Assessment of ganglioside age-related and topographic specificity in human brain by Orbitrap mass spectrometry

Lipidomics of Huntington's Disease: A Comprehensive Review of Current Status and Future Directions

BACKGROUND

Huntington's disease (HD) is a multifaceted neurological disorder characterized by the progressive deterioration of motor, cognitive, and psychiatric functions. Despite a limited understanding of its pathogenesis, research has implicated abnormal trinucleotide cytosine-adenine-guanine CAG repeat expansion in the huntingtin gene (HTT) as a critical factor. The development of innovative strategies is imperative for the early detection of predictive biomarkers, enabling timely intervention and mitigating irreversible cellular damage. Lipidomics, a comprehensive analytical approach, has emerged as an indispensable tool for systematically characterizing lipid profiles and elucidating their role in disease pathology.

METHOD

A MedLine search was performed to identify studies that use lipidomics for the characterization of HD. Search terms included "Huntington disease"; "lipidomics"; "biomarker discovery"; "NMR"; and "Mass spectrometry".

RESULTS

This review highlights the significance of lipidomics in HD diagnosis and treatment, exploring changes in brain lipids and their functions. Recent breakthroughs in analytical techniques, particularly mass spectrometry and NMR spectroscopy, have revolutionized brain lipidomics research, enabling researchers to gain deeper insights into the complex lipidome of the brain.

CONCLUSIONS

A comprehensive understanding of the broad spectrum of lipidomics alterations in HD is vital for precise diagnostic evaluation and effective disease management. The integration of lipidomics with artificial intelligence and interdisciplinary collaboration holds promise for addressing the clinical variability of HD.

The alteration and role of glycoconjugates in Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by abnormal protein deposition. With an alarming 30 million people affected worldwide, AD poses a significant public health concern. While inhibiting key enzymes such as β-site amyloid precursor protein-cleaving enzyme 1 and γ-secretase or enhancing amyloid-β clearance, has been considered the reasonable strategy for AD treatment, their efficacy has been compromised by ineffectiveness. Furthermore, our understanding of AD pathogenesis remains incomplete. Normal aging is associated with a decline in glucose uptake in the brain, a process exacerbated in patients with AD, leading to significant impairment of a critical post-translational modification: glycosylation. Glycosylation, a finely regulated mechanism of intracellular secondary protein processing, plays a pivotal role in regulating essential functions such as synaptogenesis, neurogenesis, axon guidance, as well as learning and memory within the central nervous system. Advanced glycomic analysis has unveiled that abnormal glycosylation of key AD-related proteins closely correlates with the onset and progression of the disease. In this context, we aimed to delve into the intricate role and underlying mechanisms of glycosylation in the etiopathology and pathogenesis of AD. By highlighting the potential of targeting glycosylation as a promising and alternative therapeutic avenue for managing AD, we strive to contribute to the advancement of treatment strategies for this debilitating condition.

Human Cerebellum Gangliosides: A Comprehensive Analysis by Ion Mobility Tandem Mass Spectrometry

The human cerebellum is an ultraspecialized region of the brain responsible for cognitive functions and movement coordination. The fine mechanisms through which the process of aging impacts such functions are not well understood; therefore, a rigorous exploration of this brain region at the molecular level is deemed necessary. Gangliosides, sialylated glycosphingolipids, highly and specifically expressed in the human central nervous system, represent possible molecular markers of cerebellum development and aging. In this context, for a comprehensive determination of development- and age-specific components, we have conducted here a comparative profiling and structural determination of the gangliosides expressed in fetal cerebellum in two intrauterine developmental stages and aged cerebellum by ion mobility separation (IMS) mass spectrometry (MS) and tandem MS (MS/MS). Due to the high sensitivity and efficiency of separation provided by IMS MS, no less than 551 chemically distinct species were identified, which represents 4.5 times more gangliosides than ever discovered in this brain region. The detailed assessment of fetal vs aged cerebellum gangliosidome showed marked discrepancies not only in the general number of the species expressed, but also in their sialylation patterns, the modifications of the glycan core, and the composition of the ceramides. All of these characteristics are potential markers of cerebellum development and aging. The structural analysis by collision-induced dissociation (CID) documented the occurrence of GD1b (d18:1/18:0) isomer in the fetal cerebellum in the second gestational trimester, with all probability of GQ1b (t18:1/18:0) in the near-term fetus and of GQ1b (d18:1/18:0) in aged cerebellum.

Advances in Mass Spectrometry of Gangliosides Expressed in Brain Cancers

Gangliosides are highly abundant in the human brain where they are involved in major biological events. In brain cancers, alterations of ganglioside pattern occur, some of which being correlated with neoplastic transformation, while others with tumor proliferation. Of all techniques, mass spectrometry (MS) has proven to be one of the most effective in gangliosidomics, due to its ability to characterize heterogeneous mixtures and discover species with biomarker value. This review highlights the most significant achievements of MS in the analysis of gangliosides in human brain cancers. The first part presents the latest state of MS development in the discovery of ganglioside markers in primary brain tumors, with a particular emphasis on the ion mobility separation (IMS) MS and its contribution to the elucidation of the gangliosidome associated with aggressive tumors. The second part is focused on MS of gangliosides in brain metastases, highlighting the ability of matrix-assisted laser desorption/ionization (MALDI)-MS, microfluidics-MS and tandem MS to decipher and structurally characterize species involved in the metastatic process. In the end, several conclusions and perspectives are presented, among which the need for development of reliable software and a user-friendly structural database as a search platform in brain tumor diagnostics.

Robust quantitation of gangliosides and sulfatides in human brain using UHPLC-MRM-MS: Method development and application in Alzheimer's disease

Gangliosides (GAs) and sulfatides (STs) are acidic glycosphingolipids that are particularly abundant in the nervous system and are closely related to aging and neurodegenerative disorders. To explore their roles in brain diseases, in-depth molecular profiling, including structural variations of sphingoid backbone, fatty acyl group, and sugar chain of GAs and STs was performed. A total of 210 GAs and 38 STs were characterized in the inferior frontal gyrus (IFG) of human brain, with 90 GAs discovered in brain tissues for the first time. Influential MS parameters for detecting GAs and STs in multiple reaction monitoring (MRM) mode were systematically examined and optimized to minimize in-source fragmentation, resulting in remarkable signal intensity enhancement for GAs and STs, especially for polysialylated species. To eliminate analytical variations, isotopic interference-free internal standards were prepared by simple and fast reduction reaction. The final established method facilitated the simultaneous quantitation of 184 GAs and 30 STs from 25 subtypes, which represents the highest number of GAs quantitated among all quantitation methods recorded in literature so far. The method was further validated and applied to reveal the aberrant change of GAs and STs in the IFG of 12 Alzheimer's disease (AD) patients. Four GAs exhibited high classification capacity for AD (AUC ≥0.80) and were thereby considered the most promising signatures for AD. These findings suggested the close correlation between GAs and the pathogenesis of AD, highlighting the achievements of our robust method for investigating the roles of GAs and STs in various physiological states and diseases.

Brain lipidomics: From functional landscape to clinical significance

Lipids are crucial components of cellular function owing to their role in membrane formation, intercellular signaling, energy storage, and homeostasis maintenance. In the brain, lipid dysregulations have been associated with the etiology and progression of neurodegeneration and other neurological pathologies. Hence, brain lipids are emerging as important potential targets for the early diagnosis and prognosis of neurological diseases. This review aims to highlight the significance and usefulness of lipidomics in diagnosing and treating brain diseases. We explored lipid alterations associated with brain diseases, paying attention to organ-specific characteristics and the functions of brain lipids. As the recent advances in brain lipidomics would have been impossible without advances in analytical techniques, we provide up-to-date information on mass spectrometric approaches and integrative analysis with other omic approaches. Last, we present the potential applications of lipidomics combined with artificial intelligence techniques and interdisciplinary collaborative research for treating brain diseases with clinical heterogeneities.

Ion Mobility Mass Spectrometry Reveals Rare Sialylated Glycosphingolipid Structures in Human Cerebrospinal Fluid

Gangliosides (GGs) represent an important class of biomolecules associated with the central nervous system (CNS). In view of their special role at a CNS level, GGs are valuable diagnostic markers and prospective therapeutic agents. By ion mobility separation mass spectrometry (IMS MS), recently implemented by us in the investigation of human CNS gangliosidome, we previously discovered a similarity between GG profiles in CSF and the brain. Based on these findings, we developed IMS tandem MS (MS/MS) to characterize rare human CSF glycoforms, with a potential biomarker role. To investigate the oligosaccharide and ceramide structures, the ions detected following IMS MS separation were submitted to structural analysis by collision-induced dissociation (CID) MS/MS in the transfer cell. The IMS evidence on only one mobility feature, together with the diagnostic fragment ions, allowed the unequivocal identification of isomers in the CSF. Hence, by IMS MS/MS, GalNAc-GD1c(d18:1/18:1) and GalNAc-GD1c(d18:1/18:0) having both Neu5Ac residues and GalNAc attached to the external galactose were for the first time discovered and structurally characterized. The present results demonstrate the high potential of IMS MS/MS for biomarker discovery and characterization in body fluids, and the perspectives of method implementation in clinical analyses targeting the early diagnosis of CNS diseases through molecular fingerprints.

Gangliosides as Biomarkers of Human Brain Diseases: Trends in Discovery and Characterization by High-Performance Mass Spectrometry

Gangliosides are effective biochemical markers of brain pathologies, being also in the focus of research as potential therapeutic targets. Accurate brain ganglioside mapping is an essential requirement for correlating the specificity of their composition with a certain pathological state and establishing a well-defined set of biomarkers. Among all bioanalytical methods conceived for this purpose, mass spectrometry (MS) has developed into one of the most valuable, due to the wealth and consistency of structural information provided. In this context, the present article reviews the achievements of MS in discovery and structural analysis of gangliosides associated with severe brain pathologies. The first part is dedicated to the contributions of MS in the assessment of ganglioside composition and role in the specific neurodegenerative disorders: Alzheimer’s and Parkinson’s diseases. A large subsequent section is devoted to cephalic disorders (CD), with an emphasis on the MS of gangliosides in anencephaly, the most common and severe disease in the CD spectrum. The last part is focused on the major accomplishments of MS-based methods in the discovery of ganglioside species, which are associated with primary and secondary brain tumors and may either facilitate an early diagnosis or represent target molecules for immunotherapy oriented against brain cancers.

Overview of sialylation status in human nervous and skeletal muscle tissues during aging

Sialic acids (Sias) are a large and heterogeneous family of electronegatively charged nine-carbon monosaccharides containing a carboxylic acid and are mostly found as terminal residues in glycans of glycoproteins and glycolipids such as gangliosides. They are linked to galactose or N-acetylgalactosamine via α2,3 or α2,6 linkage, or to other Sias via α2,8 or more rarely α2,9 linkage, resulting in mono, oligo and polymeric forms. Given their characteristics, Sias play a crucial role in a multitude of human tissue biological processes in physiological and pathological conditions, ranging from development and growth to adult life until aging. Here, we review the sialylation status in human adult life focusing on the nervous and skeletal muscle tissues, which both display significant structural and functional changes during aging, strongly impacting on the whole human body and, therefore, on the quality of life. In particular, this review highlights the fundamental roles played by different types of glycoconjugates Sias in several cellular biological processes in the nervous and skeletal muscle tissues during adult life, also discussing how changes in Sia content during aging may contribute to the physiological decline of physical and nervous functions and to the development of age-related degenerative pathologies. Based on our current knowledge, further in-depth investigations could help to develop novel prophylactic strategies and therapeutic approaches that, by maintaining and/or restoring the correct sialylation status in the nervous and skeletal muscle tissues, could contribute to aging slowing and the prevention of age-related pathologies.

Gangliosides of Human Glioblastoma Multiforme: A Comprehensive Mapping and Structural Analysis by Ion Mobility Tandem Mass Spectrometry

Glioblastoma multiforme (GBM), a malignant, highly aggressive, grade IV brain tumor, which rapidly infiltrates into the nearby tissue, has drawn a significant amount of attention because of its poor prognosis and the limited treatment options available. In GBM, nearly all tumor cells exhibit aberrant cell-surface glycosylation patterns due to the alteration of their biosynthesis or postsynthesis modification process. Since gangliosides (GGs) are acknowledged as tumor-associated antigens, we have carried out here a comprehensive profiling of native ganglioside mixtures extracted and purified from GBM specimens. For this purpose, high performance ion mobility separation mass spectrometry (IMS MS) was thoroughly optimized to allow the discovery of GBM-specific structures and the assessment of their roles as tumor markers or possible associated antigens. GG separation by IMS according to the charge state, carbohydrate chain length, degree of sialylation, and ceramide composition led to the identification of no less than 160 distinct components, which represents 3-fold the number of structures identified before. The detected GGs and asialo-GGs were found characterized by a high heterogeneity in their ceramide and glycan compositions, encompassing up five Neu5Ac residues. The tumor was found dominated in equal and high proportions by GD3 and GT1 forms, with a particular incidence of C24:1 fatty acids in the ceramide. By the occurrence of only one mobility feature and the diagnostic fragment ions, the IMS tandem MS conducted using collision-induced dissociation (CID) disclosed for the first time the presence of GT1c(d18:1/24:1) newly proposed here as a potential GBM marker.

Characterization of Glycosphingolipids and Their Diverse Lipid Forms through Two-Stage Matching of LC-MS/MS Spectra

Glycosphingolipids (GSLs) play a key role in various biological and pathological events. Thus, determination of the complete GSL compositions in human tissues is essential for comparative and functional studies of GSLs. In this work, a new strategy was developed for GSL characterization and glycolipidomics analysis based on two-stage matching of experimental and reference MS/MS spectra. In the first stage, carbohydrate fragments, which contain only glycans and thus are conserved within a GSL species, are directly matched to yield a species identification. In the second stage, glycolipid fragments from the matched GSL species, which contain both the lipid and glycans and thus shift due to lipid structural changes, are treated according to lipid rule-based matching to characterize the lipid compositions. This new strategy uses the whole spectrum for GSL characterization. Furthermore, simple databases containing only a single lipid form per GSL species can be utilized to identify multiple GSL lipid forms. It is expected that this method will help accelerate glycolipidomics analysis and disclose new and diverse lipid forms of GSLs.

Developments and applications of separation and microfluidics methods coupled to electrospray mass spectrometry in glycomics of nervous system gangliosides

Gangliosides are particularly abundant in the nervous system (NS) where their pattern and structure in a certain milieu or a defined region exhibit a pronounced specificity. Since gangliosides are useful biomarkers for diagnosis of NS ailments, a clear-cut mapping of individual components represents a prerequisite for designing ganglioside-based diagnostic procedures, treatments, or vaccines. These bioclinical aspects and the high diversity of ganglioside species claim for development of specific analytical strategies. This review summarizes the state-of-the-art in the implementation of separation techniques and microfluidics coupled to MS, which have contributed significantly to the advancement of the field. In the first part, the review discusses relevant approaches based on HPLC MS and CE coupled to ESI MS and their applications in the characterization of gangliosides expressed in healthy and diseased NS. A considerable section is dedicated to microfluidics MS and ion mobility separation MS, developed for the study of brain gangliosidome and its changes triggered by various factors, as well as for ganglioside biomarker discovery in neurodegenerative diseases and brain cancer. In the last part of the review, the benefits and perspectives in ganglioside research of these high-performance techniques are presented.

High resolution mass spectrometry provides novel insights into the ganglioside pattern of brain cavernous hemangioma

In this study we have optimized nanoelectrospray ionization (nanoESI) high resolution mass spectrometry (HR MS) performed on Orbitrap instrument in the negative ion mode for the determination of the composition and structure of gangliosides extracted from human brain cavernous hemangioma. The optimized HR MS platform, allowed the discrimination of 62 ions, corresponding to 52 different ganglioside species, which represents roughly twice the number of species existing in the current inventory of human brain hemangioma-associated gangliosides. The experiments revealed a ganglioside pattern dominated by GD-type of structures as well as an elevated incidence of species characterized by a low degree of sialylation and short glycan chains, including asialo GA1 (d18:1/18:0), which offer a new perspective upon the ganglioside composition in this benign tumor. Many of the structures are characteristic for this type of tumor only and are to be considered in further investigations for their potential use in early brain hemangioma diagnosis based on molecular markers. The detailed fragmentation analysis performed by collision-induced dissociation (CID) tandem MS provided information of structural elements related to the glycan core and ceramide moiety, which confirmed the molecular configuration of GD3 (d18:1/24:1) and GD3 (d18:1/24:2) species with potential biomarker role.

Novel Molecular Mechanisms of Gangliosides in the Nervous System Elucidated by Genetic Engineering

Acidic glycosphingolipids, i.e., gangliosides, are predominantly and consistently expressed in nervous tissues of vertebrates at high levels. Therefore, they are considered to be involved in the development and function of nervous systems. Recent studies involving genetic engineering of glycosyltransferase genes have revealed novel aspects of the roles of gangliosides in the regulation of nervous tissues. In this review, novel findings regarding ganglioside functions and their modes of action elucidated mainly by studies of gene knockout mice are summarized. In particular, the roles of gangliosides in the regulation of lipid rafts to maintain the integrity of nervous systems are reported with a focus on the roles in the regulation of neuro-inflammation and neurodegeneration via complement systems. In addition, recent advances in studies of congenital neurological disorders due to genetic mutations of ganglioside synthase genes and also in the techniques for the analysis of ganglioside functions are introduced.

Glycosylation changes in inflammatory diseases

Glycosylation is one of the most important modifications of proteins and lipids, and cell surface glycoconjugates are thought to play important roles in a variety of biological functions including cell-cell and cell-substrate interactions, bacterial adhesion, cell immunogenicity and cell signaling. Alterations of glycosylation are observed in a number of inflammatory diseases. Pro-inflammatory cytokines have been shown to modulate cell surface glycosylation by regulating the expression of glycosyltransferases and sulfotransferases involved in the biosynthesis of glycan chains, inducing the expression of specific carbohydrate antigens at the cell surface that can be recognized by different types of lectins or by bacterial adhesins, contributing to the development of diseases. Glycosylation can also regulate biological functions of immune cells by recruiting leukocytes to inflammation sites with pro- or anti-inflammatory effects. Cell surface proteoglycans provide a large panel of binding sites for many mediators of inflammation, and regulate their bio-availability and functions. In this review, we summarize the current knowledge of the glycosylation changes occurring in mucin type O-linked glycans, glycosaminoglycans, as well as in glycosphingolipids, with a particular focus on cystic fibrosis and neurodegenerative diseases, and their consequences on cell interactions and disease progression.

Analysis of Glycosphingolipid Glycans by Lectin Microarrays

Glycosphingolipids (GSLs) are ubiquitous glycoconjugates of cell membranes. Identification of unknown GSL-glycan structures is still a major challenge. To address this challenge, we developed a novel strategy for analysis of GSL-glycans from cultured cells based on a lectin microarray that can directly detect and reveal glycopatterns of GSL extracts without the need for glycan release. There were six steps to perform the analysis of GSL-glycans: (i) extraction of GSLs from cell pellets, (ii) quantification of GSL-glycans using orcinol-sulfuric acid reaction, (iii) preparation of lyso-GSLs by using sphingolipid ceramide N-deacylase, (iv) fluorescence labeling of lyso-GSLs, (v) detection by a lectin microarray, (vi) data acquisition and analysis. Simultaneously, a supplementary verification analysis for GSL-glycans was performed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Optimized experimental conditions, which consisted of the blocking buffer, incubation buffer, and appropriate GSL concentration, were investigated by analyzing the glycopatterns of a standard ganglioside (GM1a) via lectin microarray. The analysis of GSL-glycans from human hepatocarcinoma cell lines (MHCC97L, MHCC97H, and HCCLM3) showed that there were 27 lectins (e.g., WFA, MAL-II, and LTL) to give significantly different signals compared with a normal human liver cell line (HL-7702), indicating up- and/or down-regulations of corresponding glycopatterns such as α1-2 fucosylation and α2-3 sialylation, and changes of certain glycostructures such as Galβ1-3GalNAcβ1-4(NeuAcα2-3)Galβ1-4Glc:Cer and GalNAcα1-3(Fucα1-2)Galβ1-3GlcNAcβ1-3Galβ1-4Glc:Cer. The lectin microarray analysis of lyso-GSLs labeled by fluorescence has proven to be credible, which can provide the glycopatterns and detailed linkage information on GSL-glycans.

Gangliosides in Inflammation and Neurodegeneration

Gangliosides play roles in the regulation of cell signaling that are mediated via membrane microdomains, lipid rafts. In this review, functions of gangliosides in the maintenance of nervous systems with a focus on regulation of inflammation and neurodegeneration are addressed. During analyses of various ganglioside-lacking mutant mice, we demonstrated that nervous tissues exhibited inflammatory reactions and subsequent neurodegeneration. Among inflammation-related genes, factors of the complement system showed up-regulation with aging. Analyses of architectures and compositions of lipid rafts in nervous tissues from these mutant mice revealed that dysfunctions of complement regulatory proteins based on disrupted lipid rafts were main factors to induce the inflammatory reactions resulting in neurodegeneration. Ganglioside changes in development and senescence, and implication of them in the integrity of cell membranes and cellular phenotypes in physiological and pathological conditions including Alzheimer disease have been summarized. Novel directions to further analyze mechanisms for ganglioside functions in membrane microdomains have been also addressed.

Ion mobility mass spectrometry provides novel insights into the expression and structure of gangliosides in the normal adult human hippocampus

General work-flow for ganglioside analysis by IM-MS.