Novel Thermosensitive Hydrogel Promotes Spinal Cord Repair by Regulating Mitochondrial Function

The repair of spinal cord injury (SCI) is still a tough clinical challenge and needs innovative therapies. Mitochondrial function is significantly compromised after SCI and has emerged as an important factor causing neuronal apoptosis and hindering functional recovery. In this study, umbilical cord mesenchymal stem cells (UCMSC), which are promising seed cells for nerve regeneration, and basic fibroblast growth factor (bFGF) that have been demonstrated to have a variety of effects on neural regeneration were jointly immobilized in extracellular matrix (ECM) and heparin-poloxamer (HP) to create a polymer bioactive system that brings more hope and possibility for the treatment of SCI. Our results in vitro and in vivo showed that the UCMSCbFGF-ECM-HP thermosensitive hydrogel has good therapeutic effects, mainly in reducing apoptosis and improving the mitochondrial function. It showed promising utility for the functional recovery of impaired mitochondrial function by promoting mitochondrial fusion, reducing pathological mitochondrial fragmentation, increasing mitochondrial energy supply, and improving the metabolism of MDA, LDH, and ROS. In addition, we uncovered a distinct molecular mechanism underlying the protective effects associated with activating p21-activated kinase 1 (PAK1) and mitochondrial sirtuin 4 (SIRT4) by the UCMSC-bFGF-ECM-HP hydrogel. The expansion of new insights into the molecular relationships between PAK1 and SIRT4, which links the mitochondrial function in SCI, can lay the foundation for future applications and help to provide promising interventions of stem-cell-based biological scaffold therapies and potential therapeutic targets for the clinical formulation of SCI treatment strategies.