Retinoid pathway members function in human oocyte maturation

Abstract

Disruption of retinoid homeostasis has been associated with abnormalities during embryonic development in rodents and mammals. Its precise role in the process of human follicular development presently is not well understood. Our study evaluates retinol (Rl), retinol binding protein (RBP) and transthyretin (TTR) levels in follicular fluids (FF) and determines their content in mature large (L) and small (S) follicles from healthy young and older women undergoing assisted reproduction treatment. Observational cohort study. Serum and FF from lead follicles (LF, ≥16 mm) and small (SF, ≤12 mm) was obtained from 17 IVF patients at time of vaginal oocyte retrieval. Patients were divided in two age groups as follows: young (≤34 years) and reproductively old (≥40 years). FF samples and plasma were purified by ultracentrifugation. Quantification of RBP and TTR in samples and in fractions was conducted by western blot with protein specific antibodies. Retinol was determined by TLC. Data were evaluated as relative units (rU) based on spot intensity. Standard deviations were used to compare content in fractions. Comparison with distribution in corresponding blood plasma has been performed. RI, RBP, and TTR are present in both FF and plasma. FF levels of RBP are 1.6 (±0.2) times higher in LF (140 rU/ml ± 25 vs. 87 rU/ml ± 12) than in SF. TTR level in LF is 120 rU/ml ± 17 vs. 75 rU/ml ± 14 in SF. RI level in LF is 145 rU/ml ± 21 vs. 103 rU/ml ± 11 in SF. RI, RBP, and TTR content in plasma is 10–15% higher than in the corresponding FFs (Figure 1, Table 1). In response to hCG the plasma level of RI and RBP is found to increase by 21% (±2.8%) compared to pre hCG plasma. A positive correlation was found between RI and RBP content and number of mature eggs. Table 1FF contentFollicleRetinol (rU)RBP (rU)TTR (rU)Large145140120Small1038775 Open table in a new tab RI and RBP are necessary components of FF in the process of follicular maturation. Both RBP and TTR are possibly involved in the follicular RI trafficking. The RI and RBP levels in plasma as well as in FF are potential markers for follicular competence to support oocyte maturation.