Biosponges Embedded with GDNF Enhance Neuromuscular Recovery Following Volumetric Muscle Loss

Volumetric muscle loss (VML) injuries result in an irrecoverable loss of muscle mass and function. VML injury causes loss of both contractile tissue and associated neuromuscular junctions (NMJs). Biosponge (BSG) scaffolds, composed of gelatin, collagen, and laminin-111, have improved recovery following VML. However, improvements in NMJ quantity were not observed. Glial cell line-derived neurotrophic factor (GDNF) is known to promote motor unit survival and stimulate neurite outgrowth. In this work, BSG scaffolds were electrostatically coupled with GDNF via gelatin nanoparticles (GNPs) to support myofiber regeneration and preserve NMJs post-VML in a rodent model. In vitro determination of release kinetics revealed an initial burst release of surface-bound GDNF with almost an equivalent amount of electrostatically bound GDNF retained within the BSG post 1 week of incubation at 37°C in phosphate-buffered saline. To create the VML injury in male Lewis rats (10-12 weeks old), ∼20% of the muscle mass was removed from the tibialis anterior (TA) muscle of both hindlimbs. Relative to BSG + GNP alone, treatment with BSG + GNP + GDNF showed a significant increase (∼25%) in peak isometric torque at 6 weeks postinjury. Qualitative and quantitative histological analysis of NMJs revealed an enhanced overlap between pre and postsynaptic structures in the BSG + GNP + GDNF group. Additionally, the incorporation of GDNF slowed BSG remodeling and degradation. Overall, these results suggest that BSG-mediated GDNF delivery is an effective strategy for mitigating NMJ loss and enhancing muscle recovery following VML.