CSPALPHA/DNAJC5 IS ESSENTIAL FOR THE MAINTENANCE OF ADULT NERVOUS SYSTEM HOMEOSTASIS

The continuous maintenance of synaptic proteins is fundamental for neuronal viability and function throughout life, yet the underlying molecular mechanisms remain incompletely understood. The co-chaperone Cysteine String Protein alpha (CSPα/DNAJC5) protects synapses from degeneration. Mutations in DNAJC5 cause neuronal ceroid lipofuscinosis (CLN4/Kufs disease), a neurodegenerative disorder affecting young adults. CSPα/DNAJC5 KO mice exhibit early lethality, limiting the study of its function in aging. To overcome this limitation, we developed a tamoxifen-inducible conditional knockout mouse model (UBCCreERT2:Dnajc5^flox/flox) that allows temporal deletion of CSPα/DNAJC5 in adulthood. Acute loss of CSPα/DNAJC5 in these mice resulted in severe neurological decline and premature death, revealing its critical function in the mature nervous system. The phenotype occurred without lipofuscin accumulation, confirming that CSPα/DNAJC5 deficiency does not mimic CLN4 pathology, as described (Lopez-Begines, Borjini et al., Science Advances, 2025). Transcriptomic profiling of cortical tissue revealed dysregulation in genes associated with lipid metabolism, synaptic integrity, glial-neuronal signaling, and myelination. Although systemic adeno-associated virus (AAV) delivery of CSPα/DNAJC5 using the PHP.eB capsid achieved widespread neuronal transduction, it failed to rescue the severe neurological phenotype. This suggests that once neuronal dysfunction starts, delivered CSPα/DNAJC5 may be insufficient to reverse the damage, possibly due to inadequate viral load and/or the necessity for earlier intervention before neurodegeneration becomes irreversible. Our results demonstrate that CSPα/DNAJC5 is indispensable for sustaining neuronal function in the mature and aging adult brain. This study highlights novel molecular pathways potentially involved in CSPα/DNAJC5-related neurodegeneration.