney development. Kidneys from embryonic (E) 16-, 17-, 18-day-old mouse fetuses, and postnatal (P) 1-, 3-, 5-, 7-, 14-, 21-day-old pups were embedded in Epon. Semi-thin serial sections from two E17 kidneys underwent computer assisted 3D tubule tracing. The tracing was combined with a newly developed immunohistochemical technique, which enables immunohistochemistry on glutaraldehyde fixated plastic embedded sections. Thereby, the microstructure could be described in detail, and the immunochemistry can be performed using exactly the same sections. The study showed that Bcl-2 and Bax were strongly expressed in mature proximal convoluted tubules at all time points, less strongly expressed in proximal straight tubules, and only weakly in immature proximal tubules and distal tubules. No expression was detected in ureteric bud and other earlier developing structures, such as comma bodies, S shaped bodies, glomeruli, etc. Tubules expressing Bcl-2 only were occasionally observed. The present study showed that, during kidney development, Bcl-2 and Bax are expressed differently in the proximal and distal tubules, although these two tubule segments are almost equally equipped with mitochondria. The functional significance of the different expression of Bcl-2 and Bax in proximal and distal tubules is unknown. However, the findings of the present study suggest that the mitochondrial function differs between mature proximal tubules and in the rest of the tubules. The function of Bcl-2 and Bax during tubulogenesis still needs to be investigated.

Upregulation of nestin protects podocytes from apoptosis induced by puromycin aminonucleoside

BACKGROUND

Nestin is an intermediate filament protein widely used as a marker of stem cells or progenitor cells. Nestin is also highly expressed in the glomerular podocyte, a type of terminally differentiated epithelial cell. Little is known about the significance of nestin in podocytes.

METHODS

Puromycin aminonucleoside (PAN) was injected into the rats to produce a PAN nephrosis model. Transmission electronic microscopy and terminal dUTP nick end-labeling assay were used to examine the podocyte foot process (FP) effacement and apoptosis, respectively. A mouse podocyte cell line was cultured and incubated with PAN. Immunoblot was used to examine the level of nestin expression both in vivo and in vitro. Enhanced green fluorescence protein-tagged plasmids containing nestin shRNA were transfected into the cultured podocytes to silence nestin expression. F-actin arrangement within cultured podocytes was investigated by immunofluorescence, while the apoptosis rate was examined by both Hoechst stain and flow cytometry.

RESULTS

In the PAN-induced rat nephrosis model, podocyte nestin expression was increased in the absence of apparent podocyte apoptosis, even though the FP was significantly effaced. In the cultured mouse podocytes, PAN upregulated nestin expression in a time-dependent manner within 24 h of treatment. Notably, no significant apoptosis occurred, however knocking down nestin expression resulted in a remarkable derangement of actin cytoskeleton and an increase in apoptosis in the cultured podocytes 24 h after being incubated with PAN.

CONCLUSIONS

Upregulation of nestin expression during PAN nephrosis could protect podocytes from apoptosis and that this process is mediated by maintaining the regular arrangement of actin cytoskeleton.

Cardiac and renal cell therapies: similarities and differences

Patients with terminal cardiac or renal disease have few therapeutic options besides organ transplantation. Optimally, cell therapies would be used both in acute and chronic stages of such diseases. In the injured myocardium, the main therapeutic goal is reestablishment of adequate perfusion and cardiac output. This can be achieved by stem cell (SC) infusions, and currently several clinical trials have provided promising results. Considering the heart's low intrinsic capacity for regeneration and its paucity of resident cardiac SCs, we believe that induction of angiogenesis must be the primary goal, thereby promoting activation of resident SCs as well as mobilization of perivascular mesenchymal SCs that can mediate myocardial regeneration. Renal tissue, in contrast to the myocardium, has a high intrinsic capacity to respond to injuries and thus repair itself. Infusion of bone marrow (BM) cells or of their sub-populations protects the injured renal tissue and elicits immediate activation and proliferation of resident cells, which are able to undertake repair and regeneration of structures of both mesenchymal and epithelial origin. Experimental evidence indicates that infused cells function essentially through paracrine pathways, decreasing inflammation and fibrosis. In both severe cardiac and renal disorders, cell therapies appear to be a promising therapeutic option.

Comprehensive transcriptome and immunophenotype analysis of renal and cardiac MSC-like populations supports strong congruence with bone marrow MSC despite maintenance of distinct identities

Cells resembling bone marrow mesenchymal stem cells (MSC) have been isolated from many organs but their functional relationships have not been thoroughly examined. Here we compared the immunophenotype, gene expression, multipotency and immunosuppressive potential of MSC-like colony-forming cells from adult murine bone marrow (bmMSC), kidney (kCFU-F) and heart (cCFU-F), cultured under uniform conditions. All populations showed classic MSC morphology and in vitro mesodermal multipotency. Of the two solid organ-specific CFU-F, only kCFU-F displayed suppression of T-cell alloreactivity in vitro, albeit to a lesser extent than bmMSC. Quantitative immunophenotyping using 81 phycoerythrin-conjugated CD antibodies demonstrated that all populations contained high percentages of cells expressing diagnostic MSC surface markers (Sca1, CD90.2, CD29, CD44), as well as others noted previously on murine MSC (CD24, CD49e, CD51, CD80, CD81, CD105). Illumina microarray expression profiling and bioinformatic analysis indicated a correlation of gene expression of 0.88-0.92 between pairwise comparisons. All populations expressed approximately 66% of genes in the pluripotency network (Plurinet), presumably reflecting their stem-like character. Furthermore, all populations expressed genes involved in immunomodulation, homing and tissue repair, suggesting these as conserved functions for MSC-like cells in solid organs. Despite this molecular congruence, strong biases in gene and protein expression and pathway activity were seen, suggesting organ-specific functions. Hence, tissue-derived MSC may also retain unique properties potentially rendering them more appropriate as cellular therapeutic agents for their organ of origin.

Reciprocal expression of connexin 40 and 45 during phenotypical changes in renin-secreting cells

Gap junctional coupling of renin-producing cells is of major functional importance for the control of renin synthesis and release. This study was designed to determine the relevance of the vascular gap junction protein connexin 45 (Cx45) for the control of renin expression and secretion. By crossbreeding mice which drive Cre recombinase under the control of the endogenous renin promoter with mice harboring floxed Cx45 gene alleles, we generated viable mice with a deletion of Cx45 in the renin cell lineage. These mice were normotensive, and renin cells in their kidneys were normal with regard to localization and number. Sodium deficiency induced typical recruitment of renin-producing cells along afferent arterioles, whereas sodium overload resulted in a decrease in the number of cells expressing renin. Regulation of renin secretion by perfusion pressure, catecholamines, and angiotensin II from isolated kidneys of mice with renin cell-specific deletion of Cx45 was normal. Analyzing Cx45 promoter activity in cells of the preglomerular arteriolar tree by using mice driving the reporter gene LacZ under the control of the Cx45 promoter revealed strong staining in smooth muscle cells of the media, whereas renin-expressing cells were almost devoid of LacZ staining. Conversely, renin-producing cells, but not vascular smooth muscle cells expressed the gap junction protein Cx40. These findings suggest that Cx45 plays no major functional role in renin-producing cells, probably because the expression of Cx45 is downregulated in these cells. Since renin-producing cells in the adult kidney can reversibly transform into vascular smooth muscle cells and vice versa, our findings on connexin expression indicate that these phenotype switches are paralleled by characteristic reciprocal changes in the transcriptional activity of Cx40 and Cx45 genes.

The regenerative potential of the kidney: what can we learn from developmental biology?

Cell turnover in the healthy adult kidney is very slow but the kidney has a strong capacity for regeneration after acute injury. Although many molecular aspects of this process have been clarified, the source of the newly-formed renal epithelial cells is still being debated. Several studies have shown, moreover, that the repair of injured renal epithelium starts from mature tubular cells, which enter into an activated proliferative state characterized by the reappearance of mesenchymal markers detectable during nephrogenesis, thus pointing to a marked plasticity of renal epithelial cells. The regenerative potential of mature epithelial cells might stem from their almost unique morphogenetic process. Unlike other tubular organs, all epithelial and mesenchymal cells in the kidney derive from the same germ layer, the mesoderm. In a fascinating view of vertebrate embryogenesis, the mesoderm might be seen as a cell layer capable of oscillating between epithelial and mesenchymal states, thus acquiring a remarkable plasticity that lends it an extended potential for innovation and a better control of three-dimensional body organization. The renal papilla contains a population of cells with the characteristic of adult stem cells. Mesenchymal stromal stem cells (MSC) have been found to reside in the connective tissue of most organs, including the kidney. Recent studies indicate that the MSC compartment extends throughout the body postnatally as a result of its perivascular location. Developmental biology suggests that this might be particularly true of the kidney and that the papilla might represent the perivascular renal stem cell niche. The perivascular niche hypothesis fits well with the evolving concept of the stem cell niche as an entity of action. It is its dynamic capability that makes the niche concept so important and essential to the feasibility of regenerative medicine.

Adult human CD133/1(+) kidney cells isolated from papilla integrate into developing kidney tubules

Approximately 60,000 patients in the United States are waiting for a kidney transplant due to genetic, immunologic and environmentally caused kidney failure. Adult human renal stem cells could offer opportunities for autologous transplant and repair of damaged organs. Current data suggest that there are multiple progenitor types in the kidney with distinct localizations. In the present study, we characterize cells derived from human kidney papilla and show their capacity for tubulogenesis. In situ, nestin(+) and CD133/1(+) cells were found extensively intercalated between tubular epithelia in the loops of Henle of renal papilla, but not of the cortex. Populations of primary cells from the renal cortex and renal papilla were isolated by enzymatic digestion from human kidneys unsuited for transplant and immuno-enriched for CD133/1(+) cells. Isolated CD133/1(+) papillary cells were positive for nestin, as well as several human embryonic stem cell markers (SSEA4, Nanog, SOX2, and OCT4/POU5F1) and could be triggered to adopt tubular epithelial and neuronal-like phenotypes. Isolated papillary cells exhibited morphologic plasticity upon modulation of culture conditions and inhibition of asymmetric cell division. Labeled papillary cells readily associated with cortical tubular epithelia in co-culture and 3-dimensional collagen gel cultures. Heterologous organ culture demonstrated that CD133/1(+) progenitors from the papilla and cortex became integrated into developing kidney tubules. Tubular epithelia did not participate in tubulogenesis. Human renal papilla harbor cells with the hallmarks of adult kidney stem/progenitor cells that can be amplified and phenotypically modulated in culture while retaining the capacity to form new kidney tubules. This article is part of a Special Issue entitled: Polycystic Kidney Disease.

Nestin is a novel marker for renal tubulointerstitial injury in immunoglobulin A nephropathy

AIM

Nestin, an intermediate filament originally identified as a marker of neural progenitor cells, is transiently expressed in endothelial cells and tubuloepithelial cells during kidney development. However, in adult kidneys, podocytes are the only cells that express nestin. In this study, we examined tubulointerstitial nestin expression in human glomerulonephritis.

METHODS

Renal biopsy specimens obtained from 41 adult patients with immunoglobulin (Ig)A nephropathy were studied. Nestin expression was determined by immunohistochemical staining and estimated by digital image analysis. To identify the phenotype of nestin-positive cells, a double immunofluorescent study was performed for nestin and CD34 (a marker for endothelial cells) or alpha-smooth muscle actin (alpha-SMA, a marker for myofibroblasts).

RESULTS

In normal kidney, nestin expression was restricted to the podocytes and was not detected in tubular cells and tubulointerstitial cells. In contrast, increased nestin expression was observed at tubulointerstitial areas of IgA nephropathy. The degree of tubulointerstitial nestin expression was positively correlated with tubulointerstitial fibrosis (r = 0.546, P < 0.001). The double immunofluorescent study showed that most nestin-positive cells in the interstitium were co-stained with CD34 or alpha-SMA, suggesting that peritubular endothelial cells and tubulointerstitial myofibroblasts express nestin during the progression of tubulointerstitial injury. In addition, strong nestin expression was associated with deterioration of renal function.

CONCLUSION

Nestin expression is associated with tubulointerstitial injury and predicts renal prognosis in IgA nephropathy. Nestin could be a new marker for peritubular endothelial cell injury and tubulointerstitial fibrosis.

Mesenchymal stem cells, used as bait, disclose tissue binding sites: a tool in the search for the niche?

We developed an ex vivo approach characterizing renal mesenchymal stem cell (MSC) adhesion to kidney sections. Specificity of MSC adhesion was confirmed by demonstrating a) 3T3 cells displayed 10-fold lower adhesion, and b) MSC adhesion was CXCR4/stromal-derived factor-1 (SDF-1)-dependent. MSC adhesion was asymmetrical, with postischemic sections exhibiting more than twofold higher adhesion than controls, and showed preference to perivascular areas. Pretreating kidney sections with cyclic arginine-glycine-aspartic acid peptide resulted in increased MSC adhesion (by displacing resident cells), whereas blockade of CXCR4 with AMD3100 and inhibition of alpha4beta1(VLA4) integrin or vascular cellular adhesion molecule-1, reduced adhesion. The difference between adhered cells under cyclic arginine-glycine-aspartic acid peptide-treated and control conditions reflected prior occupancy of binding sites with endogenous cells. The AMD3100-inhibitable fraction of adhesion reflected CXCR4-dependent adhesion, whereas maximal adhesion was interpreted as kidney MSC-lodging capacity. MSC obtained from mice overexpressing caveolin-1 exhibited more robust adhesion than those obtained from knockout animals, consistent with CXCR4 dimerization in caveolae. These data demonstrate a) CXCR4/SDF-1-dependent adhesion increases in ischemia; b) CXCR4/SDF-1 activation is dependent on MSC surface caveolin-1; and c) occupancy of MSC binding sites is decreased, while d) capacity of MSC binding sites is expanded in postischemic kidneys. In conclusion, we developed a cell-bait strategy to unmask renal stem cell binding sites, which may potentially shed light on the MSC niche(s) and its characteristics.

Renal capsule as a stem cell niche

Renal resident stem cells were previously reported within the renal tubules and papillary area. The aim of the present study was to determine whether renal capsules harbor stem cells and whether this pool can be recruited to the renal parenchyma after ischemic injury. We demonstrated the presence of label-retaining cells throughout the renal capsule, at a density of ∼10 cells/mm(2), and their close apposition to the blood vessels. By flow cytometry, in vitro cultured cells derived from the renal capsule were positive for mesenchymal stem cell (MSC) markers (CD29+, vimentin+, Sca-1+, nestin+) but did not express hematopoietic and endothelial stem cell markers. Moreover, renal capsule-derived cells also exhibited self-renewal, clonogenicity, and multipotency in differentiation conditions, all favoring stem cell characteristics and identifying them with MSC. In situ labeling of renal capsules with CM-DiI CellTracker demonstrated in vivo a directed migration of CM-DiI-labeled cells to the ischemic renal parenchyma, with the rate of migration averaging 30 μm/h. Decapsulation of the kidneys during ischemia resulted in a modest, but statistically significant, deceleration of recovery of plasma creatinine compared with ischemic kidneys with intact renal capsule. Comparison of these conditions allows the conclusion that renal capsular cells may contribute ∼25-30% of the recovery from ischemia. In conclusion, the data suggest that the renal capsule may function as a novel stem cell niche harboring MSC capable of participating in the repair of renal injury.

Proliferation and migration of label-retaining cells of the kidney papilla

The kidney papilla contains a population of cells with several characteristics of adult stem cells, including the retention of proliferation markers during long chase periods (i.e., they are label-retaining cells [LRCs]). To determine whether the papillary LRCs generate new cells in the normal adult kidney, we examined cell proliferation throughout the kidney and found that the upper papilla is a site of enhanced cell cycling. Using genetically modified mice that conditionally expressed green fluorescence protein fused to histone 2B, we observed that the LRCs of the papilla proliferated only in its upper part, where they associate with "chains" of cycling cells. The papillary LRCs decreased in number with age, suggesting that the cells migrated to the upper papilla before entering the cell cycle. To test this directly, we marked papillary cells with vital dyes in vivo and found that some cells in the kidney papilla, including LRCs, migrated toward other parts of the kidney. Acute kidney injury enhanced both cell migration and proliferation. These results suggest that during normal homeostasis, LRCs of the kidney papilla (or their immediate progeny) migrate to the upper papilla and form a compartment of rapidly proliferating cells, which may play a role in repair after ischemic injury.

Stem cell therapy for the kidney?

The kidney has a remarkable capacity to regenerate after injury, as it is not a terminally differentiated organ. This regenerative potential is somehow incomplete, however, and as the insult continues, progressive and irreversible scarring results in chronic renal disease. Dialysis and organ transplantation are nonspecific and incomplete methods of renal replacement therapy. Stem cells may provide a more efficacious method for both prevention and amelioration of renal disease of many etiologies. Although many reports have claimed the existence of renal-specific stem or progenitor cells isolated and characterized by various methods, the results have been diverse and debatable. The bone marrow stem cells seem to play a minor role in renal regeneration after acute ischemia in mice through transdifferentiation and cell fusion, but their immediate paracrine effects result in considerable improvements in renal function. Therefore, as in stem cell therapy for the heart, bone marrow-derived stem cells show promise in regeneration of the kidney. Although more research is needed in the basic science of renal regeneration, clinical research in animals has demonstrated the versatility of stem cell therapy. The first phase of clinical trials of bone marrow mesenchymal cells in protection against acute kidney injury may begin shortly. This will enable further exploration of stem cell therapy in renal patients with multiple comorbidities.

Review article: endothelial progenitor cells in renal disease

This brief overview is intended to provide basic information about endothelial progenitors, their definition and consensus markers used for their detection, describe the pathways of their mobilization and homing and highlight the mechanisms and manifestations of their incompetence that occurs in some chronic kidney diseases. Discussion is geared towards the potential role of endothelial progenitor cells in organ regeneration, in particular, in kidney regeneration. The concept we attempted to promote attributes to the incompetence of endothelial progenitor cells in failed regeneration and ensuing progression of chronic kidney disease. This field of inquiry remains insufficiently explored, especially in renal diseases. Promising areas for future exploration are emphasized.

Infiltration of nestin-expressing cells in interstitial fibrosis in chronic cyclosporine nephropathy

BACKGROUND

Nestin-expressing cells play a role in the repair process of injured tissues and organs. This study examined the nestin-expressing cells in interstitial fibrosis in experimental chronic cyclosporine A (CsA) nephropathy.

METHODS

Sprague Dawley rats were treated daily for 1 or 4 weeks with CsA (15 mg/kg) or vehicle (VH; olive oil, 1 mg/kg). Nestin mRNA expression was evaluated with reverse transcriptional-polymerase chain reaction, and nestin-expressing cells were detected immunohistochemically. Localization of nestin was performed with double labeling studies for vimentin, aquaporin 1, or calbindin D28K.

RESULTS

Nestin mRNA expression was not different between VH- and CsA-treated rat kidneys. Nestin-expressing cells were rarely observed in the cortex in the VH group, but CsA-induced renal injury caused an increase in nestin-expressing cells in the cortex in a time-dependent manner. Nestin-expressing cells in the CsA group were localized to the area of interstitial fibrosis, and the number of nestin-expressing cells well correlated with the score of interstitial fibrosis (r=0.898). Nestin-expressing cells did not express vimentin, aquaporin 1, or calbindin D28K.

CONCLUSIONS

CsA-induced renal injury recruits nestin-expressing cells to injured areas, and these cells might be involved in reparative fibrosis in the progression of chronic CsA nephropathy.

Roles of angiopoietins in kidney development and disease

Angiopoietins are a family of growth factors, the best studied being angiopoietin 1 (Ang-1), which binds to and tyrosine-phosphorylates endothelial Tie-2, causing enhanced survival and cell-cell stabilization. Ang-2 and Tie-1 downregulate Ang-1-induced Tie-2 signaling, and angiopoietin actions are further modified by vascular endothelial growth factor A and integrins. Metanephric capillaries express Tie genes, whereas metanephric mesenchyme, maturing tubules, and mature podocytes express Ang-1. Ang-1 null embryos begin to form blood vessels, but subsequent vascular remodeling fails, and analyses of chimeric wild-type/Tie null mutant embryos show that Tie genes are needed for renal endothelial survival. Ang-2 is transiently expressed in renal arterial smooth muscle and mesangial cells, and tubules around adult vasa rectae express Ang-2. Ang-2 null mice have increased pericytes around kidney cortical peritubular capillaries, perhaps an indirect consequence of upregulated Tie-2 signaling. Ang-1 therapies attenuate peritubular capillary loss in adult models of tubulointerstitial disease, although, in one study, this was accompanied by enhanced inflammation and fibrosis. Podocyte-directed Ang-2 transgenic overexpression causes glomerular endothelial apoptosis, downregulated nephrin expression, and increased albuminuria, and glomerular Ang-2 is upregulated in hyperglycemic and immune-mediated glomerulopathies. Thus, angiopoietins affect podocyte as well as glomerular endothelial biology, and imbalanced angiopoietin signaling contributes to glomerular pathobiology.

Nestin expression in repopulating mesangial cells promotes their proliferation

We investigated whether the intermediate filament protein and neural stem cell marker nestin characterizes the glomerular progenitor/reserve cell population immigrating the glomerulus after mesangial cell (MC) injury in the rat (anti-Thy1 nephritis). Nestin expression was investigated by immunohistochemistry and real-time PCR during anti-Thy1 nephritis. Migration and proliferation assays were used to characterize the function of nestin in isolated MCs after nestin knockdown by siRNA. After MC injury during anti-Thy1 nephritis, glomerular nestin was transiently increased during the repopulation phase. At the peak of mesangial proliferation and expansion (day 5) most OX-7-positive MCs expressed nestin largely colocalizing with the activation marker alpha-smooth muscle actin and the proliferation marker PCNA. In contrast to a healthy, non-injured mesangium in vivo, MCs in culture are considered to be in an 'activated, injured state' and express nestin in a generalized distribution with condensed localization around the nucleus as well as intensive staining of cell protrusions such as filopodia. During cell cycle, the percentage of MCs with high nestin levels was increased during S- aupnd G2-phase. Blocking of nestin using specific siRNA resulted in inhibition of cell proliferation but not cell migration. In conclusion, nestin is constitutively expressed in podocytes, but is a marker for repopulating MCs after experimental MC injury in vivo. Nestin promotes MC proliferation in vitro, suggesting a supporting role for nestin during repair reaction.

Glial cell line-derived neurotrophic growth factor increases motility and survival of cultured mesenchymal stem cells and ameliorates acute kidney injury

Glial cell line-derived neurotrophic growth factor (GDNF), a member of the transforming growth factor family, is necessary for renal organogenesis and exhibits changes in expression in models of renal disease. Nestin is an intermediate filament protein originally believed to be a marker of neuroepithelial stem cells and recently proposed as a marker of mesenchymal stem cells (MSC). Having demonstrated the participation of nestin-expressing cells in renoprotection during acute renal ischemia, we hypothesized that growth factors and transcription factors similar to those operating in the nervous system should be also operant in the kidney and may be induced after noxious stimuli, such as an ischemic episode. Using cultured kidney-derived MSC, which abundantly express nestin, we confirmed expression of GDNF by these cells and demonstrated the GDNF-induced expression of GDNF. The cellular expression of nestin paralleled that of GDNF: serum starvation decreased the expression, whereas application of GDNF resulted in a dose-dependent increase in nestin expression. Immunohistochemical and Western blot analyses of kidneys obtained from control and postischemic mice showed that expression of GDNF was much enhanced in the renal cortex, a pattern similar to the previously reported expression of nestin. Based on the observed GDNF-induced GDNF expression, we next explored the effect of supplemental GDNF administered early after ischemia on renal function postischemia. GDNF-treated mice were protected against acute ischemia. To address potential mechanisms of the observed renoprotection, in vitro studies showed that GDNF accelerated MSC migration in a wound-healing assay. Hypoxia did not accelerate, but rather slightly reduced, the motility of MSC and reduced the expression of GDNF in MSC by approximately twofold. Furthermore, GDNF was cytoprotective against oxidative stress-induced apoptotic death of MSC. Collectively, these data establish 1) an autoregulatory circuit of GDNF-induced GDNF expression in renal MSC; 2) induction of GDNF expression in postischemic kidneys; 3) the ability of exogenous GDNF to ameliorate ischemic renal injury; and 4) a possible contribution of GDNF-induced motility and improved survival of MSC to renoprotection.