Stem Cells

Pluripotent (Pluri=Very many) -> Can differentiate into cells of all 3 germ layers. 1)Endoderm -> Lung/Thyroid/Pancreatic cells. 2)Mesoderm -> Smooth/Skeletal/Cardiac muscle, Blood cells. 3)Ectoderm -> Epidermis, Neurons, Pigment cells.
1. Embryonic stem cells (ESC) from Inner cell mass of Blastocyst (3-4 days p.c.) express Stage-specific embryonic antigen +ve (mouse=SSEA-1, human=SSEA-4) -> Cloning of animals from ESC possible -> Requires mouse fibroblast feeder layer
  1. mouse ESC can be plated as single cells / human ESC need to be plated as colonies.
2. Induced pluripotent stem cells (iPSC) in 2006(mouse) and 2007(human). Yamanaka factors most used (mouse/human)=Oct4, Sox2, Klf4, c-Myc with retrovirus. Thompson factors (human)=Oct4, Sox2, Nanog, Lin28 with lentivirus. Issues: tumorigenic, viral use, not exactly like ESC. Improvement=direct reprogramming: from fibroblast to target cell without iPSC step, short bursts of reprogramming factors (Oct4, Sox2, Klf4) then differentiation medium, faster
3. Very small embryonic-like stem cells (VSEL) from bone marrow, cord blood, muscles (CXCR4+, Oct4+, Nanog+, Rex1+) -> small (5-7µm) and "hide" in stem cell niches -> mobilized into peripheral blood to site of injury
Totipotent (Toti=Total) -> Can differentiate into all cells in an organism = Zygote
Multipotent (Multi=Many) -> Can differentiate into cells of tissue or germ layer where they reside
1. Adult (Precursor) stem cells -> Plasticity (give rise to cells of other germ layers) potentially from: transdifferentiation, cell fusion, epigenetics, artifact
  1. Hematopoietic stem cells from red bone marrow (CD34+, Lin-) -> myeloid (erythrocyte=RBC, leukocytes=WBC) or lymphoid progenitor (T/B lymphocytes) -> all blood cells
  2. Mesenchymal non-hematopoietic stromal (connective tissue) stem cells from Wharton's Jelly, adipose tissue, bone marrow (CD73+, CD105+) -> osteoblasts(bone), chondrocytes(cartilage), adipocytes(fat)
  3. Neural stem cells from subventricular zone -> neurons, glia, oligodendrocytes -> grown in vitro as neurospheres
  4. Retinal stem cells from 0.2% of pigmented ciliary margin (CHX10+, Nestin+) -> controversial
  5. Hair follicle bulge stem cells (CD34+, NFATc1, Sox9, Lgr5)
  6. Lung stem cells from each segments -> Clara/BASC/AEC stem/progenitors -> Clara cells (dormant until injury) are progenitors of the Bronchiolar epithelium -> During injury the lungs attracts Hepatocyte growth factor producing Mesenchymal stem cells (with SDF1) that come from the bone marrow (CXCR4+) -> these HGF producing MSC are found in the alveolar epithelium and interact with surrounding cells.
Tumorigenic (Tumor-forming) -> Can differentiate into cells of specific cancer sample = Cancer stem cells
1. Niches normally prevent tumorigenesis by controlling stem cells quiescence+self-renewal+differentiation. In cancer the niche doesn't control the cancer stem cells.
2. Cancer cells are not self-sufficient -> "Cancer stem cells exploit normal mechanisms to develop and metastasize" -> early metastasis can't be diagnosed -> loss of adhesion = metastasis -> only 0.02% of cancer cells metastasize. Prostate is very sensitive to androgens and faces down.
3. Lung cancer from sustained proliferation and no P53 to stop growth -> Lung tumor initiating cells (TIC) are CD166+ -> plasticity of cancer cells might create new TIC -> pemetrexed is the best treatment against TIC = inhibits GLDC -> DNA damage response (DDR) also plays a role in TIC. Summary= TIC exist in solid tumors, TIC are chemo/radio resistant, TIC might be proliferating, TIC-marker expression might be plastic, TIC have unregulated DDR
Therapeutic use of SC: Bone marrow transplantation and Skin/Corneal grafts
Stem cell niche is a specific tissue location where stem cells reside for an indefinite period of time with the ability to self-renew and produce progeny. The niche is composed of surrounding cellular and extracellular microenvironmental components (extracellular matrix, blood vessels, niche cells, progeny cells) and their signals (endocrine, paracrine, autocrine, physical) -> Identified from lineage tracing where cells are marked and progeny analyzed. Label stays=stem cell clones. Label fades=transient clones (only daughter cells)
1. Cell-cell and extracellular matrix adhesion control cell shape, function and development. Cell-adhesion molecules help communication between cells and their environment. Extracellular matrix controls anchorage, receptor binding and biomechanical forces. Adherens, desmosomal, hemidesmosomal, tight and gap JUNCTIONS.
2. Three types of niches 1)Simple=stem&partner cell=hematopoietic stem cell/intestinal crypt niches 2)Complex=2+stem&1/2+partner cells 3)Storage=stem cells are quiescent until activated by external signals to divide and migrate
  1. Hematopoietic stem cell niches are in the red bone marrow -> regulated by CXCL12 -> maintained by the CXCL12 abundant reticular cells
  2. Intestinal crypt niches are in the intestinal epithelium -> regulated by BMP&Wnt epithelium renewed every 3-5 days -> stem cells in the crypt (Lgr5+) divide once a day -> maintained by paneth cells -> transit amplifying cells do 4-5 divisions every 12 hours
  3. Neural stem cell niches are in the subventricular&subgranular zone -> Complex niches due to complexity of nervous system -> regulated by BMP&BDNF. Subventricular zone contains astrocytes surrounded by transit amplifying+neuroblast+endothelial+ependymal cells. Subgranular zone contains astrocytes surrounded by transit amplifying+granule+endothelial cells
  4. Hair follicle stem cell niches are in the hair follicle bulge -> regulated by BMP&Wnt -> once activated will migrate downward for hair regeneration or upward for skin regeneration
3. Nurturer=cell adhesion&signalling molecules, secretes growth factors+cytokines for stem cell self-renewal. Collaborator=collaborates with stem cells to organize their own niche and maintain their population. Inducer=for repair&regeneration the stem cells are induced to proliferate to replace lost differentiated cells. Messenger=located between stem cells and environment as messenger of larger systemic chances. Old age=weakening with age leading to decrease cell adhesion and stem cell renewal. Villain=controlled by cancer stem cells to help them grow and metastasise.
4. Future research to better understand cells+molecules involved in niches and cross-talk+signalling pathways to restore or engineer stem cell niches
The Liver (4% of body mass) has 4 lobes -> made up of lobules containing 6x portal triads + 1 central vein + 80% filled with hepatocytes (20% from Kupffer/Stellate/Immune/Nerve/Mesenchymal cells) -> plasma glucose&ammonia regulation, bile production, detoxification -> huge regenerative potential (max 75% of liver loss) by compensation -> Prometheus and the eagle -> regenerative properties from normal toxic removal function = must regenerate via hepatocyte proliferation (hepatocyte growth factor) -> Regeneration steps: 1)Initiation(re-enter cell cycle), 2)Proliferation, 3)Correction of overgrowth(apoptosis), 4)Termination(space reconstruction) -> Can be cut and transplanted. Main pathway of interest is the Hippo pathway = regulates organ size through cell proliferation and apoptosis
The Brain (2% of body weight) has 100 billion neurons+1,000 cell types+10^15 synapses+40,000 genes -> ischemic stroke/hemorrhage/tumors have poor recovery -> huntington's/parkinson's/alzheimer's disease -> parkinson's from loss of dopaminergic neurons -> drugs not effective in long term -> cell transplantation to replace substantia nigra -> human fetal brain cells transplanted survive but have no long term treatment effects with high risk of side effects -> limitations as cells don't all survive and integrate+limited availability of human fetal cells. ESC and iPSC derived dopamine neurons show potential for recovery in vivo. Beneficial effect of cells likely to be from paracrine factors release. Stroke leads to migration of precursor cells to stroke site. Fluoxetine leads to proliferation (↑DG, ↓SVZ) which increases neurotrophic levels. Metformin leads to neurogenesis in SVZ and hippocampus. Aging leads to decreased neurogenesis and population.
1. Grafted neural progenitor cells can survive/migrate/differentiate in OHC and animals cured from bacterial meningitis. Grafted hippocampal neural progenitor cells can survive/migrate/differentiate into neurons in the damaged area of the hippocampus in vitro and in vivo. Conclusion=Grafted hippocampal neural progenitor cells are potential therapies to repair damaged hippocampus of patients who had bacterial meningitis.
SC require a specific stromal environment to survive. Potency = Ability to differentiate into other cell types. Potens = Having Power

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Stem Cells

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	Created by William Hariton almost 9 years ago