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Enzymopathy disorders are the result of missing or defective enzymes. Among these enzymopathies, mucopolysaccharidosis type I is a rare genetic lysosomal storage disorder caused by mutations in the gene encoding alpha-L-iduronidase (IDUA), which ultimately causes toxic buildup of glycosaminoglycans (GAGs). There is currently no cure and standard treatments provide insufficient relief to the skeletal structure and central nervous system (CNS). Human memory T (Tm) cells migrate throughout the body's tissues and can persist for years, making them an attractive approach for cellular-based, systemic enzyme replacement therapy. Here, we tested genetically engineered, IDUA-expressing Tm cells as a cellular therapy in an immunodeficient mouse model of MPS I. Our results demonstrate that a single dose of engineered Tm cells leads to detectable IDUA enzyme levels in the blood for up to 22 weeks and reduced urinary GAG excretion. Furthermore, engineered Tm cells take up residence in nearly all tested tissues, producing IDUA and leading to metabolic correction of GAG levels in the heart, lung, liver, spleen, kidney, bone marrow, and the CNS, although only minimal improved cognition was observed. Our study indicates that genetically engineered Tm cells hold great promise as a platform for cellular-based enzyme replacement therapy for the treatment of mucopolysaccharidosis type I and potentially many other enzymopathies and protein deficiencies., Competing Interests: Declaration of interests A patent has been filed by the University of Minnesota covering technologies described in this manuscript., (Published by Elsevier Inc.)

Lysosomal storage disorders (LSDs) are a type of inherited metabolic disorders in which biomolecules, accumulate as a specific substrate in lysosomes due to specific individual enzyme deficiencies. Despite the fact that LSDs are incurable, various approaches, including enzyme replacement therapy, hematopoietic stem cell transplantation, or gene therapy are now available. Therefore, a timely diagnosis is a critical initial step in patient treatment. The-state-of-the-art in LSD diagnostic uses, in the first stage, enzymatic activity determination by fluorimetry or by mass spectrometry (MS) with the aid of dry blood spots, based on different enzymatic substrate structures. Due to its sensitivity, high precision, and ability to screen for an unprecedented number of diseases in a single assay, multiplexed tandem MS-based enzyme activity assays for the screening of LSDs in newborns have recently received a lot of attention. Here, (i) we review the current approaches used for simultaneous enzymatic activity determination of LSDs in dried blood spots using multiplex-LC-MS/MS; (ii) we explore the need for designing novel enzymatic substrates that generate different enzymatic products with distinct molecular masses in multiplexed-MS studies; and (iii) we give examples of the relevance of affinity-MS technique as a basis for reversing undesirable immune-reactivity in enzyme replacement therapy., (© 2023 John Wiley & Sons Ltd.)

Neuropathic lysosomal storage diseases (NLSDs), including ceroid lipofuscinosis neuronal 3 (CLN3) disease and Gaucher disease type 2 (GD2), are typically present in adolescents; however, there are no approved therapies. CLN3 disease is the most common of the 13 types of neuronal ceroid lipofuscinosis, and Gaucher disease is the most common type of lysosomal storage disease. These NLSDs share oxidative stress and lysosomal dysfunction with Parkinson's disease. In this study, we used patient-derived cells (PDCs) and resorcinol to develop a therapeutic agent based on peroxisome proliferator-activated receptor γ (PPARγ) activation. PPARγ is a major regulator of autophagy and reactive oxygen species (ROS). Resorcinol, a polyphenolic compound, has been reported to exhibit PPARγ agonistic potential. Protein levels were analyzed by immunoblotting and immunofluorescence microscopy. Changes in cellular metabolism, including ROS levels, lipid droplet content, and lysosomal activity, were measured by flow cytometry. Resorcinol reduced ROS levels by suppressing hypoxia-inducible factor 1α levels in CLN3-PDCs. Resorcinol upregulated autophagy and reduced lipid accumulation in CLN3-PDCs; however, these effects were abolished by autophagy inhibitors. Resorcinol increased nuclear PPARγ levels in CLN3-PDCs, and PPARγ antagonists abolished the therapeutic effects of resorcinol. Moreover, Resorcinol upregulated nuclear PPARγ levels and lysosomal activity in GD2-PDCs, and reduced lipid accumulation and ROS levels. In summary, resorcinol alleviated the shared pathogenesis of CLN3 disease and GD2 through PPARγ upregulation. These findings suggest that resorcinol is a potential therapeutic candidate for alleviating NLSD progression., Competing Interests: Declaration of Competing Interest All authors have no conflicts of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Lysosomal degradation pathways coordinate the clearance of superfluous and damaged cellular components. Compromised lysosomal degradation is a hallmark of many degenerative diseases, including lysosomal storage diseases (LSDs), which are caused by loss-of-function mutations within both alleles of a lysosomal hydrolase, leading to lysosomal substrate accumulation. Gaucher's disease, characterized by <15% of normal glucocerebrosidase function, is the most common LSD and is a prominent risk factor for developing Parkinson's disease. Here, we show that either of two structurally distinct small molecules that modulate PIKfyve activity, identified in a high-throughput cellular lipid droplet clearance screen, can improve glucocerebrosidase function in Gaucher patient-derived fibroblasts through an MiT/TFE transcription factor that promotes lysosomal gene translation. An integrated stress response (ISR) antagonist used in combination with a PIKfyve modulator further improves cellular glucocerebrosidase activity, likely because ISR signaling appears to also be slightly activated by treatment by either small molecule at the higher doses employed. This strategy of combining a PIKfyve modulator with an ISR inhibitor improves mutant lysosomal hydrolase function in cellular models of additional LSD., Competing Interests: Competing interests statement:W.C.H., L.A.M., D.R., and J.W.K. are inventors on the patent “PIKfyve Modulators for Treatment of Lysosomal Storage Diseases,” U.S. Ser. No. 63/675,391.

Lysosomes catabolize and recycle lipids and other biological molecules to maintain cellular homeostasis in diverse nutrient environments. Lysosomal lipid catabolism relies on the stimulatory activity of bis(monoacylglycero)phosphate (BMP), an enigmatic lipid whose levels are altered across myriad lysosome-associated diseases. Here, we review the discovery of BMP over half a century ago and its structural properties that facilitate the activation of lipid hydrolases and recruitment of their coactivators. We further discuss the current, yet incomplete, understanding of BMP catabolism and anabolism. To conclude, we discuss its role in lysosome-associated diseases and the potential for modulating its levels by pharmacologically activating and inhibiting the BMP synthase to therapeutically target lysosomal storage disorders, drug-induced phospholipidosis, Alzheimer's disease, Parkinson's disease, frontotemporal dementia, cancer, and viral infection.

Together with its β-subunit OSTM1, ClC-7 performs 2Cl - /H + exchange across lysosomal membranes. Pathogenic variants in either gene cause lysosome-related pathologies, including osteopetrosis and lysosomal storage. CLCN7 variants can cause recessive or dominant disease. Different variants entail different sets of symptoms. Loss of ClC-7 causes osteopetrosis and mostly neuronal lysosomal storage. A recently reported de novo CLCN7 mutation (p.Tyr715Cys) causes widespread severe lysosome pathology (hypopigmentation, organomegaly, and delayed myelination and development, "HOD syndrome"), but no osteopetrosis. We now describe two additional HOD individuals with the previously described p.Tyr715Cys and a novel p.Lys285Thr mutation, respectively. Both mutations decreased ClC-7 inhibition by PI(3,5)P 2 and affected residues lining its binding pocket, and shifted voltage-dependent gating to less positive potentials, an effect partially conferred to WT subunits in WT/mutant heteromers. This shift predicts augmented pH gradient-driven Cl - uptake into vesicles. Overexpressing either mutant induced large lysosome-related vacuoles. This effect depended on Cl - /H + -exchange, as shown using mutants carrying uncoupling mutations. Fibroblasts from the p.Y715C patient also displayed giant vacuoles. This was not observed with p.K285T fibroblasts probably due to residual PI(3,5)P 2 sensitivity. The gain of function caused by the shifted voltage-dependence of either mutant likely is the main pathogenic factor. Loss of PI(3,5)P 2 inhibition will further increase current amplitudes, but may not be a general feature of HOD. Overactivity of ClC-7 induces pathologically enlarged vacuoles in many tissues, which is distinct from lysosomal storage observed with the loss of ClC-7 function. Osteopetrosis results from a loss of ClC-7, but osteoclasts remain resilient to increased ClC-7 activity., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Lysosomes are highly dynamic organelles that maintain cellular homeostasis and regulate fundamental cellular processes by integrating multiple metabolic pathways. Lysosomal ion channels such as TRPML1-3, TPC1/2, ClC6/7, CLN7, and TMEM175 mediate the flux of Ca 2+ , Cl - , Na + , H + , and K + across lysosomal membranes in response to osmotic stimulus, nutrient-dependent signals, and cellular stresses. These ion channels serve as the crucial transducers of cell signals and are essential for the regulation of lysosomal biogenesis, motility, membrane contact site formation, and lysosomal homeostasis. In terms of pathophysiology, genetic variations in these channel genes have been associated with the development of lysosomal storage diseases, neurodegenerative diseases, inflammation, and cancer. This review aims to discuss the current understanding of the role of these ion channels in the central nervous system and to assess their potential as drug targets.

PIKfyve is an endosomal lipid kinase that synthesizes phosphatidylinositol 3,5-biphosphate from phosphatidylinositol 3-phsphate. Inhibition of PIKfyve activity leads to lysosomal enlargement and cytoplasmic vacuolation, attributed to impaired lysosomal fission processes and homeostasis. However, the precise molecular mechanisms underlying these effects remain a topic of debate. In this study, we present findings from PIKfyve-deficient zebrafish embryos, revealing enlarged macrophages with giant vacuoles reminiscent of lysosomal storage disorders. Treatment with mTOR inhibitors or effective knockout of mTOR partially reverses these abnormalities and extend the lifespan of mutant larvae. Further in vivo and in vitro mechanistic investigations provide evidence that PIKfyve activity is essential for mTOR shutdown during early zebrafish development and in cells cultured under serum-deprived conditions. These findings underscore the critical role of PIKfyve activity in regulating mTOR signaling and suggest potential therapeutic applications of PIKfyve inhibitors for the treatment of lysosomal storage disorders.

Lysosomes are the terminal end of catabolic pathways in the cell, as well as signaling centers performing important functions such as the recycling of macromolecules, organelles, and nutrient adaptation. The importance of lysosomes in human health is supported by the fact that the deficiency of most lysosomal genes causes monogenic diseases called as a group Lysosomal Storage Diseases (LSDs). A common phenotypic hallmark of LSDs is the expansion of the lysosomal compartment that can be detected by using conventional imaging methods based on immunofluorescence protocols or overexpression of tagged lysosomal proteins. These methods require the alteration of the cellular architecture (i.e., due to fixation methods), can alter the behavior of cells (i.e., by the overexpression of proteins), and require sample preparation and the accurate selection of compatible fluorescent markers in relation to the type of analysis, therefore limiting the possibility of characterizing cellular status with simplicity. Therefore, a quantitative and label-free methodology, such as Quantitative Phase Imaging through Digital Holographic (QPI-DH), for the microscopic imaging of lysosomes in health and disease conditions may represent an important advance to study and effectively diagnose the presence of lysosomal storage in human disease. Here we proof the effectiveness of the QPI-DH method in accomplishing the detection of the lysosomal compartment using mouse embryonic fibroblasts (MEFs) derived from a Mucopolysaccharidosis type III-A (MSP-IIIA) mouse model, and comparing them with wild-type (WT) MEFs. We found that it is possible to identify label-free biomarkers able to supply a first pre-screening of the two populations, thus showing that QPI-DH can be a suitable candidate to surpass fluorescent drawbacks in the detection of lysosomes dysfunction. An appropriate numerical procedure was developed for detecting and evaluate such cellular substructures from in vitro cells cultures. Results reported in this study are encouraging about the further development of the proposed QPI-DH approach for such type of investigations about LSDs., (© 2024 International Society for Advancement of Cytometry.)

Mutations in Drosophila Swiss cheese (SWS) gene or its vertebrate orthologue neuropathy target esterase (NTE) lead to progressive neuronal degeneration in flies and humans. Despite its enzymatic function as a phospholipase is well established, the molecular mechanism responsible for maintaining nervous system integrity remains unclear. In this study, we found that NTE/SWS is present in surface glia that forms the blood-brain barrier (BBB) and that NTE/SWS is important to maintain its structure and permeability. Importantly, BBB glia-specific expression of Drosophila NTE/SWS or human NTE in the sws mutant background fully rescues surface glial organization and partially restores BBB integrity, suggesting a conserved function of NTE/SWS. Interestingly, sws mutant glia showed abnormal organization of plasma membrane domains and tight junction rafts accompanied by the accumulation of lipid droplets, lysosomes, and multilamellar bodies. Since the observed cellular phenotypes closely resemble the characteristics described in a group of metabolic disorders known as lysosomal storage diseases (LSDs), our data established a novel connection between NTE/SWS and these conditions. We found that mutants with defective BBB exhibit elevated levels of fatty acids, which are precursors of eicosanoids and are involved in the inflammatory response. Also, as a consequence of a permeable BBB, several innate immunity factors are upregulated in an age-dependent manner, while BBB glia-specific expression of NTE/SWS normalizes inflammatory response. Treatment with anti-inflammatory agents prevents the abnormal architecture of the BBB, suggesting that inflammation contributes to the maintenance of a healthy brain barrier. Considering the link between a malfunctioning BBB and various neurodegenerative diseases, gaining a deeper understanding of the molecular mechanisms causing inflammation due to a defective BBB could help to promote the use of anti-inflammatory therapies for age-related neurodegeneration., Competing Interests: MT, AY, JH, BB, DT, HS No competing interests declared, (© 2024, Tsap et al.)

Lysosomal Storage Disorders (LSDs), which share common phenotypes, including enlarged lysosomes and defective lysosomal storage, are caused by mutations in lysosome-related genes. Although gene therapies and enzyme replacement therapies have been explored, there are currently no effective routine therapies against LSDs. During lysosome reformation, which occurs when the functional lysosome pool is reduced, lysosomal lipids and proteins are recycled to restore lysosome functions. Here we report that the sorting nexin protein SNX8 promotes lysosome tubulation, a process that is required for lysosome reformation, and that loss of SNX8 leads to phenotypes characteristic of LSDs in human cells. SNX8 overexpression rescued features of LSDs in cells, and AAV-based delivery of SNX8 to the brain rescued LSD phenotypes in mice. Importantly, by screening a natural compound library, we identified three small molecules that enhanced SNX8-lysosome binding and reversed LSD phenotypes in human cells and in mice. Altogether, our results provide a potential solution for the treatment of LSDs., (© 2024. The Author(s).)

Accumulation of sphingolipids, especially sphingosines, in the lysosomes is a key driver of several lysosomal storage diseases. The transport mechanism for sphingolipids from the lysosome remains unclear. Here, we identified SPNS1, which shares the highest homology to SPNS2, a sphingosine-1-phosphate (S1P) transporter, functions as a transporter for lysolipids from the lysosome. We generated Spns1-KO cells and mice and employed lipidomic and metabolomic approaches to reveal SPNS1 ligand identity. Global KO of Spns1 caused embryonic lethality between E12.5 and E13.5 and an accumulation of sphingosine, lysophosphatidylcholines (LPC), and lysophosphatidylethanolamines (LPE) in the fetal livers. Similarly, metabolomic analysis of livers from postnatal Spns1-KO mice presented an accumulation of sphingosines and lysoglycerophospholipids including LPC and LPE. Subsequently, biochemical assays showed that SPNS1 is required for LPC and sphingosine release from lysosomes. The accumulation of these lysolipids in the lysosomes of Spns1-KO mice affected liver functions and altered the PI3K/AKT signaling pathway. Furthermore, we identified 3 human siblings with a homozygous variant in the SPNS1 gene. These patients suffer from developmental delay, neurological impairment, intellectual disability, and cerebellar hypoplasia. These results reveal a critical role of SPNS1 as a promiscuous lysolipid transporter in the lysosomes and link its physiological functions with lysosomal storage diseases.

Lysosomal storage disorders (LSDs), which are characterized by genetic and metabolic lysosomal dysfunctions, constitute over 60 degenerative diseases with considerable health and economic burdens. However, the mechanisms driving the progressive death of functional cells due to lysosomal defects remain incompletely understood, and broad-spectrum therapeutics against LSDs are lacking. Here, we found that various gene abnormalities that cause LSDs, including Hexb, Gla, Npc1, Ctsd and Gba, all shared mutual properties to robustly autoactivate neuron-intrinsic cGAS-STING signalling, driving neuronal death and disease progression. This signalling was triggered by excessive cytoplasmic congregation of the dsDNA and DNA sensor cGAS in neurons. Genetic ablation of cGAS or STING, digestion of neuronal cytosolic dsDNA by DNase, and repair of neuronal lysosomal dysfunction alleviated symptoms of Sandhoff disease, Fabry disease and Niemann-Pick disease, with substantially reduced neuronal loss. We therefore identify a ubiquitous mechanism mediating the pathogenesis of a variety of LSDs, unveil an inherent connection between lysosomal defects and innate immunity, and suggest a uniform strategy for curing LSDs., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Lysosomes are membrane-enclosed organelles that digest intracellular material. They contain more than 50 different enzymes that can degrade a variety of macromolecules including nucleic acids, proteins, polysaccharides, and lipids. In addition to functioning within lysosomes, lysosomal enzymes are also secreted. Alterations in the levels and activities of lysosomal enzymes dysregulates lysosomes, which can lead to the intralysosomal accumulation of biological material and the development of lysosomal storage diseases (LSDs) in humans. Dictyostelium discoideum has a long history of being used to study the trafficking and functions of lysosomal enzymes. More recently, it has been used as a model system to study several LSDs. In this chapter, we outline the methods for assessing the activity of several lysosomal enzymes in D. discoideum (α-galactosidase, β-galactosidase, α-glucosidase, β-glucosidase, β-N-acetylglucosaminidase, α-mannosidase, cathepsin B, cathepsin D, cathepsin F, palmitoyl protein thioesterase 1, and tripeptidyl peptidase 1)., (© 2024. The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Lysosomal storage diseases are inborn errors of metabolism that arise due to loss of function mutations in genes encoding lysosomal enzymes, protein co-factors or lysosomal membrane proteins. As a consequence of the genetic defect, lysosomal function is impaired and substrates build up in the lysosome leading to 'storage'. A sub group of these disorders are the sphingolipidoses in which sphingolipids accumulate in the lysosome. In this review, I will discuss how the study of these rare lysosomal disorders reveals unanticipated links to other rare and common human diseases using Niemann-Pick disease type C as an example., (© 2023 The Author(s).)

Lysosomal Storage Disorders (LSDs) are a diverse group of inherited, monogenic diseases caused by functional defects in specific lysosomal proteins. The lysosome is a cellular organelle that plays a critical role in catabolism of waste products and recycling of macromolecules in the body. Disruption to the normal function of the lysosome can result in the toxic accumulation of storage products, often leading to irreparable cellular damage and organ dysfunction followed by premature death. The majority of LSDs have no curative treatment, with many clinical subtypes presenting in early infancy and childhood. Over two-thirds of LSDs present with progressive neurodegeneration, often in combination with other debilitating peripheral symptoms. Consequently, there is a pressing unmet clinical need to develop new therapeutic interventions to treat these conditions. The blood-brain barrier is a crucial hurdle that needs to be overcome in order to effectively treat the central nervous system (CNS), adding considerable complexity to therapeutic design and delivery. Enzyme replacement therapy (ERT) treatments aimed at either direct injection into the brain, or using blood-brain barrier constructs are discussed, alongside more conventional substrate reduction and other drug-related therapies. Other promising strategies developed in recent years, include gene therapy technologies specifically tailored for more effectively targeting treatment to the CNS. Here, we discuss the most recent advances in CNS-targeted treatments for neurological LSDs with a particular emphasis on gene therapy-based modalities, such as Adeno-Associated Virus and haematopoietic stem cell gene therapy approaches that encouragingly, at the time of writing are being evaluated in LSD clinical trials in increasing numbers. If safety, efficacy and improved quality of life can be demonstrated, these therapies have the potential to be the new standard of care treatments for LSD patients., (© 2023 The Authors. Journal of Inherited Metabolic Disease published by John Wiley & Sons Ltd on behalf of SSIEM.)

Lysosomes are specialized organelles with an acidic pH that act as recycling hubs for intracellular and extracellular components. They harbour numerous different hydrolytic enzymes to degrade substrates like proteins, peptides, and glycolipids. Reduced catalytic activity of lysosomal enzymes can cause the accumulation of these substrates and loss of lysosomal integrity, resulting in lysosomal dysfunction and lysosomal storage disorders (LSDs). Post-mitotic cells, such as neurons, seem to be highly sensitive to damages induced by lysosomal dysfunction, thus LSDs often manifest with neurological symptoms. Interestingly, some LSDs and Parkinson's disease (PD) share common cellular pathomechanisms, suggesting convergence of aetiology of the two disease types. This is further underlined by genetic associations of several lysosomal genes involved in LSDs with PD. The increasing number of lysosome-associated genetic risk factors for PD makes it necessary to understand functions and interactions of lysosomal proteins/enzymes both in health and disease, thereby holding the potential to identify new therapeutic targets. In this review, we highlight genetic and mechanistic interactions between the complex lysosomal network, LSDs and PD, and elaborate on methodical challenges in lysosomal research., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: The most common form of neuronal ceroid lipofuscinosis (NCL) is juvenile CLN3 disease (JNCL), a currently incurable neurodegenerative disorder caused by mutations in the CLN3 gene. Based on our previous work and on the premise that CLN3 affects the trafficking of the cation-independent mannose-6 phosphate receptor and its ligand NPC2, we hypothesised that dysfunction of CLN3 leads to the aberrant accumulation of cholesterol in the late endosomes/lysosomes (LE/Lys) of JNCL patients' brains., Methods: An immunopurification strategy was used to isolate intact LE/Lys from frozen autopsy brain samples. LE/Lys isolated from samples of JNCL patients were compared with age-matched unaffected controls and Niemann-Pick Type C (NPC) disease patients. Indeed, mutations in NPC1 or NPC2 result in the accumulation of cholesterol in LE/Lys of NPC disease samples, thus providing a positive control. The lipid and protein content of LE/Lys was then analysed using lipidomics and proteomics, respectively., Findings: Lipid and protein profiles of LE/Lys isolated from JNCL patients were profoundly altered compared to controls. Importantly, cholesterol accumulated in LE/Lys of JNCL samples to a comparable extent than in NPC samples. Lipid profiles of LE/Lys were similar in JNCL and NPC patients, except for levels of bis(monoacylglycero)phosphate (BMP). Protein profiles detected in LE/Lys of JNCL and NPC patients appeared identical, except for levels of NPC1., Interpretation: Our results support that JNCL is a lysosomal cholesterol storage disorder. Our findings also support that JNCL and NPC disease share pathogenic pathways leading to aberrant lysosomal accumulation of lipids and proteins, and thus suggest that the treatments available for NPC disease may be beneficial to JNCL patients. This work opens new avenues for further mechanistic studies in model systems of JNCL and possible therapeutic interventions for this disorder., Funding: San Francisco Foundation., Competing Interests: Declaration of interests The authors declare no competing financial interests., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Over the recent decades, the use of extracellular vesicles (EVs) has attracted considerable attention. Herein, we report the development of a novel EV-based drug delivery system for the transport of the lysosomal enzyme tripeptidyl peptidase-1 (TPP1) to treat Batten disease (BD). Endogenous loading of macrophage-derived EVs was achieved through transfection of parent cells with TPP1-encoding p DNA. More than 20% ID/g was detected in the brain following a single intrathecal injection of EVs in a mouse model of BD, ceroid lipofuscinosis neuronal type 2 (CLN2) mice. Furthermore, the cumulative effect of EVs repetitive administrations in the brain was demonstrated. TPP1-loaded EVs (EV-TPP1) produced potent therapeutic effects, resulting in efficient elimination of lipofuscin aggregates in lysosomes, decreased inflammation, and improved neuronal survival in CLN2 mice. In terms of mechanism, EV-TPP1 treatments caused significant activation of the autophagy pathway, including altered expression of the autophagy-related proteins LC3 and P62, in the CLN2 mouse brain. We hypothesized that along with TPP1 delivery to the brain, EV-based formulations can enhance host cellular homeostasis, causing degradation of lipofuscin aggregates through the autophagy-lysosomal pathway. Overall, continued research into new and effective therapies for BD is crucial for improving the lives of those affected by this condition.

Vertebrate cells rely on mannose-6-phosphate (M6P) modifications to deliver most lumenal hydrolases to the lysosome. As a critical trafficking signal for lysosomal enzymes, the M6P biosynthetic pathway has been thoroughly investigated. However, its regulatory mechanism is largely unknown. Here, we summarize three recent studies that independently discovered LYSET/TMEM251/GCAF as a key regulator of the M6P pathway. LYSET/TMEM251 directly interacts with GNPT, the enzyme that catalyzes the transfer of M6P, and is critical for its activity and stability. Deleting LYSET/TMEM251 impairs the GNPT function and M6P modifications. Consequently, lysosomal enzymes are mistargeted for secretion. Defective lysosomes fail to degrade cargoes such as endocytic vesicles and autophagosomes, leading to a newly identified lysosomal storage disease in humans. These discoveries open up a new direction in the regulation of the M6P biosynthetic pathway. Abbreviations: ER: endoplasmic reticulum; GNPT: GlcNAc-1-phosphotransferase; KO: knockout; LMP: lysosome membrane protein; LYSET: lysosomal enzyme trafficking factor; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; M6P: mannose-6-phosphate; MBTPS1/S1P: membrane-bound transcription factor peptidase, site 1; MPR: mannose-6-phosphate receptor; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TGN: trans-Golgi network.

Sialidases are found in viruses, bacteria, fungi, avians, and mammals. Mammalian sialidases differ in their specificity, optimum pH, subcellular localization, and tissue expression. To date, four genes encoding mammalian sialidases (NEU1-4) have been cloned. This review examines the functional impact of NEU4 sialidase on complex physiological and cellular processes. The intracellular localization and trafficking of NEU4 and its potential target molecules are discussed along with its impact on cancer, lysosomal storage disease, and cellular differentiation. Modulation of NEU4 expression may be essential not only for the breakdown of sialylated glycoconjugates, but also in the activation or inactivation of functionally important cellular events., (© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Identification of genetic modulators of lysosomal enzyme activities and glycosphingolipids (GSLs) may facilitate the development of therapeutics for diseases in which they participate, including Lysosomal Storage Disorders (LSDs). To this end, we used a systems genetics approach: we measured 11 hepatic lysosomal enzymes and many of their natural substrates (GSLs), followed by modifier gene mapping by GWAS and transcriptomics associations in a panel of inbred strains. Unexpectedly, most GSLs showed no association between their levels and the enzyme activity that catabolizes them. Genomic mapping identified 30 shared predicted modifier genes between the enzymes and GSLs, which are clustered in three pathways and are associated with other diseases. Surprisingly, they are regulated by ten common transcription factors, and their majority by miRNA-340p. In conclusion, we have identified novel regulators of GSL metabolism, which may serve as therapeutic targets for LSDs and may suggest the involvement of GSL metabolism in other pathologies.

Lysosomal storage disorders (LSD) are a group of inherited metabolic diseases mainly caused by a deficiency of lysosomal hydrolases, resulting in a gradual accumulation of non-degraded substrates in different tissues causing the characteristic clinical manifestations of such disorders. Confirmatory tests of suspected LSD individuals include enzymatic and genetic testing. A well-oriented clinical suspicion can improve the cost-effectiveness of confirmatory tests and reduce the time expended to achieve the diagnosis. Thus, this work aims to retrospectively study the influence of clinical orientation on the diagnostic yield of enzymatic tests in LSD by retrieving clinical, biochemical, and genetic data obtained from subjects with suspicion of LSD. Our results suggest that the clinical manifestations at the time of diagnosis and the initial clinical suspicion can have a great impact on the diagnostic yield of enzymatic tests, and that clinical orientation performed in specialized clinical departments can contribute to improve it. In addition, the analysis of enzymatic tests as the first step in the diagnostic algorithm can correctly guide subsequent confirmatory genetic tests, in turn increasing their diagnostic yield. In summary, our results suggest that initial clinical suspicion plays a crucial role on the diagnostic yield of confirmatory enzymatic tests in LSD., Competing Interests: Conflict of interest All authors declare no conflict of interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Glycosphingolipids (GSLs) are a diverse group of membrane components occurring mainly on the surfaces of mammalian cells. They and their metabolites have a role in intercellular communication, serving as versatile biochemical signals (Kaltner et al, Biochem J 476(18):2623-2655, 2019) and in many cellular pathways. Anionic GSLs, the sialic acid containing gangliosides (GGs), are essential constituents of neuronal cell surfaces, whereas anionic sulfatides are key components of myelin and myelin forming oligodendrocytes. The stepwise biosynthetic pathways of GSLs occur at and lead along the membranes of organellar surfaces of the secretory pathway. After formation of the hydrophobic ceramide membrane anchor of GSLs at the ER, membrane-spanning glycosyltransferases (GTs) of the Golgi and Trans-Golgi network generate cell type-specific GSL patterns for cellular surfaces. GSLs of the cellular plasma membrane can reach intra-lysosomal, i.e. luminal, vesicles (ILVs) by endocytic pathways for degradation. Soluble glycoproteins, the glycosidases, lipid binding and transfer proteins and acid ceramidase are needed for the lysosomal catabolism of GSLs at ILV-membrane surfaces. Inherited mutations triggering a functional loss of glycosylated lysosomal hydrolases and lipid binding proteins involved in GSL degradation cause a primary lysosomal accumulation of their non-degradable GSL substrates in lysosomal storage diseases (LSDs). Lipid binding proteins, the SAPs, and the various lipids of the ILV-membranes regulate GSL catabolism, but also primary storage compounds such as sphingomyelin (SM), cholesterol (Chol.), or chondroitin sulfate can effectively inhibit catabolic lysosomal pathways of GSLs. This causes cascades of metabolic errors, accumulating secondary lysosomal GSL- and GG- storage that can trigger a complex pathology (Breiden and Sandhoff, Int J Mol Sci 21(7):2566, 2020)., (© 2023. The Author(s), under exclusive license to Springer Nature Switzerland AG.)

Introduction: Lysosomal storage disorders (LSDs) are rare disorders and pose a diagnostic challenge for clinicians owing to their generalized symptomatology. In this study, we aim to classify LSDs into two broad categories, namely, Gaucher disease (GD) and Niemann-Pick/Niemann-Pick-like diseases (NP/NP-like diseases) based on the morphology of the storage cells in the bone marrow (BM) aspiration smears and trephine biopsy sections., Materials and Method: This retrospective study includes 32 BM specimens morphologically diagnosed as LSDs at our institute, in the last 10 years. Subsequently, they were subclassified into GD and NP/NP-like diseases. Further, we have compared and analyzed the clinical, hematological, and biochemical parameters for the two groups of LSDs., Results: Based on BM morphology, 59.4% (n = 19) cases were diagnosed as NP/NP-like diseases and 40.6% (n = 13) cases as GD. Abdominal distension and failure to thrive were the most common clinical manifestations in both groups of LSDs. Anemia and thrombocytopenia were frequently seen in either of the LSDs. On the assessment of metabolic profile, elevated total/direct bilirubin and liver enzymes were more commonly seen in NP/NP-like diseases when compared with GD., Conclusion: We have classified LSDs into GD and NP/NP-like diseases based on the morphology of the storage cells in the BM specimen. The hallmark findings on BM biopsy annexed with the comparative features of the two proposed categories can aid the clinician in clinching the diagnosis. Formulation of such a methodology will prove instrumental for patient care in an underresourced setting., Competing Interests: None

Lysosomal storage disorders (LSDs) are inherited metabolic diseases caused by genetic defects in lysosomal enzymes or related factors. LSDs are associated with excessive accumulation of natural substrates in lysosomes leading to central nervous system and peripheral tissue damage. Abnormal autophagy is also involved in pathogenesis, although the underlying mechanisms remain unclear. We demonstrated that impairment of lysosome-autophagosome fusion is due to suppressed endocytosis in LSDs. The fusion was reduced in several LSD cells and the brains of LSD model mice, suggesting that the completion of autophagy is suppressed by the accumulation of substrates. In this brain, the expression of the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins, VAMP8 and Syntaxin7, was decreased on the lysosomal surface but not intracellular. This aberrant autophagy preceded the development of pathological phenotypes in LSD-model mice. Furthermore, the enzyme deficiency leading to the substrate accumulation could suppress endocytosis, and the inhibited endocytosis decreased SNARE proteins localized on lysosomes. These findings suggest that the shortage of SNARE proteins on lysosomes is one of the reasons for the impairment of lysosome-autophagosome fusion in LSD cells. Defects in lysosomal enzyme activity suppress endocytosis and decrease the supply of intracellular SNARE proteins recruited to lysosomes. This shortage of lysosomal SNARE proteins impairs lysosome-autophagosome fusion in lysosomal storage disorders., (© 2022 SSIEM.)

Lysosomal storage disorders (LSD) are a group of rare life-threatening diseases caused by a lysosomal dysfunction, usually due to the lack of a single enzyme required for the metabolism of macromolecules, which leads to a lysosomal accumulation of specific substrates, resulting in severe disease manifestations and early death. There is currently no definitive cure for LSD, and despite the approval of certain therapies, their effectiveness is limited. Therefore, an appropriate nanocarrier could help improve the efficacy of some of these therapies. Liposomes show excellent properties as drug carriers, because they can entrap active therapeutic compounds offering protection, biocompatibility, and selectivity. Here, we discuss the potential of liposomes for LSD treatment and conduct a detailed analysis of promising liposomal formulations still in the preclinical development stage from various perspectives, including treatment strategy, manufacturing, characterization, and future directions for implementing liposomal formulations for LSD., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The authors declare the following financial interests/personal relationships that might be considered potential competing interests: S.S., J.V., and N.V. are the inventors of patent WO/2014/001509 licensed to Biopraxis Research AIE and patent WO/2006/079889 owned by Nanomol Technologies SL and are stockholders in Nanomol Technologies SL. J.T-M., J.M-M., S.S., A.C., J.V., E.G-M., and N.V. are the inventors of patent application EP21382062.4., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Mammalian cells can generate amino acids through macropinocytosis and lysosomal breakdown of extracellular proteins, which is exploited by cancer cells to grow in nutrient-poor tumors. Through genetic screens in defined nutrient conditions, we characterized LYSET, a transmembrane protein (TMEM251) selectively required when cells consume extracellular proteins. LYSET was found to associate in the Golgi with GlcNAc-1-phosphotransferase, which targets catabolic enzymes to lysosomes through mannose-6-phosphate modification. Without LYSET, GlcNAc-1-phosphotransferase was unstable because of a hydrophilic transmembrane domain. Consequently, LYSET-deficient cells were depleted of lysosomal enzymes and impaired in turnover of macropinocytic and autophagic cargoes. Thus, LYSET represents a core component of the lysosomal enzyme trafficking pathway, underlies the pathomechanism for hereditary lysosomal storage disorders, and may represent a target to suppress metabolic adaptations in cancer.

Lysosomal storage diseases (LSDs) comprise a group of inherited monogenic disorders characterized by lysosomal dysfunctions due to undegraded substrate accumulation. They are caused by a deficiency in specific lysosomal hydrolases involved in cellular catabolism, or non-enzymatic proteins essential for normal lysosomal functions. In LSDs, the lack of degradation of the accumulated substrate and its lysosomal storage impairs lysosome functions resulting in the perturbation of cellular homeostasis and, in turn, the damage of multiple organ systems. A substantial number of studies on the pathogenesis of LSDs has highlighted how the accumulation of lysosomal substrates is only the first event of a cascade of processes including the accumulation of secondary metabolites and the impairment of cellular trafficking, cell signalling, autophagic flux, mitochondria functionality and calcium homeostasis, that significantly contribute to the onset and progression of these diseases. Emerging studies on lysosomal biology have described the fundamental roles of these organelles in a variety of physiological functions and pathological conditions beyond their canonical activity in cellular waste clearance. Here, we discuss recent advances in the knowledge of cellular and molecular mechanisms linking lysosomal positioning and trafficking to LSDs.

Mitochondrial dysfunction has been recognised a major contributory factor to the pathophysiology of a number of lysosomal storage disorders (LSDs). The cause of mitochondrial dysfunction in LSDs is as yet uncertain, but appears to be triggered by a number of different factors, although oxidative stress and impaired mitophagy appear to be common inhibitory mechanisms shared amongst this group of disorders, including Gaucher's disease, Niemann-Pick disease, type C, and mucopolysaccharidosis. Many LSDs resulting from defects in lysosomal hydrolase activity show neurodegeneration, which remains challenging to treat. Currently available curative therapies are not sufficient to meet patients' needs. In view of the documented evidence of mitochondrial dysfunction in the neurodegeneration of LSDs, along with the reciprocal interaction between the mitochondrion and the lysosome, novel therapeutic strategies that target the impairment in both of these organelles could be considered in the clinical management of the long-term neurodegenerative complications of these diseases. The purpose of this review is to outline the putative mechanisms that may be responsible for the reported mitochondrial dysfunction in LSDs and to discuss the new potential therapeutic developments.

Lysosomes have many roles, including degrading macromolecules and signalling to the nucleus 1 . Lysosomal dysfunction occurs in various human conditions, such as common neurodegenerative diseases and monogenic lysosomal storage disorders (LSDs) 2-4 . For most LSDs, the causal genes have been identified but, in some, the function of the implicated gene is unknown, in part because lysosomes occupy a small fraction of the cellular volume so that changes in lysosomal contents are difficult to detect. Here we develop the LysoTag mouse for the tissue-specific isolation of intact lysosomes that are compatible with the multimodal profiling of their contents. We used the LysoTag mouse to study CLN3, a lysosomal transmembrane protein with an unknown function. In children, the loss of CLN3 causes juvenile neuronal ceroid lipofuscinosis (Batten disease), a lethal neurodegenerative LSD. Untargeted metabolite profiling of lysosomes from the brains of mice lacking CLN3 revealed a massive accumulation of glycerophosphodiesters (GPDs)-the end products of glycerophospholipid catabolism. GPDs also accumulate in the lysosomes of CLN3-deficient cultured cells and we show that CLN3 is required for their lysosomal egress. Loss of CLN3 also disrupts glycerophospholipid catabolism in the lysosome. Finally, we found elevated levels of glycerophosphoinositol in the cerebrospinal fluid of patients with Batten disease, suggesting the potential use of glycerophosphoinositol as a disease biomarker. Our results show that CLN3 is required for the lysosomal clearance of GPDs and reveal Batten disease as a neurodegenerative LSD with a defect in glycerophospholipid metabolism., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Treatment of neurological lysosomal storage disorders (LSDs) are limited because of impermeability of the blood-brain barrier (BBB) to macromolecules. Nanoformulations targeting BBB transcytosis are being explored, but the status of these routes in LSDs is unknown. We studied nanocarriers (NCs) targeted to the transferrin receptor (TfR), ganglioside GM1 or ICAM1, associated to the clathrin, caveolar or cell adhesion molecule (CAM) routes, respectively. We used brain endothelial cells and mouse models of acid sphingomyelinase-deficient Niemann Pick disease (NPD), and postmortem LSD patients' brains, all compared to respective controls. NC transcytosis across brain endothelial cells and brain distribution in mice were affected, yet through different mechanisms. Reduced TfR and clathrin expression were found, along with decreased transcytosis in cells and mouse brain distribution. Caveolin-1 expression and GM1 transcytosis were also reduced, yet increased GM1 levels seemed to compensate, providing similar NC brain distribution in NPD vs. control mice. A tendency to lower NHE-1 levels was seen, but highly increased ICAM1 expression in cells and human brains correlated with increased transcytosis and brain distribution in mice. Thus, transcytosis-related alterations in NPD and likely other LSDs may impact therapeutic access to the brain, illustrating the need for these mechanistic studies., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The mannose-6-phosphate (M6P) pathway is responsible for the transport of hydrolytic enzymes to lysosomes. N-acetylglucosamine-1-phosphotransferase (GNPT) catalyzes the first step of tagging these hydrolases with M6P, which when recognized by receptors in the Golgi diverts them to lysosomes. Genetic defects in the GNPT subunits, GNPTAB and GNPTG, cause the lysosomal storage diseases mucolipidosis types II and III. To better understand its function, we determined partial three-dimensional structures of the GNPT complex. The catalytic domain contains a deep cavity for binding of uridine diphosphate- N -acetylglucosamine, and the surrounding residues point to a one-step transfer mechanism. An isolated structure of the gamma subunit of GNPT reveals that it can bind to mannose-containing glycans in different configurations, suggesting that it may play a role in directing glycans into the active site. These findings may facilitate the development of therapies for lysosomal storage diseases.

Tissue-resident macrophages of the brain, including microglia, are implicated in the pathogenesis of various CNS disorders and are possible therapeutic targets by their chemical depletion or replenishment by hematopoietic stem cell therapy. Nevertheless, a comprehensive understanding of microglial function and the consequences of microglial depletion in the human brain is lacking. In human disease, heterozygous variants in CSF1R, encoding the Colony-stimulating factor 1 receptor, can lead to adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) possibly caused by microglial depletion. Here, we investigate the effects of ALSP-causing CSF1R variants on microglia and explore the consequences of microglial depletion in the brain. In intermediate- and late-stage ALSP post-mortem brain, we establish that there is an overall loss of homeostatic microglia and that this is predominantly seen in the white matter. By introducing ALSP-causing missense variants into the zebrafish genomic csf1ra locus, we show that these variants act dominant negatively on the number of microglia in vertebrate brain development. Transcriptomics and proteomics on relatively spared ALSP brain tissue validated a downregulation of microglia-associated genes and revealed elevated astrocytic proteins, possibly suggesting involvement of astrocytes in early pathogenesis. Indeed, neuropathological analysis and in vivo imaging of csf1r zebrafish models showed an astrocytic phenotype associated with enhanced, possibly compensatory, endocytosis. Together, our findings indicate that microglial depletion in zebrafish and human disease, likely as a consequence of dominant-acting pathogenic CSF1R variants, correlates with altered astrocytes. These findings underscore the unique opportunity CSF1R variants provide to gain insight into the roles of microglia in the human brain, and the need to further investigate how microglia, astrocytes, and their interactions contribute to white matter homeostasis., (© 2022. The Author(s).)

Although neurologic symptoms occur in two-thirds of lysosomal storage disorders (LSDs), for most we do not understand the mechanisms underlying brain dysfunction. A major unanswered question is if the pathogenic hallmark of LSDs, storage accumulation, induces functional defects directly or is a disease bystander. Also, for most LSDs we do not know the impact of loss of function in individual cell types. Understanding these critical questions are essential to therapy development. Here, we determine the impact of genetic rescue in distinct cell types on neural circuit dysfunction in CLN3 disease, the most common pediatric dementia and a paradigmatic neurodegenerative LSD. We restored Cln3 expression via AAV-mediated gene delivery and conditional genetic rescue in a CLN3 disease mouse model. Surprisingly, we found that low-level rescue of Cln3 expression in neurons alone normalized clinically relevant electrophysiologic markers of network dysfunction, despite the presence of substantial residual histopathology, in contrast to restoring expression in astrocytes. Thus, loss of CLN3 function in neurons, not storage accumulation, underlies neurologic dysfunction in CLN3 disease. This impliesies that storage clearance may be an inappropriate target for therapy development and an ineffectual biomarker., Competing Interests: Declaration of interests B.L.D. is a founder of Spark Therapeutics and Spirovant and is on the scientific advisory boards of Intellia Therapeutics, Homology Medicines, Prevail Therapeutics, Resilience, Moment Bio, Spirovant, Saliogen and Panorama Medicines. The other authors declare no competing interests., (Copyright © 2022 The American Society of Gene and Cell Therapy. Published by Elsevier Inc. All rights reserved.)

The major function of the lysosome is to degrade unwanted materials such as lipids, proteins, and nucleic acids; therefore, deficits of the lysosomal system can result in improper degradation and trafficking of these biomolecules. Diseases associated with lysosomal failure can be lethal and are termed lysosomal storage disorders (LSDs), which affect 1 in 5000 live births collectively. LSDs are inherited metabolic diseases caused by mutations in single lysosomal and non-lysosomal proteins and resulting in the subsequent accumulation of macromolecules within. Most LSD patients present with neurodegenerative clinical symptoms, as well as damage in other organs. The discovery of new biomarkers is necessary to understand and monitor these diseases and to track therapeutic progress. Over the past ten years, mass spectrometry (MS)-based proteomics has flourished in the biomarker studies in many diseases, including neurodegenerative, and more specifically, LSDs. In this review, biomarkers of disease pathophysiology and monitoring of LSDs revealed by MS-based proteomics are discussed, including examples from Niemann-Pick disease type C, Fabry disease, neuronal ceroid-lipofuscinoses, mucopolysaccharidosis, Krabbe disease, mucolipidosis, and Gaucher disease.

Pelizaeus-Merzbacher-like disease type 1 (PMLD1) is a hypomyelinating disorder arising in patients with mutations in GJC2, encoding Connexin47 (Cx47). PMLD1 causes nystagmus, cerebellar ataxia, spasticity and changes in CNS white matter detected by MRI. At least one mutation (p.I33M) yields a much milder phenotype, spastic paraplegia type 44 (SPG44). Cx47 contributes to gap junction communication channels between oligodendrocytes (OLs), the myelinating cells in the central nervous system (CNS), and between OLs and astrocytes. Prior studies in cell lines have shown that PMLD1 mutants such as p.P87S display defective protein trafficking, intracellular retention in the ER and loss-of-function. Here we show that when expressed in primary OLs, three PMLD1 associated mutants (p.P87S, p.Y269D and p.M283T) show ER retention of Cx47 and evidence of activation of the cellular stress (unfolded protein response, UPR) and apoptotic pathways. On the other hand, the milder SPG44 associated mutation p.I33M shows a wild-type-like subcellular distribution and no activation of the UPR or apoptotic pathways. These studies provide new insight into a potential element of toxic gain of function underlying the mechanism of PMLD1 that should help guide future therapeutic approaches., (Copyright © 2022. Published by Elsevier Inc.)

The majority of lysosomal storage diseases affect the brain. Treatment of the brain with intravenous enzyme replacement therapy is not successful, because the recombinant lysosomal enzymes do not cross the blood-brain barrier (BBB). Biologic drugs, including lysosomal enzymes, can be re-engineered for BBB delivery as IgG-enzyme fusion proteins. The IgG domain of the fusion protein is a monoclonal antibody directed against an endogenous receptor-mediated transporter at the BBB, such as the insulin receptor or the transferrin receptor. This receptor transports the IgG across the BBB, in parallel with the endogenous receptor ligand, and the IgG acts as a molecular Trojan horse to ferry into brain the lysosomal enzyme genetically fused to the IgG. The IgG-enzyme fusion protein is bi-functional and retains both high affinity binding for the BBB receptor, and high lysosomal enzyme activity. IgG-lysosomal enzymes are presently in clinical trials for treatment of the brain in Mucopolysaccharidosis., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author. Published by Elsevier B.V. All rights reserved.)

Lysosomal storage diseases (LSDs) are inherited metabolic diseases caused by deficiency of lysosomal enzymes, essential for the normal development of the brain and other organs. Approximately two-thirds of the patients suffering from LSD exhibit neurological deficits and impose an escalating challenge to the medical and scientific field. The advent of induced pluripotent stem cell (iPSC) technology has aided researchers in efficiently generating functional neuronal and non-neuronal cells through directed differentiation protocols, as well as in decoding the cellular, subcellular, and molecular defects associated with LSDs using two-dimensional cultures and cerebral organoid models. This review highlights the information assembled from patient-derived iPSCs on neurodevelopmental and neuropathological defects identified in LSDs. Multiple studies have identified neural progenitor cell migration and differentiation defects, substrate accumulation, axon growth and myelination defects, impaired calcium homeostasis, and altered electrophysiological properties, using patient-derived iPSCs. In addition, these studies have also uncovered defective lysosomes, mitochondria, endoplasmic reticulum, Golgi complex, autophagy and vesicle trafficking and signaling pathways, oxidative stress, neuroinflammation, blood-brain barrier dysfunction, neurodegeneration, gliosis, and altered transcriptomes in LSDs. The review also discusses the therapeutic applications such as drug discovery, repurposing of drugs, synergistic effects of drugs, targeted molecular therapies, gene therapy, and transplantation applications of mutation-corrected lines identified using patient-derived iPSCs for different LSDs.

Hypomyelinating leukodystrophies (HLDs) are a rare group of heterogeneously genetic disorders characterized by persistent deficit of myelin observed on magnetic resonance imaging (MRI). To identify a new disease-associated gene of HLD, trio-based whole exome sequencing was performed for unexplained patients with HLD. Functional studies were performed to confirm the phenotypic effect of candidate protein variants. Two de novo heterozygous variants, c.227T>G p.(L76R) or c.227T>C p.(L76P) in TMEM163 were identified in two unrelated HLD patients. TMEM163 protein is a zinc efflux transporter localized within the plasma membrane, lysosomes, early endosomes, and other vesicular compartments. It has not been associated with hypomyelination. Functional zinc flux assays in HeLa cells stably-expressing TMEM163 protein variants, L76R and L76P, revealed distinct attenuation or enhancement of zinc efflux, respectively. Experiments using a zebrafish model with knockdown of tmem163a and tmem163b (morphants) showed that loss of tmem163 causes dysplasia of the larvae, locomotor disability and myelin deficit. Expression of human wild type TMEM163 mRNAs in morphants rescues the phenotype, while the TMEM163 L76P and L76R mutants aggravated the condition. Moreover, poor proliferation, elevated apoptosis of oligodendrocytes, and reduced oligodendrocytes and neurons were also observed in zebrafish morphants. Our findings suggest an unappreciated role for TMEM163 protein in myelin development and add TMEM163 to a growing list of genes associated with hypomyelination leukodystrophy.

A distinct set of channels and transporters regulates the ion fluxes across the lysosomal membrane. Malfunctioning of these transport proteins and the resulting ionic imbalance is involved in various human diseases, such as lysosomal storage disorders, cancer, as well as metabolic and neurodegenerative diseases. As a consequence, these proteins have stimulated strong interest for their suitability as possible drug targets. A detailed functional characterization of many lysosomal channels and transporters is lacking, mainly due to technical difficulties in applying the standard patch-clamp technique to these small intracellular compartments. In this review, we focus on current methods used to unravel the functional properties of lysosomal ion channels and transporters, stressing their advantages and disadvantages and evaluating their fields of applicability.

Neuronal ceroid lipofuscinosis type 7 (CLN7) disease is a lysosomal storage disease caused by mutations in the facilitator superfamily domain containing 8 (MFSD8) gene, which encodes a membrane-bound lysosomal protein, MFSD8. To test the effectiveness and safety of adeno-associated viral (AAV) gene therapy, an in vitro study demonstrated that AAV2/MFSD8 dose dependently rescued lysosomal function in fibroblasts from a CLN7 patient. An in vivo efficacy study using intrathecal administration of AAV9/MFSD8 to Mfsd8- /- mice at P7-P10 or P120 with high or low dose led to clear age- and dose-dependent effects. A high dose of AAV9/MFSD8 at P7-P10 resulted in widespread MFSD8 mRNA expression, tendency of amelioration of subunit c of mitochondrial ATP synthase accumulation and glial fibrillary acidic protein immunoreactivity, normalization of impaired behaviors, doubled median life span, and extended normal body weight gain. In vivo safety studies in rodents concluded that intrathecal administration of AAV9/MFSD8 was safe and well tolerated. In summary, these results demonstrated that the AAV9/MFSD8 vector is both effective and safe in preclinical models.

It is well established that lysosomal glucocerebrosidase gene (GBA) variants are a risk factor for Parkinson's disease (PD), with increasing evidence suggesting a loss of function mechanism. One question raised by this genetic association is whether variants of genes involved in other aspects of sphingolipid metabolism are also associated with PD. Recent studies in sporadic PD have identified variants in multiple genes linked to diseases of glycosphingolipid (GSL) metabolism to be associated with PD. GSL biosynthesis is a complex pathway involving the coordinated action of multiple enzymes in the Golgi apparatus. GSL catabolism takes place in the lysosome and is dependent on the action of multiple acid hydrolases specific for certain substrates and glycan linkages. The finding that variants in multiple GSL catabolic genes are over-represented in PD in a heterozygous state highlights the importance of GSLs in the healthy brain and how lipid imbalances and lysosomal dysfunction are associated with normal ageing and neurodegenerative diseases. In this article we will explore the link between lysosomal storage disorders and PD, the GSL changes seen in both normal ageing, lysosomal storage disorders (LSDs) and PD and the mechanisms by which these changes can affect neurodegeneration., (© 2021. The Author(s).)

CLN7 neuronal ceroid lipofuscinosis is an inherited lysosomal storage neurodegenerative disease highly prevalent in children. CLN7/MFSD8 gene encodes a lysosomal membrane glycoprotein, but the biochemical processes affected by CLN7-loss of function are unexplored thus preventing development of potential treatments. Here, we found, in the Cln7 ∆ex2 mouse model of CLN7 disease, that failure in autophagy causes accumulation of structurally and bioenergetically impaired neuronal mitochondria. In vivo genetic approach reveals elevated mitochondrial reactive oxygen species (mROS) in Cln7 ∆ex2 neurons that mediates glycolytic enzyme PFKFB3 activation and contributes to CLN7 pathogenesis. Mechanistically, mROS sustains a signaling cascade leading to protein stabilization of PFKFB3, normally unstable in healthy neurons. Administration of the highly selective PFKFB3 inhibitor AZ67 in Cln7 ∆ex2 mouse brain in vivo and in CLN7 patients-derived cells rectifies key disease hallmarks. Thus, aberrant upregulation of the glycolytic enzyme PFKFB3 in neurons may contribute to CLN7 pathogenesis and targeting PFKFB3 could alleviate this and other lysosomal storage diseases., (© 2022. The Author(s).)

CLC proteins comprise Cl - channels and anion/H + antiporters involved in several fundamental physiological processes. ClC-7 is a lysosomal Cl - /H + antiporter that together with its beta subunit Ostm1 has a critical role in the ionic homeostasis of lysosomes and of the osteoclasts' resorption lacuna, although the specific underlying mechanism has so far remained elusive. Mutations in ClC-7 cause osteopetrosis, but also a form of lysosomal storage disease and neurodegeneration. Interestingly, both loss-of- and gain-of-function mutations of ClC-7 can be pathogenic, but the mechanistic implications of this finding are still unclear. This review will focus on the recent advances in our understanding of the biophysical properties of ClC-7 and of its role in human diseases with a focus on osteopetrosis and neurodegeneration.

Sphingolipidoses is a cluster of genetic rare disorders regarding glycosphingolipid metabolism, classified as lysosomal storage disorders (LSD). Here, we focus on eight inheritable diseases, including GM1 gangliosidosis, GM2 gangliosidosis, Fabry disease, Gaucher's disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease A and B, and Farber disease. Mostly, pathogenic mutations in the key enzyme are loss-function, resulting in accumulation of substrates and deficiency of products. Thus, cellular overload of substrates causes lipotoxicity, which is deleterious to cellular and organ function. In the terms of clinical manifestations in sphingolipidoses, multiple systems and organs, especially central nervous system (CNS) are usually affected. As for diagnosis strategy, enzymatic activity assay and genetic sequencing are helpful. Up till now, limited treatment approaches have approved for treating sphingolipidoses, with some potential strategies for further evaluation. In general, enzyme replacement therapy (ERT), substrate reduction therapy (SRT), and molecular chaperones are feasible choices for enzyme deficiency disorders, but these therapies are limited to relieve CNS lesions and symptoms due to prevention from blood-brain barrier. Other possible treatments such as gene therapy, bone marrow transplantation (BMT), and hematopoietic stem cell transplantation (HSCT) need further evaluation., (© 2022. The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd.)

Lysosomal Storage Diseases are multisystemic disorders determined by genetic variants, which affect the proteins involved in lysosomal function and cellular metabolism. Different therapeutic approaches, which are based on the physiologic mechanisms that regulate lysosomal function, have been proposed for these diseases. Currently, enzyme replacement therapy, gene therapy, or small molecules have been approved or are under clinical development to treat lysosomal storage disorders. The present article reviews the main therapeutic strategies that have been proposed so far, highlighting possible limitations and future perspectives.

We performed a systematic review of the literature to evaluate the incidence and types of lysosomal storage disorders (LSD) in case series of nonimmune hydrops fetalis (NIHF). PubMed, Ovid, and clinicaltrials.gov were reviewed for case series evaluating the workup of NIHF diagnosed in utero or in the neonatal period in human subjects from 1979 to August 2020. Retrospective case series with at least five cases of fetal and/or neonatal NIHF with its workup mentioned were identified. Idiopathic NIHF was defined as NIHF without an apparent cause after initial standard-of-care workup. In total, 22 case series with 2678 total cases of NIHF were identified. The overall incidence of LSD was 6.6% (177/2663) in NIHF cases that were tested for any LSD, and 8.2% (177/2151) in idiopathic NIHF cases. The most common LSD identified in cases of NIHF were mucopolysaccharidosis type VII, galactosialidosis, infantile sialic acid storage disease, Gaucher disease, GM1 gangliosidosis, and sialidosis. More than 40% of the most common LSD causes of NIHF have a potential postnatal treatment. LSD testing for NIHF allows for early diagnosis, better counseling and appropriate management, planning for possible early treatment, and counseling for recurrence risk., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Lysosomal storage diseases (LSDs) are a heterogeneous group of approximately 70 monogenic metabolic disorders whose diagnosis represents an arduous challenge for clinicians due to their variability in phenotype penetrance, clinical manifestations, and high allelic heterogeneity. In recent years, the approval of disease-specific therapies and the rapid emergence of novel rapid diagnostic methods has opened, for a set of selected LSDs, the possibility for inclusion in extensive national newborn screening (NBS) programs. Herein, we evaluated the clinical utility and diagnostic validity of a targeted next-generation sequencing (tNGS) panel (called NBS&#95;LSDs), designed ad hoc to scan the coding regions of six genes ( GBA , GAA , SMPD1 , IDUA1 , GLA , GALC ) relevant for a group of LSDs candidate for inclusion in national NBS programs (MPSI, Pompe, Fabry, Krabbe, Niemann Pick A-B and Gaucher diseases). A standard group of 15 samples with previously known genetic mutations was used to test and validate the entire flowchart. Analytical accuracy, sensitivity, and specificity, as well as turnaround time and costs, were assessed. Results showed that the Ion AmpliSeq and Ion Chef System-based high-throughput NBS&#95;LSDs tNGS panel is a fast, accurate, and cost-effective process. The introduction of this technology into routine NBS procedures as a second-tier test along with primary biochemical assays will allow facilitating the identification and management of selected LSDs and reducing diagnostic delay.