P450 oxidoreductase: Novel regulator of steroid synthesis and metabolism in health and disease

The human adrenal gland produces the hormone dehydroepiandrosterone (DHEA), which is a major precursor for the production of androgens, i.e. active male hormones, in both men and women. Too much androgen in women can cause irregular periods, infertility, acne and increases the risk to diabetes and high blood pressure, summarised by the term polycystic ovary syndrome. This condition affects 5-10% of all women. We have discovered two novel mechanisms that regulate the production and the breakdown, respectively, of DHEA. Patients who have a mutation, i.e. a small spelling error in their genetic code, affecting one of the two factors we have identified, POR and PAPSS2, suffer from androgen excess. Our research will aim to find out by what mechanisms disruption of POR and PAPSS2 causes androgen excess. POR and PAPSS2 also play an important role in regulating the metabolism of drugs and hormones in the liver and thus our research will also give important insights in these mechanisms. Clarification of these two novel regulatory pathways in human physiology and disease carries clear translational potential, i.e. comes with the possibility of applying new knowledge to the development of novel therapies.

The proposed research will investigate the role of two novel metabolic pathways in human health and disease. We recently discovered that mutations in P450 oxidoreductase (POR) and PAPS synthase 2 (PAPSS2) disrupt dehydroepiandrosterone (DHEA) synthesis and metabolism, respectively, resulting in androgen excess, a major feature of the polycystic ovary syndrome (PCOS). POR has a pivotal role as electron donor to all microsomal cytochrome P450 (CYP) enzymes including key enzymes of steroidogenesis and hepatic drug metabolism. In this proposal we will define the differential impact of variant POR on steroidogenesis and hepatic drug detoxification. POR deficiency is unique in that affected children of both sexes can present with disordered sex development. Undervirilisation in boys is readily explained by impaired DHEA synthesis, which however is incongruous with virilisation in affected girls. We have proposed that this apparent contradiction is explained by an alternative androgen pathway in early human life, with recent evidence supporting this hypothesis. We will examine the role of the alternative androgen pathway in human sex development, analysing its expression and activity during pregnancy and the early neonatal period in normal and disordered sex development. DHEA is the major precursor of androgen synthesis via the classic pathway unless inactivated to DHEAS by DHEA sulfotransferase, which requires the universal sulfate donor PAPS for catalytic activity. We have identified inactivating mutations in PAPSS2 encoding human PAPS synthase 2 in a girl presenting with premature pubarche followed by development of PCOS. We have established PAPSS2 deficiency as a novel monogenic cause of androgen excess, revealing DHEA sulfation as a gatekeeper to human androgen synthesis. We will identify and characterise further cases of PAPSS2 deficiency in premature pubarche and PCOS. Furthermore, we will examine whether common variation in PAPSS2 contributes to PCOS susceptibility by performing dense tagSNP genotyping in large PCOS and control cohorts. Finally, we will analyse the differential effects of the two PAPS synthase isoforms to clarify why ubiquitously expressed PAPSS1 cannot compensate for the loss of PAPSS2 activity. Taken together, this programme of research will investigate the physiological and clinical significance of two crucial metabolic pathways, the provision of electrons by POR to microsomal CYP enzymes and the provision of PAPS to sulfotransferases. The clinical significance of an improved understanding of these systems cannot be underestimated and includes a major modulatory role of POR and PAPS in hepatic phase 1 and phase 2 detoxification, current key targets of pharmacogenomics.