Stem Cell Microenvironments and Beyond

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EC

PEC

Ang1

Calc

Serpin, Tfpi2,

Timpf4

Laminin-2

Fibronectin

Calcr

Tie-2

Integrin α7β1

M-Cadherin

MA

FI

MF

qSC

FAP

BL

RL

Fig. 8.1 The quiescent niche. Under homeostatic conditions, the SC and its niche are in a quies-
cent (q) state. The qSC receives signals that keep it dormant, such as angiopoietin 1 (Ang1) from
periendothelial cells (PECs) and calcitonin (Calc) from the bloodstream, but at the same time
actively contributes to the niche state by secreting protease inhibitors (Serpin, Tfpi2, Timpf4). The
SC is attached with M-cadherin to the myofiber (MF) and with integrin to the basal lamina (BL).
Fibro/adipogenic progenitors (FAPs) and macrophages (MAs) are present in low numbers and are
mainly inactive. Further abbreviations: Calcr calcitonin receptor; EC endothelial cell; FI fibro-
blast; RL reticular lamina; Tie-2 receptor for Ang1

8 Plasticity of the Muscle Stem Cell Microenvironment