Stem Cell Microenvironments and Beyond

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EC

PEC

MA

FI

agMF

agSC

FAP

RL BL

Wnt

IL-6

TGF-β

FGF-2

Fibronectin

Notch receptor

Laminin-2 M-Cadherin

Integrin α7β1

TGF-β receptor

FGFR1

IL-6 receptor

Fig. 8.3 The aged niche. The aged myofiber (agMF) has a smaller diameter, fewer myonuclei and
reduced levels of Delta, a ligand of Notch, which is crucial to SC proliferation. Further changes to
the niche include increased fibroblast (FI) numbers and a denser basal and reticular lamina (BL,
RL) with reduced fibronectin levels, active macrophages (MAs) secreting TGF-β, as well as
increased levels of FGF-2, IL-6 and Wnt signaling molecules. Further abbreviations: EC endothe-
lial cell; FA P, fibro/adipogenic progenitor; PEC, periendothelial cell

8 Plasticity of the Muscle Stem Cell Microenvironment