Mast cells and neutrophils mediate peripheral motor pathway degeneration in ALS
Emiliano Trias, … , Olivier Hermine, Luis Barbeito
Emiliano Trias, … , Olivier Hermine, Luis Barbeito
Published October 4, 2018
Citation Information: JCI Insight. 2018;3(19):e123249. https://doi.org/10.1172/jci.insight.123249.
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Research Article Inflammation Neuroscience

Mast cells and neutrophils mediate peripheral motor pathway degeneration in ALS

Abstract

Neuroinflammation is a recognized pathogenic mechanism underlying motor neuron degeneration in amyotrophic lateral sclerosis (ALS), but the inflammatory mechanisms influencing peripheral motor axon degeneration remain largely unknown. A recent report showed a pathogenic role for c-Kit–expressing mast cells mediating inflammation and neuromuscular junction denervation in muscles from SOD1G93A rats. Here, we have explored whether mast cells infiltrate skeletal muscles in autopsied muscles from ALS patients. We report that degranulating mast cells were abundant in the quadriceps muscles from ALS subjects but not in controls. Mast cells were associated with myofibers and motor endplates and, remarkably, interacted with neutrophils forming large extracellular traps. Mast cells and neutrophils were also abundant around motor axons in the extensor digitorum longus muscle, sciatic nerve, and ventral roots of symptomatic SOD1G93A rats, indicating that immune cell infiltration extends along the entire peripheral motor pathway. Postparalysis treatment of SOD1G93A rats with the tyrosine kinase inhibitor drug masitinib prevented mast cell and neutrophil infiltration, axonal pathology, secondary demyelination, and the loss of type 2B myofibers, compared with vehicle-treated rats. These findings provide further evidence for a yet unrecognized contribution of immune cells in peripheral motor pathway degeneration that can be therapeutically targeted by tyrosine kinase inhibitors.

Authors

Emiliano Trias, Peter H. King, Ying Si, Yuri Kwon, Valentina Varela, Sofía Ibarburu, Mariángeles Kovacs, Ivan C. Moura, Joseph S. Beckman, Olivier Hermine, Luis Barbeito

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Figure 2

Neutrophils infiltrate into the degenerating skeletal muscle of ALS patients and interact with mast cells and NMJs.

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Neutrophils infiltrate into the degenerating skeletal muscle of ALS pati...
(A) Representative confocal tile reconstruction showing the infiltration of elastase-positive (red) neutrophils into 2 postmortem quadriceps samples from ALS patients and 1 control donor (upper panels). High magnification in panels of the second row show how neutrophils from ALS patients form aggregates resembling neutrophil extracellular traps. Neutrophils from control donors were seen associated with blood vessels and constitute small single cells that do not aggregate. Dotted lines delimit myofibers. Scale bars: 100 μm in low-magnification panels, 10 μm in high-magnification panels. (B) Representative high-magnification confocal images showing the infiltration of myeloperoxidase (MPO, green) into the degenerating quadriceps ALS muscles. Few or no MPO-positive cells are observed in control donors. Scale bars: 10 μm. The graph to the right shows the quantitative analysis of total elastase-positive neutrophils present in 10-μm sections of quadriceps muscle for each ALS patient and control. The graph inset shows the quantitative analysis of elastase-positive neutrophil infiltration for pooled ALS patients compared with pooled controls. Data were analyzed by Kruskal-Wallis followed by Dunn’s multiple-comparisons test (graph) and Mann-Whitney test, 2-tailed (graph inset) and are expressed as mean ± SEM; P < 0.05 was considered statistically significant. (C) Representative confocal surface 3D reconstruction showing neutrophil extracellular traps in quadriceps of an ALS case. Scale bar: 20 μm. (D) Representative 3D confocal reconstruction showing the interaction of elastase-positive neutrophils (red) with NMJs motor endplates (yellow). Scale bar: 10 μm. (E) Representative 3D confocal surface reconstruction showing the interaction of elastase-positive neutrophils (red) with degranulating chymase-positive mast cells (green). No degranulating mast cells or neutrophil–mast cell interactions are observed in control donors. Scale bar: 20 μm. (F) Representative confocal microphotograph showing the proximity of chymase-positive mast cells (green) to motor endplates (yellow) in the quadriceps muscle of an ALS patient. Scale bar: 10 μm.