The Key to Spinal Cord Recovery: Harnessing p21 Inhibition to Boost Neural Stem/Progenitor Cell Proliferation

Spinal cord injury (SCI) is a devastating traumatic condition of the central nervous system (CNS), usually resulting in irreversible motor and sensory deficits that severely compromise patients' quality of life. Harnessing the untapped potential of endogenous neural stem/progenitor cells (NSPCs) may yield revolutionary therapeutic techniques for overcoming the limited NSPC proliferative capacity following SCI in adults. Single-cell sequencing results demonstrated that the limited proliferative capacity of NSPCs after SCI is associated with the upregulation of the p21. Herein, we developed a cationic liposome-based delivery system encapsulating p21 small interfering RNA (^P21siRNA@LP) to enhance NSPC proliferation following SCI. ^P21siRNA@LP significantly increased the primary NSPC proliferation rate (145.4% on day 1 and 144.7% on day 3, respectively) while maintaining differentiation capacity in vitro. Transcriptomic and functional characterization showed that ^P21siRNA@LP modulated the expression of cyclin-dependent kinases in NSPCs, enhancing cell cycle pathways (enrichment score: 0.6691) and proliferation, with extracellular matrix reorganization (col1a1, col5a1) and gliogenesis (olig1/2) identified as key regulation pathways. Gelatin hydrogels incorporating ^P21siRNA@LP promoted dense tissue cable formation in T9 SCI rats, facilitating NSPC migration and proliferation at lesion sites, which accelerated locomotor function recovery. These findings emphasize cell cycle manipulation as a promising method to spinal cord regeneration, providing a basis for future therapeutic advances in CNS disorders.