What Does MicroRNA Expression Say about Human Preimplantation Blastocysts: A Descriptive Analytical Study

Abstract

Embryo quality is critical in in vitro fertilization treatment, significantly influencing the pregnancy success. While preimplantation genetic testing offers a reliable assessment of embryonic chromosomal status, the investigations of the embryo’s molecular characteristics remain less implemented. MiRNAs, known for their post- transcription regulatory functions, have emerged as promising markers for genetic disruptions. These small non-coding RNAs found both inside and outside cells and typically exhibit altered profiles in disorders with genetic abnormalities. In this study, we utilised next-generation sequencing to explore the miRNA expression profile in 122 cryopreserved human blastocysts collected from CRGH, London. The comprehensive miRNA profiling revealed abundant and stable miRNAs expression in blastocysts, with a substantial increase in the levels of miRNAs encoded in key miRNA clusters, such as C19CM and miR-17/92. Functional analysis linked these miRNAs to crucial biological pathways, including protein modification, cell cycle progression, response to low oxygen levels, and apoptosis. A series of differential miRNAs expression analyses were conducted to identify potential associations between miRNA expression and embryo competence. The findings revealed consistent and significant dysregulation in the miRNA profile in blastocysts with various types of aneuploidies compared to euploid ones. Additionally, differences in miRNA levels were observed among blastocysts at different blastulation days (day5 versus day 6) and between those with varying TE morphology grades. The miRNA expression profile was also assessed in relation to parental factors known to influence implantation potential and pregnancy outcomes. The results indicated that advanced reproductive age, both maternal and paternal, high ovarian stimulation dosage and impaired sperm parameters are potentially associated with altered miRNA expression in the examined blastocysts. Notably, one miRNA, hsa- miR-184, was consistently upregulated across these investigations. The dysregulated miRNAs in these analyses were commonly involved in cell cycle dynamics, metabolic processes and signalling pathways. Understanding the molecular differences between good- and poor-quality embryos through miRNA expression could enhance our knowledge of the underlying causes of poor embryonic development and outcomes. Hypothetically, these miRNAs hold promise as biomarkers for evaluating the quality of preimplantation blastocysts, contributing to advancements in reproductive treatment.