Stem Cells

Question 1

What different potencies can stem cells have?

Answer 1

Totipotent - unlimited differentiation capacity
Pluripotent - most tissues of an organism
Multipotent - particular cell types (organ)

Question 2

What are ESCs?

Answer 2

An embryonic stem cell is derived and cultured from the inner cell mass of the blastocyst.
pluripotent, 220 cell types.

Question 3

What are adult stem cells?

Answer 3

undifferentiated cells that occur in a differentiated tissue.
Only multipotent, cells from the tissue they originated in.

Question 4

Explain the difference between stem cell symmetric and asymmetric division.

Answer 4

Sym = self-renewal
Asym = Production of a progenitor cell that will end up as a terminally differentiated cell.
Retains one daughter cell in the stem cell niche

Question 5

HSCs

Answer 5

Long term HSCs (self-renew) asymmetrically divide to produce short term HSCs (high CD34). Then form multipotent progenitor cells (high CD34 & FLK2) that can form all blood cell types (lineage restricted progenitors).
RBC, WBC, T & B Cells

Question 6

NSCs

Answer 6

Neural stem cells found in sub ventricular and sub granular zone.
Lineage restricted progenitors = oligodendrocytes, neurons
NSCs can express different markers and have different activity based on location.

Question 7

Explain how the regulation of neurogenesis is increased and decreased.

Answer 7

Positive - learning, sleep, exercise - new neurons made, increasing memory capacity and detail.
Negative - stress, alcohol, lack of sleep, injuries and disease - neurodegenerative (ischaemia, epilepsy)
drugs - opiates, anti-depressants

Question 8

GSCs

Answer 8

Located in the intestinal crypts.
Lineage restricted progenitors = paneth, goblet, endocrine and columnar cells.
They become transiently amplifying cells at the base of the crypt, move upwards toward the villus where they differentiate and replace the cells that die by apoptosis at the villus tip.

Question 9

What is the stem cell niche?

Answer 9

The microenvironment surrounding stem cells, provides support and signals regulating self renewal and differentiation.
Direct contact to the niche, soluble factors and intermediate cell contacts.

Question 10

List the 4 pathways that work in combination to help with the self-renewal and proliferation of adult stem cells.

Answer 10

1 - LIF
Leukaemia inhibitory factor. LIF binds LIFR which stimulates the JAK/STAT (Klf4 -> SOX2) and PI3K/MAPK (Nanog) pathways. SOX2 + Nanog increase Oct3/4.
All for increased self renewal of stem cells.
2 - Wnt
Wnt ligand binds to LRP5/6 and Frizzled receptor to inactivate the destruction complex and increase the cellular levels of B-catenin so it can bind TCF and transcribe Wnt target genes.
3 - Notch
Membrane bound Notch ligand is bound by Delta Jagged that causes Notch to be cleaved and activated. The cut intracellular domain can move to the nucleus, activate CSL and transcribe Notch target genes.
4 - SHH
Hh binds and inhibits Patched receptor, activates Smoothened receptor. Leads to transcription of Shh target genes (Wnt + Ptc (+ve feedback))

Question 11

3 sources of embryonic stem cells.

What are the main differences between these methods?

Answer 11

• Obtained from IVF
• SCNT (isolate from the blastocyst)
• iPSCs = induced pluripotentcy using reprogramming factors in culture (Oct3/4/SOX2/Klf4)

All embryonic stem cells could possible form tumours, where adult stem cells can’t.
IVF is the only one not genetically matched to patient, however is the only one not to give genetic abnormalities.

Question 12

What is stem cell therapy?

Answer 12

An injection of stem cells with therapeutic use. Therapeutic efficacy is exclusively attributed to the potency (function) of the donor cells presented in any quality and purity.

Question 13

What are the two types of bone marrow transplants and compare them.

Answer 13

ALLOGENIC = BM harvested from a donor after patient has undergone chemo, then BM reinfused.
AUTOLOGOUS = BM harvested before chemo, purged, frozen. Patient undergoes chemo, BM thawed and reinfused.

Autologous = no rejection and no diseases passed. No tissue matching required.

Question 14

How can gene therapy be combined with stem cell therapy to modify stem cells and reimplant?

Answer 14

• Cells from same patient can be harvested, turned into iPSCs, modified to cure mutation and reimplanted.
• Drug screening on iPSCs
• Stimulate stem cell proliferation for cells lost in a particular disease. Vectors/proteins/small molecule inhibitors can achieve this.

Question 15

How to restore stem cell function? (4)

Answer 15

• Genetic modification by reprogramming factors
• Detrimental epigenetic modifications removed by dedifferentiation
• Transcriptional network missing, TF delivered to stem cell
• Reprogramming an aged niche.

Question 16

3 types of neurodegeneration with examples.

Answer 16

1. Paracrine systems - Parkinson’s - loss of dopamine secreting neurons.
2. Selective degeneration - ALS - single phenotype replaced.
   3 - Global degeneration - Stroke - multiple phenotypes replaced.

Question 17

Describe Parkinson’s disease, the possible treatments and how stem cell therapy can be applied.

Answer 17

Parkinson’s = neurodegenerative movement disorder cause by a loss of dopaminergic neurons and a loss of dopamine levels.
Treatments = deep brain stimulation, protection with trophic factors, cell therapy
Cell therapy = replacement of lost neurons.
Tried but with limited success using both ESCs and iPSCs.
Conversion from differentiated cell straight to neuron can be achieved by factors. (no amplification or 100% efficiency)

Question 18

Stem cell ethics?

Answer 18

• What source? - status of the embryo, do benefits outweigh violation? IVF/Abortions
• Restrictions? - code of conduct for handlers? only used for life threatening research?
• Therapeutic cloning allowed? Reproductive cloning.