Defect in endometrial stem cells: key player in recurrent pregnancy losses?

Posted By Braverman IVF & Reproductive Immunology || 16-Mar-2016

Recent article on stem cells in relation to recurrent pregnancy losses:

Analysis by Braverman Reproductive Immunology

A new study, published last week in the journal Stem cells, suggest that a lack of endometrial mesenchymal stem cells (eMSC) in the lining of the womb could be responsible for reccurent pregnancy losses (Lucas, 2016).
Largely commented in recent journal publications as the first work showing a cause for reccurent pregnancy losses, the British study, although very promising, showed a correlation between women suffering from RPL and a lack of eMSC but no demonstration of causality.

In the following blog, we will tell you a little more about endometrial stem cells as they relate to pregnancy, we will then focus on the main findings of the current study to finally conclude on the potential of eMSC use to treat early pregnancy disorders.

  1. Human endometrial mesenchymal stem cells
  1. Endometrial mesenchymal stem cell (eMSC) and uterine regeneration

The endometrium sheds and regenerates each month as part of the menstrual cycle but also after parturition (1).
Endometrial stem cells play key roles in regulating endometrial regeneration.
During the proliferative phase of the menstrual cycle, the estradiol induces the migration of eMSC to the endometrium. In addition, endometrial cells secrete an angiogenic factor (PDGF-BB) that will bind on PDGF receptors localized on eMSC thus leading to their recruitment that allows renewal of cells in the endometrium (2).

  1. eMSC and their role during implantation

Endometrial stem cells play key roles in regulating endometrial regeneration and receptivity, essential step to support a successful implantation and placental development.

Implantation is a key step in a pregnancy, that requires a fine-tune communication between the maternal endometrium and the invading embryo.

To allow the establishment of a pregnancy, the endometrium has to be receptive thus endometrial cells undergo a transformation into decidual cells in response to elevated circulating progesterone concentration, through a process called decidualization (3).

It has been believed for a long time that the endometrium has a passive role during implantation allowing the “assault” of the invading embryo.
In fact, recent studies showed that the endometrium and its decidual cells have a much more proactive role by encapsulating the early embryo to determine its potential to develop and lead to a healthy pregnancy. In return, the decidual cells can adapt and support a slightly “weaker” embryo to allow implantation.

This novel notion of endometrium acting as a biosensor of embryo quality was first developed by a member of our team (4) and requires the transformation of endometrial stromal cells into decidual cells thus involving the eMSC (5).

An impairment of decidualization, with the dysregulation of some key factors, has been described in biopsies samples from patient suffering from reccurent pregnancy losses (RPL) (6).

  1. eMSC and their role in immunomodulation

Endometrial MSCs have anti-inflammatory and immunomodulatory properties (7).
In a proinflammatory environment, stem cells exposed to the inflammatory cytokine tumour necrosis factor-a (TNFα) and/or interferon-gamma (IFNγ) are activated to secrete anti-inflammatory factors (8).

They are able to synthesize mediators suppressing dendritic, T, B and NK cell activation including but not limited to IL-10, prostaglandin E2, IDO, TGFb, HLA-G (9) or IL-4 (10) thus leading to a decrease in IFNγ and TNFα production.
MSCs can also switch macrophages from an inflammatory M1 to a reparative M2 phenotype (7).
MSCs also promote the formation of regulatory T cells (Treg), which play key roles in inducing an anti-inflammatory macrophage phenotype (11). In addition, MSC can also inhibit natural killer cell proliferation (12).

Altogether, these data suggest that MSC may contribute to maternal immunotolerance and endometrial MSC’s disruption could potentially play a role in miscarriage.

  1. Focus on the study: the facts

Researchers at the University of Warwick studied 183 endometrial biopsy samples from RPL patients and subfertile patients with no history of RPL (control group).
They analyzed the methylome (methylation pattern) and transcriptome (gene expression levels) of endometrial cells, in addition to in vitro studies and found that:

- endometrial stromal cells from RPL women lack a specific epigenetic signature associated with pluripotent cells in other words these endometrial cells have lower stem cells as seen by a lower level of DNMT3A, a key marker of CpH methylation (feature of stem cells).

- endometrial stromal cells from RPL women have reduced levels of HMGB2, a marker of stem cell aging so basically these cells have more DNA-damage, which leads to MSC senescence.

- the depletion of endometrial stem cell correlates with the severity of RPL phenotype.

Altogether, the study shows that eMSC deficiency with premature senescence correlate with infertility status and could be involved in RPL but a direct cause for RPL is not demonstrated in the study.

3.Endometrial mesenchymal stem cell: potential target to treat pregnancy failure

a.Use of stem cells as a therapy in RPL patients

Mesenchymal stem cells are plastic, adherent cells, that could proliferate and differentiate in multilineage (they can give rise to multiple and different cell types).
We have seen that endometrial MSCs (MSC from endometrial origin) may play key roles in regulating endometrial receptivity by secreting several factors (13).
In obese women with higher first trimester losses when compared to overweight or lean control women, studies on endometrial biopsies showed a lower number of eMSC which can explain the higher risk of miscarriages in obese women as the endometrium does not have optimal capacity to remodel upon embryo implantation (14).
The use of stem cells in regenerative medicine to treat infertility disorders linked to endometrial dysfunction has already been trialed. In a patient with Asherman syndrome (very thin endometrial lining) who was not responsive to estrogen therapy, transplant from her own bone marrow-MSC (autologous) resulted in endometrial regeneration and a clinical pregnancy following IVF embryo transfer (15).
Small injuries have been shown to improve MSC engraftment (16). Because endometrial “scratch” increase IVF success rates (17), MSC transplant in combination to endometrial “scratch” may potentially improve endometrium regeneration and receptivity in RPL patients.

  1. eMSC: easy accessible and non-invasive source of stem cells

Bone marrow is a commonly used source of mesenchymal stem cells (MSCs) for cell-based therapies but it requires at least local anesthesia.

The endometrium has a very important regenerative capacity with over 500 menstrual cycles occurring during a women’s life, where the upper layer “functionalis” of its bilayer structure is shed during menses and is replenished from the basalis layer at the following cycle (18).

Endometrial MSC have been shown to be present on the functional layer of the endometrium, they may be isolated from endometrial biopsies or more easily from menstrual blood (19).

After cell culture and purification using specific antibody, eMSC have been isolated and display the same properties as bone-marrow MSC (20).

Very few clinical trial have been using eMSC. Allogenic intravenous eMSCadministration (eMSC obtained from another individual) has been used in patients with multiple sclerosis (21), Duchenne muscular dystrophy (22) or congestive heart failure (23). Despite showing beneficial effects with no long term side effects, no conclusions could have been made as the trials were case studies only, with no control groups. Several clinical trials are underway and should bring valuable insight in the use of eMSC in liver cirrhosis or type I diabetes.

In the reproductive field, the effect of eMSC on embryo implantation following embryo transfer is under evaluation (24). To determine if eMSC could improve implantation rate, eMSC are deposited into the uterine cavity just prior to embryo transfer during an IVF cycle compared to a control group (no cells). Secondary outcomes measured endometrial volume and vascularity by ultrasound. To date, no results were published.

4.Role of Neupogen (G-CSF) on MSC

G-CSF has long been used as a method to enrich stem cell in the blood stream (25).
In a review focusing on autologous transplant (self-transfer of stem cell), the only factor that had a significant impact on stem cells engraftment (when the transplanted cells start to grow and make healthy blood cells) was the use of G-CSF prior to collecting stem cells from either blood or marrow (26).

G-CSF seemed to increase the pace of MSC engraftment when MSC were mobilized after G-CSF treatment.

Several studies have suggested that bone marrow mesenchymal stem cells can give rise to endometrial cells including stroma, epithelial and endothelial cell type (27).

In patients receiving HLA-mismatch bone-marrow transplant (donor and recipient have different HLA haplotype), endometrial cells with the donor HLA “signature” were found in the recipient endometrium at a high level with 48% of epithelial cells and 50% of stromal cells of donor origin (28).
In another study, using the Y-chromosome as a marker of bone marrow-derived cells in the endometrium (as the donor was a male), recipient patient showed 10% of endometrial cells derived from the donor bone marrow stem cells (29).

Based on these facts, we propose that one of the multiple beneficial effects of G-CSF in women attempting to conceive could be mediated through the regeneration and thickening of the endometrium with G-CSF:

  • increasing MSC in the bone marrow
  • bone marrow stem cells can then migrate to and regenerate the endometrium, helping to support a pregnancy.

Many disorders have been treated with MSC transplant including but not limited to multiple sclerosis, systemic sclerosis, systemic lupus erythematosus or rheumatoid arthritis (RA) suggesting that MSC alterations could be involved in the development of autoimmune conditions.

In systemic sclerosis patients, early senescence of bone marrow MSC has been shown (30). In a similar way, MSCs from SLE patients have been described as defective with an abnormal morphology and early sign of senescence (31) and MSCs of RA patients show altered phenotype (32).

Because MSCs have well known immune-modulatory properties as well as immune-suppressive potentials, we believe that immune related pregnancy loss may be a consequence of low MSC levels which can be boost by G-CSF, therapy already in use in our practice.

Endometrial MSC deficiency as a cause of RPL may be one of many etiologies.
Although it requires further investigations and clinical trials, transplant of eMSC prior to conception after G-CSF infusion may be a valid and promising therapy to treat patients with reccurent implantation failure or recurrent pregnancy losses.
But you might be well aware that in most cases, RPL patients suffer from multiple dysregulations requiring a thorough workup to pinpoint the specific causes leading to these losses.
We, at Braverman Reproductive Immunology, keep analyzing the latest discoveries in the Reproduction field, to include new diagnosis and develop even more adapted therapy regimen to provide you with the best possible care.


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