Introduction

An increasing number of patients with end-stage renal failure are undergoing dialysis therapy worldwide. It causes both medical and medicoeconomic problems. Renal transplantation has proven a successful therapy for most patients with end-stage renal failure, as the therapy results in a significant improvement in the patients quality of life, prolongs survival and is considered cost-effective [1]. However, the annual increase in the number of new patients with end-stage renal disease who need a renal transplant, and the widening gap between the demand for and the supply of donor kidneys have led to a progressive shortage of donor organs for transplant. This has become a serious issue and is worsened by the problem of limited graft survival due to immune rejection [1].

Among the strategies to overcome these problems is kidney regeneration using stem cells. Stem cells may be divided into two large categories: organ-specific or somatic stem cells and pluripotent stem cells. In contrast to organ-specific stem cells that generally have a limited potential for growth and differentiation, pluripotent stem cells, such as embryonic stem cells (ESCs) [24] and induced pluripotent stem (iPS) cells [57], have a virtually unlimited replicative capacity on culture dishes and are theoretically able to give rise to any cell type in the body. Stem cells have increasingly been used as a model system for understanding developmental mechanisms. In addition, in vitro culture and differentiation of stem cells offer unique opportunities for disease modeling, drug discovery, toxicology and cell replacement therapy [8]. The generation of specific functional cell types from ESCs has been demonstrated, including neural cells (several kinds of neuron and glia), vascular endothelia and smooth muscle, cardiomyocytes, hematopoietic cells, pancreatic insulin-producing cells and hepatocyte-like cells [8]. However, the protocol for in vitro differentiation of pluripotent stem cells into renal lineage cells has not been fully established.

Other approaches to regenerate kidney have also been investigated using organ-specific local stem cells within the kidney and bone marrow-derived hematopoietic stem cells [9]. Kidney regeneration using mesenchymal stem cells localized in bone marrow has also been examined [10]. However, the approaches are still being developed and the role of these stem cells in kidney regeneration remains to be well defined.

Therapeutic approaches using human ESCs face two major problems. One is the ethical issue derived from the use of human fertilized eggs, and the other is immune rejection in any cell or tissue transplantation due to histocompatibility antigenic differences between ESCs and patients. These problems have been overcome by a breakthrough experiment by Takahashi and Yamanaka. They identified four factors normally found in ESCs, Oct3/4, Sox2, c-Myc and Klf4, that were sufficient to reprogram both mouse and human somatic cells to closely resemble mouse and human ESCs [57]. They named these iPS cells. Since iPS cells can be generated from somatic cells of patients, clinical approaches using iPS cells are not associated with the two above problems (use of human fertilized egg and immune rejection). In the next natural step after iPS cell creation, significant progress has been made in redifferentiating iPS cells into somatic cells. As is the case with ESCs, iPS cells have been redifferentiated into several somatic tissues, including active motor neurons [11], insulin-secreting islet-like clusters [12], hepatocyte-like cells [13,14] and a number of cardiovascular cells (arterial endothelium, venous endothelium, lymphatic endothelium, cardiomyocytes), but not kidney [15,16].

This chapter first summarizes the mechanisms of kidney development and the research on the directed differentiation of ESCs into renal lineages based on the knowledge of kidney development. In vitro generation of kidney using the undifferentiated cell mass in amphibian eggs, similar to mammalian pluripotent stem cells in that the cell mass can differentiate into various organs in vitro, is also described as a reference to kidney regeneration in mammals. Recent advances in the iPS cell research and technology are then reviewed, and finally the future direction of iPS cells in the field of regenerative nephrology is described.

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Induced Pluripotent Stem Cell - an overview ...