Network modulation to improve gene therapy in CLN3 disease

PROJECT SUMMARY
Two-thirds of lysosomal storage disorders (LSD) affect the brain, yet most LSD treatments do not improve
central nervous system (CNS) symptoms. Several trials of brain-directed gene therapy have failed to show
clinical benefit despite restoring protein expression in the CNS. Outcomes are especially poor in subjects who
have developed neurologic deficits, suggesting rescue of expression alone may be insufficient to correct
function once diseased neuronal circuits are established.
In CLN3 Disease, a representative LSD and the most common cause of pediatric dementia, patients develop
blindness, seizures, and dementia. Several CLN3 disease mouse models have been developed. While all
recapitulate the storage accumulation seen in patients, behavioral phenotypes are subtle and variable. To
overcome this limitation, we identified robust, reproducible phenotypes on network-level electrophysiology
studies in two CLN3 models, a knockout and a human mutation model. Unlike histopathology, physiologic
measures directly reflect function and, therefore, may be a better readout for therapy development.
Our work suggests CLN3 disease, traditionally considered a degenerative disorder, disrupts early
neurodevelopment, especially in the hippocampus, a vulnerable region in CLN3 disease. On in vitro voltage
sensitive dye imaging (VSDI) and in vivo electroencephalogram (EEG) recordings, Cln3-/- mice have decreased
excitability of the hippocampal dentate gyrus (DG), faster EEG background activity, and loss of hippocampal
sharp wave ripples, oscillations that encode new memories. Also, DG neurogenesis is upregulated, perhaps as
a compensatory mechanism, early (2mo) but not later (6mo) in disease. Similar network changes arise in other
models of neurodegeneration including Alzheimer’s disease (AD). Deep brain stimulation of the entorhinal
cortex has been shown to improve outcomes in mouse models of AD.
Previously, we found that very early Cln3 gene replacement at p0 corrects network dynamics in a Cln3
knockout mouse. Our central hypothesis is that abnormal neuronal circuit development will limit the
window of time, i.e. ‘therapeutic window’, when gene replacement will improve network physiology in
CLN3 disease. Furthermore, we predict that altering activity in a key circuit could modify the therapeutic
window and efficacy of gene therapy. Our Specific Aims are to: 1) define abnormal dentate gyrus development
in CLN3 disease mice, 2) determine the therapeutic window for correction of hippocampal circuit dynamics by
gene replacement, and 3) test if modifying entorhinal cortex activity alters circuit defects and response to gene
therapy. In this way we will use CLN3 Disease as a representative LSD, to explore the relationship between
network activity and response to gene therapy. Our long-term goal is to develop network-directed therapies
that, when combined with gene replacement, improve outcomes in LSDs.

Grant Number: 5R01NS126279-03
NIH Institute/Center: NIH
Principal Investigator: Rebecca Ahrens-Nicklas