This proposal will test the hypothesis that decreasing Filamin A (FLNA) levels or function in tuberous sclerosis complex (TSC) prevents cortical malformations and associated seizure activity. TSC is caused by mutations in TSC1 or TSC2 leading to mTOR complex 1 (mTORC1) hyperactivity and cortical malformations associated with seizures and worsening of cognitive and psychiatric deficits. The mTORC1 inhibitor rapamycin is the only therapeutic option, does not rescue all defects, and has mild to life-threatening complications emphasizing the need to find novel drug targets. We recently reported that the level of the actin cross-linking molecule FLNA is increased in Tsc1null neurons and that this increase is responsible for dendrite abnormalities. In addition, FLNA regulates the migration of cortical neurons during development. These findings are attractive with respect to TSC for the following reasons: (1) Neuronal dysmorphogenesis (including dendritic abnormality) and stalled migration are hallmarks of TSC-related cortical malformations. (2) FLNA increase in Tsc1null neurons as well as in cells expressing a constitutively active Rheb (the mTORC1 canonical activator) was not mTORC1-dependent but rather ERK1/2-dependent, opening a novel pharmacological option for a possible combination therapy, and (3) Our preliminary data show that normalizing FLNA levels using shRNA or administrating the new FLNA modulator, PTI-125, during development prevents neuronal misplacement and dysmorphogenesis in our new model of TSC-related cortical malformations. To address our hypothesis we have the following three aims.
In Aim 1, we will determine whether FLNA controls development of cortical pyramidal neurons in vivo and whether decreasing FLNA levels during development prevents cortical malformations.
In Aim 2, we will examine whether there is a time-window in neonates for treatments aimed at preventing cortical malformations and reducing or eliminating associated seizure activity. Our new murine model of focal cortical malformations is associated with a high rate of daily convulsive seizures. Finally in Aim 3, we will investigate how increased FLNA levels leads to dysmorphogenesis and stalled migration, which may identify novel FLNA binding partners involved in cortical defects in TSC. Most experiments will use in utero electroporation to selectively manipulate the development of layer 2/3 cortical pyramidal neurons. This is a 2 PIs grant. The Bordey lab will be in charge of Aim 1 and 2, and the Calderwood lab will be in charge of Aim 3. Both labs will heavily interact on a weekly basis due to the need for tool (plasmid) development and the need for cell biology and in vivo experiments in Aim 2 and 3, respectively. Dr. Bordey is an expert on neuronal development and TSC, and Dr. Calderwood is a cell biologist with extensive expertise on FLNA.

Public Health Relevance

This proposal aims at preventing and/or rescuing brain malformations and associated seizure activity in disorders involving the PI3K-AKT pathway such as in tuberous sclerosis complex (TSC). TSC is a monogenic disorder leading to hyperactive mTOR complex 1 (mTORC1) and developmental malformations associated with seizures that are often refractory to treatments and worsen cognitive and psychiatric deficits. We identified that increased levels of an actin binding molecule Filamin A (FLNA) is responsible for some of the brain defects leading us to identify novel pathogenic FLNA binding partners and examine whether normalizing FLNA levels or decreasing its activity using a newly developed modulator rescue brain malformations and prevent seizures.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
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Clinical Neuroplasticity and Neurotransmitters Study Section (CNNT)
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Mamounas, Laura
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Yale University
Schools of Medicine
New Haven
United States
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Huang, Tianxiang; Nguyen, Lena H; Lin, Tiffany V et al. (2018) In utero electroporation-based translating ribosome affinity purification identifies age-dependent mRNA expression in cortical pyramidal neurons. Neurosci Res :
Iwamoto, Daniel V; Huehn, Andrew; Simon, Bertrand et al. (2018) Structural basis of the filamin A actin-binding domain interaction with F-actin. Nat Struct Mol Biol 25:918-927
Hsieh, Lawrence S; Wen, John H; Miyares, Laura et al. (2017) Outbred CD1 mice are as suitable as inbred C57BL/6J mice in performing social tasks. Neurosci Lett 637:142-147
Zhang, Longbo; Huang, Tianxiang; Bordey, Angélique (2016) Tsc1 haploinsufficiency is sufficient to increase dendritic patterning and Filamin A levels. Neurosci Lett 629:15-18