Priority Research Paper Volume 14, Issue 1 pp 28—53

Reduced growth rate of aged muscle stem cells is associated with impaired mechanosensitivity


Figure 7. Attenuated mechanosensitivity to PFSS in aged MuSCs. (A) MuSC gene expression in response to PFSS, showing upregulation of Cdk4, Timp1, c-fos, IL-6, Ptk2, Itga5, Itgb5, Itga7, Yap, Ctgf, Cyr61, Tead1, Tead2, Tead3, and Tead4, in young MuSCs, and Timp1, Ctgf, and Cyr61 in aged MuSCs. Young MuSCs, n = 10 (from 4 young mice). Aged MuSCs, n = 8 (from 3 aged mice). (B) Confocal top view (XY) and cross-sectional (XZ) live cell images of young and aged MuSCs stained for F-actin filaments (red), and nuclei (green), before (static) and during (1 s, 5 s) fluid shear stress treatment, illustrating the change in cell apex-height as a result of fluid shear stress. The change in cell apex-height is highlighted with solid and dotted lines in XZ images. Arrows indicate the direction of fluid flow (C, D) CFSS induced MuSC deformation and decreased the cell apex-height of young and aged MuSCs at the start of CFSS treatment (1 s). Aged MuSCs remained deformed after 5 s of treatment, whereas young MuSCs regained their initial cell apex-height. Young MuSCs, n = 13 (from 3 young mice). Aged MuSCs, n = 10 (from 3 aged mice). (E) Nano-indentation of MuSCs revealed a similar Young’s modulus (~450 Pa) of young and aged MuSCs. The coefficient of variation was large in aged MuSCs (61%) compared to young MuSCs (27%). (F) Force-indentation curves showing large variation in force required to indent aged MuSCs compared to young MuSCs. (G) Confocal cross-sectional micrographs of young MuSC stained for F-actin filaments (red) and nucleus (green) before and during nano-indentation, illustrating cell deformation (dotted line). Young and aged MuSCs, n = 10 cells (from 1 young mouse and 1 aged mouse). Abbreviations: MuSCs: muscle stem cells; PFSS: pulsating fluid shear stress; CFSS: constant fluid shear stress. Values are mean ± SEM. *Significant effect of PFSS, p < 0.05. #Significant difference between age groups, p < 0.05. Scale bar; 10 μm.