Neuronal HDAC3 knockdown promotes propriospinal detour pathway formation and locomotor recovery in a mouse model of spinal cord injury

Propriospinal detour pathways facilitate motor recovery after spinal cord injury (SCI). Here, through a screen of epigenetic modulators, we demonstrated that small interfering RNA (siRNA)-mediated knockdown of histone deacetylase 3, delivered by extracellular vesicles (EVsiHDAC3), promoted neurite outgrowth in murine spinal neurons and human induced pluripotent stem cell-derived sensory and motor neurons. To enhance in vivo efficacy, we developed a neurotrophic nanoparticle platform using gelatin methacryloyl microspheres conjugated with an optimized rabies glycoprotein-derived peptide. Spinal delivery of the EVsiHDAC3-loaded platform (oGHDAC3) or adeno-associated virus-mediated neuronal HDAC3 deletion facilitated propriospino-lumbar detour circuit formation and improved locomotion after staggered double hemisection SCI in mice. Chemogenetic silencing of propriospinal relay neurons compromised recovered stepping upon oGHDAC3 treatment. We observed no therapeutic effects of oGHDAC3 after full spinal transection in mice, further suggesting that spared intraspinal circuits serve as the neural substrates for locomotion recovery. Mechanistically, Stat3 deletion in interlesional neurons, combined with mTOR inactivation, abolished the beneficial effects of oGHDAC3. Finally, combining oGHDAC3 with CLP290, a KCC2 agonist, further improved detour circuit functionality, resulting in consistent weight-supported stepping. Our findings suggest that integrating siRNA-mediated HDAC3 inhibition with a neurotropic bionanomaterial platform could be a translatable approach for restoring motor function after incomplete SCI.