Supplemental information to: Female mice with HSD17B1 inactivation show mild hyperandrogenism without notable impact on reproductive function or bone

17β-hydroxysteroid dehydrogenase 1 (HSD17B1) is the primary enzyme responsible for the activation of estrone (E1) to estradiol (E2) in ovaries and extra-gonadal tissues of both humans and rodents. In the present study, molecular modelling indentified the substitution of His222 in the human HSD17B1 enzyme with glycine in the mouse as the key determinant for the different steroid specificity between the species. Furthermore, Ser143Ala mutation at the active site of mouse HSD17B1 resulted in a total loss of E1 to E2 conversion by HSD17B1. This resulted in elevated intraovarian and circulating E1 concentrations in adult HSD17B1 Ser143Ala knock-in (KI) females, but no changes in E2 concentrations were observed compared to the wild-type mice. Androstenedione and dihydrotestosterone were also elevated in the HSD17B1-KI ovaries, associated with elevated circulating luteinizing hormone (LH). However, the effect of HSD17B1 inactivation on female reproductive development and function was mild, primarily resulting in a slight decrease in ovarian weight in older HSD17B1-KI mice, without notable effects on fertility. Expression of genes related to steroid biosynthesis, mitochondrial metabolism, and known markers of PCOS was found to be upregulated in adult HSD17B1-KI ovaries. However, no alterations in the structure or function of extra-gonadal tissues were observed, and the uterus and bone phenotypes in the HSD17B1-KI females were unaffected. Our results demonstrate that the blockade of HSD17B1-dependent E2 synthesis is successfully compensated for in mouse in vivo, resulting in only a mild ovarian estrogen and androgen imbalance, but no significant adverse effects on reproductive or bone health.

17β-羟类固醇脱氢酶1（17β-hydroxysteroid dehydrogenase 1，HSD17B1）是人类与啮齿类动物卵巢及性腺外组织中，将雌酮（E1）转化为雌二醇（E2）的核心活化酶。本研究通过分子建模发现，人类HSD17B1酶的组氨酸222位点被替换为小鼠的甘氨酸，是导致两物种间类固醇特异性差异的关键决定因素。此外，小鼠HSD17B1活性位点处的丝氨酸143丙氨酸（Ser143Ala）突变，可使HSD17B1完全丧失将E1转化为E2的能力。该突变会使成年HSD17B1 Ser143Ala敲入（KI）雌性小鼠的卵巢内及循环系统中的E1水平升高，但与野生型小鼠相比，其E2浓度未出现明显变化。HSD17B1-KI小鼠的卵巢中，雄烯二酮与二氢睾酮的水平同样升高，且伴随循环系统中黄体生成素（LH）水平的上升。然而，HSD17B1失活对雌性小鼠生殖发育与功能的影响较为轻微，仅会使高龄HSD17B1-KI小鼠的卵巢重量出现轻度下降，并未对其生育能力造成显著影响。成年HSD17B1-KI小鼠的卵巢中，与类固醇生物合成、线粒体代谢及已知多囊卵巢综合征（Polycystic Ovary Syndrome，PCOS）标志物相关的基因表达均出现上调。但研究未观察到性腺外组织的结构与功能出现任何改变，HSD17B1-KI雌性小鼠的子宫与骨骼表型也未受影响。本研究结果表明，依赖HSD17B1的E2合成通路被阻断后，小鼠体内可通过代偿机制成功弥补该缺陷，仅造成轻度的卵巢雌激素与雄激素失衡，并未对生殖健康或骨骼健康造成显著不良影响。