A paracrine interaction between granulosa cells and leukocytes in the preovulatory follicle causes the increase in follicular G-CSF levels

Abstract

Objective Follicular granulocyte colony-stimulating factor (G-CSF) is a new biomarker of oocyte quality and embryo implantation in in vitro fertilization (IVF) cycles. Its role in reproduction is poorly understood. Our study aimed to investigate the mechanisms and cells responsible for G-CSF production in the preovulatory follicle. Design Laboratory research study. Setting Single-center study. Interventions Granulosa cells and leukocytes were isolated from the follicular fluids (FF) or the blood of women undergoing IVF and from the blood of a control group of women with spontaneous ovulatory cycles to perform cocultures. Main outcome measure G-CSF-secreted protein was quantified in the conditioned media of cocultures. Results G-CSF secretion was considerably increased in cocultures of granulosa cells and leukocytes. This effect was maximal when leukocytes were isolated from the blood of women in the late follicular phase of the menstrual cycle or from the FF of women undergoing IVF. The leukocyte population isolated from the FF samples of women undergoing IVF had a higher proportion of granulocytes than that isolated from the corresponding blood samples. Leukocytes induced the synthesis and secretion of G-CSF by granulosa cells. Among a range of other FF cytokines/chemokines, only growth-regulated oncogene alpha (GROα) was also increased. Conclusion The notable rise in G-CSF at the time of ovulation coincides with the accumulation of follicular granulocytes, which stimulate G-CSF production by granulosa cells via paracrine interactions. High follicular G-CSF concentrations may occur in follicles with optimal granulosa-leukocyte interactions, which could explain the increased implantation rate of embryos arising from these follicles.

Contribution of immunology to build precision medicine in reproduction: present and future

“…However, its function in reproduction is still poorly known. The significant increase in G-CSF during ovulation corresponds with the accumulation of follicular granulocytes, which stimulate G-CSF production by granulosa cells via paracrine interactions [66]. High follicular G-CSF concentrations may occur in follicles with good granulosa-leukocyte interactions, which could explain why embryos derived from these follicles have a higher implantation rate.…”

“…It also plays an important role in immunity and inflammatory responses. In recent research using an ultra-sensitive enzyme-linked immunosorbent assay (ELISA), particularly designed for the detection of follicular G-CSF, the chance of successful implantation was found to be 3.3 times greater for embryos produced from high-G-CSF follicles than for those derived from low-G-CSF follicles [66]. It's still unclear how follicular G-CSF contributes to both oocyte maturation and ovulation, and how it's produced and secreted locally are two key questions.…”

“…It might also interact with cells in the local microenvironment to induce cytokines and growth factors which are necessary for embryo development and implantation. Recently, high follicular G-CSF concentrations were correlated with the presence within the follicle of granulocytes emphasizing the importance of early granulosa-leukocyte interactions, which could explain the increased implantation rate of embryos arising from these follicles [66]. The clinical performance of an ultra-sensitive FF G-CSF immunoassay has been conducted to confirm the correlation between FF G-CSF concentration and live birth potential of the corresponding embryo after IVF.…”

A single‐cell gene expression atlas of human follicular aspirates: Identification of leukocyte subpopulations and their paracrine factors

“…In addition, a paracrine interaction between leukocytes and granulosa cells stimulated granulosa cell secretion of granulocyte-colony stimulating factor (G-CSF), known to induce neutrophil differentiation and activation. 18 Previous studies using animal models provided experimental evidence supporting the functional significance of leukocytes in the ovulatory process. [19][20][21][22] The perfusion of leukocytes into rat ovaries showed a threefold increase in the ovulation rate.…”

“…Leukocytes recruited to the ovulatory follicle are suggested to be involved in follicle wall rupture and angiogenesis during the periovulatory period 10 by producing and secreting tissue proteases, such as metalloproteinases (MMPs) 13–15 and vascular endothelial growth factor (VEGF), 16,17 respectively. In addition, a paracrine interaction between leukocytes and granulosa cells stimulated granulosa cell secretion of granulocyte‐colony stimulating factor (G‐CSF), known to induce neutrophil differentiation and activation 18 . Previous studies using animal models provided experimental evidence supporting the functional significance of leukocytes in the ovulatory process 19–22 .…”