Succinic acid modified chitosan hydrogel mediates in-situ bioenergetic remodeling of neural cells for neuronal differentiation and spinal cord injury repair

Abstract

A primary challenge in spinal cord injury repair is the presence of an energy deficit, exacerbated by the injury itself, thereby intensifying the dilemma of insufficient energy. Hence, we posit a hypothesis suggesting that the adoption of a direct energy-supply material strategy has the potential to enhance in situ cellular energy levels, facilitating the acceleration of neuronal differentiation and axonal elongation. We successfully designed a degradable bioenergetic hydrogel by introducing succinic acid (SA), a key intermediate in tricarboxylic acid (TCA) cycle, into chitosan (CS) as an energy-active unit, which was released in a sustained degradation-mediated fashion once implanted. The degraded energy-active units, after being internalized, increased bioenergetic levels via oxidative phosphorylation (OXPHOS) by facilitating TCA flux, thereby contributing to a at least 1.5-fold increase in the expression levels of neuronal differentiation-related markers in vitro, as well as the enhanced spinal cord injury repair and functional recovery in vivo. Further mechanism analysis demonstrated that the upregulation of the bioenergetic basis had the potential to induce neuronal differentiation through the AMP-activated protein kinase-mammalian target of rapamycin (AMPK-mTOR) axis. Additionally, the adenosine triphosphate (ATP) itself acted as a signaling molecule via the P2X7 receptor, leading to the upregulation of intracellular calcium ion-MAPK signal cascades, ultimately promoting neuronal differentiation. Overall, these findings have the potential to significantly alter our understanding of cell metabolism and energy homeostasis, transforming them from passive observers to critical factors in guiding nerve regeneration, and may have implications for future design of bioenergetic-active materials.