Expression Profile of New Gene Markers and Signaling Pathways Involved in Immunological Processes in Human Cumulus-Oophorus Cells.

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.

Engulfment of spermatozoa by cumulus cells and the role of CD36.

The function of cumulus cells after sperm penetration is not well understood. The present study examined the phagocytic action of cumulus cells on sperm after dispersion of cumulus-oocyte complexes. In a co-incubation system of cauda sperm and cumulus cells, the sperm heads were beginning to vanish after 2.5h and 77%±1.34 of sperm heads had disappeared at 30 h. Most of the sperm heads were engulfed by cumulus cells. Immunofluorescent studies showed that cumulus cells were expressing the CD36 molecule, and sperm were exposing phosphatidylserine (PS). Anti-CD36 antibody and annexin V inhibited the engulfment of sperm by cumulus cells by 26.0% and 40.5%, respectively. These results suggested that the cumulus cells recognized the PS molecules on sperm via CD36 and this molecular interaction possibly triggered the phagocytosis of sperm by cumulus cells. These results suggest that cumulus cells might play a role in inhibiting undesired immune reactions induced by sperm antigens.

Immune-like mechanisms in ovulation.

Ovulation is the unique biological process by which a mature oocyte (egg) and surrounding somatic cells, the cumulus cell-oocyte complex (COC), are released from the surface of the ovary into the oviduct for transport and fertilization. Ovulation is similar to an inflammatory response: the follicles become hyperemic, produce prostaglandins and synthesize a hyaluronan-rich extracellular matrix. However, this view of ovulation might be too restrictive and needs to be broadened to encompass the innate immune cell surveillance-response system. This hypothesis is being proposed because ovarian granulosa cells and cumulus cells express and respond to innate immune cell-related surveillance proteins (Toll-like receptors 2 and 4) and cytokines, such as interleukin 6 (IL-6), during ovulation.