Authors :
Presenting Author: Aastha Dheer, Ph.D – Mayo foundation for medical education & research
Long-Jun Wu, Professor – Mayo foundation for medical education & research
Rationale:
Microglia are key players in maintaining brain homeostasis and exhibit phenotypic alterations in response to epileptic stimuli. However, it is still relatively unknown if these alterations are pro- or anti-epileptic. To unravel this dilemma, we employed chemogenetic manipulation of microglia via of the artificial Gi-Dreadd receptor within a kainic acid (KA) induced murine seizure model. Methods:
We used adult (~8 weeks old), male, Cx3cr1CreER/WT: R26LSL-hM4Di/WT mice (Gi-Dreadd) which specifically express Gi-Dreadd in microglia under the inducible CX3CR1 promoter. Age matched, Cx3cr1CreER/WT mice without Gi-Dreadd expression were used as Controls. Intracerebroventricular (i.c.v.) injection of kainic acid (0.15 μg in 5 μL sterile PBS) was administered to induce seizures which were recorded as per the modified Racine scale. Following seizure onset, Clozapine-N-Oxide (5 mg/kg body weight, i.p.) was administered 20 minutes after KA injection to activate Gi-Dreadd. Fluorescent immunostaining was performed on post-fixed tissues to study expression and morphological alterations between groups. Transciptomic profiling was carried out by bulk RNA sequencing of microglia. Results:
Our results indicate that Gi-Dreadd activation can reduce seizure severity. Additionally, we observed increased interaction between microglia and neuronal soma, which correlated with reduced neuronal hyperactivity. Interestingly, prolonged activation of microglial Gi-Dreadds by repeated doses over three days, arrested microglia in a less active, homeostatic-like state, which associated with increased neuronal loss after KA induced seizures. RNAseq analysis revealed that prolonged activation of Gi-Dreadd interferes with interferon β signaling and microglia proliferation.
Conclusions: Our findings highlight the importance of microglial activation not only during
status epilepticus (SE) but also within later seizure induced pathology.
Funding:
This work was supported by the following grants from the National Institutes of Health: R01NS088627 (L.-J.W.) and R01NS112144 (L.-J.W.).