Fig. 7: Neutrophil depletion impairs skeletal muscle regeneration.

Analysis of TA muscles after 10 days from glycerol-induced injury. a Immunostaining for myosin heavy chain isoforms was utilized to detect type 2a (green), type 2x (black), and type 2b myofibers (red): these histological analyses indicate defective muscle regeneration in mice with neutrophil depletion. b–d Gaussian plots indicate that neutrophil depletion impairs the growth of newly formed myofibers in post-injury muscles whereas there is no effect of neutrophil depletion on myofiber size in contralateral uninjured muscles. e Quantitation of myofiber sizes (Feret’s minimal diameter) based on the average values obtained from the individual muscles in a group. There is an overall significant decline in the size of type 2x and 2b myofibers in post-injury muscles from neutrophil-depleted mice compared to post-injury muscles from mock-treated mice. f There is an overall similar myofiber type composition of uninjured and post-injury TA muscles. However, post-injury muscles (both from neutrophil-depleted and mock-treated mice) display higher levels of type 2x myofibers. g The number of type 2x and 2b myofibers increases in post-injury versus uninjured muscles and the number of type 2b myofibers is significantly higher in the muscles from neutrophil-depleted mice. In e–g, the graphs display the mean ±SD with n = 6 (from 6 independent control mice) and n = 4 (from 4 independent neutrophil-depleted mice) biologically independent muscles; *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 (two-way ANOVA with Tukey post hoc test), ns = not significant. h The normalized twitch force of post-injury muscles from neutrophil-depleted mice is reduced compared to that of post-injury muscles from mock-treated mice. i Similar deficits in muscle force production are found for the normalized tetanic force of muscles from neutrophil-depleted versus mock-treated mice. Neutrophil depletion does not impact twitch and tetanic force production by uninjured muscles (h, i). In h, i, the graphs display the mean ± SD with n = 6 (from 6 independent control mice) and n = 4 (from 4 independent neutrophil-depleted mice) biologically independent muscles; *P < 0.05, ****P < 0.0001 (two-way ANOVA with Sidak post hoc test). Source data are provided in the Source data file.