Figure 5: Collagen VI affects SC self-renewal by regulating muscle stiffness in vivo.

(a) Measurement of elastic modulus of wild-type and Col6a1^–/– TA muscles under standard conditions (−) and 4 days after injury (+). Data are shown as mean±s.e.m. of three independent replicates (*P<0.05; unequal variance Student’s t-test; n=10 animals, each group). Error bars indicate s.d. (b) Quantification of Pax7⁺MyoD^–, Pax7⁺MyoD⁺, and Pax7^–MyoD⁺ cell populations in sorted wild-type SCs, following 7 days culture on biomimetic structures. Data are shown as mean±s.e.m of two independent replicates (^#P<0.01 for the Pax7⁺MyoD^– population; *P<0.01 for the Pax7⁺MyoD⁺ population; ^§P<0.01 for the Pax7^–MyoD⁺ population; unequal variance Student’s t-test; n=8 wells, each group). (c) Schematic diagram of the experimental approach for grafting cultured SCs grown on 7 kPa or 12 kPa in Col6a1^–/– TA muscles. (d) Real-time PCR analysis of GFP DNA content in Col6a1^–/– TA under untreated condition (−) or after grafting. Data are shown as mean±s.e.m of three independent replicates (*P<0.05; unequal variance Student’s t-test; n=6 animals, each group). (e) Analysis of centrally nucleated fibers (CNF) in Col6a1^–/– TA under untreated condition (−) or 7 days after grafting. Data are shown as mean±s.e.m. of three independent replicates (**P<0.01; unequal variance Student’s t-test; n=6 animals, each group). (f) Quantification of SCs in Col6a1^–/– TA under untreated condition (−) or 7 days after grafting. Data are shown as mean±s.e.m. of three independent replicates (**P<0.01; unequal variance Student’s t-test; n=6 animals, each group). (g) Left panel, representative images of Col6a1^–/– TA grafted with cultured SCs, showing SCs localized in centrally nucleated fibers (CNFs, arrows). Scale bar, 25 μm. Right panel, quantification of SCs in CNFs of Col6a1^–/– TA under untreated condition (−) or 7 days after grafting. Data are shown as mean±s.e.m. of three independent replicates (**P<0.01; unequal variance Student’s t-test; n=6 animals, each group). 7 kPaSC, wild-type SCs cultured on 7 kPa; 12 kPaSC, wild-type SCs cultured on 12 kPa; Col VI, collagen VI; MG, matrigel; WT, wild-type.