The intracellular location and function of proteins of neuronal ceroid lipofuscinoses

Cathepsin regulation on microglial function

Microglia, the resident mononuclear phagocyte population in the brain, have long been implicated in the pathology of neurodegenerative age-associated disorders. However, activated microglia have now been identified as homeostatic keepers in the brain, because they are involved in the initiation and resolution of neuropathology. The complex roles of activated microglia appear to be linked to change from inflammatory and neurotoxic to anti-inflammatory and neuroprotective phenotypes. Increased expression and secretion of various cathepsins support roles of activated microglia in chronic neuroinflammation, the neurotoxic M1-like polarization and neuronal death. Moreover, changes in expression and localization of microglial cathepsin B play a critical role in the acceleration of the brain aging. Beyond the role as brain-resident macrophages, many lines of evidence have shown that microglia have essential roles in the maturation and maintenance of neuronal circuits in the developing and adult brain. Cathepsin S secreted from microglia induces the diurnal variation of spine density of cortical neurons though proteolytic modification of peri-synaptic extracellular matrix molecules. In this review, I highlight the emerging roles of cathepsins that support the roles of microglia in both normal healthy and pathological brains. In addition, I discuss cathepsin inhibitors as potential therapeutic targets for brain disorders.

An Autophagy Modifier Screen Identifies Small Molecules Capable of Reducing Autophagosome Accumulation in a Model of CLN3-Mediated Neurodegeneration

Alterations in the autophagosomal–lysosomal pathway are a major pathophysiological feature of CLN3 disease, which is the most common form of childhood-onset neurodegeneration. Accumulating autofluorescent lysosomal storage material in CLN3 disease, consisting of dolichols, lipids, biometals, and a protein that normally resides in the mitochondria, subunit c of the mitochondrial ATPase, provides evidence that autophagosomal–lysosomal turnover of cellular components is disrupted upon loss of CLN3 protein function. Using a murine neuronal cell model of the disease, which accurately mimics the major gene defect and the hallmark features of CLN3 disease, we conducted an unbiased search for modifiers of autophagy, extending previous work by further optimizing a GFP-LC3 based assay and performing a high-content screen on a library of ~2000 bioactive compounds. Here we corroborate our earlier screening results and identify expanded, independent sets of autophagy modifiers that increase or decrease the accumulation of autophagosomes in the CLN3 disease cells, highlighting several pathways of interest, including the regulation of calcium signaling, microtubule dynamics, and the mevalonate pathway. Follow-up analysis on fluspirilene, nicardipine, and verapamil, in particular, confirmed activity in reducing GFP-LC3 vesicle burden, while also demonstrating activity in normalizing lysosomal positioning and, for verapamil, in promoting storage material clearance in CLN3 disease neuronal cells. This study demonstrates the potential for cell-based screening studies to identify candidate molecules and pathways for further work to understand CLN3 disease pathogenesis and in drug development efforts.

Diagnosis of lysosomal storage disorders: current techniques and future directions

Lysosomal storage disorders represent a group of over 45 distinct genetic diseases. The broad spectrum of clinical presentation of this group of disorders has led to the development of diagnostic protocols to facilitate their rapid and accurate diagnosis. However, with the development of new therapies, testing for many of these disorders now extends beyond diagnosis of affected individuals. The efficacy of many current and proposed therapies will rely heavily upon early detection and treatment prior to the onset of irreversible pathology. Newborn screening holds the promise of early detection. However, presymptomatic diagnosis raises a number of issues relating to patient management and treatment. Methods for prognoses and monitoring therapy in asymptomatic individuals will be required.

Lysosomes and lysosomal cathepsins in cell death

Lysosomes are the key degradative compartments of the cell. Lysosomal cathepsins, which are enclosed in the lysosomes, help to maintain the homeostasis of the cell's metabolism by participating in the degradation of heterophagic and autophagic material. Following the targeted lysosomal membrane's destabilization, the cathepsins can be released into the cytosol and initiate the lysosomal pathway of apoptosis through the cleavage of Bid and the degradation of the anti-apoptotic Bcl-2 homologues. Cathepsins can also amplify the apoptotic signaling, when the lysosomal membranes are destabilized at a later stage of apoptosis, initiated by other stimuli. However, the functional integrity of the lysosomal compartment during apoptosis enables efficient autophagy, which can counteract apoptosis by providing the energy source and by disposing the damaged mitochondria, which generate the ROS. Impairing autophagy by disabling the lysosome function is being investigated as an adjuvant therapeutic approach to sensitize cells to apoptosis-inducing agents. Destabilization of the lysosomal membranes by the lysosomotropic detergents seems to be a promising strategy in this context as it would not only disable autophagy, but also promote apoptosis through the initiation of the lysosomal pathway. In contrast, the impaired autophagy and lysosomal degradation linked with the increased oxidative stress underlie degenerative changes in the aging neurons. This further suggests that lysosomes and lysosomal cathepsins have a dual role in cell death. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Experimental priapism is associated with increased oxidative stress and activation of protein degradation pathways in corporal tissue

Priapism is a debilitating disease for which there is at present no clinically accepted pharmacologic intervention. It has been estimated that priapism lasting more than 24 hours in patients is associated with a 44–90% rate of erectile dysfunction (ED). In this investigation we determined in two animal models of priapism (opiorpin-induced priapism in the rat and priapism in a mouse model of sickle cell disease) if there is evidence for an increase in markers of oxidative stress in corporal tissue. In both animal models we demonstrate that priapism results in increased levels of lipid peroxidation, glutathione S-transferase activity, and oxidatively damaged proteins in corporal tissue. Using Western blot analysis we demonstrated there is up regulation of the ubiquitination ligase proteins, Nedd-4 and Mdm-2, and the lysososomal autophage protein, LC3. The anti-apoptotic protein, Bcl-2, was also up regulated. Overall, we demonstrate that priapism is associated with increased oxidative stress in corporal tissue and the activation of protein degradation pathways. Since oxidative stress is known to mediate the development of ED resulting from several etiologies (for example ED resulting from diabetes and aging) we suggest that damage to erectile tissue resulting from priapism might be prevented by treatments targeting oxidative stress.

Oxidative stress status accompanying diabetic bladder cystopathy results in the activation of protein degradation pathways

OBJECTIVE

• To investigate the role that oxidative stress plays in the development of diabetic cystopathy.

MATERIALS AND METHODS

• Comparative gene expression in the bladder of non-diabetic and streptozotocin (STZ)-induced 2-month- old diabetic rats was carried out using microarray analysis. • Evidence of oxidative stress was investigated in the bladder by analyzing glutathione S-transferase activity, lipid peroxidation, and carbonylation and nitrosylation of proteins. • The activity of protein degradation pathways was assessed using Western blot analysis.

RESULTS

• Analysis of global gene expression showed that detrusor smooth muscle tissue of STZ-induced diabetes undergoes significant enrichment in targets involved in the production or regulation of reactive oxygen species (P = 1.27 × 10(-10)). The microarray analysis was confirmed by showing that markers of oxidative stress were all significantly increased in the diabetic bladder. • It was hypothesized that the sequelae to oxidative stress would be increased protein damage and apoptosis. • This was confirmed by showing that two key proteins involved in protein degradation (Nedd4 and LC3B) were greatly up-regulated in diabetic bladders compared to controls by 12.2 ± 0.76 and 4.4 ± 1.0-fold, respectively, and the apoptosis inducing protein, BAX, was up-regulated by 6.76 ± 0.76-fold.

CONCLUSION

• Overall, the findings obtained in the present study add to the growing body of evidence showing that diabetic cystopathy is associated with oxidative damage of smooth muscle cells, and results in protein damage and activation of apoptotic pathways that may contribute to a deterioration in bladder function.

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.

Atypical CLN2 with later onset and prolonged course: a neuropathologic study showing different sensitivity of neuronal subpopulations to TPP1 deficiency

This is the first neuropathology report of a male patient (born 1960-died 1975) with an extremely rare, atypical variant of CLN2 that has been diagnosed only in five families so far. The clinical history started during his preschool years with relatively mild motor and psychological difficulties, but with normal intellect and vision. Since age six there were progressive cerebellar and extrapyramidal symptomatology, amaurosis, and mental deterioration. Epileptic seizures were absent. The child died aged 15 years in extreme cachexy. Neuropathology revealed neurolysosomal storage of autofluorescent, curvilinear and subunit c of mitochondrial ATP synthase (SCMAS) rich material. The neuronal storage led to laminar neuronal depopulation in the cerebral cortex and to a practically total eradication of the cerebellar cortical neurons. The other areas of the central nervous system including hippocampus, which are usually heavily affected in classical forms of CLN2, displayed either a lesser degree or absence of neuronal storage, or storage without significant neuronal loss. Transformation of the stored material to the spheroid like perikaryal inclusions was rudimentary. The follow-up, after 30 years, showed heterozygous values of TPP1 (tripeptidylpeptidase 1) activity in the white blood cells of both parents and the sister. DNA analysis of CLN2 gene identified a paternal frequent null mutation c.622C > T (p.Arg208 X) in the 6th exon and a maternal novel mutation c.1439 T > G in exon 12 (p.Val480Gly). TPP1 immunohistochemistry using a specific antibody gave negative results in the brain and other organs. Our report supports the notion that the spectrum of CLN2 phenotypes may be surprisingly broad. The study revealed variable sensitivities in neuronal subpopulations to the metabolic defect which may be responsible for the variant's serious course.

Genetics and epilepsy

The term “epilepsy” describes a heterogeneous group of disorders, most of them caused by interactions between several or even many genes and environmental factors. Much rarer are the genetic epilepsies that are due to single-gene mutations or defined structural chromosomal aberrations, such as microdeletions. The discovery of several of the genes underlying these rare genetic epilepsies has already considerably contributed to our understanding of the basic mechanisms epileptogenesis. The progress made in the last 15 years in the genetics of epilepsy is providing new possibilities for diagnosis and therapy. Here, different genetic epilepsies are reviewed as examples, to demonstrate the various pathways that can lead from genes to seizures.

Immune system irregularities in lysosomal storage disorders

Lysosomal storage disorders (LSDs) are genetically inherited diseases characterized by the accumulation of disease-specific biological materials such as proteolipids or metabolic intermediates within the lysosome. The lysosomal compartment's central importance to normal cellular function can be appreciated by examining the various pathologies that arise in LSDs. These disorders are invariably fatal, and many display profound neurological impairment that begins in childhood. However, recent studies have revealed that several LSDs also have irregularities in the function of the immune system. Gaucher disease, mucopolysaccharidosis VII, and alpha-mannosidosis are examples of a subset of LSD patients that are predisposed towards immune suppression. In contrast, GM2 gangliosidosis, globoid cell leukodystrophy, Niemann-Pick disease type C1 and juvenile neuronal ceroid lipofuscinosis are LSDs that are predisposed towards immune system hyperactivity. Antigen presentation and processing by dedicated antigen presenting cells (APCs), secretion of pore-forming perforins by cytotoxic-T lymphocytes, and release of pro-inflammatory mediators by mast cells are among the many crucial immune system functions in which the lysosome plays a central role. Although the relationship between the modification of the lysosomal compartment in LSDs and modulation of the immune system remains unknown, there is emerging evidence for early neuroimmune responses in a variety of LSDs. In this review we bridge biochemical studies on the lysosomal compartment's role in the immune system with clinical data on immune system irregularities in a subset of LSDs.

Proteomic analysis of cathepsin B- and L-deficient mouse brain lysosomes

Cathepsins B and L are lysosomal cysteine proteases which have been implicated in a variety of pathological processes such as cancer, tumor angiogenesis, and neurodegeneration. However, only a few protein substrates have thus far been described and the mechanisms by which cathepsins B and L regulate cell proliferation, invasion, and apoptosis are poorly understood. Combined deficiency of both cathepsins results in early-onset neurodegeneration in mice reminiscent of neuronal ceroid lipofuscinoses in humans. Therefore, we intended to quantify accumulated proteins in brain lysosomes of double deficient mice. A combination of subcellular fractionation and LC-MS/MS using isobaric tagging for relative and absolute quantitation (iTRAQ) allowed us to simultaneously assess wildtype and cathepsin B(-/-)L(-/-) cerebral lysosomes. Altogether, 19 different proteins were significantly increased in cathepsin B(-/-)L(-/-) lysosomes. Most elevated proteins had previously been localized to neuronal biosynthetic, recycling/endocytic or lysosomal compartments. A more than 10-fold increase was observed for Rab14, the Delta/Notch-like epidermal growth factor-related receptor (DNER), calcyon, and carboxypeptidase E. Intriguingly, immunohistochemistry demonstrated that Rab14 and DNER specifically stain swollen axons in double deficient brains. Since dense accumulations of expanded axons are the earliest phenotypic and pathognomonic feature of cathepsin B(-/-)L(-/-) brains, our data suggest a role for cathepsins B and L in recycling processes during axon outgrowth and synapse formation in the developing postnatal central nervous system.

Skin biopsy: a useful tool in the diagnosis of lysosomal storage diseases

In this report, the authors summarize their 19-year experience with over 200 biochemically proven cases of lysosomal storage diseases using electron microscopic screening of more than 950 skin biopsies. They found that electron microscopy (EM) is a highly sensitive, efficient, cost-effective, and rapid diagnostic screening tool for evaluation of lysosomal storage diseases in skin biopsies. Although EM is more expensive than a single enzyme assay, it can exclude more than 90% of cases in which lysosomal storage disease is being considered. EM is critical for diagnosis of neuronal ceroid lipofuscinosis and mucolipidosis IV and is the most cost-effective screening tool in patients with previously unrecognized storage diseases.

Diagnosis of neuronal ceroid lipofuscinosis (Batten disease) by electron microscopy in peripheral blood specimens

Neuronal ceroid lipopofuscinosis (Batten disease, NCL) represents a group of common childhood neurodegenerative diseases with a shared feature of deposition of abnormal metabolic products in neurons and other tissues, including peripheral blood lymphocytes. In most forms of NCL no specific enzyme defect is known and the diagnosis relies primarily on ultrastructural identification of characteristic membrane-bound inclusions containing the abnormal metabolic product. All buffy-coat specimens examined during a 7-year period (1997-2004) for the exclusion or confirmation of the diagnosis NCL were reviewed. From a total of 265 samples, 9 were inadequate and NCL was diagnosed in 56. Five showed granular osmophilic deposits of infantile Batten disease (NCL1), 10 showed curvilinear profiles of classical late infantile Batten disease (NCL2), and 17 showed vacuolated lymphocytes with fingerprint profiles, indicating classical juvenile Batten disease (NCL3). 24 samples (43%) demonstrated compact electron-dense deposits with fingerprint profiles in the absence of vacuolated lymphocytes, indicative of variant forms NCL. Ultrastructual examination of peripheral blood allows reliable and specific diagnosis of subtypes of Batten disease, including variants, and is a useful, minimally invasive test for the diagnosis of NCL in childhood.

Occurrence of and mortality from childhood neuronal ceroid lipofuscinoses in norway

The aim of this study was to estimate the prevalence of, incidence of, and survival from childhood neuronal lipofuscinoses in Norway. All children with neuronal ceroid lipofuscinoses living in Norway are referred to the Tambartun National Resource Centre for the Visually Impaired. We based the data collection on the medical records at Tambartun. We identified 70 children with neuronal ceroid lipofuscinoses who were born in Norway from 1957 to 1998. Seven had a diagnosis of late infantile neuronal ceroid lipofuscinoses, and 63 had the juvenile form of neuronal ceroid lipofuscinoses. In 2005, the prevalence of childhood neuronal ceroid lipofuscinoses was 8.3 per million inhabitants in Norway, and all children were diagnosed with the juvenile form. The average annual incidence rate of childhood neuronal ceroid lipofuscinoses was 1.8 per 100,000 live births using the years from 1957 to 1978 and 3.9 using the years from 1978 to 1999. The trend in incidence increased at an annual rate of about 3.3% per year (P = .001), averaged over this period. Restricted to the most recent period (1967-1998), the trend was much weaker (1.4% increase per year; P = .3), and confidence intervals included the possibility of no trend. The median age at death of children diagnosed with late infantile neuronal ceroid lipofuscinoses was 12 years (95% confidence interval 9-14) and 26 years (95% confidence interval 25-30) for children diagnosed with the juvenile form. The results did not support the hypothesis that children with neuronal ceroid lipofuscinoses born in 1975 or later lived longer than those born from 1957 to 1975 (relative risk 1.0, 95% confidence interval 0.36-2.8). Mortality was similar for both genders (hazard ratio 0.97, 95% confidence interval 0.4-2.2).

Progress towards understanding disease mechanisms in small vertebrate models of neuronal ceroid lipofuscinosis

Model systems provide an invaluable tool for investigating the molecular mechanisms underlying the NCLs, devastating neurodegenerative disorders that affect the relatively inaccessible tissues of the central nervous system. These models have enabled the assessment of behavioural, pathological, cellular, and molecular abnormalities, and also allow for development and evaluation of novel therapies. This review highlights the relative advantages of the two available small vertebrate species, the mouse and zebrafish, in modelling NCL disease, summarising how these have been useful in NCL research and their potential for the development and testing of prospective disease treatments. A panel of mouse mutants is available representing all the cloned NCL gene disorders (Cathepsin D, CLN1, CLN2, CLN3, CLN5, CLN6, CLN8). These NCL mice all have progressive neurodegenerative phenotypes that closely resemble the pathology of human NCL. The analysis of these models has highlighted several novel aspects underlying NCL pathogenesis including the selective nature of neurodegeneration, evidence for glial responses that precede neuronal loss and identification of the thalamus as an important pathological target early in disease progression. Studies in mice have also highlighted an unexpected heterogeneity underlying NCL phenotypes, and novel potential NCL-like mouse models have been described including mice with mutations in cathepsins, CLC chloride channels, and other lysosome-related genes. These new models are likely to provide significant new information on the spectrum of NCL disease. Information on NCL mice is available in the NCL Mouse Model Database (). There are homologs of most of the NCL genes in zebrafish, and NCL zebrafish models are currently in development. This model system provides additional advantages to those provided by NCL mouse models including high-throughput mutational, pharmacogenetic and therapeutic technique analyses. Mouse and zebrafish models are an important shared resource for NCL research, offering a unique possibility to dissect disease mechanisms and to develop therapeutic approaches.

Lysosomal storage disease upon disruption of the neuronal chloride transport protein ClC-6

Mammalian CLC proteins function as Cl(-) channels or as electrogenic Cl(-)/H(+) exchangers and are present in the plasma membrane and intracellular vesicles. We now show that the ClC-6 protein is almost exclusively expressed in neurons of the central and peripheral nervous systems, with a particularly high expression in dorsal root ganglia. ClC-6 colocalized with markers for late endosomes in neuronal cell bodies. The disruption of ClC-6 in mice reduced their pain sensitivity and caused moderate behavioral abnormalities. Neuronal tissues showed autofluorescence at initial axon segments. At these sites, electron microscopy revealed electron-dense storage material that caused a pathological enlargement of proximal axons. These deposits were positive for several lysosomal proteins and other marker proteins typical for neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disease. However, the lysosomal pH of Clcn6(-/-) neurons appeared normal. CLCN6 is a candidate gene for mild forms of human NCL. Analysis of 75 NCL patients identified ClC-6 amino acid exchanges in two patients but failed to prove a causative role of CLCN6 in that disease.

Oxidative stress and neurodegeneration: where are we now?

The brain and nervous system are prone to oxidative stress, and are inadequately equipped with antioxidant defense systems to prevent 'ongoing' oxidative damage, let alone the extra oxidative damage imposed by the neurodegenerative diseases. Indeed, increased oxidative damage, mitochondrial dysfunction, accumulation of oxidized aggregated proteins, inflammation, and defects in protein clearance constitute complex intertwined pathologies that conspire to kill neurons. After a long lag period, therapeutic and other interventions based on a knowledge of redox biology are on the horizon for at least some of the neurodegenerative diseases.

Gene expression profiling in vLINCL CLN6-deficient fibroblasts: Insights into pathobiology

The CLN6 vLINCL is caused by molecular defects in CLN6 gene coding for an ER resident transmembrane protein whose function is unknown. In the present study gene expression profiling of CLN6-deficient fibroblasts using cDNA microarray was undertaken in order to provide novel insights into the molecular mechanisms underlying this neurodegenerative fatal disease. Data were validated by qRT-PCR. Statistically significant alterations of expression were observed for 12 transcripts. The two most overexpressed genes, versican and tissue factor pathway inhibitor 2, are related to extracellular matrix (ECM), predicting changes in ECM-related proteins in CLN6-deficient cells. Transcript profiling also suggested alterations in signal transduction pathways, apoptosis and the immune/inflammatory response. Up-regulated genes related to steroidogenesis or signalling, and the relationship between cholesterol dynamics and glycosphingolipid sorting, led to investigation of free cholesterol and gangliosides in CLN6-deficient fibroblasts. Cholesterol accumulation in lysosomes suggests a homeostasis block as a result of CLN6p deficiency. The cholesterol imbalance may affect structure/function of caveolae and lipid rafts, disrupting signalling transduction pathways and sorting cell mechanisms. Alterations in protein/lipid intracellular trafficking would affect the composition and function of endocytic compartments, including lysosomes. Dysfunctional endosomal/lysosomal vesicles may act as one of the triggers for apoptosis and cell death, and for a secondary protective inflammatory response. In conclusion, the data reported provide novel clues into molecular pathophysiological mechanisms of CLN6-deficiency, and may also help in developing disease biomarkers and therapies for this and other neurodegenerative diseases.

Batten disease: features to facilitate early diagnosis

AIMS

To ascertain the clinical and electrophysiological features in patients with juvenile neuronal ceroid lipofuscinosis (jNCL/Batten disease) and to identify those features that facilitate early diagnosis.

METHODS

Nine patients with jNCL were identified retrospectively and their case notes reviewed. All had undergone an extensive clinical examination, including electrophysiology. Blood and molecular genetic testing confirmed the diagnosis.

RESULTS

Age at onset ranged from 4-8 years. At presentation, two of nine patients had normal fundi; only two of nine patients had a bull's eye maculopathy. The electroretinogram (ERG) findings in this series included undetectable rod specific ERGs, an electronegative maximal response, reduced and delayed cone flicker ERGs, reduction in the b:a ratio in the photopic single flash ERG, and an undetectable pattern ERG. Vacuolated lymphocytes on peripheral blood film testing were present in eight of nine patients. Five of eight patients were homozygous for the 1.02 kb deletion on the CLN3 gene on molecular genetic testing; two of eight patients were heterozygous for that deletion.

CONCLUSION

jNCL should be considered in children of 10 years and under presenting with visual loss and fundal changes ranging from normal through to pigmentary/atrophic changes or a bull's eye maculopathy. Electrophysiology may suggest jNCL. Although currently untreatable, early diagnosis is important to institute appropriate counselling and support.

Mechanisms of neurodegeneration in neuronal ceroid-lipofuscinoses

Neuronal ceroid-lipofuscinoses (NCL) are a group of neurodegenerative diseases and autosomal recessive lysosomal storage disorders. We examined the involvement of cell death, oxidative stress, and glutamate excitotoxicity using immunohistochemistry against Bcl-2, Bcl-x, oxidative products to proteins, lipids and DNA, calcium-binding proteins (calbindin-D28K, parvalbumin, calretinin), and glial glutamate transporters (excitatory amino acid transporters 1 and 2), in addition to terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL) in the brains from three cases of late infantile form of NCL (LINCL) and one case of juvenile form of NCL (JNCL) to investigate the neurodegenerative mechanisms. In the cerebral and cerebellar cortex, all of three LINCL cases demonstrated neurons with TUNEL-immunoreactive nuclei, whereas the JNCL case did not show TUNEL-immunoreactive nuclei. The coexistence of the nuclear TUNEL-immunoreactivity nuclei and cytoplasmic deposition of 4-hydroxy-2-nonenal-modified protein in the frontal cortex and hypoglossal nucleus may suggest a possible interrelationship between DNA fragmentation and lipid oxidation in LINCL. Additionally, glycoxidation of protein and oxidative stress to DNA seemed to be involved in the cerebellar and cerebral degeneration, respectively. Interneurons immunoreactive for calbindin-D28K and parvalbumin were severely reduced in the cerebral cortex, whereas those for calretinin were comparatively well preserved in LINCL, indicating the possibility of altered GABAergic system. The disturbance of expression of glial glutamate transporters seemed to be heterogeneous and mild. These findings suggest the possibility of new treatments for neurodegeneration in LINCL using antioxidative agents and/or GABAergic medications.

Behavioral assessment in mouse models of neuronal ceroid lipofuscinosis using a light-cued T-maze

Learning impairment is a common feature of the neuronal ceroid lipofuscinoses (NCL), a family of lysosomal storage disorders associated with progressive neurodegeneration. Murine models for the neuronal ceroid lipofuscinoses include the well-characterized motor neuron degeneration (mnd/mnd) model for one variant of late infantile NCL (CLN8), and the more recently generated models for the infantile (CLN1) and juvenile (CLN3) forms of NCL. To determine whether these mouse models exhibit behavioral deficits analogous to the learning impairment characteristic of the human disorders, the performance of these animals on an associative learning task was assessed. The abilities of affected and normal control mice to associate a light stimulus with a food reward were evaluated in 14-16-week-old animals using a T-maze. Normal mice were able to reach a criterion for having learned to make the association within a mean of 9.4 trials. The CLN8 and CLN3 mice, on the other hand, required means of 26.2 and 27.5 trials, respectively, to reach the same performance criterion (p<0.05), whereas none of the CLN1 mice were able to reach the criterion within a limit of 30 trials. The poor performance of the mutant mice did not appear to result from impaired retinal function; mice of all three strains exhibited retinal electrophysiological responses to dim light flashes and displayed robust pupillary light reflexes. Associative learning deficits appear to be an early disease phenotype in the NCL mouse models that will be useful for assessing the efficacy of therapeutic interventions such as gene or stem cell therapies.

Physiological functions of CLC Cl- channels gleaned from human genetic disease and mouse models

The CLC gene family encodes nine different Cl() channels in mammals. These channels perform their functions in the plasma membrane or in intracellular organelles such as vesicles of the endosomal/lysosomal pathway or in synaptic vesicles. The elucidation of their cellular roles and their importance for the organism were greatly facilitated by mouse models and by human diseases caused by mutations in their respective genes. Human mutations in CLC channels are known to cause diseases as diverse as myotonia (muscle stiffness), Bartter syndrome (renal salt loss) with or without deafness, Dent's disease (proteinuria and kidney stones), osteopetrosis and neurodegeneration, and possibly epilepsy. Mouse models revealed blindness and infertility as further consequences of CLC gene disruptions. These phenotypes firmly established the roles CLC channels play in stabilizing the plasma membrane voltage in muscle and possibly in neurons, in the transport of salt and fluid across epithelia, in the acidification of endosomes and synaptic vesicles, and in the degradation of bone by osteoclasts.

Loss of the chloride channel ClC-7 leads to lysosomal storage disease and neurodegeneration

ClC-7 is a chloride channel of late endosomes and lysosomes. In osteoclasts, it may cooperate with H(+)-ATPases in acidifying the resorption lacuna. In mice and man, loss of ClC-7 or the H(+)-ATPase a3 subunit causes osteopetrosis, a disease characterized by defective bone resorption. We show that ClC-7 knockout mice additionally display neurodegeneration and severe lysosomal storage disease despite unchanged lysosomal pH in cultured neurons. Rescuing their bone phenotype by transgenic expression of ClC-7 in osteoclasts moderately increased their lifespan and revealed a further progression of the central nervous system pathology. Histological analysis demonstrated an accumulation of electron-dense material in neurons, autofluorescent structures, microglial activation and astrogliosis. Like in human neuronal ceroid lipofuscinosis, there was a strong accumulation of subunit c of the mitochondrial ATP synthase and increased amounts of lysosomal enzymes. Such alterations were minor or absent in ClC-3 knockout mice, despite a massive neurodegeneration. Osteopetrotic oc/oc mice, lacking a functional H(+)-ATPase a3 subunit, showed no comparable retinal or neuronal degeneration. There are important medical implications as defects in the H(+)-ATPase and ClC-7 can underlie human osteopetrosis.

Retrovirally transduced bone marrow has a therapeutic effect on brain in the mouse model of mucopolysaccharidosis IIIB

Mucopolysaccharidosis IIIB (MPS IIIB) is a lysosomal storage disorder caused by mutations in NAGLU, the gene encoding alpha-N-acetylglucosaminidase. The disease is characterized by profound mental retardation and eventual neurodegeneration, but relatively mild somatic manifestations. There is no available therapy. We have used a mouse knockout model of the disease to test therapy by genetically modified bone marrow. Bone marrow from Naglu -/- male mice was transduced with human NAGLU cDNA in an MND-MFG vector, and transplanted into 6- to 8-week-old lethally irradiated female -/- mice. Sham-treated mice received bone marrow transduced with eGFP cDNA in an MND vector. alpha-N-Acetylglucosaminidase activity in plasma and leukocytes, measured 3 and 6 months after transplantation, varied from marginal to nearly 30 times wild-type. A low level of alpha-N-acetylglucosaminidase activity, as little as provided by transplantation of unmodified Naglu +/+ bone marrow, could normalize biochemical defects (glycosaminoglycan storage and beta-hexosaminidase elevation) in liver and spleen, but a very high level was required for an effect on kidney. Effects on the brain were best seen by examination of cellular morphology using light and electron microcopy. Mice that expressed very high levels of alpha-N-acetylglucosaminidase in blood had an increased number of normal-appearing neurons in the cortex and other parts of the brain, while microglia with engorged lysosomes had almost completely disappeared. Immunohistochemistry showed a marked decrease of staining for subunit c of mitochondrial ATP synthase and for Lamp1, markers of neuronal and microglial pathology, respectively, as well as a decrease in staining for glial fibrillary acid protein, a marker of activated astrocytes. These results show that genetically modified cells of hematopoietic origin can reduce the pathologic manifestations of MPS IIIB in the Naglu -/- mouse brain.