👤 Mark Turmaine

Retinal degeneration and visual impairment are the first signs of juvenile neuronal ceroid lipofuscinosis caused by CLN3 mutations, followed by inevitable progression to blindness. We investigated retinal degeneration in Cln3(Δex1-6) null mice, revealing classic 'fingerprint' lysosomal storage in the retinal pigment epithelium (RPE), replicating the human disease. The lysosomes contain mitochondrial F0-ATP synthase subunit c along with undigested membranes, indicating a reduced degradative capacity. Mature autophagosomes and basal phagolysosomes, the terminal degradative compartments of autophagy and phagocytosis, are also increased in Cln3(Δex1) (-6) RPE, reflecting disruption to these key pathways that underpin the daily phagocytic turnover of photoreceptor outer segments (POS) required for maintenance of vision. The accumulated autophagosomes have post-lysosome fusion morphology, with undigested internal contents visible, while accumulated phagosomes are frequently docked to cathepsin D-positive lysosomes, without mixing of phagosomal and lysosomal contents. This suggests lysosome-processing defects affect both autophagy and phagocytosis, supported by evidence that phagosomes induced in Cln3(Δex1) (-) (6)-derived mouse embryonic fibroblasts have visibly disorganized membranes, unprocessed internal vesicles and membrane contents, in addition to reduced LAMP1 membrane recruitment. We propose that defective lysosomes in Cln3(Δex1) (-) (6) RPE have a reduced degradative capacity that impairs the final steps of the intimately connected autophagic and phagocytic pathways that are responsible for degradation of POS. A build-up of degradative organellar by-products and decreased recycling of cellular materials is likely to disrupt processes vital to maintenance of vision by the RPE. Show less

Batten disease or JNCL, is the juvenile form of Neuronal Ceroid Lipofuscinosis (NCL) an autosomal recessive neurodegenerative disorder. Since retinal degeneration is an early consequence of Batten disease, we examined the eyes of Cln3 knockout mice (1-20 months of age), along with heterozygotes and appropriate controls, to determine whether or not the Cln3 defect would lead to characteristic retinal degeneration and visual loss. Accumulation of autofluorescent material and intracellular inclusions were markedly increased in Cln3 knockout retinal ganglion cells, as well as most other nuclear layers. Nerve fiber density was also significantly decreased in Cln3 knockout retinae. Apoptosis was observed in the photoreceptor layer of Cln3 knockout. However, the degree of retinal degeneration up to age 20 months was not extensive. Fundus examinations of Cln3 knockout mice showed no significant abnormalities, while electroretinograms remained robust through 11 months of age. In summary, it appears that accumulation of autofluorescent material, carbohydrate storage material, as well as apoptotic cell death are retinal manifestations of the Cln3 defect that do not appear to extinguish retinal function in this mouse model of Batten disease. Show less