Protective effect and localization by optical imaging of human renal CD133+ progenitor cells in an acute kidney injury model

Enriched human embryonic stem cells-derived CD133+, CD24+ renal progenitors engraft and restore function in a gentamicin-induced kidney injury in mice

Introduction

Acute kidney injury (AKI) is a common health problem that leads to high morbidity and potential mortality. The failure of conventional treatments to improve forms of this condition highlights the need for innovative and effective treatment approaches. Regenerative therapies with Renal Progenitor Cells (RPCs) have been proposed as a promising new strategy. A growing body of evidence suggests that progenitor cells differentiated from different sources, including human embryonic stem cells (hESCs), can effectively treat AKI.

Methods

Here, we describe a method for generating RPCs and directed human Embryoid Bodies (EBs) towards CD133+CD24+ renal progenitor cells and evaluate their functional activity in alleviating AKI.

Results

The obtained results show that hESCs-derived CD133+CD24+ RPCs can engraft into damaged renal tubules and restore renal function and structure in mice with gentamicin-induced kidney injury, and significantly decrease blood urea nitrogen levels, suppress oxidative stress and inflammation, and attenuate histopathological disturbances, including tubular necrosis, tubular dilation, urinary casts, and interstitial fibrosis.

Conclusion

The results suggest that RPCs have a promising regenerative potential in improving renal disease and can lay the foundation for future cell therapy and disease modeling.

Role of mitochondria in endogenous renal repair

Renal tubules have potential to regenerate and repair after mild-to-moderate injury. Proliferation of tubular epithelial cells represents the initial step of this reparative process. Although for many years, it was believed that proliferating cells originated from a pre-existing intra-tubular stem cell population, there is now consensus that surviving tubular epithelial cells acquire progenitor properties to regenerate the damaged kidney. Scattered tubular-like cells (STCs) are dedifferentiated adult renal tubular epithelial cells that arise upon injury and contribute to renal self-healing and recovery by replacing lost neighboring tubular epithelial cells. These cells are characterized by the co-expression of the stem cell surface markers CD133 and CD24, as well as mesenchymal and kidney injury markers. Previous studies have shown that exogenous delivery of STCs ameliorates renal injury and dysfunction in murine models of acute kidney injury, underscoring the regenerative potential of this endogenous repair system. Although STCs contain fewer mitochondria than their surrounding terminally differentiated tubular epithelial cells, these organelles modulate several important cellular functions, and their integrity and function are critical to preserve the reparative capacity of STCs. Recent data suggest that the microenviroment induced by cardiovascular risk factors, such as obesity, hypertension, and renal ischemia may compromise STC mitochondrial integrity and function, limiting the capacity of these cells to repair injured renal tubules. This review summarizes current knowledge of the contribution of STCs to kidney repair and discusses recent insight into the key role of mitochondria in modulating STC function and their vulnerability in the setting of cardiovascular disease.

Traditional Chinese Medicine and renal regeneration: experimental evidence and future perspectives

Repair of acute kidney injury (AKI) is a typical example of renal regeneration. AKI is characterized by tubular cell death, peritubular capillary (PTC) thinning, and immune system activation. After renal tubule injury, resident renal progenitor cells, or renal tubule dedifferentiation, give rise to renal progenitor cells and repair the damaged renal tubule through proliferation and differentiation. Mesenchymal stem cells (MSCs) also play an important role in renal tubular repair. AKI leads to sparse PTC, affecting the supply of nutrients and oxygen and indirectly aggravating AKI. Therefore, repairing PTC is important for the prognosis of AKI. The activation of the immune system is conducive for the body to clear the necrotic cells and debris generated by AKI; however, if the immune activation is too strong or lengthy, it will cause damage to renal tubule cells or inhibit their repair. Macrophages have been shown to play an important role in the repair of kidney injury. Traditional Chinese medicine (TCM) has unique advantages in the treatment of AKI and a series of studies have been conducted on the topic in recent years. Herein, the role of TCM in promoting the repair of renal injury and its molecular mechanism is discussed from three perspectives: repair of renal tubular epithelial cells, repair of PTC, and regulation of macrophages to provide a reference for the treatment and mechanistic research of AKI.

Great potential of renal progenitor cells in kidney: From the development to clinic

The mammalian renal organ represents a pinnacle of complexity, housing functional filtering units known as nephrons. During embryogenesis, the depletion of niches containing renal progenitor cells (RPCs) and the subsequent incapacity of adult kidneys to generate new nephrons have prompted the formulation of protocols aimed at isolating residual RPCs from mature kidneys and inducing their generation from diverse cell sources, notably pluripotent stem cells. Recent strides in the realm of regenerative medicine and the repair of tissues using stem cells have unveiled critical signaling pathways essential for the maintenance and generation of human RPCs in vitro. These findings have ushered in a new era for exploring novel strategies for renal protection. The present investigation delves into potential transcription factors and signaling cascades implicated in the realm of renal progenitor cells, focusing on their protection and differentiation. The discourse herein elucidates contemporary research endeavors dedicated to the acquisition of progenitor cells, offering crucial insights into the developmental mechanisms of these cells within the renal milieu and paving the way for the formulation of innovative treatment modalities.

Renal ischemia alters the transcriptomic and epigenetic profile of inflammatory genes in swine scattered tubular-like cells

BACKGROUND

Scattered tubular-like cells (STCs) are differentiated renal tubular cells that during recovery from ischemic injury dedifferentiate to repair other injured renal cells. Renal artery stenosis (RAS), often associated with chronic inflammatory injury, compromises the integrity and function of STCs, but the underlying mechanisms remain unknown. We hypothesized that RAS alters the transcriptomic and epigenetic profile of inflammatory genes in swine STCs.

METHODS

STCs were harvested from pig kidneys after 10 weeks of RAS or sham (n=6 each). STC mRNA profiles of inflammatory genes were analyzed using high-throughput mRNA-sequencing (seq) and their DNA methylation (5mC) and hydroxymethylation (5hmC) profiles by DNA immunoprecipitation and next-generation sequencing (MeDIP-seq) (n=3 each), followed by an integrated (mRNA-seq/MeDIP-seq) analysis. STC protein expression of candidate differentially expressed (DE) genes and common proinflammatory proteins were subsequently assessed in vitro before and after epigenetic (Bobcat339) modulation.

RESULTS

mRNA-seq identified 57 inflammatory genes up-regulated in RAS-STCs versus Normal-STCs (>1.4 or <0.7-fold, P<0.05), of which 14% exhibited lower 5mC and 5% higher 5hmC levels in RAS-STCs versus Normal-STCs, respectively. Inflammatory gene and protein expression was higher in RAS-STCs compared with Normal-STCs but normalized after epigenetic modulation.

CONCLUSIONS

These observations highlight a novel modulatory mechanism of this renal endogenous repair system and support development of epigenetic or anti-inflammatory therapies to preserve the reparative capacity of STCs in individuals with RAS.

Renovascular Disease Induces Senescence in Renal Scattered Tubular-Like Cells and Impairs Their Reparative Potency

Scattered tubular-like cells (STCs), dedifferentiated renal tubular epithelial cells, contribute to renal self-healing, but severe injury might blunt their effectiveness. We hypothesized that ischemic renovascular disease (RVD) induces senescence in STC and impairs their reparative potency. CD24+/CD133+ STCs were isolated from swine kidneys after 16 weeks of RVD or healthy controls. To test their reparative capabilities in injured kidneys, control or RVD-STC (5×10⁵) were prelabeled and injected into the aorta of 2 kidneys, 1-clip (2k,1c) mice 2 weeks after surgery. Murine renal function and oxygenation were studied in vivo 2 weeks after injection using micro-magnetic resonance imaging, and fibrosis, tubulointerstitial injury, capillary density, and expression of profibrotic and inflammatory genes ex vivo. STC isolated from swine RVD kidneys showed increased gene expression of senescence and senescence-associated secretory phenotype markers and positive SA-β-gal staining. Delivery of normal pig STCs in 2k,1c mice improved murine renal perfusion, blood flow, and glomerular filtration rate, and downregulated profibrotic and inflammatory gene expression. These renoprotective effects were blunted using STC harvested from RVD kidneys, which also failed to attenuate hypoxia, fibrosis, tubular injury, and capillary loss in injured mouse 2k,1c kidneys. Hence, RVD may induce senescence in endogenous STC and impair their reparative capacity. These observations implicate cellular senescence in the pathophysiology of ischemic kidney disease and support senolytic therapy to permit self-healing of senescent kidneys.

Renal Progenitor Cells Have Higher Genetic Stability and Lower Oxidative Stress than Mesenchymal Stem Cells during In Vitro Expansion

In vitro senescence of multipotent cells has been commonly associated with DNA damage induced by oxidative stress. These changes may vary according to the sources of production and the studied lineages, which raises questions about the effect of growing time on genetic stability. This study is aimed at evaluating the evolution of genetic stability, viability, and oxidative stress of bone marrow mesenchymal stem cells (MSCBMsu) and renal progenitor cells of the renal cortex (RPCsu) of swine (Sus scrofa domesticus) in culture passages. P2, P5, and P9 were used for MSCBMsu and P1, P2, and P3 for RPCsu obtained by thawing. The experimental groups were submitted to MTT, apoptosis and necrosis assays, comet test, and reactive substance measurements of thiobarbituric acid (TBARS), nitrite, reduced glutathione (GSH), and catalase. The MTT test curve showed a mean viability of 1.14 ± 0.62 and 1.12 ± 0.54, respectively, for MSCBMsu and RPCsu. The percentages of MSCBMsu and RPCsu were presented, respectively, for apoptosis, an irregular and descending behavior, and necrosis, ascending and irregular. The DNA damage index showed higher intensity among the MSCBMsu in the P5 and P9 passages (p < 0.05). In the TBARS evaluation, there was variation among the lines of RPCsu and MSCBMsu, presenting the last most significant variations (p < 0.05). In the nitrite values, we identified only among the lines, in the passages P1 and P2, with the highest averages displayed by the MSCBMsu lineage (p < 0.05). The measurement of antioxidant system activity showed high standards, identifying differences only for GSH values, in the RPCsu lineage, in P3 (p < 0.05). This study suggests that the maintenance of cell culture in the long term induces lower regulation of oxidative stress, and RPCsu presents higher genetic stability and lower oxidative stress than MSCBMsu during in vitro expansion.

Stem cells: a potential treatment option for kidney diseases

The prevalence of kidney diseases is emerging as a public health problem. Stem cells (SCs), currently considered as a promising tool for therapeutic application, have aroused considerable interest and expectations. With self-renewal capabilities and great potential for proliferation and differentiation, stem cell therapy opens new avenues for the development of renal function and structural repair in kidney diseases. Mounting evidence suggests that stem cells exert a therapeutic effect mainly by replacing damaged tissues and paracrine pathways. The benefits of various types of SCs in acute kidney disease and chronic kidney disease have been demonstrated in preclinical studies, and preliminary results of clinical trials present its safety and tolerability. This review will focus on the stem cell-based therapy approaches for the treatment of kidney diseases, including various cell sources used, possible mechanisms involved, and outcomes that are generated so far, along with prospects and challenges in clinical application.

Renal ischemia alters expression of mitochondria-related genes and impairs mitochondrial structure and function in swine scattered tubular-like cells

Scattered tubular-like cells (STCs) are dedifferentiated surviving tubular epithelial cells that repair neighboring injured cells. Experimental renal artery stenosis (RAS) impairs STC reparative potency by inducing mitochondrial injury, but the exact mechanisms of mitochondrial damage remain unknown. We hypothesized that RAS alters expression of mitochondria-related genes, contributing to mitochondrial structural damage and dysfunction in swine STCs. CD24⁺/CD133⁺ STCs were isolated from pig kidneys after 10 wk of RAS or sham (n = 3 each). mRNA sequencing was performed, and nuclear DNA (nDNA)-encoded mitochondrial genes and mitochondrial DNA (mtDNA)-encoded genes were identified. Mitochondrial structure, ATP generation, biogenesis, and expression of mitochondria-associated microRNAs were also assessed. There were 96 nDNA-encoded mitochondrial genes upregulated and 12 mtDNA-encoded genes downregulated in RAS-STCs versus normal STCs. Functional analysis revealed that nDNA-encoded and mtDNA-encoded differentially expressed genes were primarily implicated in mitochondrial respiration and ATP synthesis. Mitochondria from RAS STCs were swollen and showed cristae remodeling and loss and decreased ATP production. Immunoreactivity of the mitochondrial biogenesis marker peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α and expression of the mitochondria-associated microRNAs miR-15a, miR-181a, miR-196a, and miR-296-3p, which target several mtDNA genes, were higher in RAS-STCs compared with normal STCs, suggesting a potential modulation of mitochondria-related gene expression. These results demonstrate that RAS induces an imbalance in mtDNA- and nDNA-mitochondrial gene expression, impairing mitochondrial structure and function in swine STCs. These observations support development of gene gain- and loss-of-function strategies to ameliorate mitochondrial damage and preserve the reparative potency of STCs in patients with renal ischemia.

Stem cell delivery to kidney via minimally invasive ultrasound-guided renal artery injection in mice

Cell-based therapies are promising treatments for various kidney diseases. However, the major hurdle in initiating therapeutic responses is the inefficiency of injection routes to deliver cells to the kidney parenchyma. Systemic injection, such as intravenous injection only delivers a small proportion of cells to the kidney. Whereas direct delivery, such as renal artery injection requires surgical procedures. A minimally invasive renal artery injection was therefore developed to enhance cell delivery to kidney. In this study, luciferase expressing human adipocyte derived stem cells (ADSC) were labelled with gold nanorods (GNR) and injected into the renal artery using ultrasound guidance. The ADSCs were tracked using bioluminescence and photoacoustic imaging serially over 7 days. Imaging confirmed that the majority of signal was within the kidney, indicative of successful injection and that the cells remained viable for 3 days. Histology showed co-localization of GNRs with ADSC staining throughout the kidney with no indication of injury caused by injection. These findings demonstrate that ultrasound-guided renal artery injection is feasible in mice and can successfully deliver a large proportion of cells which are retained within the kidney for 3 days. Therefore, the techniques developed here will be useful for optimising cell therapy in kidney diseases.

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

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

Renal Artery Stenosis Alters Gene Expression in Swine Scattered Tubular-Like Cells

Background: Scattered tubular-like cells (STCs) proliferate and differentiate to support neighboring injured renal tubular cells during recovery from insults. Renal artery stenosis (RAS) induces renal ischemia and hypertension and leads to loss of kidney function, but whether RAS alters renal endogenous repair mechanisms, such as STCs, remains unknown. We hypothesize that RAS in swine modifies the messenger RNA (mRNA) profile of STCs, blunting their in vitro reparative capacity. Methods: CD24+/CD133+ STCs were isolated from pig kidneys after 10-weeks of RAS or sham (n = 3 each) and their gene cargo analyzed using high-throughput mRNAseq. Expression profiles for upregulated and downregulated mRNAs in RAS-STCs were functionally interpreted by gene ontology analysis. STC activation was assessed by counting the total number of STCs in pig kidney sections using flow cytometry, whereas cell proliferation was assessed in vitro. Results: Of all expressed genes, 1430 genes were upregulated and 315 downregulated in RAS- versus Normal-STCs. Expression of selected candidate genes followed the same fold change directions as the mRNAseq findings. Genes upregulated in RAS-STCs were involved in cell adhesion, extracellular matrix remodeling, and kidney development, whereas those downregulated in RAS-STCs are related to cell cycle and cytoskeleton. The percentage of STCs from dissociated kidney cells was higher in RAS versus Normal pigs, but their proliferation rate was blunted. Conclusions: Renal ischemia and hypertension in swine induce changes in the mRNA profile of STCs, associated with increased STC activation and impaired proliferation. These observations suggest that RAS may alter the reparative capacity of STCs.

Renovascular disease induces mitochondrial damage in swine scattered tubular cells

Scattered tubular-like cells (STCs) contribute to repair neighboring injured renal tubular cells. Mitochondria mediate STC biology and function but might be injured by the ambient milieu. We hypothesized that the microenviroment induced by the ischemic and metabolic components of renovascular disease impairs STC mitochondrial structure and function in swine, which can be attenuated with mitoprotection. CD24⁺/CD133⁺ STCs were quantified in pig kidneys after 16 wk of metabolic syndrome (MetS) or lean diet (Lean) with or without concurrent renal artery stenosis (RAS) (n = 6 each). Pig STCs were isolated and characterized, and mitochondrial structure, membrane potential, and oxidative stress were assessed in cells untreated or incubated with the mitoprotective drug elamipretide (1 nM for 6 h). STC-protective effects were assessed in vitro by their capacity to proliferate and improve viability of injured pig tubular epithelial cells. The percentage of STCs was higher in MetS, Lean + RAS, and MetS + RAS kidneys compared with Lean kidneys. STCs isolated from Lean + RAS and MetS + RAS pigs showed mitochondrial swelling and decreased matrix density, which were both restored by mitoprotection. In addition, mitochondrial membrane potential and ATP production were reduced and production of reactive oxygen species elevated in MetS, Lean + RAS, and MetS + RAS STCs. Importantly, mitoprotection improved mitochondrial structure and function as well as the capacity of MetS + RAS STCs to repair injured tubular cells in vitro. Renovascular disease in swine is associated with a higher prevalence of STCs but induces structural and functional alterations in STC mitochondria, which impair their reparative potency. These observations suggest a key role for mitochondria in the renal reparative capacity of STCs.

Gadolinium-Labelled Cell Scaffolds to Follow-up Cell Transplantation by Magnetic Resonance Imaging

Cell scaffolds are often used in cell transplantation as they provide a solid structural support to implanted cells and can be bioengineered to mimic the native extracellular matrix. Gadolinium fluoride nanoparticles (Gd-NPs) as a contrast agent for Magnetic Resonance Imaging (MRI) were incorporated into poly(lactide-co-glycolide)/chitosan scaffolds to obtain Imaging Labelled Cell Scaffolds (ILCSs), having the shape of hollow spherical/ellipsoidal particles (200-600 μm diameter and 50-80 μm shell thickness). While Gd-NPs incorporated into microparticles do not provide any contrast enhancement in T1-weighted (T1w) MR images, ILCSs can release Gd-NPs in a controlled manner, thus activating MRI contrast. ILCSs seeded with human mesenchymal stromal cells (hMSCs) were xenografted subcutaneously into either immunocompromised and immunocompetent mice without any immunosuppressant treatments, and the transplants were followed-up in vivo by MRI for 18 days. Immunocompromised mice showed a progressive activation of MRI contrast within the implants due to the release of Gd-NPs in the extracellular matrix. Instead, immunocompetent mice showed poor activation of MRI contrast due to the encapsulation of ILCSs within fibrotic capsules and to the scavenging of released Gd-NPs by phagocytic cells. In conclusion, the MRI follow-up of cell xenografts can report the host cell response to the xenograft. However, it does not strictly report on the viability of transplanted hMSCs.

Premobilization of CD133+ cells by granulocyte colony- stimulating factor attenuates ischemic acute kidney injury induced by cardiopulmonary bypass

Ischemic acute kidney injury (IAKI) is a common but severe complication after a cardiopulmonary bypass (CPB). Multiple studies have demonstrated that peripheral CD133+ or differentiated cells are able to home and repair the damaged tissues, but the number of available CD133+ cells is limited, and no efficient method published previously to mobilize them immediately. We analyzed the relationship between CD133+ cells and renal function in CPB patients, in addition, the efficacy of granulocyte colony-stimulating factor (G-CSF) pre-mobilized CD133+ cells in treating of mouse IAKI model have been investigated. In the clinical study, the prospective cohort study analyzed the correlation between BUN/Crea level and the peripheral CD133+ cell numbers. CPB was associated with postoperative renal dysfunction. The significant negative correlation was observed between patients' Crea and CD133+ cells (P < 0.05). The proposed mechanism studies were performed on the mouse IAKI model. The experimental mice were treated by G-CSF to mobilize CD133+ cells before implementing CPB. Data on cell count, inflammatory index, renal function/injury, and CD133+ cell mobilization were analyzed. The result demonstrated that pretreatment by G-CSF resulted in tremendous increase in the number of mouse peripheral blood and renal CD133+ cells, significantly reduces renal tissue inflammation and dramatically improves the renal function after CPB. In summary, we concluded that premobilization of CD133+ cells abated CPB induced IAKI, by promoting both repairing damaged epithelium and by its anti-inflammatory activity. Our findings stress the remarkable applications of CD133+ or differentiated cells-based therapies for potential preventing ischemic acute kidney injury.

Application potential of stem/progenitor cell-derived extracellular vesicles in renal diseases

Extracellular vesicles (EVs) are nanometer-sized and membrane-bound vesicles, including exosomes and microvesicles. EVs can deliver bioactive macromolecules such as proteins, lipids, and nucleic acids, allowing intercellular communication in multicellular organisms. EVs are secreted by all cell types including stem/progenitor cells. Stem/progenitor cell-derived EVs have been identified to exert immunomodulatory effects on target cells through transferring protein molecules as well as regulatory effects on the phenotype of target cells through fusion with the target cells membrane and/or through direct endocytosis by target cells to transfer nucleic acid substances (such as mRNA, miRNA) to the target cells. In both human and animal models, the use of stem/progenitor cells (such as bone marrow mesenchymal stromal cells) has been shown to promote the recovery of kidney diseases such as acute kidney injury and chronic kidney disease. Stem/progenitor cell-derived extracellular vesicles are an important mechanism by which stem/progenitor cells might repair kidney injury. Here, this review will discuss the latest advances concerning the application potential of stem/progenitor cell-derived extracellular vesicles in renal diseases, including the aspects as follows: anti-inflammatory, proliferation-promoting and anti-apoptotic, proangiogenic, antifibrotic and renal cancer progression-promoting. Therefore, stem/progenitor cell-derived extracellular vesicles may be a promising treatment tool for renal diseases.

Renal Injury Repair: How About the Role of Stem Cells

Renal failure is one of the most important causes of mortality and morbidity all over the world. Acute kidney injury (AKI) is a major clinical problem that affects up to 5% of all hospitalized patients. Although the kidney has a remarkable capacity for regeneration after acute injury, the mortality among patients with severe AKI remains dismally high, and in clinical practice, most patients cannot be cured completely and suffer from chronic kidney disease (CKD). Recently, the incidence and prevalence of CKD have increased, largely as a result of the enhanced prevalence of diabetes and obesity. The progressive nature of CKD and the ensuing end-stage renal disease (ESRD) place a substantial burden on global healthcare resources. Currently, dialysis and transplantation remain the only treatment options. Finding new therapeutic methods to fight AKI and CKD remains an ongoing quest. Although the human renal histological structure is complex, stem cell therapies have been applied to repair injured kidneys. The curative effects of mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), induced pluripotent stem cells (iPSCs), and nephron progenitor cells (NPCs) on renal repair have also been reported by researchers. This review focuses on stem cell therapy and mechanisms for renal injury repair.

Receptor-Ligand Interaction Mediates Targeting of Endothelial Colony Forming Cell-derived Exosomes to the Kidney after Ischemic Injury

Endothelial colony forming cell (ECFC)-derived exosomes protect mice against ischemic kidney injury, via transfer of microRNA-(miR)-486-5p. Mechanisms mediating exosome recruitment to tissues are unclear. We hypothesized that ECFC exosomes target ischemic kidneys, involving interaction between exosomal CXC chemokine receptor type 4 (CXCR4) and stromal cell-derived factor (SDF)-1α. Ischemia-reperfusion was induced in mice by bilateral renal vascular clamp, with intravenous infusion of exosomes at reperfusion. Optical imaging determined exosome biodistribution, and miR-486-5p was measured by real-time PCR. Human umbilical vein endothelial cells (HUVECs) were cultured to study the CXCR4/SDF-1α interaction. Targeting of administered exosomes to ischemic kidneys was detected 30 min and 4 hrs after reperfusion. Exosomes increased miR-486-5p levels only in kidneys, within proximal tubules, glomeruli, and endothelial cells. Uptake of fluorescently-labeled exosomes into HUVECs, and exosomal transfer of miR-486-5p were enhanced by hypoxia, effects blocked by neutralizing antibody to SDF-1α or by the CXCR4 inhibitor plerixafor. Infusion of ECFC exosomes prevented ischemic kidney injury in vivo, an effect that was not observed when exosomes were pre-incubated with plerixafor. These data indicate that ECFC exosomes selectively target the kidneys after ischemic injury, with rapid cellular transfer of miR486-5p. Targeting of exosomes may involve interaction of CXCR4 with endothelial cell SDF-1α.

Regenerating the kidney using human pluripotent stem cells and renal progenitors

INTRODUCTION

Chronic kidney disease is a major health-care problem worldwide and its cost is becoming no longer affordable. Indeed, restoring damaged renal structures or building a new kidney represents an ambitious and ideal alternative to renal replacement therapy. Streams of research have explored the possible application of pluripotent stem cells (SCs) (embryonic SCs and induced pluripotent SCs) in different strategies aimed at regenerate functioning nephrons and at understanding the mechanisms of kidney regeneration.

AREAS COVERED

In this review, we will focus on the main potential applications of human pluripotent SCs to kidney regeneration, including those leading to rebuilding new kidneys or part of them (organoids, scaffolds, biological microdevices) as well as those aimed at understanding the pathophysiological mechanisms of renal disease and regenerative processes (modeling of kidney disease, genome editing). Moreover, we will discuss the role of endogenous renal progenitors cells in order to understand and promote kidney regeneration, as an attractive alternative to pluripotent SCs.

EXPERT OPINION

Opportunities and pitfalls of all these strategies will be underlined, finally leading to the conclusion that a deeper knowledge of the biology of pluripotent SCs is mandatory, in order to allow us to hypothesize their clinical application.

Stem cell extracellular vesicles and kidney injury

Extracellular vesicles (EVs) appear as a new promising cell-free therapy for acute and chronic renal diseases. EVs retain characteristics of the cell of origin and those derived from stem cells may mimic their regenerative properties per se. In fact, EVs contain many active molecules such as proteins and RNA species that act on target cells through different mechanisms, stimulating proliferation and angiogenesis and reducing apoptosis and inflammation. There are several reports that demonstrate a general regenerative potential of EVs derived from mesenchymal stromal cells (MSCs) of different sources in kidney injury models. In addition, a promising new approach is the use of EVs in the graft perfusion solution for kidney conditioning before transplant. Here we summarize the application of EVs released by stem cells in preclinical models of acute and chronic renal damage, comparing animal models, use of EVs of different cell origin and of their sub-fractions, doses, route of administration and efficacy of treatment.

Extracellular Vesicles in Renal Pathophysiology

Extracellular vesicles are a heterogeneous population of microparticles released by virtually all living cells which have been recently widely investigated in different biological fields. They are typically composed of two primary types (exosomes and microvesicles) and are recently commanding increasing attention as mediators of cellular signaling. Indeed, these vesicles can affect recipient cells by carrying and delivering complex cargos of biomolecules (including proteins, lipids and nucleic acids), protected from enzymatic degradation in the environment. Their importance has been demonstrated in the pathophysiology of several organs, in particular in kidney, where different cell types secrete extracellular vesicles that mediate their communication with downstream urinary tract cells. Over the past few years, evidence has been shown that vesicles participate in kidney development and normal physiology. Moreover, EVs are widely demonstrated to be implicated in cellular signaling during renal regenerative and pathological processes. Although many EV mechanisms are still poorly understood, in particular in kidney, the discovery of their role could help to shed light on renal biological processes which are so far elusive. Lastly, extracellular vesicles secreted by renal cells gather in urine, thus becoming a great resource for disease or recovery markers and a promising non-invasive diagnostic instrument for renal disease. In the present review, we discuss the most recent findings on the role of extracellular vesicles in renal physiopathology and their potential implication in diagnosis and therapy.

Human Kidney-Derived Cells Ameliorate Acute Kidney Injury Without Engrafting into Renal Tissue

Previous studies have suggested that CD133⁺ cells isolated from human kidney biopsies have the potential to ameliorate injury following intravenous (IV) administration in rodent models of kidney disease by integrating into damaged renal tissue and generating specialized renal cells. However, whether renal engraftment of CD133⁺ cells is a prerequisite for ameliorating injury has not yet been unequivocally resolved. Here, we have established a cisplatin‐induced nephropathy model in immunodeficient rats to assess the efficacy of CD133⁺ human kidney cells in restoring renal health, and to determine the fate of these cells after systemic administration. Specifically, following IV administration, we evaluated the impact of the CD133⁺ cells on renal function by undertaking longitudinal measurements of the glomerular filtration rate using a novel transcutaneous device. Using histological assays, we assessed whether the human kidney cells could promote renal regeneration, and if this was related to their ability to integrate into the damaged kidneys. Our results show that both CD133⁺ and CD133⁻ cells improve renal function and promote renal regeneration to a similar degree. However, this was not associated with engraftment of the cells into the kidneys. Instead, after IV administration, both cell types were exclusively located in the lungs, and had disappeared by 24 hours. Our data therefore indicate that renal repair is not mediated by CD133⁺ cells homing to the kidneys and generating specialized renal cells. Instead, renal repair is likely to be mediated by paracrine or endocrine factors. Stem Cells Translational Medicine2017;6:1373–1384

The effects of glomerular and tubular renal progenitors and derived extracellular vesicles on recovery from acute kidney injury

Background

Mesenchymal stromal cells (MSCs) and renal stem/progenitors improve the recovery of acute kidney injury (AKI) mainly through the release of paracrine mediators including the extracellular vesicles (EVs). Several studies have reported the existence of a resident population of MSCs within the glomeruli (Gl-MSCs). However, their contribution towards kidney repair still remains to be elucidated. The aim of the present study was to evaluate whether Gl-MSCs and Gl-MSC-EVs promote the recovery of AKI induced by ischemia-reperfusion injury (IRI) in SCID mice. Moreover, the effects of Gl-MSCs and Gl-MSC-EVs were compared with those of CD133⁺ progenitor cells isolated from human tubules of the renal cortical tissue (T-CD133⁺ cells) and their EVs (T-CD133⁺-EVs).

Methods

IRI was performed in mice by clamping the left renal pedicle for 35 minutes together with a right nephrectomy. Immediately after reperfusion, the animals were divided in different groups to be treated with: Gl-MSCs, T-CD133⁺ cells, Gl-MSC-EVs, T-CD133⁺-EVs or vehicle. To assess the role of vesicular RNA, EVs were either isolated by floating to avoid contamination of non-vesicles-associated RNA or treated with a high dose of RNase. Mice were sacrificed 48 hours after surgery.

Results

Gl-MSCs, and Gl-MSC-EVs both ameliorate kidney function and reduce the ischemic damage post IRI by activating tubular epithelial cell proliferation. Furthermore, T-CD133⁺ cells, but not their EVs, also significantly contributed to the renal recovery after IRI compared to the controls. Floating EVs were effective while RNase-inactivated EVs were ineffective. Analysis of the EV miRnome revealed that Gl-MSC-EVs selectively expressed a group of miRNAs, compared to EVs derived from fibroblasts, which were biologically ineffective in IRI.

Conclusions

In this study, we demonstrate that Gl-MSCs may contribute in the recovery of mice with AKI induced by IRI primarily through the release of EVs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0478-5) contains supplementary material, which is available to authorized users.

Human CD133+ Renal Progenitor Cells Induce Erythropoietin Production and Limit Fibrosis After Acute Tubular Injury

Persistent alterations of the renal tissue due to maladaptive repair characterize the outcome of acute kidney injury (AKI), despite a clinical recovery. Acute damage may also limit the renal production of erythropoietin, with impairment of the hemopoietic response to ischemia and possible lack of its reno-protective action. We aimed to evaluate the effect of a cell therapy using human CD133⁺ renal progenitor cells on maladaptive repair and fibrosis following AKI in a model of glycerol-induced rhabdomyolysis. In parallel, we evaluated the effect of CD133⁺ cells on erythropoietin production. Administration of CD133⁺ cells promoted the restoration of the renal tissue, limiting the presence of markers of injury and pro-inflammatory molecules. In addition, it promoted angiogenesis and protected against fibrosis up to day 60. No effect of dermal fibroblasts was observed. Treatment with CD133⁺ cells, but not with PBS or fibroblasts, limited anemia and increased erythropoietin levels both in renal tissue and in circulation. Finally, CD133⁺ cells contributed to the local production of erythropoietin, as observed by detection of circulating human erythropoietin. CD133⁺ cells appear therefore an effective source for cell repair, able to restore renal functions, including erythropoietin release, and to limit long term maldifferentiation and fibrosis.

Imaging technologies for monitoring the safety, efficacy and mechanisms of action of cell-based regenerative medicine therapies in models of kidney disease

The incidence of end stage kidney disease is rising annually and it is now a global public health problem. Current treatment options are dialysis or renal transplantation, which apart from their significant drawbacks in terms of increased morbidity and mortality, are placing an increasing economic burden on society. Cell-based Regenerative Medicine Therapies (RMTs) have shown great promise in rodent models of kidney disease, but clinical translation is hampered due to the lack of adequate safety and efficacy data. Furthermore, the mechanisms whereby the cell-based RMTs ameliorate injury are ill-defined. For instance, it is not always clear if the cells directly replace damaged renal tissue, or whether paracrine effects are more important. Knowledge of the mechanisms responsible for the beneficial effects of cell therapies is crucial because it could lead to the development of safer and more effective RMTs in the future. To address these questions, novel in vivo imaging strategies are needed to monitor the biodistribution of cell-based RMTs and evaluate their beneficial effects on host tissues and organs, as well as any potential adverse effects. In this review we will discuss how state-of-the-art imaging modalities, including bioluminescence, magnetic resonance, nuclear imaging, ultrasound and an emerging imaging technology called multispectral optoacoustic tomography, can be used in combination with various imaging probes to track the fate and biodistribution of cell-based RMTs in rodent models of kidney disease, and evaluate their effect on renal function.

Autologous Cells for Kidney Bioengineering

Worldwide, increasing numbers of patients are developing end-stage renal disease, and at present, the only treatment options are dialysis or kidney transplantation. Dialysis is associated with increased morbidity and mortality, poor life quality and high economic costs. Transplantation is by far the better option, but there are insufficient numbers of donor kidneys available. Therefore, there is an urgent need to explore alternative approaches. In this review, we discuss how this problem could potentially be addressed by using autologous cells and appropriate scaffolds to develop 'bioengineered' kidneys for transplantation. In particular, we will highlight recent breakthroughs in pluripotent stem cell biology that have led to the development of autologous renal progenitor cells capable of differentiating to all renal cell types and will discuss how these cells could be combined with appropriate scaffolds to develop a bioengineered kidney.

Non-Transgenic Mouse Models of Kidney Disease

Animal models are essential tools to understand the mechanisms underlying the development and progression of renal disease and to study potential therapeutic approaches. Recently, interventional models suitable to induce acute and chronic kidney disease in the mouse have become a focus of interest due to the wide availability of genetically engineered mouse lines. These models differ by their damaging mechanism (cell toxicity, immune mechanisms, surgical renal mass reduction, ischemia, hypertension, ureter obstruction etc.), functional and histomorphological phenotype and disease evolution. The susceptibility to a damaging mechanism often depends on strain and gender. The C57BL/6 strain, the most commonly used genetic background of transgenic mice, appears to be relatively resistant against developing glomerulosclerosis, proteinuria and hypertension. This review serves to provide a comprehensive overview of interventional mouse models of acute and chronic kidney disease.

Gadolinium-Decorated Silica Microspheres as Redox-Responsive MRI Probes for Applications in Cell Therapy Follow-Up

The redox microenvironment within a cell graft can be considered as an indicator to assess whether the graft is metabolically active or hypoxic. We present a redox-responsive MRI probe based on porous silica microparticles whose surface has been decorated with a Gd-chelate through a disulphide bridge. Such microparticles are designed to be interspersed with therapeutic cells within a biocompatible hydrogel. The onset of reducing conditions within the hydrogel is paralleled by an increased clearance of Gd, that can be detected by MRI.

Therapeutic use of human renal progenitor cells for kidney regeneration

The ability of the human kidney to repair itself is limited. Consequently, repeated injury can trigger a maladaptive response that is characterized by fibrosis and loss of renal function. The transcription patterns that characterize nephrogenesis in fetal renal progenitor cells (RPCs) are only partially activated during renal repair in adults. Nevertheless, evidence suggests that segment-restricted progenitor resident cells support renal healing in adults. In this Review, we discuss the evidence for the existence of functional human RPCs in adults and their role in renal repair, and consider the controversial issue of whether RPCs are a fixed population or arise through phenotypical plasticity of tubular cells that is mediated by the microenvironment. We also discuss the strategies for generating renal progenitor cells from pluripotent stem cells or differentiated cells and their use in therapy. Finally, we examine preclinical data on the therapeutic use of human fetal cells, adult progenitor cells and adult renal cells.

Trophic Factors from Tissue Stem Cells for Renal Regeneration

Stem cell therapies against renal injury have been advancing. The many trials for renal regeneration are reported to be effective in many kinds of renal injury models. Regarding the therapeutic mechanism, it is believed that stem cells contribute to make regeneration via not only direct stem cell differentiation in the injured space but also indirect effect via secreted factors from stem cells. Direct differentiation from stem cells to renal composed cells has been reported. They differentiate to renal composed cells and make functions. However, regarding renal regeneration, stem cells are discussed to secrete many kinds of growth factors, cytokines, and chemokines in paracrine or autocrine manner, which protect against renal injury, too. In addition, it is reported that stem cells have the ability to communicate with nearby cells via microvesicle-related RNA and proteins. Taken together from many reports, many secreted factors from stem cells were needed for renal regeneration orchestrally with harmony. In this review, we focused on the effects and insights of stem cells and regenerative factors from stem cells.

Renal progenitors derived from human iPSCs engraft and restore function in a mouse model of acute kidney injury

Acute kidney injury (AKI) is one of the most relevant health issues, leading to millions of deaths. The magnitude of the phenomenon remarks the urgent need for innovative and effective therapeutic approaches. Cell-based therapy with renal progenitor cells (RPCs) has been proposed as a possible strategy. Studies have shown the feasibility of directing embryonic stem cells or induced Pluripotent Stem Cells (iPSCs) towards nephrogenic intermediate mesoderm and metanephric mesenchyme (MM). However, the functional activity of iPSC-derived RPCs has not been tested in animal models of kidney disease. Here, through an efficient inductive protocol, we directed human iPSCs towards RPCs that robustly engrafted into damaged tubuli and restored renal function and structure in cisplatin-mice with AKI. These results demonstrate that iPSCs are a valuable source of engraftable cells with regenerative activity for kidney disease and create the basis for future applications in stem cell-based therapy.

Potential advantages of acute kidney injury management by mesenchymal stem cells

Mesenchymal stem cells are currently considered as a promising tool for therapeutic application in acute kidney injury (AKI) management. AKI is characterized by acute tubular injury with rapid loss of renal function. After AKI, inflammation, oxidative stress and excessive deposition of extracellular matrix are the molecular events that ultimately cause the end-stage renal disease. Despite numerous improvement of supportive therapy, the mortality and morbidity among patients remain high. Therefore, exploring novel therapeutic options to treat AKI is mandatory. Numerous evidence in animal models has demonstrated the capability of mesenchymal stem cells (MSCs) to restore kidney function after induced kidney injury. After infusion, MSCs engraft in the injured tissue and release soluble factors and microvesicles that promote cell survival and tissue repairing. Indeed, the main mechanism of action of MSCs in tissue regeneration is the paracrine/endocrine secretion of bioactive molecules. MSCs can be isolated from several tissues, including bone marrow, adipose tissue, and blood cord; pre-treatment procedures to improve MSCs homing and their paracrine function have been also described. This review will focus on the application of cell therapy in AKI and it will summarize preclinical studies in animal models and clinical trials currently ongoing about the use of mesenchymal stem cells after AKI.