Filamin A in TSC and FCDII

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.

Grant Number: 1R21NS142517-01
NIH Institute/Center: NIH
Principal Investigator: Angelique Bordey