Effects of CX3CR1 and CXCR2 antagonists on running-dependent intramuscular neutrophil recruitments and myokine upregulation

Abstract

Muscle contractile activity stimulates intramuscular recruitment of immune cells including neutrophils emerging to serve as a prerequisite for exerting proper muscular performance, although the underlying mechanisms and their contributions to myokine upregulation remain ill-defined. We previously reported that pharmacological inhibition of CX3CR1, a fractalkine receptor, dampens gnawing-dependent neutrophil recruitment into masseter muscles along with compromising their masticatory activity. By employing a running exercise model, we herein demonstrated that hindlimb muscles require collaborative actions of both CX3CR1- and CXCR2-mediated signals for achieving neutrophil recruitment, upregulation of myokines including interleukin (IL)-6, enhanced GLUT4 translocation, and adequate endurance capability. Mechanistically, we revealed that a combination of CX3CR1 and CXCR2 antagonists, i.e., AZD8797 and SB2205002, inhibits exercise-inducible ICAM-1 and fractalkine upregulations in the area of the endothelium and muscle-derived CXCL1 upregulation, both of which apparently contribute to the intramuscular neutrophil accumulation in working muscles. Intriguingly, we also observed that 2 h of running results in intramuscular augmentation of innate lymphoid type 2 cells (ILC2s) markers, i.e., Bcl11b mRNA levels and anti-GATA-3-antibody-positive signals, and that these effects are completely abolished by administration of the combination of CX3CR1 and CXCR2 antagonists. Taken together, our findings strongly suggest that the exercise-evoked regional interplay among working myofibers, the adjacent endothelium and recruited immune cells including neutrophils and possibly ILC2s, mediated through these local factors, plays a key role in organization of the intramuscular microenvironment supporting the performance of hindlimb muscles during running.

Molecular insights of exercise therapy in disease prevention and treatment

“…The great scientific interest in exercise-induced signaling molecules with glucose-lowering effects 145 , 147 , 148 , 150 , 151 , 153 , 154 was particularly fostered by the fact that hyperglycemia is associated with an increased risk for various diseases. 156 , 157 Understanding insulin-independent mechanisms of glucose uptake by skeletal muscle in response to exercise was therefore considered a topic with high therapeutic potential.…”

“…In summary, skeletal muscle is stimulated by various exerkines in an autocrine, paracrine, and/or endocrine fashion and the structural and functional adaptions induced by exerkine signaling range from classic endurance adaptions, 95 , 146 , 148 , 149 , 152 via anti-sarcopenic effects, 51 , 52 , 152 , 166 through to anti-diabetic and metabolic effects. 145 , 147 , 148 , 150 , 151 , 153 , 154 Besides mechanistic insights into the molecular foundations of exercise adaptions, these studies highlight how the knowledge of specific exerkine receptor signaling in a target tissue can be transferred to potential other target tissues that express the same exerkine receptor. 146 , 147 , 152 Adopting a hypothesis-driven research strategy and maintaining a clear focus on the origin and potential targets of established exerkines holds the potential to advance our understanding of the pan-tissue benefits of exercise with potential clinical implications in different diseases.…”