Human amniotic fluid as a potential new source of organ specific precursor cells for future regenerative medicine applications

Human amniotic-fluid-derived stem cells: a unique source for regenerative medicine

INTRODUCTION

The first application of tissue engineering was based on the use of differentiated cells from the adult organism, which was associated with an invasiveness and high risk of diseased cells' transplantation. Over the years, the range of available cell populations for tissue engineering has widened.

AREAS COVERED

We review the comprehensive information concerning the characteristic features of amniotic-fluid-derived stem cells (AFSCs). We also review the potential applications of these cells in clinical practice.

EXPERT OPINION

AFSCs hold promise for the future treatment of many incurable diseases. However, such cell-based therapies have some limitations, and there are questions relating to the use of stem cells, which should be carefully analyzed before translation of these cells into clinical practice.

Human second trimester amniotic fluid cells are able to create embryoid body-like structures in vitro and to show typical expression profiles of embryonic and primordial germ cells

Human amniotic fluid-derived stem cells (AFSCs) represent a novel class of broadly multipotent stem cells sharing characteristics of both embryonic and adult stem cells. However, both the origin of these cells and their actual properties in terms of pluripotent differentiation potential are still debated. In order to verify the presence of features of pluripotency in human second trimester AFSCs, we have investigated the ability of these cells to form in vitro three-dimensional aggregates, known as embryoid bodies (EBs), and to express specific genes of embryonic stem cells (ESCs) and primordial germ cells (PGCs). EBs were obtained after 5 days of AFSC culture in suspension and showed positivity for alkaline phosphatase (AP) staining and for specific markers of pluripotency (OCT4 and SOX2). Moreover, EB-derived cells showed the expression of specific transcripts of the three germ layers. RT-PCR analysis, carried out at different culture times (second, third, fourth, fifth, and eighth passages), revealed the presence of specific markers of ESCs (such as FGF4 and DAPPA4), as well as of markers typical of PGCs and, in particular, genes involved in early stages of germ cell development (Fragilis, Stella, Vasa, c-Kit, Rnf17). Finally, the expression of genes related to the control of DNA methylation (DNMT3A, DNMT3b1, DNMT1, DNMT3L, MBD1, MBD2, MBD3, MDB4, MeCP2), as well as the lack of inactivation of the X-chromosome in female samples, was also demonstrated. Taken together, these data provide further evidence for the presence of common features among human AFSCs, PGCs, and ESCs.

A novel source of cultured podocytes

Amniotic fluid is in continuity with multiple developing organ systems, including the kidney. Committed, but still stem-like cells from these organs may thus appear in amniotic fluid. We report having established for the first time a stem-like cell population derived from human amniotic fluid and possessing characteristics of podocyte precursors. Using a method of triple positive selection we obtained a population of cells (hAKPC-P) that can be propagated in vitro for many passages without immortalization or genetic manipulation. Under specific culture conditions, these cells can be differentiated to mature podocytes. In this work we compared these cells with conditionally immortalized podocytes, the current gold standard for in vitro studies. After in vitro differentiation, both cell lines have similar expression of the major podocyte proteins, such as nephrin and type IV collagen, that are characteristic of mature functional podocytes. In addition, differentiated hAKPC-P respond to angiotensin II and the podocyte toxin, puromycin aminonucleoside, in a way typical of podocytes. In contrast to immortalized cells, hAKPC-P have a more nearly normal cell cycle regulation and a pronounced developmental pattern of specific protein expression, suggesting their suitability for studies of podocyte development for the first time in vitro. These novel progenitor cells appear to have several distinct advantages for studies of podocyte cell biology and potentially for translational therapies.

Routine clonal expansion of mesenchymal stem cells derived from amniotic fluid for perinatal applications

INTRODUCTION

Stem cells (SCs) isolated from amniotic fluid (AF) are a promising source for autologous perinatal cell therapy. The aim of this study was to develop a routine isolation, selection, and expansion protocol of clonal SC lines from redundant clinical amniocentesis samples.

MATERIALS AND METHODS

Amniotic fluids were collected between 15 and 22 weeks of gestation, and SCs were isolated by CD117-based and mechanical selection protocols. SCs were characterized by mesenchymal SC marker expression and differentiation protocols. Cells were manipulated with a lentiviral vector system expressing the β-galactosidase reporter gene and were injected into immunodeficient newborn mouse pups. Qualitative assessment was performed to detect the infused cells after 1 week.

RESULTS

A total of 78 clonal AF SC populations were successfully isolated by mechanical selection from 21 consecutive amniocentesis samples. They were positive for mesenchymal SC cluster of differentiation markers and could be differentiated into the different lineages. SCs were stably labeled using β-galactosidase and were detected in the lungs and hearts of the neonatal mice.

CONCLUSION

We demonstrate that mesenchymal SCs can be routinely isolated and clonally expanded from mid-gestation human AF using mechanical isolation. They can easily be transduced and be tested for perinatal treatment in animal models.

Amniotic fluid as a source of pluripotent and multipotent stem cells for organ regeneration

PURPOSE OF REVIEW

Amniotic fluid, due to its contact to the fetus during development, is considered an important diagnostic tool to evaluate the health status of the fetus during pregnancy. However, amniotic fluid also contains a heterogeneous cellular population that can be safely collected by amniocentesis and easily cultured. Many different cell types have been found within amniotic fluid and currently some of them are being tested for their possible use for cellular therapy.

RECENT FINDINGS

Potential of pluripotent and multipotent cells isolated from the amniotic fluid has been tested and in-vitro differentiations toward various cell types have been successfully performed. Furthermore, in-vivo studies are highlighting the benefits and mechanisms of amniotic fluid cells for therapy, with particular focus on kidney and lung diseases.

SUMMARY

Amniotic fluid may represent a precious source for easily and safely retrievable cell types that may be used for regenerative medicine purposes.

Spindle shaped human mesenchymal stem/stromal cells from amniotic fluid promote neovascularization

Human amniotic fluid obtained at amniocentesis, when cultured, generates at least two morphologically distinct mesenchymal stem/stromal cell (MSC) subsets. Of these, the spindle shaped amniotic fluid MSCs (SS-AF-MSCs) contain multipotent cells with enhanced adipogenic, osteogenic and chondrogenic capacity. Here, we demonstrate, for the first time, the capacity of these SS-AF-MSCs to support neovascularization by umbilical cord blood (UCB) endothelial colony forming cell (ECFC) derived cells in both in vitro and in vivo models. Interestingly, although the kinetics of vascular tubule formation in vitro were similar when the supporting SS-AF-MSCs were compared with the best vasculogenic supportive batches of bone marrow MSCs (BMSCs) or human dermal fibroblasts (hDFs), SS-AF-MSCs supported vascular tubule formation in vivo more effectively than BMSCs. In NOD/SCID mice, the human vessels inosculated with murine vessels demonstrating their functionality. Proteome profiler array analyses revealed both common and distinct secretion profiles of angiogenic factors by the SS-AF-MSCs as opposed to the hDFs and BMSCs. Thus, SS-AF-MSCs, which are considered to be less mature developmentally than adult BMSCs, and intermediate between adult and embryonic stem cells in their potentiality, have the additional and very interesting potential of supporting increased neovascularisation, further enhancing their promise as vehicles for tissue repair and regeneration.

Chondrogenic differentiation of menstrual blood-derived stem cells on nanofibrous scaffolds

Cartilage tissue engineering is a promising technology to restore and repair cartilage lesions in the body. In recent years, significant advances have been made using stem cells as a cell source for clinical goals of cartilage tissue engineering. Menstrual blood-derived stem cells (MenSCs) is a novel population of stem cells that demonstrate the potential and differentiate into a wide range of tissues including the chondrogenic lineage. Incorporation of cell culture with extracellular matrix (ECM) like substratum plays an important role in cartilage tissue regeneration by providing attachment sites as well as bioactive signals for cells to grow and differentiate into chondrogenic lineage. The electrospun nanofibers are a class of polymer-based biomaterials that have been extensively utilized in tissue engineering as ECM-like scaffold. This chapter discusses potential of electrospun nanofibers for cell-based cartilage tissue engineering and presents detailed protocols on immunophenotyping characterization and chondrogenic differentiation of MenSCs seeded in poly-ε-caprolactone (PCL) nanofibers. The isolated MenSCs are characterized using flow cytometry, seeded on the nanofibers, imaged using scanning electron microscopy, and subsequently differentiated into chondrogenic lineage in culture medium containing specific growth factors and cytokines. Immunofluorescence and alcian blue staining are used to evaluate the development of seeded MenSCs in PCL nanofibrous scaffold into chondrogenic lineage.

Efficient direct reprogramming of mature amniotic cells into endothelial cells by ETS factors and TGFβ suppression

ETS transcription factors ETV2, FLI1, and ERG1 specify pluripotent stem cells into induced vascular endothelial cells (iVECs). However, iVECs are unstable and drift toward nonvascular cells. We show that human midgestation c-Kit(-) lineage-committed amniotic cells (ACs) can be reprogrammed into vascular endothelial cells (rAC-VECs) without transitioning through a pluripotent state. Transient ETV2 expression in ACs generates immature rAC-VECs, whereas coexpression with FLI1/ERG1 endows rAC-VECs with a vascular repertoire and morphology matching mature endothelial cells (ECs). Brief TGFβ-inhibition functionalizes VEGFR2 signaling, augmenting specification of ACs into rAC-VECs. Genome-wide transcriptional analyses showed that rAC-VECs are similar to adult ECs in which vascular-specific genes are expressed and nonvascular genes are silenced. Functionally, rAC-VECs form stable vasculature in Matrigel plugs and regenerating livers. Therefore, short-term ETV2 expression and TGFβ inhibition with constitutive ERG1/FLI1 coexpression reprogram mature ACs into durable rAC-VECs with clinical-scale expansion potential. Banking of HLA-typed rAC-VECs establishes a vascular inventory for treatment of diverse disorders.

Applications of amniotic membrane and fluid in stem cell biology and regenerative medicine

The amniotic membrane (AM) and amniotic fluid (AF) have a long history of use in surgical and prenatal diagnostic applications, respectively. In addition, the discovery of cell populations in AM and AF which are widely accessible, nontumorigenic and capable of differentiating into a variety of cell types has stimulated a flurry of research aimed at characterizing the cells and evaluating their potential utility in regenerative medicine. While a major focus of research has been the use of amniotic membrane and fluid in tissue engineering and cell replacement, AM- and AF-derived cells may also have capabilities in protecting and stimulating the repair of injured tissues via paracrine actions, and acting as vectors for biodelivery of exogenous factors to treat injury and diseases. Much progress has been made since the discovery of AM and AF cells with stem cell characteristics nearly a decade ago, but there remain a number of problematic issues stemming from the inherent heterogeneity of these cells as well as inconsistencies in isolation and culturing methods which must be addressed to advance the field towards the development of cell-based therapies. Here, we provide an overview of the recent progress and future perspectives in the use of AM- and AF-derived cells for therapeutic applications.

Potential antitumor therapeutic strategies of human amniotic membrane and amniotic fluid-derived stem cells

As stem cells are capable of self-renewal and can generate differentiated progenies for organ development, they are considered as potential source for regenerative medicine and tissue replacement after injury or disease. Along with this capacity, stem cells have the therapeutic potential for treating human diseases including cancers. According to the origins, stem cells are broadly classified into two types: embryonic stem cells (ESCs) and adult stem cells. In terms of differentiation potential, ESCs are pluripotent and adult stem cells are multipotent. Amnion, which is a membranous sac that contains the fetus and amniotic fluid and functions in protecting the developing embryo during gestation, is another stem cell source. Amnion-derived stem cells are classified as human amniotic membrane-derived epithelial stem cells, human amniotic membrane-derived mesenchymal stem cells and human amniotic fluid-derived stem cells. They are in an intermediate stage between pluripotent ESCs and lineage-restricted adult stem cells, non-tumorigenic, and contribute to low immunogenicity and anti-inflammation. Furthermore, they are easily available and do not cause any controversial issues in their recovery and applications. Not only are amnion-derived stem cells applicable in regenerative medicine, they have anticancer capacity. In non-engineered stem cells transplantation strategies, amnion-derived stem cells effectively target the tumor and suppressed the tumor growth by expressing cytotoxic cytokines. Additionally, they also have a potential as novel delivery vehicles transferring therapeutic genes to the cancer formation sites in gene-directed enzyme/prodrug combination therapy. Owing to their own advantageous properties, amnion-derived stem cells are emerging as a new candidate in anticancer therapy.

Changes in CDKN2D , TP53, and miR125a expression: potential role in the evaluation of human amniotic fluid-derived mesenchymal stromal cell fitness

Human amniotic fluid-derived mesenchymal stromal cells (hAMSC) have become one of the main cell populations used in regenerative medicine and for the study of various clinical disorders. These cells have a great capacity for proliferation and differentiation and do not form teratomas when transplanted into animal models, and their stemness seems to be between embryonic cells and adult mesenchymal cells. Before their use in cell therapy, they must be cultured and expanded in vitro, but the effect this process has on their fitness, a determining factor for the success or failure of cell therapy, is unknown. We undertook a follow-up of gene and microRNAs (miRNAs) expression using microarray of hAMSC for the first 15 passages. Significant changes were noted in the expression of various mRNAs and miRNAs, particularly down-regulation of TP53, increased expression of hsa-miR-125a and up-regulation of CDKN2D . The variations in TP53 and hsa-miR-125a may act as an indicator of the stemness of the hAMSC, whereas CDKN2D may indicate the begging of early senescence process in a p53-independent mechanism. The genes described in this study will help evaluate the fitness of hAMSC, thus guaranteeing their biological quality for use in regenerative medicine.

CD117(+) amniotic fluid stem cells: state of the art and future perspectives

Broadly multipotent stem cells can be isolated from amniotic fluid by selection for the expression of the membrane stem cell factor receptor c-Kit, a common marker for multipotential stem cells. They have clonogenic capability and can be directed into a wide range of cell types representing the three primary embryonic lineages. Amniotic fluid stem cells maintained for over 250 population doublings retained long telomeres and a normal karyotype. Clonal human lines verified by retroviral marking were induced to differentiate into cell types representing each embryonic germ layer, including cells of adipogenic, osteogenic, myogenic, endothelial, neuronal and hepatic lineages. AFS cells could be differentiate toward cardiomyogenic lineages, when co-cultured with neonatal cardiomyocytes, and have the potential to generate myogenic and hematopoietic lineages both in vitro and in vivo. Very recently first trimester AFS cells could be reprogrammed without any genetic manipulation opening new possibilities in the field of fetal/neonatal therapy and disease modeling. In this review we are aiming to summarize the knowledge on amniotic fluid stem cells and highlight the most promising results.

Amniotic fluid stem cells to study mTOR signaling in differentiation

The protein kinase mTOR is the central player within a pathway, which is known to be involved in the regulation of e.g., cell size, cell cycle, apoptosis, autophagy, aging and differentiation. mTOR activity responds to many signals, including cellular stress, oxygen, nutrient availability, energy status and growth factors. Deregulation of this enzyme is causatively involved in the molecular development of monogenic human diseases, cancer, obesity, type 2 diabetes or neurodegeneration. Recently, mTOR has also been demonstrated to control stem cell homeostasis. A more detailed investigation of this new mTOR function will be of highest relevance to provide more explicit insights into stem cell regulation in the near future. Different cellular tools, including adult stem cells, embryonic stem cells or induced pluripotent stem cells could be used to investigate the role of mTOR in mammalian stem cell biology. Here we discuss the potential of amniotic fluid stem cells to become a promising cellular model to study the role of signaling cascades in stem cell homeostasis.

Amniotic fluid stem cells: future perspectives

The existence of stem cells in human amniotic fluid was reported for the first time almost ten years ago. Since this discovery, the knowledge about these cells has increased dramatically. Today, amniotic fluid stem (AFS) cells are widely accepted as a new powerful tool for basic research as well as for the establishment of new stem-cell-based therapy concepts. It is possible to generate monoclonal genomically stable AFS cell lines harboring high proliferative potential without raising ethical issues. Many different groups have demonstrated that AFS cells can be differentiated into all three germ layer lineages, what is of relevance for both, the scientific and therapeutical usage of these cells. Of special importance for the latter is the fact that AFS cells are less tumorigenic than other pluripotent stem cell types. In this paper, we have summarized the current knowledge about this relatively young scientific field. Furthermore, we discuss the relevant future perspectives of this promising area of stem cell research focusing on the next important questions, which need to be answered.

Human amniotic fluid stem cells as a model for functional studies of genes involved in human genetic diseases or oncogenesis

Besides their putative usage for therapies, stem cells are a promising tool for functional studies of genes involved in human genetic diseases or oncogenesis. For this purpose induced pluripotent stem (iPS) cells can be derived from patients harbouring specific mutations. In contrast to adult stem cells, iPS cells are pluripotent and can efficiently be grown in culture. However, iPS cells are modulated due to the ectopic induction of pluripotency, harbour other somatic mutations accumulated during the life span of the source cells, exhibit only imperfectly cleared epigenetic memory of the source cell, and are often genomically instable. In addition, iPS cells from patients only allow the investigation of mutations, which are not prenatally lethal. Embryonic stem (ES) cells have a high proliferation and differentiation potential, but raise ethical issues. Human embryos, which are not transferred in the course of in vitro fertilization, because of preimplantation genetic diagnosis of a genetic defect, are still rarely donated for the establishment of ES cell lines. In addition, their usage for studies on gene functions for oncogenesis is hampered by the fact the ES cells are already tumorigenic per se. In 2003 amniotic fluid stem (AFS) cells have been discovered, which meanwhile have been demonstrated to harbour the potential to differentiate into cells of all three germ layers. Monoclonal human AFS cell lines derived from amniocenteses have a high proliferative potential, are genomically stable and are not associated with ethical controversies. Worldwide amniocenteses are performed for routine human genetic diagnosis. We here discuss how generation and banking of monoclonal human AFS cell lines with specific chromosomal aberrations or monogenic disease mutations would allow to study the functional consequences of disease causing mutations. In addition, recently a protocol for efficient and highly reproducible siRNA-mediated long-term knockdown of endogenous gene functions in AFS cells was established. Since AFS cells are not tumorigenic, gene modulations not only allow to investigate the role of endogenous genes involved in human genetic diseases but also may help to reveal putative oncogenic gene functions in different biological models, both in vitro and in vivo. This concept is discussed and a "proof of principle", already obtained via modulating genes involved in the mammalian target of rapamycin (mTOR) pathway in AFS cells, is presented.

Human amniotic fluid-derived c-kit(+) and c-kit (-) stem cells: growth characteristics and some differentiation potential capacities comparison

Amniotic fluid (AF) contains heterogeneous and multipotential cell types. A pure mesenchymal stem cells group can be sorted from AF using flow cytometry. In order to evaluate a possible therapeutic application of these cells, the human AF-derived c-kit(+) stem cells (c-kit(+) AFS) were compared with the c-kit(-) (unselected) stem cells (c-kit(-) AFS). Our findings revealed that the optimal period to obtain c-kit(+) AFS cells was between 16 and 22 weeks of gestation. Following cell sorting, c-kit(+) AFS cells shared similar morphological and proliferative characteristics as the c-kit(-) AFS cells. Both c-kit(+) and c-kit(-) AFS cells had the characteristics of mesenchymal stem cells through surface marker identification by flow cytometric and immunocytochemical analysis. Both c-kit(+) and c-kit(-) AFS cells could differentiate along adipogenic and osteogenic lineages. However, the myocardial differentiation capacity was enhanced in c-kit(+) AFS cells by detecting GATA-4, cTnT, α-actin, Cx43 mRNA and protein expression after myocardial induction; whereas induced c-kit(-) AFS cells were only detected with GATA-4 mRNA and protein expression. The c-kit(+) AFS cells could have potential clinical application for myogenesis in cardiac regenerative therapy.

Characterization and Chondrogenic Differentiation of Menstrual Blood-Derived Stem Cells on a Nanofibrous Scaffold

Introduction

The recent identification of menstrual blood-derived stem cells (MenSCs) as a unique population of stem cells has created enormous promise for tissue engineering. In this study, after characterization of MenSCs in comparison with bone marrow-derived stem cells (BMSCs), the potential of MenSCs seeded into electrospun, biodegradable, nanofibrous scaffolds in order to engineer cartilage was evaluated.

Methods

MenSCs and BMSCs were isolated by discontinuous density gradient centrifugation and plastic adherence. After characterization of MenSCs compared with BMSCs, MenSC differentiation into chondrocytes was investigated on a nanofibrous scaffold with specific growth and differentiation factors. The scaffold was prepared from polycaprolactone (PCL) and its surface was modified by plasma treatment.

Results

Flow cytometric analysis of expanded cells showed that MenSCs typically express some surface and intracellular markers associated with BMSCs. But marked expression of OCT-4 and the absence of STRO1 distinguished them from mesenchymal stem cells obtained from bone marrow. Based on scanning electron microscope images, the MenSCs were strongly anchored to the highly porous scaffold, which they penetrated and proliferated on. The scaffold contained an extensive cartilage-like extracellular matrix with about 50% greater glycosaminoglycan content than control MenSCs differentiated in a two-dimensional (2D) culture system (p<0.05). Considerable amounts of proteoglycan were produced by the cells differentiated on the scaffold, as demonstrated by Alcian blue staining. Unlike undifferentiated MenSCs, cells differentiated on the scaffold had strong immunoreactivity with monoclonal antibody against collagen type II.

Conclusions

The evidence presented in this study introduces MenSCs as a suitable stem cell population candidate for cartilage tissue engineering.

Injection of amniotic fluid stem cells delays progression of renal fibrosis

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

Human amniotic fluid stem cells seeded in fibroin scaffold produce in vivo mineralized matrix

This study investigated the potential of amniotic fluid stem cells (AFSCs) to synthesize mineralized extracellular matrix (ECM) within different porous scaffolds of collagen, poly-D,L-lactic acid (PDLLA), and silk fibroin. The AFSCs were initially differentiated by using an osteogenic medium in two-dimensional culture, and expression of specific bone proteins and the physiologic mineral production by the AFSCs were analyzed. In particular, during differentiation process, AFSCs expressed proteins like Runt-related transcription factor 2 (Runx2), Osterix, Osteopontin, and Osteocalcin with a sequential expression, analogous to those occurring during osteoblast differentiation, and produced extracellular calcium stores. AFSCs were then cultured on three-dimensional (3D) scaffolds and evaluated for their ability to differentiate into osteoblastic cells in vivo. Stem cells were cultured in vitro for 1 week in collagen, fibroin, and PDLLA scaffolds. The effect of predifferentiation of the stem cells in scaffolds on the subsequent bone formation in vivo was determined in a rat subcutaneous model. With the addition of a third dimension, osteogenic differentiation and mineralized ECM production by AFSCs were significantly higher. This study demonstrated the strong potential of AFSCs to produce 3D mineralized bioengineered constructs in vivo and suggests that fibroin may be an effective scaffold material for functional repair of critical size bone defects.

The potential use of stem cells derived from human amniotic fluid in renal diseases

Amniotic fluid (AF) contains a variety of cell types derived from fetal tissues that can easily grow in culture. These cells can be obtained during amniocentesis for prenatal screening of fetal genetic diseases, usually performed during the second trimester of pregnancy. Of particular interest, some expanded sub-populations derived from AF cells are capable of extensive self-renewal and maintain prolonged undifferentiated proliferation, which are defining properties of stem cells. These human AF stem cells (hAFSCs) exhibit multilineage potential and can differentiate into the three germ layers. They have high proliferation rates and express mesenchymal and embryonic markers, but do not induce tumor formation. In this study, hAFSCs derived from amniocentesis performed at 16–20 weeks of pregnancy were isolated, grown in culture, and characterized by flow cytometry and by their potential ability to differentiate into osteogenic, adipogenic, and chondrogenic lineages. After 4–7 passages, 5 × 10⁵ hAFSCs were inoculated under the kidney capsule of Wistar rats that were subjected to an experimental model of chronic renal disease, the 5/6 nephrectomy model (Nx). After 30 days, Nx rats treated with hAFSCs displayed significant reductions in blood pressure, proteinuria, macrophages, and α-smooth muscle actin expression compared with Nx animals. These preliminary results suggest that hAFSCs isolated and expanded from AF obtained by routine amniocentesis can promote renoprotection in the Nx model. Considering that the AF cells not used for fetal karyotyping are usually discarded, and that their use does not raise ethical issues, they may represent an alternative source of stem cells for cell therapy and regenerative medicine.

Amniotic Fluid as a Rich Source of Mesenchymal Stromal Cells for Transplantation Therapy

Stem cells isolated from amniotic fluid are known to be able to differentiate into different cells types, thus being considered as a powerful tool for cellular therapy of different human diseases. In the last 4 years, amniotic fluid-derived stem (AFS) cells have been shown to express embryonic and adult stem cell markers. These cells can be considered an intermediate stage between embryonic stem cells and adult stem cells. AFS cells can give rise to adipogenic, osteogenic, myogenic, endothelial, neurogenic, and hepatic lineages, inclusive of all embryonic germ layers. AFS cells have a high renewal capacity and can be expanded for over 250 doublings without any detectable loss of chromosomal telomere length. Taken together, all these data provide evidence that amniotic fluid represents a new and very promising source of stem cells for research, as well as clinical applications. Certainly stem cells from amniotic fluid will be useful both for a customized cell supply for newly born children and for banking cells to be used for therapeutic cell transplantation in immunogically matched recipients. Further investigations are also warranted to fully explore the amniotic cells' potential for adult human disorders.

Comparison of equine bone marrow-, umbilical cord matrix and amniotic fluid-derived progenitor cells

The aim of the study was to compare in vitro the stemness features of horse progenitor cells derived from bone marrow (BM-MSCs), amniotic fluid (AF-MSCs) and umbilical cord matrix (EUC-MSCs). It has been suggested that there may be a stem cell population within both umbilical cord matrix and amniotic fluid. However, little knowledge exists about the characteristics of these progenitor cells within these sources in the equine species. This study wanted to investigate an alternative and non-invasive stem cell source for the equine tissue engineering and to learn more about the properties of these cells for future cell banking. Bone marrow, umbilical cord and amniotic fluid samples were harvested from different horses. Cells were analyzed for proliferation, immunocytochemical, stem cell gene expression and multilineage plasticity. BM- and AF-MSCs took similar time to reach confluence and showed comparable plating efficiency. All cell lines expressed identical stem cell markers and capability to differentiate towards osteogenic lineage. Almost all cell lines differentiated into the adipogenic lineage as demonstrated by cytochemical staining, even if no adipose gene expression was detectable for AF-MSCs. AF- and EUC-MSCs showed a limited chondrogenic differentiation compared with BM-MSCs as demonstrated by histological and biochemical analyses. These findings suggest that AF-MSCs appeared to be a readily obtainable and highly proliferative cell line from an uninvasive source that may represent a good model system for stem cell biology. More studies are needed to investigate their multilineage potential. EUC-MSCs need to be further investigated regarding their particular behavior in vitro represented by spheroid formation.

Comparative analysis of the retinal potential of embryonic stem cells and amniotic fluid-derived stem cells

Photoreceptors have recently been generated from mouse and human embryonic stem cells (ESCs), although ethics concerns impede their utilization for cell replacement therapy for retinal disease. Extra-embryonic tissues have received attention as alternative therapeutic sources of stem cells. Human and mouse amniotic fluid-derived stem cells (AFCs) have been reported to be multipotent and express embryonic and adult stem cell markers. Here, in vitro conditions that generate retinal cells from ESCs were used to analyze and compare the retinal potential of murine AFCs and ESCs. We show that AFCs express pluripotency markers (Nanog, Sox2, and Oct3/4) as well as retinal transcription factor genes (Et, Lhx2, Tll1, Six6, Otx2, Pax6, and Fgf15). AFCs from amniotic fluid of Fgf15.gfp, Nrl.gfp, and Crx.gfp embryos cultured in retinal proliferation and differentiation conditions failed to switch on these retinal transgenes. AFCs cultured in retinal-promoting conditions, effective on ESCs, showed reduced expression of retinal markers. Retinal co-cultures activated retinal genes in ESCs but not in AFCs, and migration assays in retinal explants showed limited migration of AFCs compared with ESCs. Unlike ESCs, AFCs do not express the early embryonic ectodermal gene Utf1 and Western analysis of AFCs identified only the B isoform of Oct3/4, rather than the isoform A present in ESCs. We conclude that AFCs have restricted potential and differ considerably from ESCs and retinal progenitor cells. Reprogramming to induce pluripotency or new differentiation protocols will be required to confer retinal potential to AFCs as expression of a subset of pluripotency and retinal markers is not sufficient.

Cell-free fetal nucleic acids in amniotic fluid

BACKGROUND

Research into cell-free fetal (cff) nucleic acids has primarily focused on maternal plasma; however, cff DNA and RNA are also detectable in other body fluids such as amniotic fluid (AF). In AF, cff DNA is present in much greater concentrations than in maternal plasma and represents a pure fetal sample uncontaminated by maternal- and trophoblast-derived nucleic acids. The aim of this review was to summarize the current knowledge on cff nucleic acids in AF and to outline future research directions.

METHODS

MEDLINE and PREMEDLINE were searched up to August 2010 for original investigations of cell-free RNA or DNA in AF. Sixteen studies were included in the review.

RESULTS

AF cff DNA represents a physiologically separate pool from cff DNA in maternal plasma. The placenta is not a major source of nucleic acids in AF. It is feasible to isolate cff nucleic acids from small volumes of discarded AF supernatant in sufficient quality and quantity to perform microarray studies and downstream applications such as pathway analysis. This 'discovery-driven approach' has resulted in new information on the pathogenesis of Down syndrome and polyhydramnios. There is otherwise a paucity of information relating to the basic biology and clinical applications of cff nucleic acids in AF.

CONCLUSIONS

AF supernatant is a valuable and widely available but under-utilized biological resource. Further studies of cff nucleic acids in AF may lead to new insights into human fetal development and ultimately new approaches to antenatal treatment of human disease.

Biological characteristics of stem cells from foetal, cord blood and extraembryonic tissues

Foetal stem cells (FSCs) can be isolated during gestation from many different tissues such as blood, liver and bone marrow as well as from a variety of extraembryonic tissues such as amniotic fluid and placenta. Strong evidence suggests that these cells differ on many biological aspects such as growth kinetics, morphology, immunophenotype, differentiation potential and engraftment capacity in vivo. Despite these differences, FSCs appear to be more primitive and have greater multi-potentiality than their adult counterparts. For example, foetal blood haemopoietic stem cells proliferate more rapidly than those found in cord blood or adult bone marrow. These features have led to FSCs being investigated for pre- and post-natal cell therapy and regenerative medicine applications. The cells have been used in pre-clinical studies to treat a wide range of diseases such as skeletal dysplasia, diaphragmatic hernia and respiratory failure, white matter damage, renal pathologies as well as cancers. Their intermediate state between adult and embryonic stem cells also makes them an ideal candidate for reprogramming to the pluripotent status.