Monash Biomedicine Discovery Institute, Department of Anatomy and Developmental Biology, Development and Stem Cells Program, Monash University, Clayton, VIC, Australia.
Monash Biomedicine Discovery Institute, Department of Anatomy and Developmental Biology, Development and Stem Cells Program, Monash University, Clayton, VIC, Australia.
EBioMedicine. 2024 Aug;106:105262. doi: 10.1016/j.ebiom.2024.105262. Epub 2024 Jul 30.
An estimated 1 in 350 women carry germline BRCA1/2 mutations, which confer an increased risk of developing breast and ovarian cancer, and may also contribute to subfertility. All mature, sex steroid-producing ovarian follicles are drawn from the pool of non-renewable primordial follicles, termed the 'ovarian reserve'. The clinical implications of early ovarian reserve exhaustion extend beyond infertility, to include the long-term adverse health consequences of loss of endocrine function and premature menopause. We aimed to determine whether conditional loss of Brca1 in oocytes impacts ovarian follicle numbers, oocyte quality and fertility in mice with advancing maternal age. We also aimed to determine the utility of AMH as a marker of ovarian function, by assessing circulating AMH levels in mice and women with BRCA1/2 mutations, and correlating this with ovarian follicle counts.
In this study, we addressed a longstanding question in the field regarding the functional consequences of BRCA1 inactivation in oocytes. To recapitulate loss of BRCA1 protein function in oocytes, we generated mice with conditional gene deletion of Brca1 in oocytes using Gdf9-Cre recombinase (WT: Brca1Gdf9; cKO: Brca1Gdf9).
While the length of the fertile lifespan was not altered between groups after a comprehensive breeding trial, conditional loss of Brca1 in oocytes led to reduced litter size in female mice. Brca1 cKO animals had a reduced ovarian reserve and oocyte maturation was impaired with advanced maternal age at postnatal day (PN)300, compared to WT animals. Serum anti-Müllerian hormone (AMH) concentrations (the gold-standard indirect marker of the ovarian reserve used in clinical practice) were not predictive of reduced primordial follicle number in Brca1 cKO mice versus WT. Furthermore, we found no correlation between follicle number or density and serum AMH concentrations in matched samples from a small cohort of premenopausal women with BRCA1/2 mutations.
Together, our data demonstrate that BRCA1 is a key regulator of oocyte number and quality in females and suggest that caution should be used in relying on AMH as a reliable marker of the ovarian reserve in this context.
This work was made possible through Victorian State Government Operational Infrastructure Support and Australian Government NHMRC IRIISS. This work was supported by funding from the Australian Research Council (ALW - DE21010037 and KJH - FT190100265), as well as the National Breast Cancer Foundation (IIRS-22-092) awarded to ALW and KJH. LRA, YML, LT, EOKS and MG were supported by Australian Government Research Training Program Scholarships. LRA, YML and LT were also supported by a Monash Graduate Excellence Scholarship. YC, SG and XC were supported by Monash Biomedicine Discovery Institute PhD Scholarships. LRA was also supported by a Monash University ECPF24-6809920940 Fellowship. JMS was supported by NHMRC funding (2011299). MH was supported by an NHMRC Investigator Grant (1193838).
据估计，每 350 名女性中就有 1 名携带胚系 BRCA1/2 突变，这会增加患乳腺癌和卵巢癌的风险，并且可能还会导致生育能力下降。所有成熟的、产生性激素的卵泡都来自不可再生的原始卵泡池，称为“卵巢储备”。早期卵巢储备衰竭的临床意义不仅限于不孕，还包括内分泌功能丧失和过早绝经带来的长期不良健康后果。我们旨在确定卵母细胞中 BRCA1 的条件性缺失是否会影响小鼠的卵巢卵泡数量、卵母细胞质量和生育能力，以及随着母体年龄的增长。我们还旨在通过评估携带 BRCA1/2 突变的小鼠和女性的循环 AMH 水平，并将其与卵巢卵泡计数相关联，来确定 AMH 是否可用作卵巢功能的标志物。
在这项研究中，我们解决了该领域长期存在的一个问题，即 BRCA1 失活对卵母细胞的功能后果。为了在卵母细胞中重现 BRCA1 蛋白功能的缺失，我们使用 Gdf9-Cre 重组酶（WT：Brca1Gdf9；cKO：Brca1Gdf9）生成了卵母细胞中 Brca1 条件性基因缺失的小鼠。
尽管在全面繁殖试验后，两组之间的可育寿命长度没有改变，但卵母细胞中 BRCA1 的条件性缺失导致母鼠的产仔数减少。与 WT 动物相比，Brca1 cKO 动物的卵巢储备减少，并且卵母细胞成熟受损，在产后 300 天，随着母体年龄的增长而受损。血清抗苗勒管激素（AMH）浓度（临床实践中用于间接标记卵巢储备的金标准标志物）不能预测 Brca1 cKO 小鼠与 WT 相比原始卵泡数量减少。此外，我们在来自 BRCA1/2 突变的少量绝经前女性的匹配样本中发现，卵泡数量或密度与血清 AMH 浓度之间没有相关性。
总之，我们的数据表明 BRCA1 是雌性卵母细胞数量和质量的关键调节剂，并表明在这种情况下，在依赖 AMH 作为可靠的卵巢储备标志物时应谨慎行事。
这项工作得益于维多利亚州政府的运营基础设施支持和澳大利亚政府 NHMRC IRIISS。这项工作得到了澳大利亚研究理事会（ALW-DE21010037 和 KJH-FT190100265）以及国家乳腺癌基金会（IIRS-22-092）的资助，该基金会授予 ALW 和 KJH。LRA、YML、LT、EOKS 和 MG 得到了澳大利亚政府研究培训计划奖学金的支持。LRA、YML 和 LT 还得到了蒙纳士大学卓越研究生奖学金的支持。YC、SG 和 XC 得到了蒙纳士生物医学发现研究所博士奖学金的支持。LRA 还得到了蒙纳士大学 ECPF24-6809920940 奖学金的支持。JMS 得到了 NHMRC 资助（2011299）。MH 得到了 NHMRC 研究员资助（1193838）。
