Loss of pigment-laden stellate cells: a severe alteration of the isocortex in juvenile neuronal ceroid-lipofuscinosis

Current Insights in Elucidation of Possible Molecular Mechanisms of the Juvenile Form of Batten Disease

The neuronal ceroid lipofuscinoses (NCLs) collectively constitute one of the most common forms of inherited childhood-onset neurodegenerative disorders. They form a heterogeneous group of incurable lysosomal storage diseases that lead to blindness, motor deterioration, epilepsy, and dementia. Traditionally the NCL diseases were classified according to the age of disease onset (infantile, late-infantile, juvenile, and adult forms), with at least 13 different NCL varieties having been described at present. The current review focuses on classic juvenile NCL (JNCL) or the so-called Batten (Batten-Spielmeyer-Vogt; Spielmeyer-Sjogren) disease, which represents the most common and the most studied form of NCL, and is caused by mutations in the CLN3 gene located on human chromosome 16. Most JNCL patients carry the same 1.02-kb deletion in this gene, encoding an unusual transmembrane protein, CLN3, or battenin. Accordingly, the names CLN3-related neuronal ceroid lipofuscinosis or CLN3-disease sometimes have been used for this malady. Despite excessive in vitro and in vivo studies, the precise functions of the CLN3 protein and the JNCL disease mechanisms remain elusive and are the main subject of this review. Although the CLN3 gene is highly conserved in evolution of all mammalian species, detailed analysis of recent genomic and transcriptomic data indicates the presence of human-specific features of its expression, which are also under discussion. The main recorded to date changes in cell metabolism, to some extent contributing to the emergence and progression of JNCL disease, and human-specific molecular features of CLN3 gene expression are summarized and critically discussed with an emphasis on the possible molecular mechanisms of the malady appearance and progression.

Exogenous Flupirtine as Potential Treatment for CLN3 Disease

CLN3 disease is a fatal neurodegenerative disorder affecting children. Hallmarks include brain atrophy, accelerated neuronal apoptosis, and ceramide elevation. Treatment regimens are supportive, highlighting the importance of novel, disease-modifying drugs. Flupirtine and its new allyl carbamate derivative (compound 6) confer neuroprotective effects in CLN3-deficient cells. This study lays the groundwork for investigating beneficial effects in Cln3^Δex7/8 mice. WT/Cln3^Δex7/8 mice received flupirtine/compound 6/vehicle for 14 weeks. Short-term effect of flupirtine or compound 6 was tested using a battery of behavioral testing. For flupirtine, gene expression profiles, astrogliosis, and neuronal cell counts were determined. Flupirtine improved neurobehavioral parameters in open field, pole climbing, and Morris water maze tests in Cln3^Δex7/8 mice. Several anti-apoptotic markers and ceramide synthesis/degradation enzymes expression was dysregulated in Cln3^Δex7/8 mice. Flupirtine reduced astrogliosis in hippocampus and motor cortex of male and female Cln3^Δex7/8 mice. Flupirtine increased neuronal cell counts in male mice. The newly synthesized compound 6 showed promising results in open field and pole climbing. In conclusion, flupirtine improved behavioral, neuropathological and biochemical parameters in Cln3^Δex7/8 mice, paving the way for potential therapies for CLN3 disease.

A multimodal approach to identify clinically relevant biomarkers to comprehensively monitor disease progression in a mouse model of pediatric neurodegenerative disease

While research has accelerated the development of new treatments for pediatric neurodegenerative disorders, the ability to demonstrate the long-term efficacy of these therapies has been hindered by the lack of convincing, noninvasive methods for tracking disease progression both in animal models and in human clinical trials. Here, we unveil a new translational platform for tracking disease progression in an animal model of a pediatric neurodegenerative disorder, CLN6-Batten disease. Instead of looking at a handful of parameters or a single "needle in a haystack", we embrace the idea that disease progression, in mice and patients alike, is a diverse phenomenon best characterized by a combination of relevant biomarkers. Thus, we employed a multi-modal quantitative approach where 144 parameters were longitudinally monitored to allow for individual variability. We use a range of noninvasive neuroimaging modalities and kinematic gait analysis, all methods that parallel those commonly used in the clinic, followed by a powerful statistical platform to identify key progressive anatomical and metabolic changes that correlate strongly with the progression of pathological and behavioral deficits. This innovative, highly sensitive platform can be used as a powerful tool for preclinical studies on neurodegenerative diseases, and provides proof-of-principle for use as a potentially translatable tool for clinicians in the future.

Loss of Cln5 leads to altered Gad1 expression and deficits in interneuron development in mice

The Finnish-variant late infantile neuronal ceroid lipofuscinosis, also known as CLN5 disease, is caused by mutations in the CLN5 gene. Cln5 is strongly expressed in the developing brain and expression continues into adulthood. CLN5, a protein of unknown function, is implicated in neurodevelopment but detailed investigation is lacking. Using Cln5-/- embryos of various ages and cells harvested from Cln5-/- brains we investigated the hitherto unknown role of Cln5 in the developing brain. Loss of Cln5 results in neuronal differentiation deficits and delays in interneuron development during in utero period. Specifically, the radial thickness of dorsal telencephalon was significantly decreased in Cln5-/- mouse embryos at embryonic day 14.5 (E14.5), and expression of Tuj1, an important neuronal marker during development, was down-regulated. An interneuron marker calbindin and a mitosis marker p-H3 showed down-regulation in ganglionic eminences. Neurite outgrowth was compromised in primary cortical neuronal cultures derived from E16 Cln5-/- embryos compared with WT embryos. We show that the developmental deficits of interneurons may be linked to increased levels of the repressor element 1-silencing transcription factor, which we report to bind to glutamate decarboxylase (Gad1), which encodes GAD67, a rate-limiting enzyme in the production of gamma-aminobutyric acid (GABA). Indeed, adult Cln5-/- mice presented deficits in hippocampal parvalbumin-positive interneurons. Furthermore, adult Cln5-/- mice presented deficits in hippocampal parvalbumin-positive interneurons and showed age-independent cortical hyper excitability as measured by electroencephalogram and auditory-evoked potentials. This study highlights the importance of Cln5 in neurodevelopment and suggests that in contrast to earlier reports, CLN5 disease is likely to develop during embryonic stages.

Exogenous Galactosylceramide as Potential Treatment for CLN3 Disease

OBJECTIVE

CLN3 disease is the commonest of the neuronal ceroid lipofuscinoses, a group of pediatric neurodegenerative disorders. Functions of the CLN3 protein include antiapoptotic properties and facilitating anterograde transport of galactosylceramide from Golgi to lipid rafts. This study confirms the beneficial effects of long-term exogenous galactosylceramide supplementation on longevity, neurobehavioral parameters, neuronal cell counts, astrogliosis, and diminution in brain and serum ceramide levels in Cln3 ^Δex7/8 knock-in mice. Additionally, the impact of galactosylceramide on ceramide synthesis enzymes is documented.

METHODS

A group of 72 mice received galactosylceramide or vehicle for 40 weeks. The effect of galactosylceramide supplementation on Cln3 ^Δex7/8 mice was determined by performing behavioral tests, measuring ceramide in brains and serum, and assessing impact on longevity, subunit C storage, astrogliosis, and neuronal cell counts.

RESULTS

Galactosylceramide resulted in enhanced grip strength of forelimbs in male and female mice, better balance on the accelerating rotarod in females, and improved motor coordination during pole climbing in male mice. Brain and serum ceramide levels as well as apoptosis rates were lower in galactosylceramide-treated Cln3 ^Δex7/8 mice. Galactosylceramide also increased neuronal cell counts significantly in male and female mice and tended to decrease subunit C storage in specific brain regions. Astrogliosis dropped in females compared to a slight increase in males after galactosylceramide. Galactosylceramide increased the lifespan of affected mice.

INTERPRETATION

Galactosylceramide improved behavioral, neuropathological, and biochemical parameters in Cln3 ^Δex7/8 mice, paving the way for effective therapy for CLN3 disease and use of serum ceramide as a potential biomarker to track impact of therapies. ANN NEUROL 2019;86:729-742.

Therapeutic landscape for Batten disease: current treatments and future prospects

Batten disease (also known as neuronal ceroid lipofuscinoses) constitutes a family of devastating lysosomal storage disorders that collectively represent the most common inherited paediatric neurodegenerative disorders worldwide. Batten disease can result from mutations in 1 of 13 genes. These mutations lead to a group of diseases with loosely overlapping symptoms and pathology. Phenotypically, patients with Batten disease have visual impairment and blindness, cognitive and motor decline, seizures and premature death. Pathologically, Batten disease is characterized by lysosomal accumulation of autofluorescent storage material, glial reactivity and neuronal loss. Substantial progress has been made towards the development of effective therapies and treatments for the multiple forms of Batten disease. In 2017, cerliponase alfa (Brineura), a tripeptidyl peptidase enzyme replacement therapy, became the first globally approved treatment for CLN2 Batten disease. Here, we provide an overview of the promising therapeutic avenues for Batten disease, highlighting current FDA-approved clinical trials and prospective future treatments.

Osmoregulation of ceroid neuronal lipofuscinosis type 3 in the renal medulla

Recessive inheritance of mutations in ceroid neuronal lipofuscinosis type 3 (CLN3) results in juvenile neuronal ceroid lipofuscinosis (JNCL), a childhood neurodegenerative disease with symptoms including loss of vision, seizures, and motor and mental decline. CLN3p is a transmembrane protein with undefined function. Using a Cln3 reporter mouse harboring a nuclear-localized bacterial beta-galactosidase (beta-Gal) gene driven by the native Cln3 promoter, we detected beta-Gal most prominently in epithelial cells of skin, colon, lung, and kidney. In the kidney, beta-Gal-positive nuclei were predominant in medullary collecting duct principal cells, with increased expression along the medullary osmotic gradient. Quantification of Cln3 transcript levels from kidneys of wild-type (Cln3(+/+)) mice corroborated this expression gradient. Reporter mouse-derived renal epithelial cultures demonstrated a tonicity-dependent increase in beta-Gal expression. RT-quantitative PCR determination of Cln3 transcript levels further supported osmoregulation at the Cln3 locus. In vivo, osmoresponsiveness of Cln3 was demonstrated by reduction of medullary Cln3 transcript abundance after furosemide administration. Primary cultures of epithelial cells of the inner medulla from Cln3(lacZ/lacZ) (CLN3p-null) mice showed no defect in osmolyte accumulation or taurine flux, arguing against a requirement for CLN3p in osmolyte import or synthesis. CLN3p-deficient mice with free access to water showed a mild urine-concentrating defect but, upon water deprivation, were able to concentrate their urine normally. Unexpectedly, we found that CLN3p-deficient mice were hyperkalemic and had a low fractional excretion of K(+). Together, these findings suggest an osmoregulated role for CLN3p in renal control of water and K(+) balance.

[Mechanisms of juvenile neuronal ceroid lipofuscinosis (JNCL)]

Juvenile neuronal ceroid lipofuscinosis (JNCL) is one type of the neuronal ceroid lipofuscinosis (NCLs), which is a group of pediatric neurodegenerative disorders. The symptoms of JNCL are retinal degeneration (rd), seizures, cognitive, and motor decline. The pathogenesis, summarized in this review, include apoptosis, autophagy, dysfunction in the structure associated with plasmalemma, oxidative stress and disruption of nitric oxide signaling, dysfunction of the mitochondrial and lysosome, unbalanced intracellular pH, and other relative mechanisms. Among them, only apoptosis and autophagy are well known. In apoptosis, the defects in CLN3 result in ceramide accumulation and upstream of mitochondrial membrane per-meabilization, which eventually induce caspase-dependent and caspase-independent cell death. Autophagy exists but is disrupted because the immaturity of autophagic vacuoles leads to the failure of autophagy circulation. Understanding of the pathogenesis, especially the pathways of cell death in JNCL, is helpful to explore the mechanism of neurodegenerative dis-orders, such as JNCL.

Developmental impairments of select neurotransmitter systems in brains of Cln3(Deltaex7/8) knock-in mice, an animal model of juvenile neuronal ceroid lipofuscinosis

The neuronal ceroidlipofuscinoses (NCL) are a group of neurodegenerative disorders and are the most common lysosomal storage diseases of infancy and childhood. Juvenile NCL is caused by CLN3 mutation, producing retinal degeneration, uncontrollable seizures, cognitive and motor decline, and early death before the age of 30 years. To study the pathogenetic mechanisms of the disease, Cln3 knock-in mice (Cln3(Deltaex7/8)) have been generated, which reproduce the 1.02-kb deletion in the CLN3 gene observed in more than 85% of juvenile NCL patients. To characterize the impact of the common Cln3 mutation on development of autofluorescent storage material, gliosis, glucose metabolism, oxidative stress, and transmitter receptors during postnatal brain maturation, brain tissue of Cln3(Deltaex7/8) mice at the ages of 3, 4, 5, 6, 9, and 19 months was subjected to immunocytochemistry to label gliotic markers and nitric oxide synthases; photometric assays to assess enzyme activities of glycolysis and antioxidative defense systems; and level of reactive nitrogen species as well as quantitative receptor autoradiography to detect select cholinergic, glutamatergic, and GABAergic receptor subtypes. The developmental increase in cerebral cortical autofluorescent lipofuscin-like deposition is accompanied by a significant astro- and microgliosis, increased activities of lactate dehydrogenase and phosphofructokinase, decreased level of glutathione peroxidase, enhanced amount of reactive nitrogen species, and lowered binding levels of N-methyl-D-aspartate- and M1-muscarinic acetylcholine receptors in select brain regions but hardly in GABA(A) receptor sites compared with wild-type mice. Detailed elucidation of the sequence of pathological events during postnatal development highlights new potential strategies for symptomatic treatment of the disease.

Batten disease (JNCL) is linked to disturbances in mitochondrial, cytoskeletal, and synaptic compartments

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.

IgG entry and deposition are components of the neuroimmune response in Batten disease

Patients and a mouse model of Batten disease, the juvenile form of neuronal ceroid lipofuscinosis (JNCL), raise autoantibodies against GAD65 and other brain-directed antigens. Here we investigate the adaptive component of the neuroimmune response. Cln3(-/-) mice have autoantibodies to GAD65 in their cerebrospinal fluid and elevated levels of brain bound immunoglobulin G (IgG). IgG deposition was found within human JNCL autopsy material, a feature that became more evident with increased age in Cln3(-/-) mice. The lymphocyte infiltration present in human and murine JNCL occurred late in disease progression, and was not capable of central/intrathecal IgG production. In contrast, we found evidence for an early systemic immune dysregulation in Cln3(-/-) mice. In addition evidence for a size-selective breach in the blood-brain barrier integrity in these mice suggests that systemically produced autoantibodies can access the JNCL central nervous system and contribute to a progressive inflammatory response.

Progress towards understanding disease mechanisms in small vertebrate models of neuronal ceroid lipofuscinosis

Model systems provide an invaluable tool for investigating the molecular mechanisms underlying the NCLs, devastating neurodegenerative disorders that affect the relatively inaccessible tissues of the central nervous system. These models have enabled the assessment of behavioural, pathological, cellular, and molecular abnormalities, and also allow for development and evaluation of novel therapies. This review highlights the relative advantages of the two available small vertebrate species, the mouse and zebrafish, in modelling NCL disease, summarising how these have been useful in NCL research and their potential for the development and testing of prospective disease treatments. A panel of mouse mutants is available representing all the cloned NCL gene disorders (Cathepsin D, CLN1, CLN2, CLN3, CLN5, CLN6, CLN8). These NCL mice all have progressive neurodegenerative phenotypes that closely resemble the pathology of human NCL. The analysis of these models has highlighted several novel aspects underlying NCL pathogenesis including the selective nature of neurodegeneration, evidence for glial responses that precede neuronal loss and identification of the thalamus as an important pathological target early in disease progression. Studies in mice have also highlighted an unexpected heterogeneity underlying NCL phenotypes, and novel potential NCL-like mouse models have been described including mice with mutations in cathepsins, CLC chloride channels, and other lysosome-related genes. These new models are likely to provide significant new information on the spectrum of NCL disease. Information on NCL mice is available in the NCL Mouse Model Database (). There are homologs of most of the NCL genes in zebrafish, and NCL zebrafish models are currently in development. This model system provides additional advantages to those provided by NCL mouse models including high-throughput mutational, pharmacogenetic and therapeutic technique analyses. Mouse and zebrafish models are an important shared resource for NCL research, offering a unique possibility to dissect disease mechanisms and to develop therapeutic approaches.

Thalamocortical neuron loss and localized astrocytosis in the Cln3Δex7/8 knock-in mouse model of Batten disease

Juvenile neuronal ceroid lipofuscinosis (JNCL) is the result of mutations in the Cln3 gene. The Cln3 knock-in mouse (Cln3Deltaex7/8) reproduces the most common Cln3 mutation and we have now characterized the CNS of these mice at 12 months of age. With the exception of the thalamus, Cln3Deltaex7/8 homozygotes displayed no significant regional atrophy, but a range of changes in individual laminar thickness that resulted in variable cortical thinning across subfields. Stereological analysis revealed a pronounced loss of neurons within individual laminae of somatosensory cortex of affected mice and the novel finding of a loss of sensory relay thalamic neurons. These affected mice also exhibited profound astrocytic reactions that were most pronounced in the neocortex and thalamus, but diminished in other brain regions. These data provide the first direct evidence for neurodegenerative and reactive changes in the thalamocortical system in JNCL and emphasize the localized nature of these events.

Hippocampal pathology in the human neuronal ceroid-lipofuscinoses: distinct patterns of storage deposition, neurodegeneration and glial activation

The neuronal ceroid-lipofuscinoses (NCLs) are recessively inherited lysosomal storage diseases, currently classified into 8 forms (CLN1-CLN8). Collectively, the NCLs constitute the most common group of progressive encephalopathies of childhood, and present with visual impairment, psychomotor deterioration and severe seizures. Despite recent identification of the underlying disease genes, the mechanisms leading to neurodegeneration and epilepsy in the NCLs remain poorly understood. To investigate these events, we examined the patterns of storage deposition, neurodegeneration, and glial activation in the hippocampus of patients with CLN1, CLN2, CLN3, CLN5 and CLN8 using histochemistry and immunohistochemistry. These different forms of NCL shared distinct patterns of neuronal degeneration in the hippocampus, with heavy involvement of sectors CA2-CA4 but relative sparing of CA1. This selective pattern of degeneration was also observed in immunohistochemically identified interneurons, which exhibited a graded severity of loss according to phenotype, with calretinin-positive interneurons relatively spared. Furthermore, glial activation was also regionally specific, with microglial activation most pronounced in areas of greatest neuronal loss, and astrocyte activation prominent in areas where neuronal loss was less evident. In conclusion, the NCLs share a common pattern of selective hippocampal pathology, distinct from that seen in the majority of temporal lobe epilepsies.

Mice with Ppt1Δex4 mutation replicate the INCL phenotype and show an inflammation-associated loss of interneurons

Infantile Neuronal Ceroid Lipofuscinosis (INCL) results from mutations in the palmitoyl protein thioesterase (PPT1, CLN1) gene and is characterized by dramatic death of cortical neurons. We generated Ppt1Deltaex4 mice by a targeted deletion of exon 4 of the mouse Ppt1 gene. Similar to the clinical phenotype, the homozygous mutants show loss of vision from the age of 8 weeks, seizures after 4 months and paralysis of hind limbs at the age of 5 months. Autopsy revealed a dramatic loss of brain mass and histopathology demonstrated accumulation of autofluorescent granular osmiophilic deposits (GRODS), both characteristic of INCL. At 6 months, the homozygous Ppt1Deltaex4 mice showed a prominent loss of GABAergic interneurons in several brain areas. The transcript profiles of wild-type and mutant mouse brains revealed that most prominent alterations involved parts of the immune response, implicating alterations similar to those of the aging brain and neurodegeneration. These findings make the Ppt1Deltaex4 mouse an interesting model for the inflammation-associated death of interneurons.

A mouse model for Finnish variant late infantile neuronal ceroid lipofuscinosis, CLN5, reveals neuropathology associated with early aging

Neuronal ceroid lipofuscinoses (NCL) comprise the most common group of childhood encephalopathies caused by mutations in eight genetic loci, CLN1-CLN8. Here, we have developed a novel mouse model for the human vLINCL (CLN5) by targeted deletion of exon 3 of the mouse Cln5 gene. The Cln5-/- mice showed loss of vision and accumulation of autofluorescent storage material in the central nervous system (CNS) and peripheral tissues without prominent brain atrophy. The ultrastructure of the storage material accurately replicated the abnormalities in human patients revealing mixture of lamellar profiles including fingerprint profiles as well as curvilinear and rectilinear bodies in electronmicroscopic analysis. Prominent loss of a subset of GABAergic interneurons in several brain areas was seen in the Cln5-/- mice. Transcript profiling of the brains of the Cln5-/- mice revealed altered expression in several genes involved in neurodegeneration, as well as in defense and immune response, typical of age-associated changes in the CNS. Downregulation of structural components of myelin was detected and this agrees well with the hypomyelination seen in the human vLINCL patients. In general, the progressive pathology of the Cln5-/- brain mimics the symptoms of the corresponding neurodegenerative disorder in man. Since the Cln5-/- mice do not exhibit significant brain atrophy, these mice could serve as models for studies on molecular processes associated with advanced aging.

Late onset neurodegeneration in the Cln3−/− mouse model of juvenile neuronal ceroid lipofuscinosis is preceded by low level glial activation

Mouse models of neuronal ceroid lipofuscinosis (NCL) exhibit many features of the human disorder, with widespread regional atrophy and significant loss of GABAergic interneurons in the hippocampus and neocortex. Reactive gliosis is a characteristic of all forms of NCL, but it is unclear whether glial activation precedes or is triggered by neuronal loss. To explore this issue we undertook detailed morphological characterization of the Cln3 null mutant (Cln3(-/-)) mouse model of juvenile NCL (JNCL) that revealed a delayed onset neurodegenerative phenotype with no significant regional atrophy, but with widespread loss of hippocampal interneurons that was first evident at 14 months of age. Quantitative image analysis demonstrated upregulation of markers of astrocytic and microglial activation in presymptomatic Cln3(-/-) mice at 5 months of age, many months before significant neuronal loss occurs. These data provide evidence for subtle glial responses early in JNCL pathogenesis.

Regional and cellular neuropathology in the palmitoyl protein thioesterase-1 null mutant mouse model of infantile neuronal ceroid lipofuscinosis

Infantile neuronal ceroid lipofuscinosis (INCL) is one of a group of fatal hereditary lysosomal storage disorders. Palmitoyl protein thioesterase 1 null mutant mice (PPT1-/-) now exist that accurately recapitulate many important disease features. The severely affected PPT1-/- mouse CNS exhibited reduced volume of both cortical and subcortical regions, but with sparing of the cerebellum. Pronounced differences existed in the extent of cortical thinning between different regions, due to lamina-specific effects upon neuronal survival. A dramatic reduction in cortical and hippocampal interneuron number was also evident, with different extents of specific interneuron loss depending upon the region and phenotypic marker. These neuronal changes were accompanied by widespread astrocytosis and localized microglial activation in restricted cortical and subcortical regions. This characterization of PPT1-/- mice not only provides defined pathological landmarks for understanding disease pathogenesis, but also provides an invaluable resource for subsequently judging the efficacy of therapeutic strategies.

The mouse ortholog of the neuronal ceroid lipofuscinosis CLN5 gene encodes a soluble lysosomal glycoprotein expressed in the developing brain

Neuronal ceroid lipofuscinoses (NCLs) are recessively inherited neurodegenerative lysosomal storage disorders characterized by progressive motor and mental retardation, visual failure, and epileptic seizures. Finnish variant late infantile NCL (vLINCL(Fin)) is caused by mutations in the CLN5 gene. We have isolated the mouse Cln5 gene and analyzed its spatiotemporal expression in the central nervous system (CNS) by in situ hybridization and immunohistochemistry. Cln5 was expressed throughout the embryonic brain already at E15 and the expression steadily increased during development. Prominent expression was observed in cerebellar Purkinje cells, cerebral neurons, hippocampal pyramidal cells, and hippocampal interneurons. The expression pattern correlated with those CNS regions that get degenerated in CLN5 patients. In vitro expression of Cln5 in COS-1, HeLa, and neuronal cells further implied that mouse Cln5 is a soluble lysosomal glycoprotein, closely resembling human CLN5.

Selectivity and types of cell death in the neuronal ceroid lipofuscinoses

Cloning of the individual genes that are mutated in the neuronal ceroid lipofuscinoses (NCLs), or Batten disease, has opened up new avenues of research into the pathogenesis of these fatal autosomal recessive storage disorders. Genetically accurate mouse models have now been generated for each major form of the disorder, together with several variant forms. Ongoing analysis of these mice is revealing significant new data about the staging and progression of disease phenotypes. Combined with data from human autopsy tissues and large animal models, it is now clear that neurodegeneration is initially selective in the NCL CNS, targeting specific regions and particular cell populations. There is also evidence of selective glial activation that appears to precede obvious neurodegeneration, becoming more widespread with disease progression. Currently, there is debate over the mechanisms of cell death that operate in each form of NCL, with evidence of both apoptosis and autophagy. It is likely that these mechanisms may encompass a spectrum of cell death events, depending upon the specific context of each neuronal population. Taken together, these data have significant clinical implications for the development and targeting of appropriate therapeutic strategies, and for providing the landmarks to judge their efficacy.

Palmitoyl protein thioesterase 1 is targeted to the axons in neurons

Palmitoyl protein thioesterase 1 (PPT1) is a depalmitoylating enzyme whose deficiency leads to infantile neuronal ceroid lipofuscinosis. The disease is characterized by early loss of vision and massive neuronal death. Although PPT1 is expressed in many tissues, a deficiency of PPT1 damages neurons only in the cerebral and cerebellar cortexes and retina; other cell types remain relatively unaffected. We previously demonstrated that PPT1 is present in the synaptosomes and synaptic vesicles of neurons. To understand the crucial role of PPT1 for neuronal cells, we further investigated the expression and targeting of PPT1 in retinal, hippocampal, and cortical neurons during their maturation in culture. We found that PPT1 activity increases by neuronal maturation and is highest in retinal neuron cultures. In retinal neurons the expression of PPT1 precedes that of the synaptic vesicle protein 2 and synaptophysin, indicating a significant role for PPT1 in the early development of neuronal cells. We also found by quantitative confocal immunofluorescence microscopy that PPT1 is targeted preferably to axons in mature neurons, as indicated by its colocalization with the axonal marker microtubule-associated protein 1. In axons PPT1 is targeted specifically to axonal varicosities and presynaptic terminals, as indicated by its significant colocalization with growth-associated protein 43 and synaptophysin. Axonal localization of PPT1 was confirmed by double labeling with synaptophysin and postembedding immunoelectron microscopy. The polarized axonal targeting of PPT1 may well indicate a role for PPT1 in the exocytotic pathway of neurons.

Altered levels of high-energy phosphate compounds in fibroblasts from different forms of neuronal ceroid lipofuscinoses: further evidence for mitochondrial involvement

The pathogenesis of neurodegeneration in neuronal ceroid lipofuscinosis (NCL) is still not clear despite progress in mutation analysis of these diseases. We have recently observed anomalies at the level of the mitochondrial ATPsynthase (complex V of the respiratory chain) in fibroblasts from children with CLN1, CLN2, CLN3 and in an ovine model (OCL6). The measurements were carried out in vitro. If these alterations were of relevance in vivo as well, contents of high-energy phosphate compounds should be reduced. In the present study, we measured levels of creatine phosphate (CP), ATP, ADP and AMP in fibroblasts from children with CLN1, CLN2, CLN3 and in OCL6. ATP was reduced to about 50% of normal in CLN1, CLN2 and CLN3, ADP was about 30% of normal in these cells, and CP was 50% of normal in CLN1 and CLN2 but remained normal in CLN3. In fibroblasts of NCL-sheep, however, CP and ADP were increased to 690% and 220% of normal, respectively, while ATP remained normal. If the anomalies found in cellular energy metabolism in fibroblasts were expressed in neurons from NCL patients and NCL sheep 'slow-onset excitotoxicity' could occur leading to cellular dysfunction and eventually to cell death.

Apparent loss and hypertrophy of interneurons in a mouse model of neuronal ceroid lipofuscinosis: evidence for partial response to insulin-like growth factor-1 treatment

The neuronal ceroid lipofuscinoses (NCL) are progressive neurodegenerative disorders with onset from infancy to adulthood that are manifested by blindness, seizures, and dementia. In NCL, lysosomes accumulate autofluorescent proteolipid in the brain and other tissues. The mnd/mnd mutant mouse was first characterized as exhibiting adult-onset upper and lower motor neuron degeneration, but closer examination revealed early, widespread pathology similar to that seen in NCL. We used the autofluorescent properties of accumulated storage material to map which CNS neuronal populations in the mnd/mnd mouse show NCL-like pathological changes. Pronounced, early accumulation of autofluorescent lipopigment was found in subpopulations of GABAergic neurons, including interneurons in the cortex and hippocampus. Staining for phenotypic markers normally present in these neurons revealed progressive loss of staining in the cortex and hippocampus of mnd/mnd mice, with pronounced hypertrophy of remaining detectable interneurons. In contrast, even in aged mutant mice, many hippocampal interneurons retained staining for glutamic acid decarboxylase. Treatment with insulin-like growth factor-1 partially restored interneuronal number and reduced hypertrophy in some subregions. These results provide the first evidence for the involvement of interneurons in a mouse model of NCL. Moreover, our findings suggest that at least some populations of these neurons persist in a growth factor-responsive state.

Anomalies of mitochondrial ATP synthase regulation in four different types of neuronal ceroid lipofuscinosis

Several neuronal ceroid lipofuscinoses (NCL) show storage of subunit c of mitochondrial ATP synthase. The neurodegenerative process, however, remains obscure. We previously reported a decreased basal ATP synthase activity in fibroblasts from late-infantile NCL (CLN2) and juvenile NCL (CLN3) patients. We have now extended the study of the ATP synthase system to an ovine NCL (a model for the late-infantile NCL variant, CLN6) and the infantile NCL (CLN1). In fibroblasts from healthy sheep, active regulation of ATP synthase in response to cellular energy demand was present similar to human cells: ATP synthase was down-regulated under conditions of anoxia or functional uncoupling and was up-regulated in response to calcium. In fibroblasts from NCL sheep, basal ATP synthase activity was slightly elevated and down-regulation in response to anoxia or uncoupling of mitochondria also occurred. Calcium produced an unexpected down-regulation to 55% of basal activity. Activities of respiratory chain enzymes did not differ between healthy and NCL sheep. In fibroblasts from CLN1 patients, basal ATP synthase activity was reduced and regulation of the enzyme was absent. Activities of respiratory chain complexes II and IV were reduced. The defect of ATP synthase regulation found in fibroblasts from NCL sheep and infantile NCL patients is different from the ATP synthase deficiencies demonstrated in late-infantile and juvenile NCL, but problems of mitochondrial energy production, if also expressed in brain, would be a common feature of several NCL forms. Deficient ATP supply could result in degeneration of neurons, especially in those with high energy requirements.

Ovine ceroid lipofuscinosis (OCL6): postulated mechanism of neurodegeneration

It is proposed that ceroid lipofuscinosis in Southhampshire sheep (OCLSouthhampshire) be also known as OCL6 as it is syntenic with CLN6 of humans. Histopathological studies show a severe and progressive neurodegeneration of the cerebral cortex which sometimes appears to have a laminar pattern and which is accompanied by a severe midcortical astrocytosis. Other studies have shown that fibroblasts maintained in tissue culture have abnormal regulation of ATP synthase. If this was reflected in neurons, then selective neuron death is likely to be the result of energy-linked excitotoxicity of neurons receiving abundant glutamate input. Increased sensitivity of the NMDA receptor due to inefficient repolarization of the neuron membrane would allow increased cellular uptake of calcium, increased formation of free radicals, and neuron death. The general hypothesis, as developed for other chronic neurodegenerative diseases, is partly based on application of various drugs that block or mediate parts of the pathway involved. The same approach could be used to help test the hypothesis in OCL6 lambs and if successful some of the drugs might have therapeutic potential. As patterns of neurodegeneration are similar in various other forms of ceroid lipofuscinosis accumulating subunit c of mitochondrial ATP synthase, the model may have more general application than merely to CLN6.

The neuronal ceroid-lipofuscinoses

The neuronal ceroid lipofuscinoses (NCL) are a relatively frequent group of progressive neurodegenerative disorders in children with similar, but not identical, clinical and morphological features, entailing different clinical groups, some of which have been found to represent different genetic entities, ie, infantile (INCL) or CLN1, late-infantile (LINCL) or CLN2, juvenile (JNCL) or CLN3, and a Finnish variant of LINCL or CLN5. Within the clinical pentad are included seizures, motor disturbances, visual impairment, dementia, and familial occurrence in an autosomal-recessive fashion. The ultrastructure of accruing lipopigments is diagnostically required to recognize an individual patient's NCL by showing granular lipopigments in INCL, curvilinear profiles (with or without fingerprint profiles) in LINCL and fingerprint profiles (with or without curvilinear profiles) in JNCL. Identification of genes for INCL and JNCL, together with electron microscopy in LINCL, allows safe prenatal diagnosis which is still impossible by biochemical techniques, unlike other lysosomal disorders. However, both cause and pathogenesis of the individual forms of NCL are still unknown, and therapy is gravely insufficient.

The neuronal ceroid-lipofuscinoses

The neuronal ceroid-lipofuscinoses, a group of progressive neurodegenerative diseases in children and in adults, have now been recognized for some 90 years, and the childhood forms represent one of the largest groups of progressive neurodegenerative diseases in children. Apart from a core group of major clinical forms-the infantile, the late-infantile, the juvenile, and the adult forms--numerous atypical patients afflicted with neuronal ceroid-lipofuscinosis have now been identified, constituting 10% to 20% of all patients with neuronal ceroid-lipofuscinosis. These "atypical" patients have, over the past 10 years, prompted the suggestion of 15 atypical variants or minor syndromes, many of them displaying the lipopigments of classic curvilinear and fingerprint ultrastructure, but others displaying granular osmiophilic deposits. The former lipopigments contain the subunit C of the mitochondrial adenosine triphosphate synthase, but lipopigments of the granular osmiophilic deposits including the classic infantile type Santavuori-Haltia, apparently do not, the latter type exhibiting sphingolipid activator proteins. The nosologic significance of both the subunit C of the adenosine triphosphate synthase and the sphingolipid activator proteins, although they make up a considerable amount of the crude auto-fluorescent lipopigments in neuronal ceroid-lipofuscinosis, is still unclear. In spite of numerous pathogenetic principles invoked, such as a defect in lipid peroxidation, abnormalities of dolichols and dolichol phosphates, and defects in protease inhibitors, precise pathogenesis and etiology of the neuronal ceroid-lipofuscinoses remain elusive. Recent promising molecular genetic studies have, however, revealed the gene for infantile neuronal ceroid-lipofuscinosis, CLN1, on chromosome 1p32; the gene for juvenile neuronal ceroid-lipofuscinosis, CLN3, on chromosome 16p12.1-11.2; and the gene for a Finnish variant of late-infantile neuronal ceroid-lipofuscinosis, CLN5, on chromosome 13q31-32. The genes for classic late-infantile neuronal ceroid-lipofuscinosis, CLN2, and for adult neuronal ceroid-lipofuscinosis, CLN4, have not been located, the former having been excluded from chromosomes 1 and 16. However, the gene products of the normal allelic forms have not yet been identified. A considerable number of sporadic animal models is now available, largely equivalent to the juvenile and infantile forms of neuronal ceroid-lipofuscinosis, with those of the English setter and the South Hampshire sheep evaluated best. Recently, several mouse models have been added to this list of autosomal-recessive models, again the one most thoroughly studied being the motor-neuron disease mouse. Progress has also been made in the prenatal diagnosis of neuronal ceroid-lipofuscinosis: now the infantile, late-infantile, and juvenile forms can be recognized prenatally by a combined genetic and electron microscopic approach.

Diagnoses of neuronal ceroid-lipofuscinosis by immunochemical methods

The neuronal ceroid-lipofuscinoses (NCL), also known as Batten disease, are a not uncommon group of disorders affecting infants, children, and young adults. The abnormal ultrastructural profiles seen in NCL are used for standard diagnosis; however, they can be missed, and are also found in other neurodegenerative conditions. Furthermore, there is an overlap between the types of inclusion profiles among the different forms of NCL. Therefore, a more specific and biochemically-based marker is necessary to confirm the diagnosis of NCL. Antibodies raised against the storage material from the ovine form of NCL (mitochondrial ATP synthase subunit c) were utilized to determine whether NCL could be distinguished from other metabolic-neurodegenerative disorders. By immunoblotting and immunohistochemistry, several brain samples of well-evaluated NCL cases confirmed increased accumulations in all NCL cases except in the brain of an infantile-onset NCL patient. The immunoblot studies of skin fibroblasts and brain were sensitive but not highly specific to NCL, due to the recognition of this material in normal controls as well as in other neurogenetic diseases. Immunocytochemistry of skin fibroblasts clearly distinguished LINCL and JNCL cases from controls, and with further refinement has the potential for becoming a diagnostic tool.

Pigment variant of neuronal ceroid-lipofuscinosis

A 6-year-old girl had progressive ataxia, and visual disturbances resulting in blindness. She died in her sleep at age 22 years. She shared with her sister and paternal relatives bilateral pes cavus deformities and impaired deep-tendon reflexes which suggested Charcot-Marie-Tooth disease. Her sister, who also had both polyneuropathy and a progressive central nervous system (CNS) disease, did not have pigmentary retinopathy. At autopsy, the patient was found to have neuronal ceroid-lipofuscinosis (NCL) marked by intraneuronal accumulation of autofluorescent granular lipopigments in ballooned perikarya and conspicuous extraneuronal pigmentation of subcortical grey matter, but without axonal spheroids. These findings indicate a pigment variant of NCL and represent one of very few patients recorded. The ultrastructure of the intraneuronal pigments was uniformly granular, while that of the extraneuronal pigments found within processes of the neuropil and glial perikarya was more variegated. In addition to those patients with the pigment variant of NCL, described earlier by Jakob and Kolkmann [1973: Acta Neuropathol (Berl) 26:225-236], and Jervis and Pullarkat [1978: Neurology 28:500-503], our patient shared clinical symptoms with those described in a family afflicted with polyneuropathy and NCL by Wisniewski et al. [1987: J Child Neurol 2:33-41]. Currently, it is unclear whether they have similar atypical forms of juvenile NCL (JNCL). We conclude that the spectrum of pigment variants in lysosomal diseases is heterogeneous: only few and recently described patients have had NCL, while others most likely had other forms of lipidosis.

Comparative biology of the neuronal ceroid-lipofuscinoses (NCL): an overview

Multiple forms of ceroid-lipofuscinosis occur in human beings and animals. They are characterized by brain and retinal atrophy associated with selective necrosis of neurons. This neurodegenerative disease appears associated with the disease process rather than storage of fluorescent lipopigment per se, and there is now growing evidence that pathogenesis may involve mitochondria rather than a primary defect of lysosomal catabolism. Of the forms of ceroid-lipofuscinosis studied, most but not all reflect accumulation of subunit c of mitochondrial ATP synthase. If there is a common denominator between all forms other than the presence of fluorescent lipopigment, then it may be the accumulation of hydrophobic protein. Analogous diseases in animals can be expected to reflect the same spectrum of biochemical changes, and they warrant in-depth study to help understand the pathogenesis and heterogeneity of the group.

Morphological alterations in neocortical and cerebellar GABAergic neurons in a canine model of juvenile Batten disease

The pathogenesis of brain dysfunction in a canine model of juvenile Batten disease was studied with techniques designed to determine sequential changes in mitochondrial morphology and cytochrome oxidase (CO) activity, and in neurons and synapses using gamma-aminobutyric acid (GABA) as a neurotransmitter. Histochemical and immunocytochemical methods were employed. Mitochondrial alterations were found in a select population of nonpyramidal neurons in neocortex and claustrum, and in cerebellar basket cells. Proportions of affected neurons at any one time remained constant over the disease course, with morphologically-abnormal mitochondria first being recognized at age 6 months. Enlarged mitochondria were readily identifiable at the light microscope (LM) level as large CO-positive or mitochondrial antibody-positive granular structures. Colabelling with antibodies to GABA or to parvalbumin (PV) indicated that most of these cells were GABAergic. Ultrastructurally, atypical mitochondria were characterized by globular enlargement, intramitochondrial membranous inclusions, and disorganized internal structure. CO activity in all other cell somata and in neuropil was diminished compared with normal, age-matched tissue. Glutamic acid decarboxylase (GAD), PV, and GABA studies demonstrated loss of GABAergic neurons and synapses in cortex and cerebellum of affected dogs. These results indicate that abnormal mitochondria are present in neurons in Batten disease, and suggest that suboptimal mitochondrial function may play a role in the pathogenic mechanisms of brain dysfunction in this disorder.

The neuronal ceroid-lipofuscinoses (Batten disease): comparative aspects

The ceroid-lipofuscinoses are a group of inherited neurodegenerative diseases of human beings characterized by the accumulation of a fluorescent lipopigment in neurons and other cells within the body. There is usually atrophy of both brain and retina with preferential loss of particular neurons. Biochemically, the diseases divide into at least two groups, i.e. those that accumulate subunit c of mitochondrial ATP synthase and those that do not. Dolichol pyrophosphate linked oligosaccharides are also present in storage material. As the underlying biochemical anomalies are not known, the various clinicopathological entities are classified on clinical grounds, by age of onset and, to a lesser extent, by the course of the disease. The best recognized diseases are infantile, late infantile, early juvenile, juvenile and adult onset forms but other variants occur indicating considerable heterogeneity within the group. The infantile, late infantile and juvenile diseases are not allelic. Analogous diseases occur in a variety of animal species. That in the sheep has been extensively studied as a model of the human disease and is the prototype subunit c storage disease.

Routes of excretion of neuronal lysosomal dense bodies after ventricular infusion of leupeptin in the rat: a study using ubiquitin and PGP 9.5 immunocytochemistry

To determine the rate and routes of removal of lysosomal, lipofuscin-like dense bodies from neurons, the protease inhibitor, leupeptin, was infused into the lateral ventricle of rats for up to nine days. After seven days a number of animals were then allowed to recover. The formation and later disappearance of dense bodies was followed by morphology and immunocytochemistry. After 48 h of infusion lysosomal dense bodies in large numbers appeared in cortical, hippocampal and cerebellar neurons, which also showed increased ubiquitin immunoreactivity, as well as in other cell types. By 3-4 days ubiqutin-immunoreactive dense bodies were equally distributed between neurons and astroglia. After seven to nine days of infusion ubiquitin immunoreactive dense bodies filled neuronal perikarya, dendrites and expanded initial segments of many axons and were abundant in glial processes. All dense bodies studied by electron microscopy were ubiquitin immunoreactive. After four days of recovery dense bodies were markedly fewer in neuronal perikarya, and virtually all were now within glial processes. From 7 to 28 days of recovery, when most neurons appeared normal, lipofuscin bodies remained in axon initial segments and in reduced numbers in glial processes, particularly around blood vessels and beneath the pia of hippocampus and of cerebellar cortex. Thus, neurons probably have a steady passage of short lived proteins through the lysosomal excretory pathway. The observed temporal sequence of events on recovery suggests that secondary lysosomes probably pass rapidly from neuronal perikarya and dendrites to astrocytes and thus to the vascular bed or pia-arachnoid. The mechanism of cell-to-cell transfer is not clear from this study.

Neuronal ceroid-lipofuscinoses: the current status

In view of the epidemiological connotation of childhood neuronal ceroid-lipofuscinosis (NCL) as one of the most frequent progressive lysosomal diseases and neurodegenerative disorders in children, the recognition of the individual clinical forms of childhood NCL is still based on invasive diagnostic electronmicroscopy which, currently, may be applied also for prenatal diagnosis. Like other inherited disorders, the NCL group has finally also benefited from the genetic breakthroughs of localization of the genes for infantile NCL and juvenile NCL on chromosomes 1 and 16, respectively. This review concerns recent advances in morphological studies, broadening of the clinical spectrum of childhood NCL, new biochemical findings, and preliminary therapeutic results. Hereditary animal models, largely for human juvenile NCL, have been successfully employed in elucidation of the nosology of NCL, but the basic defect in human, canine and ovine NCL remains unknown.

Lectin histochemistry in brains with juvenile form of neuronal ceroid-lipofuscinosis (Batten disease)

Defective utilization of dolichols in the synthesis of glycoprotein leads to an accumulation of the storage, pigment "ceroid" lipofuscin, containing high-mannose-type glycoconjugates, in brains affected by neuronal ceroid-lipofuscinoses (NCL). We have employed lectin histochemistry to study the distribution of such compounds and the composition of other glycoconjugates in brains of patients with a juvenile form of the disease (JNCL). Concanavalin A detected the high-mannose glycoconjugates in all neurons of brains with JNCL, in lipofuscin-containing neurons of aging brains and in some neurons of age-matched control brains. Three other lectins (soybean agglutinin, Peanut agglutinin and Ulex europaeus agglutinin-I) recognized sugar moieties in neurons containing lipofuscin in patients only with JNCL and not in age-matched or aging brains. The results led to the conclusion, that the binding pattern of these three lectins may differentiate between storage materials of NCL and aging brains.

Neuronal types in the claustrum of man

Neuronal types of the human claustrum have been investigated by means of a transparent Golgi technique which enables one to study the characteristics of not only the cellular processes but also the marking features of the nuclei, the cellular organelles, and the paraplasmic substances of various types of nerve cells. Five varieties of neurons have been distinguished: Type I represents a class of spiny nerve cells varying to a certain extent in size and shape. These cells contain fine and widely dispersed lipofuscin granules which can only faintly be tinged by aldehydefuchsin. Type II cells are large aspiny neurons. Their cell bodies contain a great number of deeply stained coarse pigment granules. Type III cells are large aspiny neurons devoid of pigment deposits. Type IV is a small pigment-laden aspiny neuron. Type V is a small aspiny neuron devoid of lipofuscin granules. The pattern of pigmentation revealed by the different types of nerve cells turns out to be highly characteristic. It can well be used for classification of the various types of nerve cells which occur within the reaches of the claustrum.

Pigmentoarchitectonic pathology of the isocortex in juvenile neuronal ceroid-lipofuscinosis: axonal enlargements in layer IIIab and cell loss in layer V

Pigment preparations of 800 micrometer thickness and Golgi studies of the isocortex in juvenile neuronal ceroid-lipofuscinosis, morphologically proven by electron microscopy, revealed: 1. giant axonal dilatations of IIIab-pyramids. These expansions exceeded by far those found in pyramidal cell axons of other isocortical layers. 2. severe numerical reduction of neurons in the ganglionic layer.