Decreased gremlin 1 expression in women with BMI ≥35 kg/m² is mediated by interleukin 10 and interleukin 1β in the follicular fluid

Objective: To determine how body mass index (BMI) affects the follicular fluid cytokine milieu and investigate how this inflammatory environment impacts cumulus signaling.

Design: Experimental study.

Setting: Tertiary hospital based research laboratory.

Patients: Women with normal (18.5 to 24.9 kg/m²) and obese (35 to 42 kg/m²) BMI undergoing controlled ovarian stimulation for intracytoplasmic sperm injection (ICSI).

Interventions: Cumulus cell treatment with obese follicular fluid, interleukin (IL) 10, and IL-1β.

Main outcome measures: Follicular fluid cytokine concentrations between normal and obese women were compared using multiplex bead assay. Differential cumulus cell gene expression of GREM1, HAS2, PTGS2, and VCAN were measured using quantitative reverse polymerase chain reaction (RT-qPCR) while protein levels were determined by flow cytometry and confocal microscopy.

Results: Compared to women with normal BMI, women with BMI ≥35 kg/m² undergoing ICSI had higher follicular concentrations of IL-10 (9.46 pg/mL [0.59-19.16] vs 53.39 pg/mL [14.97-236.37], p=0.004) and IL-1β (1.92 pg/mL [1.92-5.18] vs 5.18 pg/mL [1.92-16.33], p=0.017), as well as decreased relative cumulus cell expression of GREM1 (1.01 [0.66-1.40] vs 0.51 [0.38-0.74], p=0.03), a surrogate marker of positive ICSI outcomes. Furthermore, elevated IL-10 and IL-1β appear to be responsible for decreasing GREM1 expression in women with BMI ≥35 kg/m².

Conclusion: Our findings suggest that follicular inflammation associated with obesity impacts cumulus cell signaling. At a molecular level, derangements to the immune system resulting in decreased GREM1 expression may be a partial explanation for the suboptimal ICSI outcomes observed with obesity.