Evidence for mast cells contributing to neuromuscular pathology in an inherited model of ALS
Emiliano Trias, … , Joseph S. Beckman, Luis Barbeito
Emiliano Trias, … , Joseph S. Beckman, Luis Barbeito
Published October 19, 2017
Citation Information: JCI Insight. 2017;2(20):e95934. https://doi.org/10.1172/jci.insight.95934.
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Research Article Inflammation Neuroscience

Evidence for mast cells contributing to neuromuscular pathology in an inherited model of ALS

Abstract

Evidence indicates that neuroinflammation contributes to motor neuron degeneration in amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease leading to progressive muscular paralysis. However, it remains elusive whether inflammatory cells can interact with degenerating distal motor axons, influencing the progressive denervation of neuromuscular junctions (NMJs). By analyzing the muscle extensor digitorum longus (EDL) following paralysis onset in the SOD1G93A rat model, we have observed a massive infiltration and degranulation of mast cells, starting after paralysis onset and correlating with progressive NMJ denervation. Remarkably, mast cells accumulated around degenerating motor axons and NMJs, and were also associated with macrophages. Mast cell accumulation and degranulation in paralytic EDL muscle was prevented by systemic treatment over 15 days with masitinib, a tyrosine kinase inhibitor currently in clinical trials for ALS exhibiting pharmacological activity affecting mast cells and microglia. Masitinib-induced mast cell reduction resulted in a 35% decrease in NMJ denervation and reduced motor deficits as compared with vehicle-treated rats. Masitinib also normalized macrophage infiltration, as well as regressive changes in Schwann cells and capillary networks observed in advanced paralysis. These findings provide evidence for mast cell contribution to distal axonopathy and paralysis progression in ALS, a mechanism that can be therapeutically targeted by masitinib.

Authors

Emiliano Trias, Sofía Ibarburu, Romina Barreto-Núñez, Valentina Varela, Ivan C. Moura, Patrice Dubreuil, Olivier Hermine, Joseph S. Beckman, Luis Barbeito

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Figure 4

Masitinib treatment prevented neuromuscular junction (NMJ) denervation.

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Masitinib treatment prevented neuromuscular junction (NMJ) denervation. ...
(A) Masitinib or vehicle was administered as described above and whole mounted extensor digitorum longus (EDL) muscles were processed for IHC. The panels show representative confocal images used to assess the innervation pattern of NMJs in different experimental conditions. α-Bungarotoxin-FITC (α-BTX, red) staining was used to analyze motor endplates. Synaptophysin–Alex Fluor 555 and heavy chain of neurofilaments–Alexa Fluor 555 (green) were used to visualize the motor axon branches and presynaptic terminals. Insets show higher-magnification images of innervated (yellow colocalization) or denervated (red) NMJs. Arrowheads indicate typical denervated motor endplates. Scales bars: 50 μm and 10 μm for insets. (B) The graph represents the quantitative analysis of NMJ occupancy defined as the overlapping of synaptophysin and α-BTX staining and expressed as percentage with respect to the nonTg condition. Note the massive loss of innervation occurring between onset and advanced paralysis in vehicle-treated rats and its prevention by masitinib. n = 4–5 animals/condition; at least 100 NMJs were analyzed per muscle, per animal. Data are expressed as mean ± SEM; data were analyzed by Kruskal-Wallis followed by Dunn’s multiple comparison test, *P < 0.01. (C) The inverted screen test was used to measure motor function. For each animal, hang time from an inverted grid was recorded in seconds and expressed as percent of the value of asymptomatic rats (100%). n = 14 and n = 22 for vehicle- and masitinib-treated groups, respectively. Data are expressed as mean ± SEM; data were analyzed by Mann-Whitney U test, 2-tailed, *P < 0.01.