Batten disease: four genes and still counting

Neuronal Ceroid-Lipofuscinosis in a Holstein Steer

A young, partially blind Holstein steer was affected by mild cerebral atrophy. Formalin-fixed cerebral gray matter was diffusely yellow brown. Microscopically, there were eosinophilic, autofluorescent granules primarily in the cytoplasm of cerebral neurons. There was also extensive retinal atrophy with complete loss of the rod and cone layers. Ultrastructural examination of affected cerebral neurons revealed a mixture of granular osmiophilic and lamellar patterns in the cytoplasmic storage bodies. This suggests the existence of neuronal ceroid-lipofuscinosis in the Holstein breed.

The Batten disease gene CLN3 confers resistance to endoplasmic reticulum stress induced by tunicamycin

Mutations in CLN3 gene cause juvenile neuronal ceroid lipofuscinosis (JNCL or Batten disease), an early-onset neurodegenerative disorder that is characterized by the accumulation of ceroid lipofuscin within lysosomes. The function of the CLN3 protein remains unclear and is presumed to be related to Endoplasmic reticulum (ER) stress. To investigate the function of CLN3 in the ER stress signaling pathway, we measured proliferation and apoptosis in cells transfected with normal and mutant CLN3 after treatment with the ER stress inducer tunicamycin (TM). We found that overexpression of CLN3 was sufficient in conferring increased resistance to ER stress. Wild-type CLN3 protected cells from TM-induced apoptosis and increased cell proliferation. Overexpression of wild-type CLN3 enhanced expression of the ER chaperone protein, glucose-regulated protein 78 (GRP78), and reduced expression of the proapoptotic protein CCAAT/-enhancer-binding protein homologous protein (CHOP). In contrast, overexpression of mutant CLN3 or siRNA knockdown of CLN3 produced the opposite effect. Together, our data suggest that the lack of CLN3 function in cells leads to a failure of management in the response to ER stress and this may be the key deficit in JNCL that causes neuronal degeneration.

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

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

Saccharomyces cerevisiae Lacking Btn1p Modulate Vacuolar ATPase Activity to Regulate pH Imbalance in the Vacuole

The vacuolar H(+)-ATPase (V-ATPase) along with ion channels and transporters maintains vacuolar pH. V-ATPase ATP hydrolysis is coupled with proton transport and establishes an electrochemical gradient between the cytosol and vacuolar lumen for coupled transport of metabolites. Btn1p, the yeast homolog to human CLN3 that is defective in Batten disease, localizes to the vacuole. We previously reported that Btn1p is required for vacuolar pH maintenance and ATP-dependent vacuolar arginine transport. We report that extracellular pH alters both V-ATPase activity and proton transport into the vacuole of wild-type Saccharomyces cerevisiae. V-ATPase activity is modulated through the assembly and disassembly of the V(0) and V(1) V-ATPase subunits located in the vacuolar membrane and on the cytosolic side of the vacuolar membrane, respectively. V-ATPase assembly is increased in yeast cells grown in high extracellular pH. In addition, at elevated extracellular pH, S. cerevisiae lacking BTN1 (btn1-Delta), have decreased V-ATPase activity while proton transport into the vacuole remains similar to that for wild type. Thus, coupling of V-ATPase activity and proton transport in btn1-Delta is altered. We show that down-regulation of V-ATPase activity compensates the vacuolar pH imbalance for btn1-Delta at early growth phases. We therefore propose that Btn1p is required for tight regulation of vacuolar pH to maintain the vacuolar luminal content and optimal activity of this organelle and that disruption in Btn1p function leads to a modulation of V-ATPase activity to maintain cellular pH homeostasis and vacuolar luminal content.

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.

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

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.

A role in vacuolar arginine transport for yeast Btn1p and for human CLN3, the protein defective in Batten disease

In Saccharomyces cerevisiae, transport of arginine into the vacuole has previously been shown to be facilitated by a putative H+/arginine antiport. We confirm that transport of arginine into isolated yeast vacuoles requires ATP and we demonstrate a requirement for a functional vacuolar H+-ATPase. We previously reported that deletion of BTN1 (btn1-delta), an ortholog of the human Batten disease gene CLN3, resulted in a decrease in vacuolar pH during early growth. We report that this altered vacuolar pH in btn1-delta strains underlies a lack of arginine transport into the vacuole, which results in a depletion of endogenous vacuolar arginine levels. This arginine transport defect in btn1-delta is complemented by expression of either BTN1 or the human CLN3 gene and strongly suggests a function for transport of, or regulation of the transport of, basic amino acids into the vacuole or lysosome for yeast Btn1p, and human CLN3 protein, respectively. We propose that defective transport at the lysosomal membrane caused by an absence of functional CLN3 is the primary biochemical defect that results in Batten disease.

Functional categorization of gene expression changes in the cerebellum of a Cln3-knockout mouse model for Batten disease

Juvenile neuronal ceroid lipofuscinosis (JNCL or Batten Disease) is the most common progressive neurodegenerative disorder of childhood. The disease is inherited in an autosomal recessive manner and is the result of mutations in the CLN3 gene. One brain region severely affected in Batten disease is the cerebellum. Using a mouse model for Batten disease which shares pathological similarities to the disease in humans we have used oligonucleotide arrays to profile approximately 19000 mRNAs in the cerebellum. We have identified reproducible changes of twofold or more in the expression of 756 gene products in the cerebellum of 10-week-old Cln3-knockout mice as compared to wild-type controls. We have subsequently divided these genes with altered expression into 14 functional categories. We report a significant alteration in expression of genes associated with neurotransmission, neuronal cell structure and development, immune response and inflammation, and lipid metabolism. An apparent shift in metabolism toward gluconeogenesis is also evident in Cln3-knockout mice. Further experimentation will be necessary to understand the contribution of these changes in expression to a disease state. Detailed analysis of the functional consequences of altered expression of genes in the cerebellum of the Cln3-knockout mice may provide valuable clues in understanding the molecular basis of the pathological mechanisms underlying Batten disease.

The neuronal ceroid lipofuscinoses: mutations in different proteins result in similar disease

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.

Molecular genetic testing for neuronal ceroid lipofuscinoses

Eight different NCL forms have been recognized to be encoded by genes CLN1-8. CLN1,2,3,5,and 8 have been cloned, and at least 85 mutations have been detected. Molecular technology can now be applied to genetic testing for NCLs; testing is now available in clinic diagnostic and research laboratories for CLN genes that have been cloned. Molecular genetic testing makes it possible not only to confirm clinical and pathological diagnoses but also to offer pre-symptom diagnosis and carrier screening for NCL families. In addition, DNA-based mutation analysis may predict prenatal outcome more accurately for pregnant women in NCL families.

Production and characterization of recombinant human CLN2 protein for enzyme-replacement therapy in late infantile neuronal ceroid lipofuscinosis

Late infantile neuronal ceroid lipofuscinosis (LINCL) is a fatal recessive childhood disease caused by mutations in the CLN2 gene, which encodes the lysosomal enzyme tripeptidyl peptidase I. As a step towards understanding the protein and developing therapeutics for the disease, we have produced and characterized recombinant human CLN2 (ceroid lipofuscinosis, neuronal 2) protein from Chinese-hamster ovary cells engineered to secrete high levels of the enzyme. The protein was secreted as an inactive soluble proenzyme of approximately 65 kDa that appears as a monomer by gel filtration. Upon acidification, the protein is processed to mature form and acquires activity. The enzyme is efficiently delivered to the lysosomes of LINCL fibroblasts by mannose 6-phosphate-receptor-mediated endocytosis (EC(50) approximately 2 nM), where it remains active for long periods of time (t(1/2) approximately 12 days). In addition, the enzyme is taken up by rat cerebellar granule neurons by mannose 6-phosphate-dependent and -independent mechanisms. Treatment of LINCL fibroblasts with recombinant CLN2 protein restores normal enzyme activity and ameliorates accumulation of the major storage protein, mitochondrial ATP synthase subunit c.

Molecular diagnosis of and carrier screening for the neuronal ceroid lipofuscinoses

The neuronal ceroid lipofuscinoses (NCLs) are a large group of autosomal recessive lysosomal storage disorders with both enzymatic deficiency and structural protein dysfunction. Three typical forms, the infantile (INCL), late-infantile (LINCL), and juvenile (JNCL), are among the most common childhood-onset neurodegenerative disorders. They result from mutations on genes CLN1, CLN2, and CLN3, respectively. We determined that the mutations 223A --> G and 451C --> T in CLN1, T523-1G --> C, and 636 C --> T in CLN2, and deletion of a 1.02-kb genomic fragment in CLN3 are the five common mutations for NCL. To offer clinical genetic testing for the NCLs, we have developed simple and quick PCR-based molecular tests for detecting INCL-, LINCL-, and JNCL-affected individuals from 180 NCL families (27 INCL, 76 LINCL, and 77 JNCL). The sensitivity of testing to detect NCL patients among clinically suspected individuals was determined to be 78% (21/27) for INCL, 66% (54/76) for LINCL, and 75% (58/77) for JNCL. When molecular screening for carriers was conducted among the normal siblings or parents of the probands, we identified two carriers out of three individuals tested for INCL, 20/56 (35.7%) carriers for LINCL, and 48/106 (45.3%) carriers for JNCL families. In addition, 5% (9/180) of NCL patients revealed genetic heterogeneity and were reclassified. Seven patients previously diagnosed as having JNCL were now found to carry mutations of CLN2 (5/7) or CLN1 (2/7) and 2 with late-infantile onsets were identified as carrying mutations of CLN1. Our data demonstrate the importance of DNA testing to detect accurately both affected individuals and carriers in NCL families.

Gene targets related to phospholipid and fatty acid metabolism in schizophrenia and other psychiatric disorders: an update

Phospholipids make up about 60% of the brain's dry weight and play key roles in many brain signal tranduction mechanisms. A recent review(1)identified the increasing evidence that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. This current paper reviews the main pathways of phospholipid metabolism, emphasizing the role of phospholipases of the A2 in signal tranduction processes. It also updates the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.

Tripeptidyl-peptidase I deficiency in classical late-infantile neuronal ceroid lipofuscinosis brain tissue. Evidence for defective peptidase rather than proteinase activity

Brain tissue from patients with classical late-infantile neuronal ceroid lipofuscinosis (LINCL, an infantile form of Batten disease) is deficient in the lysosomal enzyme tripeptidyl-peptidase I (EC 3.4.14.9). The activities of other lysosomal enzymes are either increased or decreased. Tripeptidyl-peptidase I is a pepstatin-insensitive exo-tripeptidase, with little or no endo-proteolytic activity, that is active on small peptides but not on large proteins. Using haemoglobin and casein as substrates for proteolytic activity, we were unable to demonstrate any significant defect in pepstatin-sensitive or pepstatin-insensitive proteinase activity in brain tissue or cultured skin fibroblasts of LINCL patients. These observations suggest that the lysosomal storage of undegraded, small peptides in LINCL results from the absence of peptidase rather than proteinase activity.

Molecular basis of the neuronal ceroid lipofuscinoses: mutations in CLN1, CLN2, CLN3, and CLN5

The neuronal ceroid lipofuscinoses (NCLs), also referred to as Batten disease, are a group of neurodegenerative disorders characterised by the accumulation of an autofluorescent lipopigment in many cell types. Different NCL types are distinguished according to age of onset, clinical phenotype, ultrastructural characterisation of the storage material, and chromosomal location of the disease gene. At least eight genes underlie the NCLs, of which four have been isolated and mutations characterised: CLN1, CLN2, CLN3, CLN5. Two of these genes encode lysosomal enzymes, and two encode transmembrane proteins, at least one of which is likely to be in the lysosomal membrane. The basic defect in the NCLs appears to be associated with lysosomal function.