Grafted human ESC-derived astroglia repair spinal cord injury via activation of host anti-inflammatory microglia in the lesion area

Grafted astroglia/astrocytes exhibit neuroprotective effects and improve functional recovery after injury to the central nervous system. This study sought to elucidate their ability to repair spinal cord lesions and the underlying mechanisms. Methods: Complete spinal transection, transplantation of astroglia generated from human ESC-derived neural progenitor cells (NPC-Astros) or Olig2-GFP knock-in progenitors (Olig2PC-Astros), and immunostaining were used to determine the survival of astroglia. CUBIC tissue-clearing, immunostaining, electromyography, and functional tests such as the Basso Mouse Scale score and gait analysis were applied to analyze the recovery of the lesion area, axon regeneration, synapse formation, and motor function. Sholl analysis, immunostaining, depletion of anti-inflammatory microglia, and western blotting were employed to explore the cellular and molecular mechanisms underlying spinal cord repair. Results: Grafted NPC- or Olig2PC-Astros survived in the lesion area and assisted wound healing by reducing scar formation and promoting regrowth of descending serotonergic axons and synapse reformation beyond the lesion area. These positive effects resulted in increased Basso Mouse Scale scores and improved hindlimb function as determined by electromyography and gait analysis. Activated microglia in the lesion area were shifted towards an anti-inflammatory phenotype after transplantation of NPC- or Olig2PC-Astros, and depletion of anti-inflammatory microglia reversed the observed improvements in the lesion area and axon regeneration. Transplantation of NPC- or Olig2PC-Astros elevated the expression of interleukin-4 and promoted the phenotypic shift of microglial via interleukin-4 downstream signaling. Conclusion: Our findings indicate that grafted human ESC-derived NPC- or Olig2PC-Astros promote recovery of the injured spinal cord by shifting microglia towards an anti-inflammatory state in the lesion area and activating interleukin-4 signaling.