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October 11, 2017

Amniotic Fluid Cells Show Higher Pluripotency-Related Gene Expression Than Allantoic Fluid Cells

Amniotic Fluid-Derived Stem Cells Are Highly Amenable to Reprogramming

Amniotic Fluid Cells Show Higher Pluripotency-Related Gene Expression Than Allantoic Fluid Cells

The ovine developmental model and its corresponding fetal fluid cavities. (a, b) The ovine fetus (A) is surrounded by the inner amniotic fluid cavity (B), which is separated from the outer allantoic fluid cavity (C) drained through the umbilical cord (D). The fetal fluid cavities are surrounded by the uterine wall, which is covered by single placentoma units (E). (c, d) Three-dimensional computed tomography reconstruction of the ovine anatomy and the fetal fluid volumina (by the use of 10 mL Optiray 300 for amniotic fluid and 20 mL Optiray for allantoic fluid) show in vivo architecture of the ovine fetal fluid compartments as previously described in the schematic. Scale bar = 0.5 cm.

  • Amniotic fluid represents an abundant source of multipotent stem cells, which are currently being explored, as a versatile cell source for autologous cell-based therapies. These amniotic fluid-derived stem cells (AFSCs) have a phenotype similar to bone marrow-derived (multipotent) mesenchymal stem cells (BMSCs) [1]. However, human AFSCs are often referred to as “broadly multipotent” given the expression of factors involved in the maintenance of pluripotency in embryonic stem cells (ESCs), such as OCT4, NANOG, and SSEA-4 [2,3]. AFSCs have also been differentiated into cell types of all three germ layers, including adipogenic, osteogenic, myogenic, hepatic, neuronal, and endothelial lineages [4], either using an unselected or a small preselected population of c-kit (CD117)-positive cells [2]. These characteristics make AFSCs highly amenable to reprogramming, which further supports their higher “stemness” compared with postnatal multipotent stem cell sources [5–8].

    So far, the origin of human AFSCs during intrauterine development in general as well as the origin of this broadly multipotent cellular fraction in particular is not fully understood yet. AFSCs represent a heterogeneous population of cells and ultimately several sources of origin have been proposed, including embryonic (such as the urinary tract, the skin, the urogenital, respiratory, or gastrointestinal tract) as well as extraembryonic tissues (such as the placental tissue or the amniotic fetal adnexa) [9]. Also the origin of the amniotic fluid itself varies with increasing gestational age, whereas at the beginning, the production is mainly due to active water and electrolyte transport across the amniochorionic membrane and fetal skin. In the second half of gestation most of the fluid is produced by the fetus itself, either by secretion from the respiratory tract or by production of urine [10,11]. This further suggests that the origin of cells may also vary with different stages of gestation. However, anatomical and ethical limitations prevent further studies concerning the origin of AFSCs in humans.

    On the contrary, the ovine developmental model uniquely enables investigation of prenatal extraembryonic (stem) cell compartments [12]. Although being structurally and ontogenetically similar to the human fetal anatomy [13] and thus, serving as a standard in vivo animal model for several fetal therapeutic interventions involving AFSCs [12,14–21], it maintains two separate extraembryonic fluid compartments over the entire duration of pregnancy, the allantoic and the amniotic fluid cavities (Figure 1).

    In human embryogenesis, the allantois is only present in the first 3–5 weeks after conception and afterward it involutes to form the intraembryonic urachus [22]. Interestingly, in sheep the allantoic fluid compartment mainly collects fetal urine, which is drained from the urinary bladder through the urachus [8]. It therefore represents a model that allows for a direct comparison of fetal fluid-derived cells originating from the efferent urinary tract and the allantoic fetal adnexa with cells derived from the fetus itself and amniotic fetal adnexa directly surrounding the fetus. A comparison of the pluripotency-related gene expression of fetal fluid-derived cells from different compartments would shed some first light on the actual origin of the (broadly) multipotent cellular component of human amniotic fluid cells, in particular on whether these cells seem to originate from efferent urinary tissues or not.

    Therefore, the present study compares the expression of pluripotency-related genes between cells isolated from the amniotic versus the allantoic fluid cavity in the ovine developmental model over gestation in a strictly paired fashion.

  • Abstract

    Amniotic fluid represents an abundant source of multipotent stem cells, referred as broadly multipotent given their differentiation potential and expression of pluripotency-related genes. However, the origin of this broadly multipotent cellular fraction is not fully understood. Several sources have been proposed so far, including embryonic and extraembryonic tissues. In this regard, the ovine developmental model uniquely allows for direct comparison of fetal fluid-derived cells from two separate fetal fluid cavities, the allantois and the amnion, over the entire duration of gestation. As allantoic fluid mainly collects fetal urine, cells originating from the efferent urinary tract can directly be compared with cells deriving from the extraembryonic amniotic tissues and the fetus. This study shows isolation of cells from the amniotic [ovine amniotic fluid cells (oAFCs)] and allantoic fluid [ovine allantoic fluid cells (oALCs)] in a strictly paired fashion with oAFCs and oALCs derived from the same fetus. Both cell types showed cellular phenotypes comparable to standard mesenchymal stem cells (MSCs), with trilineage differentiation potential, and expression of common ovine MSC markers. However, the expression of MSC markers per single cell was higher in oAFCs as measured by flow cytometry. oAFCs exhibited higher proliferative capacities and showed significantly higher expression of pluripotency-related genes OCT4, STAT3, NANOG, and REX1 by quantitative real-time polymerase chain reaction compared with paired oALCs. No significant decrease of pluripotency-related gene expression was noted over gestation, implying that cells with high differentiation potential may be isolated at the end of pregnancy. In conclusion, this study suggests that cells with highest stem cell characteristics may originate from the fetus itself or the amniotic fetal adnexa rather than from the efferent urinary tract or the allantoic fetal adnexa.

  • To read the full version of this articl please visit the original article and its references.

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