Rare Incorporation of Bone Marrow-Derived Cells Into Kidney After Folic Acid-Induced Injury

NAC Pre-Administration Prevents Cardiac Mitochondrial Bioenergetics, Dynamics, Biogenesis, and Redox Alteration in Folic Acid-AKI-Induced Cardio-Renal Syndrome Type 3

The incidence of kidney disease is increasing worldwide. Acute kidney injury (AKI) can strongly favor cardio-renal syndrome (CRS) type 3 development. However, the mechanism involved in CRS development is not entirely understood. In this sense, mitochondrial impairment in both organs has become a central axis in CRS physiopathology. This study aimed to elucidate the molecular mechanisms associated with cardiac mitochondrial impairment and its role in CRS development in the folic acid-induced AKI (FA-AKI) model. Our results showed that 48 h after FA-AKI, the administration of N-acetyl-cysteine (NAC), a mitochondrial glutathione regulator, prevented the early increase in inflammatory and cell death markers and oxidative stress in the heart. This was associated with the ability of NAC to protect heart mitochondrial bioenergetics, principally oxidative phosphorylation (OXPHOS) and membrane potential, through complex I activity and the preservation of glutathione balance, thus preventing mitochondrial dynamics shifting to fission and the decreases in mitochondrial biogenesis and mass. Our data show, for the first time, that mitochondrial bioenergetics impairment plays a critical role in the mechanism that leads to heart damage. Furthermore, NAC heart mitochondrial preservation during an AKI event can be a valuable strategy to prevent CRS type 3 development.

Environmental Cadmium Exposure and Dental Indices in Orthodontic Patients

BACKGROUND

Previous studies have shown that environmental cadmium exposure could disrupt salivary gland function and is associated with dental caries and reduced bone density. Therefore, this cross-sectional study attempted to determine whether tooth decay with tooth loss following cadmium exposure is associated with some dental or skeletal traits such as malocclusions, sagittal skeletal pattern, and tooth decay.

METHODS

Between August 2019 and June 2020, 60 orthodontic patients with no history of previous orthodontics, functional appliances, or surgical treatment were examined. The patients were stratified into two groups according to their urine cadmium concentrations: high (>1.06 µg/g creatinine, n = 28) or low (<1.06 µg/g creatinine, n = 32).

RESULTS

The patients were 25.07 ± 4.33 years old, and most were female (female/male: 51/9 or 85%). The skeletal relationship was mainly Class I (48.3%), followed by Class II (35.0%) and Class III (16.7%). Class I molar relationships were found in 46.7% of these patients, Class II molar relationships were found in 15%, and Class III molar relationships were found in 38.3%. The mean decayed, missing, and filled surface (DMFS) score was 8.05 ± 5.54, including 2.03 ± 3.11 for the decayed index, 0.58 ± 1.17 for the missing index, and 5.52 ± 3.92 for the filled index. The mean index of complexity outcome and need (ICON) score was 53.35 ± 9.01. The facial patterns of these patients were within the average low margin (26.65 ± 5.53 for Frankfort-mandibular plane angle (FMA)). There were no significant differences in the above-mentioned dental indices between patients with high urine cadmium concentrations and those with low urine cadmium concentrations. Patients were further stratified into low (<27, n = 34), average (27-34, n = 23), and high (>34, n = 3) FMA groups. There were no statistically significant differences in the urine cadmium concentration among the three groups. Nevertheless, a marginally significant p-value of 0.05 for urine cadmium concentration was noted between patients with low FMA and patients with high FMA.

CONCLUSION

This analysis found no association between environmental cadmium exposure and dental indices in our orthodontic patients.

Stem/progenitor cell in kidney: characteristics, homing, coordination, and maintenance

Renal failure has a high prevalence and is becoming a public health problem worldwide. However, the renal replacement therapies such as dialysis are not yet satisfactory for its multiple complications. While stem/progenitor cell-mediated tissue repair and regenerative medicine show there is light at the end of tunnel. Hence, a better understanding of the characteristics of stem/progenitor cells in kidney and their homing capacity would greatly promote the development of stem cell research and therapy in the kidney field and open a new route to explore new strategies of kidney protection. In this review, we generally summarize the main stem/progenitor cells derived from kidney in situ or originating from the circulation, especially bone marrow. We also elaborate on the kidney-specific microenvironment that allows stem/progenitor cell growth and chemotaxis, and comment on their interaction. Finally, we highlight potential strategies for improving the therapeutic effects of stem/progenitor cell-based therapy. Our review provides important clues to better understand and control the growth of stem cells in kidneys and develop new therapeutic strategies.

Acute kidney injury pathology and pathophysiology: a retrospective review

Acute kidney injury (AKI) is the clinical term used for decline or loss of renal function. It is associated with chronic kidney disease (CKD) and high morbidity and mortality. However, not all causes of AKI lead to severe consequences and some are reversible. The underlying pathology can be a guide for treatment and assessment of prognosis. The Kidney Disease: Improving Global Outcomes guidelines recommend that the cause of AKI should be identified if possible. Renal biopsy can distinguish specific AKI entities and assist in patient management. This review aims to show the pathology of AKI, including glomerular and tubular diseases.

Chronic impairment of mitochondrial bioenergetics and β-oxidation promotes experimental AKI-to-CKD transition induced by folic acid

Recent studies suggest that mitochondrial bioenergetics and oxidative stress alterations may be common mechanisms involved in the progression of renal damage. However, the evolution of the mitochondrial alterations over time and the possible effects that their prevention could have in the progression of renal damage are not clear. Folic acid (FA)-induced kidney damage is a widely used experimental model to induce acute kidney injury (AKI), which can evolve to chronic kidney disease (CKD). Therefore, it has been extensively applied to study the mechanisms involved in AKI-to-CKD transition. We previously demonstrated that one day after FA administration, N-acetyl-cysteine (NAC) pre-administration prevented the development of AKI induced by FA. Such therapeutic effect was related to mitochondrial preservation. In the present study, we characterized the temporal course of mitochondrial bioenergetics and redox state alterations along the progression of renal damage induced by FA. Mitochondrial function was studied at different time points and showed a sustained impairment in oxidative phosphorylation capacity and a decrease in β-oxidation, decoupling, mitochondrial membrane potential depolarization and a pro-oxidative state, attributed to the reduction in activity of complexes I and III and mitochondrial cristae effacement, thus favoring the transition from AKI to CKD. Furthermore, the mitochondrial protection by NAC administration before AKI prevented not only the long-term deterioration of mitochondrial function at the chronic stage, but also CKD development. Taken together, our results support the idea that the prevention of mitochondrial dysfunction during an AKI event can be a useful strategy to prevent the transition to CKD.

Characterization of Matricellular Protein Expression Signatures in Mechanistically Diverse Mouse Models of Kidney Injury

Fibrosis is the most common pathophysiological manifestation of Chronic Kidney Disease (CKD). It is defined as excessive deposition of extracellular matrix (ECM) proteins. Embedded within the ECM are a family of proteins called Matricellular Proteins (MCPs), which are typically expressed during chronic pathologies for ECM processing. As such, identifying potential MCPs in the pathological secretome of a damaged kidney could serve as diagnostic/therapeutic targets of fibrosis. Using published RNA-Seq data from two kidney injury mouse models of different etiologies, Folic Acid (FA) and Unilateral Ureteral Obstruction (UUO), we compared and contrasted the expression profile of various members from well-known MCP families during the Acute and Fibrotic injury phases. As a result, we identified common and distinct MCP expression signatures between both injury models. Bioinformatic analysis of their differentially expressed MCP genes revealed similar top annotation clusters from Molecular Function and Biological Process networks, which are those commonly involved in fibrosis. Using kidney lysates from FA- and UUO-injured mice, we selected MCP genes from our candidate list to confirm mRNA expression by Western Blot, which correlated with injury progression. Understanding the expressions of MCPs will provide important insight into the processes of kidney repair, and may validate MCPs as biomarkers and/or therapeutic targets of CKD.

Found in Translation: Reasons for Optimism in the Pursuit to Prevent Chronic Kidney Disease After Acute Kidney Injury

Purpose of review:

The current review will discuss on the progress of studying the transition phase between acute kidney injury (AKI) and chronic kidney disease (CKD) through improved animal models, common AKI and CKD pathways, and how human studies may inform different translational approaches.

Sources of information:

PubMed and Google Scholar.

Methods:

A narrative review was performed using the main terms “acute kidney injury,” “chronic kidney disease,” “end-stage renal disease,” “animal models,” “review,” “decision-making,” and “translational research.”

Key findings:

The last decade has shown much progress in the study of AKI, including evidence of a pathophysiological link between AKI and CKD. We are now in a phase of redesigning animal models and discovering mechanisms that can replicate the pathological conditions of the AKI-to-CKD continuum. Translating these findings into the clinic is a barrier that must be overcome. To this end, current efforts include prediction of AKI onset and maladaptive repair, detecting patients susceptible to the progression of chronic maladaptive repair, and understanding shared signaling mechanisms between AKI and CKD.

Limitations:

This is a narrative review of the literature that is partially influenced by the knowledge, perspectives, and experiences of the authors and their research background.

Implications:

Overall, this new knowledge from the AKI-to-CKD continuum will help bridge the discontinuity that exists between animal models and patients, resulting in more effective translational biomarkers and therapeutics to test in known AKI pathologies thereby preventing the chronicity of kidney injury progression.

Protective effects of N-acetyl-cysteine in mitochondria bioenergetics, oxidative stress, dynamics and S-glutathionylation alterations in acute kidney damage induced by folic acid

Folic acid (FA)-induced acute kidney injury (AKI) is a widely used model for studies of the renal damage and its progression to chronic state. However, the molecular mechanisms by which FA induces AKI remain poorly understood. Since renal function depends on mitochondrial homeostasis, it has been suggested that mitochondrial alterations contribute to AKI development. Additionally, N-acetyl-cysteine (NAC) can be a protective agent to prevent mitochondrial and renal dysfunction in this model, given its ability to increase mitochondrial glutathione (GSH) and to control the S-glutathionylation levels, a reversible post-translational modification that has emerged as a mechanism able to link mitochondrial energy metabolism and redox homeostasis. However, this hypothesis has not been explored. The present study demonstrates for the first time that, at 24 h, FA induced mitochondrial bioenergetics, redox state, dynamics and mitophagy alterations, which are involved in the mechanisms responsible for the AKI development. On the other hand, NAC preadministration was able to prevent mitochondrial bioenergetics, redox state and dynamics alterations as well as renal damage. The protective effects of NAC on mitochondria and renal function could be related to its observed capacity to preserve the S-glutathionylation process and GSH levels in mitochondria. Taken together, our results support the idea that these mitochondrial processes can be targets for the prevention of the renal damage and its progression in FA-induced AKI model.

Kidney disease models: tools to identify mechanisms and potential therapeutic targets

Acute kidney injury (AKI) and chronic kidney disease (CKD) are worldwide public health problems affecting millions of people and have rapidly increased in prevalence in recent years. Due to the multiple causes of renal failure, many animal models have been developed to advance our understanding of human nephropathy. Among these experimental models, rodents have been extensively used to enable mechanistic understanding of kidney disease induction and progression, as well as to identify potential targets for therapy. In this review, we discuss AKI models induced by surgical operation and drugs or toxins, as well as a variety of CKD models (mainly genetically modified mouse models). Results from recent and ongoing clinical trials and conceptual advances derived from animal models are also explored.

Identification and isolation of kidney-derived stem cells from transgenic rats with diphtheria toxin-induced kidney damage

Adult stem cells have been well characterized in numerous organs, with the exception of the kidneys. Therefore, the present study aimed to identify and isolate kidney-derived stem cells. A total of 12 Fischer 344 transgenic rats expressing the human diphtheria toxin receptor in podocyte cells of the kidney, were used in the present study. The rats were administered 5-bromo-2′-deoxyuridine (BrdU) in order to detect cellular proliferation. After 60 days, the rats were treated with the diphtheria toxin (DT), in order to induce kidney injury. Immunohistochemical analysis indicated that the number of BrdU-positive cells were increased following DT treatment. In addition, the expression of octamer-binding transcription factor 4 (Oct-4), a stem cell marker, was detected and suggested that kidney-specific stem cells were present in the DT-treated tissue samples. Furthermore, tissue samples exhibited repair of the DT-induced injury. Further cellular culturing was conducted in order to isolate the kidney-specific stem cells. After 5 weeks of culture, the majority of the cells were non-viable, with the exception of certain specialized, unique cell types, which were monomorphic and spindle-shaped in appearance. The unique cells were isolated and subjected to immunostaining and reverse transcription-polymerase chain reaction analyses in order to reconfirm the expression of Oct-4 and to detect the expression of Paired box 2 (Pax-2), which is necessary for the formation of kidney structures. The unique cells were positive for Oct-4 and Pax-2; thus suggesting that the identified cells were kidney-derived stem cells. The results of the present study suggested that the unique cell type identified in the kidneys of the DT-treated rats were kidney-specific stem cells that may have been involved in the repair of DT-induced tissue injury. In addition, these cells may provide a useful cell line for studying the fundamental characteristics of kidney stem cells, as well as identifying kidney-specific stem cell markers.

Increasing Proliferation of Intrinsic Tubular Cells after Renal Ischemia-reperfusion Injury in Adult Rat

The kidney is capable of regeneration following injury. However, whether renal stem/progenitor cells contribute to the repair process after injury, as well as the origin of the cells that repair and replace damaged renal tubule cells remains debated. Therefore, better understanding of the repair process will be critical to developing new strategies for the treatment of acute renal failure. Using an ischemia-reperfusion injury mode and an immunocytochemistry method, we counted the number of BrdU-positive cells in damged regions at different durations of reperfusion. We found that BrdU, a cell proliferative marker, was mainly incorporated in the tubular cells of both medulla and cortex 1 day after reperfusion. The number of BrdU-positive cells reached a peak at 3 days and lasted for two months after injury. BrdU-positive cells were barely found in the renal glomerulus and the parietal layer of Bowman's capsule after injury, and only a few were found in the intersititium. PAX2, an embryonic renal marker, was also increased in renal tubule cells. Confocal images show that BrdU-positive cells co-expressed PAX2, but not the activated form of caspase-3, a cell death marker. Our data suggest that renal stem-like cells or dedifferentiation of surviving renal tubular cells in both the medulla and cortex may predominantly contribute to the repair process after renal ischemia-reperfusion injury in rat.

Translational value of animal models of kidney failure

Acute kidney injury (AKI) and chronic kidney disease (CKD) are associated with decreased renal function and increased mortality risk, while the therapeutic armamentarium is unsatisfactory. The availability of adequate animal models may speed up the discovery of biomarkers for disease staging and therapy individualization as well as design and testing of novel therapeutic strategies. Some longstanding animal models have failed to result in therapeutic advances in the clinical setting, such as kidney ischemia-reperfusion injury and diabetic nephropathy models. In this regard, most models for diabetic nephropathy are unsatisfactory in that they do not evolve to renal failure. Satisfactory models for additional nephropathies are needed. These include anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis, IgA nephropathy, anti-phospholipase-A2-receptor (PLA2R) membranous nephropathy and Fabry nephropathy. However, recent novel models hold promise for clinical translation. Thus, the AKI to CKD translation has been modeled, in some cases with toxins of interest for human CKD such as aristolochic acid. Genetically modified mice provide models for Alport syndrome evolving to renal failure that have resulted in clinical recommendations, polycystic kidney disease models that have provided clues for the development of tolvaptan, that was recently approved for the human disease in Japan; and animal models also contributed to target C5 with eculizumab in hemolytic uremic syndrome. Some ongoing trials explore novel concepts derived from models, such TWEAK targeting as tissue protection for lupus nephritis. We now review animal models reproducing diverse, genetic and acquired, causes of AKI and CKD evolving to kidney failure and discuss the contribution to clinical translation and prospects for the future.

Protective effects of mesenchymal stem cells with CXCR4 up-regulation in a rat renal transplantation model

The homing of mesenchymal stem cells to injured tissue, which is important for the correction of conditions such as ischemia-reperfusion injury (IRI) and immunolesions, has been performed previously, but with poor efficiency. Substantial improvements in engraftment are required to derive clinical benefits from MSC transplantation. Chemokines are the most important factors that control cellular migration. Stromal derived factor-1 (SDF-1) is up-regulated during tissue/organ ischemia damage, and its cognate receptor, chemokine receptor 4 (CXCR4), is involved in stem cell migration. The aim of our study was to investigate CXCR4 expression in MSCs and to validate both its role in mediating migration to transplanted kidneys and its immunoregulatory effects in renal protection. Specifically, the present study was designed to investigate the short-term tissue homing of MSCs carrying genetically modified CXCR4 in a rat renal transplantation model. We tested the hypothesis that MSCs with CXCR4 over-expression can more efficiently regulate immunological reactions. Lentiviral vectors were used to over-express CXCR4 or to introduce a short hairpin ribonucleic acid (shRNA) construct targeting endogenous CXCR4 in rat MSCs. MSCs were labeled with enhanced green fluorescent protein (eGFP). After cell sorting, recipient kidneys were regionally perfused; recipient animals were injected with transduced MSCs, native MSCs, or PBS via tail vein following renal transplantation; and the effects of MSC injection were observed.

Protection of mesenchymal stem cells on acute kidney injury

The aim of the present study was to determine the protection of allogeneic bone marrow mesenchymal stem cells (BMSCs) on an ischaemia/reperfusion (I/R)‑induced acute kidney injury (AKI) rat model and to investigate the underlying mechanisms. The BMSCs were isolated and cultured from adult Sprague‑Dawley (SD) rats and the I/R‑induced AKI model was established by bilateral clamping of renal pedicles for 60 min. Following successfully establishing the AKI model, 1x106 BMSCs were administered by intrarenal injection. All animals were randomly divided into four groups (n=10 in each): 1 (sham control), 2 (I/R), 3 (I/R+culture medium) and 4 (I/R+BMSCs). Serum levels of creatinine (Cr) and blood urea nitrogen (BUN) were measured in all four groups at 24 and 72 h. Three days post‑surgery, the level of inflammatory factors, including interleukin‑6 (IL‑6), tumour necrosis factor‑α (TNF‑α) and vascular endothelial growth factor (VEGF) in the kidney was analysed by quantitative polymerase chain reaction. Three days following surgery, mRNA expression levels of IL‑6 and TNF‑α were significantly lower, however, the expression level of VEGF was significantly higher in group 4 compared with groups 2 and 3 (P<0.05). By contrast, the immunofluorescence results showed that the injected BMSCs differentiated into vascular endothelial cells. In conclusion, the present study identified that intrarenal administration of BMSCs improved I/R‑induced AKI through the anti‑inflammatory effect and a paracrine mechanism and therefore, may be hypothesised for the use in clinical trials.

Differential expression of functional Fc-receptors and additional immune complex receptors on mouse kidney cells

The precise mechanisms by which circulating immune complexes accumulate in the kidney to form deposits in glomerulonephritis are not well understood. In particular, the role of resident cells within glomeruli of the kidney has been widely debated. Immune complexes have been shown to bind one glomerular cell type (mesangial cells) leading to functional responses such as pro-inflammatory cytokine production. To further assess the presence of functional immunoreceptors on resident glomerular cells, cultured mouse renal epithelial, endothelial, and mesangial cells were treated with heat-aggregated mouse IgG or preformed murine immune complexes. Mesangial and renal endothelial cells were found to bind IgG complexes, whereas glomerular epithelial cell binding was minimal. A blocking antibody for Fc-gamma receptors reduced binding to mesangial cells but not renal endothelial cells, suggesting differential immunoreceptor utilization. RT-PCR and immunostaining based screening of cultured renal endothelial cells showed limited low-level expression of known Fc-receptors and Ig binding proteins. The interaction between mesangial cells and renal endothelial cells and immune complexes resulted in distinct, cell-specific patterns of chemokine and cytokine production. This novel pathway involving renal endothelial cells likely contributes to the predilection of circulating immune complex accumulation within the kidney and to the inflammatory responses that drive kidney injury.

Bone marrow-derived cells can acquire renal stem cells properties and ameliorate ischemia-reperfusion induced acute renal injury

Background

Bone marrow (BM) stem cells have been reported to contribute to tissue repair after kidney injury model. However, there is no direct evidence so far that BM cells can trans-differentiate into renal stem cells.

Methods

To investigate whether BM stem cells contribute to repopulate the renal stem cell pool, we transplanted BM cells from transgenic mice, expressing enhanced green fluorescent protein (EGFP) into wild-type irradiated recipients. Following hematological reconstitution and ischemia-reperfusion (I/R), Sca-1 and c-Kit positive renal stem cells in kidney were evaluated by immunostaining and flow cytometry analysis. Moreover, granulocyte colony stimulating factor (G-CSF) was administrated to further explore if G-CSF can mobilize BM cells and enhance trans-differentiation efficiency of BM cells into renal stem cells.

Results

BM-derived cells can contribute to the Sca-1⁺ or c-Kit⁺ renal progenitor cells population, although most renal stem cells came from indigenous cells. Furthermore, G-CSF administration nearly doubled the frequency of Sca-1+ BM-derived renal stem cells and increased capillary density of I/R injured kidneys.

Conclusions

These findings indicate that BM derived stem cells can give rise to cells that share properties of renal resident stem cell. Moreover, G-CSF mobilization can enhance this effect.

Silencing of hypoxia-inducible factor-1α gene attenuated angiotensin II-induced renal injury in Sprague-Dawley rats

Although it has been shown that upregulation of hypoxia-inducible factor (HIF)-1α is protective in acute ischemic renal injury, long-term overactivation of HIF-1α is implicated to be injurious in chronic kidney diseases. Angiotensin II (Ang II) is a well-known pathogenic factor producing chronic renal injury and has also been shown to increase HIF-1α. However, the contribution of HIF-1α to Ang II-induced renal injury has not been evidenced. The present study tested the hypothesis that HIF-1α mediates Ang II-induced renal injury in Sprague-Dawley rats. Chronic renal injury was induced by Ang II infusion (200 ng/kg per minute) for 2 weeks in uninephrectomized rats. Transfection of vectors expressing HIF-1α small hairpin RNA into the kidneys knocked down HIF-1α gene expression by 70%, blocked Ang II-induced HIF-1α activation, and significantly attenuated Ang II-induced albuminuria, which was accompanied by inhibition of Ang II-induced vascular endothelial growth factor, a known glomerular permeability factor, in glomeruli. HIF-1α small hairpin RNA also significantly improved the glomerular morphological damage induced by Ang II. Furthermore, HIF-1α small hairpin RNA blocked Ang II-induced upregulation of collagen and α-smooth muscle actin in tubulointerstitial region. There was no difference in creatinine clearance and Ang II-induced increase in blood pressure. HIF-1α small hairpin RNA had no effect on Ang II-induced reduction in renal blood flow and hypoxia in the kidneys. These data suggested that overactivation of HIF-1α-mediated gene regulation in the kidney is a pathogenic pathway mediating Ang II-induced chronic renal injuries, and normalization of overactivated HIF-1α may be used as a treatment strategy for chronic kidney damages associated with excessive Ang II.

Kidney repair and stem cells: a complex and controversial process

Over the last decade, stem cells have been the topic of much debate and investigation for their regenerative potential in the case of renal injury. This review focuses on bone marrow stem cells (BMSC) for renal repair and the potential origins of the controversial results between studies. Some authors have shown that BMSC can differentiate into renal cells and reverse renal dysfunction while others obtained contradictory results. One significant variation between these studies is the choice of BMSC used. According to the literature and our own experience, unfractionated bone marrow cells and hematopoietic stem cells are able to lead to long-term cell tissue engraftment and repair, whereas mesenchymal stem cells have a short-term paracrine effect. Detection of the bone-marrow-derived cells is also an important source of error. However, the major difference between studies is the model of kidney injury used. Two categories of models have to be distinguished: acute and chronic kidney disease. However, variation within these categories also exists. The outcomes of various strategies for BMSC transplantation after injury to the kidney must be compared within a single model and cannot be transposed from one model to another.

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.

Kidney preservation by bone marrow cell transplantation in hereditary nephropathy

The prospect of cell-based therapy for kidney disease remains controversial despite its immense promise. We had previously shown that transplanting bone marrow and hematopoietic stem cells could generate renal cells and lead to the preservation of kidney function in a mouse model for cystinosis (Ctns(-/-)) that develops chronic kidney injury, 4 months post transplantation. Here, we determined the long-term effects of bone marrow stem cell transplantation on the kidney disease of Ctns(-/-) mice 7 to 15 months post transplantation. Transfer of bone marrow stem cells expressing a functional Ctns gene provided long-term protection to the kidney. Effective therapy, however, depended on achieving a relatively high level of donor-derived blood cell engraftment of Ctns-expressing cells, which was directly linked to the quantity of these cells within the kidney. In contrast, kidney preservation was dependent neither on renal cystine content nor on the age of the mice at the time of transplant. Most of the bone marrow-derived cells within the kidney were interstitial and not epithelial, suggesting that the mechanism involved an indirect protection of the tubules. Thus, our model may help in developing strategies to enhance the potential success of cell-based therapy for kidney injury and in understanding some of the discrepancies currently existing in the field.

Folic acid induces acute renal failure (ARF) by enhancing renal prooxidant state

Systemic administration of folic acid (FA) in mice was used for studying the pathogenesis associated with acute renal failure (ARF). However, the mechanism by which FA induces ARF remains poorly understood. The present study therefore, was planned to investigate the effect of folic acid administration on prooxidant state and associated ultrastructural changes in renal tissue. Balb/c male mice of 4-6 weeks old were divided into control and two folic acid treatment groups (Groups A and B). The animals in group A were administered intraperitoneal injection of folic acid (100 mg kg(-1) body weight) for a period of 7 consecutive days while the animal in group B were administered a single intraperitoneal dose of folic acid (250 mg kg(-1) body weight). The renal tissues were collected and used for the analyses of lipid peroxidative indices and activities of antioxidant enzymes in renal tissues. To corroborate biochemical findings scanning electron microscopy (SEM) in renal tissue was studied. Folic acid treated animals demonstrated marked renal hypertrophy accompanied by severe impairment of renal function. Glutathione levels (GSH) and antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) levels were significantly decreased and LPO levels increased following FA treatment. SEM results further substantiated the observed biochemical changes as evident by severe inflammation in glomeruli, swelling in primary and secondary pedicels, blebbing in villi, and tremendous deprivation of erythrocytes (RBCs) in FA treated kidneys. The present study therefore suggests that acute administration of folic acid leads to the generation of oxidative stress and altered membrane architecture responsible for folic acid induced ARF.

Stem cell technology for the treatment of acute and chronic renal failure

Acute and chronic renal failure are disorders with high rates of morbidity and mortality. Current treatment is based upon conventional dialysis to provide volume regulation and small solute clearance. There is growing recognition that renal failure is a complex disease state requiring a multifactorial therapy to address the short-comings of the conventional monofactorial approach. Kidney transplantation remains the most effective treatment, however, organ availability lags far behind demand. Many key kidney functions including gluconeogenesis, ammoniagenesis, metabolism of glutathione, catabolism of important peptide hormones, growth factors, and cytokines critical to multiorgan homeostasis and immunomodulation are provided by renal tubule cells. Therefore, cell-based therapies are promising multifactorial treatment approaches. In this review, current stem cell technologies including adult stem cells, embryonic stem cells and induced pluripotent stem cells will be discussed as cell sources for the treatment of acute and chronic renal failure.

Mesenchymal stromal cells: current understanding and clinical status

Multipotent mesenchymal stromal cells (MSCs) represent a rare heterogeneous subset of pluripotent stromal cells that can be isolated from many different adult tissues that exhibit the potential to give rise to cells of diverse lineages. Numerous studies have reported beneficial effects of MSCs in tissue repair and regeneration. After culture expansion and in vivo administration, MSCs home to and engraft to injured tissues and modulate the inflammatory response through synergistic downregulation of proinflammatory cytokines and upregulation of both prosurvival and antiinflammatory factors. In addition, MSCs possess remarkable immunosuppressive properties, suppressing T-cell, NK cell functions, and also modulating dentritic cell activities. Tremendous progress has been made in preclinical studies using MSCs, including the ability to use allogeneic cells, which has driven the application of MSCs toward the clinical setting. This review highlights our current understanding into the biology of MSCs with particular emphasis on the cardiovascular and renal applications, and provides a brief update on the clinical status of MSC-based therapy.

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.

Advances in early kidney specification, development and patterning

The kidney is a model developmental system for understanding mesodermal patterning and organogenesis, a process that requires regional specification along multiple body axes, the proliferation and differentiation of progenitor cells, and integration with other tissues. Recent progress in the field has highlighted the essential roles of intrinsic nuclear factors and secreted signaling molecules in specifying renal epithelial stem cells and their self-renewal, in driving the complex dynamics of epithelial cell branching morphogenesis, and in nephron patterning. How these developments influence and advance our understanding of kidney development is discussed.

Stem cell therapy for the kidney?

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

Bone-marrow-derived cells that home to acoustic deafened cochlea preserved their hematopoietic identity

The high degree of bone marrow cell (BMC) plasticity has prompted us to test its restoration possibility in inner ear repair. Our aim was to determine the potential of these cells to transdifferentiate into specialized cochlea cell types after acoustic injury and BMC mobilization. Lethally irradiated mice were transplanted with BMCs from green fluorescent protein (GFP) transgenic mice and subjected to acoustic deafening 3 months later. In a separate experiment, stem cell factor and granulocyte colony-stimulating factor were administered to test the effect of BMC mobilization on bone marrow-derived cell (BMDC) transdifferentiation. All mice showed almost complete chimerism 3 months after bone marrow transplantation. Upon acoustic trauma, robust BMDC migration was observed in the deafened cochlea. GFP+ cell migration was most prominent during the first week after acoustic deafening, and these cells accumulated significantly at the spiral ligament, perilymphatic compartment walls, and limbus regions. Most of the BMDCs expressed CD45 and CD68 and were identified as macrophages. Upregulation of stromal-derived factor 1 (SDF-1) was also observed in the spiral ligament during the first week after acoustic deafening. Cytokine treatment resulted in increased BMC mobilization in the systemic circulation. However, the presence of any stem cell progenitors or the differentiation of BMDCs into any cell types expressing cochlea sensory, supporting, fibrocytic, or neuronal markers were not detected in the deafened cochlea. In conclusion, we have demonstrated the homing capability of BMDCs to the deafened cochlea, and these cells displayed mature hematopoietic properties without spontaneous transdifferentiation to any cochlea cell types after acoustic trauma or bone marrow mobilization.

Do stem cells exist in the adult kidney?

Adult stem cells exist in many organs and play a critical role in normal cell turnover and the response to injury. The existence of adult stem cells in the mammalian kidney remains controversial. Kidney stem cells have been isolated and characterized by many groups, often with discrepant results. This article will review the current state of knowledge regarding adult kidney stem cells and discuss future directions for kidney stem cell research.

[Regenerative therapy in nephrology. Repair or construction?]

Animal experiments and analyses of human renal tissues show that regeneration of degraded renal tubules is caused by adjacent surviving tubules. Differentiation, migration, proliferation and redifferentiation are regulated by local growth factors. Renal stem cells can also participate in this process. Mesenchymal stem cells play a pivotal role in renal regeneration and if these are still present in the adult kidney, they could be the source material for repair and regeneration following injury. The exact location and role of resident mesenchymal stem cells which have been demonstrated in the kidneys is still unclear. New surface markers and a better characterisation of the many cell populations possibly participating in the regeneration process are necessary in order to clarify their complex interaction. It is also unclear whether mesenchymal stem cells from bone marrow or other organs are also involved. In addition to structural regeneration, the stem cells also play a role in the functional recovery following acute renal failure. Artificial regeneration of human kidneys is difficult due to their functional and spatial complexity. By the additional use of cells in dialysis machines it may be possible to improve the quality of filtration and also replace other renal functions. Initial results using this new technique in clinical phase I/II studies on patients with acute renal failure are promising.

Phenotypic transitions and fibrosis in diabetic nephropathy

The cause of renal fibrosis in diabetic nephropathy is widely believed to be phenotypic switching of fibroblasts to an activated state. However, emerging evidence suggests that diabetes also alters the phenotype of normal, non-fibroblast kidney cells, such as mesangial cells, tubular epithelial cells, and bone marrow-derived progenitors. Experiments have shown that cytokines, high glucose, and advanced glycation end products induce profibrotic changes in kidney cell phenotype by the processes of myofibroblast transdifferentiation and epithelial-mesenchymal transition. As a result, differentiated kidney cells become reprogrammed to secrete and accumulate extracellular matrix. This revised view implies that inhibiting phenotypic transitions in nonfibroblasts might limit fibrosis in diabetic nephropathy.

Blocking tumor necrosis factor-α inhibits folic acid-induced acute renal failure

Systemic administration of mice with folic acid (FA) has been used for studying the pathogenesis of acute renal failure. However, the molecular mechanisms by which FA induces acute renal failure remain poorly understood. We found that CD-1 mice treated with FA developed acute renal failure characterized by increased blood urea nitrogen, necrosis, and apoptosis of tubular epithelial cells. Compared to control mice, tumor necrosis factor-alpha (TNF-alpha) was markedly elevated in blood and kidneys of these FA-treated mice, accompanied by markedly reduced expression of anti-apoptotic protein BclxL in their kidneys. In vivo administration of FA-treated CD-1 mice with neutralizing anti-TNF-alpha antibody restored the expression of BclxL in kidneys and inhibited the necrosis and apoptosis of renal tubular epithelial cells, leading to the amelioration of acute renal failure. In ex vivo cultures, we found that FA enhanced production of TNF-alpha, decreased expression of BclxL protein, and induced apoptosis of mouse cortical tubule (MCT) cells. Addition of neutralizing anti-TNF-alpha antibody, but not control IgG, in the cultures markedly blocked the apoptotic death of FA-treated MCT cells and restored expression of BclxL to the same levels as those MCT cells cultured in the absence of FA. All these results suggest that TNF-alpha is a critical inflammatory cytokine responsible for FA-mediated acute renal failure. Furthermore, in vivo administration of anti-TNF-alpha antibody may be proved as an effective approach for acute renal failure prevention and treatment.

Isolation and characterization of kidney-derived stem cells

Acute kidney injury is followed by regeneration of damaged renal tubular epithelial cells. The purpose of this study was to test the hypothesis that renal stem cells exist in the adult kidney and participate in the repair process. A unique population of cells that behave in a manner that is consistent with a renal stem cell were isolated from rat kidneys and were termed multipotent renal progenitor cells (MRPC). Features of these cells include spindle-shaped morphology; self-renewal for >200 population doublings without evidence for senescence; normal karyotype and DNA analysis; and expression of vimentin, CD90 (thy1.1), Pax-2, and Oct4 but not cytokeratin, MHC class I or II, or other markers of more differentiated cells. MRPC exhibit plasticity that is demonstrated by the ability of the cells to be induced to express endothelial, hepatocyte, and neural markers by reverse transcriptase-PCR and immunohistochemistry. The cells can differentiate into renal tubules when injected under the capsule of an uninjured kidney or intra-arterially after renal ischemia-reperfusion injury. Oct4 expression was seen in some tubular cells in the adult kidney, suggesting these cells may be candidate renal stem cells. It is proposed that MRPC participate in the regenerative response of the kidney to acute injury.

Stem Cells and Kidney Disease

Functional recovery in acute renal failure is well known, and the adult kidney is generally recognized to have the capacity to regenerate and repair. Several groups have reported the contribution of bone marrow-derived cells in this process, and others have confirmed the existence of adult stem cells in the kidney, including slow-cycling cells, side population cells, CD133+ cells and rKS56 cells. However, recent data demonstrated that in vivo differentiation of bone marrow-derived cells into renal tubular cells may not occur at all, or is at most a minor component of the repair process. Moreover, it is now generally accepted that stem cells and multipotent cells contribute to the regenerative process by producing protective and regenerative factors rather than by directly differentiating to replace damaged cells. Therefore, for clinical regenerative medicine in kidney disease, the focus of stem cell biology will shift from multiple differentiation of cells or cell-therapy to multiple functions of the cells, such as the production of bone morphologic protein-7 and other regenerative factors.

Nephrogenic factors promote differentiation of mouse embryonic stem cells into renal epithelia

Embryonic stem (ES) cells have been induced to differentiate in vitro into a broad spectrum of specialized cell types, including hematopoietic, pancreatic, and neuronal cell types. Such ES-derived cells can provide a valuable source of progenitor cell types. Whereas undifferentiated ES cells can become integrated into a developing kidney and contribute to tubular epithelia, the ability to generate renal precursor cells in vitro has not been reported. This study used a combination of nephrogenic growth factors to differentiate ES cells into renal epithelial cells that are capable of integrating into a developing kidney with very high efficiency. Using a combination of retinoic acid, Activin-A, and Bmp7, cultured ES cells can be induced to express markers specific for the intermediate mesoderm, from which the kidneys arise. Embryoid bodies that are cultured in the presence of nephrogenic factors can respond to inductive signals and form epithelial structures in vitro. When injected into developing kidney rudiments, treated ES cells contribute to tubular epithelia with near 100% efficiency. These methods may facilitate the large-scale culture of renal epithelial precursor cells for a variety of applications.

Adult stem cells in the repair of the injured renal tubule

The capacity of the kidney to regenerate functional tubules following episodes of acute injury is an important determinant of patient morbidity and mortality in the hospital setting. After severe injury or repeated episodes of injury, kidney recovery can be significantly impaired or even fail completely. Although significant advances have been made in the clinical management of such cases, there is no specific therapy that can improve the rate or effectiveness of the repair process. Recent studies have indicated that adult stem cells, either in the kidney itself or derived from the bone marrow, could participate in this repair process and might therefore be utilized clinically to treat acute renal failure. This review will focus on our current understanding of these stem cells, the controversies surrounding their in vivo capacity to repopulate the renal tubule, and further investigations that will be required before stem cell therapy can be considered for use in the clinical setting.

Stem cell approaches for the treatment of renal failure

The inadequacy of current treatment modalities and insufficiency of donor organs for cadaveric transplantation have driven a search for improved methods of dealing with renal failure. The rising concept of cell-based therapeutics has provided a framework around which new approaches are being generated, and its combination with advances in stem cell research stands to bring both fields to clinical fruition. This budding partnership is presently in its very early stages, but an examination of the cell-based therapies currently under development clearly shows the magnitude of the role that stem cells will ultimately play. The issue over reports of unexpected plasticity in adult stem cell differentiation remains a focus of debate, and evidence for bone marrow-derived stem cell contributions to renal repair has been challenged. The search for adult renal stem cells, which could have a considerable impact on much of the work discussed here, appears to be narrowing. The use of embryonic tissue in research continues to provide valuable insights but will be the subject of intense societal scrutiny and debate before it reaches the stage of clinical application. Embryonic stem (ES) cells, with their ability to generate all, or nearly all, of the cell types in the adult body and a possible source of cells genetically identical to the donor, hold great promise but face ethical and political hurdles for human use. Immunoisolation of heterologous cells by encapsulation creates opportunities for their safe use as a component of implanted or ex vivo devices.

Bone marrow transplantation can attenuate the progression of mesangial sclerosis

Bone marrow (BM) transplantation has been shown to provide beneficial effects in injured organs, including heart, liver, and kidney. We explored the therapeutic potential of BM transplantation (BMT) in Wilms' tumor suppressor 1 (Wt1) heterozygous mice, which represent a model of mesangial sclerosis. After transplantation of wild-type BM, there is statistically significantly lower urinary albumin and increased survival in Wt1+/- recipients. Control BMT using Wt1+/- donors showed no significant beneficial effects. The long-term beneficial effect of BMT was dependent on the dose of irradiation applied to the recipients before BMT. At a lethal dose of 1,000 cGy, the decrease in albuminuria and prolongation of lifespan in Wt1+/- mice were transient, with maximal amelioration at 12 weeks and resumption of albuminuria by 24 weeks after BMT. This was, at least in part, due to irradiation and not Wt1 heterozygosity because wild-type recipients also developed albuminuria within 24 weeks of BMT with 1,000 cGy. In contrast, Wt1+/- mice transplanted after 400 cGy showed long-term improvement in albuminuria and lifespan. Approximately 0.4% of podocytes were marrow derived, a level that is unlikely to be responsible for the therapeutic effects. In addition, donor BM cells formed rings surrounding the glomeruli, and approximately one third of the cells in these rings were macrophages. In conclusion, transplantation of wild-type BM attenuates progression of mesangial sclerosis in the Wt1+/- model of renal disease, and the mechanism by which this occurs may involve engraftment of BM-derived cells in the renal parenchyma.