Steroid hormones play a crucial role in supporting a successful pregnancy and ensuring proper fetal development. The placenta is one of the principal tissues in steroid production and metabolism, expressing a vast range of steroidogenic enzymes. Nevertheless, a comprehensive characterization of steroidogenic pathways in the human placenta and potential developmental changes occurring during gestation are poorly understood. Furthermore, the specific contribution of trophoblast cells in steroid release is largely unknown. Thus, this study aimed to (i) identify gestational age-dependent changes in the gene expression of key steroidogenic enzymes and (ii) explore the role of trophoblast cells in steroid biosynthesis and metabolism. Quantitative and Droplet Digital PCR analysis of 12 selected enzymes was carried out in the first trimester (n = 13) and term (n = 20) human placentas. Primary trophoblast cells (n = 5) isolated from human term placentas and choriocarcinoma-derived cell lines (BeWo, BeWo b30 clone, and JEG-3) were further screened for gene expression of enzymes involved in placental synthesis/metabolism of steroids. Finally, de novo steroid synthesis by primary human trophoblasts was evaluated, highlighting the functional activity of steroidogenic enzymes in these cells. Collectively, we provide insights into the expression patterns of steroidogenic enzymes as a function of gestational age and delineate the cellular origin of steroidogenesis in the human placenta.

Department of Nephrology and Hypertension Department of Biomedical Research Inselspital University of Bern Freiburgstrasse 15 3010 Bern Switzerland

Department of Pharmacology and Toxicology Faculty of Pharmacy in Hradec Kralove Charles University Akademika Heyrovskeho 1203 500 05 Hradec Kralove Czech Republic

Institute of Biochemistry and Molecular Medicine University of Bern Bühlstrasse 28 3012 Bern Switzerland

Pediatric Endocrinology Diabetology and Metabolism Department of Pediatrics Department of Biomedical Research Inselspital Bern University Hospital University of Bern Freiburgstrasse 15 3010 Bern Switzerland

Sitem Center for Translational Medicine and Biomedical Entrepreneurship and Sitem Insel AG University of Bern Freiburgstrasse 3 3010 Bern Switzerland

Swiss National Centre of Competence in Research TransCure University of Bern 3012 Bern Switzerland

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