Mo Lan, Huang Hong-Ying, Zhu Xin-Hua, Shapiro Ellen, Hasty David L, Wu Xue-Ru
Department of Urology, Kaplan Comprehensive Cancer Center, New York University School of Medicine, New York, New York 10010, USA.
Kidney Int. 2004 Sep;66(3):1159-66. doi: 10.1111/j.1523-1755.2004.00867.x.
The tubular fluid of the mammalian kidney is often supersaturated with mineral salts, but crystallization rarely occurs under normal conditions. The unique ability of the kidney to avoid harmful crystal formation has long been attributed to the inhibitory activity of the urinary macromolecules, although few in vivo studies have been carried out to examine this hypothesis. Here we examined the role of Tamm-Horsfall protein (THP), the principal urinary protein, in urinary defense against renal calcium crystal formation, using a THP knockout model that we recently developed.
Wild-type and THP knockout mice were examined for the spontaneous formation of renal calcium crystals using von Kossa staining. The susceptibility of these mice to experimentally induced renal crystal formation was evaluated by administering mice with ethylene glycol, a precursor of oxalate, and vitamin D(3), which increases calcium absorption. Renal calcium crystals were visualized by von Kossa stain, dark field microscopy with polarized light and scanning electron microscopy.
Inactivating the THP gene in mouse embryonic stem cells results in spontaneous formation of calcium crystals in adult kidneys. Excessive intake of calcium and oxalate, precursors of the most common type of human renal stones, dramatically increases both the frequency and the severity of renal calcium crystal formation in THP-deficient, but not in wild-type mice. Under high calcium/oxalate conditions, the absence of THP triggers a marked, adaptive induction in renal epithelial cells of osteopontin (OPN), a potent inhibitor of bone mineralization and vascular calcification. Thus, OPN may serve as an inducible inhibitor of calcium crystallization, whereas THP can serve as a constitutive and apparently more effective inhibitor.
These results provide the first in vivo evidence that THP is a critical urinary defense factor and suggest that its deficiency could be an important contributing factor in human nephrolithiasis, a condition afflicting tens of millions of people in the world annually.
哺乳动物肾脏的肾小管液中矿物质盐常常处于过饱和状态，但在正常情况下很少发生结晶。长期以来，肾脏避免有害晶体形成的独特能力一直归因于尿中大分子的抑制活性，尽管很少有体内研究来检验这一假说。在此，我们使用我们最近构建的Tamm-Horsfall蛋白（THP）基因敲除模型，研究了主要尿蛋白THP在尿液防御肾钙晶体形成中的作用。
使用冯·科萨染色法检测野生型和THP基因敲除小鼠肾钙晶体的自发形成情况。通过给小鼠喂食乙二醇（草酸盐的前体）和维生素D3（可增加钙吸收）来评估这些小鼠对实验性诱导肾晶体形成的易感性。通过冯·科萨染色、偏光暗视野显微镜和扫描电子显微镜观察肾钙晶体。
在小鼠胚胎干细胞中使THP基因失活会导致成年小鼠肾脏中自发形成钙晶体。摄入过多的钙和草酸盐（人类最常见肾结石类型的前体）会显著增加THP基因敲除小鼠肾钙晶体形成的频率和严重程度，但野生型小鼠不会。在高钙/草酸盐条件下，缺乏THP会触发肾上皮细胞中骨桥蛋白（OPN）的显著适应性诱导，骨桥蛋白是骨矿化和血管钙化的有效抑制剂。因此，骨桥蛋白可能作为钙结晶的诱导性抑制剂，而THP可作为组成性且显然更有效的抑制剂。
这些结果提供了首个体内证据，表明THP是关键的尿液防御因子，并提示其缺乏可能是人类肾结石的一个重要促成因素，肾结石每年困扰着全球数千万人。
