Yosypiv Ihor V, Boh Mary K, Spera Melissa A, El-Dahr Samir S
Section of Pediatric Nephrology, Department of Pediatrics, Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, New Orleans, Louisiana 70112, USA.
Kidney Int. 2008 Nov;74(10):1287-93. doi: 10.1038/ki.2008.378. Epub 2008 Jul 23.
Mutations of genes in the renin-angiotensin system are associated with congenital abnormalities of the kidney and urinary tract. The major signaling pathway for branching morphogenesis during kidney development is the c-Ret receptor tyrosine kinase whose ligand is GDNF and whose downstream target is Wnt11. We determined whether angiotensin II, an inducer of ureteric bud branching in vitro, influences the GDNF/c-Ret/Wnt11 pathway. Mouse metanephroi were grown in the presence or absence of angiotensin II or an angiotensin type 1 receptor (AT1R) antagonist and gene expression was measured by whole mount in situ hybridization. Angiotensin II induced the expression of c-Ret and Wnt11 in ureteric bud tip cells. GDNF, a Wnt11-regulated gene expressed in the mesenchyme, was also upregulated by angiotensin II but this downregulated Spry1, an endogenous inhibitor of Ret tyrosine kinase activity in an AT1R-dependent manner. Angiotensin II also decreased Spry1 mRNA levels in cultured ureteric bud cells. Exogenous angiotensin II preferentially stimulated ureteric bud tip cell proliferation in vivo while AT1R blockade increased cell apoptosis. Our findings suggest AT1R-mediated inhibition of the Spry1 gene increases c-Ret tyrosine kinase activity leading to upregulation of its downstream target Wnt11. Enhanced Wnt11 expression induces GDNF in adjacent mesenchyme causing focal bursts of ureteric bud tip cell proliferation, decreased tip cell apoptosis and branching.
肾素-血管紧张素系统中的基因突变与肾脏和尿路的先天性异常有关。肾脏发育过程中分支形态发生的主要信号通路是c-Ret受体酪氨酸激酶，其配体是胶质细胞系衍生神经营养因子（GDNF），其下游靶点是Wnt11。我们确定了血管紧张素II（一种体外输尿管芽分支诱导剂）是否影响GDNF/c-Ret/Wnt11通路。在有或无血管紧张素II或血管紧张素1型受体（AT1R）拮抗剂的情况下培养小鼠后肾，通过全胚胎原位杂交测量基因表达。血管紧张素II诱导输尿管芽尖细胞中c-Ret和Wnt11的表达。GDNF是一种在间充质中表达的Wnt11调节基因，也被血管紧张素II上调，但这以AT1R依赖的方式下调了Ret酪氨酸激酶活性的内源性抑制剂Spry1。血管紧张素II还降低了培养的输尿管芽细胞中Spry1 mRNA水平。外源性血管紧张素II在体内优先刺激输尿管芽尖细胞增殖，而AT1R阻断则增加细胞凋亡。我们的研究结果表明，AT1R介导的对Spry1基因的抑制增加了c-Ret酪氨酸激酶活性，导致其下游靶点Wnt11上调。Wnt11表达增强诱导相邻间充质中的GDNF，导致输尿管芽尖细胞增殖局部爆发、尖细胞凋亡减少和分支。
