Mechanistic insights into Juvenile Neuronal Ceroid Lipofuscinosis using targeted gene delivery

Juvenile Neuronal Ceroid Lipofuscinosis (JNCL) is a neurodegenerative lysosomal storagedisease caused by an autosomal recessive mutation in CLN3. Symptom onset occurs between5-10 years of age with blindness and intractable seizures, followed by progressive cognitive andmotor deterioration, and premature death (late teens-early 20s). JNCL is typified by neuronalapoptosis; however, neuronal death in the CLN3?ex7/8 mouse model occurs later in the diseaseprocess (12 months) compared to astrocyte activation, which is an early event (1-3 months) andpredicts regions of eventual neuronal loss. Our preliminary data reveal reduced Ca2+ signaling,glutamate transporter, and glutamine synthetase expression in CLN3?ex7/8 astrocytes, whichmanifests as impaired glutamate clearance. This is expected to influence neuronal apoptosis,since excessive extracellular glutamate has been implicated in neuron excitotoxicity duringJNCL. This suggests that aberrant astrocyte activity may impact neuronal dysfunction and late-stage apoptosis, which mandates a systematic assessment to alleviate this confound andseparate the cell autonomous contributions of CLN3 mutation in neurons vs. astrocytes. To thisend, our group has developed novel self-complementary (sc) adeno-associated virus 9(scAAV9) constructs to probe cell type-specific effects of CLN3 action, where human CLN3(hCLN3) is preferentially targeted to neurons (synapsin-hCLN3), astrocytes (GFAP-hCLN3), orboth populations using the methyl-CpG-binding protein 2 (MeCP2) promoter (MeCP2-hCLN3) toexamine effects on disease mechanisms and pathology. We will utilize these viruses as tools totest the hypothesis that neuron loss in JNCL is influenced by distinct cell autonomous actionsof CLN3 in neurons and astrocytes. The effects of cell type selective CLN3 expression ondisease attributes will be examined in the following Specific Aims: 1) Examine the effects ofrestoring CLN3 expression in neurons vs. astrocytes on behavioral, pathological, andphysiological deficits in JNCL; 2) Examine the effects of CLN3 mutation in neurons vs.astrocytes on neurotransmitter perturbations in JNCL; and 3) Examine cell autonomous effectsof CLN3 on proteostasis. This work will be the first to directly demonstrate cell autonomouseffects of CLN3 mutation and how this contributes to neuronal loss in JNCL. This wouldsignificantly expand our understanding of the major cell types driving neuropathology anddelineate how/where therapies should be targeted to exert the greatest impact on JNCLpathogenesis.