Human mesenchymal stem cells in rodent whole-embryo culture are reprogrammed to contribute to kidney tissues

Generation of a felinized swine endothelial cell line by expression of feline decay-accelerating factor

Embryonic stem cell research has facilitated the generation of many cell types for the production of tissues and organs for both humans and companion animals. Because ≥30% of pet cats suffer from chronic kidney disease (CKD), xenotransplantation between pigs and cats has been studied. For a successful pig to cat xenotransplant, the immune reaction must be overcome, especially hyperacute rejection. In this study, we isolated the gene for feline decay-accelerating factor (fDAF), an inhibitor of complement proteins, and transfected a swine endothelial cell line with fDAF to "felinize" the pig cells. These fDAF-expressing cells were resistant to feline serum containing anti-pig antibodies, suggesting that felinized pig cells were resistant to hyperacute rejection. Our results suggest that a "felinized" pig kidney can be generated for the treatment of CKD in cats in the future.

Cell-cell interactions driving kidney morphogenesis

The mammalian kidney forms via cell-cell interactions between an epithelial outgrowth of the nephric duct and the surrounding nephrogenic mesenchyme. Initial morphogenetic events include ureteric bud branching to form the collecting duct (CD) tree and mesenchymal-to-epithelial transitions to form the nephrons, requiring reciprocal induction between adjacent mesenchyme and epithelial cells. Within the tips of the branching ureteric epithelium, cells respond to mesenchyme-derived trophic factors by proliferation, migration, and mitosis-associated cell dispersal. Self-inhibition signals from one tip to another play a role in branch patterning. The position, survival, and fate of the nephrogenic mesenchyme are regulated by ECM and secreted signals from adjacent tip and stroma. Signals from the ureteric tip promote mesenchyme self-renewal and trigger nephron formation. Subsequent fusion to the CDs, nephron segmentation and maturation, and formation of a patent glomerular basement membrane also require specialized cell-cell interactions. Differential cadherin, laminin, nectin, and integrin expression, as well as intracellular kinesin and actin-mediated regulation of cell shape and adhesion, underlies these cell-cell interactions. Indeed, the capacity for the kidney to form via self-organization has now been established both via the recapitulation of expected morphogenetic interactions after complete dissociation and reassociation of cellular components during development as well as the in vitro formation of 3D kidney organoids from human pluripotent stem cells. As we understand more about how the many cell-cell interactions required for kidney formation operate, this enables the prospect of bioengineering replacement structures based on these self-organizing properties.

Current strategies and challenges in engineering a bioartificial kidney

Renal replacement therapy was an early pioneer in both extra-corporeal organ replacement and whole organ transplantation. Today, the success of this pioneering work is directly demonstrated in the millions of patients worldwide successfully treated with dialysis and kidney transplantation. However, there remain significant shortcomings to current treatment modalities that limit clinical outcomes and quality of life. To address these problems, researchers have turned to using cell-based therapies for the development of a bioartificial kidney. These approaches aim to recapitulate the numerous functions of the healthy kidney including solute clearance, fluid homeostasis and metabolic and endocrine functions. This review will examine the state-of-the-art in kidney bioengineering by evaluating the various techniques currently being utilized to create a bioartificial kidney. These promising new technologies, however, still need to address key issues that may limit the widespread adoption of cell therapy including cell sourcing, organ scaffolding, and immune response. Additionally, while these new methods have shown success in animal models, it remains to be seen whether these techniques can be successfully adapted for clinical treatment in humans.

Adipose tissue-derived mesenchymal stem cells in long-term dialysis patients display downregulation of PCAF expression and poor angiogenesis activation

We previously demonstrated that mesenchymal stem cells (MSCs) differentiate into functional kidney cells capable of urine and erythropoietin production, indicating that they may be used for kidney regeneration. However, the viability of MSCs from dialysis patients may be affected under uremic conditions. In this study, we isolated MSCs from the adipose tissues of end-stage kidney disease (ESKD) patients undergoing long-term dialysis (KD-MSCs; mean: 72.3 months) and from healthy controls (HC-MSCs) to compare their viability. KD-MSCs and HC-MSCs were assessed for their proliferation potential, senescence, and differentiation capacities into adipocytes, osteoblasts, and chondrocytes. Gene expression of stem cell-specific transcription factors was analyzed by PCR array and confirmed by western blot analysis at the protein level. No significant differences of proliferation potential, senescence, or differentiation capacity were observed between KD-MSCs and HC-MSCs. However, gene and protein expression of p300/CBP-associated factor (PCAF) was significantly suppressed in KD-MSCs. Because PCAF is a histone acetyltransferase that mediates regulation of hypoxia-inducible factor-1α (HIF-1α), we examined the hypoxic response in MSCs. HC-MSCs but not KD-MSCs showed upregulation of PCAF protein expression under hypoxia. Similarly, HIF-1α and vascular endothelial growth factor (VEGF) expression did not increase under hypoxia in KD-MSCs but did so in HC-MSCs. Additionally, a directed in vivo angiogenesis assay revealed a decrease in angiogenesis activation of KD-MSCs. In conclusion, long-term uremia leads to persistent and systematic downregulation of PCAF gene and protein expression and poor angiogenesis activation of MSCs from patients with ESKD. Furthermore, PCAF, HIF-1α, and VEGF expression were not upregulated by hypoxic stimulation of KD-MSCs. These results suggest that the hypoxic response may be blunted in MSCs from ESKD patients.

Directed differentiation of pluripotent stem cells to kidney cells

Regenerative medicine affords a promising therapeutic strategy for the treatment of patients with chronic kidney disease. Nephron progenitor cell populations exist only during embryonic kidney development. Understanding the mechanisms by which these populations arise and differentiate is integral to the challenge of generating new nephrons for therapeutic purposes. Pluripotent stem cells (PSCs), comprising embryonic stem cells, and induced pluripotent stem cells (iPSCs) derived from adults, have the potential to generate functional kidney cells and tissue. Studies in mouse and human PSCs have identified specific approaches to the addition of growth factors, including Wnt and fibroblast growth factor, that can induce PSC differentiation into cells with phenotypic characteristics of nephron progenitor populations with the capacity to form kidney-like structures. Although significant progress has been made, further studies are necessary to confirm the production of functional kidney cells and to promote their three-dimensional organization into bona fide kidney tissue. Human PSCs have been generated from patients with kidney diseases, including polycystic kidney disease, Alport syndrome, and Wilms tumor, and may be used to better understand phenotypic consequences of naturally occurring genetic mutations and to conduct "clinical trials in a dish". The capability to generate human kidney cells from PSCs has significant translational applications, including the bioengineering of functional kidney tissue, use in drug development to test compounds for efficacy and toxicity, and in vitro disease modeling.

Kidney regeneration with stem cells: an overview

BACKGROUND

Kidney regeneration is currently gaining considerable attention in place of kidney dialysis as the ultimate therapeutic strategy for renal failure. However, because of anatomical complications, the kidney is believed to be the hardest organ to regenerate. Such a complicated organ is virtually impossible to imagine being completely rebuilt de novo from stem cells. Nevertheless, several research groups are attempting this large challenge.

SUMMARY

There are 4 major strategies for de novo kidney regeneration from stem cells. These strategies include the use of: (i) a decellularized cadaveric scaffold, (ii) blastocyst decomplementation, (iii) a nephrogenic niche for growing a xeno-embyro, and (iv) self-assembly potential. All of these strategies may be applicable in the clinical setting, but a substantial preparation period appears to be required.

KEY MESSAGES

Although many outstanding problems remain for kidney regeneration, including ethical issues and the formation of chimeric structures, trials provide hope for dialysis patients and kidney regeneration is expected to be a reality in the future.

Mouse embryonic development in a serum-free whole embryo culture system

Mid-gestation stage mouse embryos were cultured utilizing a serum-free culture medium prepared from commercially available stem cell media supplements in an oxygenated rolling bottle culture system. Mouse embryos at E10.5 were carefully isolated from the uterus with intact yolk sac and in a process involving precise surgical maneuver the embryos were gently exteriorized from the yolk sac while maintaining the vascular continuity of the embryo with the yolk sac. Compared to embryos prepared with intact yolk sac or with the yolk sac removed, these embryos exhibited superior survival rate and developmental progression when cultured under similar conditions. We show that these mouse embryos, when cultured in a defined medium in an atmosphere of 95% O2 / 5% CO2 in a rolling bottle culture apparatus at 37 °​C for 16-40 hr, exhibit morphological growth and development comparable to the embryos developing in utero. We believe this method will be useful for investigators needing to utilize whole embryo culture to study signaling interactions important in embryonic organogenesis.

Advances in tissue engineering through stem cell-based co-culture

Stem cells are the future in tissue engineering and regeneration. In a co-culture, stem cells not only provide a target cell source with multipotent differentiation capacity, but can also act as assisting cells that promote tissue homeostasis, metabolism, growth and repair. Their incorporation into co-culture systems seems to be important in the creation of complex tissues or organs. In this review, critical aspects of stem cell use in co-culture systems are discussed. Direct and indirect co-culture methodologies used in tissue engineering are described, along with various characteristics of cellular interactions in these systems. Direct cell-cell contact, cell-extracellular matrix interaction and signalling via soluble factors are presented. The advantages of stem cell co-culture strategies and their applications in tissue engineering and regenerative medicine are portrayed through specific examples for several tissues, including orthopaedic soft tissues, bone, heart, vasculature, lung, kidney, liver and nerve. A concise review of the progress and the lessons learned are provided, with a focus on recent developments and their implications. It is hoped that knowledge developed from one tissue can be translated to other tissues. Finally, we address challenges in tissue engineering and regenerative medicine that can potentially be overcome via employing strategies for stem cell co-culture use.

Bone marrow-derived mesenchymal stem cells protect against cisplatin-induced acute kidney injury in rats by inhibiting cell apoptosis

Acute kidney injury (AKI) is a common syndrome with a high mortality and morbidity rate. Recent developments in stem cell research have shown great promise for the treatment of AKI. The aim of this study was to investigate the therapeutic potential and anti-apoptotic mechanisms of action of bone marrow-derived mesenchymal stem cells (BM-MSCs) in the treatment of AKI induced by cisplatin in vivo and in vitro. In vivo, adult male Sprague-Dawley rats (n=24) were administered BM-MSCs intravenously one day after cisplatin injection. The rats were sacrificed four days after the cisplatin injection and the effects of BM-MSCs on cisplatin-induced AKI, as well as the anti-apoptotic mechanisms involved were investigated. In vitro, NRK-52E cells, a rat renal proximal tubular cell line, were incubated in conditioned medium or complete medium in the presence or absence of cisplatin, followed by cell proliferation and apoptosis assays. The infusion of BM-MSCs preserved renal function, ameliorated renal tubular lesions, reduced apoptosis and accelerated tubular cell regeneration in the rats with cisplatin-induced AKI. The infusion of BM-MSCs also inhibited the activation of two mitogen-activated protein kinases, p38 and ERK, downregulated the expression of Bax and cleaved caspase-3, and upregulated the expression of Bcl-2. BM-MSC-conditioned medium improved NRK-52E cell viability and inhibited apoptosis. In conclusion, our results demonstrate that injecting rats with BM-MSCs protects renal function and structure in cisplatin-induced AKI by inhibiting cell apoptosis in vivo. BM-MSC-conditioned medium protects renal cells from apoptosis induced by cisplatin in vitro. Hence, the infusion of BM-MSCs should be considered as a possible therapeutic strategy for the treatment of AKI.

Renal anemia: from incurable to curable

Renal anemia has been recognized as a characteristic complication of chronic kidney disease. Although many factors are involved in renal anemia, the predominant cause of renal anemia is a relative deficiency in erythropoietin (EPO) production. To date, exogenous recombinant human (rh)EPO has been widely used as a powerful drug for the treatment of patients with renal anemia. Despite its clinical effectiveness, a potential risk for increased mortality has been suggested in patients who receive rhEPO, in addition to the economic burden of rhEPO administration. The induction of endogenous EPO is another therapeutic approach that might have advantages over rhEPO administration. However, the physiological and pathophysiological regulation of EPO are not fully understood, and this lack of understanding has hindered the development of an endogenous EPO inducer. In this review, we will discuss the current treatment for renal anemia and its drawbacks, provide an overview of EPO regulation in healthy and diseased conditions, and propose future directions for therapeutic trials that more directly target the underlying pathophysiology of renal anemia.

Organogenesis for kidney regeneration

PURPOSE OF REVIEW

The kidney has an elaborate and complicated structure comprising several cell types. Damage or destruction of the kidney thus necessitates reconstruction of all the component cell types to regenerate a functional three-dimensional renal structure. Therefore, despite all the recent advances in our understanding and technical approaches to stem cell and developmental biology, the anatomical complexity of the renal system makes de-novo kidney regeneration the most difficult challenge for organ regenerative therapy.

RECENT FINDINGS

To build a transplantable neo-kidney, some investigators propose using organogenesis. We suggest the metanephros of the developing kidney and blastocyst complementation can potentially generate a whole kidney with the required three-dimensional structure and renal function to produce urine and erythropoietin. In addition, some researchers are investigating the in-vitro differentiation of pluripotent stem cells into mature renal cells for in-vivo use.

SUMMARY

We review the current challenges to making a transplantable neo-kidney using stem cells.

Cellular interactions via conditioned media induce in vivo nephron generation from tubular epithelial cells or mesenchymal stem cells

There are some successful reports of kidney generation by utilizing the natural course of kidney development, namely, the use of an artificially treated metanephros, blastocyst or ureteric bud. Under a novel concept of cellular interactions via conditioned media (CMs), we have attempted in vivo nephron generation from tubular epithelial cells (TECs) or mesenchymal stem cells (MSCs). Here we used 10× CMs of vascular endothelial cells (VECs) and TECs, which is the first to introduce a CM into the field of organ regeneration. We first present stimulative cross-talks induced by these CMs between VECs and TECs on cell proliferation and morphological changes. In MSCs, TEC-CM suppressed these changes, however, induced cytokeratin expression, indicating the differentiation of MSCs into TECs. As a result, glomerular and tubular structures were created following the implantation of TECs or MSCs with both CMs. Our findings suggest that the cellular interactions via CMs might induce in vivo nephron generation from TECs or MSCs. As a promoting factor, CMs could also be applied to the regeneration of other organs and tissues.

iPS cell technology-based research for the treatment of diabetic nephropathy

Regenerative medicine strategies using induced pluripotent stem (iPS) cells are among the candidate approaches to treat diabetic nephropathy caused by type 1 diabetes. Cell transplantation therapy and disease modeling with patient-derived iPS cells should be examined for diabetic renal disease. Considerable work already has been performed with regard to the generation of renal lineage cells from mouse embryonic stem cells, however, few reports have described research with human embryonic stem cells or iPS cells. Further elucidation of the mechanisms of kidney development and establishing the method for directed differentiation from human iPS cells into renal lineage cells will be required for the development of iPS cell technology-based treatment for diabetic nephropathy.

Human embryonic stem cells differentiate into functional renal proximal tubular-like cells

Renal cells are used in basic research, disease models, tissue engineering, drug screening, and in vitro toxicology. In order to provide a reliable source of human renal cells, we developed a protocol for the differentiation of human embryonic stem cells into renal epithelial cells. The differentiated stem cells expressed markers characteristic of renal proximal tubular cells and their precursors, whereas markers of other renal cell types were not expressed or expressed at low levels. Marker expression patterns of these differentiated stem cells and in vitro cultivated primary human renal proximal tubular cells were comparable. The differentiated stem cells showed morphological and functional characteristics of renal proximal tubular cells, and generated tubular structures in vitro and in vivo. In addition, the differentiated stem cells contributed in organ cultures for the formation of simple epithelia in the kidney cortex. Bioreactor experiments showed that these cells retained their functional characteristics under conditions as applied in bioartificial kidneys. Thus, our results show that human embryonic stem cells can differentiate into renal proximal tubular-like cells. Our approach would provide a source for human renal proximal tubular cells that are not affected by problems associated with immortalized cell lines or primary cells.

Advancing pig cloning technologies towards application in regenerative medicine

Regenerative medicine is expected to make a significant contribution by development of novel therapeutic treatments for intractable diseases and for improving the quality of life of patients. Many advances in regenerative medicine, including basic and translational research, have been developed and tested in experimental animals; pigs have played an important role in various aspects of this work. The value of pigs as a model species is being enhanced by the generation of specially designed animals through cloning and genetic modifications, enabling more sophisticated research to be performed and thus accelerating the clinical application of regenerative medicine. This article reviews the significant aspects of the creation and application of cloned and genetically modified pigs in regenerative medicine research and considers the possible future directions of the technology. We also discuss the importance of reproductive biology as an interface between basic science and clinical medicine.

Comparison of methods for whole-organ decellularization in tissue engineering of bioartificial organs

Organ transplantation is now a well-established procedure for the treatment of end-stage organ failure due to various causes, but is a victim of its own success in that there is a growing disparity in numbers between the donor organ pool available for transplantation and the patients eligible for such a procedure; hence, an alternative solution to the limited donor organ pool is both desirable and necessary. Tissue engineering is an interdisciplinary field that applies the principles of engineering and life sciences toward the development of functional replacement tissues for clinical use. A recent innovation in tissue and organ engineering is the technique of whole-organ decellularization, which allows the production of complex three-dimensional extracellular matrix (ECM) bioscaffolds of the entire organ with preservation of the intrinsic vascular network. These bioscaffolds can then be recellularized to create potentially functional organ constructs as a regenerative medicine strategy for organ replacement. We review the current applications and methods in using xenogeneic whole-organ ECM scaffolds to create potentially functional bioartificial organ constructs for surgical implantation, and present a comparison of specific trends within this new and developing technique.

Xenotransplanted embryonic kidney provides a niche for endogenous mesenchymal stem cell differentiation into erythropoietin-producing tissue

Recent findings have demonstrated that stem cells can differentiate into mature tissue when supplied with a niche containing factors identical to those in the normal developmental program. A niche for the development of an organ can be provided by xenotransplantation of a similar developing organ. However, this process has many technical, safety, and ethical concerns. Here, we established xenotransplantation models that control endogenous mesenchymal stem cell (MSC) differentiation into mature erythropoietin (EPO)-producing tissue in a niche provided by a developing xenometanephros. Transplantation of rat metanephroi into mouse omentum, and similarly pig metanephroi into cat omentum, led to the recruitment of host cells and EPO production. EPO-expressing cells were not differentiated from integrating vessels because they did not coexpress endothelial markers (Tie-2 and VE-cadherin). Instead, EPO-expressing cells were shown to be derived from circulating host cells, as shown by enhanced green fluorescent protein (EGFP) expression in the grown transplants of chimeric mice bearing bone marrow from a transgenic mouse expressing EGFP under the control of the EPO promoter. These results suggest that donor cell recruitment and differentiation in a xenotransplanted developing organ may be consistent between species. The cells responsible for EPO expression were identified as MSCs by injecting human bone marrow-derived MSCs and endothelial progenitor cells into NOD/SCID mice. Furthermore, using metanephroi from transgenic ER-E2F1 suicide-inducible mice, the xenotissue component could be eliminated, leaving autologous EPO-producing tissue. Our findings may alleviate adverse effects due to long-lasting immunosuppression and help mitigate ethical concerns.

De novo kidney regeneration with stem cells

Recent studies have reported on techniques to mobilize and activate endogenous stem-cells in injured kidneys or to introduce exogenous stem cells for tissue repair. Despite many recent advantages in renal regenerative therapy, chronic kidney disease (CKD) remains a major cause of morbidity and mortality and the number of CKD patients has been increasing. When the sophisticated structure of the kidneys is totally disrupted by end stage renal disease (ESRD), traditional stem cell-based therapy is unable to completely regenerate the damaged tissue. This suggests that whole organ regeneration may be a promising therapeutic approach to alleviate patients with uncured CKD. We summarize here the potential of stem-cell-based therapy for injured tissue repair and de novo whole kidney regeneration. In addition, we describe the hurdles that must be overcome and possible applications of this approach in kidney regeneration.

In vivo maturation of functional renal organoids formed from embryonic cell suspensions

The shortage of transplantable organs provides an impetus to develop tissue-engineered alternatives. Producing tissues similar to immature kidneys from simple suspensions of fully dissociated embryonic renal cells is possible in vitro, but glomeruli do not form in the avascular environment. Here, we constructed renal organoids from single-cell suspensions derived from E11.5 kidneys and then implanted these organoids below the kidney capsule of a living rat host. This implantation resulted in further maturation of kidney tissue, formation of vascularized glomeruli with fully differentiated capillary walls, including the slit diaphragm, and appearance of erythropoietin-producing cells. The implanted tissue exhibited physiologic functions, including tubular reabsorption of macromolecules, that gained access to the tubular lumen on glomerular filtration. The ability to generate vascularized nephrons from single-cell suspensions marks a significant step to the long-term goal of replacing renal function by a tissue-engineered kidney.

Application of regenerative medicine for kidney diseases

Following recent advancements of stem cell research, the potential for organ regeneration using somatic stem cells as an ultimate therapy for organ failure has increased. However, anatomically complicated organs such as the kidney and liver have proven more refractory to stem cell-based regenerative techniques. At present, kidney regeneration is considered to require one of two approaches depending on the type of renal failure, namely acute renal failure (ARF) and chronic renal failure (CRF).The kidney has the potential to regenerate itself provided that the damage is not too severe and the kidney's structure remains intact. Regenerative medicine for ARF should therefore aim to activate or support this potent. In cases of the irreversible damage to the kidney, which is most likely in patients with CRF undergoing long-term dialysis, self-renewal is totally lost. Thus, regenerative medicine for CRF will likely involve the establishment of a functional whole kidney de novo. This article reviews the challenges and recent advances in both approaches and discusses the potential approach of these novel strategies for clinical application.

The KIDSTEM European Research Training Network: Developing a Stem Cell Based Therapy to Replace Nephrons Lost through Reflux Nephropathy

The incidence and prevalence of end stage renal disease (ESRD) continues to grow worldwide at a rate that is far in excess of the growth rate of the general population. In children and young adults the most common cause of ESRD is vesicoureteric reflux (VUR), a condition where urine from the bladder re-enters the kidney, predisposing to pyelonephritis, renal scarring, and in the most severe cases, ESRD. However, there is usually a time-window of several years from initial diagnosis of VUR to the development of ESRD, which presents an opportunity to design therapies aimed at preventing disease progression by repairing renal tissue before it becomes nonfunctional. Advances in our understanding of kidney development coupled with recent progress in stem cell science and tissue engineering, present an unprecedented opportunity to design a stem cell-based therapy for this clinical problem. KIDSTEM will investigate the properties of several different stem cell types (kidney stem cells, embryonic stem cells, amniotic fluid stem cells and mesenchymal stem cells) to determine which is most appropriate for the generation of functional renal tissue promoted by specifically designed biomaterials to facilitate the generation of functional nephrons.

Developmental engineering the kidney: leveraging principles of morphogenesis for renal regeneration

Multiple methodological approaches are currently under active development for application in tissue engineering and regenerative medicine of tubular and solid organs. Most recently, developmental engineering (TE/RM), or the leveraging of embryonic and morphological paradigms to recapitulate aspects of organ development, has been proposed as a strategy for the sequential, iterative de novo assembly of tissues and organs as discrete developmental modules ex vivo, prior to implantation in vivo. In this article, we focus on the kidney to highlight in detail how principles of developmental biology are impacting approaches to TE of this complex solid organ. Ultimately, such methodologies may facilitate the establishment of clinically relevant therapeutic strategies for regeneration of renal structure and function, greatly impacting treatment regimens for chronic kidney disease.

Bone marrow cells contribute to tubular epithelium regeneration following acute kidney injury induced by mercuric chloride

BACKGROUND & OBJECTIVES

Acute tubular necrosis (ATN) caused by renal ischaemia, renal hypo-perfusion, or nephrotoxic substances is the most common form of acute kidney injury (AKI). There are a few treatment options for this life-threatening disease and the mortality rate exceeds 50 per cent. In critical cases of AKI the only option is renal transplantation. In the present study we evaluated whether bone marrow cells (BMCs) are involved in regeneration of kidney tubules following acute tubular necrosis in the mouse.

METHODS

Six to eight week old C57BL6/J and congenic enhanced green fluorescence protein (eGFP) mice were used. The relative contributions of eGFP-expressing BMCs were compared in two different approaches to kidney regeneration in the mercuric chloride (HgCl 2 )-induced mouse model of AKI: induced engraftment and forced engraftment. In vitro differentiation of lineage-depleted (Lin - ) BMCs into renal epithelial cells was also studied.

RESULTS

In the forced engraftment approach, BMCs were found to play a role in the regeneration of tubules of renal cortex and outer medulla regions. About 70 per cent of donor-derived cells expressed megalin. In vitro culture revealed that Lin - BMCs differentiated into megalin, E-cadherin and cytokeratin-19 (CK-19) expressing renal epithelial cells.

INTERPRETATION & CONCLUSIONS

The present results demonstrate that Lin - BMCs may contribute in the regeneration of renal tubular epithelium of HgCl 2 -induced AKI. This study may also suggest a potential role of BMCs in treating AKI.

A Simplified In Vitro Teratoma Assay for Pluripotent Stem Cells Injected Into Rodent Fetal Organs

Teratoma formation assays are established methods for evaluating the pluripotency of embryonic stem (ES) cells and induced pluripotent stem (iPS) cells. Teratoma formation in immunodeficient mice takes approximately 2 months. Here, we have developed a novel assay system for developing teratomas in vitro from ES cells and iPS cells in a short period. In vitro culture of ES, iPS, and mesenchymal stem cells (MSCs) in fetal rat metanephroi for 1 week resulted in distinct cell-dependent distribution patterns: Pluripotent cells (ES and iPS cells) formed aggregated masses, whereas MSCs showed disseminated distribution. The aggregated masses that had developed from ES cells and iPS cells after 2 weeks of culture comprised teratomas, though they were largely composed of immature components. Furthermore, in vitro organ culture for 1 week followed by relay transplantation into immunodeficient mice resulted in considerably rapid growing teratomas (teratomas developed in 4 weeks) having similar pathological features as of the teratomas developed using conventional 7-week in vivo teratoma formation assays. In addition, the initial cell number required in the in vitro assay was 1 × 10³ cells, which was about 1% of the number of cells required in the conventional in vivo teratoma formation assays. These results suggest that the in vitro teratoma assay is a rapid and convenient screening system and might be an alternative method for developing teratomas for investigating the pluripotency of ES cells and iPS cells.

The effect of metanephros transplantation on blood pressure in anephric rats with induced acute hypotension

BACKGROUND

The kidney is an important organ for maintaining blood pressure. We have previously reported that transplanted metanephroi can reproduce some kidney functions. The aim of the present study was to determine the metabolic function of transplanted metanephroi with particular reference to maintaining blood pressure.

METHODS

Male Wistar rats were transplanted with metanephroi (transplanted group, n = 28), following unilateral nephrectomy. For comparison, we performed unilateral nephrectomy without transplantation in 32 rats (non-transplanted group, n = 18; haeminephrectomy control group, n = 14). The remaining kidney was removed 2 weeks after the initial operation, while control rats had a sham operation. Hypotension was induced by intravenous infusion of diltiazem hydrochloride or rapid withdrawal of blood. Mean arterial blood pressure (MAP) was invasively monitored and plasma renin activity (PRA) was analysed at multiple time points. Renin expression by metanephroi was evaluated by real-time polymerase chain reaction and immunohistochemistry.

RESULTS

Metanephroi in the transplanted group expressed renin messenger RNA. Metanephros transplantation significantly raised PRA and maintained MAP compared with the non-transplanted group. No significant differences between the transplanted and control groups were found with respect to PRA or MAP. PRA was positively correlated with metanephroi weight as well as MAP in the transplanted group.

CONCLUSION

The present study shows that transplantation of metanephroi produces PRA and contributes to raising MAP in a rat model of acute hypotension.

Regenerative medicine strategies

Applications of regenerative medicine technology may offer novel therapies for patients with injuries, end-stage organ failure, or other clinical problems. Currently, patients suffering from diseased and injured organs can be treated with transplanted organs. However, there is a severe shortage of donor organs that is worsening yearly as the population ages and new cases of organ failure increase. Scientists in the field of regenerative medicine and tissue engineering are now applying the principles of cell transplantation, material science, and bioengineering to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. The stem cell field is also advancing rapidly, opening new avenues for this type of therapy. For example, therapeutic cloning and cellular reprogramming may one day provide a potentially limitless source of cells for tissue engineering applications. While stem cells are still in the research phase, some therapies arising from tissue engineering endeavors have already entered the clinical setting successfully, indicating the promise regenerative medicine holds for the future.

Human amniotic fluid stem cell preconditioning improves their regenerative potential

Human amniotic fluid stem (hAFS) cells, a novel class of broadly multipotent stem cells that share characteristics of both embryonic and adult stem cells, have been regarded as promising candidate for cell therapy. Taking advantage by the well-established murine model of acute kidney injury (AKI), we studied the proregenerative effect of hAFS cells in immunodeficient mice injected with the nephrotoxic drug cisplatin. Infusion of hAFS cells in cisplatin mice improved renal function and limited tubular damage, although not to control level, and prolonged animal survival. Human AFS cells engrafted injured kidney predominantly in peritubular region without acquiring tubular epithelial markers. Human AFS cells exerted antiapoptotic effect, activated Akt, and stimulated proliferation of tubular cells possibly via local release of factors, including interleukin-6, vascular endothelial growth factor, and stromal cell-derived factor-1, which we documented in vitro to be produced by hAFS cells. The therapeutic potential of hAFS cells was enhanced by cell pretreatment with glial cell line-derived neurotrophic factor (GDNF), which markedly ameliorated renal function and tubular injury by increasing stem cell homing to the tubulointerstitial compartment. By in vitro studies, GDNF increased hAFS cell production of growth factors, motility, and expression of receptors involved in cell homing and survival. These findings indicate that hAFS cells can promote functional recovery and contribute to renal regeneration in AKI mice via local production of mitogenic and prosurvival factors. The effects of hAFS cells can be remarkably enhanced by GDNF preconditioning.

Metanephros transplantation inhibits the progression of vascular calcification in rats with adenine-induced renal failure

BACKGROUND/AIM

Recent research has shown that transplanted metanephroi form primitive vascularized kidneys with histologically recognizable renal features. The aim of the present study was to determine the metabolic function of transplanted metanephroi in rats with chronic renal failure (CRF), with particular reference to secondary hyperparathyroidism and vascular calcification.

METHODS

CRF was induced in 11-week-old male Wistar rats by maintaining them on a 0.75% adenine diet for 4 weeks, followed by normal diet for an additional 2 weeks. At the end of adenine loading, whole metanephroi from embryonic day 15 rats were transplanted into the omentum and epididymis of the transplantation group. Vascular calcification was evaluated 2 weeks after metanephroi transplantation.

RESULTS

Metanephros transplantation significantly reduced vascular calcium and phosphorus content and suppressed the progression of vascular calcification as indicated by von Kossa staining of the media of the thoracic aorta. However, no significant differences between the adenine-fed control and transplantation groups were found regarding the serum levels of 1,25(OH)2D3, calcium or phosphorus or the calcium × phosphorus product.

CONCLUSION

The present study has shown that transplantation of metanephroi suppresses the progression of vascular calcification via a mechanism that is independent of calcium-phosphorus dynamics.

Integration potential of mouse and human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a multipotent cell population which has been described to exert renoprotective and regenerative effects in experimental models of kidney injury. Several lines of evidence indicate that MSCs also have the ability to contribute to nephrogenesis, suggesting that the cells can be employed in stem cell-based applications aimed at de novo renal tissue generation. In this study we re-evaluate the capacity of mouse and human bone marrow-derived MSCs to contribute to the development of renal tissue using a novel method of embryonic kidney culture. Although MSCs show expression of some genes involved in renal development, their contribution to nephrogenesis is very limited in comparison to other stem cell types tested. Furthermore, we found that both mouse and human MSCs have a detrimental effect on the ex vivo development of mouse embryonic kidney, this effect being mediated through a paracrine action. Stimulation with conditioned medium from a mouse renal progenitor population increases the ability of mouse MSCs to integrate into developing renal tissue and prevents the negative effects on kidney development, but does not appear to enhance their ability to undergo nephrogenesis.

Defining and redefining the nephron progenitor population

It has long been appreciated that the mammalian kidney arises via reciprocal interactions between an epithelial ureteric epithelium and the surrounding metanephric mesenchyme. More recently, lineage tracing has confirmed that the portion of the metanephric mesenchyme closest to the advancing ureteric tips, the cap mesenchyme, represents the progenitor population for the nephron epithelia. This Six2(+)Cited1(+) population undergoes self-renewal throughout nephrogenesis while retaining the potential to epithelialize. In contrast, the Foxd1(+) portion of the metanephric mesenchyme shows no epithelial potential, developing instead into the interstitial, perivascular, and possibly endothelial elements of the kidney. The cap mesenchyme rests within a nephrogenic niche, surrounded by the stroma and the ureteric tip. While the role of Wnt signaling in nephron induction is known, there remains a lack of clarity over the intrinsic and extrinsic regulation of cap mesenchyme specification, self-renewal, and nephron potential. It is also not known what regulates cessation of nephrogenesis, but there is no nephron generation in response to injury during the postnatal period. In this review, we will examine what is and is not known about this nephron progenitor population and discuss how an increased understanding of the regulation of this population may better explain the observed variation in final nephron number and potentially facilitate the reinitiation or prolongation of nephron formation.

Differentiation of podocyte and proximal tubule-like cells from a mouse kidney-derived stem cell line

In this study we have shown that the papilla of the mouse kidney contains a population of Pax2+ cells that are detectable from the early postnatal period through to adulthood. Lineage analysis suggests that some of these Pax2+ cells are derived from the metanephric mesenchyme, a population of progenitor cells that gives rise to the nephrons during kidney organogenesis. Here we describe a method for isolating and culturing the Pax2+ population, and demonstrate that some cells within this population are multipotent stem cells, as they are clonogenic and appear to undergo unlimited self-renewal. Further, under appropriate culture conditions, these stem cells can differentiate to generate renal cell types, such as podocyte- and proximal tubule-like cells, and are also able to generate nonrenal cell types, such as adipocytes and osteocytes. The availability of a kidney-derived multipotent stem cell line with the potential to generate podocytes and proximal tubule cells in culture will expedite progress in understanding the biology of these important renal cell types, and will be a useful tool in toxicological studies and drug discovery.

Potential use of stem cells for kidney regeneration

Significant advances have been made in stem cell research over the past decade. A number of nonhematopoietic sources of stem cells (or progenitor cells) have been identified, including endothelial stem cells and neural stem cells. These discoveries have been a major step toward the use of stem cells for potential clinical applications of organ regeneration. Accordingly, kidney regeneration is currently gaining considerable attention to replace kidney dialysis as the ultimate therapeutic strategy for renal failure. However, due to anatomic complications, the kidney is believed to be the hardest organ to regenerate; it is virtually impossible to imagine such a complicated organ being completely rebuilt from pluripotent stem cells by gene or chemical manipulation. Nevertheless, several groups are taking on this big challenge. In this manuscript, current advances in renal stem cell research are reviewed and their usefulness for kidney regeneration discussed. We also reviewed the current knowledge of the emerging field of renal stem cell biology.

Proliferative capacity of stem/progenitor-like cells in the kidney may associate with the outcome of patients with acute tubular necrosis

Animal studies indicate that adult renal stem/progenitor cells can undergo rapid proliferation in response to renal injury, but whether the same is true in humans is largely unknown. To examine the profile of renal stem/progenitor cells responsible for acute tubular necrosis in human kidney, double and triple immunostaining was performed using proliferative marker and stem/progenitor protein markers on sections from 10 kidneys with acute tubular necrosis and 4 normal adult kidneys. The immunopositive cells were recorded using 2-photon confocal laser scanning microscopy. We found that dividing cells were present in the tubules of the cortex and medulla, as well as the glomerulus in normal human kidney. Proliferative cells in the parietal layer of Bowman capsule expressed CD133, and dividing cells in the tubules expressed immature cell protein markers paired box gene 2, vimentin, and nestin. After acute tubular necrosis, Ki67-positive cells in the cortex tubules significantly increased compared with normal adult kidney. These Ki67-positive cells expressed CD133 and paired box gene 2, but not the cell death marker, activated caspase-3. In addition, the number of dividing cells increased significantly in patients with acute tubular necrosis who subsequently recovered, compared with patients with acute tubular necrosis who consequently developed protracted acute tubular necrosis or died. Our data suggest that renal stem/progenitor cells may reside not only in the parietal layer of Bowman capsule but also in the cortex and medulla in normal human kidney, and the proliferative capacity of renal stem/progenitor cells after acute tubular necrosis may be an important determinant of a patient's outcome.

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.

Tissue engineering and stem cells: basic principles and applications in urology

To overcome problems of damaged urinary tract tissues and complications of current procedures, tissue engineering (TE) techniques and stem cell (SC) research have achieved great progress. Although diversity of techniques is used, urologists should know the basics. We carried out a literature review regarding the basic principles and applications of TE and SC technologies in the genitourinary tract. We carried out MEDLINE/PubMed searches for English articles until March 2010 using a combination of the following keywords: bladder, erectile dysfunction, kidney, prostate, Peyronie's disease, stem cells, stress urinary incontinence, testis, tissue engineering, ureter, urethra and urinary tract. Retrieved abstracts were checked, and full versions of relevant articles were obtained. Scientists have achieved great advances in basic science research. This is obvious by the tremendous increase in the number of publications. We divided this review in two topics; the first discusses basic science principles of TE and SC, whereas the second part delineates current clinical applications and advances in urological literature. TE and SC applications represent an alternative resource for treating complicated urological diseases. Despite the paucity of clinical trials, the promising results of animal models and continuous work represents the hope of treating various urological disorders with this technology.

Mesenchymal stem cell therapy for chronic renal failure

IMPORTANCE OF THE FIELD

Chronic kidney disease (CKD) has become a worldwide public health problem. Renal transplantation is the treatment of choice for end-stage renal disease, but is limited by a small number of organ donors and the immune barrier. To overcome these problems, new therapeutic strategies for tissue repair have recently emerged.

AREAS COVERED IN THIS REVIEW

We discuss the therapeutic potential of mesenchymal stem cells (MSCs) in kidney injury and examine the latest reports providing evidence supporting MSC efficacy in the treatment of chronic renal failure (CRF).

WHAT THE READER WILL GAIN

MSCs improve histological and functional outcomes in various CRF model systems. Paracrine effects rather than transdifferentiation might result in the prevention of progressive renal failure. In addition, MSCs can reprogram kidney cell differentiation, and modulate neo-kidney transplantation in CRF.

TAKE HOME MESSAGE

Although many practical problems remain to be addressed, treatment with MSCs will enter the mainstream of CRF treatment.

Effects of extremely low-frequency magnetic field on growth and differentiation of human mesenchymal stem cells

Human Mesenchymal Stem Cells (hMSCs) were exposed to a developed extremely low-frequency (ELF) magnetic fields (50 Hz ,20 mT ELF) system to evaluate whether exposure to (ELF) magnetic fields affects growth, metabolism, and differentiation of hMSCs. MTT method was used to determine the growth and metabolism of hMSCs following exposure to ELF magnetic fields. Na(+)/K(+) concentration and osmolality of extracellular were measured after exposured culture. Alkaline phosphatase (ALP) assay and Calcium assay, ALP staining, and Alizarin red staining were performed to evaluate the osteogenic differentiation of hMSCs under the ELF magnetic field exposure. In these experiments, the cells were exposed to ELF for up to 23 days. The results showed that exposure to ELF magnetic field could inhibit the growth and metabolism of hMSC, but have no significant effect on differentiation of hMSCs. These results suggested that ELF magnetic field may influence the early development of hMSCs related adult cells.

Stem cells derived from human amniotic fluid contribute to acute kidney injury recovery

Stem cells isolated from human amniotic fluid are gaining attention with regard to their therapeutic potential. In this work, we investigated whether these cells contribute to tubular regeneration after experimental acute kidney injury. Cells expressing stem cell markers with multidifferentiative potential were isolated from human amniotic fluid. The regenerative potential of human amniotic fluid stem cells was compared with that of bone marrow-derived human mesenchymal stem cells. We found that the intravenous injection of 3.5 × 10(5) human amniotic fluid stem cells into nonimmune-competent mice with glycerol-induced acute kidney injury was followed by rapid normalization of renal function compared with injection of mesenchymal stem cells. Both stem cell types showed enhanced tubular cell proliferation and reduced apoptosis. Mesenchymal stem cells were more efficient in inducing proliferation than amniotic fluid-derived stem cells, which, in contrast, were more antiapoptotic. Both cell types were found to accumulate within the peritubular capillaries and the interstitium, but amniotic fluid stem cells were more persistent than mesenchymal stem cells. In vitro experiments demonstrated that the two cell types produced different cytokines and growth factors, suggesting that a combination of different mediators is involved in their biological actions. These results suggest that the amniotic fluid-derived stem cells may improve renal regeneration in acute kidney injury, but they are not more effective than mesenchymal stem cells.

Achievements and challenges in bioartificial kidney development

Bioartificial kidneys (BAKs) combine a conventional hemofilter in series with a bioreactor unit containing renal epithelial cells. The epithelial cells derived from the renal tubule should provide transport, metabolic, endocrinologic and immunomodulatory functions. Currently, primary human renal proximal tubule cells are most relevant for clinical applications. However, the use of human primary cells is associated with many obstacles, and the development of alternatives and an unlimited cell source is one of the most urgent challenges. BAKs have been applied in Phase I/II and Phase II clinical trials for the treatment of critically ill patients with acute renal failure. Significant effects on cytokine concentrations and long-term survival were observed. A subsequent Phase IIb clinical trial was discontinued after an interim analysis, and these results showed that further intense research on BAK-based therapies for acute renal failure was required. Development of BAK-based therapies for the treatment of patients suffering from end-stage renal disease is even more challenging, and related problems and research approaches are discussed herein, along with the development of mobile, portable, wearable and implantable devices.

Contribution of human amniotic fluid stem cells to renal tissue formation depends on mTOR

Human amniotic fluid stem cells (hAFSCs) can be grown in large quantities, have a low risk for tumour development and harbour a high differentiation potential. They are a very promising new fetal stem cell type for cell-based therapy approaches and for studying differentiation processes without raising the ethical concerns associated with embryonic stem cells. Recently, a protocol for studies on renal development has been established in which murine embryonic kidneys are dissociated into single-cell suspension and then reaggregated to form organotypic renal structures. Using this approach, we formed chimeric renal structures via mixing murine embryonic kidney cells with monoclonal hAFSCs. We demonstrate here that hAFSCs harbour the potential to contribute to renal tissue formation accompanied by induction of specific renal marker expression. As part of the two kinase complexes mTORC1 and mTORC2, mammalian target of rapamycin (mTOR) is the key component of an important signalling pathway, which is involved in the regulation of differentiation and in the development of a wide variety of human genetic diseases many with characteristic kidney symptoms. Modulating endogenous mTOR activity via specific siRNA approaches revealed that contribution of hAFSCs to renal tissue formation is regulated by mTORC1 and mTORC2. These findings (i) demonstrate renal differentiation potential of hAFSCs, (ii) prove chimeric cultures of mixtures of murine embryonic kidney cells and hAFSCs to be a powerful tool to study the effects of gene knockdowns for renal structure formation and (iii) provide new insights into the role of the mTOR pathway for renal development.

A thermoreversible polymer mediates controlled release of glial cell line-derived neurotrophic factor to enhance kidney regeneration

Previously, we reported that human mesenchymal stem cells (hMSCs) that were cultivated in growing embryos differentiated in an appropriate developmental milieu, thereby facilitating the development of a functional renal unit. However, this approach required transfection with an adenovirus that expressed glial cell line-derived neurotrophic factor (GDNF) to enhance the development of hMSC-derived renal tissue, and safety issues restrict the clinical use of such viral vectors. To circumvent this problem, we tested an artificial polymer as a means to diffuse GDNF. This GDNF-polymer, which exists in liquid form at 4 degrees C but becomes a hydrogel upon heating to 37 degrees C, was used as a thermoreversible switch, allowing the injection of hMSCs at low viscosity using a mouth pipette, with subsequent slow diffusion of GDNF as it solidified. The polymer, which was dissolved in a solution of GDNF at 4 degrees C and then maintained at 37 degrees C, acted as a diffuser of GDNF for more than 48 h. LacZ-transfected hMSCs and the GDNF-polymer (at 4 degrees C) were placed in the nephrogenic sites of growing rat embryos that were maintained at 37 degrees C. Forty-eight hours later, the resultant kidney anlagen were dissected out and allowed to continue developing for 6 days in vitro. Whole-organ X-Gal staining and fluorescence activated cell sorter analysis showed that the number of hMSC-derived cells was significantly increased in developed anlagen that have been generated from hMSCs plus GDNF-polymer compared with those from hMSCs plus GDNF-containing medium and was comparable to those from adenovirus-transfected hMSCs. These findings suggest that the GDNF-polymer can be used as a diffuser of GDNF for kidney organogenesis.

Cellular maintenance and repair of the kidney

The mammalian kidney is a highly complex organ that requires the precise structural arrangement of multiple cell types for effective function. The need to filter large volumes of plasma at the glomerulus followed by active reabsorption of nearly 99% of that filtrate by the tubules creates vulnerability in both compartments for cell injury. Thus maintenance of cell viability and replacement of those cells that are lost are essential for functional stability of the kidney. This review addresses our current understanding of how cells from the glomerular, tubular, and interstitial compartments arise during development and the manner in which they may be regenerated in the adult organ. In addition, we discuss the data regarding the role of organ-specific and bone marrow-derived stem and progenitor cells in the replacement/repair process, as well as the potential for ex vivo programming of stem cells toward a renal lineage.

Paracrine/endocrine mechanism of stem cells on kidney repair: role of microvesicle-mediated transfer of genetic information

PURPOSE OF REVIEW

The mechanism of stem cell-induced kidney repair remains controversial. Engraftment of bone marrow-derived stem cells is considered a rare event and several studies point to paracrine/endocrine processes. This review focuses on microvesicle-mediated transfer of genetic information between stem cells and injured tissue as a paracrine/endocrine mechanism.

RECENT FINDINGS

The following findings support a bidirectional exchange of genetic information between stem and injured cells: microvesicles shuttle defined patterns of mRNA and microRNA, are actively released from embryonic and adult stem cells and are internalized by a receptor-mediated mechanism in target cells; transcripts delivered by microvesicles from injured cells may reprogram the phenotype of stem cells to acquire specific features of the tissue; transcripts delivered by microvesicles from stem cells may induce dedifferentiation of cells surviving injury with cell cycle reentry and tissue self-repair.

SUMMARY

Transfer of genetic information from injured cells may explain stem cell functional and phenotypic changes without the need for transdifferentiation into tissue cells. On the contrary, transfer of genetic information from stem cells may redirect altered functions in target cells suggesting that stem cells may repair damaged tissues without directly replacing parenchymal cells.

Induction of mesenchymal/epithelial marker expression in human amniotic fluid stem cells

Although dialysis and transplantation are widely applied therapies for renal failure, drawbacks such as morbidity, shortage of compatible organs and high cost are limiting factors. Recently, interest has increased in the potential use of stem cells for the repair of kidney injury, which has been considered as an alternative therapeutic strategy. Due to their high proliferation rates, their pluripotent differentiation potential, the finding that they do not induce tumour formation and the fact that they do not raise the ethical concerns connected with human embryonic stem cells, human amniotic fluid stem cells are considered to be a very promising cell source. This study demonstrates that the expression of the mesenchymal markers CD29 and CD44, the epithelial markers CD51 and ZO-1 and the podocyte markers CD2AP and NPHS2 can be induced in these cells via incubation with epidermal growth factor/platelet-derived growth factor BB and fibroblast growth factor 4/hepatocyte growth factor, respectively. Since podocytes are visceral epithelial cells in the kidneys, which form the essential part of the glomerular filtration barrier, these findings warrant further investigation of the potential use of human amniotic fluid stem cells for cell-based kidney therapies.

Mesenchymal stem cells differentiate into renin-producing juxtaglomerular (JG)-like cells under the control of liver X receptor-alpha

Renin is a key enzyme for cardiovascular and renal homeostasis and is produced by highly specialized endocrine cells in the kidney, known as juxtaglomerular (JG) cells. The nature and origin of these cells remain as mysteries. Previously, we have shown that the nuclear hormone receptor liver X receptor-alpha (LXRalpha) is a major transcriptional regulator of the expression of renin, c-myc, and other genes involved with growth/differentiation. In this study we test the hypothesis that LXRalpha plays an important role not only in renin expression but also in renin-containing cell differentiation, specifically from the mesenchymal stem cell (MSC), which may be the origin of the JG cell. Indeed, our data demonstrated that LXRalpha activation by its ligands or cAMP stimulated renin gene expression in both murine and human MSCs. Furthermore, sustained cAMP stimulation of murine MSCs overexpressing LXRalpha led to their differentiation into JG-like cells expressing renin and alpha-smooth muscle actin. These MSC-derived JG-like cells contained renin in secretory granules and released active renin in response to cAMP. In conclusion, the activation of LXRalpha stimulates renin expression and induces MSCs differentiation into renin-secreting, JG-like cells. Our results suggest that the MSC may be the origin of the juxtaglomerular cell and provide insight into novel understanding of pathophysiology of the renin-angiotensin system.

In vitro differentiation of MSC into cells with a renal tubular epithelial-like phenotype

Bone marrow mesenchymal stem (stromal) cells (MSCs) are shown to differentiate into different renal lineages in in vivo injury models. Nevertheless, the in vitro differentiation of MSCs into a renal tubular epithelial lineage has not been investigated. We hypothesize that the injured renal epithelial cells express renotypic factors that may influence the differentiation of MSCs into a renal tubular epithelial lineage. MSCs were cocultured for up to seven days with injured or uninjured murine cortical tubular renal epithelial cells (MCTs), which are separated by a physical barrier; following the coculture, MSCs were examined for the expression of two renal tubular epithelial-specific markers, kidney-specific cadherin (Ksp-cadherin) and aquaporin-1 (AQP1). MSCs differentiated into a tubular epithelial-like phenotype, as shown by the appearance of Ksp-cadherin and AQP1 by day 7 when cocultured with injured MCTs. Further, MSCs showed tubulogenic characteristics when cocultured in a three-dimensional matrix. Nonetheless, MSCs cultured with the conditioned medium from injured MCTs, cocultured with ureteric bud cells, or treated with nephrogenic factors did not differentiate into renal epithelial cells. Based on our findings, we conclude that MSCs can differentiate into a renal epithelial lineage independent of cell fusion when cocultured with injured renal cells.

Stem cells, nuclear transfer and respect for embryos

Harvesting human embryonic stem (hES) cells is a highly controversial field of research because it rests on the destruction of human embryos. Altering the procedure of nuclear transfer (NT) is suggested to generate hES cell lines without ethical obstacles by claiming that no embryo would be involved. While discussing the nature of an embryo and related central questions concerning their moral status and the respect they deserve, this paper argues that the entity created by somatic cell nuclear transfer (SCNT) or altered nuclear transfer (ANT) is an embryo and has the same moral status as a natural embryo. Respect for the embryo is expressed by the ethical principles of proportionality, probability and subsidiarity. This paper argues that the human embryo should only be taken for research with high ranking goals, which are proven in animal experimentation and for which there are no alternatives. This makes ANT obsolete and shows that SCNT to produce hES cells is premature at the present time.