Myeloid C3 causes neuronal injury prior to synapse loss [scRNA-seq]

Complement component C3 mediates pathology in several CNS neurodegenerative diseases, but the cellular and molecular mechanisms leading to neuronal injury remain unclear. Herein, we examined how C3 deletion affects glial profiles and anterior visual pathway pathology in an animal model of neuroinflammation. scRNA-seq from mouse brain and optic nerve revealed that C3 expression defined disease-associated glial subtypes which were characterized by increased mTOR activation, cell metabolism, and translation. Deletion of C3 restored these glia towards homeostatic profiles. Myeloid-derived C3 mediated injury in optic nerve axons and retinal ganglion cells (RGCs) at the peak of EAE. To elucidate the timing of pathology we examined retinas prior to symptom onset and found reductions in Brn3a, an RGC transcription factor involved in dendritic arborization and protection from apoptosis. Our study supports a direct role for C3 in activating the mTOR-ribosomal biogenesis axis in glia which subsequently mediate early neuro-axonal stress and later synapse loss. Overall design: Brains from 4 C3-tdTomato reporter mice were collected 16 days post-immunization and were dissociated, pooled, then sorted into two populations - Myeloid C3+ cells and Myeloid C3- cells. Single cell RNA-sequencing was performed using 10X Genomics 3' chemistry