Small extracellular vesicles from spared nerve injury model and sham control mice differentially regulate gene expression in primary microglia
Nerve injury outcomes might be predicted by examining small extracellular vesicles  (sEVs) in circulation, as their biomolecular cargo facilitates cellular communication and  can alter transcriptional state and behavior of recipient cells. We found that sEVs from  the serum of spared nerve injury (SNI) model male mice had seven differentially  expressed miRNAs compared to sEVs from sham-operated control mice four weeks  post-surgery. We investigated how these sEVs alter transcription in primary cortical  microglia, a crucial mediator of neuropathic pain, using RNA sequencing. While the  uptake of sEVs from both SNI model and sham groups changed gene expression in  microglia compared to PBS treatment, sEVs from the sham group induced a more  drastic change, particularly in genes involved in immune response. This was  recapitulated by increased levels of pro-inflammatory cytokines and chemokines in  microglia incubated with sEVs from sham control compared to sEVs from SNI model,  naïve mice, or PBS. However, treating microglia with sEVs from female mice showed  that serum sEVs derived from female SNI mice but not from female sham mice induced  a more pronounced microglial secretion of pro-inflammatory mediators. Our data  demonstrate that the molecular changes induced by sham surgery injuring skin and  muscles are reflected in circulating sEVs in male mice four weeks later. Thus, when  using sEVs from sham mice as control in comparative mechanistic studies after nerve  injury, sex of mice should be taken into consideration. Overall design: Comparative expression profiling using RNA-seq in primary cortical microglia treated with serum-derived small extracellular vesicles (sEVs) from spared nerve injury model and sham control mice.