Small extracellular vesicles secreted from human amniotic fluid mesenchymal stromal cells possess cardioprotective and promigratory potential.

Mesenchymal stromal cells (MSCs) exhibit antiapoptotic and proangiogenic functions in models of myocardial infarction which may be mediated by secreted small extracellular vesicles (sEVs). However, MSCs have frequently been harvested from aged or diseased patients, while the isolated sEVs often contain high levels of impurities. Here, we studied the cardioprotective and proangiogenic activities of size-exclusion chromatography-purified sEVs secreted from human foetal amniotic fluid stem cells (SS-hAFSCs), possessing superior functional potential to that of adult MSCs. We demonstrated for the first time that highly pure (up to 1.7 × 1010 particles/µg protein) and thoroughly characterised SS-hAFSC sEVs protect rat hearts from ischaemia-reperfusion injury in vivo when administered intravenously prior to reperfusion (38 ± 9% infarct size reduction, p < 0.05). SS-hAFSC sEVs did not protect isolated primary cardiomyocytes in models of simulated ischaemia-reperfusion injury in vitro, indicative of indirect cardioprotective effects. SS-hAFSC sEVs were not proangiogenic in vitro, although they markedly stimulated endothelial cell migration. Additionally, sEVs were entirely responsible for the promigratory effects of the medium conditioned by SS-hAFSC. Mechanistically, sEV-induced chemotaxis involved phosphatidylinositol 3-kinase (PI3K) signalling, as its pharmacological inhibition in treated endothelial cells reduced migration by 54 ± 7% (p < 0.001). Together, these data indicate that SS-hAFSC sEVs have multifactorial beneficial effects in a myocardial infarction setting.

Human Amniocytes Are Receptive to Chemically Induced Reprogramming to Pluripotency.

Restoring pluripotency using chemical compounds alone would be a major step forward in developing clinical-grade pluripotent stem cells, but this has not yet been reported in human cells. We previously demonstrated that VPA_AFS cells, human amniocytes cultivated with valproic acid (VPA) acquired functional pluripotency while remaining distinct from human embryonic stem cells (hESCs), questioning the relationship between the modulation of cell fate and molecular regulation of the pluripotency network. Here, we used single-cell analysis and functional assays to reveal that VPA treatment resulted in a homogeneous population of self-renewing non-transformed cells that fulfill the hallmarks of pluripotency, i.e., a short G1 phase, a dependence on glycolytic metabolism, expression of epigenetic modifications on histones 3 and 4, and reactivation of endogenous OCT4 and downstream targets at a lower level than that observed in hESCs. Mechanistic insights into the process of VPA-induced reprogramming revealed that it was dependent on OCT4 promoter activation, which was achieved independently of the PI3K (phosphatidylinositol 3-kinase)/AKT/mTOR (mammalian target of rapamycin) pathway or GSK3ß inhibition but was concomitant with the presence of acetylated histones H3K9 and H3K56, which promote pluripotency. Our data identify, for the first time, the pluripotent transcriptional and molecular signature and metabolic status of human chemically induced pluripotent stem cells.

5' isomiR variation is of functional and evolutionary importance.

We have sequenced miRNA libraries from human embryonic, neural and foetal mesenchymal stem cells. We report that the majority of miRNA genes encode mature isomers that vary in size by one or more bases at the 3' and/or 5' end of the miRNA. Northern blotting for individual miRNAs showed that the proportions of isomiRs expressed by a single miRNA gene often differ between cell and tissue types. IsomiRs were readily co-immunoprecipitated with Argonaute proteins in vivo and were active in luciferase assays, indicating that they are functional. Bioinformatics analysis predicts substantial differences in targeting between miRNAs with minor 5' differences and in support of this we report that a 5' isomiR-9-1 gained the ability to inhibit the expression of DNMT3B and NCAM2 but lost the ability to inhibit CDH1 in vitro. This result was confirmed by the use of isomiR-specific sponges. Our analysis of the miRGator database indicates that a small percentage of human miRNA genes express isomiRs as the dominant transcript in certain cell types and analysis of miRBase shows that 5' isomiRs have replaced canonical miRNAs many times during evolution. This strongly indicates that isomiRs are of functional importance and have contributed to the evolution of miRNA genes.

Placenta as a reservoir of stem cells: an underutilized resource?

INTRODUCTION: Both embryonic and adult tissues are sources of stem cells with therapeutic potential but with some limitations in the clinical practice such as ethical considerations, difficulty in obtaining and tumorigenicity. As an alternative, the placenta is a foetal tissue that can be obtained during gestation and at term, and it represents a reservoir of stem cells with various potential. SOURCES OF DATA: We reviewed the relevant literature concerning the main stem cells that populate the placenta. AREAS OF AGREEMENT: Recently, the placenta has become useful source of stem cells that offer advantages in terms of proliferation and plasticity when compared with adult cells and permit to overcome the ethical and safety concern inherent in embryonic stem cells. In addition, the placenta has the advantage of containing epithelia, haematopoietic and mesenchymal stem cells. These stem cells possess immunosuppressive properties and have the capacity of suppress in vivo inflammatory responses. AREAS OF CONTROVERSY: Some studies describe a subpopulation of placenta stem cells expressing pluripotency markers, but for other studies, it is not clear whether pluripotent stem cells are present during gestation beyond the first few weeks. Particularly, the expression of some pluripotency markers such as SSEA-3, TRA-1-60 and TRA-1-81 has been reported by us, but not by others. GROWING POINTS: Placenta stem cells could be of great importance after delivery for banking for autologous and allogeneic applications. The beneficial effects of these cells may be due to secretion of bioactive molecules that act through paracrine actions promoting beneficial effects. AREAS TIMELY FOR DEVELOPING RESEARCH: Understanding the role of placenta stem cells during pregnancy and their paracrine actions could help in the study of some diseases that affect the placenta during pregnancy.

Transplantation of human fetal blood stem cells in the osteogenesis imperfecta mouse leads to improvement in multiscale tissue properties.

Osteogenesis imperfecta (OI or brittle bone disease) is a disorder of connective tissues caused by mutations in the collagen genes. We previously showed that intrauterine transplantation of human blood fetal stem/stromal cells in OI mice (oim) resulted in a significant reduction of bone fracture. This work examines the cellular mechanisms and mechanical bone modifications underlying these therapeutic effects, particularly examining the direct effects of donor collagen expression on bone material properties. In this study, we found an 84% reduction in femoral fractures in transplanted oim mice. Fetal blood stem/stromal cells engrafted in bones, differentiated into mature osteoblasts, expressed osteocalcin, and produced COL1a2 protein, which is absent in oim mice. The presence of normal collagen decreased hydroxyproline content in bones, altered the apatite crystal structure, increased the bone matrix stiffness, and reduced bone brittleness. In conclusion, expression of normal collagen from mature osteoblast of donor origin significantly decreased bone brittleness by improving the mechanical integrity of the bone at the molecular, tissue, and whole bone levels.

Valproic acid confers functional pluripotency to human amniotic fluid stem cells in a transgene-free approach.

Induced pluripotent stem cells (iPSCs) with potential for therapeutic applications can be derived from somatic cells via ectopic expression of a set of limited and defined transcription factors. However, due to risks of random integration of the reprogramming transgenes into the host genome, the low efficiency of the process, and the potential risk of virally induced tumorigenicity, alternative methods have been developed to generate pluripotent cells using nonintegrating systems, albeit with limited success. Here, we show that c-KIT+ human first-trimester amniotic fluid stem cells (AFSCs) can be fully reprogrammed to pluripotency without ectopic factors, by culture on Matrigel in human embryonic stem cell (hESC) medium supplemented with the histone deacetylase inhibitor (HDACi) valproic acid (VPA). The cells share 82% transcriptome identity with hESCs and are capable of forming embryoid bodies (EBs) in vitro and teratomas in vivo. After long-term expansion, they maintain genetic stability, protein level expression of key pluripotency factors, high cell-division kinetics, telomerase activity, repression of X-inactivation, and capacity to differentiate into lineages of the three germ layers, such as definitive endoderm, hepatocytes, bone, fat, cartilage, neurons, and oligodendrocytes. We conclude that AFSC can be utilized for cell banking of patient-specific pluripotent cells for potential applications in allogeneic cellular replacement therapies, pharmaceutical screening, and disease modeling.

Publisher Correction: Human mid-trimester amniotic fluid (stem) cells lack expression of the pluripotency marker OCT4A.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Comparative osteogenic transcription profiling of various fetal and adult mesenchymal stem cell sources.

Human mesenchymal stem cells (MSC) from adult and fetal tissues are promising candidates for cell therapy but there is a need to identify the optimal source for bone regeneration. We have previously characterized MSC populations in first trimester fetal blood, liver, and bone marrow and we now evaluate their osteogenic differentiation potential in comparison to adult bone marrow MSC. Using quantitative real-time RT-PCR, we demonstrated that 16 osteogenic-specific genes (OC, ON, BSP, OP, Col1, PCE, Met2A, OPG, PHOS1, SORT, ALP, BMP2, CBFA1, OSX, NOG, IGFII) were expressed in both fetal and adult MSC under basal conditions and were up-regulated under osteogenic conditions both in vivo and during an in vitro 21-day time-course. However, under basal conditions, fetal MSC had higher levels of osteogenic gene expression than adult MSC. Upon osteogenic differentiation, fetal MSC produced more calcium in vitro and reached higher levels of osteogenic gene up-regulation in vivo and in vitro. Second, we observed a hierarchy within fetal samples, with fetal bone marrow MSC having greater osteogenic potential than fetal blood MSC, which in turn had greater osteogenic potential than fetal liver MSC. Finally, we found that the level of gene expression under basal conditions was positively correlated with both calcium secretion and gene expression after 21 days in osteogenic conditions. Our findings suggest that stem cell therapy for bone dysplasias such as osteogenesis imperfecta may benefit from preferentially using first trimester fetal blood or bone marrow MSC over fetal liver or adult bone marrow MSC.

Splicing speckles are not reservoirs of RNA polymerase II, but contain an inactive form, phosphorylated on serine2 residues of the C-terminal domain.

"Splicing speckles" are major nuclear domains rich in components of the splicing machinery and polyA(+) RNA. Although speckles contain little detectable transcriptional activity, they are found preferentially associated with specific mRNA-coding genes and gene-rich R bands, and they accumulate some unspliced pre-mRNAs. RNA polymerase II transcribes mRNAs and is required for splicing, with some reports suggesting that the inactive complexes are stored in splicing speckles. Using ultrathin cryosections to improve optical resolution and preserve nuclear structure, we find that all forms of polymerase II are present, but not enriched, within speckles. Inhibition of polymerase activity shows that speckles do not act as major storage sites for inactive polymerase II complexes but that they contain a stable pool of polymerase II phosphorylated on serine(2) residues of the C-terminal domain, which is transcriptionally inactive and may have roles in spliceosome assembly or posttranscriptional splicing of pre-mRNAs. Paraspeckle domains lie adjacent to speckles, but little is known about their protein content or putative roles in the expression of the speckle-associated genes. We find that paraspeckles are transcriptionally inactive but contain polymerase II, which remains stably associated upon transcriptional inhibition, when paraspeckles reorganize around nucleoli in the form of caps.

Human mid-trimester amniotic fluid (stem) cells lack expression of the pluripotency marker OCT4A.

Expression of OCT4A is one of the hallmarks of pluripotency, defined as a stem cell's ability to differentiate into all the lineages of the three germ layers. Despite being defined as non-tumorigenic cells with high translational potential, human mid-trimester amniotic fluid stem cells (hAFSCs) are often described as sharing features with embryonic stem cells, including the expression of OCT4A, which could hinder their clinical potential. To clarify the OCT4A status of hAFSCs, we first undertook a systematic review of the literature. We then performed extensive gene and protein expression analyses to discover that neither frozen, nor fresh hAFSCs cultivated in multipotent stem cell culture conditions expressed OCT4A, and that the OCT4A positive results from the literature are likely to be attributed to the expression of pseudogenes or other OCT4 variants. To address this issue, we provide a robust protocol for the assessment of OCT4A in other stem cells.

Micro-computed tomography reconstructions of tibiae of stem cell transplanted osteogenesis imperfecta mice.

Micro-computed tomography (micro-CT) is commonly used to assess bone quality and to evaluate the outcome of experimental therapies in animal models of bone diseases. Generating large datasets is however challenging and data are rarely made publicly available through shared repositories. Here we describe a dataset of micro-CT reconstructed scans of the proximal part of 21 tibiae from wild-type mice, osteogenesis imperfecta mice (homozygous oim/oim) and oim/oim mice transplanted with human amniotic fluid stem cells. The dataset contains, for each sample, 991 8-bit Bitmap reconstructed images and a 3D reconstruction of the bone in the PLY format, available at the online repository Figshare. In line with the increasing effort to make scientific datasets open-access, our data can be downloaded and used by other researchers to compare their observations with ours and to directly test scientific questions on osteogenesis imperfecta bones without the need to generate complete datasets.

The presence of human mesenchymal stem cells of renal origin in amniotic fluid increases with gestational time.

BACKGROUND: Established therapies for managing kidney dysfunction such as kidney dialysis and transplantation are limited due to the shortage of compatible donated organs and high costs. Stem cell-based therapies are currently under investigation as an alternative treatment option. As amniotic fluid is composed of fetal urine harboring mesenchymal stem cells (AF-MSCs), we hypothesized that third-trimester amniotic fluid could be a novel source of renal progenitor and differentiated cells. METHODS: Human third-trimester amniotic fluid cells (AFCs) were isolated and cultured in distinct media. These cells were characterized as renal progenitor cells with respect to cell morphology, cell surface marker expression, transcriptome and differentiation into chondrocytes, osteoblasts and adipocytes. To test for renal function, a comparative albumin endocytosis assay was performed using AF-MSCs and commercially available renal cells derived from kidney biopsies. Comparative transcriptome analyses of first, second and third trimester-derived AF-MSCs were conducted to monitor expression of renal-related genes. RESULTS: Regardless of the media used, AFCs showed expression of pluripotency-associated markers such as SSEA4, TRA-1-60, TRA-1-81 and C-Kit. They also express the mesenchymal marker Vimentin. Immunophenotyping confirmed that third-trimester AFCs are bona fide MSCs. AF-MSCs expressed the master renal progenitor markers SIX2 and CITED1, in addition to typical renal proteins such as PODXL, LHX1, BRN1 and PAX8. Albumin endocytosis assays demonstrated the functionality of AF-MSCs as renal cells. Additionally, upregulated expression of BMP7 and downregulation of WT1, CD133, SIX2 and C-Kit were observed upon activation of WNT signaling by treatment with the GSK-3 inhibitor CHIR99201. Transcriptome analysis and semiquantitative PCR revealed increasing expression levels of renal-specific genes (e.g., SALL1, HNF4B, SIX2) with gestational time. Moreover, AF-MSCs shared more genes with human kidney cells than with native MSCs and gene ontology terms revealed involvement of biological processes associated with kidney morphogenesis. CONCLUSIONS: Third-trimester amniotic fluid contains AF-MSCs of renal origin and this novel source of kidney progenitors may have enormous future potentials for disease modeling, renal repair and drug screening.

Neuroprotection of the hypoxic-ischemic mouse brain by human CD117+CD90+CD105+ amniotic fluid stem cells.

Human amniotic fluid contains two morphologically-distinct sub-populations of stem cells with regenerative potential, spindle-shaped (SS-hAFSCs) and round-shaped human amniotic fluid stem cells (RS-hAFSCs). However, it is unclear whether morphological differences correlate with functionality, and this lack of knowledge limits their translational applications. Here, we show that SS-hAFSCs and RS-hAFSCs differ in their neuro-protective ability, demonstrating that a single contralateral injection of SS-hAFSCs into hypoxic-ischemic P7 mice conferred a 47% reduction in hippocampal tissue loss and 43-45% reduction in TUNEL-positive cells in the hippocampus and striatum 48 hours after the insult, decreased microglial activation and TGFß1 levels, and prevented demyelination. On the other hand, RS-hAFSCs failed to show such neuro-protective effects. It is possible that SS-hAFSCs exert their neuroprotection via endoglin-dependent inhibition of TGFß1 signaling in target cells. These findings identify a sub-population of CD117+CD90+CD105+ stem cells as a promising source for the neuro-protection of the developing brain.

Embryonic Stem Cell-Derived Mesenchymal Stem Cells (MSCs) Have a Superior Neuroprotective Capacity Over Fetal MSCs in the Hypoxic-Ischemic Mouse Brain.

Human mesenchymal stem cells (MSCs) have huge potential for regenerative medicine. In particular, the use of pluripotent stem cell-derived mesenchymal stem cells (PSC-MSCs) overcomes the hurdle of replicative senescence associated with the in vitro expansion of primary cells and has increased therapeutic benefits in comparison to the use of various adult sources of MSCs in a wide range of animal disease models. On the other hand, fetal MSCs exhibit faster growth kinetics and possess longer telomeres and a wider differentiation potential than adult MSCs. Here, for the first time, we compare the therapeutic potential of PSC-MSCs (ES-MSCs from embryonic stem cells) to fetal MSCs (AF-MSCs from the amniotic fluid), demonstrating that ES-MSCs have a superior neuroprotective potential over AF-MSCs in the mouse brain following hypoxia-ischemia. Further, we demonstrate that nuclear factor (NF)-κB-stimulated interleukin (IL)-13 production contributes to an increased in vitro anti-inflammatory potential of ES-MSC-conditioned medium (CM) over AF-MSC-CM, thus suggesting a potential mechanism for this observation. Moreover, we show that induced pluripotent stem cell-derived MSCs (iMSCs) exhibit many similarities to ES-MSCs, including enhanced NF-κB signaling and IL-13 production in comparison to AF-MSCs. Future studies should assess whether iMSCs also exhibit similar neuroprotective potential to ES-MSCs, thus presenting a potential strategy to overcome the ethical issues associated with the use of embryonic stem cells and providing a potential source of cells for autologous use against neonatal hypoxic-ischemic encephalopathy in humans. Stem Cells Translational Medicine 2018;7:439-449.

Osterix induces osteogenic gene expression but not differentiation in primary human fetal mesenchymal stem cells.

The transcription factor osterix (Osx) is a key regulator of osteoblast differentiation and induces bone formation in embryonic but not adult stem cells. We investigated the effect of up-regulating Osx on an intermediate stem cell type, first trimester fetal mesenchymal stem cells (MSCs), which are more expandable than adult MSCs. Human fetal (hf ) MSCs were transduced with a lentiviral vector encoding human Osx. In undifferentiating MSCs cultures, forced expression of Osx stimulated osteopontin and alkaline phosphatase expression. However, Osx did not up-regulate osteocalcin, a late marker of osteoblast differentiation or result in extracellular calcium crystals, indicating that Osx does not directly mediate terminal differentiation in primary hfMSCs. To understand the downstream effects of Osx expression in primary hfMSCs, we next investigated the regulatory relationship between Osx, and the transcription factors Dlx5, Runx2, and Msx2. Osx induced Dlx5 but did not affect Runx2 and Msx2, whereas stealth ribonucleic acid interference of Osx inhibited Dlx5 without affecting expression of Runx2 and Msx2. In conclusion, Osx regulates osteogenic gene expression in hfMSCs but is insufficient to induce terminal osteogenic differentiation.

TGFß-induced osteogenic potential of human amniotic fluid stem cells via CD73-generated adenosine production.

The human amniotic fluid stem cell (hAFSC) population consists of two morphologically distinct subtypes, spindle-shaped and round-shaped cells (SS-hAFSCs and RS-hAFSCs). Whilst SS-hAFSCs are routinely expanded in mesenchymal-type (MT) conditions, we previously showed that they acquire broader differentiation potential when cultured under embryonic-type (ET) conditions. However, the effects of culture conditions on RS-hAFSCs have not been determined. Here, we show that culturing RS-hAFSCs under ET conditions confers faster proliferation and enhances the efficiency of osteogenic differentiation of the cells. We show that this occurs via TGFß-induced activation of CD73 and the associated increase in the generation of extracellular adenosine. Our data demonstrate that culture conditions are decisive for the expansion of hAFSCs and that TGFß present in ET conditions causes the phenotype of RS-hAFSCs to revert to an earlier state of stemness. Cultivating RS-hAFSCs in ET conditions with TGFß may therefore increase their therapeutic potential for clinical applications.

Fetal stem cells: betwixt and between.

Fetal stem cells can be isolated not only from fetal blood and hemopoietic organs in early pregnancy, but from a variety of somatic organs as well as amniotic fluid and placenta throughout gestation. Fetal blood is a rich source of hemopoietic stem cells, which proliferate more rapidly than those in cord blood or adult bone marrow. First-trimester fetal blood, liver, and bone marrow also contain a population of mesenchymal stem cells, which appear to be more primitive with greater multipotentiality than their adult counterparts. Fetal stem cells may thus represent an intermediate cell type in the current debate focusing on dichotomized adult versus embryonic stem cells, and thus prove advantageous as a source for downstream cell therapy applications. They have also been implicated in fetomaternal trafficking in pregnancy, and in long-term microchimerism in postreproductive women.

Induced pluripotent stem (iPS) cells from human fetal stem cells.

Pluripotency defines the ability of stem cells to differentiate into all the lineages of the three germ layers and self-renew indefinitely. Somatic cells can regain the developmental potential of embryonic stem cells following ectopic expression of a set of transcription factors or, in certain circumstances, via modulation of culture conditions and supplementation with small molecule, that is, induced pluripotent stem (iPS) cells. Here, we discuss the use of fetal tissues for reprogramming, focusing in particular on stem cells derived from human amniotic fluid, and the development of chemical reprogramming. We next address the advantages and disadvantages of deriving pluripotent cells from fetal tissues and the potential clinical applications.

Counteracting bone fragility with human amniotic mesenchymal stem cells.

The impaired maturation of bone-forming osteoblasts results in reduced bone formation and subsequent bone weakening, which leads to a number of conditions such as osteogenesis imperfecta (OI). Transplantation of human fetal mesenchymal stem cells has been proposed as skeletal anabolic therapy to enhance bone formation, but the mechanisms underlying the contribution of the donor cells to bone health are poorly understood and require further elucidation. Here, we show that intraperitoneal injection of human amniotic mesenchymal stem cells (AFSCs) into a mouse model of OI (oim mice) reduced fracture susceptibility, increased bone strength, improved bone quality and micro-architecture, normalised bone remodelling and reduced TNFα and TGFß sigalling. Donor cells engrafted into bones and differentiated into osteoblasts but importantly, also promoted endogenous osteogenesis and the maturation of resident osteoblasts. Together, these findings identify AFSC transplantation as a countermeasure to bone fragility. These data have wider implications for bone health and fracture reduction.