Sex-specific effects of microbiome perturbations on cerebral Aβ amyloidosis and microglia phenotypes.

We demonstrated that an antibiotic cocktail (ABX)-perturbed gut microbiome is associated with reduced amyloid-β (Aβ) plaque pathology and astrogliosis in the male amyloid precursor protein (APP)SWE /presenilin 1 (PS1)ΔE9 transgenic model of Aβ amyloidosis. We now show that in an independent, aggressive APPSWE/PS1L166P (APPPS1-21) mouse model of Aβ amyloidosis, an ABX-perturbed gut microbiome is associated with a reduction in Aβ pathology and alterations in microglial morphology, thus establishing the generality of the phenomenon. Most importantly, these latter alterations occur only in brains of male mice, not in the brains of female mice. Furthermore, ABX treatment lead to alterations in levels of selected microglial expressed transcripts indicative of the "M0" homeostatic state in male but not in female mice. Finally, we found that transplants of fecal microbiota from age-matched APPPS1-21 male mice into ABX-treated APPPS1-21 male restores the gut microbiome and partially restores Aβ pathology and microglial morphology, thus demonstrating a causal role of the microbiome in the modulation of Aβ amyloidosis and microglial physiology in mouse models of Aβ amyloidosis

High-fat diet-induced brain region-specific phenotypic spectrum of CNS resident microglia

Diets high in fat (HFD) are known to cause an immune response in the periphery as well as the central nervous system. In peripheral adipose tissue, this immune response is primarily mediated by macrophages that are recruited to the tissue. Similarly, reactivity of microglia, the innate immune cells of the brain, has been shown to occur in the hypothalamus of mice fed a high-fat diet. To characterize the nature of the microglial response to diets high in fat in a temporal fashion, we studied the phenotypic spectrum of hypothalamic microglia of mice fed high-fat diet for 3 days and 8 weeks by assessing their tissue reaction and inflammatory signature. While we observed a significant increase in Iba1+ myeloid cells and a reaction of GFAP+ astrocytes in the hypothalamus after 8 weeks of HFD feeding, we found the hypothalamic myeloid cell reaction to be limited to endogenous microglia and not mediated by infiltrating myeloid cells. Moreover, obese humans were found to present with signs of hypothalamic gliosis and exacerbated microglia dystrophy, suggesting a targeted microglia response to diet in humans as well. Notably, the glial reaction occurring in the mouse hypothalamus was not accompanied by an increase in pro-inflammatory cytokines, but rather by an anti-inflammatory reaction. Gene expression analyses of isolated microglia not only confirmed this observation, but also revealed a downregulation of microglia genes important for sensing signals in the microenvironment. Finally, we demonstrate that long-term exposure of microglia to HFD in vivo does not impair the cell’s ability to respond to additional stimuli, like lipopolysaccharide. Taken together, our findings support the notion that microglia react to diets high in fat in a region-specific manner in rodents as well as in humans; however, this response changes over time as it is not exclusively pro-inflammatory nor does exposure to HFD prime microglia in the hypothalamus. Electronic supplementary material The online version of this article (doi:10.1007/s00401-016-1595-4) contains supplementary material, which is available to authorized users

Charakterisierung der Art und Konsequenz der Mikrogliareaktion auf Hochfett- Ernährung

Obesity is a disease affecting millions of people worldwide. In adipose tissue, obesity leads to chronic low-level inflammation mediated by infiltrating macrophages, which ultimately results in insulin resistance. Recent work exploring the effects of obesity and metabolic disease on the central nervous system (CNS) revealed that long-term high fat diet (HFD) leads to brain inflammation and leptin resistance in the hypothalamus. Microglia, the brain’s intrinsic immune cells, play an essential role in physiological brain functions, including pruning of neuronal synapses and regulation of brain development, and respond to disease or injury to the CNS. Fitting with the notion that diets high in fat content are harmful to the brain, an altered microglia phenotype was detected in the hypothalamus of rats as early as 3 days after the start of HFD. The first aim of this thesis was to further elucidate the response of microglia to short-term and prolonged HFD exposure. The analyses of whole hypothalamic tissue and isolated microglia of HFD-fed mice revealed a distinct response of microglia to diet, including a shift in the microglia gene expression profile from pro-inflammatory in response to short-term HFD exposure to an anti-inflammatory or rather subdued phenotype following prolonged HFD. To dissect the role hypothalamic microglia might play in the regulation of body weight homeostasis, the CD11b-HSVTK mouse model was used, which allows for a specific and inducible depletion of microglia. Following microglia depletion, endogenous microglia are replaced by bone marrow-derived myeloid cells. This process appears to induce metabolic changes in CD11b-HSVTK mice that are independent of the diet such that microglia- depleted CD11b-HSVTK mice displayed a reduced body weight compared to wild- type mice when fed with either chow or HFD. From the performed analyses it can be concluded that the body weight phenotype is due to the phenomenon of myeloid cell repopulation that is taking place in microglia-depleted mice. Taken together, the response of microglia to diets high in fat is not solely pro-inflammatory, but changes over prolonged exposure to HFD, which may represent a neuroprotective response. This shift in the microglia response should be further explored, and kept in mind when devising CNS-targeted treatment strategies for obesity. Moreover, the function microglia may exert in the regulation of body weight homeostasis in the hypothalamus remains unclear and requires further investigation.Übergewicht ist weltweit eines der größten Gesundheitsprobleme und ein Risikofaktor für chronische Krankheiten wie Diabetes, Herz-Kreislauf- Erkrankungen und Krebs. Untersuchungen der letzten Jahre haben gezeigt, dass bei Übergewicht durch Makrophagen ausgelöste Entzündungsprozesse in metabolisch aktiven Organen eine entscheidende Rolle spielen und zu Insulin- und Leptinresistenz führen können. Neben der Entzündung in der Peripherie konnte auch eine mit Übergewicht assoziierte Entzündung im zentralen Nervensystem (ZNS), speziell im Hypothalamus, detektiert werden. Mikroglia, die intrinsischen Immunzellen des Gehirns, spielen eine wesentliche Rolle in der Gehirnentwicklung und bei physiologischen Gehirnfunktionen, einschließlich der Bildung von neuronalen Synapse, und reagieren auf pathologische Prozesse oder Verletzungen des ZNS. Entsprechend der Vorstellung, dass fettreiche Ernährung schädlich für das Gehirn ist, wurde eine Reaktion der Mikroglia bereits 3 Tage nach Beginn einer fettreichen Diät (high fat diet, HFD) im Hypothalamus von Ratten beobachtet. Das erste Ziel dieser Arbeit war es, aufzuklären, auf welche Weise Mikroglia auf HFD reagieren. Die Analyse von Hypothalamusgewebe sowie isolierter Mikroglia aus dem Hypothalamus von HFD gefütterten Mäusen offenbarte eine deutliche Antwort der Mikroglia auf die fettreiche Ernährung. Diese war anfänglich (nach 3 Tagen) geprägt von der Expression pro-entzündlicher Marker, die sich bei längerer Fütterung (8 Wochen) zu einem anti-entzündlichen Expressionsprofil veränderte. Um bestimmen zu können, ob hypothalamische Mikroglia eine Rolle bei der Regulation des Körpergewichts spielen, wurde das CD11b-HSVTK Mausmodell genutzt, welches eine spezifische Depletion der Mikroglia ermöglicht. Das Ausschalten der Mikroglia führt zu einem Einwandern von aus dem Knochenmark stammenden myeloiden Zellen, die die endogenen Mikroglia ersetzen. Dieser Prozess scheint Stoffwechselveränderungen in den CD11b-HSVTK Mäusen auszulösen, die dazu führten, dass diese Mäuse ein geringeres Körpergewicht aufwiesen als die transgen-negativen Kontrolltiere und zwar unabhängig davon, ob sie mit HFD oder Kontrollfutter gefüttert wurden. Aus den durchgeführten Analysen lässt sich schließen, dass der Phänotyp der Veränderung des Körpergewichts auf die Einwanderung der peripheren myeloiden Zellen in das ZNS nach Depletion der endogenen Mikrogliazellen zurückgeführt werden kann. Zusammengefasst zeigen die Ergebnisse dieser Arbeit, dass die Reaktion der Mikroglia auf eine fettreiche Ernährung nicht ausschließlich pro-entzündlich, sondern dass sie sich im Laufe einer längeren fettreichen Ernährung verändert und letztlich eine neuro-protektive Rolle übernehmen könnte. Diese funktionelle Verschiebung der Mikroglia-Aktivität gilt es in künftigen Studien weiter zu untersuchen und dies gleichermaßen zu beachten, wenn es darum geht, Behandlungsstrategien zu entwickeln, die darauf abzielen, Mikroglia bei HFD zu manipulieren. Darüber hinaus ist eine mögliche Beteiligung der Mikroglia im Hypothalamus an der Regulation des Körpergewichts weiterhin unklar und sollte Gegenstand weiterer, dezidierter Untersuchungen sein

TREMendous 2 Be Social

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Differential contribution of microglia and monocytes in neurodegenerative diseases

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Targeted Blood Brain Barrier Opening With Focused Ultrasound Induces Focal Macrophage/Microglial Activation in Experimental Autoimmune Encephalomyelitis

International audienceExperimental autoimmune encephalomyelitis (EAE) is a model of multiple sclerosis (MS). EAE reflects important histopathological hallmarks, dissemination, and diversity of the disease, but has only moderate reproducibility of clinical and histopathological features. Focal lesions are less frequently observed in EAE than in MS, and can neither be constrained to specific locations nor timed to occur at a pre-specified moment. This renders difficult any experimental assessment of the pathogenesis of lesion evolution, including its inflammatory, degenerative (demyelination and axonal degeneration), and reparatory (remyelination, axonal sprouting, gliosis) component processes. We sought to develop a controlled model of inflammatory, focal brain lesions in EAE using focused ultrasound (FUS). We hypothesized that FUS induced focal blood brain barrier disruption (BBBD) will increase the likelihood of transmigration of effector cells and subsequent lesion occurrence at the sonicated location. Lesion development was monitored with conventional magnetic resonance imaging (MRI) as well as with magnetic resonance elastography (MRE) and further analyzed by histopathological means. EAE was induced in 12 6–8 weeks old female C57BL/6 mice using myelin oligodendrocyte glycoprotein (MOG) peptide. FUS-induced BBBD was performed 6, 7, and 9 days after immunization in subgroups of four animals and in an additional control group. MRI and MRE were performed on a 7T horizontal bore small animal MRI scanner. Imaging was conducted longitudinally 2 and 3 weeks after disease induction and 1 week after sonication in control animals, respectively. The scan protocol comprised contrast-enhanced T1-weighted and T2-weighted sequences as well as MRE with a vibration frequency of 1 kHz. Animals were sacrificed for histopathology after the last imaging time point. The overall clinical course of EAE was mild. A total of seven EAE animals presented with focal T2w hyperintense signal alterations in the sonicated hemisphere. These were most frequent in the group of animals sonicated 9 days after immunization. Histopathology revealed foci of activated microglia/macrophages in the sonicated right hemisphere of seven EAE animals. Larger cellular infiltrates or apparent demyelination were not seen. Control animals showed no abnormalities on MRI and did not have clusters of activated microglia/macrophages at the sites targeted with FUS. None of the animals had hemorrhages or gross tissue damage as potential side effects of FUS. EAE-animals tended to have lower values of viscoelasticity and elasticity in the sonicated compared to the contralateral parenchyma. This trend was significant when comparing the right sonicated to the left normal hemisphere and specifically the right sonicated compared to the left normal cortex in animals that underwent FUS-BBBD 9 days after immunization (right vs. left hemisphere: mean viscoelasticity 6.1 vs. 7.2 kPa; p = 0.003 and mean elasticity 4.9 vs. 5.7 kPa, p = 0.024; right vs. left cortex: mean viscoelasticity 5.8 vs. 7.5 kPa; p = 0.004 and mean elasticity 5 vs. 6.5 kPa; p = 0.008). A direct comparison of the biomechanical properties of focal T2w hyperintensities with normal appearing brain tissue did not yield significant results. Control animals showed no differences in viscoelasticity between sonicated and contralateral brain parenchyma. We here provide first evidence for a controlled lesion induction model in EAE using FUS-induced BBBD. The observed lesions in EAE are consistent with foci of activated microglia that may be interpreted as targeted initial inflammatory activity and which have been described as pre-active lesions in MS. Such foci can be identified and monitored with MRI. Moreover, the increased inflammatory activity in the sonicated brain parenchyma seems to have an effect on overall tissue matrix structure as reflected by changes of biomechanical parameters

Microglial confetti party

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The TREM2-APOE Pathway Drives the Transcriptional Phenotype of Dysfunctional Microglia in Neurodegenerative Diseases

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