Adult Stem Cells

Overview

 * An adult stem cell is an undifferentiated cell found among differentiated cells in a tissue or organ, can renew itself, and can differentiate to yield the major specialized cell types of the tissue or organ
 * Have the ability to
 * Divide and create another cell like itself
 * Divide and create a cell more differentiated than itself
 * Most adult stem cells are multipotent and are generally defined by their origin
 * Bone marrow-dervied stem cells (BMSC)
 * Adipose-derived stem cells (ASC)
 * Endothelial stem cells (ESC)
 * Tissues contain adult stem cells
 * Adult stem cells have been identified in many organs and tissues
 * There are a very small number of adult stem cells in each tissue
 * Adult stem cells reside in a specific area of each tissue where they remain undifferentiated form many years until they are activated by disease or tissue injury
 * Adult tissues that are reported to contain stem cells include brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, and liver
 * Identify adult stem cells
 * Isolating the cells, growing them in cell culture, and manipulating them, often by adding growth factors or other biochemicals, to determine what differentiated cells types they can become

Differentiation of Adult Stem Cells

 * Adult stem cells can differentiate into cell types that have specialized structures and functions induced by growth factors or biochemicals
 * Bone marrow stromal cells (mesenchymal stem cells) give rise to a variety of cell types: bone cells (osteoblasts), cartilage cells (chondrocytes), fat cells (adipocytes), smooth muscle cells, endothelial cells, and cardiomyocytes
 * Neural stem cells in the brain give rise to its three major types: nerve cells (neurons) and two categories of non-neuronal cells - astrocytes and oligodendrocytes
 * The edpidermal stem cells in skin give rise to keratinocytes, which migrate to the surface of the skin and form a protective layer

Examples of Adult Stem Cells

 * Bone marrow is the most abundant source of stem cells having the ability to self-renew, proliferate, migrate, and differentiate into many types of cells
 * Hematopoietic stem cells (HSC)
 * A cell that can renew itself, can differentiate to a variety of specialized cells, can mobilize out of the bone marrow into circulating blood, and can undergo programmed cell death
 * HSCs give rise to all the blood cell types
 * Bone marrow-derived mesenchymal stem cells (MSC)
 * Multipotent stem cells that can differentiate into a variety of cell types, both in vitro and in vivo: osteoblasts, chondrocytes, adipocytes, et al.
 * MSCs are widely used for tissue engineering of bone cartilage, blood vessel, and adipose

Advantages

 * Multipotent and can differentiate into many different cell types
 * Can be isolated from the patient's body and used in the same patient to avoid rejection by immune system
 * The use of adult stem cells in research and therapy is not as controversial as embryonic stem cells, because the production of adult stem cells does not require the destruction of an embryo

Disadvantages

 * Number of adult stem cells in tissues is small
 * The isolation and identification process is not well defined
 * Ability to proliferate under in vitro culture conditions is less than in vivo