Time-course study of macrophage infiltration and inflammation in cast immobilization-induced atrophied muscle of mice.

Introduction: Macrophage infiltration may play an important role in mediating the development of muscle atrophy. However, temporal differences in the activation of muscle atrophy signaling pathways and the progress of macrophage infiltration during the atrophic phases of cast immobilization are currently unknown. Methods: C57BL/6J mice were euthanized after cast immobilization at 1, 3, 7, and 14 days. Results: Skeletal muscle macrophage numbers were unchanged on days 1 and 3 after immobilization, but were elevated on days 7 (2.7-fold, P<0.01) and 14 (4.1-fold, P<0.01). Ubiquitin ligase expression was increased 1 and 3 days after cast immobilization, as was the LC3-II/LC3-I ratio. Discussion: Atrophy signaling pathway activation, but not macrophage infiltration, was observed during the early phase after cast immobilization. Our findings indicate that macrophage infiltration may contribute very little to the early phase of muscle atrophy after cast immobilization.