Indianapolis, Ind. November 06, 2008 A major issue in the development of regenerative medicine is the cell sources used to rebuild damaged tissues. In a review of the issue published in Developmental Dynamics, researchers state that inducing regeneration in humans from the body's own tissues by chemical means is feasible, though many questions must be answered before the process can reach clinical status.
Regeneration is a regulative developmental process ubiquitous across all species. It functions throughout the life cycle to maintain or restore the normal form and function of cells, tissues and, in some cases organs, appendages and whole organisms. The roots, stems and leaves of plants, for example, have extensive regenerative capacity, and entire plants can grow from single cells or small cuttings.
The regenerative capability of most vertebrate animals, however, is restricted to certain tissues. In the absence of injury, many cell types such as epithelia and blood cells turn over rapidly, while others such as hepatocytes, myofibers, osteocytes, and most neurons, have low turnover rates or do not turn over at all. In organisms that grow throughout life, such as fish, the total number of cells in various tissues increases continuously, indicating that the number of new cells produced is higher than the number of cells lost.
By contrast, the loss of normal tissue mass and/or architecture to acute injury or disease in humans requires a more intense and qualitatively different regenerative response that restores the tissue to its original state. This response is called injury-induced regeneration.
A major issue for cell transplant therapies is the source of the cells to be used. Three sources of cells can be tapped for transplant: differentiated tissues, adult stem cells (ASCs) and derivatives of embryonic stem cells (ESCs). Adult stem cells regenerate epithelia, brain tissue, muscle, blood and bone. They have also b
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