Human amnion favours tissue repair by inducing the M1-to-M2 switch and enhancing M2 macrophage features.

Human amniotic mesenchymal cells (hAMTCs) possess interesting immunomodulatory properties, making them attractive candidates for regenerative medicine applications. Recent in vivo reports argue in favour of an important role for macrophages as targets of hAMTC-mediated suppression of inflammation and the enhancement of tissue repair. However, a comprehensive study of the effects of hAMTCs and their conditioned medium (CM) on human macrophage differentiation and function is unavailable. In the present study we found that hAMTCs and CM induce the differentiation of myeloid cells (U937 and monocytes) towards macrophages. We then investigated their effects on monocytes differentiated toward pro-inflammatory M1 and anti-inflammatory M2 macrophages. Monocytes treated under M1 conditions in the presence of hAMTCs or CMs shifted towards M2-like macrophages, which expressed CD14, CD209, CD23, CD163 and PM-2 K, possessed higher phagocytic activity and produced higher IL-10 and lower pro-inflammatory cytokines. They were also poor T cell stimulators and Th1 inducers, while they were able to increase activated and naïve suppressive Treg subsets. We show that prostaglandins, and not IL-6, play a role in determining the M2 activation status. Instead, monocytes treated under M2 conditions in the presence of hAMTCs or CM retained M2-like features, but with an enhanced anti-inflammatory profile, having a reduced expression of the co-stimulatory molecule CD80, reduced phagocytosis activity and decreased the secretion of inflammatory chemokines. Importantly, we provide evidence that macrophages re-educated by CM improve tissue regeneration/repair in wound-healing models. In conclusion, we identified new cell targets of hAMTCs and their bioactive factors and here provide insight into the beneficial effects observed when these cells are used in therapeutic approaches in vivo. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Human Amniotic Membrane-Derived Mesenchymal and Epithelial Cells Exert Different Effects on Monocyte-Derived Dendritic Cell Differentiation and Function.

We previously demonstrated that mesenchymal cells from human amniotic membrane (hAMTCs) inhibit the generation and maturation of monocyte-derived dendritic cells (DCs) in vitro. Considering the crucial role of DCs in the immune response and that epithelial cells of the human amniotic membrane (hAECs) share some of the immunoregulatory properties of hAMTCs, we investigated whether hAECs also modulate monocyte-derived DCs. We compared hAECs with hAMTCs in a cell-to-cell contact setting and their secreted factors in modulating DC differentiation and function. First, we demonstrated that primary and expanded hAMTCs strongly inhibited the differentiation of DCs and induced a shift toward M2-like macrophages. This was observed when hAMTCs were cultured in contact (hAMTC-DC(cont)) or in Transwells (hAMTC-DC(tw)) with monocytes and even when medium conditioned by hAMTCs was used instead of hAMTCs. hAECs also prevented DC development, but to a lesser extent than hAMTCs. hAECs were more effective when cultured in contact with monocytes (hAEC-DC(cont)) rather than in Transwells (hAEC-DC(tw)). The modulatory capacity of hAECs changed during passaging unlike the hAMSCs. The ability to stimulate CD4(+) and CD8(+) T-cell proliferation was almost completely abolished by hAMTC-DC(cont), whereas hAMTC-DC(tw) and hAEC-DC(cont) displayed only a reduced ability to stimulate CD8(+) T cells. Furthermore, monocytes cocultured with hAMTCs and hAECs showed some similarities, but also differences in cytokine/chemokine secretion. Similarities were observed in the inhibition of IL-12p70 and TNF-α and the increase in IL-10 in supernatants taken from monocyte-DCs cocultured with hAMTCs and hAECs in contact and Transwell settings. The inflammatory factors IL-8, CXCL9, and MIP-1α were significantly lower in hAMTC-DC(cont), hAMTC-DC(tw), and hAEC-DC(cont) conditions. In contrast, only hAMTCs (in both contact and Transwell conditions) were able to significantly increase IL-1ß and CCL2. Altogether, we demonstrated that hAMTCs and hAECs affect DC differentiation, but that hAMTCs exerted a stronger inhibitory effect, abolished T-cell proliferation, and also induced more changes in cytokine/chemokine production.

Feasibility and potential of in utero foetal membrane-derived cell transplantation.

Cells isolated from foetal membranes of human term placenta display multiple properties, including some features of stem/progenitor cells, together with immunomodulatory actions and the ability to secrete bioactive soluble factors. Whilst such properties support the potential applicability of these cells in transplantation settings aimed at regenerating/repairing tissues in adults, theoretically, using these cells in prenatal treatment strategies may also be achievable. To assess the feasibility of a foetal membrane-derived cell-based therapeutic treatment during foetal development, we firstly addressed the question of whether in utero transplantation using these cells was possible. To this end, we assessed postnatal microchimerism after transplantation of amniotic membrane-derived cells (a mixture of both mesenchymal stromal/stem cells and epithelial cells) in foetal sheep. Transplantation was performed with or without human umbilical cord blood mononuclear cells and chorionic membrane-derived mesenchymal stromal/stem cells, and was followed by a postnatal booster cell injection. Lambs were euthanized 2-4 months postnatally and their organs/tissues were analysed for microchimerism through detection of human DNA. Human DNA was found in almost all tissues of all of the lambs, with the seemingly random appearance of human cells in some of the analysed tissues suggesting long-term human microchimerism and donor cell migration after in utero/postnatal booster xenotransplation. Differences in microchimerism tissue distribution between animals transplanted with different cell types are discussed. This pilot study adds to ongoing efforts by different investigators to explore the potential of in utero cellular transplantation, and warrants further investigation of using foetal membrane-derived cells for prenatal cell therapies.

Human term placental cells: phenotype, properties and new avenues in regenerative medicine.

The human placenta has long been the subject of scientific interest due to the important roles which it performs during pregnancy in sustaining the fetus and maintaining fetomaternal tolerance. More recently, however, researchers have begun to investigate the possibility that the placenta's utility may extend beyond fetal development to act as a source of cells with clinically relevant properties. Indeed, several groups have reported the isolation of cells from different placental regions which display both multilineage differentiation potential and immunomodulatory properties in vitro. Furthermore, these cells have also been shown to secrete soluble factors involved in pathophysiological processes that may aid tissue repair. Cells with such features will clearly find application in the field of regenerative medicine for the repair/regeneration of damaged or diseased tissues or organs. In line with these promising findings, several preclinical and clinical studies conducted to date argue in strong favor of the therapeutic utility of placenta-derived cells for the treatment of several diseases. Although much work remains to be conducted in order to fully understand the properties of placental cells and the mechanisms which underlie their beneficial effects in vivo, data reported to date nonetheless provide compelling evidence in support of the placenta as a cell source for use in regenerative medicine.

Mutation in the VP1-LDV motif of the murine polyomavirus affects viral infectivity and conditions virus tissue tropism in vivo.

The first contact of a virus with the host cell surface and further entry are important steps for a successful outcome of the infection process and for the virus-associated pathogenicity. We have previously shown that the entry of the murine Polyomavirus (Py) into fibroblasts is a multi-step process involving, at least, the attachment to primary sialic acids (SA)-containing cell receptors followed by post-binding interaction with secondary receptors, such as the alpha4beta1 integrin, likely through the VP1-LDV motif. Here we report on the functional role of the VP1-LDV motif in Py infectivity and in vivo virus tissue tropism. For this purpose, we have characterized a recombinant virus mutant, PyLNV, harboring a single aa substitution in this motif (D138N). Although not critical for virus viability, the D138N substitution abrogates the post-attachment Py-alpha4beta1 interaction, rendering the PyLNV mutant virus twofold less infectious than the Py wild-type (Wt) in alpha4beta1-positive fibroblasts. To study the putative role of the VP1-LDV motif in vivo, newborn C57BL/6 mice were inoculated with PyWt or PyLNV and, after six days, organs were analyzed for the presence of viral DNA. Intriguingly, PyLNV showed an altered spectrum of in vivo replication compared with PyWt, particularly in the skin and in the kidney. The implication of Py-alpha4beta1 integrin interaction in conditioning tissue-specificity of virus replication is discussed.

The future of stem cells in liver diseases.

Preliminary experience with clinical hepatocyte transplantation during the past decade has provided proof of concept that cell therapy can be effective for the treatment of some liver diseases. Recent progress in cell biology resulting in the isolation and characterization of hepatic stem cells and progenitor cells further increased the expectation for a new approach to the treatment of genetic and chronic liver disease. Several potential sources have been identified of hepatic stem/ progenitor cells exhibiting both differentiation towards the hepatic lineage in vitro and hepatic parenchymal repopulation with liver-specific metabolic activity in liver-injured animal models. However, a few of these results proved to be poorly reproducible in different laboratories, and it was recognized that some initial optimistic conclusions were drawn from incorrect interpretation of experimental data or from insufficient knowledge of the mechanisms involved in tissue regeneration. Moreover, only modest results have emerged so far from ongoing clinical experience involving the use of putative stem cells in liver disease. There is much need for a joined effort to concentrate the resources on a specific cell population, in order to better characterize its function, to assess its safety and to develop better focused clinical trials. In conclusion, while the biological features of stem cells still justify the hope for future clinical applications, hepatic stem cell therapy has still a long way to go from bench to bedside.

Conformational changes of murine polyomavirus capsid proteins induced by sialic acid binding.

Murine polyomavirus (Py) infection initiates by the recognition of cell membrane molecules containing terminal sialic acid (SA) residues through specific binding pockets formed at the major capsid protein VP1 surface. VP1 Pockets 1, 2, and 3 bind terminal SA, Gal, and second branched SA, respectively. The consequence of recognition on viral cell entry remains elusive. In this work, we show that preincubation of Py with soluble compounds within Pocket 1 (N-acetyl or N-glycolyl neuraminic acids) increases Py cell binding and infectivity in murine 3T6 fibroblasts. In contrast, Gal does not significantly alter Py binding nor infectivity, whereas sialyllactose, in Pockets 1 and 2, decreases cell binding and infectivity. Binding experiments with Py virus-like particles confirmed the direct involvement of VP1 in this effect. To determine whether such results could reflect VP1 conformational changes induced by SA binding, protease digestion assays were performed after pretreatment of Py or virus-like particles with soluble receptor fragments. Binding of SA with the VP1 Pocket 1, but not of compounds interacting with Pocket 2, was associated with a transition of this protein from a protease-sensitive to a protease-resistant state. This effect was transmitted to the minor capsid proteins VP2 and VP3 in virus particles. Attachment of Py to cell monolayers similarly led to a VP1 trypsin-resistant pattern. Taken together, these data present evidence that initial binding of Py to terminal SA induces conformational changes in the viral capsid, which may influence subsequent virus cell entry steps.

Role of sialic acid-containing molecules and the alpha4beta1 integrin receptor in the early steps of polyomavirus infection.

Murine polyomavirus (MPyV) infection occurs through recognition of sialic acid (SA) residues present on the host cell membrane, but the nature of the molecules involved and the exact role of this interaction in virus cell entry still need to be clarified. In this work, mutations at residues R(77) or H(298) of the MPyV VP1 protein were shown to lead to a complete loss of virus infectivity, which, however, could be restored by lipofection of virus particles into the cytoplasm of the host cells. Using virus-like particles (VLPs), it was demonstrated that the non-infectivity of these mutants was due to impaired cell entry caused by total abrogation of SA-dependent cell binding. This indicates that SA residues are essential primary cell receptors for MPyV. As the alpha4beta1 integrin has been identified recently as a cell receptor for MPyV, the relationship, if any, was investigated between SA-containing and alpha4beta1 integrin receptors. The ability of mutants R(77)Q and H(298)Q and wt VLPs to bind to cells overexpressing the alpha4beta1 integrin was studied in SA-positive (BALB/c 3T3 cells and Pro-5 cells) and SA-deficient (Pro5-derived Lec-2 cells) backgrounds. Overexpression of alpha4beta1 integrin did not restore binding of mutant VLPs in any of these cell lines or, indeed, that of wt VLPs in a SA-deficient background. Moreover, evidence is provided that overexpression of the sialylated alpha4beta1 integrin enhances wt VLP cell binding, suggesting that, in addition to its function at a post-attachment level, alpha4beta1 integrin acts also as one of the SA-containing receptors for initial cell binding.

Alpha4beta1 integrin acts as a cell receptor for murine polyomavirus at the postattachment level.

The initial interaction of murine polyomavirus (Py) with host cells occurs through direct binding of the major capsid protein VP1 with cell membrane molecules containing terminal sialic acids; however, these Py receptor molecules have not yet been identified. Analysis of the capsid protein primary sequences of all murine strains revealed the presence of integrin ligand motifs in the DE and EF loops of VP1 (LDV and DLXXL, respectively) and at the N terminus of VP2 (DGE). We show that infectivity of the Py A2 strain in mouse Swiss 3T3 fibroblasts is significantly reduced only in the presence of natural integrin ligands carrying an LDV motif or antibodies directed against the alpha4 and beta1 integrin subunits. Furthermore, we demonstrate that expression of the alpha4 subunit in the alpha4-deficient BALB/c 3T3 cells increases viral infectivity. Addition of alpha4 function-blocking antibodies, prior to or after virus adsorption, blocks this increased infectivity without affecting virus binding to cells. Taken together, these data indicate that expression of alpha4 integrin enhances permissivity to Py, probably by acting as one of the postattachment receptors.