A novel technique for morphometric quantification of subarachnoid hemorrhage-induced microglia activation

Integrated analysis of gait parameters and gene expression profiles in a murine model of subarachnoid hemorrhage

Gait analysis has been widely used to examine the behavioral presentation of numerous neurological disorders. Thorough murine model evaluation of the subarachnoid hemorrhage (SAH)-associated gait deficits is missing. This study measures gait deficits using a clinically relevant murine model of SAH to examine associations between gait variability and SAH-associated gene expressions. A total of 159 dynamic and static gait parameters from the endovascular perforation murine model for simulating clinical human SAH were determined using the CatWalk system. Eighty gait parameters and the mRNA expression levels of 35 of the 88 SAH-associated genes were differentially regulated in the diseased models. Totals of 42 and 38 gait parameters correlated with the 35 SAH-associated genes positively and negatively with Pearson's correlation coefficients of >0.7 and <-0.7, respectively. p-SP1⁴⁵³ expression in the motor cortex in SAH animal models displays a significant correlation with a subset of gait parameters associated with muscular strength and coordination of limb movements. Our data highlights a strong correlation between gait variability and SAH-associated gene expression. p-SP1⁴⁵³ expression could act as a biomarker to monitor SAH pathological development and a therapeutic target for SAH.

Mesenchymal stem cell-derived extracellular vesicles promote microglial M2 polarization after subarachnoid hemorrhage in rats and involve the AMPK/NF-κB signaling pathway

Subarachnoid hemorrhage (SAH) is an acute and severe disease with high disability and mortality. Inflammatory reactions have been proven to occur throughout SAH. Extracellular vesicles derived from mesenchymal stem cells (MSCs-EVs) have shown broad potential for the treatment of brain dysfunction and neuroprotective effects through neurogenesis and angiogenesis after stroke. However, the mechanisms of EVs in neuroinflammation during the acute phase of SAH are not well known. Our present study was designed to investigate the effects of MSCs-EVs on neuroinflammation and the polarization regulation of microglia to the M2 phenotype and related signaling pathways after SAH in rats. The SAH model was induced by an improved method of intravascular perforation, and MSCs-EVs were injected via the tail vein. Post-SAH assessments included neurobehavioral tests as well as brain water content, immunohistochemistry, PCR and Western blot analyses. Our results showed that MSCs-EVs alleviated the expression of inflammatory cytokines in the parietal cortex and hippocampus 24 h and 48 h after SAH and that MSCs-EVs inhibited NF-κB and activated AMPK to reduce inflammation after SAH. Furthermore, MSC-EVs regulated the polarization of microglia toward the M2 phenotype by downregulating interleukin-1β, cluster of differentiation 16, cluster of differentiation 11b, and inducible nitric oxide synthase and upregulating the expression of cluster of differentiation 206 and arginase-1. Additionally, MSCs-EVs inhibited the neuroinflammatory response and had neuroprotective effects in the brain tissues of rats after SAH. This study may support their use as a potential treatment strategy for early SAH in the future.

Multiple Morphometric Assessment of Microglial Cells in Deafferented Spinal Trigeminal Nucleus

Microglia (MG) are the first cells to react to the abnormal incoming signals that follow an injury of sensory nerves and play a critical role in the development and maintenance of neuropathic pain, a common sequel of nerve injuries. Here we present population data on cell number, soma size, and length of processes of MG in the caudal division of the spinal trigeminal nucleus (Sp5C) in control mice and at the peak of microgliosis (7 days) following unilateral transection of the infraorbital nerve (IoN). The study is performed combining several bias- and assumption-free imaging and stereological approaches with different immunolabeling procedures, with the objective of tackling some hard problems that often hinder proper execution of MG morphometric studies. Our approach may easily be applied to low-density MG populations, but also works, with limited biases, in territories where MG cell bodies and processes form dense meshworks. In controls, and contralaterally to the deafferented side, MG cell body size and shape and branching pattern matched well the descriptions of “resting” or “surveillant” MG described elsewhere, with only moderate intersubject variability. On the superficial laminae of the deafferented side, however, MG displayed on average larger somata and remarkable diversity in shape. The number of cells and the length of MG processes per mm³ increased 5 and 2.5 times, respectively, indicating a net 50% decrease in the mean length of processes per cell. By using specific immunolabeling and cell sorting of vascular macrophages, we found only a negligible fraction of these cells in Sp5C, with no differences between controls and deafferented animals, suggesting that blood-borne monocytes play at most a very limited role in the microgliosis occurring following sensory nerve deafferentation. In sum, here we present reliable morphometric data on MG in control and deafferented trigeminal nuclei using efficient methods that we propose may equally be applied to any morphometric population analysis of these cells under different physiological or pathological conditions.

Impact of 12/15-Lipoxygenase on Brain Injury After Subarachnoid Hemorrhage

Background and Purpose- Subarachnoid hemorrhage (SAH) is a devastating form of stroke. Oxidative stress contributes to brain injury, but the mechanisms have been poorly studied. Here, we evaluated the role of 12/15-lipoxygenase (12/15-LOX), an enzyme known to cause cell death in ischemic stroke, on brain injury in a mouse model of SAH. Methods- C57Bl6 wild-type mice and Alox15 knockout mice were subjected to SAH using a direct blood injection technique. In SAH wild-type mice, half received the 12/15-LOX inhibitor ML351 and half received vehicle. Immunohistochemistry, brain edema, blood-brain barrier leakage and functional outcomes were assessed 1 and 3 days after SAH induction. Results- SAH led to increased 12/15-LOX in macrophages of the brain parenchyma, adjacent to the subarachnoid blood. Neuronal cell death after SAH was reduced by ML351 and in Alox15 knockout mice. Similarly, SAH induced brain edema, which was 12/15-LOX dependent. Finally, Alox15 gene knockout and inhibitor treatment in wild-type mice with SAH led to an improved behavioral outcome. Conclusions- 12/15-LOX is overexpressed in macrophages after SAH in mice, and inhibition of the 12/15-LOX pathway decreases brain injury and improves neurological outcome. This study suggests 12/15-LOX as a novel therapeutic target to limit brain injury after SAH.

Intravital 2-photon imaging reveals distinct morphology and infiltrative properties of glioblastoma-associated macrophages

Characterized by a dismal survival rate and limited response to therapy, glioblastoma (GBM) remains one of the most aggressive human malignancies. Recent studies of the role of tumor-associated macrophages (TAMs) in the progression of GBMs have demonstrated that TAMs are significant contributors to tumor growth, invasion, and therapeutic resistance. TAMs, which include brain-resident microglia and circulating bone marrow derived-monocytes (BMDMs), are typically grouped together in histopathological and molecular analyses due to the lack of reliable markers of distinction. To develop more effective therapies aimed at specific TAM populations, we must first understand how these cells differ both morphologically and behaviorally. Furthermore, we must develop a deeper understanding of the mechanisms encouraging their infiltration and how these mechanisms can be therapeutically exploited. In this study, we combined immunocompetent lineage tracing mouse models of GBM with high-resolution open-skull 2-photon microscopy to investigate the phenotypical and functional characteristics of TAMs. We demonstrate that TAMs are composed of 2 morphologically distinct cell types that have differential migratory propensities. We show that BMDMs are smaller, minimally branched cells that are highly migratory compared with microglia, which are larger, highly branched stationary cells. In addition, 2 populations of monocytic macrophages were observed that differed in terms of CX3CR1 expression and migratory capacity. Finally, we demonstrate the efficacy of anti-vascular endothelial growth factor A blockade for prohibiting TAM infiltration, especially against BMDMs. Taken together, our data clearly define characteristics of individual TAM populations and suggest that combination therapy with antivascular and antichemotaxis therapy may be an attractive option for treating these tumors.

Central nervous system lymphatic unit, immunity, and epilepsy: Is there a link?

The recent definition of a network of lymphatic vessels in the meninges surrounding the brain and the spinal cord has advanced our knowledge on the functional anatomy of fluid movement within the central nervous system (CNS). Meningeal lymphatic vessels along dural sinuses and main nerves contribute to cerebrospinal fluid (CSF) drainage, integrating the cerebrovascular and periventricular routes, and forming a circuit that we here define as the CNS-lymphatic unit. The latter unit is important for parenchymal waste clearance, brain homeostasis, and the regulation of immune or inflammatory processes within the brain. Disruption of fluid drain mechanisms may promote or sustain CNS disease, conceivably applicable to epilepsy where extracellular accumulation of macromolecules and metabolic by-products occur in the interstitial and perivascular spaces. Herein we address an emerging concept and propose a theoretical framework on: (a) how a defect of brain clearance of macromolecules could favor neuronal hyperexcitability and seizures, and (b) whether meningeal lymphatic vessel dysfunction contributes to the neuroimmune cross-talk in epileptic pathophysiology. We propose possible molecular interventions targeting meningeal lymphatic dysfunctions, a potential target for immune-mediated epilepsy.

Automated Morphological Analysis of Microglia After Stroke

Microglia are the resident immune cells of the brain and react quickly to changes in their environment with transcriptional regulation and morphological changes. Brain tissue injury such as ischemic stroke induces a local inflammatory response encompassing microglial activation. The change in activation status of a microglia is reflected in its gradual morphological transformation from a highly ramified into a less ramified or amoeboid cell shape. For this reason, the morphological changes of microglia are widely utilized to quantify microglial activation and studying their involvement in virtually all brain diseases. However, the currently available methods, which are mainly based on manual rating of immunofluorescent microscopic images, are often inaccurate, rater biased, and highly time consuming. To address these issues, we created a fully automated image analysis tool, which enables the analysis of microglia morphology from a confocal Z-stack and providing up to 59 morphological features. We developed the algorithm on an exploratory dataset of microglial cells from a stroke mouse model and validated the findings on an independent data set. In both datasets, we could demonstrate the ability of the algorithm to sensitively discriminate between the microglia morphology in the peri-infarct and the contralateral, unaffected cortex. Dimensionality reduction by principal component analysis allowed to generate a highly sensitive compound score for microglial shape analysis. Finally, we tested for concordance of results between the novel automated analysis tool and the conventional manual analysis and found a high degree of correlation. In conclusion, our novel method for the fully automatized analysis of microglia morphology shows excellent accuracy and time efficacy compared to traditional analysis methods. This tool, which we make openly available, could find application to study microglia morphology using fluorescence imaging in a wide range of brain disease models.

Distinction of Neurons, Glia and Endothelial Cells in the Cerebral Cortex: An Algorithm Based on Cytological Features

The estimation of the number or density of neurons and types of glial cells and their relative proportions in different brain areas are at the core of rigorous quantitative neuroanatomical studies. Unfortunately, the lack of detailed, updated, systematic and well-illustrated descriptions of the cytology of neurons and glial cell types, especially in the primate brain, makes such studies especially demanding, often limiting their scope and broad use. Here, following an extensive analysis of histological materials and the review of current and classical literature, we compile a list of precise morphological criteria that can facilitate and standardize identification of cells in stained sections examined under the microscope. We describe systematically and in detail the cytological features of neurons and glial cell types in the cerebral cortex of the macaque monkey and the human using semithin and thick sections stained for Nissl. We used this classical staining technique because it labels all cells in the brain in distinct ways. In addition, we corroborate key distinguishing characteristics of different cell types in sections immunolabeled for specific markers counterstained for Nissl and in ultrathin sections processed for electron microscopy. Finally, we summarize the core features that distinguish each cell type in easy-to-use tables and sketches, and structure these key features in an algorithm that can be used to systematically distinguish cellular types in the cerebral cortex. Moreover, we report high inter-observer algorithm reliability, which is a crucial test for obtaining consistent and reproducible cell counts in unbiased stereological studies. This protocol establishes a consistent framework that can be used to reliably identify and quantify cells in the cerebral cortex of primates as well as other mammalian species in health and disease.

Inhibition of mammalian target of rapamycin attenuates early brain injury through modulating microglial polarization after experimental subarachnoid hemorrhage in rats

Here, we aimed to study the role and underlying mechanism of mTOR in early brain injury (EBI) after subarachnoid hemorrhage (SAH). Experiment 1, the time course of mTOR activation in the cortex following SAH. Experiment 2, the role of mTOR in SAH-induced EBI. Adult SD rats were divided into four groups: sham group (n=18), SAH+vehicle group (n=18), SAH+rapamycin group (n=18), SAH+AZD8055 group (n=18). Experiment 3, we incubated enriched microglia with OxyHb. Rapamycin and AZD8055 were also used to demonstrate the mTOR's role on microglial polarization in vitro. The phosphorylation levels of mTOR and its substrates were significantly increased and peaked at 24h after SAH. Rapamycin or AZD8055 markedly decreased the phosphorylation levels of mTOR and its substrates and the activation of microglia in vivo, and promoted the microglial polarization from M1 phenotype to M2 phenotype. In addition, administration of rapamycin and AZD8055 following SAH significantly ameliorated EBI, including neuronal apoptosis, neuronal necrosis, brain edema and blood-brain barrier permeability. Our findings suggested that the rapamycin and AZD8055 could attenuate the development of EBI in this SAH model, possibly through inhibiting the activation of microglia by mTOR pathway.

Automatic Counting of Microglial Cells in Healthy and Glaucomatous Mouse Retinas

Proliferation of microglial cells has been considered a sign of glial activation and a hallmark of ongoing neurodegenerative diseases. Microglia activation is analyzed in animal models of different eye diseases. Numerous retinal samples are required for each of these studies to obtain relevant data of statistical significance. Because manual quantification of microglial cells is time consuming, the aim of this study was develop an algorithm for automatic identification of retinal microglia. Two groups of adult male Swiss mice were used: age-matched controls (naïve, n = 6) and mice subjected to unilateral laser-induced ocular hypertension (lasered; n = 9). In the latter group, both hypertensive eyes and contralateral untreated retinas were analyzed. Retinal whole mounts were immunostained with anti Iba-1 for detecting microglial cell populations. A new algorithm was developed in MATLAB for microglial quantification; it enabled the quantification of microglial cells in the inner and outer plexiform layers and evaluates the area of the retina occupied by Iba-1+ microglia in the nerve fiber-ganglion cell layer. The automatic method was applied to a set of 6,000 images. To validate the algorithm, mouse retinas were evaluated both manually and computationally; the program correctly assessed the number of cells (Pearson correlation R = 0.94 and R = 0.98 for the inner and outer plexiform layers respectively). Statistically significant differences in glial cell number were found between naïve, lasered eyes and contralateral eyes (P<0.05, naïve versus contralateral eyes; P<0.001, naïve versus lasered eyes and contralateral versus lasered eyes). The algorithm developed is a reliable and fast tool that can evaluate the number of microglial cells in naïve mouse retinas and in retinas exhibiting proliferation. The implementation of this new automatic method can enable faster quantification of microglial cells in retinal pathologies.

Immune cells subpopulations in cerebrospinal fluid and peripheral blood of patients with Aneurysmal Subarachnoid Hemorrhage

Background

There is growing evidence supporting the role of inflammation in aneurysmal subarachnoid hemorrhage (aSAH) pathophysiology and it is of great interest to elucidate which immune mechanisms are involved.

Methods

12 aSAH patients and 28 healthy controls were enrolled prospectively. We assessed leukocytes subpopulations and their activation status by flow cytometry in cerebrospinal fluid (CSF) and peripheral blood (PB) of SAH patients at the same time and in PB of controls.

Results

Monocytes and neutrophils were activated in CSF of aSAH patients. The percentage of CD14⁺⁺CD16⁺ monocytes were higher in CSF than in PB of aSAH patients, and were also increased in PB of aSAH patients compared with controls. An enhanced expression of CD69 was shown in CSF neutrophils compared with PB in aSAH patients. PB of aSAH patients showed lower percentage of total lymphocytes compared with controls PB. Additionally, lymphocytes were activated in CSF and PB of aSAH patients. CD4⁺ and CD8⁺ T cells had a decreased expression on CD3 and higher levels of CD69 in CSF compared with PB in aSAH patients. Moreover, PB CD4⁺ and CD8⁺ T cells of aSAH patients were activated compared with controls. Additionally, CD28 expression was decreased on CSF T lymphocytes.

Conclusions

Our data suggest an important recruitment of leukocytes to the site of injury in aSAH as well as an increased activation at this level. Overall, these results indicate that aSAH probably stimulates both the innate and adaptive immune responses.