CLN3, or Juvenile Batten Disease, is a lysosomal storage disease characterized by the absence of functional CLN3 protein. The CLN3 gene encodes for a transmembrane protein of unknown function, but we know it is important for endocytosis, intracellular trafficking, and autophagy. The absence of functional CLN3 protein leads to an accumulation of auto-fluorescent lipofuscin in lysosomes. Clinically, CLN3 disease is the most common form of childhood dementia and is characterized by early-onset rapid blindness and a neurodegenerative course including anxiety, dementia, seizures, movement disorders, cardiac arrhythmias, and death by 3rd decade of life. In early development, CLN3 is expressed in the whole brain, but postnatally, expression shifts towards the dentate gyrus, a hippocampus region critical in encoding short-term memory and learning.

Previously, the lab discovered that the dentate gyrus is hypoexcitable, has faster EEG background activity, and a loss of hippocampal sharp wave ripple before lysosomal storage accumulation, indicating abnormal hippocampal development. The overall goal is to develop network-directed therapies along with gene replacement using adeno-associated virus or AAV to improve the outcome of lysosomal storage disorders. We aim to determine whether there is a time point in hippocampal development beyond which gene therapy cannot improve network physiology. We hypothesize that gene therapy will not efficiently improve network physiology because, following abnormal development, gene replacement will not reverse the damage.

The EEG portion of the study aims to directly measure hippocampal activity to help us understand network dynamics in the early development of CLN3 mice. EEG measures the electrical activity in the brain. The different wave frequencies, beta, alpha, theta, and delta, correlate with a person’s wakefulness, going from slow delta to fast beta waves. Fast Fourier Transform decomposes the EEG signal into specific frequencies. We then use the ratios of slow, medium, and fast signals to measure cognitive features. We can also look at interictal spikes, which are synchronous discharges of a group of neurons that can signify seizure potential, a marker of CLN3 disease. We found a trend toward increasing interictal spikes in the EEG data from the p30 CLN3 mice. Additionally, using normalized power ratios, we discovered an increase in slow delta power, a decrease in fast alpha power, and a statistically significant increase in the delta:alpha ratio, an established measure in EEG of pathological slowing and a clinical marker of brain injuries and strokes.

We have confirmed EEG pathologic slowing in CLN3 mice as early as P30 and will determine whether there is a time point in circuit development, after which administering gene therapy would not improve network physiology. We know gene replacement in utero or at p0 corrects network abnormalities. We are dosing CLN3 mice at p0, p10, and p20 with a 1665 base pair controlled promoter intended to restore network physiology but avoid overexpression of CLN3 because it is toxic in some model organisms.