Stem cells and regenerative medicine

Question 1

Explain what a stem cell is and their biological function

Answer 1

Stem cells are a unique subset of cells that have the ability to self-renew (i.e. replicate themselves) and the capacity to differentiate into various types of mature cells

1) Embryonic Stem Cells (ESCs):

• derived from the inner cell mass of a blastocyst (an early-stage pre-implantation embryo ~ 4-5 days old)
• ESCs are pluripotent, which means they can differentiate into any cell type in the body
• The pluripotency of ESCs is maintained by a network of specific transcription factors, including Oct4, Sox2, and Nanog
• ESCs contribute to the formation of the body during embryogenesis by generating cells of all three primary germ layers: the ectoderm, endoderm, and mesoderm, which subsequently give rise to all tissues and organs in the body

2) Adult (Somatic) Stem Cells:

• Multipotent, meaning they can differentiate into a limited number of cell types related to their tissue of origin
• exist in various tissues, including bone marrow, skin, and the brain, and are vital for homeostasis and repair
• e.g. hematopoietic stem cells (HSCs) residing in the bone marrow continuously produce new blood cells
• Neural stem cells in the adult brain can differentiate into neurons and glial cells
• less likely to form tumours when transplanted, and since they can be harvested from the patient, avoiding

3) Induced Pluripotent Stem Cells (iPSCs):

• Some adult stem cells exhibit a broader differentiation potential under certain conditions - induced pluripotent stem cells (iPSCs)
• iPSCs are adult cells that have been genetically reprogrammed to an embryonic stem cell-like state, typically by the introduction of specific transcription factors (e.g., Oct4, Sox2, Klf4, and c-Myc)
• because they can be generated from the patient’s own cells, they avoid immune rejection issues associated with ESC
• However, the reprogramming process can be inefficient and may have a risk of generating mutations that could lead to cancer

Question 2

Describe and explain the therapeutic potential offered by stem cells

Answer 2

1) Regenerative Medicine and Tissue Engineering:

• Stem cells can be used to generate cells and tissues for the treatment of diseases where the body’s own cells are damaged or depleted
• E.g. In Parkinson’s, neurons are lost in certain areas of the brain
• Embryonic stem cells or induced pluripotent stem cells could potentially be directed to become these neurons and then transplanted into the patient
• Similarly, in conditions like heart disease or burns, stem cells could be used to generate heart muscle cells or skin cells
• Type 1 diabetes resulting from the destruction of insulin-producing beta cells in the pancreas could be treated by replacing these cells with new ones derived from stem cells

2) Drug Discovery and Development:

• Stem cells can be utilised as models for studying disease progression and drug action
• Researchers can create specific cell and disease-specific cell lines, study the molecular mechanisms underlying these diseases, and test the effect of various drugs on these cells
• Testing Efficacy and side effects of new drugs, reducing the need for animal testing and providing a more accurate representation of the drug’s effects on human cells

3) Understanding Disease Mechanisms:

• Disease-specific induced pluripotent stem cells can be generated from patients with specific diseases
• These cells can then be differentiated into the cell types affected by the disease, providing a cellular model to study that disease

4) Cell-based Therapies:

• E.g. Hematopoietic stem cells (HSCs), which give rise to different types of blood cells, have been used in bone marrow transplantation
• Gene editing techniques like CRISPR have allowed for the correction of genetic defects in stem cells, which can then be reintroduced back into the patient to treat genetic disorders

Gene Therapy:

• Stem cells can be manipulated in vitro for gene therapies
• Here, specific genetic alterations are introduced into stem cells, which are then grafted back into the patient’s body
• As these cells divide and differentiate, they help alleviate disease symptoms

Question 3

Explain the role of pluripotency factors in generating iPSCs

Answer 3

1) Oct4 (Octomer-binding transcription factor 4)

• Oct4 is a crucial player in maintaining the pluripotent state of embryonic stem cells (ESCs)
• Controls transcriptional regulation of genes associated with pluripotency and embryonic development
• In pluripotent cells, Oct4 contributes to a network of factors to maintain the cell’s “stemness” and prevent it from differentiating into a more specialised type
• In iPSCs, Oct4 helps maintain stemness by regulating gene expression related to pluripotency and suppressing genes associated with differentiation

2) Sox2 (Sex determining region Y-box 2):

• cooperates closely with Oct4, forming a complex that binds to DNA and regulates the transcription of numerous genes which maintains pluripotency and others for differentiation
• Thus, the Oct4-Sox2 complex essentially acts as a master regulator of stem cell identity

3) Klf4 (Kruppel-like factor 4):

• Klf4 works alongside Oct4 and Sox2, playing a part in the intricate balance of gene regulation that maintains a cell’s pluripotent state
• It is also implicated in several biological processes, including cell cycle progression, proliferation, differentiation, and apoptosis
• Klf4’s contribution in iPSCs seems to lie in its ability to assist the activation of stem cell-associated genes and the repression of genes related to differentiation

4) c-Myc (Myelocytomatosis oncogene):

• c-Myc, though not strictly necessary for the generation of iPSCs, enhances the efficiency of the reprogramming process
• c-Myc is known to regulate cell growth and proliferation, and it can contribute to the development of cancer

Question 4

Discuss various examples of therapeutic roles for stem cells in disease and injury

Answer 4

1) Blood Stem Cells and Hematopoietic Disorders:

• Hematopoietic stem cells (HSCs), found in the bone marrow and blood, have the ability to form all blood cell types, including red blood cells, white blood cells, and platelets
• Used in bone marrow transplants to treat hematopoietic disorders, such as leukaemia and lymphoma
• first use chemotherapy or radiation to eliminate the patient’s own cancerous cells, then introduce healthy HSCs that can repopulate the bone marrow and produce healthy blood cells

2) Skin Grafts and Burns

• Epidermal stem cells, found in the basal layer of the skin, can be cultivated in the lab to create skin grafts for patients with severe burns or large wounds

3) Neurodegenerative Disease:

• Stem cells could potentially be used to replace neurons lost due to neurodegenerative diseases like Alzheimer’s, Parkinson’s, and Huntington’s
• stem cells could be directed to differentiate into specific neuron types and then transplanted into the patient’s brain

4) Spinal Cord Injuries:

• After a spinal cord injury, nerve cells are damaged and lost, leading to paralysis below the level of injury

5) Heart Disease:

• Cardiomyocytes, or heart muscle cells, are not very good at regenerating after a heart attack
• This leads to scar tissue formation and can eventually result in heart failure
• Researchers are exploring the possibility of using stem cells to generate new cardiomyocytes and repair the damaged heart tissue

6) Type 1 Diabetes:

• Type 1 diabetes occurs when the insulin-producing beta cells in the pancreas are destroyed by the immune system
• stem cells could be used to generate new beta cells, providing a potential cure for this disease

7) Eye Diseases:

• Retinal diseases such as age-related macular degeneration result in the loss of photoreceptor cells in the retina, leading to vision loss
• stem cells could be used to generate new photoreceptor cells and reverse this vision loss