Microglial Burden Research Articles

Association between hippocampal microglia, AD and LATE-NC, and cognitive decline in older adults.

This study investigates the relationship between microglia inflammation in the hippocampus, brain pathologies, and cognitive decline. Participants underwent annual clinical evaluations and agreed to brain donation. Neuropathologic evaluations quantified microglial burden in the hippocampus, amyloid beta (Aβ), tau tangles, and limbic age-related transactive response DNA-binding protein 43 (TDP-43) encephalopathy neuropathologic changes (LATE-NC), and other common brain pathologies. Mixed-effect and linear regression models examined the association of microglia with a decline in global and domain-specific cognitive measures, and separately with brain pathologies. Path analyses estimated direct and indirect effects of microglia on global cognition. Hippocampal microglia were associated with a faster decline in global cognition, specifically in episodic memory, semantic memory, and perceptual speed. Tau tangles and LATE-NC were independently associated with microglia. Other pathologies, including Aβ, were not related. Regional hippocampal burden of tau tangles and TDP-43 accounted for half of the association of microglia with cognitive decline. Microglia inflammation in the hippocampus contributes to cognitive decline. Tau tangles and LATE-NC partially mediate this association.

Progranulin haploinsufficiency mediates cytoplasmic TDP-43 aggregation with lysosomal abnormalities in human microglia

BackgroundProgranulin (PGRN) haploinsufficiency due to progranulin gene (GRN) variants can cause frontotemporal dementia (FTD) with aberrant TAR DNA-binding protein 43 (TDP-43) accumulation. Despite microglial burden with TDP-43-related pathophysiology, direct microglial TDP-43 pathology has not been clarified yet, only emphasized in neuronal pathology. Thus, the objective of this study was to investigate TDP-43 pathology in microglia of patients with PGRN haploinsufficiency.MethodsTo design a human microglial cell model with PGRN haploinsufficiency, monocyte-derived microglia (iMGs) were generated from FTD–GRN patients carrying pathogenic or likely pathogenic variants (p.M1? and p.W147*) and three healthy controls.ResultsiMGs from FTD–GRN patients with PGRN deficiency exhibited severe neuroinflammation phenotype and failure to maintain their homeostatic molecular signatures, along with impaired phagocytosis. In FTD–GRN patients-derived iMGs, significant cytoplasmic TDP-43 aggregation and accumulation of lipid droplets with profound lysosomal abnormalities were observed. These pathomechanisms were mediated by complement C1q activation and upregulation of pro-inflammatory cytokines.ConclusionsOur study provides considerable cellular and molecular evidence that loss-of-function variants of GRN in human microglia can cause microglial dysfunction with abnormal TDP-43 aggregation induced by inflammatory milieu as well as the impaired lysosome. Elucidating the role of microglial TDP-43 pathology in intensifying neuroinflammation in individuals with FTD due to PGRN deficiency and examining consequential effects on microglial dysfunction might yield novel insights into the mechanisms underlying FTD and neurodegenerative disorders.

Assessing neuroinflammatory differences in FTLD‐Tau vs FTLD‐TDP using free water diffusion

AbstractBackgroundFrontotemporal lobar degeneration (FTLD) is associated with two pathological substrates: Tau and TAR‐DNA‐binding protein 43 (TDP‐43). In‐vivo detection of the pathological substrate is still not possible in FTLD‐related syndromes but progressive supranuclear palsy (PSP) is consistently associated with FTLD‐Tau while semantic‐variant primary progressive aphasia (svPPA) and FTD‐MND (FTD‐ALS) are associated with FTLD‐TDP. In the absence of disease‐specific markers in FTLD, it is necessary to identify biomarkers that can help distinguish FTLD‐Tau and FTLD‐TDP. Recent research has implicated neuroinflammation as a common feature across FTLD subtypes (Bright et al., 2019), however further research is required to investigate neuroinflammatory differences between FTLD‐Tau and FTLD‐TDP, given that microglial burden and activation may differ in FTLD subtypes (Woollacott et al., 2020). The free water fraction (FW), a metric generated from diffusion MRI (dMRI) (Pasternak et al., 2009), is a non‐specific marker of neuroinflammation (Bergamino, Walsh and Stokes, 2021). We will investigate differences in FW diffusion between patients with presumed FTLD‐Tau versus FTLD‐TDP. We hypothesize that differences in neuroinflammation between FTLD‐Tau and FTLD‐TDP can be identified using the free water measure, which may infer neuroinflammatory differences.MethodFree‐water maps were generated from dMRI datasets obtained from 43 subjects: 19 with presumed FTLD‐Tau (PSP, mean age = 70), 6 with presumed FTLD‐TDP (mean age = 67, 4 svPPA, 2 FTD‐ALS), and 19 healthy controls (mean age 63). Grey matter (GM) was segmented from T1‐weighted MRIs using FSL’s ‘fast’, projected onto the diffusion MRI space, where free‐water maps were averaged across the GM. The average free water estimates from FTLD‐Tau, FTLD‐TDP and control datasets were tested for group differences using student’s t‐tests and analysis of covariance (ANCOVA), with age as a covariate.ResultsANCOVA revealed significant differences between the groups (F = 6.47, p < 0.01). Post‐hoc tests showed significantly higher free‐water in FTLD‐Tau (p<0.01) and FTLD‐TDP (p<0.01) compared to controls. There was also higher free water in FTLD‐TDP in comparison to FTLD‐Tau, approaching significance (p = 0.0503)ConclusionOur preliminary data shows significant differences between healthy controls and patients with FTLD‐Tau and FTLD‐TDP and a trend for increased free water in FTLD‐TDP patients vs FTLD‐Tau, which may be indicative of neuroinflammatory differences.

INVESTIGATING THE NEURAL AFFECTS OF 17 ALPHA-ESTRADIOL (17Α-E2) ON APOE4 PHENOTYPES

Abstract Aging and APOE4 genotype are the primary risk factors for late onset Alzheimer’s disease (AD). Previous drugs trials for AD have focused on amyloid beta which has yielded minimal effects; hence a drug targeting aging could prove more efficacious. 17 alpha-estradiol (17α-E2) is an enantiomer of 17 beta-estradiol that has been shown to extend lifespan in male mice. We hypothesize that 17α-E2 will improve aging related phenotypes caused by the APOE4 genotype. We enrolled 10-month-old APOE3 or APOE4 targeted replacement mice and randomized them to either control or 17α-E2 diet for 20 weeks. At weeks 15 to 17, mice underwent various behavior assays and tissues were collected at the end of the 20 weeks. We observed behavioral improvement in APOE4 mice treated with 17α-E2 and asked whether this effect is associated with: (1) change in activity or anxiety, (2) change in neural stem cells, or (3) change in microglial activation. Activity levels but not neurogenesis of microglial burden were affected by APOE genotype and 17α-E2 treatment, suggesting a potential contribution to observed memory improvement in APOE4 mice treated with 17α-E2. Continued research on the neural effects of 17α-E2 pose potential benefits to mitigate the effects of aging.

MhcII Regulates Transmission of α-Synuclein-Seeded Pathology in Mice.

MHCII molecules, expressed by professional antigen-presenting cells (APCs) such as T cells and B cells, are hypothesized to play a key role in the response of cellular immunity to α-synuclein (α-syn). However, the role of cellular immunity in the neuroanatomic transmission of α-syn pre-formed fibrillar (PFF) seeds is undetermined. To illuminate whether cellular immunity influences the transmission of α-syn seeds from the periphery into the CNS, we injected preformed α-syn PFFs in the hindlimb of the Line M83 transgenic mouse model of synucleinopathy lacking MhcII. We showed that a complete deficiency in MhcII accelerated the appearance of seeded α-syn pathology and shortened the lifespan of the PFF-seeded M83 mice. To characterize whether B-cell and T-cell inherent MhcII function underlies this accelerated response to PFF seeding, we next injected α-syn PFFs in Rag1−/− mice which completely lacked these mature lymphocytes. There was no alteration in the lifespan or burden of endstage α-syn pathology in the PFF-seeded, Rag1-deficient M83+/− mice. Together, these results suggested that MhcII function on immune cells other than these classical APCs is potentially involved in the propagation of α-syn in this model of experimental synucleinopathy. We focused on microglia next, finding that while microglial burden was significantly upregulated in PFF-seeded, MhcII-deficient mice relative to controls, the microglial activation marker Cd68 was reduced in these mice, suggesting that these microglia were not responsive. Additional analysis of the CNS showed the early appearance of the neurotoxic astrocyte A1 signature and the induction of the Ifnγ-inducible anti-viral response mediated by MhcI in the MhcII-deficient, PFF-seeded mice. Overall, our data suggest that the loss of MhcII function leads to a dysfunctional response in non-classical APCs and that this response could potentially play a role in determining PFF-induced pathology. Collectively, our results identify the critical role of MhcII function in synucleinopathies induced by α-syn prion seeds.

Motor neuron TDP-43 proteinopathy in progressive supranuclear palsy and corticobasal degeneration

Abstract TDP-43 is mislocalized from the nucleus and aggregates within the cytoplasm of affected neurons in cases of amyotrophic lateral sclerosis. TDP-43 pathology has also been found in brain tissues under non-amyotrophic lateral sclerosis conditions, suggesting mechanistic links between TDP-43-related amyotrophic lateral sclerosis and various neurological disorders. This study aimed to assess TDP-43 pathology in the spinal cord motor neurons of tauopathies. We examined 106 spinal cords from consecutively autopsied cases with progressive supranuclear palsy (n = 26), corticobasal degeneration (n = 12), globular glial tauopathy (n = 5), Alzheimer’s disease (n = 21) or Pick's disease (n = 6) and neurologically healthy controls (n = 36). Ten of the progressive supranuclear palsy cases (38%) and seven of the corticobasal degeneration cases (58%) showed mislocalization and cytoplasmic aggregation of TDP-43 in spinal cord motor neurons, which was prominent in the cervical cord. TDP-43 aggregates were found to be skein-like, round-shaped, granular or dot-like and contained insoluble C-terminal fragments showing blotting pattern of amyotrophic lateral sclerosis or frontotemporal lobar degeneration. The lower motor neurons also showed cystatin-C aggregates, although Bunina bodies were absent in haematoxylin-eosin staining. The spinal cord TDP-43 pathology was often associated with TDP-43 pathology of the primary motor cortex. Positive correlations were shown between the severities of TDP-43 and four-repeat (4R)-tau aggregates in the cervical cord. TDP-43 and 4R-tau aggregates burdens positively correlated with microglial burden in anterior horn. TDP-43 pathology of spinal cord motor neuron did not develop in an age-dependent manner and was not found in the Alzheimer’s disease, Pick's disease, globular glial tauopathy and control groups. Next, we assessed SFPQ expression in spinal cord motor neurons; SFPQ is a recently identified regulator of amyotrophic lateral sclerosis/frontotemporal lobar degeneration pathogenesis, and it is also reported that interaction between SFPQ and FUS regulates splicing of MAPT exon 10. Immunofluorescent and proximity-ligation assays revealed altered SFPQ/FUS-interactions in the neuronal nuclei of progressive supranuclear palsy, corticobasal degeneration and amyotrophic lateral sclerosis-TDP cases but not in Alzheimer’s disease, Pick's disease and globular glial tauopathy cases. Moreover, SFPQ expression was depleted in neurons containing TDP-43 or 4R-tau aggregates of progressive supranuclear palsy and corticobasal degeneration cases. Our results indicate that progressive supranuclear palsy and corticobasal degeneration may have properties of systematic motor neuron TDP-43 proteinopathy, suggesting mechanistic links with amyotrophic lateral sclerosis-TDP. SFPQ dysfunction, arising from altered interaction with FUS, may be a candidate of the common pathway.

IL-10 based immunomodulation initiated at birth extends lifespan in a familial mouse model of amyotrophic lateral sclerosis

Inflammatory signaling is thought to modulate the neurodegenerative cascade in amyotrophic lateral sclerosis (ALS). We have previously shown that expression of Interleukin-10 (IL-10), a classical anti-inflammatory cytokine, extends lifespan in the SOD1-G93A mouse model of familial ALS. Here we test whether co-expression of the decoy chemokine receptor M3, that can scavenge inflammatory chemokines, augments the efficacy of IL-10. We found that recombinant adeno-associated virus (AAV)-mediated expression of IL-10, alone, or in combination with M3, resulted in modest extension of lifespan relative to control SOD1-G93A cohort. Interestingly neither AAV-M3 alone nor AAV-IL-10 + AAV-M3 extend survival beyond that of the AAV-IL-10 alone cohort. Focused transcriptomic analysis revealed induction of innate immunity and phagocytotic pathways in presymptomatic SOD1-G93A mice expressing IL-10 + M3 or IL-10 alone. Further, while IL-10 expression increased microglial burden, the IL-10 + M3 group showed lower microglial burden, suggesting that M3 can successfully lower microgliosis before disease onset. Our data demonstrates that over-expression of an anti-inflammatory cytokine and a decoy chemokine receptor can modulate inflammatory processes in SOD1-G93A mice, modestly delaying the age to paralysis. This suggests that multiple inflammatory pathways can be targeted simultaneously in neurodegenerative disease and supports consideration of adapting these approaches to treatment of ALS and related disorders.

Microglial burden, activation and dystrophy patterns in frontotemporal lobar degeneration

BackgroundMicroglial 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.MethodsImmunohistochemistry 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.ResultsThere 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.ConclusionsThis 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.

Pathological correlates of white matter hyperintensities in a case of progranulin mutation associated frontotemporal dementia

ABSTRACTWhite matter hyperintensities (WMH) are often seen on MRI brain scans in frontotemporal dementia (FTD) due to progranulin (GRN) mutations, but their pathological correlates are unknown. We examined the histological changes underlying WMH in a patient with GRN mutation associated behavioral variant FTD. In vivo and cadaveric MRI showed progressive, asymmetric frontotemporal and parietal atrophy, and asymmetrical WMH predominantly affecting frontal mid-zones. We first performed segmentation and localization analyses of WMH present on cadaveric MRI FLAIR images, then selected five different brain regions directly matched to differing severities of WMH for histological analysis. We used immunohistochemistry to assess vascular pathology, degree of spongiosis, neuronal and axonal loss, TDP-43, demyelination and astrogliosis, and microglial burden and morphology. Brain regions with significant WMH displayed severe cortical and white matter pathology, and prominent white matter microglial activation and microglial dystrophy, but only mild axonal loss and minimal vascular pathology. Our study suggests that WMH in GRN mutation carriers are not secondary to vascular pathology. Whilst cortical pathology induced axonal degeneration could contribute to white matter damage, individuals with GRN mutations could develop selective white matter vulnerability and myelin loss due to chronic, regional microglial dysfunction arising from GRN haploinsufficiency.

Phos-tau peptide immunization of amyloid-tg-mice reduced non-mutant phos-tau pathology, improved cognition and reduced amyloid plaques

Tau-immumotherapy has shown promising results in tangle/tauopathy-tg animal models. Here we immunized amyloid-mice (APPSwe/PSEN1dE9-tg, presenting amyloid-plaques, not neurofibrillary-tangles) with phos-tau peptides, previously shown by us to have high efficacy in mutant-tau tauopathy-mice. These amyloid-mice allowed us to test the effect of the vaccine in a model of familial AD patients with mutant amyloid plaque pathology, where tau pathology - once develops - is of non-mutant tau. Fourteen-month-old amyloid-mice were immunized with phos-tau peptides or vehicle. Eight weeks later, amelioration of cognitive impairment was noticed. Histological analysis revealed that the phos (non-mutant)-tau pathology (detected by us in these aged amyloid-mice while not in non-tg-mice), was lower in the phos-tau immunized amyloid-mice than in the non-immunized mice. Interestingly, we detected a decrease in amyloid plaque pathology, probably associated with the increased microglial burden, which surrounded both tau and amyloid pathology. These results point to the added value of immunizing AD-mice with the phos-tau-vaccine, targeting both tau and amyloid pathology, which may have clinical relevance. It also points to the multifaceted interplay between tau/amyloid pathologies.

The influence of HLA-DRB1*15 on motor cortical pathology in multiple sclerosis.

Multiple sclerosis (MS) is a common and heterogeneous CNS inflammatory demyelinating disease. The HLA-DRB1 locus may influence clinical outcome. MS cortical pathology is frequent and correlates with measures of clinical disability, including motoric dysfunction that is a predominant feature of disease progression. The influence of HLA-DRB1*15 on motor cortical pathology is unknown. A pathologically confirmed age- and sex-matched HLA-DRB1*15+ (n = 21) and HLA-DRB1*15- (n = 26) MS post-mortem cohort was used for detailed pathologic analyses. For each case, adjacent sections of motor cortex were stained for myelin and inflammation, to evaluate the extent and distribution of motor cortical pathology. A subset of MS cases (n = 42) had spinal cord (SC) pathologic outcome data available for comparison. Motor cortical demyelination was more pronounced in younger cases (r = -0.337, P < 0.05), with MS cases carrying the HLA-DRB1*15 allele driving this effect (r = -0.612, P < 0.01). HLA-DRB1*15+ MS cases had more severe motor cortical parenchymal (P < 0.05), perivascular (P < 0.05) and meningeal (P < 0.05) T-cell inflammation compared to HLA-DRB1*15- cases. HLA-DRB1*15 status significantly influenced the extent of motor cortical microglial burden in both NAGM (P < 0.0001) and lesions (P < 0.01) in MS cases. Relationships between the extent of motor cortical and SC pathology were limited, but when present were primarily driven by HLA-DRB1*15+ cases. HLA-DRB1*15 status has a significant association with the extent of inflammation in the MS motor cortex, the extent of demyelination in younger MS cases, and influences relationships between motor cortical and SC pathology.

Inflammation in Alzheimer’s disease: insights from immunotherapy

More than 20 years after its initial formulation, the amyloid cascade hypothesis—which postulates that build-up of toxic amyloid-β species initiates a series of events that culminates in neurodegeneration and symptoms (Hardy and Higgins, 1992)—continues to dominate thinking on the pathogenesis of Alzheimer’s disease. Although the exact sequence of events linking amyloid-β accumulation to aggregation of hyperphosphorylated tau in different neuronal compartments, neuronal loss, synaptic dysfunction and symptoms remains unknown, there is now a substantial body of evidence implicating neuroinflammation in the pathogenesis of Alzheimer’s disease. Thus activated microglia accumulate around amyloid plaques both in the brains of individuals with Alzheimer’s disease and in transgenic mice, and have been implicated in promoting neurodegeneration (Akiyama et al. , 2000). Imaging studies using the 11C- R -PK11195 PET ligand provide evidence that activated microglial accumulate in the vicinity of amyloid plaque pathology, and that activated microglial burden correlates with declining cognition (Edison et al. , 2008). Genome-wide association studies have identified a number of risk variants for Alzheimer’s disease implicated in inflammatory responses (Bettens et al. , 2013); exome sequencing has revealed polymorphisms in the microglial receptor TREM2 gene as a rare but significant risk for Alzheimer’s disease (Guerreiro et al. , 2013; Jonsson et al. , 2013); and recently, the CD33 risk allele has been shown to inhibit microglial clearance of amyloid-β (Bradshaw et al. , 2013; Griciuc et al. , 2013). Finally, an integrative network-based genetic analysis of Alzheimer’s disease brain has implicated disturbance in immune/microglial networks in the pathogenesis of the disease (Zhang et al. , 2013). If inflammation, and microglial activation in particular, are core features of Alzheimer’s disease, the exact mechanisms involved, and the roles of the different inflammatory components are far less clear. Microglia—the predominant macrophage species within the brain—can express different cell-surface …

Delayed Dominant-Negative TNF Gene Therapy Halts Progressive Loss of Nigral Dopaminergic Neurons in a Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder typified by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Recent evidence indicates that neuroinflammation may play a critical role in the pathogenesis of PD, particularly tumor necrosis factor (TNF). We have previously shown that soluble TNF (solTNF) is required to mediate robust degeneration induced by 6-hydroxydopamine (6-OHDA) or lipopolysaccharide. What remains unknown is whether TNF inhibition can attenuate the delayed and progressive phase of neurodegeneration. To test this, rats were injected in the SNpc with lentivirus encoding dominant-negative TNF (lenti-DN-TNF) 2 weeks after receiving a 6-OHDA lesion. Remarkably, when examined 5 weeks after the initial 6-OHDA lesion, no further loss of nigral DA neurons was observed. Lenti-DN-TNF also attenuated microglial activation. Together, these data suggest that TNF is likely a critical mediator of nigral DA neuron death during the delayed and progressive phase of neurodegeneration, and that microglia may be the principal cell type involved. These promising findings provide compelling reasons to perform DN-TNF gene transfer studies in nonhuman primates with the long-term goal of using it in the clinic to prevent the delayed and progressive degeneration of DA neurons that gives rise to motor symptoms in PD.

Granulocyte-colony stimulating factor (G-CSF) enhances recovery in mouse model of Parkinson's disease

Introduction: Granulocyte-colony stimulating factor (G-CSF) is used routinely in clinical practice for the treatment of neutropenia and to increase generation of hematopoietic stem cells in bone marrow donors. A growing body of literature on the neurotrophic effects of G-CSF has led to clinical trials in stroke, Alzheimer's disease (AD) and Parkinson's disease (PD). Objectives: The primary objective of this study was to determine if G-CSF administration would rescue the nigro-striatal system and restore locomotor function after completion of a sub-acute course of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration (30 mg/kg i.p. for 5 days) in 12 month-old mice. A secondary aim was to determine if G-CSF affects the neuro-inflammatory response by modulating microglial activation in striatum and midbrain. Results: MPTP-treated mice were impaired on the rotometer test after the last dose of the toxicant and remained impaired until euthanasia. MPTP-treated mice that were given an 8-day regimen of G-CSF starting 2 days after the last dose of toxicant enhanced motor performance compared to the MPTP alone group. MPTP treatment depleted striatal DA (DA) levels; G-CSF given after MPTP resulted in a partial, significant repletion of DA levels. Total microglial burden in the striatum was increased significantly in MPTP-treated mice and was reduced after G-CSF rescue. Conclusion: G-CSF enhances recovery of DA nigro-striatal function from MPTP toxicity in part by modulating the microglial response to injury. The G-CSF receptor may provide a novel target for modifying the disease process in Parkinson's disease.

Efficacy and safety of immunization with phosphorylated tau against neurofibrillary tangles in mice

As an abnormally folded and aggregated protein, tau composed of neurofibrillary tangles (NFTs) in Alzheimer's disease and other tauopathies seems to be a candidate for immunotherapy. Yet, the encephalitogenicity of full-length tau protein, recently reported by us in immunized mice, demands to carefully and selectively target pathological tau and address both efficacy (anti-NFT effect) and safety (free of encephalitis). We immunized NFT mice with NFT-related phosphorylated (phos) tau peptides, using an immunization protocol aimed to predispose a proinflammatory milieu in CNS as a set up to detect biohazard, an approach we used when the neurotoxicity of full-length tau was detected [use of complete Freund adjuvant (CFA) with pertussis toxin (PT)]. A decrease of about 40% in NFT burden in CNS was demonstrated and was accompanied with an increase in microglial burden. Anti-phos-tau antibodies were detected in serum and blood vessels in the CNS, while no encephalitogenicity (free of clinical neurological deficits, of adverse effects on brain inflammatory cells and of axonal damage) was recorded. The level of the lysosomal proteases, cathepsins D and L, was affected in the immunized mice suggesting the possible involvement of the lysosomal system in the decrease of NFTs. The robust anti-NFT effect and the lack of encephalitogenicity in NFT mice immunized with phos-tau peptides, even though CFA with PT was included in vaccine, point to their anti-NFT therapeutic potential.

Granulocyte colony stimulating factor decreases brain amyloid burden and reverses cognitive impairment in Alzheimer's mice

Granulocyte colony stimulating factor (G-CSF) is a multi-modal hematopoietic growth factor, which also has profound effects on the diseased CNS. G-CSF has been shown to enhance recovery from neurologic deficits in rodent models of ischemia. G-CSF appears to facilitate neuroplastic changes by both mobilization of bone marrow–derived cells and by its direct actions on CNS cells. The overall objective of the study was to determine if G-CSF administration in a mouse model of Alzheimer's disease (AD) (Tg APP/PS1) would impact hippocampal-dependent learning by modifying the underlying disease pathology. A course of s.c. administration of G-CSF for a period of less than three weeks significantly improved cognitive performance, decreased β-amyloid deposition in hippocampus and entorhinal cortex and augmented total microglial activity. Additionally, G-CSF reduced systemic inflammation indicated by suppression of the production or activity of major pro-inflammatory cytokines in plasma. Improved cognition in AD mice was associated with increased synaptophysin immunostaining in hippocampal CA1 and CA3 regions and augmented neurogenesis, evidenced by increased numbers of calretinin-expressing cells in dentate gyrus. Given that G-CSF is already utilized clinically to safely stimulate hematopoietic stem cell production, these basic research findings will be readily translated into clinical trials to reverse or forestall the progression of dementia in AD. The primary objective of the present study was to determine whether a short course of G-CSF administration would have an impact on the pathological hallmark of AD, the age-dependent accumulation of Aβ deposits, in a transgenic mouse model of AD (APP+ PS1; Tg). A second objective was to determine whether such treatment would impact cognitive performance in a hippocampal-dependent memory paradigm. To explain the G-CSF triggered amyloid reduction and associated reversal of cognitive impairment, several mechanisms of action were explored. (1) G-CSF was hypothesized to increase activation of resident microglia and to increase mobilization of marrow-derived microglia. The effect of G-CSF on microglial activation was examined by quantitative measurements of total microglial burden. To determine if G-CSF increased trafficking of marrow-derived microglia into brain, bone marrow–derived green fluorescent protein-expressing (GFP+) microglia were visualized in the brains of chimeric AD mice. (2) To assess the role of immune-modulation in mediating G-CSF effects, a panel of cytokines was measured in both plasma and brain. (3) To test the hypothesis that reduction of Aβ deposits can affect synaptic area, quantitative measurement of synaptophysin immunoreactivity in hippocampal CA1 and CA3 sectors was undertaken. (4) To learn whether enhanced hippocampal neurogenesis was induced by G-CSF treatment, numbers of calretinin-expressing cells were determined in dentate gyrus.

Regulator of G-Protein Signaling 10 Promotes Dopaminergic Neuron Survival via Regulation of the Microglial Inflammatory Response

Epidemiological studies suggest that chronic use of nonsteroidal anti-inflammatory drugs lowers the incidence of Parkinson's disease (PD) in humans and implicate neuroinflammatory processes in the death of dopamine (DA) neurons. Here, we demonstrate that regulator of G-protein signaling 10 (RGS10), a microglia-enriched GAP (GTPase accelerating protein) for Galpha subunits, is an important regulator of microglia activation. Flow-cytometric and immunohistochemical analyses indicated that RGS10-deficient mice displayed increased microglial burden in the CNS, and exposure to chronic systemic inflammation induced nigral DA neuron loss measured by unbiased stereology. Primary microglia isolated from brains of RGS10-deficient mice displayed dysregulated inflammation-related gene expression profiles under basal and stimulated conditions in vitro compared with that of primary microglia isolated from wild-type littermates. Similarly, knockdown of RGS10 in the BV2 microglia cell line resulted in dysregulated inflammation-related gene expression, overproduction of tumor necrosis factor (TNF), and enhanced neurotoxic effects of BV2 microglia on the MN9D dopaminergic cell line that could be blocked by addition of the TNF decoy receptor etanercept. Importantly, ablation of RGS10 in MN9D dopaminergic cells further enhanced their vulnerability to microglial-derived death-inducing inflammatory mediators, suggesting a role for RGS10 in modulating the sensitivity of dopaminergic neurons against inflammation-mediated cell death. Together, our findings indicate that RGS10 limits microglial-derived TNF secretion and regulates the functional outcome of inflammatory stimuli in the ventral midbrain. RGS10 emerges as a novel drug target for prevention of nigrostriatal pathway degeneration, the neuropathological hallmark of PD.

Glial cytoplasmic inclusions and tissue injury in multiple system atrophy: A quantitative study in white matter (olivopontocerebellar system) and gray matter (nigrostriatal system)

Glial cytoplasmic inclusions (GCIs) and microglia were quantified in 12 cases of multiple system atrophy (MSA) with special reference to their association with histologically defined lesion severity. The targets of the analysis were white matter (cerebellum, pontine base) and gray matter (putamen, substantia nigra). First, the lesion severity was defined: for white matter, the degree of demyelination and tissue rarefaction were semi-quantified on Klüver-Barrera (KB) sections as grade I (mildly injured), II (moderately injured), and III (severely injured); for gray matter, neurons and astrocytes were counted on KB and glial fibrillary acidic protein-immunostained sections, respectively. Next, the GCI burden was quantified on sections immunostained for alpha-synuclein, phosphorylated alpha-synuclein, and ubiquitin and the microglial burden was quantified on sections immunostained for HLA-DR. In white matter, the GCI and microglial burdens were the greatest when the tissue injury was mild and/or moderate (grade I and/or grade II), and they became less prominent when the tissue injury became more severe (grade III). In gray matter, in contrast, the GCI and microglial burdens failed to show significant correlations with the lesion severity. Our result suggests that the amount of GCIs as well as that of microglia is reduced when the tissue injury becomes severe in vulnerable white matter areas, but not in vulnerable gray matter areas, of MSA. It also suggests that there seems to be a difference between gray matter and white matter in the way GCIs and microglia participate in the degenerative process of MSA.

Microglial activation parallels system degeneration in progressive supranuclear palsy and corticobasal degeneration.

The role of microglia in progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) is unknown. To address this issue we examined 10 cases of PSP, 5 cases of CBD, and 4 normal controls. Microglial and tau burdens were determined with image analysis on brain sections that had been immunostained with monoclonal antibodies to HLA-DR and phospho-tau. We found that microglial activation was greater in PSP and CBD than normal controls, and that the microglial burden correlated with the tau burden in most areas. There were distinct patterns of microglial activation and tau pathology in PSP and CBD, with PSP showing more pathology in infratentorial structures and CBD showing more pathology in supratentorial structures. These results support the notion that PSP and CBD are distinct clinicopathologic entities. Microglial activation was not well correlated with tau pathology in the brainstem of PSP, which suggests that brainstem pathology in PSP is not exclusively due to tau pathology. While the results do not necessarily support a direct causal link between microglial activation and neurodegeneration in PSP or CBD, they nevertheless suggest that microglia play a role in disease pathogenesis.