Understanding Cellular Reprogramming

The journal Science had Cellular Reprogramming at the very top of its list, on the best advances made in research in year 2008. For a novice to understand cellular reprogramming it is important to know more about cells, cell growth and their role in eliminating disease.

Cells are the basic structural units of all our body systems. Stem cells differ from other cells, since they are unspecialized and have the ability to regenerate by cell division. Unspecialized cells are inconspicuous in shape, size and function. They tend to hide deep in tissues making their isolation difficult. However, when these stem cells are grown under specific conditions, they have the capability to become specialized cells. The liver has cells that are specific to secreting bile while the pancreas have cells that secrete insulin. The cells that are in the heart are different from those in the liver. Therefore if one has to grow cells in the laboratory i.e. in vitro, then the cell must be nurtured according to its function making it compatible with the function of the diseased organ.

When an egg is fertilized by a sperm and the embryo begins to grow, a cluster of 30-40 stem cells eventually transform into extremely specialized cells that with further growth and development form organs. Scientists recognize these stem cells from specialized cells from their surface proteins. The surface proteins give a cell identity to the different cell types. However, fingerprinting all cell types is a long drawn process. In the embryonic stage, all cells have genetic codes that are fully activated in expression. With development, the genetic codes get silenced as cells mature and become specialized. This was the first breakthrough of cellular reprogramming.

Scientists are now able to turn on the silenced genetic codes and give expression to certain required codes in a cell by reverting an adult stem cell into a more versatile stem cell. Thus, reprogramming is different from transgene therapy where new genetic material is introduced and altered. The need to reprogram cells is to make stem cells more versatile and adaptable to the body system. A stem cell introduced without reprogramming results in the formation of a teratoma or a tumor in the body.

Cellular therapy uses cells cultured in vitro as per the specifications and requirement of the disease after which they are introduced into the body to replenish the body with healthy cells. Our body system has different cells and depending on the characteristics of each cell type we have different organs. Stem cells do not have any specific job. To develop stems cells from the tissue of one organ and make them biocompatible with the tissue of another organ requires ‘plasticity’. Plasticity is the ability of a stem cell from one tissue to generate stem cells of another tissue type. This is achieved through guided and tailored growth which is the technique of reprogramming.

Stem cells in most body organs, renew and replace diseased or aged cells.They function to refurnish the body with cells throughout an individual's life. In Parkinson's disease, the cells in the brain responsible for controlling non-useful muscle movement, degenerate and die. Thus, progressively uncontrolled movements, tremors, and spasms increase. Till date, there is no cure for Parkinson's disease because the way to renew the specialized nerve cells that are dead has not been configured. Reprogramming of stem cells into brain cells offers a veritable hope. Researchers have learned how to differentiate embryonic stem cells into the specific type of brain cells lost in Parkinson's disease. They have transplanted adult nerve stem cells into rat brains with success. Transplantation of reprogrammed stem cells into the brains of patients may one day hold hope to a patient of Parkinson's disease, restoring movement control.

In type I diabetes, the beta cells of the pancreas that normally produce insulin are destroyed by an individual’s overactive immune system. Without insulin, the cells of the body are unable to take up glucose and so they starve.

Research is underway on understanding the unique properties of stem cells viz. regeneration and proliferation. A stem cell has no specialized function but can be groomed to become specialized. The most anticipated application in the arena of cellular reprogramming is harvesting ‘made to order’ cell lines by reprogramming cells from patients. This would be an important landmark of cellular therapy to terminate any disease.