The differential regulation of placenta trophoblast bisphosphoglycerate mutase in fetal growth restriction: preclinical study in mice and observational histological study of human placenta

Background Fetal growth restriction (FGR) is a pregnancy complication in which a newborn fails to achieve its growth potential, increasing the risk of perinatal morbidity and mortality. Chronic maternal gestational hypoxia, as well as placental insufficiency are associated with increased FGR incidence; however, the molecular mechanisms underlying FGR remain unknown.
Methods Pregnant mice were subjected to acute or chronic hypoxia (12.5% O2) resulting in reduced fetal weight. Placenta oxygen transport was assessed by blood oxygenation level dependent (BOLD) contrast magnetic resonance imaging (MRI). The placentae were analyzed via immunohistochemistry and in situ hybridization. Human placentae were selected from FGR and matched controls and analyzed by immunohistochemistry (IHC). Maternal and cord sera were analyzed by mass spectrometry.
Results We show that murine acute and chronic gestational hypoxia recapitulates FGR phenotype and affects placental structure and morphology. Gestational hypoxia decreased labyrinth area, increased the incidence of red blood cells (RBCs) in the labyrinth while expanding the placental spiral arteries (SpA) diameter. Hypoxic placentae exhibited higher hemoglobin-oxygen affinity compared to the control. Placental abundance of Bisphosphoglycerate mutase (BPGM) was upregulated in the syncytiotrophoblast and spiral artery trophoblast cells (SpA TGCs) in the murine gestational hypoxia groups compared to the control. Hif1a levels were higher in the acute hypoxia group compared to the control. In contrast, human FGR placentae exhibited reduced BPGM levels in the syncytiotrophoblast layer compared to placentae from healthy uncomplicated pregnancies. Levels of 2,3 BPG, the product of BPGM, were lower in cord serum of human FGR placentae compared to control. Polar expression of BPGM, was found in both human and mouse placentae syncytiotrophoblast, with higher expression facing the maternal circulation. Moreover, in the murine SpA TGCs expression of BPGM was concentrated exclusively in the apical cell side, in direct proximity to the maternal circulation.
Conclusions This study suggests a possible involvement of placental BPGM in maternal-fetal oxygen transfer, and in the pathophysiology of FGR.

背景 胎儿生长受限（Fetal growth restriction，FGR）是一类妊娠并发症，指新生儿无法达到其生长潜能，会提升围产期发病与死亡风险。慢性母体妊娠缺氧及胎盘功能不全与FGR发病率升高相关，但FGR的潜在分子机制仍未明确。
方法 对妊娠小鼠施加急性或慢性缺氧（氧浓度12.5%），可导致胎鼠体重下降。采用血氧水平依赖成像（blood oxygenation level dependent，BOLD）对比增强磁共振成像（magnetic resonance imaging，MRI）评估胎盘氧转运功能。通过免疫组织化学（immunohistochemistry）与原位杂交（in situ hybridization）技术分析胎盘组织。选取FGR患者与匹配对照的人体胎盘，采用免疫组织化学（immunohistochemistry，IHC）进行检测。采用质谱技术分析母体与脐带血清样本。
结果 本研究证实，小鼠急性与慢性妊娠缺氧可重现FGR表型，并对胎盘结构与形态产生影响。妊娠缺氧会缩小胎盘迷路区面积，增加迷路区内红细胞（red blood cells，RBCs）的出现概率，同时扩张胎盘螺旋动脉（spiral arteries，SpA）管径。缺氧胎盘的血红蛋白氧亲和力较对照组更高。与对照组相比，妊娠缺氧小鼠组的合体滋养层（syncytiotrophoblast）与螺旋动脉滋养层细胞（spiral artery trophoblast cells，SpA TGCs）中双磷酸甘油酸变位酶（Bisphosphoglycerate mutase，BPGM）的胎盘表达丰度显著上调。急性缺氧组的Hif1a水平较对照组更高。与之相反，与健康无并发症妊娠的胎盘相比，人类FGR胎盘的合体滋养层（syncytiotrophoblast）中BPGM水平降低。BPGM的催化产物2,3-二磷酸甘油酸（2,3 BPG）在人类FGR胎盘的脐带血清中水平较对照组更低。在人类与小鼠胎盘的合体滋养层（syncytiotrophoblast）中均观察到BPGM的极性表达，其高表达区域朝向母体循环。此外，在小鼠螺旋动脉滋养层细胞（spiral artery trophoblast cells，SpA TGCs）中，BPGM的表达仅集中于顶端细胞侧，紧邻母体循环。
结论 本研究提示，胎盘BPGM可能参与母胎间的氧气转运过程，并与FGR的病理生理机制相关。