ER and oxidative stresses are common mediators of apoptosis in both neurodegenerative and non-neurodegenerative lysosomal storage disorders and are alleviated by chemical chaperones

It is estimated that more than 40 different lysosomal storage disorders (LSDs) cumulatively affect one in 5000 live births, and in the majority of the LSDs, neurodegeneration is a prominent feature. Neuronal ceroid lipofuscinoses (NCLs), as a group, represent one of the most common (one in 12,500 births) neurodegenerative LSDs. The infantile NCL (INCL) is the most devastating neurodegenerative LSD, which is caused by inactivating mutations in the palmitoyl-protein thioesterase-1 (PPT1) gene. We previously reported that neuronal death by apoptosis in INCL, and in the PPT1-knockout (PPT1-KO) mice that mimic INCL, is at least in part caused by endoplasmic reticulum (ER) and oxidative stresses. In the present study, we sought to determine whether ER and oxidative stresses are unique manifestations of INCL or they are common to both neurodegenerative and non-neurodegenerative LSDs. Unexpectedly, we found that ER and oxidative stresses are common manifestations in cells from both neurodegenerative and non-neurodegenerative LSDs. Moreover, all LSD cells studied show extraordinary sensitivity to brefeldin-A-induced apoptosis, which suggests pre-existing ER stress conditions. Further, we uncovered that chemical disruption of lysosomal homeostasis in normal cells causes ER stress, suggesting a cross-talk between the lysosomes and the ER. Most importantly, we found that chemical chaperones that alleviate ER and oxidative stresses are also cytoprotective in all forms of LSDs studied. We propose that ER and oxidative stresses are common mediators of apoptosis in both neurodegenerative and non-neurodegenerative LSDs and suggest that the beneficial effects of chemical/pharmacological chaperones are exerted, at least in part, by alleviating these stress conditions.     

The use of dried blood spot samples in the diagnosis of lysosomal storage disorders--current status and perspectives

Dried blood spot (DBS) methods are currently available for identification of a range of lysosomal storage disorders (LSDs). These disorders are generally characterized by a deficiency of activity of a lysosomal enzyme and by a broad spectrum of phenotypes. Diagnosis of LSD patients is often delayed, which is of particular concern as therapeutic outcomes (e.g. enzyme replacement therapy) are generally more favorable in early disease stages. Experts in the field of LSDs diagnostics and screening programs convened and reviewed experiences with the use of DBS methods, and discuss the diagnostic challenges, possible applications and quality programs in this paper. Given the easy sampling and shipping and stability of samples, DBS has evident advantages over other laboratory methods and can be particularly helpful in the early identification of affected LSD patients through neonatal screening, high-risk population screening or family screening.     

Intracerebroventricular enzyme infusion corrects central nervous system pathology and dysfunction in a mouse model of metachromatic leukodystrophy

Arylsulfatase A (ASA) catalyzes the desulfation of sulfatide, a major lipid component of myelin. Inherited functional deficiencies of ASA cause the lysosomal storage disease (LSD) metachromatic leukodystrophy (MLD), which is characterized by intralysosomal accumulation of sulfatide, progressive neurological symptoms and early death. Enzyme replacement therapy (ERT) using intravenous injection of active enzyme is a treatment option for many LSDs as exogenous lysosomal enzymes are delivered to lysosomes of patient's cells via receptor-mediated endocytosis. Efficient treatment of MLD and other LSDs with central nervous system (CNS) involvement is, however, hampered by the blood-brain barrier (BBB), which limits transfer of therapeutic enzymes from the circulation to the brain parenchyma. To bypass the BBB, we infused recombinant human ASA (rhASA) by implanted miniature pumps into the cerebrospinal fluid (CSF) of a conventional and a novel, genetically aggravated ASA knockout mouse model of MLD. rhASA continuously delivered to the lateral ventricle for 4 weeks penetrated the brain parenchyma and was targeted to the lysosomes of brain cells. Histological analysis revealed complete reversal of lysosomal storage in the infused hemisphere. rhASA concentrations and sulfatide clearance declined with increasing distance from the infusion site. Correction of the ataxic gait indicated reversal of central nervous system dysfunctions. The profound histopathological and functional improvements, the requirement of low enzyme doses and the absence of immunological side effects suggest intracerebroventricular ERT to be a promising treatment option for MLD and other LSDs with prevailing CNS disease.     

A block of autophagy in lysosomal storage disorders

Most lysosomal storage disorders (LSDs) are caused by deficiencies of lysosomal hydrolases. While LSDs were among the first inherited diseases for which the underlying biochemical defects were identified, the mechanisms from enzyme deficiency to cell death are poorly understood. Here we show that lysosomal storage impairs autophagic delivery of bulk cytosolic contents to lysosomes. By studying the mouse models of two LSDs associated with severe neurodegeneration, multiple sulfatase deficiency (MSD) and mucopolysaccharidosis type IIIA (MPSIIIA), we observed an accumulation of autophagosomes resulting from defective autophagosome-lysosome fusion. An impairment of the autophagic pathway was demonstrated by the inefficient degradation of exogenous aggregate-prone proteins (i.e. expanded huntingtin and mutated alpha-synuclein) in cells from LSD mice. This impairment resulted in massive accumulation of polyubiquitinated proteins and of dysfunctional mitochondria which are the putative mediators of cell death. These data identify LSDs as 'autophagy disorders' and suggest the presence of common mechanisms in the pathogenesis of these and other neurodegenerative diseases.     

Neuronal ceroid lipofuscinoses and possible pathogenic mechanism

The neuronal ceroid lipofuscinoses (NCLs) consist of eight autosomal recessively inherited storage disorders characterized by lysosomal inclusions of autofluorescent lipofuscins and rapid neurodegenerative progression. The NCLs include eight forms that result from genetic deficiency on genes CLN(1) to CLN(8), respectively: four classic forms with clinical onset at varying ages-infantile (INCL), late-infantile (LINCL), juvenile (JNCL), and adult (ANCL)-and four variants of late-infantile onset-the Finnish variant LINCL (fLINCL), Portuguese variant LINCL (pLINCL), Turkish variant LINCL (tLINCL), and progressive epilepsy with mental retardation (EPMR). The genes CLN(1) and CLN(2) have been characterized to encode lysosomal hydrolytic enzymes, but CLN(3), CLN(5), and CLN(8) encode transmembranous proteins with unknown function. Although clinical and pathological abnormalities have been recognized to be similar in all eight forms, the molecular mechanism explaining NCL pathogenesis remains unclear. In this review, the molecular basis for NCLs and a possible pathogenic mechanism are discussed.     

Hippocampal pathology in the human neuronal ceroid-lipofuscinoses: distinct patterns of storage deposition, neurodegeneration and glial activation

The neuronal ceroid-lipofuscinoses (NCLs) are recessively inherited lysosomal storage diseases, currently classified into 8 forms (CLN1-CLN8). Collectively, the NCLs constitute the most common group of progressive encephalopathies of childhood, and present with visual impairment, psychomotor deterioration and severe seizures. Despite recent identification of the underlying disease genes, the mechanisms leading to neurodegeneration and epilepsy in the NCLs remain poorly understood. To investigate these events, we examined the patterns of storage deposition, neurodegeneration, and glial activation in the hippocampus of patients with CLN1, CLN2, CLN3, CLN5 and CLN8 using histochemistry and immunohistochemistry. These different forms of NCL shared distinct patterns of neuronal degeneration in the hippocampus, with heavy involvement of sectors CA2-CA4 but relative sparing of CA1. This selective pattern of degeneration was also observed in immunohistochemically identified interneurons, which exhibited a graded severity of loss according to phenotype, with calretinin-positive interneurons relatively spared. Furthermore, glial activation was also regionally specific, with microglial activation most pronounced in areas of greatest neuronal loss, and astrocyte activation prominent in areas where neuronal loss was less evident. In conclusion, the NCLs share a common pattern of selective hippocampal pathology, distinct from that seen in the majority of temporal lobe epilepsies.     

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. Hum Mutat 14:199–215, 1999. © 1999 Wiley‐Liss, Inc.     

Assay of heparan-N-sulfamidase in dried leukocytes impregnated in filter paper: A new tool for the identification of Mucopolisaccharidosis IIIA and potentially other lysosomal disorders

Diagnosis of lysosomal storage disorders (LSDs) is mainly based on specific enzyme assays in leucocytes. Dried blood spots have also been used as sample for the enzyme assays. However, some lysosomal enzymes such as heparan-N-sulfamidase (HNS) and others cannot be assayed by this material. We developed an assay for HNS using dried leukocytes impregnated in filter paper (DLFP) as source of enzyme, and the results allowed the correct identification of Mucopolisaccharidosis IIIA. From this proof of concept we predict that the assay of lysosomal enzymes in DLFP samples, which still needs further development, could be a useful tool for the diagnosis of LSDs, especially in regions where transportation of liquid blood samples in appropriate conditions for long distances and/or across country borders is challenging.     

Reversal of peripheral and central neural storage and ataxia after recombinant enzyme replacement therapy in alpha-mannosidosis mice

Despite the progress in the treatment of lysosomal storage disorders (LSDs) mainly by enzyme replacement therapy, only limited success was reported in targeting the appropriate lysosomal enzyme into the brain. This prevents efficient clearance of neuronal storage, which is present in many of these disorders including alpha-mannosidosis. Here we show that the neuropathology of a mouse model for alpha-mannosidosis can be efficiently treated using recombinant human alpha-mannosidase (rhLAMAN). After intravenous administration of different doses (25-500 U/kg), rhLAMAN was widely distributed among tissues, and immunohistochemistry revealed lysosomal delivery of the injected enzyme. Whereas low doses (25 U/kg) led to a significant clearance (<70%) in visceral tissues, higher doses were needed for a clear effect in central and peripheral nervous tissues. A distinct reduction (<50%) of brain storage required repeated high-dose injections (500 U/kg), whereas lower doses (250 U/kg) were sufficient for clearance of stored substrates in peripheral neurons of the trigeminal ganglion. Successful transfer across the blood-brain barrier was evident as the injected enzyme was found in hippocampal neurons, leading to a nearly complete disappearance of storage vacuoles. Importantly, the decrease in neuronal storage in the brain correlated with an improvement of the neuromotor disabilities found in untreated alpha-mannosidosis mice. Uptake of rhLAMAN seems to be independent of mannose-6-phosphate receptors, which is consistent with the low phosphorylation profile of the enzyme. These data suggest that high-dose injections of low phosphorylated enzymes might be an interesting option to efficiently treat LSDs with CNS involvement.     

Prevalence of lysosomal storage diseases in Portugal

Lysosomal storage diseases (LSDs) are a group of inherited metabolic disorders individually considered as rare, and few data on its prevalence has been reported in the literature. The overall birth prevalence of the 29 different LSDs studied in the Portuguese population was calculated to be 25/100000 live births, twice the prevalence previously described in Australia and in The Netherlands. The comparison of the prevalence profile of the LSDs presenting a prevalence higher than 0.5/100000 in the Portuguese, Dutch and Australian populations showed, in the Portuguese, the existence of a higher prevalence of GM2 gangliosidoses (B variant), mucolipidoses (II and III), Niemman-Pick type C and metachromatic leukodystrophy (MLD), and a lower prevalence of Pompe and Fabry. The highest prevalence value for a single LSD is the one of GM2 gangliosidoses (B variant), corresponding to 3/100000, a value which is significantly higher than the prevalence of the most frequent LSD in Dutch, Pompe disease (2/100000) and Australians, Gaucher's disease (GD) (1.8/100000). It is worth noting that the highest prevalence of GM2 gangliosidoses found in the Portuguese is mainly due to the existence of a unique subtype, the rare juvenile B1 variant.     

Ovine neuronal ceroid lipofuscinosis: a large animal model syntenic with the human neuronal ceroid lipofuscinosis variant CLN6.

The neuronal ceroid lipofuscinoses (NCLs) are a group of inherited degenerative neurological diseases affecting children. A number of non-allelic variants have been identified within the human population and the genes for some of these have recently been identified. The underlying mechanism for the neuropathology remains an enigma; however, pioneering studies with the naturally occurring ovine model (OCL) have led to the proposal that these diseases represent lesions in specific hydrophobic protein degradation pathways. In this study, we show linkage between OCL and microsatellite markers on OAR 7q13-15. Using interspecies chromosome painting we establish that OAR 7q13-15 is syntenic with human chromosome 15q21-23, the region which was recently defined as the location of a newly identified late infantile variant (CLN6). We propose that our ovine model represents a mutation in the gene orthologous to that mutated in the human late infantile variant CLN6. The ovine linkage flock, consisting of 56 families, represents a powerful resource for positional cloning of this NCL gene. The availability of such a large animal model will have important implications for experimentation in downstream corrective therapies.     

Measurement of lysosomal enzyme activities: A technical standard of the American College of Medical Genetics and Genomics (ACMG)

Assays that measure lysosomal enzyme activity are important tools for the screening and diagnosis of lysosomal storage disorders (LSDs). They are often ordered in combination with urine oligosaccharide and glycosaminoglycan analysis, additional biomarker assays, and/or DNA sequencing when an LSD is suspected. Enzyme testing in whole blood/leukocytes, serum/plasma, cultured fibroblasts, or dried blood spots demonstrating deficient enzyme activity remains a key component of LSD diagnosis and is often prompted by characteristic clinical findings, abnormal newborn screening, abnormal biochemical findings (eg, elevated glycosaminoglycans), or molecular results indicating pathogenic variants or variants of uncertain significance in a gene associated with an LSD. This document, which focuses on clinical enzyme testing for LSDs, provides a resource for laboratories to develop and implement clinical testing, to describe variables that can influence test performance and interpretation of results, and to delineate situations for which follow-up molecular testing is warranted.     

Diagnostic value of electron microscopy in a case of juvenile neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinoses (NCLs) represent a large group of inherited neurodegenerative disorders characterized by an abnormal accumulation of lipopigment in neuronal and extraneuronal cells. The authors present a case of juvenile neuronal ceroid lipofuscinosis in a 7-year-old boy. Ultrastructural examination of a skin biopsy disclosed deposits of curvilinear profiles and fingerprint-like structures in epithelial cells of sweat glands, endothelial cells, peripheral nerve endings, and fibroblasts. These findings allowed specific confirmation of the assumed diagnosis of juvenile neuronal ceroid lipofuscinosis. Due to the genotypic and phenotypic variability within the group of NCLs, the clinical investigation may be long and complicated. With the NCL disorders in mind, an accurate diagnosis based on ultrastructural examination of a skin biopsy may shorten this investigation, thus benefitting the patient.     

The Batten disease gene CLN3 is required for the response to oxidative stress

Mutations in the CLN3 gene cause juvenile neuronal ceroid lipofuscinosis (JNCL or Batten disease), an early onset neurodegenerative disorder. JNCL is the most common of the NCLs, a group of disorders with infant or childhood onset that are caused by single gene mutations. The NCLs, although relatively rare, share many pathological and clinical similarities with the more common late-onset neurodegenerative disorders, while their simple genetic basis makes them an excellent paradigm. The early onset and rapid disease progression in the NCLs suggests that one or more key cellular processes are severely compromised. To identify the functional pathways compromised in JNCL, we have performed a gain-of-function modifier screen in Drosophila. We find that CLN3 interacts genetically with the core stress signalling pathways and components of stress granules, suggesting a function in stress responses. In support of this, we find that Drosophila lacking CLN3 function are hypersensitive to oxidative stress yet they respond normally to other physiological stresses. Overexpression of CLN3 is sufficient to confer increased resistance to oxidative stress. We find that CLN3 mutant flies perceive conditions of increased oxidative stress correctly but are unable to detoxify reactive oxygen species, suggesting that their ability to respond is compromised. Together, our data suggest that the lack of CLN3 function leads to a failure to manage the response to oxidative stress and this may be the key deficit in JNCL that leads to neuronal degeneration.     

Newborn screening for lysosomal storage disorders

Lysosomes are intracellular organelles containing acid hydrolases that degrade biological macromolecules. Lysosomal storage disorders (LSDs) are caused by absent activity of one or more of these enzymes due to mutations of genes encoding lysosomal hydrolases or enzymes that process, target, and transport these enzymes. The specific signs and symptoms of each LSD derive from the type of material accumulated within the lysosome, the site (organ) of accumulation and the response of the body (sometimes in the form of an inflammatory or immune response) to the accumulated material. Interest for inclusion of these disorders in newborn screening programs derives from the availability of effective therapy in the form of enzyme replacement or substrate reduction therapy and bone marrow transplant that may improve long-term outcome especially if started prior to irreversible organ damage. Based on the availability of therapy and suitable screening methods, Gaucher disease, Fabry disease, Pompe disease, mucopolysaccharidosis I and II, Niemann–Pick disease, and Krabbe disease are candidates for newborn screening. Pilot newborn screening projects have been performed for some of these conditions that indicate the feasibility of this approach. This review will provide insight into these screening strategies and discuss their advantages and limitations. © 2011 Wiley-Liss, Inc.     

Diagnostic Value of Electron Microscopy in a Case of Juvenile Neuronal Ceroid Lipofuscinosis

Neuronal ceroid lipofuscinoses (NCLs) represent a large group of inherited neurodegenerative disorders characterized by an abnormal accumulation of lipopigment in neuronal and extraneuronal cells. The authors present a case of juvenile neuronal ceroid lipofuscinosis in a 7-year-old boy. Ultrastructural examination of a skin biopsy disclosed deposits of curvilinear profiles and fingerprint-like structures in epithelial cells of sweat glands, endothelial cells, peripheral nerve endings, and fibroblasts. These findings allowed specific confirmation of the assumed diagnosis of juvenile neuronal ceroid lipofuscinosis. Due to the genotypic and phenotypic variability within the group of NCLs, the clinical investigation may be long and complicated. With the NCL disorders in mind, an accurate diagnosis based on ultrastructural examination of a skin biopsy may shorten this investigation, thus benefitting the patient.     

Impaired parkin-mediated mitochondrial targeting to autophagosomes differentially contributes to tissue pathology in lysosomal storage diseases

Dysfunctional mitochondria are a well-known disease hallmark. The accumulation of aberrant mitochondria can alter cell homeostasis, thus resulting in tissue degeneration. Lysosomal storage disorders (LSDs) are a group of inherited diseases characterized by the buildup of undegraded material inside the lysosomes that leads to autophagic-lysosomal dysfunction. In LSDs, autophagic stress has been associated to mitochondrial accumulation and dysfunction. However, the mechanisms underlying mitochondrial aberrations and how these are involved in tissue pathogenesis remain largely unexplored. In normal conditions, mitochondrial clearance occurs by mitophagy, a selective form of autophagy, which relies on a parkin-mediated mitochondrial priming and subsequent sequestration by autophagosomes. Here, we performed a detailed analysis of key steps of mitophagy in a mouse model of multiple sulfatase deficiency (MSD), a severe type of LSD characterized by both neurological and systemic involvement. We demonstrated that in MSD liver reduced parkin levels resulted in inefficient mitochondrial priming, thus contributing to the accumulation of giant mitochondria that are located outside autophagic vesicles ultimately leading to cytochrome c release and apoptotic cell death. Morphological and functional changes were also observed in mitochondria from MSD brain but these were not directly associated with neuronal cell loss, suggesting a secondary contribution of mitochondria to neurodegeneration. Together, these data shed new light on the mechanisms underlying mitochondrial dysfunction in LSDs and on their tissue-specific differential contribution to the pathogenesis of this group of metabolic disorders.     

Gaucher's disease: a paradigm for interventional genetics

Gaucher's disease (GD) is one of the most prevalent lysosomal storage disorders (LSDs) and a rare genetic disease for which specific therapy is now available. GD is an autosomal, recessive, inborn error of glycosphingolipid metabolism, due to a deficiency in the enzyme acid β-glucosidase. Partial deficiency of acid β-glucosidase is associated with parenchymal disease of the liver, spleen, and bone marrow with concomittant anemia and thrombocytopenia in non-neuronopathic, type 1 GD. Severe deficiency of glucocerebrosidase caused by severe mutations is additionally associated with neurological manifestations in the less common type 2 and type 3 GD subtypes. Outside of the Ashkenazi Jewish community, a high molecular diversity is observed. Clarification of genotype/phenotype relationship and the identification of modifier loci that impact on GD phenotypes remains a critical area for research. Enzyme replacement therapy (ERT) is proven to be safe and effective in the treatment of type 1 GD, establishing imiglucerase as the current standard of care. Amelioration of hepatosplenomegaly and of hematological manifestations is usually apparent within 6–12 months, whereas the bone disease responds more slowly. ERT cannot reverse the neurological deficits in type 2 or type 3 GD. Small molecule inhibitors of glucosylceramide synthase are being developed for substrate reduction therapy. Other potential therapeutic options such as chaperon-mediated enzyme enhancement therapy and gene therapy are being explored.     

Update of the mutation spectrum and clinical correlations of over 360 mutations in eight genes that underlie the neuronal ceroid lipofuscinoses

The neuronal ceroid lipofuscinoses (NCLs) are clinically and genetically heterogeneous neurodegenerative disorders. Most are autosomal recessively inherited. Clinical features include a variable age of onset, motor and mental decline, epilepsy, visual loss, and premature death. Mutations in eight genes (PPT1/CLN1, TPP1/CLN2, CLN3, CLN5, CLN6, MFSD8/CLN7, CLN8) have been identified and several more are predicted to exist, including two provisionally named CLN4 and CLN9. Despite excessive in vitro and in vivo studies, the precise functions of the NCL proteins and the disease mechanisms remain elusive. To date 365 NCL-causing mutations are known, with 91 novel disease-causing mutations reported. These are reviewed with an emphasis on their complex correlation to phenotypes. Different mutations within the NCL spectrum can cause variable disease severity. The NCLs exemplify both phenotypic convergence or mimicry and phenotypic divergence. For example, mutations in CLN5, CLN6, MFSD8, or CLN8 can underlie the clinically similar late infantile variant NCL disease. Phenotypic divergence is exemplified by different CLN8 mutations giving rise to two very different diseases, the mild CLN8 disease, EPMR (progressive epilepsy with mental retardation), and the more severe CLN8 disease, late infantile variant. The increase in the genetic understanding of the NCLs has led to improved diagnostic approaches, and the recent proposal of a new nomenclature.     

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.