Singh Reetu R, Moritz Karen M, Bertram John F, Cullen-McEwen Luise A
Dept. of Anatomy and Cell Biology, Monash University, Clayton, Victoria 3800, Australia.
Am J Physiol Renal Physiol. 2007 Aug;293(2):F548-54. doi: 10.1152/ajprenal.00156.2007. Epub 2007 May 30.
Maternal administration of dexamethasone (DEX) for 48 h early in rat kidney development results in offspring with a reduced nephron endowment. However, the mechanism through which DEX inhibits nephrogenesis is unknown. In this study, we hypothesized that DEX may indirectly inhibit nephrogenesis by inhibiting ureteric branching morphogenesis. Whole metanephroi from embryonic day 14.5 (E14.5) rat embryos were cultured in the presence of DEX. DEX (10(-5) M) exposure for 2 days significantly inhibited ureteric branching compared with metanephroi grown in control media or DEX (10(-7) M). Culturing metanephroi for a further 3 days (in control media only) reduced total glomerular number in metanephroi previously exposed to DEX (10(-5) M) or (10(-7) M) compared with control cultures. Expression of genes known to regulate ureteric branching morphogenesis was determined by real-time PCR in metanephroi after 2 days in culture. DEX exposure in vitro decreased expression of glial cell line-derived neurotrophic factor (GDNF) and increased expression of bone morphogenetic protein-4 (BMP-4) and transforming growth factor-beta1 (TGF-beta1). Similar gene expression changes were found in E16.5 metanephroi in which the dam had been exposed to 2 days of DEX (0.2 mg.kg(-1).day(-1)) at E14.5/15.5 in vivo. However, in kidneys collected at E20.5 after in vivo exposure for 2 days, GDNF expression was increased and BMP-4 and TGF-beta1 expression decreased suggesting a biphasic response in gene expression to DEX exposure. These results show for the first time that inhibition of ureteric branching morphogenesis may be a key mechanism through which DEX exposure results in a reduced nephron endowment.
在大鼠肾脏发育早期给予地塞米松（DEX）48小时会导致后代肾单位数量减少。然而，DEX抑制肾发生的机制尚不清楚。在本研究中，我们假设DEX可能通过抑制输尿管分支形态发生间接抑制肾发生。将来自胚胎第14.5天（E14.5）大鼠胚胎的整个后肾在DEX存在下培养。与在对照培养基或DEX（10^(-7) M）中生长的后肾相比，暴露于DEX（10^(-5) M）2天显著抑制了输尿管分支。与对照培养相比，将后肾再培养3天（仅在对照培养基中）可减少先前暴露于DEX（10^(-5) M）或（10^(-7) M）的后肾中的总肾小球数量。通过实时PCR在培养2天后的后肾中测定已知调节输尿管分支形态发生的基因的表达。体外暴露于DEX会降低胶质细胞源性神经营养因子（GDNF）的表达，并增加骨形态发生蛋白-4（BMP-4）和转化生长因子-β1（TGF-β1）的表达。在E16.5后肾中发现了类似的基因表达变化，其中母鼠在E14.5/15.5时体内暴露于DEX（0.2 mg·kg^(-1)·day^(-1)）2天。然而，在体内暴露2天后于E20.5收集的肾脏中，GDNF表达增加，BMP-4和TGF-β1表达降低，表明基因表达对DEX暴露存在双相反应。这些结果首次表明，抑制输尿管分支形态发生可能是DEX暴露导致肾单位数量减少的关键机制。
