Abstracts

Rationale: Focal Cortical Dysplasias (FCDs) are classified histopathologically as either type I, characterized by subtle laminar disorganization and cytomegalic neurons (CNs), or type II, characterized by loss of cortical lamination and the presence of dysmorphic neurons (DNs) and balloon cells (BCs) (1). In previous studies, cells in FCD type II have been shown to co-express neuronal and glial markers, suggesting abnormalities in differentiation (2). We hypothesized that the morphological disparities of cells in FCD type I and type II reflect their differential developmental phenotypes and that stem cell marker proteins Foxg1, Nanog, Oct-4, SOX2, SOX3, and ZNF206 would be expressed in type II but not type I FCD. Furthermore, we hypothesized that stem cell protein expression in FCD type II is linked to activation of the mammalian target of rapamycin complex 1 (mTORC1) cascade. Methods: First, dissociated cell cultures were generated in vitro from a single FCD type IIB specimen resected during epilepsy surgery. Cells cultured from the resected FCD type IIB tissue were probed with antibodies recognizing stem cell marker proteins and phosphorylated isoform of S6 (phospho-S6), a marker of mTORC1 activation. Next, in order to examine the protein expression profile across different subtypes of FCD types I and II, sporadic type I and type II FCDs, tubers from tuberous sclerosis complex (TSC), two syndromic FCD subtypes, cortical dysplasia focal epilepsy syndrome (CDFE) and Pretzel syndrome (PS) specimens, and tissue resected from a FCD type IIB case were probed with antibodies recognizing stem cell proteins and phospho-S6. Results: Cells cultured from resected FCD type IIB tissue were found to co-express phospho-S6, SOX2, Oct-4, and Nestin. Furthermore, Foxg1, Nanog, Oct-4, SOX2, SOX3, and ZNF206 were expressed in sporadic FCD type II, tubers, PS, but not in any type I FCDs. Aberrant phospho-S6 immunoreactivity was detected in FCD type II but not in FCD type I, control cortex, or cortex adjacent to tubers. Activated c-myc and STAT3 (phospho-STAT3), which regulate SOX2 and Oct-4 expression via mTORC1, were detected in type II but not type I FCDs. Conclusions: The results of this study suggest that FCD type II but not type I express stem cell marker proteins and exhibit aberrant activation of the mTORC1 cascade. Furthermore, the results distinguish type II from type I dysplasias and may signify a disparate pathophysiology of the two types of FCDs. We demonstrate for the first time that cells from FCD can be cultured in vitro. The results of this study suggest that cells in type II dysplasias may retain the capacity for cell division and thus type II FCDs may represent a dynamic cortical lesion. References: 1. Palmini A, Najm I, Avanzini G, Babb T, et al. Terminology and classification of the cortical dysplasias. Neurology. 2004;62:S2-8 2. Englund C, Folkerth RD, Born D, Lacy JM, Hevner RF. Aberrant neuronal-glial differentiation in Taylor-type focal cortical dysplasia (type IIA/B). Acta Neuropathol. 2005;109:519-533. Funding: R01NS045877