Decoding muscle-resident Schwann cell dynamics during neuromuscular junction remodeling [scRNA-seq]

Understanding neuromuscular junction (NMJ) repair mechanisms is essential for addressing degenerative neuromuscular conditions. Here, we focus on the role of muscle-resident Schwann cells in NMJ reinnervation. Using an accepted model of progressive NMJ degeneration, Sod1-/- mice, we identified a clear NMJ regenerative window that allowed us to define cellular and molecular regulators of synapse remodeling and muscle fiber reinnervation. High-resolution imaging and single-cell RNA sequencing provide a detailed analysis of Schwann cell number, morphology, and transcriptome revealing multiple subtypes, including a previously unrecognized terminal Schwann cell (tSC) population expressing a synapse promoting signature. We also discovered a novel SPP1-driven cellular interaction between myelin Schwann cells and tSCs and show that it promotes tSC proliferation and reinnervation following nerve injury in wild type mice. Our findings offer important insights into molecular regulators critical in NMJ reinnervation that are mediated through tSCs to maintain NMJ function. Overall design: Male C57BL/6J mice (10–16 weeks old) were subjected to bitlateral peroneal nerve injuries, a 10 µL intramuscular injection of SPP1 neutralizing antibody (2 µg; AF808, R&D Systems) was administered into the tibialis anterior (TA) muscle using a Hamilton syringe and repeated every two days following the initial injury. Control mice received goat anti-mouse IgG (2 µg; 115-005-003, Jackson Immuno) on the same schedule. Muscles were harvested for scRNA sequnecing 7 days post injury (7dpi).