CD44 deficiency contributes to enhanced experimental autoimmune encephalomyelitis: a role in immune cells and vascular cells of the blood-brain barrier

CD6 triggers actomyosin cytoskeleton remodeling after binding to its receptor complex

The T cell marker CD6 regulates both T cells and target cells during inflammatory responses by interacting with its receptors. However, only a few receptors binding to the extracellular domains of CD6 have been identified, and cellular events induced by CD6 engagement with its receptors in target cells remain poorly understood. In this study, we identified CD44 as a novel CD6 receptor by proximity labeling and confirmed the new CD6-CD44 interaction by biochemical and biophysical approaches. CD44 and the other 2 known CD6 receptors, CD166 and CDCP1, were distributed diffusely on resting retinal pigment epithelium (RPE) cells but clustered together to form a receptor complex upon CD6 binding. CD6 stimulation induced dramatic remodeling of the actomyosin cytoskeleton in RPE cells mediated by activation of RhoA, and Rho-associated kinase signaling, resulting in increased myosin II phosphorylation. Such actomyosin activation triggered the disassembly of tight junctions responsible for RPE barrier integrity in a process that required all components of the tripartite CD6 receptor complex. These data provided new insights into the mechanisms by which CD6 mediates T cell-driven disruption of tissue barriers during inflammation.

Universal method for the isolation of microvessels from frozen brain tissue: A proof-of-concept multiomic investigation of the neurovasculature

The neurovascular unit, comprised of vascular cell types that collectively regulate cerebral blood flow to meet the needs of coupled neurons, is paramount for the proper function of the central nervous system. The neurovascular unit gatekeeps blood-brain barrier properties, which experiences impairment in several central nervous system diseases associated with neuroinflammation and contributes to pathogenesis. To better understand function and dysfunction at the neurovascular unit and how it may confer inflammatory processes within the brain, isolation and characterization of the neurovascular unit is needed. Here, we describe a singular, standardized protocol to enrich and isolate microvessels from archived snap-frozen human and frozen mouse cerebral cortex using mechanical homogenization and centrifugation-separation that preserves the structural integrity and multicellular composition of microvessel fragments. For the first time, microvessels are isolated from postmortem ventromedial prefrontal cortex tissue and are comprehensively investigated as a structural unit using both RNA sequencing and Liquid Chromatography with tandem mass spectrometry (LC-MS/MS). Both the transcriptome and proteome are obtained and compared, demonstrating that the isolated brain microvessel is a robust model for the NVU and can be used to generate highly informative datasets in both physiological and disease contexts.

Exploring Shared Genetic Signatures of Alzheimer's Disease and Multiple Sclerosis: A Bioinformatic Analysis Study

INTRODUCTION

Many clinical studies reported the coexistence of Alzheimer's disease (AD) and multiple sclerosis (MS), but the common molecular signature between AD and MS remains elusive. The purpose of our study was to explore the genetic linkage between AD and MS through bioinformatic analysis, providing new insights into the shared signatures and possible pathogenesis of two diseases.

METHODS

The common differentially expressed genes (DEGs) were determined between AD and MS from datasets obtained from Gene Expression Omnibus (GEO) database. Further, functional and pathway enrichment analysis, protein-protein interaction network construction, and identification of hub genes were carried out. The expression level of hub genes was validated in two other external AD and MS datasets. Transcription factor (TF)-gene interactions and gene-miRNA interactions were performed in NetworkAnalyst. Finally, receiver operating characteristic (ROC) curve analysis was applied to evaluate the predictive value of hub genes.

RESULTS

A total of 75 common DEGs were identified between AD and MS. Functional and pathway enrichment analysis emphasized the importance of exocytosis and synaptic vesicle cycle, respectively. Six significant hub genes, including CCL2, CD44, GFAP, NEFM, STXBP1, and TCEAL6, were identified and verified as common hub genes shared by AD and MS. FOXC1 and hsa-mir-16-5p are the most common TF and miRNA in regulating hub genes, respectively. In the ROC curve analysis, all hub genes showed good efficiency in helping distinguish patients from controls.

CONCLUSION

Our study first identified a common genetic signature between AD and MS, paving the road for investigating shared mechanism of AD and MS.

Integration of Genetic and Immune Infiltration Insights into Data Mining of Multiple Sclerosis Pathogenesis

Background

Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system. MS pathogenesis is closely related to the environment, genetic, and immune system, but the underlying interactions have not been clearly elucidated. This study aims to unveil the genetic basis and immune landscape of MS pathogenesis with bioinformatics.

Methods

Gene matrix was retrieved from the gene expression database NCBI-GEO. Then, bioinformatics was used to standardize the samples and obtain differentially expressed genes (DEGs). The protein-protein interaction network was constructed with DEGs on the STRING website. Cytohubba plug-in and MCODE plug-in were used to mine hub genes. Meanwhile, the CIBERSORTX algorithm was used to explore the characteristics of immune cell infiltration in MS brain tissues. Spearman correlation analysis was performed between genes and immune cells, and the correlation between genes and different types of brain tissues was also analyzed using the WGCNA method.

Results

A total of 90 samples from 2 datasets were included, and 882 DEGs and 10 hub genes closely related to MS were extracted. Functional enrichment analysis suggested the role of immune response in MS. Besides, CIBERSORTX algorithm results showed that MS brain tissues contained a variety of infiltrating immune cells. Correlation analysis suggested that the hub genes were highly relevant to chronic active white matter lesions. Certain hub genes played a role in the activation of immune cells such as macrophages and natural killer cells.

Conclusions

Our study shall provide guidance for the further study of the genetic basis and immune infiltration mechanism of MS.

Astrocyte depletion alters extracellular matrix composition in the demyelinating phase of Theiler's murine encephalomyelitis

Astrocytes produce extracellular matrix (ECM) glycoproteins contributing to the blood-brain barrier and regulating the immune response in the central nervous system (CNS). The aim of this study was to investigate the impact of astrocyte depletion upon the clinical outcome and the composition of ECM glycoproteins in a virus-induced animal model of demyelination. Glial fibrillary acidic protein (GFAP)-thymidine-kinase transgenic SJL (GFAP-knockout) and wildtype mice were infected with Theiler’s murine encephalomyelitis virus (TMEV). Astrocyte depletion was induced during the progressive, demyelinating disease phase by ganciclovir administration once daily between 56 and 77 days post infection (dpi). At 77 dpi GFAP-knockout mice showed a significant deterioration of clinical signs associated with a reduction of azan and picrosirius red stained ECM-molecules in the thoracic spinal cord. Basement-membrane-associated ECM-molecules including laminin, entactin/nidogen-1 and Kir4.1 as well as non-basement membrane-associated ECM-molecules like collagen I, decorin, tenascin-R and CD44 were significantly reduced in the spinal cord of GFAP-knockout mice. The reduction of the investigated ECM-molecules demonstrates that astrocytes play a key role in the production of ECM-molecules. The present findings indicate that the detected loss of Kir4.1 and CD44 as well as the disruption of the integrity of perineuronal nets led to the deterioration of clinical signs in GFAP-knockout mice.

Location Matters: Navigating Regional Heterogeneity of the Neurovascular Unit

The neurovascular unit (NVU) of the brain is composed of multiple cell types that act synergistically to modify blood flow to locally match the energy demand of neural activity, as well as to maintain the integrity of the blood-brain barrier (BBB). It is becoming increasingly recognized that the functional specialization, as well as the cellular composition of the NVU varies spatially. This heterogeneity is encountered as variations in vascular and perivascular cells along the arteriole-capillary-venule axis, as well as through differences in NVU composition throughout anatomical regions of the brain. Given the wide variations in metabolic demands between brain regions, especially those of gray vs. white matter, the spatial heterogeneity of the NVU is critical to brain function. Here we review recent evidence demonstrating regional specialization of the NVU between brain regions, by focusing on the heterogeneity of its individual cellular components and briefly discussing novel approaches to investigate NVU diversity.

Early onset senescence and cognitive impairment in a murine model of repeated mTBI

Mild traumatic brain injury (mTBI) results in broad neurological symptoms and an increased risk of being diagnosed with a neurodegenerative disease later in life. While the immediate oxidative stress response and post-mortem pathology of the injured brain has been well studied, it remains unclear how early pathogenic changes may drive persistent symptoms and confer susceptibility to neurodegeneration. In this study we have used a mouse model of repeated mTBI (rmTBI) to identify early gene expression changes at 24 h or 7 days post-injury (7 dpi). At 24 h post-injury, gene expression of rmTBI mice shows activation of the DNA damage response (DDR) towards double strand DNA breaks, altered calcium and cell–cell signalling, and inhibition of cell death pathways. By 7 dpi, rmTBI mice had a gene expression signature consistent with induction of cellular senescence, activation of neurodegenerative processes, and inhibition of the DDR. At both timepoints gliosis, microgliosis, and axonal damage were evident in the absence of any gross lesion, and by 7 dpi rmTBI also mice had elevated levels of IL1β, p21, 53BP1, DNA2, and p53, supportive of DNA damage-induced cellular senescence. These gene expression changes reflect establishment of processes usually linked to brain aging and suggests that cellular senescence occurs early and most likely prior to the accumulation of toxic proteins. These molecular changes were accompanied by spatial learning and memory deficits in the Morris water maze. To conclude, we have identified DNA damage-induced cellular senescence as a repercussion of repeated mild traumatic brain injury which correlates with cognitive impairment. Pathways involved in senescence may represent viable treatment targets of post-concussive syndrome. Senescence has been proposed to promote neurodegeneration and appears as an effective target to prevent long-term complications of mTBI, such as chronic traumatic encephalopathy and other related neurodegenerative pathologies.

Sex differences in EAE reveal common and distinct cellular and molecular components

Experimental autoimmune encephalomyelitis (EAE) is commonly used as an animal model for evaluating clinical, histological and immunological processes potentially relevant to the human disease multiple sclerosis (MS), for which the mode of disease induction remains largely unknown. An important caveat for interpreting EAE processes in mice is the inflammatory effect of immunization with myelin peptides emulsified in Complete Freund's Adjuvant (CFA), often followed by additional injections of pertussis toxin (Ptx) in some strains to induce EAE. The current study evaluated clinical, histological, cellular (spleen), and chemokine-driven processes in spinal cords of male vs. female C57BL/6 mice that were immunized with mouse (m)MOG-35-55/CFA/Ptx to induce EAE; immunized with saline/CFA/Ptx only (CFA, no EAE); or were untreated (Naïve, no EAE). Analysis of response curves utilized a rigorous and sophisticated methodology to parse and characterize the effects of EAE and adjuvant alone vs. the Naive baseline responses. The results demonstrated stronger pro-inflammatory responses of immune cells and their associated cytokines, chemokines, and receptors in male vs. female CFA and EAE mice that appeared to be offset partially by increased percentages of male anti-inflammatory, regulatory and checkpoint T cell, B cell, and monocyte/macrophage subsets. These sex differences in peripheral immune responses may explain the reduced cellular infiltration and differing chemokine profiles in the Central Nervous System (CNS) of male vs. female CFA immunized mice and the reduced CNS infiltration and demyelination observed in male vs. female EAE groups of mice that ultimately resulted in the same clinical EAE disease severity in both sexes. Our findings suggest EAE disease severity is governed not only by the degree of CNS infiltration and demyelination, but also by the balance of pro-inflammatory vs. regulatory cell types and their secreted cytokines and chemokines.

Astrocyte phenotypes: Emphasis on potential markers in neuroinflammation

Astrocytes, the most abundant glial cells in the central nervous system (CNS), have numerous integral roles in all CNS functions. They are essential for synaptic transmission and support neurons by providing metabolic substrates, secreting growth factors and regulating extracellular concentrations of ions and neurotransmitters. Astrocytes respond to CNS insults through reactive astrogliosis, in which they go through many functional and molecular changes. In neuroinflammatory conditions reactive astrocytes exert both beneficial and detrimental functions, depending on the context and heterogeneity of astrocytic populations. In this review we profile astrocytic diversity in the context of neuroinflammation; with a specific focus on multiple sclerosis (MS) and its best-described animal model experimental autoimmune encephalomyelitis (EAE). We characterize two main subtypes, protoplasmic and fibrous astrocytes and describe the role of intermediate filaments in the physiology and pathology of these cells. Additionally, we outline a variety of markers that are emerging as important in investigating astrocytic biology in both physiological conditions and neuroinflammation.

Diverse Roles for Hyaluronan and Hyaluronan Receptors in the Developing and Adult Nervous System

Hyaluronic acid (HA) plays a vital role in the extracellular matrix of neural tissues. Originally thought to hydrate tissues and provide mechanical support, it is now clear that HA is also a complex signaling molecule that can regulate cell processes in the developing and adult nervous systems. Signaling properties are determined by molecular weight, bound proteins, and signal transduction through specific receptors. HA signaling regulates processes such as proliferation, differentiation, migration, and process extension in a variety of cell types including neural stem cells, neurons, astrocytes, microglia, and oligodendrocyte progenitors. The synthesis and catabolism of HA and the expression of HA receptors are altered in disease and influence neuroinflammation and disease pathogenesis. This review discusses the roles of HA, its synthesis and breakdown, as well as receptor expression in neurodevelopment, nervous system function and disease.

Conventional Treatment of Glioblastoma Reveals Persistent CD44+ Subpopulations

Glioblastoma (GBM) is the most frequent and devastating primary tumor of the central nervous system with a median survival of 12 to 15 months after diagnosis. GBM is highly difficult to treat due to its delicate location, inter- and intra-tumoral heterogeneity, and high plasticity in response to treatment. In this study, we intracranially implanted primary GBM cells into mice which underwent conventional GBM treatments, including irradiation, temozolomide, and a combination. We obtained single cell suspensions through a combination of mechanical and enzymatic dissociation of brain tissue and investigated in detail the changes in GBM cells in response to conventional treatments in vivo using multi-color flow cytometry and cluster analysis. CD44 expression was elevated in all treatment groups, which was confirmed by subsequent immunohistochemistry. High CD44 expression was furthermore shown to correlate with poor prognosis of GBM and low-grade glioma (LGG) patients. Together, these results indicate a key role for CD44 in glioma pathogenesis.

CD44 expression in the cuprizone model

Numerous studies report that changes in extracellular matrix components and receptors, such as CD44, contribute to immune cell recruitment and thus lesion formation in multiple sclerosis (MS). In the present study, we used the cuprizone model to elucidate the expression pattern of CD44 in a toxin-induced MS model. Therefore, tissues of cuprizone-intoxicated mice were analyzed by real-time qRT-PCR and immunohistochemical staining against CD44. Co-localization analyses of CD44-positive cells with glial cell markers were performed by immunofluorescence labeling and in-situ hybridization. To investigate the functional importance of CD44 expression for myelination and glial cell activation, Cd44-deficient mice were used. In this study we demonstrate that CD44 expression is induced in a time-dependent manner in an autoimmune-independent model of MS. Up-regulation of CD44 expression was primarily associated to the superficial and perivascular glia limitans and demyelinated white matter structures, particularly the corpus callosum. In the demyelinated corpus callosum, CD44 was localized on GFAP⁺ astrocytes and IBA1⁺ microglial cells. Despite a robust expression induction, Cd44-deficiency did not ameliorate cuprizone-induced pathology. Although further studies will be needed to examine the functional relevance of CD44 in the cuprizone model, the spatial and temporal expression pattern of CD44 will pave the way to evaluate its precise role in different (immune and non-immune) pathological conditions.

CD44 expression in stem cells and niche microglia/macrophages following ischemic stroke

Background

CD44, an adhesion molecule in the hyaluronate receptor family, plays diverse and important roles in multiple cell types and organs. Increasing evidence is mounting for CD44 expression in various types of stem cells and niche cells surrounding stem cells. However, the precise phenotypes of CD44⁺ cells in the brain under pathologic conditions, such as after ischemic stroke, remain unclear.

Methods

In the present study, using a mouse model for cerebral infarction by middle cerebral artery (MCA) occlusion, we examined the localization and traits of CD44⁺ cells.

Results

In sham-mice operations, CD44 was rarely observed in the cortex of MCA regions. Following ischemic stroke, CD44⁺ cells emerged in ischemic areas of the MCA cortex during the acute phase. Although CD44 at ischemic areas was, in part, expressed in stem cells, it was also expressed in hematopoietic lineages, including activated microglia/macrophages, surrounding the stem cells. CD44 expression in microglia/macrophages persisted through the chronic phase following ischemic stroke.

Conclusions

These data demonstrate that CD44 is expressed in stem cells and cells in the niches surrounding them, including inflammatory cells, suggesting that CD44 may play an important role in reparative processes within ischemic areas under neuroinflammatory conditions; in particular, strokes.

A disintegrin and metalloproteinase 15-mediated glycocalyx shedding contributes to vascular leakage during inflammation

Aims

Endothelial hyperpermeability exacerbates multiple organ damage during inflammation or infection. The endothelial glycocalyx, a protective matrix covering the luminal surface of endothelial cells (ECs), undergoes enzymatic shedding during inflammation, contributing to barrier hyperpermeability. A disintegrin and metalloproteinase 15 (ADAM15) is a sheddase capable of cleaving the ectodomains of membrane-bound molecules. Herein, we tested whether and how ADAM15 is involved in glycocalyx shedding and vascular leakage during sepsis.

Methods and results

Dextran-150kD exclusion assay revealed lipopolysaccharide (LPS) significantly reduced glycocalyx thickness in mouse cremaster microvessels. Consistently, shedding products of glycocalyx constituents, including CD44 ectodomain, were detected with an increased plasma level after cecal ligation and puncture (CLP)-induced sepsis. The direct effects of CD44 ectodomain on endothelial barrier function were evaluated, which revealed CD44 ectodomain dose-dependently reduced transendothelial electrical resistance (TER) and caused cell–cell adherens junction disorganization. Furthermore, we examined the role of ADAM15 in CD44 cleavage and glycocalyx shedding. An in vitro cleavage assay coupled with liquid chromatography-tandem mass spectrometry confirmed ADAM15 cleaved CD44 at His²³⁵-Thr²³⁶ bond. In ECs with ADAM15 knockdown, LPS-induced CD44 cleavage and TER reduction were greatly attenuated, whereas, ADAM15 overexpression exacerbated CD44 cleavage and TER response to LPS. Consistently, ADAM15 knockout in mice attenuated CLP-induced increase in plasma CD44. Intravital and electron microscopic images revealed ADAM15 deficiency prevented LPS-induced glycocalyx injury in cremaster and pulmonary microvasculatures. Functionally, ADAM15^−/− mice with better-preserved glycocalyx exhibited resistance to LPS-induced vascular leakage, as evidenced by reduced albumin extravasation in pulmonary and mesenteric vessels. Importantly, in intact, functionally vital human lungs, perfusion of LPS induced a significant up-regulation of ADAM15, accompanied by elevated CD44 in the effluent and increased vascular permeability to albumin.

Conclusion

Together, our data support the critical role of ADAM15 in mediating vascular barrier dysfunction during inflammation. Its mechanisms of action involve CD44 shedding and endothelial glycocalyx injury.

Hyaluronan impairs the barrier integrity of brain microvascular endothelial cells through a CD44-dependent pathway

Hyaluronan (HA) constitutes the most abundant extracellular matrix component during brain development, only to become a minor component rapidly after birth and in adulthood to remain in specified regions. HA signaling has been associated with several neurological disorders, yet the impact of HA signaling at the blood-brain barrier (BBB) function remains undocumented. In this study, we investigated the impact of HA on BBB properties using human-induced pluripotent stem cell (iPSC) -derived and primary human and rat BMECs. The impact of HA signaling on developmental and mature BMECs was assessed by measuring changes in TEER, permeability, BMECs markers (GLUT1, tight junction proteins, P-gp) expression and localization, CD44 expression and hyaluronan levels. In general, HA treatment decreased barrier function and reduced P-gp activity with effects being more prominent upon treatment with oligomeric forms of HA (oHA). Such effects were exacerbated when applied during BMEC differentiation phase (considered as developmental BBB). We noted a hyaluronidase activity as well as an increase in CD44 expression during prolonged oxygen-glucose deprivation stress. Inhibition of HA signaling by antibody blockade of CD44 abrogated the detrimental effects of HA treatment. These results suggest the importance of HA signaling through CD44 on BBB properties.

Genome-wide association study in two populations to determine genetic variants associated with Toxoplasma gondii infection and relationship to schizophrenia risk

T. gondii (TOXO) infects over one billion people worldwide, yet the literature lacks a Genome Wide Association Study (GWAS) focused on genetic variants controlling the persistence of TOXO infection. To identify putative T. gondii susceptibility genes, we performed a GWAS using IgG seropositivity as the outcome variable in a discovery sample (n = 790) from an Ashkenazi dataset, and a second sample of predominately African Americans (The Grady Trauma Project, n = 285). We also performed a meta-analyses of the 2 cohorts. None of the SNPs in these analyses was statistically significant after Bonferroni correction for multiple comparisons. In the Ashkenazi population, the gene region of CHIA (chitinase) showed the most nominally significant association with TOXO. Prior studies have shown that the production of chitinase by macrophages in the brain responding to TOXO infection is crucial for controlling the burden of T. gondii cysts. We found a surprising number of genes involved in neurodevelopment and psychiatric disorders among our top hits even though our outcome variable was TOXO infection. In the meta-analysis combining the Ashkenazi and Grady Trauma Project samples, there was enrichment for genes implicated in schizophrenia spectrum disorders (p < .05). Upon limiting our sample to those without mental illness, two schizophrenia related genes (CNTNAP2, GABAR2) still had significant TOXO-associated variants at the p < .05 level, but did not pass the genome wide significance threshold after correction for multiple comparisons. Using Ingenuity Systems molecular network analysis, we identified molecular nodes suggesting that while different genetic variants associated with TOXO in the two population samples, the molecular pathways for TOXO susceptibility nevertheless converged on common pathways. Molecular nodes in these common pathways included NOTCH1, CD44, and RXRA. Prior studies show that CD44 participates in TOXO-induced immunopathology and that RXRA is instrumental in regulating T-helper immune responses. These data provide new insights into the pathophysiology of this common neurotropic parasite.

Cxcl17-/- mice develop exacerbated disease in a T cell-dependent autoimmune model

CXCL17 is a homeostatic chemokine in the mucosa known to chemoattract dendritic cells and macrophages but can also be expressed elsewhere under inflammatory conditions. Cxcl17^-/- mice have lower numbers of macrophages or dendritic cells in mucosal tissues. CXCL17 is also able to chemoattract suppressor myeloid cells that can recruit regulatory T cells. To explore a possible role of Cxcl17 in T cells, we studied T cell populations from Cxcl17^-/- or wild-type (WT) littermate mice. Cxcl17^-/- mice have higher numbers of CD4⁺ and CD8⁺ T cells in spleen and lymph nodes (LNs). Upon activation, they produce higher levels of several proinflammatory cytokines and chemokines. Furthermore, a Cxcl17^-/- mouse developed exacerbated disease in a T cell-dependent model of experimental autoimmune encephalomyelitis (EAE). By 18 days after immunization with myelin oligodendrocyte peptide, only 44% of Cxcl17^-/- mice were still alive vs. 90% for WT mice. During EAE, Cxcl17^-/- mice exhibited higher numbers of lymphoid and myeloid cells in spleen and LNs, whereas they had less myeloid cell infiltration in the CNS. Cxcl17^-/- mice also had higher levels of some inflammatory cytokines in serum, suggesting that they may be involved in the poor survival of these mice. Abnormal T cell function may reflect altered myeloid cell migration, or it could be due to altered T cell development in the thymus. We conclude that CXCL17 is a novel factor regulating T cell homeostasis and function.

Sialomucin CD43 regulates T helper type 17 cell intercellular adhesion molecule 1 dependent adhesion, apical migration and transendothelial migration

T helper type 17 lymphocytes (Th17 cells) infiltrate the central nervous system (CNS), induce inflammation and demyelination and play a pivotal role in the pathogenesis of multiple sclerosis. Sialomucin CD43 is highly expressed in Th17 cells and mediates adhesion to endothelial selectin (E-selectin), an initiating step in Th17 cell recruitment to sites of inflammation. CD43^-/- mice have impaired Th17 cell recruitment to the CNS and are protected from experimental autoimmune encephalomyelitis (EAE), the mouse model of multiple sclerosis. However, E-selectin is dispensable for the development of EAE, in contrast to intercellular and vascular cell adhesion molecules (ICAM-1 and VCAM-1). We report that CD43^-/- mice have decreased demyelination and T-cell infiltration, but similar up-regulation of ICAM-1 and VCAM-1 in the spinal cord, compared with wild-type (WT) mice, at the initiation of EAE. CD43^-/- Th17 cells have impaired adhesion to ICAM-1 under flow conditions in vitro, despite having similar expression of LFA-1, the main T-cell ligand for ICAM-1, as WT Th17 cells. Regardless of the route of integrin activation, CD43^-/- Th17 cell firm arrest on ICAM-1 was comparable to that of WT Th17 cells, but CD43^-/- Th17 cells failed to optimally apically migrate on immobilized ICAM-1-coated coverslips and endothelial cells, and to transmigrate under shear flow conditions in an ICAM-1-dependent manner. Collectively, these findings unveil novel roles for CD43, facilitating adhesion of Th17 cells to ICAM-1 and modulating apical and transendothelial migration, as mechanisms potentially responsible for Th17 cell recruitment to sites of inflammation such as the CNS.

Quantitative Proteomics Reveals the Dynamic Protein Landscape during Initiation of Human Th17 Cell Polarization

Th17 cells contribute to the pathogenesis of inflammatory and autoimmune diseases and cancer. To reveal the Th17 cell-specific proteomic signature regulating Th17 cell differentiation and function in humans, we used a label-free mass spectrometry-based approach. Furthermore, a comprehensive analysis of the proteome and transcriptome of cells during human Th17 differentiation revealed a high degree of overlap between the datasets. However, when compared with corresponding published mouse data, we found very limited overlap between the proteins differentially regulated in response to Th17 differentiation. Validations were made for a panel of selected proteins with known and unknown functions. Finally, using RNA interference, we showed that SATB1 negatively regulates human Th17 cell differentiation. Overall, the current study illustrates a comprehensive picture of the global protein landscape during early human Th17 cell differentiation. Poor overlap with mouse data underlines the importance of human studies for translational research.

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Quantitative proteomics analysis of early human Th17 cell polarization

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The proteome and transcriptome highly correlate during early Th17 polarization

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Poor overlap of proteome profiles of human and mouse during early Th17 polarization

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The results underline the importance of human studies for translational research

The role of T cells in the pathogenesis of Parkinson's disease

Recent evidence has shown that neuroinflammation plays a key role in the pathogenesis of Parkinson's disease (PD). However, different components of the brain's immune system may exert diverse effects on neuroinflammatory events in PD. The adaptive immune response, especially the T cell response, can trigger type 1 pro-inflammatory activities and suppress type 2 anti-inflammatory activities, eventually resulting in deregulated neuroinflammation and subsequent dopaminergic neurodegeneration. Additionally, studies have increasingly shown that therapies targeting T cells can alleviate neurodegeneration and motor behavior impairment in animal models of PD. Therefore, we conclude that abnormal T cell-mediated immunity is a fundamental pathological process that may be a promising translational therapeutic target for Parkinson's disease.

Hyaluronan in immune dysregulation and autoimmune diseases

The tissue microenvironment contributes to local immunity and to the pathogenesis of autoimmune diseases - a diverse set of conditions characterized by sterile inflammation, immunity against self-antigens, and destruction of tissues. However, the specific factors within the tissue microenvironment that contribute to local immune dysregulation in autoimmunity are poorly understood. One particular tissue component implicated in multiple autoimmune diseases is hyaluronan (HA), an extracellular matrix (ECM) polymer. HA is abundant in settings of chronic inflammation and contributes to lymphocyte activation, polarization, and migration. Here, we first describe what is known about the size, amount, and distribution of HA at sites of autoimmunity and in associated lymphoid structures in type 1 diabetes, multiple sclerosis, and rheumatoid arthritis. Next, we examine the recent literature on HA and its impact on adaptive immunity, particularly in regards to the biology of lymphocytes and Foxp3+ regulatory T-cells (Treg), a T-cell subset that maintains immune tolerance in healthy individuals. We propose that HA accumulation at sites of chronic inflammation creates a permissive environment for autoimmunity, characterized by CD44-mediated inhibition of Treg expansion. Finally, we address potential tools and strategies for targeting HA and its receptor CD44 in chronic inflammation and autoimmunity.

CD44 Promotes Inflammation and Extracellular Matrix Production During Arteriovenous Fistula Maturation

OBJECTIVE

Arteriovenous fistulae (AVF) remain the optimal conduit for hemodialysis access but continue to demonstrate poor patency and poor rates of maturation. We hypothesized that CD44, a widely expressed cellular adhesion molecule that serves as a major receptor for extracellular matrix components, promotes wall thickening and extracellular matrix deposition during AVF maturation.

APPROACH AND RESULTS

AVF were created via needle puncture in wild-type C57BL/6J and CD44 knockout mice. CD44 mRNA and protein expression was increased in wild-type AVF. CD44 knockout mice showed no increase in AVF wall thickness (8.9 versus 26.8 μm; P=0.0114), collagen density, and hyaluronic acid density, but similar elastin density when compared with control AVF. CD44 knockout mice also showed no increase in vascular cell adhesion molecule-1 expression, intercellular adhesion molecule-1 expression, and monocyte chemoattractant protein-1 expression in the AVF compared with controls; there were also no increased M2 macrophage markers (transglutaminase-2: 81.5-fold, P=0.0015; interleukin-10: 7.6-fold, P=0.0450) in CD44 knockout mice. Delivery of monocyte chemoattractant protein-1 to CD44 knockout mice rescued the phenotype with thicker AVF walls (27.2 versus 14.7 μm; P=0.0306), increased collagen density (2.4-fold; P=0.0432), and increased number of M2 macrophages (2.1-fold; P=0.0335).

CONCLUSIONS

CD44 promotes accumulation of M2 macrophages, extracellular matrix deposition, and wall thickening during AVF maturation. These data show the association of M2 macrophages with wall thickening during AVF maturation and suggest that enhancing CD44 activity may be a strategy to increase AVF maturation.

The role of endothelial HIF-1 αin the response to sublethal hypoxia in C57BL/6 mouse pups

Chronic sublethal hypoxia, a complication of premature birth, is associated with cognitive and motor handicaps. Responsiveness to and recovery from this hypoxic environment is dependent on induction of HIF-1 α in the cells affected. Microvascular endothelial-glial and microvascular endothelial-neuronal precursor interactions have been found to be dynamic and reciprocal, involving autocrine and paracrine signaling, with response and recovery correlated with baseline levels and levels of induction of HIF-1 α.To ascertain the roles of endothelial HIF-1 α in the responses of brain microvascular endothelial cells (EC) and neuronal precursors to hypoxia, we examined the effects of the presence and absence of endothelial HIF-1 α expression in culture and in cells comprising the subventricular zone (SVZ) and dentate gyrus under normoxic and hypoxic conditions. We used C57BL/6 WT and EC HIF-1 α -deficient mice and brain microvascular ECs isolated from these mice in western blots, immunofluorescence, and behavioral studies to examine the roles of EC HIF-1 α behaviors of endothelial and neuronal precursor cells (NPCs) in SVZ and hippocampal tissues under normoxic and hypoxic conditions and behaviors of these mice in open field activity tests. Analyses of ECs and SVZ and dentate gyrus tissues revealed effects of the absence of endothelial HIF-1 α on proliferation and apoptosis as well as open field activity, with both ECs and neuronal cells exhibiting decreased proliferation, increased apoptosis, and pups exhibiting gender-specific differences in open field activities. Our studies demonstrate the autocrine and paracrine effects of EC HIF-1 α-modulating proliferative and apoptotic behaviors of EC and NPC in neurogenic regions of the brain and gender-specific behaviors in normoxic and hypoxic settings.

Role of Anti-Osteopontin Antibodies in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Osteopontin (OPN) is highly expressed in demyelinating lesions in multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). OPN is cleaved by thrombin into N- (OPN-N) and C-terminal (OPN-C) fragments with different ligands and functions. In EAE, administering recombinant OPN induces relapses, whereas treatment with anti-OPN antibodies ameliorates the disease. Anti-OPN autoantibodies (autoAbs) are spontaneously produced during EAE but have never been detected in MS. The aim of the study was to evaluate anti-OPN autoAbs in the serum of MS patients, correlate them with disease course, and recapitulate the human findings in EAE. We performed ELISA in the serum of 122 patients collected cross-sectionally, and 50 patients with relapsing–remitting (RR) disease collected at diagnosis and followed longitudinally for 10 years. In the cross-sectional patients, the autoAb levels were higher in the RR patients than in the primary- and secondary-progressive MS and healthy control groups, and they were highest in the initial stages of the disease. In the longitudinal group, the levels at diagnosis directly correlated with the number of relapses during the following 10 years. Moreover, in patients with active disease, who underwent disease-modifying treatments, autoAbs were higher than in untreated patients and were associated with low MS severity score. The autoAb displayed neutralizing activity and mainly recognized OPN-C rather than OPN-N. To confirm the clinical effect of these autoAbs in vivo, EAE was induced using myelin oligodendrocyte glycoprotein MOG_35–55 in C57BL/6 mice pre-vaccinated with ovalbumin (OVA)-linked OPN or OVA alone. We then evaluated the titer of antibodies to OPN, the clinical scores and in vitro cytokine secretion by spleen lymphocytes. Vaccination significantly induced antibodies against OPN during EAE, decreased disease severity, and the protective effect was correlated with decreased T cell secretion of interleukin 17 and interferon-γ ex vivo. The best effect was obtained with OPN-C, which induced significantly faster and more complete remission than other OPN vaccines. In conclusion, these data suggest that production of anti-OPN autoAbs may favor remission in both MS and EAE. Novel strategies boosting their levels, such as vaccination or passive immunization, may be proposed as a future strategy in personalized MS therapy.

IKKβ-mediated inflammatory myeloid cell activation exacerbates experimental autoimmune encephalomyelitis by potentiating Th1/Th17 cell activation and compromising blood brain barrier

Background

The inflammatory myeloid cell activation is one of the hallmarks of experimental autoimmune encephalomyelitis (EAE), yet the in vivo role of the inflammatory myeloid cell activation in EAE has not been clearly resolved. It is well-known that IKK/NF-κB is a key signaling pathway that regulates inflammatory myeloid activation.

Methods

We investigated the in vivo role of inflammatory myeloid cell activation in myelin oligodendrocyte glycoprotein (MOG) peptides-induced EAE using myeloid cell type-specific ikkβ gene conditional knockout-mice (LysM-Cre/Ikkβ^F/F).

Results

In our study, LysM-Cre/Ikkβ^F/F mice had alleviated clinical signs of EAE corresponding to the decreased spinal demyelination, microglial activation, and immune cell infiltration in the spinal cord, compared to the wild-type mice (WT, Ikkβ^F/F). Myeloid ikkβ gene deletion significantly reduced the percentage of CD4⁺/IFN-γ⁺ (Th1) and CD4⁺/IL-17⁺ (Th17) cells but increased the percentages of CD4⁺/CD25⁺/Foxp3⁺ (Treg) cells in the spinal cord and lymph nodes, corresponding to the altered mRNA expression of IFN-γ, IL-17, IL-23, and Foxp3 in the spinal cords of LysM-Cre/Ikkβ^F/F EAE mice. Also, the beneficial effect of myeloid IKKβ deletion in EAE corresponded to the decreased permeability of the blood brain barrier (BBB).

Conclusions

Our findings strongly suggest that IKK/NF-kB-induced myeloid cell activation exacerbates EAE by activating Th1 and Th17 responses and compromising the BBB. The development of NF-κB inhibitory agents with high efficacy through specific targeting of IKKβ in myeloid cells might be of therapeutic potential in MS and other autoimmune disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0116-1) contains supplementary material, which is available to authorized users.

CD44 Influences Fibroblast Behaviors Via Modulation of Cell-Cell and Cell-Matrix Interactions, Affecting Survivin and Hippo Pathways

CD44 has been studied in a wide variety of cell types, in a diverse array of cell behaviors and in a diverse range of signaling pathways. We now document a role for CD44 in mediating fibroblast behaviors via regulation of N-cadherin, extracellular matrix expression, Survivin and the Hippo pathway. Here, we report our findings on the roles of CD44 in modulating proliferation, apoptosis, migration and invasion of murine wild-type (WT-FB) and CD44 knockout dermal fibroblasts (CD44KO-FB). As we have documented in microvascular endothelial cells lacking CD44, we found persistent increased proliferation, reduced activation of cleaved caspase 3, increased initial attachment, but decreased strength of cell attachment in high cell density, post confluent CD44KO-FB cultures. Additionally, we found that siRNA knock-down of CD44 mimicked the behaviors of CD44KO-FB, restoring the decreases in N-cadherin, collagen type I, fibronectin, Survivin, nuclear fractions of YAP and phospho-YAP and decreased levels of cleaved caspase 3 to the levels observed in CD44KO-FB. Interestingly, plating CD44KO-FB on collagen type I or fibronectin resulted in significant decreases in secondary proliferation rates compared to plating cells on non-coated dishes, consistent with increased cell adhesion compared to their effects on WT-FB. Lastly, siRNA knockdown of CD44 in WT-FB resulted in increased fibroblast migration compared to WT-FB, albeit at reduced rates compared to CD44KO-FB. These results are consistent with CD44's pivotal role in modulating several diverse behaviors important for adhesion, proliferation, apoptosis, migration and invasion during development, growth, repair, maintenance and regression of a wide variety of mesenchymal tissues.

The CD44 ligand hyaluronic acid is elevated in the cerebrospinal fluid of suicide attempters and is associated with increased blood-brain barrier permeability

BACKGROUND

The glycosaminoglycan hyaluronic acid (HA) is an important component of the extracellular matrix (ECM) in the brain. CD44 is a cell adhesion molecule that binds to HA in the ECM and is present on astrocytes, microglia and certain neurons. Cell adhesion molecules have been reported to be involved in anxiety and mood disorders. CD44 levels are decreased in the cerebrospinal fluid (CSF) of depressed individuals, and the CD44 gene has been identified in brain GWAS studies as a possible risk gene for suicidal behavior.

METHOD

We measured the CSF levels of HA and the soluble CD44 (sCD44) in suicide attempters (n=94) and in healthy controls (n=45) using ELISA and electrochemiluminescence assays. We also investigated other proteins known to interact with CD44, such as osteopontin and the matrix metalloproteinases MMP1, MMP3 and MMP9.

RESULTS

The suicide attempters had higher CSF levels of HA (p=.003) and MMP9 (p=.004). The CSF levels of HA correlated with BBB-permeability (rho=0.410, p<.001) and MMP9 correlated with sCD44 levels (rho=0.260, p=.005).

LIMITATIONS

Other relevant biological contributors to suicidal behavior is not addressed in parallel to the specific role of CD44-HA signaling. The gender distribution of the patients from whom CSF was analyzed was uneven.

CONCLUSIONS

Increased BBB-permeability and HA levels might be a results of increased neuroinflammation and can play a role in the pathobiology of suicidal behavior. The CD44 signaling pathway might be considered a novel target for intervention in mood disorders.

Hyaluronan synthesis is necessary for autoreactive T-cell trafficking, activation, and Th1 polarization

The extracellular matrix polysaccharide hyaluronan (HA) accumulates at sites of autoimmune inflammation, including white matter lesions in multiple sclerosis (MS), but its functional importance in pathogenesis is unclear. We have evaluated the impact of 4-methylumbelliferone (4-MU), an oral inhibitor of HA synthesis, on disease progression in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Treatment with 4-MU decreases the incidence of EAE, delays its onset, and reduces the severity of established disease. 4-MU inhibits the activation of autoreactive T cells and prevents their polarization toward a Th1 phenotype. Instead, 4-MU promotes polarization toward a Th2 phenotpye and induction of Foxp3(+) regulatory T cells. Further, 4-MU hastens trafficking of T cells through secondary lymphoid organs, impairs the infiltration of T cells into the CNS parenchyma, and limits astrogliosis. Together, these data suggest that HA synthesis is necessary for disease progression in EAE and that treatment with 4-MU may be a potential therapeutic strategy in CNS autoimmunity. Considering that 4-MU is already a therapeutic, called hymecromone, that is approved to treat biliary spasm in humans, we propose that it could be repurposed to treat MS.

CD43 Functions as an E-Selectin Ligand for Th17 Cells In Vitro and Is Required for Rolling on the Vascular Endothelium and Th17 Cell Recruitment during Inflammation In Vivo

Endothelial E- and P-selectins mediate lymphocyte trafficking in inflammatory processes by interacting with lymphocyte selectin ligands. These are differentially expressed among different T cell subsets and function alone or in cooperation to mediate T cell adhesion. In this study, we characterize the expression and functionality of E-selectin ligands in Th type 17 lymphocytes (Th17 cells) and report that CD43 functions as a Th17 cell E-selectin ligand in vitro that mediates Th17 cell rolling on the vascular endothelium and recruitment in vivo. We demonstrate Th17 cells express CD44, P-selectin glycoprotein ligand (PSGL)-1, and CD43. Few PSGL-1(-/-)CD43(-/-) Th17 cells accumulated on E-selectin under shear flow conditions compared with wild-type cells. CD43(-/-) Th17 cell accumulation on E-selectin was impaired as compared with wild-type and PSGL-1(-/-), and similar to that observed for PSGL-1(-/-)CD43(-/-) Th17 cells, indicating that CD43 alone is a dominant ligand for E-selectin. Notably, this finding is Th17 cell subset specific because CD43 requires cooperation with PSGL-1 in Th1 cells for binding to E-selectin. In vivo, Th17 cell recruitment into the air pouch was reduced in CD43(-/-) mice in response to CCL20 or TNF-α, and intravital microscopy studies demonstrated that CD43(-/-) Th17 cells had impaired rolling on TNF-α-treated microvessels. Furthermore, CD43(-/-) mice were protected from experimental autoimmune encephalomyelitis and had impaired recruitment of Th17 cells in the spinal cord. Our findings demonstrate that CD43 is a major E-selectin ligand in Th17 cells that functions independent of PSGL-1, and they suggest that CD43 may hold promise as a therapeutic target to modulate Th17 cell recruitment.

[A case of multiple sclerosis with bilateral intermediate uveitis]

We describe a case of 20-year-old woman with visual impairment in her left eye. Her left visual acuity was 0.07 and an ophthalmoscopic examination demonstrated bilateral intermediate uveitis (IU). A neurological examination on admission revealed lower nasal quadrantanopsia in her left eye and an exaggerated right patellar tendon reflex. A T2-weighted MRI showed multiple high-intensity lesions in the bilateral periventricular region, corpus callosum, medulla. A short T1 inversion recovery MRI also showed a swollen left retrobulbar optic nerve and posterior thoracic cord lesion at Th 9 level. The latter longitudinal length was approximately 20 mm. Laboratory investigation demonstrated no abnormalities including an anti-aquaporin-4 antibody. A cerebrospinal fluid examination revealed an increased IgG-index (1.21) with oligoclonal IgG babds. Initially, a diagnosis of retrobulbar optic neuritis with IU was made. She received subtenon corticosteroid injection with intravenous methylprednisolone pulse and oral prednisolone therapy. An immediate improvement of her visual symptoms and MRI abnormalities was observed. Approximately 1 year later, a new high-intensity lesion in the right internal capsule was present on a follow-up T2-weighted brain MRI, established a diagnosis of multiple sclerosis (MS) based on the McDonald criteria in 2010. Previous reports in Japan demonstrated few cases of uveitis in patients with MS and this is the first report of MS with IU in Japan.

Multivariate analysis of subjective responses to d-amphetamine in healthy volunteers finds novel genetic pathway associations

RATIONALE

Researchers studying behavioral and physiologic effects of d-amphetamine have explored individual response differences to the drug. Concurrently, genome-wide analyses have identified several single-nucleotide polymorphisms (SNPs) associated with these traits. Univariate methods can identify SNPs associated with behavioral and physiological traits, but multivariate analyses allow identification of clusters of related biologically relevant SNPs and behavioral components.

OBJECTIVES

The aim of the study was to identify clusters of related biologically relevant SNPs and behavioral components in the responses of healthy individuals to d-amphetamine using multivariate analysis.

METHODS

Individuals (N = 375) without substance abuse histories completed surveys and detailed cardiovascular monitoring during randomized, blinded sessions: d-amphetamine (10 and 20 mg) and placebo. We applied parallel independent component analysis (Para-ICA) to data previously analyzed with univariate approaches, revealing new associations between genes and behavioral responses to d-amphetamine.

RESULTS

Three significantly associated (p < .001) phenotype-genotype pairs emerged. The first component included physiologic measures of systolic and diastolic blood pressure (BP) and mean arterial pressure (MAP) along with SNPs in calcium and glutamatergic signaling pathways. The second associated components included the "Anger" items from the Profile of Mood States (POMS) questionnaire and the marijuana effects from the Addiction Research Center Inventory (Cuyas, Verdejo-Garcia et al.), with enriched genetic pathways involved in cardiomyopathy and MAPK signaling. The final pair included "Anxious," "Fatigue," and "Confusion" items from the POMS questionnaire, plus functional pathways related to cardiac muscle contraction and cardiomyopathy.

CONCLUSIONS

Multifactorial genetic networks related to calcium signaling, glutamatergic and dopaminergic synapse function, and amphetamine addiction appear to mediate common behavioral and cardiovascular responses to d-amphetamine.

PECAM-1 isoforms, eNOS and endoglin axis in regulation of angiogenesis

Vascular development and maintenance of proper vascular function through various regulatory mechanisms are critical to our wellbeing. Delineation of the regulatory processes involved in development of the vascular system and its function is one of the most important topics in human physiology and pathophysiology. Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), a cell adhesion molecule with proangiogenic and proinflammatory activity, has been the subject of numerous studies. In the present review, we look at the important roles that PECAM-1 and its isoforms play during angiogenesis, and its molecular mechanisms of action in the endothelium. In the endothelium, PECAM-1 not only plays a role as an adhesion molecule but also participates in intracellular signalling pathways which have an impact on various cell adhesive mechanisms and endothelial nitric oxide synthase (eNOS) expression and activity. In addition, recent studies from our laboratory have revealed an important relationship between PECAM-1 and endoglin expression. Endoglin is an essential molecule during angiogenesis, vascular development and integrity, and its expression and activity are compromised in the absence of PECAM-1. In the present review we discuss the roles that PECAM-1 isoforms may play in modulation of endothelial cell adhesive mechanisms, eNOS and endoglin expression and activity, and angiogenesis.

Modulation of Sox10, HIF-1α, Survivin, and YAP by Minocycline in the Treatment of Neurodevelopmental Handicaps following Hypoxic Insult

Premature infants are at an increased risk of developing cognitive and motor handicaps due to chronic hypoxia. Although the current therapies have reduced the incidence of these handicaps, untoward side effects abound. Using a murine model of sublethal hypoxia, we demonstrated reduction in several transcription factors that modulate expression of genes known to be involved in several neural functions. We demonstrate the induction of these genes by minocycline, a tetracycline antibiotic with noncanonical functions, in both in vitro and in vivo studies. Specifically, there was induction of genes, including Sox10, Hif1a, Hif2a, Birc5, Yap1, Epo, Bdnf, Notch1 (cleaved), Pcna, Mag, Mobp, Plp1, synapsin, Adgra2, Pecam1, and reduction in activation of caspase 3, all known to affect proliferation, apoptosis, synaptic transmission, and nerve transmission. Minocycline treatment of mouse pups reared under sublethal hypoxic conditions resulted in improvement in open field testing parameters. These studies demonstrate beneficial effects of minocycline treatment following hypoxic insult, document up-regulation of several genes associated with improved cognitive function, and support the possibility of minocycline as a potential therapeutic target in the treatment of neurodevelopmental handicaps observed in the very premature newborn population. Additionally, these studies may aid in further interpretation of the effects of minocycline in the treatment trials and animal model studies of fragile X syndrome and multiple sclerosis.

Differences in CD44 Surface Expression Levels and Function Discriminates IL-17 and IFN-γ Producing Helper T Cells

CD44 is a prominent activation marker which distinguishes memory and effector T cells from their naïve counterparts. It also plays a role in early T cell signaling events as it is bound to the lymphocyte-specific protein kinase and thereby enhances T cell receptor signalling. Here, we investigated whether IFN-γ and IL-17 producing T helper cells differ in their CD44 expression and their dependence of CD44 for differentiation. Stimulation of CD4⁺ T cells with allogeneic dendritic cells resulted in the formation of three distinguishable populations: CD44⁺, CD44⁺⁺ and CD44⁺⁺⁺. In vitro and in vivo generated allo-reactive IL-17 producing T helper cells were mainly CD44⁺⁺⁺ as compared to IFN-γ⁺ T helper cells, which were CD44⁺⁺. This effect was enhanced under polarizing conditions. T helper 17 polarization led to a shift towards the CD44⁺⁺⁺ population, whereas T helper 1 polarization diminished this population. Furthermore, blocking CD44 decreased IL-17 secretion, while IFN-γ was barely affected. Titration experiments revealed that low T cell receptor and CD28 stimulation supported T helper 17 rather than T helper 1 development. Under these conditions CD44 could act as a co-stimulatory molecule and replace CD28. Indeed, rested CD44⁺⁺⁺CD4⁺ T cells contained already more total and especially phosphorylated zeta-chain-associated protein kinase 70 as compared to CD44⁺⁺ cells. Our results support the notion, that CD44 enhances T cell receptor signaling strength by delivering lymphocyte-specific protein kinase, which is required for induction of IL-17 producing T helper cells.

A hydrogel-endothelial cell implant mimics infantile hemangioma: modulation by survivin and the Hippo pathway

Microvascular endothelial cells cultured in three-dimensional hydrogel scaffolds form a network of microvessel structures when implanted subcutaneously in mice, inosculate with host vessels, and over time remodel into large ectatic vascular structures resembling hemangiomas. When compared with infantile hemangiomas, similarities were noted, including a temporal progression from a morphological appearance of a proliferative phase to the appearance of an involuted phase, mimicking the proliferative and involutional phases of infantile hemangioma. Consistent with the progression of a proliferative phase to an involuted phase, both the murine implants and human biopsy tissue exhibit reduced expression of Ajuba, YAP, and Survivin labeling as they progressed over time. Significant numbers of CD45+, CD11b+, Mac3+ mononuclear cells were found at the 2-week time point in our implant model that correlated with the presence of CD45+, CD68+ mononuclear cells observed in biopsies of human proliferative-phase hemangiomas. At the 4-week time point in our implant model, only small numbers of CD45+ cells were detected, which again correlated with our findings of significantly diminished CD45+, CD68+ mononuclear cells in human involutional-phase hemangiomas. The demonstration of mononuclear cell infiltration transiently in the proliferative phase of these lesions suggests that the vascular proliferation and/or regression may be driven in part by an immune response. Gross and microscopic morphological appearances of human proliferative and involutional hemangiomas and our implant model correlate well with each other as do the expression levels of Hippo pathway components (Ajuba and YAP) and Survivin and correlate with proliferation in these entities. Inhibitors of Survivin and Ajuba (which we have demonstrated to inhibit proliferation and increase apoptosis in murine hemangioendothelioma cell tissue culture) may have potential as other beneficial treatments for proliferating infantile hemangiomas. This implant model may have potential as a modest through-put screen for testing and development of therapeutics targeted at the proliferative phase of infantile hemangiomas, reducing the subsequent postinvolutional scarring or deformities sometimes associated with these lesions.

CD44: molecular interactions, signaling and functions in the nervous system

CD44 is the major surface hyaluronan (HA) receptor implicated in intercellular and cell-matrix adhesion, cell migration and signaling. It is a transmembrane, highly glycosylated protein with several isoforms resulting from alternative gene splicing. The CD44 molecule consists of several domains serving different functions: the N-terminal extracellular domain, the stem region, the transmembrane domain and the C-terminal tail. In the nervous system, CD44 expression occurs in both glial and neuronal cells. The role of CD44 in the physiology and pathology of the nervous system is not entirely understood, however, there exists evidence suggesting it might be involved in the axon guidance, cytoplasmic Ca²⁺ clearance, dendritic arborization, synaptic transmission, epileptogenesis, oligodendrocyte and astrocyte differentiation, post-traumatic brain repair and brain tumour development.

Korean Red Ginseng and Ginsenoside-Rb1/-Rg1 Alleviate Experimental Autoimmune Encephalomyelitis by Suppressing Th1 and Th17 Cells and Upregulating Regulatory T Cells

The effects of Korean red ginseng extract (KRGE) on autoimmune disorders of the nervous system are not clear. We investigated whether KRGE has a beneficial effect on acute and chronic experimental autoimmune encephalomyelitis (EAE). Pretreatment (daily from 10 days before immunization with myelin basic protein peptide) with KRGE significantly attenuated clinical signs and loss of body weight and was associated with the suppression of spinal demyelination and glial activation in acute EAE rats, while onset treatment (daily after the appearance of clinical symptoms) did not. The suppressive effect of KRGE corresponded to the messenger RNA (mRNA) expression of proinflammatory cytokines (tumor necrosis factor-α [TNF-α] and interleukin [IL]-1β), chemokines (RANTES, monocyte chemotactic protein-1 [MCP-1], and macrophage inflammatory protein-1α [MIP-1α]), adhesion molecules (intercellular adhesion molecule-1 [ICAM-1], vascular cell adhesion molecule-1 [VCAM-1], and platelet endothelial cell adhesion molecule [PECAM-1]), and inducible nitric oxide synthase in the spinal cord after immunization. Interestingly, in acute EAE rats, pretreatment with KRGE significantly reduced the population of CD4(+), CD4(+)/IFN-γ(+), and CD4(+)/IL-17(+) T cells in the spinal cord and lymph nodes, corresponding to the downregulation of mRNA expression of IFN-γ, IL-17, and IL-23 in the spinal cord. On the other hand, KRGE pretreatment increased the population of CD4(+)/Foxp3(+) T cells in the spinal cord and lymph nodes of these rats, corresponding to the upregulation of mRNA expression of Foxp3 in the spinal cord. Interestingly, intrathecal pretreatment of rats with ginsenosides (Rg1 and Rb1) significantly decreased behavioral impairment. These results strongly indicate that KRGE has a beneficial effect on the development and progression of EAE by suppressing T helper 1 (Th1) and Th17 T cells and upregulating regulatory T cells. Additionally, pre- and onset treatment with KRGE alleviated neurological impairment of myelin oligodendrocyte glycoprotein(35-55)-induced mouse model of chronic EAE. These results warrant further investigation of KRGE as preventive or therapeutic strategies for autoimmune disorders, such as multiple sclerosis.

Age-related changes in spleen of Dark Agouti rats immunized for experimental autoimmune encephalomyelitis

The study was undertaken considering age-related changes in susceptibility to experimental autoimmune encephalomyelitis (EAE) and a putative role of spleen in pathogenesis of this disease. The phenotypic and functional characteristics of T splenocytes were examined in young (3-month-old), middle-aged (8-month-old) and aged (26-month-old) Dark Agouti rats immunized for EAE with rat spinal cord in complete Freund's adjuvant. The rat susceptibility to EAE induction, as well as the number of activated CD4+CD134+ lymphocytes retrieved from their spinal cords progressively decreased with aging. To the contrary, in rats immunized for EAE the number of activated CD4+ splenocytes, i.e., CD4+CD134+, CD4+CD25+FoxP3- and CD4+CD40L+ cells, progressively increased with aging. This was associated with age-related increase in (i) CD4+ splenocyte surface expression of CD44, the molecule suggested to be involved in limiting emigration of encephalitogenic CD4+ cells from spleen into blood and (ii) frequency of regulatory T cells, including CD4+CD25+FoxP3+ cells, which are also shown to control encephalitogenic cell migration from spleen into the central nervous system. In favor of expansion of T-regulatory cell pool in aged rats was the greater concentration of IL-10 in unstimulated, Concanavalin A (ConA)- and myelin basic protein (MBP)-stimulated splenocyte cultures from aged rats compared with the corresponding cultures from young ones. Consistent with the age-related increase in the expression of CD44, which is shown to favor Th1 effector cell survival by interfering with CD95-mediated signaling, the frequency of apoptotic cells among CD4+ splenocytes, despite the greater frequency of CD95+ cells, was diminished in splenocyte cultures from aged compared with young rats. In addition, in control, as well as in ConA- and MBP-stimulated splenocyte cultures from aged rats, despite of impaired CD4+ cell proliferation, IFN-γ concentrations were greater than in corresponding cultures from young rats. This most likely reflected increased abundance of IFN-γ-producing cells in splenocyte cultures from aged compared with young rats. The diminished CD4+ cell proliferation in response to ConA and MBP in splenocyte cultures from aged compared with young rats could be, at least partly, associated with an enhanced splenic expression of iNOS mRNA in aged rats. Thus, the study suggests that age-associated changes leading to entrapping of activated CD4+ cells in the spleen could contribute to the restriction in development of EAE in aged rats.

Adhesion molecule-mediated hippo pathway modulates hemangioendothelioma cell behavior

Hemangioendotheliomas are categorized as intermediate-grade vascular tumors that are commonly localized in the lungs and livers. The regulation of this tumor cell's proliferative and apoptotic mechanisms is ill defined. We recently documented an important role for Hippo pathway signaling via endothelial cell adhesion molecules in brain microvascular endothelial cell proliferation and apoptosis. We found that endothelial cells lacking cell adhesion molecules escaped from contact inhibition and exhibited abnormal proliferation and apoptosis. Here we report on the roles of adherens junction molecule modulation of survivin and the Hippo pathway in the proliferation and apoptosis of a murine hemangioendothelioma (EOMA) cell. We demonstrated reduced adherens junction molecule (CD31 and VE-cadherin) expression, increased survivin and Ajuba expression, and a reduction in Hippo pathway signaling resulting in increased proliferation and decreased activation of effector caspase 3 in postconfluent EOMA cell cultures. Furthermore, we confirmed that YM155, an antisurvivin drug that interferes with Sp1-survivin promoter interactions, and survivin small interference RNA (siRNA) transfection elicited induction of VE-cadherin, decreased Ajuba expression, increased Hippo pathway and caspase activation and apoptosis, and decreased cell proliferation. These findings support the importance of the Hippo pathway in hemangioendothelioma cell proliferation and survival and YM155 as a potential therapeutic agent in this category of vascular tumors.

CCR2+ Ly6C(hi) inflammatory monocyte recruitment exacerbates acute disability following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating type of stroke that lacks a specific treatment. An intense immune response develops after ICH, which contributes to neuronal injury, disability, and death. However, the specific mediators of inflammation-induced injury remain unclear. The objective of the present study was to determine whether blood-derived CCR2+ Ly6C(hi) inflammatory monocytes contribute to disability. ICH was induced in mice and the resulting inflammatory response was quantified using flow cytometry, confocal microscopy, and neurobehavioral testing. Importantly, blood-derived monocytes were distinguished from resident microglia by differential CD45 staining and by using bone marrow chimeras with fluorescent leukocytes. After ICH, blood-derived CCR2+ Ly6C(hi) inflammatory monocytes trafficked into the brain, outnumbered other leukocytes, and produced tumor necrosis factor. Ccr2(-/-) mice, which have few circulating inflammatory monocytes, exhibited better motor function following ICH than control mice. Chimeric mice with wild-type CNS cells and Ccr2(-/-) hematopoietic cells also exhibited early improvement in motor function, as did wild-type mice after inflammatory monocyte depletion. These findings suggest that blood-derived inflammatory monocytes contribute to acute neurological disability. To determine the translational relevance of our experimental findings, we examined CCL2, the principle ligand for the CCR2 receptor, in ICH patients. Serum samples from 85 patients were collected prospectively at two hospitals. In patients, higher CCL2 levels at 24 h were independently associated with poor functional outcome at day 7 after adjusting for potential confounding variables. Together, these findings suggest that inflammatory monocytes worsen early disability after murine ICH and may represent a therapeutic target for patients.

CD44 regulation of endothelial cell proliferation and apoptosis via modulation of CD31 and VE-cadherin expression

CD44 has been implicated in a diverse array of cell behaviors and in a diverse range of signaling pathway activations under physiological and pathophysiological conditions. We have documented a role for CD44 in mediating vascular barrier integrity via regulation of PECAM-1 (CD31) expression. We now report our findings on the roles of CD44 in modulating proliferation and apoptosis of microvascular endothelial cells via its modulation of CD31 and VE-cadherin expression and the Hippo pathway. In this report, we demonstrate persistent increased proliferation and reduced activations of both effector and initiator caspases in high cell density, postconfluent CD44 knock-out (CD44KO), and CD31KO cultures. We found that reconstitution with murine CD44 or CD31 restored the proliferative and caspase activation rates to WT levels. Moreover, we have confirmed that the CD31 ecto-domain plays a key role in specific caspase cascades as well as cell adhesion-mediated cell growth and found that CD31 deficiency results in a reduction in VE-cadherin expression. Last, we have shown that both CD44KO and CD31KO endothelial cells exhibit a reduced VE-cadherin expression correlating with increased survivin expression and YAP nuclear localization, consistent with inactivation of the Hippo pathway, resulting in increased proliferation and decreased apoptosis. These findings support the concept that CD44 mediates several of its effects on endothelia through modulation of adhesion protein expression, which, in addition to its known modulation of junctional integrity, matrix metalloproteinase levels and activation, interactions with cortical membrane proteins, and selected signaling pathways, plays a key role as a critical regulator of vascular function.

White matter astrocytes in health and disease

Myelination by oligodendrocytes is a highly specialized process that relies on intimate interactions between the axon and the oligodendrocytes. Astrocytes have an important part in facilitating myelination in the CNS, however, comparatively less is known about how they affect myelination. This review therefore summarizes the literature and explores lingering questions surrounding differences between white matter and gray matter astrocytes, how astrocytes support myelination, how their dysfunction in pathological states contributes to myelin pathologies and how astrocytes may facilitate remyelination. We discuss how astrocytes in the white matter are specialized to promote myelination and myelin maintenance by clearance of extracellular ions and neurotransmitters and by secretion of pro-myelinating factors. Additionally, astrocyte-oligodendrocyte coupling via gap junctions is crucial for both myelin formation and maintenance, due to K(+) buffering and possibly metabolic support for oligodendrocytes via the panglial syncytium. Dysfunctional astrocytes aberrantly affect oligodendrocytes, as exemplified by a number of leukodystrophies in which astrocytic pathology is known as the direct cause of myelin pathology. Conversely, in primary demyelinating diseases, such as multiple sclerosis, astrocytes may facilitate remyelination. We suggest that specific manipulation of astrocytes could help prevent myelin pathologies and successfully restore myelin sheaths after demyelination.

CD44 regulates vascular endothelial barrier integrity via a PECAM-1 dependent mechanism

Vascular integrity is a critical parameter in normal growth and development. Loss of appropriate vascular barrier function is present in various immune- and injury-mediated pathological conditions. CD44 is an adhesion molecule expressed by multiple cell types, including endothelial cells (EC). The goal of the present study was to examine how loss of CD44 affected vascular permeability. Using C57BL/6 WT and CD44-KO mice, we found no significant permeability to Evan's Blue in either strain at baseline. However, there was significantly increased histamine-induced permeability in CD44-deficient mice compared to WT counterparts. Similar results were observed in vitro, where CD44-deficient endothelial monolayers were also impermeable to 40kD-FITC dextran in the absence of vasoactive challenge, but exhibited enhanced and prolonged permeability following histamine. However, CD44-KO monolayers have reduced baseline barrier strength by electrical resistance, which correlated with increased permeability, at baseline, to smaller molecular weight 4-kD FITC-dextran, suggesting weakly formed endothelial junctions. The CD44-KO EC displayed several characteristics consistent with impaired barrier function/dysfunctional EC junctions, including differential expression, phosphorylation, and localization of endothelial junction proteins, increased matrix metalloprotease expression, and altered cellular morphology. Reduced platelet endothelial cell adhesion molecule-1 (PECAM-1) expression by CD44-KO EC in vivo and in vitro was also observed. Reconstitution of murine CD44 or PECAM-1 restored these defects to near WT status, suggesting CD44 regulates vascular permeability and integrity through a PECAM-1 dependent mechanism.