Heat stress could promote skeletal muscle regeneration via early recruitment and invasion of macrophages into the necrotic muscle fibers (e.g., Takeuchi et al., 2014; Hatade et al., 2014). Macrophages play important roles in myoblasts proliferation, differentiation and fusion by producing some cytokines and be involved in muscle regeneration (e.g., Tidball, 2005; Arnold et al., 2007). But in the regeneration process, the mechanisms for the macrophages recruitment via the heat stress is unclear. Monocyte Chemoattractant Protein‐1 (MCP‐1) is involved in the migration, and this chemokine is produced by the satellite cells (e.g., Chazaud et al., 2003). Spatial distributions and chronological changes of the MCP‐1, Pax7 (a specific marker of satellite cells) and CD68 (a pan‐macrophages marker) were examined by using the immunohistochemistry via heat stress after crush injury to the extensor digitorum longus muscle of rats. In the present study, 8‐week old male Wistar rats weighing 180–200g were used. According to the crush method described by Furuta (2001) and our earlier reports (Takeuchi et al., 2014; Hatade et al., 2014), animals were anesthetized by an isoflurane and exposed the muscle. Next, the middle part of the muscle belly was crushed for 30s using forceps, to which a weight (500g) was attached. After the muscle crush injury, animals were randomly divided into heat and non‐heat groups. In the heat group, packs filled with hot water (42 degrees C) were percutaneously applied to the muscle for 20 min soon after the injury and in the non‐heat group were not. At 6, 12 and 24 h (n = 1, respectively) after the injury, animals were sacrificed, muscles were harvested and frozen cross sections (10 μm) of the injured muscle were prepared by cutting with a cryostat. Some sections were used for hematoxylin and eosin staining, the others were used for immunohistochemistry. At 6 h after the injury, macrophages were recruited around the degenerating muscle fibers in the non‐heat group. In the heat group, recruitment of the macrophages was higher than the non‐heat group. Similarly, recruitment and infiltration of macrophages in the heat group were higher than those in the non‐heat group at 12 h and 24 h after the injury. In addition, at 6 h after the injury of the heat group, the MCP‐1 was expressed in the satellite cells, whereas in the non‐heat group it was seen after 12 h, suggesting that the heat stress soon after the skeletal muscle injury might promote more rapid MCP‐1 expression of the satellite cells.Support or Funding InformationNoneThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
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May 1, 2023
Hiroshi Fujimaki + 6
