Effective treatment of the central nervous system in lysosomal storage diseases: save that brain!
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Cathepsin D-deficient (CD-/-) mice have been shown to manifest seizures and become blind near the terminal stage [approximately postnatal day (P) 26]. We therefore examined the morphological, immunocytochemical, and biochemical features of CNS tissues of these mice. By electron microscopy, autophagosome/autolysosome-like bodies containing part of the cytoplasm, granular osmiophilic deposits, and fingerprint profiles were demonstrated in the neuronal perikarya of CD-/- mouse brains after P20. Autophagosomes and granular osmiophilic deposits were detected in neurons at P0 but were few in number, whereas they increased in the neuronal perikarya within days after birth. Some large-sized neurons having autophagosome/autolysosome-like bodies in the perikarya appeared in the CNS tissues, especially in the thalamic region and the cerebral cortex, at P17. These lysosomal bodies occupied the perikarya of almost all neurons in CD-/- mouse brains obtained from P23 until the terminal stage. Because these neurons exhibited autofluorescence, it was considered that ceroid lipofuscin may accumulate in lysosomal structures of CD-/- neurons. Subunit c of mitochondrial ATP synthase was found to accumulate in the lysosomes of neurons, although the activity of tripeptidyl peptidase-I significantly increased in the brain. Moreover, neurons near the terminal stage were often shrunken and possessed irregular nuclei through which small dense chromatin masses were scattered. These results suggest that the CNS neurons in CD-/- mice show a new form of lysosomal accumulation disease with a phenotype resembling neuronal ceroid lipofuscinosis.
The neuronal ceroid lipofuscinoses (NCLs) constitute a group of neurodegenerative storage diseases characterized by progressive psychomotor retardation, blindness and premature death. Pathologically, there is accumulation of autofluorescent material in lysosome-derived organelles in a variety of cell types, but neurons in the central nervous system appear to be selectively affected and undergo progressive death. In this report we show that a novel form of NCL, congenital ovine NCL, is caused by a deficiency in the lysosomal aspartyl proteinase cathepsin D. A single nucleotide mutation in the cathepsin D gene results in conversion of an active site aspartate to asparagine, leading to production of an enzymatically inactive but stable protein. This results in severe cerebrocortical atrophy and early death, providing strong evidence for an important role of cathepsin D in neuronal development and/or homeostasis.
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.
Lysosomal diseases comprise a group of inherited disorders resulting from defects of lysosomal enzymes and their cofactors, and in many of them the nervous system is affected. Recently, enzyme replacement therapy with recombinant lysosomal enzymes has been clinically available for several lysosomal diseases. Such enzyme replacement therapies can improve non-neurological disorders but is not effective for neurological ones. In this review, we discuss the molecular pathologies of lysosomal diseases from the protein structural aspect, current enzyme replacement therapies, and attempts to develop enzyme replacement therapies effective for lysosomal diseases associated with neurological disorders, i.e., production of enzymes, brain-specific delivery and incorporation of lysosomal enzymes into cells.
Multiple lines of evidence implicate lysosomes in a variety of pathogenic events that produce neurodegeneration. Genetic mutations that cause specific enzyme deficiencies account for more than 40 lysosomal storage disorders. These mostly pre-adult diseases are associated with abnormal brain development and mental retardation. Such disorders are characterized by intracellular deposition and protein aggregation, events also found in age-related neurodegenerative diseases including (i) Alzheimer's disease and related tauopathies (ii) Lewy body disorders and synucleinopathies such as Parkinson's disease, and (iii) Huntington's disease and other polyglutamine expansion disorders. Of particular interest for this review is evidence that alterations to the lysosomal system contribute to protein deposits associated with different types of age-related neurodegeneration. Lysosomes are in fact highly susceptible to free radical oxidative stress in the aging brain, leading to the gradual loss of their processing capacity over the lifespan of an individual. Several studies point to this lysosomal disturbance as being involved in amyloidogenic processing, formation of paired helical filaments, and the aggregation of alpha-synuclein and mutant huntingtin proteins. Most notably, experimentally induced lysosomal dysfunction, both in vitro and in vivo, recapitulates important pathological features of age-related diseases including the link between protein deposition and synaptic loss.
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alpha-N-acetylgalactosaminidase (alpha-NAGA) deficiency is a rare hereditary lysosomal storage disease, and only three alpha-NAGA-deficient patients with angiokeratoma corporis diffusum (Kanzaki) have been described. We report a further case in a 47-year-old Japanese woman, the product of a consanguineous marriage. The remarkable findings in this patient were her normal intelligence, Ménière's syndrome, disturbance of peripheral sensory nerves, hearing loss and cardiac hypertrophy. alpha-NAGA enzyme activity in her plasma was 0.77% of the normal value. Other enzyme activities, such as alpha-galactosidase, beta-galactosidase, alpha-L-fucosidase, beta-mannosidase and aspartylglucosaminidase, were within normal limits. A large quantity of amino acid O-glycans was detected in her urine. Gene analysis revealed a novel point mutation (G-->A transition) at nucleotide 11018 (986 in the cDNA) resulting in an Arg-329-Gln substitution. Kanzaki disease has the same enzyme defect as Schindler disease, but the manifestations are quite different.
The term "neuronal ceroid lipofuscinosis" (NCL) describes a complex of inherited neurodegenerative conditions associated with storage of lipopigments in brain tissue. In 1989 Dyken proposed a classification of NCL based on the age, clinical symptoms, and ultrastructural aspects of the lipopigments. At the ultrastructural level it is possible to distinguish 5 different patterns of osmiophilic lipopigments: usual lipofuscin, fingerprint deposits, granular profiles, curvilinear bodies, and microtubular aggregates. The concept that each ultrastructural pattern was the counterpart of a specific clinical type has been proved not to be true. Advances in molecular genetic techniques have allowed the identification of defective genes and their protein products in several NCL clinical forms. Ceroid lipofuscin deposits may be ultrastructurally observed not only in neuronal cells, but also in several other sites, such as trophoblastic cells, thus permitting prenatal diagnosis. In spite of recent advances in immunohistochemical identification of biochemical markers, the ultrastructural identification of lipofuscinic pigments remains the gold standard to identify NCL, together with clinical aspects and respective gene defects. This study describes the ultrastructural aspects observed in 8 cases of NCL syndromes (3 juvenile, 3 infantile, 1 late infantile, and 1 congenital clinical form). In these patients, genetic analysis was also performed.
Tripeptidyl-peptidase I (TPPI) is an acidic lysosomal peptidase that removes tripeptides from an unmodified N-terminus of small proteins and polypeptides. In humans, TPP I constitutes an integral part of the lysosomal proteolytic apparatus, which, includes numerous hydrolytic enzymes, mostly cysteine proteases (cathepsin B, C, H, K, L, and others), but also serine (cathepsin A) and aspartic (cathepsin D) proteases. The combination of endo- and exopeptidase activities of these enzymes allows for efficient digestion of the diverse proteins transported to the lysosomes, releasing free amino acids and dipeptides that are transported back to the cytoplasm and reused according to the metabolic needs of the cell. The role of TPP I in normal lysosome functioning is underscored by the genetic association of the enzyme with one form of a group of the developmental neurodegenerative disorders of childhood--the neuronal ceroid lipofuscinoses (NCLs). The scope of this article is to review the most recent data, mostly from author's laboratory, on the biology and pathology of TPP I. NCLs are also shortly reviewed with the special emphasis on CLN2 form resulting from mutations in TPP I gene.
Neuronal storage disorders are fatal neurodegenerative diseases of humans and animals that are caused by inherited deficiencies of lysosomal hydrolase activity. Affected individuals often appear normal at birth but eventually develop progressive neurologic symptoms including sensory and motor deficits, mental retardation, and seizures. We have examined efficacy of bone marrow transplantation as a means of enzyme replacement, using cats with the lysosomal storage disease alpha-mannosidosis. Treated animals showed little or no progression of neurologic signs 1-2 years after transplant, whereas untreated cats became severely impaired and reached endstage disease by 6 months of age. Increased lysosomal alpha-mannosidase activity was found in brain tissue of the treated animals, and electron microscopy revealed no evidence of lysosomal storage within most neurons. Histochemical localization of acidic alpha-D-mannoside mannohydrolase (EC 3.2. 1.24), using 5-bromo-4-chloro-3-indolyl alpha-D-mannopyranoside, showed that functional enzyme was present in neurons, glial cells, and cells associated with blood vessels. This study provides direct evidence that bone marrow transplantation as treatment for a neuronal storage disease can lead to significant levels of a missing lysosomal hydrolase within neurons of the central nervous system and to compensation for the genetic metabolic defect.
The application of techniques based on in vivo magnetic resonance to the study of leukodystrophies is evaluated. Magnetic resonance imaging (MRI), the most important neuroimaging modality for patients with leukodystrophies, has proven invaluable for the detection of the extent and etiology of white-matter involvement, diagnosis, and monitoring of disease progression. Proton magnetic resonance spectroscopy, which can detect several brain metabolites, including those related to axonal function and myelination, can provide additional diagnostic and prognostic information and, in some cases, allows a rare insight into the biochemical pathology of leukodystrophies. The potential of other advanced magnetic resonance techniques, including diffusion tensor imaging, magnetization transfer contrast, and molecular imaging, is also discussed. In the future, anatomic and physiologic magnetic resonance techniques are expected to be integrated into a single examination that will provide a detailed characterization of white-matter diseases in children.
Gene transfer into the central nervous system (CNS) is one of the foremost scientific challenges today. To give a brief survey of possible approaches to gene therapy in diseases affecting the CNS, we have selected the lysosomal storage diseases (LDS), which are an excellent model of both early-onset infantile neurological forms and late-onset adult psychiatric forms. Lysosomal storage diseases represent a group of about 50 monogenic metabolic disorders resulting from a deficiency in intralysosomal enzymes involved in macromolecule catabolism. The clinical severity, including neuropsychiatric symptoms, and the absence of an efficient therapy for the majority of these disorders prompted the various trials of gene therapy now in progress. Most of the genes encoding the normal lysosomal enzymes have been cloned, and the size of the corresponding cDNAs is generally compatible with their transfer by recombinant vectors. New vectors with improved immunogenicity, transduction efficacy, insert capacity, and specificity of targeting are under development. Here we discuss several gene therapy strategies for the correction of LSD-induced anomalies in the CNS. Interesting results have been obtained by animal model brain, which raises hopes that large-scale clinical trials may soon be started.
Dysmyelinating diseases, or leukodystrophies, encompass a wide spectrum of inherited neurodegenerative disorders affecting the integrity of myelin in the brain and peripheral nerves. Most of these disorders fall into one of three categories-lysosomal storage diseases, peroxisomal disorders, and diseases caused by mitochondrial dysfunction-and each leukodystrophy has distinctive clinical, biochemical, pathologic, and radiologic features. Magnetic resonance (MR) imaging has become the primary imaging modality in patients with leukodystrophy and plays an important role in the identification, localization, and characterization of underlying white matter abnormalities in affected patients. MR imaging has also been extensively used to monitor the natural progression of various white matter disorders and the response to therapy. Although the MR imaging features of leukodystrophy are often nonspecific, systematic analysis of the finer details of disease involvement may permit a narrower differential diagnosis, which the clinician can then further refine with knowledge of patient history, clinical testing, and metabolic analysis.
OBJECTIVE: To evaluate the degree of possible peripheral nervous system (PNS) involvement in addition to CNS manifestations in Salla disease, a free sialic acid storage disorder leading to severe mental retardation with a wide clinical variation. BACKGROUND: Salla disease is a lysosomal storage disorder that affects the white matter of the CNS. MRI findings and recent 1H MRS study results provide evidence for delayed central myelination, but there is no previous evidence for PNS involvement in this disease. The gene coding for a presumptive sialic acid transport protein has recently been identified, and the first disease-causing mutations have been characterized. METHODS: Nerve conduction studies; evoked potentials to visual (VEP), brainstem auditory (BAEP), and somatosensory stimuli (SEP); and EEG were carried out on 22 patients (age range 2 months to 57 years) with biochemically and genetically confirmed Salla disease. Brain MRI were available on 14 patients. RESULTS: Nerve conduction studies revealed abnormalities in nearly half of the patients (10/21). The four severely disabled patients and the oldest patient had greatly reduced nerve conduction velocities and prolonged distal latencies compatible with demyelinating polyneuropathy. In addition, SEP was abnormal in the majority of the patients, but VEP and BAEP in only a few cases. PNS involvement was clearly associated with both the phenotypic severity and MRI findings. CONCLUSIONS: The results indicate that dysmyelination in Salla disease occurs not only in the CNS but also in the peripheral nervous system, contributing to the phenotypic variation, which can now be correlated with the molecular basis of the disease.
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An inherited disease associated with deficiencies of beta-galactosidase and alpha-neuraminidase has been identified recently in sheep. The clinical signs, the deficiency of lysosomal enzymes, and the familial nature of the disorder suggested that the condition was a lysosomal storage disease. Four affected sheep were necropsied and their tissues were examined by histopathologic and histochemical methods to determine if the lesions were consistent with a lysosomal storage disease. Central nervous system neurons were enlarged with finely to coarsely granular cytoplasmic material, or less often, neurons were distended with multiple, variably-sized vacuoles. Loss of neurons without gliosis was evident and the Nissl substance was either dispersed and fragmented or condensed around the nuclei of remaining neurons. Neurons of intestinal and other peripheral ganglia, retinal ganglion cells, and heart Purkinje fibers were enlarged similarly. White matter of the cerebrum and spinal cord had numerous spheroid to ellipsoid axonal enlargements. Periportal hepatocytes and renal epithelial cells were enlarged with marked vacuolation. The neuronal storage material stained intensely with periodic acid-Schiff/alcian blue, with Luxol fast blue, for acid phosphatase, and moderately with oil red O stains. Renal and hepatocyte storage material stained intensely with oil red O and moderately with periodic acid-Schiff/alcian blue and Sudan black B stains. The lesions in these sheep were consistent with those of a lysosomal storage disease. Both neuronal and visceral storage occurred, but the neuronal storage was more severe.