Understanding Stem Cells: Characteristics and Types

• Stem cell research holds the potential to end the suffering of millions and benefit almost everyone
• Stem cells can replace damaged cells, allow the study of development/genetics, and can be used to test drugs and chemicals

What are Stem Cells?

• Stem cells are the first cells to form after a fertilized egg divides
• They are undifferentiated and have the potential to become specialized cells like liver, brain, cartilage, or skin
• They have the ability to continuously divide

Stem Cell Characteristics

• Stem cells are 'blank cells' (unspecialized)
• They proliferate and renew themselves for long periods of time
• They can differentiate into specialized cell types
• They express the transcription factor Oct-4
• Stem cells can be induced to continue proliferating or to differentiate
• They lack the G1 checkpoint in the cell cycle
• ES cells spend most of their time in the S phase of the cell cycle, during which they synthesize DNA
• Unlike differentiated somatic cells, ES cells do not require any external stimulus to initiate DNA replication
• They do not show X inactivation
• In every somatic cell of a female mammal, one of the two X chromosomes becomes permanently inactivated, but X inactivation does not occur in undifferentiated ES cells

Stem Cells and Adult Tissues

• Stem cells divide to produce one daughter cell that remains a stem cell and one that divides and differentiates
• Hematopoietic (blood-forming) stem cells were the first to be identified
• There are several distinct types of blood cells with specialized functions: erythrocytes, granulocytes, macrophages, platelets, and lymphocytes all derived from the same population of stem cells

Types of Stem Cells

• Embryonic stem cells compose the early human embryo
• During early stages of development the embryo are called Totipotent, meaning they can differentiate into any cell types
• Four days after fertilization, the embryo enters the blastocyst stage
• Cells of the inner cell mass of the developing embryo are called Pluripotent, meaning they can make almost any cell types

• Embryonic Stem Cells are mainly from IVF

Pluripotent Stem Cells

• Pluripotent Stem Cells have the potential to become any type of cell

Adult Stem Cells

• Adult stem cells are undifferentiated cells in tissues of adults
• They occur in small numbers
• They are multipotent and can develop into two or more different cell lines, but not any type of cells
• Bone marrow can develop into several blood cell types
• Unipotent cells can develop into only one cell line
• Multipotent stem cells are limited in what the cells can become

IPS Cells

• IPS Cells are Induced Pluripotent Stem Cells

Creating IPS Cells

• Isolate cells from a patient, the patient's skin or fibroblasts, which are grown in a dish
• Treat cells with "reprogramming" factors
• Wait a few weeks
• Pluripotent stem cells are formed
• Culture conditions are changed to stimulate cells to differentiate into a variety of cell types
• Some important factors in creation of IPS Cells are Apoptosis, senescence, Klf4, c-Myc, Somatic Cells,Tumor Cells, Immortalization, open chromatin, Oct-3/4, Nullipotent ES-like Cells, Sox2 and Pluripotent iPS Cells

The Generation of IPS Cells From Adult Fibroblast Cells

• Cells are taken from a normal mouse and engineered to allow selection of induced pluripotent stem (iPS) cells
• Next uses Gene delivery(Oct3/4, Sox2, Kif4, c-Myc) selection, and growth in culture
• Injection of iPS cells into blastocyst
• Implantation into surrogate mother

IPSCs – Clinical Applications

• IPSCs are clinically applicable, meaning they have the ability to differentiate into many cell types
• Are vastly renewable
• Are easily accessible
• Are Individual-specific i.e. personalized or non-immunogenic

Where To Find Stem Cells

• Bone marrow
• Skin
• Fat tissue
• Teeth
• Mammary tissue
• Many other tissues

Bone Marrow

• Bone marrow is found in spongy bone where blood cells form
• Used to replace damaged or destroyed bone marrow with healthy bone marrow stem cells.
• Help treat patients diagnosed with leukemia, aplastic anemia, and lymphomas

Separation of Stem Cells

• Cells in suspension are tagged with fluorescent markers specific for undifferentiated stem cells
• Labeled cells are sent under pressure through a small nozzle and pass through an electric field
• A cell generates a negative charge if it fluoresces and a positive charge if it does not

Stem Cells and the Maintenance of Adult Tissues

• Most adult tissues have stem cells, which reside in distinct microenvironments or niches
• Niches provide the environmental signals that maintain stem cells throughout life and control the balance between self-renewal and differentiation

Tissue Growth

• Hyperplasia is tissue growth through cell multiplication
• Hypertrophy is enlargement of preexisting cells (e.g., muscle growth through exercise)
• Neoplasia is the growth of a tumor (benign or malignant) through the growth of abnormal tissue

Tissue Repair

• Regeneration is the replacement of damaged cells with original cells, this is seen with skin injuries and liver regeneration
• Fibrosis is the replacement of damaged cells with scar tissue, and function is not restored.
• Keloid is healing with excessive fibrosis (raised shiny scars)

Tissue Engineering

• The production of tissues and organs in the lab
• A framework of collagen or biodegradable polyester fibers is used
• Seeded with human cells
• Grown in "bioreactor" (inside of mouse)
• This process supplies nutrients and oxygen to growing tissue
• Skin grafts are already available
• Research is in progress on heart valves, coronary arteries, bone, liver, tendons

Therapeutic Cloning

• Involves an unfertilized egg with chromosomes removed
• Adult somatic cell from patient
• Next is Transfer nucleus to enucleated egg
• Culture is grown to early embryo
• Culture embryonic stem cells
• Differentiate to desired cell type (e.g., neurons)
• Transplant back to patient

Potential Uses of Stem Cells

• Pluripotent stem cells offer the possibility of a renewable source of replacement cells and tissues, which could be used to treat a variety of diseases, conditions, and disabilities including Parkinson's disease, spinal cord injury, burns, heart disease, arthritis, and diabetes
• Adult stem cells are currently being used for treatments for leukemia
• Scientists expect to use embryonic stem cells to make organs that can replace damaged ones, like liver and heart
• Studies show leukemia patients treated with stem cells emerge free of disease
• Injections of stem cells can reduce pancreatic cancers in some patients
• Adult Stem Cells may be helpful in jumpstarting repair of eroded cartilage in Rheumatoid Arthritis

Type I Diabetes

• Pancreatic cells do not produce insulin
• Embryonic Stems Cells might be trained to become pancreatic islets cells needed to secrete insulin

Potential Problems with Adult Stem Cells

• Source/Cell lines may have mutations
• Delivery to target areas
• Prevention of rejection
• Suppressing tumors
• Mutations can lead to leukemia

Why the Controversy Over Stem Cells?

• Embryonic Stem cells are derived from extra blastocysts that would otherwise be discarded following IVF
• Extracting stem cells destroys the developing blastocyst (embryo)
  • Is an embryo a person?
  • Is it morally acceptable to use embryos for research?
  • When do we become “human beings?"