Polycystic ovary syndrome (PCOS) is a common endocrine disorder in women, and characterized by chronic inflammation and oxidative stress [19]. It has been reported that CD24 regulates a variety of immune cells and plays an important role in autoimmune diseases, inflammatory diseases and cancer. However, few studies have investigated the role of correlation between CD24 expression and clinical outcomes of PCOS patients treated by IVF.
In the present study, the results of RT-PCR and Immunohistochemistry staining revealed significant upregulation in CD24 expressions at both the mRNA and protein levels in the cumulus granulosa cells between the PCOS and control groups. Wissing et al [13] first reported obvious upregulation of CD24 expression in GCs after human chorionic gonadotropin (hCG) administration, which he defined as an ovulation-regulated gene. Dong, Jun-Peng et al [15] revealed remarkably lower CD24 protein expression in GCs from early growing follicles of mice, compared to antral follicles and the corpus luteum, suggesting that the expression of CD24 transcripts in GCs may be ovulation-dependent. Subsequently, they confirmed that the CD24-EGFR-ERK1/2 signalling pathway is involved in the hCG-induced upregulation of prostaglandin synthase and prostaglandin transporter expression in GCs. An animal experiment showed that suppressing EGFR levels by treating PCOS mice with EGFR inhibitor promoted a huge improvement in the ovulatory function and sex hormone levels, including the oestrus cycle, LH/FSH ratio, testosterone levels, morphology of the ovary and probability of ovulation. Then it demonstrated that EGF/EGFR signaling affected the proliferation of cumulus granulosa cells, oocyte maturation and meiosis, and played a potential role in the pathogenesis of PCOS [20]. Based on the above results, it can be speculated that the high expression of CD24 in GCs of PCOS patients may be related to abnormal oocyte development and ovulation disorder, but the specific mechanism needs to be further investigated.
Then we found that CD24 mRNA expression in GCs was positively correlated with serum AMH and BMI of infertile patients. Anti-Müllerian hormone (AMH) was shown to be synthesized by ovary in the 1980s. AMH concentrations are 2 to 4 folds higher in both the serum and the follicular fluid of women with PCOS [21, 22]. The high serum AMH level observed in women with PCOS might be due to both the increased number of antral follicles and their GCs [23, 24]. Moreover, serum AMH has been established as a reliable marker of ovarian reserve, the prediction of POI and PCOS, and the evidence strongly points to the involvement in the pathogenesis of PCOS [25, 26]. CD24 mRNA expression in GCs positively correlated with serum AMH levels, further suggesting that granulosa cell CD24 may be associated with ovulation disorders and follicular development abnormalities in PCOS. CD24 has been shown to be a marker of preadipocytes and its expression is lost in mature adipose tissue, recent studies have found that dynamic upregulation of CD24 is necessary for mature adipocyte development [27, 28]. In this study, there was a significant positive correlation between CD24 mRNA expression and BMI index (r = 0. 646, p = 0. 005), further suggesting that CD24 may be involved in pathophysiological processes such as adiposity, insulin resistance, and abnormal metabolism in PCOS patients [29, 30].
Due to changes in the follicular microenvironment and granulosa cell dysfunction, PCOS patients are often associated with ovulation disorders and reduced oocyte maturation [31]. Consistent with the reports [32], our study found that there were no significant differences in 2PN formation rate, transferable embryo rate, cleaved embryo rate, number of good quality embryos and good quality embryo rate between the PCOS group and control group (p > 0.05). In addition, Results showed that there was a significant positive correlation between CD24 expression in GCs and oocytes retrieved, 2PN, transferable embryos, high-quality embryos and cleaved embryos. Therefore, we conclude that CD24 is associated with the laboratory outcome, and we speculate that CD24 may be involved in regulating oocyte maturation and embryo development.
Though the clinical pregnancy rate did not reach a statistically significant difference between the two groups, we discovered that the CD24 mRNA expression of GCs was remarkably higher in pregnant people than in non-pregnant (p < 0.05). Furthermore, multiple linear regression analysis indicated that larger sample size is needed to draw firm conclusions regarding the possible predictive effect of CD24 mRNA expression in relation to the clinical pregnancy rate.
Our study has the limitations as a single center project with smaller sample size. We also need further experiments to prove the correlation among CD24 and other indicators such as ID4, PTGES, PTGS2, AKR1C1, SLCO2A1, ABCC4, SFRP4, IRS1, and IGFBP5, and their predictive value in PCOS by assisted reproductive therapy.