Danielle Te Vruchte

Background: Parkinson’s disease (PD) is a prevalent neurodegenerative disorder characterized by progressive motor dysfunction and broad cellular impairment, including significant disruptions in lysosomal function, lipid metabolism, and intracellular trafficking. Glycosphingolipids (GSLs), critical for various cellular processes, depend on effective lysosomal degradation. Aberrant GSL metabolism has been linked to PD pathology, and glycoprotein non-metastatic melanoma protein B (GPNMB) has emerged as a biomarker associated with lysosomal dysfunction and lipid imbalance in PD Objectives: To assess the relationship between GPNMB and GSL levels in cerebrospinal fluid (CSF) and plasma from PD patients and controls within the BioFIND cohort. We also investigated potential sex differences and associations with PD-related biomarkers such as α-synuclein Methods: GSL species and GPNMB protein levels were quantified using high-performance liquid chromatography (HPLC) and ELISA assays, respectively, in matched CSF and plasma samples from PD patients and controls Results: Levels of the paraglobosides GSL species, alpha-2,3SpG and pGb were significantly elevated in the plasma of PD patients compared to healthy controls, while levels of the ganglioside GD1a and the lacto-series GSL, Le ^b combined (GD1a + Le ^b ), were significantly reduced in PD. GPNMB levels positively correlated with several GSL species in both plasma and CSF. Plasma GSLs and GPNMB concentrations were significantly higher in females compared to males, independent of PD diagnosis. CSF GPNMB correlated positively with age and α-synuclein concentrations Interpretation: Our findings confirm that GSL metabolism is altered in PD. They also highlight significant sex-based biochemical variations in GSL and GPNMB levels, emphasizing the need for sex-specific analyses in PD biomarker research. The relationship between GSLs and GPNMB supports their potential as interconnected biomarkers of lipid pathology in PD.

Gangliosides are abundant neuronal glycosphingolipids, yet their roles in organizing the plasma membrane and supporting neuronal function remain poorly defined. Mutations in the biosynthetic enzymes ST3GAL5 or B4GALNT1 cause severe neurodevelopmental disorders, yet their cellular consequences are unclear. Using isogenic human iPSC-derived cortical neurons, we show that loss of these enzymes eliminates major neuronal gangliosides but produces strikingly divergent outcomes. ST3GAL5 deficiency reprograms the glycosphingolipid repertoire toward non-neuronal species and abolishes network-level electrical activity. In contrast, B4GALNT1-deficient neurons retain near-normal excitability, supported by accumulation of simple sialylated precursors (GM3/GD3). Quantitative proteomics reveals a profound loss of plasma membrane proteins, including ion channels and synaptic organizers, only in ST3GAL5-deficient neurons. These findings identify sialylated glycosphingolipids as essential scaffolds for plasma membrane organization and neuronal excitability, providing a mechanistic basis for the severe phenotype caused by loss of GM3 synthase in humans. TEASER: Human neuronal models reveal why loss of GM3 synthase causes severe neurodevelopmental disease

Developmental delay and seizures with or without movement abnormalities (OMIM 617836) caused by heterozygous pathogenic variants in the DHDDS gene (DHDDS-CDG) is a rare genetic disease that belongs to the progressive encephalopathy spectrum. It results in developmental delay in affected children, accompanied by myoclonus, seizures, ataxia and tremor, which worsens over time. DHDDS encodes a subunit of a DHDDS/NUS1 cis-prenyltransferase ( cis- PTase), a branch point enzyme of the mevalonate pathway essential for N-linked glycosylation. We describe the first mouse model of this disease, Dhdds ^R37H+/- strain, heterozygous for the human recurrent de novo c.110G>A:p.R37H pathogenic variant. Dhdds ^R37H+/- mice present with seizures, myoclonus and memory deficits associated with reduced density or/and maturity of inhibitory interneurons in the cortex. Multiomics analyses of mouse CNS tissues, together with the enzymatic/structural characterization of the R37H DHDDS mutant protein, reveal that the variant produces a catalytically inactive enzyme and results in a brain dolichol deficit, aberrant glycosylation of brain glycoproteins, including those involved in synaptic transmission, and major perturbations in the CNS proteome and lipidome. Acetazolamide, a carbonic anhydrase inhibitor clinically approved for treatment of glaucoma, epilepsy, and intracranial hypertension, and successfully used “off-label” to treat genetic movement disorders, drastically reduces seizure susceptibility to pentylenetetrazol in Dhdds ^R37H+/- mice, suggesting potential therapeutic value of using this drug in human DHDDS-CDG patients. Together, our results define cis- PTase as a master regulator of CNS development and function and establish that its monoallelic debilitating variants cause a novel Congenital Disorder of Glycosylation, associated with aberrant levels of neuronal proteins and lipids. Graphical

Interest in the role of cellular glycosphingolipids (GSLs) in health and disease led to us developing a sensitive method to analyse the full complement of GSL structures present in mammalian cells, fluids and tissues. The original qualitative method we developed was published in 2004 and measured the oligosaccharides selectively released from glycosphingolipids using a ceramide glycanase enzyme derived from the medicinal leech. We have now updated and refined this protocol with the focus on achieving sensitive and reproducible quantitation of GSLs in cell line samples. The method uses the fluorescent compound anthranilic acid (2-AA) to label oligosaccharides prior to analysis using normal-phase high-performance liquid chromatography. The labelling procedure is rapid, selective, and easy to perform. With the inclusion of a 2AA-labelled chitotriose calibration standard, it is possible to obtain accurate and reproducible molar quantities of individual GSL species.

Interest in the role of cellular glycosphingolipids (GSLs) in health and disease led to us developing a sensitive method to analyse the full complement of GSL structures present in mammalian cells, fluids and tissues. The original qualitative method we developed was published in 2004 and measured the oligosaccharides selectively released from glycosphingolipids using a ceramide glycanase enzyme derived from the medicinal leech. We have now updated and refined this protocol with the focus on achieving sensitive and reproducible quantitation of GSLs in animal tissues. The method uses the fluorescent compound anthranilic acid (2-AA) to label oligosaccharides prior to analysis using normal-phase high-performance liquid chromatography. The labelling procedure is rapid, selective, and easy to perform. With the inclusion of a 2AA-labelled chitotriose calibration standard, it is possible to obtain accurate and reproducible molar quantities of individual GSL species.

Interest in the role of cellular glycosphingolipids (GSLs) in health and disease led to us developing a sensitive method to analyse the full complement of GSL structures present in mammalian cells, fluids and tissues. The original qualitative method we developed was published in 2004 and measured the oligosaccharides selectively released from glycosphingolipids using a ceramide glycanase enzyme derived from the medicinal leech. We have now updated and refined this protocol with the focus on achieving sensitive and reproducible quantitation of GSLs in control and patient cerebrospinal fluid samples. The method uses the fluorescent compound anthranilic acid (2-AA) to label oligosaccharides prior to analysis using normal-phase high-performance liquid chromatography. The labelling procedure is rapid, selective, and easy to perform. With the inclusion of a 2AA-labelled chitotriose calibration standard, it is possible to obtain accurate and reproducible molar quantities of individual GSL species.

Background: Alteration in glycosphingolipids (GSLs) in Parkinson's disease (PD) still needs to be determined.Objectives: We evaluated if PD subjects show abnormal GSLs levels compared to healthy controls (HC) and if GSLs correlate with clinical features.Methods: We analyzed GSLs and glucosylceramide (GlcCer) in plasma using two normal‐phase high‐performance liquid chromatography assays; clinico‐demographic data were extracted.Results: Eighty PD subjects and 25 HCs were analyzed. Levels of GlcCer, GD1b, Gb4, GalNAcGA1, and b‐series were higher in PD patients than in HCs; total GSLs, GT1b, GM1a, GM3, GM2, and a‐series levels were lower in PD patients than in HCs. Changes in GSLs were present in PD subjects, with GlcCer levels similar to those in HCs. The results were similar after excluding certain GBA1 mutation carriers. Movement Disorder Society Unified Parkinson's Disease Rating Scale, Part III, correlated with Gb4 and Montreal Cognitive Assessment with GD1b levels.Conclusions: Multiple GSL abnormalities in plasma were detected in patients with and without GlcCer changes, indicating a broader shift in lipid homeostasis. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.

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.

Invariant natural killer T (iNKT) cells are a specialised subset of T cells that are restricted to the MHC class I like molecule, CD1d. The ligands for iNKT cells are lipids, with the canonical superagonist being α‐galactosylceramide, a non‐mammalian glycosphingolipid. Trafficking of CD1d through the lysosome is required for the development of murine iNKT cells. Niemann‐Pick type C (NPC) disease is a lysosomal storage disorder caused by dysfunction in either of two lysosomal proteins, NPC1 or NPC2, resulting in the storage of multiple lipids, including glycosphingolipids. In the NPC1 mouse model, iNKT cells are virtually undetectable, which is likely due to the inability of CD1d to be loaded with the selecting ligand due to defective lysosomal function and/or CD1d trafficking. However, in this study we have found that in NPC1 patients iNKT cells are present at normal frequencies, with no phenotypic or functional differences. In addi‐tion, antigen‐presenting cells derived from NPC1 patients are functionally competent to present several different CD1d/iNKT‐cell ligands. This further supports the hypothesis that there are different trafficking requirements for the development of murine and human iNKT cells, and a functional lysosomal/late‐endosomal compartment is not required for human iNKT‐cell development.