Glycosphingolipid composition of a new immortalized human cerebromicrovascular endothelial cell line

Preferential delivery of lipid-ligand conjugated DNA/RNA heteroduplex oligonucleotide to ischemic brain in hyperacute stage

Antisense oligonucleotide (ASO) is a major tool used for silencing pathogenic genes. For stroke in the hyperacute stage, however, the ability of ASO to regulate genes is limited by its poor delivery to the ischemic brain owing to sudden occlusion of the supplying artery. Here we show that, in a mouse model of permanent ischemic stroke, lipid-ligand conjugated DNA/RNA heteroduplex oligonucleotide (lipid-HDO) was unexpectedly delivered 9.6 times more efficiently to the ischemic area of the brain than to the contralateral non-ischemic brain and achieved robust gene knockdown and change of stroke phenotype, despite a 90% decrease in cerebral blood flow in the 3 h after occlusion. This delivery to neurons was mediated via receptor-mediated transcytosis by lipoprotein receptors in brain endothelial cells, the expression of which was significantly upregulated after ischemia. This study provides proof-of-concept that lipid-HDO is a promising gene-silencing technology for stroke treatment in the hyperacute stage.

Uptake of severe acute respiratory syndrome coronavirus 2 spike protein mediated by angiotensin converting enzyme 2 and ganglioside in human cerebrovascular cells

Introduction

There is clinical evidence of neurological manifestations in coronavirus disease-19 (COVID-19). However, it is unclear whether differences in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)/spike protein (SP) uptake by cells of the cerebrovasculature contribute to significant viral uptake to cause these symptoms.

Methods

Since the initial step in viral invasion is binding/uptake, we used fluorescently labeled wild type and mutant SARS-CoV-2/SP to study this process. Three cerebrovascular cell types were used (endothelial cells, pericytes, and vascular smooth muscle cells), in vitro.

Results

There was differential SARS-CoV-2/SP uptake by these cell types. Endothelial cells had the least uptake, which may limit SARS-CoV-2 uptake into brain from blood. Uptake was time and concentration dependent, and mediated by angiotensin converting enzyme 2 receptor (ACE2), and ganglioside (mono-sialotetrahexasylganglioside, GM1) that is predominantly expressed in the central nervous system and the cerebrovasculature. SARS-CoV-2/SPs with mutation sites, N501Y, E484K, and D614G, as seen in variants of interest, were also differentially taken up by these cell types. There was greater uptake compared to that of the wild type SARS-CoV-2/SP, but neutralization with anti-ACE2 or anti-GM1 antibodies was less effective.

Conclusion

The data suggested that in addition to ACE2, gangliosides are also an important entry point of SARS-CoV-2/SP into these cells. Since SARS-CoV-2/SP binding/uptake is the initial step in the viral penetration into cells, a longer exposure and higher titer are required for significant uptake into the normal brain. Gangliosides, including GM1, could be an additional potential SARS-CoV-2 and therapeutic target at the cerebrovasculature.

Why Is N-Glycolylneuraminic Acid Rare in the Vertebrate Brain?

The sialic acids N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) differ by a single oxygen atom and are widely found at the terminal position of glycans on vertebrate cell surfaces. In animals capable of synthesizing Neu5Gc, most tissues and cell types express both sialic acids, in proportions that vary between species. However, it has long been noted that Neu5Gc is consistently expressed at trace to absent levels in the brains of all vertebrates studied to date. Although several reports have claimed to find low levels of Neu5Gc-containing glycans in neural tissue, no study definitively excludes the possibility of contamination with glycans from non-neural cell types. This distribution of a molecule - prominently but variably expressed in extraneural tissues but very low or absent in the brain - is, to our knowledge, unique. The evolutionarily conserved brain-specific suppression of Neu5Gc may indicate that its presence is toxic to this organ; however, no studies to date have directly addressed this very interesting question. Here we provide a historical background to this issue and discuss potential mechanisms causing the suppression of Neu5Gc expression in brain tissue, as well as mechanisms by which Neu5Gc may exert the presumed toxicity. Finally, we discuss future approaches towards understanding the mechanisms and implications of this unusual finding.

In vitro models of the blood-brain barrier

The chapter provides an introduction and brief overview of currently available in vitro blood-brain barrier models, pointing out the major advantages and disadvantages of the respective models and potential applications. Bovine brain microvessel endothelial cell isolation, culture, and transendothelial permeability measurement procedures are discussed in detail as a model system for a laboratory to begin brain vascular investigations.

Sulfoglucuronosyl paragloboside promotes endothelial cell apoptosis in inflammation: elucidation of a novel glycosphingolipid-signaling pathway

Sulfoglucuronosyl paragloboside (SGPG), a minor glycosphingolipid of endothelial cells, is a ligand for L-selectin and has been implicated in neuro-inflammatory diseases, such as Guillian-Barré syndrome. Inflammatory cytokines, such as TNFα and IL-1β, up-regulate SGPG expression by stimulating gene expression for glucuronosyltransferases, both P and S forms (GlcATp and GlcATs), and the human natural killer antigen (HNK-1) sulfotransferase (HNK-1 ST). Transfection of a human cerebromicrovascular endothelial cell (SV-HCEC) line with HNK-1 ST siRNA down-regulated SGPG expression, inhibited cytokine-stimulated T-cell adhesion, and offered protection against apoptosis. However, the precise mechanisms of SGPG elevation in endothelial cell apoptosis and the maintenance of blood-brain or blood-nerve barrier integrity in inflammation have not been elucidated. Blocking SGPG expression inhibited cytokine-mediated stimulation of NF-κB activity but stimulated MAP kinase activity. Furthermore, elevation of SGPG by over-expression of GlcATp and GlcATs triggered endothelial cell apoptosis, with GlcATs being more potent than GlcATp. Although SGPG-mediated endothelial cell apoptosis was preceded by inhibiting the intracellular NF-κB activity, interfering with Akt and ERK activation and stimulating caspase 3 in SV-HCECs, HNK-1ST siRNA transfection also interfered with IκB phosphorylation but stimulated ERK activation. Our data indicate that SGPG is a critical regulatory molecule for maintaining endothelial cell survival and blood-brain or blood-nerve barrier function.

Advances on the compositional analysis of glycosphingolipids combining thin-layer chromatography with mass spectrometry

Glycosphingolipids (GSLs), composed of a hydrophilic carbohydrate chain and a lipophilic ceramide anchor, play pivotal roles in countless biological processes, including infectious diseases and the development of cancer. Knowledge of the number and sequence of monosaccharides and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains, is essential for exploring the function of GSLs. As part of the investigation of the vertebrate glycome, GSL analysis is undergoing rapid expansion owing to the application of novel biochemical and biophysical technologies. Mass spectrometry (MS) takes part in the network of collaborations to further unravel structural and functional aspects within the fascinating world of GSLs with the ultimate aim to better define their role in human health and disease. However, a single-method analytical MS technique without supporting tools is limited yielding only partial structural information. Because of its superior resolving power, robustness, and easy handling, high-performance thin-layer chromatography (TLC) is widely used as an invaluable tool in GSL analysis. The intention of this review is to give an insight into current advances obtained by coupling supplementary techniques such as TLC and mass spectrometry. A retrospective view of the development of this concept and the recent improvements by merging (1) TLC separation of GSLs, (2) their detection with oligosaccharide-specific proteins, and (3) in situ MS analysis of protein-detected GSLs directly on the TLC plate, are provided. The procedure works on a nanogram scale and was successfully applied to the identification of cancer-associated GSLs in several types of human tumors. The combination of these two supplementary techniques opens new doors by delivering specific structural information of trace quantities of GSLs with only limited investment in sample preparation.

Sulfoglucuronosyl paragloboside is a ligand for T cell adhesion: regulation of sulfoglucuronosyl paragloboside expression via nuclear factor kappaB signaling

Inflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta stimulate glucuronosyltransferase genes (S and P) in endothelial cells (ECs) and up-regulate sulfoglucuronosyl paragloboside (SGPG) expression, which serves as a ligand for T cell adhesion. However, the mechanism of cytokine-mediated gene up-regulation has not been elucidated. To evaluate the precise mechanism of SGPG up-regulation, we have specifically inhibited the SGPG synthesis in the cerebromicrovascular EC line (SV-HCECs), a transformed brain ECs of human origin. SV-HCECs were transfected with small interfering RNA designed to mimic the human natural killer epitope-1 sulfotransferase (HNK-1ST), the ultimate enzyme that transfers the sulfate group to glucuronic acid for SGPG synthesis. An inhibition of SGPG expression along with a reduction of human CD4(+) cell adhesion was observed in siRNA HNK-1ST (siHNK-1)-transfected cells after TNFalpha stimulation. A thorough screening of the signaling system confirmed that TNFalpha/IL-1beta stimulation up-regulated nuclear factor kappaB (NFkappaB) signaling in SV-HCECs. siHNK-1 transfection interfered with the SGPG up-regulation after TNFalpha/IL-1beta stimulation in transfected cells and reduced the T cell adhesion. Hence, our study indicates that T cell-SGPG adhesion in SV-HCECs may proceed through NFkappaB activation. In addition, siHNK-1 transfection reduced the NFkappaB activity compared with cells that were transfected with scrambled siRNA, before and after TNFalpha/IL-1beta stimulation. This is the first report indicating that NFkappaB signaling is involved in SGPG gene expression in brain ECs by an unknown mechanism. Its down-regulation by inhibiting HNK-1ST expression may have a potential use in preventing the T cell invasion and consequently nerve damage during inflammation.

Expression of Neutral Glycosphingolipids in the Brain and Spleen of Mice Lacking TNF Receptor 1

We investigated the expression of neutral glycosphingolipids (GSLs) in the brain and spleen of mice lacking the gene for the tumor necrosis factor-alpha receptor p55 (TNFR1). Neutral GSLs of the ganglio-, globo-, and neolacto-series were determined in the tissues of homozygous (TNFR1-/-) and control heterozygous (TNFR1+/-) animals by high performance thin layer chromatography (HPTLC) overlay immunostaining with specific antibodies. The spleen of homozygous TNFR1 knockout mice lacked glucosylceramide substituted with palmitic acid, GlcCer(C16), and showed severe reduction in the expression of GlcCer(C24). In addition, gangliotetraosylceramide substituted with palmitic acid, Gg4Cer(C16), and globotetraosylceramide, Gb4Cer, were down-regulated in the TNFR1-/- spleen in comparison with the heterozygous control. The brain of both groups of animals (TNFR1-/- and TNFR1+/-) did not express detectable levels of Gg4Cer, Gb5Cer and Gb4Cer, but the brain of TNFR1 knockout mice expressed abundant globotriaosylceramide, Gb3Cer, compared to no expression in control heterozygous mice. nLcCer(C24) had slightly higher (1.4 fold) expression in the brain of TNFR1-/- mice compared with the control animals. This study provides in vivo evidence that TNF signaling via the TNFR1 is involved in the acquisition of a divergent GSL assembly in the brain, an immunologically privileged organ, and the spleen, typical secondary lymphoid organ.

Glycosphingolipid antigens in neural tumor cell lines and anti-glycosphingolipid antibodies in sera of patients with neural tumors

To characterize biomarkers in neural tumors, we analyzed the acidic lipid fractions of 13 neural tumor cell lines using enzyme-linked immunoabsorbent assay (ELISA) and high-performance thin-layer chromatography (HPTLC) immunostaining. Sulfated glucuronosyl glycosphingolipids (SGGLs) are cell surface molecules that are endowed with the Human Natural Killer-1 (HNK-1) carbohydrate epitope. These glycosphingolipids (GSLs) were expressed in all cell lines with concentrations ranging from 210 to 330 ng per 2 x 10(6) cells. Sulfoglucuronosyl paragloboside (SGPG) was the prominent species with lesser amounts of sulfoglucuronosyl lactosaminyl paragloboside (SGLPG) in these tumor cell lines as assessed by quantitative HPTLC immunostaining. Among the gangliosides surveyed, GD3 and 9-O-acetylated GD3 (OAc-GD3) were expressed in all tumor cell lines. In contrast, fucosyl-GM1 was not found to restrict to small cell lung carcinoma cells. In addition, we have analyzed serum antibody titers against SGPG, GD3, and OAc-GD3 in patients with neural tumors by ELISA and HPTLC immunostaining. All sera had high titers of antibodies of the IgM isotype against SGPG (titers over 1:3,200), especially in tumors such as meningiomas, germinomas, orbital tumors, glioblastomas, medulloblastomas, and subependymomas. Serum in a patient with subependymomas also had a high anti-SGGL antibody titer of the IgG and IgA types (titers over 12,800). The titer of anti-GD3 antibody was also elevated in patients with subependymomas and medulloblastomas; the latter cases also had a high titer of antibody against OAc-GD3. Our data indicate that certain GSL antigens, especially SGGLs, GD3, and OAc-GD3, are expressed in neural tumor cells and may be considered as tumor-associated antigens that represent important biomarkers for neural tumors. Furthermore, antibody titers in sera of patients with these tumors may be of diagnostic value for monitoring the presence of tumor cells and tumor progression.

Host defenses to Rickettsia rickettsii infection contribute to increased microvascular permeability in human cerebral endothelial cells

Rickettsiae are arthropod-borne intracellular bacterial pathogens that primarily infect the microvascular endothelium leading to systemic spread of the organisms and the major pathophysiological effect, increased microvascular permeability, and edema in vital organs such as the lung and brain. Much work has been done on mechanisms of immunity to rickettsiae, as well as the responses of endothelial cells to rickettsial invasion. However, to date, no one has described the mechanisms of increased microvascular permeability during acute rickettsiosis. We sought to establish an in vitro model of human endothelial-target rickettsial infection using the etiological agent of Rocky Mountain spotted fever, Rickettsia rickettsii, and human cerebral microvascular endothelial cells. Endothelial cells infected with R. rickettsii exhibited a dose-dependent decrease in trans-endothelial electrical resistance, which translates into increased monolayer permeability. Additionally, we showed that the addition of pro-inflammatory stimuli essential to rickettsial immunity dramatically enhanced this effect. This increase in permeability correlates with dissociation of adherens junctions between endothelial cells and is not dependent on the presence of nitric oxide. Taken together, these results demonstrate for the first time that increased microvascular permeability associated with rickettsial infection is partly attributable to intracellular rickettsiae and partly attributable to the immune defenses that have evolved to protect the host from rickettsial spread.

Tumor necrosis factor-alpha up-regulates glucuronosyltransferase gene expression in human brain endothelial cells and promotes T-cell adhesion

Stimulation of human brain microvascular endothelial cells (SV-HCECs) with tumor necrosis factor-alpha (TNF-alpha) up-regulates sulfoglucuronosyl paragloboside (SGPG) synthesis in a dose- and time-dependent manner. After TNF-alpha exposure at a concentration of 50 ng/ml for 24 hr, we observed a seven- to tenfold elevation of SGPG concentration. Interleukin-1beta (IL-1beta) at a concentration of 10 ng/ml and the combined doses of TNF-alpha and IL-1beta were less effective than TNF-alpha alone. TNF-alpha also stimulated T-cell (Jurkat) adhesion with SV-HCECs via SGPG-L-selectin recognition: this was determined by double-label immunofluorescent staining with SGPG and L-selectin antibodies. The number of T cells bound to SV-HCECs after different cytokine stimulations was proportional to the SGPG concentration, and the cell attachment was inhibited by anti-SGPG and anti-L-selectin antibodies, respectively. Our data unequivocally establish that inflammatory cytokines, particularly TNF-alpha, stimulate the glucuronosyltransferse, GlcAT-P, and GlcAT-S, gene expression in brain endothelial cells and promote T-cell adhesion via SGPG-L-selectin recognition, a preliminary step for onset of neuroinflammation.

The blood-brain barrier transmigrating single domain antibody: mechanisms of transport and antigenic epitopes in human brain endothelial cells

Antibodies against receptors that undergo transcytosis across the blood-brain barrier (BBB) have been used as vectors to target drugs or therapeutic peptides into the brain. We have recently discovered a novel single domain antibody, FC5, which transmigrates across human cerebral endothelial cells in vitro and the BBB in vivo. The purpose of this study was to characterize mechanisms of FC5 endocytosis and transcytosis across the BBB and its putative receptor on human brain endothelial cells. The transport of FC5 across human brain endothelial cells was polarized, charge independent and temperature dependent, suggesting a receptor-mediated process. FC5 taken up by human brain endothelial cells co-localized with clathrin but not with caveolin-1 by immunochemistry and was detected in clathrin-enriched subcellular fractions by western blot. The transendothelial migration of FC5 was reduced by inhibitors of clathrin-mediated endocytosis, K+ depletion and chlorpromazine, but was insensitive to caveolae inhibitors, filipin, nystatin or methyl-beta-cyclodextrin. Following internalization, FC5 was targeted to early endosomes, bypassed late endosomes/lysosomes and remained intact after transcytosis. The transcytosis process was inhibited by agents that affect actin cytoskeleton or intracellular signaling through PI3-kinase. Pretreatment of human brain endothelial cells with wheatgerm agglutinin, sialic acid, alpha(2,3)-neuraminidase or Maackia amurensis agglutinin that recognizes alpha(2,3)-, but not with Sambucus nigra agglutinin that recognizes alpha(2,6) sialylgalactosyl residues, significantly reduced FC5 transcytosis. FC5 failed to recognize brain endothelial cells-derived lipids, suggesting that it binds luminal alpha(2,3)-sialoglycoprotein receptor which triggers clathrin-mediated endocytosis. This putative receptor may be a new target for developing brain-targeting drug delivery vectors.

Glycosphingolipid composition of primary cultured human brain microvascular endothelial cells

Glycosphingolipid (GSL) antigens have been considered to be involved in the pathogenesis of autoimmune neurologic disorders including multiple sclerosis. To establish the GSL pattern specific for endothelial cells forming blood-brain barrier (BBB), we established a method to yield sufficient quantities of highly purified human brain microvascular endothelial cells (HBMECs) and compared their GSL composition to that of human umbilical cord vein endothelial cells (HUVECs), as the representative of endothelial cells not forming BBB. The major gangliosides were GM3 and sialyl paragloboside (LM1), and the major neutral GSLs were lactosylceramide (LacCer), globotriaosylceramide (Gb3), and globoside (Gb4). Trace amounts of GM1, GD1a, GD1b, GT1b, and sulfoglucuronosyl paragloboside (SGPG) could be detected by the high performance thin layer chromatography-overlay method. SGPG was detected only at a nonconfluent state in an amount almost 1/30 that of in nonconfluent HUVECs. Conversely, GM3 and LM1 increased significantly after confluency. The amount of Gb3 in HBMECs was almost as twice that in HUVECs. The significance of these differences in GSL content between HBMECs and HUVECs and between confluent and nonconfluent states is obscure. It might be related, however, to the defense mechanism at the BBB and to the susceptibility of the central nervous system in some disorders that target cell surface GSL, such as hemolytic uremic syndrome.

Recent studies on the roles of antiglycosphingolipids in the pathogenesis of neurological disorders

Evidence is mounting to suggest a causal role of humoral immunity arising from antiglycosphingolipid (GSL) antibodies in a variety of neurological disorders. These disorders include the demyelinating and axonal forms of Guillain-Barre syndrome, multifocal motor neuropathy, chronic inflammatory demyelinating polyradiculoneuropathy, and IgM paraproteinemia. Many claims have been made regarding other neurological disorders, which should be carefully scrutinized for their validity, based on several criteria proposed in this review. These criteria include 1) characterization of the causative antigens and immunoglobulins, 2) correlation of the pathological lesions and clinical manifestation of the antigens, 3) establishment of animal models using pure GSLs as the antigens, 4) immunopathogenic mechanisms of the neurodenerative process, 5) mechanisms for the malfunctioning of blood-nerve barrier and the ensuing leakage of circulating antibodies into peripheral nerve parenchyma, and 6) the roles of anti-GSL antibodies that may cause humorally mediated nerve dysfunction and injury as well as interference with ion channel function at the node of Ranvier, where carbohydrate epitopes are located. Finally, the origin of the anti-GSL antibodies is discussed in light of the recent circumstantial evidence pointing to a molecular mimicry mechanism with infectious agents. With a better understanding of the immunopathogenic mechanisms, it will then be possible to devise rational and effective diagnostic and therapeutic strategies for the treatment of these neurological disorders.