Lack of apolipoprotein-E exacerbates experimental allergic encephalomyelitis

Myelin repair in Alzheimer's disease: a review of biological pathways and potential therapeutics

This literature review investigates the significant overlap between myelin-repair signaling pathways and pathways known to contribute to hallmark pathologies of Alzheimer's disease (AD). We discuss previously investigated therapeutic targets of amyloid, tau, and ApoE, as well as other potential therapeutic targets that have been empirically shown to contribute to both remyelination and progression of AD. Current evidence shows that there are multiple AD-relevant pathways which overlap significantly with remyelination and myelin repair through the encouragement of oligodendrocyte proliferation, maturation, and myelin production. There is a present need for a single, cohesive model of myelin homeostasis in AD. While determining a causative pathway is beyond the scope of this review, it may be possible to investigate the pathological overlap of myelin repair and AD through therapeutic approaches.

Lowering blood cholesterol does not affect neuroinflammation in experimental autoimmune encephalomyelitis

Background

Multiple sclerosis (MS) is a chronic disabling disease of the central nervous system (CNS) commonly affecting young adults. There is increasing evidence that environmental factors are important in the development and course of MS. The metabolic syndrome (MetS) which comprises dyslipidemia has been associated with a worse outcome in MS disease. Furthermore, the lipid-lowering drug class of statins has been proposed to improve MS disease course. However, cholesterol is also rate-limiting for myelin biogenesis and promotes remyelination in MS animal models. Thus, the impact of circulating blood cholesterol levels during the disease remains debated and controversial.

Methods

We assessed the role of circulating cholesterol on the murine model of MS, the experimental autoimmune encephalomyelitis (EAE) disease using two different approaches: (1) the mouse model of familial hypercholesterolemia induced by low-density lipoprotein receptor (LDLr) deficiency, and (2) the use of the monoclonal anti-PCSK9 neutralizing antibody alirocumab, which reduces LDLr degradation and consequently lowers blood levels of cholesterol.

Results

Elevated blood cholesterol levels induced by LDLr deficiency did not worsen clinical symptoms of mice during EAE. In addition, we observed that the anti-PCSK9 antibody alirocumab did not influence EAE disease course, nor modulate the immune response in EAE.

Conclusions

These findings suggest that blood cholesterol level has no direct role in neuro-inflammatory diseases and that the previously shown protective effects of statins in MS are not related to circulating cholesterol.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02409-x.

Co-Ultramicronized Palmitoylethanolamide/Luteolin Facilitates the Development of Differentiating and Undifferentiated Rat Oligodendrocyte Progenitor Cells

Oligodendrocytes, the myelin-producing cells of the central nervous system (CNS), have limited capability to bring about repair in chronic CNS neuroinflammatory demyelinating disorders such as multiple sclerosis (MS). MS lesions are characterized by a compromised pool of undifferentiated oligodendrocyte progenitor cells (OPCs) unable to mature into myelin-producing oligodendrocytes. An attractive strategy may be to replace lost OLs and/or promote their maturation. N-palmitoylethanolamine (PEA) is an endogenous fatty acid amide signaling molecule with anti-inflammatory and neuroprotective actions. Recent studies show a co-ultramicronized composite of PEA and the flavonoid luteolin (co-ultraPEALut) to be more efficacious than PEA in improving outcome in CNS injury models. Here, we examined the effects of co-ultraPEALut on development of OPCs from newborn rat cortex cultured under conditions favoring either differentiation (Sato medium) or proliferation (fibroblast growth factor-2 and platelet-derived growth factor (PDGF)-AA-supplemented serum-free medium ("SFM")). OPCs in SFM displayed high expression of PDGF receptor alpha gene and the proliferation marker Ki-67. In Sato medium, in contrast, OPCs showed rapid decreases in PDGF receptor alpha and Ki-67 expression with a concomitant rise in myelin basic protein (MBP) expression. In these conditions, co-ultraPEALut (10 μM) enhanced OPC morphological complexity and expression of MBP and the transcription factor TCF7l2. Surprisingly, co-ultraPEALut also up-regulated MBP mRNA expression in OPCs in SFM. MBP expression in all cases was sensitive to inhibition of mammalian target of rapamycin. Within the context of strategies to promote endogenous remyelination in MS which focus on enhancing long-term survival of OPCs and stimulating their differentiation into remyelinating oligodendrocytes, co-ultraPEALut may represent a novel pharmacological approach.

Myeloid apolipoprotein E controls dendritic cell antigen presentation and T cell activation

Cholesterol homeostasis has a pivotal function in regulating immune cells. Here we show that apolipoprotein E (apoE) deficiency leads to the accumulation of cholesterol in the cell membrane of dendritic cells (DC), resulting in enhanced MHC-II-dependent antigen presentation and CD4⁺ T-cell activation. Results from WT and apoE KO bone marrow chimera suggest that apoE from cells of hematopoietic origin has immunomodulatory functions, regardless of the onset of hypercholesterolemia. Humans expressing apoE4 isoform (ε4/3–ε4/4) have increased circulating levels of activated T cells compared to those expressing WT apoE3 (ε3/3) or apoE2 isoform (ε2/3–ε2/2). This increase is caused by enhanced antigen-presentation by apoE4-expressing DCs, and is reversed when these DCs are incubated with serum containing WT apoE3. In summary, our study identifies myeloid-produced apoE as a key physiological modulator of DC antigen presentation function, paving the way for further explorations of apoE as a tool to improve the management of immune diseases.

Cholesterol homeostasis can modulate immunity via multiple pathways. Here the authors show that apolipoprotein E, an important regulator of cholesterol, produced by myeloid cells can regulate T cell activation by controlling the antigen presentation activity of dendritic cells in both humans and mice.

Low-Density Lipoprotein Receptor Deficiency Attenuates Neuroinflammation through the Induction of Apolipoprotein E

Objective

We aimed to determine the role of the low-density lipoprotein receptor (LDLr) in neuroinflammation by inducing experimental autoimmune encephalomyelitis (EAE) in ldlr knock out mice.

Methods

MOG_35-55 induced EAE in male and female ldlr^-/- mice was assessed clinically and histopathologically. Expression of inflammatory mediators and apolipoprotein E (apoE) was investigated by qPCR. Changes in protein levels of apoE and tumor necrosis factor alpha (TNFα) were validated by western blot and ELISA, respectively.

Results

Ldlr^-/--attenuated EAE disease severity in female, but not in male, EAE mice marked by a reduced proinflammatory cytokine production in the central nervous system of female ldlr^-/- mice. Macrophages from female ldlr^-/- mice showed a similar decrease in proinflammatory mediators, an impaired capacity to phagocytose myelin and enhanced secretion of the anti-inflammatory apoE. Interestingly, apoE/ldlr double knock out abrogated the beneficial effect of ldlr depletion in EAE.

Conclusion

Collectively, we show that ldlr^-/- reduces EAE disease severity in female but not in male EAE mice, and that this can be explained by increased levels of apoE in female ldlr^-/- mice. Although the reason for the observed sexual dimorphism remains unclear, our findings show that LDLr and associated apoE levels are involved in neuroinflammatory processes.

Apolipoprotein E as a novel therapeutic neuroprotection target after traumatic spinal cord injury

Apolipoprotein E (apoE), a plasma lipoprotein well known for its important role in lipid and cholesterol metabolism, has also been implicated in many neurological diseases. In this study, we examined the effect of apoE on the pathophysiology of traumatic spinal cord injury (SCI). ApoE-deficient mutant (apoE^-/-) and wild-type mice received a T9 moderate contusion SCI and were evaluated using histological and behavioral analyses after injury. At 3days after injury, the permeability of spinal cord-blood-barrier, measured by extravasation of Evans blue dye, was significantly increased in apoE^-/- mice compared to wild type. The inflammation and spared white matter was also significantly increased and decreased, respectively, in apoE^-/- mice compared to the wild type ones. The apoptosis of both neurons and oligodendrocytes was also significantly increased in apoE^-/- mice. At 42days after injury, the inflammation was still robust in the injured spinal cord in apoE^-/- but not wild type mice. CD45+ leukocytes from peripheral blood persisted in the injured spinal cord of apoE^-/- mice. The spared white matter was significantly decreased in apoE^-/- mice compared to wild type ones. Locomotor function was significantly decreased in apoE^-/- mice compared to wild type ones from week 1 to week 8 after contusion. Treatment of exogenous apoE mimetic peptides partially restored the permeability of spinal cord-blood-barrier in apoE^-/- mice after SCI. Importantly, the exogenous apoE peptides decreased inflammation, increased spared white matter and promoted locomotor recovery in apoE^-/- mice after SCI. Our results indicate that endogenous apoE plays important roles in maintaining the spinal cord-blood-barrier and decreasing inflammation and spinal cord tissue loss after SCI, suggesting its important neuroprotective function after SCI. Our results further suggest that exogenous apoE mimetic peptides could be a novel and promising neuroprotective reagent for SCI.

Expression profiles of cholesterol metabolism-related genes are altered during development of experimental autoimmune encephalomyelitis in the rat spinal cord

Increased evidence suggests that dysregulation of cholesterol metabolism may be a key event contributing to progression of multiple sclerosis (MS). Using an experimental autoimmune encephalomyelitis (EAE) model of MS we revealed specific changes in the mRNA and protein expression of key molecules involved in the maintaining of cholesterol homeostasis in the rat spinal cord: 3-hydroxy-3-methylglutaryl-coenzyme-A reductase (HMGCR), apolipoprotein E (ApoE) and cholesterol 24-hydroxylase (CYP46A1) during the course of disease. The presence of myelin lipid debris was seen only at the peak of EAE in demyelination loci being efficiently removed during the recovery period. Since CYP46A1 is responsible for removal of cholesterol excess, we performed a detailed profiling of CYP46A1 expression and revealed regional and temporal specificities in its distribution. Double immunofluorescence staining demonstrated CYP46A1 localization with neurons, infiltrated macrophages, microglia and astrocytes in the areas of demyelination, suggesting that these cells play a role in cholesterol turnover in EAE. We propose that alterations in the regulation of cholesterol metabolism at the onset and peak of EAE may add to the progression of disease, while during the recovery period may have beneficial effects contributing to the regeneration of myelin sheath and restoration of neuronal function.

Investigation of sex-specific effects of apolipoprotein E on severity of EAE and MS

Background

Despite pleiotropic immunomodulatory effects of apolipoprotein E (apoE) in vitro, its effects on the clinical course of experimental autoimmune encephalomyelitis (EAE) and multiple sclerosis (MS) are still controversial. As sex hormones modify immunomodulatory apoE functions, they may explain contentious findings. This study aimed to investigate sex-specific effects of apoE on disease course of EAE and MS.

Methods

MOG_35-55 induced EAE in female and male apoE-deficient mice was assessed clinically and histopathologically. apoE expression was investigated by qPCR. The association of the MS severity score (MSSS) and APOE rs429358 and rs7412 was assessed across 3237 MS patients using linear regression analyses.

Results

EAE disease course was slightly attenuated in male apoE-deficient (apoE^−/−) mice compared to wildtype mice (cumulative median score: apoE^−/− = 2 [IQR 0.0–4.5]; wildtype = 4 [IQR 1.0–5.0]; n = 10 each group, p = 0.0002). In contrast, EAE was more severe in female apoE^−/− mice compared to wildtype mice (cumulative median score: apoE^−/− = 3 [IQR 2.0–4.5]; wildtype = 3 [IQR 0.0–4.0]; n = 10, p = 0.003). In wildtype animals, apoE expression during the chronic EAE phase was increased in both females and males (in comparison to naïve animals; p < 0.001). However, in MS, we did not observe a significant association between MSSS and rs429358 or rs7412, neither in the overall analyses nor upon stratification for sex.

Conclusions

apoE exerts moderate sex-specific effects on EAE severity. However, the results in the apoE knock-out model are not comparable to effects of polymorphic variants in the human APOE gene, thus pinpointing the challenge of translating findings from the EAE model to the human disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0429-y) contains supplementary material, which is available to authorized users.

Genetics ignite focus on microglial inflammation in Alzheimer's disease

In the past five years, a series of large-scale genetic studies have revealed novel risk factors for Alzheimer’s disease (AD). Analyses of these risk factors have focused attention upon the role of immune processes in AD, specifically microglial function. In this review, we discuss interpretation of genetic studies.  We then focus upon six genes implicated by AD genetics that impact microglial function: TREM2, CD33, CR1, ABCA7, SHIP1, and APOE. We review the literature regarding the biological functions of these six proteins and their putative role in AD pathogenesis. We then present a model for how these factors may interact to modulate microglial function in AD.

"Disease modifying nutricals" for multiple sclerosis

The association between vitamin D and multiple sclerosis has (re)-opened new interest in nutrition and natural compounds in the prevention and treatment of this neuroinflammatory disease. The dietary amount and type of fat, probiotics and biologicals, salmon proteoglycans, phytoestrogens and protease inhibitor of soy, sodium chloride and trace elements, and fat soluble vitamins including D, A and E were all considered as disease-modifying nutraceuticals. Studies in experimental autoimmune encephalomyelitis mice suggest that poly-unsaturated fatty acids and their 'inflammation-resolving' metabolites and the gut microflora may reduce auto-aggressive immune cells and reduce progression or risk of relapse, and infection with whipworm eggs may positively change the gut-brain communication. Encouraged by the recent interest in multiple sclerosis-nutrition nature's pharmacy has been searched for novel compounds with anti-inflammatory, immune-modifying and antioxidative properties, the most interesting being the scorpion toxins that inhibit specific potassium channels of T cells and antioxidative compounds including the green tea flavonoid epigallocatechin-3-gallate, curcumin and the mustard oil glycoside from e.g. broccoli and sulforaphane. They mostly also inhibit pro-inflammatory signaling through NF-κB or toll-like receptors and stabilize the blood brain barrier. Disease modifying functions may also complement analgesic and anti-spastic effects of cannabis, its constituents, and of 'endocannabinoid enhancing' drugs or nutricals like inhibitors of fatty acid amide hydrolase. Nutricals will not solve multiple sclerosis therapeutic challenges but possibly support pharmacological interventions or unearth novel structures.

Apolipoprotein E mediation of neuro-inflammation in a murine model of multiple sclerosis

Apolipoprotein E (ApoE) functions as a ligand in receptor-mediated endocytosis of lipoprotein particles and has been demonstrated to play a role in antigen presentation. To explore the contribution of ApoE during autoimmune central nervous system (CNS) demyelination, we examined the clinical, cellular immune function, and pathologic consequences of experimental autoimmune encephalomyelitis (EAE) induction in ApoE knockout (ApoE(-/-)) mice. We observed reduced clinical severity of EAE in ApoE(-/-) mice in comparison to WT mice that was concomitant with an early reduction of dendritic cells (DCs) followed by a reduction of additional innate cells in the spinal cord at the peak of disease without any differences in axonal damage. While T cell priming was enhanced in ApoE(-/-) mice, reduced severity of EAE was also observed in ApoE(-/-) recipients of encephalitogenic wild type T cells. Expression of ApoE during EAE was elevated within the CNS of wild type mice, particularly by innate cells such as DCs. Overall, ApoE promotes clinical EAE, likely by mediation of inflammation localized within the CNS.

Toward biomarkers in multiple sclerosis: new advances

Multiple sclerosis is an autoimmune disease that commonly affects young adults. If initially characterized by acute relapses, it is later followed by only incomplete remission. Over years, progressive disability and irreversible deficit lead to chronic neurological deficits in the majority of patients. The clinical course is protracted and unpredictable, and no biological marker is useful in predicting the evolution of autoaggression and disability. It is difficult to diagnose and to monitor disease progression after the initial symptoms or even during the major clinical manifestations, and it is difficult to treat. In this review, the authors report recent advances in the field, focusing on the search of new antigens as a marker of the disease, in their relevance to the pathophysiology and diagnosis of the disease.

Amyloid fibrils composed of hexameric peptides attenuate neuroinflammation

The amyloid-forming proteins tau, αB crystallin, and amyloid P protein are all found in lesions of multiple sclerosis (MS). Our previous work established that amyloidogenic peptides from the small heat shock protein αB crystallin (HspB5) and from amyloid β fibrils, characteristic of Alzheimer's disease, were therapeutic in experimental autoimmune encephalomyelitis (EAE), reflecting aspects of the pathology of MS. To understand the molecular basis for the therapeutic effect, we showed a set of amyloidogenic peptides composed of six amino acids, including those from tau, amyloid β A4, major prion protein (PrP), HspB5, amylin, serum amyloid P, and insulin B chain, to be anti-inflammatory and capable of reducing serological levels of interleukin-6 and attenuating paralysis in EAE. The chaperone function of the fibrils correlates with the therapeutic outcome. Fibrils composed of tau 623-628 precipitated 49 plasma proteins, including apolipoprotein B-100, clusterin, transthyretin, and complement C3, supporting the hypothesis that the fibrils are active biological agents. Amyloid fibrils thus may provide benefit in MS and other neuroinflammatory disorders.

Apolipoprotein E and its mimetic peptide suppress Th1 and Th17 responses in experimental autoimmune encephalomyelitis

Apolipoprotein E (apoE) has been detected to possess anti-inflammatory properties that can contribute to protection against experimental autoimmune encephalomyelitis (EAE). However, its impact on Th1 and Th17 responses in EAE is unclear. In this study, we induced EAE in apoE-/- mice and wild-type mice. We observed that the absence of apoE resulted in the increased proportion of Th1 and Th17 cells in the spleens and brains, as well as up-regulated expressions of proinflammatory cytokines (IL-17, IFN-γ, TNF-α, IL-12, IL-1β and IL-6) and transcription factors (RORγt and T-bet) in the CNS. ApoE-/- mice also showed the increased release of proinflammatory cytokines by macrophages in vitro. In addition, we used a mimetic peptide of apoE, which mimic the functions of apoE except for lipid transport. ApoE mimetic peptide could reverse the above negative effect in EAE. Thus, apoE can modulate Th1 and Th17 responses, likely through its inhibitory effect on the secretion of cytokines by macrophages. Our result also suggests that apoE mimetic peptide might be developed into a therapeutic agent for multiple sclerosis.

Apolipoprotein E Mimetic Promotes Functional and Histological Recovery in Lysolecithin-Induced Spinal Cord Demyelination in Mice

Objective

Considering demyelination is the pathological hallmark of multiple sclerosis (MS), reducing demyelination and/or promoting remyelination is a practical therapeutic strategy to improve functional recovery for MS. An apolipoprotein E (apoE)-mimetic peptide COG112 has previously demonstrated therapeutic efficacy on functional and histological recovery in a mouse experimental autoimmune encephalomyelitis (EAE) model of human MS. In the current study, we further investigated whether COG112 promotes remyelination and improves functional recovery in lysolecithin induced focal demyelination in the white matter of spinal cord in mice.

Methods

A focal demyelination model was created by stereotaxically injecting lysolecithin into the bilateral ventrolateral funiculus (VLF) of T8 and T9 mouse spinal cords. Immediately after lysolecithin injection mice were treated with COG112, prefix peptide control or vehicle control for 21 days. The locomotor function of the mice was measured by the beam walking test and Basso Mouse Scale (BMS) assessment. The nerve transmission of the VLF of mice was assessed in vivo by transcranial magnetic motor evoked potentials (tcMMEPs). The histological changes were also examined by by eriochrome cyanine staining, immunohistochemistry staining and electron microscopy (EM) method.

Results

The area of demyelination in the spinal cord was significantly reduced in the COG112 group. EM examination showed that treatment with COG112 increased the thickness of myelin sheaths and the numbers of surviving axons in the lesion epicenter. Locomotor function was improved in COG112 treated animals when measured by the beam walking test and BMS assessment compared to controls. TcMMEPs also demonstrated the COG112-mediated enhancement of amplitude of evoked responses.

Conclusion

The apoE-mimetic COG112 demonstrates a favorable combination of activities in suppressing inflammatory response, mitigating demyelination and in promoting remyelination and associated functional recovery in animal model of CNS demyelination. These data support that apoE-mimetic strategy may represent a promising therapy for MS and other demyelination disorders.

Paradoxical effects of apolipoprotein E on cognitive function and clinical progression in mice with experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an inflammatory demyelinating disease characterized by sensory, motor, and cognitive impairments. Apolipoprotein E (apoE) plays an important role in cholesterol and lipid metabolism in the brain and in susceptibility to cognitive impairment and pathology following brain injury. Studies in mice with a mild form of experimental autoimmune encephalomyelitis (EAE), an MS animal model, support only protective roles for apoE in MS. We examined behavioral and cognitive changes prior to onset of clinical disease and the onset and progression of a more severe form of EAE in female Apoe(-/-) and C57Bl/6 wild-type mice. Apoe(-/-) mice had a later day of onset, a later day of peak symptoms and disease severity, and a lower cumulative disease index compared to wild type mice. Apoe(-/-) mice also showed decreased CD4+ cell invasion following EAE induction compared to wild type mice, and less spinal cord demyelination at 17 but not 30 days following EAE induction. In contrast, EAE-challenged Apoe(-/-) mice showed reduced exploratory activity, rotorod performance, and impaired contextual fear conditioning compared to wild type animals. These data indicate paradoxical effects of apoE on EAE-induced behavioral and cognitive changes and the onset and progression of clinical disease.

The immune-modulatory role of apolipoprotein E with emphasis on multiple sclerosis and experimental autoimmune encephalomyelitis

Apolipoprotein E (apoE) is a 34.2 kDa glycoprotein characterized by its wide tissue distribution and multiple functions. The nonlipid-related properties of apoE include modulating inflammation and oxidation, suppressing T cell proliferation, regulating macrophage functions, and facilitating lipid antigen presentation by CD1 molecules to natural killer T (NKT) cells, and so forth. Increasing studies have revealed that APOE ε allele might be associated with multiple sclerosis (MS), although evidence is still not sufficient enough. In this review, we summarized the current progress of the immunomodulatory functions of apoE, with special focus on the association of APOE ε allele with the clinical features of MS and of its animal model experimental autoimmune encephalomyelitis (EAE).

Impact of apolipoprotein E (ApoE) polymorphism on brain ApoE levels

Inheritance of the apoE4 allele (epsilon4) increases the risk of developing Alzheimer's disease; however, the mechanisms underlying this association remain elusive. Recent data suggest that inheritance of epsilon4 may lead to reduced apoE protein levels in the CNS. We therefore examined apoE protein levels in the brains, CSF and plasma of epsilon2/2, epsilon3/3, and epsilon4/4 targeted replacement mice. These apoE mice showed a genotype-dependent decrease in apoE levels; epsilon2/2 >epsilon3/3 >epsilon4/4. Next, we sought to examine the relative contributions of apoE4 and apoE3 in the epsilon3/4 mouse brains. ApoE4 represented 30-40% of the total apoE. Moreover, the absolute amount of apoE3 per allele was similar between epsilon3/3 and epsilon3/4 mice, implying that the reduced levels of total apoE in epsilon3/4 mice can be explained by the reduction in apoE4 levels. In culture medium from epsilon3/4 human astrocytoma or epsilon3/3, epsilon4/4 and epsilon3/4 primary astrocytes, apoE4 levels were consistently lower than apoE3. Secreted cholesterol levels were also lower from epsilon4/4 astrocytes. Pulse-chase experiments showed an enhanced degradation and reduced half-life of newly synthesized apoE4 compared with apoE3. Together, these data suggest that astrocytes preferentially degrade apoE4, leading to reduced apoE4 secretion and ultimately to reduced brain apoE levels. Moreover, the genotype-dependent decrease in CNS apoE levels, mirror the relative risk of developing AD, and suggest that low levels of total apoE exhibited by epsilon4 carriers may directly contribute to the disease progression, perhaps by reducing the capacity of apoE to promote synaptic repair and/or Abeta clearance.

Identification of differentially expressed proteins in experimental autoimmune encephalomyelitis (EAE) by proteomic analysis of the spinal cord

The present study used isobaric tags for relative and absolute quantitation (iTRAQ) to identify novel targets in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. The expression of 41 proteins was significantly altered in the inflamed spinal cord. Twenty of these are implicated in EAE for the first time and many have previously been shown to play a role in antigen processing, inflammation, neuroprotection, or neurodegeneration.

Apolipoprotein E deficiency enhances the antigen-presenting capacity of Schwann cells

Apolipoprotein E (apoE) has immunomodulatory properties and has been implicated in the pathogenic mechanism of autoimmune diseases. Previously, the authors found that apoE deficiency increased the susceptibility to experimental autoimmune neuritis (EAN), an animal model for human Guillain-Barré syndrome. To further elucidate the mechanism behind apoE deficiency exacerbating EAN, the authors investigated the role of major target and important antigen-presenting cells of the peripheral nerve system, Schwann cells (SCs), in apoE knockout mice. Treatment of apoE deficient SCs with recombinant mouse interferon-gamma and lipopolysaccharide resulted in higher MHC-II and CD40 expression as compared with normal SCs derived from wild-type mice. The increased MHC-II and CD40 expression on SCs was accompanied by lower levels of intracellular IL-6 production within SCs of apoE deficiency, which is confirmed by the neutralization with anti IL-6 antibody. The increased antigen-presenting capacity of apoE deficient SCs was further explored by enhancement of T cell proliferation co-cultured with P0 peptide 180-199 specific T cells derived from EAN mice immunized with the P0 peptide. In conclusion, apoE may protect mice from EAN and probably also from chronic inflammatory demyelinating polyneuropathy by affecting the antigen-presenting function of SCs via influence of IL-6 production.

Multifunctional regulators of cell growth are differentially expressed in anergic murine B cells

Defective anergy is a major cause of failed tolerance and is amenable to therapeutic manipulation. To better define the molecular basis of anergy in B cells tolerized by matrix self-antigen, we used complementary approaches of representational difference analysis (RDA) and microarray to identify genes differentially transcribed in anergic as compared to non-tolerant B cells isolated from a well-characterized murine autoantibody transgenic model. Forty RDA clones representing 16 genes were isolated from receptor-stimulated B cells and independently confirmed as differentially expressed in tolerant cells using custom microarray, dot blotting and/or quantitative PCR. Differential expression was conserved in tolerant cells from two different transgenic founder lineages and from two genetically disparate backgrounds. Prominent among recovered gene fragments were genes encoding multifunctional proteins not previously implicated in B cell biology, but with roles in biologic processes fundamental to the tolerance phenotype, including cell growth, proliferation and differentiation. RDA also identified a novel transcript not previously reported in nucleic acid databases. To further explore dependence on receptor stimulation and to identify additional genes, commercial oligonucleotide arrays were probed with labeled B cell transcripts and analyzed for genes differentially expressed in resting as well as stimulated cells and in both B6 and MRL mouse strains. Arrays identified differential expression of a subset of RDA genes as well as 46 additional genes, including subsets engaged in signal transduction, transcriptional regulation, cell growth and apoptosis. Immunoblotting confirmed differential protein expression for galectin-3 and galectin-1, two interactive members of the galectin family, suggesting a novel role for galectins as regulators of immune tolerance.

Role of apolipoproteins in gammadelta and NKT cell-mediated innate immunity

Recent findings reveal unanticipated connections between the fields of lipid metabolism and immunology. They concern gammadelta and NKT cells, nonconventional T cell populations that do not recognize protein antigens and are involved in immunity against cancer, defense against infections, or in regulation of classical immune responses. In this review, we summarize data linking perturbations of apolipoprotein levels and nonconventional T cells with inflammatory processes such as autoimmune diseases or atherosclerosis. We integrate and discuss recent findings on the implication of apolipoproteins in antigen recognition by gammadelta and NKT cells, with emphasis on apolipoproteins A-I and E. These findings also provide indications that apolipoproteins influence antitumor immunosurveillance.

Apolipoprotein E-derived peptides ameliorate clinical disability and inflammatory infiltrates into the spinal cord in a murine model of multiple sclerosis

Apolipoprotein E (apoE), well known to play a role in lipid transport and cholesterol metabolism, also exerts anti-inflammatory and neuroprotective effects in the central nervous system. Recent clinical and genetic studies display an association between apoE genotype (APOE) and the progression and severity of multiple sclerosis, raising the possibility that modulation of apoE may be a novel treatment for multiple sclerosis. Using a murine experimental autoimmune encephalomyelitis (EAE) model of human multiple sclerosis, we found that a peptidomimetic of apoE protein, COG133, substantially reduces the clinical symptoms of EAE and promotes remission from the disability when administered before or after onset of disease. Most notably, fusion of COG133 to a protein transduction domain creates COG112, a modified apoE-mimetic peptide with significantly enhanced anti-inflammatory bioactivities in vitro, and improved therapeutic effects on EAE in vivo, which renders a nearly full remission from the disability. Histopathological analysis showed that COG112 and COG133 attenuated demyelination and significantly diminished the number of peripheral cells infiltrating into the spinal cord. ApoE mimetics also interfered with several mechanisms relevant to the pathogenesis of EAE and multiple sclerosis, including activation of macrophages, subsequent production of nitric oxide and inflammatory cytokines, and lymphocyte proliferation. These data suggest that apoE mimetics represent a multidimensional therapeutic for multiple sclerosis capable of inhibiting the inflammatory cascade, modulating immune cell function, and reducing clinical signs, which may have novel utility for the treatment of inflammatory autoimmune diseases.

Allelic association of sequence variants in the herpes virus entry mediator-B gene (PVRL2) with the severity of multiple sclerosis

Discrepant findings have been reported regarding an association of the apolipoprotein E (APOE) gene with the clinical course of multiple sclerosis (MS). To resolve these discrepancies, we examined common sequence variation in six candidate genes residing in a 380-kb genomic region surrounding and including the APOE locus for an association with MS severity. We genotyped at least three polymorphisms in each of six candidate genes in 1,540 Caucasian MS families (729 single-case and multiple-case families from the United States, 811 single-case families from the UK). By applying the quantitative transmission/disequilibrium test to a recently proposed MS severity score, the only statistically significant (P=0.003) association with MS severity was found for an intronic variant in the Herpes Virus Entry Mediator-B Gene PVRL2. Additional genotyping extended the association to a 16.6 kb block spanning intron 1 to intron 2 of the gene. Sequencing of PVRL2 failed to identify variants with an obvious functional role. In conclusion, the analysis of a very large data set suggests that genetic polymorphisms in PVRL2 may influence MS severity and supports the possibility that viral factors may contribute to the clinical course of MS, consistent with previous reports.

Serum lipoproteins: Trojan horses of the immune response?

T cells recognizing lipid antigens presented by CD1 molecules have an important role in the immune response. Several lipid antigens for CD1-restricted T cells have been identified, as have some rules of CD1 loading and CD1-restricted presentation. Little is known, however, about the delivery of lipid antigens from either extracellular compartments or CD1-negative cells to CD1-expressing antigen-presenting cells (APCs). A recent study provides evidence for a role for apolipoprotein E in binding lipid antigens and delivering them to APCs.

Serum uric acid, dehydroepiandrosterone sulphate, and apolipoprotein E genotype in benign vs. progressive multiple sclerosis

The majority of patients with multiple sclerosis (MS) experience gradual progression of disability, either as secondary progressive MS (SPMS) or primary progressive MS (PPMS). A subgroup with relapsing-remitting MS shows a benign course with little or no disease progression and minimal disability decades after the first manifestations, so called benign MS (BMS). In our search to identify factors that are associated with progression of MS, we investigated serum levels of uric acid and dehydroepiandrostenedione sulphate (DHEAS), and apolipoprotein (apo)E genotype in 28 patients with BMS, 33 with SPMS, 21 with PPMS, and 29 healthy individuals. We found no significant changes in uric acid levels and apoE genotype between the four groups. Mean DHEAS levels were lower in MS patients compared with healthy controls (P = 0.049), but there were no significant differences between the clinical subgroups of MS. In patients with SPMS and PPMS there was no correlation between progression rate and serum levels of either uric acid or DHEAS. Our results suggest that serum levels of uric acid and DHEAS, and apoE genotype do not differ between patients with a benign and progressive course of MS.

Heterogeneous expression of apolipoprotein-E by human macrophages

Apolipoprotein-E (apoE) is expressed at high levels by macrophages. In addition to its role in lipid transport, macrophage-derived apoE plays an important role in immunoregulation. Previous studies have identified macrophage subpopulations that differ substantially in their ability to synthesize specific cytokines and enzymes, however, potential heterogeneous macrophage apoE expression has not been studied. Here we examined apoE expression in human THP-1 macrophages and monocyte-derived macrophages (MDM). Using immunocytochemistry and flow cytometry methods we reveal a striking heterogeneity in macrophage apoE expression in both cell types. In phorbol-ester-differentiated THP-1 macrophages, 5% of the cells over-expressed apoE at levels more than 50-fold higher than the rest of the population. ApoE over-expressing THP-1 macrophages contained condensed/fragmented nuclei and increased levels of activated caspase-3 indicating induction of apoptosis. In MDM, 3-5% of the cells also highly over-expressed apoE, up to 50-fold higher than the rest of the population; however, this was not associated with obvious nuclear alterations. The apoE over-expressing MDM were larger, more granular, and more autofluorescent than the majority of cells and they contained numerous vesicle-like structures that appeared to be coated by apoE. Flow cytometry experiments indicated that the apoE over-expressing subpopulation of MDM were positive for CD14, CD11b/Mac-1 and CD68. These observations suggest that specific macrophage subpopulations may be important for apoE-mediated immunoregulation and clearly indicate that subpopulation heterogeneity should be taken into account when investigating macrophage apoE expression.