Proteomic Approaches to Unravel the Molecular Dynamics of Early Pregnancy in Farm Animals: An In-Depth Review

Predictive potential of combined secretomics and image-based morphometry as a non-invasive method for selecting implanting embryos

BACKGROUND

Non-invasive selection of human embryos for in vitro fertilization purposes is still a major challenge to pursue. Therefore, this study aims to identify non-invasive morphometric and secretomic parameters that reliably select the embryos with the highest likelihood of implantation prior to embryo transfer (ET).

METHODS

Prospective single-centre cohort study. Thirty-two day 5 blastocysts derived from 28 couples undergoing intracytoplasmic sperm injection (ICSI) and ET between January 2023 and April 2023. Patients were split according to their implantation outcome, confirmed with serum beta-human chorionic gonadotropin (b-hCG) levels > 5 mIU/mL nine days post-SET. Ninety-two proteins involved in embryonic developmental programming were measured in spent blastocyst media (SBM) using a protein extension assay. Sparse PLS-DA (sPLS-DA) was used for principal component analysis. Forty-seven morphometric parameters related to the trophoblast, inner cell mass and blastocele dimension were evaluated in microphotographs of day 5 embryos with ImageJ software. T-test and Mann-Whitney tests were respectively used to compare morphometric measurements and normalized expression of secreted protein (NPx) levels between embryos that implanted or not. Predictive value of models of implantation based on embryo morphometric parameters and secreted proteins.

RESULTS

Chi-squared tests showed no significant differences in transferred blastocyst stage, quality, and state between subgroups. Implanting blastocysts (n = 14) presented significantly different morphometric shape descriptors (i.e., internal circularity, internal roundness, internal axis ratio, internal angle and trophoblast mean width) than non-implanting blastocysts (n = 13). Among the quantifiable proteins (86/92) in SBM from eleven implanting and nine non-implanting blastocysts, NPx and sPLS-DA analysis revealed three differentially expressed proteins. Matrilin-2 (MATN2) and legumain (LGMN) were significantly elevated (p < 0.01 in both cases) while thymosin beta-10 (TMSB10) was significantly decreased (p < 0.05) in implanting embryos. Predictive models based exclusively on morphometric or secreted protein profiles accurately discriminated implantation outcomes (AUC > 0.71). The model integrating the blastocysts' internal circularity, internal roundness, internal axis ratio and the NPx of MATN2 and TMSB10 in SBM had exceptional negative and positive predictive power for implantation outcomes (100% and 90.91%, respectively; AUC = 0.93).

CONCLUSIONS

Morphometric shape descriptors and NPx levels of MATN2 and TMSB10 in SBM emerge as promising candidate markers for non-invasive embryo selection.

Preimplantation trophectoderm: A 'quick-fix' protector for embryo survival?

The trophectoderm (TE) epithelium forms the outer layer of the mammalian blastocyst and generates the blastocoel through vectorial transport. Its differentiation during cleavage, studied mainly in mouse, is integrated with blastocyst morphogenesis with key roles for cell polarisation, asymmetric cell divisions, cell signalling, regulatory transcription factors and cellular inheritance. The TE provides a physical and cellular protection to the emerging lineages of the embryo essential for the integrity of blastocyst development. Here, two examples of TE differentiation are considered in some detail where this immediate protective function for embryo survival is assessed: (i) cellular processes from TE at the polar-mural junctional zone in the early blastocyst that later form filopodia traversing the blastocoel, and (ii) the endocytic system which matures and polarises during differentiation. Understanding the broad role for TE in regulating early morphogenesis and environmental protection of the embryo, including these two examples, have clinical as well as biological relevance.

Simple method for isolation and culture of primary buffalo (Bubalus bubalis) endometrial epithelial cells (pBuEECs) and its characterization using high throughput proteomics approach

Early embryonic mortality resulting from insufficient interaction between the embryo and the uterus leads to the failure of pregnancy in livestock animals. Thus, it is imperative to comprehend the multifaceted process of implantation at molecular levels, which requires synchronized feto-maternal interaction. The in-vitro models serve as valuable tools to investigate the specific stages of implantation. The present study was undertaken to develop a simple method to isolate and culture the primary buffalo endometrial epithelial cells (pBuEECs), followed by proteome profiling of the proliferating cells. Collagenase I was used to separate uterine epithelial cells (UECs) from the ipsilateral uterine horn, and then the cells were separated using a cell strainer. After being seeded on culture plates, UECs developed colonies with characteristic epithelial shape and expressed important markers such as cytokeratin 18 (KRT18), progesterone receptor (PGR), β-estrogen receptor (ESR1), and leukemia inhibitory factor (LIF), which were confirmed by PCR. The purity of epithelial cells was assessed using cytokeratin 18 immunostaining, which indicated approximately 99% purity in cultured cells. The proteome profiling of pBuEECs via high-throughput tandem mass spectrometry (MS), identified a total of 3383 proteins. Bioinformatics analysis revealed enrichment in various biological processes, including cellular processes, metabolic processes, biological regulation, localization, signaling, and developmental processes. Moreover, the KEGG pathway analysis highlighted associations with the ribosome, proteosome, oxidative phosphorylation, spliceosome, and cytoskeleton regulation pathways. In conclusion, these well characterized cells offer valuable in-vitro model to enhance the understanding of implantation and uterine pathophysiology in livestock animals, particularly buffaloes.