Abstracts

Rationale: Cortical dysplasia (CD) is a disorder characterized by malformation of the cortex and is commonly associated with aberrant activation of the mTOR pathway and epilepsy. In addition, recent studies have revealed the induction of inflammatory responses such as increased proliferation and activation of microglia and astrocytes (micro- and astrogliosis) and elevated levels of proinflammatory cytokines in dysplastic tissue resected from CD patients, suggesting a role for neuroinflammation in the pathophysiology of epilepsy. The mTOR pathway is known to regulate a variety of immune processes; however, the link between mTOR dysregulation, neuroinflammation, and epilepsy remains unclear. In the current study, we investigated whether markers of inflammation were abnormal in the previously described neuronal subset-specific PTEN knockout (NS-PTEN KO) mouse model of CD with hyperactive mTOR signaling and epilepsy.Methods: Immunohistochemistry was performed in coronal brain sections obtained from 7-9 week-old NS-PTEN KO and WT mice. We used antibodies against IBA1 and CD11b (microglial markers), GFAP (astrocytic marker), NeuN (neuronal marker), and p-S6 (phosphorylated ribosomal S6 protein, a marker for mTOR pathway activation), and evaluated immunostaining of these markers in the hippocampal formation. Results: Staining for IBA1 and CD11b was markedly stronger in the hippocampi of NS-PTEN KO compared WT mice. Many of the IBA1- and CD11b-stained microglia in the KO group were hypertrophied compared to those in the WT group. Staining for p-S6 was notably more intense in the KO group compared to the WT group. This was evident in the granule cell layer dentate gyrus where the majority of cells lacking PTEN reside although scattered p-S6 staining was also observed in CA1 and CA3 regions. p-S6 staining co-localized with NeuN in both the KO and WT groups, and also with CD11b in the KO group. In addition, more intense staining for GFAP was also observed in the hippocampi of KO compared to WT mice.Conclusions: Our findings reveal evidence of micro- and astroglial activation in the hippocampus of NS-PTEN KO mice. Furthermore, p-S6 staining co-localizes with activated microglia in the NS-PTEN KO mice, suggesting a role for mTOR hyperactivity in this inflammatory process. Future studies will evaluate the effects of rapamycin, an mTOR inhibitor and immunosuppressant with seizure-attenuating effects, on these findings.