CLN3, the protein associated with batten disease: structure, function and localization

Quantifying physical decline in juvenile neuronal ceroid lipofuscinosis (Batten disease)

OBJECTIVE

To use the Unified Batten Disease Rating Scale (UBDRS) to measure the rate of decline in physical and functional capability domains in patients with juvenile neuronal ceroid lipofuscinosis (JNCL) or Batten disease, a neurodegenerative lysosomal storage disorder. We have evaluated the UBDRS in subjects with JNCL since 2002; during that time, the scale has been refined to improve reliability and validity. Now that therapies are being proposed to prevent, slow, or reverse the course of JNCL, the UBDRS will play an important role in quantitatively assessing clinical outcomes in research trials.

METHODS

We administered the UBDRS to 82 subjects with JNCL genetically confirmed by CLN3 mutational analysis. Forty-four subjects were seen for more than one annual visit. From these data, the rate of physical impairment over time was quantified using multivariate linear regression and repeated-measures analysis.

RESULTS

The UBDRS Physical Impairment subscale shows worsening over time that proceeds at a quantifiable linear rate in the years following initial onset of clinical symptoms. This deterioration correlates with functional capability and is not influenced by CLN3 genotype.

CONCLUSION

The UBDRS is a reliable and valid instrument that measures clinical progression in JNCL. Our data support the use of the UBDRS to quantify the rate of progression of physical impairment in subjects with JNCL in clinical trials.

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.

Parent-reported benefits of flupirtine in juvenile neuronal ceroid lipofuscinosis (Batten disease; CLN3) are not supported by quantitative data

Juvenile neuronal ceroid lipofuscinosis (JNCL; CLN3 disease; Batten disease) is an autosomal recessive neurodegenerative disease of childhood that typically presents at school age with vision loss followed by progressive cognitive decline, motor dysfunction, seizures, and behavior problems. No therapy has been shown to slow the progression of disease in JNCL patients, and all current treatments are symptomatic. Flupirtine has been shown in vitro to reduce apoptosis in CLN3 lymphocytes. Based on that preclinical study, several children with JNCL were given flupirtine by their parents. The purpose of this study was to determine if there was evidence of attenuated disease progression in any JNCL symptom domain. We administered a survey to parents of JNCL children to qualitatively assess flupirtine efficacy. We used the Unified Batten Disease Rating Scale (UBDRS) to determine specific aspects of disease progression and investigated three age-related factors: loss of independent ambulation, loss of intelligible speech, and loss of ability to perform independent activities of daily living. The median scores for the UBDRS physical, behavior, and capability subscales were determined in flupirtine-exposed subjects and compared to age-, sex-, and genotype-matched subjects who had never taken flupirtine. Twenty-one percent of survey responders reported administering flupirtine to their JNCL child, and 56% of these families perceived beneficial changes that they attributed to flupirtine. However, our quantitative, prospectively obtained data did not show any change in JNCL disease progression that could be attributed to flupirtine. This study highlights the need for prospective experimental therapeutic research.

The Batten disease gene CLN3 is required for the response to oxidative stress

Mutations in the CLN3 gene cause juvenile neuronal ceroid lipofuscinosis (JNCL or Batten disease), an early onset neurodegenerative disorder. JNCL is the most common of the NCLs, a group of disorders with infant or childhood onset that are caused by single gene mutations. The NCLs, although relatively rare, share many pathological and clinical similarities with the more common late-onset neurodegenerative disorders, while their simple genetic basis makes them an excellent paradigm. The early onset and rapid disease progression in the NCLs suggests that one or more key cellular processes are severely compromised. To identify the functional pathways compromised in JNCL, we have performed a gain-of-function modifier screen in Drosophila. We find that CLN3 interacts genetically with the core stress signalling pathways and components of stress granules, suggesting a function in stress responses. In support of this, we find that Drosophila lacking CLN3 function are hypersensitive to oxidative stress yet they respond normally to other physiological stresses. Overexpression of CLN3 is sufficient to confer increased resistance to oxidative stress. We find that CLN3 mutant flies perceive conditions of increased oxidative stress correctly but are unable to detoxify reactive oxygen species, suggesting that their ability to respond is compromised. Together, our data suggest that the lack of CLN3 function leads to a failure to manage the response to oxidative stress and this may be the key deficit in JNCL that leads to neuronal degeneration.

Altered sensitivity of cerebellar granule cells to glutamate receptor overactivation in the Cln3(Δex7/8)-knock-in mouse model of juvenile neuronal ceroid lipofuscinosis

The juvenile onset form of neuronal ceroid lipofuscinoses (JNCL) is a recessively inherited lysosomal storage disorder characterized by progressive neurodegeneration. JNCL results from mutations in the CLN3 gene that encodes a lysosomal membrane protein with unknown function. Utilizing a Cln3-knock-out mouse model of JNCL that was created on the 129S6/SvEv genetic background, we have previously demonstrated that CLN3-deficient cerebellar granule cells (CGCs) have a selectively increased sensitivity to AMPA-type glutamate receptor-mediated toxicity. Our recent findings that CGCs from 129S6/SvEv and C57BL/6J wild type (WT) mice have significant differences in glutamate receptor expression and in excitotoxic vulnerability indicated that the genetic background possibly have a strong influence on how glutamate receptor function is dysregulated in CLN3-deficient neurons. Indeed, here we show that in the Cln3(Δex7/8)-knock-in mouse model, that is on the C57BL/6J genetic background, mimics the most frequent mutation observed in JNCL patients and considered a null mutant, the sensitivity of CGCs to both AMPA- and NMDA-type glutamate receptor overactivations is altered. Cultured wild type and Cln3(Δex7/8) CGCs were equally sensitive to AMPA toxicity after 2 or 3 weeks in vitro, whereas the subunit-selective AMPA receptor agonist, CPW-399, induced significantly more cell death in mature, 3-week-old Cln3(Δex7/8) cultures. NMDA receptor-mediated toxicity changed during in vitro development: Cln3(Δex7/8) CGCs were less sensitive to high concentration of NMDA after 2 weeks in culture but became more vulnerable than their WT counterparts after 3 weeks in vitro. Abnormally altered glutamate receptor function in the cerebellum may result in motor deficits, and we confirmed that 7-week-old Cln3(Δex7/8) mice, similarly to Cln3-knock-out mice, have a motor coordination deficit as measured by an accelerating rotarod. Our results demonstrate altered glutamate receptor function in Cln3(Δex7/8) neurons and suggest that both AMPA and NMDA receptors are potential therapeutic targets in JNCL.

Temporary inhibition of AMPA receptors induces a prolonged improvement of motor performance in a mouse model of juvenile Batten disease

Mutations in the CLN3 gene cause juvenile Batten disease, a fatal pediatric neurodegenerative disorder. The Cln3-knockout (Cln3(Δex1-6)) mouse model of the disease displays many pathological characteristics of the human disorder including a deficit in motor coordination. We have previously found that attenuation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type glutamate receptor activity in one-month-old Cln3(Δex1-6) mice resulted in an immediate improvement of their motor skills. Here we show that at a later stage of the disease, in 6-7-month-old Cln3(Δex1-6) mice, acute inhibition of AMPA receptors by a single intraperitoneal injection (1mg/kg) of the non-competitive AMPA antagonist, EGIS-8332, does not have an immediate effect. Instead, it induces a delayed but prolonged improvement of motor skills. Four days after the injection of the AMPA antagonist, Cln3(Δex1-6) mice reached the same motor skill level as their wild type (WT) counterparts, an improvement that persisted for an additional four days. EGIS-8332 was rapidly eliminated from the brain as measured by HPLC-MS/MS. Histological analysis performed 8 days after the drug administration revealed that EGIS-8332 did not have any impact upon glial activation or the survival of vulnerable neuron populations in 7-month-old Cln3(Δex1-6) mice. We propose that temporary inhibition of AMPA receptors can induce a prolonged correction of the pre-existing abnormal glutamatergic neurotransmission in vivo for juvenile Batten disease.

Screening for calcium channel modulators in CLN3 siRNA knock down SH-SY5Y neuroblastoma cells reveals a significant decrease of intracellular calcium levels by selected L-type calcium channel blockers

BACKGROUND

Defects of the CLN3 gene on chromosome 16p12.1 lead to the juvenile form of neuronal ceroid-lipofuscinosis (JNCL, Batten Disease), the most common recessive inherited neurodegenerative disorder in children. Dysregulation of intracellular calcium homeostasis in the absence of a functional CLN3 protein (CLN3P, Battenin) has been linked to synaptic dysfunction and accelerated apoptosis in vulnerable neuronal cells. Prolonged increase of intracellular calcium concentration is considered to be a significant trigger for neuronal apoptosis and cellular loss in JNCL.

METHODS

We examined the potential effect of 41 different calcium channel modulators on intracellular calcium concentration in CLN3 siRNA knock down SH-SY5Y neuroblastoma cells.

RESULTS

Six drugs belonging to the group of voltage dependent L-type channel blockers show significant lowering of the increased intracellular calcium levels in CLN3 siRNA knock down cells.

CONCLUSIONS

Our studies provide important new data suggesting possible beneficial effects of the tested drugs on calcium flux regulated pathways in neuronal cell death. Therapeutic intervention in this untreatable disease will likely require drugs that cross the blood-brain barrier as did all of the positively screened drugs in this study.

GENERAL SIGNIFICANCE

Better comprehension of the mechanism of neurodegeneration in rare recessive disorders, such as neuronal ceroid-lipofuscinoses, is likely to help to better understand mechanisms involved in more complex genetic neurodegenerative conditions, such as those associated with aging.

pH-dependent localization of Btn1p in the yeast model for Batten disease

Btn1p the yeast homolog of human CLN3, which is associated with juvenile Batten disease has been implicated in several cellular pathways. Yeast cells lacking BTN1 are unable to couple ATP hydrolysis and proton pumping activities by the vacuolar ATPase (V-ATPase). In this work, we demonstrate that changes in extracellular pH result in altered transcription of BTN1, as well as a change in the glycosylation state and localization of Btn1p. At high pH, Btn1p expression was increased and the protein was mainly located in vacuolar membranes. However, low pH decreased Btn1p expression and changed its location to undefined punctate membranes. Moreover, our results suggest that differential Btn1p localization may be regulated by its glycosylation state. Underlying pathogenic implications for Batten disease of altered cellular distribution of CLN3 are discussed.

A knock-in reporter mouse model for Batten disease reveals predominant expression of Cln3 in visual, limbic and subcortical motor structures

Juvenile neuronal ceroid lipofuscinosis (JNCL) or Batten disease is an autosomal recessive neurodegenerative disorder of children caused by mutation in CLN3. JNCL is characterized by progressive visual impairment, cognitive and motor deficits, seizures and premature death. Information about the localization of CLN3 expressing neurons in the nervous system is limited, especially during development. The present study has systematically mapped the spatial and temporal localization of CLN3 reporter neurons in the entire nervous system including retina, using a knock-in reporter mouse model. CLN3 reporter is expressed predominantly in post-migratory neurons in visual and limbic cortices, anterior and intralaminar thalamic nuclei, amygdala, cerebellum, red nucleus, reticular formation, vestibular nuclei and retina. CLN3 reporter in the nervous system is mainly expressed during the first postnatal month except in the dentate gyrus, parasolitary nucleus and retina, where it is still strongly expressed in adulthood. The predominant distribution of CLN3 reporter neurons in visual, limbic and subcortical motor structures correlates well with the clinical symptoms of JNCL. These findings have also revealed potential target brain regions and time periods for future investigations of the disease mechanisms and therapeutic intervention.

A novel interaction of CLN3 with nonmuscle myosin-IIB and defects in cell motility of Cln3(-/-) cells

Juvenile neuronal ceroid lipofuscinosis (JNCL) is a pediatric lysosomal storage disorder characterized by accumulation of autofluorescent storage material and neurodegeneration, which result from mutations in CLN3. The function of CLN3, a lysosomal membrane protein, is currently unknown. We report that CLN3 interacts with cytoskeleton-associated nonmuscle myosin-IIB. Both CLN3 and myosin-IIB are ubiquitously expressed, yet mutations in either produce dramatic consequences in the CNS such as neurodegeneration in JNCL patients and Cln3(-/-) mouse models, or developmental deficiencies in Myh10(-/-) mice, respectively. A scratch assay revealed a migration defect associated with Cln3(-/-) cells. Inhibition of nonmuscle myosin-II with blebbistatin in WT cells resulted in a phenotype that mimics the Cln3(-/-) migration defect. Moreover, inhibiting lysosome function by treating cells with chloroquine exacerbated the migration defect in Cln3(-/-). Cln3(-/-) cells traversing a transwell filter under gradient trophic factor conditions displayed altered migration, further linking lysosomal function and cell migration. The myosin-IIB distribution in Cln3(-/-) cells is elongated, indicating a cytoskeleton defect caused by the loss of CLN3. In summary, cells lacking CLN3 have defects that suggest altered myosin-IIB activity, supporting a functional and physical interaction between CLN3 and myosin-IIB. We propose that the migration defect in Cln3(-/-) results, in part, from the loss of the CLN3-myosin-IIB interaction.

Interactions of the proteins of neuronal ceroid lipofuscinosis: clues to function

Neuronal ceroid lipofuscinoses (NCL) are caused by mutations in eight different genes, are characterized by lysosomal accumulation of autofluorescent storage material, and result in a disease that causes degeneration of the central nervous system (CNS). Although functions are defined for some of the soluble proteins that are defective in NCL (cathepsin D, PPT1, and TPP1), the primary function of the other proteins defective in NCLs (CLN3, CLN5, CLN6, CLN7, and CLN8) remain poorly defined. Understanding the localization and network of interactions for these proteins can offer clues as to the function of the NCL proteins and also the pathways that will be disrupted in their absence. Here, we present a review of the current understanding of the localization, interactions, and function of the proteins associated with NCL.

Genotype does not predict severity of behavioural phenotype in juvenile neuronal ceroid lipofuscinosis (Batten disease)

AIM

The primary aim of this investigation was to examine genotype and clinical phenotype differences in individuals with juvenile neuronal ceroid lipofuscinosis (JNCL) who were homozygous for a common disease-causing deletion or compound heterozygous. The secondary aim was to cross-validate the Child Behavior Checklist (CBCL) and the Unified Batten Disease Rating Scale (UBDRS), a disease-specific JNCL rating scale.

METHOD

Sixty individuals (28 males, 32 females; mean age 15y 1mo, SD 4y 9mo, range 5y 8mo--31y 1mo) with JNCL completed the UBDRS.

RESULTS

No significant genotype and clinical phenotype differences were identified when comparing individuals homozygous for the deletion with a heterogeneous group of compound heterozygous individuals. There were significant correlations among related behaviour items and scales on the CBCL and UBDRS (Spearman's rho ranging from 0.39 [p<0.05] to 0.72 [p<0.01]). Behaviour and physical function ratings were uncorrelated, supporting divergent validity of these two constructs in JNCL.

INTERPRETATION

Previous reports of genotype and clinical phenotype differences were unsupported in this investigation, which did not find differences between individuals homozygous or heterozygous for the CLN3 deletion. The CBCL, an already validated measure of behaviour problems, appears valid for use in JNCL and cross-validates well with the UBDRS.

Molecular characterisation of ‘transmembrane protein 192’ (TMEM192), a novel protein of the lysosomal membrane

Transmembrane protein 192 (TMEM192) has been previously identified in proteomic analyses of lysosomal membranes. TMEM192 does not exhibit any significant homology to known protein families and possesses four potential transmembrane segments. To approach the molecular role of TMEM192, a detailed biochemical characterisation of this protein was performed. Expression constructs of fusion proteins containing TMEM192 and appended epitope tags were constructed. In HeLa cells these proteins were detected in membranes of lysosomes/late endosomes. To examine endogenous TMEM192, a TMEM192-specific antibody was generated and validated. With this antibody colocalisation of endogenous TMEM192 with lysosomal and late endosomal markers was demonstrated. Using Percoll density gradient centrifugation and immunoblotting, co-sedimentation of major portions of both TMEM192 and the lysosomal proteins LAMP-2 and cathepsin D into high-density fractions was observed. Interestingly, in contrast to many other lysosomal proteins no N-glycosylation of TMEM192 could be detected. Western blotting of reduced and non-reduced samples and co-immunoprecipitation experiments indicated TMEM192 to be a homodimer with one or more interchain disulphide bridges. TMEM192 was found to be strongly expressed in human kidney, liver, lung and pancreas tissue. The widespread tissue distribution could suggest an important role of TMEM192 for lysosomal function.

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.

Juvenile neuronal ceroid lipofuscinosis (JNCL) and the eye

Juvenile neuronal ceroid lipofuscinoses, or Batten disease, is the most common type of NCL in the United States and Europe. This devastating disorder presents with vision failure and progresses to include seizures, motor dysfunction, and dementia. Death usually occurs in the third decade, but some patients die before age twenty. Though the mechanism of visual failure remains poorly understood, recent advances in molecular genetics have improved diagnostic testing and suggested possible therapeutic strategies. The ophthalmologist plays a crucial role in both early diagnosis and documentation of progression of juvenile neuronal ceroid lipofuscinoses. We update Batten disease research, particularly as it relates to the eye, and present various theories on the pathophysiology of retinal degeneration.

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.

Spectral properties and mechanisms that underlie autofluorescent accumulations in Batten disease

Neuronal Ceroid Lipofuscinoses (NCLs) have an incidence of 1 in 12,500 live births. These devastating neurodegenerative lysosomal storage diseases are characterized by the lysosomal accumulation of autofluorescent storage material (AFSM) similar to that seen in aging cells. Using patient derived lymphoblasts from three genetically distinct NCLs we report that AFSM for each NCL has distinct spectral properties. Moreover, by using pharmacological inhibitors to disrupt various biochemical pathways in normal control lymphoblasts we have determined that disruptions in microtubule assembly and non-muscle myosin II function results in accumulation of lysosomal AFSM. Interestingly, inhibition of autophagy did not result in AFSM. We conclude that cellular disturbances outside the lysosome in addition to compromised function of this organelle can result in accumulation of lysosomal AFSM in NCLs and possibly as a result of cellular aging.

Endolysosomal phospholipidosis and cytosolic lipid droplet storage and release in macrophages

This review summarizes the current knowledge of endolysosomal and cytoplasmic lipid storage in macrophages induced by oxidized LDL (Ox-LDL), enzymatically degraded LDL (E-LDL) and other atherogenic lipoprotein modifications, and their relation to the adapter protein 3 (AP-3) dependent ABCA1 and ABCG1 cellular lipid efflux pathways. We compare endolysosomal lipid storage caused either through drug induced phospholipidosis, inheritable endolysosomal and cytosolic lipid storage disorders and Ox-LDL or E-LDL induced phagosomal uptake and cytosolic lipid droplet storage in macrophages. Ox-LDL is resistant to rapid endolysosomal hydrolysis and is trapped within the endolysosomal compartment generating lamellar bodies which resemble the characteristics of phospholipidosis. Various inherited lysosomal storage diseases including sphingolipidosis, glycosphingolipidosis and cholesterylester storage diseases also present a phospholipidosis phenotype. In contrast E-LDL resembling coreless unesterified cholesterol enriched LDL-particles, with a multilamellar, liposome-like structure, lead to rapid phagosomal degradation and cytosolic lipid droplet accumulation. As a consequence the uptake of E-LDL through type I and type II phagocytosis leads to increased lipid droplet formation and moderate upregulation of ABCA1 and ABCG1 while uptake of Ox-LDL leads to a rapid expansion of the lysosomal compartment and a pronounced upregulation of the ABCA1/ABCG1/AP-3 lipid efflux pathway.

Interactions between the juvenile Batten disease gene, CLN3, and the Notch and JNK signalling pathways

Mutations in the gene CLN3 are responsible for the neurodegenerative disorder juvenile neuronal ceroid lipofuscinosis or Batten disease. CLN3 encodes a multi-spanning and hydrophobic transmembrane protein whose function is unclear. As a consequence, the cell biology that underlies the pathology of the disease is not well understood. We have developed a genetic gain-of-function system in Drosophila to identify functional pathways and interactions for CLN3. We have identified previously unknown interactions between CLN3 and the Notch and Jun N-terminal kinase signalling pathways and have uncovered a potential role for the RNA splicing and localization machinery in regulating CLN3 function.

Novel families of vacuolar amino acid transporters

Amino acids are compartmentalized in the vacuoles of microorganisms and plants. In Saccharomyces cerevisiae, basic amino acids accumulate preferentially into vacuoles but acidic amino acids are almost excluded from them. This indicates that selective machineries operate at the vacuolar membrane. The members of the amino acid/auxin permease family and the major facilitator superfamily involved in the vacuolar compartmentalization of amino acids have been recently identified in studies using S. cerevisiae. Homologous genes for these transporters are also found in plant and mammalian genomes. The physiological significance in response to nitrogen starvation can now be discussed.

JNCL patients show marked brain volume alterations on longitudinal MRI in adolescence

Juvenile neuronal ceroid lipofuscinosis (JNCL, CLN3) is an inherited lysosomal disease. We used longitudinal MRI, for the first time, to evaluate the rate of brain volume alterations in JNCL. Six patients (mean ages of 12.4 years and 17.3 years) and 12 healthy controls were studied twice with 1.5 T MRI. White matter (WM), gray matter (GM) and CSF volumes were measured from the sets of T1-weighted 3-dimensional MR images using a fully automated image-processing procedure. The brain volume alterations were calculated as percentage change per year. The GM and whole brain volumes decreased and the CSF volume increased significantly more in the patients than in controls (p-values for the null hypothesis of equal means were 0.001, 0.004, and 0.005, respectively). We found no difference in the WM volume change between the populations. In patients, the GM volume decreased 2.4 % (SD 0.5 %, p 0.0001 for the null hypothesis of zero mean change between observations), the whole brain volume decreased 1.1 % (SD 0.5 %, p = 0.003), and the CSF volume increased 2.7 % (SD 1.8 %, p = 0.01) per year. In normal controls, only the mean white matter volume was significantly altered (0.8 % increase, SD 0.7 %, and p = 0.001).

CONCLUSION

We demonstrated by longitudinal MRI that the annual rate of the gray matter loss in adolescent JNCL patients is as high as 2.4 %.

Phenotypic characterization of a mouse model of juvenile neuronal ceroid lipofuscinosis

Juvenile neuronal ceroid lipofuscinosis (JNCL) is an autosomal recessively inherited neurodegenerative disorder that results from mutations in the CLN3 gene. JNCL is characterized by accumulation of autofluorescent lysosomal storage bodies, vision loss, seizures, progressive cognitive and motor decline, and premature death. Studies were undertaken to characterize the neuronal ceroid lipofuscinosis phenotype in a Cln3 knockout mouse model. Progressive accumulation of autofluorescent storage material was observed in brain and retina of affected mice. The Cln3(-/-) mice exhibited progressively impaired inner retinal function, altered pupillary light reflexes, losses of inner retinal neurons, and reduced brain mass. Behavioral changes included reduced spontaneous activity levels and impaired learning and memory. In addition, Cln3(-/-) mice had significantly shortened life spans. These phenotypic features indicate that the mouse model will be useful for investigating the mechanisms underlying the disease pathology in JNCL and provide quantitative markers of disease pathology that can be used for evaluating the efficacies of therapeutic interventions.

Intermediate levels of neuronal palmitoyl-protein Delta-9 desaturase in heterozygotes for murine Batten disease

We recently demonstrated reduced activity of a novel palmitoyl-protein Delta-9 desaturase in neuronal tissues from mice with the cln3 Juvenile Neuronal Ceroid-Lipofuscinosis (Batten disease) gene ablated. In this follow-up study we have been able to obtain tissues from heterozygous cln3 mice and report that the enzyme activity in brain and pancreas from the heterozygotes is intermediate at 40% of the wild-type activity and consistent with recessive inheritance. Neuronal tissues from the CLN1 knock-out mouse demonstrated normal enzymatic activity pointing to the specificity of the desaturase function to CLN3. Non-neuronal tissues did not have measurable desaturase activity in wild-type or knock-out mice using this assay system. This may be due to lack of sensitivity of our assay system in these tissues or failure to activate the enzyme in these tissues. This is the first report of a heterozygous abnormality in Batten disease and provides important confirmation that this is the function of the CLN3 protein in neuronal tissues.

Thalami and corona radiata in juvenile NCL (CLN3): a voxel-based morphometric study

Juvenile neuronal ceroid lipofuscinosis (CLN3) is characterized by progressive cerebral atrophy. The purpose of this study was to re-evaluate the three-dimensional magnetic resonance (3D-MR) images of patients with CLN3 using voxel-based morphometry (VBM) to achieve a detailed understanding of the affected brain regions. T1-weighted 3D-MR images of 15 patients with CLN3 (age range: 12-25 years, mean age 17.6 years) and 15 age- and sex-matched controls were analyzed using VBM. VBM showed strikingly focal alterations in the brains of CLN3 patients: the gray matter volume was significantly decreased in the dorsomedial part of the thalami of CLN3 patients. In addition, the volume of the white matter was significantly decreased in the corona radiata, containing cortical efferents and afferents in the transition between the internal capsule and the subcortical white matter. These data suggest that the dorsomedial part of the thalamus and the corona radiata may have a central, previously unrecognized role in the pathogenesis of CLN3.

Neuropsychological symptoms of juvenile-onset batten disease: experiences from 2 studies

Juvenile neuronal ceroid lipofuscinosis (Batten disease) is a progressive and fatal autosomal-recessive inherited lysosomal storage disorder of childhood. Core symptoms include vision loss, seizures, and mental and motor decline. This article presents data from 2 studies of neuropsychological function in juvenile neuronal ceroid lipofuscinosis. In the first cross-sectional pilot study, 15 children with genetic or clinicopathologic confirmation of juvenile neuronal ceroid lipofuscinosis completed a brief test of attention (mean age = 14.3 +/- 2.9 years, range = 8.75-18.74 years; 7 males, 8 females). Average attention performances were significantly below age-expected normative data. A second longitudinal study was then initiated to study neuropsychological function in greater depth, including change in function over time. The authors have enrolled 18 children to date (mean age = 12.88 +/- 3.59 years, range = 6.26-18.65; 11 males, 7 females). Of these, 5 children have completed a second (annual) re-evaluation. Results thus far indicate significant impairment in domains of auditory attention, memory, estimated verbal intellectual function, and verbal fluency. Neuropsychological impairment was significantly correlated with disease duration and with motor function as assessed by a disease-specific clinical neurologic rating scale. There was no significant difference between males and females in neuropsychological test performance. Neuropsychological function was worse among children with a positive seizure history. Juvenile neuronal ceroid lipofuscinosis-affected children exhibited significant and pervasive impairments on tests of auditory attention, verbal memory and repetition, verbal fluency, and an estimate of verbal intellectual ability. Preliminary follow-up data from an annual reassessment showed progressive declines in cognitive function, in particular on a task of working memory. Neuropsychological deficits are pervasive and progressive. Future research will focus on clarifying the relationship among disease duration, motor function, and neuropsychological performances, including the relative sensitivity of neuropsychological testing at different stages of motor impairment or disease duration.

Absence of Btn1p in the yeast model for juvenile Batten disease may cause arginine to become toxic to yeast cells

Lymphoblast cell lines established from individuals with juvenile Batten disease (JNCL) bearing mutations in CLN3 and yeast strains lacking Btn1p (btn1-Delta), the homolog to CLN3, have decreased intracellular levels of arginine and defective lysosomal/vacuolar transport of arginine. It is important to establish the basis for this decrease in arginine levels and whether restoration of arginine levels would be of therapeutic value for Batten disease. Previous studies have suggested that synthesis and degradation of arginine are unaltered in btn1-Delta. Using the yeast model for the Batten disease, we have determined that although btn1-Delta results in decreased intracellular arginine levels, it does not result from altered arginine uptake, arginine efflux or differences in arginine incorporation into peptides. However, expression of BTN1 is dependent on arginine and Gcn4p, the master regulator of amino acid biosynthesis. Moreover, deletion of GCN4 (gcn4-Delta), in combination with btn1-Delta, results in a very specific growth requirement for arginine. In addition, increasing the intracellular levels of arginine through overexpression of Can1p, the plasma membrane basic amino acid permease, results in increased cell volume and a severe growth defect specific to basic amino acid availability for btn1-Delta, but not wild-type cells. Therefore, elevation of intracellular levels of arginine in btn1-Delta cells is detrimental and is suggestive that btn1-Delta and perhaps mutation of CLN3 predispose cells to keep arginine levels lower than normal.

Progressive oxidative damage in the central nervous system of a murine model for juvenile Batten disease

Oxidative damage is a known contributor to the pathogenesis of neurodegenerative diseases. Juvenile Batten disease is a progressive neurodegenerative disorder of childhood that results from mutation in Cln3. We have performed an initial characterization of the oxidative burden throughout the CNS in a Cln3(-/-) mouse model for juvenile Batten disease. A survey of multiple regions of the Cln3(-/-) mouse brain revealed a specific reduction of total glutathione, a tripeptide antioxidant molecule, in the cerebellum. Further analysis revealed an increase in protein oxidation not only in the cerebellum but also in the thalamus and primary motor cortex. Additionally, the thalamus was found to have an increase in the amount of a potent antioxidant enzyme, manganese superoxide dismutase (MnSOD), which may be in response to an increase in deleterious superoxide radicals. Colocalization studies indicate that microglia are localized directly adjacent to neurons expressing MnSOD, indicating that microglial activation may be related to the observed oxidative damage. This study helps to provide an initial measure of regions within the CNS of Cln3(-/-) mice that are specifically affected by the loss of CLN3 function and may serve to identify at the neuroanatomical level, the sequence of events that plays a role in the pathogenesis and clinical course of juvenile Batten disease.

Distinct patterns of serum immunoreactivity as evidence for multiple brain-directed autoantibodies in juvenile neuronal ceroid lipofuscinosis

Autoantibodies to glutamic acid decarboxylase (GAD65) have been reported in sera from the Cln3(-/-) mouse model of juvenile neuronal ceroid lipofuscinosis (JNCL), and in individuals with this fatal paediatric neurodegenerative disorder. To investigate the existence of other circulating autoreactive antibodies, we used sera from patients with JNCL and other forms of neuronal ceroid lipofuscinosis (NCL) as primary antisera to stain rat and human central nervous system sections. JNCL sera displayed characteristic patterns of IgG, but not IgA, IgE or IgM immunoreactivity that was distinct from the other forms of NCL. Immunoreactivity of JNCL sera was not confined to GAD65-positive (GABAergic) neurons, but also stained multiple other cell populations. Preadsorption of JNCL sera with recombinant GAD65 reduced the intensity of the immunoreactivity, but did not significantly change its staining pattern. Moreover, sera from Stiff Person Syndrome and Type I Diabetes, disorders in which GAD65 autoantibodies are present, stained with profiles that were markedly different from JNCL sera. Collectively, these studies provide evidence of the presence of autoreactive antibodies within multiple forms of NCL, and are not exclusively directed towards GAD65.

CLN3P, the Batten's disease protein, is a novel palmitoyl-protein Delta-9 desaturase

OBJECTIVE

Batten's disease, one of the most common recessively inherited, untreatable, neurodegenerative diseases of humans, is characterized by progressive neuronal loss and intraneuronal proteolipid storage. Although the gene for the disorder was cloned more than a decade ago, the function of the encoded protein, CLN3P, has not been defined thus far.

METHODS

Sequence analysis using the Pfam server identified a low stringency match to a fatty acid desaturase domain in the N-terminal sequence of CLN3P. We developed a fatty acid desaturase assay based on measurement of desaturase products by gas chromatography/mass spectrometry.

RESULTS

We show that CLN3P is a novel palmitoyl-protein Delta-9 desaturase, which converts membrane-associated palmitoylated proteins to their respective palmitoleated derivatives. We have further demonstrated that this palmitoyl-protein Delta-9 desaturase activity is deficient in cln3(-/-) mouse pancreas and is completely ablated in neuroblastoma cells by RNA inhibition.

INTERPRETATION

We propose that palmitoyl-protein desaturation defines a new mechanism of proteolipid modification, and that deficiency of this process leads to the signs and symptoms of Batten's 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.

Characterizing pathogenic processes in Batten disease: Use of small eukaryotic model systems

The neuronal ceroid lipofuscinoses (NCLs) are neurodegenerative disorders. Nevertheless, small model organisms, including those lacking a nervous system, have proven invaluable in the study of mechanisms that underlie the disease and in studying the functions of the conserved proteins associated to each disease. From the single-celled yeast, Saccharomyces cerevisiae and Schizosaccharomyces pombe, to the worm, Caenorhabditis elegans and the fruitfly, Drosophila melanogaster, biochemical and, in particular, genetic studies on these organisms have provided insight into the NCLs.

From genes to systems: new global strategies for the characterization of NCL biology

Neuronal ceroid lipofuscinoses (NCL) are rare neurological disorders with a uniform phenotype, caused by mutations in seven known genes. NCL provide a unique model to characterize molecular pathways critical for normal neuronal development and pathological neuronal degeneration. Systems biology based approach utilizes the rapidly developing tools of genomics, proteomics, lipidomics and metabolomics and aims at thorough understanding of the functions of cells, tissues and whole organisms by molecular analysis and biocomputing-assisted modeling. The systems level understanding of NCL is now possible by utilizing different model organisms. Initial work has revealed disturbed metabolic pathways in several NCL disorders and most analyses have utilized the infantile (INCL/CLN1) and juvenile (JNCL/CLN3) disease modeling and utilized mainly human and mouse samples. To date, the data obtained from transcript and lipidomic profiling has pinpointed the role of lipid metabolism and synaptic function in the infantile NCL. Changes in glutamate utilization and amino acid metabolism have been a common theme emerging from the transcript and metabolite profiling of the juvenile NCL. Further experimental models are being developed and systematic sample collection as well as data integration projects are needed. The combined analyses of the global information should provide means to expose all the NCL-associated molecular pathways.

Over-expression of CLN3P, the Batten disease protein, inhibits PANDER-induced apoptosis in neuroblastoma cells: further evidence that CLN3P has anti-apoptotic properties

Juvenile neuronal ceroid-lipofuscinosis (JNCL) or Batten/Spielmeyer-Vogt-Sjogren disease (OMIM #204200) is one of a group of nine clinically related inherited neurodegenerative disorders (CLN1-9). JNCL results from mutations in CLN3 on chromosome 16p12.1. The neuronal loss in Batten disease has been shown to be due to a combination of apoptosis and autophagy suggesting that CLN3P, the defective protein, may have an anti-neuronal death function. PANDER (PANcreatic-DERived factor) is a novel cytokine that was recently cloned from pancreatic islet cells. PANDER is specifically expressed in the pancreatic islets, small intestine, testis, prostate, and neurons of the central nervous system, and has been demonstrated to induce apoptosis. In this study, we over-expressed CLN3P in SH-SY5Y neuroblastoma cells and monitored the effects on PANDER-induced apoptosis. CLN3P significantly increased the survival rate of the SH-SY5Y cells in this system. This study provides additional evidence that the function of CLN3P is related to preventing neuronal apoptosis.

The Niemann-Pick C1 protein in recycling endosomes of presynaptic nerve terminals

Niemann-Pick type C (NPC) disease is a fatal, neurodegenerative disorder caused in 95% of cases by loss of function of NPC1, a ubiquitous endosomal transmembrane protein. A biochemical hallmark of NPC deficiency is cholesterol accumulation in the endocytic pathway. Although cholesterol trafficking defects are observed in all cell types, neurons are the most vulnerable to NPC1 deficiency, suggesting a specialized function for NPC1 in neurons. We investigated the subcellular localization of NPC1 in neurons to gain insight into the mechanism of action of NPC1 in neuronal metabolism. We show that NPC1 is abundant in axons of sympathetic neurons and is present in recycling endosomes in presynaptic nerve terminals. NPC1 deficiency causes morphological and biochemical changes in the presynaptic nerve terminal. Synaptic vesicles from Npc1(-/-) mice have normal cholesterol content but altered protein composition. We propose that NPC1 plays a previously unrecognized role in the presynaptic nerve terminal and that NPC1 deficiency at this site might contribute to the progressive neurological impairment in NPC disease.

Selectively increased sensitivity of cerebellar granule cells to AMPA receptor-mediated excitotoxicity in a mouse model of Batten disease

Batten disease, a lysosomal storage disorder, is caused by mutations in the CLN3 gene. The Cln3-knockout (Cln3-/-) mouse model of the disease exhibits many characteristic pathological features of the human disorder. Here, we show that Cln3-/- mice, similarly to Batten disease patients, have a deficit in cerebellar motor coordination. To explore the possible cellular cause of this functional impairment, we compared the vulnerability of wild type (WT) and Cln3-/- cerebellar granule cell cultures to different toxic insults. We have found that cultured Cln3-/- cerebellar granule cells are selectively more vulnerable to AMPA-type glutamate receptor-mediated toxicity than their WT counterparts. This selective sensitivity was also observed in organotypic cerebellar slice cultures. Our results suggest that lack of the CLN3 protein has a significant influence on the function of AMPA receptors in cerebellar granule neurons, and that AMPA receptor dysregulation may be a major contributor to the cerebellar dysfunction in Batten disease.

Thematic review series: lipid posttranslational modifications. Structural biology of protein farnesyltransferase and geranylgeranyltransferase type I

More than 100 proteins necessary for eukaryotic cell growth, differentiation, and morphology require posttranslational modification by the covalent attachment of an isoprenoid lipid (prenylation). Prenylated proteins include members of the Ras, Rab, and Rho families, lamins, CENPE and CENPF, and the gamma subunit of many small heterotrimeric G proteins. This modification is catalyzed by the protein prenyltransferases: protein farnesyltransferase (FTase), protein geranylgeranyltransferase type I (GGTase-I), and GGTase-II (or RabGGTase). In this review, we examine the structural biology of FTase and GGTase-I (the CaaX prenyltransferases) to establish a framework for understanding the molecular basis of substrate specificity and mechanism. These enzymes have been identified in a number of species, including mammals, fungi, plants, and protists. Prenyltransferase structures include complexes that represent the major steps along the reaction path, as well as a number of complexes with clinically relevant inhibitors. Such complexes may assist in the design of inhibitors that could lead to treatments for cancer, viral infection, and a number of deadly parasitic diseases.

You say lipofuscin, we say ceroid: defining autofluorescent storage material

Accumulation of intracellular autofluorescent material or "aging pigment" has been characterized as a normal aging event. Certain diseases also exhibit a similar accumulation of intracellular autofluorescent material. However, autofluorescent storage material associated with aging and disease has distinct characteristics. Lipofuscin is a common term for aging pigments, whereas ceroid is used to describe pathologically derived storage material, for example, in the neuronal ceroid lipofuscinoses (NCLs). NCLs are a family of neurodegenerative diseases that are characterized by an accumulation of autofluorescent storage material (ceroid) in the lysosome, which has been termed "lipofuscin-like". There have been many studies that describe this autofluorescent storage material, but what is it? Is this accumulation lipofuscin or ceroid? In this review we will try to answer the following questions: (1) What is lipofuscin and ceroid? (2) What contributes to the accumulation of this storage material in one or the other? (3) Does this material have an effect on cellular function? Studying parallels between the accumulation of lipofuscin and ceroid may provide insight into the biological relevance of these phenomena.

Defective lysosomal arginine transport in juvenile Batten disease

Mutations in the CLN3 gene, which encodes a lysosomal membrane protein, are responsible for the neurodegenerative disorder juvenile Batten disease. A previous study on the yeast homolog to CLN3, designated Btn1p, revealed a potential role for CLN3 in the transport of arginine into the yeast vacuole, the equivalent organelle to the mammalian lysosome. Lysosomes isolated from lymphoblast cell lines, established from individuals with juvenile Batten disease-bearing mutations in CLN3, but not age-matched controls, demonstrate defective transport of arginine. Furthermore, we show that there is a depletion of arginine in cells derived from individuals with juvenile Batten disease. We have, therefore, characterized lysosomal arginine transport in normal lysosomes and show that it is ATP-, v-ATPase- and cationic-dependent. This and previous studies have shown that both arginine and lysine are transported by the same transport system, designated system c. However, we report that lysosomes isolated from juvenile Batten disease lymphoblasts are only defective for arginine transport. These results suggest that the CLN3 defect in juvenile Batten disease may affect how intracellular levels of arginine are regulated or distributed throughout the cell. This assertion is supported by two other experimental approaches. First, an antibody to CLN3 can block lysosomal arginine transport and second, expression of CLN3 in JNCL cells using a lentiviral vector can restore lysosomal arginine transport. CLN3 may have a role in regulating intracellular levels of arginine possibly through control of the transport of this amino acid into lysosomes.