IL-1β is associated with decreased expression of GREM1 in obese women undergoing in vitro fertilization with intracytoplasmic sperm injection (IVF-ICSI)

Abstract

To investigate obesity associated inflammatory factors in follicular fluid that may affect gene expression in cumulus cells of women undergoing IVF-ICSI. Prospective cohort study. Follicular fluid and cumulus cells were collected during oocyte retrieval in women undergoing IVF-ICSI, and grouped based on body mass index (BMI). Cytokine levels were measured from the follicular fluid using enzyme-linked immunosorbent assay (ELISA). Expression of 4 genes (GREM1, HAS2, PTGS2, VCAN), which have been positively correlated with oocyte maturity and/or pregnancy outcome in cumulus cells, was determined by quantitative reverse transcription polymerase chain reaction (RT-qPCR). Mann Whitney tests were utilized to compare cohorts by BMI and reported as medians with interquartile ranges. Cumulus cells of normal BMI (21.1 kg/m2 to 23.6 kg/m2) women were cultured with IL-1β to investigate its impact on gene expression. Change in gene expression following IL-1β was analyzed by paired t test. P values <0.05 were considered significant. A total of 68 women were included in the ELISA analysis. Women were grouped based on BMI with 57 women having BMI <35 kg/m2 and 11 women having BMI ≥35 kg/m2. Women with BMI ≥35 kg/m2 had increased levels of IL-1β in the follicular fluid as compared to women with lower BMI (5.18 pg/mL vs 1.92 pg/mL, p=0.02). Gene expression from cumulus cells was measured from a representative cohort based on BMI, with 6 in the normal group (BMI 21.1 kg/m2 to 23.6 kg/m2) and 6 in the obese group (35.6 kg/m2 to 42.0 kg/m2). The obese group had a significantly lower relative expression of GREM1 compared to the normal group (0.51 [0.38, 0.74] vs 1.01 [0.66, 1.40], p=0.03). No differences were seen with HAS2 (0.73 [0.49, 1.17] vs 1.06 [0.65, 1.78], p=0.39), PTGS2 (1.54 [1.09, 3.11] vs 0.58 [0.47, 4.19], p=0.22), or VCAN (0.88 [0.61, 1.56] vs 0.93 [0.63, 1.56], p=0.82). Given increased levels of IL-1β in follicular fluid of obese women, cumulus cells from women with normal BMI were cultured with IL-1β to investigate the impact on GREM1 expression. Following IL-1β incubation, GREM1 levels significantly decreased in cumulus cells of normal BMI women (p=0.02) similar to the obese cohort. Compared to women with normal BMI, obese women had higher levels of pro-inflammatory IL-1β in the follicular fluid and had lower cumulus cell expression of GREM1. Decreased expression of GREM1 in cumulus cells of normal BMI women following culture with IL-1β suggests that this pro-inflammatory cytokine may play a role in suppressing GREM1 levels in obese women. These molecular discrepancies may give insight into physiologic differences in oocyte development and cycle outcomes in obese women undergoing IVF-ICSI. Further studies are required to correlate these molecular findings to clinical outcomes.