50. Sonic Hedgehog Agonists Within Engineered Hydrogel Induce Repair Schwann Cell Phenotype in Peripheral Nerve Injury

PURPOSE: Peripheral nerve injuries often lead to significant functional impairments. This project developed an innovative hydrogel consisting of F127-SS-DA, a biocompatible polymer capable of self-assembling into micelles and featuring disulfide linkages for controlled drug release of Sonic Hedgehog (Shh) agonists. The overall goal is to use this hydrogel to reprogram SCs into a repair phenotype, preventing chronic denervation, and enhancing functional recovery. METHODS: Primary rat SCs were cultured with Smoothened agonist (SAG) and purmorphamine (PUR) to identify dosing and effects to their repair phenotype. Isolated rat dorsal root ganglion (DRG) neurons were co-cultured along with these SCs to measure changes to axonal extension. Hyaluronic acid (HA)-based hydrogels were designed and optimized to incorporate antioxidative micelles (F127-SS-DA) for sustained release of PUR. PUR release kinetics were assessed for 26 days. Laminin- or fibronectin-derived peptides (YIGSR, RGD, IKVAV) were also conjugated with HA hydrogels to support SC culture in 3D. Lastly, we injected small volumes (30 µL) of infrared-labeled hydrogel into sciatic nerve isolated from Thy1-GFP rats ex vivo and performed whole-mount confocal imaging to observe the distribution of the hydrogel along axons. RESULTS: Higher concentrations of SAG and PUR elevated c-Jun expression and altered the morphology of primary SCs to a repair phenotype. These changes were associated with a marked increase in the expression of repair-associated genes in a dose-dependent manner. Consequently, drug-treated SCs enhanced neurite elongation from neurons compared to non-treated SCs. The F127-SS-DA hydrogel containing adhesive peptides was able to support SC attachment and migration, demonstrating biocompatibility. Release kinetics demonstrated that this hydrogel was able to release therapeutically effective doses of PUR (2.5-10 μM). The hydrogel was able to induce c-Jun expression and repair morphology in cultured SCs. Finally, intrafascicular loading of the hydrogel within nerve preserved axonal trajectories. CONCLUSION: Our engineered hydrogel system offers an innovative strategy to treat nerve injury by reprograming SCs to promote axonal regeneration. This mechanism is particularly relevant after nerve transection wherein axons are acutely severed, and in chronic denervation stemming from compressive neuropathy or delayed intervention. By promoting a repair phenotype in SCs, this approach has significant potential to improve nerve regeneration and functional recovery of motor and sensory function in multiple clinical contexts.