Conditioned medium from renal tubular epithelial cells initiates differentiation of human mesenchymal stem cells

Differentiated kidney tubular cell-derived extracellular vesicles enhance maturation of tubuloids

The prevalence of end-stage kidney disease (ESKD) is rapidly increasing with the need for regenerative therapies. Adult stem cell derived kidney tubuloids have the potential to functionally mimic the adult kidney tubule, but still lack the expression of important transport proteins needed for waste removal. Here, we investigated the potential of extracellular vesicles (EVs) obtained from matured kidney tubular epithelial cells to modulate in vitro tubuloids functional maturation. We focused on organic anion transporter 1 (OAT1), one of the most important proteins involved in endogenous waste excretion. First, we show that EVs from engineered proximal tubule cells increased the expression of several transcription factors and epithelial transporters, resulting in improved OAT1 transport capacity. Next, a more in-depth proteomic data analysis showed that EVs can trigger various biological pathways, including mesenchymal-to-epithelial transition, which is crucial in the tubular epithelial maturation. Moreover, we demonstrated that the combination of EVs and tubuloid-derived cells can be used as part of a bioartificial kidney to generate a tight polarized epithelial monolayer with formation of dense cilia structures. In conclusion, EVs from kidney tubular epithelial cells can phenotypically improve in vitro tubuloid maturation, thereby enhancing their potential as functional units in regenerative or renal replacement therapies.

Current advances of stem cell-based therapy for kidney diseases

Kidney diseases are a prevalent health problem around the world. Multidrug therapy used in the current routine treatment for kidney diseases can only delay disease progression. None of these drugs or treatments can reverse the progression to an end-stage of the disease. Therefore, it is crucial to explore novel therapeutics to improve patients’ quality of life and possibly cure, reverse, or alleviate the kidney disease. Stem cells have promising potentials as a form of regenerative medicine for kidney diseases due to their unlimited replication and their ability to differentiate into kidney cells in vitro. Mounting evidences from the administration of stem cells in an experimental kidney disease model suggested that stem cell-based therapy has therapeutic or renoprotective effects to attenuate kidney damage while improving the function and structure of both glomerular and tubular compartments. This review summarises the current stem cell-based therapeutic approaches to treat kidney diseases, including the various cell sources, animal models or in vitro studies. The challenges of progressing from proof-of-principle in the laboratory to widespread clinical application and the human clinical trial outcomes reported to date are also highlighted. The success of cell-based therapy could widen the scope of regenerative medicine in the future.

Characterization of Extracellular Vesicles from Preconditioned Human Adipose-Derived Stromal/Stem Cells

Cell-free therapy using extracellular vesicles (EVs) from adipose-derived mesenchymal stromal/stem cells (ASCs) seems to be a safe and effective therapeutic option to support tissue and organ regeneration. The application of EVs requires particles with a maximum regenerative capability and hypoxic culture conditions as an in vitro preconditioning regimen has been shown to alter the molecular composition of released EVs. Nevertheless, the EV cargo after hypoxic preconditioning has not yet been comprehensively examined. The aim of the present study was the characterization of EVs from hypoxic preconditioned ASCs. We investigated the EV proteome and their effects on renal tubular epithelial cells in vitro. While no effect of hypoxia was observed on the number of released EVs and their protein content, the cargo of the proteins was altered. Proteomic analysis showed 41 increased or decreased proteins, 11 in a statistically significant manner. Furthermore, the uptake of EVs in epithelial cells and a positive effect on oxidative stress in vitro were observed. In conclusion, culture of ASCs under hypoxic conditions was demonstrated to be a promising in vitro preconditioning regimen, which alters the protein cargo and increases the anti-oxidative potential of EVs. These properties may provide new potential therapeutic options for regenerative medicine.

3-D Human Renal Tubular Organoids Generated from Urine-Derived Stem Cells for Nephrotoxicity Screening

The development of human cell-based systems to replace the use of rodents or the two-dimensional culture of cells for studying nephrotoxicity is urgently needed. Human urine-derived stem cells were differentiated into renal tubular epithelial cells in three-dimensional (3-D) culture after being induced by a kidney extracellular matrix. Levels of CYP2E1 and KIM-1 in 3-D organoids were significantly increased in response to acetone and cisplatin. This 3-D culture system provides an alternative tool for nephrotoxicity screening and research.

Epithelial differentiation of human adipose-derived stem cells (hASCs) undergoing three-dimensional (3D) cultivation with collagen sponge scaffold (CSS) via an indirect co-culture strategy

BACKGROUND

Three-dimensional (3D) cultivation with biomaterials was proposed to facilitate stem cell epithelial differentiation for wound healing. However, whether human adipose-derived stem cells (hASCs) on collagen sponge scaffold (CSS) better differentiate to keratinocytes remains unclear.

METHODS

3D cultivation with CSS on hASC epidermal differentiation co-cultured with HaCaT cells at air-liquid interface (ALI) was compared with two-dimensional (2D) form and cultivation without "co-culture" or "ALI." Cellular morphology, cell adhesion, and growth condition were evaluated, followed by the protein and gene expression of keratin 14 (K14, keratinocyte specific marker).

RESULTS

Typical cobblestone morphology of keratinocytes was remarkably observed in co-cultured hASCs at ALI, but those seeded on the CSS exhibited more keratinocyte-like cells under an invert microscope and scanning electron microscope. Desired cell adhesion and proliferation were confirmed in 3D differentiation groups by rhodamine-labeled phalloidin staining, consistent with H&E staining. Compared with those cultured in 2D culture system or without "ALI," immunofluorescence staining and gene expression analysis revealed hASCs co-cultured over CSS expressed K14 at higher levels at day 15.

CONCLUSIONS

CSS is positive to promote epithelial differentiation of hASCs, which will foster a deeper understanding of artificial dermis in skin wound healing and regeneration.

Isolation, Characterization, Differentiation and Immunomodulatory Capacity of Mesenchymal Stromal/Stem Cells from Human Perirenal Adipose Tissue

Mesenchymal stromal/stem cells (MSCs) are immature multipotent cells, which represent a rare population in the perivascular niche within nearly all tissues. The most abundant source to isolate MSCs is adipose tissue. Currently, perirenal adipose tissue is rarely described as the source of MSCs. MSCs were isolated from perirenal adipose tissue (prASCs) from patients undergoing tumor nephrectomies, cultured and characterized by flow cytometry and their differentiation potential into adipocytes, chondrocytes, osteoblasts and epithelial cells. Furthermore, prASCs were stimulated with lipopolysaccharide (LPS), lipoteichoic acid (LTA) or a mixture of cytokines (cytomix). In addition, prASC susceptibility to human cytomegalovirus (HCMV) was investigated. The expression of inflammatory readouts was estimated by qPCR and immunoassay. HCMV infection was analyzed by qPCR and immunostaining. Characterization of cultured prASCs shows the cells meet the criteria of MSCs and prASCs can undergo trilineage differentiation. Cultured prASCs can be induced to differentiate into epithelial cells, shown by cytokeratin 18 expression. Stimulation of prASCs with LPS or cytomix suggests the cells are capable of initiating an inflammation-like response upon stimulation with LPS or cytokines, whereas, LTA did not induce a significant effect on the readouts (ICAM-1, IL-6, TNFα, MCP-1 mRNA and IL-6 protein). HCMV broadly infects prASCs, showing a viral load dependent cytopathological effect (CPE). Our current study summarizes the isolation and culture of prASCs, clearly characterizes the cells, and demonstrates their immunomodulatory potential and high permissiveness for HCMV.

Genetic communication by extracellular vesicles is an important mechanism underlying stem cell-based therapy-mediated protection against acute kidney injury

Stem cell-based therapy appears to be a promising new candidate for acute kidney injury (AKI) management. Traditionally, it has been accepted that the mechanism underlying the regenerative effect of stem cells is based on their paracrine/endocrine activity, including release of bioactive factors that act on injured renal cells and presentation of proangiogenic, antiapoptotic, antioxidative, and immunomodulatory effects. Recently, multiple studies have confirmed that extracellular vesicles (EVs) are a kind of vesicle rich in a broad variety of biologically active molecules, including lipids, proteins, and, in particular, nucleic acids. EVs are able to transfer genetic information to target cells, alter target gene regulatory networks, and exert biological effects. Stem cell-derived EVs (SC-EVs) are emerging as potent genetic information sources that deliver mRNAs and miRNAs to injured renal cells and exert renoprotective effects during AKI. On the other hand, EVs originating from injured renal cells also contain genetic information that is believed to be able to influence phenotypic and functional changes in stem cells, favoring renal recovery. In this review, we summarize studies providing evidence of genetic communication during the application of stem cells in preclinical AKI models, aiming to clarify the mechanism and describe the therapeutic effects of stem cell-based therapy in AKI patients.

Collagen I Promotes Adipocytogenesis in Adipose-Derived Stem Cells In Vitro

A hallmark of ageing is the redistribution of body fat. Particularly, subcutaneous fat decreases paralleled by a decrease of skin collagen I are typical for age-related skin atrophy. In this paper, we hypothesize that collagen I may be a relevant molecule stimulating the differentiation of adipose-derived stem cells (ASCs) into adipocytes augmenting subcutaneous fat. In this context lipogenesis, adiponectin, and collagen I receptor expression were determined. Freshly isolated ASCs were characterized by stemness-associated surface markers by FACS analysis and then transdifferentiated into adipocytes by specific medium supplements. Lipogenesis was evaluated using Nile Red staining and documented by fluorescence microscopy or quantitatively measured by using a multiwell spectrofluorometer. Expression of adiponectin was measured by real-time RT-PCR and in cell-free supernatants by ELISA, and expression of collagen I receptors was observed by western blot analysis. It was found that supports coated with collagen I promote cell adhesion and lipogenesis of ASCs. Interestingly, a reverse correlation to adiponectin expression was observed. Moreover, we found upregulation of the collagen receptor, discoidin domain-containing receptor 2; receptors of the integrin family were absent or downregulated. These findings indicate that collagen I is able to modulate lipogenesis and adiponectin expression and therefore may contribute to metabolic dysfunctions associated with ageing.

Novel cellular mechanism that mediates the collecting duct formation during postnatal renal development

We have previously demonstrated that kidney embryonic structures are present in rats, and are still developing until postnatal Day 20. Consequently, at postnatal Day 10, the rat renal papilla contains newly formed collecting duct (CD) cells and others in a more mature stage. Performing primary cultures, combined with immunocytochemical and time-lapse analysis, we investigate the cellular mechanisms that mediate the postnatal CD formation. CD cells acquired a greater degree of differentiation, as we observed that they gradually lose the ability to bind BSL-I lectin, and acquire the capacity to bind Dolichos biflorus. Because CD cells retain the same behavior in culture than in vivo, and by using DBA and BSL-I as markers of cellular lineage besides specific markers of epithelial/mesenchymal phenotype, the experimental results strongly suggest the existence of mesenchymal cell insertion into the epithelial CD sheet. We propose such a mechanism as an alternative strategy for CD growing and development.

Urothelium with barrier function differentiated from human urine-derived stem cells for potential use in urinary tract reconstruction

Background

Autologous urothelial cells are often obtained via bladder biopsy to generate the bio-engineered urethra or bladder, while urine-derived stem cells (USC) can be obtained by a non-invasive approach. The objective of this study is to develop an optimal strategy for urothelium with permeability barrier properties using human USC which could be used for tissue repair in the urinary tract system.

Methods

USC were harvested from six healthy adult individuals. To optimize urothelial differentiation, five different differentiation methods were studied. The induced cells were assessed for gene and protein expression markers of urothelial cells via RT-PCR, Western blotting, and immunofluorescent staining. Barrier function and ultrastructure of the tight junction were assessed with permeability assays and transmission electron microscopy (TEM). Induced cells were both cultured on trans-well membranes and small intestinal submucosa, then investigated under histology analysis.

Results

Differentiated USC expressed significantly higher levels of urothelial-specific transcripts and proteins (Uroplakin III and Ia), epithelial cell markers (CK20 and AE1/AE3), and tight junction markers (ZO-1, ZO-2, E-cadherin, and Cingulin) in a time-dependent manner, compared to non-induced USC. In vitro assays using fluorescent dye demonstrated a significant reduction in permeability of differentiated USC. In addition, transmission electron microscopy confirmed appropriate ultrastructure of urothelium differentiated from USC, including tight junction formation between neighboring cells, which was similar to positive controls. Furthermore, multilayered urothelial tissues formed 2 weeks after USC were differentiated on intestine submucosal matrix.

Conclusion

The present study illustrates an optimal strategy for the generation of differentiated urothelium from stem cells isolated from the urine. The induced urothelium is phenotypically and functionally like native urothelium and has proposed uses in in vivo urological tissue repair or in vitro urethra or bladder modeling.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1035-6) contains supplementary material, which is available to authorized users.

Adipose-Derived Mesenchymal Stem Cells: A New Tool for the Treatment of Renal Fibrosis

As chronic kidney disease progresses, kidney tissue inevitably undergoes cell loss, accumulation of extracellular matrix, and kidney tissue fibrosis, eventually leading to end-stage renal disease. With the continuous innovation of cell therapy technology, mesenchymal stem cells are used in numerous fields, including cardiovascular diseases, diabetes, and kidney tissue injury repair. Adipose-derived mesenchymal stem cells (AMSCs), a type of pluripotent stem cells, have the potential for self-renewal and proliferation with low immunogenicity and significant anti-inflammatory properties. AMSCs can promote impaired cell regeneration and remodeling in renal lesions, thus avoiding further worsening of renal disease and even blocking or reversing the process of renal fibrosis. In this review, we discuss the mechanisms involved in the treatment of renal fibrosis with AMSCs and summarize the potential hazards that may exist in cell therapy.

Development of xeno-free epithelial differentiation media for adherent, non-expanded adipose stromal vascular cell cultures

INTRODUCTION

Reconstruction of respiratory epithelium is critical for the fabrication of bioengineered airway implants. Epithelial differentiation is typically achieved using bovine pituitary extract (BPE). Due to the xenogenic nature and undefined composition of BPE, an alternative for human clinical applications, devoid of BPE, must be developed. The goal of this study was to develop two different BPE-free media, with and without select pituitary hormone (PH), which could initiate epithelial differentiation for use in human implantation.

METHODS

The ability of the two BPE-free media to initiate epithelial differentiation of adherent, non-expanded stromal-vascular cells grown on porcine small intestinal submucosa was compared to traditional BPE-containing media (M1). Nanostring^® was used to measure differences in gene expression of stemness (MSC), basal cell (basal), and ciliated markers (muco-cil), and staining was performed support the gene data.

RESULTS

Compared to baseline, both BPE-free media upregulated epithelial and stemness genes, however this was to a lower degree than BPE-containing media. In general, the expression of basal cell markers (COL17A1, DSG3, ITGA6, KRT6A, LOXL2) and secreted mucous proteins (PLUNC, MUC5B, SCGB2A1) was upregulated. The gene expression of ciliated markers C9orf24, TUBA3 and DNCL2B but not of the key transcription factor for cilagenesis FOXJ1 were upregulated, indicating that mucus-secreting cell differentiation occurs more rapidly than ciliogenesis. The ability of the adherent stromal vascular cells to upregulate gene expression of both epithelial and stemness markers suggests maintenance of the self-renewal capacity of undifferentiated and/or basal cell-like cells contributing to proliferation and ensuring a persisting source of cells for regenerative medicine applications.

CONCLUSION

This study provides the initial step to defining a BPE-free epithelial differentiation medium for clinical translation. Thus, either of the proposed BPE-free medium are viable alternatives to BPE-containing medium for partial epithelial differentiation for human translational applications.

Directing adipose-derived stem cells into keratinocyte-like cells: impact of medium composition and culture condition

BACKGROUND

Adipose-derived stem cells (ASC) are known to transdifferentiate into a wide range of different cell species in vitro including along the epidermal lineage. This property makes them a promising tool for regenerative medicine to restore the epidermal barrier.

OBJECTIVE

This study is dedicated to identify in vitro conditions enabling transdifferentiation to a keratinocyte-like phenotype. In particular, the impact of different culture conditions (media compositions, 2D, 3D cultures) and extracellular matrix (ECM) molecules was evaluated.

METHODS

Adipose-derived stem cells derived from subcutaneous abdominal fat were characterized by stemness-associated markers and subjected to different media. Epithelial differentiation in 2D cultures was monitored by pan-cytokeratin expression using flow cytometry and immunocytochemistry. To evaluate the impact of different ECM molecules on epidermal stratification, 3D cultures were produced, lifted to the air-liquid interface (ALI) and examined by histological analysis and quantitative real-time RT-PCR.

RESULTS

We identified a medium composition containing retinoic acid, hydrocortisone, ascorbic acid and BMP-4 enabling maximum pan-cytokeratin expression in 2D cultures. Moreover, adhesion to type IV collagen further promotes the pan-cytokeratin expression. When cultures were lifted to the ALI, significant stratification was observed, particularly in supports coated with type IV collagen or fibronectin. Moreover, epidermal differentiation markers (involucrin, cytokeratin 1 and 14) become induced.

CONCLUSION

Conditions with hampered wound healing such as non-healing ulcers demand new treatment regimes. The here introduced optimized protocols for transdifferentiation of ASC into keratinocyte-like cells may help to establish more effective treatment procedures.

Renal Differentiation of Mesenchymal Stem Cells Seeded on Nanofibrous Scaffolds Improved by Human Renal Tubular Cell Lines-Conditioned Medium

Kidney injuries and renal dysfunctions are one of the most important clinical problems, and tissue engineering could be a valuable method for solving it. The objective of this study was to investigate the synergistic effect of renal cell line-conditioned medium and Polycaprolactone (PCL) nanofibers on renal differentiation of human mesenchymal stem cells (MSCs). In the current study, after stem cells isolation and characterization, PCL nanofibrous scaffold was fabricated using electrospinning methods and characterized morphologically, mechanically, and for biocompatibility. The renal differentiation of seeded MSCs on the surface of PCL nanofibers with and without human renal tubular cell lines-conditioned medium was investigated by evaluation of eight important renal-related genes expression by real-time reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemistry. Fabricated nanofibrous scaffolds were good in all characterized items. Almost highest expression of all genes was detected in stem cells seeded on PCL under conditioned media in comparison with the stem cells seeded on PCL, tissue culture polystyrene (TCPS) under renal induction medium, and TCPS under conditioned medium. According to the results, PCL nanofibers in contribution with conditioned medium can provide the optimal conditions for renal differentiation of MSCs and could be a promising candidate for renal tissue engineering application.

RUNX2 promotes epithelial differentiation of ADSCs and burn wound healing via targeting E-cadherin

Epithelial differentiation of adipose-derived stem cells (ADSCs) is mediated by sophisticated interactions of various molecular functions and biological processes, including transcriptional regulation. Runt-related transcription factor 2 (RUNX2) increases osteoblast and adipocyte differentiation of ADSCs. However, the role of RUNX2 in epithelial differentiation of ADSCs is unknown. We first showed that ADSCs possess the potential to differentiate into epithelial lineage. Then, we employed the effect of RUNX2 on epithelial differentiation of ADSCs. Our data showed that RUNX2 promoted epithelial differentiation of ADSCs. Overexpression or knockdown of RUNX2 resulted in increase or decrease of E-cadherin expression, respectively. Abatement of E-cadherin in ADSCs attenuated RUNX2-activated epithelial conversion of ADSCs and epithelial markers cytokeratin 18 (CK18) and zonula occludens protein-1 (ZO-1). We also evaluated the effect of RUNX2 on burn wound healing in vivo. The wound re-epithelialization were accelerated by RUNX2. The wound closure indexs, demis regeneration and revascularization were all improved. Furthermore, RUNX2 binding directly to the E-cadherin promoter region was characterized in ADSCs by chromatin immunoprecipitation (ChIP) and luciferase promoter reporter assays. Taken together, the study demonstrates the role of RUNX2 in epithelial differentiation of ADSCs and suggests that RUNX2 promotes E-cadherin expression, at least in part, through its direct binding to the promoter.

Microencapsulated macrophages releases conditioned medium able to prevent epithelial to mesenchymal transition

Epithelial to mesenchymal transition (EMT) has emerged as a key process in the development of renal fibrosis. In fact, EMT-derived fibroblasts contribute to the progression of chronic renal disease. In addition, anti-inflammatory M2 macrophages have exhibited a great influence on renal fibrosis. However, because of the high impact that the inputs of different environmental cytokines have on their phenotype, macrophages can easily lose this property. We aim to known if microencapsulated macrophages on M2-inducing alginate matrices could preserve macrophage phenotype and thus release factors able to act on epithelial cells to prevent the epithelial differentiation towards mesenchymal cells. We reproduced an in vitro model of EMT by treating adipose-derived stem cells with all-trans retinoic acid (ATRA) and induced their transformation toward epithelia. Dedifferentiation of epithelial cells into a mesenchymal phenotype occurred when ATRA was retired, thus simulating EMT. Results indicate that induction of M2 phenotype by IL-10 addition in the alginate matrix produces anti-inflammatory cytokines and increases the metabolic activity and the viability of the encapsulated macrophages. The released conditioned medium modulates EMT and maintains healthy epithelial phenotype. This could be used for in vivo cell transplantation, or alternatively as an external releaser able to prevent epithelial to mesenchymal transformation for future anti-fibrotic therapies.

Proteomic Profiling of Neuroblastoma Cells Adhesion on Hyaluronic Acid-Based Surface for Neural Tissue Engineering

The microenvironment of neuron cells plays a crucial role in regulating neural development and regeneration. Hyaluronic acid (HA) biomaterial has been applied in a wide range of medical and biological fields and plays important roles in neural regeneration. PC12 cells have been reported to be capable of endogenous NGF synthesis and secretion. The purpose of this research was to assess the effect of HA biomaterial combining with PC12 cells conditioned media (PC12 CM) in neural regeneration. Using SH-SY5Y cells as an experimental model, we found that supporting with PC12 CM enhanced HA function in SH-SY5Y cell proliferation and adhesion. Through RP-nano-UPLC-ESI-MS/MS analyses, we identified increased expression of HSP60 and RanBP2 in SH-SY5Y cells grown on HA-modified surface with cotreatment of PC12 CM. Moreover, we also identified factors that were secreted from PC12 cells and may promote SH-SY5Y cell proliferation and adhesion. Here, we proposed a biomaterial surface enriched with neurotrophic factors for nerve regeneration application.

Mesenchymal Stromal Cells Epithelial Transition Induced by Renal Tubular Cells-Derived Extracellular Vesicles

Mesenchymal-epithelial interactions play an important role in renal tubular morphogenesis and in maintaining the structure of the kidney. The aim of this study was to investigate whether extracellular vesicles (EVs) produced by human renal proximal tubular epithelial cells (RPTECs) may induce mesenchymal-epithelial transition of bone marrow-derived mesenchymal stromal cells (MSCs). To test this hypothesis, we characterized the phenotype and the RNA content of EVs and we evaluated the in vitro uptake and activity of EVs on MSCs. MicroRNA (miRNA) analysis suggested the possible implication of the miR-200 family carried by EVs in the epithelial commitment of MSCs. Bone marrow-derived MSCs were incubated with EVs, or RPTEC-derived total conditioned medium, or conditioned medium depleted of EVs. As a positive control, MSCs were co-cultured in a transwell system with RPTECs. Epithelial commitment of MSCs was assessed by real time PCR and by immunofluorescence analysis of cellular expression of specific mesenchymal and epithelial markers. After one week of incubation with EVs and total conditioned medium, we observed mesenchymal-epithelial transition in MSCs. Stimulation with conditioned medium depleted of EVs did not induce any change in mesenchymal and epithelial gene expression. Since EVs were found to contain the miR-200 family, we transfected MSCs using synthetic miR-200 mimics. After one week of transfection, mesenchymal-epithelial transition was induced in MSCs. In conclusion, miR-200 carrying EVs released from RPTECs induce the epithelial commitment of MSCs that may contribute to their regenerative potential. Based on experiments of MSC transfection with miR-200 mimics, we suggested that the miR-200 family may be involved in mesenchymal-epithelial transition of MSCs.

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.

Epithelial cells in culture: injured or differentiated cells?

Isolation of epithelial cells for cell culture is based on destruction of epithelial integrity. The consequences are manifold: cell polarity and specific cell functions are lost; cells acquire non-epithelial characteristics and start to proliferate. This situation may also occur in situ when parts of the epithelium are lost, either by apoptosis or necrosis by organ or tissue injury. During recovery from this injury, surviving epithelial cells proliferate and may restore epithelial integrity and finally re-differentiate into functional epithelial cells. In vitro, this re-differentiation is mostly not complete due to sub-optimal culture conditions. Therefore cultured epithelial cells resemble wounded or injured epithelia rather than healthy and well differentiated epithelia. The value of an in vitro cell model is the extent to which it helps to understand the function of the cells in situ. A variety of parameters influence the state of differentiation of cultured cells in vitro. Although each of these parameters had been studied, the picture how they co-ordinately influence the state of differentiation of epithelial cells in vitro is incomplete. Therefore we discuss the influence of the isolation method and cell culture on epithelial cells, and outline strategies to achieve highly differentiated epithelial cells for the use as an in vitro model.

miRNA let-7e targeting MMP9 is involved in adipose-derived stem cell differentiation toward epithelia

miRNA let-7e is involved in stem cell differentiation, and metalloproteinases are among its potential target genes. We hypothesized that the inhibitory action of let-7e on regulation of MMP9 expression could represent a crucial mechanism during differentiation of adipose-derived stem cells (ASCs). ASCs were differentiated with all-trans retinoic acid (ATRA) to promote differentiation, and the effect of let-7 silencing during differentiation was tested. Results indicate that ASCs cultured with ATRA differentiated into cells of the epithelial lineage. We found that ASCs cultured with ATRA or transfected with miRNA let-7e expressed epithelial markers such as cytokeratin-18 and early renal organogenesis markers such as Pax2, Wt1, Wnt4 and megalin. Conversely, the specific knockdown of miRNA let-7e in ASCs significantly decreased the expression of these genes, indicating its vital role during the differentiation process. Using luciferase reporter assays, we also showed that MMP9 is a direct target of miRNA let-7e. Thus, our results suggest that miRNA let-7e acts as a matrix metalloproteinase-9 (MMP9) inhibitor and differentiation inducer in ASCs.

Mesenchymal stem cell-conditioned medium enhances osteogenic and chondrogenic differentiation of human embryonic stem cells and human induced pluripotent stem cells by mesodermal lineage induction

Human mesenchymal stem cells (hMSCs) have the ability to differentiate into mesenchymal lineages. In this study, we hypothesized that treatment of embryoid bodies (EBs) composed of either human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) with a hMSC-conditioned medium (CM) can stimulate the induction of the mesodermal lineage and subsequent differentiation toward the osteogenic and chondrogenic lineage. Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) analysis indicated that the hMSC-CM treatment increased gene expression related to the mesodermal lineage and decreased gene expression related to the endodermal and ectodermal lineage in EBs. Fourteen days after culturing the mesodermal lineage-induced EBs in the osteogenic or chondrogenic differentiation medium, we observed enhanced osteogenic and chondrogenic differentiation compared with untreated EBs, as evaluated using qRT-PCR, cytochemistry, immunocytochemistry, and flow cytometry. This method may be useful for enhancing the osteogenic or chondrogenic differentiation of hESCs or hiPSCs.

Label retention identifies a multipotent mesenchymal stem cell-like population in the postnatal thymus

Thymic microenvironments are essential for the proper development and selection of T cells critical for a functional and self-tolerant adaptive immune response. While significant turnover occurs, it is unclear whether populations of adult stem cells contribute to the maintenance of postnatal thymic epithelial microenvironments. Here, the slow cycling characteristic of stem cells and their property of label-retention were used to identify a K5-expressing thymic stromal cell population capable of generating clonal cell lines that retain the capacity to differentiate into a number of mesenchymal lineages including adipocytes, chondrocytes and osteoblasts suggesting a mesenchymal stem cell-like phenotype. Using cell surface analysis both culture expanded LRCs and clonal thymic mesenchymal cell lines were found to express Sca1, PDGFRα, PDGFRβ,CD29, CD44, CD49F, and CD90 similar to MSCs. Sorted GFP-expressing stroma, that give rise to TMSC lines, contribute to thymic architecture when reaggregated with fetal stroma and transplanted under the kidney capsule of nude mice. Together these results show that the postnatal thymus contains a population of mesenchymal stem cells that can be maintained in culture and suggests they may contribute to the maintenance of functional thymic microenvironments.

Transdifferentiation of adipose-derived stem cells into keratinocyte-like cells: engineering a stratified epidermis

Skin regeneration is an important area of research in the field of tissue-engineering, especially for cases involving loss of massive areas of skin, where current treatments are not capable of inducing permanent satisfying replacements. Human adipose-derived stem cells (ASC) have been shown to differentiate in-vitro into both mesenchymal lineages and non-mesenchymal lineages, confirming their transdifferentiation ability. This versatile differentiation potential, coupled with their ease of harvest, places ASC at the advancing front of stem cell-based therapies. In this study, we hypothesized that ASC also have the capacity to transdifferentiate into keratinocyte-like cells and furthermore are able to engineer a stratified epidermis. ASC were successfully isolated from lipoaspirates and cell sorted (FACS). After sorting, ASC were either co-cultured with human keratinocytes or with keratinocyte conditioned media. After a 14-day incubation period, ASC developed a polygonal cobblestone shape characteristic of human keratinocytes. Western blot and q-PCR analysis showed the presence of specific keratinocyte markers including cytokeratin-5, involucrin, filaggrin and stratifin in these keratinocyte-like cells (KLC); these markers were absent in ASC. To further evaluate if KLC were capable of stratification akin to human keratinocytes, ASC were seeded on top of human decellularized dermis and cultured in the presence or absence of EGF and high Ca²⁺ concentrations. Histological analysis demonstrated a stratified structure similar to that observed in normal skin when cultured in the presence of EGF and high Ca²⁺. Furthermore, immunohistochemical analysis revealed the presence of keratinocyte markers such as involucrin, cytokeratin-5 and cytokeratin-10. In conclusion this study demonstrates for the first time that ASC have the capacity to transdifferentiate into KLC and engineer a stratified epidermis. This study suggests that adipose tissue is potentially a readily available and accessible source of keratinocytes, particularly for severe wounds encompassing large surface areas of the body and requiring prompt epithelialization.

Tumor necrosis factor receptor 2: its contribution to acute cellular rejection and clear cell renal carcinoma

Tumor necrosis factor receptor 2 (TNFR2) is a type I transmembrane glycoprotein and one of the two receptors that orchestrate the complex biological functions of tumor necrosis factor (TNF, also designed TNF-α). Accumulating experimental evidence suggests that TNFR2 plays an important role in renal disorders associated with acute cellular rejection and clear cell renal carcinoma but its exact role in these settings is still not completely understood. This papers reviews the factors that may mediate TNFR2 induction in acute cellular rejection and clear cell renal carcinoma and its contribution to these conditions and discusses its therapeutic implications. A greater understanding of the function of TNFR2 may lead to the development of new anti-TNF drugs.

Keratinocyte growth factor and thiazolidinediones and linolenic acid differentiate characterized mammary fat pad adipose stem cells isolated from prepubertal Korean black goat to epithelial and adipogenic lineage

The study was conducted to know and investigate the mechanism involved during mesenchymal to epithelial transition to unravel questions related to mammary gland development in prepubertal Korean black goat. We, therefore, biopsied mammary fat pad and isolated adipose cells and characterized with stemness factors (CD34, CD13, CD44, CD106, and vimentin) immunologically and through their genetic expression. Furthermore, characterized cells were differentiated to adipogenic (thiazolidinediones and α-linolenic acid) and epithelial (keratinocyte growth factor) lineages. Thiazolidinediones/or in combination with α-linolenic acid demonstrated significant upregulation of adipo-Q, PPAR-γ, CEBP-α, LPL, and resistin. Adipose stem cells in induction mixture (5 μg/ml insulin, 1 μg/ml hydrocortisone, and 10 ng/ml epidermal growth factor) and subsequent treatment with 10 ng/ml keratinocyte growth factor revealed their trans-differentiating ability to epithelial lineage. From 2 d onwards, the cells under keratinocyte growth factor influenced cells to assume rectangular (2-4 d) to cuboidal (8-10 d) shapes. Ayoub-Shklar stain developed brownish-red pigment in the transformed cells. Though, expressions of K8 and K18 were noted to be highly significant (p < 0.01) but expressions of epithelial membrane antigens and epithelial specific antigens were also significant (p < 0.05) compared to 0 d. Conclusively, epithelial transformations of mammary adipose stem cells would add up knowledge to develop therapeutic regimen to deal with mammary tissue injury and diseases.

Adipose and mammary epithelial tissue engineering

Breast reconstruction is a type of surgery for women who have had a mastectomy, and involves using autologous tissue or prosthetic material to construct a natural-looking breast. Adipose tissue is the major contributor to the volume of the breast, whereas epithelial cells comprise the functional unit of the mammary gland. Adipose-derived stem cells (ASCs) can differentiate into both adipocytes and epithelial cells and can be acquired from autologous sources. ASCs are therefore an attractive candidate for clinical applications to repair or regenerate the breast. Here we review the current state of adipose tissue engineering methods, including the biomaterials used for adipose tissue engineering and the application of these techniques for mammary epithelial tissue engineering. Adipose tissue engineering combined with microfabrication approaches to engineer the epithelium represents a promising avenue to replicate the native structure of the breast.

Effects of multiple agents on epithelial differentiation of rabbit adipose-derived stem cells in 3D culture

Mesenchymal stem cells have been given particular attention in tissue regeneration research due to their multipotency and proliferative activity. In this study, we investigated the possibility of epithelial differentiation of rabbit adipose-derived stem cells (rASCs) in an in vitro 3D culture system. The experimental procedure was performed with different contributing factors including all-trans retinoic acid (ATRA), epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), and hydrocortisone in air-liquid interface culture, for modulating proliferation and providing a synergistic effect on epithelial differentiation of rASCs. After induction, immunofluorescence staining, western blot analysis, flow cytometry analysis, and quantitative real-time polymerase chain reaction assay have been performed to detect the expression of epithelial-specific markers and mesenchymal marker alpha-smooth muscle actin (α-SMA). The growth pattern and viability of cells were evaluated by transmission electron microscopy and Hoechst 33258 assay, respectively. After treated with optimized induction medium (including 2.5 μM ATRA, 20 ng/mL EGF, 10 ng/mL KGF, 10 ng/mL HGF, and 0.5 μg/mL hydrocortisone), rASCs were observed to display a stratified epithelial-like morphology, with the expression of cytokeratin 19 and cytokeratin 13 in 63.69%±2.63% and 22.17%±1.51%, respectively, and the relative expression level of cytokeratin 19 increased to 3.152 compared with 0.151 before induction. The expression of α-SMA decreased to 19.40%±1.45% after induction, but almost no expression of involucrin was detected. The results showed that the establishment of an epithelial-specific microenvironment may be a feasible way for epithelial differentiation of ASCs in vitro, and provided an alternative for research on epithelium regeneration.

Human mesenchymal stem cells differentiate into keratocyte-like cells in keratocyte-conditioned medium

Culturing corneal keratocytes is difficult because keratocytes growing in a monolayer rapidly lose their stellate morphology and cease to express keratocyte markers such as keratocan, lumican and aldehyde dehydrogenase 1 family, member A1 (ALDH1A1). Conversely, mesenchymal stem cells (MSCs) can be easily expanded in cell culture, and they have a variety of differentiation pathways. We studied the feasibility of using MSCs as a source for corneal tissue engineering. Based on the observation that keratocytes have MSC-like properties, similar to bone marrow-derived MSCs (BM-MSCs), we hypothesized that MSCs would differentiate into corneal keratocyte-like cells in keratocyte-conditioned medium (KCM). We measured changes in the expression of keratocyte markers through quantitative real-time polymerase chain reaction (qRT-PCR) and found that human MSC's cultured in KCM expressed both keratocan and ALDH1A1. Western blot analysis demonstrated that human MSCs cultured in KCM steadily increased their expression of lumican and ALDH1A1, while they lost expression of α-smooth muscle actin (α-SMA). Immunocytochemistry indicated that human MSCs grown in KCM acquired characteristics similar to those of keratocytes. These results suggest that KCM can direct human MSCs to differentiate into keratocyte-like cells.

Adipose-derived mesenchymal stromal/stem cells: tissue localization, characterization, and heterogeneity

Adipose tissue as a stem cell source is ubiquitously available and has several advantages compared to other sources. It is easily accessible in large quantities with minimal invasive harvesting procedure, and isolation of adipose-derived mesenchymal stromal/stem cells (ASCs) yields a high amount of stem cells, which is essential for stem-cell-based therapies and tissue engineering. Several studies have provided evidence that ASCs in situ reside in a perivascular niche, whereas the exact localization of ASCs in native adipose tissue is still under debate. ASCs are isolated by their capacity to adhere to plastic. Nevertheless, recent isolation and culture techniques lack standardization. Cultured cells are characterized by their expression of characteristic markers and their capacity to differentiate into cells from meso-, ecto-, and entodermal lineages. ASCs possess a high plasticity and differentiate into various cell types, including adipocytes, osteoblasts, chondrocytes, myocytes, hepatocytes, neural cells, and endothelial and epithelial cells. Nevertheless, recent studies suggest that ASCs are a heterogeneous mixture of cells containing subpopulations of stem and more committed progenitor cells. This paper summarizes and discusses the current knowledge of the tissue localization of ASCs in situ, their characterization and heterogeneity in vitro, and the lack of standardization in isolation and culture methods.

Transdifferentiation of human adipose-derived stem cells into urothelial cells: potential for urinary tract tissue engineering

Autologous urothelial cells (UCs) provide a cell source for urinary tissue engineering because they can be used safely due to their lack of immunogenicity. However, these cells cannot be harvested under the following circumstances: malignancy, infection and organ loss, etc. Human adipose-derived stem cells (HADSCs) possess the traits of high differentiation potential and ease of isolation, representing a promising resource for tissue engineering and regenerative medicine. Nevertheless, HADSCs have been poorly investigated in urology and the optimal approaches to induce HADSCs into urothelium are still under investigation. In this study, we hypothesized that the change of microenvironment by a conditioned medium was essential for the transdifferentiation of HADSCs into UCs. We then used a conditioned medium derived from urothelium to alternate the microenvironment of HADSCs. After 14 days of culture in a conditioned medium, about 25-50% HADSCs changed their morphology into polygonal epithelium-like shapes. In addition, these cells expressed up-regulating of urothelial lineage-specific markers (uroplakin 2and cytokeratin-18) and down-regulating of mesenchymal marker (vimentin) in RNA and protein level, respectively, which confirmed that HADSCs were induced into urothelial lineage cells. We also measured the growth factors in the conditioned medium in order to analyze the molecular mechanisms regulating transdifferentiation. We observed that the expression levels of PDGF-BB and VEGF were significantly higher than those of the control group after 14 days induction, suggesting they were abundantly secreted into the medium during the culturing period. In conclusion, HADSCs showed in vitro the upregulation of markers for differentiation towards urothelial cells by culturing in an urothelial-conditioned medium, which provides an alternative cell source for potential use in urinary tract tissue engineering.

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

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

During epithelial differentiation of human adipose-derived stromal/stem cells, expression of zonula occludens protein-1 is induced by a combination of retinoic acid, activin-A and bone morphogenetic protein-7

BACKGROUND AIMS

Adipose-derived stromal/stem cells (ASC) possess a multilineage differentiation potential, can be used from an autologous origin, and are, therefore, attractive candidates for clinical applications to repair or regenerate damaged tissues and organs. Beside their well-known differentiation into cells of mesodermal origin, ASC are able to differentiate into cells of ecto- and endodermal origin.

METHODS

Previous studies have shown that all trans retinoic acid (ATRA) induces the expression of cytokeratin 18 (CK18), indicating the beginning of differentiation into the epithelial lineage. Nevertheless, ATRA does not induce the expression of other epithelial markers. Therefore, we tested the additional influence of two growth factors on the onset of epithelial differentiation of ASC. The cells were cultured with ATRA, Activin A (ActA) and bone morphogenetic protein-7 (BMP-7), either alone or in combination. Differentiation into the epithelial lineage was assessed by the expression of the characteristic epithelial markers CK18 and zonula occludens protein 1 (ZO-1) using Western blot, immunofluorescence staining and polymerase chain reaction (PCR) analysis.

RESULTS

The mixture of all three factors induced epithelial differentiation of ASC without enhancing cell proliferation. Upon induction, the ASC showed phenotypic changes consistent with an epithelial phenotype. The addition of the growth factors ActA and BMP-7 enhanced the inductive effect of ATRA, as shown by the de novo expression of ZO-1 in addition to CK18 expression.

CONCLUSIONS

Our study highlights the onset of the epithelial differentiation of ASC induced by culture with a combination of ATRA, ActA and BMP-7.

In search of the skeletal stem cell: isolation and separation strategies at the macro/micro scale for skeletal regeneration

Skeletal stem cells (SSCs) show great capacity for bone and cartilage repair however, current in vitro cultures are heterogeneous displaying a hierarchy of differentiation potential. SSCs represent the diminutive true multipotent stem cell fraction of bone marrow mononuclear cell (BMMNC) populations. Endeavours to isolate SSCs have generated a multitude of separation methodologies. SSCs were first identified and isolated by their ability to adhere to culture plastic. Once isolated, further separation is achieved via culture in selective or conditioned media (CM). Indeed, preferential SSC growth has been demonstrated through selective in vitro culture conditions. Other approaches have utilised cell morphology (size and shape) as selection criteria. Studies have also targeted SSCs based on their preferential adhesion to specified compounds, individually or in combination, on both macro and microscale platforms. Nevertheless, most of these methods which represent macroscale function with relatively high throughput, yield insufficient purity. Consequently, research has sought to downsize isolation methodologies to the microscale for single cell analysis. The central approach is identification of the requisite cell populations of SSC-specific surface markers that can be targeted for isolation by either positive or negative selection. SELEX and phage display technology provide apt means to sift through substantial numbers of candidate markers. In contrast, single cell analysis is the paramount advantage of microfluidics, a relatively new field for cell biology. Here cells can be separated under continuous or discontinuous flow according to intrinsic phenotypic and physicochemical properties. The combination of macroscale quantity with microscale specificity to generate robust high-throughput (HT) technology for pure SSC sorting, isolation and enrichment offers significant implications therein for skeletal regenerative strategies as a consequence of lab on chip derived methodology.

Epithelial differentiation of human adipose-derived stem cells

The versatile differentiation potential of adipose-derived stem cells (ASC) into cells of mesodermal, entodermal, and ectodermal origin places these cells at the forefront of cell-based therapies and cell transplantation. Epithelial differentiation of ASC may either be initiated by direct cell-cell or cell-matrix contacts, by chemical factors like retinoic acid, or via secreted cellular factors like cytokines, interleukins, or growth factors included in conditioned media.This protocol describes methods to induce the in vitro differentiation of ASC from human adipose tissue into the epithelial lineage, and describes the methods used to verify this induced differentiation. We present two differentiation protocols based on either retinoic acid or conditioned medium of cultured epithelial cells.

Exosomes/microvesicles as a mechanism of cell-to-cell communication

Microvesicles (MVs) are circular fragments of membrane released from the endosomal compartment as exosomes or shed from the surface membranes of most cell types. An increasing body of evidence indicates that they play a pivotal role in cell-to-cell communication. Indeed, they may directly stimulate target cells by receptor-mediated interactions or may transfer from the cell of origin to various bioactive molecules including membrane receptors, proteins, mRNAs, microRNAs, and organelles. In this review we discuss the pleiotropic biologic effects of MVs that are relevant for communication among cells in physiological and pathological conditions. In particular, we discuss their potential involvement in inflammation, renal disease, and tumor progression, and the evidence supporting a bidirectional exchange of genetic information between stem and injured cells. The transfer of gene products from injured cells may explain stem cell functional and phenotypic changes without the need of transdifferentiation into tissue cells. On the other hand, transfer of gene products from stem cells may reprogram injured cells to repair damaged tissues.

Achievements and challenges in bioartificial kidney development

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

Human adipose-derived mesenchymal stem cells in vitro: evaluation of an optimal expansion medium preserving stemness

BACKGROUND AIMS

The potential of cultured adipose-derived stem cells (ASC) in regenerative medicine and new cell therapeutic concepts has been shown recently by many investigations. However, while the method of isolation of ASC from liposuction aspirates depending on plastic adhesion is well established, a standard expansion medium optimally maintaining the undifferentiated state has not been described.

METHODS

We cultured ASC in five commonly used culture media (two laboratory-made media and three commercially available media) and compared them with a standard medium. We analyzed the effects on cell morphology, proliferation, hepatocyte growth factor (HGF) expression, stem cell marker profile and differentiation potential. Proliferation was measured with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and a fluorescent assay. Release of HGF was assessed by an immunoassay. Expression of characteristic stem cell-related transcription factors and markers was evaluated by quantitative polymerase chain reaction (qPCR) (Nanog, Sox-2, Rex-1, nestin and Oct-4) and flow cytometry (CD44, CD73, CD90, CD105 and CD166), and differentiation was shown by adipogenic medium.

RESULTS

The morphology and expansion of ASC were significantly affected by the media used, whereas none of the media influenced the ASC potential to differentiate into adipocytes. Furthermore, two of the media induced an increase in expression of transcription factors, an increased secretion of HGF and a decrease in CD105 expression.

CONCLUSIONS

Culture of ASC in one of these two media before using the cells in cell therapeutic approaches may have a benefit on their regenerative potential.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Expression of a functional epidermal growth factor receptor on human adipose-derived mesenchymal stem cells and its signaling mechanism

Adult stem cells act as a pluripotent source of regenerative cells during tissue injury. Despite expanded research in stem cell biology, understanding how growth and migration of adipose-derived adult mesenchymal stem cells (ASC) are governed by interactions with growth factors is very limited. One important property of ASC is the presence of the epidermal growth factor (EGF) receptor and the cellular response to soluble EGF. Expression of the EGF receptor was proven by PCR and Western blotting. Signal transduction was analyzed by Western blotting and PhosFlow assay. EGF caused robust phosphorylation of SHC and ERK1/2, which could be inhibited by EGF receptor antagonist AG1478 and MEK inhibitor PD98059. ASC proliferation was determined by MTT assay. Stem cell migration was analyzed in a modified Boyden chamber. Incubation with EGF led to cell proliferation and induced cell migration, but did not change the undifferentiated state of the cells. In the kidney, injured renal tubular cells express high amounts of EGF. Therefore, our results may highlight a mechanism underlying renal regeneration. Thus, future in vivo studies that focus on the effects of EGF on recruitment of ASC to sites of injury are necessary.