Abstract
Immune cells are involved in skeletal muscle regeneration. The mechanism by which Treg cells are involved in the regeneration of injured skeletal muscle is still unclear. The purpose of this study was to explore the role of programmed death-1 in contused skeletal muscle regeneration, and to clarify the regulation of programmed death-1 on Treg cell generation and macrophage polarization, in order to deepen our understanding of the relationship between the immune system and injured skeletal muscle regeneration. The results show that programmed death-1 knockdown reduced the number of Treg cells and impaired contused skeletal muscle regeneration compared with those of wild-type mice. The number of pro-inflammatory macrophages in the contused skeletal muscle of programmed death-1 knockout mice increased, and the expression of pro-inflammatory factors and oxidative stress factors increased, while the number of anti-inflammatory macrophages and the expression of anti-inflammatory factors, antioxidant stress factors, and muscle regeneration-related factors decreased. These results suggest that programmed death-1 can promote contused skeletal muscle regeneration by regulating Treg cell generation and macrophage polarization.
Highlights
Skeletal muscle injury is a common injury in sports medicine [1], and skeletal muscle contusion is a common form of sports-related skeletal muscle injury [2]
On the first day after skeletal muscle injury, wild-type mice and PD-1 knockout mice showed a large amount of muscle fiber swelling, necrosis, and inflammatory cell infiltration, but there was no significant difference between the two groups
The morphological results showed that wild-type mice had recovered to nearly normal levels on day 14 after skeletal muscle injury, but this was not the case in the PD-1−/− mice
Summary
Skeletal muscle injury is a common injury in sports medicine [1], and skeletal muscle contusion is a common form of sports-related skeletal muscle injury [2]. The regeneration process in skeletal muscle injury is divided into three stages. The first stage occurs early in the injury, when the muscle fiber structure is destroyed, and there is swelling, necrosis, and a large number of infiltrating inflammatory cells. The second stage occurs 5–10 days after injury. At this time, muscle satellite cells are activated and proliferate, differentiate, and fuse with injured muscle fibers or residual myotubes to repair the damaged skeletal muscle. Muscle satellite cells are activated and proliferate, differentiate, and fuse with injured muscle fibers or residual myotubes to repair the damaged skeletal muscle This stage is called the injury repair period. The third stage is the tissue shaping phase, which usually occurs
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