Nerve regeneration within a chitosan conduit after immediate and delayed nerve repair
Peripheral nerve injuries represent a significant clinical challenge due to their limited regenerative capacity. Surgical repair strategies include immediate nerve repair, performed shortly after injury, and delayed nerve repair, conducted after a prolonged period when primary intervention is not feasible. Understanding the molecular and genetic mechanisms underlying both strategies is essential for optimizing functional recovery. This study compares the transcriptional landscape of delayed and immediate nerve repair over time to elucidate key pathways involved in nerve regeneration. A rat model of sciatic nerve injury was used, where an 8-mm nerve gap was repaired using a chitosan conduit either immediately or after a 3-month delay. Regenerated nerves were collected at 7-, 14-, and 21-days post-repair. RNA sequencing was performed to analyze transcriptomic changes across time points, and differentially expressed genes were identified and subjected to Gene Ontology enrichment analysis to identify functional pathways and regulatory networks involved in nerve regeneration. Distinct transcriptional profiles were observed across time points after immediate and delayed repair when comparing regenerating nerves with a healthy nerve. At 7 days, both exhibited a robust inflammatory response with upregulation of genes related to cytokine signaling and myeloid cell activation. By 14 days, many pathways related to response to lipoprotein particles and phagocytosis were upregulated, with delayed repair showing downregulation of myelination-associated genes. At 21 days, immune response activation, phagocytosis and lipoprotein particle activated pathways remained upregulated in both conditions. These findings suggest that immediate repair induces a faster regenerative response, whereas delayed repair follows a slower trajectory but engages similar molecular pathways. Despite initial differences, both strategies eventually converge on key regenerative mechanisms. These insights emphasize the benefits of early intervention while highlighting the potential for delayed repair to achieve functional recovery. Future research will focus on enhancing delayed repair outcomes through targeted molecular approaches. Overall design: Median nerves of adult female Rattus norvegicus were cut to obtain a 8 mm gap and repaired with a 10 mm chitosan conduit.  Two experimental groups were created: immediate repair (animals repaired immediately after injury) and delayed repair (repair carried out 3 months after injury). The nerves regenerated within the conduits were collected 7, 14, 21 days after repair. RNA was extracted and sent to Novogene SRL for Illumina Next-Generation sequencing.