Cathepsin S contributes to microglia‐mediated olfactory dysfunction through the regulation of Cx3cl1–Cx3cr1 axis in a Niemann–Pick disease type C1 model

Microglia can aggravate olfactory dysfunction by mediating neuronal death in the olfactory bulb (OB) of a murine model of Niemann–Pick disease type C1 (NPC1), a fatal neurodegenerative disorder accompanied by lipid trafficking defects. In this study, we focused on the crosstalk between neurons and microglia to elucidate the mechanisms underlying extensive microgliosis in the NPC1‐affected brain. Microglia in the OB of NPC1 mice strongly expressed CX3C chemokine receptor 1 (Cx3cr1), a specific receptor for the neural chemokine C‐X3‐C motif ligand 1 (Cx3cl1). In addition, a high level of Cx3cl1 was detected in NPC1 mouse‐derived CSF due to enhanced catalytic activity of Cathepsin S (Ctss), which is responsible for Cx3cl1 secretion. Notably, nasal delivery of Cx3cl1 neutralizing antibody or Ctss inhibitor could inhibit the Cx3cl1–Cx3cr1 interaction and support neuronal survival through the suppression of microglial activation, leading to an improvement in the olfactory function in NPC1 mice. Relevant in vitro experiments revealed that intracellular cholesterol accumulation could act as a strong inducer of abnormal Ctss activation and, in turn, stimulated the Cx3cl1–Cx3cr1 axis in microglia via p38 mitogen‐activated protein kinase signaling. Our data address the significance of Cx3cl1–Cx3cr1 interaction in the development of microglial neurotoxicity and suggest that Ctss is a key upstream regulator. Therefore, this study contributes to a better understanding of the crosstalk between neurons and microglia in the development of the neurodegeneration and provides a new perspective for the management of olfactory deficits and other microglia‐dependent neuropathies. GLIA 2016;64:2291–2305     

Reduced microglial CX3CR1 expression delays neurofibromatosis‐1 glioma formation

Although traditional models of carcinogenesis have largely focused on neoplastic cells, converging data have revealed the importance of non‐neoplastic stromal cells in influencing tumor growth and progression. Leveraging a genetically engineered mouse model of neurofibromatosis type 1 (NF1)‐associated optic glioma, we now demonstrate that stromal microglia express the CX3CR1 chemokine receptor, such that reduced CX3CR1 expression decreases optic nerve microglia. Moreover, genetic reduction of Cx3cr1 expression in Nf1 optic glioma mice delays optic glioma formation. Coupled with previous findings demonstrating that microglia maintain optic glioma growth, these new findings provide a strong preclinical rationale for the development of future stroma‐directed glioma therapies in children. ANN NEUROL 2013;73:303–308     

Resident microglia,rather than blood‐derived macrophages,contribute to the earlier and more pronounced inflammatory reaction in the immature compared with the adult hippocampus after hypoxia‐ischemia

The mechanisms of neuronal injury after hypoxia–ischemia (HI) are different in the immature and the adult brain, but microglia activation has not been compared. The purpose of this study was to phenotype resident microglia and blood‐derived macrophages in the hippocampus after HI in neonatal (postnatal day 9, P9) or adult (3 months of age, 3mo) mice. Unilateral brain injury after HI was induced in Cx3cr1^GFP/+Ccr2^RFP/+ male mice on P9 (n = 34) or at 3mo (n = 53) using the Vannucci model. Resident microglia (Cx3cr1‐GFP+) proliferated and were activated earlier after HI in the P9 (1–3 days) than that in the 3mo hippocampus, but remained longer in the adult brain (3–7 days). Blood‐derived macrophages (Ccr2‐RFP+) peaked 3 days after HI in both immature (P9) and adult (3mo) hippocampi but were twice as frequent in adult brains, 41% vs. 21% of all microglia/macrophages. CCL2 expression was three times higher in the P9 hippocampi, indicating that the proinflammatory response was more pronounced in the immature brain after HI. This corresponded well with the higher numbers of galectin‐3‐positive resident microglia in the P9 hippocampi, but did not correlate with CD16/32‐ or CD206‐positive resident microglia or blood‐derived macrophages. In conclusion, resident microglia, rather than infiltrating blood‐derived macrophages, proliferate and are activated earlier in the immature than in the adult brain, but remain increased longer in the adult brain. The inflammatory response is more pronounced in the immature brain, and this correlate well with galectin‐3 expression in resident microglia. GLIA 2015;63:2220–2230     

CX3CR1 deficiency induces an early protective inflammatory environment in ischemic mice

The studies on fractalkine and its unique receptor CX3CR1 in neurological disorders yielded contrasting results. We have explored the consequences of CX3CR1 deletion in ischemic (30′ MCAo) mice on: (1) brain infarct size; (2) microglia dynamism and morphology; (3) expression of markers of microglia/macrophages (M/M) activation and polarization. We observed smaller infarcts in cx3cr1^?/? (26.42 ± 7.41 mm³, mean ± sd) compared to wild type (36.29 ± 11.57) and cx3cr1^?/+ (34.49 ± 8.91) mice. We longitudinally analyzed microglia by in vivo two‐photon microscopy before, 1 and 24 h after transient ischemia. Microglia were stationary in both cx3cr1^?/? and cx3cr1^?/+ mice throughout the study. In cx3cr1^?/? mice, they displayed a significantly higher number of ramifications >10 μm at baseline and at 24 h after ischemia compared to cx3cr1^?/+ mice, indicating that CX3CR1 deficiency impaired the development of microglia hypertrophic/amoeboid morphology. At 24 h after ischemia, we performed post mortem quantitative immunohistochemistry for different M/M markers. In cx3cr1^?/? immunoreactivity for CD11b (M/M activation) and for CD68 (associated with phagocytosis) were decreased, while that for CD45^high (macrophage and leukocyte recruitment) was increased. In addition, immunoreactivity for Ym1 (M2 polarization) was enhanced, while that for iNOS (M1) was decreased. Our data show that in cx3cr1^?/? mice protection from ischemia at early time points after injury is associated with a protective inflammatory milieu, characterized by the promotion of M2 polarization markers.     

Glycogen synthase kinase‐3β phosphorylates synphilin‐1 in vitro

α‐Synuclein is known to be a major component of Lewy bodies and glial cytoplasmic inclusions in the brains of patients with α‐synucleinopathies. Synphilin‐1, an α‐synuclein‐associated protein, is also present in these inclusions. However, little is known about the post‐translational modifications of synphilin‐1. In the present study, it is reported that synphilin‐1 is phosphorylated by glycogen synthase kinase‐3βin vitro. It is well known that protein phosphorylation is involved in various physiological phenomena, including signal transduction and protein degradation. Therefore, phosphorylation of synphilin‐1 may play an important role in the function of this protein in the brain.     

Microglial phagocytosis and activation underlying photoreceptor degeneration is regulated by CX3CL1‐CX3CR1 signaling in a mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP), a disease characterized by the progressive degeneration of mutation‐bearing photoreceptors, is a significant cause of incurable blindness in the young worldwide. Recent studies have found that activated retinal microglia contribute to photoreceptor demise via phagocytosis and proinflammatory factor production, however mechanisms regulating these contributions are not well‐defined. In this study, we investigate the role of CX3CR1, a microglia‐specific receptor, in regulating microglia‐mediated degeneration using the well‐established rd10 mouse model of RP. We found that in CX3CR1‐deficient (CX3CR1^GFP/GFP) rd10 mice microglial infiltration into the photoreceptor layer was significantly augmented and associated with accelerated photoreceptor apoptosis and atrophy compared with CX3CR1‐sufficient (CX3CR1^GFP/+) rd10 littermates. CX3CR1‐deficient microglia demonstrated increased phagocytosis as evidenced by (1) having increased numbers of phagosomes in vivo, (2) an increased rate of phagocytosis of fluorescent beads and photoreceptor cellular debris in vitro, and (3) increased photoreceptor phagocytosis dynamics on live cell imaging in retinal explants, indicating that CX3CR1 signaling in microglia regulates the phagocytic clearance of at‐risk photoreceptors. We also found that CX3CR1 deficiency in retinal microglia was associated with increased expression of inflammatory cytokines and microglial activation markers. Significantly, increasing CX3CL1‐CX3CR1 signaling in the rd10 retina via exogenous intravitreal delivery of recombinant CX3CL1 was effective in (1) decreasing microglial infiltration, phagocytosis and activation, and (2) improving structural and functional features of photoreceptor degeneration. These results indicate that CX3CL1‐CX3CR1 signaling is a molecular mechanism capable of modulating microglial‐mediated degeneration and represents a potential molecular target in therapeutic approaches to RP. GLIA 2016;64:1479–1491     

Mapping and kinetics of microglia/neuron cell‐to‐cell contacts in the 6‐OHDA murine model of Parkinson's disease

As neuroinflammatory processes are involved in the pathogenesis of Parkinson's disease (PD), we provide several key data describing the time‐course of microglial accumulation in relation with behavioral alterations and neurodegeneration in a murine model of PD induced by intrastriatal injection of 6‐hydroxydopamine (6‐OHDA). Our study argues for a major role of microglia which accumulation is somehow early and transient in spite of the neuronal loss progression. Moreover, we observed less 6‐OHDA‐induced neurodegeneration associated with less inflammatory reaction in DAP‐12 Knock‐In mice. The direct cell‐to‐cell contacts that may support physical interactions between microglia and altered dopaminergic neurons are ill‐defined, while it is currently hypothesized that microglia support an immune‐mediated amplification of neurodegeneration by establishing a molecular cross talk with neurons. Indeed, we sought to map microglia/neuron appositions in substantia nigra (SN) of 6‐OHDA injected C57Bl/6 mice and CX3CR1/^GFP/+ mice. Confocal immunofluorescence analyses followed by 3D reconstitutions reveal close appositions between the soma of TH+ neurons and microglial cell bodies and ramifications. Interestingly, some microglial ramifications penetrated TH⁺ somas and about 40% of GFP⁺ microglial cells in the injured SN harbored TH⁺ intracytoplasmic inclusions. These results suggest a direct cross talk between neurons and microglia that may exert a microphagocytic activity toward TH+ neurons. Altogether, these results obtained in a murine PD model may participate in the understanding of microglial cells' function in neurodegenerative diseases. GLIA 2013;61:1645–1658     

Common polymorphisms of chemokine (C‐X3‐C motif) receptor 1 gene modify amyotrophic lateral sclerosis outcome: A population‐based study

Introduction: In the brain, the chemokine (C‐X3‐C motif) receptor 1 (1CX3CR1) gene is expressed only by microglia, where it acts as a key mediator of the neuron–microglia interactions. We assessed whether the 2 common polymorphisms of the CX3CR1 gene (V249I and T280M) modify amyotrophic lateral sclerosis (ALS) phenotype. Methods: The study included 755 ALS patients diagnosed in Piemonte between 2007 and 2012 and 369 age‐matched and sex‐matched controls, all genotyped with the same chips. Results: Neither of the variants was associated with an increased risk of ALS. Patients with the V249I V/V genotype had a 6‐month‐shorter survival than those with I/I or V/I genotypes (dominant model, P = 0.018). The T280M genotype showed a significant difference among the 3 genotypes (additive model, P = 0.036). Cox multivariable analysis confirmed these findings. Discussion: We found that common variants of the CX3CR1 gene influence ALS survival. Our data provide further evidence for the role of neuroinflammation in ALS. Muscle Nerve 57 : 212–216, 2018     

α‐Synuclein activates innate immunity but suppresses interferon‐γ expression in murine astrocytes

Glial activation and neuroinflammation contribute to pathogenesis of neurodegenerative diseases, linked to neuron loss and dysfunction. α‐Synuclein (α‐syn), as a metabolite of neuron, can induce microglia activation to trigger innate immune response. However, whether α‐syn, as well as its mutants (A53T, A30P, and E46K), induces astrocyte activation and inflammatory response is not fully elucidated. In this study, we used A53T mutant and wild‐type α‐syns to stimulate primary astrocytes in dose‐ and time‐dependent manners (0.5, 2, 8, and 20 μg/ml for 24 hr or 3, 12, 24, and 48 hr at 2 μg/ml), and evaluated activation of several canonical inflammatory pathway components. The results showed that A53T mutant or wild‐type α‐syn significantly upregulated mRNA expression of toll‐like receptor (TLR)2, TLR3, nuclear factor‐κB and interleukin (IL)‐1β, displaying a pattern of positive dose–effect correlation or negative time–effect correlation. Such upregulation was confirmed at protein levels of TLR2 (at 20 μg/ml), TLR3 (at most doses), and IL‐1β (at 3 hr) by western blotting. Blockage of TLR2 other than TLR4 inhibited TLR3 and IL‐1β mRNA expressions. By contrast, interferon (IFN)‐γ was significantly downregulated at mRNA, protein, and protein release levels, especially at high concentrations of α‐syns or early time‐points. These findings indicate that α‐syn was a TLRs‐mediated immunogenic agent (A53T mutant stronger than wild‐type α‐syn). The stimulation patterns suggest that persistent release and accumulation of α‐syn is required for the maintenance of innate immunity activation, and IFN‐γ expression inhibition by α‐syn suggests a novel immune molecule interaction mechanism underlying pathogenesis of neurodegenerative diseases.     

Anti‐inflammatory effects of pioglitazone on iron‐induced oxidative injury in the nigrostriatal dopaminergic system

H. C. Yu, S. F. Feng, P. L. Chao and A. M. Y. Lin (2010) Neuropathology and Applied Neurobiology 36, 612–622
Anti‐inflammatory effects of pioglitazone on iron‐induced oxidative injury in the nigrostriatal dopaminergic system Aims: Transition metals, oxidative stress and neuroinflammation have been proposed as part of a vicious cycle in central nervous system neurodegeneration. Our aim was to study the anti‐inflammatory effect of pioglitazone, a peroxisome proliferative activated receptor‐γ agonist, on iron‐induced oxidative injury in rat brain. Methods: Intranigral infusion of ferrous citrate (iron) was performed on anaesthetized rats. Pioglitazone (20 mg/kg) was orally administered. Oxidative injury was investigated by measuring lipid peroxidation in the substantia nigra (SN) and dopamine content in the striatum. Western blot assay and DNA fragmentation were employed to study the involvement of α‐synuclein aggregation, neuroinflammation as well as activation of endoplasmic reticulum (ER) and mitochondrial pathways in iron‐induced apoptosis. Results: Intranigral infusion of iron time‐dependently increased α‐synuclein aggregation and haem oxygenase‐1 levels. Furthermore, apoptosis was demonstrated by TUNEL‐positive cells and DNA fragmentation in the iron‐infused SN. Systemic pioglitazone was found to potentiate iron‐induced elevation in nuclear peroxisome proliferative activated receptor‐γ levels. However, pioglitazone inhibited iron‐induced α‐synuclein aggregation, elevations in interleukin‐1β and interleukin‐6 mRNA levels as well as increases in oxygenase‐1, cyclo‐oxygenase II, nitric oxide synthase and ED‐1 protein levels, an indicator of activated microglia. Moreover, iron‐induced DNA laddering as well as activation of ER and mitochondrial pathways were attenuated by pioglitazone. In addition, pioglitazone decreased iron‐induced elevation in lipid peroxidation in the infused SN and depletion in striatal dopamine level. Conclusions: Our results suggest that pioglitazone prevents iron‐induced apoptosis via both ER and mitochondrial pathways. Furthermore, inhibition of α‐synuclein aggregation and neuroinflammation may contribute to the pioglitazone‐induced neuroprotection in central nervous system.     

Cerebrospinal fluid Tau/α‐synuclein ratio in Parkinson's disease and degenerative dementias

Although alpha‐synuclein is the main constituent of Lewy bodies, cerebrospinal fluid determination on its own does not seem fundamental for the diagnosis of synucleinopathies. We evaluated whether the combination of classical biomarkers, Aβ_1–42, total tau, phosphorylated tau, and α‐synuclein can improve discrimination of Parkinson's disease, dementia with Lewy bodies, Alzheimer's disease, and frontotemporal dementia. Aβ_1–42, total tau, phosphorylated tau, and α‐synuclein were measured in a series of patients with Parkinson's disease (n = 38), dementia with Lewy bodies (n = 32), Alzheimer's disease (n = 48), frontotemporal dementia (n = 31), and age‐matched control patients with other neurological diseases (n = 32). Mean α‐synuclein levels in cerebrospinal fluid were significantly lower in the pathological groups than in cognitively healthy subjects. An inverse correlation of α‐synuclein with total tau (r = ?0.196, P < .01) was observed. In the group of patients with Parkinson's disease, Aβ_1–42, total tau, and phosphorylated tau values were similar to controls, whereas total tau/α‐synuclein and phosphorylated tau/α‐synuclein ratios showed the lowest values. Cerebrospinal fluid α‐synuclein alone did not provide relevant information for Parkinson's disease diagnosis, showing low specificity (area under the curve, 0.662; sensitivity, 94%; specificity, 25%). Instead, a better performance was obtained with the total tau/α‐syn ratio (area under the curve, 0.765; sensitivity, 89%; specificity, 61%). Combined determination of α‐synuclein and classical biomarkers in cerebrospinal fluid shows differential patterns in neurodegenerative disorders. In particular, total tau/α‐synuclein and phosphorylated tau/α‐synuclein ratios can contribute to the discrimination of Parkinson's disease. © 2011 Movement Disorder Society     

Microglia replenished OHSC: A culture system to study in vivo like adult microglia

Recent data suggest that ramified microglia fulfil various tasks in the brain. However, to investigate this unique cell type cultured primary microglia are only a poor model. We here describe a method to deplete and repopulate organotypic hippocampal slice cultures (OHSC) with ramified microglia isolated from adult mouse brain creating microglia‐replenished OHSC (Mrep‐OHSC). Replenished microglia integrate into the tissue and ramify to a degree indistinguishable from their counterparts in the mouse brain. Moreover, wild‐type slices replenished with microglia from TNFα‐deficient animals provide similar results as OHSC prepared from microglia‐specific TNFα‐knockout mice (CX3CR1^cre/TNFα^fl/fl). Furthermore, this study demonstrates that replenished microglia in OHSC maintain original functions and properties acquired in vivo. Microglia from ERCC1^Δ/ko mice, a mouse model of accelerated aging, maintain enhanced Mac2 expression and their activated phenotype after replenishment to wild‐type OHSC tissue. Thus, the present study demonstrates that Mrep‐OHSC are a unique tool to construct chimeric brain slices allowing studying the function of different phenotypes of in vivo like microglia in a tissue culture setting. GLIA 2016 GLIA 2016;64:1285–1297     

Randomized,placebo‐controlled trial of flax oil in pediatric bipolar disorder

Gracious BL, Chirieac MC, Costescu S, Finucane TL, Youngstrom EA, Hibbeln JR. Randomized, placebo‐controlled trial of flax oil in pediatric bipolar disorder.
Bipolar Disord 2010: 12: 142–154. © 2010 The Authors.
Journal compilation © 2010 John Wiley & Sons A/S. Objectives: This clinical trial evaluated whether supplementation with flax oil, containing the omega‐3 fatty acid α‐linolenic acid (α‐LNA), safely reduced symptom severity in youth with bipolar disorder. Methods: Children and adolescents aged 6–17 years with symptomatic bipolar I or bipolar II disorder (n = 51), manic, hypomanic, mixed, or depressed, were randomized to either flax oil capsules containing 550 mg α‐LNA per 1 gram or an olive oil placebo adjunctively or as monotherapy. Doses were titrated to 12 capsules per day as tolerated over 16 weeks. Primary outcomes included changes in the Young Mania Rating Scale, Child Depression Rating Scale‐Revised, and Clinical Global Impressions‐Bipolar ratings using Kaplan‐Meier survival analyses. Results: There were no significant differences in primary outcome measures when compared by treatment assignment. However, clinician‐rated Global Symptom Severity was negatively correlated with final serum omega‐3 fatty acid compositions: %α‐LNA (r = ?0.45, p < 0.007), % eicosapentaenoic acid (EPA) (r = ?0.47, p < 0.005); and positively correlated with final arachidonic acid (AA) (r = 0.36, p < 0.05) and docosapentaenoic acid (DPA) n‐6 (r = 0.48, p < 0.004). The mean duration of treatment for α‐LNA was 11.8 weeks versus 8 weeks for placebo; however, the longer treatment duration for α‐LNA was not significant after controlling for baseline variables. Subjects discontinued the study for continued depressive symptoms. Conclusions: Studies of essential fatty acid supplementation are feasible and well tolerated in the pediatric population. Although flax oil may decrease severity of illness in children and adolescents with bipolar disorder who have meaningful increases in serum EPA percent levels and/or decreased AA and DPA n‐6 levels, individual variations in conversion of α‐LNA to EPA and docosahexaenoic acid as well as dosing burden favor the use of fish oil both for clinical trials and clinical practice. Additionally, future research should focus on adherence and analysis of outcome based on changes in essential fatty acid tissue compositions, as opposed to group randomization alone.     

Systemic exosomal siRNA delivery reduced alpha‐synuclein aggregates in brains of transgenic mice

Alpha‐synuclein (α‐Syn) aggregates are the main component of Lewy bodies, which are the characteristic pathological feature in Parkinson's disease (PD) brain. Evidence that α‐Syn aggregation can be propagated between neurones has led to the suggestion that this mechanism is responsible for the stepwise progression of PD pathology. Decreasing α‐Syn expression is predicted to attenuate this process and is thus an attractive approach to delay or halt PD progression. We have used α‐Syn small interfering RNA (siRNA) to reduce total and aggregated α‐Syn levels in mouse brains. To achieve widespread delivery of siRNAs to the brain we have peripherally injected modified exosomes expressing Ravies virus glycoprotein loaded with siRNA. Normal mice were analyzed 3 or 7 days after injection. To evaluate whether this approach can decrease α‐Syn aggregates, we repeated the treatment using transgenic mice expressing the human phosphorylation‐mimic S129D α‐Syn, which exhibits aggregation. In normal mice we detected significantly reduced α‐Syn messenger RNA (mRNA) and protein levels throughout the brain 3 and 7 days after treatment with RVG‐exosomes loaded with siRNA to α‐Syn. In S129D α‐Syn transgenic mice we found a decreased α‐Syn mRNA and protein levels throughout the brain 7 days after injection. This resulted in significant reductions in intraneuronal protein aggregates, including in dopaminergic neurones of the substantia nigra. This study highlights the therapeutic potential of RVG‐exosome delivery of siRNA to delay and reverse brain α‐Syn pathological conditions. © 2014 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.     

Engineering synucleinopathy‐resistant human dopaminergic neurons by CRISPR‐mediated deletion of the SNCA gene

An emerging treatment for Parkinson's disease (PD) is cell replacement therapy. Authentic midbrain dopaminergic (mDA) neuronal precursors can be differentiated from human embryonic stem cells (hESCs) and human induced pluripotent stem cells (iPSCs). These laboratory‐generated mDA cells have been demonstrated to mature into functional dopaminergic neurons upon transplantation into preclinical models of PD. However, clinical trials with human fetal mesenchephalic cells have shown that cell replacement grafts in PD are susceptible to Lewy body formation suggesting host‐to‐graft transfer of α‐synuclein pathology. Here, we have used CRISPR/Cas9n technology to delete the endogenous SNCA gene, encoding for α‐synuclein, in a clinical‐grade hESC line to generate SNCA^+/? and SNCA^?/? cell lines. These hESC lines were first differentiated into mDA neurons, and then challenged with recombinant α‐synuclein preformed fibrils (PFFs) to seed the formation for Lewy‐like pathology as measured by phosphorylation of serine‐129 of α‐synuclein (pS129‐αSyn). Wild‐type neurons were fully susceptible to the formation of protein aggregates positive for pS129‐αSyn, while SNCA^+/? and SNCA^?/? neurons exhibited significant resistance to the formation of this pathological mark. This work demonstrates that reducing or completely removing SNCA alleles by CRISPR/Cas9n‐mediated gene editing confers a measure of resistance to Lewy pathology.     

CX3CR1 Disruption Differentially Influences Dopaminergic Neuron Degeneration in Parkinsonian Mice Depending on the Neurotoxin and Route of Administration

Parkinson’s disease (PD) is characterized by progressive degeneration of dopaminergic neurons accompanied by an inflammatory reaction. The neuron-derived chemokine fractalkine (CX3CL1) is an exclusive ligand for the receptor CX3CR1 expressed on microglia. The CX3CL1/CX3CR1 signaling is important for sustaining microglial activity. Using a recently developed PD model, in which the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxin is delivered intranasally, we hypothesized that CX3CR1 could play a role in neurotoxicity and glial activation. For this, we used CX3CR1 knock-in mice and compared results with those obtained using the classical PD models through intraperitonal MPTP or intrastriatal 6-hydroxydopamine (6-OHDA). The striatum from all genotypes (CX3CR1^+/+, CX3CR1^+/GFP and CX3CR1-deficient mice) showed a significant dopaminergic depletion after intranasal MPTP inoculation. In contrast to that, we could not see differences in the number of dopaminergic neurons in the substantia nigra of CX3CR1-deficient animals. Similarly, after 6-OHDA infusion, the CX3CR1 deletion decreased the amphetamine-induced turning behavior observed in CX3CR1^+/GFP mice. After the 6-OHDA inoculation, a minor dopaminergic neuronal loss was observed in the substantia nigra from CX3CR1-deficient mice. Distinctly, a more extensive neuronal cell loss was observed in the substantia nigra after the intraperitoneal MPTP injection in CX3CR1 disrupted animals, corroborating previous results. Intranasal and intraperitoneal MPTP inoculation induced a similar microgliosis in CX3CR1-deficient mice but a dissimilar change in the astrocyte proliferation in the substantia nigra. Nigral astrocyte proliferation was observed only after intraperitoneal MPTP inoculation. In conclusion, intranasal MPTP and 6-OHDA lesion in CX3CR1-deficient mice yield no nigral dopaminergic neuron loss, linked to the absence of astroglial proliferation.     

6‐hydroxydopamine‐induced Parkinson's disease‐like degeneration generates acute microgliosis and astrogliosis in the nigrostriatal system but no bioluminescence imaging‐detectable alteration in adult neurogenesis

Parkinson's disease is a slowly progressing neurodegenerative disorder caused by loss of dopaminergic neurons in the substantia nigra (SN), leading to severe impairment in motor and non‐motor functions. Endogenous subventricular zone (SVZ) neural stem cells constantly give birth to new cells that might serve as a possible source for regeneration in the adult brain. However, neurodegeneration is accompanied by neuroinflammation and dopamine depletion, potentially compromising regeneration. We therefore employed in vivo imaging methods to study striatal deafferentation (N‐ω‐fluoropropyl‐2β‐carbomethoxy‐3β‐(4‐[¹²³I]iodophenyl)nortropane single photon emission computed tomography, DaTscan^™) and neuroinflammation in the SN and striatum (N,N‐diethyl‐2‐(2‐(4‐(2‐[¹⁸F]fluoroethoxy)phenyl)‐5,7‐dimethylpyrazolo[1,5‐a]pyrimidin‐3‐yl)acetamide positron emission tomography, [¹⁸F]DPA‐714 PET) in the intranigral 6‐hydroxydopamine Parkinson's disease mouse model. Additionally, we transduced cells in the SVZ with a lentivirus encoding firefly luciferase and followed migration of progenitor cells in the SVZ–olfactory bulb axis via bioluminescence imaging under disease and control conditions. We found that activation of microglia in the SN is an acute process accompanying the degeneration of dopaminergic cell bodies in the SN. Dopaminergic deafferentation of the striatum does not influence the generation of doublecortin‐positive neuroblasts in the SVZ, but generates chronic astrogliosis in the nigrostriatal system.     

Alpha‐synuclein transfers from neurons to oligodendrocytes

The origin of α‐synuclein (α‐syn)‐positive glial cytoplasmic inclusions found in oligodendrocytes in multiple system atrophy (MSA) is enigmatic, given the fact that oligodendrocytes do not express α‐syn mRNA. Recently, neuron‐to‐neuron transfer of α‐syn was suggested to contribute to the pathogenesis of Parkinson's disease. In this study, we explored whether a similar transfer of α‐syn might occur from neurons to oligodendrocytes, which conceivably could explain how glial cytoplasmic inclusions are formed. We studied oligodendrocytes in vitro and in vivo and examined their ability to take up different α‐syn assemblies. First, we treated oligodendrocytes with monomeric, oligomeric, and fibrillar forms of α‐syn proteins and investigated whether α‐syn uptake is dynamin‐dependent. Second, we injected the same α‐syn species into the mouse cortex to assess their uptake in vivo. Finally, we monitored the presence of human α‐syn within rat oligodendroglial cells grafted in the striatum of hosts displaying Adeno‐Associated Virus‐mediated overexpression of human α‐syn in the nigro‐striatal pathway. Here , we show that oligodendrocytes take up recombinant α‐syn monomers, oligomers and, to a lesser extent, fibrils in vitro in a concentration and time‐dependent manner, and that this process is inhibited by dynasore. Further, we demonstrate in our injection model that oligodendrocytes also internalize α‐syn in vivo. Finally, we provide the first direct evidence that α‐syn can transfer to grafted oligodendroglial cells from host rat brain neurons overexpressing human α‐syn. Our findings support the hypothesis of a neuron‐to‐oligodendrocyte transfer of α‐syn, a mechanism that may play a crucial role in the progression and pathogenesis of MSA. GLIA 2014;62:387–398