ApoE-Deficient Promotes Blood–Brain Barrier Disruption in Experimental Autoimmune Encephalomyelitis via Alteration of MMP-9

APOE from patient-derived astrocytic extracellular vesicles alleviates neuromyelitis optica spectrum disorder in a mouse model

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune astrocytopathy of the central nervous system, mediated by antibodies against aquaporin-4 water channel protein (AQP4-Abs), resulting in damage of astrocytes with subsequent demyelination and axonal damage. Extracellular communication through astrocyte-derived extracellular vesicles (ADEVs) has received growing interest in association with astrocytopathies. However, to what extent ADEVs contribute to NMOSD pathogenesis remains unclear. Here, through proteomic screening of patient-derived ADEVs, we observed an increase in apolipoprotein E (APOE)-rich ADEVs in patients with AQP4-Abs-positive NMOSD. Intracerebral injection of the APOE-mimetic peptide APOE130-149 attenuated microglial reactivity, neuroinflammation, and brain lesions in a mouse model of NMOSD. The protective effect of APOE in NMOSD pathogenesis was further established by the exacerbated lesion volume in APOE-deficient mice, which could be rescued by exogenous APOE administration. Genetic knockdown of the APOE receptor lipoprotein receptor-related protein 1 (LRP1) could block the restorative effects of APOE130-149 administration. The transfusion ADEVs derived from patients with NMOSD and healthy controls also alleviated astrocyte loss, reactive microgliosis, and demyelination in NMOSD mice. The slightly larger beneficial effect of patient-derived ADEVs as compared to ADEVs from healthy controls was further augmented in APOE-/- mice. These results indicate that APOE from astrocyte-derived extracellular vesicles could mediate disease-modifying astrocyte-microglia cross-talk in NMOSD.

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.

Plasma Apolipoproteins Predicting the Occurrence and Severity of Diabetic Retinopathy in Patients With Type 2 Diabetes Mellitus

OBJECTIVE

Apolipoproteins are amphipathic molecules and the major components of plasma lipoproteins. This study aims to investigate the effects of dysregulated apolipoprotein (apo) profiles and their ratios on type 2 diabetes mellitus (T2DM) and diabetic retinopathy (DR) further to test the hypothesis that altered serum level of apolipoproteins is strong biomarkers for DR.

RESEARCH DESIGN AND METHODS

This case-control study consists of 157 patients with T2DM including DM without DR, non-proliferative DR (NPDR), and proliferative DR (PDR). Fifty-eight age- and sex-matched healthy subjects were enrolled as normal controls. Blood biochemistry profile including serum levels of glucose, glycated hemoglobin (HbA1c), lipid profile [total cholesterol (TC), Triglycerides (TG), high and low-density lipoprotein (HDL-C and LDL-C)] was estimated. Apolipoproteins (apos, A-I, A-II, B, C-II, C-III, and E) was evaluated by protein chips (Luminex technology). Apolipoprotein ratios and arteriosclerosis-associated plasma indices were calculated. The Kruskal-Wallis test, independent sample t-test or Mann-Whitney U test, and multivariate regression analysis were performed to investigate the association of serum lipid biomarkers and the DR severity.

RESULTS

Serum level of apoA-I was negatively correlated with TC-(HDL-C)/HDL-C (p < 0.001), fasting glucose (p < 0.001), HbA1c (p < 0.001), and (p<0.001), while apoE, apoC-II/apoC-III, apoA-II/apoA-I were positively correlated with above traditional biomarkers (p < 0.001). Single variable logistic analysis results showed that body mass index (BMI) (p = 0.023), DM duration (p < 0.001), apoE (p < 0.001), apoC-II/apo C-III (p < 0.001), apoE/apoC-II (p < 0.001), atherogenic index (p = 0.013), fasting glucose (p < 0.001), HbA1c (p < 0.001), LPA (p = 0.001), and LDL-C/HDL-C (p = 0.031) were risk factors for the occurrence and severity of DR. Multivariate logistic regression mode showed that apoC-II/apoC-III and apoB/non-HDL-C (p < 0.001) as well as apoE/apoC-II (p = 0.001) were the independent risk factors for the occurrence and severity of DR-apopA-I and apoA-II are protective factors for DR-after controlling for the duration of DM, HbA1c, fasting glucose, and LPA.

CONCLUSIONS

apoE, apoC-II/apoC-III, apoE/apoC-II, and apoB/non-HDL-C could be used as novel biomarkers for occurrence and severity of DR, whereas apoA-I and apoA-II resulted as protective factors for DR.

Astrocytes in the Traumatic Brain Injury: the Good and the Bad

Astrocytes control many processes of the nervous system in health and disease, and respond to injury quickly. Astrocytes produce neuroprotective factors in the injured brain to clear cellular debris and to orchestrate neurorestorative processes that are beneficial for neurological recovery after traumatic brain injury (TBI). However, astrocytes also become dysregulated and produce cytotoxic mediators that hinder CNS repair by induction of neuronal dysfunction and cell death. Hence, we discuss the potential role of astrocytes in neuropathological processes such as neuroinflammation, neurogenesis, synaptogenesis and blood-brain barrier repair after TBI. Thus, an improved understanding of the dual role of astrocytes may advance our knowledge of post-brain injury recovery, and provide opportunities for the development of novel therapeutic strategies for TBI.

Exposure to traffic-generated air pollution promotes alterations in the integrity of the brain microvasculature and inflammation in female ApoE-/- mice

Traffic-generated air pollutants have been correlated with alterations in blood-brain barrier (BBB) integrity, which is associated with pathologies in the central nervous system (CNS). Much of the existing literature investigating the effects of air pollution in the CNS has predominately been reported in males, with little known regarding the effects in females. As such, this study characterized the effects of inhalation exposure to mixed vehicle emissions (MVE), as well as the presence of female sex hormones, in the CNS of female ApoE^-/- mice, which included cohorts of both ovariectomized (ov-) and ovary-intact (ov+) mice. Ov + and ov- were placed on a high-fat diet and randomly grouped to be exposed to either filtered-air (FA) or MVE (200 PM/m³: 50 μg PM/m³ gasoline engine + 150 μg PM/m³ from diesel engine emissions) for 6 h/d, 7d/wk, for 30d. MVE-exposure resulted in altered cerebral microvascular integrity and permeability, as determined by the decreased immunofluorescent expression of tight junction (TJ) proteins, occludin, and claudin-5, and increased IgG extravasation into the cerebral parenchyma, compared to FA controls, regardless of ovary status. Associated with the altered cerebral microvascular integrity, we also observed an increase in matrix metalloproteinases (MMPs) -2/9 activity in the MVE ov+, MVE ov-, and FA ov- groups, compared to FA ov+. There was also elevated expression of intracellular adhesion molecule (ICAM)-1, inflammatory interleukins (IL-1, IL-1β), and tumor necrosis factor (TNF-α) mRNA in the cerebrum of MVE ov + and MVE ov- animals. IκB kinase (IKK) subunits IKKα and IKKβ mRNA expressions were upregulated in the cerebrum of MVE ov- and FA ov- mice. Our findings indicate that MVE exposure mediates altered integrity of the cerebral microvasculature correlated with increased MMP-2/9 activity and inflammatory signaling, regardless of female hormones present.

[APOΕ gene polymorphism and markers of brain damage in the outcomes of severe traumatic brain injury in children]

OBJECTIVE

To compare apolipoprotein E (APOE) genotypes with outcomes and levels of neuromarkers in children with severe traumatic brain injury (TBI).

MATERIAL AND METHODS

APOE polymorphisms were genotyped in 69 children with severe TBI. The following markers of brain damage were identified: neuron-specific enolase (NSE), glial protein S100b, content of autoantibodies (aAB) to glutamate receptors (to the NR2 subunit of NMDA receptors), aAB to S100b and brain-derived neurotrophic factor (BDNF).

RESULTS AND CONCLUSION

There was no association between APOE 3/3, 3/4, 3/2 genotypes and outcomes assessed by the Glasgow Outcome Scale (GOS). The greatest number of favorable outcomes was noted in the group of APOE 3/3 genotype carriers (60%). The ratio of favorable outcomes to unfavorable outcomes was equal (50%:50%) in groups with APOE 3/4 and APOE 3/2 genotypes. An association between APOE polymorphism and BDNF was found: there were normal BDNF levels in the APOE 3/3 group and reduced levels in the APOE 3/2 group. The correlation between neuromarkers and GOS scores was shown for BDNF and aAB to S100b. In children with favorable TBI outcomes, normal BDNF levels and a lower level of aAB to S100b were observed. Regardless of APOE genotypes, almost all children with severe TBI (95%) showed a significant increase in aAB to glutamate receptors in the remote period and most children had an increase in aAB to S100b in the blood. This fact can be explained by the presence of cerebral hypoxia, activation of autoimmune processes and increased BBB permeability, which may be enhanced by increased NO content and intensification of oxidative processes in children with severe TBI.

Sex-dependent effect of APOE on Alzheimer's disease and other age-related neurodegenerative disorders

The importance of apolipoprotein E (APOE) in late-onset Alzheimer's disease (LOAD) has been firmly established, but the mechanisms through which it exerts its pathogenic effects remain elusive. In addition, the sex-dependent effects of APOE on LOAD risk and endophenotypes have yet to be explained. In this Review, we revisit the different aspects of APOE involvement in neurodegeneration and neurological diseases, with particular attention to sex differences in the contribution of APOE to LOAD susceptibility. We discuss the role of APOE in a broader range of age-related neurodegenerative diseases, and summarize the biological factors linking APOE to sex hormones, drawing on supportive findings from rodent models to identify major mechanistic themes underlying the exacerbation of LOAD-associated neurodegeneration and pathology in the female brain. Additionally, we list sex-by-genotype interactions identified across neurodegenerative diseases, proposing APOE variants as a shared etiology for sex differences in the manifestation of these diseases. Finally, we present recent advancements in 'omics' technologies, which provide a new platform for more in-depth investigations of how dysregulation of this gene affects the development and progression of neurodegenerative diseases. Collectively, the evidence summarized in this Review highlights the interplay between APOE and sex as a key factor in the etiology of LOAD and other age-related neurodegenerative diseases. We emphasize the importance of careful examination of sex as a contributing factor in studying the underpinning genetics of neurodegenerative diseases in general, but particularly for LOAD.

Dimethyl itaconate, an itaconate derivative, exhibits immunomodulatory effects on neuroinflammation in experimental autoimmune encephalomyelitis

Background

Inflammatory stimuli induce immunoresponsive gene 1 (IRG1) expression that in turn catalyzes the production of itaconate from the tricarboxylic acid cycle. Itaconate has recently emerged as a regulator of immune cell functions, especially in macrophages. Studies show that itaconate is required for the activation of anti-inflammatory transcription factor Nrf2 by LPS in mouse and human macrophages, and LPS-activated IRG1^-/- macrophages that lack endogenous itaconate production exhibit augmented inflammatory responses. Moreover, dimethyl itaconate (DMI), an itaconate derivative, inhibits IL-17-induced IκBς activation in keratinocytes and modulates IL-17-IκBς pathway-mediated skin inflammation in an animal model of psoriasis. Currently, the effect of itaconate on regulating macrophage functions and peripheral inflammatory immune responses is well established. However, its effect on microglia (MG) and CNS inflammatory immune responses remains unexplored. Thus, we investigated whether itaconate possesses an immunomodulatory effect on regulating MG activation and CNS inflammation in animal models of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE).

Methods

Chronic C57BL/6 EAE was induced followed by DMI treatment. The effect of DMI on disease severity, blood-brain barrier (BBB) disruption, MG activation, peripheral Th1/Th17 differentiation, and the CNS infiltration of Th1/Th17 cells in EAE was determined. Primary MG was cultured to study the effect of DMI on MG activation. Relapsing-remitting SJL/J EAE was induced to assess the therapeutic effect of DMI.

Results

Our results show DMI ameliorated disease severity in the chronic C57BL/6 EAE model. Further analysis of the cellular and molecular mechanisms revealed that DMI mitigated BBB disruption, inhibited MMP3/MMP9 production, suppressed microglia activation, inhibited peripheral Th1/Th17 differentiation, and repressed the CNS infiltration of Th1 and Th17 cells. Strikingly, DMI also exhibited a therapeutic effect on alleviating severity of relapse in the relapsing-remitting SJL/J EAE model.

Conclusions

We demonstrate that DMI suppresses neuroinflammation and ameliorates disease severity in EAE through multiple cellular and molecular mechanisms, suggesting that DMI can be developed as a novel therapeutic agent for the treatment of MS/EAE through its immunomodulatory and anti-inflammatory properties.

Dual roles of astrocytes in plasticity and reconstruction after traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of fatality and disability worldwide. Despite its high prevalence, effective treatment strategies for TBI are limited. Traumatic brain injury induces structural and functional alterations of astrocytes, the most abundant cell type in the brain. As a way of coping with the trauma, astrocytes respond in diverse mechanisms that result in reactive astrogliosis. Astrocytes are involved in the physiopathologic mechanisms of TBI in an extensive and sophisticated manner. Notably, astrocytes have dual roles in TBI, and some astrocyte-derived factors have double and opposite properties. Thus, the suppression or promotion of reactive astrogliosis does not have a substantial curative effect. In contrast, selective stimulation of the beneficial astrocyte-derived molecules and simultaneous attenuation of the deleterious factors based on the spatiotemporal-environment can provide a promising astrocyte-targeting therapeutic strategy. In the current review, we describe for the first time the specific dual roles of astrocytes in neuronal plasticity and reconstruction, including neurogenesis, synaptogenesis, angiogenesis, repair of the blood-brain barrier, and glial scar formation after TBI. We have also classified astrocyte-derived factors depending on their neuroprotective and neurotoxic roles to design more appropriate targeted therapies.

Pyk2-dependent phosphorylation of LSR enhances localization of LSR and tricellulin at tricellular tight junctions

Tight junctions (TJs) are cellular junctions within the mammalian epithelial cell sheet that function as a physical barrier to molecular transport within the intercellular space. Dysregulation of TJs leads to various diseases. Tricellular TJs (tTJs), specialized structural variants of TJs, are formed by multiple transmembrane proteins (e.g., lipolysis-stimulated lipoprotein receptor [LSR] and tricellulin) within tricellular contacts in the mammalian epithelial cell sheet. However, the mechanism for recruiting LSR and tricellulin to tTJs is largely unknown. Previous studies have identified that tyrphostin 9, the dual inhibitor of Pyk2 (a nonreceptor tyrosine kinase) and receptor tyrosine kinase platelet-derived growth factor receptor (PDGFR), suppresses LSR and tricellulin recruitment to tTJs in EpH4 (a mouse mammary epithelial cell line) cells. In this study, we investigated the effect of Pyk2 inhibition on LSR and tricellulin localization to tTJs. Pyk2 inactivation by its specific inhibitor or repression by RNAi inhibited the localization of LSR and downstream tricellulin to tTJs without changing their expression level in EpH4 cells. Pyk2-dependent changes in subcellular LSR and tricellulin localization were independent of c-Jun N-terminal kinase (JNK) activation and expression. Additionally, Pyk2-dependent LSR phosphorylation at Tyr-237 was required for LSR and tricellulin localization to tTJs and decreased epithelial barrier function. Our findings indicated a novel mechanism by which Pyk2 regulates tTJ assembly and epithelial barrier function in the mammalian epithelial cell sheet.

Dual Roles of Astrocyte-Derived Factors in Regulation of Blood-Brain Barrier Function after Brain Damage

The blood-brain barrier (BBB) is a major functional barrier in the central nervous system (CNS), and inhibits the extravasation of intravascular contents and transports various essential nutrients between the blood and the brain. After brain damage by traumatic brain injury, cerebral ischemia and several other CNS disorders, the functions of the BBB are disrupted, resulting in severe secondary damage including brain edema and inflammatory injury. Therefore, BBB protection and recovery are considered novel therapeutic strategies for reducing brain damage. Emerging evidence suggests key roles of astrocyte-derived factors in BBB disruption and recovery after brain damage. The astrocyte-derived vascular permeability factors include vascular endothelial growth factors, matrix metalloproteinases, nitric oxide, glutamate and endothelin-1, which enhance BBB permeability leading to BBB disruption. By contrast, the astrocyte-derived protective factors include angiopoietin-1, sonic hedgehog, glial-derived neurotrophic factor, retinoic acid and insulin-like growth factor-1 and apolipoprotein E which attenuate BBB permeability resulting in recovery of BBB function. In this review, the roles of these astrocyte-derived factors in BBB function are summarized, and their significance as therapeutic targets for BBB protection and recovery after brain damage are discussed.

Apolipoprotein E in lipoprotein metabolism, health and cardiovascular disease

Apolipoprotein E (apoE), a 34 kDa circulating glycoprotein of 299 amino acids, predominantly synthesised in the liver, associates with triglyceride-rich lipoproteins to mediate the clearance of their remnants after enzymatic lipolysis in the circulation. Its synthesis in macrophages initiates the formation of high density-like lipoproteins to effect reverse cholesterol transport to the liver. In the nervous system apoE forms similar lipoproteins which perform the function of distributing lipids amongst cells. ApoE accounts for much of the variation in plasma lipoproteins by three common variants (isoforms) that influence low-density lipoprotein concentration and the risk of atherosclerosis. ApoE2 generally is most favourable and apoE4 least favourable for cardiovascular and neurological health. The apoE variants relate to different amino acids at positions 112 and 158: cysteine in both for apoE2, arginine at both sites for apoE4, and respectively cysteine and arginine for apoE3 that is viewed as the wild type. Paradoxically, under metabolic stress, homozygosity for apoE2 may result in dysbetalipoproteinaemia in adults owing to impaired binding of remnant lipoproteins to the LDL receptor and related proteins as well as heparan sulphate proteoglycans. This highly atherogenic condition is also seen with other mutations in apoE, but with autosomal dominant inheritance. Mutations in apoE may also cause lipoprotein glomerulopathy. In the central nervous system apoE binds amyloid β-protein and tau protein and fragments may incur cellular damage. ApoE4 is a strong risk factor for the development of Alzheimer's disease. ApoE has several other physiological effects that may influence health and disease, including supply of docosahexaenoic acid for the brain and modulating immune and inflammatory responses. Genotyping of apoE may have application in disorders of lipoprotein metabolism as well as glomerulopathy and may be relevant to personalised medicine in understanding cardiovascular risk, and the outcome of nutritional and therapeutic interventions. Quantitation of apoE will probably not be clinically useful. ApoE is also of interest as it may generate peptides with biological function and could be employed in nanoparticles that may allow crossing of the blood-brain barrier. Therapeutic options may emerge from these newer insights.

Potential implications of Apolipoprotein E in early brain injury after experimental subarachnoid hemorrhage: Involvement in the modulation of blood-brain barrier integrity

Apolipoprotein E (Apoe) genetic polymorphisms have been implicated in the long term outcome of subarachnoid haemorrhage (SAH), but little is known about the effect of Apoe on the early brain injury (EBI) after SAH. This study investigated the potential role of APOE in EBI post-SAH. Multiple techniques were used to determine the early BBB disruption in EBI post-SAH in a murine model using wild-type (WT) and Apoe^−/− (KO) mice. Progressive BBB disruption (Evans blue extravasation and T2 hyperintensity in magnetic resonance imaging) was observed before the peak of endogenous APOE expression elevation at 48h after SAH. Moreover, Apoe^−/− mice exhibited more severe BBB disruption charcteristics after SAH than WT mice, including higher levels of Evans blue and IgG extravasation, T2 hyperintensity in magnetic resonance imaging, tight junction proteins degradation and endothelial cells death. Mechanistically, we found that APOE restores the BBB integrity in the acute stage after SAH via the cyclophilin A (CypA)-NF-κB-proinflammatory cytokines-MMP-9 signalling pathway. Consequently, although early BBB disruption causes neurological dysfunctions after SAH, we capture a different aspect of the effects of APOE on EBI after SAH that previous studies had overlooked and open up the idea of BBB disruption as a target of APOE-based therapy for EBI amelioration research in the future.

Matrix metalloproteinase-9 activity and a downregulated Hedgehog pathway impair blood-brain barrier function in an in vitro model of CNS tuberculosis

Central nervous system tuberculosis (CNS TB) has a high mortality and morbidity associated with severe inflammation. The blood-brain barrier (BBB) protects the brain from inflammation but the mechanisms causing BBB damage in CNS TB are uncharacterized. We demonstrate that Mycobacterium tuberculosis (Mtb) causes breakdown of type IV collagen and decreases tight junction protein (TJP) expression in a co-culture model of the BBB. This increases permeability, surface expression of endothelial adhesion molecules and leukocyte transmigration. TJP breakdown was driven by Mtb-dependent secretion of matrix metalloproteinase (MMP)-9. TJP expression is regulated by Sonic hedgehog (Shh) through transcription factor Gli-1. In our model, the hedgehog pathway was downregulated by Mtb-stimulation, but Shh levels in astrocytes were unchanged. However, Scube2, a glycoprotein regulating astrocyte Shh release was decreased, inhibiting Shh delivery to brain endothelial cells. Activation of the hedgehog pathway by addition of a Smoothened agonist or by addition of exogenous Shh, or neutralizing MMP-9 activity, decreased permeability and increased TJP expression in the Mtb-stimulated BBB co-cultures. In summary, the BBB is disrupted by downregulation of the Shh pathway and breakdown of TJPs, secondary to increased MMP-9 activity which suggests that these pathways are potential novel targets for host directed therapy in CNS TB.

Pentoxifylline exerts anti-inflammatory effects on cerebral ischemia reperfusion‑induced injury in a rat model via the p38 mitogen-activated protein kinase signaling pathway

Pentoxifylline exhibits complex functions with extensive pharmacological effects and is used therapeutically due to its therapeutic effects and rapid metabolism in the body, with no cumulative effects and few side effects. The present study investigated the effects of pentoxifylline on cerebral ischemia reperfusion‑induced injury (IRI) through suppression of inflammation in rats. Hematoxylin and eosin staining was performed to evaluate the number of neurocytes, and ELISAs were applied to measure tumor necrosis factor‑α, interleukin‑6, malondialdehyde and superoxide dismutase activities. Treatment with pentoxifylline significantly recovered the cerebral ischemia reperfusion‑induced neurological deficit score and cerebral infarct volume in rats. In addition, pentoxifylline treatment significantly reversed the cerebral ischemia reperfusion‑induced interleukin‑6, tumor necrosis factor‑α, malondialdehyde and superoxide dismutase levels in vivo. Furthermore, pentoxifylline significantly inhibited cyclooxygenase‑2 and inducible nitric oxide synthase mRNA and protein expression in cerebral IRI mice. Treatment with pentoxifylline also significantly suppressed the expression of cleaved caspase‑3 and p38 mitogen‑activated protein kinase (MAPK) protein in cerebral IRI mice. These results indicate that the protective effects of pentoxifylline on cerebral IRI may occur via the p38 MAPK signaling pathway.

ApoE Influences the Blood-Brain Barrier Through the NF-κB/MMP-9 Pathway After Traumatic Brain Injury

Apolipoprotein E (ApoE), encoded by the ApoE gene (APOE), influences the outcomes of traumatic brain injury (TBI), but the mechanism remains unclear. The present study aimed to investigate the effects of different ApoEs on the outcome of TBI and to explore the possible mechanisms. Controlled cortical impact (CCI) was performed on APOEε3 (E3) and APOEε4 (E4) transgenic mice, APOE-KO (KO) mice, and wild type (WT) mice to construct an in vivo TBI model. Neurological deficits, blood brain barrier (BBB) permeability and brain edema were detected at days 1, 3, and 7 after TBI. The results revealed no significant differences among the four groups at day 1 or day 3 after injury, but more severe deficits were found in E4 and KO mice than in E3 and WT mice. Furthermore, a significant loss of tight junction proteins was observed in E4 and KO mice compared with E3 and WT mice at day 7. Additionally, more expression and activation of NF-κB and MMP-9 were found in E4 mice compared with E3 mice. Different ApoEs had distinct effects on neuro-function and BBB integrity after TBI. ApoE3, but not E4, might inhibit the NF-κB/MMP-9 pathway to alleviate BBB disruption and improve TBI outcomes.

Hydrogen sulfide protects against the development of experimental cerebral malaria in a C57BL/6 mouse model

Hydrogen sulfide (H2S) has anti‑inflammatory and neuroprotective properties, particularly during pathological processes. Experimental cerebral malaria (ECM), which is caused by vascular leakage into the brain, is characterized by inflammation, neurological deficits and cerebral hemorrhage. The present study investigated the correlation between ECM genesis and the levels of H2S. The results indicated that the levels of H2S derived from the brain decreased over time following ECM infection, and that the low H2S bioavailability was partially caused by decreased expression of the H2S generating enzyme, cystathionine‑β‑synthase. Administration of NaHS (an exogenous donor of H2S) provided protection against ECM. NaHS inhibited the destruction of the blood brain barrier and the secretion of proinflammatory biomarkers, including interluekin‑18, matrix metalloproteinase‑9 and serum cluster of differentiation 40 into the brain during ECM. In conclusion, these results suggested that low levels of H2S in brain contributed to the progression of ECM, and that H2S donor administration may represent a potential protective therapy against ECM.

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.

Gas6 Promotes Oligodendrogenesis and Myelination in the Adult Central Nervous System and After Lysolecithin-Induced Demyelination

A key aim of therapy for multiple sclerosis (MS) is to promote the regeneration of oligodendrocytes and remyelination in the central nervous system (CNS). The present study provides evidence that the vitamin K-dependent protein growth arrest specific 6 (Gas6) promotes such repair in in vitro cultures of mouse optic nerve and cerebellum. We first determined expression of Gas6 and TAM (Tyro3, Axl, Mer) receptors in the mouse CNS, with all three TAM receptors increasing in expression through postnatal development, reaching maximal levels in the adult. Treatment of cultured mouse optic nerves with Gas6 resulted in significant increases in oligodendrocyte numbers as well as expression of myelin basic protein (MBP). Gas6 stimulation also resulted in activation of STAT3 in optic nerves as well as downregulation of multiple genes involved in MS development, including matrix metalloproteinase-9 (MMP9), which may decrease the integrity of the blood-brain barrier and is found upregulated in MS lesions. The cytoprotective effects of Gas6 were examined in in vitro mouse cerebellar slice cultures, where lysolecithin was used to induce demyelination. Cotreatment of cerebellar slices with Gas6 significantly attenuated demyelination as determined by MBP immunostaining, and Gas6 activated Tyro3 receptor through its phosphorylation. In conclusion, these results demonstrate that Gas6/TAM signaling stimulates the generation of oligodendrocytes and increased myelin production via Tyro3 receptor in the adult CNS, including repair after demyelinating injury. Furthermore, the effects of Gas6 on STAT3 signaling and matrix MMP9 downregulation indicate potential glial cell repair and immunoregulatory roles for Gas6, indicating that Gas6-TAM signaling could be a potential therapeutic target in MS and other neuropathologies.

The role of the low-density lipoprotein receptor–related protein 1 (LRP-1) in regulating blood-brain barrier integrity

The blood-brain barrier (BBB) is a protective structure that helps maintaining the homeostasis in cerebral microenvironment by limiting the passage of molecules into the brain. BBB is formed by closely conjugated endothelial cells, with astrocytic endfeet surrounded and extracellular matrix (ECM) consolidated. Numerous neurological diseases can cause disturbance of BBB, leading to brain edema and neurological dysfunctions. The low-density lipoprotein (LDL) receptor–related protein 1 (LRP-1), a member of the LDL receptor gene family, is involved in a lot of important processes in the brain under both physiological and pathological conditions. As a membrane receptor, LRP-1 interacts with a variety of ligands and mediates the internalization of several important substances. LRP-1 is found responsible for inducing the opening of BBB following ischemic attack. It has also been reported that LRP-1 regulates several tight junction proteins and mediates the clearance of major ECM-degrading proteinases. In this review, we briefly discussed the role of LRP-1 in regulating BBB integrity by modulating tight junction proteins, endothelial cells and the remodeling of ECM.

The role of APOE in cerebrovascular dysfunction

The ε4 allele of the apolipoprotein E gene (APOE4) is associated with cognitive decline during aging, is the greatest genetic risk factor for Alzheimer's disease and has links to other neurodegenerative conditions that affect cognition. Increasing evidence indicates that APOE genotypes differentially modulate the function of the cerebrovasculature (CV), with apoE and its receptors expressed by different cell types at the CV interface (astrocytes, pericytes, smooth muscle cells, brain endothelial cells). However, research on the role of apoE in CV dysfunction has not advanced as quickly as other apoE-modulated pathways. This review will assess what aspects of the CV are modulated by APOE genotypes during aging and under disease states, discuss potential mechanisms, and summarize the therapeutic significance of the topic. We propose that APOE4 induces CV dysfunction through direct signaling at the CV, and indirectly via modulation of peripheral and central pathways. Further, that APOE4 predisposes the CV to damage by, and exacerbates the effects of, additional risk factors (such as sex, hypertension, and diabetes). ApoE4-induced detrimental CV changes include reduced cerebral blood flow (CBF), modified neuron-CBF coupling, increased blood-brain barrier leakiness, cerebral amyloid angiopathy, hemorrhages and disrupted transport of nutrients and toxins. The apoE4-induced detrimental changes may be linked to pericyte migration/activation, astrocyte activation, smooth muscle cell damage, basement membrane degradation and alterations in brain endothelial cells.

Bexarotene reduces blood-brain barrier permeability in cerebral ischemia-reperfusion injured rats

BACKGROUND

Matrix metalloproteinase-9 (MMP-9) over-expression disrupts the blood-brain barrier (BBB) in the ischemic brain. The retinoid X receptor agonist bexarotene suppresses MMP-9 expression in endothelial cells and displays neuroprotective effects. Therefore, we hypothesized that bexarotene may have a beneficial effect on I/R-induced BBB dysfunction.

METHODS

A total of 180 rats were randomized into three groups (n = 60 each): (i) a sham-operation group, (ii) a cerebral ischemia-reperfusion (I/R) group, and (iii) an I/R+bexarotene group. Brain water content was measured by the dry wet weight method. BBB permeability was analyzed by Evans Blue staining and the magnetic resonance imaging contrast agent Omniscan. MMP-9 mRNA expression, protein expression, and activity were assessed by reverse transcription polymerase chain reaction, Western blotting, and gelatin zymography, respectively. Apolipoprotein E (apoE), claudin-5, and occludin expression were analyzed by Western blotting.

RESULTS

After 24 h, 48 h, and 72 h post-I/R, several effects were observed with bexarotene administration: (i) brain water content and BBB permeability were significantly reduced; (ii) MMP-9 mRNA and protein expression as well as activity were significantly decreased; (iii) claudin-5 and occludin expression were significantly increased; and (iv) apoE expression was significantly increased.

CONCLUSIONS

Bexarotene decreases BBB permeability in rats with cerebral I/R injury. This effect may be due in part to bexarotene's upregulation of apoE expression, which has been previously shown to reduce BBB permeability through suppressing MMP-9-mediated degradation of the tight junction proteins claudin-5 and occludin. This work offers insight to aid future development of therapeutic agents for cerebral I/R injury in human patients.

"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.

Inhibition of p21-activated kinase 1 by IPA-3 attenuates secondary injury after traumatic brain injury in mice

The p21-activated kinase 1 (PAK1) is up-regulated in the brain following traumatic brain injury (TBI). Inhibition of PAK1 has been found to alleviate brain edema in a rat model of subarachnoid hemorrhage. Suppressing PAK1 activity might represent a novel therapeutics of attenuating secondary injury following TBI. Here we confirmed that the mRNA and protein levels of PAK1 and the protein level of p-PAK1 were significantly increased after inducing TBI in mice via M.A. Flierl's weight-drop model. A single intraperitoneal administration of IPA-3, a specific PAK1 inhibitor, immediately after TBI significantly reduced the protein level of p-PAK1, cleaved caspase-3 level, the number of apoptotic cells at the lesion sites of TBI mice. It also reduced brain water content and the blood-brain barrier permeability in TBI mice. Furthermore, the administration of IPA-3 significantly reduced the neurological severity score and increased the grip test score in TBI mice. Taken together, we demonstrate that PAK1 inhibition by IPA-3 may attenuate the secondary injury following TBI, suggesting it might be a promising neuroprotective strategy for preventing the development of secondary injury after TBI.