The adult stem cells refer to the undifferentiated cells that are found all through the body after the body has undergone development (Jurukovski, 2012). The adult stem cells multiply through division in order to replenish the cells that are dying as well as regenerating the tissues that have been damaged. These cells are also referred to as somatic stem cells and are found in juvenile and adult animals as well as human bodies. The ability of the adult stem cells to divide or have an indefinite self–renewal has gathers great interest in science. The cells have been suggested as having the capability of generating all types of cells from which they have been taken (Jurukovski, 2012).
The use of adult stem cells is not considered to have controversies like the embryonic stem cells. This is because the cells are derived from tissues samples that are taken from human rather than the destroyed human embryos. The application of the adult stem cells has been studied both in human and in models such as rats and mice. The adult stem cells are divided into either multipotent or unipotent cells. The multipotent cells refer to the cells that are produced in the bone marrow and are involved production of a number of blood cell types. The unipotent cells refer to only the cells that are epidermal produced (Jurukovski, 2012).
A stem cell usually has two main properties such as being self-renewal and having the potential for multipotency. Self-renewal is the ability for a cell to undergo numerous cell division cycles while still maintaining the state of undifferentiated. Multipotency, which is also known as multidifferentiative potential, refers to the ability of the cell to generate progeny of different distinct cell types such as glial cells and neurons. This is unlike the unipotent cells that are only capable of producing a single type of cells (Mlsna, 2010).
Some researchers, however, do not see the property of multipotency as an essential requirement for a stem cell. They believe that there also exists stem cell that are unipotent and at the same time self-renewing (Mlsna, 2010). The two properties can be shown with ease especially in the in vitro setups where methods like the clonogenic assay are used. These methods are used to characterize the progeny of a single cell. However, some of the cell cultures that are used in vitro have potential of altering the behavior of the cells. It has been challenging to provide evidence that a particular subgroup of cells has the properties of stem cell in, an in vivo setup. This has resulted into a considerable debate as to whether some of the adult stem cells that have been proposed are indeed stem cells.
Just like the embryonic stem cells, the adult stem cells have the capability of differentiating into a variety of cell types. However, they are usually restricted to a number of lineages, unlike the embryonic stem cells. Transdifferentiation refers to the ability of a particular stem cell that belongs to one lineage changing to another lineage. For example, neural stem cells that are harvested from the brain are usually derived from the ectoderm cells and can differentiate to form endoderm, mesoderm and ectoderm (Clarke, et al., 2000). Similarly, stem cells taken from the bone marrow and usually derived from mesoderm may differentiate forming lungs, liver, gastrointestinal tract as well as the skin (Krause, et al., 2001). This calls for a specific lineage of adult stem cells to be used in stem cell therapy, a practice which is not easy.
Transdifferentiation is usually induced through the modification of the growth medium when the cells are cultured in vitro. In an in vivo, setup, transdifferentiation is attained by transplanting the stem cells into an organ in the body that is different from the organ where the stem cells were originally isolated. There still no common understanding on the therapeutic relevance in the plasticity of the adult stem cells among scientists. Recent studies have indicated the presence of pluripotent stem cells in blood and tissues in adults although dormant (Kucia, et al., 2006).
Research on the adult stem cell has focused mainly on understanding the molecular mechanisms that control both self-renewal and differentiation. One of the pathways that have been suggested includes the Notch pathway (Dontu, et al., 2004). Some of the adult stem cells hematopoietic, mammary, intestinal mesenchymal, endothelial and neural stem cells. in the process of differentiating, stem cells form an intermediate cell type before they can achieve full differentiated state. This intermediate cell is referred to as a progenitor or precursor cell. The distinguishing feature between the precursor and the stem cell are shown in Figure 1 below (Bethesda, 2009).
Figure 1: Distinguishing features between a precursor and stem cells
One of applications where adult stem cell has been used is in the treatment of leukemia and other related blood or bone cancers (Science Daily, 2012). The cells have also been used in the treatment of a number of diseases such as spinal cord injury, peripheral vascular disease and liver cirrhosis. There has also been commercial application of the Mesenchymal Stem Cells. The treatment with the cells is either through direct injection or cell replacement is done at the site of where repair is needed. The vascular delivery is not used since it undergoes the pulmonary first pass effect (Fischer, et al., 2009).
Works Cited
Bethesda, M. D., 2009. 4. The Adult Stem Cell. [Online] Available at: http://stemcells.nih.gov/info/scireport/pages/chapter4.aspx[Accessed 28 April 2013].
Clarke, D. L., et al. "Generalized Potential of Adult Neural Stem Cells." Science 288.5471 (2000): 1660–1663.
Dontu, G., et al. "Role of Notch signaling in cell-fate determination of human mammary stem/progenitor cells." Breast Cancer Research 6.6 (2004): R605–6015.
Fischer, U. M., M. T Harting and F. Jimenez. "Pulmonary passage is a major obstacle for intravenous stem cell delivery: the pulmonary first-pass effect." Stem Cells and Development 18.5 (2009): 683–692.
Jurukovski, V. "Tissues." 2012. 27 April 2013.
Krause, D. S., et al. " Multi-Organ, Multi-Lineage Engraftment by a Single Bone Marrow-Derived Stem Cell." Cell 105.3 (2001): 369–377.
Kucia, M., et al. "A population of very small embryonic-like (VSEL) CXCR4+SSEA-1+Oct-4+ stem cells identified in adult bone marrow." Leukemia 20.5 (2006): 857–869.
Mlsna, Lucas. "Stem Cell Based Treatments and Novel Considerations for Conscience Clause Legislation." 2010. 28 April 2013.
Science Daily. "Adult stem cell." 2012. 27 April 2013.
