A mutation in the ovine cathepsin D gene causes a congenital lysosomal storage disease with profound neurodegeneration

Autosomal dominant adult neuronal ceroid lipofuscinosis: a novel form of NCL with granular osmiophilic deposits without palmitoyl protein thioesterase 1 deficiency

We describe the neuropathological and biochemical autopsy findings in 3 patients with autosomal dominant adult neuronal ceroid lipofuscinosis (ANCL, Parry type; MIM 162350), from a family with 6 affected individuals in 3 generations. Throughout the brain of these patients, there was abundant intraneuronal lysosomal storage of autofluorescent lipopigment granules. Striking loss of neurons in the substantia nigra was found. In contrast, little neuronal cell loss occurred in other cerebral areas, despite massive neuronal inclusions. Visceral storage was present in gut, liver, cardiomyocytes, skeletal muscle, and in the skin eccrine glands. The storage material showed highly variable immunoreactivity with antiserum against subunit c of mitochondrial ATP synthase, but uniform strong immunoreactivity for saposin D (sphingolipid activating protein D). Protein electrophoresis of isolated storage material revealed a major protein band of about 14 kDa, recognized in Western blotting by saposin D antiserum (but not subunit c of mitochondrial ATPase (SCMAS) antiserum). Electron microscopy showed ample intraneuronal granular osmiophilic deposits (GRODs), as occurs in CLN1 and congenital ovine NCL. These forms of NCL are caused by the deficiencies of palmitoyl protein thioesterase 1 and cathepsin D, respectively. However, activities of these enzymes were within normal range in our patients. Thus we propose that a gene distinct from the cathepsin D and CLN1-CLN8 genes is responsible for this autosomal dominant form of ANCL.

The genetic spectrum of human neuronal ceroid-lipofuscinoses

The neuronal ceroid lipofuscinoses (NCL), also known as Batten disease, are a group of inherited severe neurodegenerative disorders primarily affecting children. They are characterised by the accumulation of autofluorescent storage material in many cells. Children suffer from visual failure, seizures, progressive physical and mental decline and premature death, associated with the loss of cortical neurones. Six genes have been identified that cause human NCL (CLN1, CLN2, CLN3, CLN5, CLN6, CLN8), and approximately 150 mutations have been described. The majority of mutations result in a characteristic disease course for each gene. However, mutations associated with later disease onset or a more protracted disease course have also been described. At least seven common mutations exist, either with a world-wide distribution or associated with families from specific countries. All mutations are described in the NCL Mutation Database (http://www.uc.ac.uk/ncl).

Two motifs target Batten disease protein CLN3 to lysosomes in transfected nonneuronal and neuronal cells

Batten disease is a neurodegenerative disorder resulting from mutations in CLN3, a polytopic membrane protein, whose predominant intracellular destination in nonneuronal cells is the lysosome. The topology of CLN3 protein, its lysosomal targeting mechanism, and the development of Batten disease are poorly understood. We provide experimental evidence that both the N and C termini and one large loop domain of CLN3 face the cytoplasm. We have identified two lysosomal targeting motifs that mediate the sorting of CLN3 in transfected nonneuronal and neuronal cells: an unconventional motif in the long C-terminal cytosolic tail consisting of a methionine and a glycine separated by nine amino acids [M(X)9G], and a more conventional dileucine motif, located in the large cytosolic loop domain and preceded by an acidic patch. Each motif on its own was sufficient to mediate lysosomal targeting, but optimal efficiency required both. Interestingly, in primary neurons, CLN3 was prominently seen both in lysosomes in the cell body and in endosomes, containing early endosomal antigen-1 along neuronal processes. Because there are few lysosomes in axons and peripheral parts of dendrites, the presence of CLN3 in endosomes of neurons may be functionally important. Endosomal association of the protein was independent of the two lysosomal targeting motifs.

Enhanced expression of manganese-dependent superoxide dismutase in human and sheep CLN6 tissues

Neuronal ceroid lipofuscinosis type 6 and its sheep model (OCL6) are lysosomal storage disorders caused by mutations in the CLN6 gene product of unknown function. It has been proposed that mitochondrial dysfunction, including defects in mitochondrial protein degradation, organelle enlargement and functional changes in oxidative phosphorylation, may contribute to the disease pathology. To further explore the disease mechanisms underlying CLN6, protein expression was compared between normal and affected tissues. Using two-dimensional electrophoretic separation of proteins, MS and immunoblotting, MnSOD (manganese-dependent superoxide dismutase) was found to be significantly and specifically increased in fibroblasts and brain extracts of both human and sheep affected with CLN6. Both the activity and expression of MnSOD mRNA were enhanced in affected fibroblasts. Confocal fluorescence microscopy and immunohistochemical studies revealed the presence of MnSOD in mitochondria of CLN6 fibroblasts and in CLN6 brain sections within both neurons and hypertrophic astrocytes. These data suggest that oxidative stress and/or the production of pro-inflammatory cytokines are characteristic features of human and sheep CLN6, resulting in elevated expression of MnSOD, which may be important for diagnostic purposes.

Stress-induced apoptosis is impaired in cells with a lysosomal targeting defect but is not affected in cells synthesizing a catalytically inactive cathepsin D

The role of cathepsin D in stress-induced cell death has been investigated by using ovine fibroblasts exhibiting a missense mutation in the active site of cathepsin D. The cathepsin D (lysosomal aspartic protease) deficiency did not protect cells against toxicity induced by doxorubicin and other cytotoxic agents, neither did it protect cells from caspase activation. Moreover, the cathepsin D inhibitor, pepstatin A, did not prevent stress-induced cell death in human fibroblasts or lymphoblasts. The possible role of lysosomal ceramide or sphingosine-mediated activation of cathepsin D in apoptosis was also excluded by using human cells either overexpressing or deficient in acid ceramidase. However, a normal lysosomal function seems to be required for efficient cell death, as indicated by the finding that fibroblasts from patients with mucolipidosis II were partially resistant to staurosporine, sphingosine and TNF-induced apoptosis, suggesting a key role of lysosomes in cell death.

Involvement of two different cell death pathways in retinal atrophy of cathepsin D-deficient mice

To understand the mechanisms of retinal atrophy in cathepsin D-deficient mice, the postnatal development of their retinae was analyzed. TUNEL-positive cells appeared abundantly in the outer nuclear layer (ONL) and slightly in the inner nuclear layer (INL). Nitric oxide synthase (NOS) was induced in microglial cells which invaded retinal layers and phagocytosed dead cell debris, while NOS inhibitors prevented cell death in the INL but not in the ONL. Caspases 9 and 3 were activated only in the ONL after P15. Moreover, no atrophic change was detected in the retina of mice deficient in cathepsin B or L. These results suggest that cathepsin D is essential for the metabolic maintenance of retinal photoreceptor cells and that its deficiency induces apoptosis of the cells, while the loss of INL neurons is mediated by NO from microglial cells.

A replacement of the active-site aspartic acid residue 293 in mouse cathepsin D affects its intracellular stability, processing and transport in HEK-293 cells

The substitution of an active-site aspartic acid residue by asparagine in the lysosomal protease cathepsin D (CTSD) results in a loss of enzyme activity and severe cerebrocortical atrophy in a novel form of neuronal ceroid lipofuscinosis in sheep [Tyynelä, Sohar, Sleat, Gin, Donnelly, Baumann, Haltia and Lobel (2000) EMBO J. 19, 2786-2792]. In the present study we have introduced the corresponding mutation by replacing aspartic acid residue 293 with asparagine (D293N) into the mouse CTSD cDNA to analyse its effect on synthesis, transport and stability in transfected HEK-293 cells. The complete inactivation of mutant D293N mouse CTSD was confirmed by a newly developed fluorimetric quantification system. Moreover, in the heterologous overexpression systems used, mutant D293N mouse CTSD was apparently unstable and proteolytically modified during early steps of the secretory pathway, resulting in a loss of mass by about 1 kDa. In the affected sheep, the endogenous mutant enzyme was stable but also showed the shift in its molecular mass. In HEK-293 cells, the transport of the mutant D293N mouse CTSD to the lysosome was delayed and associated with a low secretion rate compared with wild-type CTSD. These data suggest that the mutation may result in a conformational change which affects stability, processing and transport of the enzyme.

The neuronal ceroid-lipofuscinoses

The neuronal ceroid-lipofuscinoses (NCLs) collectively constitute the most common group of neurodegenerative diseases in childhood and usually show an autosomal recessive mode of inheritance. Despite varying ages of onset and clinical course characterized in most instances by progressive mental and motor deterioration, blindness, epileptic seizures, and premature death, all forms of NCL show unifying histopathological features. There is accumulation of autofluorescent, periodic acid-Schiff-, and Sudan black B-positive granules that are resistant to lipid solvents in the cytoplasm of most nerve cells and. to a lesser degree, of many other cell types. The storage process is associated with progressive and selective neuronal loss and gliosis with secondary white matter lesions. The ultrastructure of the storage deposits varies between different forms of NCL and, along with the age of onset, has provided the basis for the traditional classification of NCLs. Recent molecular genetic findings have established that defects in at least 7 different genes underlie the various forms of NCL. The purpose of this paper is to provide an overview of the NCLs, review recent molecular genetic and biochemical findings, and discuss their impact on our views on the classification and pathogenesis of these devastating brain disorders.

Cathepsin D exon 2 polymorphism associated with general intelligence in a healthy older population

General intelligence is a heritable trait that is a risk factor for both the onset of dementia and the rate of cognitive decline in community-dwelling older persons. Previous studies screening for quantitative trait loci (QTLs) that influence general intelligence in healthy individuals have identified four loci, two of which are located within the genes insulin-like growth factor 2 receptor (IGF2R) and the Msx1 homeobox. Here, we report the finding of another QTL associated with general intelligence that is located within exon 2 of the cathepsin D (CTSD) gene. A group of 767 healthy adults with a follow-up period of over 15 years have been analyzed for cross-sectional and longitudinal trends in cognitive change using the Heim intelligence test score (AH4-1). We observed a significant association (P = 0.01) between a functional C > T (Ala > Val) transition within exon 2 of the CTSD gene that increases the secretion of pro-CTSD from the cell, and the AH4-1 score at initial testing on entry to the longitudinal study. Interestingly, CTSD is transported by IGF2R from the trans Golgi network to the lysosome.

Detection of procathepsin D in rat milk

The presence of procathepsin D, a zymogen of the soluble lysosomal aspartic proteinase cathepsin D, was detected in rat milk using Western blot analysis and assay of proteolytic activity in acidic buffers. No other forms of cathepsin D were found. Two different polyclonal anti-procathepsin D antibodies were used for immunochemical detection of procathepsin D. Both antibodies we found to recognize rat procathepsin D. Proteolytic activity in acidic buffers was detected using a fluorogenic substrate specific for cathepsin D and was abolished by pepstatin A, a specific inhibitor of aspartic proteinases. This study represents third demonstration of presence of procathepsin D in mammal breast milk. Potential sources and physiological functions are discussed.

Lysosomal degradation of cholecystokinin-(29-33)-amide in mouse brain is dependent on tripeptidyl peptidase-I: implications for the degradation and storage of peptides in classical late-infantile neuronal ceroid lipofuscinosis

Tripeptidyl peptidase-I (TPP-I) is a lysosomal exopeptidase which removes tripeptides from the N-terminus of small peptides. Mutations in the TPP-I gene result in a lethal neurodegenerative disease, classical late-infantile neuronal ceroid lipofuscinosis (CLN2). This disease is characterized by the accumulation of proteinaceous and autofluorescent material within the lysosomes of neurons, which undergo massive cell death during the course of the disease. The absence of TPP-I may result in the lysosomal accumulation of small peptides and proteins, which eventually compromises lysosomal functions critical to the survival of neurons. To investigate the metabolism of small peptides, we have studied the degradation of cholecystokinin-(29-33)-amide (GWMDF-NH2; cholecystokinin C-terminal pentapeptide) by lysosomal fractions isolated from mouse brain and several other tissues. GWMDF-NH2 is cleaved at only one peptide bond by brain lysosomes, to produce GWM and DF-NH2. Inhibitor studies demonstrate that this reaction is catalysed by TPP-I. In contrast, lysosomal fractions from other mouse tissues additionally cleave a second peptide bond to produce GW and MDF-NH2. Inhibitor studies indicate that this reaction is catalysed by dipeptidyl peptidase-I (DPP-I; cathepsin C). Inhibitors of TPP-I are sufficient to completely block the degradation of GWMDF-NH2 by brain, but inhibitors of both TPP-I and DPP-I are required to completely inhibit the degradation of GWMDF-NH2 by other mouse tissues. Enzyme assays confirm the low activity of DPP-I in brain. An unrelated neuropeptide, neuromedin B, is degraded by a pathway that is partially dependent on TPP-I. These results indicate that TPP-I is required for the partial or complete digestion of certain neuropeptides by brain lysosomes. In the absence of TPP-I, neuropeptides or their degradation products will accumulate in brain lysosomes and may contribute to the pathogenesis of CLN2. Other tissues are spared because they express another peptidase, DPP-I, which has extensive activity on peptides and can compensate for the loss of TPP-I.

Status Epilepticus Induces Changes in the Expression and Localization of Endogenous Palmitoyl-Protein Thioesterase 1

Kainic acid (KA)-induced experimental epilepsy, a model of excitotoxicity, leads to selective neuronal death and synaptic restructuring. We used this model to investigate the effects of neuronal hyperactivation on palmitoyl-protein thioesterase 1 (PPT1), the deficiency of which causes drastic neurodegeneration. Immunological stainings showed that epileptic seizures in adult rats led to a progressive and remarkable increase of PPT1 in limbic areas of the brain. Within 1 week, the maximal expression was observed in CA3 and CA1 pyramidal neurons of the hippocampus. In the surviving pyramidal neurons, PPT1 localized in vesicular structures in cell soma and neuritic extensions. After seizures, colocalization of PPT1 with synaptic membrane marker (NMDAR2B) was enhanced. Further, synaptic fractionation revealed that after seizures PPT1 was readily observed on the presynaptic side of synaptic junction. These data suggest that PPT1 may protect neurons from excitotoxicity and have a role in synaptic plasticity.

The effects of lysosomotropic agents on normal and INCL cells provide further evidence for the lysosomal nature of palmitoyl-protein thioesterase function

Fatty acylation of proteins on cysteine residues is a common post-translational modification that plays roles in protein-membrane and protein-protein interactions. Recently, we described a lysosomal palmitoyl-protein thioesterase that removes long-chain fatty acids from lipid-modified cysteine residues in proteins. Deficiency in palmitoyl-protein thioesterase results in a human lysosomal storage disorder, infantile neuronal ceroid lipofuscinosis (INCL), which primarily affects the central nervous system. The pathological hallmark of the disorder is the accumulation of granular osmiophilic deposits (GROD) that resemble lipofuscin, or aging pigment. In previous work, we have shown that [35S]cysteine-labeled lipid thioesters derived from fatty acylated proteins accumulate in cultured cells derived from palmitoyl-protein thioesterase-deficient patients. In the present work, we show that the lipid cysteine thioesters accumulate in the lysosomal fraction, and we further show that the appearance of these compounds in the organic phase is blocked by inhibitors of lysosomal proteolysis, demonstrating through biochemical means the lysosomal nature of the site of palmitoyl-protein thioesterase action. Furthermore, substrates for palmitoyl-protein thioesterase accumulate even in normal cells after leupeptin or chloroquine treatment. This was demonstrated by subjecting extracts of treated cells to exhaustive proteolysis to release protein-bound cysteine lipid for analysis. Cysteamine, a lysosomotropic drug recently proposed for the treatment of INCL, was found to have effects similar to leupeptin and chloroquine, suggesting that its mechanism of action may be more complex than previously understood.

Neuronal loss and brain atrophy in mice lacking cathepsins B and L

Cathepsins B and L are widely expressed cysteine proteases implicated in both intracellular proteolysis and extracellular matrix remodeling. However, specific roles remain to be validated in vivo. Here we show that combined deficiency of cathepsins B and L in mice is lethal during the second to fourth week of life. Cathepsin B(-/-)/L(-/-) mice reveal a degree of brain atrophy not previously seen in mice. This is because of massive apoptosis of select neurons in the cerebral cortex and the cerebellar Purkinje and granule cell layers. Neurodegeneration is accompanied by pronounced reactive astrocytosis and is preceded by an accumulation of ultrastructurally and biochemically unique lysosomal bodies in large cortical neurons and by axonal enlargements. Our data demonstrate a pivotal role for cathepsins B and L in maintenance of the central nervous system.

CLC-3 deficiency leads to phenotypes similar to human neuronal ceroid lipofuscinosis

BACKGROUND

CLC-3 is a member of the CLC chloride channel family and is widely expressed in mammalian tissues. To determine the physiological role of CLC-3, we generated CLC-3-deficient mice (Clcn3-/- ) by targeted gene disruption.

RESULTS

Together with developmental retardation and higher mortality, the Clcn3-/- mice showed neurological manifestations such as blindness, motor coordination deficit, and spontaneous hyperlocomotion. In histological analysis, the Clcn3-/- mice showed a pattern of progressive degeneration of the retina, hippocampus and ileal mucosa, which resembled the phenotype observed in cathepsin D knockout mice. The defect of cathepsin D results in a lysosomal accumulation of ceroid lipofuscin containing the mitochondrial F1F0 ATPase subunit c. In immunohistochemistry and Western blot analysis, we found that the subunit c was heavily accumulated in the lysosome of Clcn3-/- mice. Furthermore, we detected an elevation in the endosomal pH of the Clcn3-/- mice.

CONCLUSIONS

These results indicated that the neurodegeneration observed in the Clcn3-/- mice was caused by an abnormality in the machinery which degrades the cellular protein and was associated with the phenotype of neuronal ceroid lipofuscinosis (NCL). The elevated endosomal pH could be an important factor in the pathogenesis of NCL.

Neuronal ceroid lipofuscinosis in Merino sheep

OBJECTIVE

To characterise neuronal ceroid lipofuscinosis (NCL) in Merino sheep.

DESIGN

A prospective clinical, pathological, biochemical and genetic study.

PROCEDURE

NCL cases were studied from a medium-wool Merino flock, the stud of origin of its replacement rams, and an experimental flock established at the University of Sydney.

RESULTS

Behavioural changes and visual impairment were first detected at 7 to 12 months of age and progressed, with associated motor disturbances and at later stages seizures, to premature death by 27 months of age. At necropsy there was severe cerebrocortical atrophy associated with neuronal loss, astrocytosis and the presence in neurons of eosinophilic intracytoplasmic storage bodies with the characteristics of a lipopigment. In the retina there was progressive loss of photoreceptor cells. Storage bodies isolated from fresh brain, liver and pancreas formed electron-dense aggregates and coarse multilamellar and fine fingerprint profiles ultrastructurally, and consisted mainly of the hydrophobic protein, subunit c of mitochondrial ATP synthase. A homozygosity mapping approach localised the gene causing the disease in Merino sheep to the chromosomal region (OAR7q13-15) associated with NCL in South Hampshire sheep.

CONCLUSION

NCL in Merino sheep is a subunit c-storing disease, clinically and pathologically similar to NCL in South Hampshire sheep. We propose that the disease in both breeds represents mutation at the same gene locus in chromosomal region OAR7q13-15.

The origin of fluorescence in the neuronal ceroid lipofuscinoses (Batten disease) and neuron cultures from affected sheep for studies of neurodegeneration

Lipofuscin and ceroid are usually held responsible for impaired cellular performance, via oxidative damage and the irreversible accumulation of fluorescent products of lipid peroxidation. The neuronal ceroid lipofuscinoses (NCLs, Batten disease) are inherited neurodegenerative diseases characterized by intracellular accumulation of fluorescent lipofuscin-like bodies. However these bodies are lysosomes packed with a particular protein, subunit c of mitochondrial ATP synthase; not the result of oxidative damage. No individual storage body component was fluorescent nor were solutions of total storage bodies. UV-vis spectra confirmed the lack of a fluorophor. Crystals of non-fluorescent albumin and reconstituted storage bodies were fluorescent in glycerol suspensions. This fluorescence is probably caused by interference of light reflected from the protein array, as is often observed in protein crystals. Other lipofuscins may be secondary lysosomes with a high protein content and the source of fluorescence the same. The neurodegeneration associated with lipofuscin accumulation may be caused by that accumulation, or may be a separate manifestation of aging. Neuronal cell cultures offer a way to study these processes. Subunit c accumulation has been observed in cerebral bipolar neurons cultured from 90 day NCL affected sheep foetuses. Neurons from different parts of the brain behave differently. Normal 108 day cerebellar granule neurons migrated into clumps when cultured with tri-iodothyronine, but affected cerebellar neurons did not, nor did normal or affected cerebral neurons.

Flupirtine blocks apoptosis in batten patient lymphoblasts and in human postmitotic CLN3- and CLN2-deficient neurons

Multiple gene defects cause Batten disease. Accelerated apoptosis accounts for neurodegeneration in the late infantile and juvenile forms that are due to defects in the CLN3 and CLN2 genes. Extensive neuronal death is seen in CLN2- and CLN3-deficient human brain as well as in CLN6-deficient sheep brain and retina. When neurons in late infantile and juvenile brain survive, they manage to do so by upregulating the neuroprotective molecule Bcl-2. The CLN3 gene has antiapoptotic properties at the molecular level. We show that the CLN2 gene is neuroprotective: it enhances growth of NT2 cells and maintains survival of human postmitotic hNT neurons. Conversely, blocking CLN3 or CLN2 expression in hNT neurons with adenoviral antisense-CLN3 or antisense-CLN2-AAV2 constructs causes apoptosis. The drug flupirtine is a triaminopyridine derivative that acts as a nonopioid analgesic. Flupirtine upregulates Bcl-2, increases glutathione levels, activates an inwardly rectifying potassium channel, and delays loss of intermitochondrial membrane calcium retention capacity. We show that flupirtine aborts etoposide-induced apoptosis in CLN1-, CLN2-, CLN3-, and CLN6-deficient as well as normal lymphoblasts. Flupirtine also prevents the death of CLN3- and CLN2-deficient postmitotic hNT neurons at the mitochondrial level. We show that a mechanism of neuroprotection exerted by flupirtine involves complete functional antagonism of N-methyl-D-aspartate or N-methyl-D-aspartate-induced neuronal apoptosis. Flupirtine may be useful as a drug capable of halting the progression of neurodegenerative diseases caused by dysregulated apoptosis.

The gene mutated in variant late-infantile neuronal ceroid lipofuscinosis (CLN6) and in nclf mutant mice encodes a novel predicted transmembrane protein

The neuronal ceroid lipofuscinoses (NCLs) are a group of autosomal recessive neurodegenerative diseases characterized by the accumulation of autofluorescent lipopigment in various tissues and by progressive cell death in the brain and retina. The gene for variant late-infantile NCL (vLINCL), CLN6, was previously mapped to chromosome 15q21-23 and is predicted to be orthologous to the genes underlying NCL in nclf mice and in South Hampshire and Merino sheep. The gene underlying this disease has been identified with six different mutations found in affected patients and with a 1-bp insertion in the orthologous Cln6 gene in the nclf mouse. CLN6 encodes a novel 311-amino acid protein with seven predicted transmembrane domains, is conserved across vertebrates and has no homologies with proteins of known function. One vLINCL mutation, affecting a conserved amino acid residue within the predicted third hydrophilic loop of the protein, has been identified, suggesting that this domain may play an important functional role.

Neurodegenerative disease: the neuronal ceroid lipofuscinoses (Batten disease)

In the past decade there have been significant advances in our understanding of the molecular genetic basis of the neuronal ceroid lipofuscinoses, a clinically and genetically heterogeneous group of childhood neurodegenerative storage disorders. Recent research progress is reviewed here, to summarize new disease gene identification, diagnostics, treatment, protein functional studies and investigations into the underlying molecular pathogenesis of these devastating disorders.

Involvement of nitric oxide released from microglia-macrophages in pathological changes of cathepsin D-deficient mice

Cathepsin D (CD) deficiency has been shown to induce ceroid-lipofuscin storage in lysosomes of mouse CNS neuron (Koike et al., 2000). To understand the behavior of microglial cells corresponding to these neuronal changes, CD-deficient (CD-/-) mice, which die at approximately postnatal day (P) 25 by intestinal necrosis, were examined using morphological as well as biochemical approaches. Light and electron microscopic observations revealed that microglia showing large round cell bodies with few processes appeared in the cerebral cortex and thalamus after P16. At P24, microglia often encircled neurons that were occupied with autolysosomes, indicating increased phagocytic activity. These morphologically transformed microglia markedly expressed inducible nitric oxide synthase (iNOS), which was also detected in the intestine of the mice. To assess the role of microglial nitric oxide (NO) in neuropathological changes in CD-/- mice, l-N(G)-nitro-arginine methylester (l-NAME), a competitive NOS inhibitor, or S-methylisothiourea hemisulfate (SMT), an iNOS inhibitor, was administered intraperitoneally for 13 consecutive days. The total number of terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive cells counted in the thalamus was found to be significantly decreased by chronic treatment of l-NAME or SMT, whereas neither the neuronal accumulation of ceroid-lipofuscin nor the microglial phagocytic activity was affected by these treatments. Moreover, the chronic treatment of l-NAME or SMT completely suppressed hemorrhage-necrotic changes in the small intestine of CD-/- mice, resulting in normal growth of the body weight of the mice. These results suggest that NO production via iNOS activity in microglia and peripheral macrophages contributes to secondary tissue damages such as neuronal apoptosis and intestinal necrosis, respectively.

Involvement of nitric oxide released from microglia-macrophages in pathological changes of cathepsin D-deficient mice

Cathepsin D (CD) deficiency has been shown to induce ceroid-lipofuscin storage in lysosomes of mouse CNS neuron (Koike et al., 2000). To understand the behavior of microglial cells corresponding to these neuronal changes, CD-deficient (CD-/-) mice, which die at approximately postnatal day (P) 25 by intestinal necrosis, were examined using morphological as well as biochemical approaches. Light and electron microscopic observations revealed that microglia showing large round cell bodies with few processes appeared in the cerebral cortex and thalamus after P16. At P24, microglia often encircled neurons that were occupied with autolysosomes, indicating increased phagocytic activity. These morphologically transformed microglia markedly expressed inducible nitric oxide synthase (iNOS), which was also detected in the intestine of the mice. To assess the role of microglial nitric oxide (NO) in neuropathological changes in CD-/- mice, l-N(G)-nitro-arginine methylester (l-NAME), a competitive NOS inhibitor, or S-methylisothiourea hemisulfate (SMT), an iNOS inhibitor, was administered intraperitoneally for 13 consecutive days. The total number of terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive cells counted in the thalamus was found to be significantly decreased by chronic treatment of l-NAME or SMT, whereas neither the neuronal accumulation of ceroid-lipofuscin nor the microglial phagocytic activity was affected by these treatments. Moreover, the chronic treatment of l-NAME or SMT completely suppressed hemorrhage-necrotic changes in the small intestine of CD-/- mice, resulting in normal growth of the body weight of the mice. These results suggest that NO production via iNOS activity in microglia and peripheral macrophages contributes to secondary tissue damages such as neuronal apoptosis and intestinal necrosis, respectively.

Congenital ovine neuronal ceroid lipofuscinosis--a cathepsin D deficiency with increased levels of the inactive enzyme

We recently showed that a form of neuronal ceroid lipofuscinosis (NCL) in white Swedish landrace sheep is caused by a missense mutation in the cathepsin D gene resulting in complete inactivation of the enzyme. Despite the lack of cathepsin D activity, the brains of the cathepsin D deficient sheep showed strongly increased staining for cathepsin D in immunohistochemistry. By Western blotting, a 5-10 fold increase in the level of cathepsin D was confirmed. These results indicate that the missense mutation in congenital NCL sheep results in the synthesis of an inactive yet stable cathepsin D.

Neuronal ceroid lipofuscinosis in Australian Merino sheep: a new animal model

In 1997, neuronal ceroid lipofuscinosis (NCL) was identified for the first time in Merino sheep in Australia. A homozygosity mapping approach localized the disease gene in Merino sheep to the same region on chromosome 7 in which NCL was recently mapped in South Hampshire sheep. This region shows conserved synteny with the region on human chromosome 15 in which the human late infantile NCL variant CLN6 was mapped. NCL in Merino and South Hampshire sheep are therefore potential animal models for the human late infantile variant CLN6.

Developmental changes in the expression of neuronal ceroid lipofuscinoses-linked proteins

Neuronal ceroid lipofuscinoses (NCL) form a distinct group of storage diseases where the normal development of the central nervous system is interrupted and neurons of the neocortex begin to degenerate. Mutations in genes encoding three lysosomal enzymes are the causes for three early-onset forms of NCLs: palmitoyl-protein thioesterase 1 (PPT1) is deficient in human infantile NCL, tripeptidyl peptidase 1 (TTP1) in late-infantile NCL, and cathepsin D in congenital ovine NCL. We wanted to compare the developmental expression profiles of these enzymes in rat brain. In conclusion, the PPT1 expression pattern differed from the two other lysosomal enzymes implicated in NCL diseases, thus suggesting a distinctive role for PPT1 in brain development.