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

Raman spectroscopy analysis of human amniotic fluid cells from fetuses with myelomeningocele

Prenatal surgery for the treatment of spina bifida (myelomeningocele, MMC) significantly enhances the neurological prognosis of the patient. To ensure better protection of the spinal cord by large defects, the application of skin grafts produced with cells gained from the amniotic fluid is presently studied. In order to determine the most appropriate cells for this purpose, we tried to shed light on the extremely complex amniotic fluid cellular composition in healthy and MMC pregnancies. We exploited the potential of micro-Raman spectroscopy to analyse and characterize human amniotic fluid cells in total and putative (cKit/CD117-positive) stem cells of fetuses with MMC in comparison with amniotic fluid cells from healthy individuals, human fetal dermal fibroblasts and adult adipose derived stem cells. We found that (i) the differences between healthy and MMC amniocytes can be attributed to specific spectral regions involving collagen, lipids, sugars, tryptophan, aspartate, glutamate, and carotenoids, (ii) MMC amniotic fluid contains two particular cell populations which are absent or reduced in normal pregnancies, (iii) the cKit-negative healthy amniocyte subpopulation shares molecular features with human fetal fibroblasts. On the one hand we demonstrate a different amniotic fluid cellular composition in healthy and MMC pregnancies, on the other our work confirms micro-Raman spectroscopy to be a valuable tool for discriminating cell populations in unknown mixtures of cells.

Tissue-specific populations from amniotic fluid-derived mesenchymal stem cells manifest variant in vitro and in vivo properties

Amniotic fluid derived mesenchymal stem cells (AFMSCs), shed along the fetal development, exhibit superior multipotency and immunomodulatory properties compared to MSCs derived from other somatic tissues (e.g., bone marrow and fat). However, AFMSCs display heterogeneity due to source ambiguity, making them an underutilized stem cells source for translational clinical trials. Consequently, there is an urgent need to identify a method to purify the AFMSCs for clinical use. We found that the AFMSCs can be categorized into three distinct groups: kidney-specific AFMSCs (AFMSCs-K), lung-specific AFMSCs (AFMSCs-L), and AFMSCs with an undefined tissue source (AFMSCs-X). This classification was based on tissue-specific gene expression pattern of single cell colony. Additionally, we observed that AFMSCs-X, a minority population within the AFMSCs, exhibited the highest multipotency, proliferation, resistance to senescence and immuno-modulation. Our results showed that AFMSCs-X significantly improved survival rates and reduced bacterial colony forming units (CFU) in cecal ligation and puncture (CLP)-induced septic mice. Therefore, our study introduces a novel classification method to enhance the consistency and efficacy of AFMSCs. These subpopulations, originating from different tissue source, may offer a valuable and innovative resource of cells for regenerative medicine purposes.

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

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

Body fluid-derived stem cells - an untapped stem cell source in genitourinary regeneration

Somatic stem cells have been obtained from solid organs and tissues, including the bone marrow, placenta, corneal stroma, periosteum, adipose tissue, dental pulp and skeletal muscle. These solid tissue-derived stem cells are often used for tissue repair, disease modelling and new drug development. In the past two decades, stem cells have also been identified in various body fluids, including urine, peripheral blood, umbilical cord blood, amniotic fluid, synovial fluid, breastmilk and menstrual blood. These body fluid-derived stem cells (BFSCs) have stemness properties comparable to those of other adult stem cells and, similarly to tissue-derived stem cells, show cell surface markers, multi-differentiation potential and immunomodulatory effects. However, BFSCs are more easily accessible through non-invasive or minimally invasive approaches than solid tissue-derived stem cells and can be isolated without enzymatic tissue digestion. Additionally, BFSCs have shown good versatility in repairing genitourinary abnormalities in preclinical models through direct differentiation or paracrine mechanisms such as pro-angiogenic, anti-apoptotic, antifibrotic, anti-oxidant and anti-inflammatory effects. However, optimization of protocols is needed to improve the efficacy and safety of BFSC therapy before therapeutic translation.

Amniotic Fluid Stem Cells: What They Are and What They Can Become

In the last two decades, fetal amniotic fluid stem cells progressively attracted attention in the context of both basic research and the development of innovative therapeutic concepts. They exhibit broadly multipotent plasticity with the ability to differentiate into cells of all three embryonic germ layers and low immunogenicity. They are convenient to maintain, highly proliferative, genomically stable, non-tumorigenic, perfectly amenable to genetic modifications, and do not raise ethical concerns. However, it is important to note that among the various fetal amniotic fluid cells, only c-Kit+ amniotic fluid stem cells represent a distinct entity showing the full spectrum of these features. Since amniotic fluid additionally contains numerous terminally differentiated cells and progenitor cells with more limited differentiation potentials, it is of highest relevance to always precisely describe the isolation procedure and characteristics of the used amniotic fluid-derived cell type. It is of obvious interest for scientists, clinicians, and patients alike to be able to rely on up-todate and concisely separated pictures of the utilities as well as the limitations of terminally differentiated amniotic fluid cells, amniotic fluid-derived progenitor cells, and c-Kit+ amniotic fluid stem cells, to drive these distinct cellular models towards as many individual clinical applications as possible.

Clinical and molecular cytogenetic findings and pregnancy outcomes of fetuses with isochromosome Y

BACKGROUND

The mosaic forms and clinical phenotypes of fetuses with isochromosome Y are difficult to predict. Therefore, we summarized the cases of nine fetuses with isochromosome Y identified in prenatal diagnosis with a combination of molecular cytogenetic techniques, providing clinical evidence for prenatal genetic counseling.

METHODS

The prenatal diagnosis and pregnancy outcomes of nine fetuses with isochromosome Y were obtained by a  retrospective analysis. Isochromosome Y was identified prenatally by different approaches, such as conventional karyotyping, chromosomal microarray analysis (CMA), quantitative fluorescent polymerase chain reaction (QF-PCR) and fluorescence in situ hybridization (FISH).

RESULTS

Seven idic(Y) fetuses and two i(Y) fetuses were identified. One fetus was complete for i(Y)(p10), and the rest with 45,X had mosaic forms. A break and fusion locus was identified in Yp11.3 in one fetus, in Yq11.22 in six fetuses and in Yp10 in two fetuses. The CMA results suggested that different deletions and duplications were found on the Y chromosome. The deletion fragments ranged from 4.7 Mb to the entire Y chromosome, and the duplication fragments ranged from 10.4 to 18.0 Mb. QF-PCR analysis suggested that the AZF region was intact in one fetus, four fetuses had AZFb+c+d deletion, one fetus had AZFa+b+c+d deletion, and one fetus had AZFc+d deletion. Finally, four healthy male neonates were delivered successfully, but the parents of the remaining five fetuses, including three healthy and two unhealthy fetuses, chose to terminate their pregnancies.

CONCLUSION

The fetus and neonate phenotype of prenatally detected isochromosome Y usually is that of a normally developed male, ascertained in the absence of other indicators of a fetal structural anomaly. Our study provides clinical reference materials for risk assessment and permits better prenatally counseling and preparation of parents facing the birth of isochromosome Y fetuses.

CD24 for Cardiovascular Researchers: A Key Molecule in Cardiac Immunology, Marker of Stem Cells and Target for Drug Development

The study of the membrane protein, CD24, and its emerging role in major disease processes, has made a huge leap forward in the past two decades. It appears to have various key roles in oncogenesis, tumor progression and metastasis, stem cell maintenance and immune modulation. First described in the 1980s as the homologous human protein to the mouse HSA (Heat Stable Antigen), it was reported as a surface marker in developing hematopoietic cell lines. The later discovery of its overexpression in a large number of human neoplasms, lead cancer researchers to discover its various active roles in critical checkpoints during cancer development and progression. Targeting CD24 in directed drug development showed promising results in cancer treatment. More recently, the chimeric CD24-Fc protein has shown exciting results in clinical trials as a specific modulator of auto-inflammatory syndromes. This report is aimed to summarize the relevant literature on CD24 and tie it together with recent advancements in cardiovascular research. We hypothesize that CD24 is a promising focus of research in the understanding of cardiovascular disease processes and the development of novel biological therapies.

Amniotic fluid-derived exosomes improved spermatogenesis in a rat model of azoospermia

AIMS

This study aimed to explore the therapeutic effects of amniotic fluid-derived extracellular vesicles including exosomes (AF-Exos) on the recovery of sperm production capacity in a rat model of azoospermia.

MAIN METHODS

The non-obstructive azoospermia (NOA) was induced in rats using intratesticular administration of Busulfan. Azoospermia was confirmed by testis histology. AF-Exos samples containing 10 or 40 μg exosomal proteins were injected into testicular tissue of NOA rats. After two months, the recovery of spermatogenesis was monitored via histopathological staining, spermiogram, and hormonal analysis. Immunohistochemistry staining for OCT-3/4 was used to identify of spermatogonial progenitors. The expression of DAZL and VASA, was also measured.

KEY FINDINGS

AF-Exos exhibited sphere-shaped morphology with the mean diameter and zeta potential of 50 ± 7.521 nm and -7.16 mV. Immunoblots revealed that isolated nanoparticles were CD63, CD9, and CD81 positive. Histopathological evaluation revealed that spermatogenesis was improved significantly in NOA rats after AF-Exos injection. Data showed that the sperm parameters and spermatogenesis index were significantly improved after AF-Exos injection compared to azoospermic groups. OCT-3/4⁺ cells were increased in NOA rats after AF-Exos injection, showing the restoration of spermatogenesis. In the present study, both doses of exosome (10 and 40 μg) restored the testicular function of NOA rats. DAZL and VASA were increased significantly in animals who received 40 μg exosomal protein compared to azoospermic rats. Except in a high dose of AF-Exos (40 μg) for Testosterone and FSH, no statistically significant differences were found regarding hormones post-exosome injection.

SIGNIFICANCE

Our study demonstrated that AF-Exos regenerated spermatogenesis and improved sperm quality in NOA rats.

The Amniotic Fluid Cell-Free Transcriptome Provides Novel Information about Fetal Development and Placental Cellular Dynamics

The amniotic fluid (AF) is a complex biofluid that reflects fetal well-being during development. AF con be divided into two fractions, the supernatant and amniocytes. The supernatant contains cell-free components, including placenta-derived microparticles, protein, cell-free fetal DNA, and cell-free fetal RNA from the fetus. Cell-free mRNA (cfRNA) analysis holds a special position among high-throughput analyses, such as transcriptomics, proteomics, and metabolomics, owing to its ease of profiling. The AF cell-free transcriptome differs from the amniocyte transcriptome and alters with the progression of pregnancy and is often associated with the development of various organ systems including the fetal lung, skin, brain, pancreas, adrenal gland, gastrointestinal system, etc. The AF cell-free transcriptome is affected not only by normal physiologies, such as fetal sex, gestational age, and fetal maturity, but also by pathologic mechanisms such as maternal obesity, and genetic syndromes (Down, Edward, Turner, etc.), as well as pregnancy complications (preeclampsia, intrauterine growth restriction, preterm birth, etc.). cfRNA in the amniotic fluid originates from the placenta and fetal organs directly contacting the amniotic fluid as well as from the fetal plasma across the placenta. The AF transcriptome may reflect the fetal and placental development and therefore aid in the monitoring of normal and abnormal development.

Loss of decay-accelerating factor triggers podocyte injury and glomerulosclerosis

Kidney glomerulosclerosis commonly progresses to end-stage kidney failure, but pathogenic mechanisms are still poorly understood. Here, we show that podocyte expression of decay-accelerating factor (DAF/CD55), a complement C3 convertase regulator, crucially controls disease in murine models of adriamycin (ADR)-induced focal and segmental glomerulosclerosis (FSGS) and streptozotocin (STZ)-induced diabetic glomerulosclerosis. ADR induces enzymatic cleavage of DAF from podocyte surfaces, leading to complement activation. C3 deficiency or prevention of C3a receptor (C3aR) signaling abrogates disease despite DAF deficiency, confirming complement dependence. Mechanistic studies show that C3a/C3aR ligations on podocytes initiate an autocrine IL-1β/IL-1R1 signaling loop that reduces nephrin expression, causing actin cytoskeleton rearrangement. Uncoupling IL-1β/IL-1R1 signaling prevents disease, providing a causal link. Glomeruli of patients with FSGS lack DAF and stain positive for C3d, and urinary C3a positively correlates with the degree of proteinuria. Together, our data indicate that the development and progression of glomerulosclerosis involve loss of podocyte DAF, triggering local, complement-dependent, IL-1β–induced podocyte injury, potentially identifying new therapeutic targets.

Balzer M, Park J, Zhou T, Ma Z, Sullivan KM, Hu H, Sheng X, Liu H, Wei Y, Boustany-Kari CM, Patel U, Almaani S, Palmer M, Townsend R, Blady S, Hogan J, Morton L, Susztak K. Urinary Single-Cell Profiling Captures the Cellular Diversity of the Kidney

BACKGROUND

Microscopic analysis of urine sediment is probably the most commonly used diagnostic procedure in nephrology. The urinary cells, however, have not yet undergone careful unbiased characterization.

METHODS

Single-cell transcriptomic analysis was performed on 17 urine samples obtained from five subjects at two different occasions, using both spot and 24-hour urine collection. A pooled urine sample from multiple healthy individuals served as a reference control. In total 23,082 cells were analyzed. Urinary cells were compared with human kidney and human bladder datasets to understand similarities and differences among the observed cell types.

RESULTS

Almost all kidney cell types can be identified in urine, such as podocyte, proximal tubule, loop of Henle, and collecting duct, in addition to macrophages, lymphocytes, and bladder cells. The urinary cell-type composition was subject specific and reasonably stable using different collection methods and over time. Urinary cells clustered with kidney and bladder cells, such as urinary podocytes with kidney podocytes, and principal cells of the kidney and urine, indicating their similarities in gene expression.

CONCLUSIONS

A reference dataset for cells in human urine was generated. Single-cell transcriptomics enables detection and quantification of almost all types of cells in the kidney and urinary tract.

Regeneration and tissue engineering: How pediatric surgeons contributed to building a new field to change the future of medicine

The authors highlight the speciality field of regenerative medicine and its application to health care. Academic pediatric surgeons have been the early pioneers here sharing exciting discovery and the opportunities for research enterprise. An overview of current and future therapeutics is provided for the reader.

Unravelling Heterogeneity of Amplified Human Amniotic Fluid Stem Cells Sub-Populations

Human amniotic fluid stem cells (hAFSCs) are broadly multipotent immature progenitor cells with high self-renewal and no tumorigenic properties. These cells, even amplified, present very variable morphology, density, intracellular composition and stemness potential, and this heterogeneity can hinder their characterization and potential use in regenerative medicine. Celector^® (Stem Sel ltd.) is a new technology that exploits the Non-Equilibrium Earth Gravity Assisted Field Flow Fractionation principles to characterize and label-free sort stem cells based on their solely physical characteristics without any manipulation. Viable cells are collected and used for further studies or direct applications. In order to understand the intrapopulation heterogeneity, various fractions of hAFSCs were isolated using the Celector^® profile and live imaging feature. The gene expression profile of each fraction was analysed using whole-transcriptome sequencing (RNAseq). Gene Set Enrichment Analysis identified significant differential expression in pathways related to Stemness, DNA repair, E2F targets, G2M checkpoint, hypoxia, EM transition, mTORC1 signalling, Unfold Protein Response and p53 signalling. These differences were validated by RT-PCR, immunofluorescence and differentiation assays. Interestingly, the different fractions showed distinct and unique stemness properties. These results suggest the existence of deep intra-population differences that can influence the stemness profile of hAFSCs. This study represents a proof-of-concept of the importance of selecting certain cellular fractions with the highest potential to use in regenerative medicine.

Enhanced efficiency in isolation and expansion of hAMSCs via dual enzyme digestion and micro-carrier

A two-stage method of obtaining viable human amniotic stem cells (hAMSCs) in large-scale is described. First, human amniotic stem cells are isolated via dual enzyme (collagenase II and DNAase I) digestion. Next, relying on a culture of the cells from porous chitosan-based microspheres in vitro, high purity hAMSCs are obtained in large-scale. Dual enzymatic (collagenase II and DNase I) digestion provides a primary cell culture and first subculture with a lower contamination rate, higher purity and a larger number of isolated cells. The obtained hAMSCs were seeded onto chitosan microspheres (CM), gelatin-chitosan microspheres (GCM) and collagen-chitosan microspheres (CCM) to produce large numbers of hAMSCs for clinical trials. Growth activity measurement and differentiation essays of hAMSCs were realized. Within 2 weeks of culturing, GCMs achieved over 1.28 ± 0.06 × 107 hAMSCs whereas CCMs and CMs achieved 7.86 ± 0.11 × 106 and 1.98 ± 0.86 × 106 respectively within this time. In conclusion, hAMSCs showed excellent attachment and viability on GCM-chitosan microspheres, matching the hAMSCs' normal culture medium. Therefore, dual enzyme (collagenase II and DNAase I) digestion may be a more useful isolation process and culture of hAMSCs on porous GCM in vitro as an ideal environment for the large-scale expansion of highly functional hAMSCs for eventual use in stem cell-based therapy.

Molecular characterization of bovine amniotic fluid derived stem cells with an underlying focus on their comparative neuronal potential at different passages

BACKGROUND

The excellence in the field of stem cell therapy demands alternative and more convenient stem cells for potential applications. Researchers have opted for least invasive and broadly multipotent cells with minimum ethical concerns. Bovine amniotic fluid derived mesenchymal stem cells (BAF-MSCs) due to their ease of collection and owing similar gestational length to that of human could be presumed as an attractive large animal model for biomedical and biotechnology research.

METHODS

Bovine amniotic fluid derived stem cells were isolated from abattoir based samples and characterized for epithelial, neuronal, mesenchymal and pluripotent markers by qPCR and immunofluorescence studies at P1, P3, P5 and P7 alongside population doubling time, growth curve and multilineage differentiation studies.

RESULTS

The cells were explored for unique expression of Sox2, which was observed to be up regulated with increase in passage number and Nestin was found to be downregulated during further passaging of mesenchymal cells in this study. The cells also co-expressed Oct ¾ at initial passages which diminished within further passages. Evidence regarding diversity and heterogeneity in different cell population in amniotic fluid was recorded by positive expression of epithelial cell markers like pan Cytokeratin and p63 during early passages. The study suggested that cells with higher expression of Sox2 generated comparatively larger neurospheres with comparative strong expression of Sox2 and Nestin by immunofluorescence staining and qPCR analysis. Besides BAF-MSCs derived neurospheres were also shown to express pro-neuronal markers like ß-III Tubulin, GAP43 and ASCL-1.

CONCLUSIONS

This study explores and characterizes BAF-MSCs for their multipotent and neurogenic potentials and their use for clinical applications, though more detailed studies are needed to determine the exact pathways linked with neurogenic capacities of these cells and their morphological assessments at different gestational ages in bovines. The knowledge from the bovine model after detailed studies, proven safety and efficacy could also be used to understand substitutive strategies to investigate MSCs physiology at different trimesters and potential application of these cells for human and veterinary regenerative medicine provided the animal ethics are carefully monitored.

Bioengineering of Fetal Skin: Differentiation of Amniotic Fluid Stem Cells into Keratinocytes

PURPOSE

Open fetal spina bifida repair has become a novel clinical standard of care. In very large spina bifida lesions, the skin defect cannot be covered primarily, asking for alternative solutions. We hypothesize that amniotic fluid stem cells (AFSC) could be differentiated into keratinocytes that could then be used to bioengineer autologous skin usable for in utero back coverage.

METHODS

To obtain human AFSC, amniotic fluid samples obtained from fetal surgeries were subjected to immunoselection for c-kit. C-kit-positive samples and controls were cultured with the additives morphogenetic protein 4 and vitamin C to induce differentiation towards keratinocytes. This process was monitored by measuring the expression of K8 and K14 via immunohistochemical staining, flow cytometry, and polymerase chain reaction.

RESULTS

After immunoselection and expansion, most cells were positive for K8, but none for K14. After completion of the differentiation protocol, cell colonies with keratinocyte-like appearance could be observed, but cells remained positive for K8 and negative for K14, indicating failed differentiation into keratinocytes.

CONCLUSIONS

Culturing of keratinocyte-like cells from AFSC, harvested intraoperatively, was not feasible in this setting. The reasons for failure must be investigated and eliminated, as bioengineering of fetal skin for clinical use during fetal surgery for spina bifida remains an attractive goal.

Identification of amniotic fluid metabolomic and placental transcriptomic changes associated with abnormal development of cloned pig fetuses

Piglets cloned by somatic cell nuclear transfer (SCNT) show a high incidence of malformations and a high death rate during the perinatal period. To investigate the underlying mechanisms for abnormal development of cloned pig fetuses, we compared body weight, amniotic fluid (AF) metabolome, and placental transcriptome between SCNT- and artificial insemination (AI)-derived pig fetuses. Results showed that the body weight of SCNT pig fetuses was significantly lower than that of AI pig fetuses. The identified differential metabolites between the two groups of AF were mainly involved in bile acids and steroid hormones. The levels of all detected bile acids in SCNT AF were significantly higher than those in AI AF. The increase in the AF bile acid levels in SCNT fetuses was linked with the downregulation of placental bile acid transporter expression and the abnormal development of placental folds (PFs), both of which negatively affected the transfer of bile acids from AF across the placenta into the mother's circulation. Alteration in the AF steroid hormone levels in cloned fetuses was associated with decreased expression of enzymes responsible for steroid hormone biosynthesis in the placenta. In conclusion, cloned pig fetuses undergo abnormal intrauterine development associated with alteration of bile acid and steroid hormone levels in AF, which may be due to the poor development of PFs and the erroneous expression of bile acid transporters and enzymes responsible for steroid hormone biosynthesis in the placentas.

Renogenic characterization and in vitro differentiation of rat amniotic fluid stem cells into renal proximal tubular- and juxtaglomerular-like cells

The aim of the present study was to investigate the renogenic characteristics of amniotic fluid stem cells (AFSCs) and to evaluate their in vitro differentiation potential into renal proximal tubular-like cells and juxtaglomerular-like cells. We culture expanded AFSCs derived from rat amniotic fluid. The AFSCs grew as adherent spindle-shaped cells and expressed mesenchymal markers CD73, CD90, and CD105 as well as renal progenitor markers WT1, PAX2, SIX2, SALL1, and CITED1. AFSCs exhibited an in vitro differentiation potential into renal proximal tubular epithelial-like cells, as shown by the upregulation of expression of proximal tubular cell-specific genes like AQP1, CD13, PEPT1, GLUT5, OAT1, and OCT1. AFSCs could also be differentiated into juxtaglomerular-like cells as demonstrated by the expression of renin and α-SMA. The AFSCs also expressed pluripotency markers OCT4, NANOG, and SOX2 and could be induced into embryoid bodies with differentiation into all the three germ layers, highlighting the pluripotent nature of these cells. Our results show that amniotic fluid contains a population of primitive stem cells that express renal-progenitor markers and also possess the propensity to differentiate into two renal lineage cell types and, thus, may have a therapeutic potential in renal regenerative medicine.

Advances in perinatal stem cells research: a precious cell source for clinical applications

Perinatal tissues possess numerous types of stem (stromal) cells, which are considered effective candidates for cell therapy. These tissues possess common characteristics of both embryonic and adult stem cells, and cell therapists have begun to use perinatal stem cells to treat several diseases. Despite their benefits, these cells are considered biological waste and usually discarded after delivery. This review highlights the characteristics and potential clinical applications in regenerative medicine of perinatal stem cell sources - cord blood hematopoietic stem cells, umbilical cord mesenchymal stem cells, amniotic membrane stem cells, amniotic fluid stem cells, amniotic epithelial cells and chorionic mesenchymal stem cells.

Amniotic fluid cells: current progress and emerging challenges in renal regeneration

Amniotic fluid (AF) contains a heterogeneous population of cells that have been identified to possess pluripotent and progenitor-like characteristics. These cells have been applied in various regenerative medicine applications ranging from in vitro cell differentiation to tissue engineering to cellular therapies for different organs including the heart, the liver, the lung, and the kidneys. In this review, we examine the different methodologies used for the derivation of amniotic fluid stem cells and renal progenitors, and their application in renal repair and regeneration. Moreover, we discuss the recent achievements and newly emerging challenges in our understanding of their biology, their immunoregulatory characteristics, and their paracrine-mediated therapeutic potential for the treatment of acute and chronic kidney diseases.

Human Adipose-Derived and Amniotic Fluid-Derived Stem Cells: A Preliminary In Vitro Study Comparing Myogenic Differentiation Capability

Background

Around the world, disabilities due to musculoskeletal disorders have increased and are a major health problem worldwide. In recent years, stem cells have been considered to be powerful tools for musculoskeletal tissue engineering. Human adipose-derived stem cells (hADSCs) and amniotic fluid-derived stem cells (hAFSCs) undergo typical differentiation process into cells of mesodermal origin and can be used to treat muscular system diseases. The aim of the present study was to compare the biological characteristic of stem cells isolated from different human tissues (adipose tissue and amniotic fluid) with respect to myogenic capacity and skeletal and smooth muscle differentiation under the same conditions.

Material/Methods

hAFSCs and hADSCs were isolated during standard medical procedures and widely characterized by specific markers expression and differentiation potential. Both cell types were induced toward smooth and striated muscles differentiation, which was assessed with the use of molecular techniques.

Results

For phenotypic characterization, both stem cell types were assessed for the expression of OCT-4, SOX2, CD34, CD44, CD45, and CD90. Muscle-specific markers appeared in both stem cell types, but the proportion of positive cells showed differences depending on the experimental conditions used and the source from which the stem cells were isolated.

Conclusions

In this study, we demonstrated that hADSCs and hAFSCs have different capability of differentiation toward both muscle types. However, hADSCs seem to be a better source for myogenic protocols and can promote skeletal and smooth muscle regeneration through either direct muscle differentiation or by paracrine mechanism.

Biological characterization and pluripotent identification of ovine amniotic fluid stem cells

Mesenchymal stem cells derived from amniotic fluid have become one of the most potential stem cell source for cell-based therapy for the reason they can be harvested at low cost and without ethical problems. Here, we obtained amniotic fluid stem cells (AFSCs) from ovine amniotic fluid and studied the expansion capacity, cell markers expression, karyotype, and multilineage differentiation ability. In our work, AFSCs were subcultured to passage 62. The cell markers, CD29, CD44, CD73 and OCT4 which analyzed by RT-PCR were positive; CD44, CD73, CD90, CD105, NANOG, OCT4 analyzed by immunofluorescence and flow cytometry were also positive. The growth curves of different passages were all typically sigmoidal. The different passages cells took on a normal karyotype. In addition, AFSCs were successfully induced to differentiate into adipocytes, osteoblasts and chondrocytes. The results suggested that the AFSCs isolated from ovine maintained normal biological characteristics and their multilineage differentiation potential provides many potential applications in cell-based therapies and tissue engineering.

Urine-derived podocytes-lineage cells: A promising tool for precision medicine in Alport Syndrome

Alport Syndrome (ATS) is a rare genetic disorder caused by collagen IV genes mutations, leading to glomerular basement membrane damage up to end-stage renal disease. Podocytes, the main component of the glomerular structure, are the only cells able to produce all the three collagens IV alpha chains associated with ATS and thus, they are key players in ATS pathogenesis. However, podocytes-targeted therapeutic strategies have been hampered by the difficulty of non-invasively isolating them and transcripts-based diagnostic approaches are complicated by the inaccessibility of other COL4 chains-expressing cells. We firstly isolated podocyte-lineage cells from ATS patients' urine samples, in a non-invasive way. RT-PCR analysis revealed COL4A3, COL4A4, and COL4A5 expression. Transcripts analysis on RNA extracted from patient's urine derived podocyte-lineage cells allowed defining the pathogenic role of intronic variants, namely one mutation in COL4A3 (c.3882+5G>A), three mutations in COL4A4 (c.1623+2T>A, c.3699_3706+1del, c.2545+143T>A), and one mutation in COL4A5 (c.3454+2T>C). Therefore, our cellular model represents a novel tool, essential to unequivocally prove the effect of spliceogenic intronic variants on transcripts expressed exclusively at a glomerular level. This process is a key step for providing the patient with a definite molecular diagnosis and with a proper recurrence risk. The established system also opens up the possibility of testing personalized therapeutic approaches on disease-relevant cells.

The amniotic fluid as a source of mesenchymal stem cells with lung-specific characteristics

The amniotic fluid is a clinically accessible source of mesenchymal stem cells (AF-MSC) during gestation, which enables autologous cellular therapy for perinatal disorders. The origin of AF-MSC remains elusive: renal and neuronal progenitors have been isolated from the AF-MSC pool, yet no cells with pulmonary characteristics. We analyzed gene expression of pulmonary and renal markers of 212 clonal lines of AF-MSC isolated from amniocentesis samples. AF-MSC were cultured on dishes coated with extracellular matrix (ECM) proteins from decellularized fetal rabbit lungs. In vivo differentiation potential of AF-MSC that expressed markers suggestive of lung fate was tested by renal subcapsular injections in immunodeficient mice. Of all the isolated AF-MSC lines, 26% were positive for lung endodermal markers FOXA2 and NKX2.1 and lacked expression of renal markers (KSP). This AF-MSC subpopulation expressed other lung-specific factors, including IRX1, P63, FOXP2, LGR6, SFTC, and PDPN. Pulmonary marker expression decreased over passages when AF-MSC were cultured under conventional conditions, yet remained more stable when culturing the cells on lung ECM-coated dishes. Renal subcapsular injection of AF-MSC expressing lung-specific markers resulted in engrafted cells that were SPTB positive. These data suggest that FOXA2+/NKX2.1+/KSP- AF-MSC lines have lung characteristics which are supported by culture on lung ECM-coated dishes.

Application of the amniotic fluid metabolome to the study of fetal malformations, using Down syndrome as a specific model

Although monitoring and diagnosis of fetal diseases in utero remains a challenge, metabolomics may provide an additional tool to study the etiology and pathophysiology of fetal diseases at a functional level. In order to explore specific markers of fetal disease, metabolites were analyzed in two separate sets of experiments using amniotic fluid from fetuses with Down syndrome (DS) as a model. Both sets included 10–15 pairs of controls and cases, and amniotic fluid samples were processed separately; metabolomic fingerprinting was then conducted using UPLC-MS. Significantly altered metabolites involved in respective metabolic pathways were compared in the two experimental sets. In addition, significantly altered metabolic pathways were further compared with the genomic characters of the DS fetuses. The data suggested that metabolic profiles varied across different experiments, however alterations in the 4 metabolic pathways of the porphyrin metabolism, bile acid metabolism, hormone metabolism and amino acid metabolism, were validated for the two experimental sets. Significant changes in metabolites of coproporphyrin III, glycocholic acid, taurochenodeoxycholate, taurocholate, hydrocortisone, pregnenolone sulfate, L-histidine, L-arginine, L-glutamate and L-glutamine were further confirmed. Analysis of these metabolic alterations was linked to aberrant gene expression at chromosome 21 of the DS fetus. The decrease in coproporphyrin III in the DS fetus may portend abnormal erythropoiesis, and unbalanced glutamine-glutamate concentration was observed to be closely associated with abnormal brain development in the DS fetus. Therefore, alterations in amniotic fluid metabolites may provide important clues to understanding the etiology of fetal disease and help to develop diagnostic testing for clinical applications.

Amniotic fluid as a source of engraftable stem cells

The ability of stem cells to differentiate into various lineages has made them powerful tools of regenerative medicine and applicable to multiple human diseases. Of particular interest, amniotic fluid-derived stem cells (AFSC) have been characterized to express both adult and embryonic cell markers, indicating them as cells within an intermediate stage between embryonic and adult phenotype. AFSC can differentiate into cells of all three germ layers, including hepatic, myogenic, osteogenic, and neurogenic cell types. Furthermore, AFSC have minimal replicative senescence, retaining the ability to divide effectively for over 250 doublings. These facts indicate that amniotic fluid may exist as a promising donor source of stem cells for the treatment of multiple clinically relevant conditions. Of particular interest is the convenience of harvesting stem cells from the amniotic fluid stem for the treatment of newborns, as well as for banking or cryopreserving purposes to be used at a later date. Importantly, the promise of amniotic fluid as a source of stem cells merits ongoing research into their potential therapeutic applications. This paper is a review article. Referred literature in this paper has been listed in the references section. The datasets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors' experiences.

Highly potent stem cells from full-term amniotic fluid: A realistic perspective

Amniotic fluid (AF) is now known to harbor highly potent stem cells, making it an excellent source for cell therapy. However, most of the stem cells isolated are from AF of mid-term pregnancies in which the collection procedure involves an invasive technique termed amniocentesis. This has limited the access in getting the fluid as the technique imposes certain level of risks to the mother as well as to the fetus. Alternatively, getting AF from full-term pregnancies or during deliveries would be a better resolution. Unfortunately, very few studies have isolated stem cells from AF at this stage of gestation, the fluid that is merely discarded. The question remains whether full-term AF harbors stem cells of similar potency as of the stem cells of mid-term AF. Here, we aim to review the prospect of having this type of stem cells by first looking at the origin and contents of AF particularly during different gestation period. We will then discuss the possibility that the AF, at full term, contains a population of highly potent stem cells. These stem cells are distinct from, and probably more potent than the AF mesenchymal stem cells (AF-MSCs) isolated from full-term AF. By comparing the studies on stem cells isolated from mid-term versus full-term AF from various species, we intend to address the prospect of having highly potent amniotic fluid stem cells from AF of full-term pregnancies in human and animals.

Direct Isolation and Characterization of Human Nephron Progenitors

Mature nephrons originate from a small population of uninduced nephrogenic progenitor cells (NPs) within the cap mesenchyme. These cells are characterized by the coexpression of SIX2 and CITED1. Many studies on mouse models as well as on human pluripotent stem cells have advanced our knowledge of NPs, but very little is known about this population in humans, since it is exhausted before birth and strategies for its direct isolation are still limited. Here we report an efficient protocol for direct isolation of human NPs without genetic manipulation or stepwise induction procedures. With the use of RNA‐labeling probes, we isolated SIX2⁺CITED1⁺ cells from human fetal kidney for the first time. We confirmed their nephrogenic state by gene profiling and evaluated their nephrogenic capabilities in giving rise to mature renal cells. We also evaluated the ability to culture these cells without complete loss of SIX2 and CITED1 expression over time. In addition to defining the gene profile of human NPs, this in vitro system facilitates studies of human renal development and provides a novel tool for renal regeneration and bioengineering purposes. Stem Cells Translational Medicine2017;6:419–433

Decellularized Renal Matrix and Regenerative Medicine of the Kidney: A Different Point of View

Over the past years, extracellular matrix (ECM) obtained from whole organ decellularization has been investigated as a platform for organ engineering. The ECM is composed of fibrous and nonfibrous molecules providing structural and biochemical support to the surrounding cells. Multiple decellularization techniques, including ours, have been optimized to maintain the composition, microstructure, and biomechanical properties of the native renal ECM that are difficult to obtain during the generation of synthetic substrates. There are evidences suggesting that in vivo implanted renal ECM has the capacity to induce formation of vasculature-like structures, but long-term in vivo transplantation and filtration activity by these tissue-engineered constructs have not been investigated or reported. Therefore, even if the process of renal decellularization is possible, the repopulation of the renal matrix with functional renal cell types is still very challenging. This review aims to summarize the current reports on kidney tissue engineering with the use of decellularized matrices and addresses the challenges in creating functional kidney units. Finally, this review discusses how future studies investigating cell-matrix interaction may aid the generation of a functional renal unit that would be transplantable into patients one day.

Amniotic Fluid Derived Stem Cells with a Renal Progenitor Phenotype Inhibit Interstitial Fibrosis in Renal Ischemia and Reperfusion Injury in Rats

Objectives

Mesenchymal stem cells derived from human amniotic fluid (hAFSCs) are a promising source for cellular therapy, especially for renal disorders, as a subpopulation is derived from the fetal urinary tract. The purpose of this study was to evaluate if hAFSCs with a renal progenitor phenotype demonstrate a nephroprotective effect in acute ischemia reperfusion (I/R) model and prevent late stage fibrosis.

Methods

A total of 45 male 12-wk-old Wistar rats were divided into three equal groups;: rats subjected to I/R injury and treated with Chang Medium, rats subjected to I/R injury and treated with hAFSCs and sham-operated animals. In the first part of this study, hAFSCs that highly expressed CD24, CD117, SIX2 and PAX2 were isolated and characterized. In the second part, renal I/R injury was induced in male rats and cellular treatment was performed 6 hours later via arterial injection. Functional and histological analyses were performed 24 hours, 48 hours and 2 months after treatment using serum creatinine, urine protein to creatinine ratio, inflammatory and regeneration markers and histomorphometric analysis of the kidney. Statistical analysis was performed by analysis of variance followed by the Tukey’s test for multiple comparisons or by nonparametric Kruskal-Wallis followed by Dunn. Statistical significance level was defined as p <0.05.

Results

hAFSCs treatment resulted in significantly reduced serum creatinine level at 24 hours, less tubular necrosis, less hyaline cast formation, higher proliferation index, less inflammatory cell infiltration and less myofibroblasts at 48h. The treated group had less fibrosis and proteinuria at 2 months after injury.

Conclusion

hAFSCs contain a renal progenitor cell subpopulation that has a nephroprotective effect when delivered intra-arterially in rats with renal I/R injury, and reduces interstitial fibrosis on long term follow-up.

Therapeutic use of human renal progenitor cells for kidney regeneration

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

Rat full term amniotic fluid harbors highly potent stem cells

Amniotic fluid stem cells (AFSCs) are commonly isolated from mid-term amniotic fluid (AF) of animals and human collected via an invasive technique, amniocentesis. Alternatively, AFSCs could be collected at full-term. However, it is unclear whether AFSCs are present in the AF at full term. Here, we aimed to isolate and characterize stem cells isolated from AF of full term pregnant rats. Three stem cell lines have been established following immuno-selection against the stem cell marker, c-kit. Two of the new lines expressed multiple markers of pluripotency until more than passage 90. Further, they spontaneously differentiated into derivatives of the three primary germ layers through the formation of good quality embryoid bodies (EBs), and can be directly differentiated into neural lineage. Their strong stemness and potent neurogenic properties highlight the presence of highly potent stem cells in AF of full-term pregnancies, which could serve as a potential source of stem cells for regenerative medicine.

Isolation and in vitro characterization of bovine amniotic fluid derived stem cells at different trimesters of pregnancy

Amniotic fluid (AF) is a source of multipotent mesenchymal stem cells (MSCs), very promising cells for tissue engineering in clinical application. The aim of this work was to isolate and characterize cells isolated from bovine AF as alternative sources of primitive multipotent stem cells in a species that could be a large-animal model for biomedical and biotechnology researches. Samples were recovered, at slaughterhouse, from 39 pregnant cows at different trimesters of pregnancy and cells were cultured in vitro. At passages (P) 3 and 7 differentiation towards chondrogenic, osteogenic and adipogenic lineages was induced. Flow cytometry analysis for CD90, CD105, CD73, CD44, CD34, CD45 and CD14 was performed, immunocytochemistry (ICC) for Oct4, SSEA4, α-SMA, Vimentin, N- and E- Cadherin and CK and qPCR analysis for OCT4, NANOG and SOX2 were carried out. The cell yield was significantly higher in the first trimester compared to the second and the third one (P < 0.05). Cells were isolated from 25/39 samples and cell population appeared heterogeneous. Two main cell types were identified in samples from all trimesters: round- (RS) and spindle-shaped (SS) cells. 17/25 samples showed both populations (mixed, MX). Both cell types showed MSC-markers and differentiation capability with some variability related to the passages. The SS-population also expressed low levels of stemness markers such as NANOG and SSEA4 but not OCT4. Bovine AF shows a heterogeneous cell population containing also MSCs, multipotent cells that represent an intermediate stage between embryonic stem cells and adult ones.

Intramuscular Transplantation of Pig Amniotic Fluid-Derived Progenitor Cells Has Therapeutic Potential in a Mouse Model of Myocardial Infarction

Acute myocardial infarction (MI) is a fatal event that causes a large number of deaths worldwide. MI results in pathological remodeling and decreased cardiac function, which could lead to heart failure and fatal arrhythmia. Cell therapy is a potential strategy to repair the damage through enhanced angiogenesis or by modulation of the inflammatory process via paracrine signaling. Amniotic fluid-derived progenitor cells (AFPCs) have been reported to differentiate into several lineages and can be used without ethical concerns or risk of teratoma formation. Since pigs are anatomically, physiologically, and genetically similar to humans, and pregnant pigs can be an abundant source of AFPCs, we used porcine AFPCs (pAFPCs) as our target cells. Intramyocardial injection of AFPCs has been shown to cure MI in animal models. However, intramuscular transplantation of cells has not been extensively investigated. In this study, we investigated the therapeutic potential of intramuscular injection of pAFPCs on acute MI. MI mice were divided into 1) PBS control, 2) medium cell dose (1 × 106 cells per leg; cell-M), and 3) high cell dose (4 × 106 cells per leg; cell-H) groups. Cells or PBS were directly injected into the hamstring muscle 20 min after MI surgery. Four weeks after MI surgery, the cell-M and cell-H groups exhibited significantly better ejection fraction, significantly greater wall thickness, smaller infarct scar sizes, and lower LV expansion index compared to the PBS group. Using in vivo imaging, we showed that the hamstring muscles from animals in the cell-M and cell-H groups had RFP-positive signals. In summary, intramuscular injection of porcine AFPCs reduced scar size, reduced pathological remodeling, and preserved heart function after MI.

Human Urine as a Noninvasive Source of Kidney Cells

Urine represents an unlimited source of patient-specific kidney cells that can be harvested noninvasively. Urine derived podocytes and proximal tubule cells have been used to study disease mechanisms and to screen for novel drug therapies in a variety of human kidney disorders. The urinary kidney stem/progenitor cells and extracellular vesicles, instead, might be promising for therapeutic treatments of kidney injury. The greatest advantages of urine as a source of viable cells are the easy collection and less complicated ethical issues. However, extensive characterization and in vivo studies still have to be performed before the clinical use of urine-derived kidney progenitors.

Second and third trimester amniotic fluid mesenchymal stem cells can repopulate a de-cellularized lung scaffold and express lung markers

BACKGROUND/PURPOSE

This study examined the potential of amniotic fluid mesenchymal stem cells (AF-MSCs) to generate lung precursor cells in vitro and on a xenologous three-dimensional de-cellularized lung scaffold.

METHODS

AF-MSCs were isolated from human amniotic fluid obtained from 17-37 weeks gestation. Lung differentiation was induced on Matrigel or on de-cellularized rat lungs intra-tracheally injected with AF-MSCs by culturing with a modification of small airway growth medium (mSAGM) lacking retinoic acid (RA) and triodothyronine (T3) with addition of fibroblast growth factor-10 (FGF10). Cells and scaffolds were characterized by immunofluorescence and RT-PCR for markers of viability, proliferation, and lung distal airway differentiation (TTF-1(+) and SPC(+)) in the absence of markers of brain (TuJ1(-)) and thyroid (Pax8(-)).

RESULTS

After culture in mSAGM on either Matrigel or lung scaffolds, there were TTF-1(+)/TuJ1(-)/Pax8(-) cells, indicating a lung precursor phenotype. In addition, SPC(+) cells also evolved suggesting a more mature lung phenotype.

CONCLUSIONS

We demonstrate that mid- to late-trimester AF-MSCs can be induced to develop into lung precursor cells when cultured on the appropriate extracellular matrix (ECM), making them a viable source for use in cell therapy or development of an ex vivo tissue engineered lung.

Stem cells, cell therapies, and bioengineering in lung biology and diseases. Comprehensive review of the recent literature 2010-2012

A conference, "Stem Cells and Cell Therapies in Lung Biology and Lung Diseases," was held July 25 to 28, 2011 at the University of Vermont to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy and ex vivo bioengineering approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, to discuss and debate current controversies, and to identify future research directions and opportunities for basic and translational research in cell-based therapies for lung diseases. The goal of this article, which accompanies the formal conference report, is to provide a comprehensive review of the published literature in lung regenerative medicine from the last conference report through December 2012.

Engraftment of mouse amniotic fluid-derived progenitor cells after in utero transplantation in mice

BACKGROUND/PURPOSE

Amniotic fluid-derived progenitor cells (AFPCs) are oligopotent and shed from the fetus into the amniotic fluid. It was reported that AFPCs express stem cell-like markers and are capable of differentiating into specific cell type in in vitro experiments. However, no study has fully investigated the potentiality and destiny of these cells in in vivo experiments.

METHODS

Ds-red transgenic mice (on Day 13.5 of pregnancy) were transplanted in utero with enhanced green fluorescent protein-labeled mouse AFPC (EGFP-mAFPCs). After birth, baby mice were euthanized at 3-week intervals beginning 3 weeks postnatally, and the specimens were examined by polymerase chain reaction, histology, and flow cytometry.

RESULTS

Our results demonstrate the transplantability of mAFPCs into all three germ layers and the potential of mAFPCs in the study of progenitor cell homing, differentiation, and function. Engraftment of EGFP-mAFPCs was detected in the intestine, kidney, muscle, skin, bladder, heart, stomach, etc., at 3 weeks after delivery.

CONCLUSION

This model using EGFP-mAFPCs injected in utero may provide an ideal method for determining the fate of transplanted cells in recipients and these findings may justify a clinical trial of in utero transplantation during gestation for patients who have inherited genetic disorders.

Amniotic fluid-derived mesenchymal stem cells prevent fibrosis and preserve renal function in a preclinical porcine model of kidney transplantation

It is well known that ischemia/reperfusion injuries strongly affect the success of human organ transplantation. Development of interstitial fibrosis and tubular atrophy is the main deleterious phenomenon involved. Stem cells are a promising therapeutic tool already validated in various ischemic diseases. Amniotic fluid-derived mesenchymal stem cells (af-MSCs), a subpopulation of multipotent cells identified in amniotic fluid, are known to secrete growth factors and anti-inflammatory cytokines. In addition, these cells are easy to collect, present higher proliferation and self-renewal rates compared with other adult stem cells (ASCs), and are suitable for banking. Consequently, af-MSCs represent a promising source of stem cells for regenerative therapies in humans. To determine the efficiency and the safety of af-MSC infusion in a preclinical porcine model of renal autotransplantation, we injected autologous af-MSCs in the renal artery 6 days after transplantation. The af-MSC injection improved glomerular and tubular functions, leading to full renal function recovery and abrogated fibrosis development at 3 months. The strong proof of concept generated by this translational porcine model is a first step toward evaluation of af-MSC-based therapies in human kidney transplantation.

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.