Filamin A in TSC and FCDII

Yale University, New Haven CT

Investigators

Abstract

ABSTRACT Tuberous sclerosis complex (TSC) and focal cortical dysplasia type II (FCDII) are devastating neurological disorders caused by somatic mutations in mTOR pathway genes leading to mTOR complex 1 (mTORC1) hyperactivity and focal malformations of cortical development. In ~90% of patients, these abnormalities cause epileptic seizures that respond poorly to medications, including the mTORC1 inhibitor, and so often require invasive surgical procedures that suffer from limited efficacy and adverse complications. There is thus a critical need to identify new therapeutic targets in these disorders. Recent data from our lab established the importance of the actin-crosslinking and scaffolding molecule, filamin A (FLNA), in disease pathogenesis and we found that normalizing FLNA function led to strong seizure reduction in an FCDII mouse model. Notably, the mTORC1-independence of FLNA dysregulation underscores the need to understand the molecular alterations that underlie disease pathogenesis and suggests that therapeutic targeting of FLNA, or its interaction partners, may provide novel avenues for treating seizures in TSC/FCDII. We first identified increased FLNA expression in TSC transgenic mice that was further validated in human TSC and FCDII cortical tissue. Importantly, normalizing FLNA expression using shRNA reduced neuronal dysmorphogenesis and seizure activity in our mouse model. We also found that neuronal overexpression of FLNA triggered dendritic abnormalities and preliminary data show that this is independent of FLNA actin binding, suggesting these effects are generated via one or more of FLNA binding partners. Therapeutic targeting of large scaffolding proteins capable of many protein-protein interactions is challenging, however, the small molecule PTI-125 has been reported to modulate FLNA. While the mechanism of action of PTI-125 is controversial, PTI-125 alleviated seizures in our mouse model of TCS/FCDII without reducing FLNA levels. We hypothesize that this may be due to modulation of FLNA function, either via changes in FLNA conformation that alter its interactome or through changes in the expression of individual binding partners or their signaling activities. Here we propose to test the hypothesis that the role of FLNA in TSC/FCDII stems from functional alterations in the FLNA-interactome. This exploratory proposal aims to identify FLNA- interacting proteins (Aim 1) that contribute to neuronal defects and seizures in TSC/FCDII (Aim 2), providing insights into disease mechanisms and possibly revealing new therapeutic targets. It may also reveal mechanisms of action for PTI-125, which we find inhibits seizures in mouse TSC models and others propose for Alzheimer’s disease therapy.