About stem cell

INTRODUCTION:

''Everything you'll ever need to know is within you; the secrets of the universe are imprinted on the cells of your body''.   Dan Millman

Inspired by the above quote, and with the recent scientific advances and the current achievements in the field of Cell biology, Stem cells are now being considered as the master cells of the body - these are the cells from which all the other cells types with specialized functions are developed. If given the right laboratory or the body conditions, stem cells divides to form some more cells, called the daughter cells. These daughter cells can either become new stem cells (self-renewal) or become specialized cells (differentiation) with a more specific function, such as blood cells, brain cells, heart muscle or bone. Stem cells are unique - no other cell in the body has the ability to self-renew or to differentiate. And therefore scientists have focussed to trap its potentials.

Where do stem cells come from?

Researchers have discovered several sources of stem cells:

  • Embryonic stem cells. These stem cells come from embryos that are four to five days old in their blastocyst stage and have about 150 cells. These are the pluripotent stem cells, and they can be divided into more stem cells or they can specialize and become any type of body cell. Because of this versatility, embryonic stem cells have the highest potential for use to regenerate or repair diseased tissue and organs in people.
  • Adult stem cells. These stem cells are found in small numbers in most adult tissues, such as bone marrow. Adult stem cells are also found in children and in placentas and umbilical cords. Because of that, a more precise term is somatic stem cell, meaning "of the body." This research has led to early-stage clinical trials to test usefulness and safety in people.
  • Adult cells can be altered to become embryonic stem cells. Researchers can transform regular adult cells into stem cells in laboratory studies. By altering, the researchers were able to reprogram the cells to act similarly to embryonic stem cells. Though it can be done under laboratory conditions but it is not safe to use on humans, therefore researches are still being carried out to further develop on this technique.
  • Amniotic fluid stem cells. Researchers have also discovered stem cells in amniotic fluid. Amniotic fluid fills the sac that surrounds and protects a developing fetus in the uterus. These amniotic fluid were drawn from pregnant women during a procedure called amniocentesis

Application:

1. stem cells to heal ourselves:

Granulocyte colony-stimulating factor G-CSF is a factor which stimulates the production of neutrophils (white blood cell). G-CSF is a cytokine that belongs to the family of drugs called hematopoietic (blood-forming) agents. Also called filgrastim.It is a type of glycoprotein,growth factor produced by a number of different tissues to stimulate the bone marrow  to produce granulocytes and stem cells. G-CSF then later stimulates the bone marrow to release them into the blood. It also stimulates the survival, proliferation, differentiation, and function of neutrophil precursors and mature neutrophils. G-CSF regulate them using Janus kinase (JAK)/signal transducer and activator of transcription (STAT) and Ras /mitogen-activated protein (MAP) kinase and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signal transduction pathway. G-CSF is also known as colony-stimulating factor 3 (CSF 3).

According to researches, Scientists have found that bone marrow produces two types of stem cells : mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) - these are classified depending  considerably on the types of damage and disease that can be treatable. "It's promoting self-healing".

MSCs grow into muscle and bone, and so have the potential to repair cardiac tissue in case of heart attacks, or to accelerate healing of broken bones or ligaments. They also reduces inflammation, and so could be used to treat autoimmune diseases. EPCs repair blood vessels and form new ones, so they have the potential to restore vital blood supplies to tissues damaged by stroke or heart attacks. Here the scientists could predict that they could initialize the production of both the types of stem cells in ample amount from the bone marrow of mice and induce it to help the body to regenerate its lost mechanisms.

Stem cells are the major source for the development, maintenance and repair of all types of tissues due to their capacity of increased  proliferation and differentiation into number of multiple effectors cells. The fact that aging is initialised by a diminished capacity to adequately maintain tissue homeostasis has suggested that a decline in stem cell function may be central to the process of tissue aging.

Indeed stem cells from several tissues have been shown to be functionally decline with advancing age. In hematopoietic stem cells (HSC) this is the cell  with a decreased competitive repopulating ability, a skewing of lineage potential from lymphopoiesis to myelopoiesis [1]. This is the major region for the  contribution to the loss of immune function [2], increased incidence of leukaemia [3] and onset of anaemia [4] occurring with age. Similarly neural stem cells (NSC) have been shown to be reduced in numbers and proliferative potential in the subventricular zone and in dentate gyrus of the hippocampus with age [5], [6] and [7]. Moreover diminished neurogenesis has been observed in the olfactory bulb of old mice [5], where NSC migrate and contribute to neurogenesis. Neurogenesis is thought to be important for sensory and cognitive functions such as memory and learning [8], and therefore NSC aging has been linked to the decline of those activities in older people.

Understanding genes and their interactions leading to stem cell aging is vital to open up opportunities for drug discovery and strategies to identify compounds capable of extending tissue survival and repair. Preventive targeting of young stem cells, which show predisposition to an accelerated aging is more likely to be successful rather than targeting of aged stem cells which have undergone profound and complex changes and unlikely to be reverted by any intervention. Given that aging is considered a continuous process starting early in development and occurring at different pace in each individual the identification of when and whose stem cells require intervention is difficult but important for design of any therapy.

Down syndrome (DS) has been identified as a model to study early events occurring in stem cells with age. Down Syndrome is associated with many of the signs of premature tissue aging including early abnormalities typical of Alzheimer disease (AD), T-cell deficiency, increased incidence of Myelodysplastic-type disease and leukaemia [9],[10], [11], [12] and [13]; and can be detected from an early phase in development to the presence of trisomy 21. Here they have tried to prove that stem cells in Down Syndrome shows premature ageing signs.The Mean telomere restriction fragment length (mTRF) of peripheral blood lymphocytes declines more rapidly in individuals with Down Syndrome than in normal individuals which shows an accelerated HSC telomere shortening [14]. The accelerated telomere shortening is already present in fetal life and is associated with stem cell deficiency as shown by a reduction in cells possessing the phenotype of HSC (detected as CD34+ cells) in fetal blood and bone marrow (BM) of children suffereing from Down Syndrome and in the number of long term culture initiating cells in their BM [14]. Moreover NSC derived from the cortical tissue of DS fetuses at 17-19 weeks of gestation show severely reduced replicative capacity and early loss of neuronal differentiation capacity after 10 weeks in culture [15].

In the study scientists used HSC and NSC from patients affected by Down Syndrome at very early stages of development, to identify the early changes in gene expression occurring in HSC and NSC with age. They have used a combination of genomic analysis and mathematical modelling, by which they identified a dysregulation of the Notch/Wnt pathway and showed that changes in Down syndrome stem cells reflected molecular events occurring in stem cells of older people. They data which they have produced are consistent with the hypothesis that Down Syndrome is an invaluable model to determine the molecular markers predisposing to stem cell aging and is suitable to unveil new molecular targets for intervention.

For the conduction of the experiment, Researches obtained the bone marrow from the iliac crest of Down Syndrome children (1-5 years) who suffered with no clinical hematological abnormalities undergoing cardiac surgery and from the age matched relatively hematologically healthy children having similar significant surgery but with parental consent. Bone marrow were also collected from the  individuals between 60-80 years old clear from a haematological malignancy. Long term hematopoietic stem cells were isolated by labeling mononuclear cells with CD45 APC, CD34 PE and CD38 FITC (BD biosciences). CD45+CD34+CD38- (200-1000 cells) were sorted on FACS Aria sorter (Becton Dickenson) following propidium iodide (10 g/ml, Fluka) was added to exclude dead cells. The gating strategy used is represented in the given figure.

Fig. 1. Representative example of the gating strategy used to obtain PI-/CD45+/CD34+/CD38- HSC. (A) A region for live bone marrow cells (PI negative) was drawn (R1); (B) Cells contained in the R1 region were plotted and CD45+ cells (leucocyte cells) were further selected in the R2 region; (C) The cells contained in both the R1 and R2 regions were plotted and a R3 region was drawn around the lymphocyte population; (D) The cells common to all three regions were plotted for CD34 and CD38 expression and the CD34+ and CD38- population was identified (R4) and sorted; (E) CD34+ CD38- population after sort; (F) CD34+ CD38+ population after sort.

After this the purity was measured which was found to be > 95%. 
 

The NSC human fetal tissue was obtained from the Birth Defects Laboratory at the University of Washington, Seattle and the Tissue Bank for Developmental Disorders at the University of Maryland. Neurospheres were generated from two trisomy 21 cortex samples and two gestationally age matched controls (12 and 18 weeks gestation). Cortical precursors were isolated from fetal brain were induced to proliferate as free-floating neurospheres [16]. After 2 weeks, neurospheres were grown in DMEM/Ham's F12 media with penicillin, streptomycin, amphotericin B (PSA, 1%) and supplemented with N2 (1%; Life Technologies) and 20 ng/ml EGF.

2.2. PolyA RT-PCR

PolyA RT-PCR was carried out for the 200 to 1000 HSC cells

2.3. Microarray analysis

Microarray analysis was carried out of the c DNA sample cells at the Paterson Institute for Cancer Research microarray facility.

2.4. Data analysis

After this the Identification of age related genes were carried out based on the hypothesis that Down Syndrome samples show accelerated aging when compared to normal samples and also the fact that aging is a continuous process with changes.Here the differences between HSC samples and NSC samples was built as ?XHSC-NSC=?Dev+

Where, X is the gene expression level, the first term on the right hand side is the difference due to the different developmental stages, the second term includes various sources of noise

Later was they performed transcriptional regulation and pathway analysis.

2.5. Real time quantitative PCR

PCR primer pairs was designed for mRNA sequence within 500 bp of the 3' end of each gene and then it was carried out.

In the above study they tested the hypothesis that changes in gene expression in HSC and NSC of patients affected by DS reflect changes occurring in stem cells with age. The profiles of genes expressed in HSC and NSC from DS patients shows the pathways associated with cellular aging including a down regulation of DNA repair genes and increases in proapoptotic genes, s-phase cell cycle genes, inflammation and angiogenesis genes. Here in the experiment conducted, Notch signalling was identified as a potential hub, which if deregulated may drive stem cell aging. These data suggests that Down syndrome is a valuable model to study early events in stem cell aging and can further be helpful to determine its characteristics.

Another recent application of the stem cell is the use of Magnetised stem cell to treat arthriritis, where the magnets are being used to control the transformation of the stem cells into specific tissues.

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