👤 Jill M Weimer

Development of therapies for CLN3 disease, a rare pediatric lysosomal storage disorder, has been hindered by the lack of etiological insights and translatable biomarkers to clinics. We used a deep multi-omics approach to discover blood-based biomarkers using longitudinal serum samples from a porcine model of CLN3 disease. Comprehensive metabolomics was combined with a nanoparticle-based LC-MS-based proteomic profiling coupled with TMTpro 18-plex to generate quantitative data on 769 metabolites and 2634 proteins, collectively the most exhaustive multi-omics profile conducted on serum from a porcine model. This was previously impossible due to lack of efficient deep serum proteome profiling technologies compatible with model organisms. Here we show that the presymptomatic disease state is characterized by elevations in glycerophosphodiester species and lysosomal proteases, while later timepoints are enriched with species involved in immune cell activation and sphingolipid metabolism. Cathepsin S (CTSS), Cathepsin B (CTSB), glycerophosphoinositol, and glycerophosphoethanolamine captured a large portion of the genotype-correlated variation between healthy and diseased animals, suggesting that an index score based on these analytes could have great utility in the clinic. This study's findings demonstrate the potential of deep multi-omics profiling for uncovering disease-specific biomarkers, providing valuable insights for understanding disease and facilitating the identification of potential drug targets, thus offering valuable insights for therapeutic interventions. Show less

Innate lymphoid cells (ILCs) are rare, tissue-resident innate lymphocytes that functionally mirror CD4+ T helper cell lineages but lack antigen receptors. Type 3 ILCs (ILC3s) are enriched in the gut, airways, and mucosal lymphoid tissues, where they regulate inflammation and promote barrier integrity. To define the regulatory architecture of primary human ILC3s, we map promoter-anchored chromosomal contacts using high-resolution, low-input Promoter Capture Hi-C (PCHi-C) in these cells alongside CD4+ T cells. By combining statistical detection with a PCHi-C-adapted Activity-by-Contact approach, we link promoters to distal regulatory elements, identifying hundreds of ILC3-specific contacts. We use these maps to connect genome-wide association study (GWAS) risk variants for Crohn's disease to target genes using multiCOGS, a Bayesian framework that integrates PCHi-C with summary-statistic imputation and multivariate fine-mapping. This analysis highlights both known and unanticipated candidates, including Show less

CLN3 Batten disease is a lethal pediatric neurodegenerative disease caused by mutations in the CLN3 gene. Typically, the disease manifests as vision loss in early childhood and progresses to neurological dysfunction and death in young adulthood. Most therapeutic developments have focused on treating the brain and may not protect against vision loss, which greatly affects quality of life. We have previously shown that a splice-switching antisense oligonucleotide (ASO) delivered to the central nervous system can reduce neurological disease burden in mouse models of CLN3 disease. Here, we apply a similar ASO approach for treating retinal dysfunction in a pig model of CLN3 Batten disease, which is more representative of human vision. A single intravitreal injection of ASO induces robust exon skipping in the retina for up to 12 months. The ASO treatment resulted in higher amplitudes on electroretinograms, suggesting mitigation of retinal dysfunction at early timepoints of disease. One ASO that efficiently induces exon skipping in vivo was well-tolerated and targets a region conserved in humans, making it a promising candidate for clinical translation. Our findings demonstrate the utility of an ASO-based approach to treat retinal dysfunction in CLN3 Batten disease and support broader ASO applications for treating ocular diseases. Show less

CLN3 Batten disease (also known as juvenile neuronal ceroid lipofuscinosis) is a lysosomal storage disorder that typically initiates with retinal degeneration but is followed by seizure onset, motor decline and premature death. Patient-derived CLN3 disease induced pluripotent stem cell-RPE cells show defective phagocytosis of photoreceptor outer segment (POS). Because modifier genes are implicated in CLN3 disease, our goal here was to investigate a direct link between CLN3 mutation and POS phagocytosis defect. Isogenic control and CLN3 mutant stem cell lines were generated by CRISPR-Cas9-mediated biallelic deletion of exons 7 and 8. A transgenic CLN3Δ7-8/Δ7-8 (CLN3) Yucatan miniswine was also used to study the impact of CLN3Δ7-8/Δ7-8 mutation on POS phagocytosis. POS phagocytosis by cultured RPE cells was analyzed by Western blotting and immunohistochemistry. Electroretinogram, optical coherence tomography and histological analysis of CLN3Δ7-8/Δ7-8 and wild-type miniswine eyes were carried out at 6, 36, or 48 months of age. CLN3Δ7-8/Δ7-8 RPE (CLN3 RPE) displayed decreased POS binding and consequently decreased uptake of POS compared with isogenic control RPE cells. Furthermore, wild-type miniswine RPE cells phagocytosed CLN3Δ7-8/Δ7-8 POS less efficiently than wild-type POS. Consistent with decreased POS phagocytosis, lipofuscin/autofluorescence was decreased in CLN3 miniswine RPE at 36 months of age and was followed by almost complete loss of photoreceptors at 48 months of age. CLN3Δ7-8/Δ7-8 mutation (which affects ≤85% of patients) affects both RPE and POS and leads to photoreceptor cell loss in CLN3 disease. Furthermore, both primary RPE dysfunction and mutant POS independently contribute to impaired POS phagocytosis in CLN3 disease. Show less

CLN3 Batten disease (also known as Juvenile Neuronal Ceroid Lipofuscinosis; JNCL) is a lysosomal storage disorder that typically initiates with retinal degeneration but is followed by seizure onset, motor decline and premature death. Patient-derived CLN3 disease iPSC-RPE cells show defective phagocytosis of photoreceptor outer segments (POSs). Because modifier genes are implicated in CLN3 disease, our goal here was to investigate a direct link between Isogenic control and Show less

CLN3 disease (also known as CLN3 Batten disease or Juvenile Neuronal Ceroid Lipofuscinosis) is a rare pediatric neurodegenerative disorder caused by biallelic mutations in CLN3. While extensive efforts have been undertaken to understand CLN3 disease etiology, pathology, and clinical progression, little is known about the impact of CLN3 disease on parents and caregivers. Here, we investigated CLN3 disease progression, clinical care, and family experiences using semi-structured interviews with 39 parents of individuals with CLN3 disease. Analysis included response categorization by independent observers and quantitative methods. Parents reported patterns of disease progression that aligned with previous reports. Insomnia and thought- and mood-related concerns were reported frequently. "Decline in visual acuity" was the first sign/symptom noticed by n = 28 parents (70%). A minority of parents reported "behavioral issues" (n = 5, 12.5%), "communication issues" (n = 3, 7.5%), "cognitive decline" (n = 1, 2.5%), or "seizures" (n = 1, 2.5%) as the first sign/symptom. The mean time from the first signs or symptoms to a diagnosis of CLN3 disease was 2.8 years (SD = 4.1). Misdiagnosis was common, being reported by n = 24 participants (55.8%). Diagnostic tests and treatments were closely aligned with observed symptoms. Desires for improved or stabilized vision (top therapeutic treatment concern for n = 14, 32.6%), cognition (n = 8, 18.6%), and mobility (n = 3, 7%) dominated parental concerns and wishes for therapeutic correction. Family impacts were common, with n = 34 (81%) of respondents reporting a financial impact on the family and n = 20 (46.5%) reporting marital strain related to the disease. Collectively, responses demonstrated clear patterns of disease progression, a strong desire for therapies to treat symptoms related to vision and cognition, and a powerful family impact driven by the unrelenting nature of disease progression. Show less

Lysosomal storage disorders (LSDs) are a genetically and clinically diverse group of diseases characterized by lysosomal dysfunction. Batten disease is a family of severe LSDs primarily impacting the central nervous system. Here we show that AF38469, a small molecule inhibitor of sortilin, improves lysosomal and glial pathology across multiple LSD models. Live-cell imaging and comparative transcriptomics demonstrates that the transcription factor EB (TFEB), an upstream regulator of lysosomal biogenesis, is activated upon treatment with AF38469. Utilizing CLN2 and CLN3 Batten disease mouse models, we performed a short-term efficacy study and show that treatment with AF38469 prevents the accumulation of lysosomal storage material and the development of neuroinflammation, key disease associated pathologies. Tremor phenotypes, an early behavioral phenotype in the CLN2 disease model, were also completely rescued. These findings reveal sortilin inhibition as a novel and highly efficacious therapeutic modality for the treatment of multiple forms of Batten disease. Show less

Genetic mutations that disrupt open reading frames and cause translation termination are frequent causes of human disease and are difficult to treat due to protein truncation and mRNA degradation by nonsense-mediated decay, leaving few options for traditional drug targeting. Splice-switching antisense oligonucleotides offer a potential therapeutic solution for diseases caused by disrupted open reading frames by inducing exon skipping to correct the open reading frame. We have recently reported on an exon-skipping antisense oligonucleotide that has a therapeutic effect in a mouse model of CLN3 Batten disease, a fatal pediatric lysosomal storage disease. To validate this therapeutic approach, we generated a mouse model that constitutively expresses the Show less

Mouse models of CLN3 Batten disease, a rare lysosomal storage disorder with no cure, have improved our understanding of CLN3 biology and therapeutics through their ease of use and a consistent display of cellular pathology. However, the translatability of murine models is limited by disparities in anatomy, body size, life span and inconsistent subtle behavior deficits that can be difficult to detect in CLN3 mutant mouse models, thereby limiting their use in preclinical studies. Here, we present a longitudinal characterization of a novel miniswine model of CLN3 disease that recapitulates the most common human pathogenic variant, an exon 7-8 deletion (CLN3Δex7/8). Progressive pathology and neuron loss is observed in various regions of the CLN3Δex7/8 miniswine brain and retina. Additionally, mutant miniswine present with retinal degeneration and motor abnormalities, similar to deficits seen in humans diagnosed with the disease. Taken together, the CLN3Δex7/8 miniswine model shows consistent and progressive Batten disease pathology, and behavioral impairment mirroring clinical presentation, demonstrating its value in studying the role of CLN3 and safety/efficacy of novel disease-modifying therapeutics. Show less

CLN8-Batten disease (CLN8 disease) is a rare neurodegenerative disorder characterized phenotypically by progressive deterioration of motor and cognitive abilities, visual symptoms, epileptic seizures, and premature death. Mutations in CLN8 results in characteristic Batten disease symptoms and brain-wide pathology including accumulation of lysosomal storage material, gliosis, and neurodegeneration. Recent investigations of other subforms of Batten disease (CLN1, CLN3, CLN6) have emphasized the influence of biological sex on disease and treatment outcomes; however, little is known about sex differences in the CLN8 subtype. To determine the impact of sex on CLN8 disease burden and progression, we utilized a Cln8 Several notable sex differences were observed in the presentation of brain pathology, including Cln8 Taken together, our results provide further evidence of biologic sex as a modifier of Batten disease progression and outcome, thus warranting consideration when conducting investigations and monitoring therapeutic impact. Show less

CLN3 Batten disease is a rare pediatric neurodegenerative lysosomal disorder caused by biallelic disease-associated variants in We performed an exhaustive metabolomic screen using serum samples from a novel minipig model of CLN3 Batten disease and validated findings in CLN3 pig serum samples from 4 ages exhibited large elevations in 4 glycerophosphodiester species: glycerophosphoinositol (GPI), glycerophosphoethanolamine (GPE), glycerophosphocholine (GPC), and glycerophosphoserine (GPS). GPI and GPE exhibited the largest elevations, with similar elevations found in GPE and GPI could have utility as biomarkers of CLN3 disease status. GPI, in particular, shows consistent elevations across a diverse cohort of individuals with CLN3. This raises the potential to use these biomarkers as a blood-based diagnostic test or as an efficacy measure for disease-modifying therapies. Show less

Batten disease is unique among lysosomal storage disorders for the early and profound manifestation in the central nervous system, but little is known regarding potential neuron-specific roles for the disease-associated proteins. We demonstrate substantial overlap in the protein interactomes of three transmembrane Batten proteins (CLN3, CLN6, and CLN8), and that their absence leads to synaptic depletion of key partners (i.e., SNAREs and tethers) and altered synaptic SNARE complexing Show less

Mutations in CLN3 lead to photoreceptor cell loss in CLN3 disease, a lysosomal storage disorder characterized by childhood-onset vision loss, neurological impairment, and premature death. However, how CLN3 mutations cause photoreceptor cell death is not known. Here, we show that CLN3 is required for phagocytosis of photoreceptor outer segment (POS) by retinal pigment epithelium (RPE) cells, a cellular process essential for photoreceptor survival. Specifically, a proportion of CLN3 in human, mouse, and iPSC-RPE cells localized to RPE microvilli, the site of POS phagocytosis. Furthermore, patient-derived CLN3 disease iPSC-RPE cells showed decreased RPE microvilli density and reduced POS binding and ingestion. Notably, POS phagocytosis defect in CLN3 disease iPSC-RPE cells could be rescued by wild-type CLN3 gene supplementation. Altogether, these results illustrate a novel role of CLN3 in regulating POS phagocytosis and suggest a contribution of primary RPE dysfunction for photoreceptor cell loss in CLN3 disease that can be targeted by gene therapy. Show less

CLN3 Batten disease (CLN3 disease) is a pediatric lysosomal storage disorder that presents with progressive blindness, motor and cognitive decline, seizures, and premature death. CLN3 disease results from mutations in CLN3 with the most prevalent mutation, a 966 bp deletion spanning exons 7-8, affecting ~ 75% of patients. Mouse models with complete Cln3 deletion or Cln3 Show less

Mycophenolate, an immunosuppressant, is commonly used off-label for autoimmune neurological conditions. In CLN3 disease, a neurodegenerative disorder of childhood, preclinical and clinical data suggest secondary autoimmunity and inflammation throughout the central nervous system are key components of pathogenesis. We tested the short-term tolerability of mycophenolate in individuals with CLN3 disease, in preparation for possible long-term efficacy trials of this drug. We conducted a randomized, double-blind, placebo-controlled, crossover study of mycophenolate in 19 ambulatory individuals with CLN3 disease to determine the safety and tolerability of short-term administration (NCT01399047). The study included two 8-week treatment periods with a 4-week intervening washout. Mycophenolate was well tolerated. 89.5% of participants completed the mycophenolate arm, on the assigned study dose (95% CI: 66.9-98.7%), and there were no significant differences in tolerability rates between mycophenolate and placebo arms (10.5%; 95% CI: -3.3-24.3%, p = 0.21). All reported adverse events were mild in severity; the most common adverse events on mycophenolate were vomiting (31.6%; 95% CI: 12.6-56.6%), diarrhea (15.8%; 95% CI: 3.4-39.6%), and cough (15.8%; 95% CI: 3.4-39.6%). These did not occur at a significantly increased frequency above placebo. There were no definite effects on measured autoimmunity or clinical outcomes in the setting of short-term administration. Study of long-term exposure is needed to test the impact of mycophenolate on key clinical features and CLN3 disease trajectory. Show less

CLN3-Batten disease is a rare, autosomal recessive disorder involving seizures, visual, motor and cognitive decline, and premature death. The Cln3Δex7/8 mouse model recapitulates several phenotypic characteristics of the most common 1.02kb disease-associated deletion. Identification of reproducible biomarker(s) to facilitate longitudinal monitoring of disease progression and provide readouts for therapeutic response has remained elusive. One factor that has complicated the identification of suitable biomarkers in this mouse model has been that variations in animal husbandry appear to significantly influence readouts. In the current study, we cross-compared a number of biological parameters in blood from Cln3Δex7/8 mice and control, non-disease mice on the same genetic background from multiple animal facilities in an attempt to better define a surrogate marker of CLN3-Batten disease. Interestingly, we found that significant differences between Batten and non-disease mice found at one site were generally not maintained across different facilities. Our results suggest that colony variation in the Cln3Δex7/8 mouse model of CLN3-Batten disease can influence potential biomarkers of the disease. Show less

Obesity, type 2 diabetes and associated metabolic diseases are characterized by low-grade systemic inflammation which involves interplay of nutrition and monocyte/macrophage functions. We suggested that some factors such as nutrient components, neuropeptides involved in the control of gastrointestinal functions, and gastrointestinal hormones might influence immune cell functions and in this way contribute to the disease pathogenesis. The aim of this study was to investigate the mRNA expression of twelve nutrition-associated receptors in peripheral blood mononuclear cells (PBMC), isolated monocytes and monocyte-derived macrophages and their regulation under the switching from the high-carbohydrate low-fat diet to the low-carbohydrate high-fat (LC/HFD) isocaloric diet in healthy humans. The mRNA expression of receptors for short chain fatty acids (GPR41, GPR43), bile acids (TGR5), incretins (GIPR, GLP1R), cholecystokinin (CCKAR), neuropeptides VIP and PACAP (VIPR1, VIPR2), and neurotensin (NTSR1) was detected in PBMC and monocytes, while GPR41, GPR43, GIPR, TGR5, and VIPR1 were found in macrophages. Correlations of the receptor expression in monocytes with a range of metabolic and inflammatory markers were found. In non-obese subjects, the dietary switch to LC/HFD induced the increase of GPR43 and VIPR1 expression in monocytes. No significant differences of receptor expression between normal weight and moderately obese subjects were found. Our study characterized for the first time the expression pattern of nutrition-associated receptors in human blood monocytes and its dietary-induced changes linking metabolic responses to nutrition with immune functions in health and metabolic diseases. Show less

Juvenile neuronal ceroid lipofuscinosis (JNCL), or Batten disease, is a neurodegenerative disease resulting from a mutation in CLN3, which presents clinically with visual deterioration, seizures, motor impairments, cognitive decline, hallucinations, loss of circadian rhythm, and premature death in the late-twenties to early-thirties. Using a Cln3 null (Cln3(-/-)) mouse, we report here several deficits in the cerebellum in the absence of Cln3, including cell loss and early onset motor deficits. Surprisingly, early onset glial activation and selective neuronal loss within the mature fastigial pathway of the deep cerebellar nuclei (DCN), a region critical for balance and coordination, are seen in many regions of the Cln3(-/-) cerebellum. Additionally, there is a loss of Purkinje cells (PC) in regions of robust Bergmann glia activation in Cln3(-/-) mice and human JNCL post-mortem cerebellum. Moreover, the Cln3(-/-) cerebellum had a mis-regulation in granule cell proliferation and maintenance of PC dendritic arborization and spine density. Overall, this study defines a novel multi-faceted, early-onset cerebellar disruption in the Cln3 null brain, including glial activation, cell loss, and aberrant cell proliferation and differentiation. These early alterations in the maturation of the cerebellum could underlie some of the motor deficits and pathological changes seen in JNCL patients. Show less

HP1 proteins are thought to be modulators of chromatin organization in all mammals, yet their exact physiological function remains unknown. In a first attempt to elucidate the function of these proteins in vivo, we disrupted the murine Cbx1 gene, which encodes the HP1-beta isotype, and show that the Cbx1(-/-) -null mutation leads to perinatal lethality. The newborn mice succumbed to acute respiratory failure, whose likely cause is the defective development of neuromuscular junctions within the endplate of the diaphragm. We also observe aberrant cerebral cortex development in Cbx1(-/-) mutant brains, which have reduced proliferation of neuronal precursors, widespread cell death, and edema. In vitro cultures of neurospheres from Cbx1(-/-) mutant brains reveal a dramatic genomic instability. Our results demonstrate that HP1 proteins are not functionally redundant and that they are likely to regulate lineage-specific changes in heterochromatin organization. Show less

Batten disease, or juvenile neuronal ceroid lipofuscinosis (JNCL), results from mutations in the CLN3 gene. This disorder presents clinically around the age of 5 years with visual deficits progressing to include seizures, cognitive impairment, motor deterioration, hallucinations, and premature death by the third to fourth decade of life. The motor deficits include coordination and gait abnormalities, myoclonic jerks, inability to initiate movements, and spasticity. Previous work from our laboratory has identified an early reduction in catechol-O-methyltransferase (COMT), an enzyme responsible for the efficient degradation of dopamine. Alterations in the kinetics of dopamine metabolism could cause the accumulation of undegraded or unsequestered dopamine leading to the formation of toxic dopamine intermediates. We report an imbalance in the catabolism of dopamine in 3 month Cln3(-/-) mice persisting through 9 months of age that may be causal to oxidative damage within the striatum at 9 months of age. Combined with the previously reported inflammatory changes and loss of post-synaptic D1alpha receptors, this could facilitate cell loss in striatal projection regions and underlie a general locomotion deficit that becomes apparent at 12 months of age in Cln3(-/-) mice. This study provides evidence for early changes in the kinetics of COMT in the Cln3(-/-) mouse striatum, affecting the turnover of dopamine, likely leading to neuron loss and motor deficits. These data provide novel insights into the basis of motor deficits in JNCL and how alterations in dopamine catabolism may result in oxidative damage and localized neuronal loss in this disorder. Show less

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. Show less

Juvenile neuronal ceroid lipofuscinosis (JNCL) is an autosomal recessive disorder of childhood caused by mutations in CLN3. Although visual deterioration is typically the first clinical sign to manifest in affected children, loss of Cln3 in a mouse model of JNCL does not recapitulate this retinal deterioration. This suggests that either the loss of CLN3 does not directly affect retinal cell survival or that nuclei involved in visual processing are affected prior to retinal degeneration. Having previously demonstrated that Cln3(-/-) mice have decreased optic nerve axonal density, we now demonstrate a decrease in nerve conduction. Examination of retino-recipient regions revealed a decreased number of neurons within the dorsal lateral geniculate nucleus (LGNd). We demonstrate decreased transport of amino acids from the retina to the LGN, suggesting an impediment in communication between the retina and projection nuclei. This study defines a novel path of degeneration within the LGNd, providing a mechanism for causation of JNCL visual deficits. Show less

Juvenile Neuronal Ceroid Lipofuscinosis (JNCL), or Batten disease, is a childhood neurodegenerative disease that is characterized clinically by progressive visual loss, seizures, dementia, and motor incoordination. Children affected with this disease tend to develop normally for the first 5 years of life. However, once disease onset occurs, they decline rapidly and die in their late 20s to early 30s. Though this represents the typical disease course, the onset and severity of disease symptoms can vary. This variability is presumed to be the result of both differences in the causative genetic mutation in the CLN3 gene as well as environmental influences. Most cases of JNCL are caused by a 1 kb deletion in the CLN3 gene, resulting in a frameshift mutation predicted to leave the first 153 amino acids of the CLN3 protein intact, followed by the addition of 28 novel amino acids. Here we report the discovery of a novel mutation identified as a G to T transversion at nucleotide 49 (G49T) in exon 2 of CLN3, introducing a premature stop codon (E17X) near the N-terminus. This mutation represents the most 5' mutation described to date. The patient examined in this study was heterozygous for the common 1 kb deletion and E17X. She had classical disease progression, suggesting that this mutation in CLN3 mimics the more prevalent 1 kb deletion and that progression of JNCL is predominantly the result of loss of CLN3 function. Show less

Hook1 is a member of a family of microtubule-binding proteins. Studies on the Drosophila homolog of Hook1 have suggested a role in the maturation and trafficking of internalized proteins to the late endosome. A weak interaction between Hook1 and the lysosomal/late endosomal protein, CLN3, was recently reported. Mutations in CLN3 result in the neurological disorder Batten disease. Here we show a novel interaction between Hook1 and Ankyrin G, an adaptor protein that binds the spectrin-actin cytoskeleton and targets proteins to the peripheral membrane. Although we demonstrate co-localization of Hook1 and Ankyrin G, Hook1 also localizes to additional regions of the cell devoid of Ankyrin G where it likely interacts with other proteins. There is no disruption of the Hook1-Ankyrin G interaction or localization in tissue derived from a Cln3-knockout mouse despite a nearly threefold increase in the expression of Hook1. However, mutation of CLN3 could lead to alterations in the functioning and positioning of organelles and membrane proteins through this Hook1-Ankyrin G interaction. Show less

Batten disease, an inherited neurodegenerative storage disease affecting children, results from the autosomal recessive inheritance of mutations in Cln3. The function of the CLN3 protein remains unknown. A key to understanding the pathology of this devastating disease will be to elucidate the function of CLN3 at the cellular level. CLN3 has proven difficult to study as it is predicted to be a membrane protein expressed at relatively low levels. This article is a critical review of various approaches used in examining the structure, trafficking, and localization of CLN3. We conclude that CLN3 is likely resident in the lysosomal/endosomal membrane. Different groups have postulated conflicting orientations for CLN3 within this membrane. In addition, CLN3 undergoes several posttranslational modifications and is trafficked through the endoplasmic reticulum and Golgi. Recent evidence also suggests that CLN3 traffics via the plasma membrane. Although the function of this protein remains elusive, it is apparent that genetic alterations in Cln3 may have a direct affect on lysosomal function. Show less

The neuronal ceroid-lipofuscinoses (NCL) are the most common group of progressive neurodegenerative diseases in children, with an incidence as high as one in 12,500 live births. The main features of this disease are failure of psychomotor development, impaired vision, seizures, and premature death. Many biochemical and physiological studies have been initiated to determine the cellular defect underlying the disease, although only a few traits have been truly associated with the disorders. One of the paradox's of the NCL-diseases is the characteristic accumulation of autofluorescent hydrophobic material in the lysosomes of neurons and other cell types. However, the accumulation of this lysosomal storage material, which no doubt contributes to the neurologic disease, does not apparently lead to disease outside the CNS, and how these cellular alterations relate to the neurodegeneration in NCLs is unknown. Mutations have been identified in six distinct genes/proteins, namely CLN1, which encodes PPT1, a protein thiolesterase; CLN2, which encodes TPP1, a serine protease; and CLN3, CLN5, CLN6, and CLN8, which encode novel transmembrane proteins. Mutation in any one of these CLN-proteins results in a distinct type of NCL-disease. However, there are many shared similarities in the pathology of these diseases. The most obvious connection between PPT1, TPP1, CLN3, CLN5, CLN6, and CLN8 is their subcellular localization. To date, three of the four proteins whose subcellular localization has been confirmed, namely PPT1, TPP1, and CLN3, reside in the lysosome. We review the function of the CLN-proteins and discuss the possibility that a disruption in a common biological process leads to an NCL-disease. Show less