Granulosa cell biomarkers to predict oocyte and embryo quality in assisted reproductive technology

With the development of human assisted reproductive technology (ART), an objective, accurate, and non-invasive method to assess the quality and viability of oocytes and embryos remains one of the most significant goals. Granulosa cells (GCs) play an essential role in oocyte development. GCs can differentiate into mural GCs (MGCs) and cumulus cells (CCs) under the influence of oocytes. MGCs promote the growth and development of follicles by secreting cytokines and steroid hormones. Simultaneously, CCs can form cumulus-oocyte complexes to communicate with oocytes through gap junctions and promote oocyte growth and maturation. Seeking suitable biomarkers in GCs provides a direction for the non-invasive assessment of oocyte and embryo abilities during ART procedures. To date, only a few studies have investigated potentially effective GC biomarkers during ART processes, such as the apoptosis of GCs, transcriptomic characteristics of GCs, quality and quantity of mitochondria in GCs, and telomere length of such cells. These are potential reference indices for screening high-quality oocytes and embryos. Independent studies on MGCs and CCs can provide more effective results. Although there is scope for optimization and improvement, the results have become increasingly accurate with the constant advances in technology. Due to the heterogeneity of the study population and technical limitations, clinical tests for GCs cannot be performed as part of routine tests, but their prospects are promising. This article reviews the biomarkers that have been studied in MGCs and CCs.