Morphologic Characterization and Lifespan of Terminal Schwann Cells
Alison K. Snyder-Warwick, MD; Albina Jablonka, PhD
Plastic Surgery, Washington University in St. Louis, St. Louis, MO
Purpose: Functional reconstruction of peripheral nerve injuries is limited by a critical therapeutic window during which native musculature can be reinnervated. Non-myelinating Schwann cells at the neuromuscular junction (NMJ) called terminal Schwann cells are relatively understudied and may contribute to the temporal restrictions on muscle reinnervation. In addition the lifespan of terminal Schwann cells (and all Schwann cells) is unknown. We describe our preliminary morphologic observations of the development and lifespan of this unique cell type.
Methodology: The sternomastoid muscles of wild type and transgenic S100-GFP mice were evaluated with confocal microscopy at different developmental timepoints from embryonic day 14.5 to a maximum age of 29 months. Neuromuscular junctions were evaluated with immunostaining using S100 antibody (for glial cell identification), alpha-bungarotoxin (for motor endplate staining), DAPI (for nuclear staining), and neurofilament (for axonal staining).
Results: Terminal Schwann cells are identified at the NMJ beginning around postnatal day 6 or 7. Approximately 3 to 5 terminal Schwann cells are noted per NMJ. In mature NMJs, terminal Schwann cells have characteristic round nuclei with a centrally located, round nucleolus. No obvious morphologic changes are noted in the NMJs of 9 month old mice compared to younger adults, but by 14 months of age, terminal Schwann cells and motor endplates become disjointed; NMJs often have endplates in isolation or terminal Schwann cells in isolation, with fewer NMJs having colocalization of both elements. By 29 months of age, fewer terminal Schwann cells are present at each NMJ with some NMJs having an absence of terminal Schwann cells. Motor endplates become fragmented with increasing age beyond 12 months.
Conclusions: Terminal Schwann cells can be identified at the NMJ with characteristic morphologic features. Interruption of the colocalization of motor endplates with terminal Schwann cells is notable with age beyond 14 months. Quantitative studies are underway to better define this phenomenon.
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