铁离子缺乏调控胚胎肾脏发育缺陷的分子机理研究

Iron is an essential nutrient required for cell growth and development. Iron is also a growth factor required for nephrogenesis. Iron deficiency in pregnancy is a common worldwide public health problem, and can cause developmental defects of embryonic kidney, which is generally manifested as chronic kidney diseases in later life. Hence, it is of importance to understand how the required quantity of maternal iron is delivered to different cell lineages of the embryonic kidney for organogenesis while to prevent the occurrence of kidney defects. We herein generated a mouse model of iron deficient pregnancy and a conditional gene knockout mouse model for cell-specific Tfr1 deletion in the embryonic kidney. By using these mouse models, we demonstrated that iron deficiency in pregnancy led to embryonic kidney hypoplasia and even anephria, and specific deletion Tfr1 gene in cap mesenchyme resulted in reduced glomeruli in the embryonic kidney, indicating that iron deficiency likely interacted with embryonic kidney cells directly which eventually resulted in defective development of embryonic kidney. In this proposal, we are going take advantage of these mouse models to investigate the molecular basis for how iron deficiency in pregnancy induces developmental defects in the embryonic kidney and to understand the genetic basis of iron delivery in the developing kidney. These studies are particularly important for efficient intervention and prevention of defective embryonic kidney development caused by iron deficiency in pregnancy.

铁离子是细胞生长和发育所必需的营养元素，是胚胎肾发育的必需生长因子。妊娠妇女铁离子缺乏可导致胚胎肾发育缺陷，出生及成年后通常逐渐表现为慢性肾病。因此，研究铁离子是如何从母体运输到胚胎肾的不同谱系细胞供其生长和发育为不同组织、同时防止铁离子缺乏引起组织发育缺陷的分子机理，对于更科学合理、更有效地早期预防和干预由铁离子缺乏导致的胚胎肾缺陷具有重要的理论指导意义。我们建立和论证了模拟妇女妊娠前后铁离子缺乏的小鼠模型和细胞特异性Tfr1基因敲除小鼠模型，前期的结果表明小鼠孕期前后铁离子缺乏可导致胚胎小肾甚至无肾，而特异性敲除肾单位前体细胞的铁离子转运基因Tfr1可导致肾小球数目减少，说明铁离子缺乏很可能是直接影响胚胎肾细胞而导致缺陷的。本研究将利用这些小鼠模型，在前期研究的基础上，系统研究母体孕期前后铁离子缺乏对胚胎肾中不同组织发育的影响以及分子细胞机理，阐明胚胎肾发育过程中铁离子运输的分子机制。

铁缺乏是最广泛、影响最广的微量营养缺乏，可导致贫血、流产、早产、器官发育缺陷、低体重胎儿等疾病。我国慢性肾病的发病率高达13％，但是铁缺乏的影响以及如何调控这些疾病的发生不清楚。本项目建立了多种小鼠模型进行了研究，发现了妊娠期缺铁导致胚胎肾发育缺陷、出生后肾功能不全和囊性肾病，具体表现为肾单位显著减少，近曲小管膨大形成囊泡，表明妊娠期缺铁是囊性肾病的重要病因之一。利用基因表达芯片和RNA-Seq技术，发现缺铁导致E15.5胚胎和出生后肾脏～300个基因的表达显著下调，其中43％为近曲小管特异表达基因，同时低氧诱导因子alpha调控的264个基因显著上调，同时低氧诱导因子alpha抑制剂可显著抑制囊性肾病。这些结果说明铁缺乏对近曲小管发育影响更显著，而出生后肾脏囊性疾病的发生与铁缺乏导致的低氧信号通路过度激活密切有关。我们建立了肾脏谱系特异性转铁蛋白铁（Tf-Fe）缺乏的Tfr1组织特异性基因敲除，研究了胚胎肾脏不同谱系细胞Tf-Fe缺乏对肾脏发育及肾脏疾病发生的影响及其机制，发现胚胎肾间充质细胞Tf-Fe缺乏导致胚胎肾退化和出生后特异性肾删除，但对其它器官的发育无明显影响，表明Tf-Fe是维持胚胎肾起始后发育进程中所必需的营养因子，与肾脏发育起始无关。发现了肾单位Tf-Fe缺乏导致囊性肾病，而在小鼠出生后8天腹腔注射补充葡聚糖铁可显著抑制肾脏囊性肾病的发生，表明Tf-Fe缺乏是妊娠期囊性肾病的主要原因，出生后早期补充铁是干预这一疾病的有效手段。发现了胚胎肾脏输尿管芽特异性Tf-Fe缺乏抑制胚胎肾脏发育，出生后这些小鼠肾脏表现出慢性囊性肾病和纤维化。发现了铁缺乏可显著抑制纤毛基因BBS等的表达、导致肾小管表皮细胞纤毛病变，说明纤毛病变是铁缺乏导致肾囊泡的一种重要分子机制。结论：利用多种铁缺乏小鼠模型，我们研究发现铁缺乏是囊性肾病的重要病因，阐明了病理发生的低氧信号通路过表达和纤毛病变机制，发现了出生后补铁可显著抑制缺铁囊性肾病，这对于有效治疗缺铁引起的肾脏疾病奠定了理论基础并提供了有效手段。