A lysosome-plasma membrane-sphingolipid axis linking lysosomal storage to cell growth arrest

Linking glycosphingolipid metabolism to disease-related changes in the plasma membrane proteome

Glycosphingolipids (GSLs) are vital components of the plasma membrane (PM), where they play crucial roles in cell function. GSLs form specialised membrane microdomains that organise lipids and proteins into functional platforms for cell adhesion and signalling. GSLs can also influence the function of membrane proteins and receptors, via direct protein-lipid interactions thereby affecting cell differentiation, proliferation, and apoptosis. Research into GSL-related diseases has primarily focussed on lysosomal storage disorders, where defective enzymes lead to the accumulation of GSLs within lysosomes, causing cellular dysfunction and disease. However, recent studies are uncovering the broader cellular impact of GSL imbalances including on a range of organelles and cellular compartments such as the mitochondria, endoplasmic reticulum and PM. In this review we describe the mechanisms by which GSL imbalances can influence the PM protein composition and explore examples of the changes that have been observed in the PM proteome upon GSL metabolic disruption. Identifying and understanding these changes to the PM protein composition will enable a more complete understanding of lysosomal storage diseases and provide new insights into the pathogenesis of other GSL-related diseases, including cancer and neurodegenerative disorders.

Lysosome dynamics during human endometrial stromal cells decidualization: effect of para-nonylphenol

During the process of decidualization, the stromal cells of the endometrium change dynamically to create a favorable environment for embryo implantation. Lysosome activity has often been associated with physiological changes in the endometrium during the preimplantation period and early pregnancy. In this study, the effect of para-nonylphenol (p-NP), an endocrine disruptor, on human immortalized endometrial stromal cells (tHESCs) was investigated. After exposure to p-NP (1 nM and 1 pM), the cells were examined for the decidualization markers connexin-43, insulin like growth factor binding protein 1 (IGFBP1), and prolactin. In addition, the effect of p-NP on lysosome biogenesis and exocytosis was investigated by examining the expression and localization of the transcription factor EB (TFEB) and that of the lysosomal-associated membrane protein 1 (LAMP-1). Finally, we evaluated the effect of p-NP on extracellular matrix (ECM) remodeling using a fibronectin assay. Our results showed that p-NP reduced the expression of prolactin protein, increased the nuclear localization of TFEB, and induced the increase and translocation of the lysosomal protein LAMP-1 to the membrane of tHESCs. The data indicate an impairment of decidualization and suggest an increase in lysosomal biogenesis and exocytosis, which is supported by the higher release of active cathepsin D by tHESCs. Given the importance of cathepsins in the processing and degradation of the ECM during trophoblast invasiveness and migration into the decidua, our results appear to be clear evidence of the negative effects of p-NP on endometrial processes that are fundamental to reproductive success and the establishment of pregnancy.NEW & NOTEWORTHY Endocrine disruptors, such as para-nonylphenol, affect the decidualization of human endometrial stromal cells with an impact on decidualization itself, lysosome biogenesis and exocytosis, and extracellular matrix remodeling. All these alterations may negatively impact embryo implantation with the success of reproduction and the establishment of pregnancy.

Applying Multimodal Mass Spectrometry to Image Tumors Undergoing Ferroptosis Following In Vivo Treatment with a Ferroptosis Inducer

Epithelial ovarian cancer (EOC) is the most common form of ovarian cancer. The poor prognosis generally associated with this disease has led to the search for improved therapies such as ferroptosis-inducing agents. Ferroptosis is a form of regulated cell death that is dependent on iron and is characterized by lipid peroxidation. Precise mapping of lipids and iron within tumors exposed to ferroptosis-inducing agents may provide insight into processes of ferroptosis in vivo and ultimately assist in the optimal deployment of ferroptosis inducers in cancer therapy. In this work, we present a method for combining matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) with secondary ion mass spectrometry (SIMS) to analyze changes in spatial lipidomics and metal composition, respectively, in ovarian tumors following exposure to a ferroptosis inducer. Tumors were obtained by injecting human ovarian cancer tumor-initiating cells into mice, followed by treatment with the ferroptosis inducer erastin. SIMS imaging detected iron accumulation in the tumor tissue, and sequential MALDI-MS imaging of the same tissue section displayed two chemically distinct regions of lipids. One region was associated with the iron-rich area detected with SIMS, and the other region encompassed the remainder of the tissue section. Bulk lipidomics confirmed the lipid assignments putatively assigned from the MALDI-MS data. Overall, we demonstrate the ability of multimodal MSI to identify the spatial locations of iron and lipids in the same tissue section and associate these regions with clinical pathology.

GM1 ganglioside exerts protective effects against glutamate-excitotoxicity via its oligosaccharide in wild-type and amyotrophic lateral sclerosis motor neurons

Alterations in glycosphingolipid metabolism have been linked to the pathophysiological mechanisms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting motor neurons. Accordingly, administration of GM1, a sialic acid-containing glycosphingolipid, is protective against neuronal damage and supports neuronal homeostasis, with these effects mediated by its bioactive component, the oligosaccharide head (GM1-OS). Here, we add new evidence to the therapeutic efficacy of GM1 in ALS: Its administration to WT and SOD1G93A motor neurons affected by glutamate-induced excitotoxicity significantly increased neuronal survival and preserved neurite networks, counteracting intracellular protein accumulation and mitochondria impairment. Importantly, the GM1-OS faithfully replicates GM1 activity, emphasizing that even in ALS the protective function of GM1 strictly depends on its pentasaccharide.

Cross-talk between CFTR and sphingolipids in cystic fibrosis

Cystic fibrosis (CF) is the most common inherited, life-limiting disorder in Caucasian populations. It is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR), which lead to an impairment of protein expression and/or function. CFTR is a chloride/bicarbonate channel expressed at the apical surface of epithelial cells of different organs. Nowadays, more than 2100 CFTR genetic variants have been described, but not all of them cause CF. However, around 80-85% of the patients worldwide are characterized by the presence, at least in one allele, of the mutation F508del. CFTR mutations cause aberrant hydration and secretion of mucus in hollow organs. In the lungs, this condition favors bacterial colonization, allowing the development of chronic infections that lead to the onset of the CF lung disease, which is the main cause of death in patients. In recent years, evidence has reported that CFTR loss of function is responsible for alterations in a particular class of bioactive lipids, called sphingolipids (SL). SL are ubiquitously present in eukaryotic cells and are mainly asymmetrically located within the external leaflet of the plasma membrane, where they organize specific platforms capable of segregating a selected number of proteins. CFTR is associated with these platforms that are fundamental for its functioning. Considering the importance of SL in CFTR homeostasis, we attempt here to provide a critical overview of the literature to determine the role of these lipids in channel stability and activity, and whether their modulation in CF could be a target for new therapeutic approaches.

Ellagic acid and its metabolites urolithins A/B ameliorate most common disease phenotypes in cellular and mouse models for lysosomal storage disorders by enhancing extracellular vesicle secretion

Niemann Pick diseases types A (NPDA) and C (NPDC) are lysosomal storage disorders (LSDs) leading to cognitive impairment, neurodegeneration, and early death. NPDA and NPDC have different genetic origins, being caused by mutations in the acid sphingomyelinase (ASM) or the cholesterol transport protein NPC1, respectively. However, they share a common pathological hallmark in the accumulation of lipids in the endolysosomal compartment. Here, we tested the hypothesis that polyphenols reduce lipid overload in NPD cells by enhancing the secretion of extracellular vesicles (ECVs). We show that among the polyphenols tested, the ellagic acid metabolites, urolithin A and B, were the safest and most efficient in increasing ECV secretion. They reduced levels of accumulating lipids and lysosomal size and permeabilization in cultured bone marrow-derived macrophages and neurons from ASMko and NPC1 mutant mice, which mimic NPDA and NPDC, respectively. Moreover, oral treatment with ellagic acid reduced lipid levels, ameliorated lysosomal alterations, and diminished microglia activation in the brain of NPD mice. These results support the therapeutic value of ECV secretion and polyphenols for NPDs, which may also help treat other LSDs characterized by intracellular lipid overload.

Proceedings of workshop: "Neuroglycoproteins in health and disease", INNOGLY cost action

The Cost Action "Innovation with glycans: new frontiers from synthesis to new biological targets" (INNOGLY) hosted the Workshop "Neuroglycoproteins in health and disease", in Alicante, Spain, on March 2022. This event brought together an european group of scientists that presented novel insights into changes in glycosylation in diseases of the central nervous system and cancer, as well as new techniques to study protein glycosylation. Herein we provide the abstracts of all the presentations.

β-Glucocerebrosidase Deficiency Activates an Aberrant Lysosome-Plasma Membrane Axis Responsible for the Onset of Neurodegeneration

β-glucocerebrosidase is a lysosomal hydrolase involved in the catabolism of the sphingolipid glucosylceramide. Biallelic loss of function mutations in this enzyme are responsible for the onset of Gaucher disease, while monoallelic β-glucocerebrosidase mutations represent the first genetic risk factor for Parkinson’s disease. Despite this evidence, the molecular mechanism linking the impairment in β-glucocerebrosidase activity with the onset of neurodegeneration in still unknown. In this frame, we developed two in vitro neuronal models of β-glucocerebrosidase deficiency, represented by mouse cerebellar granule neurons and human-induced pluripotent stem cells-derived dopaminergic neurons treated with the specific β-glucocerebrosidase inhibitor conduritol B epoxide. Neurons deficient for β-glucocerebrosidase activity showed a lysosomal accumulation of glucosylceramide and the onset of neuronal damage. Moreover, we found that neurons react to the lysosomal impairment by the induction of their biogenesis and exocytosis. This latter event was responsible for glucosylceramide accumulation also at the plasma membrane level, with an alteration in lipid and protein composition of specific signaling microdomains. Collectively, our data suggest that β-glucocerebrosidase loss of function impairs the lysosomal compartment, establishing a lysosome–plasma membrane axis responsible for modifications in the plasma membrane architecture and possible alterations of intracellular signaling pathways, leading to neuronal damage.

Massive Accumulation of Sphingomyelin Affects the Lysosomal and Mitochondria Compartments and Promotes Apoptosis in Niemann-Pick Disease Type A

Niemann-Pick type A disease (NPA) is a rare lysosomal storage disorder caused by mutations in the gene coding for the lysosomal enzyme acid sphingomyelinase (ASM). ASM deficiency leads to the consequent accumulation of its uncatabolized substrate, the sphingolipid sphingomyelin (SM), causing severe progressive brain disease. To study the effect of the aberrant lysosomal accumulation of SM on cell homeostasis, we loaded skin fibroblasts derived from a NPA patient with exogenous SM to mimic the levels of accumulation characteristic of the pathological neurons. In SM-loaded NPA fibroblasts, we found the blockage of the autophagy flux and the impairment of the mitochondrial compartment paralleled by the altered transcription of several genes, mainly belonging to the electron transport chain machinery and to the cholesterol biosynthesis pathway. In addition, SM loading induces the nuclear translocation of the transcription factor EB that promotes the lysosomal biogenesis and exocytosis. Interestingly, we obtained similar biochemical findings in the brain of the NPA mouse model lacking ASM (ASMKO mouse) at the neurodegenerative stage. Our work provides a new in vitro model to study NPA etiopathology and suggests the existence of a pathogenic lysosome-plasma membrane axis that with an impairment in the mitochondrial activity is responsible for the cell death.

Therapeutic advantages of combined gene/cell therapy strategies in a murine model of GM2 gangliosidosis

Genetic deficiency of β-N-acetylhexosaminidase (Hex) functionality leads to accumulation of GM2 ganglioside in Tay-Sachs disease and Sandhoff disease (SD), which presently lack approved therapies. Current experimental gene therapy (GT) approaches with adeno-associated viral vectors (AAVs) still pose safety and efficacy issues, supporting the search for alternative therapeutic strategies. Here we leveraged the lentiviral vector (LV)-mediated intracerebral (IC) GT platform to deliver Hex genes to the CNS and combined this strategy with bone marrow transplantation (BMT) to provide a timely, pervasive, and long-lasting source of the Hex enzyme in the CNS and periphery of SD mice. Combined therapy outperformed individual treatments in terms of lifespan extension and normalization of the neuroinflammatory/neurodegenerative phenotypes of SD mice. These benefits correlated with a time-dependent increase in Hex activity and a remarkable reduction in GM2 storage in brain tissues that single treatments failed to achieve. Our results highlight the synergic mode of action of LV-mediated IC GT and BMT, clarify the contribution of treatments to the therapeutic outcome, and inform on the realistic threshold of corrective enzymatic activity. These results have important implications for interpretation of ongoing experimental therapies and for design of more effective treatment strategies for GM2 gangliosidosis.

Molecular and mesoscopic geometries in autophagosome generation. A review

Autophagy is an essential process in cell self-repair and survival. The centre of the autophagic event is the generation of the so-called autophagosome (AP), a vesicle surrounded by a double membrane (two bilayers). The AP delivers its cargo to a lysosome, for degradation and re-use of the hydrolysis products as new building blocks. AP formation is a very complex event, requiring dozens of specific proteins, and involving numerous instances of membrane biogenesis and architecture, including membrane fusion and fission. Many stages of AP generation can be rationalised in terms of curvature, both the molecular geometry of lipids interpreted in terms of 'intrinsic curvature', and the overall mesoscopic curvature of the whole membrane, as observed with microscopy techniques. The present contribution intends to bring together the worlds of biophysics and cell biology of autophagy, in the hope that the resulting cross-pollination will generate abundant fruit.

Ceramide-Induced Lysosomal Biogenesis and Exocytosis in Early-Onset Preeclampsia Promotes Exosomal Release of SMPD1 Causing Endothelial Dysfunction

Aberrant ceramide build-up in preeclampsia, a serious disorder of pregnancy, causes exuberant autophagy-mediated trophoblast cell death. The significance of ceramide accumulation for lysosomal biogenesis in preeclampsia is unknown. Here we report that lysosome formation is markedly increased in trophoblast cells of early-onset preeclamptic placentae, in particular in syncytiotrophoblasts. This is accompanied by augmented levels of transcription factor EB (TFEB). In vitro and in vivo experiments demonstrate that ceramide increases TFEB expression and nuclear translocation and induces lysosomal formation and exocytosis. Further, we show that TFEB directly regulates the expression of lysosomal sphingomyelin phosphodiesterase (L-SMPD1) that degrades sphingomyelin to ceramide. In early-onset preeclampsia, ceramide-induced lysosomal exocytosis carries L-SMPD1 to the apical membrane of the syncytial epithelium, resulting in ceramide accumulation in lipid rafts and release of active L-SMPD1 via ceramide-enriched exosomes into the maternal circulation. The SMPD1-containing exosomes promote endothelial activation and impair endothelial tubule formation in vitro. Both exosome-induced processes are attenuated by SMPD1 inhibitors. These findings suggest that ceramide-induced lysosomal biogenesis and exocytosis in preeclamptic placentae contributes to maternal endothelial dysfunction, characteristic of this pathology.

Sphingolipids as multifaceted mediators in ovarian cancer

Ovarian cancer is the most lethal gynaecological malignancy. It is commonly diagnosed at advanced stage when it has metastasised to the abdominal cavity and treatment becomes very challenging. While current standard therapy involving debulking surgery and platinum + taxane-based chemotherapy is associated with high response rates initially, the large majority of patients relapse and ultimately succumb to chemotherapy-resistant disease. In order to improve survival novel strategies for early detection and therapeutics against treatment-refractory disease are urgently needed. A promising new target against ovarian cancer is the sphingolipid pathway which is commonly hijacked in cancer to support cell proliferation and survival and has been shown to promote chemoresistance and metastasis in a wide range of malignant neoplasms. In particular, the sphingosine kinase 1-sphingosine 1-phosphate receptor 1 axis has been shown to be altered in ovarian cancer in multiple ways and therefore represents an attractive therapeutic target. Here we review the roles of sphingolipids in ovarian cancer progression, metastasis and chemoresistance, highlighting novel strategies to target this pathway that represent potential avenues to improve patient survival.

Metabolic features of recurrent major depressive disorder in remission, and the risk of future recurrence

Recurrent major depressive disorder (rMDD) is a relapsing-remitting disease with high morbidity and a 5-year risk of recurrence of up to 80%. This was a prospective pilot study to examine the potential diagnostic and prognostic value of targeted plasma metabolomics in the care of patients with rMDD in remission. We used an established LC-MS/MS platform to measure 399 metabolites in 68 subjects with rMDD (n = 45 females and 23 males) in antidepressant-free remission and 59 age- and sex-matched controls (n = 40 females and 19 males). Patients were then followed prospectively for 2.5 years. Metabolomics explained up to 43% of the phenotypic variance. The strongest biomarkers were gender specific. 80% of the metabolic predictors of recurrence in both males and females belonged to 6 pathways: (1) phospholipids, (2) sphingomyelins, (3) glycosphingolipids, (4) eicosanoids, (5) microbiome, and (6) purines. These changes traced to altered mitochondrial regulation of cellular redox, signaling, energy, and lipid metabolism. Metabolomics identified a chemical endophenotype that could be used to stratify rrMDD patients at greatest risk for recurrence with an accuracy over 0.90 (95%CI = 0.69-1.0). Power calculations suggest that a validation study of at least 198 females and 198 males (99 cases and 99 controls each) will be needed to confirm these results. Although a small study, these results are the first to show the potential utility of metabolomics in assisting with the important clinical challenge of prospectively identifying the patients at greatest risk of recurrence of a depressive episode and those who are at lower risk.

Glycosphingolipids

Glycosphingolipids are amphiphilic plasma membrane components formed by a glycan linked to a specific lipid moiety. In this chapter we report on these compounds, on their role played in our cells to maintain the correct cell biology.In detail, we report on their structure, on their metabolic processes, on their interaction with proteins and from this, their property to modulate positively in health and negatively in disease, the cell signaling and cell biology.

The multifaceted role of cell cycle regulators in the coordination of growth and metabolism

Adapting to changes in nutrient availability and environmental conditions is a fundamental property of cells. This adaptation requires a multi‐directional coordination between metabolism, growth, and the cell cycle regulators (consisting of the family of cyclin‐dependent kinases (CDKs), their regulatory subunits known as cyclins, CDK inhibitors, the retinoblastoma family members, and the E2F transcription factors). Deciphering the mechanisms accountable for this coordination is crucial for understanding various patho‐physiological processes. While it is well established that metabolism and growth affect cell division, this review will focus on recent observations that demonstrate how cell cycle regulators coordinate metabolism, cell cycle progression, and growth. We will discuss how the cell cycle regulators directly regulate metabolic enzymes and pathways and summarize their involvement in the endolysosomal pathway and in the functions and dynamics of mitochondria.

APOL1 polymorphism modulates sphingolipid profile of human podocytes

Apolipoprotein L1 (APOL1) wild type (G0) plays a role in the metabolism of sphingolipids, glycosphingolipids, sphingomyelin and ceramide, which constitute bioactive components of the lipid rafts (DRM). We asked whether APOL1 variants (APOL1-Vs) G1 and G2 carry the potential to alter the metabolism of sphingolipids in human podocytes. The sphingolipid pattern in HPs overexpressing either APOL1G0 or APOL1-Vs was analysed by using a thin mono- and bi-dimensional layer chromatography, mass-spectrometry and metabolic labelling with [1-³H]sphingosine. HP G0 and G1/G2-Vs exhibit a comparable decrease in lactosylceramide and an increase in the globotriaosylceramide content. An analysis of the main glycohydrolases activity involved in glycosphingolipid catabolism showed an overall decrease in the activeness of the tested enzymes, irrespective of the type of APOL1-Vs expression. Similarly, the high throughput cell live-based assay showed a comparable increased action of the plasma membrane glycosphingolipid-glycohydrolases in living cells independent of the genetic APOL1 expression profile. Importantly, the most significative modification of the sphingolipid pattern induced by APOL1-Vs occurred in DRM resulted with a drastic reduction of radioactivity associated with sphingolipids. G1/G2-Vs present a decrease amount of globotriaosylceramide and globopentaosylceramide compared to G0. Additionally, ceramide at the DRM site and lactosylceramide in general, showed a greatest fall in G1/G2 in comparison with G0. Additionally, the levels of glucosylceramide decreased only in the DRM of human podocytes overexpressing G1/G2-Vs. These findings suggest that altered sphingolipidsprofiles may contribute to the deranged functionality of the plasma membrane in APOL1 risk milieu.

Synthesis and Therapeutic Applications of Iminosugars in Cystic Fibrosis

Iminosugars are sugar analogues endowed with a high pharmacological potential. The wide range of biological activities exhibited by these glycomimetics associated with their excellent drug profile make them attractive therapeutic candidates for several medical interventions. The ability of iminosugars to act as inhibitors or enhancers of carbohydrate-processing enzymes suggests their potential use as therapeutics for the treatment of cystic fibrosis (CF). Herein we review the most relevant advances in the field, paying attention to both the chemical synthesis of the iminosugars and their biological evaluations, resulting from in vitro and in vivo assays. Starting from the example of the marketed drug NBDNJ (N-butyl deoxynojirimycin), a variety of iminosugars have exhibited the capacity to rescue the trafficking of F508del-CFTR (deletion of F508 residue in the CF transmembrane conductance regulator), either alone or in combination with other correctors. Interesting results have also been obtained when iminosugars were considered as anti-inflammatory agents in CF lung disease. The data herein reported demonstrate that iminosugars hold considerable potential to be applied for both therapeutic purposes.

The oligosaccharide portion of ganglioside GM1 regulates mitochondrial function in neuroblastoma cells

The crucial role of ganglioside GM1 in the regulation of neural homeostasis has been assessed by several studies. Recently we shed new light on the molecular basis underlying GM1 effects demonstrating that GM1 oligosaccharide directly binds TrkA receptor and triggers MAPK pathway activation leading to neuronal differentiation and protection. Following its exogenous administration, proteomic analysis revealed an increased expression of proteins involved in several biochemical mechanisms, including mitochondrial bioenergetics. Based on these data, we investigated the possible effect of GM1 oligosaccharide administration on mitochondrial function. We show that wild-type Neuro2a cells exposed to GM1 oligosaccharide displayed an increased mitochondrial density and an enhanced mitochondrial activity together with reduced reactive oxygen species levels. Interestingly, using a Neuro2a model of mitochondrial dysfunction, we found an increased mitochondrial oxygen consumption rate as well as increased complex I and II activities upon GM1 oligosaccharide administration. Taken together, our data identify GM1 oligosaccharide as a mitochondrial regulator that by acting at the plasma membrane level triggers biochemical signaling pathway inducing mitochondriogenesis and increasing mitochondrial activity. Although further studies are necessary, the capability to enhance the function of impaired mitochondria points to the therapeutic potential of the GM1 oligosaccharide for the treatment of pathologies where these organelles are compromised, including Parkinson's disease.

Gangliosides in the differentiation process of primary neurons: the specific role of GM1-oligosaccharide

It has been recently reported by our group that GM1-oligosaccharide added to neuroblastoma cells or administered to mouse experimental model mimics the neurotrophic and neuroprotective properties of GM1 ganglioside. In addition to this, differently from GM1, GM1-oligosaccharide is not taken up by the cells, remaining solubilized into the extracellular environment interacting with cell surface proteins. Those characteristics make GM1-oligosaccharide a good tool to study the properties of the endogenous GM1, avoiding to interfere with the ganglioside natural metabolic pathway. In this study, we show that GM1-oligosaccharide administered to mice cerebellar granule neurons by interacting with cell surface induces TrkA-MAP kinase pathway activation enhancing neuron clustering, arborization and networking. Accordingly, in the presence of GM1-oligosaccharide, neurons show a higher phosphorylation rate of FAK and Src proteins, the intracellular key regulators of neuronal motility. Moreover, treated cells express increased level of specific neuronal markers, suggesting an advanced stage of maturation compared to controls. In parallel, we found that in the presence of GM1-oligosaccharide, neurons accelerate the expression of complex gangliosides and reduce the level of the simplest ones, displaying the typical ganglioside pattern of mature neurons. Our data confirms the specific role of GM1 in neuronal differentiation and maturation, determined by its oligosaccharide portion. GM1-oligosacchairide interaction with cell surface receptors triggers the activation of intracellular biochemical pathways responsible for neuronal migration, dendrites emission and axon growth.

Parkinson's disease recovery by GM1 oligosaccharide treatment in the B4galnt1+/- mouse model

Given the recent in vitro discovery that the free soluble oligosaccharide of GM1 is the bioactive portion of GM1 for neurotrophic functions, we investigated its therapeutic potential in the B4galnt1^+/− mice, a model of sporadic Parkinson’s disease. We found that the GM1 oligosaccharide, systemically administered, reaches the brain and completely rescues the physical symptoms, reduces the abnormal nigral α-synuclein content, restores nigral tyrosine hydroxylase expression and striatal neurotransmitter levels, overlapping the wild-type condition. Thus, this study supports the idea that the Parkinson’s phenotype expressed by the B4galnt1^+/− mice is due to a reduced level of neuronal ganglioside content and lack of interactions between the oligosaccharide portion of GM1 with specific membrane proteins. It also points to the therapeutic potential of the GM1 oligosaccharide for treatment of sporadic Parkinson’s disease.

Novel bicistronic lentiviral vectors correct β-Hexosaminidase deficiency in neural and hematopoietic stem cells and progeny: implications for in vivo and ex vivo gene therapy of GM2 gangliosidosis

The favorable outcome of in vivo and ex vivo gene therapy approaches in several Lysosomal Storage Diseases suggests that these treatment strategies might equally benefit GM2 gangliosidosis. Tay-Sachs and Sandhoff disease (the main forms of GM2 gangliosidosis) result from mutations in either the HEXA or HEXB genes encoding, respectively, the α- or β-subunits of the lysosomal β-Hexosaminidase enzyme. In physiological conditions, α- and β-subunits combine to generate β-Hexosaminidase A (HexA, αβ) and β-Hexosaminidase B (HexB, ββ). A major impairment to establishing in vivo or ex vivo gene therapy for GM2 gangliosidosis is the need to synthesize the α- and β-subunits at high levels and with the correct stoichiometric ratio, and to safely deliver the therapeutic products to all affected tissues/organs. Here, we report the generation and in vitro validation of novel bicistronic lentiviral vectors (LVs) encoding for both the murine and human codon optimized Hexa and Hexb genes. We show that these LVs drive the safe and coordinate expression of the α- and β-subunits, leading to supranormal levels of β-Hexosaminidase activity with prevalent formation of a functional HexA in SD murine neurons and glia, murine bone marrow-derived hematopoietic stem/progenitor cells (HSPCs), and human SD fibroblasts. The restoration/overexpression of β-Hexosaminidase leads to the reduction of intracellular GM2 ganglioside storage in transduced and in cross-corrected SD murine neural progeny, indicating that the transgenic enzyme is secreted and functional. Importantly, bicistronic LVs safely and efficiently transduce human neurons/glia and CD34+ HSPCs, which are target and effector cells, respectively, in prospective in vivo and ex vivo GT approaches. We anticipate that these bicistronic LVs may overcome the current requirement of two vectors co-delivering the α- or β-subunits genes. Careful assessment of the safety and therapeutic potential of these bicistronic LVs in the SD murine model will pave the way to the clinical development of LV-based gene therapy for GM2 gangliosidosis.

Exploring the effect of chirality on the therapeutic potential of N-alkyl-deoxyiminosugars: anti-inflammatory response to Pseudomonas aeruginosa infections for application in CF lung disease

In the frame of a research program aimed to explore the relationship between chirality of iminosugars and their therapeutic potential, herein we report the synthesis of N-akyl l-deoxyiminosugars and the evaluation of the anti-inflammatory properties of selected candidates for the treatment of Pseudomonas aeruginosa infections in Cystic Fibrosis (CF) lung disease. Target glycomimetics were prepared by the shortest and most convenient approach reported to date, relying on the use of the well-known PS-TPP/I₂ reagent system to prepare reactive alkoxyalkyl iodides, acting as key intermediates. Iminosugars ent-1-3 demonstrated to efficiently reduce the inflammatory response induced by P. aeruginosa in CuFi cells, either alone or in synergistic combination with their d-enantiomers, by selectively inhibiting NLGase. Surprisingly, the evaluation in murine models of lung disease showed that the amount of ent-1 required to reduce the recruitment of neutrophils was 40-fold lower than that of the corresponding d-enantiomer. The remarkably low dosage of the l-iminosugar, combined with its inability to act as inhibitor for most glycosidases, is expected to limit the onset of undesired effects, which are typically associated with the administration of its d-counterpart. Biological results herein obtained place ent-1 and congeners among the earliest examples of l-iminosugars acting as anti-inflammatory agents for therapeutic applications in Cystic Fibrosis.

The Neuroprotective Role of the GM1 Oligosaccharide, II3Neu5Ac-Gg4, in Neuroblastoma Cells

Recently, we demonstrated that the GM1 oligosaccharide, II³Neu5Ac-Gg₄ (OligoGM1), administered to cultured murine Neuro2a neuroblastoma cells interacts with the NGF receptor TrkA, leading to the activation of the ERK1/2 downstream pathway and to cell differentiation. To understand how the activation of the TrkA pathway is able to trigger key biochemical signaling, we performed a proteomic analysis on Neuro2a cells treated with 50 μM OligoGM1 for 24 h. Over 3000 proteins were identified. Among these, 324 proteins were exclusively expressed in OligoGM1-treated cells. Interestingly, several proteins expressed only in OligoGM1-treated cells are involved in biochemical mechanisms with a neuroprotective potential, reflecting the GM1 neuroprotective effect. In addition, we found that the exogenous administration of OligoGM1 reduced the cellular oxidative stress in Neuro2a cells and conferred protection against MPTP neurotoxicity. These results confirm and reinforce the idea that the molecular mechanisms underlying the GM1 neurotrophic and neuroprotective effects depend on its oligosaccharide chain, suggesting the activation of a positive signaling starting at plasma membrane level.

GM1 promotes TrkA-mediated neuroblastoma cell differentiation by occupying a plasma membrane domain different from TrkA

Recently, we highlighted that the ganglioside GM1 promotes neuroblastoma cells differentiation by activating the TrkA receptor through the formation of a TrkA-GM1 oligosaccharide complex at the cell surface. To study the TrkA-GM1 interaction, we synthesized two radioactive GM1 derivatives presenting a photoactivable nitrophenylazide group at the end of lipid moiety, 1 or at position 6 of external galactose, 2; and a radioactive oligosaccharide portion of GM1 carrying the nitrophenylazide group at position 1 of glucose, 3. The three compounds were singly administered to cultured neuroblastoma Neuro2a cells under established conditions that allow cell surface interactions. After UV activation of photoactivable compounds, the proteins were analyzed by PAGE separation. The formation of cross-linked TrkA-GM1 derivatives complexes was identified by both radioimaging and immunoblotting. Results indicated that the administration of compounds 2 and 3, carrying the photoactivable group on the oligosaccharide, led to the formation of a radioactive TrkA complex, while the administration of compound 1 did not. This underlines that the TrkA-GM1 interaction directly involves the GM1 oligosaccharide, but not the ceramide. To better understand how GM1 relates to the TrkA, we isolated plasma membrane lipid rafts. As expected, GM1 was found in the rigid detergent-resistant fractions, while TrkA was found as a detergent soluble fraction component. These results suggest that TrkA and GM1 belong to separate membrane domains: probably TrkA interacts by 'flopping' down its extracellular portion onto the membrane, approaching its interplay site to the oligosaccharide portion of GM1.

Validation of anti-glucocerebrosidase antibodies for western blot analysis on protein lysates of murine and human cells

Gaucher disease (GD) is a rare lysosomal storage disorder caused by mutations in the GBA1 gene, encoding the lysosome-resident glucocerebrosidase enzyme involved in the hydrolysis of glucosylceramide. The discovery of an association between mutations in GBA1 and the development of synucleinopathies, including Parkinson disease, has directed attention to glucocerebrosidase as a potential therapeutic target for different synucleinopathies. These findings initiated an exponential growth in research and publications regarding the glucocerebrosidase enzyme. The use of various commercial and custom-made glucocerebrosidase antibodies has been reported, but standardized in-depth validation is still not available for many of these antibodies. This work details the evaluation of several previously reported glucocerebrosidase antibodies for western blot analysis, tested on protein lysates of murine gba+/+ and gba−/− immortalized neurons and primary human wild-type and type 2 GD fibroblasts.

Acute Gaucher Disease-Like Condition in an Indian Infant with a Novel Biallelic Mutation in the Prosaposin Gene

This is the first reported case of prosaposin ( PSAP ) mutation from India manifesting as an acute neuronal Gaucher disease-like condition. A 2-month-old male baby presented with encephalopathy, resistant tonic-clonic seizures, moderate hepatosplenomegaly, hypotonia, and cherry red spot in the retinae. The child had anemia, thrombocytopenia, elevated chitotriosidase, and normal activity of acid sphingomyelinase and low normal activity of β-glucosidase 1 (β-glucocerebrosidase 1, GBA). The child succumbed in the fourth month of life due to persistent respiratory distress and refractory seizures. The clinical phenotype, cherry red spots, elevated chitotriosidase, and lysosomal assays led to the suspicion of Gaucher disease. Exome sequencing revealed a homozygous stop codon mutation in the PSAP gene (c.G1228T, p.Glu410ter). Prenatal diagnosis in the next pregnancy revealed a carrier fetus, who was unaffected postnatally. The diagnosis of specific activator deficiency such as saposin C and saposin D deficiency (in the current study) should be considered and tested for when Gaucher disease is suspected in an infant with partially deficient or near normal GBA activity.

Biochemical Characterization of the GBA2 c.1780G>C Missense Mutation in Lymphoblastoid Cells from Patients with Spastic Ataxia

The GBA2 gene encodes the non-lysosomal glucosylceramidase (NLGase), an enzyme that catalyzes the conversion of glucosylceramide (GlcCer) to ceramide and glucose. Mutations in GBA2 have been associated with the development of neurological disorders such as autosomal recessive cerebellar ataxia, hereditary spastic paraplegia, and Marinesco-Sjogren-Like Syndrome. Our group has previously identified the GBA2 c.1780G>C [p.Asp594His] missense mutation, in a Cypriot consanguineous family with spastic ataxia. In this study, we carried out a biochemical characterization of lymphoblastoid cell lines (LCLs) derived from three patients of this family. We found that the mutation strongly reduce NLGase activity both intracellularly and at the plasma membrane level. Additionally, we observed a two-fold increase of GlcCer content in LCLs derived from patients compared to controls, with the C₁₆ lipid being the most abundant GlcCer species. Moreover, we showed that there is an apparent compensatory effect between NLGase and the lysosomal glucosylceramidase (GCase), since we found that the activity of GCase was three-fold higher in LCLs derived from patients compared to controls. We conclude that the c.1780G>C mutation results in NLGase loss of function with abolishment of the enzymatic activity and accumulation of GlcCer accompanied by a compensatory increase in GCase.

Neuronal membrane dynamics as fine regulator of sphingolipid composition

Sphingolipid metabolism is an intricate network of several interdependent and co-regulated pathways. In addition to the mainstream biosynthetic and catabolic pathways, several processes, even if less important in contributing to the final tissue sphingolipid composition from the quantitative point of view, might become relevant when sphingolipid metabolism is for any reason dysregulated and concur to the onset of neuronal pathologies. The main subcellular sites involved in the mainstream metabolic pathway are represented by the Golgi apparatus (for the biosynthesis) and by the lysosomes (for catabolism). On the other hand, the minor collateral pathways are associated with the plasma membrane and membranes of other organelles, and likely play important roles in the local regulation of membrane dynamics and contribute to maintain a perfect membrane organization functional to the physiology of the cell. In this review, we will consider few aspects of the sphingolipid metabolic pathway depending by the dynamic of the membranes that seems to become relevant in neurodegenerative diseases.

Sphingolipids and neuronal degeneration in lysosomal storage disorders

Ceramide, sphingomyelin, and glycosphingolipids (both neutral and acidic) are characterized by the presence in the lipid moiety of an aliphatic base known as sphingosine. Altogether, they are called sphingolipids and are particularly abundant in neuronal plasma membranes, where, via interactions with the other membrane lipids and membrane proteins, they play a specific role in modulating the cell signaling processes. The metabolic pathways determining the plasma membrane sphingolipid composition are thus the key point for functional changes of the cell properties. Unnatural changes of the neuronal properties are observed in sphingolipidoses, lysosomal storage diseases occurring when a lysosomal sphingolipid hydrolase is not working, leading to the accumulation of the substrate and to its distribution to all the cell membranes interacting with lysosomes. Moreover, secondary accumulation of sphingolipids is a common trait of other lysosomal storage diseases. This article is part of the Special Issue "Lysosomal Storage Disorders".