CLN5 disease, caused by mutations in the CLN5 gene, is a form of neuronal ceroid lipofuscinoses (Batten disease). Patients suffer progressive motor dysfunction, vision loss, seizures, and dementia, leading to premature death. Here, we report a preclinical study of AAV9-mediated gene therapy in a Cln5-/- mouse model. Single-dose AAV9 carrying human CLN5 driven by the CAG or human synapsin 1 promoter (hSYN) was administered via intracerebroventricular injection into neonatal and juvenile Cln5-/- mice. Treatment efficacy was evaluated by assessment of neurodegeneration, neuroinflammation, locomotor function, and survival. AAV9 expressing CLN5 driven by the hSYN promoter significantly alleviated neurodegeneration, improved biochemical and glycosphingolipid profiles, neuropathological and locomotor function, and extended lifespan of the Cln5-/- mice. However, gene transfer employing the CAG promoter demonstrated limited therapeutic efficacy. Furthermore, delayed intervention in juveniles provided superior therapeutic response compared with early neonatal intervention and normalized lifespan. Finally, blood plasma neurofilament light that is significantly elevated in the Cln5-/- mice is restored to normal wildtype levels following treatment. These results indicate that brain-directed adeno-associated virus (AAV) gene therapy could be a promising treatment strategy for CLN5 disease and efficacy might be monitored using a noninvasive blood plasma biomarker.

CLN5 disease, a form of juvenile dementia within the neuronal ceroid lipofuscinosis (NCL), is associated with mutations in the CLN5 gene encoding the lysosomal bis(monoacylglycero)phosphate (BMP) synthase, essential for BMP production and lysosomal function. Limited knowledge of cellular mechanisms and unclear drug targets hinder translating this to children's treatment, which remains symptomatic. We developed and characterized a new cln5 knock-out zebrafish model that replicates key features and molecular signatures of the human disease. Loss of Cln5 function in vivo altered axonal growth of retinal ON-bipolar cells and disrupted calcium homeostasis in the cerebellum, revealing new disease features. Additionally, multi-omic analyses at different developmental stages revealed an impaired glucose metabolism as an original finding in NCL. A novel biomarker, PHGDH, was validated in zebrafish and human skin fibroblasts harboring pathogenic variants in CLN5, and in CLN7. We also tested metformin which improved the expression of PHGDH in patient-derived cells, and rescued zebrafish behavior. This work demonstrates the profound metabolic impact of CLN5 dysfunction, offering a promising avenue toward targeted therapies for juvenile dementia.