STEM CELLS IN THE KIDNEY

当输尿管芽侵入后肾间充质并诱导其转化为肾单位的上皮时，肾脏开始发育。后肾间充质最终被分割成肾小球、近端、袢和远端上皮。我们先前已经证明后肾间充质含有能够产生所有肾单位节段的干细胞。干细胞是慢循环细胞，因此当用DNA复制期间掺入的标记物标记时，它们保留标记。他们也是 多能性的，存在于组织的区域中，该区域被保护免受环境的影响，这是一个经常缺氧的小生境。我们最近发现，成人肾脏含有标记保留细胞，当作为单细胞培养时，其分化为上皮细胞或平滑肌细胞，偶尔细胞获得神经元样表型。值得注意的是，这些成体干细胞主要存在于乳头中。我们将根据这些细胞在克隆培养物中生长的要求、增殖能力以及分化为上皮内皮细胞、平滑肌细胞和成纤维细胞谱系的能力来表征这些细胞。乳头状环境（缺氧、高渗透压、ECM蛋白生长因子等）对生长潜力的作用， 还将研究这些细胞在克隆培养物中的分化。在第二个目标中，我们将使用微阵列研究它们的基因表达。目的是鉴定膜蛋白受体及其分泌的蛋白质和生长因子。这些发现将有助于我们制定战略，为它们的扩张创造适当的文化条件。我们发现，诱导缺血性急性肾小管坏死引起的变化，在这些乳头状干细胞的丰度和分布，我们将研究他们的途径和这些干细胞的后代的部分纳入。同样，我们将研究输尿管梗阻对这些位于乳头的细胞存活的影响。最后，我们将测试某些 其受体将在关于保护、预防或改善肾脏疾病的微阵列研究中鉴定。肾脏中成体干细胞的发现有望为肾脏疾病的发病机制和治疗提供重要的基础和临床见解。

Kidney development begins when the ureteric bud invades the metanephric mesenchyme and induces it to convert to the epithelium of the nephron. Metanephric mesenchyme eventually gets segmented into glomerulus, proximal, loop and distal epithelia. We had shown previously that the metanephric mesenchyme contains stem cells capable of generating all of the nephron segments. Stem cells are slow cycling cells hence when labeled with a marker that is incorporated during DNA replication they retain the label. They are also pluripotent and exist in regions of a tissue that is protected from the environment, a niche that is often hypoxic. We recently discovered that adult kidneys contain label-retaining cells that when cultured as single cells differentiate into epithelial or smooth muscle cells with an occasional cell acquiring a neuron like phenotype. Remarkably, these adult stem cells are present mostly in the papilla. We will characterize these cells in terms of their requirement for growth in clonal cultures, their proliferative ability, and their capacity to differentiate to epithelial endothelial, smooth muscle and fibroblastic lineages. The role of the papillary environment (hypoxia, hyper-osmolality, ECM proteins growth factors etc) on the potential for growth and differentiation of these cells in clonal cultures will also be studied. In a second Aim, we will study their gene expression using microarrays. The aim here is to identify the membrane protein receptors and the proteins and growth factors that they secrete. These findings will help us in developing strategies to develop appropriate culture conditions for their expansion. We found that induction of ischemic acute tubular necrosis induced a change in abundance and distribution in these papillary stem cells and we will study their pathway and the segment of incorporation of the progeny of these stem cells. Similarly we will study the effect of ureteric obstruction on the survival of these cells located in the papilla. Finally, we will test the effect of certain growth factors whose receptors will be identified in the microarray studies on protection, prevention or improvement of the renal disease. The discovery of adult stem cells in the kidney promises to yield important basic and clinical insight into the pathogenesis and treatment of renal disease.