Lecture 20 Flashcards
What gene do quiescent satellite cells express?
Pax7
Where do satellite cells typically reside?
between sarcolemma and basal lamina
What genes lead to muscle precursor cells?
Pax7
Pax3
CD34
Why are satellite cells activated?
To repair damaged muscle fibers.
What differentiates satellite cells?
Not all satellite cells are the same. This depends on the type of transcription factors they express.
Near what structures are satellite cells typically found? Why is this the case?
Blood vessels; this allows them to be regulated systemically.
What are the theories of how satellite cells proliferate?
Theory A: Asymmetric cell division (satellite cell divides to make 1 quiescent satellite cell and 1 activated satellite cell)
Theory B: Satellite cell divides and some return to quiescence
What do satellite cells change into in the process of repairing muscle?
Satellite cells form myoblasts which form myotubes and repair muscle fibers.
Why do satellite cells express Pax7?
Pax7 is required for development and maintenance of satellite cells.
What happens to Pax7 expressiong when myoblast wants to start differentiation?
Pax7 is downregulated
Which muscles typically express Pax3?
Diaphragm and body wall muscles.
What is the function of Myf5 during post natal myogenesis?
Expressed in a sub-population of quiescent satellite cells and in all activated satellite cells and is expressed through myotube fusion
How do damaged fibers recruit satellite cells to repair them?
Damaged muscle fibers release HGF which activates satellite cells. This results in upregulation of myf5 and myoD
How are activated satellite cells converted to myoblasts?
To go from an activated satellite cell to a myoblast Pax7 is downregulated and primary myogenic regulatory factors are upregulated.
If muscle injury is repaired why do muscles atrophy?
Muscle atrophy occurs with age and in genetic disease.
Is muscle atrophy due to systemic factors or failure to regenerate?
Muscle atrophy is due to systemic factors.
- This was proven in an experiment where young-old heterochronic parabiotic mice expressed ‘young’ muscle regeneration.
- Young muscles put into old mice lose regenerative ability and vice versa. This suggests that it’s due to systemic changes causing a lack of ability to regenerate.
Do satellite cells decrease in quality with age?
Satellite cells don’t wear out very quickly and have a high regenerative potential.
What are some stem cells that can be used instead of satellite cells for muscle transplants?
Mesangioblasts
Pericytes
AC133
Muscle-derived stem cells
Bone marrow
Side population
Where are mesangioblasts derived from?
Blood vessels
What tissue can be formed from mesangioblasts?
Smooth, cardiac, and skeletal muscle, bone, and fat.
Are mesangioblasts involved in muscle repair?
No, but they can be harnessed for therapeutic use.
What are mesangioblasts?
Mesangioblasts are mesoderm derived stem cells found in blood vessels.
Where are pericytes located?
Pericytes are found beneeath basal lamina of small blood vessels.
What are pericytes?
Blood vessel associated stem cells from post-natal stage muscle.
What is the benefits of using pericytes for muscle repair?
Suitable for intravascular delivery.
What is the benefit of transplanting pericytes into muscles?
pericytes have a higher muscle regenerative potential than satellite cells.
Are pericytes involved in muscle repair?
No, but can be harnessed for therapeutic use.
How abundant are AC133+ cells in the body?
AC133+ make up 1% of total mononucleated cells of the body regardless of age.
What are AC133+ cells?
Blood and skeletal-muscle derived cells that express glycosylated epitope CD133 antigen.
Which AD133+ cells can produce myogenic cells?
Both blood and muscle derived AD133+ cells can produce myogenic cells.
What is the advantage of using AD133+ cells over myoblasts?
AD133+ proliferate better than myoblasts.
AD133+ have fusion index almost as high as Myoblasts
Do AD133+ and bone marrow derived stem cells normally contribute to muscle regeneration?
No
What are the benefits of using muscle derived stem cells?
Muscle derived stem cells have good myogenic potential in vivo
What are Muscle-Derived Stem Cells?
A population of stem cells located in muscle interstitial space and are positive for CD34.
Muscle-derived stem cells express different markers to satellite cells.
What were the results of experiments in which dystrophic mice were injected with MDSCs?
Muscle derived stem cells have demonstrated the ability to regenerate in dystrophic mice when injected into muscle directly or into vasculature.
How are muscle derived stem cells extracted from muscles?
Identified by preplating from muscle biopsy and may be a predecessor of the satellite cell
What are side population cells?
Population of stem cells identified by their unique ability to efflux DNA-binding dye.
Where are side population cells located?
SP cells are located in both skeletal muscle and bone marrow.
SP cells are located outside of muscle fibers and are associated with the vasculature
What gene/s do SP cells express?
SP cells express Sca1 and do not express satellite cell markers (Pax7, Desmin)
Why are SP cells a good canditate for myotherapy?
SP have myogenic potential when injected into regenerating muscles.
What is cell therapy?
Cell therapy is the delivery of new muscle cells to wasting muscle in an effort to restore muscle strength and function
What are the criteria for ideal stem cell for treating muscle wasting?
- Be expandable outside of the body.
- Not going to be rejected.
- Delivered systemically.
- Survive, proliferate and migrate in host muscle.
- Differentiate into muscle fibers to replace lost fibers.
- Replace satellite cell pool with functional stem cells.
- Be capable of expressing muscle genes
- Must replenish muscle strength.
What are some other cells that can be used to produce muscle?
Adipose stem cells
induced pluripotent cells
What are the satellite cell/myoblast transplants that have been attempted?
- Myoblast transplantation
- Satellite cell transplantation
- Myofiber-associated satellite cell transplantation
What happened when myoblast transplantation was performed in vivo?
Up to 10% dystrophin positive fibers in immunosuppressed patients and had poor survival in vivo with limited migration from injection sites and were unable to provide long term regeneration.
What are the problems of satellite cell transplantation?
Satellite cells need to be injected into muscles.
Poor contribution in absence of regenerating environment.
Poor survival in vivo.
Multiple injections required for therapeutic benefit.
What was the result of transplanting an entire fibre in mice?
Transplantation of entire fiber gives good engraftment of the muscle with good regenerative capacity.
What are the advantages and disadvantages of mesangioblast transplants?
Pros:
Can be delivered systemically.
Demonstrated to relieve dystrophy in dystrophic dog.
Cons:
Difficult to purify and poorly defined cell population.
What are some obstacles to cell therapy for muscle disease?
Fibrosis/adipose tissue affect ability of cells to engraft.
Will host immune response affect graft?
When is MyoD upregulated and when is it downregulated?
Upregulated during proliferation
Downregulated during myoblast fusion
When is myogenin produced?
It is upregulated by MyoD and Myf5.
