อัพเดตเมื่อ: ม.ค. 18
What are stem cells?
Stem cells are distinctive human cells that can develop into many varieties of cell types, from intestine cells to heart cells. In some manifestations, they also have the potential to repair damaged tissues.
Importance of Stem Cells.
Stem cells are crucial for living things for many purposes. In the 3-5 days old embryo, known as a blastocyst, the inner cells generate the whole body of the organism, which include all of the many specialized cell types and part of the body such as the heart, liver, skin, lung, eggs sperm and other tissues. In some adult tissues, such as the brain , bone marrow, and brain, separate populations of adult stem cells promote replacements for cells that are broken or death through injury, wear and tear, or disease.
Given their special regenerative abilities, stem cells offer new potentials for treating diseases such as diabetes, OA knee, and heart disease.
There are three types of stem cells:
Adult Stem Cells (ASCs)
ASCs are un-transform cells found living within specific differentiated tissues in our bodies that can renew themselves or generate brand new cells that can fill up dead or damaged tissue. You may as well see the name “somatic stem cell” used to refer to adult stem cells. The term “somatic” refers to non-progenitive cells in the body (sperms or eggs). ASCs are typically scantly in native tissues, which have rendered them difficult to study and extract for research basics.
Occupying most tissues of the human body, discrete populations of ASCs generate cells to put back those that are lost through regular repair, injury, or disease. ASCs are found throughout one’s lifetime in tissues such as the bone marrow, placenta, umbilical cord, gut, skin, fat tissue, brain, muscle, etc. In 1948, the first ASCs were extracted and used in the production of blood. There was an expansion of his procedure in 1968 when the primary adult bone marrow cells were used in clinical treatment for blood disease.
Types of Adult Stem Cells:
Mesenchymal Stem Cells
Neural Stem Cells
Skin Stem Cells
Epithelial Stem Cells
Hematopoietic Stem Cells (Blood Stem Cells)
Embryonic Stem Cells (ESCs)
Approximately 6 days after fertilization, the embryo (at this stage, called a blastocyst), carries an inner cell mass that is capable of generating all the specialized tissues that are building blocks of the human body. Obtained from the inner cell mass of an embryo that has been fertilized laboratory, ESCs are used for research purposes following informed consent. ESCs are not collected from eggs fertilized in a woman’s body.
These pluripotent stem cells, cells that are known to develop into cells and tissues of the three primary germ layers which can become almost any cell type and are only found during the early phase of development.
Tumor formation from Embryogenic stem cells.
When implanted into immunocompromised mice, human embryonic stem cells (hESCs) give rise to teratoma, a type of tumor made up of several different types of tissue, such as hair, muscle, bone, or teeth. The ability to form teratoma is a requisite typical of pluripotent stem cells.
The similarities and differences between adult and embryonic stem cells?
Embryonic and adult stem cells each have upside and downside regarding potential use for cell-based regenerative treatment. One of the significant differences between adult and embryonic stem cells is their different potential in the number and varieties of differentiated cell types they can become. Embryonic stem cells can suit all cell types of the body due to pluripotency. Adult stem cells, on the other hand, are thought to be limited to differentiating into divergent cell types of their tissue of beginning.
Embryonic stem cells can be grown comparatively quickly in culture. Adult stem cells are rare in fully grown tissues, so isolating these cells from an adult tissue is challenging, and techniques to expand their numbers in cell culture have not yet been worked out. This is an important distinction, as vast numbers of cells are needed for stem cell replacement treatment.
Scientists think that tissues derived from embryonic and adult stem cells may differ in the chance of being rejected after transplantation. We don't yet know for sure whether tissues obtain from embryonic stem cells would cause transplant rejection since relatively few clinical studies have tested the safety of transplanted cells received from embryonic stem cells.
Adult stem cells and tissues obtained from them are currently assume less likely to initiate rejection after transplantation. This is because a patient's cells could be multiplied in culture, coaxed into taking a specific cell type (differentiation), and then re-implanted into the patient. This use of adult stem cells and tissues obtained from the patient's adult stem cells would mean a significant reduction in the chance that the immune system rejects the cells. This means a considerable advantage, as immune rejection need not be circumvented through the use of immunosuppressive drugs, which may themselves cause unwanted side-effects.
Induced Pluripotent Stem Cells (iPSCs)
Induced pluripotent stem cells are stem cells that are produced in the laboratory, a middling between adult stem cells and embryonic stem cells. iPSCs are designed through the introduction of embryonic genes into a somatic cell (a skin cell, for example) that cause it to regress to a “stem cell-like” state. These cells, like ESCs, are considered pluripotent but only being discovered in 2007, these man-made stem cells are still a long way from clinical use.
In an article from the University of Nebraska Medical Center it was stated,
genetic reprogramming to produce embryonic-like cells, is novel and needs many more years of study before use in clinical treatment.
The first iPS cells were created by using viruses to insert extra copies of three to four genes known to be essential in embryonic stem cells into the specialized cell. It is not yet totally understood how pluripotency is induced by these three or four “reprogramming” genes, and this question is the focus of ongoing studies. Furthermore, recent studies have focused on alternative methods of reprogramming cells using techniques that are safer for use in clinical settings.
THE PROBLEMS OF iPSC - PRODUCTION EFFICIENCY AND APPLICATION SAFETY IN CELL TRANSPLANT THERAPY
Since iPSCs come from a genetic reprogramming technique, another serious problem is the gene set itself that is used for the initiation of pluripotency. The abnormal transcription of cancer gene can lead to tumor development from cells derived from iPSCs because of the expression of cancer gene (a gene, which in a specific situation can change a cell into a tumor cell) is associated with the creating of multiple tumors known in oncogenetic. In particular, the overexpression of the cancer gene causes mice outer layer cell change to become cancer, the aberrant expression of Sox2[cancer gene] causes the development of lump and colon carcinomas, breast tumors.
Comparison of Different Types of Stem Cells
The adult Stem cell in depth
There are many adult stem cells, maybe one or more for each tissue of the body. For the sake of brevity, the focus will be on the few that have been widely studied.
Neuro-stem cells (NSCs) The neuro-stem cells (NSCs) can turn into a fantastic array of neurons and neural-related cells such as astrocytes and oligodendrocytes.
hematopoietic stem cell (HSC) The longest studied and most clinically related adult stem cell is the hematopoietic stem cell (HSC). HAC is a not fully developed cell that can develop into all types of blood cells, including red blood cells, white blood cells, and platelets. Hematopoietic stem cells are found in the systemic blood and the bone marrow. Also called a blood stem cell.
Mesenchymal Stem Cells [MSC]
A stable, safe, and highly accessible stem cells. Mesenchymal stem cells (MSCs) are adult stem cells that can be extracted from human and animal origin. Human MSCs are the non-hematopoietic, multipotent stem cells with the capacity to become into middle germ cell layer lineage such as adipocytes [fat cell] osteocytes [bone cell], and chondrocytes [cartilage cell] as well neurocytes [nerve cell ] and inner cell layer lineages such as liver cell. Human- MSCs have been cultured multiple times in a specific medium without any severe malformation. Moreover, MSCs have immunomodulatory features, produce cytokines (substances that affect other cells), and immune receptors which regulate the microenvironment in the host tissue. Multilineage potential, balancing immunity, and create of anti-inflammatory molecules makes MSCs a useful tool in the treatment of chronic diseases. MSCs are present not only in fetal tissues but also in specific adult tissues. Efficient populations of MSCs have been found in the bone marrow. Cells which manifests characteristics of MSCs were isolated from amniotic fluid, adipose tissue, amniotic membrane, endometrium, dental tissues, menstrual blood, limb bud, peripheral blood, fetal membrane and placenta, salivary gland, sub-amniotic umbilical cord lining membrane, skin and foreskin, Wharton’s jelly and synovial fluid.
Adult Stem Cell properties
Through division, stem cells can renew themselves for long periods. All adult stem cells can split into two daughter cells, at least one daughter cell remains as a stem cell.
Multipotent: Although still able to change into different cell types, adult stem cells are limited to cells of a particular cell line.
The Healer: Adult stem cells are exquisitely reactive to the composite microenvironment in which they introduced. Importantly, in injury microenvironments or implantations, for adult stem cells, the first job is “fixing” the injury before responding to the differentiation requirement of the site or organism. This “sensory” activity is responsive to the phenomenally changing microenvironment of an injury or regenerative site since an injury site goes through essential changes from its start to the final regenerative resolution
Cell Dominant: Adult stem cells are the dominant producer in their live-cell activities. In clusters of varieties cells in tissues or at sites of injury, their secretory products control or are commanding in the tissue field related to the other cells
Immuno-Modulator: All adult stem cells produce molecules that mainly provide a barrier or protector to inhibit all of the interrogators of the immune system from entering an injury or developmental tissue field. This protector or modulatory activity is the first line of shielding against the establishment of autoimmune conditions.
Provider, Stimulator: Adult Stem Cells produce bioactive factors that structure both physically and molecularly the injury or developmental (regenerative) functions. The secreted factors contribute to a progressively and dynamically changing microenvironment that supports regenerative activities (not the maintenance of the innervated muscle).
Regenerative: Adult stem cells allow regenerative microenvironments and under the appropriate conditions; the result may be the start of their self-differentiation cascade.
Homing: Adult Stem cells have a unique ability to “home in” on sites of tissue injury, damage, or inflammation
Adult Stem Cells Regenerative Ability: “The younger, the better “
Adult stem cells, or known as somatic stem cells, are found everywhere in our body in every tissues and organ after development and function as self-renewing cell pools to refill dying cells and regenerate damaged tissues throughout our life. Nevertheless, adult stem cells appear to age with the person. As stem cells age, their functional ability also declines. Specifically, this regenerative ability seems to worsen with age, as injuries in older individuals heal more slowly than in childhood. For instance, healing of a fractured bone takes a much longer time in the elderly than in young individuals. There is a considerable amount of evidence showing that deterioration of adult stem cells in adulthood can become an essential player in the start of several diseases in aging such as coronary heart disease, diabetes, Alzheimer's, osteoarthritis etc.
Mesenchymal Stem Cells from the Umbilical cord.
Among the adult stem cells, type Mesenchymal stem cells from the umbilical cord are the youngest cell type.
Wharton’s jelly mesenchymal stem cells (WJ-MSCs) are a type of stem cells with high differentiative ability, an immuno-privileged condition and easy access for extraction. Umbilical cord stem cells offer dominance character over other types of stem cells as a source of therapeutic cells. First, UCM cells are obtained from a noncontroversial, inexhaustible source, and can be collected noninvasively without surgery at low cost. Second, unlike human embryonic stem cells, umbilical cord stem cells did not cause teratomas[tumor].
1.Stanford Children’s health “what are stem cells?” 2.University of Nebraska Medical Center “The importance of stem cells” 3.University of Nebraska Medical Center “Types of Stem Cells” 4.Pamela Gehron Robey, Ph.D. Cell sources for bone regeneration The good the bad and the ugly [but promising]. Tissue Engineering Volume 17 November 6, 2011 5.Prokhorova TA et al. Teratoma formation by human embryonic stem cells is site dependent and enhanced by the presence of Matrigel. Stem Cells Dev. 2009 Jan-Feb; 18(1):47-54. 6.National Cancer Institute, https://www.cancer.gov/publications/dictionaries/cancer- terms/def/hematopoietic-stem-cell 7.International Society for Stem Cells Research. Stem Cells Facts