Gattone V H, Maser R L, Tian C, Rosenberg J M, Branden M G
Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City 66160-7400, USA.
Dev Genet. 1999;24(3-4):309-18. doi: 10.1002/(SICI)1520-6408(1999)24:3/4<309::AID-DVG14>3.0.CO;2-5.
Currently, there is little understanding of what factors regulate the development of urine concentrating capability in normal or polycystic kidney. The present study examined the developmental expression of genes associated with urine concentration in developing mice, including C57BL/6J-cpk/cpk mice with autosomal recessive-infantile (AR) polycystic kidney disease (PKD). Concentration of urine requires: 1) medullary collecting ducts (CD) located within a hypertonic interstitium, 2) CD cell expression of functional arginine vasopressin V2 receptors (AVP-V2R), and 3) the presence of appropriate CD water channels (aquaporins, AQP 2 and 3). An increase in urine osmolarity, normally seen between 1 and 3 weeks of age, was absent in cpk cystic mice. Aldose reductase mRNA expression (a gene upregulated by medullary hyperosmolarity) increased in normal mice, but remained low in the cystic kidney, suggesting the absence of a hypertonic medullary interstitium. AVP-V2R, AQP2, and AQP3 mRNA expression normally increase between 7 and 14 days. However, all were dramatically overexpressed even at 7 days of age in the cpk kidney in vivo, but decreased in vitro. Activation of the AVP-V2 receptor stimulates the production of cAMP, a substance known to promote cyst enlargement. To determine if CD cAMP, generated from increased AVP-V2Rs, was accelerating the PKD, cystic mice and their normal littermates were treated with OPC31260, a relatively specific AVP-V2R antagonist. OPC31260 treatment of cystic mice led to an amelioration of the cystic enlargement and azotemia. Treatment also decreased renal AQP2 mRNA but increased AVP-V2R and AQP3 mRNA expression in vivo. AVP upregulates the expression of AVP-V2R, AQP2, and AQP3 mRNAs in vitro. Renal EGF, known to inhibit AVP-V2R activity, downregulates AVP-V2R mRNA in vitro. Brief in vivo EGF treatment, known to decrease PKD in cpk mice, led to increased expression of AVP-V2R, AQP2, and AQP3 mRNAs at 2 weeks in both normal and cystic mice but no change was evident at 3 weeks of age. In conclusion, the development of urinary concentration ability correlates with the development of an increased medullary osmotic gradient which is diminished in murine ARPKD. However, CD genes associated with this process are overexpressed in vivo but underexpressed in vitro in the cystic kidney. The overexpression and/or overactivity of the AVP-V2R appears to contribute to the progression of PKD since an AVP-V2R antagonist inhibits cystic renal enlargement in the cpk mouse.
目前，对于正常或多囊肾中调节尿液浓缩能力发展的因素了解甚少。本研究检测了发育中小鼠中与尿液浓缩相关基因的发育表达情况，包括患有常染色体隐性婴儿型（AR）多囊肾病（PKD）的C57BL/6J-cpk/cpk小鼠。尿液浓缩需要：1）位于高渗间质中的髓质集合管（CD）；2）功能性精氨酸加压素V2受体（AVP-V2R）的CD细胞表达；3）合适的CD水通道（水通道蛋白，AQP 2和3）的存在。cpk囊性小鼠在1至3周龄时通常出现的尿渗透压升高情况并未出现。醛糖还原酶mRNA表达（一种受髓质高渗上调的基因）在正常小鼠中增加，但在囊性肾中保持低水平，提示不存在高渗的髓质间质。AVP-V2R、AQP2和AQP3 mRNA表达通常在7至14天之间增加。然而，在体内cpk肾中，即使在7日龄时所有这些基因也都显著过表达，但在体外却降低。AVP-V2受体的激活会刺激cAMP的产生，cAMP是一种已知会促进囊肿增大的物质。为了确定由增加的AVP-V2R产生的CD cAMP是否正在加速PKD，对囊性小鼠及其正常同窝小鼠用相对特异性的AVP-V2R拮抗剂OPC31260进行治疗。用OPC31260治疗囊性小鼠导致囊肿增大和氮质血症得到改善。治疗还降低了肾AQP2 mRNA，但在体内增加了AVP-V2R和AQP3 mRNA表达。AVP在体外上调AVP-V2R、AQP2和AQP3 mRNA的表达。已知抑制AVP-V2R活性的肾表皮生长因子（EGF）在体外下调AVP-V2R mRNA。已知能减少cpk小鼠PKD的短暂体内EGF治疗导致正常和囊性小鼠在2周龄时AVP-V2R、AQP2和AQP3 mRNA表达增加，但在3周龄时无明显变化。总之，尿液浓缩能力的发展与髓质渗透梯度增加的发展相关，而在小鼠ARPKD中髓质渗透梯度减小。然而，与该过程相关的CD基因在体内过表达，但在囊性肾体外表达不足。AVP-V2R的过表达和/或过度活性似乎促成了PKD的进展，因为AVP-V2R拮抗剂可抑制cpk小鼠的囊性肾增大。
