Changes In Microglia Research Articles

Association between glial and synaptic fluid biomarkers and brain [18F]FDG‐PET signal

AbstractBackgroundBeyond the hypometabolic signature, indexed by [18F]FDG‐PET imaging, seen in the brain of Alzheimer’s disease (AD) patients, a transient brain glucose hypermetabolism has been recently identified in the early stages of AD. The cellular source of this dual metabolic response remains controversial, with glial cells gaining a lot of attention. In light of this, whether glial and synaptic fluid biomarkers are associated with [18F]FDG‐PET signal in the early stages of AD remains debatable. Thus, we evaluated the association of astrocyte, microglial and synaptic fluid biomarkers with [18F]FDG‐PET signal in an AD rat model.Method[18F]FDG‐PET imaging was conducted in ten‐month‐old (early amyloid stage) APP/PS1 (TgF344‐AD, n = 8‐17) and wild‐type (WT, n = 8‐15) rats. Glial (GFAP and sTREM2), synaptic (neurogranin), and amyloid biomarkers (Aß1‐40 and Aß1‐42) were quantified in the cerebrospinal fluid (CSF) and plasma through a multiplex immunoassay. T‐statistical maps of brain [18F]FDG‐PET and those fluid biomarkers were conducted at the voxel level using RMINC. Differences were considered statistically significant at p<0.05 (t>2).ResultA large hypermetabolic cluster was identified in ten‐month‐old TgF344‐AD (Fig. 1AB, local maxima, t(13) = 4.28). We found positive correlations between CSF TREM2 and brain [18F]FDG‐PET signal (Fig. 2AC, local maxima, t(13) = 4.12). In addition, we identified a positive correlation between plasma GFAP and brain [18F]FDG‐PET signal (Fig. 2BC, local maxima, t(13) = 10.62). Plasma TREM2, CSF GFAP, and plasma neurogranin did not associate with brain glucose metabolism.ConclusionOur findings suggest that CSF TREM2 and plasma GFAP are associated with brain metabolism before amyloid load reaches a plateau. Stronger association of plasma GFAP, rather than CSF GFAP, with brain pathology corroborates cross‐sectional human studies. One could argue that [18F]FDG‐PET hypermetabolism identified is likely a response to astrocyte and microglial changes.

Microglial phenotype and proinflammatory gene induction in human prefrontal cortex in Alcohol Use Disorder overlap with Alzheimer’s Disease

AbstractBackgroundAlcohol Use Disorder (AUD) and heavy alcohol abuse are associated with dementia. However, studies focused on Alzheimer’s disease (AD) tend to exclude heavy alcohol drinking patients. We hypothesize microglial phenotype changes in AUD contribute to degeneration that parallels AD.MethodOrbital frontal cortex (OFC) from moderate drinking controls and heavy drinking AUD individuals paired by age were obtained from the New South Wales Tissue Resource Center in Sydney Australia. Tissue blocks were used for RTPCR gene mRNA and paraffin sections for immunohistochemistry assessment of microglial and proinflammatory genes and proteins, respectively. Fluoro‐Jade B, TUNEL stain and neuron marker NeuN were used to assess degeneration.ResultAUD OFC expressed increased levels of proinflammatory HMGB1, RAGE, and multiple Toll‐like receptors (TLR). In addition, AUD OFC increased expression of the TLR adaptor protein myeloid differentiation primary response 88 (MyD88), NFκB, and proinflammatory cytokines, chemokines, and their corresponding receptors. Iba1, a marker of monocytes and microglia, is increased in AUD, but not mRNA levels. Macrophage‐1 antigen, a complement receptor, is increased in AUD cortex as is CX3C chemokine receptor 1 (CX3CR1), the fractalkine receptor. OX42 staining (CD11b) in also increased. Microglial markers P2ry12, and CSF1R also show greater cellular staining in human AUD. The lysosomal scavenger receptor marker CD68 is also increased in AUD cortex. CX3CR1 and CD11b mRNA are increased in AUD cortex, but not CD68. Interestingly, TMEM119, a specific microglial marker, is decreased in AUD, both mRNA and protein staining in contrast to other markers increasing. Assessment of DNA oxidation using 8‐hydroxy‐2'‐deoxyguanosine (8‐OHdG) a biomarker of oxidative DNA/RNA damage 8‐OHdG+IR indicated AUD more than doubled cortical cells with this marker. Induction of HMGB1‐TLR‐MyD88‐NFκB proinflammatory signaling pathways, oxidative stress and microglial activation correlate with markers of neurodegeneration.ConclusionThe increased expression of TLR receptors, MyD88 and NFkB and increased proinflammatory cytokines are consistent with increased microglial activation and oxidative stress induced degeneration. Studies support alcohol activated microglia‐monocytes as driving loss of NeuN and other neurodegeneration markers. The reduced TMEM119 level with other markers increasing may indicate monocytes are replacing microglia in AUD cortex.

Astrocyte signaling regulates microglial and oligodendrocyte subpopulation changes in a diet‐based model of small cerebral vessel disease

AbstractBackgroundVascular contributions to cognitive impairment and dementia (VCID) is the second leading cause of dementia behind Alzhiemer’s disease. Hyperhomocysteinemia (HHcy)‐inducing diets in mice recapitulate aspects of VCID including small cerebrovessel pathology, vascular inflammation and cognitive decline. Recently, we found signs of astrocytic Ca2+‐dysregulation and hyperactivation of calcineurin/NFAT activity in mice treated with HHcy diet (Sompol et al., 2023 J Neurosci 43:1797). Inhibition of astrocytic NFATs normalized cerebrovascular, synaptic, and cognitive function in HHcy mice, suggesting that reactive astrocytes alter the brain milieu during development of HHcy and small cerebrovessel pathology. Here, we used scRNA‐seq to further characterize the impact of astrocytic calcineurin/NFATs on multiple brain cell types in the context of HHcy.MethodSeven‐to‐eight week‐old male C57BL/6J mice received intrahippocampal injections of AAV2/5‐Gfa2‐EGFP (control) or AAV expressing the NFAT inhibitor VIVIT (i.e. AAV2/5‐Gfa2‐VIVIT‐EGFP). Mice were then fed with control chow(CT) or HHcy‐inducing chow enriched in methionine and deficient in folate and vitamins B6 and B12. After15 weeks of diet, brains were extracted and hippocampi dissected away, pooled and dissociated for transcriptional analyses. scRNA‐seq was used to identify diet and AAV‐dependent cell specific gene expression changes according to our previous work (Lee et al, 2023, Cell Reports, 112196).Result31 cell clusters were identified and assigned to 1 of 12 unique cell types using established gene markers. Analysis of differentially‐expressed genes showed that microglia and oligodendrocytes were most sensitive to diet and/or AAV treatment. In HHcy mice treated with control AAV (HHcy–EGFP), predominant microglial subpopulations exhibited upregulation of several disease‐associated microglial genes (e.g. Apoe, Il1b, Ccl5, Cebpb, Cybb) and downregulation of common homeostatic genes (e.g. P2ry12, Gpr34, Fcrls, Sparc). Oligodendrocyte subpopulations in the same mice also exhibited upregulation of disease related genes (e.g. Serpina3n, H2‐D1, C4b, Klk6). However, these patterns were mitigated in HHcy mice treated with AAV‐Gfa2‐VIVIT, who exhibited expression patterns in line with CT diet mice. Analyses of DEGs in other cell types and association with immunometabolic pathways are in progress.ConclusionResults suggest that reactive astrocyte signaling strongly regulates molecular phenotypes of other local glial cells and provides a potential target for preventing/resolving pathologic glial activity in VCID and other ADRDs.

Jedi‐1/MEGF12‐mediated phagocytosis controls the pro‐neurogenic properties of microglia in the ventricular‐subventricular zone

AbstractBackgroundThe act of engulfing cellular debris profoundly shapes phagocyte phenotypes and, thus, determines tissue‐specific phagocyte function. A population of microglia with unique characteristics resides in the ventricular‐subventricular zone (V‐SVZ) neurogenic niche in neonatal mice. It is unclear whether these microglia perform phagocytosis and to what extent their phagocytic activity would support neurogenesis. We asked whether V‐SVZ‐resident microglia phagocytose apoptotic neurons and investigated whether the novel receptor Jedi‐1 mediates this process.MethodWhole brain tissue or micro‐dissected V‐SVZ was collected from wild‐type and Jedi‐1 knockout (JKO) pups at postnatal day 7 (P7) and processed for immunofluorescent labeling, cytokine analysis, LC‐MS analysis of lipid mediators, microglia‐enriched culture and engulfment assays, or bulk RNA sequencing. Proliferating cells were labeled during a one‐hour pulse of EdU, delivered to the pups subcutaneously at P7. Microglia‐specific deletion of Jedi‐1 was induced with Tamoxifen, administered to the lactating dam twice daily from P1‐P3. In vivo rescue was performed via intracerebral injection of interleukin‐1 receptor antagonist at P4, followed by tissue collection at P7 for downstream analysis.ResultWe show that V‐SVZ microglia express Jedi‐1 and that Jedi‐1 is necessary for microglial phagocytosis both in vitro and in vivo. Furthermore, we show that loss of Jedi‐1 transforms microglial identity, leading to a neuroinflammatory phenotype consistent with that observed in neurodegenerative diseases and the aging brain. We demonstrate that loss of Jedi‐1 reduces the proliferation and neuronal differentiation of neural precursor cells in the V‐SVZ and that this effect is due to the loss of Jedi‐1 specifically in microglia. Finally, we provide evidence that the neurogenesis deficit is due to elevated interleukin‐1β levels and that in vivo inhibition of IL‐1 signaling rescues neurogenesis in the Jedi‐1 knockout V‐SVZ.ConclusionThe discovery that Jedi‐1 activation engenders pro‐neurogenic microglia reveals previously unknown aspects of postnatal neurogenesis and microglial function. It also provides a platform for future research on pathways that dictate microglial phenotypic changes at all life stages, both in health and in disease. Finally, these findings may provide opportunities to explore neuroprotective/neuroregenerative microglial‐targeted therapies.

Blockage of the fractalkine pathway reduces hyperalgesia and prevents morphological glial alterations-Comparison between inflammatory and neuropathic orofacial pain in male rats.

This study aimed to evaluate the effects of inhibitors of the fractalkine pathway in hyperalgesia in inflammatory and neuropathic orofacial pain in male rats and the morphological changes in microglia and satellite glial cells (SGCs). Rats were submitted to zymosan-induced arthritis of the temporomandibular joint or infraorbital nerve constriction, and treated intrathecally with a P2 X7 antagonist, a cathepsin S inhibitor or a p-38 mitogen-activated protein kinase (MAPK) inhibitor. Mechanical hyperalgesia was evaluated 4 and 6 h following arthritis induction or 7 and 14 days following nerve ligation. The expression of the receptor CX3 CR1 , phospho-p-38 MAPK, ionized calcium-binding adapter molecule-1 (Iba-1), and glutamine synthetase and the morphological changes in microglia and SGCs were evaluated by confocal microscopy. In both inflammatory and neuropathic models, untreated animals presented a higher expression of CX3 CR1 and developed hyperalgesia and up-regulation of phospho-p-38 MAPK, which was prevented by all drugs (p < .05). The number of microglial processes endpoints and the total branch length were lower in the untreated animals, but the overall immunolabeling of Iba-1 was altered only in neuropathic rats (p < .05). The mean area of SGCs per neuron was significantly altered only in the inflammatory model (p < .05). All morphological alterations were reverted by modulating the fractalkine pathway (p < .05). In conclusion, the blockage of the fractalkine pathway seemed to be a possible therapeutic strategy for inflammatory and neuropathic orofacial pain, reducing mechanical hyperalgesia by impairing the phosphorylation of p-38 MAPK and reverting morphological alterations in microglia and SGCs.

Microglia shape AgRP neuron postnatal development via regulating perineuronal net plasticity.

The hypothalamus plays a crucial role in controlling metabolism and energy balance, with Agouti-related protein (AgRP) neurons and proopiomelanocortin (POMC) neurons being essential components of this process. The proper development of these neurons is important for metabolic regulation in later life. Microglia, the resident immune cells in the brain, have been shown to significantly influence neurodevelopment. However, their role in shaping the postnatal development of hypothalamic neural circuits remains underexplored. In this study, we investigated the dynamic changes of microglia in the hypothalamic arcuate nucleus (ARC) during lactation and their impact on the maturation of AgRP and POMC neurons. We demonstrated that microglial depletion during a critical period of ARC neuron maturation increases the number of AgRP neurons and fiber density, with less effect on POMC neurons. This depletion also resulted in increased neonatal feeding behavior. Mechanistically, microglia can engulf perineuronal net (PNN) components surrounding AgRP neurons both in vivo and ex vivo. The absence of microglia leads to increased PNN formation and enhanced leptin sensitivity in ARC. Our findings suggest that microglia participate in the postnatal development of AgRP neurons by regulating the plasticity of PNN formation. This study contributes to a better understanding of microglia's role in shaping hypothalamic neural circuits during postnatal development and their impact on metabolism regulation.

Amyloid plaques and normal ageing have differential effects on microglial Ca2+ activity in the mouse brain

In microglia, changes in intracellular calcium concentration ([Ca2+]i) may regulate process motility, inflammasome activation, and phagocytosis. However, while neurons and astrocytes exhibit frequent spontaneous Ca2+ activity, microglial Ca2+ signals are much rarer and poorly understood. Here, we studied [Ca2+]i changes of microglia in acute brain slices using Fluo-4–loaded cells and mice expressing GCaMP5g in microglia. Spontaneous Ca2+ transients occurred ~ 5 times more frequently in individual microglial processes than in their somata. We assessed whether microglial Ca2+ responses change in Alzheimer's disease (AD) using AppNL−G−F knock-in mice. Proximity to Aβ plaques strongly affected microglial Ca2+ activity. Although spontaneous Ca2+ transients were unaffected in microglial processes, they were fivefold more frequent in microglial somata near Aβ plaques than in wild-type microglia. Microglia away from Aβ plaques in AD mice showed intermediate properties for morphology and Ca2+ responses, partly resembling those of wild-type microglia. By contrast, somatic Ca2+ responses evoked by tissue damage were less intense in microglia near Aβ plaques than in wild-type microglia, suggesting different mechanisms underlying spontaneous vs. damage-evoked Ca2+ signals. Finally, as similar processes occur in neurodegeneration and old age, we studied whether ageing affected microglial [Ca2+]i. Somatic damage-evoked Ca2+ responses were greatly reduced in microglia from old mice, as in the AD mice. In contrast to AD, however, old age did not alter the occurrence of spontaneous Ca2+ signals in microglial somata but reduced the rate of events in processes. Thus, we demonstrate distinct compartmentalised Ca2+ activity in microglia from healthy, aged and AD-like brains.

Microglia sense astrocyte dysfunction and prevent disease progression in an Alexander disease model.

Alexander disease (AxD) is an intractable neurodegenerative disorder caused by GFAP mutations. It is a primary astrocyte disease with a pathological hallmark of Rosenthal fibres within astrocytes. AxD astrocytes show several abnormal phenotypes. Our previous study showed that AxD astrocytes in model mice exhibit aberrant Ca2+ signals that induce AxD aetiology. Here, we show that microglia have unique phenotypes with morphological and functional alterations, which are related to the pathogenesis of AxD. Immunohistochemical studies of 60TM mice (AxD model) showed that AxD microglia exhibited highly ramified morphology. Functional changes in microglia were assessed by Ca2+ imaging using hippocampal brain slices from Iba1-GCaMP6-60TM mice and two-photon microscopy. We found that AxD microglia showed aberrant Ca2+ signals, with high frequency Ca2+ signals in both the processes and cell bodies. These microglial Ca2+ signals were inhibited by pharmacological blockade or genetic knockdown of P2Y12 receptors but not by tetrodotoxin, indicating that these signals are independent of neuronal activity but dependent on extracellular ATP from non-neuronal cells. Our single-cell RNA sequencing data showed that the expression level of Entpd2, an astrocyte-specific gene encoding the ATP-degrading enzyme NTPDase2, was lower in AxD astrocytes than in wild-type astrocytes. In situ ATP imaging using the adeno-associated virus vector GfaABC1D ATP1.0 showed that exogenously applied ATP was present longer in 60TM mice than in wild-type mice. Thus, the increased ATP level caused by the decrease in its metabolizing enzyme in astrocytes could be responsible for the enhancement of microglial Ca2+ signals. To determine whether these P2Y12 receptor-mediated Ca2+ signals in AxD microglia play a significant role in the pathological mechanism, a P2Y12 receptor antagonist, clopidogrel, was administered. Clopidogrel significantly exacerbated pathological markers in AxD model mice and attenuated the morphological features of microglia, suggesting that microglia play a protective role against AxD pathology via P2Y12 receptors. Taken together, we demonstrated that microglia sense AxD astrocyte dysfunction via P2Y12 receptors as an increase in extracellular ATP and alter their morphology and Ca2+ signalling, thereby protecting against AxD pathology. Although AxD is a primary astrocyte disease, our study may facilitate understanding of the role of microglia as a disease modifier, which may contribute to the clinical diversity of AxD.

Specificity and efficiency of tamoxifen-mediated Cre induction is equivalent regardless of age

Temporally controlling Cre recombination through tamoxifen (Tam) induction has many advantages for biomedical research. Most studies report early post-natal/juvenile (<2 m.o.) Tam induction, but age-related neurodegeneration and aging studies can require Cre induction in older mice (>12 m.o.). While anecdotally reported as problematic, there are no published comparisons of Tam-mediated Cre induction at early and late ages. Here, microglial-specific Cx3cr1creERT2 mice were crossed to a floxed NuTRAP reporter to compare Cre induction at early (3-6 m.o.) and late (20 m.o.) ages. Specificity and efficiency of microglial labeling at 21-22 m.o. were identical in mice induced with Tam at early and late ages. Age-related microglial translatomic changes were also similar regardless of Tam induction age. Each Cre and flox mouse line should be independently validated, however, these findings demonstrate that Tam-mediated Cre induction can be performed even into older mouse ages and should be generalizable to other inducible Cre models.

Morphological and metabolic changes in microglia exposed to cadmium: Cues on neurotoxic mechanisms

Microglial cells play a key role in protecting the central nervous system from pathogens and toxic compounds and are involved in the pathogenesis of different neurodegenerative diseases. Cadmium is a widespread toxic heavy metal, released into the environment at a rate of 30,000 tons/year by anthropogenic activities; it is easily uptaken by the human body through diet and cigarette smoke, as well as by occupational exposure. Once inside the body, cadmium enters the cells and substitutes to zinc and other divalent cations altering many biological functions. Its extremely long half-life makes it a serious health threat. Recent data suggest a role for heavy metals in many neurodegenerative diseases; however, the role of cadmium is still to be elucidated. In this work we report the investigation of cadmium toxicity towards murine BV2 microglial cells, a widely used model for the study of neurodegeneration. Results show that increasing cadmium concentrations increase oxidative stress, a proposed mechanism of neurodegeneration, but also that BV2 cells can keep oxidative stress under control by increasing glutathione reduction. Moreover, cadmium induces alterations of cell morphology and metabolism leading to mitochondrial impairment, without switching the cells to Warburg effect. Finally cadmium induces the release of proinflammatory cytokines, but does not markedly switch BV2 cells to M1 phenotype.

Exposure to Δ9-tetrahydrocannabinol leads to a rise in caspase-3, morphological changes in microglial, and astrocyte reactivity in the cerebellum of rats.

The present study aimed to elucidate the effect of 10mg/kg Δ9-tetrahydrocannabinol (THC) on cerebellar neuronal and glial morphology, apoptosis and inflammatory gene expression using a series of histological assays including stereology, Sholl analysis, immunofluorescence and real-time qPCR in male Wistar rats. A decrease in the number of Purkinje neurons and the thickness of the granular layer in the cerebellum was reported in THC-treated rats. Increased expression of Iba-1 and arborization of microglial processes were evidence of microgliosis and morphological changes in microglia. In addition, astrogliosis and changes in astrocyte morphology were other findings associated with THC administration. THC also led to an increase in caspase-3 positive cells and a decrease in autophagy and inflammatory gene expression such as mTOR, BECN1 and LAMP2. However, there were no significant changes in the volume of molecular layers and white matter, the spatial arrangement of granular layers and white matter, or the spatial arrangement of granular layers and white matter in the cerebellum. Taken together, our data showed both neuroprotective and neurodegenerative properties of THC in the cerebellum, which require further study in the future.

Alzheimer's disease-induced phagocytic microglia express a specific profile of coding and non-coding RNAs.

Alzheimer's disease (AD) is a neurodegenerative disease and the main cause of dementia in the elderly. AD pathology is characterized by accumulation of microglia around the beta-amyloid (Aβ) plaques which assumes disease-specific transcriptional signatures, as for the disease-associated microglia (DAM). However, the regulators of microglial phagocytosis are still unknown. We isolated Aβ-laden microglia from the brain of 5xFAD mice for RNA sequencing to characterize the transcriptional signature in phagocytic microglia and to identify the key non-coding RNAs capable of regulating microglial phagocytosis. Through spatial sequencing, we show the transcriptional changes of microglia in the AD mouse brain in relation to Aβ proximity. Finally, we show that phagocytic messenger RNAs are regulated by miR-7a-5p, miR-29a-3p and miR-146a-5p microRNAs and segregate the DAM population into phagocytic and non-phagocytic states. Our study pinpoints key regulators of microglial Aβ clearing capacity suggesting new targets for future therapeutic approaches.

A microglial activity state biomarker panel differentiates FTD-granulin and Alzheimer’s disease patients from controls

BackgroundWith the emergence of microglia-modulating therapies there is an urgent need for reliable biomarkers to evaluate microglial activation states.MethodsUsing mouse models and human induced pluripotent stem cell-derived microglia (hiMGL), genetically modified to yield the most opposite homeostatic (TREM2-knockout) and disease-associated (GRN-knockout) states, we identified microglia activity-dependent markers. Non-targeted mass spectrometry was used to identify proteomic changes in microglia and cerebrospinal fluid (CSF) of Grn- and Trem2-knockout mice. Additionally, we analyzed the proteome of GRN- and TREM2-knockout hiMGL and their conditioned media. Candidate marker proteins were tested in two independent patient cohorts, the ALLFTD cohort (GRN mutation carriers versus non-carriers), as well as the proteomic data set available from the EMIF-AD MBD study.ResultsWe identified proteomic changes between the opposite activation states in mouse microglia and CSF, as well as in hiMGL cell lysates and conditioned media. For further verification, we analyzed the CSF proteome of heterozygous GRN mutation carriers suffering from frontotemporal dementia (FTD). We identified a panel of six proteins (FABP3, MDH1, GDI1, CAPG, CD44, GPNMB) as potential indicators for microglial activation. Moreover, we confirmed three of these proteins (FABP3, GDI1, MDH1) to be significantly elevated in the CSF of Alzheimer’s (AD) patients. Remarkably, each of these markers differentiated amyloid-positive cases with mild cognitive impairment (MCI) from amyloid-negative individuals.ConclusionsThe identified candidate proteins reflect microglia activity and may be relevant for monitoring the microglial response in clinical practice and clinical trials modulating microglial activity and amyloid deposition. Moreover, the finding that three of these markers differentiate amyloid-positive from amyloid-negative MCI cases in the AD cohort suggests that these proteins associate with a very early immune response to seeded amyloid. This is consistent with our previous findings in the Dominantly Inherited Alzheimer’s Disease Network (DIAN) cohort, where soluble TREM2 increases as early as 21 years before symptom onset. Moreover, in mouse models for amyloidogenesis, seeding of amyloid is limited by physiologically active microglia further supporting their early protective role. The biological functions of some of our main candidates (FABP3, CD44, GPNMB) also further emphasize that lipid dysmetabolism may be a common feature of neurodegenerative disorders.

Chronic Administration of Ion Channel Blockers Impact Microglia Morphology and Function in a Murine Model of Alzheimer's Disease.

As the population ages, a high prevalence of multimorbidity will affect the way physicians need to think about drug interactions. With microglia's important involvement in the pathology and progression of Alzheimer's disease (AD), understanding whether systemically administered drugs intended for other affections could impact microglia function, already impacted by the presence of beta-amyloid, is important. The aim of this study was to evaluate morphological changes of microglia, using in vivo 2-photon laser scanning microscopy, in a murine model of AD under systemic administration of sodium or calcium ion channel blockers in order to establish potential effects that these drugs might have on microglia under neuro-inflammatory conditions. A total of 30 mice (age 14-16 weeks, weight 20-25 g) were used, with 25 APP randomly divided into three groups. The remaining animals were CX3CR1GFP/GFP male mice (n = 5) used as WT controls. After baseline behavior testing, all animals received daily intraperitoneal injections for 30 days according to the assigned group [WT (n = 5), Control (n = 5), Carbamazepine (n = 10), and Verapamil (n = 10)]. The results showed that the Verapamil treatment improved short-term memory and enhanced exploratory behavior in APP mice. The Carbamazepine treatment also improved short-term memory but did not elicit significant changes in anxiety-related behavior. Both Verapamil and Carbamazepine reduced the surveillance speed of microglia processes and changed microglia morphology in the cortex compared to the Control group. Due to their complex molecular machinery, microglia are potentially affected by drugs that do not target them specifically, and, as such, investigating these interactions could prove beneficial in our management of neurodegenerative pathologies.

Live imaging of microglia during sleeping sickness reveals early and heterogeneous inflammatory responses.

Invasion of the central nervous system (CNS) is the most serious consequence of Trypanosoma brucei infection, which causes sleeping sickness. Recent experimental data have revealed some more insights into the disease during the meningoencephalitic stage. However, detailed cellular processes befalling the CNS during the disease are poorly understood. To further address this issue, we implanted a cranial window on the cortex of B6.129P2(Cg)-Cx3cr1tm1Litt/J mice, infected them with Trypanosoma brucei expressing RFP via intraperitoneal injection, and monitored microglial cells and parasites longitudinally over 30 days using in vivo 2-photon imaging. We correlated the observed changes with histological analyses to evaluate the recruitment of peripheral immune cells. We uncovered an early involvement of microglia that precedes invasion of the CNS by the parasite. We accomplished a detailed characterization of the progressive sequence of events that correlates with microglial morphological changes and microgliosis. Our findings unveiled a heterogeneous microglial response in places of initial homeostatic disruption near brain barriers and pointed out an exceptional capability of microglia to hamper parasite proliferation inside the brain. We also found early signs of inflammation in the meninges, which synchronize with the microglial response. Moreover, we observed a massive infiltration of peripheral immune cells into the parenchyma as a signature in the final disease stage. Overall, our study provides new insights into the host-pathogen immune interactions in the meningeal and parenchymal compartments of the neocortex.

Microglia contribute to cognitive decline in hypercholesterolemic LDLr-/- mice.

Familial hypercholesterolemia (FH) is caused by mutations in the gene that encodes the low-density lipoprotein (LDL) receptor, which leads to an excessive increase in plasma LDL cholesterol levels. Previous studies have shown that FH is associated with gliosis, blood-brain barrier dysfunction, and memory impairment, but the mechanisms associated with these events are still not fully understood. Therefore, we aimed to investigate the role of microgliosis in the neurochemical and behavioral changes associated with FH using LDL receptor knockout (LDLr-/-) mice. We noticed that microgliosis was more severe in the hippocampus of middle-aged LDLr-/- mice, which was accompanied by microglial morphological changes and alterations in the immunocontent of synaptic protein markers. At three months of age, the LDLr-/- mice already showed increased microgliosis and decreased immunocontent of claudin-5 in the prefrontal cortex (PFC). Subsequently, 6-month-old male C57BL/6 wild-type and LDLr-/- mice were treated once daily for 30 days with minocycline (a pharmacological inhibitor of microglial cell reactivity) or vehicle (saline). Adult LDLr-/- mice displayed significant hippocampal memory impairment, which was ameliorated by minocycline treatment. Non-treated LDLr-/- mice showed increased microglial density in all hippocampal regions analyzed, a process that was not altered by minocycline treatment. Region-specific microglial morphological analysis revealed different effects of genotype or minocycline treatment on microglial morphology, depending on the hippocampal subregion analyzed. Moreover, 6-month-old LDLr-/- mice exhibited a slight but not significant increase in IBA-1 immunoreactivity in the PFC, which was reduced by minocycline treatment without altering microglial morphology. Minocycline treatment also reduced the presence of microglia within the perivascular area in both the PFC and hippocampus of LDLr-/- mice. However, no significant effects of either genotype or minocycline treatment were observed regarding the phagocytic activity of microglia in the PFC and hippocampus. Our results demonstrate that hippocampal microgliosis, microglial morphological changes, and the presence of these glial cells in the perivascular area, but not increased microglial phagocytic activity, are associated with cognitive deficits in a mouse model of FH.

Atorvastatin rescues hyperhomocysteinemia-induced cognitive deficits and neuroinflammatory gene changes

BackgroundEpidemiological data suggests statins could reduce the risk of dementia, and more specifically, Alzheimer’s disease (AD). Pre-clinical data suggests statins reduce the risk of dementia through their pleiotropic effects rather than their cholesterol lowering effects. While AD is a leading cause of dementia, it is frequently found co-morbidly with cerebral small vessel disease and other vascular contributions to cognitive impairment and dementia (VCID), which are another leading cause of dementia. In this study, we determined if atorvastatin ameliorated hyperhomocysteinemia (HHcy)-induced VCID.MethodsWild-type (C57Bl6/J) mice were placed on a diet to induce HHcy or a control diet each with or without atorvastatin for 14 weeks. Mice underwent novel object recognition testing before tissue collection. Plasma total cholesterol and total homocysteine as well as related metabolites were measured. Using qPCR and NanoString technology, we profiled glial cell-associated gene expression changes. Finally, microglial morphology, astrocyte end feet, and microhemorrhages were analyzed using histological methods.ResultsAtorvastatin treatment of HHcy in mice led to no changes in total cholesterol but decreases in total homocysteine in plasma. While HHcy decreased expression of many glial genes, atorvastatin rescued these gene changes, which mostly occurred in oligodendrocytes and microglia. Microglia in HHcy mice with atorvastatin were trending towards fewer processes compared to control with atorvastatin, but there were no atorvastatin effects on astrocyte end feet. While atorvastatin treatment was trending towards increasing the area of microhemorrhages in HHcy mice in the frontal cortex, it only slightly (non-significantly) reduced the number of microhemorrhages. Finally, atorvastatin treatment in HHcy mice led to improved cognition on the novel object recognition task.ConclusionsThese data suggest that atorvastatin rescued cognitive changes induced by HHcy most likely through lowering plasma total homocysteine and rescuing gene expression changes rather than impacts on vascular integrity or microglial changes.

Sequences of Alterations in Inflammation and Autophagy Processes in Rd1 Mice.

(1) Background: the aim of this work was to study microglia and autophagy alterations in a one retinitis pigmentosa (RP) model at different stages of the disease (when rods are dying and later, when there are almost no rods, and cones are the cells that die. (2) Methods: rd1 mice were used and retinas obtained at postnatal days (PN) 11, 17, 28, 35, and 42. Iba1 (ionized calcium-binding adapter molecule 1) was the protein selected to study microglial changes. The macroautophagy markers Beclin-1, Atg5, Atg7, microtubule-associated protein light chain 3 (LC3), and lysosomal-associated membrane protein 2 (LAMP2) (involved in chaperone-mediated autophagy (CMA)) were determined. (3) Results: the expression of Iba1 was increased in rd1 retinas compared to the control group at PN17 (after the period of maximum rod death), PN28 (at the beginning of the period of cone death), and PN42. The number of activated (ameboid) microglial cells increased in the early ages of the retinal degeneration and the deactivated forms (branched cells) in more advanced ages. The macroautophagy markers Atg5 at PN11, Atg7 and LC3II at PN17, and Atg7 again at PN28 were decreased in rd1 retinas. At PN35 and PN42, the results reveal alterations in LAMP2A, a marker of CMA in the retina of rd1 mice. (4) Conclusions: we can conclude that during the early phases of retinal degeneration in the rd1 mouse, there is an alteration in microglia and a decrease in the macroautophagy cycle. Subsequently, the CMA is decreased and later on appears activated as a compensatory mechanism.

Microglial and Astrocytic Responses in the Human Midcingulate Cortex in Huntington's Disease.

Patients with Huntington's disease can present with variable difficulties of motor functioning, mood, and cognition. Neurodegeneration occurs in the anterior cingulate cortex of some patients with Huntington's disease and is linked to the presentation of mood symptomatology. Neuroinflammation, perpetrated by activated microglia and astrocytes, has been reported in Huntington's disease and may contribute to disease progression and presentation. This study sought to quantify the density of mutant huntingtin protein and neuroinflammatory glial changes in the midcingulate cortex of postmortem patients with Huntington's disease and determine if either correlates with the presentation of mood, motor, or mixed symptomatology. Free-floating immunohistochemistry quantified 1C2 immunolabeling density as an indicative marker of mutant huntingtin protein, and protein and morphological markers of astrocyte (EAAT2, Cx43, and GFAP), and microglial (Iba1 and HLA-DP/DQ/DR) activation. Relationships among the level of microglial activation, mutant huntingtin burden, and case characteristics were explored using correlative analysis. We report alterations in activated microglia number and morphology in the midcingulate cortex of Huntington's disease cases with predominant mood symptomatology. An increased proportion of activated microglia was observed in the midcingulate of all Huntington's disease cases and positively correlated with 1C2 burden. Alterations in the astrocytic glutamate transporter EAAT2 were observed in the midcingulate cortex of patients associated with mood symptoms. This study presents pathological changes in microglia and astrocytes in the midcingulate cortex in Huntington's disease, which coincide with mood symptom presentation. These findings further the understanding of neuroinflammation in Huntington's disease, a necessary step for developing inflammation-targeted therapeutics. ANN NEUROL 2023;94:895-910.

Seizure-induced increase in microglial cell population in the developing zebrafish brain

Epilepsy is a chronic brain disorder characterized by unprovoked and recurrent seizures, of which 60% are of unknown etiology. Recent studies implicate microglia in the pathophysiology of epilepsy. However, their role in this process, in particular following early-life seizures, remains poorly understood due in part to the lack of suitable experimental models allowing the in vivo imaging of microglial activity. Given the advantage of zebrafish larvae for minimally-invasive imaging approaches, we sought for the first time to describe the microglial responses after acute seizures in two different zebrafish larval models: a chemically-induced epileptic model by the systemic injection of kainate at 3 days post-fertilization, and the didys552 genetic epilepsy model, which carries a mutation in scn1lab that leads to spontaneous epileptiform discharges. Kainate-treated larvae exhibited transient brain damage as shown by increased numbers of apoptotic nuclei as early as one day post-injection, which was followed by an increase in the number of microglia in the brain. A similar microglial phenotype was also observed in didys552-/- mutants, suggesting that microglia numbers change in response to seizure-like activity in the brain. Interestingly, kainate-treated larvae also displayed a decreased seizure threshold towards subsequent pentylenetetrazole-induced seizures, as shown by higher locomotor and encephalographic activity in comparison with vehicle-injected larvae. These results are comparable to kainate-induced rodent seizure models and suggest the suitability of these zebrafish seizure models for future studies, in particular to elucidate the links between epileptogenesis and microglial dynamic changes after seizure induction in the developing brain, and to understand how these modulate seizure susceptibility.