Stem cells’ therapeutic potential in treating Preeclampsia

Preeclampsia (PE) is a hypertensive disorder in pregnancy and the leading cause of death and disability, for both mothers and babies. With the greatest morbidity and mortality, PE affects 5% to 7% of all pregnant women but is responsible for over 70 000 maternal deaths and 500 000 fetal deaths worldwide every year. The occurrence of PE is seven times higher in developing countries compared to developed countries and can range between 1.8% and 16.7% in developing countries (1).

Despite this, the only cure at present is to deliver the placenta and the baby. The potential for long-term complications however remains after delivery.

It is a multifaceted disease of which the pathogenesis is not well understood. The main pathogenic processes that are implicated in PE development are a maternal immune response, oxidative stress, and inflammatory processes that lead to endothelial dysfunction. A review of clinical features, diagnosis, and differential diagnosis in PE was published in January 2023 which highlights mostly all the factors involved in PE pathogenesis.

An efficient prognostic test for preeclampsia would enable early diagnosis, directed observations, and timely delivery; however, currently these options are restricted. In the last 2 years first-trimester screening algorithm was published after development and validation to predict preterm preeclampsia, with poor utility for term disease, where the greatest burden lies. Biomarkers such as sFlt-1 and placental growth factor are also currently being used clinically in cases of presumed preterm preeclampsia; their elevated negative predictive value facilitates confident exclusion of disease in women with normal results, but the sensitivity is modest. There has been a collaborative attempt to detect possible novel biomarkers that might increase predictive value. These largely originate from organs involved in preeclampsia’s pathogenesis, including placental, cardiovascular, and urinary biomarkers. A review of these biomarkers was published in December 2021 (2).

These two above-mentioned reviews highlight the research in PE over the past decades and with this summary, we wish to highlight novel findings related to stem cells and possible therapeutic applications that have emerged over the past 2 years.

Fetal microchimerism (FMc) in PE

After almost forty years of study, the biological role of fetal microchimerism (FMc) remains enigmatic. Transmission of fetal cells to the mother begins soon after implantation and increases with gestational age. Feto-maternal microchimerism (FMM) on the other hand, involves bidirectional cross-placental trafficking during pregnancy, leading to a microchimeric state that can persist for years. In this way, a pregnant woman will harbour cells from her mother, as well as cells from her child.

Fetal microchimerism (FMc) is present as undifferentiated or differentiated cells throughout the maternal tissues. FMc has been linked to autoimmune tolerance and tissue repair but also with autoimmune diseases and cancer, creating the probability that they exercise numerous and opposing effects in a mother’s body. Evidence indicates that different pregnancy and birth complications, caesarean sections, antepartum hemorrhages, and PE, might alter the functional fate of FMc.

Figure 1:  Fetal cells (pink circles) traffic into and set up in the maternal organism (FMc). Maternal cells (purple circles) also traffic into and remain in the fetal body (MMc).

Bi-directional cell trafficking between mother and fetus is also modified in PE and has been proposed to contribute to the underlying aetiology. The fundamental mechanism whereby the host immune system is controlled is uncertain, but seems to entail HLA class II molecules, Couples that have a high level of HLA class II compatibility have a higher risk of PE. Since pregnant women with PE exhibit significantly lower levels of maternally-derived micro-chimerism, the question arises whether preeclampsia and post-partum development of autoimmune conditions occur due to the failure of the grandmothers’ cells to sufficiently regulate an unsuitable micro-chimeric pattern.

Current evidence indicates that FMc within the maternal peripheral blood mononuclear cell (PBMC) compartment, which is characterised by incomplete clearance, immune competence, and pluripotency, may underpin the maternal immune dysfunction seen in PE and may lead to long-term persistence after PE pregnancy. This FMc within the maternal circulation can permanently persist decades after pregnancy and is known to arise at greater frequency in PE, which can potentially affect local and systemic immune programming.

Figure 2. Representation of the different organs where FMc have been localized in humans and the diseases associated. (Blanca Cómitre-Mariano, et al. Feto-maternal microchimerism: Memories from pregnancy, iScience, Volume 25, Issue 1, 2022)

In a recent study conducted by a group at the Department of Obstetrics and Gynaecology, University of Washington, they found a significant increase in FMc concentration in immune cell subsets in PE cases compared to controls, primarily in B cell, and NK cell lymphocyte populations. There was no substantial difference in FMc frequency or concentration within the stem cell population between PE and controls (3).

Regarding the role of natural killer cells (NKCs) in pregnancy. NKCs are among the most abundant immune cells in the uterus during the first trimester of pregnancy, but their numbers decrease substantially after the placenta forms. A new study, by scientists in China, discovered that a specific subset of NKCs in the human uterine lining secretes growth-promoting factors called pleiotrophin and osteoglycin, which participate in extensive developmental processes. This subset of cells made up a smaller proportion of natural killer cells in the uterine lining of patients who experienced recurrent spontaneous abortion (42%) compared to healthy females (81%). These results suggest that inadequate secretion of growth-promoting factors by a particular subset of natural killer cells may be responsible for restricted fetal development in humans. The researchers identified a specific subset of uterine natural killer cells that secrete growth-promoting factors in humans and mice, and further demonstrated that transfer of these cells can reverse impaired fetal growth in pregnant mice (4).

Mesenchymal stem cells (MSCs) in PE

Mesenchymal stem cells (MSCs) have earned increasing attention due to their easy cultivation, low immunogenicity and expansion in vitro.  MSCs are the most extensively studied stem cells currently being investigated for treatment of many diseases.

MSCs act as injury sensors and are recruited to the injury site in reaction to stress signals (inflammation, hypoxia, and the like) and then engage in tissue repair. Besides this, MSCs react to growth signals and take part in programmed tissue development, MSCs replace injured tissue by both differentiating into tissue cells directly and secreting trophic cytokines to promote the proliferation of tissue cells indirectly. Likewise, inflammatory signals can also encourage MSCs to develop an immunosuppressive phenotype thus inhibiting inflammation/immune triggering in injured tissue. MSCs-assisted angiogenesis facilitates damaged tissue to restore the vascular system and regain blood supply. More intriguingly, MSCs express low levels of HLA Class I and II and high levels of HLA-G, therefore, MSCs show relative low immunogenicity after allotransplantation. Paracrine nutrition, anti-inflammation/immune-modulation, multi-differentiation, damage sensing and low immunogenicity characteristics have made MSCs transplantation a potent therapy in tissue repair and systematic inflammation/immune disorders.

In recent years, MSCs or their secreted cargo (exosomes) have been studied in various animal models of PE and showed encouraging result, which inspired further investigations into the therapeutic effects and mechanisms of MSC-based therapies in PE. 

Figure 3. In situ and bone marrow recruited MSCs to participate in endometrium/decidual and placenta development by direct differentiating into endothelial, vascular smooth muscle cells, and stromal cells to form vascular and stromal tissue de novo and promote the proliferation of preexisting vascular cells and the stromal cells to build the vascular network and stromal in tissue. Progesterone/cAMP induces decidual stromal cell (DSCs) like changes in MSCs and expresses high levels of receptive markers which may promote blastocyte adhesion, implantation, and fetal antigen tolerance. MSCs secret multiple cytokines to promote proliferation and invasion of trophoblast (TB) which may foster villous expansion and maternal spinal arterial remodeling. (S Jin. Et al. The pathological and therapeutic roles of mesenchymal stem cells in preeclampsia. Front. Med., 28 July 2022.Volume 9 – 2022 | https://doi.org/10.3389/fmed.2022.923334)

Remodelling of the uterine vasculature in PE

In the past few decades researchers have investigated the role of remodelling of the uterine vasculature as one of the underlying mechanisms of PE, intrauterine growth restrictions and preterm births. It is well known that the remodelling of the uterine vasculature by invasive extravillous trophoblasts (EVTs) is a vital part of human placentation. This remodelling involves alterations in the arterial system from a high-pressure low flow system to a low-pressure high flow system. These changes results in significant structural and functional changes in large and small arteries and veins in the arterial walls. Insufficient EVT penetration can lead to severe obstetrical complications like PE, intrauterine growth restriction, and preterm birth.

A specific transcription factor has been extensively studied in this remodelling process, Glial cells missing-1 (GCM1) is crucial for proper placentation in mice and is highly expressed in human syncytiotrophoblast (ST) and EVTs. GCM1 is classically believed as a master regulator of ST formation, but little is known about its involvement in the growth and function of EVTs. Researchers have shown that GCM1 is highly expressed in human trophoblast stem (TS) cells differentiated into either ST or EVTs. RNA sequencing analysis of GCM1-deficient TS cells revealed downregulation of EVT-associated genes and enrichment in transcripts related to WNT signalling, which was linked to decreased expression of the EVT master regulator ASCL2 and the WNT antagonist NOTUM. Therefore, this research highlighted an essential role of GCM1 during ST and EVT development and suggest that GCM1 regulates differentiation of human TS cells into EVTs by inducing expression of ASCL2 and NOTUM (5).

The same research group further identified a mitochondrial creatine kinase 1 (CKMT1) as a key GCM1 target crucial for syncytiotrophoblast differentiation and reveal decreased CKMT1 expression in PE.

They found that the induction efficiency of cytotrophoblast is determined by functional antagonism of the placental transcription factor GCM1 and the stemness regulator ΔNp63α. ΔNp63α reduces GCM1 transcriptional activity, whereas GCM1 inhibits ΔNp63α oligomerization and autoregulation. EGF/CASVY cocktail activated ΔNp63α, thereby partially inhibiting GCM1 activity and reverting term cytotrophoblasts into stem cells (6). By applying hypoxia condition, they reduced GCM1 activity and successfully induce term cytotrophoblasts into TS cells. They found that trophoblast stem (TS) term cells can easily be established from every individual’s placenta and propagated for lifetime storage as an abundant source of stem cells, which may offer enormous potential for autologous cell therapy.

Exosomes in PE

It is well known that poor placentation secretes exosomes as well as anti-angiogenic factors that results in increased immune responsiveness, proinflammatory cytokines and anti-angiogenic factors. On the other hand, anti-inflammatory cytokines and pro-angiogenic factors are decreased. Preeclampsia (PE)-specific exosomes derived from damaged trophoblasts are secreted and may transport RNA, DNA, and proteins to distant maternal organs, causing multiple-organ failure, especially due to endothelial dysfunction. Evidence suggests that the pathogenesis of PE may be ameliorated by the immunosuppressive and anti-inflammatory effects of mesenchymal stem cell (MSC)-derived exosomes (7).

Another group investigating during transfection experiments the role of human umbilical cord mesenchymal stem cell (hucMSC)-derived exosomes in PE, by using these exosomes transmitting microRNA-342-5p (miR-342-5p) by targeting programmed cell death 4 (PDCD4). They concluded in their study that the HucMSC-Exo carrying elevated miR-342-5p prevents the development of PE in a rat model through downregulating of the gene PDCD4. This study illustrates the way that ex vivo manipulation of these exosomes could aid in developing therapeutic strategies for PE in future (8).

Therefore, exosomes may be involved in the pathogenesis of PE and have great potential for the treatment of this disease. PE pathogenesis could be improved or prevented by inhibiting exosome effects or preventing their binding to target organs. By first examining the effects of exosomes released from the preeclamptic placenta on various organs by searching for proteins, RNA, and DNA in the exosomes. Exosomes could be used as markers to predict the onset of PE and to follow the course of this disease. In 2012 Marleau, suggested that the anticancer effects of molecular targeted drugs could be enhanced by removing exosomes from the circulating blood via hemodialysis. This approach may also be used to treat PE via the removal of STB EVs. The use of various exosome-based methods may aid the identification of the best solution for PE prevention and treatment (9).

Conclusion

Preeclampsia remains one of the most serious pregnancy complications with a substantial vestige of both maternal and perinatal morbidity. Early detection improves outcomes, yet at present there is no reliable screening test to predict its development – especially at term gestations where the greatest burden of disease exists.

Many potential biomarkers have been discovered through investigative studies using samples from well-known disease. These studies have produced hypotheses for potential biomarkers, with less focus on prediction. It is possible that combining biomarkers derived from multiple organ and cellular sources may yield the best predictive performance. Utilising large prospective cohort collections in unselected populations provides the best avenue for discovering novel biomarkers, but these markers – or combinations – must be rigorously validated in external cohorts to ensure they achieve their potential to improve outcomes for pregnant mothers and their babies. Thus the development of multiple biomarkers with exact test outcomes will offer a multi- dimensional focus to complete the antenatal and postnatal care of PE. The main intent hereof is to provide rapid bedside prediction of women with suspected PE. Numerous biochemical factors in combination with superior therapeutic methodologies, which have been shown to be valuable and expandable into widespread clinical practice, will be incorporated into the management standard of patients with suspected or confirmed PE over the coming years. Currently there is no therapy to reverse the process once started and although various stem cell therapeutic approaches have shown improved outcomes in PE, these treatments are still in the investigative phase and not yet approved. However, these stem cell therapies might prove invaluable in future by virtue of their mode of action, whereby they act as sensors and are recruited to the site of injury in reaction to stress signals, thus effecting their “healing” principles at the exact sites of inflammation, hypoxia, and the like, in accordance with the multifactorial mode of pathogenesis of PE.

References

• https://www.ncbi.nlm.nih.gov/books/NBK570611/#:~:text=PE%20is%20a%20hypertensive%20disorder,%25%20in%20high%2Dincome%20countries.
• https://doi.org/10.1016/j.ebiom.2021.103780;https://www.uptodate.com/contents/preeclampsia-clinical-features-and-diagnosis.
• McCartney SA, Kolarova T, Kanaan SB, Chae A, Laughney CI, Nelson JL, Gammill HS, Shree R. Increased fetal microchimerism in immune and stem cell subsets in PE. Am J Reprod Immunol. 2023 Mar;89(3):e13666. doi: 10.1111/aji.13666. Epub 2022 Dec 16. PMID: 36482289.
• Binqing Fu, Yonggang Zhou, Xiang Ni, Xianhong Tong, Xiuxiu Xu, Zhongjun Dong, Rui Sun, Zhigang Tian, Haiming Wei. Natural Killer Cells Promote Fetal Development through the Secretion of Growth-Promoting Factors. Immunity, 2017; 47 (6): 1100 DOI: 10.1016/j.immuni.2017.11.018.
• Wang, LJ., Chen, CP., Lee, YS. et al. Functional antagonism between ΔNp63α and GCM1 regulates human trophoblast stemness and differentiation. Nat Commun 13, 1626 (2022).
• Wang, LJ., Chen, CP., Lee, YS. et al. Functional antagonism between ΔNp63α and GCM1 regulates human trophoblast stemness and differentiation. Nat Commun 13, 1626 (2022).
• (Matsubara K, Matsubara Y, Uchikura Y, Sugiyama T. Pathophysiology of Preeclampsia: The Role of Exosomes. Int J Mol Sci. 2021 Mar 4;22(5):2572. doi: 10.3390/ijms22052572. PMID: 33806480; PMCID: PMC7961527.
• Yi Chen et al. Exosomal microRNA-342-5p from human umbilical cord mesenchymal stem cells inhibits PE in rats. Front Physiol 2022 Oct 14;13:1037597.
• Marleau A.M., Chen C.S., Joyce J.A., Tullis R.H. Exosome removal as a therapeutic adjuvant in cancer. J. Transl. Med. 2012;10:134. doi: 10.1186/1479-5876-10-134.