EPO/BMP/Alk3信号通路介导低出生体重大鼠肾单位发育障碍的机制

Accumulated evidence demonstrated the association between low birth weight (LBW) and reduced nephron number at birth. Children born with LBW are at increased risk of developing chronic kidney diseases in late life. Previous studies demonstrated that the reduced number of nephrons leads to hyperfiltration, which in turn causes systemic hypertension and progressive deterioration of renal structures and functions. The molecular mechanisms of nephron reduction associated with LBW induced by prematurity or intrauterine growth retardation, however, remains unclear. Erythropoietin (EPO) is a cytokine that regulates erythropoiesis through the EPO receptor (EPOR). Previous studies have shown nonerythropoietic protective effects of EPO in the brain and kidneys. A number of interesting work recently showed that endogenous EPO/EPOR signaling promotes cell survival in the embryonic brain, and contributes to neural proliferation in the adult brain in regions associated with neurogenesis, suggesting that EPO contributes directly to the development in the organs. However, the role of EPO in the development of the kidneys is unclear. This project will use LBW rats induced by intrauterine growth retardation. Our preliminary data showed that the protein expression of EPO, EPOR, bone morphogenetic protein-2 (BMP2) and its receptor Alk3, that are critical for nephron development, was significantly lower in the LBW rats than that in the controls. In addition, exogenous EPO may increase the number of nephrons in LBW rats. Therefore, we hypothesized that EPO, acting EPOR and BMP/Alk3 signaling, may play a role in nephron formation in the developing kidney. The goals of this study are to investigate the effects of EPO/EPOR, and the associated molecular pathways of BMP/Alk3 signaling, in nephron number reduction induced by intrauterine growth retardation in rats, and to investigate whether exogenous EPO may have protective effects. The data gained will provide new insights into understanding of the molecular mechanisms related to reduced nephron number associated with LBW or fetal growth restriction.

早产或宫内发育迟缓导致的低出生体重（LBW）常伴有肾单位数目减少，而肾单位减少是引起日后肾损伤的危险因素。我们前期研究发现，促红细胞生成素（EP0）和受体(EPOR)及肾发育调控因子骨形成蛋白（BMP）和受体（Alk3）的蛋白表达在LBW 大鼠肾组织明显受抑制；而外源性EPO可以上调BMP蛋白、促进LBW大鼠肾单位发育，提示EPO可能通过BMP/Alk3信号通路介导LBW大鼠肾单位发育障碍。本项目拟通过观察EPO沉默表达、过表达时胎肾发育和肾单位数目及BMP/Alk3信号通路的变化，结合免疫共沉淀和免疫荧光双标技术，研究EPO通过EPOR作用于BMP/Alk3信号通路，从而调控LBW大鼠肾单位发育的机制。从EPO/EPOR/BMP/Alk3信号通路对肾发育调控研究相关机制有其原创新颖价值。期望为LBW儿肾单位发育障碍的防治，为早期干预肾损伤提供新线索和潜在的靶标。

早产、宫内发育迟缓或其他因素导致的低出生体重常伴有肾单位数目减少，而肾单位数目减少是引起日后进行性肾损伤发生的重要机制。因此，积极纠正与低出生体重密切相关的肾单位数目减少，早期干预发育阶段的肾损伤、对预防日后肾功能衰竭的发生发展，具有极其深远的意义。本项目（1）通过建立生长受限的低出生体重大鼠模型，评估宫内发育迟缓诱导的低出生体重大鼠肾脏发育和肾单位数目的变化，揭示了低出生体重大鼠肾单位数目减少与成年期肾损伤的相关联系。（2）通过建立在离体肾单位发育障碍模型；动态检测内源性促红细胞生成素（EPO）和其受体及BMP/Alk3信号通路关键蛋白在大鼠肾组织中的表达，揭示了内源性EPO及BMP/Alk3信号通路在肾单位发育中的作用；并通过探讨EPO是否通过EPO受体及BMP/Alk3信号通路而起作用，揭示低出生体重大鼠肾单位数目减少和肾发育障碍的机制，及肾单位数目减少的低出生体重大鼠在成年期发生肾损伤的可能机制。（3）通过在离体实验，在肾单位数目发育关键期，给予外源性EPO，动态观测肾脏发育和肾单位数目的变化，揭示外源性EPO具有促进肾单位发育及减少低出生体重大鼠在成年期发生肾损伤的潜力。（4）通过在离体实验，阐明外源性EPO通过EPO受体调控BMP/Alk3信号通路及细胞增殖与凋亡，促进肾单位发育的机制；及外源性EPO通过调控p38 MAPK及细胞增殖与凋亡，减少LBW大鼠在成年期发生肾损伤的可能机制。本项目为阐明与低出生体重密切相关的肾单位发育障碍的机制提供新线索；为低出生体重儿肾单位发育障碍的防治，从而早期预防成年期肾损伤，提供理论依据和潜在的干预靶标。