Review: Endothelial progenitor cells in pregnancy and obstetric pathologies

Fetal endothelial colony-forming cells: Possible targets for prevention of the fetal origins of adult diseases

Endothelial colony-forming cells (ECFCs), a subset of circulating and resident endothelial progenitor cells, are capable of self-renewal and de novo vessel formation, and are known key regulators of vascular integrity and homeostasis. Numerous studies have found that exposure to hostile environment during the fetal development exerts a profound influence on the level and function of ECFCs, which may be the underlying factor linking endothelial dysfunction to cardiovascular disease of the offspring in later life. Herein, we focus on the latest findings regarding the effects of pregnancy-related disorders on the frequency and function of fetal ECFCs. Subsequently, we discuss about placental ECFCs and put forward some details that should be paid attention to in the process of ECFC isolation and culture. Overall, the information presented in this review highlight the potential of ECFCs as a future biomarker or even therapeutic targets for the pregnancy-related adverse maternal and fetal outcomes.

Endothelial progenitor cells in pregnancy-related diseases

Placental neovascularization plays a crucial role in fetomaternal circulation throughout pregnancy and is dysregulated in several pregnancy-related diseases, including preeclampsia, gestational diabetes mellitus, and fetal growth restriction. Endothelial progenitor cells (EPCs) are a heterogeneous population of cells that differentiate into mature endothelial cells, which influence vascular homeostasis, neovascularization, and endothelial repair. Since their discovery in 1997 by Asahara et al., the role of EPCs in vascular biology has garnered a lot of interest. However, although pregnancy-related conditions are associated with changes in the number and function of EPCs, the reported findings are conflicting. This review discusses the discovery, isolation, and classification of EPCs and highlights discrepancies between current studies. Overviews of how various diseases affect the numbers and functions of EPCs, the role of EPCs as biomarkers of pregnancy disorders, and the potential therapeutic applications involving EPCs are also provided.

microRNA-646 inhibits angiogenesis of endothelial progenitor cells in pre-eclamptic pregnancy by targeting the VEGF-A/HIF-1α axis

Pre-eclampsia is a complication that occurs during pregnancy, the pathological feature of which is a change in vascular endothelial homeostasis. microRNA (miR)-646 is an anti-angiogenic miRNA that has been indicated to exhibit potential anti-angiogenic effects in endothelial cells cultured in vitro and in ischemia-induced angiogenesis. However, whether miR-646 has therapeutic potential in placental angiogenesis in pre-eclampsia remains to be determined. In the current study, human peripheral blood-derived endothelial progenitor cells (EPCs) were isolated to study the coordination between miR-646, vascular endothelial growth factor (VEGF)-A and hypoxia-inducible factor (HIF)-1α expression in preeclampsia EPCs. EPCs were isolated from human peripheral blood to demonstrate a potential interaction between miR-646 and targets (VEGF-A) in vitro. The number of EPCs and the expression of miR-646 in patients with preeclampsia was detected, and the effects of miR-646 on EPC function and preeclampsia angiogenesis was assessed. Clinical specimens demonstrated that miR-646 expression was enhanced in pregnancy with preeclampsia. The results indicated that miR-646 suppressed EPCs multiplication, differentiation and migration. miR-646 was observed to exert an anti-angiogenic function by suppressing the expression of angiogenic cytokines VEGF-A and HIF-1α. Additionally, luciferase results displayed that miR-646 downregulated VEGF-A expression by directly binding to a specific sequence in its 3'-untranslated region. The results of the current study demonstrated that the miR-646/VEGF-A/HIF-1α axis is significant for angiogenic properties of EPCs in vitro and in vivo placental vasculogenesis. The results of the present study provide a new insight into microRNA regulation of vessel homeostasis and angiogenesis, and a basis for alternative treatments for patients with pre-eclampsia.

Maternal endothelial function, circulating endothelial cells, and endothelial progenitor cells in pregnancies conceived with or without in vitro fertilization

In women who conceived with or without assisted reproduction, we evaluated endothelial function by EndoPAT [reactive hyperemia index (RHI)], circulating numbers of endothelial cells (CEC) and endothelial progenitor cells (EPC), and their function before during and after pregnancy. In vitro fertilization (IVF) pregnancies were stratified by method of conception and corpus luteum (CL) number-controlled ovarian stimulation (>1 CL) or programmed (0 CL) cycles and spontaneous singleton pregnancies (1 CL). We observed 1) comparable gestational decline of RHI in the three participant groups secondary to gestational rise of baseline preocclusion pulse-wave amplitude (PWA) incorporated into the RHI calculation by EndoPAT software; 2) progressive rise in "normalized" RHI throughout pregnancy (calculated by substituting prepregnancy baseline preocclusion PWA into the RHI equation), greater in spontaneous conception vs. IVF cohorts; 3) similar gestational increase of maximum PWA and time to maximum PWA after the ischemia stimulus among the three participant groups; 4) modest gestational increase of ischemia response (reactive hyperemia) in the spontaneous conception group and no change or significant decline, respectively, in women who conceived using programmed or controlled ovarian stimulation cycles; 5) enhanced basal nitric oxide production by early (primitive) outgrowth EPC during pregnancy in women who conceived spontaneously, but not through IVF; and 6) gestational increase in CEC in all three participant cohorts, more pronounced in women who conceived by IVF using programmed cycles. On balance, the evidence supported enhanced endothelial function during pregnancy in spontaneous conceptions but less so in IVF pregnancies using either controlled ovarian stimulation or programmed cycles.

Intravenous human endothelial progenitor cell administration into aged mice enhances embryo development and oocyte quality by reducing inflammation, endoplasmic reticulum stress and apoptosis

Stem cell therapy has been proposed to restore the function and structure of injured tissues. In the present study, we investigated the ability of human endothelial progenitor cells (hEPCs) to attenuate ovarian aging and dysfunction. Female ICR mice aged 4 and 6 months were injected with cultured hEPCs. Cultured hEPCs were injected intravenously twice with 5 × 104 cells with a 4 day interval. After pregnant mare serum gonadotropin and human chorionic gonadotropin stimulation, oocytes and ovaries of aged mice were collected, cumulus-free oocytes were activated by SrCl2 and gene expression levels related to inflammation, apoptosis, follicle development and endoplasmic reticulum (ER) stress in ovaries were compared. Administration of hEPCs attenuated the level of inflammatory cytokines and adverse apoptotic factor, as well as reducing ER stress in the ovaries. Increased cleavage and blastocyst formation rates and cell numbers in blastocysts from hEPCs-treated aged mice vs. same aged control mice demonstrated a protective function of hEPCs against reproductive aging. Based on these data, we suggest that treatment with hEPCs attenuates reproductive aging and dysfunction potentially via regulation of inflammation, apoptosis and ER stress.

Reduction of maternal circulating endothelial progenitor cells in human pregnancies with intrauterine growth restriction

INTRODUCTION

Circulating endothelial progenitor cells (EPCs) may play a crucial role during pregnancy by sustaining adequate placentation and fetal growth. Unambiguous demonstration of EPC increase during pregnancy has been hampered so far by lack of standardized methods for EPC quantification. In this study we used the currently most accepted phenotype for EPC detection for investigating whether maternal circulating EPCs might increase during normal pregnancy and whether they may fail to increase in pregnancy complicated by idiopathic intrauterine growth restriction (IUGR), a leading cause of perinatal mortality and morbidity characterized by insufficient placental perfusion.

METHODS

Twenty-one non-pregnant women, 44 women during healthy pregnancy progression (9, 13 and 22 women in the first, second and third trimester, respectively) and 11 with pregnancy complicated by idiopathic IUGR were recruited in a cross-sectional study. EPCs in maternal blood were identified as CD45(dim)/CD34+ / KDR+ cells by flow cytometry. Plasmatic cytokines were measured by ELISA.

RESULTS

We observed a significant and progressive increase of EPCs in normal pregnancy, yet detectable in early pregnancy but even more pronounced in the third trimester. The increase of EPCs was impaired in IUGR-complicated pregnancies at comparable gestational age. The circulating levels of placental growth-factor and stromal-derived-factor-1 were significantly lower in IUGR than normal pregnancies, possibly contributing to EPC impairment.

CONCLUSIONS

EPC count in maternal circulation may have a great potential as a novel biomarker for pregnancy monitoring and may represent the target of novel therapeutic strategies designed to prevent adverse pregnancy outcomes often occurring in IUGR.