Omar Shmoury

Neuronal ceroid lipofuscinosis type 6 (CLN6) is a fatal, autosomal recessive neurodegenerative disorder characterized by cognitive/motor impairment, vision loss, as well as neuronal loss and gliosis in the brain, and premature death. Onset typically occurs in childhood. No approved pharmacological treatments exist that halt or reverse disease progression. A novel flupirtine benzyl carbamate was orally administered to male and female Cln6^nclf mice from 4 to 28 weeks of age to evaluate its neuroprotective and antispastic effects. Drug treatment produced significant, sex-dependent phenotypic improvements. Treated mice of both sexes exhibited reduced hindlimb spasticity, but only treated males demonstrated diminution in locomotor hyperactivity and recovery of visuospatial performance. In the brains of male and female Cln6^nclf mice, flupirtine benzyl carbamate significantly decreased astrocytosis, microgliosis and mitochondrial ATP synthase subunit C (SCMAS) accumulation, increased neuronal marker expression and reduced the number of TUNEL-positive cells. The treatment failed to rescue photoreceptor loss or clear retinal SCMAS storage. These outcomes result in distinct sex-specific differences in neuronal vulnerability and drug responsiveness. Overall, these findings demonstrate that flupirtine benzyl carbamate diminishes key motor, visual and pathological deficits in CLN6 disease, highlighting its promise as a potential disease-modifying therapy for CLN6 in humans despite sex-specific differences.

Neuronal ceroid lipofuscinoses (NCLs) are a group of autosomal recessive neurogenetic disorders caused by mutations in 14 different genes. CLN6 disease manifests as variant late-infantile NCL (vLINCL) or as an adult variant. In childhood, symptoms include speech delay, vision loss, cognitive and motor decline, seizures, and early death. An in-depth characterization of a naturally occurring Cln6 mutant mouse (Cln6^nclf) is presented, with implications for translational research. The expanded phenotype provides data showing early death, vision loss, and motor deficits in male and female Cln6^nclf mice. Diminished visual acuity in Cln6^nclf mice was noted at 28 weeks of age, but the pathological loss of retinal layers began as early as 2 weeks or postnatal day 14 (P14). Apoptosis was confirmed by TUNEL staining in the Cln6^nclf mouse brain at P8 and in the retina at P12. A peak in glial fibrillary acidic protein (GFAP) expression was established as a normal developmental phenomenon in the wild-type and Cln6^nclf mouse brain cerebellum and the CA2–CA3 regions of the hippocampus at P8. In Cln6^nclf mice, GFAP levels were elevated at P12 in the cerebellum and hippocampus. In the retina, a developmental peak in gliosis was absent, with increased astrogliosis noted at P6 and P8 in female and male Cln6^nclf mice, respectively. This highlights the lack of a sex-dependent response in wild-type mice. These novel data position the Cln6^nclf mouse model as a useful tool for screening potential therapeutics for human CLN6 disease.

Neurological diseases, including neurodegenerative and neurodevelopmental disorders, affect nearly one in six of the world’s population. The burden of the resulting deaths and disability is set to rise during the next few decades as a consequence of an aging population. To address this, zebrafish have become increasingly prominent as a model for studying human neurological diseases and exploring potential therapies. Zebrafish offer numerous benefits, such as genetic homology and brain similarities, complementing traditional mammalian models and serving as a valuable tool for genetic screening and drug discovery. In this comprehensive review, we highlight various drug delivery techniques and systems employed for therapeutic interventions of neurological diseases in zebrafish, and evaluate their suitability. We also discuss the challenges encountered during this process and present potential advancements in innovative techniques.