From bedside to cell biology: A century of history on lysosomal dysfunction

High-frequency spinal cord stimulation produces long-lasting analgesic effects by restoring lysosomal function and autophagic flux in the spinal dorsal horn

High-frequency spinal cord stimulation (HF-SCS) has been established as an effective therapy for neuropathic pain. However, the analgesic mechanisms involved in HF-SCS remain to be clarified. In our study, adult rat neuropathic pain was induced by spinal nerve ligation. Two days after modeling, the rats were subjected to 4 hours of HF-SCS (motor threshold 50%, frequency 10,000 Hz, and pulse width 0.024 ms) in the dorsal horn of the spinal cord. The results revealed that the tactile allodynia of spinal nerve-injured rats was markedly alleviated by HF-SCS, and the effects were sustained for 3 hours after the stimulation had ceased. HF-SCS restored lysosomal function, increased the levels of lysosome-associated membrane protein 2 (LAMP2) and the mature form of cathepsin D (matu-CTSD), and alleviated the abnormally elevated levels of microtubule-associated protein 1A/B-light chain 3 (LC3)-II and sequestosome 1 (P62) in spinal nerve-injured rats. HF-SCS also mostly restored the immunoreactivity of LAMP2, which was localized in neurons in the superficial layers of the spinal dorsal horn in spinal nerve-injured rats. In addition, intraperitoneal administration of 15 mg/kg chloroquine for 60 minutes reversed the expression of the aforementioned proteins and shortened the timing of the analgesic effects of HF-SCS. These findings suggest that HF-SCS may exhibit long-lasting analgesic effects on neuropathic pain in rats through improving lysosomal dysfunction and alleviating autophagic flux. This study was approved by the Laboratory Animal Ethics Committee of China Medical University, Shenyang, China (approval No. 2017PS196K) on March 1, 2017.

Next-Generation Molecular Investigations in Lysosomal Diseases: Clinical Integration of a Comprehensive Targeted Panel

Diagnosis of lysosomal disorders (LDs) may be hampered by their clinical heterogeneity, phenotypic overlap, and variable age at onset. Conventional biological diagnostic procedures are based on a series of sequential investigations and require multiple sampling. Early diagnosis may allow for timely treatment and prevent clinical complications. In order to improve LDs diagnosis, we developed a capture-based next generation sequencing (NGS) panel allowing the detection of single nucleotide variants (SNVs), small insertions and deletions, and copy number variants (CNVs) in 51 genes related to LDs. The design of the LD panel covered at least coding regions, promoter region, and flanking intronic sequences for 51 genes. The validation of this panel consisted in testing 21 well-characterized samples and evaluating analytical and diagnostic performance metrics. Bioinformatics pipelines have been validated for SNVs, indels and CNVs. The clinical output of this panel was tested in five novel cases. This capture-based NGS panel provides an average coverage depth of 474× which allows the detection of SNVs and CNVs in one comprehensive assay. All the targeted regions were covered above the minimum required depth of 30×. To illustrate the clinical utility, five novel cases have been sequenced using this panel and the identified variants have been confirmed using Sanger sequencing or quantitative multiplex PCR of short fluorescent fragments (QMPSF). The application of NGS as first-line approach to analyze suspected LD cases may speed up the identification of alterations in LD-associated genes. NGS approaches combined with bioinformatics analyses, are a useful and cost-effective tool for identifying the causative variations in LDs.

Heparan sulfate proteoglycans: The sweet side of development turns sour in mucopolysaccharidoses

Heparan sulfate proteoglycans (HSPGs) are complex carbohydrate-modified proteins ubiquitously expressed on cell surfaces, extracellular matrix and basement membrane of mammalian tissues. Beside to serve as structural constituents, they regulate multiple cellular activities. A critical involvement of HSPGs in development has been established, and perturbations of HSPG-dependent pathways are associated with many human diseases. Recent evidence suggest a role of HSPGs in the pathogenesis of mucopolysaccharidoses (MPSs) where the accumulation of undigested HS results in the loss of cellular functions, tissue damage and organ dysfunctions accounting for clinical manifestations which include central nervous system (CNS) involvement, degenerative joint disease and reduced bone growth. Current therapies are not curative but only ameliorate the disease symptoms. Here, we highlight the link between HSPG functions in the development of CNS and musculoskeletal structures and the etiology of some MPS phenotypes, suggesting that HSPGs may represent potential targets for the therapy of such incurable diseases.

The new frame for Mucopolysaccharidoses

Mucopolysaccharidoses (MPS) are genetic, progressive, lysosomal storage disorders affecting virtually all organs and systems. The first MPS were clinically identified about 100 years ago. Nowadays, the enzyme defects and related genes are known for all 11 different enzyme defects. Treatments are available for many MPS but these have only partial efficacy, especially when started late. The problems to solve are: 1) the need for an earlier diagnosis (neonatal screening? improving the awareness of physicians?); 2) prompt access to therapies; 3) improving the efficacy of the available treatments; 4) finding new treatments; and 5) the availability of specialist experts in MPS who can meet the traditional needs of MPS patients. This introduction to the IJP Supplement on MPS is a brief comment on the different papers accepted for this volume, which are in turn the elaboration of the lectures given at a meeting on the future of mucopolysaccharidoses held in Milan on 8-9 May 2017.

Fast, sensitive method for trisaccharide biomarker detection in mucopolysaccharidosis type 1

Certain recessively inherited diseases result from an enzyme deficiency within lysosomes. In mucopolysaccharidoses (MPS), a defect in glycosaminoglycan (GAG) degradation leads to GAG accumulation followed by progressive organ and multiple system dysfunctions. Current methods of GAG analysis used to diagnose and monitor the diseases lack sensitivity and throughput. Here we report a LC-MS method with accurate metabolite mass analysis for identifying and quantifying biomarkers for MPS type I without the need for extensive sample preparation. The method revealed 225 LC-MS features that were >1000-fold enriched in urine, plasma and tissue extracts from untreated MPS I mice compared to MPS I mice treated with iduronidase to correct the disorder. Levels of several trisaccharides were elevated >10000-fold. To validate the clinical relevance of our method, we confirmed the presence of these biomarkers in urine, plasma and cerebrospinal fluid from MPS I patients and assessed changes in their levels after treatment.

LRRK2, GBA and SMPD1 Founder Mutations and Parkinson's Disease in Ashkenazi Jews

BACKGROUND/AIM

Parkinson's disease (PD) is associated with mutations in LRRK2, GBA, and SMPD1 genes. We describe the clinical characteristics of PD patients related to their carrier status of the Ashkenazi founder mutations in the aforementioned genes.

METHODS

Ashkenazi PD patients (n = 270) were recruited following informed consent, and tested for the founder Ashkenazi mutations in the above genes. Clinical characteristics were compared between carriers and noncarriers. Homozygotes for mutations in GBA or LRRK2, and those who carried mutations in two causative genes were excluded from the analysis.

RESULTS

Five (1.85%), 54 (20%), and 22 (8.1%) PD patients carried mutations in SMPD1, GBA or LRRK2, respectively. By post hoc Bonferroni analysis, GBA carriers were singled at a significantly earlier age at diagnosis compared to noncarriers (58.06 ± 10.84 and 62.65 ± 10.86 years, respectively; p = 0.036), and due to bilateral manifestation at diagnosis compared to all other PD groups (n = 8, 15.7% compared to n = 2, 1.1%, respectively; p < 0.001). Other clinical manifestations were comparable between groups.

CONCLUSION

Although only GBA mutation carriers, compared to noncarriers, reached statistical significance regarding age at diagnosis, it appears that LRRK2 and SMPD1 mutation carriers may reach significance with larger group numbers.

Overview of immune abnormalities in lysosomal storage disorders

The critical relevance of the lysosomal compartment for normal cellular function can be proved by numbering the clinical phenotypes that arise in lysosomal storage disorders (LSDs), a group of around 70 different monogenic autosomal or X-linked syndromes, caused by specific lysosomal enzyme deficiencies: all LSDs are characterized by progressive accumulation of heterogeneous biologic materials in the lysosomes of various parts of the body such as viscera, skeleton, skin, heart, and central nervous system. At least a fraction of LSDs has been associated with mixed abnormalities involving the immune system, while some patients with LSDs may result more prone to autoimmune phenomena. A large production of proinflammatory cytokines has been observed in Gaucher and Fabry diseases, and wide different autoantibody production has been also reported in both. Many immune-mediated reactions are crucial to the pathogenesis of different inflammatory signs in mucopolysaccharidoses, and subverted heparan sulphate catabolism might dysregulate cellular homeostasis in the brain of these patients. Furthermore, an inappropriate activation of microglia is implicated in the neurodegenerative foci of Niemann-Pick disease, in which abnormal signalling pathways are activated by impaired sphingolipid metabolism. In addition, not the simple impaired catabolism of gangliosides per se, but also the production of anti-ganglioside autoantibodies contributes to the neurological disease of gangliosidoses. Even if the exact relationship between the modification of lysosomal activities and modulation of the immune system remains obscure, there is emerging evidence of different impaired immunity responses in a variety of LSDs: in this review we investigate and summarize the immune abnormalities and/or clinical data about immune system irregularities which have been described in a subset of LSDs.

Arylsulfatase K is the Lysosomal 2-Sulfoglucuronate Sulfatase

The degradation of glycosaminoglycans (GAGs) involves a series of exolytic glycosidases and sulfatases that act sequentially on the nonreducing end of the polysaccharide chain. Enzymes have been cloned that catalyze all of the known linkages with the exception of the removal of the 2-O-sulfate group from 2-sulfoglucuronate, which is found in heparan sulfate and dermatan sulfate. Here, we show using synthetic disaccharide substrates that arylsulfatase K is the glucuronate-2-sulfatase. Arylsulfatase K acts selectively on 2-sulfoglucuronate and lacks activity against 2-sulfoiduronate, whereas iduronate-2-sulfatase (IDS) desulfates synthetic disaccharides containing 2-sulfoiduronate but not 2-sulfoglucuronate. As arylsulfatase K has all of the properties expected of a lysosomal enzyme, we conclude that arylsulfatase K is the long sought lysosomal glucuronate-2-sulfatase, which we designate GDS.

The lysosomotropic drug LeuLeu-OMe induces lysosome disruption and autophagy-independent cell death in Trypanosoma brucei

BACKGROUND

Trypanosoma brucei is a blood-borne, protozoan parasite that causes African sleeping sickness in humans and nagana in animals. The current chemotherapy relies on only a handful of drugs that display undesirable toxicity, poor efficacy and drug-resistance. In this study, we explored the use of lysosomotropic drugs to induce bloodstream form T. brucei cell death via lysosome destabilization.

METHODS

We measured drug concentrations that inhibit cell proliferation by 50% (IC<sub>50<sub>) for several compounds, chosen based on their lysosomotropic effects previously reported in Plasmodium falciparum. The lysosomal effects and cell death induced by L-leucyl-L-leucyl methyl ester (LeuLeu-OMe) were further analyzed by flow cytometry and immunofluorescence analyses of different lysosomal markers. The effect of autophagy in LeuLeu-OMe-induced lysosome destabilization and cytotoxicity was also investigated in control and autophagy-deficient cells.

RESULTS

LeuLeu-OMe was selected for detailed analyses due to its strong inhibitory profile against T. brucei with minimal toxicity to human cell lines in vitro. Time-dependent immunofluorescence studies confirmed an effect of LeuLeu-OMe on the lysosome. LeuLeu-OMe-induced cytotoxicity was also found to be dependent on the acidic pH of the lysosome. Although an increase in autophagosomes was observed upon LeuLeu-OMe treatment, autophagy was not required for the cell death induced by LeuLeu-OMe. Necrosis appeared to be the main cause of cell death upon LeuLeu-OMe treatment.

CONCLUSIONS

LeuLeu-OMe is a lysosomotropic agent capable of destabilizing lysosomes and causing necrotic cell death in bloodstream form of T. brucei.

The contribution of Niemann-Pick SMPD1 mutations to Parkinson disease in Ashkenazi Jews

INTRODUCTION

Parkinson disease is noted for its association with mutations in GBA and the p.G2019S mutation in LRRK2. This study aimed to evaluate the frequency of Ashkenazi founder mutations in sphingomyelin phosphodiesterase 1 (SMPD1) in Ashkenazi patients diagnosed with Parkinson's disease (PD); and their impact on PD phenotypic expression. SMPD1 underlies the lysosomal storage disease - Niemann-Pick.

METHODS

A case (n = 287) control (n = 400) study was undertaken. All patients underwent a physical, neurobehavioral and neurologic examination that incorporated the Unified Parkinson's Disease Rating Scale. Three founder SMPD1 Ashkenazi mutations (c.996delC (fsP330), p.L302P and p.R496L) were investigated in patients and controls, previously evaluated for carriage of founder mutations in GBA and the p.G2019S mutation in LRRK2.

RESULTS

Nine (3.1%) PD patients compared to two (0.5%) individuals from the control group were found to carry one of the three Ashkenazi SMPD1 founder mutations (p = 0.007). The overall clinical characteristics of PD patients carrying SMPD1 mutations were similar to those of PD patients with no mutations in SMPD1, GBA and LRRK2 (n = 189).

CONCLUSION

We maintain that disruptive mutations in SMPD1 constitute a risk factor for PD.

Glycosaminoglycans are potential pharmacological targets for classic DNA minor groove binder drugs berenil and pentamidine

It is shown that the antiprotozoal drugs berenil and pentamidine, conventional minor groove binders of DNA, form non-covalent complexes with polyanionic glycosaminoglycans.