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Summary: Objective: Microglial abnormalities have been reported in pathologic specimens from patients with tuberous sclerosis complex (TSC), a genetic disorder characterized by epilepsy, intellectual disability, and autism. However, the pathogenic role of microglia in epilepsy in TSC is poorly understood, particularly whether microglia defects may be a primary contributor to epileptogenesis or are secondary to seizures or simply epiphenomena. In this study, we tested the hypothesis that Tsc1 gene inactivation in microglia is sufficient to cause epilepsy in mouse models of TSC. Methods: Using a chemokine receptor, Cx3cr1, to target microglia, conventional Tsc1Cx3cr1‐CreCKO (conditional knockout) mice and postnatal‐inducible Tsc1Cx3cr1‐CreERCKO mice were generated and assessed for molecular and histopathologic evidence of microglial abnormalities, mechanistic target of rapamycin 1 (mTORC1) pathway activation, and epilepsy. Results: Tsc1Cx3cr1‐CreCKO mice exhibited a high efficiency of microglia Tsc1 inactivation, mTORC1 activation, increased microglial size and number, and robust epilepsy, which were rapamycin‐dependent. However, Cre reporter studies demonstrated that constitutive Cx3cr1 expression affected not only microglia, but also a large percentage of cortical neurons, confounding the role of microglia in epileptogenesis in Tsc1 Cx3cr1‐CreCKO mice. In contrast, postnatal inactivation of Tsc1 utilizing a tamoxifen‐inducible Cx3cr1‐CreER resulted in a more‐selective microglia Tsc1 inactivation with high efficiency, mTORC1 activation, and increased microglial size and number, but no documented epilepsy. Significance: Microglia abnormalities may contribute to epileptogenesis in the context of neuronal involvement in TSC mouse models, but selective Tsc1 gene inactivation in microglia alone may not be sufficient to cause epilepsy, suggesting that microglia have more supportive roles in the pathogenesis of seizures in TSC. [ABSTRACT FROM AUTHOR]

Objective Epilepsy is one of the most prominent symptoms of tuberous sclerosis complex ( TSC), a genetic disorder, and may be related to developmental defects resulting from impaired TSC1 or TSC2 gene function in astrocytes and neurons. Inactivation of the Tsc1 gene driven by a glial-fibrillary acidic protein ( GFAP) promoter during embryonic brain development leads to widespread pathologic effects on astrocytes and neurons, culminating in severe, progressive epilepsy in mice ( Tsc1 GFAP-Cre mice). However, the developmental timing and cellular specificity relevant to epileptogenesis in this model has not been well defined. The present study evaluates the effect of postnatal Tsc1 gene inactivation on pathologic features of astrocytes and neurons and development of epilepsy. Methods An inducible Tsc1 knock-out mouse was created utilizing a tamoxifen-driven GFAP-Cre ER line ( Tsc1 GFAP-Cre ER mice) with TSC1 reduction induced postnatally at 2 and 6 weeks of age, and compared to conventional Tsc1 GFAP-Cre mice with prenatal TSC1 reduction. Western blotting, immunohistochemistry, histology, and video-electroencephalography ( EEG) assessed mechanistic target of rapamycin (mTOR) pathway activation, astrogliosis, neuronal organization, and spontaneous seizures, respectively. Results Tsc1 gene inactivation at 2 weeks of age was sufficient to cause astrogliosis and mild epilepsy in Tsc1 GFAP-Cre ER mice, but the phenotype was much less severe than that observed with prenatal Tsc1 gene inactivation in Tsc1 GFAP-Cre mice. Both astrocytes and neurons were affected by prenatal and postnatal Tsc1 gene activation to a degree similar to the severity of epilepsy, suggesting that both cellular types may contribute to epileptogenesis. Significance These findings support a model in which the developmental timing of TSC1 loss dictates the severity of neuronal and glial abnormalities and resulting epilepsy. [ABSTRACT FROM AUTHOR]

Objective Tuberous sclerosis complex (TSC) is a genetic disorder, characterized by tumor formation in multiple organs and severe neurologic manifestations, including epilepsy, intellectual disability, and autism. Abnormalities of both neurons and astrocytes have been implicated in contributing to the neurologic phenotype of TSC, but the role of microglia in TSC has not been investigated. The objectives of this study were to characterize microglial activation in a mouse model of TSC, involving conditional inactivation of the Tsc1 gene predominantly in glial cells ( Tsc1GFAPCKO mice), and to test the hypothesis that microglial activation contributes to epileptogenesis in this mouse model. Methods Microglial and astrocyte activation was examined in Tsc1GFAPCKO mice by ionized calcium binding adaptor molecule 1 and glial fibrillary acidic protein immunohistochemistry. Cytokine and chemokine expression was evaluated with quantitative polymerase chain reaction. Seizures were monitored by video-electroencephalography (EEG). The effect of minocycline in inhibiting microglial and astrocyte activation, cytokine expression, and seizures was tested. Results Microglial cell number and size were increased in cortex and hippocampus of 3- to 4-week-old Tsc1GFAPCKO mice, which correlated with the onset of seizures. Minocycline treatment prevented the increase in number and cell size of microglia in 4-week-old Tsc1GFAPCKO mice. However, minocycline treatment had no effect on astrocyte proliferation and cytokine/chemokine expression and the progression of seizures in Tsc1GFAPCKO mice. Significance Microglia cell number and size are abnormal in Tsc1GFAPCKO mice, and minocycline treatment inhibits this microglia activation, but does not suppress seizures. Microglia may play a role in the neurologic manifestations of TSC, but additional studies are needed in other models and human studies to determine whether microglia are critical for epileptogenesis in TSC. [ABSTRACT FROM AUTHOR]