In recent times, attention has been drawn to a particular area of biological science involving the use of stem cells. In biology, these are a type of undifferentiated cells which are capable of being multipotent or even pluripotent (embryonic stem cells only). This truly remarkable characteristic has intrigued and ultimately inspired scientists to develop techniques that can be applied to the medical field.
However we must appreciate that there are two types of stem cell. Adult and embryonic. Embryonic stem cells are derived from a 'small hollow ball of cells' called a blastocyst. This is one of the immediate results of fertilisation. What scientists are interested in is the inner cell mass - these cells are undifferentiated but more importantly they are pluripotent. This means that they have the capacity to develop into any type of cell in the body. Conversely, adult stem cells are considered multipotent, meaning they have the capability to develop into one type of cell however the variety is limited. In the human body, the most common extraction point for adult stem cells is bone marrow (although many other tissues and organs are known to produce stem cells, including the brain, heart and skin). Interestingly, foetuses have also been found to have stem cells.
Some adult stem cells such as fibroblasts can actually be reprogrammed genetically for them to 'behave like embryonic stem cells'. These are known as induced pluripotent stem cells.
Another fascinating property of stem cells is that during asymmetric division, two daughter cells are produced with contrasting characteristics. One cell is the result of self-renewal, whilst the other the result of differentiation. This explains how our body is able to heal and repair itself - any type of cell can be made available to any site where it is needed. This ability for these cells to replicate themselves and differentiate is a marvel of genetics. So how is this controlled? An engaging article in a Biological Sciences Review magazine gave me an insight.
Differentiation of stem cells is dependent on 'changing the expression of the self-renewal and pluripotency control genes'. Scientists have carefully monitored which genes switch on or off during differentiation for a variety of cell types. The result is, we can identity which genes control differentiation for a vast array of cell types. An example given is that for the production of cartilage cells (chondroctyes), adult stem cells need to 'express high levels of the gene SOX-9. This gene encourages the expression of a different gene called COL2A1 as a consequence. As genes code for polypeptides, it follows that COL2A1 codes for the production of the type-2 collagen protein. Cartilage largely comprises of this protein.
When adult stem cells are used in medicine, scientists tend to use induced pluripotent stem cells (see above) as their diversity for differentiation is a significant advantage. However for medical applications in the body, sometimes we require the aid of biomaterials to supplement the use of implanted stem cells. The example used in this article is treatment of back pain due to a slipped disc. The pain is caused by an indentation into the spinal cord by a disc, causing a compression. Intevertebral disc cells are produced by stem cells in a lab, which can them be cultured and left to proliferate. One approach to treating the condition is to 'seed' the cells into a synthetic hydrogel. This compound exists as a gel at body temperature, it is also thermosensitive. This gel can then be 'injected into the damaged disc, where it would form a gel and act like a shock absorber, similar to a natural disc'.
The potential of stem cells in medical application is exciting and promising with continuous ongoing research. Diseases such as Alzheimer's and muscular dystrophy could one day be in combat with emerging stem cell treatments to improve the lives of those who endure the pain of these conditions.
Credit to Dr Stephen Richardson, lecturer in cell tissue engineering at the University of Manchester who wrote for the Biological Sciences Review (Volume 26, Number 4)
A very profound area of research, hoping to make big strides in the next few years!
ReplyDelete