Abstract
The function of the immune system extends from defense against external pathogens to the recognition and elimination of mutated or dying cells, aiding elimination of malignant potential and/or maintaining homeostasis. The many cell types of the immune system secrete a broad range of factors to enable cellular signaling that is vital to physiological processes. Additionally, in the ovary, follicular selection and maturation, as well as ovulation, are directly regulated by the nearby immune cells. Additionally, ovulation and rupture of the follicle have been observed to resemble a local inflammatory response. Cells of the cumulus–oocyte complex (COC) show evolving gene expression profiles throughout the oocytes’ lifespan, including genes associated with immunological processes. Analysis of these genes allows the identification of useful molecular markers, as well as highlighting gene functions and interactions in these cells. Cumulus cells were obtained from hormonally stimulated patients undergoing an in vitro fertilization procedure and studied under long-term culture conditions. The microarray technique made it possible to compare the level of CCs’ gene expression on the 1st, 7th, 15th and 30th day of cultivation. Additionally, RNA microarray analysis was performed to map gene expression in these cells, associated with immunological processes and associated cytokine signaling. Subsequently, the use of DAVID software allowed us to identify the “defense response to other organism”, “defense response”, “defense response to virus”, “cytokine secretion”, “cytokine production” and “cytokine-mediated signaling pathway” GO BP terms, as well as allowing further analysis of the most differentially expressed genes associated with these processes. Of the 122 genes involved, 121 were upregulated and only one was downregulated. The seven most upregulated genes related to the abovementioned terms were ANXA3, IFIT1, HLA-DPA1, MX1, KRT8, HLA-DRA and KRT18. Therefore, genes involved in immunological defense processes are upregulated in CC cultures and could serve as useful molecular markers of growth and development in the COC, as well as the proliferation of granulosa and cumulus cells.
Highlights
At the pre-antral to antral follicle transition, granulosa cells surrounding the oocyte differentiate into mural cells and cumulus cells (CCs), which are physically separated by the formation of the antrum
The Human Genome U219 Array Strip was used for the microarray gene expression analysis of human cumulus-oophorus cells (CCs), allowing for the study of gene expression of 22,480 transcripts at 1, 7, 15 and 30 days of in vitro culture
The list of differentially expressed genes (DEGs) was uploaded to the DAVID software platform, which allowed us to assign the genes to 775 GO BP, 33 GO MF and 125 GO CC gene ontology terms
Summary
At the pre-antral to antral follicle transition, granulosa cells surrounding the oocyte differentiate into mural cells and cumulus cells (CCs), which are physically separated by the formation of the antrum. Successful ovulation and the development of a competent oocyte are dependent on support by the surrounding CCs, which play a role in the metabolism of pyruvate and glucose in the oocyte and continue to proliferate during cumulus expansion, a process occurring just before ovulation [1]. Similar to the oocyte, which releases growth factors influencing the activity in neighboring cumulus cells, the CCs themselves produce cytokines and factors released during ovulation. Bi-directional signaling between CCs and the oocyte in the COC is vital and takes place both through gap junctions (GJs) and paracrine factors. By arresting meiosis in the oocyte, CCs have an important influence on the development and viability of the oocyte [2,3]
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