Osteopontin modulates microglial activation states and attenuates inflammatory responses after subarachnoid hemorrhage in rats

Aims: Osteopontin (OPN) has demonstrated neuroprotective effects in various stroke models. Its role in neuroinflammation after brain injury remains to be elucidated. This study aims to clarify the effect of OPN on neuroinflammation, particularly on the functional states of microglia after subarachnoid hemorrhage (SAH). Methods: 77 rats were randomly divided into the following groups: Sham, SAH 24 h, SAH + rOPN, SAH + Vehicle (PBS), SAH + OPN siRNA, and SAH + Scr siRNA, SAH + rOPN+Fib-14 and SAH + rOPN+DMSO. Modified Garcia and beam balance tests were used to evaluate neurobehavioral outcomes. Semi-quantitative immunofluorescence staining was performed to measure expression of myeloperoxidase (MPO) and microglia activation state markers CD16, CD206 after SAH and recombinant OPN treatment. The quantification of microglia activation and functional markers CD16, CD206, TNF-alpha and IL-10 were further evaluated using Western-blotting. Results: Nasal administration of rOPN improved neurological dysfunction, attenuated neutrophil infiltration, and decreased expression of phenotypic and functional markers of pro-inflammatory microglia CD16 and TNF-alpha. It also promoted an anti-inflammatory microglial state, as evidenced by increased expression of CD206 and IL-10. Furthermore, after blocking the phosphorylation of FAK signaling, the effects of rOPN on microglial activation states were partially reversed. The downstream pathways of STAT3 and NF-kappa B also exhibited consistent changes, suggesting the involvement of the STAT3 and NF-kappa B pathways in OPN's modulation of microglial activation via integrin-FAK signaling. Conclusion: OPN attenuates inflammatory responses after SAH by promoting an anti-inflammatory microglial state, potentially mediated through the integrin-FAK-STAT3 and NF-kappa B signaling pathways.

Automated summary

This study found that Osteopontin (OPN) can attenuate inflammatory responses after subarachnoid hemorrhage (SAH) by promoting an anti-inflammatory microglial state. This effect may be mediated through the integrin-FAK-STAT3 and NF-kappa B signaling pathways.