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

Characteristics and Therapeutic Potential of Human Amnion-Derived Stem Cells

Stem cells including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs) and adult stem cells (ASCs) are able to repair/replace damaged or degenerative tissues and improve functional recovery in experimental model and clinical trials. However, there are still many limitations and unresolved problems regarding stem cell therapy in terms of ethical barriers, immune rejection, tumorigenicity, and cell sources. By reviewing recent literatures and our related works, human amnion-derived stem cells (hADSCs) including human amniotic mesenchymal stem cells (hAMSCs) and human amniotic epithelial stem cells (hAESCs) have shown considerable advantages over other stem cells. In this review, we first described the biological characteristics and advantages of hADSCs, especially for their high pluripotency and immunomodulatory effects. Then, we summarized the therapeutic applications and recent progresses of hADSCs in treating various diseases for preclinical research and clinical trials. In addition, the possible mechanisms and the challenges of hADSCs applications have been also discussed. Finally, we highlighted the properties of hADSCs as a promising source of stem cells for cell therapy and regenerative medicine and pointed out the perspectives for the directions of hADSCs applications clinically.

Amniotic fluid-derived stem cells mixed with platelet rich plasma for restoration of rat alveolar bone defect

Stem cells isolated from the amniotic fluid have been shown as a promising candidate for cell therapy and tissue engineering. However, the experimental and preclinical applications of amniotic fluid-derived stem cells (AFSCs) in the very field of maxillofacial bone tissue engineering are still limited. In this study, rat AFSCs were successfully harvested and characterized in vitro. The rat AFSCs showed typical fibroblastoid morphology, stable proliferation activity and multi-differentiation potential. Flow-cytometry analysis demonstrated that these cells were positive for CD29, CD44, and CD90, while negative for hematopoietic markers such as CD34 and CD45. The regenerative performance of AFSCs-premixed with platelet rich plasma (PRP) gel in restoration of alveolar bone defect was further investigated using a modified rat maxillary alveolar defect model. Micro-computer tomography and histological examination showed a superior regenerative capacity of AFSCs-premixed with PRP gel at both 4 and 8 weeks after operation comparing with control groups. Moreover, the implanted AFSCs can survive in the defect site and directly participate in the bone tissue regeneration. Taken together, these results indicated the feasibility of an AFSCs-based alveolar bone tissue engineering strategy for alveolar defect restoration.

Transplantation of rat embryonic stem cell-derived retinal progenitor cells preserves the retinal structure and function in rat retinal degeneration

INTRODUCTION

Degenerative retinal diseases like age-related macular degeneration (AMD) are the leading cause of blindness. Cell transplantation showed promising therapeutic effect for such diseases, and embryonic stem cell (ESC) is one of the sources of such donor cells. Here, we aimed to generate retinal progenitor cells (RPCs) from rat ESCs (rESCs) and to test their therapeutic effects in rat model.

METHODS

The rESCs (DA8-16) were cultured in N2B27 medium with 2i, and differentiated to two types of RPCs following the SFEBq method with modifications. For rESC-RPC1, the cells were switched to adherent culture at D10, while for rESC-RPC2, the suspension culture was maintained to D14. Both RPCs were harvested at D16. Primary RPCs were obtained from P1 SD rats, and some of them were labeled with EGFP by infection with lentivirus. To generate Rax::EGFP knock-in rESC lines, TALENs were engineered to facilitate homologous recombination in rESCs, which were cotransfected with the targeting vector and TALEN vectors. The differentiated cells were analyzed with live image, immunofluorescence staining, flow cytometric analysis, gene expression microarray, etc. RCS rats were used to mimic the degeneration of retina and test the therapeutic effects of subretinally transplanted donor cells. The structure and function of retina were examined.

RESULTS

We established two protocols through which two types of rESC-derived RPCs were obtained and both contained committed retina lineage cells and some neural progenitor cells (NPCs). These rESC-derived RPCs survived in the host retinas of RCS rats and protected the retinal structure and function in early stage following the transplantation. However, the glia enriched rESC-RPC1 obtained through early and longer adherent culture only increased the b-wave amplitude at 4 weeks, while the longer suspension culture gave rise to evidently neuronal differentiation in rESC-RPC2 which significantly improved the visual function of RCS rats.

CONCLUSIONS

We have successfully differentiated rESCs to glia enriched RPCs and retinal neuron enriched RPCs in vitro. The retinal neuron enriched rESC-RPC2 protected the structure and function of retina in rats with genetic retinal degeneration and could be a candidate cell source for treating some degenerative retinal diseases in human trials.

Comparative study between amniotic-fluid mesenchymal stem cells and retinal pigmented epithelium (RPE) stem cells ability to differentiate towards RPE cells

Dysfunction of the retinal pigmented epithelium (RPE) is one of the first effects of dry age-related macular degeneration (AMD) with consequent blindness. Hence, patients affected by this retinal disorder could benefit from a cell-based transplantation strategy for RPE. Actually, an effective protocol to approach this problem is lacking, though recently, it has been postulated the existence of a subpopulation of RPE stem cells (RPESCs) derived from adult RPE and able to reconstitute a functional RPE. On the other hand, the evidence related to the differentiative potential of human mesenchymal stem cells (MSCs) is continuously increasing. Among others, amniotic fluid-derived MSCs (AF-MSCs) may be a promising candidate, since these cells are characterized by high proliferation and differentiative potential. In this study, AF-MSCs and RPESCs were isolated, characterized to assay their stemness and induced to neuronal/retinal differentiation; specific RPE markers were then analyzed. Our results indicate that RPESCs are more suitable candidates for RPE replacement than AF-MSCs.

In situ vascularization of injectable fibrin/poly(ethylene glycol) hydrogels by human amniotic fluid-derived stem cells

One of the greatest challenges in regenerative medicine is generating clinically relevant engineered tissues with functional blood vessels. Vascularization is a key hurdle faced in designing tissue constructs larger than the in vivo limit of oxygen diffusion. In this study, we utilized fibrin-based hydrogels to serve as a foundation for vascular formation, poly(ethylene glycol) (PEG) to modify fibrinogen and increase scaffold longevity, and human amniotic fluid-derived stem cells (AFSC) as a source of vascular cell types (AFSC-EC). AFSC hold great potential for use in regenerative medicine strategies, especially those involving autologous congenital applications, and we have shown previously that AFSC-seeded fibrin-PEG hydrogels have the potential to form three-dimensional vascular-like networks in vitro. We hypothesized that subcutaneously injecting these hydrogels in immunodeficient mice would both induce a fibrin-driven angiogenic host response and promote in situ AFSC-derived neovascularization. Two weeks postinjection, hydrogels were sectioned, and the following was demonstrated: the average maximum invasion distance of host murine cells into the subcutaneous fibrin/PEG scaffold was 147 ± 90 µm after 1 week and 395 ± 138 µm after 2 weeks; the average number of cell-lined lumen per square millimeter was significantly higher in hydrogels seeded with stem cells or cocultures containing stem cells (MSC, 36.5 ± 11.4; AFSC, 47.0 ± 18.9; AFSC/AFSC-EC, 32.8 ± 11.6; and MSC/HUVEC, 43.1 ± 25.1) versus endothelial cell types alone (AFSC-EC, 9.7 ± 6.1; HUVEC, 14.2 ± 8.8); and a subset of these lumen were characterized by the presence of red blood cells. Select areas of cell-seeded hydrogels contained CD31(+) lumen surrounded by α-smooth muscle cell support cells, whereas control hydrogels with no cells only showed infiltration of α-smooth muscle cell-positive host cells.

Capillary-like network formation by human amniotic fluid-derived stem cells within fibrin/poly(ethylene glycol) hydrogels

A major limitation in tissue engineering strategies for congenital birth defects is the inability to provide a significant source of oxygen, nutrient, and waste transport in an avascular scaffold. Successful vascularization requires a reliable method to generate vascular cells and a scaffold capable of supporting vessel formation. The broad potential for differentiation, high proliferation rates, and autologous availability for neonatal surgeries make amniotic fluid-derived stem cells (AFSC) well suited for regenerative medicine strategies. AFSC-derived endothelial cells (AFSC-EC) express key proteins and functional phenotypes associated with endothelial cells. Fibrin-based hydrogels were shown to stimulate AFSC-derived network formation in vitro but were limited by rapid degradation. Incorporation of poly(ethylene glycol) (PEG) provided mechanical stability (65%±9% weight retention vs. 0% for fibrin-only at day 14) while retaining key benefits of fibrin-based scaffolds-quick formation (10±3 s), biocompatibility (88%±5% viability), and vasculogenic stimulation. To determine the feasibility of AFSC-derived microvasculature, we compared AFSC-EC as a vascular cell source and AFSC as a perivascular cell source to established sources of these cell types-human umbilical vein endothelial cells (HUVEC) and mesenchymal stem cells (MSC), respectively. Cocultures were seeded at a 4:1 endothelial-to-perivascular cell ratio, and gels were incubated at 37°C for 2 weeks. Mechanical testing was performed using a stress-controlled rheometer (G'=95±10 Pa), and cell-seeded hydrogels were assessed based on morphology. Network formation was analyzed based on key parameters such as vessel thickness, length, and area, as well as the degree of branching. There was no statistical difference between individual cultures of AFSC-EC and HUVEC in regard to these parameters, suggesting the vasculogenic potential of AFSC-EC; however, the development of robust vessels required the presence of both an endothelial and a perivascular cell source and was seen in AFSC cocultures (70%±20% vessel length, 90%±10% vessel area, and 105%±10% vessel thickness compared to HUVEC/MSC). At a fixed seeding density, the coculture of AFSC with AFSC-EC resulted in a synergistic effect on network parameters similar to MSC (150% vessel length, 147% vessel area, 150% vessel thickness, and 155% branching). These results suggest that AFSC-EC and AFSC have significant vasculogenic and perivasculogenic potential, respectively, and are suited for in vivo evaluation.

Perinatal stem cells: A promising cell resource for tissue engineering of craniofacial bone

In facing the mounting clinical challenge and suboptimal techniques of craniofacial bone defects resulting from various conditions, such as congenital malformations, osteomyelitis, trauma and tumor resection, the ongoing research of regenerative medicine using stem cells and concurrent advancement in biotechnology have shifted the focus from surgical reconstruction to a novel stem cell-based tissue engineering strategy for customized and functional craniofacial bone regeneration. Given the unique ontogenetical and cell biological properties of perinatal stem cells, emerging evidence has suggested these extraembryonic tissue-derived stem cells to be a promising cell source for extensive use in regenerative medicine and tissue engineering. In this review, we summarize the current achievements and obstacles in stem cell-based craniofacial bone regeneration and subsequently we address the characteristics of various types of perinatal stem cells and their novel application in tissue engineering of craniofacial bone. We propose the promising feasibility and scope of perinatal stem cell-based craniofacial bone tissue engineering for future clinical application.

Derivation of traceable and transplantable photoreceptors from mouse embryonic stem cells

Retinal degenerative diseases resulting in the loss of photoreceptors are one of the major causes of blindness. Photoreceptor replacement therapy is a promising treatment because the transplantation of retina-derived photoreceptors can be applied now to different murine retinopathies to restore visual function. To have an unlimited source of photoreceptors, we derived a transgenic embryonic stem cell (ESC) line in which the Crx-GFP transgene is expressed in photoreceptors and assessed the capacity of a 3D culture protocol to produce integration-competent photoreceptors. This culture system allows the production of a large number of photoreceptors recapitulating the in vivo development. After transplantation, integrated cells showed the typical morphology of mature rods bearing external segments and ribbon synapses. We conclude that a 3D protocol coupled with ESCs provides a safe and renewable source of photoreceptors displaying a development and transplantation competence comparable to photoreceptors from age-matched retinas.

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De novo isolation of Crx-GFP embryonic stem cell lines to trace photoreceptors

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3D culture system fine-tuning to generate many integration-competent photoreceptors

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Revealing in-vitro- and in-vivo-developing retina similarities

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Characterization of the most appropriate stage to transplant photoreceptors

Regenerative medicine for congenital malformations

This is a review of the progress in regenerative medicine and concepts behind the field of tissue engineering and cell transplantation as it applies to congenital malformations. It is based on the Journal of Pediatric Surgery invited lecture to the BAPS/EUPSA Congress in Rome, Italy, June 2012.

Genome-wide analysis reveals the unique stem cell identity of human amniocytes

Human amniotic fluid contains cells that potentially have important stem cell characteristics, yet the programs controlling their developmental potency are unclear. Here, we provide evidence that amniocytes derived from multiple patients are marked by heterogeneity and variability in expression levels of pluripotency markers. Clonal analysis from multiple patients indicates that amniocytes have large pools of self-renewing cells that have an inherent property to give rise to a distinct amniocyte phenotype with a heterogeneity of pluripotent markers. Significant to their therapeutic potential, genome-wide profiles are distinct at different gestational ages and times in culture, but do not differ between genders. Based on hierarchical clustering and differential expression analyses of the entire transcriptome, amniocytes express canonical regulators associated with pluripotency and stem cell repression. Their profiles are distinct from human embryonic stem cells (ESCs), induced-pluripotent stem cells (iPSCs), and newborn foreskin fibroblasts. Amniocytes have a complex molecular signature, coexpressing trophoblastic, ectodermal, mesodermal, and endodermal cell-type-specific regulators. In contrast to the current view of the ground state of stem cells, ESCs and iPSCs also express high levels of a wide range of cell-type-specific regulators. The coexpression of multilineage differentiation markers combined with the strong expression of a subset of ES cell repressors in amniocytes suggests that these cells have a distinct phenotype that is unlike any other known cell-type or lineage.

Isolation of canine mesenchymal stem cells from amniotic fluid and differentiation into hepatocyte-like cells

Recent findings have demonstrated that amniotic fluid cells are an interesting and potential source of mesenchymal stem cells (MSCs). In this study, we isolated MSCs from canine amniotic fluid and then characterized their multilineage differentiation ability. Canine amniotic fluid stem (cAFS) cells at passage 5 had a fibroblast-like morphology instead of forming colonies and were positive for pluripotent stem cell markers such as OCT4, NANOG, and SOX2. Flow cytometry analysis showed the expression of MSC surface markers CD44, CD29, and CD90 on the cAFS cells. In addition, these cells were cultured under conditions favorable for adipogenic, chondrogenic, and osteogenic induction. The results of this experiment confirmed the mesenchymal nature of cAFS cells and their multipotent potential. Interestingly, although the cells exhibited a fibroblast-like morphology after hepatogenic induction, reverse transcription-polymerase chain reaction revealed that the expression of several hepatic genes, such as albumin, tyrosine aminotransferase, and alpha-1 antiproteinase, increased following maturation and differentiation. These findings indicated that cAFS cells have functional properties similar to those of hepatocytes. Taken together, the results of our study demonstrated that cAFS cells with mesenchymal characteristics can be successfully isolated from canine amniotic fluid and possess functional properties characteristic of hepatocytes. The findings of our work suggest that cAFS cells have the potential to be a resource for cell-based therapies in a canine model of hepatic disease.

Gene expression and functional annotation of the human ciliary body epithelia

Purpose

The ciliary body (CB) of the human eye consists of the non-pigmented (NPE) and pigmented (PE) neuro-epithelia. We investigated the gene expression of NPE and PE, to shed light on the molecular mechanisms underlying the most important functions of the CB. We also developed molecular signatures for the NPE and PE and studied possible new clues for glaucoma.

Methods

We isolated NPE and PE cells from seven healthy human donor eyes using laser dissection microscopy. Next, we performed RNA isolation, amplification, labeling and hybridization against 44×k Agilent microarrays. For microarray conformations, we used a literature study, RT-PCRs, and immunohistochemical stainings. We analyzed the gene expression data with R and with the knowledge database Ingenuity.

Results

The gene expression profiles and functional annotations of the NPE and PE were highly similar. We found that the most important functionalities of the NPE and PE were related to developmental processes, neural nature of the tissue, endocrine and metabolic signaling, and immunological functions. In total 1576 genes differed statistically significantly between NPE and PE. From these genes, at least 3 were cell-specific for the NPE and 143 for the PE. Finally, we observed high expression in the (N)PE of 35 genes previously implicated in molecular mechanisms related to glaucoma.

Conclusion

Our gene expression analysis suggested that the NPE and PE of the CB were quite similar. Nonetheless, cell-type specific differences were found. The molecular machineries of the human NPE and PE are involved in a range of neuro-endocrinological, developmental and immunological functions, and perhaps glaucoma.

Whole-organ tissue engineering: decellularization and recellularization of three-dimensional matrix scaffolds

The definitive treatment for end-stage organ failure is orthotopic transplantation. However, the demand for transplantation far exceeds the number of available donor organs. A promising tissue-engineering/regenerative-medicine approach for functional organ replacement has emerged in recent years. Decellularization of donor organs such as heart, liver, and lung can provide an acellular, naturally occurring three-dimensional biologic scaffold material that can then be seeded with selected cell populations. Preliminary studies in animal models have provided encouraging results for the proof of concept. However, significant challenges for three-dimensional organ engineering approach remain. This manuscript describes the fundamental concepts of whole-organ engineering, including characterization of the extracellular matrix as a scaffold, methods for decellularization of vascular organs, potential cells to reseed such a scaffold, techniques for the recellularization process and important aspects regarding bioreactor design to support this approach. Critical challenges and future directions are also discussed.