Molecular genetics of the NCLs -- status and perspectives

Intraventricular Cerliponase Alfa Treatment in a Patient with Advanced Neuronal Ceroid Lipofuscinosis Type 2

Neuronal ceroid lipofuscinosis type 2 (CLN2) is an autosomal recessive lysosomal disease caused by decreased activity of the enzyme tripeptidyl peptidase 1 (TPP1) due to pathogenic variants in the TPP1 gene. Cerliponase alfa, a recombinant proenzyme form of TPP1, has shown efficacy in preventing motor and language function decline in early-stage CLN2. However, the safety and effects of this therapy in advanced-stage CLN2 are unclear. We herein report a case of intraventricular cerliponase alfa treatment for over a year in a patient with advanced-stage CLN2. The results suggest the safety and potential efficacy of treatment at an advanced stage of CLN2.

Clinical features of two Japanese siblings of neuronal ceroid lipofuscinosis type 1 (CLN1) complicated with TypeⅡ diabetes mellitus

Neuronal ceroid lipofuscinosis type1(CLN1), is a one form of the group of neuronal ceroid lipofuscinoses (NCLs), which is a neurodegenerative disorder characterized by progressive psychomotor deterioration, ataxia, epilepsy, and visual impairment. Neurological manifestations occur at a wide range of ages, from infancy to adulthood, but are most common in infancy. The prevalence of CLN1 is unclear; however, it is very rare in Japan and Europe. In Japan, only a few cases have been reported, two of infantile- and one of juvenile-onset type. Nonetheless, the clinical characteristics of Japanese patients and their relationship with the genotype have not been sufficiently investigated. Here, we report the cases of two siblings that presented with juvenile-onset (a 22-year-old man and a 29-year-old woman) CLN1 associated with type II diabetes mellitus. In both cases, visual impairment followed by learning disability was observed from school-age, and retinitis pigmentosa was noted on ophthalmological examination. These patients presented type II diabetes mellitus during their later teenage years. Brain magnetic resonance imaging (MRI) revealed marked atrophy of the cerebrum and cerebellum. The clinical symptoms lead to suspect NCLs. Decreased PPT1 enzyme activity in dried blood spot (DBS)and leukocytes were observed, and the genetic analysis revealed heterozygous missense variants in PPT1, c.550G > A/c.664 A > G (p. Glu184Lys/p. Lys216Glu). The latter variant of this patients was novel variant. The residual enzymatic activity of PPT1 in these cases is higher than that in the infantile type. CLN1 mutant cells are known to have altered subcellular expression and localization, enhanced lipid raft-mediated endocytosis, abnormal autophagy, and mitochondrial dysfunction. Although the prevalence of diabetes mellitus is high and the possibility of coincidental complications cannot be ruled out, we concluded that mitochondrial abnormalities are involved in insulin resistance and may be implicated in the development of type II diabetes mellitus. Further studies are needed to prove the correlation between CLN1 and diabetes mellitus.

Phenotypic Variability of Retinal Disease Among a Cohort of Patients With Variants in the CLN Genes

Purpose

To describe the phenotype of CLN-associated retinal dystrophy in a subset of patients at the Columbia University Medical Center, United States, and the Hospital das Clínicas de Pernambuco, Brazil, in comparison to the published literature.

Methods

Eleven patients with confirmed biallelic variants in the CLN genes were evaluated via dilated fundus examination, clinical imaging, and full-field electroretinogram. A thorough literature search was conducted to determine previously published variants and associated phenotypes.

Results

Genetic testing confirmed the presence of variants in CLN3, CLN7/MFSD8, CLN8, and GRN/CLN11. Five novel variants were identified, and four novel phenotypes of previously published alleles were described. The phenotype differed among patients with variants in the same gene and sometimes among patients with the same allele.

Conclusions

Substantial phenotypic variability among variants in the CLN genes makes identification of genotype-phenotype or allele-phenotype correlations challenging. Further study is required to establish an extensive database for adequate patient counseling.

A novel deletion variant in CLN3 with highly variable expressivity is responsible for juvenile neuronal ceroid lipofuscinoses

Mutations in CLN3 (OMIM: 607042) are associated with juvenile neuronal ceroid lipofuscinoses (JNCL)-a rare neurodegenerative disease with early retinal degeneration and progressive neurologic deterioration. The study aimed to determine the underlying genetic factors justifying the NCL phenotype in a large Iraqi consanguineous family. Four affected individuals with an initial diagnosis of NCL were recruited. By doing neuroimaging and also pertinent clinical examinations, e.g. fundus examination, due to heterogeneity of neurodevelopmental disorders, the proband was subjected to the paired-end whole-exome sequencing to identify underlying genetic factors. The candidate variant was also confirmed by Sanger sequencing. Various in silico predictions were used to show the pathogenicity of the variant. This study revealed a novel homozygous frameshift variant-NM_000086.2: c.1127del; p.(Leu376Argfs*15)-in the exon 14 of the CLN3 gene as the most likely disease-causing variant. Three out of 4 patients showed bilateral vision loss (< 7 years) and retinal degeneration with macular changes in both eyes. Electroencephalography demonstrated the loss of normal posterior alpha rhythm and also low amplitude multifocal slow waves. Brain magnetic resonance imaging of the patients with a high degree of deterioration showed mild cerebral and cerebellar cortical atrophy, mild ventriculomegaly, thinning of the corpus callosum and vermis, and non-specific periventricular white matter signal changes in the occipital area. The novel biallelic deletion variant of CLN3 was identified that most probably led to JNCL with variable expressivity of the phenotype. This study also expanded our understanding of the clinical and genetic spectrum of JNCL.

A tailored mouse model of CLN2 disease: A nonsense mutant for testing personalized therapies

The Neuronal Ceroid Lipofuscinoses (NCLs), also known as Batten disease, result from mutations in over a dozen genes. Although, adults are susceptible, the NCLs are frequently classified as pediatric neurodegenerative diseases due to their greater pediatric prevalence. Initial clinical presentation usually consists of either seizures or retinopathy but develops to encompass both in conjunction with declining motor and cognitive function. The NCLs result in premature death due to the absence of curative therapies. Nevertheless, preclinical and clinical trials exist for various therapies. However, the genotypes of NCL animal models determine which therapeutic approaches can be assessed. Mutations of the CLN2 gene encoding a soluble lysosomal enzyme, tripeptidyl peptidase 1 (TPP1), cause late infantile NCL/CLN2 disease. The genotype of the original mouse model of CLN2 disease, Cln2^-/-, excludes mutation guided therapies like antisense oligonucleotides and nonsense suppression. Therefore, the purpose of this study was to develop a model of CLN2 disease that allows for the assessment of all therapeutic approaches. Nonsense mutations in CLN2 disease are frequent, the most common being CLN2^R208X. Thus, we created a mouse model that carries a mutation equivalent to the human p.R208X mutation. Molecular assessment of Cln2^R207X/R207X tissues determined significant reduction in Cln2 transcript abundance and TPP1 enzyme activity. This reduction leads to the development of neurological impairment (e.g. tremors) and neuropathology (e.g. astrocytosis). Collectively, these assessments indicate that the Cln2^R207X/R207X mouse is a valid CLN2 disease model which can be used for the preclinical evaluation of all therapeutic approaches including mutation guided therapies.

The neuronal ceroid lipofuscinoses: Opportunities from model systems

The neuronal ceroid lipofuscinoses are a group of severe and progressive neurodegenerative disorders, generally with childhood onset. Despite the fact that these diseases remain fatal, significant breakthroughs have been made in our understanding of the genetics that underpin these conditions. This understanding has allowed the development of a broad range of models to study disease processes, and to develop new therapeutic approaches. Such models have contributed significantly to our knowledge of these conditions. In this review we will focus on the advantages of each individual model, describe some of the contributions the models have made to our understanding of the broader disease biology and highlight new techniques and approaches relevant to the study and potential treatment of the neuronal ceroid lipofuscinoses. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)".

Mice homozygous for c.451C>T mutation in Cln1 gene recapitulate INCL phenotype

Objective

Nonsense mutations account for 5–70% of all genetic disorders. In the United States, nonsense mutations in the CLN1/PPT1 gene underlie >40% of the patients with infantile neuronal ceroid lipofuscinosis (INCL), a devastating neurodegenerative lysosomal storage disease. We sought to generate a reliable mouse model of INCL carrying the most common Ppt1 nonsense mutation (c.451C>T) found in the United States patient population to provide a platform for evaluating nonsense suppressors in vivo.

Methods

We knocked-in c.451C>T nonsense mutation in the Ppt1 gene in C57 embryonic stem (ES) cells using a targeting vector in which LoxP flanked the Neo cassette, which was removed from targeted ES cells by electroporating Cre. Two independently targeted ES clones were injected into blastocysts to generate syngenic C57 knock-in mice, obviating the necessity for extensive backcrossing.

Results

Generation of Ppt1-KI mice was confirmed by DNA sequencing, which showed the presence of c.451C>T mutation in the Ppt1 gene. These mice are viable and fertile, although they developed spasticity (a “clasping” phenotype) at a median age of 6 months. Autofluorescent storage materials accumulated throughout the brain regions and in visceral organs. Electron microscopic analysis of the brain and the spleen showed granular osmiophilic deposits. Increased neuronal apoptosis was particularly evident in cerebral cortex and abnormal histopathological and electroretinographic (ERG) analyses attested striking retinal degeneration. Progressive deterioration of motor coordination and behavioral parameters continued until eventual death.

Interpretation

Our findings show that Ppt1-KI mice reliably recapitulate INCL phenotype providing a platform for testing the efficacy of existing and novel nonsense suppressors in vivo.

Oral cysteamine bitartrate and N-acetylcysteine for patients with infantile neuronal ceroid lipofuscinosis: a pilot study

BACKGROUND

Infantile neuronal ceroid lipofuscinosis is a devastating neurodegenerative lysosomal storage disease caused by mutations in the gene (CLN1 or PPT1) encoding palmitoyl-protein thioesterase-1 (PPT1). We have previously reported that phosphocysteamine and N-acetylcysteine mediate ceroid depletion in cultured cells from patients with this disease. We aimed to assess whether combination of oral cysteamine bitartrate and N-acetylcysteine is beneficial for patients with neuronal ceroid lipofuscinosis.

METHODS

Children between 6 months and 3 years of age with infantile neuronal ceroid lipofuscinosis with any two of the seven most lethal PPT1 mutations were eligible for inclusion in this pilot study. All patients were recruited from physician referrals. Patients received oral cysteamine bitartrate (60 mg/kg per day) and N-acetylcysteine (60 mg/kg per day) and were assessed every 6-12 months until they had an isoelectric electroencephalogram (EEG, attesting to a vegetative state) or were too ill to travel. Patients were also assessed by electroretinography, brain MRI and magnetic resonance spectroscopy (MRS), and electron microscopic analyses of leukocytes for granular osmiophilic deposits (GRODs). Children also underwent physical and neurodevelopmental assessments on the Denver scale. Outcomes were compared with the reported natural history of infantile neuronal ceroid lipofuscinosis and that of affected older siblings. This trial is registered with ClinicalTrials.gov, number NCT00028262.

FINDINGS

Between March 14, 2001, and June 30, 2012, we recruited ten children with infantile neuronal ceroid lipofuscinosis; one child was lost to follow-up after the first visit and nine patients (five girls and four boys) were followed up for 8 to 75 months. MRI showed abnormalities similar to those in previous reports; brain volume and N-acetyl aspartic acid (NAA) decreased steadily, but no published quantitative MRI or MRS studies were available for comparison. None of the children acquired new developmental skills, and their retinal function decreased progressively. Average time to isoelectric EEG (52 months, SD 13) was longer than reported previously (36 months). At the first follow-up visit, peripheral leukocytes in all nine patients showed virtually complete depletion of GRODs. Parents and physicians reported less irritability, improved alertness, or both in seven patients. No treatment-related adverse events occurred apart from mild gastrointestinal discomfort in two patients, which disappeared when liquid cysteamine bitartrate was replaced with capsules.

INTERPRETATION

Our findings suggest that combination therapy with cysteamine bitartrate and N-acetylcysteine is associated with delay of isoelectric EEG, depletion of GRODs, and subjective benefits as reported by parents and physicians. Our systematic and quantitative report of the natural history of patients with infantile neuronal ceroid lipofuscinosis provides a guide for future assessment of experimental therapies.

FUNDING

National Institutes of Health.

A murine model of variant late infantile ceroid lipofuscinosis recapitulates behavioral and pathological phenotypes of human disease

Neuronal ceroid lipofuscinoses (NCLs; also known collectively as Batten Disease) are a family of autosomal recessive lysosomal storage disorders. Mutations in as many as 13 genes give rise to ∼10 variants of NCL, all with overlapping clinical symptomatology including visual impairment, motor and cognitive dysfunction, seizures, and premature death. Mutations in CLN6 result in both a variant late infantile onset neuronal ceroid lipofuscinosis (vLINCL) as well as an adult-onset form of the disease called Type A Kufs. CLN6 is a non-glycosylated membrane protein of unknown function localized to the endoplasmic reticulum (ER). In this study, we perform a detailed characterization of a naturally occurring Cln6 mutant (Cln6^nclf) mouse line to validate its utility for translational research. We demonstrate that this Cln6^nclf mutation leads to deficits in motor coordination, vision, memory, and learning. Pathologically, we demonstrate loss of neurons within specific subregions and lamina of the cortex that correlate to behavioral phenotypes. As in other NCL models, this model displays selective loss of GABAergic interneuron sub-populations in the cortex and the hippocampus with profound, early-onset glial activation. Finally, we demonstrate a novel deficit in memory and learning, including a dramatic reduction in dendritic spine density in the cerebral cortex, which suggests a reduction in synaptic strength following disruption in CLN6. Together, these findings highlight the behavioral and pathological similarities between the Cln6^nclf mouse model and human NCL patients, validating this model as a reliable format for screening potential therapeutics.

Progressive retinal degeneration and glial activation in the CLN6 (nclf) mouse model of neuronal ceroid lipofuscinosis: a beneficial effect of DHA and curcumin supplementation

Neuronal ceroid lipofuscinosis (NCL) is a group of neurodegenerative lysosomal storage disorders characterized by vision loss, mental and motor deficits, and spontaneous seizures. Neuropathological analyses of autopsy material from NCL patients and animal models revealed brain atrophy closely associated with glial activity. Earlier reports also noticed loss of retinal cells and reactive gliosis in some forms of NCL. To study this phenomenon in detail, we analyzed the ocular phenotype of CLN6^nclf mice, an established mouse model for variant-late infantile NCL. Retinal morphometry, immunohistochemistry, optokinetic tracking, electroretinography, and mRNA expression were used to characterize retinal morphology and function as well as the responses of Müller cells and microglia. Our histological data showed a severe and progressive degeneration in the CLN6^nclf retina co-inciding with reactive Müller glia. Furthermore, a prominent phenotypic transformation of ramified microglia to phagocytic, bloated, and mislocalized microglial cells was identified in CLN6^nclf retinas. These events overlapped with a rapid loss of visual perception and retinal function. Based on the strong microglia reactivity we hypothesized that dietary supplementation with immuno-regulatory compounds, curcumin and docosahexaenoic acid (DHA), could ameliorate microgliosis and reduce retinal degeneration. Our analyses showed that treatment of three-week-old CLN6^nclf mice with either 5% DHA or 0.6% curcumin for 30 weeks resulted in a reduced number of amoeboid reactive microglia and partially improved retinal function. DHA-treatment also improved the morphology of CLN6^nclf retinas with a preserved thickness of the photoreceptor layer in most regions of the retina. Our results suggest that microglial reactivity closely accompanies disease progression in the CLN6^nclf retina and both processes can be attenuated with dietary supplemented immuno-modulating compounds.

Regional brain atrophy in mouse models of neuronal ceroid lipofuscinosis: a new rostrocaudal perspective

The neuronal ceroid lipofuscinoses (Batten disease) are collectively the most common inherited neurodegenerative disorder of childhood. Mouse models of neuronal ceroid lipofuscinosis represent a powerful resource for investigating the underlying disease mechanisms, which remain poorly understood. Here we present a new rostrocaudal analysis of regional brain volume rather than focusing on central nervous system structures that can be affected. This has revealed an earlier onset of regional atrophy than was suspected in infantile neuronal ceroid lipofuscinosis (or CLN1 disease, infantile), with a greater involvement of rostral structures. We have also provided the first description of regional atrophy in severely affected mice with the juvenile variant (CLN3 disease, juvenile). These data reveal new perspectives on how the central nervous system is affected in these disorders, which have implications for judging the efficacy of therapeutic strategies in preclinical studies.

The role of nonsense-mediated decay in neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinosis (NCL), commonly referred to as Batten disease, is a group of autosomal recessive neurodegenerative diseases of childhood characterized by seizures, blindness, motor and cognitive decline and premature death. Currently, there are over 400 known mutations in 14 different genes, leading to five overlapping clinical variants of NCL. A large portion of these mutations lead to premature stop codons (PTCs) and are predicted to predispose mRNA transcripts to nonsense-mediated decay (NMD). Nonsense-mediated decay is associated with a number of other genetic diseases and is an important regulator of disease pathogenesis. We contend that NMD targets PTCs in NCL gene transcripts for degradation. A number of PTC mutations in CLN1, CLN2 and CLN3 lead to a significant decrease in mRNA transcripts and a corresponding decrease in protein levels and function in patient-derived lymphoblast cell lines. Inhibiting NMD leads to an increased transcript level, and where protein function is known, increased activity. Treatment with read-through drugs also leads to increased protein function. Thus, NMD provides a promising therapeutic target that would allow read-through of transcripts to enhance protein function and possibly ameliorate Batten disease pathogenesis.

Biometals in rare neurodegenerative disorders of childhood

Copper, iron, and zinc are just three of the main biometals critical for correct functioning of the central nervous system (CNS). They have diverse roles in many functional processes including but not limited to enzyme catalysis, protein stabilization, and energy production. The range of metal concentrations within the body is tightly regulated and when the balance is perturbed, debilitating effects ensue. Homeostasis of brain biometals is mainly controlled by various metal transporters and metal sequestering proteins. The biological roles of biometals are vastly reviewed in the literature with a large focus on the connection to neurological conditions associated with ageing. Biometals are also implicated in a variety of debilitating inherited childhood disorders, some of which arise soon following birth or as the child progresses into early adulthood. This review acts to highlight what we know about biometals in childhood neurological disorders such as Wilson's disease (WD), Menkes disease (MD), neuronal ceroid lipofuscinoses (NCLs), and neurodegeneration with brain iron accumulation (NBIA). Also discussed are some of the animal models available to determine the pathological mechanisms in these childhood disorders, which we hope will aid in our understanding of the role of biometals in disease and in attaining possible therapeutics in the future.

Diagnosis of neuronal ceroid lipofuscinosis: mutation detection strategies

The neuronal ceroid lipofuscinoses (NCL) are a group of rare genetically inherited neurodegenerative disorders in children. These diseases are classified by age of onset (congenital, infantile, late-infantile, juvenile and adult-onset) and by the gene bearing mutations (CLN10/CTSD, CLN1/PPT1, CLN2/TPP1, CLN3, CLN5, CLN6, CLN7/MFSD8 and CLN8). Enzyme activity assays are helpful in identifying several of these disorders; however confirmation of the mutation in the gene causing these diseases is vital for definitive diagnosis. There exists considerable heterogeneity in the NCLs as a whole and within each type of NCL both in phenotype (disease manifestation and progression) and genotype (type of mutation), which complicates NCL diagnosis. In order to streamline the diagnostic process, the age of symptom onset, geography and/or ethnicity, and enzyme activity may be considered together. However, these ultimately serve to guide targeting the correct route to genetic confirmation of an NCL through mutational analysis. Herein, an effective protocol to diagnose NCLs using these criteria is presented.

Neuronal ceroid lipofuscinosis type CLN2: a new rationale for the construction of phenotypic subgroups based on a survey of 25 cases in South America

Tripeptidyl-peptidase 1 (TPP1) null or residual activity occurs in neuronal ceroid lipofuscinosis (NCL) with underlying TPP1/CLN2 mutations. A survey of 25 South American CLN2 affected individuals enabled the differentiation of two phenotypes: classical late-infantile and variant juvenile, each in approximately 50% of patients, with residual TPP1 activity occurring in approximately 32%. Each individual was assigned to one of three subgroups: (I) n=11, null TPP1 activity in leukocytes; (II) n=8, residual TPP1 activity of 0.60-15.85 nmol/h/mg (nr 110-476); (III) n=6, activity not measured in leukocytes. Curvilinear bodies (CB) appeared in almost all studied CLN2 subjects; the only exceptions occurred in cases of subgroup II: two individuals had combined CBs/fingerprints (FPs), and one case had pure FPs. There were 15 mutations (4 first published in this paper, 3 previously observed in South America by our group, and 8 previously observed by others). In subgroup I, mutations were either missense or nonsense; in subgroups II and III, mutations prevailed at the non-conserved intronic site, c.887-10A>G (intron 7), and to a lesser extent at c.89+5G>C (intron 2), in heterozygous combinations. Grouping phenotypically and genetically known individuals on the basis of TPP1 activity supported the concept that residual enzyme activity underlies a protracted disease course. The prevalence of intronic mutations at non-conserved sites in subgroup II individuals indicates that some alternative splicing might allow some residual TPP1 activity.

Molecular epidemiology of childhood neuronal ceroid-lipofuscinosis in Italy

Background

To review the descriptive epidemiological data on neuronal ceroid lipofuscinoses (NCLs) in Italy, identify the spectrum of mutations in the causative genes, and analyze possible genotype-phenotype relations.

Methods

A cohort of NCL patients was recruited through CLNet, a nationwide network of child neurology units. Diagnosis was based on clinical and pathological criteria following ultrastructural investigation of peripheral tissues. Molecular confirmation was obtained during the diagnostic procedure or, when possible, retrospectively.

Results

One hundred eighty-three NCL patients from 156 families were recruited between 1966 and 2010; 124 of these patients (from 88 families) were tested for known NCL genes, with 9.7% of the patients in this sample having not a genetic diagnosis. Late infantile onset NCL (LINCL) accounted for 75.8% of molecularly confirmed cases, the most frequent form being secondary to mutations in CLN2 (23.5%). Juvenile onset NCL patients accounted for 17.7% of this cohort, a smaller proportion than found in other European countries. Gene mutations predicted severe protein alterations in 65.5% of the CLN2 and 78.6% of the CLN7 cases. An incidence rate of 0.98/100,000 live births was found in 69 NCL patients born between 1992 and 2004, predicting 5 new cases a year. Prevalence was 1.2/1,000,000.

Conclusions

Descriptive epidemiology data indicate a lower incidence of NCLs in Italy as compared to other European countries. A relatively high number of private mutations affecting all NCL genes might explain the genetic heterogeneity. Specific gene mutations were associated with severe clinical courses in selected NCL forms only.

Use of model organisms for the study of neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinoses are a group of fatal progressive neurodegenerative diseases predominantly affecting children. Identification of mutations that cause neuronal ceroid lipofuscinosis, and subsequent functional and pathological studies of the affected genes, underpins efforts to investigate disease mechanisms and identify and test potential therapeutic strategies. These functional studies and pre-clinical trials necessitate the use of model organisms in addition to cell and tissue culture models as they enable the study of protein function within a complex organ such as the brain and the testing of therapies on a whole organism. To this end, a large number of disease models and genetic tools have been identified or created in a variety of model organisms. In this review, we will discuss the ethical issues associated with experiments using model organisms, the factors underlying the choice of model organism, the disease models and genetic tools available, and the contributions of those disease models and tools to neuronal ceroid lipofuscinosis research. This article is part of a Special Issue entitled: The Neuronal Ceroid Lipofuscinoses or Batten Disease.

Cln5-deficiency in mice leads to microglial activation, defective myelination and changes in lipid metabolism

CLN5 disease, late infantile variant phenotype neuronal ceroid lipofuscinosis, is a severe neurodegenerative disease caused by mutations in the CLN5 gene, which encodes a lysosomal protein of unknown function. Cln5-deficiency in mice leads to loss of thalamocortical neurons, and glial activation, but the underlying mechanisms are poorly understood. We have now studied the gene expression of Cln5 in the mouse brain and show that it increases gradually with age and differs between neurons and glia, with the highest expression in microglia. In Cln5(-/-) mice, we documented early and significant microglial activation that was already evident at 3 months of age. Loss of Cln5 also leads to defective myelination in vitro and in the developing mouse brain. This was accompanied by early alterations in serum lipid profiles, dysfunctional cellular metabolism and lipid transport in Cln5(-/-) mice. Taken together, these data provide significant new information about events associated with Cln5-deficiency, revealing altered myelination and disturbances in lipid metabolism, together with an early neuroimmune response.

Evaluation of neurodegeneration in a mouse model of infantile batten disease by magnetic resonance imaging and magnetic resonance spectroscopy

Neuronal ceroid lipofuscinoses (NCLs) represent a group of common hereditary childhood neurodegenerative storage disorders that have no effective treatment. Mutations in eight different genes cause various forms of NCLs. Infantile NCL (INCL), the most lethal disease, is caused by inactivating mutations in the palmitoyl-protein thioesterase-1 (PPT1) gene. The availability of Ppt1-knockout (Ppt1-KO) mice, which recapitulate virtually all clinical and pathological features of INCL, provides an opportunity to test the effectiveness of novel therapeutic strategies in vivo. However, such studies will require noninvasive methods that can be used to perform serial evaluations of the same animal receiving an experimental therapy. Thus, the development of noninvasive method(s) of evaluation is urgently needed. Here, we report our evaluation of the progression of neurodegeneration in Ppt1-KO mice starting at 3 months of age by MRI and MR spectroscopy (MRS) and repeating these tests using the same mice at 4, 5 and 6 months of age. Our results showed progressive cerebral atrophy, which was associated with histological loss of neuronal content and increase in astroglia. Remarkably, while the brain volumes in Ppt1-KO mice progressively declined with advancing age, the MRS signals, which were significantly lower than those of their wild-type littermates, remained virtually unchanged from 3 to 6 months of age. In addition, our results also showed an abnormality in cerebral blood flow in these mice, which showed progression with age. Our findings provide methods to serially examine the brains of mouse models of neurodegenerative diseases (e.g. Ppt1-KO mice) using noninvasive and nonlethal procedures such as MRI and MRS. These methods may be useful in studies to understand the progression of neuropathology in animal models of neurodegenerative diseases as they allow repeated evaluations of the same animal in which experimental therapies are tested.

Brain transcriptome perturbations in the Hfe(-/-) mouse model of genetic iron loading

Severe disruption of brain iron homeostasis can cause fatal neurodegenerative disease, however debate surrounds the neurologic effects of milder, more common iron loading disorders such as hereditary hemochromatosis, which is usually caused by loss-of-function polymorphisms in the HFE gene. There is evidence from both human and animal studies that HFE gene variants may affect brain function and modify risks of brain disease. To investigate how disruption of HFE influences brain transcript levels, we used microarray and real-time reverse transcription polymerase chain reaction to assess the brain transcriptome in Hfe(-/-) mice relative to wildtype AKR controls (age 10 weeks, n≥4/group). The Hfe(-/-) mouse brain showed numerous significant changes in transcript levels (p<0.05) although few of these related to proteins directly involved in iron homeostasis. There were robust changes of at least 2-fold in levels of transcripts for prominent genes relating to transcriptional regulation (FBJ osteosarcoma oncogene Fos, early growth response genes), neurotransmission (glutamate NMDA receptor Grin1, GABA receptor Gabbr1) and synaptic plasticity and memory (calcium/calmodulin-dependent protein kinase IIα Camk2a). As previously reported for dietary iron-supplemented mice, there were altered levels of transcripts for genes linked to neuronal ceroid lipofuscinosis, a disease characterized by excessive lipofuscin deposition. Labile iron is known to enhance lipofuscin generation which may accelerate brain aging. The findings provide evidence that iron loading disorders can considerably perturb levels of transcripts for genes essential for normal brain function and may help explain some of the neurologic signs and symptoms reported in hemochromatosis patients.

Late infantile neuronal ceroid lipofuscinosis and dopamine deficiency

Neuronal ceroid lipofuscinosis is a severe neurodegenerative lysosomal storage disorder. Gamma-aminobutyric acid and glutamate deficiency have been reported with CLN1, CLN3, and CLN6. Isolated biopterin/neopterin without dopamine deficiency has been reported in 1 patient with a CLN2 mutation. This report describes a patient with a CLN2 mutation with symptomatic biopterin and dopamine deficiency. A 4-year-old boy presented with intractable epilepsy and developmental regression starting 1 year previously. His exam showed retinopathy, scanning speech, dysmetria, and ataxic fenestrating gait with stooped posture. Electroencephalogram showed generalized spikes with occipital spikes on slow photic stimulation. Brain magnetic resonance images 1 year apart showed significant diffuse atrophy. CLN2 gene sequencing showed pathogenic compound heterozygous mutations. Cerebrospinal fluid neurotransmitters showed low homovanillic acid and tetrahydrobiopterin. Levodopa-carbidopa resulted in dramatic improvement of gait. Dopamine/biopterin deficiency is a possible secondary manifestation of CLN2 mutations. Levodopa and dopamine agonists might be useful in treating these secondary abnormalities and improving quality of life in these patients.

Intrathecal tripeptidyl-peptidase 1 reduces lysosomal storage in a canine model of late infantile neuronal ceroid lipofuscinosis

Late infantile neuronal ceroid lipofuscinosis (LINCL) is caused by mutations in the gene encoding tripeptidyl-peptidase 1 (TPP1). LINCL patients accumulate lysosomal storage materials in the CNS accompanied by neurodegeneration, blindness, and functional decline. Dachshunds homozygous for a null mutation in the TPP1 gene recapitulate many symptoms of the human disease. The objectives of this study were to determine whether intrathecal (IT) TPP1 treatment attenuates storage accumulation and functional decline in TPP1-/- Dachshunds and to characterize the CNS distribution of TPP1 activity. TPP1 was administered to one TPP1-/- and one homozygous wild-type (WT) dog. An additional TPP1-/- and WT dog received vehicle. Four IT administrations of 32 mg TPP1 formulated in 2.3 mL of artificial cerebrospinal fluid (aCSF) or vehicle were administered monthly via the cerebellomedullary cistern from four to seven months of age. Functional decline was assessed by physical and neurological examinations, electrophysiology, and T-maze performance. Neural tissues were collected 48 h after the fourth administration and analyzed for TPP1 activity and autofluorescent storage material. TPP1 was distributed at greater than WT levels in many areas of the CNS of the TPP1-/- dog administered TPP1. The amount of autofluorescent storage was decreased in this dog relative to the vehicle-treated affected control. No improvement in overall function was observed in this dog compared to the vehicle-treated TPP1-/- littermate control. These results demonstrate for the first time in a large animal model of LINCL widespread delivery of biochemically active TPP1 to the brain after IT administration along with a decrease in lysosomal storage material. Further studies with this model will be necessary to optimize the dosing route and regimen to attenuate functional decline.

Cysteine cathepsins: from structure, function and regulation to new frontiers

It is more than 50 years since the lysosome was discovered. Since then its hydrolytic machinery, including proteases and other hydrolases, has been fairly well identified and characterized. Among these are the cysteine cathepsins, members of the family of papain-like cysteine proteases. They have unique reactive-site properties and an uneven tissue-specific expression pattern. In living organisms their activity is a delicate balance of expression, targeting, zymogen activation, inhibition by protein inhibitors and degradation. The specificity of their substrate binding sites, small-molecule inhibitor repertoire and crystal structures are providing new tools for research and development. Their unique reactive-site properties have made it possible to confine the targets simply by the use of appropriate reactive groups. The epoxysuccinyls still dominate the field, but now nitriles seem to be the most appropriate “warhead”. The view of cysteine cathepsins as lysosomal proteases is changing as there is now clear evidence of their localization in other cellular compartments. Besides being involved in protein turnover, they build an important part of the endosomal antigen presentation. Together with the growing number of non-endosomal roles of cysteine cathepsins is growing also the knowledge of their involvement in diseases such as cancer and rheumatoid arthritis, among others. Finally, cysteine cathepsins are important regulators and signaling molecules of an unimaginable number of biological processes. The current challenge is to identify their endogenous substrates, in order to gain an insight into the mechanisms of substrate degradation and processing. In this review, some of the remarkable advances that have taken place in the past decade are presented. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

The yeast Batten disease orthologue Btn1 controls endosome-Golgi retrograde transport via SNARE assembly

The human Batten disease gene CLN3 and yeast orthologue BTN1 encode proteins of unclear function. We show that the loss of BTN1 phenocopies that of BTN2, which encodes a retromer accessory protein involved in the retrieval of specific cargo from late endosomes (LEs) to the Golgi. However, Btn1 localizes to Golgi and regulates soluble N-ethyl-maleimide sensitive fusion protein attachment protein receptor (SNARE) function to control retrograde transport. Specifically, BTN1 overexpression and deletion have opposing effects on phosphorylation of the Sed5 target membrane SNARE, on Golgi SNARE assembly, and on Golgi integrity. Although Btn1 does not interact physically with SNAREs, it regulates Sed5 phosphorylation by modulating Yck3, a palmitoylated endosomal kinase. This may involve modification of the Yck3 lipid anchor, as substitution with a transmembrane domain suppresses the deletion of BTN1 and restores trafficking. Correspondingly, deletion of YCK3 mimics that of BTN1 or BTN2 with respect to LE-Golgi retrieval. Thus, Btn1 controls retrograde sorting by regulating SNARE phosphorylation and assembly, a process that may be adversely affected in Batten Disease patients.

Juvenile neuronal ceroid lipofuscinosis: clinical course and genetic studies in Spanish patients

BACKGROUND

Juvenile neuronal ceroid lipofuscinosis (JNCL, NCL3, Batten disease) is usually caused by a 1.02-kb deletion in the CLN3 gene. Mutations in the CLN1 gene may be associated with a variant form of JNCL (vJNCL). We report the clinical course and molecular studies in 24 patients with JNCL collected from 1975 to 2010 with the aim of assessing the natural history of the disorder and phenotype/genotype correlations.

PATIENTS AND METHODS

Patients were classified into the groups of vJNCL with mutations in the CLN1 gene and/or granular osmiophilic deposit (GROD) inclusion bodies (n = 11) and classic JNCL (cJNCL) with mutations in the CLN3 gene and/or fingerprint (FP) profiles (n = 13). Psychomotor impairment included regression of acquired skills, cognitive decline, and clinical manifestations of the disease. We used Kaplan-Meier analyses to estimate the age of onset of psychomotor impairment.

RESULTS

Patients with vJNCL showed learning delay at an earlier age (median 4 years, 95% confidence interval [CI] 3.1-4.8) than those in the cJNCL group (median 8 years, 95% CI 6.2-9.7) (P = 0.001) and regression of acquired skills at a younger age. Patients with vJNCL showed a more severe and progressive clinical course than those with cJNCL. There may be a Gypsy ancestry for V181L missense mutation in the CLN1 gene.

CONCLUSIONS

The rate of disease progression may be useful to diagnose vJNCL or cJNCL, which should be confirmed by molecular studies in CLN1/CLN3 genes. Further studies of genotype/phenotype correlation will be helpful for understanding the pathogenesis of this disease.

Deficient mitochondrial Ca(2+) buffering in the Cln8(mnd) mouse model of neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinoses (NCLs) are a group of genetic childhood-onset progressive brain diseases characterized by a decline in mental and motor capacities, epilepsy, visual loss and premature death. Using patch clamp, fluorescence imaging and caged Ca(2+) photolysis, we evaluated the mechanisms of neuronal Ca(2+) clearance in Cln8(mnd) mice, a model of the human NCL caused by mutations in the CLN8 gene. In Cln8(mnd) hippocampal slices, Ca(2+) clearance efficiency in interneurons and, to some extent, principal neurons declined with age. In cultured Cln8(mnd) hippocampal neurons, clearance of large Ca(2+) loads was inefficient due to impaired mitochondrial Ca(2+) uptake. In contrast, neither Ca(2+) uptake by sarco/endoplasmic reticulum Ca(2+) ATPase, nor Ca(2+) extrusion through plasma membrane was affected by the Cln8 mutation. Excitotoxic glutamate challenge caused Ca(2+) deregulation more readily in Cln8(mnd) than in wt neurons. We propose that neurodegeneration in human CLN8 disorders is primarily caused by reduced mitochondrial Ca(2+) buffering capacity.

Neuronal ceroid lipofuscinosis in Qatar: report of a novel mutation in ceroid-lipofuscinosis, neuronal 5 in the Arab population

This study sought to genetically define the first family diagnosed with neuronal ceroid lipofuscinosis from Qatar. Onset was in late infancy (3 years), and sequencing in the affected children revealed a novel homozygous c.613C>T change in exon 3 of ceroid-lipofuscinosis, neuronal 5, corresponding to a missense mutation of a conserved amino acid, p.Pro205Ser. The clinical manifestations of the disease in this family largely resemble those of ceroid-lipofuscinosis, neuronal 5 disease, variant late infantile that was first described in Finland and include mental decline, visual deterioration, ataxia, and epileptic seizures. This description of ceroid-lipofuscinosis, neuronal 5 disease in an Arab family adds to the clinical and molecular diversity of the variant late-infantile neuronal ceroid lipofuscinoses, which were originally reported in Europe and are increasingly recognized in other populations.

The neuronal ceroid lipofuscinoses: the same, but different?

The NCLs (neuronal ceroid lipofuscinoses) (also known as Batten disease) are a group of at least ten fatal inherited storage disorders. Despite the identification of many of the disease-causing genes, very little is known about the underlying disease mechanisms. However, now that we have mouse or large-animal models for most forms of NCL, we can investigate pathogenesis and compare what happens in the brain in different types of the disease. Broadly similar neuropathological themes have emerged, including the highly selective nature of neuron loss, early effects upon the presynaptic compartment, together with an early and localized glial activation. These events are especially pronounced within the thalamocortical system, but it is clear that where and when they occur varies markedly between different forms of NCL. It is now becoming apparent that, despite having pathological endpoints that resemble one another, these are reached by a sequence of events that is specific to each subtype of NCL.

Distinct early molecular responses to mutations causing vLINCL and JNCL presage ATP synthase subunit C accumulation in cerebellar cells

Variant late-infantile neuronal ceroid lipofuscinosis (vLINCL), caused by CLN6 mutation, and juvenile neuronal ceroid lipofuscinosis (JNCL), caused by CLN3 mutation, share clinical and pathological features, including lysosomal accumulation of mitochondrial ATP synthase subunit c, but the unrelated CLN6 and CLN3 genes may initiate disease via similar or distinct cellular processes. To gain insight into the NCL pathways, we established murine wild-type and CbCln6(nclf/nclf) cerebellar cells and compared them to wild-type and CbCln3(Δex7/8/Δex7/8) cerebellar cells. CbCln6(nclf/nclf) cells and CbCln3(Δex7/8/Δex7/8) cells both displayed abnormally elongated mitochondria and reduced cellular ATP levels and, as cells aged to confluence, exhibited accumulation of subunit c protein in Lamp 1-positive organelles. However, at sub-confluence, endoplasmic reticulum PDI immunostain was decreased only in CbCln6(nclf/nclf) cells, while fluid-phase endocytosis and LysoTracker® labeled vesicles were decreased in both CbCln6(nclf/nclf) and CbCln3(Δex7/8/Δex7/8) cells, though only the latter cells exhibited abnormal vesicle subcellular distribution. Furthermore, unbiased gene expression analyses revealed only partial overlap in the cerebellar cell genes and pathways that were altered by the Cln3(Δex7/8) and Cln6(nclf) mutations. Thus, these data support the hypothesis that CLN6 and CLN3 mutations trigger distinct processes that converge on a shared pathway, which is responsible for proper subunit c protein turnover and neuronal cell survival.

Immunosuppression alters disease severity in juvenile Batten disease mice

Autoantibodies to brain proteins are present in Juvenile Neuronal Ceroid Lipofuscinosis (Batten disease) patients and in the Cln3-/- mouse model of this disease, suggesting an autoimmune component to pathogenesis. Using genetic or pharmaceutical approaches to attenuate this immune response in Cln3-/- mice, we demonstrate decreased neuroinflammation, decreased deposition of immunoglobulin G in the brain and protection of vulnerable neuron populations. Moreover, immune suppression results in a significant improvement in motor performance providing for the first plausible therapeutic approach for juvenile Batten disease.

Disruption of adaptive energy metabolism and elevated ribosomal p-S6K1 levels contribute to INCL pathogenesis: partial rescue by resveratrol

The infantile neuronal ceroid lipofuscinosis (INCL) is a devastating neurodegenerative lysosomal storage disease. Despite our knowledge that palmitoyl-protein thioesterase-1 (PPT1)-deficiency causes INCL, the molecular mechanism(s) of neurodegeneration and the drastically reduced lifespan of these patients remain poorly understood. Consequently, an effective treatment for this disease is currently unavailable. We previously reported that oxidative stress-mediated abnormality in mitochondria activates caspases-9 pathway of apoptosis in INCL fibroblasts and in neurons of Ppt1-knockout (Ppt1-KO) mice, which mimic INCL. Since mitochondria play critical roles in maintaining cellular energy homeostasis, we hypothesized that oxidative stress-mediated disruption of energy metabolism and homeostasis may contribute to INCL pathogenesis. We report here that, in cultured INCL fibroblasts and in the brain tissues of Ppt1-KO mice, the NAD(+)/NADH ratio, the levels of phosphorylated-AMPK (p-AMPK), peroxisome proliferator-activated receptor-γ (PPARγ) coactivator-1α (PGC-1α) and Silent Information Regulator T1 (SIRT1) are markedly down-regulated. This suggested an abnormality in AMPK/SIRT1/PGC-1α signaling pathway of energy metabolism. Moreover, we found that, in INCL fibroblasts and in the Ppt1-KO mice, phosphorylated-S6K-1 (p-S6K1) levels, which inversely correlate with lifespan, are markedly elevated. Most importantly, resveratrol (RSV), an antioxidant polyphenol, elevated the NAD(+)/NADH ratio, levels of ATP, p-AMPK, PGC-1α and SIRT1 while decreasing the level of p-S6K1 in both INCL fibroblasts and in Ppt1-KO mice, which showed a modest increase in lifespan. Our results show that disruption of adaptive energy metabolism and increased levels of p-S6K1 are contributing factors in INCL pathogenesis and provide the proof of principle that small molecules such as RSV, which alleviate these abnormalities, may have therapeutic potential.

Distinct neuropathologic phenotypes after disrupting the chloride transport proteins ClC-6 or ClC-7/Ostm1

The proteins ClC-6 and ClC-7 are expressed in the endosomal-lysosomal system. Because Clcn6-deficient mice display some features of neuronal ceroid lipofuscinosis (NCL), CLCN6 may be a candidate gene for novel forms of NCL. Using landmarks of disease progression from NCL mouse models as a guide, we examined neuropathologic alterations in the central nervous system of Clcn6(-/-), Clcn7(-/-), andgl mice. gl mice bear a mutation in Ostm1, the β-subunit critical for Clcn7 function. Severely affected Clcn7(-/-) and gl mice have remarkably similar neuropathologic phenotypes, with pronounced reactive changes and neuron loss in the thalamocortical system, similar to findings in early-onset forms of NCL. In contrast, Clcn6(-/-) mice display slowly progressive, milder neuropathologic features with very little thalamic involvement or microglial activation. These findings detail for the first time the markedly different neuropathologic consequences of mutations in these two CLC genes. Clcn7(-/-) and gl mice bear a close resemblance to the progressive neuropathologic phenotypes of early onset forms of NCL, whereas the distinct phenotype of Clcn6-deficient mice suggests that this gene could be a candidate for a later-onset form of mild neurologic dysfunction with some NCL-like features.

A missense mutation in canine CLN6 in an Australian shepherd with neuronal ceroid lipofuscinosis

The childhood neuronal ceroid lipofuscinoses (NCLs) are inherited neurodegenerative diseases that are progressive and ultimately fatal. An Australian Shepherd that exhibited a progressive neurological disorder with signs similar to human NCL was evaluated. The cerebral cortex, cerebellum, and retina were found to contain massive accumulations of autofluorescent inclusions characteristic of the NCLs. Nucleotide sequence analysis of DNA from the affected dog identified a T to C variant (c.829T>C) in exon 7 of CLN6. Mutations in the human ortholog underlie a late-infantile form of NCL in humans. The T-to-C transition results in a tryptophan to arginine amino acid change in the predicted protein sequence. Tryptophans occur at homologous positions in the CLN6 proteins from all 13 other vertebrates evaluated. The c.829T>C transition is a strong candidate for the causative mutation in this NCL-affected dog. Dogs with this mutation could serve as a model for the analogous human disorder.

[Genetics of neuronal ceroidlipofuscinoses. Aspects of genetic counseling]

Neuronal ceroid lipofuscinoses are autosomal recessive inherited disorders of neuronal cells. Neuronal ceroid lipofuscinoses belong to the lysosomal storage disorders and are characterized by accumulation of protein-lipid complexes in the lysosomal compartments of all somatic cells. This debris causes degenerative activities in the nervous system, especially in the cerebrum, the cerebellum and the afferent and efferent cranial nerves. With one exception of adult onset the disorder causes the loss of receptive, cognitive and control function in the first decade of life and an early death by the age of 20. Currently 10 loci are known which correlate to 8 genes. The genotype related phenotype and the correlated prognosis depend on the underlying gene and type of mutation. The genotype phenotype correlation is hampered by a lack of knowledge on the function of the mutant gene products. In this review we summarize the known genetic data on neuronal ceroid lipofuscinoses and comment on therapeutic approaches.

Deletion of btn1, an orthologue of CLN3, increases glycolysis and perturbs amino acid metabolism in the fission yeast model of Batten disease

The neuronal ceroid lipofuscinoses (NCLs) constitute a group of autosomal recessive neurodegenerative diseases affecting children. To date, the disease pathogenesis remains unknown, although the role of lysosomal impairment is widely recognized across the different diseases. Recently, the creation of simple models of juvenile NCL (Batten disease) has provided additional insights into the disease mechanism at the molecular level. We report defects in metabolism identified in the Schizosacchromyces pombe yeast model, where btn1, the orthologue of CLN3, has been deleted, using a metabolomics approach based on high resolution 1H and 13C NMR spectroscopy. Such changes represent the first documented metabolic changes associated with deletion of btn1. A decrease in extracellular glucose and increases in the concentration of extracellular ethanol and alanine labelling demonstrate increased glycolytic flux that may arise from vacuolar impairment, whilst amino acid changes were detected which were also in accordance with defective vacuolar functionality. That these changes were detected using a metabolomic based approach advocates its use to further analyse other yeast models of human disease to better understand the function of orthologue genes.

Autofluorescence and infrared retinal imaging in patients and obligate carriers with neuronal ceroid lipofuscinosis

PURPOSE

To measure fundus autofluorescence (FAF) in patients and obligate carriers with Neuronal Ceroid Lipofuscinosis (NCL) and document fundus abnormalities in NCL patients using standard retinal photography and confocal infra-red (IR) imaging.

METHODS

Twenty-seven patients with NCL, 50 obligate carriers of NCL, and 19 controls were imaged in IR and FAF modes by a confocal scanning laser opthalmoscope (HRA II, Heidelberg-Engineering, Inc). FAF intensities were referenced to the mean and standard deviation at the optic disk to remove inter-subject variance and then quantified along the horizontal and vertical meridians.

RESULTS

For NCL subjects, FAF images were successfully obtained in 16 eyes (9 of 27 subjects). Of these, 11 eyes had severely reduced or extinguished FAF and 5 eyes (3 subjects) could be analyzed along the meridians. An NCL subject with bilateral bull's eye maculopathy showed overall increased FAF, the remaining 3 eyes had advanced retinal degeneration and showed reduced FAF. Four patterns of macular disease were observed: 1) bull's eye atrophy 2) retinal pigment epithelium (RPE) dropout without pigmentary alterations, 3) RPE dropout with pigmentary alterations, 4) RPE dropout with pigmentary alterations and retinal flecks. Standard photography revealed focal retinal flecks in addition to severe retinal atrophy, RPE dropout, pigmentary clumping, and constricted vessels. Linear striations near the optic disc were highlighted by IR imaging. Topographical comparison of images demonstrated the focal flecks were not hyperfluorescent while the linear striations showed slight increases in FAF. For obligate carriers, FAF profiles were similar to controls with a mild increase in mean FAF intensity.

CONCLUSIONS

Patients with NCL show increases in retinal fluorophores in early stages and decreases in FAF in late stages of the disease. Obligate carriers of NCL have mildly elevated FAF but this finding is not a specific measure of the carrier state.

Novel interactions of CLN5 support molecular networking between Neuronal Ceroid Lipofuscinosis proteins

BACKGROUND

Neuronal ceroid lipofuscinoses (NCLs) comprise at least eight genetically characterized neurodegenerative disorders of childhood. Despite of genetic heterogeneity, the high similarity of clinical symptoms and pathology of different NCL disorders suggest cooperation between different NCL proteins and common mechanisms of pathogenesis. Here, we have studied molecular interactions between NCL proteins, concentrating specifically on the interactions of CLN5, the protein underlying the Finnish variant late infantile form of NCL (vLINCLFin).

RESULTS

We found that CLN5 interacts with several other NCL proteins namely, CLN1/PPT1, CLN2/TPP1, CLN3, CLN6 and CLN8. Furthermore, analysis of the intracellular targeting of CLN5 together with the interacting NCL proteins revealed that over-expression of PPT1 can facilitate the lysosomal transport of mutated CLN5FinMajor, normally residing in the ER and in the Golgi complex. The significance of the novel interaction between CLN5 and PPT1 was further supported by the finding that CLN5 was also able to bind the F1-ATPase, earlier shown to interact with PPT1.

CONCLUSION

We have described novel interactions between CLN5 and several NCL proteins, suggesting a modifying role for these proteins in the pathogenesis of individual NCL disorders. Among these novel interactions, binding of CLN5 to CLN1/PPT1 is suggested to be the most significant one, since over-expression of PPT1 was shown to influence on the intracellular trafficking of mutated CLN5, and they were shown to share a binding partner outside the NCL protein spectrum.

Variant late infantile neuronal ceroid lipofuscinosis (CLN6 gene) in Saudi Arabia

Variant late infantile neuronal ceroid lipofuscinosis is one of the multiethnically prevalent types of neuronal ceroid lipofuscinoses. Reported here are three families representing the first cases from Saudi Arabia, one of them having a novel mutation in the CLN6 gene. The CLN6-related literature is reviewed.

Protracted course of juvenile ceroid lipofuscinosis associated with a novel CLN3 mutation (p.Y199X)

The juvenile neuronal ceroid lipofuscinosis (JNCL, Batten disease, MIM 204200), is an autosomal recessive lysosomal storage disease, which is characterized by ubiquitous accumulation of the lipopigment material ceroid-lipofuscin. It manifests with loss of vision in childhood due to retinal degeneration, followed by seizures and parkinsonism leading to premature death at around 30 years. Eighty-five percent of JNCL patients carry a disease-causing 1.02 kb deletion in the CLN3 gene on chromosome 16. Here we report on a large consanguineous Lebanese family with five affected siblings. Electron microscopy of lymphocytes revealed the presence of fingerprint profiles suggesting JNCL. However, disease progression, especially of mental and motor function was slower as expected for 'classic' JNCL. We thus confirmed the diagnosis by genetic testing and found a new c.597C>A transversion in exon 8, homozygous in all affected family members and not present in 200 alleles of normal controls. The mutation generates a premature termination codon (p.Y199X) truncating the CLN3 protein by 55%. In heterozygous state mutant mRNA transcripts are expressed at the same levels as the wild-type ones, suggesting the absence of nonsense mediated messenger decay. We discuss a potential residual catalytic function of the truncated protein as a cause for the mild phenotype.

Progressive thalamocortical neuron loss in Cln5 deficient mice: Distinct effects in Finnish variant late infantile NCL

Finnish variant LINCL (vLINCL(Fin)) is the result of mutations in the CLN5 gene. To gain insights into the pathological staging of this fatal pediatric disorder, we have undertaken a stereological analysis of the CNS of Cln5 deficient mice (Cln5-/-) at different stages of disease progression. Consistent with human vLINCL(Fin), these Cln5-/- mice displayed a relatively late onset regional atrophy and generalized cortical thinning and synaptic pathology, preceded by early and localized glial responses within the thalamocortical system. However, in marked contrast to other forms of NCL, neuron loss in Cln5-/- mice began in the cortex and only subsequently occurred within thalamic relay nuclei. Nevertheless, as in other NCL mouse models, this progressive thalamocortical neuron loss was still most pronounced within the visual system. These data provide unexpected evidence for a distinctive sequence of neuron loss in the thalamocortical system of Cln5-/- mice, diametrically opposed to that seen in other forms of NCL.

Variant late infantile neuronal ceroid lipofuscinosis because of CLN1 mutations

The neuronal ceroid lipofuscinoses are a heterogeneous group of inherited degenerative disorders of the central nervous system. Cases of ceroid lipofuscinosis with cytoplasmic storage of granular osmiophilic deposits are associated with reduced activity of palmitoyl-protein thioesterase-1 (PPT-1) and mutations in CLN1, and occur from infancy to adulthood. We present clinical and diagnostic investigations in six children with variant late infantile neuronal ceroid lipofuscinosis and mutations in CLN1. The main clinical features at onset were behavioral disturbances and cognitive decline. Myoclonic jerks constituted the most prominent paroxysmal phenomenon. An electroencephalogram revealed the "vanishing" pattern described in infantile ceroid lipofuscinosis. Neurologic regression was associated with dramatic shrinkage of cortical structures, evident upon brain magnetic resonance imaging. Three unrelated children harboring the same homozygous mutation in CLN1 and a girl who carried a novel mutation resulting in skipping of multiple exons presented with a similar clinical phenotype. The most severe picture occurred in two siblings who carried a homozygous mutation predicting a prematurely truncated protein. Similar to the infantile form, the clinical evolution in this group of patients was characterized by an onset of severe neurologic impairment, peaking within a relatively short period of time, followed by a slower evolution of the disease.

S. pombe btn1, the orthologue of the Batten disease gene CLN3, is required for vacuole protein sorting of Cpy1p and Golgi exit of Vps10p

Batten disease is characterised by lysosomal dysfunction. The most common type of the disease is caused by mutations in the membrane protein CLN3, whose function is unknown. We show that the fission yeast orthologue Btn1p, previously implicated in vacuole function, is required for correct sorting of the vacuole hydrolase carboxypeptidase Y (Cpy1p). This is, in part, due to a defect in trafficking of Vps10p, the sorting receptor for Cpy1p, from the Golgi to the trans-Golgi network in btn1Delta cells. Our data also implicate btn1 in other Vps10-independent Cpy1-sorting pathways. Furthermore, btn1 affects the number, intracellular location and structure of Golgi compartments. We show that the prevacuole location of Btn1p is at the Golgi, because Btn1p colocalises predominantly with the Golgi marker Gms1p in compartments that are sensitive to Brefeldin A. Btn1p function might be linked to that of Vps34p, a phosphatidylinositol 3-kinase, because Btn1p acts as a multicopy suppressor of the severe Cpy1p vacuole protein-sorting defect of vps34Delta cells. Together, these results indicate an important role for Btn1p in the Golgi complex, which affects Golgi homeostasis and vacuole protein sorting. We propose a similar role for CLN3 in mammalian cells.

Drosophila melanogaster as a model organism of brain diseases

Drosophila melanogaster has been utilized to model human brain diseases. In most of these invertebrate transgenic models, some aspects of human disease are reproduced. Although investigation of rodent models has been of significant impact, invertebrate models offer a wide variety of experimental tools that can potentially address some of the outstanding questions underlying neurological disease. This review considers what has been gleaned from invertebrate models of neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, metabolic diseases such as Leigh disease, Niemann-Pick disease and ceroid lipofuscinoses, tumor syndromes such as neurofibromatosis and tuberous sclerosis, epilepsy as well as CNS injury. It is to be expected that genetic tools in Drosophila will reveal new pathways and interactions, which hopefully will result in molecular based therapy approaches.