Blog Junction | SBAmin.com: Reprogramming the Cell

Reprogramming Cell is perhaps the most thought provoking topic to me ever since I started blogging in applied genomics. Recently, upon reading stem cell bias article¹, I found relevant articles and book chapters on reprogramming the cell which as expected created many unsolved questions, loopholes and finally headache! This post tries to summarize development in stem cell research and current hurdles in application of stem cell based therapies with emphasis on following keywords based sub-topics: signal transduction, self-renewal, differentiation, reprogramming MAPCs, plasticity, RNAi, Dynamic DNA, cellular therapy, therapeutic transgene.

Basics of stem cell^{2, 3}:

Differentiation (-potency) power:

Totipotent: A fertilized egg having potential to generate all the cells and tissues that make up an embryo and that support its development in utero.
Pluripotent: A Stem cells that can give rise to any type of cells derived from all three embryonic germ layers—mesoderm, endoderm, and ectoderm.
Unipotent: A mature adult cell capable of differentiating along only one lineage. i.e. skin, muscle, heart, red blood cell, etc.

A Stem cell is a unspecialized cell having unique property of self-renewal for indefinite period and differentiation (pluripotency) into specialized cells (i.e. hematopoietic cell line, neurons, etc.) under appropriate conditions.

An Embryonic stem cell (ESC) is derived from the inner cell mass of the blastocyst (4-5 days old fertilized egg) at a stage before it would implant in the uterine wall. Because of legal and ethical issue, more precise definition of embryonic stem cell is one that develop from eggs that have been fertilized in vitro - in an in vitro fertilization clinic - and then donated for research purposes with informed consent of the donors. They are not derived from eggs fertilized in a woman's body. Under standardized conditions of cell culturing in-vitro, the original 30 cells of the inner cell mass by process of self-renewal yield millions of embryonic stem cells after six or more months without differentiating, meaning they are pluripotent with normal genotype which are then referred to as an embryonic stem cell line.

An Adult stem cell (Somatic stem cell; ASC) is an undifferentiated (unspecialized) cell that is characteristically found in a differentiated (specialized) tissue; Although it has indefinite self-renewal property, it becomes specialized only into certain specialized cell types of the tissue from which it is originated. i.e. a hematopoietic stem cell can give rise to different blood cells and not other tissue cells - neurons, muscle, etc. Unlike ESC, there is no evidence, at this time, of an adult stem cell that is pluripotent. Also, in-vitro culturing ASC is difficult compare to ESC. Sources of adult stem cells are bone marrow, blood stream, cornea and retina of the eye, the dental pulp of the tooth, liver, skin, gastrointestinal tract, and pancreas.

Plasticity (Transdifferentiation) is a recently debated¹ phenomenon of adult stem cell showing possibility that stem cells from one tissue may be able to give rise to cell types of a completely different tissue. i.e. blood cells from neurons or vice versa.

Niche Cellular microenvironment providing support and stimuli necessary to sustain self-renewal⁴.

Multipotent adult progenitor cells (MAPCs) are said to be an exceptional population of adult cells which may have pluripotent potential by phenomenon of plasticity (transdifferentiation). This term is surrounded by dispute currently¹.

Clone is a line of cells that is genetically identical to the originating cell.

Applied Genomics is a branch of medicine which deals with exploration of various applications to introduce current genetic cocnepts in preventing / treating diseases.

Therapeutic transgene is a novel method of gene based therapy by which new genetic material is introduced into the patient. It involves introduction or elimination of specific genes by using molecular biology techniques to physically manipulate genetic material - to alter or supplement the function of an abnormal gene by providing a copy of a normal gene, to directly repair such a gene, or to provide a gene that adds new functions or regulates the activity of other genes. Scientists usually deploy viral vector as a delivery vehicle for introducing such transgene into desired cell line.

Cellular (cell based) therapy is a type of therapy in which stem cells are cultured and differentiated in a desired specialized cell in-vitro (sometimes with integrated therapeutic transgene) which are then introduced in the body to replenish deficient or damaged unipotent adult cell line.

Signal Transduction is a mechanism by which internal and external factors bring changes in the cell structure and function. It is the most fundamental key which once understood fully, will bring dramatic shift in applied genomics. e.g. Understanding how stem cells maintain their inherent property of self-renewal and pluripotency, which signals are essential for such properties will help scientists to manipulate signal system in a desired way maintain healthy body system.

Cell Reprogramming is a concept of manipulating signal transduction mechanisms and growth factors so as to give a mature unipotent adult cell power of plasticity and become pluripotent or differentiating into at least one other different cell line.

Why ASC:

Scientists are currently focusing more on making ASC pluripotent in a hope to override ethical issues associated with ESC. Another theoretical advantage of ASC is that autologus ASCs are immune friendly and chances of immune rejections are less compare to use of donor ESCs.

Unsolved questions with ASC:

1. Source(s) of ASC in the body, their quantity.

2. How is ASC formed? - from ESC or de-novo?

3. Signals controlling ASCs self-renewal and property of not being pluripotent (switching off signals?)

4. Understanding plasticity phenomenon, if present.

5. In-vitro culturing of ASC which is currently difficult.