Stem cells
From DrugPedia: A Wikipedia for Drug discovery
Contents |
[edit] INTRODUCTION
There is still no universally acceptable definition of the term ‘stem cells’ , but stem cells have following characteristics:-
- They are unspecialized cells that renew themselves for long periods through cell division.
- Under certain physiologic condition or experimental condition, they can be induced to convert into cells with special functions for e.g. beating cells of heart muscle or insulin producing cells of pancreas.
An embryo in an initial stage i.e. 3-5 days old, is called as blastocyst . Stem cells in developing tissues give rise to various kinds of specialized cells that makes heart, lung, skin and other tissue. In adults, stem cells generate replacements for cells in tissues such as bone marrow, muscle, and brain which are lost through normal wear and tear, injury or disease. In this way it might be possible someday; stem cells will become the basis for treating disease like Parkinson’s disease, Diabetes, and Heart disease.
Stem cells can also be used for the screening new drugs and toxins, and in understanding birth defects.
[edit] EMBRYONIC STEM CELLS
These cells are derived from embryos, specifically those embryos that develop from eggs that have been fertilized in-vitro. The embryos from which human embryonic stem cells are derived are 4-5 days old and are hollow microscopic balls of cells called blastocyst.
Blastocyst includes 3 structures:-
a) The tropoblast – the layer of cells that surrounds the blastocyst.
b) The blastocoel – which is a hollow cavity inside the blastocyst.
c) The inner cell mass – it is the group of 30 cells at one end of the blastocoel.
[edit] How embryonic stem cells can be exploited?
Growing cells in a laboratory is known as cell culture. Human embryonic stem cells are isolated by transferring the inner cell mass into a culture medium. Embryonic stem cells that have been proliferated in cell culture for six or more months without differentiating are called as pluripotent and appear genetically normal and are referred to as an embryonic stem cell line. Directing the differentiation of embryonic stem cells into specific cell types, it might be possible to the resulting, differentiated cells to treat certain diseases. Disease which can be treated from cells generated from embryonic stem cells include Parkinson’s disease, Diabetes, Traumatic spinal cord injury, Purkinje cell degeneration, Dischenne’s muscular dystrophy, Heart disease and Vision & Hearing loss.
[edit] ADULT STEM CELLS
An adult stem cell is an undifferentiated cell found among the differentiated cells in a tissue or organ that can:-
a) Can renew itself
b) And, can differentiate to yield the major specialized cell types of the tissue or organ.
The main role of adult stem cells in a living organism is to maintain and repair the tissue in which they are found. Adult stem cells are also known as somatic cells. Unlike embryonic stem cells, which are defined by their origin (the inner cell mass of blastocyst), the origin of the adult stem cells in the mature tissue is unknown.
Certain kinds of stem cells have ability to differentiate into a number of different cell types, given right conditions. These cells have been identified in many organs and tissues, and their number is very small in each tissue. Stem cells reside in specific area of the tissue where they remain quiescent (non-dividing) for many years until they are activated by a disease or tissue injury. The adult tissue reported to contain stem cells include brain, bone marrow, peripheral blood, blood vessels, skeletal muscles, skin and liver. Potential treatments which might be possible involving adult stem cells include the dopamine-producing cells in the brains of Parkinson’s patients, developing insulin-producing cell for type-I Diabetes and repairing damaged heart muscle following a heart attack with cardiac muscle cells.
[edit] Types of Adult stem cells
Adult stem cells have ability to form specialized cell types of other tissues, which is known as transdifferentiation or plasticity. In a living organism, stem cells can divide for a long period and can give rise to mature cell types that have characteristic shapes and specialized structures and functions of a particular tissue.
Various types of adult stem cells can be:-
a) Hematopoietic stem cells – these cells give rise to all types of blood cells: red blood cells, neutrophils, basophills, eosinophills, monocytes, macrophages, and platelets.
b) Bone marrow stromal cells (mesenchymal stem cells) – these give rise to a variety of cell types: bone cells (osteocytes), cartilage cells(chondreocytes), fat cells (adipocytes), and other kinds of connective tissue cells such as those in tendons.
c) Neural stem cells – these cells are found in brain and give rise to its three major cell types: nerve cells (neurons) and two categories of non-neuronal cells-astrocytes and oligodendrocytes.
d) Epithelial stem cells – these are found in the lining of the digestive tract occur in deep crypts and give rise to several cell types: adsorptive cells, goblet cells, panet cells, and enteroendocrine cells.
e) Skin stem cells – these cells occur in the basal layer of the epidermis and the base of hair follicles. The epidermal stem cells give rise to keratinocytes, which migrate to the surface of the skin and form a protective layer. The follicular stem cells can give rise to both the follicle and to epidermis.
Adult stem cells are pluripotent and they exhibit plasticity or transdifferentiation. Their plasticity can be explained by following facts:
- Hematopoietic stem cells may differentiate into: three major type of brain cells (neurons, oligodendrocytes, and astrocytes); skeletal muscle cells; and liver cells.
- Bone marrow stromal cells differentiate into: cardiac muscle cells and skeletal muscle cells.
- Brain stem cells may differentiate into: blood cells and skeletal muscle cells.
[edit] CONCLUSION
Human embryonic stem cells may yield information about the complex event that occurs during human development. The differentiation of undifferentiated cells to specialized cells is related(indirectly) to the concept of turning genes on and off, as cancer and birth defects are due to abnormal cell division and differentiation, a better understanding of genetic and molecular controls of these processes may yield information about how such diseases arise and new therapies can be invented. Human stem cells could also be used to test new drugs as new medications could be tested for safety on differentiated cells generated from human pluripotent cell lines. Cancer cell lines can be used to screen potential anti-tumordrugs. Conditions have to be identical when comparing different drugs, if drugs are to be screened effectively. Perhaps the most important potential application of human stem cells is the generation of cells and tissues that could be used for cell-based therapies. Stem cells, directed to differentiate into specific cell types, offer the possibility of a renewable source of replacement cells and tissues to treat diseases including Parkinson’s and Alzheimer’s diseases, Spinal cord injury, stroke, Burns, Heart disease, Diabetes, Osteoarthritis, and Rheumatoid arthritis.
