All Stem Cells Japan

Abstract
Summary: Spinal cord injury (SCI) results in loss of nervous tissue and consequently loss of motor and
sensory function. There is no treatment available that restores the injury-induced loss of function to a degree
that an independent life can be guaranteed. Transplantation of stem cells or progenitors may support spinal
cord repair. Stem cells are characterized by self-renewal and their ability to become any cell in an organism.
Promising results have been obtained in experimental models of SCI. Stem cells can be directed to
differentiate into neurons or glia in vitro, which can be used for replacement of neural cells lost after SCI.
Neuroprotective and axon regeneration-promoting effects have also been credited to transplanted stem
cells. There are still issues related to stem cell transplantation that need to be resolved, including ethical
concerns. This paper reviews the current status of stem cell application for spinal cord repair.
 
INTRODUCTION
Stem cells proliferate, migrate, and differentiate to form organisms during embryogenesis. During adulthood,
stem cells are present within tissues/organs including the central nervous system (1–5), where they may
differentiate into neurons (6). Since the identification and characterization of stem cells, a great deal of interest has been given to their potential for treatment of spinal cord injury (SCI), traumatic brain injury, and degenerative brain diseases (7–12). Considering their characteristic abilities to self-renew and differentiate into any cell type in the body, the therapeutic promise of stem cells is justified. Before effective therapies can be developed, several issues need to be addressed and resolved. These issues range from increasing our basic knowledge about the stem cell’s biology to prevailing over moral concerns fueled by religious and/or political ideas.
 
STEM CELL DEFINITIONS
A stem cell is defined by its ability of self-renewal and its totipotency. Self-renewal is characterized by the ability to undergo an asymmetric division in which one of the resulting cells remains a ‘‘stem cell,’’ without signs of aging, and the other (daughter) cell becomes restricted to one of the germ layers. A stem cell may become quiescent and at later stages re-enter the cycle of cell division (13,14) (Figure 1).
A true stem cell is a totipotent cell; it can become any cell type present in an organism. Many consider the zygote to be the only true totipotent (stem) cell because it is able to differentiate into either a placenta cell or an embryonic cell. Others define the cells of the inner cell mass within the blastocyst as embryonic stem cells (ESCs). These cells are pluripotent because they can not become a placenta cell (Table 1). Besides ESCs, undifferentiated cells can be found among differentiated cells of a specific tissue after birth. These cells are known as adult stem cells, although a better term would be ‘‘somatic stem cell’’ because they are also present in
children and umbilical cords. There is ample evidence that adult stem cells are not restricted to a particular
germ layer and can transdifferentiate (15–19). An M. Oudega is now at the Departments of Physical Medicine and
Rehabilitation and Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
Stem Cell–Based Therapies 105 #1 important advantage of adult stem cells over ESCs is that they can be harvested without destruction of an embryo. As a result, adult stem cells have gained ample interest for their application in a variety of disorders. See More