L7.2 Myogenesis 2

Question 1

Post-natal myogenic process?

Answer 1

Question 2

Satellite cells

Answer 2

• Quiescent cell population → not actively proliferating
  
  • Responds to damage muscles
• Distinct from myonuclei & has a distinct location - satellite cell niche
  
  • Niche → localised close to BV
    
    • Allows systemic regulation of satellite cells
• Express Pax 3, 7, CD34 (the muscle precursor cells)

Question 3

What are the 2 theories of a self-renewal satellite cell?

Answer 3

• A: asymmetric cell division
  
  • Sat cell → New quiescent sat cell (populate niche) & another sat cell (enters cell cycle → prolif)
• B: Return to quiescence
  
  • Sat → activated ↑ prolif → 1 cell goes back to quiescent to repopulate niche

Question 4

Regulation: Transcription factors

Answer 4

• Pax 3, 7 (7 is required for dev & maintenance of sat cells)
  
  • In adults : pax 7 expression maintained in all sat cells & prolif myoblast
    
    • Decreased rapidly before differentiation
  • Pax 3 co-expressed in trunk muscles, but x expressed in limb muscles (only pax 7)

Question 5

Regulation: MRFs

Answer 5

• Myf5 → expressed from some quiescent cells → myotube fusion
• MyoD → From activated → prolif, down regulated when fusion starts
• Myogenin → ↓Myf5 & MyoD → ↑Myogenin

Question 6

What contributes to the failure of satellite cells? and how was this determined?

Answer 6

• Not through wearing out, but from changes in environment
• Shown in experiment:
  
  • Young muscle transplanted into old mice → LOSE regen ability, vice versa
  • And the parabiotic pairing experiment:
    
    • Fuse 2 mice together → same effect

Question 7

Other sources of stem cells?

Answer 7

Mesoangioblasts

Pericytes

AC133 cells

Bone marrow stem cells

Muscle derived stem cells

Side population cells

Question 8

Mesoangioblasts

Answer 8

• Mesoangioblasts: BV associated, acquired from embryonic stage muscles
  
  • Differentiation into different mesodermal tissues
  • X great contribution to muscle regen

Question 9

Pericytes

Answer 9

• Pericytes: BV associated, from post-natal stage muscles
  
  • Beneath basal lamina
  • Intravascular delivery
  • Large myogenic potential (compared to sat cells)
  • X great contribution to muscle regen

Question 10

AC 133 cells

Answer 10

• AC 133 cells: blood & skeletal muscles derived
  
  • 1% of total mononucleated cells
  • Have myogenic potentials

Question 11

Bone marrow stem cells

Answer 11

• circulating myogenic precursor
• Minimal contribution to muscle regen

Question 12

Muscle derived stem cells

Answer 12

• In muscle interstitial space
• +ve for CD34 & SCA1
• From pre-plating technique from muscle biopsy
• May be predecessor of sat cells
• Good myogenic potential in vivo

Question 13

Side population cells

Answer 13

• From skeletal muscles & bone marrow
• Express Sca1 but x express sat cell markers (pax 7)
• Haematopoietic (formation of blood) potential in vitro
• Muscle regen potential

Question 14

8 Criterias for stem cells to be appropriate therapy material?

Answer 14

1. Expandable in vitro, x lose SC properties
2. Immuno-privileged (immune system won’t attack it)
3. Systemically deliverable
4. Survive, prolif, migrate upon arrival
5. Ability to differentiate into muscle fibres
6. Reconstitute sat cell pool
7. Express required muscle genes
8. ↑ muscle str

Question 15

3 stages of satellite cell therapy?

Answer 15

• Myoblast transplants: initial choice:
  
  • Poor survival in vivo, x migration, x regen in long term
• Sat-cell transplants: ↑ muscle fibre formation
  
  • But need delivery directly to muscles
  • Poor in vivo survival
• Myofibre: associated sat cell transplant, transplants entire fibre, protects against age-related muscle degenration

Question 16

Mesoangioblast transplants?

Answer 16

• Ameliorate dystrophy for Duchenne’s muscular dystrophy & can be delivered systematically
• But difficult to purify & poorly defined cell population