Glucosamine-mediated immunomodulation after stroke is sexually dimorphic

Growing evidence suggests that galectin-3 (Gal-3) is instrumental in orchestrating innate immune response and microglia activation following different brain pathologies. However, its role remains controversial. We recently showed that a readily available natural product glucosamine may act as a strong modulator of Gal-3. Glucosamine is a naturally occurring sugar and a precursor in the synthesis of glycosylated proteins. It is often used as a supplement to treat symptoms of various inflammatory conditions. Our recent work suggests that by increasing the synthesis and availability of Gal-3 ligands and/or by regulating its expression levels, glucosamine may significantly modulate Gal-3 signaling. Because evidence suggests that Gal-3 might be differentially regulated after ischemic injury in the brains of female mice, here we examined and compared the immunomodulatory potential of glucosamine in male and female stroke. The mice were subjected to transient middle cerebral artery occlusion (MCAO), followed by different reperfusion periods. The short-term 5 days treatment with glucosamine (150 ​mg/kg i.p.) was initiated 2 ​hrs after stroke. To visualize the effects of glucosamine treatment on post-stroke inflammation, we took advantage of a transgenic mouse model bearing the dual reporter system luciferase/GFP under transcriptional control of a murine TLR2 promoter (TLR2-luc-GFP) allowing in vivo bioluminescence imaging of innate immune response and microglial activation. We report that after stroke, both, male and female mice strongly up-regulate the TLR2 bioluminescence signals from activated microglia, however, the observed in vivo immunomodulatory effects of glucosamine after stroke were sex-dependent. Analysis of cytokine profiles at protein level, in glucosamine-treated male mice 72hsr after stroke, revealed down regulation of pro-inflammatory cytokines, an increase in levels of anti-inflammatory cytokines including IL-4, IL13 and colony stimulating factors MCFC and GM-CSF and a significant decrease in the size of ischemic lesion in male mice. Conversely, in female mice glucosamine markedly increases the pro-inflammatory signaling and exacerbates ischemic injury. Analysis of the downstream signaling target of glucosamine/Gal-3 revealed that glucosamine administration restored PPAR-γ activity in male but not in female mice 3 days following MCAO. Together, our results suggest that glucosamine acts as a fine tuner of post-ischemic inflammation in a sex dependent-manner and may have therapeutic potential after stroke in males. Based on our results propose that targeting immune system after stroke may require adapted sex-specific therapeutic approaches.

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Immunomodulatory effects of glucosamine are sex dependent.

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Glucosamine differentially modulates galectin-3/IL4R signaling in male and female mice.

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Glucosamine restores PPAR-gamma transcriptional activity in male mice and protects against stroke in male mice.

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Glucosamine increases inflammatory signaling and exacerbates ischemic injury in female mice.

Tlr2 Deficiency is Associated with Enhanced Elements of Neuronal Repair and Caspase 3 Activation Following Brain Ischemia

The aim of this study was to apply multimodal in vivo imaging to assess the influence of altered innate immunity on brain repair after ischemic lesion. Tlr2-deficient mice were compared to wild type controls, as they lack Tlr2-mediated pro-inflammatory signaling triggered by postischemic necrosis. The ischemic lesion was induced by transient middle cerebral artery occlusion for 60 min, followed by brain imaging and analysis at four time points until 28 days after ischemia. Multimodal in vivo imaging involved a combination of 3 modalities: (1) magnetic resonance imaging by T2-weighted scans to assess brain lesion size, (2) bioluminescence imaging of Gap43-luc/gfp transgenic mice to visualize the axonal remodeling, and (3) caged-luciferin bioluminescence imaging of DEVD-luciferin allowing for visualization of caspase 3 and 7 activity in Gap43-luc/gfp mice. This enabled innovative correlation of the MRI-determined lesion size to photon fluxes obtained by bioluminescence imaging. Our data revealed that following ischemia, Tlr2-deficient mice had higher Gap43 expression and higher levels of caspases 3 and 7 activity, which was accompanied by enhanced levels of synaptic plasticity markers DLG4 and synaptophysin when compared to wild type controls. Altered inflammation in Tlr2-deficient mice was accompanied by enhanced elements of post-stroke repair, in particular during the chronic phase of recovery, but also with delayed final consolidation of the brain lesion.

Brain Response to Injuries: When Microglia Go Sexist

Microglia are the principle immune cells of the brain. Once activated, microglial cells may exhibit a wide repertoire of the context-dependent profiles ranging from highly neurotoxic to more protective and pro-regenerative cellular phenotypes. While to date the mechanisms involved in the molecular regulation of the microglia polarization phenotypes remain elusive, growing evidence suggests that gender may markedly affect the inflammatory and/or glial responses following brain injuries. In the recent years, special attention has been given to the role of microglia in sexual dimorphism, both in healthy brain and diseased brain. Here, we review recent advances revealing microglia as an important determinant of gender differences under physiological conditions and in injured brain. We also discuss how microglia-driven innate immunity and signaling pathways might be involved in the sex-dependent responses following brain ischemic injury. Finally we describe how advanced methods such as live imaging techniques may help elucidate the role of microglia in the modulation of immune responses and gender difference after stroke.

A Shift from a Pivotal to Supporting Role for the Growth-Associated Protein (GAP-43) in the Coordination of Axonal Structural and Functional Plasticity

In a number of animal species, the growth-associated protein (GAP), GAP-43 (aka: F1, neuromodulin, B-50, G50, pp46), has been implicated in the regulation of presynaptic vesicular function and axonal growth and plasticity via its own biochemical properties and interactions with a number of other presynaptic proteins. Changes in the expression of GAP-43 mRNA or distribution of the protein coincide with axonal outgrowth as a consequence of neuronal damage and presynaptic rearrangement that would occur following instances of elevated patterned neural activity including memory formation and development. While functional enhancement in GAP-43 mRNA and/or protein activity has historically been hypothesized as a central mediator of axonal neuroplastic and regenerative responses in the central nervous system, it does not appear to be the crucial substrate sufficient for driving these responses. This review explores the historical discovery of GAP-43 (and associated monikers), its transcriptional, post-transcriptional and post-translational regulation and current understanding of protein interactions and regulation with respect to its role in axonal function. While GAP-43 itself appears to have moved from a pivotal to a supporting factor, there is no doubt that investigations into its functions have provided a clearer understanding of the biochemical underpinnings of axonal plasticity.

Molecular imaging of nestin in neuroinflammatory conditions reveals marked signal induction in activated microglia

Background

Nestin is a known marker of neuronal progenitor cells in the adult brain. Following neuro- and gliogenesis, nestin is replaced by cell type-specific intermediate filaments, e.g., neurofilaments for panneuronal expression and glial fibrillary acidic protein as a specific marker of mature astrocytes. While previous work have been mostly focused on the neuronal fate of nestin-positive progenitors, in the present study, we sought to investigate in real time how nestin signals and cellular expression patterns are controlled in the context of neuroinflammatory challenge and ischemic brain injury.

Methods

To visualize effects of neuroinflammation on neurogenesis/gliogenesis, we created a transgenic model bearing the dual reporter system luciferase and GFP under transcriptional control of the murine nestin promoter. In this model, transcriptional activation of nestin was visualized from the brains of living animals using biophotonic/bioluminescence molecular imaging and a high resolution charged coupled device camera. Nestin induction profiles in vivo and in tissue sections were analyzed in two different experimental paradigms: middle cerebral artery occlusion and lipopolysaccharide-induced innate immune stimuli.

Results

We report here a context- and injury-dependent induction and cellular expression profile of nestin. While in the baseline conditions the nestin signal and/or GFP expression was restricted to neuronal progenitors, the cellular expression patterns of nestin following innate immune challenge and after stroke markedly differed shifting the cellular expression patterns towards activated microglia/macrophages and astrocytes.

Conclusions

Our results suggest that nestin may serve as a context-dependent biomarker of inflammatory response in glial cells including activated microglia/macrophages.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0816-7) contains supplementary material, which is available to authorized users.

In vitro neuroprotective effects of ciliary neurotrophic factor on dorsal root ganglion neurons with glutamate-induced neurotoxicity

Ciliary neurotrophic factor has neuroprotective effects mediated through signal transducer and Janus kinase (JAK) 2/activator of transcription 3 (STAT3) and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathways. Whether ciliary neurotrophic factor is neuroprotective for glutamate-induced excitotoxicity of dorsal root ganglion neurons is poorly understood. In the present study, the in vitro neuroprotective effects of ciliary neurotrophic factor against glutamate-induced excitotoxicity were determined in a primary culture of dorsal root ganglion neurons from Wistar rat embryos at embryonic day 15. Whether the JAK2/STAT3 and PI3K/Akt signaling pathways were related to the protective effects of ciliary neurotrophic factor was also determined. Glutamate exposure inhibited neurite outgrowth, cell viability, and growth-associated protein 43 expression and promoted apoptotic neuronal cell death, all of which were reversed by the administration of exogenous ciliary neurotrophic factor. Additionally, preincubation with either JAK2 inhibitor AG490 or PI3K inhibitor LY294002 blocked the neuroprotective effect of ciliary neurotrophic factor. These data indicate that the two pathways JAK2/STAT3 and PI3K/Akt play major roles in mediating the in vitro neuroprotective effects of ciliary neurotrophic factor on dorsal root ganglion neurons with glutamate-induced neurotoxicity.

Increased expression and colocalization of GAP43 and CASP3 after brain ischemic lesion in mouse

GAP43 is a protein involved in neurite outgrowth during development and axon regeneration reflecting its presynaptic localization in developing neurons. Recently, it has been demonstrated that GAP43 is a ligand of CASP3 involved in receptor endocytosis and is also localized post-synaptically. In this study, by using a transgenic mouse strain carrying a bioluminescent reporter for GAP43 combined with an in vivo bioluminescence assay for CASP3, we demonstrated that one day after brain ischemic lesion and, even more pronounced, four days after stroke, expression of both CASP3 and Gap43 in neurons increased more than 40 times. The in vivo approach of CASP3 and GAP43 colocalization imaging was further validated and quantified by immunofluorescence. Importantly, in 82% of GAP43 positive cells, colocalization with CASP3 was present. These findings suggested that one and four days after stroke CASP3 expression, not necessarily associated with neuronal death, increased and suggested that CASP3 and GAP43 might be part of a common molecular pathway involved in early response to ischemic events occurring after onset of stroke.

Early-stage treatment with Withaferin A reduces levels of misfolded superoxide dismutase 1 and extends lifespan in a mouse model of amyotrophic lateral sclerosis

Approximately 20% of cases of familial amyotrophic lateral sclerosis (ALS) are caused by mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Recent studies have shown that Withaferin A (WA), an inhibitor of nuclear factor-kappa B activity, was efficient in reducing disease phenotype in a TAR DNA binding protein 43 transgenic mouse model of ALS. These findings led us to test WA in mice from 2 transgenic lines expressing different ALS-linked SOD1 mutations, SOD1(G93A) and SOD1(G37R). Intraperitoneal administration of WA at a dosage of 4 mg/kg of body weight was initiated from postnatal day 40 until end stage in SOD1(G93A) mice, and from 9 months until end stage in SOD1(G37R) mice. The beneficial effects of WA in the SOD1(G93A) mice model were accompanied by an alleviation of neuroinflammation, a decrease in levels of misfolded SOD1 species in the spinal cord, and a reduction in loss of motor neurons resulting in delayed disease progression and mortality. Interestingly, WA treatment triggered robust induction of heat shock protein 25 (a mouse ortholog of heat shock protein 27), which may explain the reduced level of misfolded SOD1 species in the spinal cord of SOD1(G93A) mice and the decrease of neuronal injury responses, as revealed by real-time imaging of biophotonic SOD1(G93A) mice expressing a luciferase transgene under the control of the growth-associated protein 43 promoter. These results suggest that WA may represent a potential lead compound for drug development aiming to treat ALS.

A review of novel optical imaging strategies of the stroke pathology and stem cell therapy in stroke

Transplanted stem cells can induce and enhance functional recovery in experimental stroke. Invasive analysis has been extensively used to provide detailed cellular and molecular characterization of the stroke pathology and engrafted stem cells. But post mortem analysis is not appropriate to reveal the time scale of the dynamic interplay between the cell graft, the ischemic lesion and the endogenous repair mechanisms. This review describes non-invasive imaging techniques which have been developed to provide complementary in vivo information. Recent advances were made in analyzing simultaneously different aspects of the cell graft (e.g., number of cells, viability state, and cell fate), the ischemic lesion (e.g., blood-brain-barrier consistency, hypoxic, and necrotic areas) and the neuronal and vascular network. We focus on optical methods, which permit simple animal preparation, repetitive experimental conditions, relatively medium-cost instrumentation and are performed under mild anesthesia, thus nearly under physiological conditions. A selection of recent examples of optical intrinsic imaging, fluorescence imaging and bioluminescence imaging to characterize the stroke pathology and engrafted stem cells are discussed. Special attention is paid to novel optimal reporter genes/probes for genetic labeling and tracking of stem cells and appropriate transgenic animal models. Requirements, advantages and limitations of these imaging platforms are critically discussed and placed into the context of other non-invasive techniques, e.g., magnetic resonance imaging and positron emission tomography, which can be joined with optical imaging in multimodal approaches.

The emerging use of in vivo optical imaging in the study of neurodegenerative diseases

The detection and subsequent quantification of photons emitted from living tissues, using highly sensitive charged-couple device (CCD) cameras, have enabled investigators to noninvasively examine the intricate dynamics of molecular reactions in wide assortment of experimental animals under basal and pathophysiological conditions. Nevertheless, extrapolation of this in vivo optical imaging technology to the study of the mammalian brain and related neurodegenerative conditions is still in its infancy. In this review, we introduce the reader to the emerging use of in vivo optical imaging in the study of neurodegenerative diseases. We highlight the current instrumentation that is available and reporter molecules (fluorescent and bioluminescent) that are commonly used. Moreover, we examine how in vivo optical imaging using transgenic reporter mice has provided new insights into Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Prion disease, and neuronal damage arising from excitotoxicity and inflammation. Furthermore, we also touch upon studies that have utilized these technologies for the development of therapeutic strategies for neurodegenerative conditions that afflict humans.

Adeno-associated virus-mediated delivery of a recombinant single-chain antibody against misfolded superoxide dismutase for treatment of amyotrophic lateral sclerosis

There is emerging evidence that the misfolding of superoxide dismutase 1 (SOD1) may represent a common pathogenic event in both familial and sporadic amyotrophic lateral sclerosis (ALS). To reduce the burden of misfolded SOD1 species in the nervous system, we have tested a novel therapeutic approach based on adeno-associated virus (AAV)–mediated tonic expression of a DNA construct encoding a secretable single-chain fragment variable (scFv) antibody composed of the variable heavy and light chain regions of a monoclonal antibody (D3H5) binding specifically to misfolded SOD1. A single intrathecal injection of the AAV encoding the single-chain antibody in SOD1^G93A mice at 45 days of age resulted in sustained expression of single-chain antibodies in the spinal cord, and it delayed disease onset and extension of life span by up to 28%, in direct correlation with scFv titers in the spinal cord. The treatment caused attenuation of neuronal stress signals and reduction in levels of misfolded SOD1 in the spinal cord of SOD1^G93A mice. From these results, we propose that an immunotherapy based on intrathecal inoculation of AAV encoding a secretable scFv against misfolded SOD1 should be considered as potential treatment for ALS, especially for individuals carrying SOD1 mutations.

Effects of neuregulin-1β on growth-associated protein 43 expression in dorsal root ganglion neurons with excitotoxicity induced by glutamate in vitro

Neuregulin-1β (NRG-1β) is a growth factor with potent neuroprotective capacity. Growth-associated protein 43 (GAP-43) is expressed in dorsal root ganglion (DRG) neurons and an indicator of neuronal survival in vitro. The purpose of present study is to evaluate the effects of NRG-1β on GAP-43 expression in DRG neurons with excitotoxicity induced by glutamate (Glu) in vitro. The phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated protein kinase 1/2 (ERK1/2) signaling pathways involved in these effects were also determined. Embryonic rat DRG neurons were treated with Glu in the absence or presence of NRG-1β and PI3K inhibitor LY294002 and/or ERK1/2 inhibitor PD98059. After that, GAP-43 mRNA and GAP-43 protein levels were analyzed by real time-PCR and western blot assay, respectively. GAP-43 expression in situ was determined by immunofluorescent labeling. The results showed that the decreased GAP-43 levels induced by Glu could be partially reversed by the presence of NRG-1β. Inhibitors (LY294002, PD98059) either alone or in combination blocked the effects of NRG-1β. These data provide new insights of the actions of NRG-1β in sensory neurons.

Making the brain glow: in vivo bioluminescence imaging to study neurodegeneration

Bioluminescence imaging (BLI) takes advantage of the light-emitting properties of luciferase enzymes, which produce light upon oxidizing a substrate (i.e., D-luciferin) in the presence of molecular oxygen and energy. Photons emitted from living tissues can be detected and quantified by a highly sensitive charge-coupled device camera, enabling the investigator to noninvasively analyze the dynamics of biomolecular reactions in a variety of living model organisms such as transgenic mice. BLI has been used extensively in cancer research, cell transplantation, and for monitoring of infectious diseases, but only recently experimental models have been designed to study processes and pathways in neurological disorders such as Alzheimer disease, Parkinson disease, or amyotrophic lateral sclerosis. In this review, we highlight recent applications of BLI in neuroscience, including transgene expression in the brain, longitudinal studies of neuroinflammatory responses to neurodegeneration and injury, and in vivo imaging studies of neurogenesis and mitochondrial toxicity. Finally, we highlight some new developments of BLI compounds and luciferase substrates with promising potential for in vivo studies of neurological dysfunctions.