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Decoding muscle-resident Schwann cell dynamics during neuromuscular junction remodeling
Steve D. Guzman, Ahmad Abu-Mahfouz, Carol S. Davis, Lloyd P. Ruiz, Peter C.D. Macpherson, Susan V. Brooks
Steve D. Guzman, Ahmad Abu-Mahfouz, Carol S. Davis, Lloyd P. Ruiz, Peter C.D. Macpherson, Susan V. Brooks
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Research Article Cell biology Muscle biology

Decoding muscle-resident Schwann cell dynamics during neuromuscular junction remodeling

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Abstract

In this study, we used single-cell RNA sequencing to delineate the contributions of muscle-resident Schwann cells to neuromuscular junction (NMJ) remodeling by comparing a model of stable innervation with models of reinnervation following partial or complete denervation. We discovered multiple distinct Schwann cell subtypes, including a terminal Schwann cell subtype integral to the denervation-reinnervation cycle, identified by a transcriptomic signature indicative of cell migration and polarization. The data also characterize 3 myelin Schwann cell subtypes, which are distinguished based on enrichment of genes associated with myelin production, mesenchymal differentiation, or collagen synthesis. Importantly, SPP1 signaling emerged as a pivotal regulator of NMJ dynamics, promoting Schwann cell proliferation and muscle reinnervation across nerve injury models. These findings advance our understanding of NMJ maintenance and regeneration and underscore the therapeutic potential of targeting specific molecular pathways to treat neuromuscular and neurodegenerative disorders.

Authors

Steve D. Guzman, Ahmad Abu-Mahfouz, Carol S. Davis, Lloyd P. Ruiz, Peter C.D. Macpherson, Susan V. Brooks

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Figure 3

The remodeling of neuromuscular junctions (NMJs) is associated with greater tSC numbers, larger synaptic areas, and enhanced proliferation in S100GFP-tg Sod1–/– mice.

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The remodeling of neuromuscular junctions (NMJs) is associated with grea...
(A) Schematic of NMJ analysis, consisting of collecting NMJs images from muscle fiber bundles followed by the generation of feature masks and their measurements. Additional details on the generation of the masks are provided in Supplemental Figures 3 and 4 and Methods. (B) NMJs stained for S100B (Schwann cells; green), NF/SV2 (nerve; cyan), AChRs (α-bungarotoxin, BTX; red), and nuclei (DAPI; blue) in 2-month-old S100GFP-tg control and S100GFP-tg Sod1–/– mice. (C–E) Quantification of nerve terminal area, nerve terminal perimeter, AChR area, percentage overlap between AChR area and nerve terminal area, and tSC number and tSC area. Muscle fiber imaging from S100GFP-tg (F) and S100GFP-tg Sod1–/– (G) mice, immunostained for S100B (green), Ki67 (magenta), AChR (red), and nuclei (blue). White arrows point to extrasynaptic nuclei positive for Ki67 but lacking endogenously expressed GFP and or S100B immunostaining, while the yellow arrow highlights a perisynaptic Ki67+GFP+ nucleus. (H) Enlarged view of 2 NMJs from the highlighted region in G, detailing the S100B, Ki67, and BTX stains. (I) The same NMJs from H, but focused on BTX and Ki67, revealing multiple Ki67+ nuclei in close proximity to the endplate. (J) Quantification of extrasynaptic and perisynaptic nuclei either singly labeled for Ki67 or double labeled for Ki67 and GFP. Values for all features across all NMJs analyzed are provided in Supplemental Figure 4. Open circles indicate average for each individual mouse of no fewer than 20 NMJs analyzed per muscle and bars represent means across animals ± SEM. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001 by 2-tailed unpaired t test (C–E, vs. S100GFP-tg Sod1–/–) and (J). Scale bars: 25 μm (B) and 50 μm (F and G). In C–E, n = 4–5/group; J, n = 3/group.

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