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Microglia as target for anti-inflammatory approaches to prevent secondary brain injury after subarachnoid hemorrhage
Rebecca Heinz1, Susan Brandenburg1, Melina Nieminen-Kelhä1
1Experimental Neurosurgery, Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany.
Background:
Microglia-driven cerebral spreading inflammation is a key contributor to secondary brain injury after SAH. Genetic depletion or deactivation of microglia has been shown to ameliorate neuronal cell death. Therefore, clinically feasible anti-inflammatory approaches counteracting microglia accumulation or activation are interesting targets for SAH treatment. Here, we tested two different methods of interference with microglia-driven cerebral inflammation in a murine SAH model: (i) inflammatory preconditioning and (ii) pharmacological deactivation.
Methods:
7T-MRI-controlled SAH was induced by endovascular perforation in four groups of C57Bl/6 mice: (i) Sham-operation, (ii) SAH naïve, (iii) SAH followed by inflammatory preconditioning (LPS intraperitoneally), and (iv) SAH followed by pharmacological microglia deactivation (colony-stimulating factor-1 receptor-antagonist PLX3397 intraperitoneally). Microglia accumulation and neuronal cell death (immuno-fluorescence), as well as activation status (RT-PCR for inflammation-associated molecules from isolated microglia) were recorded at day 4 and 14. Toll-like receptor4 (TLR4) status was analyzed using FACS.
Results:
Following SAH, significant cerebral spreading inflammation occurred. Microglia accumulation and pro-inflammatory gene expression were accompanied by neuronal cell death with a maximum on day 14 after SAH. Inflammatory preconditioning as well as PLX3397-treatment resulted in significantly reduced microglia accumulation and activation as well as neuronal cell death. TLR4 surface expression in preconditioned animals was diminished as a sign for receptor activation and internalization.
Conclusions:
Microglia-driven cerebral spreading inflammation following SAH contributes to secondary brain injury. Two microglia-focused treatment strategies, (i) inflammatory preconditioning with LPS and (ii) pharmacological deactivation with PLX3397, led to significant reduction of neuronal cell death. Increased internalization of inflammation-driving TLR4 after preconditioning leaves less receptor molecules on the cell surface, providing a probable explanation for significantly reduced microglia activation. Our findings support microglia-focused treatment strategies to overcome secondary brain injury after SAH. Delayed inflammation onset provides a valuable clinical window of opportunity.
Insights
Targeting microglia with inflammatory preconditioning or PLX3397 significantly reduced brain inflammation and neuronal death after subarachnoid hemorrhage (SAH). These findings highlight microglia-focused strategies for treating secondary brain injury following SAH.
Area of Science:
- Neuroscience
- Immunology
- Pharmacology
Background:
- Microglia-driven inflammation exacerbates secondary brain injury after subarachnoid hemorrhage (SAH).
- Targeting microglia activation or accumulation offers potential therapeutic avenues for SAH.
- This study investigates two novel anti-inflammatory approaches in a murine SAH model.
Purpose of the Study:
- To evaluate the efficacy of inflammatory preconditioning and pharmacological microglia deactivation in mitigating SAH-induced brain injury.
- To assess the impact of these interventions on microglia accumulation, activation, and neuronal cell death.
- To explore the underlying mechanisms, including Toll-like receptor 4 (TLR4) expression.
Main Methods:
- Subarachnoid hemorrhage (SAH) was induced in mice via endovascular perforation.
- Experimental groups included sham, SAH-naïve, SAH with LPS-induced inflammatory preconditioning, and SAH with PLX3397 (CSF-1R antagonist) treatment.
- Microglia status, neuronal death, and TLR4 expression were analyzed at days 4 and 14 post-SAH.
Main Results:
- SAH induced significant cerebral inflammation, microglia accumulation, and neuronal cell death.
- Both inflammatory preconditioning and PLX3397 treatment markedly reduced microglia activation and neuronal injury.
- Preconditioning led to diminished TLR4 surface expression, suggesting receptor internalization and reduced activation.
Conclusions:
- Microglia-driven inflammation is a critical factor in secondary brain injury post-SAH.
- Targeting microglia through preconditioning or PLX3397 effectively reduces neuronal cell death.
- These findings support microglia-centric therapies for SAH and suggest a therapeutic window for intervention.
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