Temporal dynamics of microglia-astrocyte interaction in neuroprotective glial scar formation after intracerebral hemorrhage

The role of glial scar after intracerebral hemorrhage(ICH)remains unclear.This study aimed to investigate whether microglia-astrocyte interaction affects glial scar formation and explore the specific function of glial scar.We used a pharmacologic approach to induce microglial depletion during different ICH stages and examine how ablating microglia affects astrocytic scar formation.Spatial transcriptomics(ST)analysis was performed to explore the potential ligand-receptor pair in the modulation of microglia-astrocyte interaction and to verify the functional changes of astrocytic scars at different periods.During the early stage,sustained microglial depletion induced disorganized astrocytic scar,enhanced neutrophil infiltration,and impaired tissue repair.ST analysis indicated that microglia-derived insulin like growth factor 1(IGF1)modulated astrocytic scar formation via mechanistic target of rapamycin(mTOR)signaling activation.Moreover,repopulating microglia(RM)more strongly activated mTOR signaling,facilitating a more protective scar formation.The combination of IGF1 and osteopontin(OPN)was necessary and sufficient for RM function,rather than IGF1 or OPN alone.At the chronic stage of ICH,the overall net effect of astrocytic scar changed from protective to destructive and delayed microglial depletion could partly reverse this.The vital insight gleaned from our data is that sustained microglial depletion may not be a reasonable treatment strategy for early-stage ICH.Inversely,early-stage IGF1/OPN treatment combined with late-stage PLX3397 treatment is a promising therapeutic strategy.This prompts us to consider the complex temporal dynamics and overall net effect of microglia and astrocytes,and develop elaborate treatment strategies at precise time points after ICH.

CCL17 exerts neuroprotection through activation of CCR4/mTORC2 axis in microglia after subarachnoid haemorrhage in rats

Background and purpose C-C motif chemokine ligand 17(CCL17)presents an important role in immune regulation,which is critical in the pathophysiology of brain injury after subarachnoid haemorrhage(SAH).There is rare evidence to illustrate the function of CCL17 towards SAH.In this study,we try to reveal the therapeutic effects of CCL17 and its underlying mechanism in rat SAH model.Methods SAH rat models were assigned to receive recombinant CCL17(rCCL17)or phosphate buffer saline(PBS).AZD2098 and JR-AB2-011 were applied to investigate the C-C motif chemokine receptor 4(CCR4)/mammalian target of rapamycin complex 2(mTORC2)axis in CCL17-mediated neuroprotection.To elucidate the underlying mechanism,the in vitro kinase assay was performed in primary microglia.Microglial-specific Rictor knockdown was administered via intracerebroventricular injection of adenovirus-associated virus.Brain water content,short-term neurobehavioural evaluation,western blot analysis,quantitative RT-PCR and histological staining were performed.Results The expression of CCL17 was increased and secreted from neurons after oxyhaemoglobin stimulation.Exogenous rCCL17 significantly alleviated neuronal apoptosis,and alleviated short-term neurofunction after SAH in rats.In addition,rCCL17 increased M2-like polarisation of microglia in rats post-SAH and in primary microglia culture.The neuroprotection of rCCL17 was abolished via inhibition of either CCR4 or mTORC2.Conclusion CCL17 activated the CCR4/mTORC2 axis in microglia,which can alleviate SAH-induced neurological deficits by promoting M2-like polarisation of microglia.