From skeletal muscle damage and regeneration to the hypertrophy induced by exercise: what is the role of different macrophage subsets?

Macrophages are one of the top players when considering immune cells involved with tissue homeostasis. Recently, increasing evidence has demonstrated that macrophages could also present two major subsets during tissue healing: proliferative macrophages (M1-like), which are responsible for increasing myogenic cell proliferation, and restorative macrophages (M2-like), which are involved in the end of the mature muscle myogenesis. The participation and characterization of these macrophage subsets are critical during myogenesis to understand the inflammatory role of macrophages during muscle recovery and to create supportive strategies that can improve mass muscle maintenance.

Inflammatory response of the peripheral neuroendocrine system following downhill running.

Exploring the relationship between exercise inflammation and the peripheral neuroendocrine system is essential for understanding how acute or repetitive bouts of exercise can contribute to skeletal muscle adaption. In severe damage, some evidence demonstrates that peripheral neuroendocrine receptors might contribute to inflammatory resolution, supporting the muscle healing process through myogenesis. In this sense, the current study aimed to evaluate two classic peripheral neuronal receptors along with skeletal muscle inflammation and adaptation parameters in triceps brachii after exercise.

Skeletal muscles induce recruitment of Ly6C macrophage subtypes and release inflammatory cytokines 3 days after downhill exercise.

Macrophages are one of the most versatile cells of the immune system that can express distinct subtypes and functions depending on the physiological challenge. After skeletal muscle damage, inflammatory macrophage subtypes aid muscles to regenerate and are implicated in physical training adaption. Based on this information, this study aimed to evaluate two classic mice macrophage subtypes and determine whether some inflammatory cytokines might be involved in the muscle adaption process after exercise.

The Secretory Leukocyte Protease Inhibitor mRNA expression is involved with inflammatory control after downhill exercise in the triceps brachii intermediary head in Wistar rats.

After severe skeletal muscle damage, communication between inflammatory macrophages, myogenic cells, and modulatory secretion factors is essential to induce re-establishment of skeletal muscle structure. To analyze when characteristic gene expression of macrophages, myogenic cells, and SLPI are modulated after an exercise-induced muscle damage (EIMD) downhill protocol. Twenty-six rats were exposed to an experimental protocol of exercise and euthanized before (CTRL), immediately after (G0), and 24 (G24) and 48 (G48) hours after the exercise.

Macrophage Polarization: Implications on Metabolic Diseases and the Role of Exercise.

Macrophages are cells of the innate immune response that trigger inflammation resolution. The phenotype of "classically activated macrophages" (M1) has anti-tumoricidal and anti-bactericidal activities. On the other hand, "alternatively activated macrophages" (M2) are involved in tissue remodeling and immunomodulatory functions.

Downhill exercise-induced changes in gene expression related with macrophage polarization and myogenic cells in the triceps long head of rats.

Macrophages are one of the most heterogenic immune cells involved in skeletal muscle regeneration. After skeletal muscle damage, M1 phenotypes exhibit pro-inflammatory reaction. In a later stage, they are converted to M2 phenotypes with anti-inflammatory properties.