Expression of Key Steroidogenic Enzymes in Human Placenta and Associated Adverse Pregnancy Outcomes

Steroid hormones, including progestagens, estrogens, androgens, corticosteroids, and their precursor cholesterol, perform essential functions in the successful establishment and maintenance of pregnancy and normal fetal development. As the core endocrine organ at the prenatal stage, the human placenta is involved in the biosynthesis, metabolism, and delivery of steroid hormones. Steroidogenic pathways are tightly regulated by placenta-intrinsic cytochrome P450 and hydroxysteroid dehydrogenase. However, the relationship between placental steroidogenic enzyme expression and adverse pregnancy outcomes is controversial. In this review, we summarize the possible upstream regulatory mechanisms of placental steroidogenic enzymes in physiologic and pathophysiologic states. We also describe the human placental barrier model and examine the potential of single-cell sequencing for evaluating the primary functions and cellular origin of steroidogenic enzymes. Finally, we examine the existing evidence for the association between placental steroidogenic enzyme dysregulation and adverse pregnancy outcomes.