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Muscle regenerative capacity and aging International Conference on - - PowerPoint PPT Presentation
Muscle regenerative capacity and aging International Conference on - - PowerPoint PPT Presentation
Muscle regenerative capacity and aging International Conference on Frailty & Sarcopenia Research Charlotte A. Peterson Miami, Florida March 1-3, 2018 Satellite cells: Resident muscle stem cells Relaix & Zammit, 2012 Plasmalemma
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Relaix & Zammit, 2012
Satellite cells: Resident muscle stem cells
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Plasmalemma Basal lamina Myofibril Mitochondria Satellite cell nucleus Myonucleus
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Supplement Figure 2F: Dystrophin staining to demonstrate how CSA was determined
Pax7 IHC to identify satellite cells
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Myofiber repair and regeneration is mediated by satellite cells
Adapted from Abmayr & Pavlath Development 2012
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Normal compared to regenerated single fibers
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Pax7-DTA mouse for satellite cell depletion
>4 months of age, ~ 25g Tamoxifen: 2mg/day for 5 days IP, 2 week washout Only mice with >90% satellite cell depletion are used
V V Pax7-CreER Rosa26-flstopfl-DTA Pax7-DTA
Mauro, 1961
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100 µm
Vehicle Tamoxifen PBS BaCl2
Satellite cell-depleted muscle does not regenerate
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Adapted from Brack & Rando, Cell Stem Cell, 2012
Pax7+ Satellite Cell
Other roles for satellite cells?
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Dogma: The myonuclear domain remains constant during adult muscle growth via satellite cell fusion
Resistance training
– Satellite cell proliferation – Fusion to the myofiber – Myofiber hypertrophy
Satellite cell Myonucleus
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Model of muscle hypertrophy
Synergist ablation (SA) Imposes functional overload of plantaris muscle Substitute for resistance exercise training
0,0 0,5 0,9 1,4 1,8
CONT SA1 SA2 SA4 muscle weight (mg/g)
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Early growth response following synergist ablation is unaffected by satellite cell depletion
McCarthy et al., Development, 2011
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Hypertrophy occurs in the absence of myonuclear accretion in satellite cell-depleted muscle
nucleus inside the fiber (myonucleus) nucleus outside fiber
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Muscle growth plateaus in the absence of satellite cell participation
Fry et al., FASEB J, 2014
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ECM accumulation is increased in satellite cell-depleted muscle following 8 weeks of overload
Vehicle Tamoxifen
200 400 600 800
Sham SA-8 Vehicle Tamoxifen
*
WGA Area · Fiber-1
*
Glycoaminoglycans Tamoxifen Sham SA-8 Vehicle Collagen
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In vitro analysis of the myogenic progenitor cell (MPC)-fibroblast interaction
Insert (MPCs) Well (Fibroblasts) Well (Fibroblasts) Insert (Fibroblasts)
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Activated satellite cell/MPC secretory products inhibit ECM gene expression in fibroblasts
0,5 1 1,5 2 2,5 3
Col1a2 Col3a1 Col6a2 Fbnct + Fibroblasts + MPCs
Relative mRNA expression
* * * ‡
Fry et al., Cell Stem Cell 2017
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Brack & Rando, Cell Stem Cell 2012
Pax7+ Satellite Cell Pax7- DTA
Do satellite cells play a role in normal muscle maintenance?
Early
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Dogma: Loss of satellite cell activity causes sarcopenia
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Satellite cell depletion as a premature muscle aging model?
Muscle collected from: 5-month olds - 1 month of satellite cell depletion (young) 24-month olds - 20 months of satellite cell depletion (old) 4 24
Tamoxifen/Vehicle Pax7-DTA mouse
5
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Long term satellite cell depletion does not exacerbate sarcopenia
0,04 0,08 0,12
Plantaris Gastroc TA/EDL Soleus Plantaris Gastroc TA/EDL Soleus
Pax7+ Cells / Fiber
* * * * * * * *
Young Old Vehicle Tam
500 1000 1500 2000 2500 3000
Plantaris Gastroc TA/EDL Soleus
Mean Fiber CSA (µm2)
† † †
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Satellite cell-depleted aged muscle does not regenerate
PBS BaCl2 Vehicle Tamoxifen
Fry et al., Nature Medicine, 2016
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1 2 3 4 5 6 7 8 Vehicle Tamoxifen #Nuclei/100um Fiber Length Young Old
Myonuclear number is not altered in satellite cell- depleted muscle
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5 10 15 20 25 30 35
Vehicle Tamoxifen
#
Vehicle Tamoxifen
Increased fibrosis in lifelong satellite cell-depleted muscle
% WGA
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Growth in response to overload is impaired in aged mice regardless of satellite cell content
Lee et al., J. Gerontol., 2016
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Myonuclear accretion does not drive myofiber growth in aged muscle
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Conclusions
- Muscle regeneration, maintenance and hypertrophy have different satellite
cell requirements.
- Satellite cell-depleted muscle becomes fibrotic over time which may limit
long term growth.
- Satellite cells repress ECM production by fibroblasts which may facilitate
muscle remodeling.
- Depletion of satellite cells in adult mice impairs muscle regenerative
capacity without affecting sarcopenia.
- Satellite cell loss with age may contribute to muscle fibrosis, limiting
muscle adaptability.
- Satellite cell fusion and myonuclear accretion are insufficient to drive
myofiber growth in aged muscle.
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Take Home Messages
- Compensatory mechanisms exist in the adult mouse that
enable muscle maintenance and adaptation independent of satellite cells.
- In addition to therapeutic potential of satellite cells in treating
degenerative muscle diseases by promoting regeneration, satellite cells may be useful in reducing fibrosis associated with aging, independent of their ability to contribute nuclei to myofibers.
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