Mesenchymal stem cells in acute kidney injury

Reconstitution of kidney side population cells after ischemia-reperfusion injury by self-proliferation and bone marrow-derived cell homing

The aim of this study was to examine the contribution of side population (SP) cells from kidney and bone marrow for reconstitution of kidney SP pools after ischemia-reperfusion injury (IRI). The SP and non-SP cells in kidneys following IRI were isolated and serially assessed by fluorescence-activated cell sorting. The apoptosis, proliferation, phenotype, and paracrine actions of SP cells were evaluated in vitro and in vivo. Results indicated that the SP cells from ischemic kidney were acutely depleted within one day following renal IRI and were progressively restored to baseline within 7 days after IRI, through both proliferation of remaining kidney SP cells and homing of bone marrow-derived cells to ischemic kidney. Either hypoxia or serum deprivation alone increased apoptosis of SP cells, and a combination of both further aggravated it. Furthermore, hypoxia in vivo and in vitro induced the increase in the secretion of vascular endothelial growth factor, insulin-like growth factor 1, hepatocyte growth factor, and stromal cell-derived factor-1 α in kidney SP but not non-SP cells. In summary, these results suggest that following renal IRI, kidney SP cells are acutely depleted and then progressively restored to baseline levels by both self-proliferation and extrarenal source, that is, bone marrow-derived cell homing.

Modulation of glucose and lipid metabolism by porcine adiponectin receptor 1-transgenic mesenchymal stromal cells in diet-induced obese mice

BACKGROUND AIMS

Obesity and its associated diseases demand better therapeutic strategies. Regenerative medicine combined with gene therapy has emerged as a promising approach in various clinical applications. Adiponectin (ApN) and its receptors have been demonstrated to play beneficial roles in modulating glucose and lipid homeostasis. In the current study, we tested such an approach by transplanting mesenchymal stromal cells (MSCs) from porcine ApN receptor (pAdipoR) 1-transgenic mice into high-fat/sucrose diet (HFSD)-fed mice.

METHODS

Twenty 6-week-old Friend virus B/NJNarl male mice were randomly assigned into four groups with the control fed a chow diet (chow) and others HFSD for 10 months. The HFSD groups were then intraperitoneally injected once per week for 8 weeks with placebo (200 μL phosphate-buffered saline), wild-type MSC (WT-MSC, 2 × 10(6) cells/200 μL phosphate-buffered saline) or pAdipoR1-transgenic MSC (pR1-tMSC, 2 × 10(6) cells/200 μL phosphate-buffered saline), respectively. Body weights, blood samples, tissue histology, and gene expression and protein levels of metabolism-associated genes were analyzed.

RESULTS

Both WT-MSC and pR1-tMSC transplantations restored the messenger RNA expression of AdipoR1, with those of glucose transporter 4 and 5'-adenosine monophosphate-activated protein kinase catalytic subunit α-1 and protein levels of pyruvate kinase induced by pR1-tMSC in the muscles of HFSD-fed mice. In the liver, both WT-MSC and pR1-tMSC ameliorated HFSD-induced hepatosteatosis, with the gene expression of lipoprotein lipase and hormone-sensitive lipase upregulated by the latter. Lastly, pR1-tMSC transplantation reduced fatty acid synthase mRNA levels in the adipose tissues of HFSD-fed mice.

CONCLUSIONS

This study demonstrates the modulatory actions of MSC and pR1-tMSC on genes associated with glucose and lipid metabolism and provides insights into its therapeutic application for obesity-associated metabolic complication.

Therapeutic effects of human amniotic fluid-derived stem cells on renal interstitial fibrosis in a murine model of unilateral ureteral obstruction

Interstitial fibrosis is regarded as the main pathway for the progression of chronic kidney disease (CKD) and is often associated with severe renal dysfunction. Stem cell-based therapies may provide alternative approaches for the treatment of CKD. Human amniotic fluid-derived stem cells (hAFSCs) are a novel stem cell population, which exhibit both embryonic and mesenchymal stem cell characteristics. Herein, the present study investigated whether the transplantation of hAFSCs into renal tissues could improve renal interstitial fibrosis in a murine model of unilateral ureteral obstruction (UUO). We showed that hAFSCs provided a protective effect and alleviated interstitial fibrosis as reflected by an increase in microvascular density; additionally, hAFSCs treatment beneficially modulated protein levels of vascular endothelial growth factor (VEGF), hypoxia inducible factor-1α (HIF-1α) and transforming growth factor-β1 (TGF-β1). Therefore, we hypothesize that hAFSCs could represent an alternative, readily available source of stem cells that can be applied for the treatment of renal interstitial fibrosis.

Current developments in early diagnosis of acute kidney injury

Acute kidney injury (AKI) is a very frequent and serious clinical problem, accounting for overall high morbidity and mortality. Up to date, mortality due to AKI is virtually unchanged over the past 50 years. This may partly be explained due to a delay in initiating renal protective and appropriate therapeutic measures since until now there are no reliable early-detecting biomarkers. The gold standard, serum creatinine, displays poor specificity and sensitivity with regard to identification of the incipient phase of AKI, and this is also true for cystatin C. We aimed to review novel biomarkers of AKI in urine and serum which have now progressed to the clinical phase. The main focus refers to their diagnostic and prognostic value. For this purpose, a web-based literature search using PubMed was performed comprising the following terms: renal failure, acute kidney injury and biomarkers. New molecules such as neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), N-acetyl-β-D-glucosaminidase (NAG), monocyte chemotactic peptide (MCP-1), Il-18, liver-type fatty acid-binding protein (L-FABP) and Netrin-1 are available and represent promising new markers that, however, need to be further evaluated in the clinical setting for suitability. In clinical settings with incipient AKI, not only the development and the implementation of more sensitive, practicable and accurate biomarkers are required for well-timed treatment initiation. Just as important is a substantial improvement of refined and applicable prophylactic therapeutic options in these situations. Before full adoption in clinical practice can be accomplished, adequately powered clinical trials testing a row of biomarkers are strongly warranted.

Therapeutic potential of mesenchymal stem cells in regenerative medicine

Mesenchymal stem cells (MSCs) are stromal cells that have the ability to self-renew and also exhibit multilineage differentiation into both mesenchymal and nonmesenchymal lineages. The intrinsic properties of these cells make them an attractive candidate for clinical applications. MSCs are of keen interest because they can be isolated from a small aspirate of bone marrow or adipose tissues and can be easily expanded in vitro. Moreover, their ability to modulate immune responses makes them an even more attractive candidate for regenerative medicine as allogeneic transplant of these cells is feasible without a substantial risk of immune rejection. MSCs secrete various immunomodulatory molecules which provide a regenerative microenvironment for a variety of injured tissues or organ to limit the damage and to increase self-regulated tissue regeneration. Autologous/allogeneic MSCs delivered via the bloodstream augment the titers of MSCs that are drawn to sites of tissue injury and can accelerate the tissue repair process. MSCs are currently being tested for their potential use in cell and gene therapy for a number of human debilitating diseases and genetic disorders. This paper summarizes the current clinical and nonclinical data for the use of MSCs in tissue repair and potential therapeutic role in various diseases.

Immunomodulatory properties of dental tissue-derived mesenchymal stem cells

In addition to their well-established self-renewal and multipotent differentiation properties, mesenchymal stem cells (MSCs) also possess potent immunomodulatory functions both in vitro and in vivo, which render them a potential novel immunotherapeutic tool for a variety of autoimmune and inflammation-related diseases. The major mechanisms may involve (1) the secretion of an array of soluble factors such as prostaglandin E2 (PGE2 ), indoleamine 2, 3-dioxygenase (IDO), transforming growth factor-β (TGF-β), and human leukocyte antigen G5 (HLA-G5); (2) interactions between MSCs and immune cells such as T cells, B cells, macrophages, and dendritic cells. Recently, increasing evidence has supported that MSCs derived from dental tissues are promising alternative sources of multipotent MSCs. We here provide a thorough and extensive review about new findings in the immunomodulatory functions of MSCs derived from several dental tissues, including dental pulp, periodontal ligament, gingiva, exfoliated deciduous teeth, apical papilla, and dental follicle, respectively. The immunomodulatory properties of dental MSCs place them as a more accessible cell source than bone marrow-derived MSCs for cell-based therapy of immune and inflammation-related diseases.

Mesenchymal stem cell: an efficient mass producer of exosomes for drug delivery

Advances in biomedical research have generated an unprecedented number of potential targets for therapeutic intervention to treat disease or delay disease progression. Unfortunately, many of these targets are not druggable as they are intracellular, present in many cell types, poorly soluble or rapidly inactivated. Although synthetic drug vehicles have successfully circumvented many of these problems, natural particulates such as exosomes that intrinsically possess many attributes of a drug delivery vehicle are highly attractive as potentially better alternatives. Of the cell types known to produce exosomes, the readily available proliferative, immunosuppressive and clinically tested human mesenchymal stem cell (MSC) is the most prolific producer. Its exosomes are therapeutic in animal model of disease and exhibit immunosuppressive activity. The quality and quantity of exosome production is not compromised by immortalization to create a permanent MSC cell line. Therefore, MSC is well suited for mass production of exosomes that are ideal for drug delivery.

The therapeutic potential of mesenchymal stem cell-derived extracellular vesicles

Extracellular vesicles (EVs), membrane vesicles that are secreted by a variety of mammalian cell types, have been shown to play an important role in intercellular communication. The contents of EVs, including proteins, microRNAs, and mRNAs, vary according to the cell type that secreted them. Accordingly, researchers have demonstrated that EVs derived from various cell types play different roles in biological phenomena. Considering the ubiquitous presence of mesenchymal stem cells (MSCs) in the body, MSC-derived EVs may take part in a wide range of events. In particular, MSCs have recently attracted much attention due to the therapeutic effects of their secretory factors. MSC-derived EVs may therefore provide novel therapeutic approaches. In this review, we first summarize the wide range of functions of EVs released from different cell types, emphasizing that EVs echo the phenotype of their parent cell. Then, we describe the various therapeutic effects of MSCs and pay particular attention to the significance of their paracrine effect. We then survey recent reports on MSC-derived EVs and consider the therapeutic potential of MSC-derived EVs. Finally, we discuss remaining issues that must be addressed before realizing the practical application of MSC-derived EVs, and we provide some suggestions for enhancing their therapeutic efficiency.

Mesenchymal-like progenitors derived from human embryonic stem cells promote recovery from acute kidney injury via paracrine actions

BACKGROUND AIMS

The engraftment of mesenchymal stem cells (MSCs) is reported to promote recovery of renal function in animal models of acute kidney injury (AKI). However, it is unknown whether mesenchymal-like progenitors (MPs) derived from human embryonic stem cells (hESCs) can mediate similar therapeutic effects. We investigated the responses of recipient renal tissue to engraftment of hESC-MPs and underlying mechanisms of these effects.

METHODS

We measured blood urea nitrogen and creatinine levels of AKI mice with hESC-MPs transplantation and control mice. We performed renal morphology analysis by immunohistochemistry and electron microscopy to confirm the renoprotective effects of engrafted hESC-MPs. Proliferation, apoptosis and gene expression of tubular cells were also monitored by immunohistochemistry and real-time quantitative polymerase chain reaction to investigate the mechanisms that occurred.

RESULTS

After transplantation of hESC-MPs into mice with cisplatin-induced AKI, improvements in renal function and recovery from tubular epithelial cell injury were observed. Engrafted hESC-MPs were localized to areas of injured kidney 5 days after cisplatin induction, where they promoted tubular cell proliferation and decreased kidney cell apoptosis. The beneficial effect was further confirmed by the capability of the engrafted cells to up-regulate renal gene expression of anti-inflammatory cytokines and pro-survival cytokines. Meanwhile, infusion of these cells reduced renal gene expression of pro-inflammatory cytokines and monocyte chemotactic protein-1, a chemokine that stimulates monocyte and macrophage infiltration.

CONCLUSIONS

Our results show that infused hESC-MPs may promote recovery from AKI by regulating related cytokines.

High targeted migration of human mesenchymal stem cells grown in hypoxia is associated with enhanced activation of RhoA

INTRODUCTION

A feature which makes stem cells promising candidates for cell therapy is their ability to migrate effectively into damaged or diseased tissues. Recent reports demonstrated the increased motility of human mesenchymal stem cells (hMSC) grown under hypoxic conditions compared to normoxic cells. However, the directional migration of hMSC cultured in hypoxia has not been investigated. In this study we examined the in vitro transmembrane migration of hMSC permanently cultured in hypoxia in response to various cytokines. We also studied the involvement of RhoA, a molecule believed to play an essential role in the migration of MSC via reorganization of the cytoskeleton.

METHODS

We compared the directional migration of human hMSCs grown permanently under normal (21%, normoxic) and low O2 (5%, hypoxic) conditions until passage 4 using an in vitro transmembrane migration assay. A series of 17 cytokines was used to induce chemotaxis. We also compared the level of GTP-bound RhoA in the cell extracts of calpeptin-activated hypoxic and normoxic hMSC.

RESULTS

We found that hMSC cultured in hypoxia demonstrate markedly higher targeted migration activity compared to normoxic cells, particularly towards wound healing cytokines, including those found in ischemic and myocardial infarction. We also demonstrated for the first time that hMSC are dramatically more sensitive to activation of RhoA.

CONCLUSIONS

The results of this study indicate that high directional migration of hMSCs permanently grown in hypoxia is associated with the enhanced activation of RhoA. The enhanced migratory capacity of hypoxic hMSC would further suggest their potential advantages for clinical applications.

Stem cells and their role in renal ischaemia reperfusion injury

BACKGROUND

Ischaemia-reperfusion injury (IRI) remains one of the leading causes of acute kidney injury (AKI). IRI is an underlying multifactorial pathophysiological process which affects the outcome in both native and transplanted patients. The high morbidity and mortality associated with IRI/AKI and disappointing results from current available clinical therapeutic approaches prompt further research. Stem cells (SC) are undifferentiated cells that can undergo both renewal and differentiation into one or more cell types which can possibly ameliorate IRI.

AIM

To carry out a detailed literature analysis and construct a comprehensive literature review addressing the role of SC in AKI secondary to IRI.

METHODS

Evidence favouring the role of SC in renal IRI and evidence showing no benefits of SC in renal IRI are the two main aspects to be studied. The search strategy was based on an extensive search addressing MESH terms and free text terms.

RESULTS

The majority of studies in the field of renal IRI and stem cell therapy show substantial benefits.

CONCLUSIONS

Studies were mostly conducted in small animal models, thus underscoring the need for further pre-clinical studies in larger animal models, and results should be taken with caution. SC therapy may be promising though controversy exists in the exact mechanism. Thorough scientific exploration is required to assess mechanism, safety profile, reproducibility and methods to monitor administered SC.

Pre-conditioned mesenchymal stem cells ameliorate renal ischemic injury in rats by augmented survival and engraftment

Background

Ischemia is the major cause of acute kidney injury (AKI), associated with high mortality and morbidity. Mesenchymal stem cells (MSCs) have multilineage differentiation potential and can be a potent therapeutic option for the cure of AKI.

Methods

MSCs were cultured in four groups SNAP (S-nitroso N-acetyl penicillamine), SNAP + Methylene Blue (MB), MB and a control for in vitro analysis. Cultured MSCs were pre-conditioned with either SNAP (100 μM) or MB (1 μM) or both for 6 hours. Renal ischemia was induced in four groups (as in in vitro study) of rats by clamping the left renal padicle for 45 minutes and then different pre-conditioned stem cells were transplanted.

Results

We report that pre-conditioning of MSCs with SNAP enhances their proliferation, survival and engraftment in ischemic kidney. Rat MSCs pre-conditioned with SNAP decreased cell apoptosis and increased proliferation and cytoprotective genes’ expression in vitro. Our in vivo data showed enhanced survival and engraftment, proliferation, reduction in fibrosis, significant improvement in renal function and higher expression of pro-survival and pro-angiogenic factors in ischemic renal tissue in SNAP pre-conditioned group of animals. Cytoprotective effects of SNAP pre-conditioning were abrogated by MB, an inhibitor of nitric oxide synthase (NOS) and guanylate cyclase.

Conclusion

The results of these studies demonstrate that SNAP pre-conditioning might be useful to enhance therapeutic potential of MSCs in attenuating renal ischemia reperfusion injury.

Tissues use resident dendritic cells and macrophages to maintain homeostasis and to regain homeostasis upon tissue injury: the immunoregulatory role of changing tissue environments

Most tissues harbor resident mononuclear phagocytes, that is, dendritic cells and macrophages. A classification that sufficiently covers their phenotypic heterogeneity and plasticity during homeostasis and disease does not yet exist because cell culture-based phenotypes often do not match those found in vivo. The plasticity of mononuclear phagocytes becomes obvious during dynamic or complex disease processes. Different data interpretation also originates from different conceptual perspectives. An immune-centric view assumes that a particular priming of phagocytes then causes a particular type of pathology in target tissues, conceptually similar to antigen-specific T-cell priming. A tissue-centric view assumes that changing tissue microenvironments shape the phenotypes of their resident and infiltrating mononuclear phagocytes to fulfill the tissue's need to maintain or regain homeostasis. Here we discuss the latter concept, for example, why different organs host different types of mononuclear phagocytes during homeostasis. We further discuss how injuries alter tissue environments and how this primes mononuclear phagocytes to enforce this particular environment, for example, to support host defense and pathogen clearance, to support the resolution of inflammation, to support epithelial and mesenchymal healing, and to support the resolution of fibrosis to the smallest possible scar. Thus, organ- and disease phase-specific microenvironments determine macrophage and dendritic cell heterogeneity in a temporal and spatial manner, which assures their support to maintain and regain homeostasis in whatever condition. Mononuclear phagocytes contributions to tissue pathologies relate to their central roles in orchestrating all stages of host defense and wound healing, which often become maladaptive processes, especially in sterile and/or diffuse tissue injuries.

Bone marrow stem cells-derived microvesicles protect against renal injury in the mouse remnant kidney model

AIMS

  Several studies have demonstrated administration of mesenchymal stem cells (MSC) could reverse kidney injury by paracrine mechanisms rather than by MSC transdifferentiation. Recently, a few researchers found microvesicles (MV) derived from MSC might be a paracrine mechanism for cell-to-cell communication. The aim of this study was to investigate the repair effects of MV in a 5/6 subtotal nephrectomy (Nx) mice model.

METHODS

  The animals were randomly divided into four groups: Control, Nx, Nx + MSC and Nx + MV group. MSC were injected (1 × 10(6) /mouse) through caudal vein in Nx + MSC group at the second day after the surgery and MV were injected (30 µg/mouse) through caudal vein in Nx + MV group on alternate days. Mice were killed on day 7 after the first time of administration. Blood urea nitrogen (BUN), serum creatinine (Scr), uric acid (UA) and proteinuria were evaluated. Histopathology of kidney was analysed.

RESULTS

  In Nx mice, the levels of Scr, UA and proteinuria were significantly decreased with administration of MV and MSC (P < 0.05). The remnant kidneys of MV and MSC-treated Nx mice showed less fibrosis, interstitial lymphocyte infiltrates and less or absent tubular atrophy compared with the untreated Nx group. The Histological Score of Kidney in untreated mice was 3.13 ± 0.74, while in the MSC-treated group it was 1.67 ± 0.47 and in the MV-treated group it was 1.80 ± 0.44, nearly preserving normal morphology of the kidney (P < 0.01).

CONCLUSION

  This study showed MV protects against renal injury induced by 5/6 Nx, which could mimic the role of MSC in kidney repair. The research showed a newly potential therapeutic approach to kidney diseases.

Low serum cultured adipose tissue-derived stromal cells ameliorate acute kidney injury in rats

Current studies suggest that mesenchymal stromal cells (MSCs) improve acute kidney injury (AKI) via paracrine/endocrine effects. We established human adipose tissue-derived stromal cells (hASCs) cultured in low (2%) serum (hLASCs), which have great potential of tissue regeneration. The present study was performed to investigate the therapeutic effects of hLASCs on AKI and to clarify the mechanisms involved. In low serum, hASCs proliferated well, while human bone marrow-derived stromal cells (hBMSCs) did not. hLASCs secreted higher levels of hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) than did hASCs cultured in high (20%) serum (hHASCs) or hBMSCs cultured in high serum (hHBMSCs). AKI was induced in nude rats by folic acid, and hLASCs, hHASCs or control medium were administered into the renal subcapsules. hLASCs significantly attenuated acute renal damage, while hHASCs showed far less effect. Furthermore, interstitial fibrosis observed on day 14 was less pronounced in the hLASCs group. Cell tracking experiment showed no evidence of transdifferentiation. Intravenous injection of hLASCs or hHBMSCs or subcapsular injection of hHBMSCs did not ameliorate AKI. Concerning the mechanisms, our in vivo experiments showed that HGF knockdown by siRNA impaired the ability of hLASCs to protect the kidney from acute injury whereas VEGF knockdown did not. In conclusion, hLASCs, but not hHASCs or hHBMSCs, ameliorated AKI via paracrine effects, and HGF is one of the key mediators.

Autologous cell therapy for cisplatin-induced acute kidney injury by using non-expanded adipose tissue-derived cells

BACKGROUND AIMS

Recent studies have demonstrated that cultured mesenchymal stromal cells derived from adipose tissue are useful for regenerative cell therapy. The stromal vascular fraction (SVF) can be obtained readily without culturing and may be clinically applicable. We investigated the therapeutic effects of SVF and used it in the treatment of acute kidney injury (AKI).

METHODS

Liposuction aspirates were obtained from healthy donors who had provided written informed consent. We harvested the SVF and determined the growth factor secretion and anti-apoptotic ability with conditioned medium. To investigate the effect of SVF on AKI, cisplatin was injected into rats and SVF was administrated into the subcupsula of the kidney.

RESULTS

Both human and rat SVF cells secreted vascular endothelial growth factor-A (VEGF) and hepatocyte growth factor (HGF). Human SVF-conditioned media had an anti-apoptotic effect, which was inhibited by anti-HGF antibody (Ab) but not by anti-VEGF Ab. In vivo, SVF significantly ameliorated renal function, attenuated tubular damage and increased the cortical blood flow speed. In the SVF-treated group, VEGF levels in the cortex and HGF levels in both the cortex and medulla, especially tubules in the medulla, were significantly higher. Immunostaining revealed that SVF cells expressing VEGF and HGF and remained in the subcapsule on day 14.

CONCLUSIONS

The present study demonstrates that a subcapsular injection of non-expanded SVF cells ameliorates rat AKI, and that the mechanism probably involves secretion of renoprotective molecules. Administration of human SVF may be clinically applicable and useful as a novel autologous cell therapy against kidney diseases.

Mesenchymal stem cell-conditioned medium accelerates regeneration of human renal proximal tubule epithelial cells after gentamicin toxicity

Bone marrow-derived mesenchymal stem cells (MSCs) have the capacity to regenerate renal tubule epithelia and repair renal function without fusing with resident tubular cells. The goal of the present project was to investigate the role of MSCs secreted cytokines on tubule cell viability and regeneration after a toxic insult, using a conditionally immortalized human proximal tubule epithelial cell (ciPTEC) line. Gentamicin was used to induce nephrotoxicity, and cell viability and migration were studied in absence and presence of human MSC-conditioned medium (hMSC-CM) i.e. medium containing soluble factors produced and secreted by MSCs. Exposure of ciPTEC to 0-3000 μg/ml gentamicin for 24 h caused a significant dose-dependent increase in cell death. We further demonstrated that the nephrotoxic effect of 2000 μg/ml gentamicin was recovered partially by exposing cells to hMSC-CM. Moreover, exposure of ciPTEC to gentamicin (1500-3000 μg/ml) for 7 days completely attenuated the migratory capacity of the cells. In addition, following scrape-wounding, cell migration of both untreated and gentamicin-exposed cells was increased in the presence of hMSC-CM, as compared to exposures to normal medium, indicating improved cell recovery. Our data suggest that cytokines secreted by MSCs stimulate renal tubule cell regeneration after nephrotoxicity.

Human embryonic mesenchymal stem cell-derived conditioned medium rescues kidney function in rats with established chronic kidney disease

Chronic kidney disease (CKD) is a major health care problem, affecting more than 35% of the elderly population worldwide. New interventions to slow or prevent disease progression are urgently needed. Beneficial effects of mesenchymal stem cells (MSC) have been described, however it is unclear whether the MSCs themselves or their secretome is required. We hypothesized that MSC-derived conditioned medium (CM) reduces progression of CKD and studied functional and structural effects in a rat model of established CKD.

CKD was induced by 5/6 nephrectomy (SNX) combined with L-NNA and 6% NaCl diet in Lewis rats. Six weeks after SNX, CKD rats received either 50 µg CM or 50 µg non-CM (NCM) twice daily intravenously for four consecutive days. Six weeks after treatment CM administration was functionally effective: glomerular filtration rate (inulin clearance) and effective renal plasma flow (PAH clearance) were significantly higher in CM vs. NCM-treatment. Systolic blood pressure was lower in CM compared to NCM. Proteinuria tended to be lower after CM. Tubular and glomerular damage were reduced and more glomerular endothelial cells were found after CM. DNA damage repair was increased after CM. MSC-CM derived exosomes, tested in the same experimental setting, showed no protective effect on the kidney. In a rat model of established CKD, we demonstrated that administration of MSC-CM has a long-lasting therapeutic rescue function shown by decreased progression of CKD and reduced hypertension and glomerular injury.

Mesenchymal stem cell-like cells in classic renal angiomyolipoma

As a benign mesenchymal tumor, classic renal angiomyolipoma (AML) may obliterate the kidney parenchyma and cause renal hemorrhage. It has previously been reported that mesenchymal stem cells (MSCs) are involved in tumorigenesis; however, there have been no studies on stem cells with renal AML origin. In the present study, six females with classic renal AML received a partial or total nephrectomy. During surgery, tumor tissues were collected and culture expansion of adhesive fibroblastoid cells from these tissues was performed. We successfully isolated and cultured MSC-like cells from all six renal AML tumors. MSC characteristics, including morphology, immunophenotype and multidifferentiation potential were analyzed. Flow cytometry analysis revealed that these cells are highly similar to human bone marrow MSCs due to the expression of MSC-specific surface proteins, including CD29, CD44, CD73, CD90 and CD105. The stem cell-like nature of these cells is further supported by their adipogenic and osteogenic differentiation potentials when incubated in appropriate differentiation cocktails. Renal AML-derived adhesive cells possessing the characteristics of MSCs are described for the first time. They are a novel cell type which may be useful in future studies with regards to determining the role of stem cells in the formation and development of renal AML.

Mesenchymal stem cells in kidney inflammation and repair

Mesenchymal stem cells are a heterogeneous population of fibroblast-like stromal cells that have been isolated from the bone marrow and a number of organs and tissues including the kidney. They have multipotent and self-renewing properties and can differentiate into cells of the mesodermal lineage. Following their administration in vivo, mesenchymal stem cells migrate to damaged kidney tissue where they produce an array of anti-inflammatory cytokines and chemokines that can alter the course of injury. Mesenchymal stem cells are thought to elicit repair through paracrine and/or endocrine mechanisms that modulate the immune response resulting in tissue repair and cellular replacement. This review will discuss the features of mesenchymal stem cells and the factors they release that protect against kidney injury; the mechanisms of homing and engraftment to sites of inflammation; and further elucidate the immunomodulatory effect of mesenchymal stem cells and their ability to alter macrophage phenotype in a setting of kidney damage and repair.

Human cord blood CD133+ cells exacerbate ischemic acute kidney injury in mice

BACKGROUND

Acute kidney injury (AKI) in humans has few therapeutic options. In experimental models, administration of progenitor cells facilitates recovery from AKI. Human umbilical cord-derived CD133(+) progenitor cells promote endothelial repair in ischemic limb, heart and brain tissue.

METHODS

We examined the effects of human CD133(+) progenitor cells in bilateral ischemia-reperfusion (I/R) kidney injury in non-obese diabetic severe combined immunodeficient mice. CD133(+) cells from human cord blood were injected intravenously at the time of reperfusion and the extent of injury was determined by plasma biochemistry and kidney histology.

RESULTS

In mice with I/R, fluorescently labeled CD133(+) cells were detected in blood 2 min after injection but decreased rapidly thereafter with no evidence of homing to the kidneys. In mice subjected to I/R, CD133(+) cells significantly increased plasma urea and Cr at 24 h compared to vehicle- or CD133(-) cell-treated mice. CD133(+) cells exacerbated tubular necrosis and apoptosis, increased plasma tumor necrosis factor-α and increased kidney neutrophil infiltration. In contrast, CD133(+) cells did not affect tubular cell proliferation. Administration of CD133(+) cells to FVB/N mice post-I/R also augmented kidney injury.

CONCLUSIONS

These data indicate that human cord blood-derived CD133(+) cells unexpectedly exacerbate ischemic AKI in mice, possibly through soluble factors. Our study highlights the importance of caution in cell-based therapies for human AKI.

The role of SDF-1-CXCR4/CXCR7 axis in the therapeutic effects of hypoxia-preconditioned mesenchymal stem cells for renal ischemia/reperfusion injury

In vitro hypoxic preconditioning (HP) of mesenchymal stem cells (MSCs) could ameliorate their viability and tissue repair capabilities after transplantation into the injured tissue through yet undefined mechanisms. There is also experimental evidence that HP enhances the expression of both stromal-derived factor-1 (SDF-1) receptors, CXCR4 and CXCR7, which are involved in migration and survival of MSCs in vitro, but little is known about their role in the in vivo therapeutic effectiveness of MSCs in renal ischemia/reperfusion (I/R) injury. Here, we evaluated the role of SDF-1-CXCR4/CXCR7 pathway in regulating chemotaxis, viability and paracrine actions of HP-MSCs in vitro and in vivo. Compared with normoxic preconditioning (NP), HP not only improved MSC chemotaxis and viability but also stimulated secretion of proangiogenic and mitogenic factors. Importantly, both CXCR4 and CXCR7 were required for the production of paracrine factors by HP-MSCs though the former was only responsible for chemotaxis while the latter was for viability. SDF-1α expression was upregulated in postischemic kidneys. After 24 h systemical administration following I/R, HP-MSCs but not NP-MSCs were selectively recruited to ischemic kidneys and this improved recruitment was abolished by neutralization of CXCR4, but not CXCR7. Furthermore, the increased recruitment of HP-MSCs was associated with enhanced functional recovery, accelerated mitogenic response, and reduced apoptotic cell death. In addition, neutralization of either CXCR4 or CXCR7 impaired the improved therapeutic potential of HP-MSCs. These results advance our knowledge about SDF-1-CXCR4/CXCR7 axis as an attractive target pathway for improving the beneficial effects of MSC-based therapies for renal I/R.

Induced pluripotent stem cells without c-Myc attenuate acute kidney injury via downregulating the signaling of oxidative stress and inflammation in ischemia-reperfusion rats

Induced pluripotent stem (iPS) cells have potential for multilineage differentiation and provide a resource for stem cell-based treatment. However, the therapeutic effect of iPS cells on acute kidney injury (AKI) remains uncertain. Given that the oncogene c-Myc may contribute to tumorigenesis by causing genomic instability, herein we evaluated the therapeutic effect of iPS cells without exogenously introduced c-Myc on ischemia-reperfusion (I/R)-induced AKI. As compared with phosphate-buffered saline (PBS)-treated group, administration of iPS cells via intrarenal arterial route into kidneys improved the renal function and attenuated tubular injury score at 48 h after ischemia particularly at the dose of 5 × 10(5) iPS cells. However, a larger number of iPS cells (5 × 10(7) per rat) diminished the therapeutic effects for AKI and profoundly reduced renal perfusion detected by laser Doppler imaging in the reperfusion phase. In addition, the green fluorescence protein-positive iPS cells mobilized to the peritubular area at 48 h following ischemia, accompanied by a significant reduction in infiltration of macrophages and apoptosis of tubular cells, and a remarkable enhancement in endogenous tubular cell proliferation. Importantly, transplantation of iPS cells reduced the expression of oxidative substances, proinflammatory cytokines, and apoptotic factors in I/R kidney tissues and eventually improved survival in rats of ischemic AKI. Six months after transplantation in I/R rats, engrafted iPS cells did not result in tumor formation in kidney and other organs. In summary, considering the antioxidant, anti-inflammatory, and antiapoptotic properties of iPS cells without c-Myc, transplantation of such cells may be a treatment option for ischemic AKI.

Injection of amniotic fluid stem cells delays progression of renal fibrosis

Injection of amniotic fluid stem cells ameliorates the acute phase of acute tubular necrosis in animals by promoting proliferation of injured tubular cells and decreasing apoptosis, but whether these stem cells could be of benefit in CKD is unknown. Here, we used a mouse model of Alport syndrome, Col4a5(-/-) mice, to determine whether amniotic fluid stem cells could modify the course of progressive renal fibrosis. Intracardiac administration of amniotic fluid stem cells before the onset of proteinuria delayed interstitial fibrosis and progression of glomerular sclerosis, prolonged animal survival, and ameliorated the decline in kidney function. Treated animals exhibited decreased recruitment and activation of M1-type macrophages and a higher proportion of M2-type macrophages, which promote tissue remodeling. Amniotic fluid stem cells did not differentiate into podocyte-like cells and did not stimulate production of the collagen IVa5 needed for normal formation and function of the glomerular basement membrane. Instead, the mechanism of renal protection was probably the paracrine/endocrine modulation of both profibrotic cytokine expression and recruitment of macrophages to the interstitial space. Furthermore, injected mice retained a normal number of podocytes and had better integrity of the glomerular basement membrane compared with untreated Col4a5(-/-) mice. Inhibition of the renin-angiotensin system by amniotic fluid stem cells may contribute to these beneficial effects. In conclusion, treatment with amniotic fluid stem cells may be beneficial in kidney diseases characterized by progressive renal fibrosis.

In vivo healing of meniscal lacerations using bone marrow-derived mesenchymal stem cells and fibrin glue

Fibrin glue created from a patient's own blood can be used as a carrier to deliver cells to the specific site of an injury. An experimental model for optimizing various permutations of this delivery system in vivo was tested in this study. Harvested equine meniscal sections were reapposed with fibrin glue or fibrin glue and equine bone marrow-derived mesenchymal stem cells (BMSCs). These constructs were then implanted subcutaneously in nude mice. After harvesting of the constructs, BMSC containing constructs showed significantly increased vascularization, and histology showed subjectively decreased thickness of repair tissue and increased total bonding compared to fibrin alone constructs. This model allowed direct comparison of different meniscal treatment groups while using a small number of animals. This in vivo model could be valuable in the future to optimize fibrin and cellular treatments for meniscal lesions in the horse and potentially humans as well.

Human adipose tissue-derived mesenchymal stem cells protect kidneys from cisplatin nephrotoxicity in rats

Cisplatin has multiple cellular targets and modes of action that lead to nephrotoxicity. This suggests novel therapies that act at multiple cisplatin target sites may be effective. We tested whether human adipose tissue-derived mesenchymal stem cells (Ad-MSCs) can affect multiple target sites and protect against cisplatin-induced kidney damage. Rats were divided into four groups: control, infused with Ad-MSCs, injected with cisplatin, and cisplatin followed by infusion of Ad-MSCs. Animal survival and renal function were decreased and histological damage was increased in cisplatin-treated rats at day 3. Infusion of Ad-MSCs ameliorated renal dysfunction and tissue injury caused by cisplatin, leading to increased survival. Apoptotic cell death in the kidney was significantly reduced by infusion of Ad-MSCs. Activation of p53, JNK, and ERK and the expression of inflammation-related molecules were also decreased in the kidney that received Ad-MSCs. Very few Ad-MSCs were detected in the kidney. Conditioned medium from cultured Ad-MSCs had renal-protective functions in vivo and in vitro. Renal dysfunction and tissue damage caused by cisplatin were significantly reduced in rats treated with Ad-MSCs-conditioned medium. The viability of cultured renal proximal tubular cells exposed to cisplatin was also improved by coculture with Ad-MSCs or with conditioned medium. Release of proinflammatory mediators induced by cisplatin was inhibited in coculture with Ad-MSCs. Our results show that human Ad-MSCs exert a paracrine-protective effect on cisplatin nephrotoxicity at multiple target sites and suggest that human Ad-MSCs might be a new therapeutic approach for patients with acute kidney injury.

Enabling innovative translational research in acute kidney injury

Acute kidney injury (AKI) is a common, heterogeneous, and detrimental clinical condition that has significant attributable morbidity and mortality. Despite major advances in understanding the epidemiology, pathogenesis, and outcomes of AKI, preventive measures remain inadequate and therapeutic approaches (except for renal replacement therapy) have largely proven futile so far. Critical to the process of designing rational therapies is translational research, which involves the transition between the basic research discoveries and everyday clinical applications to prevent, diagnose, and treat human diseases. Progress in innovative approaches has been hampered due in part to the reliance on functional markers (serum creatinine and blood urea nitrogen) that are neither sensitive nor specific to diagnose AKI. This limitation has created a great deal of interest and intense investigation to identify a "troponin-like marker" that would facilitate recognition of AKI and allow for timely implementation of the precise therapeutic agent. The other major obstacle in this field is the diverse and complex nature of AKI that involves multiple independent and overlapping pathways, making it difficult to cure AKI with a single approach. In this review, we will summarize the advances, ongoing studies, and future perspectives in the field of translational research of AKI.

Cellular pathophysiology of ischemic acute kidney injury

Ischemic kidney injury often occurs in the context of multiple organ failure and sepsis. Here, we review the major components of this dynamic process, which involves hemodynamic alterations, inflammation, and endothelial and epithelial cell injury, followed by repair that can be adaptive and restore epithelial integrity or maladaptive, leading to chronic kidney disease. Better understanding of the cellular pathophysiological processes underlying kidney injury and repair will hopefully result in the design of more targeted therapies to prevent the injury, hasten repair, and minimize chronic progressive kidney disease.

Biomarkers of kidney injury

CONTEXT

Acute kidney injury (AKI) represents a common serious clinical problem. Up to date mortality due to AKI, especially in intensive care units, has not been changed significantly over the past 50 years. This is partly due to a delay in initiating renal protective and appropriate therapeutic measures since until now there are no reliable early-detecting biomarkers. The gold standard, serum creatinine, displays poor specificity and sensitivity with regard to recognition of the early period of AKI.

OBJECTIVE

Our objective was to review established markers versus novel urine and serum biomarkers of AKI in humans, which have progressed to clinical phase with regard to their diagnostic and prognostic value.

MATERIALS AND METHODS

A review was performed on the basis of literature search of renal failure, acute kidney injury, and biomarkers in Pubmed.

RESULTS

Next to established biomarkers as creatinine and cystatin C, other molecules such as neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), monocyte chemotactic peptide (MCP-1), Netrin-1, and interleukin (IL)-18 are available and represent promising new markers that, however, need to be further evaluated in the clinical setting for suitability.

DISCUSSION

In clinical settings with incipient AKI, not only the development and the implementation of more sensitive biomarkers are required for earlier treatment initiation in order to attenuate the severity of kidney injury, but also equally important remains the substantial improvement and application of refined and prophylactic therapeutic options in these situations.

CONCLUSION

Adequately powered clinical trials testing a row of biomarkers are warranted before they may qualify for full adoption in clinical practice.

Mesenchymal stem cells: from experiment to clinic

There is currently much interest in adult mesenchymal stem cells (MSCs) and their ability to differentiate into other cell types, and to partake in the anatomy and physiology of remote organs. It is now clear these cells may be purified from several organs in the body besides bone marrow. MSCs take part in wound healing by contributing to myofibroblast and possibly fibroblast populations, and may be involved in epithelial tissue regeneration in certain organs, although this remains more controversial. In this review, we examine the ability of MSCs to modulate liver, kidney, heart and intestinal repair, and we update their opposing qualities of being less immunogenic and therefore tolerated in a transplant situation, yet being able to contribute to xenograft models of human tumour formation in other contexts. However, such observations have not been replicated in the clinic. Recent studies showing the clinical safety of MSC in several pathologies are discussed. The possible opposing powers of MSC need careful understanding and control if their clinical potential is to be realised with long-term safety for patients.

Genetic tracing of the epithelial lineage during mammalian kidney repair

Developing new therapeutic approaches to treat acute kidney injury requires a detailed understanding of endogenous cellular repair. Genetic fate mapping defines cellular hierarchies in vivo and we used this technique to assess a possible contribution of non-epithelial stem cells to renal repair after ischemic injury. Mice with efficient labeling of renal epithelial cells, but not non-epithelial interstitial cells, were subjected to a single cycle or sequential cycles of kidney injury and repair. No dilution of the epithelial cell fate marker was observed despite robust epithelial cell proliferation. Thus, non-tubular cells do not have the ability to migrate across the basement membrane and differentiate into epithelial cells in this model. Instead, surviving tubular epithelial cells are responsible for repair of the damaged nephron. Future studies will need to distinguish between uniform dedifferentiation and proliferation of all epithelial cells after injury versus selective expansion of an intratubular epithelial stem cell.

Protective actions of administered mesenchymal stem cells in acute kidney injury: relevance to clinical trials

Current therapies for acute kidney injury remain primarily supportive and have failed to reduce morbidity, mortality (>50%), and associated costs. This prompted our studies in which rats with bilateral ischemia/reperfusion-induced acute kidney injury were treated with bone marrow-derived, culture-expanded allogeneic mesenchymal stem cells. Their administration into the suprarenal aorta after reflow significantly protected renal function and hastened repair, mediated by complex antiapoptotic, mitogenic, anti-inflammatory, and immune modulating actions that were not elicited by isogeneic fibroblasts. Infused mesenchymal stem cells, recruited to renal sites of injury, did not significantly differentiate into target cells but rather disappeared from kidneys and other organs within 72 h. Furthermore, at 3 months, compared with vehicle-treated controls, renal function was well preserved and interstitial fibrosis was absent. These preclinical data served as the scientific basis for a recently completed Phase I Clinical Trial (http://www.clinicaltrials.gov; # NCT00733876), in which patients at high risk for cardiac surgery-associated AKI were treated with allogeneic mesenchymal stem cells. Until now, MSC therapy in the study subjects has been safe, and none of the patients has developed postoperative AKI or subsequent loss of renal function, suggesting that this novel form of therapy may have promise in this group of high-risk patients, which will be further investigated in a Phase II Trial.

Mesenchymal stem cells as a therapeutic approach to glomerular diseases: benefits and risks

Most studies using adult stem cells (ASCs) and progenitor cells as potential therapeutics for kidney disorders have been conducted in models of acute kidney injury, where the damage mainly affects the tubulointerstitium. The results are promising, whereas the underlying mechanisms are still being discussed controversially. Glomerular diseases have not received as much attention. Likely reasons include the often insidious onset, rendering the choice of optimal treatment timing difficult, and the fact that chronic diseases may require long-term therapy. In this mini review, we summarize current strategies in adult stem cell-based therapies for glomerular diseases. In addition, we focus on possible side effects of stem cell administration that have been reported recently, that is, profibrotic actions and maldifferentiation of mesenchymal stem cells.

Ischemic kidney injury and mechanisms of tissue repair

Acute kidney injury (AKI) may result from ischemia or by the use of nephrotoxic agents. The incidence of AKI is variable, depends on comorbidities, and ranges from 5 to 35% in all hospitalized patients. The mechanisms of kidney injury exist within a large network of signaling pathways driven by interplay of inflammatory cytokines/chemokines, reactive oxygen species (ROS), and apoptotic factors. The effects and progression of injury overlap extensively with the remarkable ability of the kidney to repair itself both by intrinsic and extrinsic mechanisms that involve specific cell receptors/ligands as well as possible paracrine influences. The fact that kidney injury is usually part of a generalized comorbid condition makes it all the more challenging in terms of assessment of severity. In this review, we attempt to analyze the mechanisms of ischemic injury and repair in acute and chronic kidney disease from the perspectives of both preclinical and human studies.

In vivo effect of bone marrow-derived mesenchymal stem cells in a rat kidney transplantation model with prolonged cold ischemia

Brain death and prolonged cold ischemia are major contributors to the poorer long-term outcome of transplants from deceased donor kidney transplants, with an even higher impact if expanded criteria donors ('marginal organs') are used. Targeting ischemia-reperfusion injury-related intragraft inflammation is an attractive concept to improve the outcome of those grafts. As mesenchymal stem cells (MSCs) express both immunomodulatory and tissue repair properties, we evaluated their therapeutic efficacy in a rat kidney transplant model of prolonged cold ischemia. The in vitro immunomodulatory capacity of bone marrow-derived rat MSCs was tested in co-cultures with rat lymph node cells. For in vivo studies, Dark Agouti rat kidneys were cold preserved and transplanted into Lewis rats. Syngeneic Lewis MSCs were administered intravenously. Transplants were harvested on day 3, and inflammation was examined by quantitative RT-PCR and histology. Similarly to MSCs from other species, rat MSCs in vitro also showed a dose-dependent immunomodulatory capacity. Most importantly, in vivo administration of MSCs reduced the intragraft gene expression of different pro-inflammatory cytokines, chemokines, and intercellular adhesion molecule-1. In addition, fewer antigen-presenting cells were recruited into the renal allograft. In conclusion, rat MSCs ameliorate inflammation induced by prolonged cold ischemia in kidney transplantation.

Endogenous BMP-7 is a critical molecular determinant of the reversibility of obstruction-induced renal injuries

Although obstructive uropathies are frequently correctable through surgery, the potential for permanent renal injury remains even following the successful correction of obstructions. Little is known about the intrinsic mechanisms that determine the reversibility of renal injuries. We and others found that exogenous bone morphogenic protein 7 (BMP-7) inhibits the pathogenesis of renal injury. Here, we examine the role of endogenous BMP-7 in the outcome of renal recovery following the correction of obstructive uropathies using a reversible murine model of ureteral obstruction. The role of BMP-7 was determined by examining the regulation of BMP-7 during renal recovery and by treating with either BMP-7-neutralizing antibodies or exogenous BMP-7. While BMP-7 is upregulated following the correction of obstructions that lead to reversible renal injury, the upregulation of BMP-7 is diminished following the correction of prolonged obstructions that lead to irreversible renal injury. The activation of the BMP-7 pathway is required for several processes that contribute to renal recovery including the suppression of transforming growth factor-β-dependent profibrotic pathways, the restoration of renal architecture, and the resolution of fibrotic changes in the kidney. Importantly, the therapeutic restoration of BMP-7 enhances renal recovery following the correction of prolonged obstructions that typically lead to irreversible renal injury. Together, these findings show that, while BMP-7 plays a critical role in the repair of obstruction-induced renal injuries, the potential for renal recovery from prolonged obstruction is diminished, in part, due to the dysregulation of BMP-7. Accordingly, renal recovery from obstructive uropathies may be optimized through timely intervention and adjuvant approaches to restore BMP-7 activity.

The rise of cellular therapy

In 1938, the field of Transfusion Medicine began as the simpler entity - Blood Banking. It was a discipline that focused on collecting, processing, storing and distributing end stage blood cells, plasma and plasma fractions to patients. Over the years, the field progressed to include clinical patient services such as apheresis technology and with the development of stem cell transplantation as a standard of care, Cell Therapy. Now the discipline is also finding a niche in the area of Regenerative Medicine. The role played by Transfusion Medicine practitioners in Cell Therapy and Regenerative Medicine was predicated on many factors: (1) pre-existing, established protocols for therapeutic leukapheresis, (2) prior experience with mononuclear cell collection and processing, (3) long term familiarity with, and a clear understanding of, cGMP and cGLP guidelines, Federal regulations, and the voluntary standards established by various organizations, (4) close relationships with practitioners in clinical departments of medicine, pediatrics, oncology, surgery, and their subspecialty areas. While the initial Cell Therapy programs related primarily to hematopoietic stem cell transplantation, as Regenerative Medicine programs developed, transfusion specialists found it to be a related field that would also benefit from their input. Cell Therapy and Regenerative Medicine, now provide fertile soil for the seeds of Transfusion Medicine to grow. The once narrowly defined field of Blood Banking now encompasses involvement in major new Cellular Therapy/Regenerative Medicine research protocols related to treatment of patients with cancer as well as renal, hepatic and cardiac illnesses. This in turn provides opportunities for residents and fellows to consider robust careers in the field of Transfusion Medicine. In this manner we will move forward with one eye on the past and another on the promising future.

Mesenchymal stem cells for the treatment of systemic lupus erythematosus: is the cure for connective tissue diseases within connective tissue?

Mesenchymal stem cells (MSCs) are now known to display not only adult stem cell multipotency but also robust anti-inflammatory and regenerative properties. After widespread in vitro and in vivo preclinical testing in several autoimmune disease models, allogenic MSCs have been successfully applied in patients with severe treatment-refractory systemic lupus erythematosus. The impressive results of these uncontrolled phase I and II trials - mostly in patients with non-responding renal disease - point to the need to perform controlled multicentric trials. In addition, they suggest that there is much to be learned from the basic and clinical science of MSCs in order to reap the full potential of these multifaceted progenitor cells in the treatment of autoimmune diseases.

Injectable multidomain peptide nanofiber hydrogel as a delivery agent for stem cell secretome

Peptide hydrogels show immense promise as therapeutic materials. Here we present a rationally designed multidomain peptide that self-assembles into nanofibers approximately 8 nm wide, 2 nm high, and micrometers in length in the presence of Mg(2+). At a concentration of 1% by weight, the peptide forms an extensive nanofibers network that results in a physically cross-linked viscoelastic hydrogel. This hydrogel undergoes shear thinning and then quickly recovers nearly 100% of its elastic modulus when the shearing force is released, making it ideal for use as an injectable material. When placed in the presence of human embryonic stem cells (ESCs), the nanofibrous hydrogel acts like a sponge, soaking up the vast array of growth factors and cytokines released by the ESCs. The peptide hydrogel sponge can then be removed from the presence of the ESCs and placed in a therapeutic environment, where it can subsequently release these components. In vitro experiments demonstrate that release of stem cell secretome from these hydrogels in the presence of glomerular epithelial cells treated with high glucose significantly decreased protein permeability in a model of diabetes-induced kidney injury. Tracking experiments were then performed to determine the fate of the hydrogel upon injection in vivo. Hydrogels labeled with a Gd(3+) MRI contrast agent were injected into the abdominal cavity of mice and found to remain localized over 24 h. This implies that the hydrogel possesses sufficient rigidity to remain localized and release stem cell secretome over time rather than immediately dissolving in the abdominal cavity. Together, the shear thinning and recovery as observed by rheometry as well as secretome absorption and release in vivo demonstrate the potential of the nanofibrous multidomain peptide hydrogel as an injectable delivery agent.

Regenerative medicine of the kidney

End stage renal disease is a major health problem in this country and worldwide. Although dialysis and kidney transplantation are currently used to treat this condition, kidney regeneration resulting in complete healing would be a desirable alternative. In this review we focus our attention on current therapeutic approaches used clinically to delay the onset of kidney failure. In addition we describe novel approaches, like Tissue Engineering, Stem cell Applications, Gene Therapy, and Renal Replacement Therapy that may one day be possible alternative therapies for patients with the hope of delaying kidney failure or even stopping the progression of renal disease.

Selecting the optimal cell for kidney regeneration: fetal, adult or reprogrammed stem cells

Chronic kidney disease (CKD) is a progressive loss in renal function over a period of months or years. End-stage renal disease (ESRD) or stage 5 CKD ensues when renal function deteriorates to under 15% of the normal range. ESRD requires either dialysis or, preferentially, a kidney organ allograft, which is severely limited due to organ shortage for transplantation. To combat this situation, one needs to either increase supply of organs or decrease their demand. Two strategies therefore exist: for those that have completely lost their kidney function (ESRD), we will need to supply new kidneys. Taking into account the kidneys' extremely complex structure, this may prove to be impossible in the near future. In contrast, for those patients that are in the slow progression route from CKD to ESRD but still have functional kidneys, we might be able to halt progression by introducing stem cell therapy to diseased kidneys to rejuvenate or regenerate individual cell types. Multiple cell compartments that fall into three categories are likely to be worthy targets for cell repair: vessels, stroma (interstitium) and nephron epithelia. Different stem/progenitor cells can be linked to regeneration of specific cell types; hematopoietic progenitors and hemangioblastic cell types have specific effects on the vascular niche (vasculogenesis and angiogenesis). Multipotent stromal cells (MSC), whether derived from the bone marrow or isolated from the kidney's non-tubular compartment, may, in turn, heal nephron epithelia via paracrine mechanisms. Nevertheless, as we now know that all of the above lack nephrogenic potential, we should continue our quest to derive genuine nephron (epithelial) progenitors from differentiated pluripotent stem cells, from fetal and adult kidneys and from directly reprogrammed somatic cells.

Selective depletion of mouse kidney proximal straight tubule cells causes acute kidney injury

The proximal straight tubule (S3 segment) of the kidney is highly susceptible to ischemia and toxic insults but has a remarkable capacity to repair its structure and function. In response to such injuries, complex processes take place to regenerate the epithelial cells of the S3 segment; however, the precise molecular mechanisms of this regeneration are still being investigated. By applying the “toxin receptor mediated cell knockout” method under the control of the S3 segment-specific promoter/enhancer, Gsl5, which drives core 2 β-1,6-N-acetylglucosaminyltransferase gene expression, we established a transgenic mouse line expressing the human diphtheria toxin (DT) receptor only in the S3 segment. The administration of DT to these transgenic mice caused the selective ablation of S3 segment cells in a dose-dependent manner, and transgenic mice exhibited polyuria containing serum albumin and subsequently developed oliguria. An increase in the concentration of blood urea nitrogen was also observed, and the peak BUN levels occurred 3–7 days after DT administration. Histological analysis revealed that the most severe injury occurred in the S3 segments of the proximal tubule, in which tubular cells were exfoliated into the tubular lumen. In addition, aquaporin 7, which is localized exclusively to the S3 segment, was diminished. These results indicate that this transgenic mouse can suffer acute kidney injury (AKI) caused by S3 segment-specific damage after DT administration. This transgenic line offers an excellent model to uncover the mechanisms of AKI and its rapid recovery.