CLN3 disease disrupts very early postnatal hippocampal maturation.

CLN3 disease or juvenile neuronal ceroid lipofuscinosis (Batten disease), is a progressive, severe, neurodegenerative, lysosomal storage disorder. Previous studies have demonstrated that network-level excitability differences are present in mouse models prior to significant lysosomal storage accumulation. Here we sought to identify the earliest biochemical and functional markers of disease in the hippocampus, a brain region important in learning and memory and implicated in CLN3 disease. Using targeted hydrophilic interaction liquid chromatography high resolution mass spectrometry (LC-HRMS), we quantified levels of glycerophosphodiesters (GPDs), recently-described biomarkers of CLN3 disease, in early postnatal hippocampus. In addition, we assessed hippocampal excitability via in vitro voltage-sensitive dye imaging (VSDI) across the period of postanal hippocampal maturation (p7, p14, p21). Finally, we completed longitudinal electroencephalogram (EEG) recordings to evaluate in vivo hippocampal circuit dynamics once the hippocampal circuit was matured. Intriguingly, glycercophosphoinositol (GPI or GroPIns), but not other GPDs, were significantly elevated in CLN3 disease hippocampus in early development at p11, further supporting the hypothesis that GPI plays a key role in disease pathogenesis. Functionally, the hippocampus was significantly hypoexcitable as early as p7 and showed a very atypical pattern of maturation across early development. This aberrant development resulted in abnormal in vivo circuit function, with pathologic slowing observed on EEG recordings at p30. Collectively these data underscore the potential link between pathologic metabolism of GPI and functional defects in CLN3 disease. In addition, this work highlights that CLN3 disease is an early neurodevelopmental, and not just neurodegenerative, disorder.