Enriched environment reduces apolipoprotein E (ApoE) in reactive astrocytes and attenuates inflammation of the peri-infarct tissue after experimental stroke

Genetically Predicted Apolipoprotein E Levels with the Risk of Panvascular Diseases: A Mendelian Randomization Study

The aim of this study was to comprehensively assess the causal relationship between the overall genetic effect of circulating ApoE levels and panvascular lesions using newer genome-wide association data and two-sample bidirectional Mendelian randomization (MR) analysis. Two-way MR using single-nucleotide polymorphisms of circulating ApoE as instrumental variables was performed using the highest-priority Genome-wide association study (GWAS) data, with factor-adjusted and data-corrected statistics, to estimate causal associations between circulating ApoE levels and 10 pan-vascular diseases in > 500,000 UK Biobank participants, > 400,000 participants of Finnish ancestry, and numerous participants in a consortium of predominantly European ancestry. Meta-analysis was conducted to assess positive results. After correcting for statistical results, elevated circulating ApoE levels were shown to have a significant protective effect against Cerebral ischemia (CI) [IVW odds ratio (OR) 0.888, 95% Confidence Interval (CI): 0.823-0.958, p = 2.3 × 10-3], Coronary heart disease [IVW OR 0.950,95% CI: 0.924-0.976, p = 2.0 × 10-4] had a significant protective effect and potentially suggestive protective causality against Angina pectoris [IVW odds ratio (OR) 0.961, 95%CI: 0.931-0.991, p = 1.1 × 10-2]. There was a potential causal effect for increased risk of Heart failure (HF) [IVW ratio (OR) 1.040, 95%CI: 1.006-1.060, p = 1.8 × 10-2]. (Bonferroni threshold p < 0.0026, PFDR < 0.05) Reverse MR analysis did not reveal significant evidence of a causal effect of PVD on changes in circulating ApoE levels. Meta-analysis increases reliability of results. Elevated circulating ApoE levels were particularly associated with an increased risk of heart failure. Elevated ApoE levels reduce the risk of cerebral ischemia, coronary heart disease, and angina pectoris, reflecting a protective effect. The possible pathophysiological role of circulating ApoE levels in the development of panvascular disease is emphasized.

Environmental Enrichment in Stroke Research: an Update

Environmental enrichment (EE) refers to different forms of stimulation, where the environment is designed to improve the levels of sensory, cognitive, and motor stimuli, inducing stroke recovery in animal models. Stroke is a leading cause of mortality and neurological disability among older adults, hence the importance of developing strategies to improve recovery for such patients. This review provides an update on recent findings, compiling information regarding the parameters affected by EE exposure in both preclinical and clinical studies. During stroke recovery, EE exposure has been shown to improve both the cognitive and locomotor aspects, inducing important neuroplastic alterations, increased angiogenesis and neurogenesis, and modified gene expression, among other effects. There is a need for further research in this field, particularly in those aspects where the evidence is inconclusive. Moreover, it is necessary refine and adapt the EE paradigms for application in human patients.

Integrating single-cell and spatially resolved transcriptomic strategies to survey the astrocyte response to stroke in male mice

Astrocytes, a type of glial cell in the central nervous system (CNS), adopt diverse states in response to injury that are influenced by their location relative to the insult. Here, we describe a platform for spatially resolved, single-cell transcriptomics and proteomics, called tDISCO (tissue-digital microfluidic isolation of single cells for -Omics). We use tDISCO alongside two high-throughput platforms for spatial (Visium) and single-cell transcriptomics (10X Chromium) to examine the heterogeneity of the astrocyte response to a cortical ischemic stroke in male mice. We show that integration of Visium and 10X Chromium datasets infers two astrocyte populations, proximal or distal to the injury site, while tDISCO determines the spatial boundaries and molecular profiles that define these populations. We find that proximal astrocytes show differences in lipid shuttling, with enriched expression of Apoe and Fabp5. Our datasets provide a resource for understanding the roles of astrocytes in stroke and showcase the utility of tDISCO for hypothesis-driven, spatially resolved single-cell experiments.

Enriched Environment Effects on Myelination of the Central Nervous System: Role of Glial Cells

Myelination is regulated by various glial cells in the central nervous system (CNS), including oligodendrocytes (OLs), microglia, and astrocytes. Myelination of the CNS requires the generation of functionally mature OLs from OPCs. OLs are the myelin-forming cells in the CNS. Microglia play both beneficial and detrimental roles during myelin damage and repair. Astrocyte is responsible for myelin formation and regeneration by direct interaction with oligodendrocyte lineage cells. These glial cells are influenced by experience-dependent activities such as environmental enrichment (EE). To date, there are few studies that have investigated the association between EE and glial cells. EE with a complex combination of sensorimotor, cognitive, and social stimulation has a significant effect on cognitive impairment and brain plasticity. Hence, one mechanism through EE improving cognitive function may rely on the mutual effect of EE and glial cells. The purpose of this paper is to review recent research into the efficacy of EE for myelination and glial cells at cellular and molecular levels and offers critical insights for future research directions of EE and the treatment of EE in cognitive impairment disease.

An enriched environment prevents cognitive impairment in an Alzheimer's disease model by enhancing the secretion of exosomal microRNA-146a from the choroid plexus

Alzheimer’s disease (AD) is characterized by the extensive deposition of amyloid-β plaques and neurofibrillary tangles. We previously found that preserved function of astrocytes is associated with cognitively normal subjects with AD pathology. Here we show that an enriched environment (EE) can prevent cognitive impairment in AD model mice by ameliorating astrocytic inflammation and increasing synaptic density in the subiculum area of the hippocampus. In AD model mice treated with an EE, increased levels of microRNA (miR)-146a and down-regulation of NF-κB were observed in the hippocampus. In addition, increased levels of interferon (IFN)-γ were seen in serum from mice exposed to an EE. In vitro, enhanced miR-146a expression was observed in exosomes derived from the choroid plexus (CP) after IFN-γ treatment. In further in vitro experiments, we transfected miR-146a into Aβ/lipopolysaccharide-induced inflammatory astrocytes and showed that miR-146a ameliorated astrocytic inflammation by down-regulating tumor necrosis factor receptor-associated factor 6 and NF-κB. The present study indicates that following an EE, exosomal miR-146a derived from the CP cells is a key factor in ameliorating astrocytic inflammation, leading to synaptogenesis and correction of cognitive impairment.

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An enriched environment (EE) prevented the cognitive impairment in 5 ​× ​FAD mice.

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An EE inhibited astrocytic inflammation and increased miR-146a in hippocampus.

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An EE increased the levels of interferon-γ (IFN-γ) in serum.

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IFN-γ increased the secretion of exosomal miR-146a from cultured choroid plexus.

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Transfection of miR-146a down-regulated NF-κB in cultured astrocytes.

Plasticity-Enhancing Effects of Levodopa Treatment after Stroke

Dopaminergic treatment in combination with rehabilitative training enhances long-term recovery after stroke. However, the underlying mechanisms on structural plasticity are unknown. Here, we show an increased dopaminergic innervation of the ischemic territory during the first week after stroke induced in Wistar rats subjected to transient occlusion of the middle cerebral artery (tMCAO) for 120 min. This response was also found in rats subjected to permanent focal ischemia induced by photothrombosis (PT) and mice subjected to PT or tMCAO. Dopaminergic branches were detected in the infarct core of mice and rats in both stroke models. In addition, the Nogo A pathway was significantly downregulated in rats treated with levodopa (LD) compared to vehicle-treated animals subjected to tMCAO. Specifically, the number of Nogo A positive oligodendrocytes as well as the levels of Nogo A and the Nogo A receptor were significantly downregulated in the peri-infarct area of LD-treated animals, while the number of Oligodendrocyte transcription factor 2 positive cells increased in this region after treatment. In addition, we observed lower protein levels of Growth Associated Protein 43 in the peri-infarct area compared to sham-operated animals without treatment effect. The results provide the first evidence of the plasticity-promoting actions of dopaminergic treatment following stroke.

Postoperative Cognitive Dysfunction and the Protective Effects of Enriched Environment: A Systematic Review

BACKGROUND

Currently, the number of individuals who undergo surgery is greatly increased. As a consequence, postoperative cognitive dysfunction (POCD) has gradually gained more attention.

SUMMARY

POCD is a perioperative complication requiring sensitive preoperative and postoperative neuropsychiatric tests, and its incidence in both cardiac and noncardiac surgery is high, especially in elderly individuals. Surgical, patient, and anesthetic factors may all lead to the occurrence and development of POCD. The key mechanism of POCD may be the inflammatory response of the central nervous system during surgery, which is similar to that of Alzheimer's disease (AD). Enriched environment (EE), a factor that can significantly improve and prevent neurodegenerative diseases, may have a beneficial effect on POCD. Key Messages: This review aims to elucidate the mechanism of the occurrence and development of POCD, analyze the possible influence of EE on POCD at the molecular level, and provide a direction for its treatment.

Preclinical neurorehabilitation with environmental enrichment confers cognitive and histological benefits in a model of pediatric asphyxial cardiac arrest

Pediatric asphyxial cardiac arrest (ACA) often leaves children with physical, cognitive, and emotional disabilities that affect overall quality of life, yet rehabilitation is neither routinely nor systematically provided. Environmental enrichment (EE) is considered a preclinical model of neurorehabilitation and thus we sought to investigate its efficacy in our established model of pediatric ACA. Male Sprague-Dawley rat pups (post-natal day 16-18) were randomly assigned to ACA (9.5 min) or Sham injury. After resuscitation, the rats were assigned to 21 days of EE or standard (STD) housing during which time motor, cognitive, and anxiety-like (i.e., affective) outcomes were assessed. Hippocampal CA1 cells were quantified on post-operative day-22. Both ACA + STD and ACA + EE performed worse on beam-balance vs. Sham controls (p < 0.05) and did not differ from one another overall (p > 0.05); however, a single day analysis on the last day of testing revealed that the ACA + EE group performed better than the ACA + STD group (p < 0.05) and did not differ from the Sham controls (p > 0.05). Both Sham groups performed better than ACA + STD (p < 0.05) but did not differ from ACA + EE (p > 0.05) in the open field test. Spatial learning and declarative memory were improved and CA1 neuronal loss was attenuated in the ACA + EE vs. ACA + STD group (p < 0.05). Collectively, the data suggest that providing rehabilitation after pediatric ACA can reduce histopathology and improve motor and cognitive ability.

Enriched environment alleviates post-stroke cognitive impairment through enhancing α7-nAChR expression in rats

ABSTRACT Background: Enriched environment (EE) is a simple and effective intervention to improve cognitive function in post-stroke cognitive impairment (PSCI), partly due to the rebalancing of the cholinergic signaling pathway in the hippocampus. α7-nicotinic acetylcholine receptor (α7-nAChR) is a cholinergic receptor whose activation inhibits inflammation and promotes the recovery of neurological function in PSCI patients. However, it is still unclear whether EE can regulate α7-nAChR and activate the cholinergic anti-inflammatory pathway (CAP) in PSCI. Objective: To investigate the effects of EE on cognitive impairment, and the role of α7-nAChR in PSCI. Methods: A PSCI rat model was induced by middle cerebral artery occlusion and reperfusion (MCAO/R) and were reared in standard environment (SE) or EE for 28d, control group with sham surgery. Cognitive function was determined by Morris water maze test. The long-term potentiation (LTP) was assessed by Electrophysiology. Histopathological methods were used to determine infarct volume, α7-nAChR expression and the cytokines and cholinergic proteins expression. Results: Compared with SE group, rats in EE group had better cognitive function, higher expression of α7-nAChR positive neurons in hippocampal CA1 region. In addition, EE attenuated unfavorable changes induced by MCAO/R in cytokines and cholinergic proteins, and also enhanced LTP promoted by nicotine and attenuated by α-BGT; but showed no significantly difference in infarct volume. Conclusions: EE markedly improves cognitive impairment and enhances neuroplasticity in PSCI rats, which may be closely related to enhancement of α7-nAChR expression.

Enriched environment improves post-stroke cognitive impairment and inhibits neuroinflammation and oxidative stress by activating Nrf2-ARE pathway

INTRODUCTION

Neuroinflammation and oxidative stress are major mechanisms of post-stroke cognitive impairment (PSCI) neural injury and decreased spatial and memory capacity. Enriched environment (EE) is an effective method to improve cognitive dysfunction. However, the regulation by EE of neuroinflammation, oxidative stress and associated mechanisms in animal models remains unclear.

MATERIALS AND METHODS

In this study, a rat PSCI model was established by middle cerebral artery occlusion (MCAO). Rats were randomly divided into the control group, standard environment (SE) group and EE group for 28 days. A Morris water-maze test was used to measure cognitive function at 7, 14 and 28 days after MCAO. Rats were sacrificed on the 28th day. Quantitative PCR, immunohistochemistry and ELISA were respectively used to detect mRNA expression of NF-E2-related factor 2 (Nrf2) and Nrf2 response genes, the expression of IL-1β and levels of proinflammatory cytokines in the hippocampus.

RESULTS

EE improved mNSS scores and cognitive ability in PSCI rats. EE increased mRNA expression of the Nrf2 and Nrf2 response genes, including heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1). EE significantly decreased the level of malondialdehyde (MDA) and increased the levels of superoxide dismutase (SOD) and glutathione (GSH), in the hippocampus of PSCI rats. EE reduced the number of IL-1β positive cells in the hippocampus, and IL-1β levels in the hippocampus and serum. EE increased GFAP-positive astrocytes in the hippocampus, and BDNF levels in the hippocampus and serum.

CONCLUSIONS

EE can improve cognitive function in PSCI rats by inhibiting neuroinflammation and oxidative stress.

Triiodothyronine modulates neuronal plasticity mechanisms to enhance functional outcome after stroke

The development of new therapeutic approaches for stroke patients requires a detailed understanding of the mechanisms that enhance recovery of lost neurological functions. The efficacy to enhance homeostatic mechanisms during the first weeks after stroke will influence functional outcome. Thyroid hormones (TH) are essential regulators of neuronal plasticity, however, their role in recovery related mechanisms of neuronal plasticity after stroke remains unknown. This study addresses important findings of 3,5,3′-triiodo-L-thyronine (T₃) in the regulation of homeostatic mechanisms that adjust excitability – inhibition ratio in the post-ischemic brain. This is valid during the first 2 weeks after experimental stroke induced by photothrombosis (PT) and in cultured neurons subjected to an in vitro model of acute cerebral ischemia. In the human post-stroke brain, we assessed the expression pattern of TH receptors (TR) protein levels, important for mediating T₃ actions.

Our results show that T₃ modulates several plasticity mechanisms that may operate on different temporal and spatial scales as compensatory mechanisms to assure appropriate synaptic neurotransmission. We have shown in vivo that long-term administration of T₃ after PT significantly (1) enhances lost sensorimotor function; (2) increases levels of synaptotagmin 1&2 and levels of the post-synaptic GluR2 subunit in AMPA receptors in the peri-infarct area; (3) increases dendritic spine density in the peri-infarct and contralateral region and (4) decreases tonic GABAergic signaling in the peri-infarct area by a reduced number of parvalbumin⁺ / c-fos⁺ neurons and glutamic acid decarboxylase 65/67 levels. In addition, we have shown that T₃ modulates in vitro neuron membrane properties with the balance of inward glutamate ligand-gated channels currents and decreases synaptotagmin levels in conditions of deprived oxygen and glucose. Interestingly, we found increased levels of TRβ1 in the infarct core of post-mortem human stroke patients, which mediate T₃ actions. Summarizing, our data identify T₃ as a potential key therapeutic agent to enhance recovery of lost neurological functions after ischemic stroke.

MRI Evaluation of Axonal Remodeling After Combination Treatment With Xiaoshuan Enteric-Coated Capsule and Enriched Environment in Rats After Ischemic Stroke

Xiaoshuan enteric-coated capsule (XSEC) is a compound Chinese medicine widely used for the treatment of ischemic stroke. Enriched environment (EE) is a rehabilitative intervention designed to facilitate physical, cognitive, and social activity after brain injury. This study aimed to assess whether the XSEC and EE combination could provide synergistic efficacy in axonal remodeling compared to that with a single treatment after ischemic stroke using magnetic resonance imaging (MRI) followed by histological analysis. Rats were subjected to permanent middle cerebral artery occlusion and treated with XSEC and EE alone or in combination for 30 days. T2-weighted imaging and diffusion tensor imaging (DTI) were performed to examine the infarct volume and axonal remodeling, respectively. The co-localization of Ki67 with NG2 or CNPase was examined by immunofluorescence staining to assess oligodendrogenesis. The expressions of growth associated protein-43 (GAP-43) and growth inhibitors NogoA/Nogo receptor (NgR)/RhoA/Rho-associated kinase2 (ROCK2) were measured using western blot and qRT-PCR. The Morris water maze (MWM) was performed to evaluate the cognitive function. MRI and histological measurements indicated XSEC and EE individually benefited axonal reorganization after stroke. Notably, XSEC + EE decreased infarct volume compared with XSEC or EE monotherapy and increased ipsilateral residual volume compared with vehicle group. DTI showed XSEC + EE robustly increased fractional anisotropy while decreased axial diffusivity and radial diffusivity in the injured cortex, striatum, and external capsule. Meanwhile, diffusion tensor tractography revealed XSEC + EE elevated fiber density in the cortex and external capsule and increased fiber length in the striatum and external capsule compared with the monotherapies. These MRI measurements, confirmed by histology, showed that XSEC + EE promoted axonal restoration. Additionally, XSEC + EE amplified oligodendrogenesis, decreased the expressions of NogoA/NgR/RhoA/ROCK2, and increased the expression of GAP-43 in the peri-infarct tissues. In parallel to these findings, rats treated with XSEC + EE exhibited higher cognitive recovery than those treated with XSEC or EE monotherapy, as evidenced by MWM test. Taken together, our data implicated that XSEC + EE exerted synergistic effects on alleviating atrophy and encouraging axonal reorganization partially by promoting oligodendrogenesis and overcoming intrinsic growth-inhibitory signaling, thereby facilitating higher cognitive recovery.

Astrocytic proBDNF and Tonic GABA Distinguish Active versus Reactive Astrocytes in Hippocampus

Astrocytes are the most abundant cell type in the brain and they make close contacts with neurons and blood vessels. They respond dynamically to various environmental stimuli and change their morphological and functional properties. Both physiological and pathological stimuli can induce versatile changes in astrocytes, as this phenomenon is referred to as ‘astrocytic plasticity’. However, the molecular and cellular mechanisms of astrocytic plasticity in response to various stimuli remain elusive, except for the presence of hypertrophy, a conspicuous structural change which is frequently observed in activated or reactive astrocytes. Here, we investigated differential characteristics of astrocytic plasticity in a stimulus-dependent manner. Strikingly, a stab wound brain injury lead to hypertrophy of astrocytes accompanied by increased GABA expression and tonic GABA release in mouse CA1 hippocampus. In contrast, the mice experiencing enriched environment exhibited astrocytic hypertrophy with enhanced proBDNF immunoreactivity but without GABA signal. Based on the results, we define proBDNF-positive/GABA-negative hypertrophic astrocytes as ‘active’ astrocytes and GABA-positive hypertrophic astrocytes as ‘reactive’ astrocytes, respectively. We propose for the first time that astrocytic proBDNF can be a bona fide molecular marker of the active astrocytes, which are distinct from the reactive astrocytes which show hypertrophy but with aberrant GABA.

MicroRNA-124-loaded nanoparticles increase survival and neuronal differentiation of neural stem cells in vitro but do not contribute to stroke outcome in vivo

There is a high quest for novel therapeutic strategies to enhance recovery after stroke. MicroRNA-124 (miR-124) has been described as neuroprotective and anti-inflammatory molecule. Moreover, miR-124 is a well described enhancer of adult neurogenesis that could offer potentially beneficial effects. Herein, we used miR-124-loaded nanoparticles (miR-124 NPs) to evaluate their therapeutic potential in an in vitro and in vivo model of stroke. For that, neuroprotective and neurogenic responses were assessed in an in vitro model of stroke. Here, we found that miR-124 NPs decreased cell death and improved neuronal differentiation of subventricular zone (SVZ) neural stem cell cultures after oxygen and glucose deprivation. In contrast, intravenous injection of miR-124 NPs immediately after permanent focal ischemia induced by photothrombosis (PT) did not provide a better neurological outcome. In addition, treatment did not affect the number of 5-bromo-2'-deoxyuridine (BrdU)- and doublecortin/BrdU- positive cells in the SVZ at the study endpoint of 14 days after PT. Likewise, the ischemic insult did not affect the numbers of neuronal progenitors in the SVZ. However, in PT mice miR-124 NPs were able to specifically augment interleukin-6 levels at day 2 post-stroke. Furthermore, we also showed that NPs reached the brain parenchyma and were internalized by brain resident cells. Although, promising in vitro data could not be verified in vivo as miR-124 NPs treatment did not improve functional outcome nor presented beneficial actions on neurogenesis or post-stroke inflammation, we showed that our NP formulation can be a safe alternative for drug delivery into the brain.

Enhancing endogenous capacity to repair a stroke-damaged brain: An evolving field for stroke research

Stroke represents a severe medical condition that causes stroke survivors to suffer from long-term and even lifelong disability. Over the past several decades, a vast majority of stroke research targets neuroprotection in the acute phase, while little work has been done to enhance stroke recovery at the later stage. Through reviewing current understanding of brain plasticity, stroke pathology, and emerging preclinical and clinical restorative approaches, this review aims to provide new insights to advance the research field for stroke recovery. Lifelong brain plasticity offers the long-lasting possibility to repair a stroke-damaged brain. Stroke impairs the structural and functional integrity of entire brain networks; the restorative approaches containing multi-components have great potential to maximize stroke recovery by rebuilding and normalizing the stroke-disrupted entire brain networks and brain functioning. The restorative window for stroke recovery is much longer than previously thought. The optimal time for brain repair appears to be at later stage of stroke rather than the earlier stage. It is expected that these new insights will advance our understanding of stroke recovery and assist in developing the next generation of restorative approaches for enhancing brain repair after stroke.

SOX9 Is an Astrocyte-Specific Nuclear Marker in the Adult Brain Outside the Neurogenic Regions

Astrocytes have in recent years become the focus of intense experimental interest, yet markers for their definitive identification remain both scarce and imperfect. Astrocytes may be recognized as such by their expression of glial fibrillary acidic protein, glutamine synthetase, glutamate transporter 1 (GLT1), aquaporin-4, aldehyde dehydrogenase 1 family member L1, and other proteins. However, these proteins may all be regulated both developmentally and functionally, restricting their utility. To identify a nuclear marker pathognomonic of astrocytic phenotype, we assessed differential RNA expression by FACS-purified adult astrocytes and, on that basis, evaluated the expression of the transcription factor SOX9 in both mouse and human brain. We found that SOX9 is almost exclusively expressed by astrocytes in the adult brain except for ependymal cells and in the neurogenic regions, where SOX9 is also expressed by neural progenitor cells. Transcriptome comparisons of SOX9+ cells with GLT1+ cells showed that the two populations of cells exhibit largely overlapping gene expression. Expression of SOX9 did not decrease during aging and was instead upregulated by reactive astrocytes in a number of settings, including a murine model of amyotrophic lateral sclerosis (SOD1G93A), middle cerebral artery occlusion, and multiple mini-strokes. We quantified the relative number of astrocytes using the isotropic fractionator technique in combination with SOX9 immunolabeling. The analysis showed that SOX9+ astrocytes constitute ∼10-20% of the total cell number in most CNS regions, a smaller fraction of total cell number than previously estimated in the normal adult brain.SIGNIFICANCE STATEMENT Astrocytes are traditionally identified immunohistochemically by antibodies that target cell-specific antigens in the cytosol or plasma membrane. We show here that SOX9 is an astrocyte-specific nuclear marker in all major areas of the CNS outside of the neurogenic regions. Based on SOX9 immunolabeling, we document that astrocytes constitute a smaller fraction of total cell number than previously estimated in the normal adult mouse brain.

CX3C chemokine receptor 1 deficiency modulates microglia morphology but does not affect lesion size and short-term deficits after experimental stroke

Background

The fractalkine/CX₃C chemokine receptor 1 (CX₃CR1) pathway has been identified to play an essential role in the chemotaxis of microglia, leukocyte trafficking and microglia/macrophage recruitment. It has also been shown to be important in the regulation of the inflammatory response in the early phase after experimental stroke. The present study was performed to investigate if CX₃CR1 deficiency affects microglia during the first 14 days with consequences for tissue damage after experimental stroke.

Results

CX3CR1 deficiency significantly increased the number of intersections of GFP positive microglia in the proximal peri-infarct area at 2, 7 and 14 days following tMCAO compared to heterozygous and wildtype littermates. In addition, the length of microglial branches increased until day 7 in CX₃CR1 knockout mice while the presence of a functional CX3CR1 allele resulted in a gradual reduction of their length following tMCAO. After stroke, wildtype, heterozygous and CX3CR1 deficient mice did not show differences in the composite neuroscore and assessment of infarct volumes from CX3CR1 wildtype, heterozygous and deficient mice revealed no differences between the genotypes 7 and 14 days after stroke.

Conclusion

Results demonstrate that CX3CR1 deficiency affects the morphology of GFP positive microglia located in the proximal peri-infarct region during the first 14 days after tMCAO. Our data also indicate that CX3CR1 deficiency does not affect definite infarct volumes. Modulation of the CX3CR1 pathway may have implication for microglia function contributing to mechanisms of tissue reorganization in the post-ischemic brain.

Reactive astrogliosis in stroke: Contributions of astrocytes to recovery of neurological function

Alterations in neuronal connectivity, particularly in the "peri-infarct" tissue adjacent to the region of ischemic damage, are important contributors to the spontaneous recovery of function that commonly follows stroke. Peri-infarct astrocytes undergo reactive astrogliosis and play key roles in modulating the adaptive responses in neurons. This reactive astrogliosis shares many features with that induced by other forms of damage to the central nervous system but also differs in details that potentially influence neurological recovery. A subpopulation of astrocytes within a few hundred micrometers of the infarct proliferate and are centrally involved in the development of the glial scar that separates the damaged tissue in the infarct from surrounding normal brain. The intertwined processes of astrocytes adjacent to the infarct provide the core structural component of the mature scar. Interventions that cause early disruption of glial scar formation typically impede restoration of neurological function. Marked reactive astrogliosis also develops in cells more distant from the infarct but these cells largely remain in the spatial territories they occupied prior to stroke. These cells play important roles in controlling the extracellular environment and release proteins and other molecules that are able to promote neuronal plasticity and improve functional recovery. Treatments manipulating aspects of reactive astrogliosis can enhance neuronal plasticity following stroke. Optimising these treatments for use in human stroke would benefit from a more complete characterization of the specific responses of peri-infarct astrocytes to stroke as well as a better understanding of the influence of other factors including age, sex, comorbidities and reperfusion of the ischemic tissue.

Ocular Dominance Plasticity after Stroke Was Preserved in PSD-95 Knockout Mice

Neuronal plasticity is essential to enable rehabilitation when the brain suffers from injury, such as following a stroke. One of the most established models to study cortical plasticity is ocular dominance (OD) plasticity in the primary visual cortex (V1) of the mammalian brain induced by monocular deprivation (MD). We have previously shown that OD-plasticity in adult mouse V1 is absent after a photothrombotic (PT) stroke lesion in the adjacent primary somatosensory cortex (S1). Exposing lesioned mice to conditions which reduce the inhibitory tone in V1, such as raising animals in an enriched environment or short-term dark exposure, preserved OD-plasticity after an S1-lesion. Here we tested whether modification of excitatory circuits can also be beneficial for preserving V1-plasticity after stroke. Mice lacking postsynaptic density protein-95 (PSD-95), a signaling scaffold present at mature excitatory synapses, have lifelong juvenile-like OD-plasticity caused by an increased number of AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) -silent synapses in V1 but unaltered inhibitory tone. In fact, using intrinsic signal optical imaging, we show here that OD-plasticity was preserved in V1 of adult PSD-95 KO mice after an S1-lesion but not in PSD-95 wildtype (WT)-mice. In addition, experience-enabled enhancement of the optomotor reflex of the open eye after MD was compromised in both lesioned PSD-95 KO and PSD-95 WT mice. Basic V1-activation and retinotopic map quality were, however, not different between lesioned PSD-95 KO mice and their WT littermates. The preserved OD-plasticity in the PSD-95 KO mice indicates that V1-plasticity after a distant stroke can be promoted by either changes in excitatory circuitry or by lowering the inhibitory tone in V1 as previously shown. Furthermore, the present data indicate that an increased number of AMPA-silent synapses preserves OD-plasticity not only in the healthy brain, but also in another experimental paradigm of cortical plasticity, namely the long-range influence on V1-plasticity after an S1-lesion.

Neuroprotection by combination of resveratrol and enriched environment against ischemic brain injury in rats

OBJECTIVES

Both resveratrol (RV) and enriched environment (EE) exert beneficial effects on neurological functional recovery after an ischemic brain injury.

METHODS

The neuroprotective effect of combined treatment of RV and EE was examined in a rat model of middle cerebral artery occlusion (MCAO), aiming to further promote neurological functional recovery.

RESULTS

The combined therapy of RV and EE clearly improved locomotor activity and behaviour examination, compared to the monotherapy of RV or EE alone. Stroke severity was also markedly ameliorated by the co-treatment. Mechanistic study revealed that the combined treatment reduced oxidative stress. Moreover, the detrimental ERK1/2 signalling upregulated by MCAO injury was markedly suppressed by the co-treatment, compared to RV or EE monotherapy.

DISCUSSION

Altogether, the combined therapy of RV and EE showed a clearly enhanced neuroprotective effect, compared to RV or EE monotherapy, which might be a new strategy for the treatment of ischemic brain injury.

A Small Motor Cortex Lesion Abolished Ocular Dominance Plasticity in the Adult Mouse Primary Visual Cortex and Impaired Experience-Dependent Visual Improvements

It was previously shown that a small lesion in the primary somatosensory cortex (S1) prevented both cortical plasticity and sensory learning in the adult mouse visual system: While 3-month-old control mice continued to show ocular dominance (OD) plasticity in their primary visual cortex (V1) after monocular deprivation (MD), age-matched mice with a small photothrombotically induced (PT) stroke lesion in S1, positioned at least 1 mm anterior to the anterior border of V1, no longer expressed OD-plasticity. In addition, in the S1-lesioned mice, neither the experience-dependent increase of the spatial frequency threshold (“visual acuity”) nor of the contrast threshold (“contrast sensitivity”) of the optomotor reflex through the open eye was present. To assess whether these plasticity impairments can also occur if a lesion is placed more distant from V1, we tested the effect of a PT-lesion in the secondary motor cortex (M2). We observed that mice with a small M2-lesion restricted to the superficial cortical layers no longer expressed an OD-shift towards the open eye after 7 days of MD in V1 of the lesioned hemisphere. Consistent with previous findings about the consequences of an S1-lesion, OD-plasticity in V1 of the nonlesioned hemisphere of the M2-lesioned mice was still present. In addition, the experience-dependent improvements of both visual acuity and contrast sensitivity of the open eye were severely reduced. In contrast, sham-lesioned mice displayed both an OD-shift and improvements of visual capabilities of their open eye. To summarize, our data indicate that even a very small lesion restricted to the superficial cortical layers and more than 3mm anterior to the anterior border of V1 compromised V1-plasticity and impaired learning-induced visual improvements in adult mice. Thus both plasticity phenomena cannot only depend on modality-specific and local nerve cell networks but are clearly influenced by long-range interactions even from distant brain regions.

Adult neurogenesis and brain remodelling after brain injury: From bench to bedside?

OBJECTIVE

Brain trauma and stroke cause important disabilities. The mechanisms involved are now well described, but all therapeutics developed thus far for neuro-protection are currently unsuccessful at improving neurologic prognosis. The recently studied neuro-restorative time following brain injury may point towards a promising therapeutic approach. The purpose of this paper is to explain the mechanisms of this revolutionary concept, give an overview of related knowledge and discuss its transfer into clinical practice.

DATA SOURCES AND SYNTHESIS

An overview of the neurogenesis concept using MEDLINE, EMBASE and CENTRAL databases was carried out in May 2014. The clinicaltrials.gov registry was used to search for ongoing clinical trials in this domain.

CONCLUSION

The concept of brain remodelling upset fundamental ideas concerning the neurologic system and opened new fields of research. Therapies currently under evaluation hold promising results and could have a real prognostic impact in future years, but the translation of these therapies from the laboratory to the clinic is still far from completion.

Dynamics of major histocompatibility complex class II-positive cells in the postischemic brain--influence of levodopa treatment

Background

Cerebral ischemia activates both the innate and the adaptive immune response, the latter being activated within days after the stroke onset and triggered by the recognition of foreign antigens.

Methods

In this study we have investigated the phenotype of antigen presenting cells and the levels of associated major histocompatibility complex class II (MHC II) molecules in the postischemic brain after transient occlusion of the middle cerebral artery (tMCAO) followed by levodopa/benserazide treatment. Male Sprague Dawley rats were subjected to tMCAO for 105 minutes and received levodopa (20 mg/kg)/benserazide (15 mg/kg) for 5 days starting on day 2 after tMCAO. Thereafter, immune cells were isolated from the ischemic and contralateral hemisphere and analyzed by flow cytometry. Complementarily, the spatiotemporal profile of MHC II-positive (MHC II⁺) cells was studied in the ischemic brain during the first 30 days after tMCAO; protein levels of MHC II and the levels of inflammation associated cytokines were determined in the ischemic hemisphere.

Results

We found that microglia/macrophages represent the main MHC II expressing cell in the postischemic brain one week after tMCAO. No differences in absolute cell numbers were found between levodopa/benserazide and vehicle-treated animals. In contrast, MHC II protein levels were significant downregulated in the ischemic infarct core by levodopa/benserazide treatment. This reduction was accompanied by reduced levels of IFN-γ, TNF-α and IL-4 in the ischemic hemisphere. In the contralateral hemisphere, we exclusively detected MHC II⁺ cells in the corpus callosum. Interestingly, the number of cells was increased by treatment with levodopa/benserazide independent from the infarct size 14 days after tMCAO.

Conclusions

Results suggest that dopamine signaling is involved in the adaptive immune response after stroke and involves microglia/macrophages.

Reduction of rat brain CD8+ T-cells by levodopa/benserazide treatment after experimental stroke

The activation of inflammatory cascades in the ischemic hemisphere impairs mechanisms of tissue reorganization with consequences for recovery of lost neurological function. Recruitment of T-cell populations to the post-ischemic brain occurs and represents a significant part of the inflammatory response. This study was conducted to investigate if treatment with levodopa, potentially acting as an immunomodulator, affects the T-cell accumulation in the post-ischemic brain. Male Sprague-Dawley rats were subjected to transient occlusion of the middle cerebral artery (tMCAO) for 105 min followed by levodopa/benserazide treatment (20 mg/kg/15 mg/kg) for 5 days initiated on day 2 post-stroke. One week after tMCAO, T-cell populations were analysed from brains, and levels of interleukin (IL)-1β, chemokine (C-X-C motif) ligand 1, IL-4, IL-5, interferon gamma and IL-13 were analysed. After levodopa/benserazide treatment, we found a significant reduction of cytotoxic T-cells (CD3+ CD8+ ) in the ischemic hemisphere together with reduced levels of T-cell-associated cytokine IL-5, while other T-cell populations (CD3+, CD3+ CD4+, CD3+ CD4+ CD25+) were unchanged compared with vehicle-treated rats. Moreover, a reduced number of cells was associated with reduced levels of intercellular adhesion molecule 1, expressed in endothelial cells, in the infarct core of levodopa/benserazide-treated animals. Together, we provide the first evidence that dopamine can act as a potential immunomodulator by attenuating inflammation in the post-ischemic brain.

Enriched housing enhances recovery of limb placement ability and reduces aggrecan-containing perineuronal nets in the rat somatosensory cortex after experimental stroke

Stroke causes life long disabilities where few therapeutic options are available. Using electrical and magnetic stimulation of the brain and physical rehabilitation, recovery of brain function can be enhanced even late after stroke. Animal models support this notion, and housing rodents in an enriched environment (EE) several days after experimental stroke stimulates lost brain function by multisensory mechanisms. We studied the dynamics of functional recovery of rats with a lesion to the fore and hind limb motor areas induced by photothrombosis (PT), and with subsequent housing in either standard (STD) or EE. In this model, skilled motor function is not significantly enhanced by enriched housing, while the speed of recovery of sensori-motor function substantially improves over the 9-week study period. In particular, this stroke lesion completely obliterates the fore and hind limb placing ability when visual and whisker guidance is prevented, a deficit that persists for up to 9 weeks of recovery, but that is markedly restored within 2 weeks by enriched housing. Enriched housing after stroke also leads to a significant loss of perineuronal net (PNN) immunoreactivity; detection of aggrecan protein backbone with AB1031 antibody was decreased by 13–22%, and labelling of a glycan moiety of aggrecan with Cat-315 antibody was reduced by 25–30% in the peri-infarct area and in the somatosensory cortex, respectively. The majority of these cells are parvalbumin/GABA inhibitory interneurons that are important in sensori-information processing. We conclude that damage to the fore and hind limb motor areas provides a model of loss of limb placing response without visual guidance, a deficit also seen in more than 50% of stroke patients. This loss is amenable to recovery induced by multiple sensory stimulation and correlates with a decrease in aggrecan-containing PNNs around inhibitory interneurons. Modulating the PNN structure after ischemic damage may provide new therapies enhancing tactile/proprioceptive function after stroke.

Enriched housing down-regulates the Toll-like receptor 2 response in the mouse brain after experimental stroke

Post-ischemic inflammation plays an important role in the evolution of brain injury, recovery and repair after stroke. Housing rodents in an enriched environment provides multisensory stimulation to the brain and enhances functional recovery after experimental stroke, also depressing the release of cytokines and chemokines in the peri-infarct. In order to identify targets for late stroke treatment, we studied the dynamics of inflammation and the contribution of resident Toll-like receptor 2 (TLR2) expressing microglia cells. We took advantage of the biophotonic/bioluminescent imaging technique using the reporter mouse-expressing luciferase and GFP reporter genes under transcriptional control of the murine TLR2 promoter (TLR2-luc/GFP mice) for non-invasive in vivo analysis of TLR2 activation/response in photothrombotic stroke after differential housing. Real-time imaging at 1day after stroke, revealed up-regulation of TLR2 in response to photothrombotic stroke that subsequently declined over time of recovery (14days). The inflammatory response was persistently down-regulated within days of enriched housing, enhancing recovery of lost sensori-motor function in TLR2-luc mice without affecting infarct size. The number of YM1-expressing microglia in the peri-infarct and areas remote from the infarct was also markedly attenuated. Using a live imaging approach, we demonstrate that multisensory stimulation rapidly, persistently and generally attenuates brain inflammation after experimental stroke, reducing the TLR2 response and leading to improved neurological outcome. TLR2-expressing microglia cells may provide targets for new stroke therapeutics.

Environmental enrichment extends ocular dominance plasticity into adulthood and protects from stroke-induced impairments of plasticity

Ocular dominance (OD) plasticity in mouse primary visual cortex (V1) declines during postnatal development and is absent beyond postnatal day 110 if mice are raised in standard cages (SCs). An enriched environment (EE) promotes OD plasticity in adult rats. Here, we explored cellular mechanisms of EE in mouse V1 and the therapeutic potential of EE to prevent impairments of plasticity after a cortical stroke. Using in vivo optical imaging, we observed that monocular deprivation in adult EE mice (i) caused a very strong OD plasticity previously only observed in 4-wk-old animals, (ii) restored already lost OD plasticity in adult SC-raised mice, and (iii) preserved OD plasticity after a stroke in the primary somatosensory cortex. Using patch-clamp electrophysiology in vitro, we also show that (iv) local inhibition was significantly reduced in V1 slices of adult EE mice and (v) the GABA/AMPA ratio was like that in 4-wk-old SC-raised animals. These observations were corroborated by in vivo analyses showing that diazepam treatment significantly reduced the OD shift of EE mice after monocular deprivation. Taken together, EE extended the sensitive phase for OD plasticity into late adulthood, rejuvenated V1 after 4 mo of SC-rearing, and protected adult mice from stroke-induced impairments of cortical plasticity. The EE effect was mediated most likely by preserving low juvenile levels of inhibition into adulthood, which potentially promoted adaptive changes in cortical circuits.

Inhibition of CXCL12 signaling attenuates the postischemic immune response and improves functional recovery after stroke

After stroke, brain inflammation in the ischemic hemisphere hampers brain tissue reorganization and functional recovery. Housing rats in an enriched environment (EE) dramatically improves recovery of lost neurologic functions after experimental stroke. We show here that rats housed in EE after stroke induced by permanent occlusion of the middle cerebral artery (pMCAO), showed attenuated levels of proinflammatory cytokines in the ischemic core and the surrounding peri-infarct area, including a significant reduction in the stroke-induced chemokine receptor CXCR4 and its natural ligand stromal cell-derived factor-1 (CXCL12). To mimic beneficial effects of EE, we studied the impact of inhibiting CXCL12 action on functional recovery after transient MCAO (tMCAO). Rats treated with the specific CXCL12 receptor antagonist 1-[4-(1,4,8,11-tetrazacyclotetradec-1-ylmethyl)phenyl]methyl]-1,4,8,11-tetrazacyclo-tetradecan (AMD3100) showed improved recovery compared with saline-treated rats after tMCAO, without a concomitant reduction in infarct size. This was accompanied by a reduction of infiltrating immune cells in the ischemic hemisphere, particularly cluster of differentiation 3-positive (CD3(+)) and CD3(+)/CD4(+) T cells. Spleen atrophy and delayed death of splenocytes, induced by tMCAO, was prevented by AMD3100 treatment. We conclude that immoderate excessive activation of the CXCL12 pathway after stroke contributes to depression of neurologic function after stroke and that CXCR4 antagonism is beneficial for the recovery after stroke.

The effects of a rhythm and music-based therapy program and therapeutic riding in late recovery phase following stroke: a study protocol for a three-armed randomized controlled trial

BACKGROUND

Stroke represents one of the most costly and long-term disabling conditions in adulthood worldwide and there is a need to determine the effectiveness of rehabilitation programs in the late phase after stroke. Limited scientific support exists for training incorporating rhythm and music as well as therapeutic riding and well-designed trials to determine the effectiveness of these treatment modalities are warranted.

METHODS/DESIGN

A single blinded three-armed randomized controlled trial is described with the aim to evaluate whether it is possible to improve the overall health status and functioning of individuals in the late phase of stroke (1-5 years after stroke) through a rhythm and music-based therapy program or therapeutic riding. About 120 individuals will be consecutively and randomly allocated to one of three groups: (T1) rhythm and music-based therapy program; (T2) therapeutic riding; or (T3) control group receiving the T1 training program a year later. Evaluation is conducted prior to and after the 12-week long intervention as well as three and six months later. The evaluation comprises a comprehensive functional and cognitive assessment (both qualitative and quantitative), and questionnaires. Based on the International classification of functioning, disability, and health (ICF), the outcome measures are classified into six comprehensive domains, with participation as the primary outcome measure assessed by the Stroke Impact Scale (SIS, version 2.0.). The secondary outcome measures are grouped within the following domains: body function, activity, environmental factors and personal factors. Life satisfaction and health related quality of life constitute an additional domain.

CURRENT STATUS

A total of 84 participants were randomised and have completed the intervention. Recruitment proceeds and follow-up is on-going, trial results are expected in early 2014.

DISCUSSION

This study will ascertain whether any of the two intervention programs can improve overall health status and functioning in the late phase of stroke. A positive outcome would increase the scientific basis for the use of such interventions in the late phase after stroke.

TRIAL REGISTRATION

Clinical Trials.gov Identifier: NCT01372059.

Dietary β-carotene regulates interleukin-1β-induced expression of apolipoprotein E in astrocytes isolated from stroke-prone spontaneously hypertensive rats

Stroke-prone spontaneously hypertensive rats (SHRSP) have an abnormality in cholesterol synthesis, but the pathological relevance of this to stroke and related neuronal disorders is not yet clear. The induction of astrocyte-derived cholesterol transportation to neurons by apolipoprotein E (apoE) promotes neuronal repair after brain injuries such as stroke. Such repair is reduced by interleukin-1 beta (IL-1β) and stroke conditions. Furthermore, fibroblast growth factor 1 (FGF1) regulates the production of apoE-cholesterol-rich high density lipoproteins (HDL) and induces gliosis of astrocytes. On the other hand, high levels of plasma carotenoids reduce the risk of ischemic stroke. Thus, we investigated the expression of apoE in primary astrocytes that had been treated with IL-1β or β-carotene. In addition, we compared the expression levels of Apoe genes in astrocytes from SHRSP/Izm and normal control rats, Wistar-Kyoto rats (WKY/Izm) following hypoxia/reoxygenation (H/R). The expression levels of genes and proteins were investigated by RT-PCR, Western blotting (WB), and immunofluorescence analysis. IL-1β decreased the expression levels of the Apoe gene. Conversely, β-carotene significantly enhanced the expression levels of genes related to cholesterol regulation, including Abca1, Abcg1, Hmgcr as well as Apoe. During H/R, the gene expression levels of Apoe were decreased in the SHRSP/Izm rats in comparison with the WKY/Izm rats. These results suggest that IL-1β decreases Apoe expression levels, whereas β-carotene strongly elevates Apoe levels and inhibits FGF1-mediated gliosis of astrocytes. Furthermore, under hypoxic stress, astrocytes isolated from SHRSP/Izm rats displayed altered regulation of Apoe compared with those from WKY/Izm rats.

Effects of the sigma-1 receptor agonist 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)-piperazine dihydro-chloride on inflammation after stroke

Activation of the sigma-1 receptor (Sig-1R) improves functional recovery in models of experimental stroke and is known to modulate microglia function. The present study was conducted to investigate if Sig-1R activation after experimental stroke affects mediators of the inflammatory response in the ischemic hemisphere. Male Wistar rats were subjected to transient occlusion of the middle cerebral artery (MCAO) and injected with the specific Sig-1R agonist 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride (SA4503) or saline for 5 days starting on day 2 after MCAO. Treatment did not affect the increased levels of the pro-inflammatory cytokines interleukin 1 beta (IL-1β), tumor necrosis factor alpha (TNF-α), interferon gamma (IFN-γ), interleukin 4 (IL-4), interleukin 5 (IL-5), and interleukin 13 (IL-13) in the infarct core and peri-infarct area after MCAO. In addition, treatment with SA4503 did not affect elevated levels of nitrite, TNF-α and IL-1β observed in primary cultures of microglia exposed to combined Hypoxia/Aglycemia, while the unspecific sigma receptor ligand 1,3-di-o-tolylguanidine (DTG) significantly decreased the production of nitrite and levels of TNF-α. Analysis of the ischemic hemisphere also revealed increased levels of ionized calcium binding adaptor molecule 1 (Iba1) levels in the infarct core of SA4503 treated animals. However, no difference in Iba1 immunoreactivity was detected in the infarct core. Also, levels of the proliferation marker proliferating cell nuclear antigen (PCNA) and OX-42 were not increased in the infarct core in rats treated with SA4503. Together, our results suggest that sigma-1 receptor activation affects Iba1 expression in microglia/macrophages of the ischemic hemisphere after experimental stroke but does not affect post-stroke inflammatory mediators.

Levodopa Treatment Improves Functional Recovery After Experimental Stroke

Background and Purpose—

Delayed treatment of patients with stroke with levodopa/benserazide contributes to enhanced functional recovery, but the mechanisms involved are poorly understood. The present study was designed to investigate if levodopa/benserazide treatment improves recovery of lost neurological function and contributes to tissue reorganization in the rat brain after stroke.

Methods—

Male Wistar rats were subjected to transient occlusion of the middle cerebral artery (120 minutes) and treated with levodopa (1, 5, and 20 mg/kg)/benserazide (15 mg/kg) or saline for 12 consecutive days starting on Day 2 after transient occlusion of the middle cerebral artery. Infarct volume was determined and sensorimotor function was assessed using the rotating pole test, a 28-point neuroscore, and a cylinder test on Days 2, 7, and 14 after transient occlusion of the middle cerebral artery. The spatiotemporal expression pattern of dopamine-1 and dopamine-2 receptors and the dopamine- and cAMP-regulated neuronal phosphoprotein in reactive astrocytes were analyzed in the ischemic hemisphere as well as in cultured astrocytes.

Results—

Treatment with levodopa/benserazide significantly improved the recovery of sensorimotor function after transient occlusion of the middle cerebral artery without affecting the infarct volume. In addition, we found that different subpopulations of glial fibrillary acidic protein-positive astrocytes in the peri-infarct area express dopamine-1 receptors and dopamine-2 receptors as well as dopamine- and cAMP-regulated neuronal phosphoprotein.

Conclusions—

Our results strongly corroborate the concept of recovery enhancing actions of levodopa treatment after stroke. Also, astrocytes in the peri-infarct area may contribute to the dopamine enhanced recovery mechanisms.

Lipid metabolism and glial lipoproteins in the central nervous system

Lipoproteins in the central nervous system (CNS) are not incorporated from the blood but are formed mainly by glial cells within the CNS. In addition, cholesterol in the CNS is synthesized endogenously because the blood-brain barrier segregates the CNS from the peripheral circulation. Apolipoprotein (apo) E is a major apo in the CNS. In normal condition, apo E is secreted from glia, mainly from astrocytes, and forms cholesterol-rich lipoproteins by ATP-binding cassette transporters. Subsequently, apo E-containing glial lipoproteins supply cholesterol and other components to neurons via a receptor-mediated process. Recent findings demonstrated that receptors of the low density lipoprotein (LDL) receptor family not only internalize lipoproteins into the cells but also, like signaling receptors, transduce signals upon binding the ligands. In this review, the regulation of lipid homeostasis will be discussed as well as roles of lipoproteins and functions of receptors of LDL receptor family in the CNS. Furthermore, the relation between lipid metabolism and Alzheimer's disease (AD) is discussed.

SC1/hevin and reactive gliosis after transient ischemic stroke in young and aged rats

SC1 is a member of the SPARC family of glycoproteins that regulate cell-matrix interactions in the developing brain. SC1 is expressed in astrocytes, but nothing is known about the expression in the aged or after stroke. We found that after focal striatal ischemic infarction in adult rats, SC1 increased in astrocytes surrounding the infarct and in the glial scar, but in aged rats, SC1 was lower at the lesion edge. Glial fibrillary acidic protein (GFAP) also increased, but it was less prominent in reactive astrocytes further from the lesion in the aged rats. On the basis of their differential expression of several molecules, 2 types of reactive astrocytes with differing spatiotemporal distributions were identified. On Days 3 and 7, SC1 was prevalent in cells expressing markers of classic reactive astrocytes (GFAP, vimentin, nestin, S100β), as well as apoliprotein E (ApoE), interleukin 1β, aggrecanase 1 (ADAMTS4), and heat shock protein 25 (Hsp25). Adjacent to the lesion on Days 1 and 3, astrocytes with low GFAP levels and a "starburst" SC1 pattern expressed S100β, ApoE, and Hsp32 but not vimentin, nestin, interleukin 1β, ADAMTS4, or Hsp25. Neither cell type was immunoreactive for NG2,CC-1, CD11b, or ionized calcium-binding adapter-1. Their differing expression of inflammation-related and putatively protective molecules suggests different roles for starburst and classic reactive astrocytes in the early glial responses to ischemia.

Lack of macrophage migration inhibitory factor in mice does not affect hallmarks of the inflammatory/immune response during the first week after stroke

Background

Macrophage migration inhibitory factor (MIF) has been proposed to play a detrimental role in stroke. We recently showed that MIF promotes neuronal death and aggravates neurological deficits during the first week after experimental stroke, in mice. Since MIF regulates tissue inflammation, we studied the putative role of MIF in post-stroke inflammation.

Methods

We subjected C57BL/6 mice, Mif^-/- (MIF-KO) or Mif^+/+ (WT), to a transient occlusion of the right middle cerebral artery (tMCAo) or sham-surgery. We studied MIF expression, GFAP expression and the number of CD74-positive cells in the ischemic brain hemisphere 7 days after tMCAo using primarily immunohistochemistry. We determined IFN-γ, IL-2, IL-4, IL-5, IL-10, IL-12, KC/CXCL-1 and TNF-α protein levels in the brain (48 h after surgery) and serum (48 h and 7 days after surgery) by a multiplex immunoassay.

Results

We observed that MIF accumulates in neurons and astrocytes of the peri-infarct region, as well as in microglia/macrophages of the infarct core up to 7 days after stroke. Among the inflammatory mediators analyzed, we found a significant increase in cerebral IL-12 and KC levels after tMCAo, in comparison to sham-surgery. Importantly, the deletion of Mif did not significantly affect the levels of the cytokines evaluated, in the brain or serum. Moreover, the spleen weight 48 h and 7 days subsequent to tMCAo was similar in WT and MIF-KO mice. Finally, the extent of GFAP immunoreactivity and the number of MIF receptor (CD74)-positive cells within the ischemic brain hemisphere did not differ significantly between WT and MIF-KO mice subjected to tMCAo.

Conclusions

We conclude that MIF does not affect major components of the inflammatory/immune response during the first week after experimental stroke. Based on present and previous evidence, we propose that the deleterious MIF-mediated effects in stroke depend primarily on an intraneuronal and/or interneuronal action.

Macrophage migration inhibitory factor promotes cell death and aggravates neurologic deficits after experimental stroke

Multiple mechanisms contribute to tissue demise and functional recovery after stroke. We studied the involvement of macrophage migration inhibitory factor (MIF) in cell death and development of neurologic deficits after experimental stroke. Macrophage migration inhibitory factor is upregulated in the brain after cerebral ischemia, and disruption of the Mif gene in mice leads to a smaller infarct volume and better sensory-motor function after transient middle cerebral artery occlusion (tMCAo). In mice subjected to tMCAo, we found that MIF accumulates in neurons of the peri-infarct region, particularly in cortical parvalbumin-positive interneurons. Likewise, in cultured cortical neurons exposed to oxygen and glucose deprivation, MIF levels increase, and inhibition of MIF by (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1) protects against cell death. Deletion of MIF in Mif(-/-) mice does not affect interleukin-1β protein levels in the brain and serum after tMCAo. Furthermore, disruption of the Mif gene in mice does not affect CD68, but it is associated with higher galectin-3 immunoreactivity in the brain after tMCAo, suggesting that MIF affects the molecular/cellular composition of the macrophages/microglia response after experimental stroke. We conclude that MIF promotes neuronal death and aggravates neurologic deficits after experimental stroke, which implicates MIF in the pathogenesis of neuronal injury after stroke.

The sigma-1 receptor enhances brain plasticity and functional recovery after experimental stroke

Stroke leads to brain damage with subsequent slow and incomplete recovery of lost brain functions. Enriched housing of stroke-injured rats provides multi-modal sensorimotor stimulation, which improves recovery, although the specific mechanisms involved have not been identified. In rats housed in an enriched environment for two weeks after permanent middle cerebral artery occlusion, we found increased sigma-1 receptor expression in peri-infarct areas. Treatment of rats subjected to permanent or transient middle cerebral artery occlusion with 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride, an agonist of the sigma-1 receptor, starting two days after injury, enhanced the recovery of lost sensorimotor function without decreasing infarct size. The sigma-1 receptor was found in the galactocerebroside enriched membrane microdomains of reactive astrocytes and in neurons. Sigma-1 receptor activation increased the levels of the synaptic protein neurabin and neurexin in membrane rafts in the peri-infarct area, while sigma-1 receptor silencing prevented sigma-1 receptor-mediated neurite outgrowth in primary cortical neuronal cultures. In astrocytic cultures, oxygen and glucose deprivation induced sigma-1 receptor expression and actin dependent membrane raft formation, the latter blocked by sigma-1 receptor small interfering RNA silencing and pharmacological inhibition. We conclude that sigma-1 receptor activation stimulates recovery after stroke by enhancing cellular transport of biomolecules required for brain repair, thereby stimulating brain plasticity. Pharmacological targeting of the sigma-1 receptor provides new opportunities for stroke treatment beyond the therapeutic window of neuroprotection.

Influence of enriched environment on viral encephalitis outcomes: behavioral and neuropathological changes in albino Swiss mice

An enriched environment has previously been described as enhancing natural killer cell activity of recognizing and killing virally infected cells. However, the effects of environmental enrichment on behavioral changes in relation to virus clearance and the neuropathology of encephalitis have not been studied in detail. We tested the hypothesis that environmental enrichment leads to less CNS neuroinvasion and/or more rapid viral clearance in association with T cells without neuronal damage. Stereology-based estimates of activated microglia perineuronal nets and neurons in CA3 were correlated with behavioral changes in the Piry rhabdovirus model of encephalitis in the albino Swiss mouse. Two-month-old female mice maintained in impoverished (IE) or enriched environments (EE) for 3 months were behaviorally tested. After the tests, an equal volume of Piry virus (IEPy, EEPy)-infected or normal brain homogenates were nasally instilled. Eight days post-instillation (dpi), when behavioral changes became apparent, brains were fixed and processed to detect viral antigens, activated microglia, perineuronal nets, and T lymphocytes by immuno- or histochemical reactions. At 20 or 40 dpi, the remaining animals were behaviorally tested and processed for the same markers. In IEPy mice, burrowing activity decreased and recovered earlier (8–10 dpi) than open field (20–40 dpi) but remained unaltered in the EEPy group. EEPy mice presented higher T-cell infiltration, less CNS cell infection by the virus and/or faster virus clearance, less microgliosis, and less damage to the extracellular matrix than IEPy. In both EEPy and IEPy animals, CA3 neuronal number remained unaltered. The results suggest that an enriched environment promotes a more effective immune response to clear CNS virus and not at the cost of CNS damage.

The asparaginyl endopeptidase legumain after experimental stroke

Various proteases in the brain contribute to ischemic brain injury. We investigated the involvement of the asparaginyl endopeptidase legumain after experimental stroke. On the basis of gene array studies and in situ hybridizations, we observed an increase of legumain expression in the peri-infarct area of rats after transient occlusion of the middle cerebral artery (MCAO) for 120 mins with a maximum expression at 24 and 48 h. Immunohistochemical analyses revealed the expression of legumain in Iba1(+) microglial cells and glial fibrillary acidic protein-positive astrocytes of the peri-infarct area in mice after MCAO. Post-stroke recovery was also studied in aged legumain-deficient mice (45 to 58 weeks old). Legumain-deficient mice did not show any differences in physiologic parameters compared with respective littermates before, during MCAO (45 mins), and the subsequent recovery period of 8 days. Moreover, legumain deficiency had no effect on mortality, infarct volume, and the neurologic deficit determined by the rotating pole test, a standardized grip strength test, and the pole test. However, a reduced number of invading CD74(+) cells in the ischemic hemisphere indicates an involvement in post-stroke inflammation. We conclude that legumain is not essential for the functional deficit after MCAO but may be involved in mechanisms of immune cell invasion.

Enriched environment downregulates macrophage migration inhibitory factor and increases parvalbumin in the brain following experimental stroke

Housing rodents in an enriched environment (EE) following experimental stroke enhances neurological recovery. Understanding the underlying neural cues may provide the basis for improving stroke rehabilitation. We studied the contribution of brain macrophage migration inhibitory factor (MIF) to functional recovery after permanent middle cerebral artery occlusion (pMCAo) in rats. In the cerebral cortex, MIF is predominantly found in neurons, particularly in parvalbumin interneurons. Following pMCAo, MIF increases around the infarct core, where it is located to neurons and astrocytes. Housing rats in an EE after pMCAo resulted in a decrease of MIF protein levels in peri-infarct areas, which was accompanied by an increase in parvalbumin immunoreactive interneurons. Our data suggest that MIF is part of a signaling network involved in brain plasticity, and elevated neuronal and/or astrocytic MIF levels repress the recovery of sensory-motor function after stroke. Downregulating MIF could constitute a new therapeutic approach to promote recovery after stroke.

Effects of chronic Clozapine administration on apolipoprotein D levels and on functional recovery following experimental stroke

Elevated brain levels of apolipoprotein D (ApoD) correlate with improved neurological recovery after experimental stroke. Hence, a pharmacological induction of ApoD in the postischemic brain could be beneficial for recovery after stroke. Here we investigated the effect of Clozapine, a compound that increases the expression of ApoD, in two rat models of experimental stroke. Rats were subjected to permanent occlusion of the middle cerebral artery (pMCAO) and treated with Clozapine (i.p. 10 mg/kg body weight) or saline for 8 or 28 days starting on the second day after MCAO. ApoD levels increased by 35% in the peri-infarct area after 10 and 30 days after pMCAO, mainly in neuron-specific nuclear protein (NeuN) positive neurons and glial fibrillary acidic protein (GFAP) positive astrocytes. Clozapine did not affect the neurological deficit assessed by the rotating pole test and a grip strength test at 7 days, 14 days, 21 days, and 28 days after pMCAO. Functional outcome and the infarct size were similar in rats subjected to transient MCAO and injected with Clozapine (i.p. 10 mg/kg body weight) or saline for 26 days starting on the second day after tMCAO. We conclude that Clozapine affects cellular processes involved in peri-infarct tissue reorganization, but does not affect functional recovery after MCAO.