Membrane trafficking and mitochondrial abnormalities precede subunit c deposition in a cerebellar cell model of juvenile neuronal ceroid lipofuscinosis.

BACKGROUND: JNCL is a recessively inherited, childhood-onset neurodegenerative disease most-commonly caused by a approximately 1 kb CLN3 mutation. The resulting loss of battenin activity leads to deposition of mitochondrial ATP synthase, subunit c and a specific loss of CNS neurons. We previously generated Cln3Deltaex7/8 knock-in mice, which replicate the common JNCL mutation, express mutant battenin and display JNCL-like pathology. RESULTS: To elucidate the consequences of the common JNCL mutation in neuronal cells, we used P4 knock-in mouse cerebella to establish conditionally immortalized CbCln3 wild-type, heterozygous, and homozygous neuronal precursor cell lines, which can be differentiated into MAP-2 and NeuN-positive, neuron-like cells. Homozygous CbCln3Deltaex7/8 precursor cells express low levels of mutant battenin and, when aged at confluency, accumulate ATPase subunit c. Recessive phenotypes are also observed at sub-confluent growth; cathepsin D transport and processing are altered, although enzyme activity is not significantly affected, lysosomal size and distribution are altered, and endocytosis is reduced. In addition, mitochondria are abnormally elongated, cellular ATP levels are decreased, and survival following oxidative stress is reduced. CONCLUSIONS: These findings reveal that battenin is required for intracellular membrane trafficking and mitochondrial function. Moreover, these deficiencies are likely to be early events in the JNCL disease process and may particularly impact neuronal survival.

Cln3(Deltaex7/8) knock-in mice with the common JNCL mutation exhibit progressive neurologic disease that begins before birth.

Juvenile-onset neuronal ceroid lipofuscinosis (JNCL; Batten disease) features hallmark membrane deposits and loss of central nervous system (CNS) neurons. Most cases of the disease are due to recessive inheritance of an approximately 1 kb deletion in the CLN3 gene, encoding battenin. To investigate the common JNCL mutation, we have introduced an identical genomic DNA deletion into the murine CLN3 homologue (Cln3) to create Cln3( Deltaex7/8) knock-in mice. The Cln3( Deltaex7/8) allele produced alternatively spliced mRNAs, including a variant predicting non-truncated protein, as well as mutant battenin that was detected in the cytoplasm of cells in the periphery and CNS. Moreover, Cln3( Deltaex7/8) homozygotes exhibited accrual of JNCL-like membrane deposits from before birth, in proportion to battenin levels, which were high in liver and select neuronal populations. However, liver enzymes and CNS development were normal. Instead, Cln3( Deltaex7/8) mice displayed recessively inherited degenerative changes in retina, cerebral cortex and cerebellum, as well as neurological deficits and premature death. Thus, the harmful impact of the common JNCL mutation on the CNS was not well correlated with membrane deposition per se, suggesting instead a specific battenin activity that is essential for the survival of CNS neurons.