Figure 4.

Delivery of macrophages from aged ambulatory donors to young adult recipients following hindlimb unloading. Ex vivo force production of soleus muscles from young adult mice during early recovery (4 days) following hindlimb unloading that received intramuscular injections of macrophages from ambulatory aged mice (Mac) or PBS (Vehicle) into contralateral hindlimbs. A–D: muscles were subjected to a single-pulse stimulation to induce a twitch contraction for the measurement of specific force (A), rate of contraction (B), or rate of relaxation (C). D: raw force tracings from a single-pulse stimulation that induced a twitch contraction. E: specific force was measured across a range of stimulation frequencies from 10 to 200 Hz. F: raw force tracings from a 100 Hz stimulation. G: proinflammatory gene expression from qRT-PCR of macrophages isolated from ambulatory young adult or aged mice. Individual data points are shown with means ± SE. Unpaired t tests were performed. A–C, and G: individual data points are shown and connected with respective contralateral limbs and the mean is represented as a bar. E: data points are shown as means ± SE. Paired/unpaired t tests (A–C, and G) or a two-way ANOVA with Sidak’s multiple-comparisons test (E) was used. n = 7/group.