A novel CLN5 mutation in Turkish patient with variant late-onset neuronal ceroid lipofuscinosis and recurrent fractures that causes severe morbidity

Neuronal ceroid lipofuscinosis (NCL) is characterized by ataxia, epilepsy, mental and motor deterioration, and visual loss. The phenotype of patients is highly heterogeneous. We report a patient with late-infantile-onset psychomotor retardation, visual loss, seizure, movement disorder, and recurrent bone fractures. Clinical exome sequencing revealed a novel homozygous c.1113_1116del, p.Y371fs mutation in CLN5. No variant was detected associated with simple bone cyst. While NCL disease is difficult disease in itself, recurrent fractures significantly increased morbidity. This case report contributes to genotypic spectrum of CLN5 and emphasizes clinical importance of Turkish patients with CLN5 mutations, and non-NCL factors/diseases can adversely affect morbidity.

Deficiency of the Lysosomal Protein CLN5 Alters Lysosomal Function and Movement

Batten disease is a devastating, childhood, rare neurodegenerative disease characterised by the rapid deterioration of cognition and movement, leading to death within ten to thirty years of age. One of the thirteen Batten disease forms, CLN5 Batten disease, is caused by mutations in the CLN5 gene, leading to motor deficits, mental deterioration, cognitive impairment, visual impairment, and epileptic seizures in children. A characteristic pathology in CLN5 Batten disease is the defects in lysosomes, leading to neuronal dysfunction. In this study, we aimed to investigate the lysosomal changes in CLN5-deficient human neurons. We used an induced pluripotent stem cell system, which generates pure human cortical-like glutamatergic neurons. Using CRISPRi, we inhibited the expression of CLN5 in human neurons. The CLN5-deficient human neurons showed reduced acidic organelles and reduced lysosomal enzyme activity measured by microscopy and flow cytometry. Furthermore, the CLN5-deficient human neurons also showed impaired lysosomal movement-a phenotype that has never been reported in CLN5 Batten disease. Lysosomal trafficking is key to maintain local degradation of cellular wastes, especially in long neuronal projections, and our results from the human neuronal model present a key finding to understand the underlying lysosomal pathology in neurodegenerative diseases.

Aberrant Autophagy Impacts Growth and Multicellular Development in a Dictyostelium Knockout Model of CLN5 Disease

Mutations in CLN5 cause a subtype of neuronal ceroid lipofuscinosis (NCL) called CLN5 disease. While the precise role of CLN5 in NCL pathogenesis is not known, recent work revealed that the protein has glycoside hydrolase activity. Previous work on the Dictyostelium discoideum homolog of human CLN5, Cln5, revealed its secretion during the early stages of development and its role in regulating cell adhesion and cAMP-mediated chemotaxis. Here, we used Dictyostelium to examine the effect of cln5-deficiency on various growth and developmental processes during the life cycle. During growth, cln5^– cells displayed reduced cell proliferation, cytokinesis, viability, and folic acid-mediated chemotaxis. In addition, the growth of cln5^– cells was severely impaired in nutrient-limiting media. Based on these findings, we assessed autophagic flux in growth-phase cells and observed that loss of cln5 increased the number of autophagosomes suggesting that the basal level of autophagy was increased in cln5^– cells. Similarly, loss of cln5 increased the amounts of ubiquitin-positive proteins. During the early stages of multicellular development, the aggregation of cln5^– cells was delayed and loss of the autophagy genes, atg1 and atg9, reduced the extracellular amount of Cln5. We also observed an increased amount of intracellular Cln5 in cells lacking the Dictyostelium homolog of the human glycoside hydrolase, hexosaminidase A (HEXA), further supporting the glycoside hydrolase activity of Cln5. This observation was also supported by our finding that CLN5 and HEXA expression are highly correlated in human tissues. Following mound formation, cln5^– development was precocious and loss of cln5 affected spore morphology, germination, and viability. When cln5^– cells were developed in the presence of the autophagy inhibitor ammonium chloride, the formation of multicellular structures was impaired, and the size of cln5^– slugs was reduced relative to WT slugs. These results, coupled with the aberrant autophagic flux observed in cln5^– cells during growth, support a role for Cln5 in autophagy during the Dictyostelium life cycle. In total, this study highlights the multifaceted role of Cln5 in Dictyostelium and provides insight into the pathological mechanisms that may underlie CLN5 disease.

CLN5 and CLN3 function as a complex to regulate endolysosome function

CLN5 is a soluble endolysosomal protein whose function is poorly understood. Mutations in this protein cause a rare neurodegenerative disease, neuronal ceroid lipofuscinosis (NCL). We previously found that depletion of CLN5 leads to dysfunctional retromer, resulting in the degradation of the lysosomal sorting receptor, sortilin. However, how a soluble lysosomal protein can modulate the function of a cytosolic protein, retromer, is not known. In this work, we show that deletion of CLN5 not only results in retromer dysfunction, but also in impaired endolysosome fusion events. This results in delayed degradation of endocytic proteins and in defective autophagy. CLN5 modulates these various pathways by regulating downstream interactions between CLN3, an endolysosomal integral membrane protein whose mutations also result in NCL, RAB7A, and a subset of RAB7A effectors. Our data support a model where CLN3 and CLN5 function as an endolysosomal complex regulating various functions.

Intravitreal gene therapy protects against retinal dysfunction and degeneration in sheep with CLN5 Batten disease

Neuronal ceroid lipofuscinoses (NCL; Batten disease) are a group of inherited neurodegenerative diseases primarily affecting children. A common feature across most NCLs is the progressive loss of vision. We performed intravitreal injections of self-complementary AAV9 vectors packaged with either ovine CLN5 or CLN6 into one eye of 3-month-old CLN5-/- or CLN6-/- animals, respectively. Electroretinography (ERG) was performed every month following treatment, and retinal histology was assessed post-mortem in the treated compared to untreated eye. In CLN5-/- animals, ERG amplitudes were normalised in the treated eye whilst the untreated eye declined in a similar manner to CLN5 affected controls. In CLN6-/- animals, ERG amplitudes in both eyes declined over time although the treated eye showed a slower decline. Post-mortem examination revealed significant attenuation of retinal atrophy and lysosomal storage body accumulation in the treated eye compared with the untreated eye in CLN5-/- animals. This proof-of-concept study provides the first observation of efficacious intravitreal gene therapy in a large animal model of NCL. In particular, the single administration of AAV9-mediated intravitreal gene therapy can successfully ameliorate retinal deficits in CLN5-/- sheep. Combining ocular gene therapy with brain-directed therapy presents a promising treatment strategy to be used in future sheep trials aiming to halt neurological and retinal disease in CLN5 Batten disease.

A lysosomal enigma CLN5 and its significance in understanding neuronal ceroid lipofuscinosis

Neuronal Ceroid Lipofuscinosis (NCL), also known as Batten disease, is an incurable childhood brain disease. The thirteen forms of NCL are caused by mutations in thirteen CLN genes. Mutations in one CLN gene, CLN5, cause variant late-infantile NCL, with an age of onset between 4 and 7 years. The CLN5 protein is ubiquitously expressed in the majority of tissues studied and in the brain, CLN5 shows both neuronal and glial cell expression. Mutations in CLN5 are associated with the accumulation of autofluorescent storage material in lysosomes, the recycling units of the cell, in the brain and peripheral tissues. CLN5 resides in the lysosome and its function is still elusive. Initial studies suggested CLN5 was a transmembrane protein, which was later revealed to be processed into a soluble form. Multiple glycosylation sites have been reported, which may dictate its localisation and function. CLN5 interacts with several CLN proteins, and other lysosomal proteins, making it an important candidate to understand lysosomal biology. The existing knowledge on CLN5 biology stems from studies using several model organisms, including mice, sheep, cattle, dogs, social amoeba and cell cultures. Each model organism has its advantages and limitations, making it crucial to adopt a combinatorial approach, using both human cells and model organisms, to understand CLN5 pathologies and design drug therapies. In this comprehensive review, we have summarised and critiqued existing literature on CLN5 and have discussed the missing pieces of the puzzle that need to be addressed to develop an efficient therapy for CLN5 Batten disease.

Knockdown of CLN5 inhibits the tumorigenic properties of glioblastoma cells via the Akt/mTOR signaling pathway

Gliomas are highly malignant tumors with a rapid progression and poor prognosis. The present study investigated the cellular effects of CLN5-knockdown in the glioblastoma (GBM) U251 and U87MG cell lines. The Cell Counting Kit-8 and colony formation assays indicated that CLN5-knockdown inhibited the proliferation of GBM cells. Additionally, the results of the Transwell and scratch assays revealed that CLN5-knockdown significantly inhibited migration and invasion, and the flow cytometry analysis confirmed that apoptosis was promoted. Knockdown of CLN5 downregulated the expression levels of MMP-2, Bcl-2, cyclin D1, CDK4 and CDK6, and upregulated the expression levels of Bax and activated caspase-9. Additionally, it blocked GBM cells in the G1-phase and induced early apoptosis. Knockdown of CLN5 inhibited the activation of the Akt and mTOR signaling pathways in GBM by decreasing the levels of phosphorylated (p)-Akt and p-mTOR. The present data suggested that downregulation of CLN5 may be a potential treatment option for GBM. Knockdown of CLN5 inhibited the development of GBM via the inhibition of the Akt and mTOR signaling pathways.

Functional Analysis of a Novel CLN5 Mutation Identified in a Patient With Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinoses (NCLs) are a group of autosomal recessive inherited neurodegenerative disorders mainly affecting children, and at least 13 causative genes (CLN1 to CLN8 and CLN10 to CLN14) have been identified. Here, we reported a novel homozygous missense mutation (c.434G > C, p.Arg145Pro) identified in CLN5 gene via whole exome sequencing in a 5-year-old girl. The patient first presented paroxysmal epilepsy associated with vomiting, followed by progressive regression in walking, vision, intelligence and speaking. Combining the molecular and clinical analysis, the diagnosis of NCL could be made, although the missense mutation (c.434G > C, p.Arg145Pro) in CLN5 was evaluated to be a variant of uncertain significance according to American College of Medical Genetics and Genomics (ACMG) standard. We further performed expression and localization studies and our results provide evidence of impaired cellular trafficking of CLN5 to lysosome, indicating that this mutation might be deleterious to the function of CLN5 for its mislocalization. Our study demonstrated the efficacy of next generation sequencing in molecular diagnosis, and a deleterious effect of the variant discovered in our patient on CLN5, triggering the NCL disease.

Novel likely disease-causing CLN5 variants identified in Pakistani patients with neuronal ceroid lipofuscinosis

BACKGROUND

Neuronal ceroid lipofuscinosis (NCL) is a hereditary lysosomal storage disease with progressive brain neurodegeneration. Mutations in ceroid lipofuscinosis neuronal protein 5 (CLN5) cause CLN5 disease, a severe condition characterized by seizures, visual failure, motor decline, and progressive cognitive deterioration. This study aimed to identify causative gene variants in Pakistani consanguineous families diagnosed with NCL.

METHODS

After a thorough clinical and neuroradiological characterization, whole exome sequencing (WES) was performed in 3 patients from 2 unrelated families. Segregation analysis was subsequently performed through Sanger sequencing ANALYSIS: WES led to the identification of the 2 novel homozygous variants c.925_926del, (p.Leu309AlafsTer4) and c.477 T > C, (p.Cys159Arg).

CONCLUSION

In this study, we report two novel CLN5 cases in the Punjab region of Pakistan. Our observations will help clinicians observe and compare common and unique clinical features of NCL patients, further improving our current understanding of NCL.

A novel pathogenic frameshift variant unmasked by a large de novo deletion at 13q21.33-q31.1 in a Chinese patient with neuronal ceroid lipofuscinosis type 5

BACKGROUND

Neuronal ceroid lipofuscinosis type 5 (CLN5) is a rare form of neuronal ceroid lipofuscinoses (NCLs) which are a group of inherited neurodegenerative diseases characterized by progressive intellectual and motor deterioration, visual failure, seizures, behavioral changes and premature death. CLN5 was initially named Finnish variant late infantile NCL, it is now known to be present in other ethnic populations and with variable age of onset. Few CLN5 patients had been reported in Chinese population.

CASE PRESENTATION

In this paper, we report the symptoms of a Chinese patient who suffer from developmental regression and grand mal epilepsy for several years. The DNA was extracted from peripheral blood of proband and both parents, and then whole exome sequencing was performed using genomic DNA. Both sequence variants and copy number variants (CNVs) were analyzed and classified according to guidelines. As the result, a novel frameshift mutation c.718_719delAT/p.Met240fs in CLN5 and a de novo large deletion at 13q21.33-q31.1 which unmasked the frameshift mutation were identified in the proband. Despite the large de novo deletion, which can be classified as a pathogenic copy number variant (CNV), the patient's clinical presentation is mostly consistent with that of CLN5, except for early developmental delay which is believed due to the large deletion. Both variants were detected simultaneously by exome sequencing.

CONCLUSIONS

This is the first report of whole gene deletion in combination with a novel pathogenic sequence variant in a CLN5 patient. The two mutations detected with whole exome sequencing simultaneously proved the advantage of the sequencing technology for genetic diagnostics.

The Neuronal Ceroid Lipofuscinoses-Linked Loss of Function CLN5 and CLN8 Variants Disrupt Normal Lysosomal Function

Neuronal ceroid lipofuscinoses (NCLs) are a group of neurodegenerative disorders caused by mutations in fourteen distinct ceroid lipofuscinoses, neuronal (CLN) genes described with various severe symptoms such as seizures, visual failure, motor decline, and progressive cognitive deterioration. The current research represents novel CLN5 (c.741G > A) and CLN8 (c.565delT) mutations in two different Iranian families with late-infantile NCL (LINCL) and their relatives by using whole-exome sequencing (WES). The first family had a 10-year-old male with consanguineous parents and severe NCL symptoms, including motor clumsiness, telangiectasia, and cerebellar atrophy. The second family with a child who suffered from nystagmus rotation, motor difficulties, and seizure was a 5-year-old male with consanguineous parent. WES of probands 1 and 2 revealed homozygotic mutations in exon 4 of CLN5 (c.741G > A, p.W247X) and deletion in exon 3 (c.565delT, p.F189fs) of CLN8, respectively. Both patients' parents were heterozygous for these alterations. In concordance with previous studies, our results indicate that pathogenic mutations in CLN genes, especially CLN5 and 8, are a main cause of LINCL; these results also suggest that LINCL is not a regionally or nationally dependent disorder and can occur in any ethnic group despite the fact that some populations may be more at risk. Consequently, CLN gene screening for patients with typical signs of LINCL is recommended.

A mixed breed dog with neuronal ceroid lipofuscinosis is homozygous for a CLN5 nonsense mutation previously identified in Border Collies and Australian Cattle Dogs

The neuronal ceroid lipofuscinoses (NCLs) are a group of inherited neurodegenerative disorders characterized by progressive declines in neurological functions following normal development. The NCLs are distinguished from similar disorders by the accumulation of autofluorescent lysosomal storage bodies in neurons and many other cell types, and are classified as lysosomal storage diseases. At least 13 genes contain pathogenic sequence variants that underlie different forms of NCL. Naturally occurring canine NCLs can serve as models to develop better understanding of the disease pathologies and for preclinical evaluation of therapeutic interventions for these disorders. To date 14 sequence variants in 8 canine orthologs of human NCL genes have been found to cause progressive neurological disorders similar to human NCLs in 12 different dog breeds. A mixed breed dog with parents of uncertain breed background developed progressive neurological signs consistent with NCL starting at approximately 11 to 12 months of age, and when evaluated with magnetic resonance imaging at 21 months of age exhibited diffuse brain atrophy. Due to the severity of neurological decline the dog was euthanized at 23 months of age. Cerebellar and cerebral cortical neurons contained massive accumulations of autofluorescent storage bodies the contents of which had the appearance of tightly packed membranes. A whole genome sequence, generated with DNA from the affected dog contained a homozygous C-to-T transition at position 30,574,637 on chromosome 22 which is reflected in the mature CLN5 transcript (CLN5: c.619C > T) and converts a glutamine codon to a termination codon (p.Gln207Ter). The identical nonsense mutation has been previously associated with NCL in Border Collies, Australian Cattle Dogs, and a German Shepherd-Australian Cattle Dog mix. The current whole genome sequence and a previously generated whole genome sequence for an Australian Cattle Dog with NCL share a rare homozygous haplotype that extends for 87 kb surrounding 22: 30, 574, 637 and includes 21 polymorphic sites. When genotyped at 7 of these polymorphic sites, DNA samples from the German Shepherd-Australian Cattle Dog mix and from 5 Border Collies with NCL that were homozygous for the CLN5: c.619 T allele also shared this homozygous haplotype, suggesting that the NCL in all of these dogs stems from the same founding mutation event that may have predated the establishment of the modern dog breeds. If so, the CLN5 nonsence allele is probably segregating in other, as yet unidentified, breeds. Thus, dogs exhibiting similar NCL-like signs should be screened for this CLN5 nonsense allele regardless of breed.

Next-Generation Sequencing Analysis Reveals Novel Pathogenic Variants in Four Chinese Siblings With Late-Infantile Neuronal Ceroid Lipofuscinosis

Neuronal Ceroid Lipofuscinoses (NCLs) are progressive degenerative diseases mainly affect brain and retina. They are characterized by accumulation of autofluorescent storage material, mitochondrial ATPase subunit C, or sphingolipid activator proteins A and D in lysosomes of most cells. Heterogenous storage material in NCLs is not completely disease-specific. Most of CLN proteins and their natural substrates are not well-characterized. Studies have suggested variants of Late-Infantile NCLs (LINCLs) include the major type CLN2 and minor types CLN5, CLN6, CLN7, and CLN8. Therefore, combination of clinical and molecular analysis has become a more effective diagnosis method. We studied 4 late-infantile NCL siblings characterized by seizures, ataxia as early symptoms, followed by progressive regression in intelligence and behavior, but mutations are located in different genes. Symptoms and progression of 4 types of LINCLs are compared. Pathology of LINCLs is also discussed. We performed Nest-Generation Sequencing on these phenotypically similar families. Three novel variants c.1551+1insTGAT in TPP1, c.244G>T in CLN6, c.554-5A>G in MFSD8 were identified. Potential outcome of the mutations in structure and function of proteins are studied. In addition, we observed some common and unique clinical features of Chinese LINCL patient as compared with those of Western patients, which greatly improved our understanding of the LINCLs.

Recent Insights into NCL Protein Function Using the Model Organism Dictyostelium discoideum

The neuronal ceroid lipofuscinoses (NCLs) are a group of devastating neurological disorders that have a global distribution and affect people of all ages. Commonly known as Batten disease, this form of neurodegeneration is linked to mutations in 13 genetically distinct genes. The precise mechanisms underlying the disease are unknown, in large part due to our poor understanding of the functions of NCL proteins. The social amoeba Dictyostelium discoideum has proven to be an exceptional model organism for studying a wide range of neurological disorders, including the NCLs. The Dictyostelium genome contains homologs of 11 of the 13 NCL genes. Its life cycle, comprised of both single-cell and multicellular phases, provides an excellent system for studying the effects of NCL gene deficiency on conserved cellular and developmental processes. In this review, we highlight recent advances in NCL research using Dictyostelium as a biomedical model.

Novel Mutations in CLN5 of Chinese Patients With Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinosis is a hereditary disease, and ceroid-lipofuscinosis neuronal protein 5 (CLN5) has been proved to be associated with neuronal ceroid lipofuscinosis. Here we report 3 patients from 2 families diagnosed with CLN5 neuronal ceroid lipofuscinosis. Whole genome sequencing of DNAs from 3 patients and their families revealed 3 novel homozygous mutations, including 1 deletion CLN5.c718 719delAT and 2 missense mutations c.1082T>C and c.623G>A. We reviewed 278 papers about neuronal ceroid lipofuscinosis resulting from CLN5 mutations and compared Chinese cases with 27 European and American cases. The overall age of onset of European and American patients occur mainly at 3 to 6 years (66%, 18/27), 100% (27/27) of patients had psychomotor regression, 99% (26/27) patients presented vision decline, and 70% (19/27) of patients suffered seizures. In China, the age of onset in 3 patients was 5 years, but for 1 patient it was at 17 months. Four Chinese patients presented psychomotor deterioration and seizures; only 1 had visual problems.

An Alzheimer's Disease-Linked Loss-of-Function CLN5 Variant Impairs Cathepsin D Maturation, Consistent with a Retromer Trafficking Defect

In a whole-exome sequencing study of multiplex Alzheimer's disease (AD) families, we investigated three neuronal ceroid lipofuscinosis genes that have been linked to retromer, an intracellular trafficking pathway associated with AD: ceroid lipofuscinosis 3 (CLN3), ceroid lipofuscinosis 5 (CLN5), and cathepsin D (CTSD). We identified a missense variant in CLN5 c.A959G (p.Asn320Ser) that segregated with AD. We find that this variant causes glycosylation defects in the expressed protein, which causes it to be retained in the endoplasmic reticulum with reduced delivery to the endolysosomal compartment, CLN5's normal cellular location. The AD-associated CLN5 variant is shown here to reduce the normal processing of cathepsin D and to decrease levels of full-length amyloid precursor protein (APP), suggestive of a defect in retromer-dependent trafficking.

Secretion and function of Cln5 during the early stages of Dictyostelium development

Mutations in CLN5 cause neuronal ceroid lipofuscinosis (NCL), a currently untreatable neurodegenerative disorder commonly known as Batten disease. Several genetic models have been generated to study the function of CLN5, but one limitation has been the lack of a homolog in lower eukaryotic model systems. Our previous work revealed a homolog of CLN5 in the social amoeba Dictyostelium discoideum. We used a Cln5-GFP fusion protein to show that the protein is secreted and functions as a glycoside hydrolase in Dictyostelium. Importantly, we also revealed this to be the molecular function of human CLN5. In this study, we generated an antibody against Cln5 to show that the endogenous protein is secreted during the early stages of Dictyostelium development. Like human CLN5, the Dictyostelium homolog is glycosylated and requires this post-translational modification for secretion. Cln5 secretion bypasses the Golgi complex, and instead, occurs via an unconventional pathway linked to autophagy. Interestingly, we observed co-localization of Cln5 and GFP-Cln3 as well as increased secretion of Cln5 and Cln5-GFP in cln3- cells. Loss of Cln5 causes defects in adhesion and chemotaxis, which intriguingly, has also been reported for Dictyostelium cells lacking Cln3. Finally, autofluorescence was detected in cln5- cells, which is consistent with observations in mammalian systems. Together, our data support a function for Cln5 during the early stages of multicellular development, provide further evidence for the molecular networking of NCL proteins, and provide insight into the mechanisms that may underlie CLN5 function in humans.

Cln5 is secreted and functions as a glycoside hydrolase in Dictyostelium

Ceroid lipofuscinosis neuronal 5 (CLN5) is a member of a family of proteins that are linked to neuronal ceroid lipofuscinosis (NCL). This devastating neurological disorder, known commonly as Batten disease, affects all ages and ethnicities and is currently incurable. The precise function of CLN5, like many of the NCL proteins, remains to be elucidated. In this study, we report the localization, molecular function, and interactome of Cln5, the CLN5 homolog in the social amoeba Dictyostelium discoideum. Residues that are glycosylated in human CLN5 are conserved in the Dictyostelium homolog as are residues that are mutated in patients with CLN5 disease. Dictyostelium Cln5 contains a putative signal peptide for secretion and we show that the protein is secreted during growth and starvation. We also reveal that both Dictyostelium Cln5 and human CLN5 are glycoside hydrolases, providing the first evidence in any system linking a molecular function to CLN5. Finally, immunoprecipitation coupled with mass spectrometry identified 61 proteins that interact with Cln5 in Dictyostelium. Of the 61 proteins, 67% localize to the extracellular space, 28% to intracellular vesicles, and 20% to lysosomes. A GO term enrichment analysis revealed that a majority of the interacting proteins are involved in metabolism, catabolism, proteolysis, and hydrolysis, and include other NCL-like proteins (e.g., Tpp1/Cln2, cathepsin D/Cln10, cathepsin F/Cln13) as well as proteins linked to Cln3 function in Dictyostelium (e.g., AprA, CfaD, CadA). In total, this work reveals a CLN5 homolog in Dictyostelium and further establishes this organism as a complementary model system for studying the functions of proteins linked to NCL in humans.

Loss of Cln5 causes altered neurogenesis in a mouse model of a childhood neurodegenerative disorder

Neural stem/progenitor cells (NPCs) generate new neurons in the brain throughout an individual's lifetime in an intricate process called neurogenesis. Neurogenic alterations are a common feature of several adult-onset neurodegenerative diseases. The neuronal ceroid lipofuscinoses (NCLs) are the most common group of inherited neurodegenerative diseases that mainly affect children. Pathological features of the NCLs include accumulation of lysosomal storage material, neuroinflammation and neuronal degeneration, yet the exact cause of this group of diseases remains poorly understood. The function of the CLN5 protein, causative of the CLN5 disease form of NCL, is unknown. In the present study, we sought to examine neurogenesis in the neurodegenerative disorder caused by loss of Cln5 Our findings demonstrate a newly identified crucial role for CLN5 in neurogenesis. We report for the first time that neurogenesis is increased in Cln5-deficient mice, which model the childhood neurodegenerative disorder caused by loss of Cln5 Our results demonstrate that, in Cln5 deficiency, proliferation of NPCs is increased, NPC migration is reduced and NPC differentiation towards the neuronal lineage is increased concomitantly with functional alterations in the NPCs. Moreover, the observed impairment in neurogenesis is correlated with increased expression of the pro-inflammatory cytokine IL-1β. A full understanding of the pathological mechanisms that lead to disease and the function of the NCL proteins are critical for designing effective therapeutic approaches for this devastating neurodegenerative disorder.

CLN5 is cleaved by members of the SPP/SPPL family to produce a mature soluble protein

The Neuronal ceroid lipofuscinoses (NCLs) are a group of recessive disorders of childhood with overlapping symptoms including vision loss, ataxia, cognitive regression and premature death. 14 different genes have been linked to NCLs (CLN1-CLN14), but the functions of the proteins encoded by the majority of these genes have not been fully elucidated. Mutations in the CLN5 gene are responsible for the Finnish variant late-infantile form of NCL (Finnish vLINCL). CLN5 is translated as a 407 amino acid transmembrane domain containing protein that is heavily glycosylated, and subsequently cleaved into a mature soluble protein. Functionally, CLN5 is implicated in the recruitment of the retromer complex to endosomes, which is required to sort the lysosomal sorting receptors from endosomes to the trans-Golgi network. The mechanism that processes CLN5 into a mature soluble protein is currently not known. Herein, we demonstrate that CLN5 is initially translated as a type II transmembrane protein and subsequently cleaved by SPPL3, a member of the SPP/SPPL intramembrane protease family, into a mature soluble protein consisting of residues 93-407. The remaining N-terminal fragment is then cleaved by SPPL3 and SPPL2b and degraded in the proteasome. This work further characterizes the biology of CLN5 in the hopes of identifying a novel therapeutic strategy for affected children.

Induced Pluripotent Stem Cells Derived from a CLN5 Patient Manifest Phenotypic Characteristics of Neuronal Ceroid Lipofuscinoses

Neuronal ceroid lipofuscinoses (NCLs) are autosomal recessive progressive encephalopathies caused by mutations in at least 14 different genes. Despite extensive studies performed in different NCL animal models, the molecular mechanisms underlying neurodegeneration in NCLs remain poorly understood. To model NCL in human cells, we generated induced pluripotent stem cells (iPSCs) by reprogramming skin fibroblasts from a patient with CLN5 (ceroid lipofuscinosis, neuronal, 5) disease, the late infantile variant form of NCL. These CLN5 patient-derived iPSCs (CLN5Y392X iPSCs) harbouring the most common CLN5 mutation, c.1175_1176delAT (p.Tyr392X), were further differentiated into neural lineage cells, the most affected cell type in NCLs. The CLN5Y392X iPSC-derived neural lineage cells showed accumulation of autofluorescent storage material and subunit C of the mitochondrial ATP synthase, both representing the hallmarks of many forms of NCLs, including CLN5 disease. In addition, we detected abnormalities in the intracellular organelles and aberrations in neuronal sphingolipid transportation, verifying the previous findings obtained from Cln5-deficient mouse macrophages. Therefore, patient-derived iPSCs provide a suitable model to study the mechanisms of NCL diseases.

Proteolytic processing of the neuronal ceroid lipofuscinosis related lysosomal protein CLN5

CLN5 is a soluble lysosomal glycoprotein. Deficiency in CLN5 protein causes neuronal ceroid lipofuscinosis, an inherited neurodegenerative lysosomal storage disorder. The function of CLN5 and how it affects lysosome activity are unclear. We identified two forms of the CLN5 protein present in most of the cell lines studied. The molecular mass difference between these two forms is about 4kDa. The fibroblast cells derived from two CLN5 patients lack both forms. Using transient transfection, we showed one of these two forms is a proprotein and the other is a C-terminal cleaved mature form. Using cycloheximide chase analysis, we were able to demonstrate that the C-terminal processing occurs post-translationally. By treating cells with several pharmaceutical drugs to inhibit proteases, we showed that the C-terminal processing takes place in an acidic compartment and the protease involved is most likely a cysteine protease. This is further supported by overexpression of a CLN5 patient mutant D279N and a glycosylation mutant N401Q, showing that the C-terminal processing takes place beyond the endoplasmic reticulum, and can occur as early as from the trans Golgi network. Furthermore, we demonstrated that CLN5 is expressed in a variety of murine tissues.

Recent studies of ovine neuronal ceroid lipofuscinoses from BARN, the Batten Animal Research Network

Studies on naturally occurring New Zealand and Australian ovine models of the neuronal ceroid-lipofuscinoses (Batten disease, NCLs) have greatly aided our understanding of these diseases. Close collaborations between the New Zealand groups at Lincoln University and the University of Otago, Dunedin, and a group at the University of Sydney, Australia, led to the formation of BARN, the Batten Animal Research Network. This review focusses on presentations at the 14th International Conference on Neuronal Ceroid Lipofuscinoses (Batten Disease), recent relevant background work, and previews of work in preparation for publication. Themes include CLN5 and CLN6 neuronal cell culture studies, studies on tissues from affected and control animals and whole animal in vivo studies. Topics include the effect of a CLN6 mutation on endoplasmic reticulum proteins, lysosomal function and the interactions of CLN6 with other lysosomal activities and trafficking, scoping gene-based therapies, a molecular dissection of neuroinflammation, identification of differentially expressed genes in brain tissue, an attempted therapy with an anti-inflammatory drug in vivo and work towards gene therapy in ovine models of the NCLs. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)".

Inhibition of storage pathology in prenatal CLN5-deficient sheep neural cultures by lentiviral gene therapy

The neuronal ceroid lipofuscinoses (NCLs, Batten disease) are inherited neurodegenerative lysosomal storage diseases caused by mutations in several different genes. Mutations in CLN5 cause a variant late-infantile human disease and some cases of juvenile and adult clinical disease. NCLs also occur in animals, and a flock of New Zealand Borderdale sheep with a CLN5 splice-site mutation has been developed for model studies. Dissociated mixed neural cells from CLN5-deficient foetal sheep brains contained no obvious storage bodies at plating but these accumulated rapidly in culture, mainly in microglial cells and also in neurons and astrocytes. Accumulation was very obvious after a week, as monitored by fluorescent microscopy and immunostaining for subunit c of mitochondrial ATP synthase. Photography at intervals revealed the dynamic nature of the cultures and a flow of storage bodies between cells, specifically the phagocytosis of storage-body containing cells by microglia and incorporation of the storage bodies into the host cells. No storage was observed in cultured control cells. Transduction of cell cultures with a lentiviral vector expressing a C-terminal Myc tagged CLN5 resulted in secretion of post-translationally glycosylated and processed CLN5. Transduction of CLN5-deficient cultures with this construct rapidly reversed storage body accumulation, to less than half in only six days. These results show that storage body accumulation is reversible with enzyme correction and support the use of these cultures for testing of therapeutics prior to whole animal studies.

Topology and membrane anchoring of the lysosomal storage disease-related protein CLN5

One late infantile variant of the neurodegenerative disease neuronal ceroid lipofuscinosis (NCL) is caused by a mutation in the CLN5 gene. CLN5 encodes a lysosomal glycoprotein whose structure and function have not yet been clearly defined. In the present study, we used epitope-tagged CLN5 to determine the topology and solubility of the CLN5 protein. Our results indicated that CLN5 is synthesized as a type II transmembrane (TM) glycoprotein with a cytoplasmic N-terminus, one TM segment, and a large luminal C-terminal domain containing an amphipathic helix (AH). The cytoplasmic and TM domains were rapidly removed following signal-peptide cleavage, and the resulting mature CLN5 was tightly associated with the lumen of the membrane through the AH. CLN5 pathological mutants deprived of AH lose their membrane association, are retained in the endoplasmic reticulum, and are rapidly degraded by the proteasomal machinery. We experimentally define the topology of CLN5 and demonstrate the existence of an AH that anchors the protein to the membrane. Our work sheds light on the basic properties of CLN5 required to better understand its biological functions and involvement in NCL pathogenesis.

Atypical juvenile neuronal ceroid lipofuscinosis: A report of three cases

The diagnosis of juvenile neuronal ceroid lipofuscinosis (JNCL) is usually based on age of onset, initial clinical symptoms, clinical progression, and pathologic findings. Our cases manifested atypical clinical symptomatology and/or pathologic findings and therefore, represent variant forms of JNCL. Case 1 and 2 presented with slow developmental regression from the age of 4 years and became blind and wheelchair bound at around 8 years. Pathologic finding of lymphocytes showed fingerprint inclusion which was consistent with JNCL. Mutational analysis was positive for CLN5 which usually presents as variant late infantile NCL (LINCL) and more common in Finnish population. Case 3 presented with progressive visual loss from the age of 8 years. Clinical symptomatology and age of onset were similar to that of JNCL but was found to have low palmitoyl protein thioesterase, granular inclusion body, and CLN1 mutation, thus representing milder form of INCL. These three cases demonstrated phenotypic-genotypic variations. Pertinent issues relating diagnostic difficulties, ophthalmologic, neuroradiological, and laboratory aspects are discussed.