Regulation by GD3 of the proinflammatory response of microglia mediated by interleukin-15

Neoprzewaquinone A alters the migration, phagocytosis and energy metabolism of IL-15-induced HMC3 cells

Microglia play a major role in the immune defense system of the central nervous system and are activated in many neurological diseases. The immunomodulatory cytokine interleukin (IL)-15 is known to be involved in microglia response and inflammatory factors release. Neoprzewaquinone A (NEO) is an active compound isolated from Salvia miltiorrhiza Bunge. Our previous study has shown that NEO significantly inhibit the proliferation of IL-15-treated Mo7e cells. However, the role of NEO in the structure and function of IL-15-treated human microglial cells (HMC3) remains unclear. Thus, our study aimed to quantitatively analyze the beneficial effects of NEO on HMC3 cells following IL-15 treatment. The cell viability, phagocytosis, migration and energy metabolism were evaluated by Cell Counting Kit-8 (CCK8), scratch assay, pHrodo™ Red Zymosan BioParticles™ Conjugate, and Agilent Seahorse XF Cell Mito Test. Cephalothin (CEP) was selected as a positive drug because it has obvious inhibitory effect on IL-15 and IL-15Rɑ. Our results showed that IL-15 stimulated the proliferation, migration and phagocytosis of HMC3 cells in a time-dependent manner. Interestingly, NEO exhibited significant suppressive effects on these IL-15-induced changes, which were even superior to those observed with the CEP. Moreover, IL-15 treatment did not significantly alter energy metabolism, including glycolysis and mitochondrial respiration. NEO and CEP alone effectively reduced glycolysis, non-mitochondrial respiration, basal respiration, ATP turnover, respiration capacity, and H+ leak in HMC3 cells. Furthermore, NEO displayed a partial regulatory effect on mitochondrial function in IL-15-treated HMC3 cells. Our study confirms the effectively inhibition of NEO on IL-15-induced microglial activation and provides valuable insights into the therapeutic prospects of NEO in neuropsychiatric disorders associated with IL-15 and microglia.

The biological role and immunotherapy of gangliosides and GD3 synthase in cancers

Gangliosides are a large subfamily of glycosphingolipids that broadly exist in the nervous system and interact with signaling molecules in the lipid rafts. GD3 and GD2 are two types of disialogangliosides (GDs) that include two sialic acid residues. The expression of GD3 and GD2 in various cancers is mostly upregulated and is involved in tumor proliferation, invasion, metastasis, and immune responses. GD3 synthase (GD3S, ST8SiaI), a subclass of sialyltransferases, regulates the biosynthesis of GD3 and GD2. GD3S is also upregulated in most tumors and plays an important role in the development and progression of tumors. Many clinical trials targeting GD2 are ongoing and various immunotherapy studies targeting gangliosides and GD3S are gradually attracting much interest and attention. This review summarizes the function, molecular mechanisms, and ongoing clinical applications of GD3, GD2, and GD3S in abundant types of tumors, which aims to provide novel targets for future cancer therapy.

Brain Cancer-Activated Microglia: A Potential Role for Sphingolipids

Almost no neurological disease exists without microglial activation. Microglia has exert a pivotal role in the maintenance of the central nervous system and its response to external and internal insults. Microglia have traditionally been classified as, in the healthy central nervous system, "resting", with branched morphology system and, as a response to disease, "activated", with amoeboid morphology; as a response to diseases but this distinction is now outmoded. The most devastating disease that hits the brain is cancer, in particular glioblastoma. Glioblastoma multiforme is the most aggressive glioma with high invasiveness and little chance of being surgically removed. During tumor onset, many brain alterations are present and microglia have a major role because the tumor itself changes microglia from the pro-inflammatory state to the anti-inflammatory and protects the tumor from an immune intervention. What are the determinants of these changes in the behavior of the microglia? In this review, we survey and discuss the role of sphingolipids in microglia activation in the progression of brain tumors, with a particular focus on glioblastoma.

The Role of Glycosphingolipids in Immune Cell Functions

Glycosphingolipids (GSLs) exhibit a variety of functions in cellular differentiation and interaction. Also, they are known to play a role as receptors in pathogen invasion. A less well-explored feature is the role of GSLs in immune cell function which is the subject of this review article. Here we summarize knowledge on GSL expression patterns in different immune cells. We review the changes in GSL expression during immune cell development and differentiation, maturation, and activation. Furthermore, we review how immune cell GSLs impact membrane organization, molecular signaling, and trans-interactions in cellular cross-talk. Another aspect covered is the role of GSLs as targets of antibody-based immunity in cancer. We expect that recent advances in analytical and genome editing technologies will help in the coming years to further our knowledge on the role of GSLs as modulators of immune cell function.

Prevalence of IgG Autoantibodies against GD3 Ganglioside in Acute Zika Virus Infection

Zika virus (ZIKV) disease has become a global health emergency with devastating effects on public health. Recent evidences implicate the virus as an emergent neuropathological agent promoting serious pathologies of the human nervous system, that include destructive and malformation consequences such as development of ocular and fetal brain lesions, microcephaly in neonates, and Guillain–Barré syndrome (GBS) in adults. These neurological disorders of both central and peripheral nervous systems are thought to be associated to the neurotropic properties of the virus that has ability to infect neural stem cells as well as peripheral neurons, a hallmark of its pathogenicity. The presence of autoantibodies against gangliosides plays a pivotal role in the etiogenesis of GBS and a variety of neurological disorders. Gangliosides are a class of galactose-containing cerebrosides mainly expressed in nervous system tissues playing a critical role in the physiology of neural cells and neurogenesis. Herein, our findings indicate that patients at acute phase of ZIKV infection without any neurological signs show increased levels of IgG autoantibody against GD3 gangliosides, a class of glycolipid found to be highly expressed in neural stem cell acting in the maintenance of their self-renewal cellular capacity. It is possible that a pathological threshold of these antibodies is only acquired in secondary or subsequent infections. In the light of these evidences, we propose that the target of GD3 by autoimmune responses may possibly has an effect in the neuropathy and neurogenesis disorder seen during ZIKV infection.

Role of Cytokine-Induced Glycosylation Changes in Regulating Cell Interactions and Cell Signaling in Inflammatory Diseases and Cancer

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 number of diseases such as cancer and chronic inflammation. In that context, pro-inflammatory cytokines have been shown to modulate cell surface glycosylation by regulating the expression of glycosyltransferases involved in the biosynthesis of carbohydrate chains. These changes in cell surface glycosylation are also known to regulate cell signaling and could contribute to disease pathogenesis. This review summarizes our current knowledge of the glycosylation changes induced by pro-inflammatory cytokines, with a particular focus on cancer and cystic fibrosis, and their consequences on cell interactions and signaling.

The role of IL-15 in central nervous system disorders

IL-15 is a proinflammatory cytokine. It is produced by activated blood monocytes, macrophages, dendritic cells, and activated glial cells. It promotes T-cell proliferation, induction of cytolytic effector cells including natural killer and cytotoxic cells and stimulates B-cell to proliferate and secrete immunoglobulins. Little information is available on the exact role of IL-15 in the neurological diseases. Microglial cells are the main regulators of both innate and adaptive immune responses in the central nervous system (CNS). IL-15 may be involved in the inflammatory reactions and microglial activation of some common CNS disorders such as multiple sclerosis, Alzheimer's and Parkinson's disease, but its exact role in their pathogenesis is not clear.

Inhibitors of Glioma Growth that Reveal the Tumour to the Immune System

Treated glioblastoma patients survive from 6 to 14 months. In the first part of this review, we describe glioma origins, cancer stem cells and the genomic alterations that generate dysregulated cell division, with enhanced proliferation and diverse response to radiation and chemotherapy. We review the pathways that mediate tumour cell proliferation, neo-angiogenesis, tumor cell invasion, as well as necrotic and apoptotic cell death. Then, we examine the ability of gliomas to evade and suppress the host immune system, exhibited at the levels of antigen recognition and immune activation, limiting the effective signaling between glioma and host immune cells.The second part of the review presents current therapies and their drawbacks. This is followed by a summary of the work of our laboratory during the past 20 years, on oligosaccharide and glycosphingolipid inhibitors of astroblast and astrocytoma division. Neurostatins, the O-acetylated forms of gangliosides GD1b and GT1b naturally present in mammalian brain, are cytostatic for normal astroblasts, but cytotoxic for rat C6 glioma cells and human astrocytoma grades III and IV, with ID50 values ranging from 200 to 450 nM. The inhibitors do not affect neurons or fibroblasts up to concentrations of 4 μM or higher.At least four different neurostatin-activated, cell-mediated antitumoral processes, lead to tumor destruction: (i) inhibition of tumor neovascularization; (ii) activation of microglia; (iii) activation of natural killer (NK) cells; (iv) activation of cytotoxic lymphocytes (CTL). The enhanced antigenicity of neurostatin-treated glioma cells, could be related to their increased expression of connexin 43. Because neurostatins and their analogues show specific activity and no toxicity for normal cells, a clinical trial would be the logical next step.

Interleukin-15 regulates proliferation and self-renewal of adult neural stem cells

The role of IL-15 in the regulation of neural stem cell biology appears as a key mechanism in the control of adult neurogenesis, with direct implications for the development of pathologies with a neuroimmune component.

The impact of inflammation is crucial for the regulation of the biology of neural stem cells (NSCs). Interleukin-15 (IL-15) appears as a likely candidate for regulating neurogenesis, based on its well-known mitogenic properties. We show here that NSCs of the subventricular zone (SVZ) express IL-15, which regulates NSC proliferation, as evidenced by the study of IL-15−/− mice and the effects of acute IL-15 administration, coupled to 5-bromo-2′-deoxyuridine/5-ethynyl-2′-deoxyuridine dual-pulse labeling. Moreover, IL-15 regulates NSC differentiation, its deficiency leading to an impaired generation of neuroblasts in the SVZ–rostral migratory stream axis, recoverable through the action of exogenous IL-15. IL-15 expressed in cultured NSCs is linked to self-renewal, proliferation, and differentiation. IL-15–/– NSCs presented deficient proliferation and self-renewal, as evidenced in proliferation and colony-forming assays and the analysis of cell cycle–regulatory proteins. Moreover, IL-15–deficient NSCs were more prone to differentiate than wild-type NSCs, not affecting the cell population balance. Lack of IL-15 led to a defective activation of the JAK/STAT and ERK pathways, key for the regulation of proliferation and differentiation of NSCs. The results show that IL-15 is a key regulator of neurogenesis in the adult and is essential to understanding diseases with an inflammatory component.

Glioma growth inhibition by neurostatin and O-But GD1b

In spite of their low incidence, central nervous system tumors have elevated morbidity and mortality, being responsible for 2.3% of total cancer deaths. The ganglioside O-acetylated GD1b (O-Ac GD1b; neurostatin), present in the mammalian brain, and the semi-synthetic O-butyrylated GD1b (O-But GD1b) are potent glioma proliferation inhibitors, appearing as possible candidates for the treatment of nervous system tumors. Tumoral cell division inhibitory activity in culture correlated with growth inhibition of glioma xenotransplants in Foxn1(nu) nude mice and intracranial glioma allotransplants. Both O-Ac GD1b and O-But GD1b inhibited in vivo cell proliferation, induced cell cycle arrest, and potentiated immune cell response to the tumor. Furthermore, the increased stability of the butyrylated compound (O-But GD1b) enhanced its activity with respect to the acetylated ganglioside (neurostatin). These results are the first report of the antitumoral activity of neurostatin and a neurostatin-like compound in vivo and indicate that semi-synthetic O-acetylated and O-butyrylated gangliosides are potent antitumoral compounds that should be considered in strategies for brain tumor treatment.

Cerebral interleukin-15 shows upregulation and beneficial effects in experimental autoimmune encephalomyelitis

Interleukin (IL)-15 can cross the blood-brain barrier to act on its specific brain receptor (IL15Ralpha) and co-receptors. The important roles of neuronal IL15 and IL15Ralpha in experimental autoimmune encephalomeylitis (EAE) are suggested by the upregulation of IL15Ralpha mRNA in different regions of the brain and spinal cord, and by double-labeling immunohistochemistry showing neuronal localization of IL15 and IL15Ralpha in different neurons. Contrary to expectations, IL15 treatment lessened EAE severity. IL15 knockout mice showed heightened susceptibility to EAE with significantly higher scores that were decreased by treatment with IL15. Thus, IL15 improves this CNS autoimmune disorder as a potential therapeutic agent.

Blockade of IL-15 activity inhibits microglial activation through the NFkappaB, p38, and ERK1/2 pathways, reducing cytokine and chemokine release

Reactive glia formation is one of the hallmarks of damage to the CNS, but little information exists on the signals that direct its activation. Microglial cells are the main regulators of both innate and adaptative immune responses in the CNS. The proinflammatory cytokine IL-15 is involved in regulating the response of T and B cells, playing a key role in regulating nervous system inflammatory events. We have used a microglial culture model of inflammation induced by LPS and IFNgamma to evaluate the role of IL-15 in the proinflammatory response. Our results indicate that IL-15 is necessary for the reactive response, its deficiency (IL-15-/-) leading to the development of a defective proinflammatory response. Blockade of IL-15, both with blocking antibodies or with the ganglioside Neurostatin, inhibited the activation of the NFkappaB pathway, decreasing iNOS expression and NO production. Inhibiting IL-15 signaling also blocked the activation of the mitogen-activated protein kinase (MAPK) pathways ERK1/2 and p38. The major consequence of these inhibitory effects, analyzed using cytokine antibody arrays, was a severe decrease in the production of chemokines, cytokines and growth factors, like CCL17, CCL19, IL-12, or TIMP-1, that are essential for the development of the phenotypic changes of glial activation. In conclusion, activation of the IL-15 system seems a necessary step for the development of glial reactivity and the regulation of the physiology of glial cells. Modulating IL-15 activity opens the possibility of developing new strategies to control gliotic events upon inflammatory stimulation.

Protection of intestinal occludin tight junction protein by dietary gangliosides in lipopolysaccharide-induced acute inflammation

OBJECTIVES

Intestinal permeability and barrier function are regulated by expression of tight junction proteins. Lipopolysaccharide (LPS), tumor necrosis factor-alpha, and interleukin-1beta induce expression of nitric oxide (NO) and reduce the expression of gut tight junction proteins. The purpose of this study was to determine whether dietary gangliosides (GGs) increase the concentration of the anti-inflammatory cytokine interleukin-10 (IL-10) in response to LPS, thereby inhibiting NO production and protecting gut occludin tight junction protein from degradation.

MATERIALS AND METHODS

Rats were fed semipurified diets with (n = 16) or without (n = 16) GGs (0.1% w/w of total lipid). After 2 weeks of feeding, animals were injected with saline (n = 8/diet group) or LPS (n = 8/diet group) (IP, 3 mg mL(-1) kg(-1)). Intestinal tissue, mucosa, and blood sample were collected 6 hours post-LPS exposure. The effect of dietary GGs on production/expression of IL-10, NO, inducible NO synthase, and occludin protein was determined.

RESULTS

Dietary GGs increased IL-10 content in intestinal mucosa significantly by 32-fold (P < 0.0001) and in plasma by 2.4-fold (P < 0.001). Feeding animals a ganglioside-enriched diet decreased total NO content in intestinal mucosa and plasma by 44% and 30%, respectively, and inhibited inducible NO synthase expression following LPS exposure compared with control animals. Dietary GGs reduced the degradation of occludin tight junction protein in response to LPS.

CONCLUSIONS

Dietary GGs inhibit degradation of gut occludin tight junction protein during LPS-induced acute inflammation. Thus, dietary GGs have a role in protecting the integrity of the intestinal barrier during acute gut inflammation.

Aggravated experimental autoimmune encephalomyelitis in IL-15 knockout mice

IL-15 initially identified as a T proliferating cytokine has several structural and biological similarities with IL-2 and has been associated with a number of autoimmune diseases. Because of the scarcity of information available on the role of IL-15 in MS pathogenesis, we have investigated how the absence of IL-15 affected the development of experimental autoimmune encephalomyelitis, a mouse model of MS. Following immunization of IL-15(-/-) and C57BL/6 mice with MOG(35-55), we observed a more severe neurological impairment in the IL-15 knockout mice than in the wild-type group. The enhanced disease severity in IL-15(-/-) mice was associated with greater demyelination in the spinal cord, increased immune cell infiltration and inflammation. These events may be related to the higher CD4/CD8 ratio and the almost absent NK cell activity, congenital immune features of IL-15KO mice. Moreover, we found that the fractalkine receptor CX3CR1 was overexpressed in the spinal cord of IL-15(-/-) mice, mainly localized on infiltrating CD8(+) T cells. How these findings are contributing to the aggravated EAE development in IL-15 KO mice remain unclear and need to be further investigated.

Role of IL-15 in spinal cord and sciatic nerve after chronic constriction injury: regulation of macrophage and T-cell infiltration

The release of inflammatory mediators from immune and glial cells either in the peripheral or CNS may have an important role in the development of physiopathological processes such as neuropathic pain. Microglial, then astrocytic activation in the spinal cord, lead to chronic inflammation, alteration of neuronal physiology and neuropathic pain. Standard experimental models of neuropathic pain include an important peripheral inflammatory component, which involves prominent immune cell activation and infiltration. Among potential immunomodulators, the T-cell cytokine interleukin-15 (IL-15) has a key role in regulating immune cell activation and glial reactivity after CNS injury. Here we show, using the model of chronic constriction of the sciatic nerve (CCI), that IL-15 is essential for the development of the early inflammatory events in the spinal cord after a peripheral lesion that generates neuropathic pain. IL-15 expression in the spinal cord was identified in both astroglial and microglial cells and was present during the initial gliotic and inflammatory (NFkappaB) response to injury. The expression of IL-15 was also identified as a cue for macrophage and T-cell activation and infiltration in the sciatic nerve, as shown by intraneural injection of the cytokine and activity blockage approaches. We conclude that the regulation of IL-15 and hence the initial events following its expression after peripheral nerve injury could have a future therapeutic potential in the reduction of neuroinflammation.

Important differences between human and mouse APOE gene promoters: limitation of mouse APOE model in studying Alzheimer's disease

Apolipoprotein E (ApoE), encoded by the apolipoprotein E gene (APOE), plays an important role in the pathogenesis of Alzheimer's disease (AD). The APOE epsilon4 variant is strongly associated with AD. APOE promoter polymorphisms have also been reported to associate with higher AD risk. Mouse models of APOE expression have long been used to study the pathogenesis of AD. Elucidating the role of the APOE gene in AD requires understanding of how its regulation differs between mouse and human APOE genes, and how the differences influence AD risk. We compared the structure and function of both the human APOE gene promoter (hAPOEP) and mouse APOE gene promoter (mAPOEP) regions. Homology is less than 40% at 180 bp or more upstream of the two species' transcription start site (TSS, +1). Functional analysis revealed both similarities and important differences between the two sequences, significantly affected by human versus rodent cell line origin. We likewise probed nuclear extracts from several cell lines of different origins (astrocytic, glial, and neuronal) and mouse brain with specific hAPOEP and mAPOEP fragments. Each fragment shared DNA-protein interactions with the other but, notably, also bound distinct factors, demonstrated by gel shift and southwestern analyses. We determined possible identities for these distinct factors. These results suggest that regulation of mouse and human APOE genes may be sufficiently unique to justify the use of both the human APOE promoter sequence in transgenic rodent models and non-rodent AD models for studying factors involved in AD pathogenesis.