- Open Access
Brain region-specific enhancement of remyelination and prevention of demyelination by the CSF1R kinase inhibitor BLZ945
© The Author(s). 2018
- Received: 26 January 2018
- Accepted: 26 January 2018
- Published: 15 February 2018
Multiple sclerosis (MS) is a chronic inflammatory disease affecting the central nervous system (CNS). While multiple effective immunomodulatory therapies for MS exist today, they lack the scope of promoting CNS repair, in particular remyelination. Microglia play a pivotal role in regulating myelination processes, and the colony-stimulating factor 1 (CSF-1) pathway is a key regulator for microglia differentiation and survival. Here, we investigated the effects of the CSF-1 receptor kinase inhibitor, BLZ945, on central myelination processes in the 5-week murine cuprizone model by non-invasive and longitudinal magnetic resonance imaging (MRI) and histology. Therapeutic 2-week BLZ945 treatment caused a brain region-specific enhancement of remyelination in the striatum/cortex, which was absent in the corpus callosum/external capsule. This beneficial effect correlated positively with microglia reduction, increased oligodendrocytes and astrogliosis. Prophylactic BLZ945 treatment prevented excessive demyelination in the corpus callosum by reducing microglia and increasing oligondendrocytes. In the external capsule oligodendrocytes were depleted but not microglia and a buildup of myelin debris and axonal damage was observed. A similar microglial dysfunction in the external capsule with an increase of myelin debris was obvious in triggering receptor expressed on myeloid cells 2 (TREM2) knock-out mice treated with cuprizone. Finally, therapeutic BLZ945 treatment did not change the disease course in experimental autoimmune encephalomyelitis mice, a peripherally driven neuroinflammation model. Taken together, our data suggest that a short-term therapeutic inhibition of the CSF-1 receptor pathway by BLZ945 in the murine cuprizone model enhances central remyelination by modulating neuroinflammation. Thus, microglia-modulating therapies could be considered clinically for promoting myelination in combination with standard-of-care treatments in MS patients.
- Multiple sclerosis
- CSF1R kinase
Multiple sclerosis (MS) is a chronic immune-mediated multifocal demyelinating disease of the central nervous system (CNS) with progressive neurodegeneration. The pathology is believed to be mainly driven by the adaptive immune-system and/or autoimmune mechanisms that damage neurons and oligodendrocytes (ODs) in the CNS leading to white and grey matter degeneration. The relevance of the innate immunity of the CNS in disease initiation and progression has not been extensively investigated. Activated microglia and astrocyte together with neurodegeneration has been observed in MS patients and this neuroinflammatory condition is believed to play an important role in the grey matter damage (for review see [3, 35]). Although white matter lesions are the classical hallmarks of MS, the demyelinating events observed in the grey matter might have a more profound contribution to the permanent neurological dysfunction than assumed. Available treatments for MS primarily address the peripheral inflammation and help relapsing-remitting MS patients to gain normal neurological function again. However, a substantial number of MS patients suffer from irreversible progression of clinical disability. The progressive phase of MS is believed to be the consequence of altered central function of microglia, astrocytes and ODs. In this neuroinflammatory milieu ODs and oligodendrocyte precursor cells (OPCs) seem not to be able to exert their proper function anymore, mainly remyelination, and thus further demyelinating events in grey and white matter occur with subsequent axonal pathology. There is a high unmet medical need in MS patients to stop demyelination, enhance remyelination and prevent irreversible axonal pathology.
The cuprizone model is a toxin-induced demyelination model to study myelination processes in the CNS [22, 50, 57] without a major involvement of the peripheral immune system. The copper chelator cuprizone induces mitochondrial damage and the subsequent energy deficit in the highly energy-dependent ODs leads to apoptosis. OPCs are not affected by cuprizone intoxication and can readily proliferate and differentiate to produce new ODs with normal myelination efficiency. Thus, the cuprizone model is well suited to test regenerative treatment paradigms for MS that enhance remyelination independently of invading peripheral immune cells.
Microglia are the resident phagocytes of the brain that play an important role in modeling the CNS synaptic circuitry, keeping myelin homeostasis and removal of pathogens and cell debris (, for review see ). It has been shown that reduced neuroinflammation preserves axons  and that removal of myelin debris is essential to initiate repair by remyelination [4, 26, 40] in the cuprizone model.
The colony-stimulating factor 1 receptor (CSF1R) signaling pathway is essential for microglia survival [10, 11]. Several groups have shown that inhibition of the CSF1R pathway is neuroprotective in different disease conditions like amyotrophic lateral sclerosis , Charcot-Marie-Tooth type 1 neuropathies , catatonia in psychiatric disorders  and Alzheimer’s disease [29, 36, 48] by reducing neuroinflammation/inflammation. Here, we investigated the involvement of microglia in the de- and re-myelination processes in the murine cuprizone model. Mice were treated prophylactically and therapeutically with the CSF1R kinase inhibitor, BLZ945 [25, 41], to investigate the consequences of microglia depletion on de- and re-myelination events. Magnetic resonance imaging (MRI) was used to monitor in vivo the effects of cuprizone in several brain regions. Specifically, changes in magnetization transfer ratio (MTR) and signal intensity were used as markers of alteration in myelin levels induced by cuprizone, as confirmed by post-mortem histological analyses and in agreement with earlier work [12, 31, 49, 51, 56]. In both treatment paradigms BLZ945 enhanced myelination in certain brain regions, thus opening a new way for a novel therapy in treating myelination deficiencies in MS.
Studies described in this report were approved by the Swiss Cantonal Veterinary Authority of Basel City, Switzerland, under the license numbers 2711 and 2119.
Mice (C57BL/6 J and C57BL/6 J OlaHsd) were commercially purchased from Charles River Laboratories (Sulzfeld, Germany), Harlan Laboratories BV (Horst, The Netherlands) or obtained from Novartis Pharma AG breeding colonies (8–9 weeks old, females). TREM2 knock-out mice were purchased from UCDavis KOMP Repository (Project ID VG10093) and were then bred at Novartis Pharma AG. Genotyping of TREM2 KO mice was performed according to the provided method. All the animals were allowed to adapt for 7 days prior to the start of the experiment and housed in IVC racks (max. 4 mice/XJ Type cage). The animals were given access to food and water ad libitum. Before killing animals were perfused trans-cardiac by phosphate-buffered saline (PBS) and then with 4% paraformaldehyde (PFA). The brains were subsequently isolated and fixed in 4% PFA for 48 h at 4 °C.
Animals were treated with cuprizone for 5 weeks. Cuprizone (Bis(cyclohexanone) oxaldihydrazone, Sigma-Aldrich, Buchs, Switzerland) was mixed into rodent food pellets (0.2% w/w) by Provimi Kliba AG (Kaiseraugst, Switzerland). Animals were treated with 169, 127, 100, 85, 60, 20 and 7 mg/kg of BLZ945, once per day (qd), per os (p.o.) 10 ml/kg. BLZ945 was prepared in 0.5% methylcellulose in water and 0.1% Tween-80.
Magnetic resonance imaging (MRI)
Measurements were performed with a Biospec 70/30 spectrometer (Bruker Medical Systems, Ettlingen, Germany) operating at 7 T. The operational software of the scanner was Paravision 5.1 (Bruker). Images were acquired from anesthetized, spontaneously breathing animals using a mouse brain circularly polarized coil (Bruker, Model 1P T20063 V3; internal diameter 23 mm) for radiofrequency excitation and detection. Neither cardiac nor respiratory triggering was applied. Following a short period of introduction in a box, animals were maintained in anesthesia with 1.5% isoflurane (Abbott, Cham, Switzerland) in oxygen, administered via a nose cone. During MRI signal acquisitions, animals were placed in prone position in a cradle made of Plexiglas, the body temperature was kept at 37 ± 1 °C using a heating pad, and the respiration was monitored.
A T2-weighted, two-dimensional multislice RARE (Rapid Acquisition with Relaxation Enhancement) sequence  was used for determining the anatomical orientation and for evaluating signal intensities. This was followed by a two-dimensional multislice gradient-recalled FLASH (Fast Low-Angle Shot) acquisition  for assessment of MTR. As both sequences had the same anatomical parameters, the choice of the regions-of-interest for evaluations was performed on the RARE images and then transferred to the FLASH images. MRI images were analyzed using the ParaVision software.
The parameters of the acquisitions were the following: (a) RARE sequence: effective echo time 80 milliseconds (ms), repetition time 3280 ms, RARE factor 16, 12 averages, field of view 20 × 18 mm2, matrix size 213 × 192, pixel size 0.094 × 0.094 mm2, slice thickness 0.5 mm, 15 adjacent slices. Hermite pulses of duration/bandwidth 1 ms/5400 Hz and 0.64 ms/5344 Hz were used for radiofrequency excitation and refocusing, respectively. Fat suppression was achieved by a gauss512 pulse of 2.61 ms/1051 Hz duration/bandwidth followed by a 2-ms-long gradient spoiler. The total acquisition time was of 7 min 52.3 s; (b) FLASH sequence: echo time 2.8 ms, repetition time 252.8 ms, 4 averages, field of view 20 × 18 mm2, matrix size 213 × 192, pixel size 0.094 × 0.094 mm2, slice thickness 0.5 mm, 15 adjacent slices. A hermite pulse of 0.9 ms/6000 Hz duration/bandwidth and flipangle 30° was used for radiofrequency excitation. MTR contrast was introduced by a gauss pulse of 15 ms/182.7 Hz duration/bandwidth applied with radiofrequency peak amplitude of 7.5 μT and an irradiation offset of 2500 Hz. The acquisition was then repeated with the same parameters but without the introduction of the MTR contrast. MTR was then computed using the formula MTR = (S0-SMTR)/S0 where S0 and SMTR represent respectively the signal intensities in the FLASH acquisitions without and with the introduction of the MTR contrast. The total acquisition time for both data sets was 6 min 31.6 s.
Quantitative determination of BLZ945 in blood and brain
Sample preparation and analysis was based on a modified protein precipitation procedure followed by liquid chromatographic separation coupled with mass spectrometry for detection. Cerebella were homogenized in a gentleMACS™ Dissociator (Milteniy Biotec, # 130-093-235) by adding 20% CH3OH to a final concentration of 0.20 g/mL. Blood-EDTA samples were directly used for further preparation. Calibration, quality control, and recovery control samples were prepared by spiking blank blood and blank brain homogenate with known quantities of BLZ945 (between 0.02 and 62.5 μg/mL). For analyte determination, Labetalol hydrochloride (Sigma-Aldrich, #L1011) was used as generic internal standard (IS). Aliquots of 10 μL calibration standard, quality control, recovery control, and unknown samples were transferred to 0.75 ml 96- well- Loborack (Vitaris AG, # 51004 BC -MIC) and 3 μL IS mixture (2.5 μg/mL in 50% CH3CN) was added to each tube. For protein precipitation and extraction from the blood and brain matrix, 200 μl CH3CN was added. After vortexing for 10 min, the samples were centrifuged at 3220 g for 15 min at 4 °C. 50 μl of the upper layer was transferred to a 1.2 mL 96 deep well plate (Thermo Scientific, # AB-0787).
LC–MS–MS analysis: For quantitative analysis, a 1.5 μl aliquot of each sample, including calibration, quality control, and recovery control samples were injected with a cooled Waters™ Acquity Urbinary sample manager and HPLC system. The test article and its internal standard were separated with an ACE C18-PFP (50 × 2.1 mm ID, 3.0 μm pore size; # ACE-1110-0502) as column at 40 °C. For separation a linear gradient from 5 to 65% B in 1.7 min at a flow rate of 0.400 mL/min was applied. The total cycle time was 3.5 min. The mobile phase used was A: water with 0.1% formic acid, and B: CH3CN with 0.1% formic. For detection the column effluent was directly guided in a AB Sciex API5500 Triple quad mass spectrometer equipped with a TurboIonSpray™ interface. The detection was done in MRM positive ion mode. Quantification was based on the compound/IS ratio of the extracted ion chromatograms of the selected mass transitions 399 m/z → 242 m/z for BLZ945 and 329 m/z → 162 m/z for Labetalol (IS). The unknown sample concentration was calculated using external calibration curves. The LLOQ of the method was set to 20 ng/mL for blood, and 100 ng/mL for brain samples, and the recovery from the matrix was 95 ± 2%. All calculations were performed with AB Sciex Analyst software 1.6.2.
Histology of brains
After fixation brains were processed for paraffin embedding by dehydration through increasing ethanol series. Automated immunohistochemistry of paraffin sections was performed on 3 μm paraffin sections mounted on SuperFrost+ slides (Thermo Fisher Scientific) and automatically immunostained using the Discovery XT technology (Ventana, Roche Diagnostics). Sections were deparaffinized, rehydrated, subjected to antigen retrieval by heating with CC1 cell conditioning buffer for 28–68 min according to the antibody, incubated for 1–3 h according to the antibody at room temperature with primary antibody diluted in antibody diluent (Ventana), incubated with the respective biotinylated secondary antibody diluted in antibody diluent, reacted with DABMab kit and counterstained with Hematoxylin II and Bluing reagent (Ventana). Slides were washed with soap in hot tap water and rinsed under cold running tap water to remove the soap, then dehydrated and embedded with Pertex.
For LFB staining, slides were deparaffinized and rehydrated to 95% ethanol. Slides were then incubated in LFB solution (Solvent Blue 38 (Sigma S3382) in 95% ethanol and 10% acetic acid (Sigma 695092)) overnight at 60 °C, rinsed in 95% ethanol for 1 min, then in distilled water for 2 min and in 0.05% lithium carbonate for 5 s. Subsequently, slides were rinsed in 70% ethanol twice for 10 s, then in distilled water for 2 min. The rinsing was repeated in 0.05% lithium carbonate (Merck 105680) prepared freshly, 70% ethanol and distilled water until there was a sharp contrast between the blue of the white matter (myelin) and the colorless grey-matter. Finally, slides were dehydrated starting with 95% ethanol and mounted in Pertex.
For Ki67 and Iba1 immunofluorescence co-staining, 5 μm-thick sections were de-paraffinized, rehydrated and subjected to antigen retrieval in 10 mM citrate buffer pH 6. After blocking with 10% normal donkey serum (NDS) in 1xTBS for 20 min, sections were incubated with monoclonal IgG rabbit anti-mouse ki67 antibody overnight at 4 °C. Sections were then washed twice in TBS and incubated for 30 min at RT with biotin donkey anti-rabbit IgG (H + L). After washing twice in TBS, slides were incubated with Streptavidin, Alexa Fluor™ 546 conjugate for 30 min at RT, washed again twice in TBS and blocked in 10% NDS for 20 min at RT. This was followed by incubation with goat anti-Iba1 antibody for 1 h at RT, washing steps in TBS and incubation with donkey anti-goat IgG Alexa Fluor™ 488 for 30 min at RT. After washing in TBS, nuclei were stained with DAPI (Thermo Fisher Scientific R37606) for 10 min at RT, washed and slides were mounted with MOWIOL 4–88 Reagent solution (Merck, 475904).
Histology on the spinal cord
Lumbar spinal cord (L1-L3 spinal segments) samples were carefully dissected with the corresponding vertebrae and fixed in 10% neutral buffered formalin (Sigma-Aldrich, HT501128) for 48 h. Tissues were then transferred to decalcifying reagent Immunocal® (StatLab, 1414-32; StatLab Medical Products) for 96 h. Dehydration and paraffin infiltration were performed on a Tissue-Tek VIP 6 Vacuum Infiltration Processor (Sakura Finetek Europe). Following paraffin embedding, 5 μm-thick sections of spinal cord samples were cut and stained with Iba1 antibody, as described for brain sections.
Primary antibodies are: rabbit anti-mouse MBP (Dako A0623) 1:1000; rabbit anti-mouse GST-π (MBL 312) 1:500; Rabbit anti-Iba1 (Wako 019–19741, 50 μg/100 μl) 1:500; rabbit anti-GFAP (Dako Z0334) 1:5000; rabbit anti-mouse MOG (abcam ab32760) 1:100; rabbit anti-dMBP (Millipore AB5864) 1:3000; mouse anti-Neurofilament (Covance SMI312) 1:5000; rabbit anti-mouse ALDH1L1 (abcam ab87117) 1:1000; rabbit anti-mouse NeuN (Millipore ABN78) 1:2000; rat anti-mouse CD107a (Biorad MCA4707T) 1:200; rabbit anti-mouse NG2 (abcam ab129051) 1:200; rabbit anti-mouse ki67 (abcam ab16667, clone SP6) 1:100; goat anti-Iba1 (Thermo Fisher Scientific PA5–18039) 1:250.
Secondary detection antibodies are: Goat anti-rabbit IgG biotinylated (Jackson ImmunoResearch 111–065-144) 1:1000; Goat anti-rabbit IgG biotinylated (Vector BA-1000) 1:200 or 1:1000; Goat anti-mouse IgG biotinylated (Vector BA-9200) 1:1000; Goat anti-rat biotinylated (Vector BA-9400) 1:200; donkey anti-rabbit IgG (Jackson ImmunoResearch 711–065-152) 1:200; Streptavidin, Alexa Fluor™ 546 conjugate (Thermo Fisher Scientific S11225) 1:800; donkey anti-goat IgG Alexa Fluor™ 488 (Thermo Fisher Scientific A11055) 1:500.
Analysis of histological images
For the quantitative evaluation of microglia/astrocyte numbers and morphology based on image analysis from histological stained brain sections, a proprietary image analysis platform (ASTORIA, Automated Stored Image Analysis, Novartis Pharma AG) was developed based on MS Visual Studio 2010 and many functions from Matrox MIL V9 libraries (Matrox Inc).
For the detection and analysis of soma, proximal and distal processes, the following sequence of steps was performed (Additional file 1: Figure S14): 1. Slides with brain sections for assessment of (brown) immunohistochemically stained microglia (Iba1) or astrocyte (GFAP) soma and their proximal and distal processes were scanned with Aperio’s Scanscope (Leica Biosystems AG) at 20× magnification (Additional file 1: Figure S14A). 2. Each image was processed using the ImageScope software (V184.108.40.20629, Aperio, Leica Biosystems AG) according to the following steps: A: color deconvolution to obtain brown staining without blue; B: segmentation of brain tissue from white background through thresholding, morphological closing, filling of holes, opening and elimination of too small objects, resulting in a binary mask of the valid tissue and sample area; C: adaptive thresholding for the individual segmentation of soma, based on the average gray value of the blue channel of the color-deconvoluted brown image at sufficiently dark regions (indicative for soma). The computed threshold was used for binarization, and after size filtering yielded the soma mask image (within the valid sample region, Additional file 1: Figure S14B); D: segmentation of processes through morphological tophat transformation with a size to pick thin processes. Adaptive thresholding was applied again to segment the processes (using the previously determined gray average of brown objects), followed by binarization of the top hat image and size filtering of the resulting objects; E: subtraction of soma (that may also have been picked by top hat thresholding) to obtain an image mask of true processes (Additional file 1: Figure S14C); F: ultimate thinning of processes for length computation; G: proximal processes: A predefined number of dilations of soma was used to define a reference (marker) region for proximal soma, employing a circle around the soma center to define the cutoff boundary for proximal processes. Thinned proximal processes with marker in dilated soma and limited by circular influence zone (set of “proximal thinned processes”) were then reconstructed around the soma center. “Final proximal processes” were collected through reconstruction of all processes having markers in the “proximal thinned processes” set (Additional file 1: Figure S14D); H: soma was added to proximal processes to obtain a set of “visible microglia”; I: Distal processes: Reconstruction of processes from proximal processes only (i.e. ignoring those in background or from soma in different focus plane), then subtract circular region defining proximal processes, to yield set of distal processes (Additional file 1: Figure S14E); J: in the optical density computation for soma as well as “visible microglia” (individual soma+proximal processes complex within circular reference region, Additional file 1: Figure S14F), local background (non-visible microglia) was used for reference; K: morphometric features (size, form factor, length) were computed for soma, proximal and distal processes (Additional file 1: Figure S14G).
These image analysis algorithms were also used to quantify SMI312, dMBP, GST-π, MBP and NeuN stained sections according to the above description.
For MBP an alternative quantification with ImageJ analyzing IntDen (integrated density) with threshold was performed in addition to the one described above.
MOG peptide-induced experimental autoimmune encephalomyelitis (EAE)
Female C57BL/6 mice (Harlan, Itingen, Switzerland; n = 30) were immunized with a subcutaneous injection of rat myelin oligodendrocyte glycoprotein peptide (MOG1–125; in house produced; 200 μg/100 μl) emulsified in 4 mg/ml complete Freund adjuvant (CFA, Sigma-Aldrich) in the lower back. Pertussis toxin (200 ng per mouse; Sigma-Aldrich) was administered intraperitoneally on days 0 and 2.
Evaluation of EAE: The mice were observed and weighed daily. They were assessed for clinical signs on a scale from 0 to 5, with graduations of 0.5 for intermediate scores. 0: no clinical signs, 1: Limp tail/complete loss of tail tonus; 2: Clear hind limb weakness; 3: Complete bilateral hind limb paralysis; 4: Fore limbs and hind limbs paralysis; 5: Death. Supplementary food and gel food were provided inside the cage once first clinical signs appeared.
Lysing Matrix D tubes (MP Biomedicals, 116913500) were used for lysis of lumbar spinal cord (L4-L6 spinal segment) in 1 ml of TRIzol reagent (Thermo Fisher Scientific, 15596018). Total RNA was then isolated with TRIzol reagent according to the manufacturer’s instructions and a TURBO DNA-free™ Kit (Thermo Fisher Scientific, AM1907) was used for complete digestion of DNA.
RNA (500 ng) was reverse transcribed to cDNA using the High-Capacity RNA-to-cDNA™ Kit (Thermo Fisher Scientific, 4387406).
Quantitative PCR (qPCR) was carried out using 10 ng of cDNA per each sample and TaqMan® Universal PCR Master Mix (Thermo Fisher Scientific, 4324018). Gene-specific primers with FAM-labeled probes were from Thermo Fisher Scientific: Aif1, Mm00479862_g1; Csf1r, Mm01266652_m1; Cx3cr1, Mm02620111_s1; Tmem119, Mm00525305_m1; Trem2, Mm04209424_g1. Gapdh-specific primers (Mm99999915_g1) were used as internal control.
PCR cycling conditions on software supplied with ViiA™ 7 System (Applied Biosystems) were as follows: 50 °C for 2 min, 95 °C for 10 min, 40 cycles at 95 °C for 15 s, and 60 °C for 1 min. Data were expressed as Ct values and used for the relative quantification of targets with the ΔΔCt calculation to give N-fold differences. Data were transformed through the eq. 2-ΔΔCt.
The CSF1R kinase inhibitor BLZ945 therapeutically enhances remyelination in the cuprizone model
We next tested the CSF1R kinase inhibitor, BLZ945, in this model at a high dose of 169 mg/kg p.o. This dose has been chosen based on studies in naïve mice, revealing that BLZ945 administered daily p.o. during 5 days dose-dependently deplete microglia in the brain cortex and spinal cord (Additional file 1: Figure S3 and S4). After 4–5 days microglia depletion was maximal at the high dose of 169 mg/kg (Additional file 1: Figure S3b). After treatment stop microglia re-appeared readily already after 3 days and reached normal numbers at 7 days (Additional file 1: Figure S3b). Microglia activation (microglia soma and proximal processes normalized to distal processes) was analyzed by morphological characteristics via image analysis of Iba1-immunostained brain sections (see Material and Methods and Additional file 1: Figure S14). BLZ945 treatment induced a slight increase in activation status of the remaining microglia. However, newly generated microglia after 3 days BLZ945 removal were highly activated, while they reached normal levels after 7 days (Additional file 1: Figure S3b). Furthermore, microglia activation was dose-dependent but bell-shaped that was highest at a medium dose of 60 mg/kg BLZ945 (Additional file 1: Figure S3c). Microglia depletion in the spinal cord was additionally confirmed on gene expression level (Additional file 1: Figure S4b).
To investigate the relevance of microglia in an autoimmune disease model we therapeutically treated EAE mice, a model of human MS. Animals received two different doses (85 and 127 mg/kg, p.o., qd) of BLZ945 starting at near maximal disease 14 days after immunization (Additional file 1: Figure S9a). Treatment lasted until the end at day 28 post-immunization. No difference in clinical score for both BLZ945 groups compared to vehicle could be observed (Additional file 1: Figure S9a). The onset of EAE clinical pathology around 11–12 days post-immunization as well as the weight change was similar between the treatment and vehicle groups. Microglia depletion could be observed in the spinal cord gray matter at day 28 with treatment of 127 mg/kg BLZ945 (Additional file 1: Figure S9b, c). However, no microglia reduction after high dose BLZ945 treatment could be detected in the cortex (Additional file 1: Figure S9b, d). The microglia displayed a higher activation status in spinal cord and cortex (Additional file 1: Figure S9b, c, d). Furthermore, microglia in the cortex were highly proliferating as shown by Iba1 and Ki67 co-immunofluorescence staining (Additional file 1: Figure S9e); this was not observed in the cortex of vehicle-treated EAE mice (data not shown). This contradicts the mechanism of action of BLZ945, but as the microglia are confronted with peripheral immune cells in the EAE model their phenotypic status could be altered and other additional factors might contribute in regulating microglia homeostasis independent of the CSF1R pathway. Further work is needed to understand the microglia phenotype in the EAE model. Nevertheless, CSF1R kinase inhibition does not alter disease progression in the EAE model, a peripherally driven neuroinflammation model.
In summary, therapeutic BLZ945 treatment enhanced remyelination in specific brain regions after 5-week cuprizone intoxication, like cortex and striatum but did not change remyelination processes in the corpus callosum/external capsule.
The CSF1R kinase inhibitor BLZ945 prophylactically prevents demyelination in the cuprizone model selectively in the corpus callosum but enhances myelin debris and axonal pathology in the external capsule and cortex
In analogy to the MRI observations, differential regional effects were also observed for demyelination and Iba1-positive microglia numbers after 5 weeks BLZ945 + cuprizone treatment (Fig. 6). At this time point, vehicle mice treated with cuprizone displayed again the expected demyelination (LFB) and increase of microglia (Iba1) in the corpus callosum and external capsule (Fig. 6, red and green arrows, respectively). However, mice with BLZ945 + cuprizone treatment for 5 weeks displayed in the corpus callosum a substantial amount of remaining myelin, but a reduction of Iba1-positive microglia (Fig. 6, red arrows). Furthermore, according to the increased presence of myelin, significantly more ODs in the corpus callosum could be detected (Fig. 7e, f). No difference of SMI312-positive axon fibers was observed in corpus callosum in mice treated with BLZ945 + cuprizone (Fig. 7c, d). Contrasting observations could be seen in the external capsule. Iba1-positive microglia were only slightly affected by the CSF1R kinase inhibition (Fig. 6c, d, green arrows), but a reduction of myelin (LFB) could be observed in the external capsule (Fig. 6a, d, green arrows). However, the external capsule displayed an enhanced presence of myelin debris (Fig. 7a, b) which was accompanied by reduced axonal fibers as detected by SMI312 (Fig. 7c, d) in mice treated with BLZ945 + cuprizone. In the cortex similar observations, enhanced myelin debris, axonal pathology and reduced NeuN-positive cells in the BLZ945 + cuprizone treatment group could be detected (Additional file 1: Figure S11). Finally, the external capsule displayed a similar reduction of ODs in vehicle+cuprizone and BLZ945 + cuprizone treated mice (Fig. 7e, f) correlating with the absence of myelin in this region. Again, as for the therapeutic BLZ945 treatment (Additional file 1: Figure S6c), in mice treated prophylactically with BLZ945 in the cuprizone model a dramatic reduction in NG2-positive cells was obvious (data not shown). Important to note, besides reducing microglia and NG2-positive cells there was no change in any of the analyzed parameters in mice treated for 6 weeks with BLZ945 alone without cuprizone intoxication. GFAP-positive astrocytes and the expression of the lysosomal marker Lamp-1 (CD107a) were increased during cuprizone treatment, but both were indifferent between the vehicle+cuprizone and BLZ9459 + cuprizone groups (Additional file 1: Figure S12). The similar increase of Lamp-1 in the external capsule in both treatment groups indicates that microglia are reacting similar to the intoxication but are in their function somehow impaired as myelin was not properly cleared and thus, could be detected as myelin debris. Similar microglia dysfunction in the same brain region could also be observed in MRI scans from TREM2 (triggering receptor expressed on myeloid cells 2 protein) knock-out animals treated for 5 weeks with cuprizone revealing as well increased myelin debris in the external capsule (Additional file 1: Figure S13).
In summary, prophylactic BLZ945 treatment before and during 5-week cuprizone intoxication reduced microglia in specific brain regions, prevented demyelination in the corpus callosum while myelin debris build up due to functionally impaired microglia could be observed in the external capsule.
In this study we pharmacologically depleted microglia therapeutically and prophylactically to investigate the contribution of microglia on de- and re-myelination processes in the cuprizone model. Cuprizone intoxication is a widely accepted experimental model to investigate MS-related pathology, characterized by a direct degeneration of mature oligodendrocytes (ODs, for review see [22, 50, 57]). We used the CSF1 receptor kinase inhibitor BLZ945 that has been shown previously to alter macrophage polarization and block glioma progression in preclinical models of glioblastomas  as well as to control myelin homeostasis in adult mouse brain . We could show that BLZ945 dose-dependently depleted microglia in the central nervous system after 5 days of daily treatment consistent to a report by others that used a different CSF1R kinase inhibitor . After inhibitor removal microglia repopulate readily and more importantly show unaltered function without any apparent adverse effects . A complete absence of the CSF1 receptor on the contrary is detrimental for proper brain development .
The 2-week therapeutic treatment of BLZ945 in the 5-week cuprizone model showed a beneficial effect in the non-invasive longitudinal MRI signal intensity measurements as well as subsequent histology analysis on myelin level and OD numbers. MTR changes in these areas were not considered here, because of the small magnitude (≤2%) of MTR reductions in the cortex and striatum following the 5-week cuprizone intoxication period. The beneficial effect of BLZ945 was brain region-specific, with only the cortex and striatum showing increased remyelination whereas the effect was absent in the corpus callosum and external capsule. Other brain areas have not been analyzed in this study. The extent of beneficial effect obtained here was similar to enhanced remyelination in the cuprizone model described elsewhere  for therapeutic treatment with clemastine, a compound that is currently being tested in the clinic . Furthermore, this differential brain region effect on myelin was also observed on microglia/astrocyte numbers as well as on the microglia activation status. In cortex and striatum the BLZ945-induced microglia reduction was much more pronounced than that observed in the corpus callosum and external capsule; the reduction of microglia was even below control levels in cortex and striatum. In contrast, the astrocytes were even further increased in cortex and striatum whereas this increase was only minimal in corpus callosum and external capsule. Similarly, morphological parameters characteristic of microglia activation were mostly increased in cortex and striatum, whereas there was no change or even a reduction of these parameters in corpus callosum and external capsule. This indicates that microglia numbers and morphology is brain region specifically altered, with subsequent consequences on myelination processes.
Astrocytes and microglia are known to play an important role in myelination in the cuprizone model (for review see ). Peripheral lipopolysaccharide (LPS) treatment in the cuprizone model delayed demyelination and enhanced remyelination by inhibiting microglia but enhancing oligondrocyte proliferation . It has been also shown that astrocytes are needed to recruit microglia for clearing myelin debris and initiate repair . Additionally, proper microglia function for clearing myelin debris is needed for efficient remyelination. It has been demonstrated through cuprizone intoxication that mice lacking the triggering receptor expressed on myeloid cells 2 (TREM2) and CX3CR1 microglia were not able to properly clear myelin and thus inefficiently remyelinated upon cuprizone removal [4, 26, 40]. Others have shown that enhancing microglia phagocytosis by inhibiting soluble TNF enhances remyelination . Furthermore, laquinimod and quetiapine have been shown, via different mode of actions, to reduce microglia activation in the cuprizone model and promote myelin repair [2, 24, 52]. Microglia and astrocytes express different markers, have different polarization status (e.g. M1/M2 and A1/A2 classification) and functions during the course of the neuroinflammatory response to an insult [13, 28]. Despite the fact that M1/M2 phenotype classification for microglia has been challenged , as the boundaries between pro-inflammatory M1 and pro-resolution M2 microglia are not so well defined, it has been shown that M2 microglia promote oligodendrogenesis and thus shows enhanced remyelination [32, 55]. Thus, it might be conceivable that BLZ945 treatment alters the polarization of microglia/macrophages . In our study the microglia depletion was not complete and the remaining microglia might have adopted an activation status that could promote myelin clearance, enhanced recruitment of astrocytes and increased OD proliferation and maturation. A thorough single-cell or cell population RNAseq expression analysis would be needed to investigate the microglia phenotype after BLZ945 treatment in the cuprizone model. Important to note, in human brain differences have been observed in the dynamics of OD generation between white and gray matter , a factor that could have also contributed to the differences in BLZ945 efficacy between cortex/striatum and corpus callosum/external capsule observed here. Furthermore, brain region-specific effects have been reported with chemokine knockout mice, showing beneficial effects in cortex but not corpus callosum , indicating that region-specific pathophysiological processes do exist. It has been shown that microglia are essential for the development and homeostasis of oligodendrocyte precursor cell (OPCs) . We also could observe that BLZ945 treatment substantially reduced NG2-positive OPCs. Microglia seem to be essential in OPC maintenance as OPCs do not express CSF1R . Nevertheless, mature ODs are still being generated and are even enhanced upon therapeutic BLZ945 treatment. It seems that OD numbers and function profit from microglia depletion. It can be speculated that in our model ODs are being generated by NG2-negative OPCs/pre-mature ODs or other unknown precursor cell populations. It has been shown that BLZ945 treatment induced an increase in GFP-positive/NG2-negative cells with the Sox10 promoter-driven inducible GFP reporter mouse , indicating an enhanced maturation of ODs or prompt differentiation of OPCs upon CSF1R pathway inhibition. Similar to Hagemeyer et al.  we also did not observe any myelination, axonal fiber and OD differences in the corpus callosum/external capsule after 6 weeks high dose BLZ945 treatment without cuprizone. Importantly, after BLZ945 removal OPCs similar to microglia seem to reappear .
Our data suggest that the microglia populations in the corpus callosum and the external capsule differed extensively in their behavior during prophylactic BLZ945 treatment in the cuprizone model. When BLZ945 was given prophylactically before and during cuprizone intoxication microglia in the external capsule became insensitive towards CSF1R kinase inhibition resulting in a functional impairment. It has been reported that heterozygous CSF1R knock-out mice also have abnormal myelination and aberrant activation of microglia . This is similar to data observed in TREM2 (triggering receptor expressed on myeloid cells 2 protein) knock-out animals where microglia impairment could be observed by us and others [4, 40]. TREM2 and CSF1R presumably signal via the same adapter protein DAP12  and when dysfunctional contributes to chronic neurodegeneration in humans. Deficiency in TREM2 leads to Nasu-Hakola disease and patients with partial loss-of-function mutations in CSF1R suffer from hereditary diffuse leukoencephalopathy with spheroids (see reviews [34, 53]). This indicates that the CSF1R and TREM2 pathway may converge and even interact to exert similar downstream events. At week 5, there was a discrepancy between the MRI readouts at the level of the external capsule of cuprizone-challenged mice: whereas the signal intensities were approximately the same for the BLZ945 and vehicle groups, consistent with the similar levels of demyelination in both groups evidenced by histology, the MTR was significantly increased in BLZ945- compared to vehicle-treated animals. However, increased myelin debris was observed by histology in the external capsule of mice that had received BLZ945, suggesting that myelin debris contributed to MTR. These observations are consistent with earlier work showing that OD ablation resulted only in minor decreases in MTR due to inefficient removal of myelin debris . In the corpus callosum on the contrary, for BLZ945 given prophylactically, microglia were substantially reduced, comparable to the situation in the therapeutic BLZ945 treatment mode, and additionally microglia functionality was altered, leading to reduced demyelination, no accumulation of myelin debris and absence of axonal damage. This is in agreement with the reduced MRI signal and the increased MTR measured in the corpus callosum of cuprizone challenged animals receiving BLZ945 prophylactically. Therefore, a discrepancy between MRI signal and MTR might thus indicate poor myelin debris removal in a given area, pointing to the importance of assessing both parameters.
Microglia can also exert pro-inflammatory neurotoxic function in chronic neurodegenerative diseases, damaging neurons, synapses, neuronal processes directly or indirectly by helping spreading of toxic proteins. It has been shown that CSF1R kinase inhibition in animal models of Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), brain lesions, tauopathies and catatonia of neuropsychiatric diseases prevented or functionally improved disease progression [1, 8, 19, 30, 36, 43]. Similarly, mice lacking the chemokine Cxcl10 showed a reduction of microglia activation and as a consequence a reduced demyelination and axonal pathology . Brain areas with the strongest microglia depletion by BLZ945 also displayed enhanced myelination and OD numbers. This implicates that a reduction of microglia is beneficial for the myelination processes exerted by remaining ODs. The exact mechanisms by which microglia are inhibiting mature OD myelination remains to be elucidated. Important to note that in an experimental autoimmune encephalomyelitis (EAE) model therapeutic treatment of BLZ945 did not change disease progression despite a significant reduction of microglia cells in the spinal cord gray matter. However, microglia were not reduced in the cortex, but showed enhanced proliferation indicating that peripheral immune cells in the EAE model do alter microglia response towards BLZ945. Further studies are needed to characterize the phenotype of microglia in the EAE model. Additionally, combination therapies in the EAE model for modulating peripheral as well as central inflammatory processes may shed more light on the contribution of microglia to the pathology. Furthermore, combining cuprizone and EAE models could prove to have good translational value for studying inflammatory lesions in the forebrain [44, 45]. Nevertheless, our results indicate that microglia modulation via the CSF1R pathway seems not to play a crucial role in modifying the disease progression in the EAE model.
Taken together, the myelination processes can be positively modulated by reducing microglia and enhancing astrocytes and thereby increasing and/or preserve ODs and, finally, myelination. As this is brain region-specific and depends on disease state the timing on the intervention is crucial. Our results show for the first time beneficial effects on myelination events in the cuprizone model by CSF1R kinase inhibition. Thus, microglia-modulating mechanisms could be potentially pursued as new short-term treatment paradigms for initiating and enhancing myelination processes in combination with standard-of-care medication in MS.
We thank Marion Wiesmann for her support.
NB, PS, EG, NA, MN, SD, WF, LP and DRS designed research. NB, PS, AN, SZ, JP, LP, EG, FW and DRS performed research. NB, PS, AN, SZ, JP, EG, SD, WF and DRS analyzed data. NB and DRS wrote the paper. All authors read and approved the final manuscript.
All authors are, or have been, employees and shareholders of Novartis Pharma AG, Basel Switzerland.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- Asai H, Ikezu S, Tsunoda S, Medalla M, Luebke J, Haydar T, Wolozin B, Butovsky O, Kügler S, Ikezu T (2015) Depletion of microglia and inhibition of exosome synthesis halt tau propagation. Nat Neurosci 18:1584–1593. https://doi.org/10.1038/nn.4132 View ArticlePubMedPubMed CentralGoogle Scholar
- Brück W, Pförtner R, Pham T, Zhang J, Hayardeny L, Piryatinsky V, Hanisch U-K, Regen T, van Rossum D, Brakelmann L, Hagemeier K, Kuhlmann T, Stadelmann C, John GR, Kramann N, Wegner C (2012) Reduced astrocytic NF-κB activation by laquinimod protects from cuprizone-induced demyelination. Acta Neuropathol 124:411–424. https://doi.org/10.1007/s00401-012-1009-1 View ArticlePubMedPubMed CentralGoogle Scholar
- Calabrese M, Magliozzi R, Ciccarelli O, Geurts JJG, Reynolds R, Martin R (2015) Exploring the origins of grey matter damage in multiple sclerosis. Nat Rev Neurosci 16:147–158. https://doi.org/10.1038/nrn3900 View ArticlePubMedGoogle Scholar
- Cantoni C, Bollman B, Licastro D, Xie M, Mikesell R, Schmidt R, Yuede CM, Galimberti D, Olivecrona G, Klein RS, Cross AH, Otero K, Piccio L (2015) TREM2 regulates microglial cell activation in response to demyelination in vivo. Acta Neuropathol. doi: https://doi.org/10.1007/s00401-015-1388-1
- Chandran P, Upadhyay J, Markosyan S, Lisowski a, Buck W, Chin C-L, Fox G, Luo F, Day M (2012) Magnetic resonance imaging and histological evidence for the blockade of cuprizone-induced demyelination in C57BL/6 mice. Neuroscience 202:446–453. https://doi.org/10.1016/j.neuroscience.2011.10.051 View ArticlePubMedGoogle Scholar
- Chitu V, Gokhan S, Gulinello M, Branch CA, Patil M, Basu R, Stoddart C, Mehler MF, Richard Stanley E (2015) Phenotypic characterization of a Csf1r haploinsufficient mouse model of adult-onset leukodystrophy with axonal spheroids and pigmented glia (ALSP). Neurobiol Dis 74:219–228. https://doi.org/10.1016/j.nbd.2014.12.001 View ArticlePubMedGoogle Scholar
- Clarner T, Janssen K, Nellessen L, Stangel M, Skripuletz T, Krauspe B, Hess F-M, Denecke B, Beutner C, Linnartz-Gerlach B, Neumann H, Vallières L, Amor S, Ohl K, Tenbrock K, Beyer C, Kipp M (2015) CXCL10 Triggers Early Microglial Activation in the Cuprizone Model. J Immunol. doi: https://doi.org/10.4049/jimmunol.1401459
- Dagher NN, Najafi AR, Kayala KMN, Elmore MRP, White TE, Medeiros R, West BL, Green KN (2015) Colony-stimulating factor 1 receptor inhibition prevents microglial plaque association and improves cognition in 3xTg-AD mice. J Neuroinflammation 12:139. https://doi.org/10.1186/s12974-015-0366-9 View ArticlePubMedPubMed CentralGoogle Scholar
- Elmore MRP, Lee RJ, West BL, Green KN (2015) Characterizing newly repopulated microglia in the adult mouse: impacts on animal behavior, cell morphology, and neuroinflammation. PLoS One 10:e0122912. https://doi.org/10.1371/journal.pone.0122912 View ArticlePubMedPubMed CentralGoogle Scholar
- Elmore MRP, Najafi AR, M a K, Dagher NN, Spangenberg EE, Ra R, Kitazawa M, Matusow B, Nguyen H, West BL, Green KN (2014) Colony-stimulating factor 1 receptor signaling is necessary for microglia viability, unmasking a microglia progenitor cell in the adult brain. Neuron 82:380–397. https://doi.org/10.1016/j.neuron.2014.02.040 View ArticlePubMedPubMed CentralGoogle Scholar
- Erblich B, Zhu L, Etgen AM, Dobrenis K, Pollard JW (2011) Absence of colony stimulation factor-1 receptor results in loss of microglia, disrupted brain development and olfactory deficits. PLoS One 6:e26317. https://doi.org/10.1371/journal.pone.0026317 View ArticlePubMedPubMed CentralGoogle Scholar
- Fjær S, Bø L, Lundervold A, Myhr K-M, Pavlin T, Torkildsen O, Wergeland S (2013) Deep gray matter demyelination detected by magnetization transfer ratio in the cuprizone model. PLoS One 8:e84162. https://doi.org/10.1371/journal.pone.0084162 View ArticlePubMedPubMed CentralGoogle Scholar
- Franco R, Fernández-Suárez D (2015) Alternatively activated microglia and macrophages in the central nervous system. Prog Neurobiol 131:65–86. https://doi.org/10.1016/j.pneurobio.2015.05.003 View ArticlePubMedGoogle Scholar
- Green AJ, Gelfand JM, Cree BA, Bevan C, Boscardin WJ, Mei F, Inman J, Arnow S, Devereux M, Abounasr A, Nobuta H, Zhu A, Friessen M, Gerona R, von Büdingen HC, Henry RG, Hauser SL, Chan JR (2017) Clemastine fumarate as a remyelinating therapy for multiple sclerosis (ReBUILD): A randomised, controlled, double-blind, crossover trial. Lancet. https://doi.org/10.1016/S0140-6736(17)32346-2
- Gudi V, Gingele S, Skripuletz T, Stangel M (2014) Glial response during cuprizone-induced de- and remyelination in the CNS: lessons learned. Front Cell Neurosci 8:73. https://doi.org/10.3389/fncel.2014.00073 View ArticlePubMedPubMed CentralGoogle Scholar
- Haase A, Matthaei D, Hänicke W, Frahm J (1986) Dynamic digital subtraction imaging using fast low-angle shot MR movie sequence. Radiology 160:537–541. https://doi.org/10.1148/radiology.160.2.3523597 View ArticlePubMedGoogle Scholar
- Hagemeyer N, Hanft K-M, Akriditou M-A, Unger N, Park ES, Stanley ER, Staszewski O, Dimou L, Prinz M (2017) Microglia contribute to normal myelinogenesis and to oligodendrocyte progenitor maintenance during adulthood. Acta Neuropathol. https://doi.org/10.1007/s00401-017-1747-1
- Hennig J, Nauerth A, Friedburg H (1986) RARE imaging: a fast imaging method for clinical MR. Magn Reson Med 3:823–833. https://doi.org/10.1002/mrm.1910030602 View ArticlePubMedGoogle Scholar
- Janova H, Arinrad S, Balmuth E, Mitjans M, Hertel J, Habes M, Bittner RA, Pan H, Goebbels S, Begemann M, Gerwig UC, Langner S, Werner HB, Kittel-Schneider S, Homuth G, Davatzikos C, Völzke H, West BL, Reif A, Grabe HJ, Boretius S, Ehrenreich H, Nave K-A (2017) Microglia ablation alleviates myelin-associated catatonic signs in mice. J Clin Invest:1–12. https://doi.org/10.1172/JCI97032
- Janssen K, Rickert M, Clarner T, Beyer C, Kipp M (2015) Absence of CCL2 and CCL3 ameliorates central nervous system Grey matter but not white matter Demyelination in the presence of an intact blood–brain barrier. Mol Neurobiol:1551–1564. https://doi.org/10.1007/s12035-015-9113-6
- Karamita M, Barnum C, Möbius W, Tansey MG, Szymkowski DE, Lassmann H, Probert L (2017) Therapeutic inhibition of soluble brain TNF promotes remyelination by increasing myelin phagocytosis by microglia. JCI Insight. https://doi.org/10.1172/jci.insight.87455
- Kipp M, Clarner T, Dang J, Copray S, Beyer C (2009) The cuprizone animal model: new insights into an old story. Acta Neuropathol 118:723–736. https://doi.org/10.1007/s00401-009-0591-3 View ArticlePubMedGoogle Scholar
- Klein D, Patzko I, Schreiber D, van Hauwermeiren A, Baier M, Groh J, West BL, Martini R (2015) Targeting the CSF-1 receptor alleviates two forms of Charcot-Marie-tooth disease in mice. Glia 63:E337–E337. https://doi.org/10.1093/awv279 Google Scholar
- Kramann N, Menken L, Hayardeny L, Hanisch U-K, Brück W (2016) Laquinimod prevents cuprizone-induced demyelination independent of toll-like receptor signaling. Neurol Neuroimmunol Neuroinflamm 3:e233. https://doi.org/10.1212/NXI.0000000000000233 View ArticlePubMedPubMed CentralGoogle Scholar
- J a K, Jin Y, Walles M, Pfaar U, Sutton J, Wiesmann M, Graf D, Pflimlin-Fritschy V, Wolf T, Camenisch G, Swart P (2015) Phenotypic and metabolic investigation of a CSF-1R kinase receptor inhibitor (BLZ945) and its pharmacologically active metabolite. Xenobiotica 45:107–123. https://doi.org/10.3109/00498254.2014.945988 View ArticleGoogle Scholar
- Lampron A, Larochelle A, Laflamme N, Préfontaine P, Plante M-M, Sánchez MG, Yong VW, Stys PK, Tremblay M-È, Rivest S (2015) Inefficient clearance of myelin debris by microglia impairs remyelinating processes. J Exp Med 212:481–495. https://doi.org/10.1084/jem.20141656 View ArticlePubMedPubMed CentralGoogle Scholar
- Li Z, He Y, Fan S, Sun B (2015) Clemastine rescues behavioral changes and enhances remyelination in the cuprizone mouse model of demyelination. Neurosci Bull 31:617–625. https://doi.org/10.1007/s12264-015-1555-3 View ArticlePubMedPubMed CentralGoogle Scholar
- Liddelow SA, Guttenplan KA, Clarke LE, Bennett FC, Bohlen CJ, Schirmer L, Bennett ML, Münch AE, Chung W-S, Peterson TC, Wilton DK, Frouin A, Napier BA, Panicker N, Kumar M, Buckwalter MS, Rowitch DH, Dawson VL, Dawson TM, Stevens B, Barres BA (2017) Neurotoxic reactive astrocytes are induced by activated microglia. Nature. https://doi.org/10.1038/nature21029
- Luo J, Elwood F, Britschgi M, Villeda S, Zhang H, Ding Z, Zhu L, Alabsi H, Getachew R, Narasimhan R, Wabl R, Fainberg N, James ML, Wong G, Relton J, Gambhir SS, Pollard JW, Wyss-Coray T (2013) Colony-stimulating factor 1 receptor (CSF1R) signaling in injured neurons facilitates protection and survival. J Exp Med 210:157–172. https://doi.org/10.1084/jem.20120412 View ArticlePubMedPubMed CentralGoogle Scholar
- Martínez-Muriana A, Mancuso R, Francos-Quijorna I, Olmos-Alonso A, Osta R, Perry VH, Navarro X, Gomez-Nicola D, López-Vales R (2016) CSF1R blockade slows the progression of amyotrophic lateral sclerosis by reducing microgliosis and invasion of macrophages into peripheral nerves. Sci Rep 6:25663. https://doi.org/10.1038/srep25663 View ArticlePubMedPubMed CentralGoogle Scholar
- Merkler D, Boretius S, Stadelmann C, Ernsting T, Michaelis T, Frahm J, Brück W (2005) Multicontrast MRI of remyelination in the central nervous system. NMR Biomed 18:395–403. https://doi.org/10.1002/nbm.972 View ArticlePubMedGoogle Scholar
- Miron VE, Boyd A, Zhao J-W, Yuen TJ, Ruckh JM, Shadrach JL, van Wijngaarden P, Wagers AJ, Williams A, Franklin RJM, ffrench-Constant C (2013) M2 microglia and macrophages drive oligodendrocyte differentiation during CNS remyelination. Nat Neurosci 16:1211–1218. doi: https://doi.org/10.1038/nn.3469
- Mueggler T, Pohl H, Baltes C, Riethmacher D, Suter U, Rudin M (2012) MRI signature in a novel mouse model of genetically induced adult oligodendrocyte cell death. NeuroImage 59:1028–1036. https://doi.org/10.1016/j.neuroimage.2011.09.001 View ArticlePubMedGoogle Scholar
- Neumann H, Daly MJ (2013) Variant TREM2 as risk factor for Alzheimer’s disease. N Engl J Med 368:182–184. https://doi.org/10.1056/NEJMe1213157 View ArticlePubMedGoogle Scholar
- Nylander A, Hafler DA (2012) Multiple sclerosis. J Clin Invest 122:1180–1188. https://doi.org/10.1172/JCI58649 View ArticlePubMedPubMed CentralGoogle Scholar
- Olmos-Alonso A, Schetters STT, Sri S, Askew K, Mancuso R, Vargas-Caballero M, Holscher C, Perry VH, Gomez-Nicola D (2016) Pharmacological targeting of CSF1R inhibits microglial proliferation and prevents the progression of Alzheimer’s-like pathology. Brain 139:891–907. https://doi.org/10.1093/brain/awv379 View ArticlePubMedPubMed CentralGoogle Scholar
- Otero K, Turnbull IR, Poliani PL, Vermi W, Cerutti E, Aoshi T, Tassi I, Takai T, Stanley SL, Miller M, Shaw AS, Colonna M (2009) Macrophage colony-stimulating factor induces the proliferation and survival of macrophages via a pathway involving DAP12 and beta-catenin. Nat Immunol 10:734–743. https://doi.org/10.1038/ni.1744 View ArticlePubMedPubMed CentralGoogle Scholar
- Perry VH (2016) Microglia. Microbiol Spectr 4:1–9. https://doi.org/10.1128/microbiolspec.MCHD-0003-2015 Google Scholar
- Petković F, Campbell IL, Gonzalez B, Castellano B (2016) Astrocyte-targeted production of interleukin-6 reduces astroglial and microglial activation in the cuprizone demyelination model: implications for myelin clearance and oligodendrocyte maturation. Glia. https://doi.org/10.1002/glia.23043
- Poliani PL, Wang Y, Fontana E, Robinette ML, Yamanishi Y, Gilfillan S, Colonna M (2015) TREM2 sustains microglial expansion during aging and response to demyelination. J Clin Invest 125:2161–2170. https://doi.org/10.1172/JCI77983 View ArticlePubMedPubMed CentralGoogle Scholar
- Pyonteck SM, Akkari L, Schuhmacher AJ, Bowman RL, Sevenich L, Quail DF, Olson OC, Quick ML, Huse JT, Teijeiro V, Setty M, Leslie CS, Oei Y, Pedraza A, Zhang J, Brennan CW, Sutton JC, Holland EC, Daniel D, Joyce JA (2013) CSF-1R inhibition alters macrophage polarization and blocks glioma progression. Nat Med 19:1264–1272. https://doi.org/10.1038/nm.3337 View ArticlePubMedPubMed CentralGoogle Scholar
- Ransohoff RM (2016) A polarizing question: do M1 and M2 microglia exist? Nat Neurosci 19:987–991. https://doi.org/10.1038/nn.4338 View ArticlePubMedGoogle Scholar
- Rice R a, Spangenberg EE, Yamate-Morgan H, Lee RJ, RPS A, Hernandez MX, Tenner a J, West BL, Green KN (2015) Elimination of microglia improves functional outcomes following extensive neuronal loss in the hippocampus. J Neurosci 35:9977–9989. https://doi.org/10.1523/JNEUROSCI.0336-15.2015 View ArticlePubMedPubMed CentralGoogle Scholar
- Rüther BJ, Scheld M, Dreymueller D, Clarner T, Kress E, Brandenburg L-O, Swartenbroekx T, Hoornaert C, Ponsaerts P, Fallier-Becker P, Beyer C, Rohr SO, Schmitz C, Chrzanowski U, Hochstrasser T, Nyamoya S, Kipp M (2017) Combination of cuprizone and experimental autoimmune encephalomyelitis to study inflammatory brain lesion formation and progression. Glia 65:1900–1913. https://doi.org/10.1002/glia.23202 View ArticlePubMedGoogle Scholar
- Scheld M, Ruther BJ, Grosse-Veldmann R, Ohl K, Tenbrock K, Dreymuller D, Fallier-Becker P, Zendedel A, Beyer C, Clarner T, Kipp M (2016) Neurodegeneration triggers peripheral immune cell recruitment into the forebrain. J Neurosci 36:1410–1415. https://doi.org/10.1523/JNEUROSCI.2456-15.2016 View ArticlePubMedGoogle Scholar
- Skripuletz T, Hackstette D, Bauer K, Gudi V, Pul R, Voss E, Berger K, Kipp M, Baumgärtner W, Stangel M (2013) Astrocytes regulate myelin clearance through recruitment of microglia during cuprizone-induced demyelination. Brain 136:147–167. https://doi.org/10.1093/brain/aws262 View ArticlePubMedGoogle Scholar
- Skripuletz T, Miller E, Grote L, Gudi V, Pul R, Voss E, Skuljec J, Moharregh-Khiabani D, Trebst C, Stangel M (2011) Lipopolysaccharide delays demyelination and promotes oligodendrocyte precursor proliferation in the central nervous system. Brain Behav Immun 25:1592–1606. https://doi.org/10.1016/j.bbi.2011.05.009 View ArticlePubMedGoogle Scholar
- Spangenberg EE, Lee RJ, Najafi AR, Rice R a, Elmore MRP, Blurton-Jones M, West BL, Green KN (2016) Eliminating microglia in Alzheimer’s mice prevents neuronal loss without modulating amyloid-β pathology. Brain 1–17. https://doi.org/10.1093/brain/aww016
- Thiessen JD, Zhang Y, Zhang H, Wang L, Buist R, Del Bigio MR, Kong J, Li X-M, Martin M (2013) Quantitative MRI and ultrastructural examination of the cuprizone mouse model of demyelination. NMR Biomed 26:1562–1581. https://doi.org/10.1002/nbm.2992 View ArticlePubMedGoogle Scholar
- Torkildsen O, Brunborg LA, Myhr K-M, Bø L (2008) The cuprizone model for demyelination. Acta Neurol Scand Suppl 188:72–76. https://doi.org/10.1111/j.1600-0404.2008.01036.x View ArticlePubMedGoogle Scholar
- Turati L, Moscatelli M, Mastropietro A, Dowell NG, Zucca I, Erbetta A, Cordiglieri C, Brenna G, Bianchi B, Mantegazza R, Cercignani M, Baggi F, Minati L (2015) In vivo quantitative magnetization transfer imaging correlates with histology during de- and remyelination in cuprizone-treated mice. NMR Biomed 28:327–337. https://doi.org/10.1002/nbm.3253 View ArticlePubMedGoogle Scholar
- Wang H, Liu S, Tian Y, Wu X, He Y, Li C, Namaka M, Kong J, Li H, Xiao L (2015) Quetiapine inhibits Microglial activation by neutralizing abnormal STIM1-mediated intercellular calcium homeostasis and promotes myelin repair in a Cuprizone-induced mouse model of Demyelination. Front Cell Neurosci 9:1–11. https://doi.org/10.3389/fncel.2015.00492 Google Scholar
- Yaghmoor F, Noorsaeed A, Alsaggaf S, Aljohani W, Scholtzova H, Boutajangout A, Wisniewski T (2014) The role of TREM2 in Alzheimer’s disease and other neurological disorders. J Alzheimer’s Dis Park. https://doi.org/10.4172/2161-0460.1000160
- Yeung MSYSY, Zdunek S, Bergmann O, Bernard S, Salehpour M, Alkass K, Perl S, Tisdale J, Possnert G, Brundin L, Druid H, Frisén J (2014) Dynamics of Oligodendrocyte generation and Myelination in the human brain. Cell 159:766–774. https://doi.org/10.1016/j.cell.2014.10.011 View ArticlePubMedGoogle Scholar
- Yuan J, Ge H, Liu W, Zhu H, Chen Y, Zhang X, Yang Y, Yin Y, Chen W, Wu W, Yang Y, Lin J (2017) M2 microglia promotes neurogenesis and oligodendrogenesis from neural stem/progenitor cells via the PPARγ signaling pathway. Oncotarget 8:19855–19865. https://doi.org/10.18632/oncotarget.15774 PubMedPubMed CentralGoogle Scholar
- Zaaraoui W, Deloire M, Merle M, Girard C, Raffard G, Biran M, Inglese M, Petry KG, Gonen O, Brochet B, Franconi J-M, Dousset V (2008) Monitoring demyelination and remyelination by magnetization transfer imaging in the mouse brain at 9.4 T. MAGMA 21:357–362. https://doi.org/10.1007/s10334-008-0141-3 View ArticlePubMedPubMed CentralGoogle Scholar
- Zendedel A, Beyer C, Kipp M (2013) Cuprizone-induced demyelination as a tool to study remyelination and axonal protection. J Mol Neurosci 51:567–572. https://doi.org/10.1007/s12031-013-0026-4 View ArticlePubMedGoogle Scholar