Staining of HLA-DR, Iba1 and CD68 in human microglia reveals partially overlapping expression depending on cellular morphology and pathology

Myeloid cell modulation by a GLP-1 receptor agonist regulates retinal angiogenesis in ischemic retinopathy

Ischemic retinopathies including diabetic retinopathy are major causes of blindness. Although neurons and Müller glia are recognized as important regulators of reparative and pathologic angiogenesis, the role of mononuclear phagocytes (MPs) — particularly microglia, the resident retinal immune cells — is unclear. Here, we found MP activation in human diabetic retinopathy, especially in neovessels from human neovascular membranes in proliferative retinopathy, including TNF-α expression. There was similar activation in the mouse oxygen-induced retinopathy (OIR) model of ischemia-induced neovascularization. Glucagon-like peptide-1 receptor (GLP-1R) agonists are in clinical use for glycemic control in diabetes and are also known to modulate microglia. Herein, we investigated the effect of a long-acting GLP-1R agonist, NLY01. Following intravitreal administration, NLY01 selectively localized to MPs in retina with OIR. NLY01 modulated MPs but not retinal endothelial cell viability, apoptosis, and tube formation in vitro. In OIR, NLY01 treatment inhibited MP infiltration and activation, including MP expression of cytokines in vivo. NLY01 significantly suppressed global induction of retinal inflammatory cytokines, promoted reparative angiogenesis, and suppressed pathologic retinal neovascularization. Collectively, these findings indicate the important role of mononuclear phagocytes in regulation of retinal vascularization in ischemia and suggest modulation of MPs as a potentially new treatment strategy for ischemic retinopathies.

Neural Infection by Oropouche Virus in Adult Human Brain Slices Induces an Inflammatory and Toxic Response

Oropouche virus (OROV) is an emerging arbovirus in South and Central Americas with high spreading potential. OROV infection has been associated with neurological complications and OROV genomic RNA has been detected in cerebrospinal fluid from patients, suggesting its neuroinvasive potential. Motivated by these findings, neurotropism and neuropathogenesis of OROV have been investigated in vivo in murine models, which do not fully recapitulate the complexity of the human brain. Here we have used slice cultures from adult human brains to investigate whether OROV is capable of infecting mature human neural cells in a context of preserved neural connections and brain cytoarchitecture. Our results demonstrate that human neural cells can be infected ex vivo by OROV and support the production of infectious viral particles. Moreover, OROV infection led to the release of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) and diminished cell viability 48 h post-infection, indicating that OROV triggers an inflammatory response and tissue damage. Although OROV-positive neurons were observed, microglia were the most abundant central nervous system (CNS) cell type infected by OROV, suggesting that they play an important role in the response to CNS infection by OROV in the adult human brain. Importantly, we found no OROV-infected astrocytes. To the best of our knowledge, this is the first direct demonstration of OROV infection in human brain cells. Combined with previous data from murine models and case reports of OROV genome detection in cerebrospinal fluid from patients, our data shed light on OROV neuropathogenesis and help raising awareness about acute and possibly chronic consequences of OROV infection in the human brain.

Proteomic analysis capsule synthesis and redox mechanisms in the intracellular survival of group B Streptococcus in fish microglia

Group B Streptococcus (GBS) causes meningitis in neonates and Nile tilapia (Oreochromis niloticus). The molecular mechanisms regulating the intracellular survival of this pathogen in the host cell are complex and crucial for the progression of infection. Thus, we propose the use of GBS-infected Nile tilapia microglia as an in vitro model system simulating infection caused by homologous bacteria in humans. We used this model to evaluate the phagocytic activity, as well as the functional aspects of the capsular proteins A, B, C, and D and the major redox enzymes, and the synergistic role of mechanisms/proteins involved in blocking phagocytic process. We observed that in the intracellular phase, GBS showed enhanced synthesis of the polysaccharide capsule and used superoxide dismutase, thioredoxin, NADH oxidase, and alkyl hydroperoxide reductase to scavenge reactive oxygen species and reactive nitrogen species produced by the host cell. Furthermore, although these virulence mechanisms were effective during the initial hours of infection, they were not able to subvert microglial responses, which partially neutralized the infection. Altogether, our findings provided important information regarding the intracellular survival mechanisms of GBS and perspectives for the production of new drugs and vaccines, through the druggability analysis of specific proteins. In conclusion, tilapia microglia serve as a potent in vitro experimental model for the study of meningitis.

Multiple Sclerosis: Microglia, Monocytes, and Macrophage-Mediated Demyelination

This study examined the roles of microglia and monocytes in myelin destruction in patients with early multiple sclerosis (MS). Twenty-two cases were studied; the clinical duration was <9 weeks in 10 cases. Twenty myeloid cell subtypes or categories were identified including 2 cell types not known previously to occur in demyelinating diseases. Commencing myelin breakdown in plaques and in perivascular and subpial tissues occurred in the immediate presence of infiltrating monocytes and was effected by a homogeneous population of IgG-positive Fc receptor-bearing early phagocytes interacting with abnormal myelin. Oligodendrocyte apoptosis was observed in intact myelinated tissue bordering areas of active demyelination. Capillaries in the cerebral cortex plugged by large numbers of monocytes were common in acute cases of MS and in a patient with a neuromyelitis optica variant and extreme systemic recruitment of monocytes. In an MS patient with progressive disease, microglial nodules centered on MHC-II-positive capillaries plugged by monocytes were present in the cerebral cortex. This constitutes a new gray matter lesion in MS.

Electroacupuncture Improves M2 Microglia Polarization and Glia Anti-inflammation of Hippocampus in Alzheimer's Disease

Background: Alzheimer's disease (AD) is a neurodegenerative disease characterized by loss of recognition and memory. Neuroinflammation plays pivotal roles in the pathology of AD and affects the progression of the disease. Astrocyte and microglia, as main immune executors in the central nervous system (CNS), participate into the inflammatory response in AD. Glia polarize into different phenotypes during neurodegeneration. Pro-inflammatory glia produce cytokines (IL-1β, TNF-α, and IL-6) resulting into debris aggregates and neurotoxicity. Anti-inflammatory phenotypes produce cytokines (IL-4 and IL-10) to release the inflammation. Electroacupuncture is a useful treatment that has been found to slow the neurodegeneration in animals through experimentation and in humans through clinical trials. The aim of this study was to uncover the mechanisms of glia activation, microglia polarization, and cytokine secretion regulated by electroacupuncture as a treatment for AD. Methods: Twenty male Sprague-Dawley (SD) rats were randomly divided into four groups: Control group (Control), Normal saline group (NS), AD group (AD), and Electroacupuncture group (Acupuncture). The AD and Acupuncture groups were bilaterally injected with Aβ_{1 - 42} into the CA1 field of the hippocampus. The Acupuncture group received electroacupuncture stimulation on the acupoint "Baihui" (GV20) for 6 days per week for a total of 3 weeks. The Morris Water Maze (MWM) was used to evaluate learning and memory capacity. Immunofluorescence was used to stain GFAP and Iba1 of the DG and CA1 in the hippocampus, which, respectively, expressed the activation of astrocyte and microglia. The M1 microglia marker, inducible nitric oxide synthase (iNOS), and M2 marker Arginase 1 (Arg1) were used to analyze the polarization of microglia. The pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6), anti-inflammatory cytokines (IL-4 and IL-10), and pathway-molecules (p65 and Stat6) were tested to analyze the glia inflammatory response by immunofluorescence and polymerase chain reaction (PCR). Results: The MWM results showed that electroacupuncture improves the escape latency time and the swimming distance of AD rats. The number of GFAP and Iba1 cells significantly increased in AD rats, but electroacupuncture decreased the cells. The iNOS-positive cells were significantly increased in AD, and electroacupuncture decreased the positive cells. Electroacupuncture elevated Arg1-positive cells in AD rats. Electroacupuncture decreased the glia pro-inflammatory cytokine expression and increased the anti-inflammatory cytokine expression in AD rats. Furthermore, electroacupuncture inhibited the NF-κB pathway molecule (p65) while raising the Stat6 pathway molecule (Stat6). Conclusion: These results provide evidence that electroacupuncture improves the recognition abilities and memory of AD rats. Electroacupuncture inhibits the activation of glia and polarizes microglia toward the M2 phenotype. Electroacupuncture decreased the pro-inflammatory cytokines (IL-1β, TNF-α, and IL-6) and increased the anti-inflammatory cytokines (IL-4 and IL-10). Furthermore, electroacupuncture affects the immune responses through inhibition of NF-κB pathway but activation of Stat6 pathway.

Myosin 1f-mediated activation of microglia contributes to the photoreceptor degeneration in a mouse model of retinal detachment

Photoreceptor death and neurodegeneration is the leading cause of irreversible vision loss. The inflammatory response of microglia plays an important role in the process of neurodegeneration. In this study, we chose retinal detachment as the model of photoreceptor degeneration. We found Myosin 1f was upregulated after retinal detachment, and it was specifically expressed in microglia. Deficiency of myosin 1f protected against photoreceptor apoptosis by inhibiting microglia activation. The elimination of microglia can abolish the protective effect of myosin 1f deficiency. After stimulation by LPS, microglia with myosin 1f deficiency showed downregulation of the MAPK and AKT pathways. Our results demonstrated that myosin 1f plays a crucial role in microglia-induced neuroinflammation after retinal injury and photoreceptor degeneration by regulating two classic inflammatory pathways and thereby decreasing the expression of inflammatory cytokines. Knockout of myosin 1f reduces the intensity of the immune response and prevents cell death of photoreceptor, suggesting that myosin 1f can be inhibited to prevent a decline in visual acuity after retinal detachment.

Protective effects of Dimethyl malonate on neuroinflammation and blood-brain barrier after ischemic stroke

OBJECTIVES

After ischemic stroke, microglia will be activated and play a key role in neuroinflammation and the destruction of the blood-brain barrier (BBB), and activated microglia could polarize into pro-inflammation M1 phenotype and anti-inflammation M2 phenotype. Dimethyl malonate (DMM) could reduce reactive oxygen species and we speculate DMM could regulate microglia to protect ischemic brain.

METHODS

We used transient middle cerebral artery occlusion (tMCAO) mouse model to simulate ischemic stroke and adult male C57BL/6 mice were used in our study. 2,3,5-triphenyltetrazolium chloride staining was used to measure infarct volume. Evans Blue and Brain water content were used to evaluate the destruction of BBB. We used a five-point scale to assess the neurologic function of mice. Western blot and Immunofluorescence were used to measure microglia, pericytes and the expression of related proteins.

RESULTS

DMM reduced cerebral infarct volume, Evans blue leakage, brain water content and improved neurologic deficits after tMCAO. The number of activated microglia and M1 microglia were decreased and the number of M2 microglia and pericytes were increased after DMM treatment. The expression of tumor necrosis factor-α was reduced while protein levels of IL-10 and ZO-1 were increased through DMM treatment.

CONCLUSIONS

DMM could regulate activation and polarization of microglia to inhibit neuroinflammation and protect BBB.

Persistent neuropathology and behavioral deficits in a mouse model of status epilepticus induced by acute intoxication with diisopropylfluorophosphate

Organophosphate (OP) nerve agents and pesticides are a class of neurotoxic compounds that can cause status epilepticus (SE), and death following acute high-dose exposures. While the standard of care for acute OP intoxication (atropine, oxime, and high-dose benzodiazepine) can prevent mortality, survivors of OP poisoning often experience long-term brain damage and cognitive deficits. Preclinical studies of acute OP intoxication have primarily used rat models to identify candidate medical countermeasures. However, the mouse offers the advantage of readily available knockout strains for mechanistic studies of acute and chronic consequences of OP-induced SE. Therefore, the main objective of this study was to determine whether a mouse model of acute diisopropylfluorophosphate (DFP) intoxication would produce acute and chronic neurotoxicity similar to that observed in rat models and humans following acute OP intoxication. Adult male C57BL/6J mice injected with DFP (9.5 mg/kg, s.c.) followed 1 min later with atropine sulfate (0.1 mg/kg, i.m.) and 2-pralidoxime (25 mg/kg, i.m.) developed behavioral and electrographic signs of SE within minutes that continued for at least 4 h. Acetylcholinesterase inhibition persisted for at least 3 d in the blood and 14 d in the brain of DFP mice relative to vehicle (VEH) controls. Immunohistochemical analyses revealed significant neurodegeneration and neuroinflammation in multiple brain regions at 1, 7, and 28 d post-exposure in the brains of DFP mice relative to VEH controls. Deficits in locomotor and home-cage behavior were observed in DFP mice at 28 d post-exposure. These findings demonstrate that this mouse model replicates many of the outcomes observed in rats and humans acutely intoxicated with OPs, suggesting the feasibility of using this model for mechanistic studies and therapeutic screening.

COVID-19-related neuropathology and microglial activation in elderly with and without dementia

The actual role of SARS-CoV-2 in brain damage remains controversial due to lack of matched controls. We aim to highlight to what extent is neuropathology determined by SARS-CoV-2 or by pre-existing conditions. Findings of 9 Coronavirus disease 2019 (COVID-19) cases and 6 matched non-COVID controls (mean age 79 y/o) were compared. Brains were analyzed through immunohistochemistry to detect SARS-CoV-2, lymphocytes, astrocytes, endothelium, and microglia. A semi-quantitative scoring was applied to grade microglial activation. Thal-Braak stages and the presence of small vessel disease were determined in all cases. COVID-19 cases had a relatively short clinical course (0-32 days; mean: 10 days), and did not undergo mechanical ventilation. Five patients with neurocognitive disorder had delirium. All COVID-19 cases showed non-SARS-CoV-2-specific changes including hypoxic-agonal alterations, and a variable degree of neurodegeneration and/or pre-existent SVD. The neuroinflammatory picture was dominated by ameboid CD68 positive microglia, while only scant lymphocytic presence and very few traces of SARS-CoV-2 were detected. Microglial activation in the brainstem was significantly greater in COVID-19 cases (p = 0.046). Instead, microglial hyperactivation in the frontal cortex and hippocampus was clearly associated to AD pathology (p = 0.001), regardless of the SARS-CoV-2 infection. In COVID-19 cases complicated by delirium (all with neurocognitive disorders), there was a significant enhancement of microglia in the hippocampus (p = 0.048). Although higher in cases with both Alzheimer's pathology and COVID-19, cortical neuroinflammation is not related to COVID-19 per se but mostly to pre-existing neurodegeneration. COVID-19 brains seem to manifest a boosting of innate immunity with microglial reinforcement, and adaptive immunity suppression with low number of brain lymphocytes probably related to systemic lymphopenia. Thus, no neuropathological evidence of SARS-CoV-2-specific encephalitis is detectable. The microglial hyperactivation in the brainstem, and in the hippocampus of COVID-19 patients with delirium, appears as a specific topographical phenomenon, and probably represents the neuropathological basis of the "COVID-19 encephalopathic syndrome" in the elderly.

Beyond Activation: Characterizing Microglial Functional Phenotypes

Classically, the following three morphological states of microglia have been defined: ramified, amoeboid and phagocytic. While ramified cells were long regarded as “resting”, amoeboid and phagocytic microglia were viewed as “activated”. In aged human brains, a fourth, morphologically novel state has been described, i.e., dystrophic microglia, which are thought to be senescent cells. Since microglia are not replenished by blood-borne mononuclear cells under physiological circumstances, they seem to have an “expiration date” limiting their capacity to phagocytose and support neurons. Identifying factors that drive microglial aging may thus be helpful to delay the onset of neurodegenerative diseases, such as Alzheimer’s disease (AD). Recent progress in single-cell deep sequencing methods allowed for more refined differentiation and revealed regional-, age- and sex-dependent differences of the microglial population, and a growing number of studies demonstrate various expression profiles defining microglial subpopulations. Given the heterogeneity of pathologic states in the central nervous system, the need for accurately describing microglial morphology and expression patterns becomes increasingly important. Here, we review commonly used microglial markers and their fluctuations in expression in health and disease, with a focus on IBA1 low/negative microglia, which can be found in individuals with liver disease.

Safety evaluation of a clinical focused ultrasound system for neuronavigation guided blood-brain barrier opening in non-human primates

An emerging approach with potential in improving the treatment of neurodegenerative diseases and brain tumors is the use of focused ultrasound (FUS) to bypass the blood-brain barrier (BBB) in a non-invasive and localized manner. A large body of pre-clinical work has paved the way for the gradual clinical implementation of FUS-induced BBB opening. Even though the safety profile of FUS treatments in rodents has been extensively studied, the histological and behavioral effects of clinically relevant BBB opening in large animals are relatively understudied. Here, we examine the histological and behavioral safety profile following localized BBB opening in non-human primates (NHPs), using a neuronavigation-guided clinical system prototype. We show that FUS treatment triggers a short-lived immune response within the targeted region without exacerbating the touch accuracy or reaction time in visual-motor cognitive tasks. Our experiments were designed using a multiple-case-study approach, in order to maximize the acquired data and support translation of the FUS system into human studies. Four NHPs underwent a single session of FUS-mediated BBB opening in the prefrontal cortex. Two NHPs were treated bilaterally at different pressures, sacrificed on day 2 and 18 post-FUS, respectively, and their brains were histologically processed. In separate experiments, two NHPs that were earlier trained in a behavioral task were exposed to FUS unilaterally, and their performance was tracked for at least 3 weeks after BBB opening. An increased microglia density around blood vessels was detected on day 2, but was resolved by day 18. We also detected signs of enhanced immature neuron presence within areas that underwent BBB opening, compared to regions with an intact BBB, confirming previous rodent studies. Logistic regression analysis showed that the NHP cognitive performance did not deteriorate following BBB opening. These preliminary results demonstrate that neuronavigation-guided FUS with a single-element transducer is a non-invasive method capable of reversibly opening the BBB, without substantial histological or behavioral impact in an animal model closely resembling humans. Future work should confirm the observations of this multiple-case-study work across animals, species and tasks.

A multicenter retrospective study of heterogeneous tissue aggregates obstructing ventricular catheters explanted from patients with hydrocephalus

BACKGROUND

Implantation of ventricular catheters (VCs) to drain cerebrospinal fluid (CSF) is a standard approach to treat hydrocephalus. VCs fail frequently due to tissue obstructing the lumen via the drainage holes. Mechanisms driving obstruction are poorly understood. This study aimed to characterize the histological features of VC obstructions and identify links to clinical factors.

METHODS

343 VCs with relevant clinical data were collected from five centers. Each hole on the VCs was classified by degree of tissue obstruction after macroscopic analysis. A subgroup of 54 samples was analyzed using immunofluorescent labelling, histology and immunohistochemistry.

RESULTS

61.5% of the 343 VCs analyzed had tissue aggregates occluding at least one hole (n = 211) however the vast majority of the holes (70%) showed no tissue aggregates. Mean age at which patients with occluded VCs had their first surgeries (3.25 yrs) was lower than in patients with non-occluded VCs (5.29 yrs, p < 0.02). Mean length of time of implantation of occluded VCs, 33.22 months was greater than for non-occluded VCs, 23.8 months (p = 0.02). Patients with myelomeningocele had a greater probability of having an occluded VC (p = 0.0426). VCs with occlusions had greater numbers of macrophages and astrocytes in comparison to non-occluded VCs (p < 0.01). Microglia comprised only 2-6% of the VC-obstructing tissue aggregates. Histologic analysis showed choroid plexus occlusion in 24%, vascularized glial tissue occlusion in 24%, prevalent lymphocytic inflammation in 29%, and foreign body giant cell reactions in 5% and no ependyma.

CONCLUSION

Our data show that age of the first surgery and length of time a VC is implanted are factors that influence the degree of VC obstruction. The tissue aggregates obstructing VCs are composed predominantly of astrocytes and macrophages; microglia have a relatively small presence.

Activated microglia do not increase 18 kDa translocator protein (TSPO) expression in the multiple sclerosis brain

To monitor innate immune responses in the CNS, the 18 kDa Translocator protein (TSPO) is a frequently used target for PET imaging. The frequent assumption that increased TSPO expression in the human CNS reflects pro-inflammatory activation of microglia has been extrapolated from rodent studies. However, TSPO expression does not increase in activated human microglia in vitro. Studies of multiple sclerosis (MS) lesions reveal that TSPO is not restricted to pro-inflammatory microglia/macrophages, but also present in homeostatic or reparative microglia. Here, we investigated quantitative relationships between TSPO expression and microglia/macrophage phenotypes in white matter and lesions of brains with MS pathology. In white matter from brains with no disease pathology, normal appearing white matter (NAWM), active MS lesions and chronic active lesion rims, over 95% of TSPO+ cells are microglia/macrophages. Homeostatic microglial markers in NAWM and control tissue are lost/reduced in active lesions and chronic active lesion rims, reflecting cell activation. Nevertheless, pixel analysis of TSPO+ cells (n = 12,225) revealed that TSPO expression per cell is no higher in active lesions and chronic active lesion rims (where myeloid cells are activated) relative to NAWM and control. This data suggests that whilst almost all the TSPO signal in active lesions, chronic active lesion rims, NAWM and control is associated with microglia/macrophages, their TSPO expression predominantly reflects cell density and not activation phenotype. This finding has implications for the interpretation of TSPO PET signal in MS and other CNS diseases, and further demonstrates the limitation of extrapolating TSPO biology from rodents to humans.

Microglia in Aging and Alzheimer's Disease: A Comparative Species Review

Microglia are the primary immune cells of the central nervous system that help nourish and support neurons, clear debris, and respond to foreign stimuli. Greatly impacted by their environment, microglia go through rapid changes in cell shape, gene expression, and functional behavior during states of infection, trauma, and neurodegeneration. Aging also has a profound effect on microglia, leading to chronic inflammation and an increase in the brain's susceptibility to neurodegenerative processes that occur in Alzheimer's disease. Despite the scientific community's growing knowledge in the field of neuroinflammation, the overall success rate of drug treatment for age-related and neurodegenerative diseases remains incredibly low. Potential reasons for the lack of translation from animal models to the clinic include the use of a single species model, an assumption of similarity in humans, and ignoring contradictory data or information from other species. To aid in the selection of validated and predictive animal models and to bridge the translational gap, this review evaluates similarities and differences among species in microglial activation and density, morphology and phenotype, cytokine expression, phagocytosis, and production of oxidative species in aging and Alzheimer's disease.

Regional microglial populations in central autonomic brain regions in SUDEP

OBJECTIVE

Sudden unexpected death in epilepsy (SUDEP) may arise as a result of autonomic dysfunction during a seizure. The central autonomic networks (CANs) modulate brainstem cardiorespiratory regulation. Recent magnetic resonance imaging (MRI) studies in SUDEP have shown cortical and subcortical volume changes and altered connectivity between CAN regions, but the pathological correlate is unknown. Because neuroinflammation is both a cause and a consequence of seizures and may relate to regional brain pathology, our aim was to evaluate microglial populations in CANs in SUDEP.

METHODS

In 55 postmortem cases, including SUDEP, epilepsy controls without SUDEP and nonepilepsy controls, we quantified Iba1-expressing microglia in 14 cortical and thalamic areas that included known CAN regions.

RESULTS

Mean Iba1 labeling across all brain regions was significantly higher in SUDEP cases compared to epilepsy and nonepilepsy controls. There was significant regional variation in Iba1 labeling in SUDEP cases only, with highest labeling in the medial thalamus. Significantly higher labeling in SUDEP cases than epilepsy and nonepilepsy controls was consistently noted in the superior temporal gyrus. In cases with documented seizures up to 10 days prior to death, significantly higher mean Iba1 labeling was observed in SUDEP compared to epilepsy controls.

SIGNIFICANCE

Our findings support microglial activation in SUDEP, including cortical and subcortical regions with known autonomic functions such as the thalamus and superior temporal gyrus. This may be relevant to cellular pathomechanisms underlying cardioregulatory failure during a seizure.

Vagus nerve stimulation does not alter brainstem nuclei morphology in patients with refractory epilepsy

OBJECTIVE

To describe morphological characteristics of the brainstem nuclei in response to chronic vagus nerve stimulation (VNS) in patients with refractory epilepsy.

BACKGROUND

VNS is a treatment option for individuals with medically refractory epilepsy. While treatment with VNS may achieve up to 50% seizure reduction and is protective against sudden unexpected death in epilepsy (SUDEP), its mechanism of action is not fully understood. Long-term structural and cellular changes in response to VNS have rarely been addressed in humans.

METHODS

Four autopsy cases with history of chronic epilepsy treated with VNS (VNS+) and 4 age- and sex-matched chronic epilepsy-related death cases without VNS (VNS-) were included. Detailed clinical and postmortem data were obtained. Serial horizontal sections of the brainstem were prepared and stained with hematoxylin, eosin, and luxol fast blue (HE/LFB). Three regions of interest (ROIs) were delineated, including nucleus tractus solitarius (NTS), locus coeruleus (LC), and the rostral pontine group of raphe nuclei (rRN). Immunohistochemistry studies were performed using antibodies to GFAP, NeuN, HLA-DR, and IBA-1. Immunolabeling index was analyzed.

RESULTS

Three of the 4 VNS+ patients and all 4 control (VNS-) patients died of SUDEP. There was no laterality difference in the NeuN, GFAP, HLA-DR and IBA-1 expression in LC and NTS of VNS+ patients. Similarly, there was no difference in the rRN, LC, and NTS between the VNS+ and VNS- groups.

CONCLUSION

This study represents the first histopathological study of the long-term effects of VNS therapy in the human brain. There was no difference observed in the neuronal cell number, degree of astrocytosis, and neuroinflammation in the main brainstem vagal afferent nuclei after prolonged VNS treatment in patients with refractory epilepsy.

Acute neuroinflammation, sickness behavior and working memory responses to acute systemic LPS challenge following noradrenergic lesion in mice

Locus coeruleus (LC)-derived noradrenaline is important in cognition and decreases with age, but the impact of prior noradrenaline deficiency on vulnerability to inflammation-induced acute cognitive dysfunction is unclear. Here we assessed whether noradrenergic depletion, in female mice, impacted upon inflammation, locomotor activity and working memory directly after acute systemic immune challenge with bacterial lipopolysaccharide (LPS), a paradigm we have previously used to capture delirium-like acute cognitive deficits. Mice received 2 doses of the LC-selective noradrenergic toxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4; 50 mg/kg i.p.) and were challenged, 2 weeks later, with LPS (100 μg/kg i.p.). DSP-4 dramatically reduced noradrenaline concentrations and tyrosine hydroxylase-positive afferents in the frontal cortex and hippocampus. This did not significantly alter numbers of Pu.1-positive microglia, Iba1-positive microglial morphology or mRNA expression of microglia-associated gene transcripts (Tyrobp, Sall1, Cd68, Sra2, Clec7a) in the hippocampus or frontal cortex and produced modest reductions in Cx3cr1 and P2ry12. LPS induced blood and brain cytokine levels, cFOS activation and locomotor responses that were highly similar in DSP-4- and vehicle-treated mice, although LPS-induced plasma TNF-α was significantly reduced in those treated with DSP-4. Importantly, prior noradrenergic depletion did not predispose to LPS-induced T-maze working memory deficits. The data demonstrate that significant depletion of noradrenaline in the hippocampus and frontal cortex does not prompt acutely exaggerated neuroinflammation or leave the brain vulnerable to acute, transient working memory deficits upon low dose LPS challenge. These findings have implications for our understanding of the impact of systemic inflammation on the aging and vulnerable brain during septic encephalopathy and delirium.

Inducible knockout of Clec16a in mice results in sensory neurodegeneration

CLEC16A has been shown to play a role in autophagy/mitophagy processes. Additionally, genetic variants in CLEC16A have been implicated in multiple autoimmune diseases. We generated an inducible whole-body knockout, Clec16aΔUBC mice, to investigate the loss of function of CLEC16A. The mice exhibited a neuronal phenotype including tremors and impaired gait that rapidly progressed to dystonic postures. Nerve conduction studies and pathological analysis revealed loss of sensory axons that are associated with this phenotype. Activated microglia and astrocytes were found in regions of the CNS. Several mitochondrial-related proteins were up- or down-regulated. Upregulation of interferon stimulated gene 15 (IGS15) were observed in neuronal tissues. CLEC16A expression inversely related to IGS15 expression. ISG15 may be the link between CLEC16A and downstream autoimmune, inflammatory processes. Our results demonstrate that a whole-body, inducible knockout of Clec16a in mice results in an inflammatory neurodegenerative phenotype resembling spinocerebellar ataxia.

Peripheral Neuronopathy Associated With Ebola Virus Infection in Rhesus Macaques: A Possible Cause of Neurological Signs and Symptoms in Human Ebola Patients

Neurological signs and symptoms are the most common complications of Ebola virus disease. However, the mechanisms underlying the neurologic manifestations in Ebola patients are not known. In this study, peripheral ganglia were collected from 12 rhesus macaques that succumbed to Ebola virus (EBOV) disease from 5 to 8 days post exposure. Ganglionitis, characterized by neuronal degeneration, necrosis, and mononuclear leukocyte infiltrates, was observed in the dorsal root, autonomic, and enteric ganglia. By immunohistochemistry, RNAscope in situ hybridization, transmission electron microscopy, and confocal microscopy, we confirmed that CD68+ macrophages are the target cells for EBOV in affected ganglia. Further, we demonstrated that EBOV can induce satellite cell and neuronal apoptosis and microglial activation in infected ganglia. Our results demonstrate that EBOV can infect peripheral ganglia and results in ganglionopathy in rhesus macaques, which may contribute to the neurological signs and symptoms observed in acute and convalescent Ebola virus disease in human patients.

Genistein-3'-sodium sulfonate Attenuates Neuroinflammation in Stroke Rats by Down-Regulating Microglial M1 Polarization through α7nAChR-NF-κB Signaling Pathway

Microglial M1 depolarization mediated prolonged inflammation contributing to brain injury in ischemic stroke. Our previous study revealed that Genistein-3'-sodium sulfonate (GSS) exerted neuroprotective effects in ischemic stroke. This study aimed to explore whether GSS protected against brain injury in ischemic stroke by regulating microglial M1 depolarization and its underlying mechanisms. We established transient middle cerebral artery occlusion and reperfusion (tMCAO) model in rats and used lipopolysaccharide (LPS)-stimulated BV2 microglial cells as in vitro model. Our results showed that GSS treatment significantly reduced the brain infarcted volume and improved the neurological function in tMCAO rats. Meanwhile, GSS treatment also dramatically reduced microglia M1 depolarization and IL-1β level, reversed α7nAChR expression, and inhibited the activation of NF-κB signaling in the ischemic penumbra brain regions. These effects of GSS were further verified in LPS-induced M1 depolarization of BV2 cells. Furthermore, pretreatment of α7nAChR inhibitor (α-BTX) significantly restrained the neuroprotective effect of GSS treatment in tMCAO rats. α-BTX also blunted the regulating effects of GSS on neuroinflammation, M1 depolarization and NF-κB signaling activation. This study demonstrates that GSS protects against brain injury in ischemic stroke by reducing microglia M1 depolarization to suppress neuroinflammation in peri-infarcted brain regions through upregulating α7nAChR and thereby inhibition of NF-κB signaling. Our findings uncover a potential molecular mechanism for GSS treatment in ischemic stroke.

Upregulation of Superoxide Dismutase 2 by Astrocytes in the SIV/Macaque Model of HIV-Associated Neurologic Disease

HIV-associated neurocognitive disorders (HAND) remain prevalent despite implementation of antiretroviral therapy (ART). Development of HAND is linked to mitochondrial dysfunction and oxidative stress in the brain; therefore, upregulation of antioxidant defenses is critical to curtail neuronal damage. Superoxide dismutase 2 (SOD2) is a mitochondrial antioxidant enzyme essential for maintaining cellular viability. We hypothesized that SOD2 was upregulated during retroviral infection. Using a simian immunodeficiency virus (SIV)-infected macaque model of HIV, quantitative PCR showed elevated SOD2 mRNA in cortical gray ([GM], 7.6-fold for SIV vs uninfected) and white matter ([WM], 77-fold for SIV vs uninfected) during SIV infection. Further, SOD2 immunostaining was enhanced in GM and WM from SIV-infected animals. Double immunofluorescence labeling illustrated that SOD2 primarily colocalized with astrocyte marker glial fibrillary acidic protein (GFAP) in SIV-infected animals. Interestingly, in ART-treated SIV-infected animals, brain SOD2 RNA levels were similar to uninfected animals. Additionally, using principal component analysis in a transcriptomic approach, SOD2 and GFAP expression separated SIV-infected from uninfected brain tissue. Projection of these data into a HIV dataset revealed similar expression changes, thereby validating the clinical relevance. Together, our findings suggest that novel SOD2-enhancing therapies may reduce neuroinflammation in ART-treated HIV-infected patients.

Evidence of the Cellular Senescence Stress Response in Mitotically Active Brain Cells-Implications for Cancer and Neurodegeneration

Cellular stress responses influence cell fate decisions. Apoptosis and proliferation represent opposing reactions to cellular stress or damage and may influence distinct health outcomes. Clinical and epidemiological studies consistently report inverse comorbidities between age-associated neurodegenerative diseases and cancer. This review discusses how one particular stress response, cellular senescence, may contribute to this inverse correlation. In mitotically competent cells, senescence is favorable over uncontrolled proliferation, i.e., cancer. However, senescent cells notoriously secrete deleterious molecules that drive disease, dysfunction and degeneration in surrounding tissue. In recent years, senescent cells have emerged as unexpected mediators of neurodegenerative diseases. The present review uses pre-defined criteria to evaluate evidence of cellular senescence in mitotically competent brain cells, highlights the discovery of novel molecular regulators and discusses how this single cell fate decision impacts cancer and degeneration in the brain. We also underscore methodological considerations required to appropriately evaluate the cellular senescence stress response in the brain.

Analysis the alteration of systemic inflammation in old and young APP/PS1 mouse

The impairment of cognitive function was considered as a major clinic feature in Alzheimer's disease (AD) patients. Thus, a number of researches related to AD were focused on the changes in brain. However, as a neurodegenerative disorder with systemic inflammation, the periphery organs may also play a key role in AD pathology. Here, we pose the hypothesis that histopathology and inflammatory response of periphery organs may alter with aging in APP/PS1 mouse model. Therefore, we performed immunohistochemical staining technology to double label Aβ plaques and microglia cells in brain. The H&E staining was performed in periphery tissues and the mRNA expression of inflammatory factors IL-6, IL-10 and TNF-α were also determined. Next, the index of oxidative stress was measured. Consequently, the level of inflammatory factors was significantly increased in 24 months APP/PS1 mice. Furthermore, the enzyme activity of SOD, CAT and GSH were significantly decreased in colon and other organs. Our results demonstrated the increased inflammation response and declined antioxidative capacity of periphery organs in aged APP/PS1 mice, which suggesting that a more comprehensive perspective to study AD were necessary.

Organotypic Brain Slice Culture Microglia Exhibit Molecular Similarity to Acutely-Isolated Adult Microglia and Provide a Platform to Study Neuroinflammation

Microglia are central nervous system (CNS) resident immune cells that have been implicated in neuroinflammatory pathogenesis of a variety of neurological conditions. Their manifold context-dependent contributions to neuroinflammation are only beginning to be elucidated, which can be attributed in part to the challenges of studying microglia in vivo and the lack of tractable in vitro systems to study microglia function. Organotypic brain slice cultures offer a tissue-relevant context that enables the study of CNS resident cells and the analysis of brain slice microglial phenotypes has provided important insights, in particular into neuroprotective functions. Here we use RNA sequencing, direct digital quantification of gene expression with nCounter® technology and targeted analysis of individual microglial signature genes, to characterize brain slice microglia relative to acutely-isolated counterparts and 2-dimensional (2D) primary microglia cultures, a widely used in vitro surrogate. Analysis using single cell and population-based methods found brain slice microglia exhibited better preservation of canonical microglia markers and overall gene expression with stronger fidelity to acutely-isolated adult microglia, relative to in vitro cells. We characterized the dynamic phenotypic changes of brain slice microglia over time, after plating in culture. Mechanical damage associated with slice preparation prompted an initial period of inflammation, which resolved over time. Based on flow cytometry and gene expression profiling we identified the 2-week timepoint as optimal for investigation of microglia responses to exogenously-applied stimuli as exemplified by treatment-induced neuroinflammatory changes observed in microglia following LPS, TNF and GM-CSF addition to the culture medium. Altogether these findings indicate that brain slice cultures provide an experimental system superior to in vitro culture of microglia as a surrogate to investigate microglia functions, and the impact of soluble factors and cellular context on their physiology.

Tumor-associated macrophages based signaling pathway analysis and hub genes identification in glioma

Tumor-associated macrophages (TAMs) play a crucial role in the immune response to many malignancies, but the signaling pathways by which the glioma microenvironment cross-talk with TAMs are poorly understood. The aim of this study was to uncover the potential signaling pathways of the regulation of TAMs and identify candidate targets for therapeutic intervention of glioma through bioinformatics analysis.Chinese Glioma Genome Atlas (CGGA) and The Cancer Genome Atlas (TCGA) datasets were used to download RNA-Seq data and microarray data of human glioma specimen. Differentially expressed genes (DEGs) between CD68-high samples and CD68-low samples were sorted. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the DEGs was conducted. Protein-protein interaction (PPI) network were formed to identify the hub genes.The prognostic value of TAMs in glioma patients was confirmed. A total of 477 specific DEGs were sorted. The signaling pathway was identified in pathway enrichment and the DEGs showed prominent representations of immune response networks in glioma. The hub genes including C3, IL6, ITGB2, PTAFR, TIMP1 and VAMP8 were identified form the PPI network and they were all correlated positively with the expression of CD68 and showed the excellent prognostic value in glioma patients.TAMs can be used as a good prognostic indicator in glioma patients. By analyzing comprehensive bioinformatics data, we uncovered the underlying signaling pathway of the DEGs between glioma patients with high and low expression level of CD68. Furthermore, the 6 hub genes identified were closely associated with TAMs in glioma microenvironment and need further investigation.

The prefrontal cortex as a target for atypical antipsychotics in schizophrenia, lessons of neurodevelopmental animal models

Prefrontal cortex (PFC) inflammatory imbalance, oxidative/nitrosative stress (O/NS) and impaired neuroplasticity in schizophrenia are thought to have neurodevelopmental origins. Animal models are not only useful to test this hypothesis, they are also effective to establish a relationship among brain disturbances and behavior with the atypical antipsychotics (AAPs) effects. Here we review data of PFC post-mortem and in vivo neuroimaging, human induced pluripotent stem cells (hiPSC), and peripheral blood studies of inflammatory, O/NS, and neuroplasticity alterations in the disease as well as about their modulation by AAPs. Moreover, we reviewed the PFC alterations and the AAP mechanisms beyond their canonical antipsychotic action in four neurodevelopmental animal models relevant to the study of schizophrenia with a distinct approach in the generation of schizophrenia-like phenotypes, but all converge in O/NS and altered neuroplasticity in the PFC. These animal models not only reinforce the neurodevelopmental risk factor model of schizophrenia but also arouse some novel potential therapeutic targets for the disease including the reestablishment of the antioxidant response by the perineuronal nets (PNNs) and the nuclear factor erythroid 2-related factor (Nrf2) pathway, as well as the dendritic spine dynamics in the PFC pyramidal cells.

Dietary Protein Source Influences Brain Inflammation and Memory in a Male Senescence-Accelerated Mouse Model of Dementia

Dementia is a pathological condition characterized by a decline in memory, as well as in other cognitive and social functions. The cellular and molecular mechanisms of brain damage in dementia are not completely understood; however, neuroinflammation is involved. Evidence suggests that chronic inflammation may impair cognitive performance and that dietary protein source may differentially influence this process. Dietary protein source has previously been shown to modify systemic inflammation in mouse models. Thus, we aimed to investigate the effect of chronic dietary protein source substitution in an ageing and dementia male mouse model, the senescence-accelerated mouse-prone 8 (SAMP8) model. We observed that dietary protein source differentially modified memory as shown by inhibitory avoidance testing at 4 months of age. Also, dietary protein source differentially modified neuroinflammation and gliosis in male SAMP8 mice. Our results suggest that chronic dietary protein source substitution may influence brain ageing and memory-related mechanisms in male SAMP8 mice. Moreover, the choice of dietary protein source in mouse diets for experimental purposes may need to be carefully considered when interpreting results.

Construction of a 3D brain extracellular matrix model to study the interaction between microglia and T cells in co-culture

Neurodegenerative disorders are characterised by the activation of brain-resident microglia cells and by the infiltration of peripheral T cells. However, their interplay in disease has not been clarified yet. It is difficult to investigate complex cellular dynamics in living animals, and simple two-dimensional (2D) cell culture models do not resemble the soft 3D structure of brain tissue. Therefore, we developed a biomimetic 3D in vitro culture system for co-cultivation of microglia and T cells. As the activation and/or migration of immune cells in the brain might be affected by components of the extracellular matrix, defined 3D fibrillar collagen I-based matrices were constructed and modified with hyaluronan and/or chondroitin sulphate, resembling aspects of brain extracellular matrix. Murine microglia and spleen-derived T cells were cultured alone or in co-culture on the constructed matrices. Microglia exhibited in vivo-like morphology and T cells showed enhanced survival when co-cultured with microglia or to a minor degree in the presence of glia-conditioned medium. The open and porous fibrillar structure of the matrix allowed for cell invasion and direct cell-cell interaction, with stronger invasion of T cells. Both cell types showed no dependence on the matrix modifications. Microglia could be activated on the matrices by lipopolysaccharide resulting in interleukin-6 and tumour necrosis factor-α secretion. The findings herein indicate that biomimetic 3D matrices allow for co-cultivation and activation of primary microglia and T cells and provide useful tools to study their interaction in vitro.

Lipid Pathology of the Corpus Callosum in Schizophrenia and the Potential Role of Abnormal Gene Regulatory Networks with Reduced Microglial Marker Expression

Structural changes in the corpus callosum have been reported in schizophrenia; however, the underlying molecular mechanism remains unclear. As the corpus callosum is high in lipid content, we analyzed the lipid contents of the corpora callosa from 15 patients with schizophrenia and 15 age- and sex-matched controls using liquid chromatography coupled to tandem mass spectrometry and identified lipid combinations associated with schizophrenia. Real-time quantitative polymerase chain reaction analyses using extended samples (schizophrenia, n = 95; control, n = 91) showed low expression levels of lipid metabolism-related genes and their potential upstream transcription factors in schizophrenia. Subsequent pathway analysis identified a gene regulatory network where nuclear factor of activated T cells 2 (NFATC2) is placed most upstream. We also observed low gene expression levels of microglial markers, inflammatory cytokines, and colony-stimulating factor 1 receptor (CSF1R), which is known to regulate the density of microglia, in the corpus callosum in schizophrenia. The interactions between CSF1R and several genes in the presently identified gene network originating from NFATC2 have been reported. Collectively, this study provides evidence regarding lipid abnormalities in the corpora callosa of patients with schizophrenia and proposes the potential role of impaired “NFATC2-relevant gene network-microglial axis” as its underlying mechanism.

Single-cell mass cytometry of microglia in major depressive disorder reveals a non-inflammatory phenotype with increased homeostatic marker expression

Stress-induced disturbances of brain homeostasis and neuroinflammation have been implicated in the pathophysiology of mood disorders. In major depressive disorder (MDD), elevated levels of proinflammatory cytokines and chemokines can be found in peripheral blood, but very little is known about the changes that occur directly in the brain. Microglia are the primary immune effector cells of the central nervous system and exquisitely sensitive to changes in the brain microenvironment. Here, we performed the first single-cell analysis of microglia from four different post-mortem brain regions (frontal lobe, temporal lobe, thalamus, and subventricular zone) of medicated individuals with MDD compared to controls. We found no evidence for the induction of inflammation-associated molecules, such as CD11b, CD45, CCL2, IL-1β, IL-6, TNF, MIP-1β (CCL4), IL-10, and even decreased expression of HLA-DR and CD68 in microglia from MDD cases. In contrast, we detected increased levels of the homeostatic proteins P2Y₁₂ receptor, TMEM119 and CCR5 (CD195) in microglia from all brain regions of individuals with MDD. We also identified enrichment of non-inflammatory CD206^hi macrophages in the brains of MDD cases. In sum, our results suggest enhanced homeostatic functions of microglia in MDD.

Morphological analyzes of microglia heterogeneity and dynamics during photoreceptor degeneration in vitro: Presumptive dark microglia in porcine retina

In the adult retina, ramifying microglia interact with the outer plexiform layer (OPL) monitoring the synaptic integrity between photoreceptors and post-synaptic target cells. Microglia are reactive during photoreceptor diseases, but their disease-related function(s) are not fully understood. Retinal explant cultures are model systems used to study degenerative events including photoreceptor degeneration and gliosis. Our culture paradigm, with adult porcine retinas subjected to coculture with human A-retinal pigment epithelia-19 (ARPE) cells, is an experimental approach resulting in improved photoreceptor survival and reduced gliosis. Under the in vitro pathological conditions with photoreceptor degeneration, reactive Iba1-and CD11b-immunoreactive microglia and their processes positioned in proximity with the OPL and among photoreceptor outer segments. Coculture for 3 days with ARPE-cells resulted in a significantly increased density of microglia at the OPL. After 5 days of culture, the density of microglia at the OPL was similar between coculture and control specimens. Electron microscopy revealed the presence of two subtypes of microglia: one exhibiting a dark nucleus and cytosol with dilated endoplasmic reticulum, vacuoles, endosomes and mitochondrial variations. This subtype localized close to synaptic structures in the OPL. The other subtype appeared as pale phagocytic microglia localized among degenerating outer segments. The Iba1-and CD11b-immunoreactive microglia in degenerating retina may be of two separate subtypes, which differ in localization, subcellular morphology and perhaps function.

Bioinformatic Analysis of Neuroimmune Mechanism of Neuropathic Pain

Background

Neuropathic pain (NP) is a devastating complication following nerve injury, and it can be alleviated by regulating neuroimmune direction. We aimed to explore the neuroimmune mechanism and identify some new diagnostic or therapeutic targets for NP treatment via bioinformatic analysis.

Methods

The microarray GSE18803 was downloaded and analyzed using R. The Venn diagram was drawn to find neuroimmune-related differentially expressed genes (DEGs) in neuropathic pain. Gene Ontology (GO), pathway enrichment, and protein-protein interaction (PPI) network were used to analyze DEGs, respectively. Besides, the identified hub genes were submitted to the DGIdb database to find relevant therapeutic drugs.

Results

A total of 91 neuroimmune-related DEGs were identified. The results of GO and pathway enrichment analyses were closely related to immune and inflammatory responses. PPI analysis showed two important modules and 8 hub genes: PTPRC, CD68, CTSS, RAC2, LAPTM5, FCGR3A, CD53, and HCK. The drug-hub gene interaction network was constructed by Cytoscape, and it included 24 candidate drugs and 3 hub genes.

Conclusion

The present study helps us better understand the neuroimmune mechanism of neuropathic pain and provides some novel insights on NP treatment, such as modulation of microglia polarization and targeting bone resorption. Besides, CD68, CTSS, LAPTM5, FCGR3A, and CD53 may be used as early diagnostic biomarkers and the gene HCK can be a therapeutic target.

The impact of antidiabetic treatment on human hypothalamic infundibular neurons and microglia

Animal studies indicate that hypothalamic dysfunction plays a major role in type 2 diabetes mellitus (T2DM) development, and that insulin resistance and inflammation are important mechanisms involved in this disorder. However, it remains unclear how T2DM and antidiabetic treatments affect the human hypothalamus. Here, we characterized the proopiomelanocortin (POMC) immunoreactive (-ir) neurons, the neuropeptide-Y-ir (NPY-ir) neurons, the ionized calcium-binding adapter molecule 1-ir (iba1-ir) microglia, and the transmembrane protein 119-ir (TMEM119-ir) microglia in the infundibular nucleus (IFN) of human postmortem hypothalamus of 32 T2DM subjects with different antidiabetic treatments and 17 matched nondiabetic control subjects. Compared with matched control subjects, T2DM subjects showed a decrease in the number of POMC-ir neurons, but no changes in NPY-ir neurons or microglia. Interestingly, T2DM subjects treated with the antidiabetic drug metformin had fewer NPY-ir neurons and microglia than T2DM subjects not treated with metformin. We found that the number of microglia correlated with the number of NPY-ir neurons, but only in T2DM subjects. These results indicate that different changes in POMC and NPY neurons and microglial cells in the IFN accompany T2DM. In addition, T2DM treatment modality is associated with highly selective changes in hypothalamic neurons and microglial cells.

Microglial Phagocytosis-Rational but Challenging Therapeutic Target in Multiple Sclerosis

Multiple sclerosis (MS) is the most common autoimmune and demyelinating disease of the central nervous system (CNS), characterized, in the majority of cases, by initial relapses that later evolve into progressive neurodegeneration, severely impacting patients’ motor and cognitive functions. Despite the availability of immunomodulatory therapies effective to reduce relapse rate and slow disease progression, they all failed to restore CNS myelin that is necessary for MS full recovery. Microglia are the primary inflammatory cells present in MS lesions, therefore strongly contributing to demyelination and lesion extension. Thus, many microglial-based therapeutic strategies have been focused on the suppression of microglial pro-inflammatory phenotype and neurodegenerative state to reduce disease severity. On the other hand, the contribution of myelin phagocytosis advocating the neuroprotective role of microglia in MS has been less explored. Indeed, despite the presence of functional oligodendrocyte precursor cells (OPCs), within lesioned areas, MS plaques fail to remyelinate as a result of the over-accumulation of myelin-toxic debris that must be cleared away by microglia. Dysregulation of this process has been associated with the impaired neuronal recovery and deficient remyelination. In line with this, here we provide a comprehensive review of microglial myelin phagocytosis and its involvement in MS development and repair. Alongside, we discuss the potential of phagocytic-mediated therapeutic approaches and encourage their modulation as a novel and rational approach to ameliorate MS-associated pathology.

Microglial burden, activation and dystrophy patterns in frontotemporal lobar degeneration

Background

Microglial dysfunction is implicated in frontotemporal lobar degeneration (FTLD). Although studies have reported excessive microglial activation or senescence (dystrophy) in Alzheimer’s disease (AD), few have explored this in FTLD. We examined regional patterns of microglial burden, activation and dystrophy in sporadic and genetic FTLD, sporadic AD and controls.

Methods

Immunohistochemistry was performed in frontal and temporal grey and white matter from 50 pathologically confirmed FTLD cases (31 sporadic, 19 genetic: 20 FTLD-tau, 26 FTLD-TDP, four FTLD-FUS), five AD cases and five controls, using markers to detect phagocytic (CD68-positive) and antigen-presenting (CR3/43-positive) microglia, and microglia in general (Iba1-positive). Microglial burden and activation (morphology) were assessed quantitatively for each microglial phenotype. Iba1-positive microglia were assessed semi-quantitatively for dystrophy severity and qualitatively for rod-shaped and hypertrophic morphology. Microglia were compared in each region between FTLD, AD and controls, and between different pathological subtypes of FTLD, including its main subtypes (FTLD-tau, FTLD-TDP, FTLD-FUS), and subtypes of FTLD-tau, FTLD-TDP and genetic FTLD. Microglia were also compared between grey and white matter within each lobe for each group.

Results

There was a higher burden of phagocytic and antigen-presenting microglia in FTLD and AD cases than controls, but activation was often not increased. Burden was generally higher in white matter than grey matter, but activation was greater in grey matter. However, microglia varied regionally according to FTLD subtype and disease mechanism. Dystrophy was more severe in FTLD and AD than controls, and more severe in white than grey matter, but this also varied regionally and was particularly extensive in FTLD due to progranulin (GRN) mutations. Presence of rod-shaped and hypertrophic microglia also varied by FTLD subtype.

Conclusions

This study demonstrates regionally variable microglial involvement in FTLD and links this to underlying disease mechanisms. This supports investigation of microglial dysfunction in disease models and consideration of anti-senescence therapies in clinical trials.

Microglia in the human infant brain and factors that affect expression

The present study reports on the microglial populations present in 34 regions of the human infant brain (1-11 months), and whether developmental parameters or extrinsic factors such as cigarette smoke exposure, prone sleeping and an upper respiratory tract infection (URTI) influence their expression. Further, we compare microglia populations amongst three sudden unexpected death in infancy (SUDI) sub-groups: explained SUDI (eSUDI, n ​= ​7), sudden infant death syndrome (SIDS) I (n ​= ​8) and SIDS II (n ​= ​13). Ionised calcium binding adaptor molecule-1 (Iba1) was used to determine the morphology and area covered by microglia in a given brain region. Activation was explored using cluster-of-differentiation factor 68 (CD68) and human leukocyte antigen-DP,DQ,DR (HLA). We found regional heterogeneity in the area covered and activation status of microglia across the infant brain. The hippocampus, basal ganglia, white matter and dentate nucleus of the cerebellum showed larger areas of Iba1, while the brainstem had the smallest. Microglia in regions of the basal ganglia and cortex demonstrated positive correlations with infant developmental parameters, while in nuclei of the rostral medulla, negative correlations between microglia parameters were seen. URTI and cigarette smoke exposure were associated with a reduced microglial area in regions of the hippocampus and cortex (parietal and occipital), respectively. In the context of SIDS, a reduced microglial area was seen in SIDS II and fewer SIDS I infants demonstrated activated phenotypes in the hippocampus. Overall, we identify the distribution of microglia in the infant brain to be heterogenous, and influenced by intrinsic and extrinsic factors, and that the SIDS I group is a useful control group for future research into other infant CNS pathologies.

Phagocytosis-related NADPH oxidase 2 subunit gp91phox contributes to neurodegeneration after repeated systemic challenge with lipopolysaccharides

Repeated systemic challenge with lipopolysaccharides (LPS) can induce microglia activation and inflammatory neurodegeneration in the substantia nigra pars compacta region of mice. We now explored the role of mononuclear phagocytes associated nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX-2) in inflammatory neurodegeneration. Cybb-deficient NOX-2 knock-out (KO) and control wild type (WT) mice were treated intraperitoneally daily over four consecutive days with 1 μg/gbw/day LPS. Transcriptome analysis by RNA-seq of total brain tissue indicated increased LPS-induced upregulation of genes belonging to the reactive oxygen species and reactive nitrogen species production, complement and lysosome activation as well as apoptosis and necroptosis in WT compared to NOX-2 KO mice. Validation of up-regulated gene transcripts via qRT-PCR confirmed that LPS-challenged NOX-2 KO mice expressed lower levels of the microglial phagocytosis-related genes Nos2, Cd68, Aif1/Iba1, Cyba, Itgam, and Fcer1g compared to WT mice at Day 5 after systemic inflammatory challenge, but no significant differences in the pro-inflammatory genes Tnfα and Il1b as well as microglial IBA1 and CD68 intensities were observed between both genotypes. Furthermore, loss of tyrosine hydroxylase positive (TH+) and NeuN positive neurons in the substantia nigra pars compacta upon repeated systemic LPS application were attenuated in NOX-2 KO mice. Thus, our data demonstrate that loss of dopaminergic neurons in the substantia nigra pars compacta after repeated systemic challenge with LPS is associated with a microglial phagocytosis-related gene activation profile involving the NADPH oxidase subunit Cybb/gp91phox.

Microglia: Agents of the CNS Pro-Inflammatory Response

The pro-inflammatory immune response driven by microglia is a key contributor to the pathogenesis of several neurodegenerative diseases. Though the research of microglia spans over a century, the last two decades have increased our understanding exponentially. Here, we discuss the phenotypic transformation from homeostatic microglia towards reactive microglia, initiated by specific ligand binding to pattern recognition receptors including toll-like receptor-4 (TLR4) or triggering receptors expressed on myeloid cells-2 (TREM2), as well as pro-inflammatory signaling pathways triggered such as the caspase-mediated immune response. Additionally, new research disciplines such as epigenetics and immunometabolism have provided us with a more holistic view of how changes in DNA methylation, microRNAs, and the metabolome may influence the pro-inflammatory response. This review aimed to discuss our current knowledge of pro-inflammatory microglia from different angles, including recent research highlights such as the role of exosomes in spreading neuroinflammation and emerging techniques in microglia research including positron emission tomography (PET) scanning and the use of human microglia generated from induced pluripotent stem cells (iPSCs). Finally, we also discuss current thoughts on the impact of pro-inflammatory microglia in neurodegenerative diseases.

Preservation of optic nerve structure by complement inhibition in experimental glaucoma

Glaucoma is characterized by a progressive damage of the retina and the optic nerve. Despite a huge research interest, the exact pathomechanisms are still unknown. In the experimental autoimmune glaucoma model, rats develop glaucoma-like damage of the retina and the optic nerve after immunization with an optic nerve antigen homogenate (ONA). An early activation of the complement system, even before optic nerve degeneration, was reported in this model. Here, we investigated the effects of a monoclonal antibody against complement factor C5 on optic nerves. Rats were immunized with ONA and compared to controls. In one eye of some ONA animals, the antibody against C5 was intravitreally injected (15 μmol: ONA + C5-I or 25 μmol: ONA + C5-II) before immunization and then every 2 weeks. After 6 weeks, optic nerves were processed for histology (n = 6/group). These analyses demonstrated that the intravitreal therapy reduced the depositions of the membrane attack complex compared to ONA animals (ONA + C5-I: p = 0.005; ONA + C5-II: p = 0.002). Cellular infiltration was significantly reduced in the ONA + C5-I group (p = 0.003), but not in ONA + C5-II tissues (p = 0.41). Furthermore, SMI-32 staining revealed that neurofilament was preserved in both treatment groups compared to ONA optic nerves (both p = 0.002). A decreased amount of microglia was found in treated animals in comparison to the ONA group (ONA + C5-I: p = 0.03; ONA + C5-II: p = 0.009). We observed, for the first time, that a complement system inhibition could prevent optic nerve damage in an autoimmune glaucoma model. Therefore, complement inhibition could serve as a new therapeutic tool for glaucoma.

Kainic acid Induces production and aggregation of amyloid β-protein and memory deficits by activating inflammasomes in NLRP3- and NF-κB-stimulated pathways

Kainic acid (KA) treatment causes neuronal degeneration, which is a feature of Alzheimer’s disease (AD) symptoms such as amyloid β-protein production and memory deficits. Inflammasomes are known to be critical for the progression of AD. However, the underlying mechanism by which inflammasomes influence AD progression remains unknown. The present study investigated the damaging effect of KA on neurons by focusing on the inflammasome-mediated signaling pathways. Assessments using cultured microglia and mouse brains demonstrated that KA treatment specifically induced inflammasome activation. Mechanistic evaluations showed that KA activated two major components of inflammasomes, nucleotide binding oligomerization domain (NOD)-like receptor (NLR) protein 3 (NLRP3) and nuclear factor (NF)-κB, which resulted in the production of interleukin-1β (IL-1β) and brain-derived neurotrophic factor (BDNF). Inhibition of NLRP3 or NF-κB by Bay11-7082 caused a reduction in the KA-induced expression of interleukin (IL)-1β and BDNF. Moreover, knockdown of the expression of KA receptors (KARs) such as Grik1 and Grik3 induced suppression of NLRP3 and NF-κB, suggesting that KARs function upstream of NLRP3 and NF-κB to mediate the effects of KA on regulation of IL-1β and BDNF expression. Notably, IL-1β was shown to exert positive effects on the expression of BACE1, which is blocked by Bay11-7082. Overall, our results revealed that Bay11-7082 acts against KA-induced neuronal degeneration, amyloid β-protein (Aβ) deposition, and memory defects via inflammasomes and further highlighted the protective role of Bay11-7082 in KA-induced neuronal defects.

Combined 1-Deoxynojirimycin and Ibuprofen Treatment Decreases Microglial Activation, Phagocytosis and Dopaminergic Degeneration in MPTP-Treated Mice

Inflammation is a predominant aspect of neurodegenerative diseases and experimental studies performed in animal models of Parkinson's disease (PD) suggesting that a sustained neuroinflammation exacerbates the nigrostriatal degeneration pathway. The central role of microglia in neuroinflammation has been studied as a target for potential neuroprotective drugs for PD, for example nonsteroidal anti-inflammatory drugs (NSAIDs) and matrix metalloproteinases (MMP) inhibitors that regulates microglial activation and migration. The aim of this study was to investigate the neuroprotective response of the iminosugar 1-deoxynojirimycin (1-DNJ) and compare its effect with a combined treatment with ibuprofen. MPTP-treated mice were orally dosed with ibuprofen and/or 1-DNJ 1. Open-field test was used to evaluate behavioral changes. Immunohistochemistry for dopaminergic neurons marker (TH⁺) and microglia markers (Iba-1⁺; CD68⁺) were used to investigate neuronal integrity and microglial activation in the substantia nigra pars compacta (SNpc). The pro-inflammatory cytokines TNF-α and IL-6 were analysed by qPCR. Treatments with either 1-DNJ or Ibuprofen alone did not reduce the damage induced by MPTP intoxication. However, combined treatment with 1-DNJ and ibuprofen prevents loss of mesencephalic dopaminergic neurons, decreases the number of CD68⁺/ Iba-1⁺ cells, the microglia/neurons interactions, and the pro-inflammatory cytokines, and improves behavioral changes when compared with MPTP-treated animals. In conclusion, these data demonstrate that the combined treatment with a MMPs inhibitor (1-DNJ) plus an anti-inflammatory drug (ibuprofen) has neuroprotective effects open for future therapeutic interventions. Graphical Abstract MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) is a protoxicant that, after crossing the Blood Brain Barrier, is metabolized by astrocytic MAO-B to MPDP+, a pyridinium intermediate, which undergoes further two-electron oxidation to yield the toxic metabolite MPP+ (methyl-phenyltetrahydropyridinium) that is then selectively transported into nigral neurons via the mesencephalic dopamine transporter. In this study, we demonstrated that MPTP induced death of dopaminergic neurons, microgliosis, increase of gliapses, motor impairment and neuroinflammation in mice, which were inhibited by combined 1-deoxynojirimycin and ibuprofen treatment.

Tissue Transglutaminase Appears in Monocytes and Macrophages but Not in Lymphocytes in White Matter Multiple Sclerosis Lesions

Leukocyte infiltration is an important pathological hallmark of multiple sclerosis (MS) and is therefore targeted by current MS therapies. The enzyme tissue transglutaminase (TG2) contributes to monocyte/macrophage migration and is present in MS lesions and could be a potential therapeutic target. We examined the cellular identity of TG2-expressing cells by immunohistochemistry in white matter lesions of 13 MS patients; 9 active and chronic active lesions from 4 patients were analyzed in detail. In these active MS lesions, TG2 is predominantly expressed in leukocytes (CD45⁺) but not in cells of the lymphocyte lineage, that is, T cells (CD3⁺) and B cells (CD20⁺). In general, cells of the monocyte/macrophage lineage (CD11b⁺ or CD68⁺) are TG2⁺ but no further distinction could be made regarding pro- or anti-inflammatory macrophage subtypes. In conclusion, TG2 is abundantly present in cells of the monocyte/macrophage lineage in active white matter MS lesions. We consider that TG2 can play a role in MS as it is associated with macrophage infiltration into the CNS. As such, TG2 potentially presents a novel target for therapeutic intervention that can support available MS therapies targeting lymphocyte infiltration.

A quantitative neuropathological assessment of translocator protein expression in multiple sclerosis

The 18 kDa translocator protein (TSPO) is increasingly used to study brain and spinal cord inflammation in degenerative diseases of the CNS such as multiple sclerosis. The enhanced TSPO PET signal that arises during disease is widely considered to reflect activated pathogenic microglia, although quantitative neuropathological data to support this interpretation have not been available. With the increasing interest in the role of chronic microglial activation in multiple sclerosis, characterising the cellular neuropathology associated with TSPO expression is of clear importance for understanding the cellular and pathological processes on which TSPO PET imaging is reporting. Here we have studied the cellular expression of TSPO and specific binding of two TSPO targeting radioligands (3H-PK11195 and 3H-PBR28) in tissue sections from 42 multiple sclerosis cases and 12 age-matched controls. Markers of homeostatic and reactive microglia, astrocytes, and lymphocytes were used to investigate the phenotypes of cells expressing TSPO. There was an approximate 20-fold increase in cells double positive for TSPO and HLA-DR in active lesions and in the rim of chronic active lesion, relative to normal appearing white matter. TSPO was uniformly expressed across myeloid cells irrespective of their phenotype, rather than being preferentially associated with pro-inflammatory microglia or macrophages. TSPO+ astrocytes were increased up to 7-fold compared to normal-appearing white matter across all lesion subtypes and accounted for 25% of the TSPO+ cells in these lesions. To relate TSPO protein expression to ligand binding, specific binding of the TSPO ligands 3H-PK11195 and 3H-PBR28 was determined in the same lesions. TSPO radioligand binding was increased up to seven times for 3H-PBR28 and up to two times for 3H-PK11195 in active lesions and the centre of chronic active lesions and a strong correlation was found between the radioligand binding signal for both tracers and the number of TSPO+ cells across all of the tissues examined. In summary, in multiple sclerosis, TSPO expression arises from microglia of different phenotypes, rather than being restricted to microglia which express classical pro-inflammatory markers. While the majority of cells expressing TSPO in active lesions or chronic active rims are microglia/macrophages, our findings also emphasize the significant contribution of activated astrocytes, as well as smaller contributions from endothelial cells. These observations establish a quantitative framework for interpretation of TSPO in multiple sclerosis and highlight the need for neuropathological characterization of TSPO expression for the interpretation of TSPO PET in other neurodegenerative disorders.

Single Inflammatory Trigger Leads to Neuroinflammation in LRRK2 Rodent Model without Degeneration of Dopaminergic Neurons

BACKGROUND

Leucine-rich repeat kinase 2 (LRRK2) mutations are the most common genetic risk factor for Parkinson's disease (PD). While the corresponding pathogenic mechanisms remain largely unknown, LRRK2 has been implicated in the immune system.

OBJECTIVE

To assess whether LRRK2 mutations alter the sensitivity to a single peripheral inflammatory trigger, with ultimate impact on dopaminergic integrity, using a longitudinal imaging-based study design.

METHODS

Rats carrying LRRK2 p.G2019S and non-transgenic (NT) littermates were treated peripherally with lipopolysaccharide (LPS). They were monitored over 10 months with PET markers for neuroinflammation and dopaminergic integrity, and with behavioral testing. Tyrosine hydroxylase and CD68 expression were assessed postmortem, 12 months after LPS treatment, in the striatum and substantia nigra.

RESULTS

Longitudinal [11C]PBR28 PET imaging revealed that LPS treatment caused inflammation in the brain, increasing over time, as compared to saline (corrected p = 0.008). LPS treated LRRK2 animals exhibited significantly increased neuroinflammation in the cortex and ventral-regions compared to saline treated animals (LRRK2 and NT) at 10 months post treatment, with the increase in [11C]PBR28 binding from baseline averaging 0.128±0.045 g/mL. For LPS treated NT animals, the increase was not significant. CD68 immunohistochemistry data supported the imaging results, but without reaching statistical significance. No dopaminergic degeneration was observed.

CONCLUSION

A single peripheral inflammatory trigger elicited long lasting, progressive neuroinflammation. A trend for an exacerbated inflammatory response in LRRK2 animals compared to NT controls was observed. Translationally, this implies that repeated exposure to inflammatory triggers may be needed for LRRK2 mutation carriers to develop active PD.

Bifidobacteria shape host neural circuits during postnatal development by promoting synapse formation and microglial function

We hypothesized that early-life gut microbiota support the functional organization of neural circuitry in the brain via regulation of synaptic gene expression and modulation of microglial functionality. Germ-free mice were colonized as neonates with either a simplified human infant microbiota consortium consisting of four Bifidobacterium species, or with a complex, conventional murine microbiota. We examined the cerebellum, cortex, and hippocampus of both groups of colonized mice in addition to germ-free control mice. At postnatal day 4 (P4), conventionalized mice and Bifidobacterium-colonized mice exhibited decreased expression of synapse-promoting genes and increased markers indicative of reactive microglia in the cerebellum, cortex and hippocampus relative to germ-free mice. By P20, both conventional and Bifidobacterium-treated mice exhibited normal synaptic density and neuronal activity as measured by density of VGLUT2+ puncta and Purkinje cell firing rate respectively, in contrast to the increased synaptic density and decreased firing rate observed in germ-free mice. The conclusions from this study further reveal how bifidobacteria participate in establishing functional neural circuits. Collectively, these data indicate that neonatal microbial colonization of the gut elicits concomitant effects on the host CNS, which promote the homeostatic developmental balance of neural connections during the postnatal time period.

Hippocampal granule cell dispersion: a non-specific finding in pediatric patients with no history of seizures

Chronic epilepsy has been associated with hippocampal abnormalities like neuronal loss, gliosis and granule cell dispersion. The granule cell layer of a normal human hippocampal dentate gyrus is traditionally regarded as a compact neuron-dense layer. Histopathological studies of surgically resected or autopsied hippocampal samples primarily from temporal lobe epilepsy patients, as well as animal models of epilepsy, describe variable patterns of granule cell dispersion including focal cell clusters, broader thick segments, and bilamination or “tram-tracking”. Although most studies have implicated granule cell dispersion as a specific feature of chronic epilepsy, very few “non-seizure” controls were included in these published investigations. Our retrospective survey of 147 cadaveric pediatric human hippocampi identified identical morphological spectra of granule cell dispersion in both normal and seizure-affected brains. Moreover, sections across the entire antero-posterior axis of a control cadaveric hippocampus revealed repetitive occurrence of different morphologies of the granule cell layer – compact, focally disaggregated and bilaminar. The results indicate that granule cell dispersion is within the spectrum of normal variation and not unique to patients with epilepsy. We speculate that sampling bias has been responsible for an erroneous dogma, which we hope to rectify with this investigation.

Microinjection of a growth factor cocktail affects activated microglia in the neocortex of adult rats

Microglia, as the resident immune cells in the central nervous system, play important roles in regulating neuronal processes, such as neural excitability, synaptic activity, and apoptotic cell clearance. Growth factors can activate multiple signaling pathways in central nervous system microglia and can regulate their immune effects, but whether growth factors can affect the morphological characteristics and ultrastructure of microglia has not been reported. After microinjecting 300 nL of a growth factor cocktail, including 10 μg/mL epidermal growth factor, 10 μg/mL basic fibroblast growth factor, 10 μg/mL hepatocyte growth factor and 10 μg/mL insulin-like growth factor into adult rat cortex, we found that the number of IBA1-positive microglia around the injection area increased significantly, indicating local activation of microglia. All CD68-positive labeling co-localized with IBA1 in microglia. Cell bodies and protrusions of CD68-positive cells were strongly attached to or were engulfing neurons. Characteristic huge phagosomes were observed in activated phagocytes by electron microscopy. The phagosomes generally included non-degraded neuronal protrusions and mitochondria, yet they contained no myelin membrane or remnants, which might indicate selective phagocytosis by the phagocytes. The remnant myelin sheath after phagocytosis still had regenerative ability and formed “myelin-like” structures around phagocytes. These results show that microinjection of a growth factor cocktail into the cerebral cortex of rodents can locally activate microglia and induce selective phagocytosis of neural structures by phagocytes. The study was approved by the Institute of Laboratory Animal Science, Beijing Institute of Basic Medical Sciences (approval No. IACUC-AMMS-2014-501) on June 30, 2014.

Serum pro-BDNF levels correlate with phospho-tau staining in Alzheimer's disease

Disruption of brain-derived neurotrophic factor (BDNF) biosynthesis and/or signaling has been implicated in the pathogenesis of Alzheimer's disease (AD). We used postmortem brain and fluid samples from 20 patients with variable severity of AD and 11 controls to investigate whether BDNF levels in serum and brain tissue correlated with hippocampal pathology. Total BDNF, precursor BDNF (pro-BDNF), and mature BDNF were measured in cerebrospinal fluid, serum, and 3 postmortem brain regions. Histological markers for AD pathology, the BDNF cognate receptor (TrkB), and glia were measured in the hippocampus (HIP). Lower pro-BDNF levels were observed in the entorhinal and frontal cortices in AD cases compared with controls. AD cases also exhibited significantly lower staining densities of the cognate BDNF receptor TrkB in the HIP compared with controls, and TrkB staining was inversely correlated with both Amylo-Glo and pTau staining in the same region, suggesting a relationship between the density of the cognate BDNF receptor and accumulation of AD pathology. In addition, higher serum pro-BDNF levels correlated with lower HIP pro-BDNF levels and higher pTau staining in the HIP. Total BDNF levels in cortical regions were also negatively correlated with Amylo-Glo staining in the HIP suggesting that reduced BDNF cortical levels might influence hippocampal amyloid accumulation. These results strongly suggest that altered BDNF and TrkB receptors are involved in AD pathology and therefore warrant investigations into therapies involving the BDNF pathway.