👤 K Luiro

Juvenile neuronal ceroid lipofuscinosis (JNCL, Batten disease) is the most common progressive neurodegenerative disorder of childhood. CLN3, the transmembrane protein underlying JNCL, is proposed to participate in multiple cellular events including membrane trafficking and cytoskeletal functions. We demonstrate here that CLN3 interacts with the plasma membrane-associated cytoskeletal and endocytic fodrin and the associated Na(+), K(+) ATPase. The ion pumping activity of Na(+), K(+) ATPase was unchanged in Cln3(-/-) mouse primary neurons. However, the immunostaining pattern of fodrin appeared abnormal in JNCL fibroblasts and Cln3(-/-) mouse brains suggesting disturbances in the fodrin cytoskeleton. Furthermore, the basal subcellular distribution as well as ouabain-induced endocytosis of neuron-specific Na(+), K(+) ATPase were remarkably affected in Cln3(-/-) mouse primary neurons. These data suggest that CLN3 is involved in the regulation of plasma membrane fodrin cytoskeleton and consequently, the plasma membrane association of Na(+), K(+) ATPase. Most of the processes regulated by multifunctional fodrin and Na(+), K(+) ATPase are also affected in JNCL and Cln3-deficiency implicating that dysregulation of fodrin cytoskeleton and non-pumping functions of Na(+), K(+) ATPase may play a role in the neuronal degeneration in JNCL. Show less

Intracellular pathways leading to neuronal degeneration are poorly understood in the juvenile neuronal ceroid lipofuscinosis (JNCL, Batten disease), caused by mutations in the CLN3 gene. To elucidate the early pathology, we carried out comparative global transcript profiling of the embryonic, primary cultures of the Cln3-/- mouse neurons. Statistical and functional analyses delineated three major cellular pathways or compartments affected: mitochondrial glucose metabolism, cytoskeleton, and synaptosome. Further functional studies showed a slight mitochondrial dysfunction and abnormalities in the microtubule cytoskeleton plus-end components. Synaptic dysfunction was also indicated by the pathway analysis, and by the gross upregulation of the G protein beta 1 subunit, known to regulate synaptic transmission via the voltage-gated calcium channels. Intracellular calcium imaging showed a delay in the recovery from depolarization in the Cln3-/- neurons, when the N-type Ca2+ channels had been blocked. The data suggests a link between the mitochondrial dysfunction and cytoskeleton-mediated presynaptic inhibition, thus providing a foundation for further investigation of the disease mechanism underlying JNCL disease. Show less

The endosomal/lysosomal transmembrane protein CLN3 is mutated in the Batten disease (juvenile neuronal ceroid lipofuscinosis, JNCL). However, the molecular mechanism of JNCL pathogenesis and the exact function of the CLN3 protein have remained unclear. Previous studies have shown that deletion of BTN1, the yeast orthologue of CLN3, leads to increased expression of BTN2. BTN2 encodes Btn2p, a proposed homologue to a novel microtubule-binding protein Hook1, which regulates endocytosis in Drosophila. We analysed here the putative interconnection between CLN3 and Hook1 in the mammalian cells and discovered that overexpression of human CLN3 induces aggregation of Hook1 protein, potentially by mediating its dissociation from the microtubules. Using in vitro binding assay we were able to demonstrate a weak interaction between Hook1 and the cytoplasmic segments of CLN3. We also found receptor-mediated endocytosis to be defective in CLN3-deficient JNCL fibroblasts, connecting CLN3, Hook1 and endocytosis in the mammalian system. Moreover, co-immunoprecipitation experiments showed that Hook1 physically interacts with endocytic Rab7, Rab9 and Rab11, hence delineating a manifold role for mammalian Hook1 in membrane trafficking events. These novel interactions between the microtubule-binding Hook1 and the large family of Rab GTPases also suggest a link between CLN3 function, microtubule cytoskeleton and endocytic membrane trafficking. Show less

Batten disease (juvenile neuronal ceroid lipofuscinosis, JNCL), the most common neurodegenerative disease of childhood, is caused by mutations in the CLN3 gene encoding a putative transmembrane protein. The function of CLN3 is currently unknown but it has been shown to localize in the endosomal/lysosomal compartments of non-neuronal cells. In addition, several other intracellular localizations have been proposed and the controversy of the reports suggests that CLN3 may have different intracellular localization in different cell types. Batten disease severely affects neuronal cells but leaves other organs clinically unaffected, and thus it is of utmost importance to approach the disease mechanism by studying the expression and localization of CLN3 in the brain and neuronal cells. We have analysed here CLN3 in the mouse brain using in situ hybridization, immunohistochemical staining and western blot analysis of subcellular fractions. As visual deterioration is the hallmark of Batten disease we have set up primary retinal cultures from the mouse and analysed both endogenous mouse CLN3 and Semliki Forest virus-mediated human CLN3 localization using immunofluorescence staining and confocal microscopy. We demonstrate that CLN3 is abundantly expressed in neuronal cells, especially in the cortex, hippocampus and cerebellum of the adult mouse brain. Furthermore, our results indicate that in neurons CLN3 is not solely a lysosomal protein. It is localized in the synaptosomes but, interestingly, is not targeted to the synaptic vesicles. The novel localization of CLN3 directs attention towards molecular alterations at the synapses. This should yield important clues about the mechanisms of neurodegeneration in Batten disease. Show less