Regulation of Granulocyte Colony-Stimulating Factor and Its Receptor in Skeletal Muscle Is Dependent Upon the Type of Inflammatory Stimulus

Abstract

The cytokine granulocyte colony-stimulating factor (G-CSF) binds to its receptor (G-CSFR) to stimulate hematopoietic stem cell mobilization, myelopoiesis, and the production and activation of neutrophils. In response to exercise-induced muscle damage, G-CSF is increased in circulation and G-CSFR has recently been identified in skeletal muscle cells. While G-CSF/G-CSFR activation mediates pro- and anti-inflammatory responses, our understanding of the role and regulation in the muscle is limited. The aim of this study was to investigate, in vitro and in vivo, the role and regulation of G-CSF and G-CSFR in skeletal muscle under conditions of muscle inflammation and damage. First, C2C12 myotubes were treated with lipopolysaccharide (LPS) with and without G-CSF to determine if G-CSF modulates the inflammatory response. Second, the regulation of G-CSF and its receptor was measured following eccentric exercise-induced muscle damage and the expression levels we investigated for redox sensitivity by administering the antioxidant N-acetylcysteine (NAC). LPS stimulation of C2C12 myotubes resulted in increases in G-CSF, interleukin (IL)-6, monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor-α (TNFα) messenger RNA (mRNA) and an increase in G-CSF, IL-6, and MCP-1 release from C2C12 myotubes. The addition of G-CSF following LPS stimulation of C2C12 myotubes increased IL-6 mRNA and cytokine release into the media, however it did not affect MCP-1 or TNFα. Following eccentric exercise-induced muscle damage in humans, G-CSF levels were either marginally increased in circulation or remain unaltered in skeletal muscle. Similarly, G-CSFR levels remained unchanged in response to damaging exercise and G-CSF/G-CSFR did not change in response to NAC. Collectively, these findings suggest that G-CSF may cooperate with IL-6 and potentially promote muscle regeneration in vitro, whereas in vivo aseptic inflammation induced by exercise did not change G-CSF and G-CSFR responses. These observations suggest that different models of inflammation produce a different G-CSF response.

The effect of polyphenols on cytokine and granulocyte response to resistance exercise

“…The findings of Wright et al. () are consistent with our findings, and may suggest that resistance exercise does not elicit production of G‐CSF from skeletal muscle. Rather, production of circulating G‐CSF may be a function of systemic inflammation associated with resistance exercise (Roberts ; Wright et al.…”

“…G-CSF, however, has been demonstrated to increase (Paulsen et al 2005;Wright et al 2015), and remain unchanged (Smith et al 2000;Ross et al 2010) following exercise-induced muscle damage. Exercise volume appears to drive this response as exercise protocols with a greater volume (300 eccentric contractions of knee extensors) being reported to elicit an increase in circulating G-CSF (Paulsen et al 2005;Wright et al 2015), while lower training volumes (~50 eccentric contractions of knee flexors or hip extensors) did not (Smith et al 2000;Ross et al 2010).…”

“…Wright et al. () demonstrated no change in protein content of G‐CSF following exercise‐induced muscle damage. The findings of Wright et al.…”

“…Rather, production of circulating G‐CSF may be a function of systemic inflammation associated with resistance exercise (Roberts ; Wright et al. ). Regardless of production site, the primary action of G‐CSF and GM‐CSF is the production and activation of granulocytes from the bone marrow (Roberts ; Francisco‐Cruz et al.…”

Exercise-Induced Oxidative Stress Responses in the Pediatric Population

“…However, in cases of excessive exercise training and inadequate recovery (i.e., overtraining) a disproportionate rise of oxidative stress biomarkers is seen due to the overload of antioxidant system which may be compromised [26,27,28]. It appears that under conditions of elevated oxidant load, ingestion of antioxidant compounds (e.g., thiol-based antioxidants, lipoic acid) [29,30,31,32] and other nutritional supplements [13] may boost antioxidant reserves, help to keep oxidative stress responses under control and lower the inflammatory response. However, it has been suggested that antioxidant reserves, such as reduced glutathione (GSH), may be lower in children, especially those engaged in chronic intensive training programs suggesting that children, and probably adolescents, may be susceptible to exercise-induced oxidative damage [33,34,35].…”