An integrative analysis of endometrial steroid metabolism and transcriptome in relation to endometrial receptivity in in vitro fertilization patients

Abstract

To study the relation between the steroid concentration in endometrium, in serum and the gene expression level of steroid metabolizing enzymes in the context of endometrial receptivity in IVF patients. Case-control study of 40 IVF patients recruited in the SCRaTCH study (NTR5342), a randomized controlled trial investigating pregnancy outcome after 'endometrial scratching'. Endometrial biopsies and serum were obtained from patients with a first failed IVF cycle randomized to the endometrial scratch in the mid-luteal phase of the natural cycle prior to the next fresh embryo transfer during the second IVF cycle. Twenty women with clinical pregnancy were compared with 20 women that did not conceive after fresh embryo transfer. Cases and controls were matched for primary versus secondary infertility, embryo quality and age. Steroid concentrations in endometrial tissue homogenates and serum were measured with liquid chromatography-mass spectrometry. The endometrial transcriptome was profiled by RNA-sequencing followed by principal component analysis and differential expression analysis. False Discovery Rate-adjusted p<0.05 and log Fold Change >|0.5| were selected as threshold for differentially expressed genes. Estrogen levels were comparable in both serum (n=16) and endometrium (n=40). Androgens and 17-hydroxyprogesterone were higher in serum as compared to endometrium. Although steroid levels did not vary between pregnant and non-pregnant groups, subgroup analysis of primary infertile women showed a significantly lower estrone concentration and estrone:androstenedione ratio in serum of the pregnant group (n=5) compared to the non-pregnant group (n=2). Expression of 34 out of 46 genes encoding the enzymes controlling the local steroid metabolism was detected and estrogen receptor β gene was differentially expressed between pregnant and non-pregnant women. When only the primary infertile group was considered, 28 genes were differentially expressed between pregnant and non-pregnant women, including HSD11B2, that catalyses the conversion of cortisol into cortisone. Steroidomic and transcriptomic analyses show that steroid concentrations are regulated by the local metabolism in the endometrium. Although no differences were found in endometrial steroid concentration in the pregnant and non-pregnant IVF patients, primary infertile women showed deviations in steroid levels and gene expression, indicating that a more homogeneous patient group is required to uncover the exact role of steroid metabolism in endometrial receptivity.