Quantitative morphological study of microglial cells in the ischemic rat brain using principal component analysis

Morphological differentiation of peritumoral brain zone microglia

The Peritumoral Brain Zone (PBZ) contributes to Glioblastoma (GBM) relapse months after the resection of the original tumor, which is influenced by a variety of pathological factors. Among those, microglia are recognized as one of the main regulators of GBM progression and probably relapse. Although microglial morphology has been analyzed inside GBM and its immediate surroundings, it has not been objectively characterized throughout the PBZ. Thus, we aimed to perform a thorough characterization of microglial morphology in the PBZ and its likely differentiation not just from the tumor-associated microglia but from control tissue microglia. For this purpose, Sprague Dawley rats were intrastriatally implanted with C6 cells to induce a GBM formation. Gadolinium-based magnetic resonance imaging (MRI) was performed to locate the tumor and to define the PBZ (2 mm beyond the tumor border), thus delimitating the different regions of interest (ROIs: core tumoral zone and immediate interface; contralateral striatum as control). Brain slices were obtained and immunolabeled with the microglia marker Iba-1. Sixteen morphological parameters were measured for each cell, significative differences were found in all parameters when comparing the four ROIs. To determine if PBZ microglia could be morphologically differentiated from microglia in other ROIs, hierarchical clustering analysis was performed, revealing that microglia can be separated into four morphologically differentiated clusters, each of them mostly integrated by cells sampled in each ROI. Furthermore, a classifier based on linear discriminant analysis, including only three morphological parameters, categorized microglial cells across the studied ROIs and showed a gradual transition between them. The robustness of this classification was assessed through principal component analysis with the remaining 13 morphological parameters, corroborating the obtained results. Thus, in this study we provided objective and quantitative evidence that PBZ microglia represent a differentiable microglial morphotype that could contribute to the recurrence of GBM in this area.

Morphology and Fractal-Based Classifications of Neurons and Microglia in Two and Three Dimensions

Microglia and neurons live physically intertwined, intimately related structurally and functionally in a dynamic relationship in which microglia change continuously over a much shorter timescale than do neurons. Although microglia may unwind and depart from the neurons they attend under certain circumstances, in general, together both contribute to the fractal topology of the brain that defines its computational capabilities. Both neuronal and microglial morphologies are well-described using fractal analysis complementary to more traditional measures. For neurons, the fractal dimension has proved valuable for classifying dendritic branching and other neuronal features relevant to pathology and development. For microglia, fractal geometry has substantially contributed to classifying functional categories, where, in general, the more pathological the biological status, the lower the fractal dimension for individual cells, with some exceptions, including hyper-ramification. This chapter provides a review of the intimate relationships between neurons and microglia, by introducing 2D and 3D fractal analysis methodology and its applications in neuron-microglia function in health and disease.

Morphomigrational description as a new approach connecting cell's migration with its morphology

The examination of morphology and migration of cells plays substantial role in understanding the cellular behaviour, being described by plethora of quantitative parameters and models. These descriptions, however, treat cell migration and morphology as independent properties of temporal cell state, while not taking into account their strong interdependence in adherent cells. Here we present the new and simple mathematical parameter called signed morphomigrational angle (sMM angle) that links cell geometry with translocation of cell centroid, considering them as one morphomigrational behaviour. The sMM angle combined with pre-existing quantitative parameters enabled us to build a new tool called morphomigrational description, used to assign the numerical values to several cellular behaviours. Thus, the cellular activities that until now were characterized using verbal description or by complex mathematical models, are described here by a set of numbers. Our tool can be further used in automatic analysis of cell populations as well as in studies focused on cellular response to environmental directional signals.

Development of a Wound-Healing Protocol for In Vitro Evaluation of Urothelial Cell Growth

Urethral healing is plagued by strictures, impacting quality of life and medical costs. Various growth factors (GFs) have shown promise as therapeutic approaches to improve healing, but there is no protocol for in vitro comparison between GFs. This study focuses the development of a biomimetic in vitro urothelial healing assay designed to mimic early in vivo healing, followed by an evaluation of urothelial cell growth in response to GFs.

METHODS

Wound-healing assays were developed with human urothelial cells and used to compared six GFs (EGF, FGF-2, IGF-1, PDGF, TGF-β1, and VEGF) at three concentrations (1 ng/mL, 10 ng/mL, and 100 ng/mL) over a 48 h period. A commercial GF-containing medium (EGF, TGF-α, KGF, and Extract P) and a GF-free medium were used as controls.

RESULTS

There was a statistically significant increase in cell growth for IGF-1 at 10 and 100 ng/mL compared to both controls (p < 0.05). There was a statistically significant increase in cell growth for EGF at all concentrations compared to the GF-free medium control (p < 0.05).

CONCLUSION

This study shows the development of a clinically relevant wound-healing assay to evaluate urothelial cell growth. It is the first to compare GFs for future use in reconstructive techniques to improve urethral healing.

Daytime Light Deficiency Leads to Sex- and Brain Region-Specific Neuroinflammatory Responses in a Diurnal Rodent

Seasonal changes in peripheral inflammation are well documented in both humans and animal models, but seasonal changes in neuroinflammation, especially the impact of seasonal lighting environment on neuroinflammation remain unclear. To address this question, the present study examined the effects of environmental lighting conditions on neuroinflammation in a diurnal rodent model, Nile grass rats (Arvicanthis niloticus). Male and female grass rats were housed in either bright (brLD) or dim (dimLD) light during the day to simulate a summer or winter light condition, respectively. After 4 weeks, microglia markers Iba-1 and CD11b, as well as pro-inflammatory cytokines TNF-α and IL-6, were examined in the anterior cingulate cortex (ACC), basolateral amygdala (BLA), and dorsal hippocampus (dHipp). The results revealed that winter-like dim light during the day leads to indicators of increased neuroinflammation in a brain site- and sex-specific manner. Specifically, relatively few changes in the neuroinflammatory markers were observed in the ACC, while numerous changes were found in the BLA and dHipp. In the BLA, winter-like dimLD resulted in hyper-ramified microglia morphology and increased expression of the pro-inflammatory cytokine IL-6, but only in males. In the dHipp, dimLD led to a higher number and hyper-ramified morphology of microglia as well as increased expression of CD11b and TNF-α, but only in females. Neuroinflammatory state is thus influenced by environmental light, differently in males and females, and could play a role in sex differences in the prevalence and symptoms of psychiatric or neurological disorders that are influenced by season or other environmental light conditions. Diurnal Nile grass rats were housed under bright or dim light during the day for 4 weeks, simulating seasonal fluctuations in daytime lighting environment. Dim light housing resulted in hyper-ramified morphology of microglia (scale bar, 15 μm) and altered expression of pro-inflammatory cytokines (TNF-α) in a sex- and brain region-specific manner.

Prolonged anesthesia induces neuroinflammation and complement-mediated microglial synaptic elimination involved in neurocognitive dysfunction and anxiety-like behaviors

BACKGROUND

Perioperative neurocognitive disorders (PND) with a high incidence frequently occur in elderly surgical patients closely associated with prolonged anesthesia-induced neurotoxicity. The neuromorphopathological underpinnings of anesthesia-induced neurotoxicity have remained elusive.

METHODS

Prolonged anesthesia with sevoflurane was used to establish the sevoflurane-induced neurotoxicity (SIN) animal model. Morris water maze, elevated plus maze, and open field test were employed to track SIN rats' cognitive behavior and anxiety-like behaviors. We investigated the neuropathological basis of SIN through techniques such as transcriptomic, electrophysiology, molecular biology, scanning electron microscope, Golgi staining, TUNEL assay, and morphological analysis. Our work further clarifies the pathological mechanism of SIN by depleting microglia, inhibiting neuroinflammation, and C1q neutralization.

RESULTS

This study shows that prolonged anesthesia triggers activation of the NF-κB inflammatory pathway, neuroinflammation, inhibition of neuronal excitability, cognitive dysfunction, and anxiety-like behaviors. RNA sequencing found that genes of different types of synapses were downregulated after prolonged anesthesia. Microglial migration, activation, and phagocytosis were enhanced. Microglial morphological alterations were also observed. C1qa, the initiator of the complement cascade, and C3 were increased, and C1qa tagging synapses were also elevated. Then, we found that the "Eat Me" complement pathway mediated microglial synaptic engulfment in the hippocampus after prolonged anesthesia. Afterward, synapses were remarkably lost in the hippocampus. Furthermore, dendritic spines were reduced, and their genes were also downregulated. Depleting microglia ameliorated the activation of neuroinflammation and complement and rescued synaptic loss, cognitive dysfunction, and anxiety-like behaviors. When neuroinflammatory inhibition or C1q neutralization occurred, complement was also decreased, and synaptic elimination was interrupted.

CONCLUSIONS

These findings illustrated that prolonged anesthesia triggered neuroinflammation and complement-mediated microglial synaptic engulfment that pathologically caused synaptic elimination in SIN. We have demonstrated the neuromorphopathological underpinnings of SIN, which have direct therapeutic relevance for PND patients.

Automated detection and quantification of Enchytraeus crypticus (Oligochaeta: Enchytraeidae) in tropical artificial soil using image analysis

The effects of toxic substance in soil matrices are evaluated by assessing adult worm survival and reproduction. Throughout the test, hundreds of juvenile potworms can be found. The current method for Enchytraeus crypticus quantification in soil samples is a laborious and time-consuming procedure that involves manual counting. The present work proposes a method for quick and reliable counting of E. crypticus by using an automated image analysis algorithm applied to soil images. Comparisons between automated and manual methods conducted in double-blind trials involving a large, routine batch of tropical artificial soil samples revealed no statistically significant differences for a wide range of worm densities. The proposed method overcomes time-consuming counts in manual methods and is suited to be deployed routinely for soil toxicity studies involving large batches of samples.

The Shape of μ—How Morphological Analyses Shape the Study of Microglia

Microglia, the innate immune cells of the CNS parenchyma, serve as the first line of defense in a myriad of neurodevelopmental, neurodegenerative, and neuroinflammatory conditions. In response to the peripheral inflammation, circulating mediators, and other external signals that are produced by these conditions, microglia dynamically employ different transcriptional programs as well as morphological adaptations to maintain homeostasis. To understand these cells’ function, the field has established a number of essential analysis approaches, such as gene expression, cell quantification, and morphological reconstruction. Although high-throughput approaches are becoming commonplace in regard to other types of analyses (e.g., single-cell scRNA-seq), a similar standard for morphological reconstruction has yet to be established. In this review, we offer an overview of microglial morphological analysis methods, exploring the advantages and disadvantages of each, highlighting a number of key studies, and emphasizing how morphological analysis has significantly contributed to our understanding of microglial function in the CNS parenchyma. In doing so, we advocate for the use of unbiased, automated morphological reconstruction approaches in future studies, in order to capitalize on the valuable information embedded in the cellular structures microglia inhabit.

Label-free detection and enumeration of Giardia cysts in agitated suspensions using in situ microscopy

Laboratory procedures performed in water treatment studies frequently require the characterization of (oo)cyst suspensions. Standard methods commonly used are laborious, expensive and time-consuming, besides requiring well-trained personnel to prepare samples with fluorescent staining and perform analysis under fluorescence microscopy. In this study, an easy cost-effective in situ microscope was assessed to acquire images of Giardia cysts directly from agitated suspensions without using any chemical labels or sample preparation steps. An image analysis algorithm analyzes the acquired images, and automatically enumerates and provides morphological information of cysts within 10 min. The proposed system was evaluated at different cyst concentrations, achieving a limit of detection of ~30 cysts/mL. The proposed system overcomes cost, time and labor demands by standard methods and has the potential to be an alternative technique for the characterization of Giardia cyst suspensions in resource-limited facilities, since it is independent of experts and free of consumables.

Long-term in vivo imaging of mouse spinal cord through an optically cleared intervertebral window

The spinal cord accounts for the main communication pathway between the brain and the peripheral nervous system. Spinal cord injury is a devastating and largely irreversible neurological trauma, and can result in lifelong disability and paralysis with no available cure. In vivo spinal cord imaging in mouse models without introducing immunological artifacts is critical to understand spinal cord pathology and discover effective treatments. We developed a minimally invasive intervertebral window by retaining the ligamentum flavum to protect the underlying spinal cord. By introducing an optical clearing method, we achieve repeated two-photon fluorescence and stimulated Raman scattering imaging at subcellular resolution with up to 15 imaging sessions over 6-167 days and observe no inflammatory response. Using this optically cleared intervertebral window, we study neuron-glia dynamics following laser axotomy and observe strengthened contact of microglia with the nodes of Ranvier during axonal degeneration. By enabling long-term, repetitive, stable, high-resolution and inflammation-free imaging of mouse spinal cord, our method provides a reliable platform in the research aiming at interpretation of spinal cord physiology and pathology.

Mitigation Effects of Selenium Nanoparticles on Depression-Like Behavior Induced by Fluoride in Mice via the JAK2-STAT3 Pathway

Depression is a mental health problem with typically high levels of distress and dysfunction, and 150 mg/L fluoride (F) can induce depression-like behavior. The development of depression is correlated with neuronal atrophy, insufficient secretion of monoamine neurotransmitters, extreme deviations from the normal microglial activation status, and immune-inflammatory response. Studies found that Se supplementation was related to the improvement of depression. In this study, we applied selenium nanoparticles (SeNPs) for F-induced depression disease mitigation by regulating the histopathology, metabolic index, genes, and protein expression related to the JAK2-STAT3 signaling pathway in vivo. Results showed that F and 2 mg Se/kg BW/day SeNPs lowered the dopamine (DA) content (P < 0.05), altered the microglial morphology, ramification index as well as solidity, and triggered the microglial neuroinflammatory response by increasing the p-STAT3 nuclear translocation (P < 0.01). Furthermore, F reduced the cortical Se content and the number of surviving neurons (P < 0.05), increasing the protein expressions of p-JAK2/JAK2 and p-STAT3/STAT3 of the cortex (P < 0.01), accompanied by the depression-like behavior. Importantly, 1 mg Se/kg BW/day SeNPs alleviated the microglial ramification index as well as solidity changes and decreased the interleukin-1β secretion induced by F by suppressing the p-STAT3 nuclear translocation (P < 0.01). Likewise, 1 mg Se/kg BW/day SeNPs restored the F-disturbed dopamine and noradrenaline secretion, increased the number of cortical surviving neurons, and reduced the vacuolation area, ultimately suppressing the occurrence of depression-like behavior through inhibiting the JAK2-STAT3 pathway activation. In conclusion, 1 mg Se/kg BW/day SeNPs have mitigation effects on the F-induced depression-like behavior. The mechanism of how SeNPs repair neural functions will benefit depression mitigation. This study also indicates that inhibiting the JAK/STAT pathway can be a promising novel treatment for depressive disorders.

Sustained microglial activation in the area postrema of collagen-induced arthritis mice

Background

Central nervous system (CNS)-mediated symptoms, such as fatigue, depression, and hyperalgesia, are common complications among patients with rheumatoid arthritis (RA). However, it remains unclear how the peripheral pathology of RA spreads to the brain. Accumulated evidence showing an association between serum cytokine levels and aberrant CNS function suggests that humoral factors participate in this mechanism. In contrast to the well-known early responses of microglia (CNS-resident immune cells) in the area postrema [AP; a brain region lacking a blood–brain barrier (BBB)] to experimental inflammation, microglial alterations in the AP during chronic inflammation like RA remain unclear. Therefore, to determine whether microglia in the AP can react to persistent autoimmune-arthritis conditions, we analyzed these cells in a mouse model of collagen-induced arthritis (CIA).

Methods

Microglial number and morphology were analyzed in the AP of CIA and control mice (administered Freund’s adjuvant or saline). Immunostaining for ionized calcium-binding adaptor molecule-1 was performed at various disease phases: “pre-onset” [post-immunization day (PID) 21], “establishment” (PID 35), and “chronic” (PID 56 and 84). Quantitative analyses of microglial number and morphology were performed, with principal component analysis used to classify microglia. Interleukin-1β (IL-1β) mRNA expression was analyzed by multiple fluorescent in situ hybridization and real-time polymerase chain reaction. Behavioral changes were assessed by sucrose preference test.

Results

Microglia in the AP significantly increased in density and exhibited changes in morphology during the establishment and chronic phases, but not the pre-onset phase. Non-subjective clustering classification of cell morphology (CIA, 1,256 cells; saline, 852 cells) showed that the proportion of highly activated microglia increased in the CIA group during establishment and chronic phases. Moreover, the density of IL-1β-positive microglia, a hallmark of functional activation, was increased in the AP. Sucrose preferences in CIA mice negatively correlated with IL-1β expression in brain regions containing the AP.

Conclusions

Our findings demonstrate that microglia in the AP can sustain their activated state during persistent autoimmune arthritis, which suggests that chronic inflammation, such as RA, may affect microglia in brain regions lacking a BBB and have various neural consequences.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02657-x.

Astroglia in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is an umbrella term encompassing several neurodevelopmental disorders such as Asperger syndrome or autism. It is characterised by the occurrence of distinct deficits in social behaviour and communication and repetitive patterns of behaviour. The symptoms may be of different intensity and may vary in types. Risk factors for ASD include disturbed brain homeostasis, genetic predispositions, or inflammation during the prenatal period caused by viruses or bacteria. The number of diagnosed cases is growing, but the main cause and mechanism leading to ASD is still uncertain. Recent findings from animal models and human cases highlight the contribution of glia to the ASD pathophysiology. It is known that glia cells are not only "gluing" neurons together but are key players participating in different processes crucial for proper brain functioning, including neurogenesis, synaptogenesis, inflammation, myelination, proper glutamate processing and many others. Despite the prerequisites for the involvement of glia in the processes related to the onset of autism, there are far too little data regarding the engagement of these cells in the development of ASD.

Morphometric quantification of a pseudohyphae forming Saccharomyces cerevisiae strain using in situ microscopy and image analysis

Yeast morphology and counting are highly important in fermentation as they are often associated with productivity and can be influenced by process conditions. At present, time-consuming and offline methods are utilized for routine analysis of yeast morphology and cell counting using a haemocytometer. In this study, we demonstrate the application of an in situ microscope to obtain a fast stream of pseudohyphae images from agitated sample suspensions of a Saccharomyces cerevisiae strain, whose morphology in cell clusters is frequently found in the bioethanol fermentation industry. The large statistics of microscopic images allow for online determination of the principal morphological characteristics of the pseudohyphae, including the number of constituent cells, cell-size, number of branches, and length of branches. The distributions of these feature values are calculated online, constituting morphometric monitoring of the pseudohyphae population. By providing representative data, the proposed system can improve the effectiveness of morphological characterization, which in turn can help to improve the understanding and control of bioprocesses in which pseudohyphal-like morphologies are found.

Diverse changes in microglia morphology and axonal pathology during the course of 1 year after mild traumatic brain injury in pigs

Over 2.8 million people experience mild traumatic brain injury (TBI) in the United States each year, which may lead to long-term neurological dysfunction. The mechanical forces that are caused by TBI propagate through the brain to produce diffuse axonal injury (DAI) and trigger secondary neuroinflammatory cascades. The cascades may persist from acute to chronic time points after injury, altering the homeostasis of the brain. However, the relationship between the hallmark axonal pathology of diffuse TBI and potential changes in glial cell activation or morphology have not been established in a clinically relevant large animal model at chronic time points. In this study, we assessed the tissue from pigs subjected to rapid head rotation in the coronal plane to generate mild TBI. Neuropathological assessments for axonal pathology, microglial morphological changes, and astrocyte reactivity were conducted in specimens out to 1-year post-injury. We detected an increase in overall amyloid precursor protein pathology, as well as periventricular white matter and fimbria/fornix pathology after a single mild TBI. We did not detect the changes in corpus callosum integrity or astrocyte reactivity. However, detailed microglial skeletal analysis revealed changes in morphology, most notably increases in the number of microglial branches, junctions, and endpoints. These subtle changes were most evident in periventricular white matter and certain hippocampal subfields, and were observed out to 1-year post-injury in some cases. These ongoing morphological alterations suggest persistent change in neuroimmune homeostasis. Additional studies are needed to characterize the underlying molecular and neurophysiological alterations, as well as potential contributions to neurological deficits.

OTULIN is a new target of EA treatment in the alleviation of brain injury and glial cell activation via suppression of the NF-κB signalling pathway in acute ischaemic stroke rats

OBJECTIVE

Ovarian tumour domain deubiquitinase with linear linkage specificity (OTULIN) is a potent negative regulator of the nuclear factor-κB (NF-κB) signalling pathway, and it plays a strong neuroprotective role following acute ischemic stroke. Electroacupuncture (EA) is an effective adjuvant treatment for reducing brain injury and neuroinflammation via the inhibition of NF-κB p65 nuclear translocation, but the underlying mechanism is not clear. The present study investigated whether OTULIN was necessary for EA to mitigate brain injury and glial cell activation in a transient middle cerebral artery occlusion (tMCAO) model in rats.

METHODS

An acute ischaemic stroke model was established via tMCAO surgery in Sprague-Dawley (SD) rats. EA was performed once daily at "Baihui (GV 20)", "Hegu (LI 4)", and "Taichong (LR 3)" acupoints. The effect of EA on the spatiotemporal expression of OTULIN in the ischaemic penumbra of the cerebral cortex was detected within 7 days after reperfusion. The effects of OTULIN gene silencing on EA neurological deficits, cerebral infarct volume, neuronal damage, the activation of microglia and astrocytes, the contents of tumour necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β) and interleukin-6 (IL-6), and the expression of p-IκBa, IκBa and nucleus/cytoplasm NF-κB p65 protein were assessed.

RESULTS

EA treatment increased endogenous OTULIN expression, which peaked at 48 h. Enhanced OTULIN was primarily located in neurons, but a small amount of OTULIN was detected in microglia. OTULIN silencing obviously reversed EA neuroprotection, which was demonstrated by worsened neurobehavioural performance, cerebral infarct volume and neuronal injury. The inhibitory effect of EA on the NF-κB pathway was also attenuated by enhanced IκBα phosphorylation and NF-κB p65 nuclear translocation. EA partially inhibited the transformation of microglia and astrocytes from resting states to activated states and reduced the secretion of TNF-α, IL-1β and IL-6. However, these preventive effects were reversed after the silencing of OTULIN expression.

CONCLUSIONS

OTULIN provides a new potential therapeutic target for EA to alleviate acute ischaemic stroke-induced brain injury and the activation of glial cells, which are related to suppression of the NF-κB signalling pathway.

Time-restricted feeding prevents depressive-like and anxiety-like behaviors in male rats exposed to an experimental model of shift-work

Individuals who regularly shift their sleep timing, like night and/or shift-workers suffer from circadian desynchrony and are at risk of developing cardiometabolic diseases and cancer. Also, shift-work is are suggested to be a risk factor for the development of mood disorders such as the burn out syndrome, anxiety, and depression. Experimental and clinical studies provide evidence that food intake restricted to the normal activity phase is a potent synchronizer for the circadian system and can prevent the detrimental health effects associated with circadian disruption. Here, we explored whether adult male Wistar rats exposed to an experimental model of shift-work (W-AL) developed depressive and/or anxiety-like behaviors and whether this was associated with neuroinflammation in brain areas involved with mood regulation. We also tested whether time-restricted feeding (TRF) to the active phase could ameliorate circadian disruption and therefore would prevent depressive and anxiety-like behaviors as well as neuroinflammation. In male Wistar rats, W-AL induced depressive-like behavior characterized by hypoactivity and anhedonia and induced increased anxiety-like behavior in the open field test. This was associated with increased number of glial fibrillary acidic protein and IBA-1-positive cells in the prefrontal cortex and basolateral amygdala. Moreover W-AL caused morphological changes in the microglia in the CA3 area of the hippocampus indicating microglial activation. Importantly, TRF prevented behavioral changes and decreased neuroinflammation markers in the brain. Present results add up evidence about the importance that TRF in synchrony with the light-dark cycle can prevent neuroinflammation leading to healthy mood states in spite of circadian disruptive conditions.

Insight into Mechanobiology: How Stem Cells Feel Mechanical Forces and Orchestrate Biological Functions

The cross-talk between stem cells and their microenvironment has been shown to have a direct impact on stem cells' decisions about proliferation, growth, migration, and differentiation. It is well known that stem cells, tissues, organs, and whole organisms change their internal architecture and composition in response to external physical stimuli, thanks to cells' ability to sense mechanical signals and elicit selected biological functions. Likewise, stem cells play an active role in governing the composition and the architecture of their microenvironment. Is now being documented that, thanks to this dynamic relationship, stemness identity and stem cell functions are maintained. In this work, we review the current knowledge in mechanobiology on stem cells. We start with the description of theoretical basis of mechanobiology, continue with the effects of mechanical cues on stem cells, development, pathology, and regenerative medicine, and emphasize the contribution in the field of the development of ex-vivo mechanobiology modelling and computational tools, which allow for evaluating the role of forces on stem cell biology.

Microglial Morphometric Parameters Correlate With the Expression Level of IL-1β, and Allow Identifying Different Activated Morphotypes

Microglia are the resident macrophages in the brain. Traditionally, two forms of microglia have been described: one considered as a resting/surveillant state in which cells have a highly branched morphology, and another considered as an activated state in which they acquire a de-ramified or amoeboid form. However, many studies describe intermediate microglial morphologies which emerge during pathological processes. Since microglial form and function are closely related, it is of interest to correlate microglial morphology with the extent of its activation. To address this issue, we used a rat model of neuroinflammation consisting in a single injection of the enzyme neuraminidase (NA) within the lateral ventricle. Sections from NA-injected animals were co-immunolabeled with the microglial marker IBA1 and the cytokine IL-1β, which highlight features of the cell’s shape and inflammatory activation, respectively. Activated (IL-1β positive) microglial cells were sampled from the dorsal hypothalamus nearby the third ventricle. Images of single microglial cells were processed in two different ways to obtain (1) an accurate measure of the level of expression of IL-1β (indicating the degree of activation), and (2) a set of 15 morphological parameters to quantitatively and objectively describe the cell’s shape. A simple regression analysis revealed a dependence of most of the morphometric parameters on IL-1β expression, demonstrating that the morphology of microglial cells changes progressively with the degree of activation. Moreover, a hierarchical cluster analysis pointed out four different morphotypes of activated microglia, which are characterized not only by morphological parameters values, but also by specific IL-1β expression levels. Thus, these results demonstrate in an objective manner that the activation of microglial cells is a gradual process, and correlates with their morphological change. Even so, it is still possible to categorize activated cells according to their morphometric parameters, each category presenting a different activation degree. The physiological relevance of those activated morphotypes is an issue worth to be assessed in the future.

The Impact of the Ketogenic Diet on Glial Cells Morphology. A Quantitative Morphological Analysis

Ketogenic diet is reported to protect against cognitive decline, drug-resistant epilepsy, Alzheimer's Disease, damaging effect of ischemic stroke and many neurological diseases. Despite mounting evidence that this dietary treatment works, the exact mechanism of its protective activity is largely unknown. Ketogenic diet acts systemically, not only changing GABA signaling in neurons, but also influencing the reliance on mitochondrial respiration, known to be disrupted in many neurological diseases. Normally, human body is driven by glucose while ketogenic diet mimics starvation and energy required for proper functioning comes from fatty acids oxidation. In the brain astrocytes are believed to be the sole neural cells capable of fatty oxidation. Here we try to explain that not exclusively neurons, but also morphological changes of astroglia and/or microglia due to different metabolic state are important for the mechanism underlying the protective role of ketogenic diet. By quantifying different parameters describing cellular morphology like ramification index or fractal dimension and using Principal Component Analysis to discover the regularities between them, we demonstrate that in normal adult rat brain, ketogenic diet itself is able to change glial morphology, indicating an important role of these underappreciated cells in the brain metabolism.

The formyl peptide receptor agonist FPRa14 induces differentiation of Neuro2a mouse neuroblastoma cells into multiple distinct morphologies which can be specifically inhibited with FPR antagonists and FPR knockdown using siRNA

The N-formyl peptide receptors (FPRs) have been identified within neuronal tissues and may serve as yet undetermined functions within the nervous system. The FPRs have been implicated in the progression and invasiveness of neuroblastoma and other cancers. In this study the effects of the synthetic FPR agonist FPRa14, FPR antagonists and FPR knockdown using siRNA on mouse neuroblastoma neuro2a (N2a) cell differentiation plus toxicity were examined. The FPRa14 (1-10μM) was found to induce a significant dose-dependent differentiation response in mouse neuroblastoma N2a cells. Interestingly, three distinct differentiated morphologies were observed, with two non-archetypal forms observed at the higher FPRa14 concentrations. These three forms were also observed in the human neuroblastoma cell-lines IMR-32 and SH-SY5Y when exposed to 100μM FPRa14. In N2a cells combined knockdown of FPR1 and FPR2 using siRNA inhibited the differentiation response to FPRa14, suggesting involvement of both receptor subtypes. Pre-incubating N2a cultures with the FPR1 antagonists Boc-MLF and cyclosporin H significantly reduced FPRa14-induced differentiation to near baseline levels. Meanwhile, the FPR2 antagonist WRW4 had no significant effect on FPRa14-induced N2a differentiation. These results suggest that the N2a differentiation response observed has an FPR1-dependent component. Toxicity of FPRa14 was only observed at higher concentrations. All three antagonists used blocked FPRa14-induced toxicity, whilst only siRNA knockdown of FPR2 reduced toxicity. This suggests that the toxicity and differentiation involve different mechanisms. The demonstration of neuronal differentiation mediated via FPRs in this study represents a significant finding and suggests a role for FPRs in the CNS. This finding could potentially lead to novel therapies for a range of neurological conditions including neuroblastoma, Alzheimer's disease, Parkinson's disease and neuropathic pain. Furthermore, this could represent a potential avenue for neuronal regeneration therapies.

Activation of microglia associated with lentiviral transduction: A semiautomated method of assessment

Lentiviral transduction is a powerful tool and widely used in neuroscience research to manipulate gene expression of cells. However, the injection of lentiviral vectors in the brain is not totally benign, it potentially induces focal neuroinflammation. Upon inflammation, microglial cells get activated and can induce major changes in tissue environment, which may interfere with experimental results. In the current study, two weeks after the injection of control viral construction in the dentate gyrus (DG) of rats, an activation of microglia was detected. To access the activation status, we used a fast and accurate method of phenotype detection - measurement of fractal dimension (FD). Microglial morphology is a key indicator of neuroinflammation, therefore FD of microglial cells may serve as a reliable index of inflammation status in the brain. Here we present a detailed description of image processing procedure of images of individual microglial cells. The method allows to preserve the complex structure of microglial cells and their thin processes on the output image, which is important for accurate FD assessment.

Functional Neuronal Topography: A Statistical Approach to Micro Mapping Neuronal Location

In order to understand the relationship between neuronal organization and behavior, precise methods that identify and quantify functional cellular ensembles are required. This is especially true in the quest to understand the mechanisms of memory. Brain structures involved in memory formation and storage, as well as the molecular determinates of memory are well-known, however, the microanatomy of functional neuronal networks remain largely unidentified. We developed a novel approach to statistically map molecular markers in neuronal networks through quantitative topographic measurement. Brain nuclei and their subdivisions are well-defined - our approach allows for the identification of new functional micro-regions within established subdivisions. A set of analytic methods relevant for measurement of discrete neuronal data across a diverse range of brain subdivisions are presented. We provide a methodology for the measurement and quantitative comparison of functional micro-neural network activity based on immunohistochemical markers matched across individual brains using micro-binning and heat mapping within brain sub-nuclei. These techniques were applied to the measurement of different memory traces, allowing for greater understanding of the functional encoding within sub-nuclei and its behavior mediated change. These approaches can be used to understand other functional and behavioral questions, including sub-circuit organization, normal memory function and the complexities of pathology. Precise micro-mapping of functional neuronal topography provides essential data to decode network activity underlying behavior.

Glia and central cardiorespiratory pathology

Respiration and blood pressure are primarily controlled by somatic and autonomic motor neurones, respectively. Central cardiorespiratory control is critical in moment-to-moment survival, but it also has a role in the development and maintenance of chronic pathological conditions such as hypertension. The glial cells of the brain are non-neuronal cells with metabolic, immune, and developmental functions. Recent evidence shows that glia play an active role in supporting and regulating the neuronal circuitry which drives the cardiorespiratory system. Here we will review the activities of two key types of glial cell, microglia and astrocytes, in assisting normal central cardiorespiratory control and in pathology.

Pharmacological blockade of fatty acid amide hydrolase (FAAH) by URB597 improves memory and changes the phenotype of hippocampal microglia despite ethanol exposure

Changes in endogenous cannabinoid homeostasis are associated with both ethanol-related neuroinflammation and memory decline. Extensive research is still required to unveil the role of endocannabinoid signaling activation on hippocampal microglial cells after ethanol exposure. Either microglial morphology, phenotype and recruitment may become notably altered after chronic alcohol-related neurodegeneration. Here, we evaluated the pharmacological effects of fatty-acid amide-hydrolase (FAAH) inhibitor URB597 (0.3 mg/kg), oleoylethanolamide (OEA, 10 mg/kg), arachidonoylethanolamide (AEA, 10 mg/kg), the CB1 receptor agonist ACEA (3 mg/kg) and the CB2 receptor agonist JWH133 (0.2 mg/kg) administered for 5 days in a rat model of subchronic (2 weeks) ethanol diet (11% v/v) exposure. URB597 turned to be the most effective treatment. URB597 increased microglial (IBA-1+) cell population, and changed morphometric features (cell area and perimeter, roughness, fractal dimension, lacunarity) associated with activated microglia in the hippocampus of ethanol-exposed rats. Regarding innate immune activity, URB597 specifically increased mRNA levels of toll-like receptor 4 (TLR4), glial fibrillary acidic protein (Gfap) and the chemokine stromal cell-derived factor 1 (SDF-1α/CXCL12), and elevated the cell population expressing the chemokine receptors CX3CR1, CCR2 and CCR4 in the ethanol-exposed rat hippocampus. Contrary to ethanol effect, URB597 reduced mRNA levels of Iba-1, Tnfα, IL-6 and the monocyte chemoattractant protein-1 (MCP-1/CCL2), as well as cell population expressing iNOS. URB597 effects on hippocampal immune system were accompanied by changes in short and long-term visual recognition memory. These results suggest that FAAH inhibition may modulates hippocampal microglial recruitment and activation that can be associated with improved hippocampal-dependent memory despite ethanol exposure.

Quantifying Microglia Morphology from Photomicrographs of Immunohistochemistry Prepared Tissue Using ImageJ

Microglia are brain phagocytes that participate in brain homeostasis and continuously survey their environment for dysfunction, injury, and disease. As the first responders, microglia have important functions to mitigate neuron and glia dysfunction, and in this process, they undergo a broad range of morphologic changes. Microglia morphologies can be categorized descriptively or, alternatively, can be quantified as a continuous variable for parameters such as cell ramification, complexity, and shape. While methods for quantifying microglia are applied to single cells, few techniques apply to multiple microglia in an entire photomicrograph. The purpose of this method is to quantify multiple and single cells using readily available ImageJ protocols. This protocol is a summary of the steps and ImageJ plugins recommended to convert fluorescence and bright-field photomicrographs into representative binary and skeletonized images and to analyze them using software plugins AnalyzeSkeleton (2D/3D) and FracLac for morphology data collection. The outputs of these plugins summarize cell morphology in terms of process endpoints, junctions, and length as well as complexity, cell shape, and size descriptors. The skeleton analysis protocol described herein is well suited for a regional analysis of multiple microglia within an entire photomicrograph or region of interest (ROI) whereas FracLac provides a complementary individual cell analysis. Combined, the protocol provides an objective, sensitive, and comprehensive assessment tool that can be used to stratify between diverse microglia morphologies present in the healthy and injured brain.

Atomoxetine, a selective norepinephrine reuptake inhibitor, improves short-term histological outcomes after hypoxic-ischemic brain injury in the neonatal male rat

BACKGROUND

Despite the recent progress of perinatal medicine, perinatal hypoxic-ischemic (HI) insult remains an important cause of brain injury in neonates, and is pathologically characterized by neuronal loss and the presence of microglia. Neurotransmitters, such as norepinephrine (NE) and glutamate, are involved in the pathogenesis of hypoxic-ischemic encephalopathy via the interaction between neurons and microglia. Although it is well known that the monoamine neurotransmitter NE acts as an anti-inflammatory agent in the brain under pathological conditions, its effects on perinatal HI insult remains elusive. Atomoxetine, a selective NE reuptake inhibitor, has been used clinically for the treatment of attention-deficit hyperactivity disorder in children. Here, we investigated whether the enhancement of endogenous NE by administration of atomoxetine could protect neonates against HI insult by using the neonatal male rat model. We also examined the involvement of microglia in this process.

METHODS

Unilateral HI brain injury was induced by the combination of left carotid artery dissection followed by ligation and hypoxia (8% O₂, 2 h) in postnatal day 7 (P7) male rat pups. The pups were randomized into three groups: the atomoxetine treatment immediately after HI insult, the atomoxetine treatment at 3 h after HI insult, or the vehicle treatment group. The pups were euthanized on P8 and P14, and the brain regions including the cortex, striatum, hippocampus, and thalamus were evaluated by immunohistochemistry.

RESULTS

HI insult resulted in severe brain damage in the ipsilateral hemisphere at P14. Atomoxetine treatment immediately after HI insult significantly increased NE levels in the ipsilateral hemisphere at 1 h after HI insult and reduced the neuronal damage via the increased phosphorylation of cAMP response element-binding protein (pCREB) in all brain regions examined. In addition, the number of microglia was maintained under atomoxetine treatment compared with that of the vehicle treatment group. To determine the involvement of microglia in the process of neuronal loss by HI insult, we further examined the influence of hypoxia on rat primary cultured microglia by the quantitative real-time polymerase chain reaction. Hypoxia did not cause the upregulation of interleukin-1beta (IL-1β) mRNA expression, but decreased the microglial intrinsic nitric oxide synthase (iNOS)/arginase1 mRNA expression ratio. NE treatment further decreased the microglial iNOS/arginase1 mRNA expression ratio. In contrast, no significant neuroprotective effect was observed at P14 when atomoxetine was administered at 3 h after HI insult.

CONCLUSIONS

These findings suggested that the enhancement of intrinsic neurotransmitter NE signaling by a selective NE reuptake inhibitor, atomoxetine, reduced the perinatal HI insult brain injury. In addition, atomoxetine treatment was associated with changes of TUNEL, pCREB, and BDNF expression levels, and microglial numbers, morphology, and responses.

Glucocerebrosidase deficiency in dopaminergic neurons induces microglial activation without neurodegeneration

Mutations in the GBA1 gene encoding the lysosomal enzyme glucocerebrosidase (GBA1) are important risk factors for Parkinson's disease (PD). In vitro, altered GBA1 activity promotes alpha-synuclein accumulation whereas elevated levels of alpha-synuclein compromise GBA1 function, thus supporting a pathogenic mechanism in PD. However, the mechanisms by which GBA1 deficiency is linked to increased risk of PD remain elusive, partially because of lack of aged models of GBA1 deficiency. As knocking-out GBA1 in the entire brain induces massive neurodegeneration and early death, we generated a mouse model of GBA1 deficiency amenable to investigate the long-term consequences of compromised GBA1 function in dopaminergic neurons. DAT-Cre and GBA1-floxed mice were bred to obtain selective homozygous disruption of GBA1 in midbrain dopamine neurons (DAT-GBA1-KO). Mice were followed for motor function, neuronal survival, alpha-synuclein phosphorylation and glial activation. Susceptibility to nigral viral vector-mediated overexpression of mutated (A53T) alpha-synuclein was assessed. Despite loss of GBA1 and substrate accumulation, DAT-GBA1-KO mice displayed normal motor performances and preserved dopaminergic neurons despite robust microglial activation in the substantia nigra, without accumulation of endogenous alpha-synuclein with respect to wild-type mice. Lysosomal function was only marginally affected. Screening of micro-RNAs linked to the regulation of GBA1, alpha-synuclein or neuroinflammation did not reveal significant alterations. Viral-mediated overexpression of A53T-alpha-synuclein yielded similar neurodegeneration in DAT-GBA1-KO mice and wild-type mice. These results indicate that loss of GBA1 function in mouse dopaminergic neurons is not critical for alpha-synuclein accumulation or neurodegeneration and suggest the involvement of GBA1 deficiency in other cell types as a potential mechanism.

Regulation of Microglia Identity from an Epigenetic and Transcriptomic Point of View

Microglia have long been recognized as the endogenous innate immune elements in the central nervous system (CNS) parenchyma. Besides fulfilling local immune-related functions, they provide cross-talk between the CNS and the immune system at large. In the adult CNS, microglia are involved in maintaining brain homeostasis, modulating synaptic transmission and clearance of apoptotic cells. During embryonic development, microglia are responsible for the removal of supernumerary synapses and neurons, and neuronal network formation. The full scale of their potential abilities has been highlighted by improvements in microglia isolation methods, the development of genetically tagged mouse models, advanced imaging technologies and the application of next-generation sequencing in recent years. Genome-wide expression analysis of relatively pure microglia populations from both mouse and human CNS tissues has thereby greatly contributed to our knowledge of their biology; what defines them under homeostatic conditions and how microglia respond to processes like aging and CNS disease? How and to what degree beneficial functions of microglia can be restored in the aged or diseased brain will be the key issue to be addressed in future research.

Quantitative microglia analyses reveal diverse morphologic responses in the rat cortex after diffuse brain injury

Determining regions of altered brain physiology after diffuse brain injury is challenging. Microglia, brain immune cells with ramified and dynamically moving processes, constantly surveil the parenchyma for dysfunction which, when present, results in a changed morphology. Our purpose was to define the spatiotemporal changes in microglia morphology over 28 days following rat midline fluid percussion injury (mFPI) as a first step in exploiting microglia morphology to reflect altered brain physiology. Microglia morphology was quantified from histological sections using Image J skeleton and fractal analysis procedures at three time points and in three regions post-mFPI: impact site, primary somatosensory cortex barrel field (S1BF), and a remote region. Microglia ramification (process length/cell and endpoints/cell) decreased in the impact and S1BF but not the remote region (p < 0.05). Microglia complexity was decreased in the S1BF (p = 0.003) and increased in the remote region (p < 0.02). Rod-shaped microglia were present in the S1BF and had a 1.8:1.0 length:width ratio. An in-depth quantitative morphologic analysis revealed diverse and widespread changes to microglia morphology in the cortex post-mFPI. Due to their close link to neuronal function, changes in microglia morphology, summarized in this study, likely reflect altered physiology with diverse and widespread impact on neuronal and circuit function.

IL-17A Enhances Microglial Response to OGD by Regulating p53 and PI3K/Akt Pathways with Involvement of ROS/HMGB1

Cerebral ischemia-reperfusion injury (IRI) has a complex pathogenesis, and interleukin-17 (IL-17) is a newly identified class of the cytokine family that plays an important role in ischemic inflammation. An oxygen-glucose deprivation (OGD) model showed that IL-17A expression was significantly up-regulated in microglial cells. After IL-17A siRNA transfection, the inhibition of proliferation, and the increased apoptosis in microglial cells, induced by OGD/reperfusion, was improved, and the elevation of Caspase-3, Caspase-8, Caspase-9, and poly ADP ribose polymerase (PARP) activities was inhibited. Mass spectrometry demonstrated that IL-17A functioned through a series of factors associated with oxidative stress and apoptosis and regulated Caspase-3 activity and apoptosis in microglial cells via the p53 and PI3K/Akt signaling pathways. IL-17A, HMGB1, and ROS were regulated mutually to exhibit a synergistic effect in the OGD model of microglial cells, but the down-regulation of IL-17A or HMGB1 expression did not completely inhibit the production of ROS. These findings demonstrated that ROS might be located upstream of IL-17A and HMGB1 so that ROS can regulate HMGB1/IL-17A expression to affect the p53 and PI3K/Akt signaling pathways and therefore promote the occurrence of apoptosis in microglial cells. These findings provide a novel evidence for the role of IL-17A in ischemic cerebral diseases.

Microglia Morphological Categorization in a Rat Model of Neuroinflammation by Hierarchical Cluster and Principal Components Analysis

It is known that microglia morphology and function are closely related, but only few studies have objectively described different morphological subtypes. To address this issue, morphological parameters of microglial cells were analyzed in a rat model of aseptic neuroinflammation. After the injection of a single dose of the enzyme neuraminidase (NA) within the lateral ventricle (LV) an acute inflammatory process occurs. Sections from NA-injected animals and sham controls were immunolabeled with the microglial marker IBA1, which highlights ramifications and features of the cell shape. Using images obtained by section scanning, individual microglial cells were sampled from various regions (septofimbrial nucleus, hippocampus and hypothalamus) at different times post-injection (2, 4 and 12 h). Each cell yielded a set of 15 morphological parameters by means of image analysis software. Five initial parameters (including fractal measures) were statistically different in cells from NA-injected rats (most of them IL-1β positive, i.e., M1-state) compared to those from control animals (none of them IL-1β positive, i.e., surveillant state). However, additional multimodal parameters were revealed more suitable for hierarchical cluster analysis (HCA). This method pointed out the classification of microglia population in four clusters. Furthermore, a linear discriminant analysis (LDA) suggested three specific parameters to objectively classify any microglia by a decision tree. In addition, a principal components analysis (PCA) revealed two extra valuable variables that allowed to further classifying microglia in a total of eight sub-clusters or types. The spatio-temporal distribution of these different morphotypes in our rat inflammation model allowed to relate specific morphotypes with microglial activation status and brain location. An objective method for microglia classification based on morphological parameters is proposed.

Main points

Microglia undergo a quantifiable morphological change upon neuraminidase induced inflammation.

Hierarchical cluster and principal components analysis allow morphological classification of microglia.

Brain location of microglia is a relevant factor.

Long-Term Consumption of High-Fat Diet in Rats: Effects on Microglial and Astrocytic Morphology and Neuronal Nitric Oxide Synthase Expression

Obesity in humans is associated with cognitive decline and elevated risk of neurodegenerative diseases of old age. Variations of high-fat diet are often used to model these effects in animal studies. However, we previously reported improvements in markers of memory and learning, as well as larger hippocampi and higher metabolite concentrations in Wistar rats fed high-fat, high-carbohydrate diet (HFCD, 60 % energy from fat, 28 % from carbohydrates) for 1 year; this diet leads to mild ketonemia (Setkowicz et al. in PLoS One 10:e0139987, 2015). In the present study, we follow up on this cohort to assess glial morphology and expression of markers related to gliosis. Twenty-five male Wistar rats were kept on HFCD and twenty-five on normal chow. At 12 months of age, the animals were sacrificed and processed for immunohistochemical staining for astrocytic (glial fibrillary acidic protein), microglial (Iba1), and neuronal (neuronal nitric oxide synthetase, nNOS) markers in the hippocampus. We have found changes in immunopositive area fraction and cellular complexity, as studied by a simplified Sholl procedure. To our knowledge, this study is the first to apply this methodology to the study of glial cells in HFCD animals. GFAP and Iba1 immunoreactive area fraction in the hippocampi of HFCD-fed rats were decreased, while the mean number of intersections (an indirect measure of cell complexity) was decreased in GFAP-positive astrocytes, but not in Iba1-expressing microglia. At the same time, nNOS expression was lowered after HFCD in both the cortex and the hippocampus.

Characterizing microglia activation: a spatial statistics approach to maximize information extraction

Microglia play an important role in the pathology of CNS disorders, however, there remains significant uncertainty about the neuroprotective/degenerative role of these cells due to a lack of techniques to adequately assess their complex behaviour in response to injury. Advancing microscopy techniques, transgenic lines and well-characterized molecular markers, have made histological assessment of microglia populations more accessible. However, there is a distinct lack of tools to adequately extract information from these images to fully characterise microglia behaviour. This, combined with growing economic pressures and the ethical need to minimise the use of laboratory animals, led us to develop tools to maximise the amount of information obtained. This study describes a novel approach, combining image analysis with spatial statistical techniques. In addition to monitoring morphological parameters and global changes in microglia density, nearest neighbour distance, and regularity index, we used cluster analyses based on changes in soma size and roundness to yield novel insights into the behaviour of different microglia phenotypes in a murine optic nerve injury model. These methods should be considered a generic tool to quantitatively assess microglia activation, to profile phenotypic changes into microglia subpopulations, and to map spatial distributions in virtually every CNS region and disease state.

Homology analysis detects topological changes of Iba1 localization accompanied by microglial activation

The state of microglial activation provides important information about the central nervous system. However, a reliable index of microglial activation in histological samples has yet to be established. Here, we show that microglial activation induces topological changes of Iba1 localization that can be detected by analysis based on homology theory. Analysis of homology was applied to images of Iba1-stained tissue sections, and the 0-dimentional Betti number (b0: the number of solid components) and the 1-dimentional Betti number (b1: the number of windows surrounded by solid components) were obtained. We defined b1/b0 as the Homology Value (HV), and investigated its validity as an index of microglial activation using cerebral ischemia model mice. Microglial activation was accompanied by changes to Iba1 localization and morphology of microglial processes. In single microglial cells, the change of Iba1 localization increased b1. Conversely, thickening or retraction of microglial processes decreased b0. Consequently, microglial activation increased the HV. The HV of a tissue area increased with proximity to the ischemic core and showed a high degree of concordance with the number of microglia expressing activation makers. Furthermore, the HV of human metastatic brain tumor tissue also increased with proximity to the tumor. These results suggest that our index, based on homology theory, can be used to correctly evaluate microglial activation in various tissue images.

Hierarchical Cluster Analysis of Three-Dimensional Reconstructions of Unbiased Sampled Microglia Shows not Continuous Morphological Changes from Stage 1 to 2 after Multiple Dengue Infections in Callithrix penicillata

It is known that microglial morphology and function are related, but few studies have explored the subtleties of microglial morphological changes in response to specific pathogens. In the present report we quantitated microglia morphological changes in a monkey model of dengue disease with virus CNS invasion. To mimic multiple infections that usually occur in endemic areas, where higher dengue infection incidence and abundant mosquito vectors carrying different serotypes coexist, subjects received once a week subcutaneous injections of DENV3 (genotype III)-infected culture supernatant followed 24 h later by an injection of anti-DENV2 antibody. Control animals received either weekly anti-DENV2 antibodies, or no injections. Brain sections were immunolabeled for DENV3 antigens and IBA-1. Random and systematic microglial samples were taken from the polymorphic layer of dentate gyrus for 3-D reconstructions, where we found intense immunostaining for TNFα and DENV3 virus antigens. We submitted all bi- or multimodal morphological parameters of microglia to hierarchical cluster analysis and found two major morphological phenotypes designated types I and II. Compared to type I (stage 1), type II microglia were more complex; displaying higher number of nodes, processes and trees and larger surface area and volumes (stage 2). Type II microglia were found only in infected monkeys, whereas type I microglia was found in both control and infected subjects. Hierarchical cluster analysis of morphological parameters of 3-D reconstructions of random and systematic selected samples in control and ADE dengue infected monkeys suggests that microglia morphological changes from stage 1 to stage 2 may not be continuous.

Quantitative Evaluation of Changes in the Striatal Astrocyte Axons in Simulated Parkinsonism

Three parkinsonism models using neurotoxin 6-OHDA and pesticides rotenone and paraquat were reproduced in Wistar rats and parameters of astrocyte processes in the striatum (axon number and length, area occupied by them, and axon branching pattern) detected by immunohistochemical reaction for acid glial fibrillary protein were studied by computer morphometry. By these parameters, three morphological types of astrocytes were distinguished. Two variants of changes were found in the used parkinsonism models: 1) more intense branching and even elongation of all axons and 2) reduction of small and elongation of the main remaining stems, which manifested in polarization of glial cell. Type 1 reaction was obviously associated with compensatory increase in astrocyte interaction with neurons, while type 2 reflected astrocyte response to injury and impaired glioneuronal interactions.

Apocynin prevents mitochondrial burdens, microglial activation, and pro-apoptosis induced by a toxic dose of methamphetamine in the striatum of mice via inhibition of p47phox activation by ERK

BACKGROUND

Activation of NADPH oxidase (PHOX) plays a critical role in mediating dopaminergic neuroinflammation. In the present study, we investigated the role of PHOX in methamphetamine (MA)-induced neurotoxic and inflammatory changes in mice.

METHODS

We examined changes in mitogen-activated protein kinases (MAPKs), mitochondrial function [i.e., mitochondrial membrane potential, intramitochondrial Ca(2+) accumulation, mitochondrial oxidative burdens, mitochondrial superoxide dismutase expression, and mitochondrial translocation of the cleaved form of protein kinase C delta type (cleaved PKCδ)], microglial activity, and pro-apoptotic changes [i.e., cytosolic cytochrome c release, cleaved caspase 3, and terminal deoxynucleotidyl transferase dUDP nick-end labeling (TUNEL) positive populations] after a neurotoxic dose of MA in the striatum of mice to achieve a better understanding of the effects of apocynin, a non-specific PHOX inhibitor, or genetic inhibition of p47phox (by using p47phox knockout mice or p47phox antisense oligonucleotide) against MA-induced dopaminergic neurotoxicity.

RESULTS

Phosphorylation of extracellular signal-regulated kinases (ERK1/2) was most pronounced out of MAPKs after MA. We observed MA-induced phosphorylation and membrane translocation of p47phox in the striatum of mice. The activation of p47phox promoted mitochondrial stresses followed by microglial activation into the M1 phenotype, and pro-apoptotic changes, and led to dopaminergic impairments. ERK activated these signaling pathways. Apocynin or genetic inhibition of p47phox significantly protected these signaling processes induced by MA. ERK inhibitor U0126 did not exhibit any additional positive effects against protective activity mediated by apocynin or p47phox genetic inhibition, suggesting that ERK regulates p47phox activation, and ERK constitutes the crucial target for apocynin-mediated inhibition of PHOX activation.

CONCLUSIONS

Our results indicate that the neuroprotective mechanism of apocynin against MA insult is via preventing mitochondrial burdens, microglial activation, and pro-apoptotic signaling process by the ERK-dependent activation of p47phox.

Inflammation induced at different developmental stages affects differently the range of microglial reactivity and the course of seizures evoked in the adult rat

BACKGROUND

In the brain, inflammation occurs following a variety of types of brain damage, including epileptic seizures. Proinflammatory cytokines, like IL-1β or TNFα, can increase neuronal excitability and initiate spontaneous seizures or epileptogenesis. Recent studies indicate that the effects can be attenuated or even abolished in animals subjected to inflammation-inducing treatments at earlier developmental stages, termed "preconditioning". Immunocompetent microglial cells display particular sensitivity to subtle brain pathologies showing a morphological continuum from resting to reactive forms. Following inflammation, multiple ramified processes of resting microglia become gradually shorter, and the cells transform into macrophages. Parameters of the morphological variations were used here as indicators of the nervous tissue reactivity to seizures in adult rats experiencing inflammation at earlier stages of postnatal development.

METHODS

Systemic inflammation was induced with lipopolysaccharide (LPS) in 6-day-old or 30-day-old rats. In two-month-old survivors of the inflammatory status, seizures were evoked with pilocarpine injection. The seizure intensity was scored during a six-hour continuous observation period following the injection. Brain sections were immunostained for Iba1 to visualize microglia. Thereafter, morphology of microglial cells located in the hippocampal formation was analyzed using parameters such as solidity, circularity, ramification index, and area.

RESULTS

In naïve rats, seizure-induced transformations of microglial cells were reflected by strong changes in the parameters of their morphology. However, in the adult rats pretreated with LPS on their 6th or 30th postnatal days, the seizure-induced changes were significantly reduced, and microglial morphology remained significantly closer to normal. Significant amelioration of the acute phase of seizures was observed only when inflammation was induced in 30-day-old, but not in 6-day-old, rats.

CONCLUSIONS

The results confirm previous reports that moderate inflammation protects the nervous tissue from subsequent damage by reducing influences of proinflammatory factors on reactive glial cells. The young-age inflammation may have age-dependent effects on susceptibility to seizures induced in adulthood. This article is part of a Special Issue entitled "Status Epilepticus".

Selective estrogen receptor modulators regulate reactive microglia after penetrating brain injury

Following brain injury, microglia assume a reactive-like state and secrete pro-inflammatory molecules that can potentiate damage. A therapeutic strategy that may limit microgliosis is of potential interest. In this context, selective estrogen receptor modulators, such as raloxifene and tamoxifen, are known to reduce microglia activation induced by neuroinflammatory stimuli in young animals. In the present study, we have assessed whether raloxifene and tamoxifen are able to affect microglia activation after brain injury in young and aged animals in time points relevant to clinics, which is hours after brain trauma. Volume fraction of MHC-II(+) microglia was estimated according to the point-counting method of Weibel within a distance of 350 μm from the lateral border of the wound, and cellular morphology was measured by fractal analysis. Two groups of animals were studied: (1) young rats, ovariectomized at 2 months of age; and (2) aged rats, ovariectomized at 18 months of age. Fifteen days after ovariectomy animals received a stab wound brain injury and the treatment with estrogenic compounds. Our findings indicate that raloxifene and tamoxifen reduced microglia activation in both young and aged animals. Although the volume fraction of reactive microglia was found lower in aged animals, this was accompanied by important changes in cell morphology, where aged microglia assume a bushier and hyperplasic aspect when compared to young microglia. These data suggest that early regulation of microglia activation provides a mechanism by which selective estrogen receptors modulators (SERMs) may exert a neuroprotective effect in the setting of a brain trauma.

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

BACKGROUND

Subarachnoid hemorrhage (SAH) is a neurologic catastrophe and poor outcome is typically attributed to vasospasm; however, there is also evidence that SAH causes a pro-inflammatory state and these two phenomena may be interrelated. SAH causes activation of microglia, but the time course and degree of microglial activation after SAH and its link to poor patient outcome and vasospasm remains unknown.

NEW METHOD

Transgenic mice expressing eGFP under the control of the CX3CR1 locus, in which microglia are endogenously fluorescent, were randomly assigned to control or SAH groups. Immunohistochemistry for CD-68 and CD-31 was performed at different time points after SAH. Using confocal microscopy and MatLab software, we have developed a novel technique to detect and quantify the stages of microglial activation and return to quiescence using an automated computerized morphometric analysis.

RESULTS

We detected a statistically significant decrease in microglial process complexity 2 and 7 days following SAH. In addition, we detected a statistically significant increase in microglial domain volume 1 day following SAH; however, microglial domain volume returned to baseline by 2 days.

COMPARISON WITH EXISTING METHOD

Most techniques for microglia assessment are qualitative, not quantitative, and are therefore inadequate to address the effects of anti-inflammatory drug treatment or other therapies after SAH.

CONCLUSIONS

Using novel image analysis techniques we were able to reproducibly quantify activation of microglia following SAH, which will improve our ability to study the biology of microglial activation, and may ultimately improve management of disease progression and response to therapies directed at microglial activation.

Automated method for the rapid and precise estimation of adherent cell culture characteristics from phase contrast microscopy images

The quantitative determination of key adherent cell culture characteristics such as confluency, morphology, and cell density is necessary for the evaluation of experimental outcomes and to provide a suitable basis for the establishment of robust cell culture protocols. Automated processing of images acquired using phase contrast microscopy (PCM), an imaging modality widely used for the visual inspection of adherent cell cultures, could enable the non-invasive determination of these characteristics. We present an image-processing approach that accurately detects cellular objects in PCM images through a combination of local contrast thresholding and post hoc correction of halo artifacts. The method was thoroughly validated using a variety of cell lines, microscope models and imaging conditions, demonstrating consistently high segmentation performance in all cases and very short processing times (<1 s per 1,208 × 960 pixels image). Based on the high segmentation performance, it was possible to precisely determine culture confluency, cell density, and the morphology of cellular objects, demonstrating the wide applicability of our algorithm for typical microscopy image processing pipelines. Furthermore, PCM image segmentation was used to facilitate the interpretation and analysis of fluorescence microscopy data, enabling the determination of temporal and spatial expression patterns of a fluorescent reporter. We created a software toolbox (PHANTAST) that bundles all the algorithms and provides an easy to use graphical user interface. Source-code for MATLAB and ImageJ is freely available under a permissive open-source license. Biotechnol. Bioeng. 2014;111: 504–517. © 2013 Wiley Periodicals, Inc.

Functional morphometric analysis in cellular behaviors: shape and size matter

Cellular morphogenesis in response to biophysical and topographical cues provides insights into cytoskeletal status, biointerface communications, and phenotypic adaptations in an incessant signaling feedback that governs cellular fate. Morphometric characterization is an important element in the study of the dynamic cellular behaviors, in their interactive response to environmental influence exerted by culture system. They collectively serve to reflect cellular proliferation, migration, and differentiation, which may serve as prognostic indices for clinical and pathological diagnosis. Various parameters are proposed to categorize morphological adaptations in relation to cellular function. In this review, the underlying principles, assumptions, and limitations of morphological characterizations are discussed. The significance, challenges, and implications of quantitative morphometric characterization of cell shapes and sizes in determining cellular functions are discussed.

Novel objective classification of reactive microglia following hypoglossal axotomy using hierarchical cluster analysis

A total of 136 microglia were intracellularly labeled and their morphological features were evaluated by 3D morphometric measurement. According to hierarchical cluster analysis, microglia were objectively categorized into four groups termed types I-IV. The validity of this classification was confirmed by principal component analysis and linear discriminant analysis. Type I microglia were found in sham-operated mice and in mice sacrificed 28 days (D28) after axotomy. The appearance of type I cells was similar to so-called ramified microglia in a resting state. Type II microglia were mainly seen in D14 mice, which exhibited small cell bodies with thin and short processes. Interestingly, none of the already-known morphological types of microglia seemed to be comparable to type II cells. We thus named type II microglia "small ramified" cells. Types III and IV microglia were mainly seen in D3 and D7 mice and their appearances were similar to hypertrophied and bushy cells, respectively. Proliferating cell nuclear antigen (PCNA), a mitosis marker, was almost exclusively expressed in D3 mice. On the other hand, voltage-dependent potassium channels (Kv1.3/1.5), neurotoxicity-related molecules, were most highly expressed in D14 mice. Increased expression of Kv1.3/1.5 in D14 mice was suppressed by minocycline treatment. These findings indicate that type II and III microglia may be involved in neurotoxicity and mitosis, respectively. Type IV microglial cells are assumed to be in the process of losing mitotic activity and gaining neurotoxicity. Our data also suggest that type II microglia can be a potential therapeutic target against neurodegenerative diseases.

Oxidative stress is related to the deleterious effects of heme oxygenase-1 in an in vivo neuroinflammatory rat model

Heme oxygenase-1 (HO-1) induction is associated with beneficial or deleterious effects depending on the experimental conditions adopted and the neurodegenerative rodent models used. The present study aimed first to evaluate the effects of cerebral HO-1 induction in an in vivo rat model of neuroinflammation by intrastriatal injection of quinolinic acid (QA) and secondly to explore the role played by reactive oxygen species (ROS) and free iron (Fe²⁺) derived from heme catabolism promoted by HO-1. Chronic I.P. treatment with the HO-1 inductor and substrate hemin was responsible for a significant dose-related increase of cerebral HO-1 production. Brain tissue loss, microglial activation, and neuronal death were significantly higher in rats receiving QA plus hemin (H-QA) versus QA and controls. Significant increase of ROS production in H-QA rat brain was inhibited by the specific HO-1 inhibitor ZnPP which supports the idea that ROS level augmentation in hemin-treated animals is a direct consequence of HO-1 induction. The cerebral tissue loss and ROS level in hemin-treated rats receiving the iron chelator deferoxamine were significantly decreased, demonstrating the involvement of Fe²⁺in brain ROS production. Therefore, the deleterious effects of HO-1 expression in this in vivo neuroinflammatory model were linked to a hyperproduction of ROS, itself promoted by free iron liberation.