Altered sensitivity of cerebellar granule cells to glutamate receptor overactivation in the Cln3Δex7/8-knock-in mouse model of juvenile neuronal ceroid lipofuscinosis

The juvenile onset form of neuronal ceroid lipofuscinoses (JNCL) is a recessively inherited lysosomal storage disorder characterized by progressive neurodegeneration. JNCL results from mutations in the CLN3 gene that encodes a lysosomal membrane protein with unknown function.Utilizing a Cln3-knock-out mouse model of JNCL that was created on the 129S6/SvEv genetic background, we have previously demonstrated that CLN3-deficient cerebellar granule cells (CGCs) have a selectively increased sensitivity to AMPA-type glutamate receptor-mediated toxicity. Our recent findings that CGCs from 129S6/SvEv and C57BL/6J wild type (WT) mice have significant differences in glutamate receptor expression and in excitotoxic vulnerability indicated that the genetic background possibly have a strong influence on how glutamate receptor function is dysregulated in CLN3-deficient neurons. Indeed, here we show that in the Cln3Δex7/8-knock-in mouse model, that is on the C57BL/6J genetic background, mimics the most frequent mutation observed in JNCL patients and considered a null mutant, the sensitivity of CGCs to both AMPA- and NMDA-type glutamate receptor overactivations is altered. Cultured wild type and Cln3Δex7/8 CGCs were equally sensitive to AMPA toxicity after 2 or 3 weeks in vitro, whereas the subunit-selective AMPA receptor agonist, CPW-399, induced significantly more cell death in mature, 3-week-old Cln3Δex7/8 cultures. NMDA receptor-mediated toxicity changed during in vitro development: Cln3Δex7/8 CGCs were less sensitive to high concentration of NMDA after 2 weeks in culture but became more vulnerable than their WT counterparts after 3 weeks in vitro.Abnormally altered glutamate receptor function in the cerebellum may result in motor deficits, and we confirmed that 7-week-old Cln3Δex7/8 mice, similarly to Cln3-knock-out mice, have a motor coordination deficit as measured by an accelerating rotarod.Our results demonstrate altered glutamate receptor function in Cln3Δex7/8 neurons and suggest that both AMPA and NMDA receptors are potential therapeutic targets in JNCL.

Research highlights
► The genetic background affects mouse models of juvenile Batten disease.
► Sensitivity of Cln3Δex7/8 neurons to glutamate receptor overactivation is altered.
► AMPA and NMDA receptor expression is not changed in the Cln3Δex7/8 cerebellum.
► Seven-week-old Cln3Δex7/8-knock-in mice have a motor coordination deficit.