Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
Laboratoire d'Etude des Résidus et Contaminants dans les Aliments (LABERCA), UMR Oniris-INRA 1329, Université Bretagne Loire, Nantes, France.
PLoS Biol. 2019 Feb 14;17(2):e3000002. doi: 10.1371/journal.pbio.3000002. eCollection 2019 Feb.
Masculinization of the external genitalia in humans is dependent on formation of 5α-dihydrotestosterone (DHT) through both the canonical androgenic pathway and an alternative (backdoor) pathway. The fetal testes are essential for canonical androgen production, but little is known about the synthesis of backdoor androgens, despite their known critical role in masculinization. In this study, we have measured plasma and tissue levels of endogenous steroids in second trimester human fetuses using multidimensional and high-resolution mass spectrometry. Results show that androsterone is the principal backdoor androgen in the male fetal circulation and that DHT is undetectable (<1 ng/mL), while in female fetuses, there are significantly lower levels of androsterone and testosterone. In the male, intermediates in the backdoor pathway are found primarily in the placenta and fetal liver, with significant androsterone levels also in the fetal adrenal. Backdoor intermediates, including androsterone, are only present at very low levels in the fetal testes. This is consistent with transcript levels of enzymes involved in the alternate pathway (steroid 5α-reductase type 1 [SRD5A1], aldo-keto reductase type 1C2 [AKR1C2], aldo-keto reductase type 1C4 [AKR1C4], cytochrome P450 17A1 [CYP17A1]), as measured by quantitative PCR (qPCR). These data identify androsterone as the predominant backdoor androgen in the human fetus and show that circulating levels are sex dependent, but also that there is little de novo synthesis in the testis. Instead, the data indicate that placental progesterone acts as substrate for synthesis of backdoor androgens, which occurs across several tissues. Masculinization of the human fetus depends, therefore, on testosterone and androsterone synthesis by both the fetal testes and nongonadal tissues, leading to DHT formation at the genital tubercle. Our findings also provide a solid basis to explain why placental insufficiency is associated with disorders of sex development in humans.
人类外生殖器的男性化依赖于通过经典雄激素途径和替代（后门）途径形成 5α-二氢睾酮（DHT）。胎儿睾丸对于经典雄激素的产生至关重要，但尽管它们在男性化中起着重要作用，但对后门雄激素的合成知之甚少。在这项研究中，我们使用多维和高分辨率质谱法测量了人类胎儿妊娠中期的内源性类固醇的血浆和组织水平。结果表明，雄甾酮是男性胎儿循环中的主要后门雄激素，而 DHT 无法检测到（<1ng/mL），而在女性胎儿中，雄甾酮和睾酮的水平显着较低。在男性中，后门途径的中间体主要存在于胎盘和胎儿肝脏中，胎儿肾上腺中也存在显着的雄甾酮水平。包括雄甾酮在内的后门中间体仅在胎儿睾丸中以非常低的水平存在。这与参与替代途径的酶（类固醇 5α-还原酶 1 型[SRD5A1]、醛酮还原酶 1C2 型[AKR1C2]、醛酮还原酶 1C4 型[AKR1C4]、细胞色素 P450 17A1 [CYP17A1]）的转录水平一致，如定量 PCR（qPCR）所示。这些数据将雄甾酮鉴定为人类胎儿中的主要后门雄激素，并表明循环水平与性别有关，但睾丸中几乎没有从头合成。相反，数据表明胎盘孕酮作为后门雄激素合成的底物，发生在多个组织中。因此，人类胎儿的男性化取决于胎儿睾丸和非性腺组织的睾酮和雄甾酮合成，导致在生殖器芽中形成 DHT。我们的发现也为解释为什么胎盘功能不全与人类性别发育障碍有关提供了坚实的基础。
