P-540 Improper placentation due to skewed Oct4-Cdx2 expression may be a leading factor in idiopathic recurrent pregnancy loss (RPL) cases from Assam, India.
Authors: Begum A , Kashyap N , Das C R , Datta R , Buzarbaruah S M , Bose P D , Bose S 
Published: June 2023

Abstract

Study question
Does the differential expression of key embryonic stem cell (ESC) markers due to upstream signaling cascade(s) deregulation influence RPL pathogenesis in the studied population?

Summary answer
Imbalanced Oct4-Cdx2 expression linked differential ESCs polarization due to β-catenin signaling deregulation during the peri-implantation period impacts RPL pathogenesis in the studied population.

What is known already
RPL affects approximately 2-5% of women globally and around 7% Indian women in reproductive age group; with 50% of case etiology being unclear. Proper placentation is indispensable for establishment, continuation, and success of a pregnancy; and it depends largely on a healthy balance between apoptosis and stem cell differentiation that aids proper trophoblast invasion. These differentiation events are tightly controlled by the interplay of oxygen tension, hormones, growth factors, other signaling molecules and most importantly by transcription factors including those deciding the stem cell lineage like Oct4, NANOG, and Cdx2, wherein, β-catenin is known to enhance Oct-4 activity in ESCs.

Study design, size, duration
The sample size was predicted using Raosoft software utilizing the prevalence rate of RPL. Overall 87 women with 2 or more pregnancy losses before completion of 20 weeks of gestation were enrolled as RPL cases with informed consent, whereas, for the control group, 107 women volunteers undergoing medical termination of pregnancy (MTP) were enrolled as gestation-week-matched comparative study group for experimental data analysis.

Participants/materials, setting, methods
Products of conception (POC) was collected from the MTP and RPL cases. POCs were collected in 2vials for every subject: (i) 4% buffered formalin for fixation and preparation of microscopic slides for immunofluorescence (IF) based protein expression of Oct4 and Cdx2; (ii) RNA later solution for site specific transcriptional analysis of Oct4, NANOG, Cdx2, and β-catenin utilizing Realtime PCR. The difference in expression was analyzed using SPSS statistical software.

Main results and the role of chance
IF based site specific protein expression data confirmed higher expression of OCT4 in RPL cases compared to MTP controls, whereas CDX2 expression was found to be low in RPL compared to MTP subjects. The Realtime PCR amplification of cDNA using β-actin as internal normalization control for Oct4 (25.76 ± 10.17 folds) and NANOG (18.32 ± 6.67folds) showed increased expression whereas the Cdx2 expression was downregulated (0.487 ± 0.186 folds) in RPL cases compared to MTP controls, indicating a shift towards pluripotency which is a non-favorable environment for the ongoing pregnancy since cell polarization for initiation of differentiation to different cell lineages is required at that time of gestation. The cdx2 and oct4 expression correlated inversely and significantly {Pearson’s correlation= −0.838, p = 0.009; Spearman’s rho= −0.786; p = 0.016}. The realtime PCR amplification of β-catenin, the key molecule involved in direct enhancing of Oct4 expression during gestation was found to be increased in RPL cases compared to MTP controls. Statistically, the β-catenin-Oct4 expression correlated positively significantly.

Limitations, reasons for caution
Being a patient based study, the present study is limited to being an associative study only; and therefore secondary validation of the data for causal association using cell lines or suitable model system futuristically may add valuable scientific inputs and aid clinical intervention modalities for controlling RPL.

Wider implications of the findings
As the majority of RPL pathogenesis etiology is undefined limiting the possibilities of clinical interventions therefore we presume the present data can layout possible therapeutic interventions by regulating key regulators influencing skewed ESC profile aiding proper placentation leading to successful pregnancy in a subpopulation of cases with RPL history.

Trial registration number
Not applicable