M1 microglia-derived exosomes promote A1 astrocyte activation and aggravate ischemic injury via miR-331-5p/MAVS/NF-kB pathway

Ischemic stroke (IS) is one of the most serious neurological diseases, characterized by high mortality and disability rates. Glia cells, particularly microglia and astrocytes, occupy a pivotal position in the progression of IS. In response to stroke, microglia undergo polarization, transforming into either pro-inflammatory M1 phenotype or anti-inflammatory M2 phenotype. Analogously, astrocytes would polarize to pro-inflammatory A1 phenotype or anti-inflammatory A2 phenotype. It has been documented that A1 astrocytes can be activated by M1 microglia, although precise underlying mechanism remains elusive. In our study, we emulated ischemic injury using a middle cerebral artery occlusion/reperfusion (MCAO/R) model in mice and an oxygen-glucose deprivation/reoxygenation (OGD/R) model in primary astrocytes. Our findings revealed that M1 microglia could activate A1 astrocytes by secreting exosomes. According to RNA sequencing, circSTRN3 was enriched in M1 microglia-derived exosomes. Based on the review of literature and bioinformatics analysis, it was suggested that circSTRN3 could sponge miR-331-5p, while miR-331-5p could bind to MAVS and participate in the activation of NF-kB pathway and A1 astrocytes. Western blotting and qRT-PCR experiments verified this process. Furtherly, overexpression of circSTRN3 could aggravate neurological deficits, increase infarct volume, and promote cell death in MCAO/R model, whereas miR-331-5p inhibited this process. Furthermore, we conducted tests on circSTRN3 and miR-331-5p in exosomes isolated from the peripheral blood of IS patients, thereby confirming the correlation among circSTRN3, miR-331-5p, and the stroke severity score. Taken together, our study indicated that M1 microglia-derived exosomes could promote A1 astrocyte activation and exacerbate ischemic brain injury through the circSTRN3-miR331-5P/MAVS/NF-KB pathway. Overall design: circRNA profiles of exosomes from microglia after previous normoxia condition(M0) or OGD/R model(M1)