Immune and satellite cells : important role players in muscle recovery after injury

[摘要] ENGLISH ABSTRACT: Muscle injuries are associated with changes in skeletal muscle as well as the immunesystem. All studies investigating possible treatment modalities have found both positive andnegative effects on muscle recovery. Since no universally accepted treatment modalityexists, this thesis aims to determine whether a plant-derived antioxidant, proanthocyanidolicoligomer (PCO), might prove beneficial as treatment for sports injuries in order for athletes toreturn to the sports field quicker. The difference in recovery of muscle following both chronic(supplementation started 14 days prior to injury and continued thereafter) and acutesupplementation (supplementation started two hours after injury) were also investigated.Both chronic and acute PCO supplementation in a rat hindlimb contusion injury modelresulted in earlier muscle recovery, verified by an earlier satellite cell response compared tothe placebo group. This effect was most prominent already at the four hour time pointfollowing injury, compared to day seven and three after chronic and acute placebo treatmentrespectively. PCO supplementation also resulted in quicker foetal myosin heavy chain(MHCf) expression compared to placebo treatment. Chronic supplementation specificallyresulted in a blunted circulatory pro-inflammatory cytokine response, whilst allowing for asignificant increase in IL-10, an anti-inflammatory cytokine, on day three (in the PCO grouponly). At tissue level, the response of the muscle pro-inflammatory cytokines, TNF-and IL-6, coincided with the satellite cell response. Macrophage infiltration into the injured musclealso followed a similar pattern to that seen for the pro-inflammatory cytokines. Macrophagesinvaded the injured area quicker when supplemented with PCO chronically, however,macrophage infiltration could not explain the cytokine response seen with acutesupplementation. Both chronic and acute supplementation with PCO was responsible for aseverely blunted neutrophil response, a novel finding of this particular antioxidant.The main findings of the in vivo rodent study were that PCO was able to blunt the neutrophilresponse, whilst allowing for earlier macrophage infiltration. To establish possiblemechanisms by which PCO might exert these beneficial effects, further analysis included determining macrophage phenotypes and neutrophil numbers in circulation. An in vitroneutrophil migration assay was also employed to further elucidate PCO's ability to bluntneutrophil infiltration into the injured area. For this study, conditioned plasma were harvestedfrom experimental animals and added together with neutrophils from control rats andgranulocyte colony stimulating factor (G-CSF) to the insert of the migration chamber. Achemotactic factor, N-formyl methionine-leucine-phenylalanine (fMLP), was added to thebottom well and neutrophils were allowed to migrate for two hours. Results from this studyindicated that neutrophil migration was attenuated in vitro in the presence of conditionedplasma from PCO supplemented rats only.The studies in this thesis on the effect of PCO on parameters of muscle and the immunesystem led to the following main conclusions: a) PCO supplementation resulted in earliermuscle recovery as a result of earlier satellite cell activation and MHCf synthesis; b) PCOfavours an anti-inflammatory cytokine reaction, whilst blunting the pro-inflammatory cytokineresponse; and c) PCO blunted the neutrophil response whilst facilitating earlier macrophageinfiltration into the injured area. The specific mechanism of action of PCO to blunt theneutrophil response specifically, possibly includes the ability to suppress adhesion moleculeexpression on the neutrophils themselves. However, this warrants further investigation.

[发布机构] Stellenbosch University