Epigenetic control of microglial immune responses

Microglia, the major population of brain-resident macrophages, are now recognized as a heterogeneous population comprising several cell subtypes with different (so far mostly supposed) functions in health and disease. A number of studies have performed molecular characterization of these different microglial activation states over the last years making use of omics technologies, that is transcriptomics, proteomics and, less frequently, epigenomics profiling. These approaches offer the possibility to identify disease mechanisms, discover novel diagnostic biomarkers, and develop new therapeutic strategies. Here, we focus on epigenetic profiling as a means to understand microglial immune responses beyond what other omics methods can offer, that is, revealing past and present molecular responses, gene regulatory networks and potential future response trajectories, and defining cell subtype-specific disease relevance through mapping non-coding genetic variants. We review the current knowledge in the field regarding epigenetic regulation of microglial identity and function, provide an exemplary analysis that demonstrates the advantages of performing joint transcriptomic and epigenomic profiling of single microglial cells and discuss how comprehensive epigenetic analyses may enhance our understanding of microglial pathophysiology

Altern und Entzündung im peripheren Nervensystem

Aging is known to be a risk factor for structural abnormalities and functional decline in the nervous system. Characterizing age-related changes is important to identify putative pathways to overcome deleterious effects and improve life quality for the elderly. In this study, the peripheral nervous system of 24-month-old aged C57BL/6 mice has been investigated and compared to 12-month-old adult mice. Aged mice showed pathological alterations in their peripheral nerves similar to nerve biopsies from elderly human individuals, with nerve fibers showing demyelination and axonal damage. Such changes were lacking in nerves of adult 12-month-old mice and adult, non-aged humans. Moreover, neuromuscular junctions of 24-month-old mice showed increased denervation compared to adult mice. These alterations were accompanied by elevated numbers of macrophages in the peripheral nerves of aged mice. The neuroinflammatory conditions were associated with impaired myelin integrity and with a decline of nerve conduction properties and muscle strength in aged mice. To determine the pathological impact of macrophages in the aging mice, macrophage depletion was performed in mice by oral administration of CSF-1R specific kinase (c-FMS) inhibitor PLX5622 (300 mg/kg body weight), which reduced the number of macrophages in the peripheral nerves by 70%. The treated mice showed attenuated demyelination, less muscle denervation and preserved muscle strength. This indicates that macrophage-driven inflammation in the peripheral nerves is partially responsible for the age-related neuropathy in mice. Based on previous observations that systemic inflammation can accelerate disease progression in mouse models of neurodegenerative diseases, it was hypothesized that systemic inflammation can exacerbate the peripheral neuropathy found in aged mice. To investigate this hypothesis, aged C57BL/6 mice were intraperitoneally injected with a single dose of lipopolysaccharide (LPS; 500 μg/kg body weight) to induce systemic inflammation by mimicking bacterial infection, mostly via activation of Toll-like receptors (TLRs). Altered endoneurial macrophage activation, highlighted by Trem2 downregulation, was found in LPS injected aged mice one month after injection. This was accompanied by a so far rarely observed form of axonal perturbation, i.e., the occurrence of “dark axons” characterized by a damaged cytoskeleton and an increased overall electron density of the axoplasm. At the same time, however, LPS injection reduced demyelination and muscle denervation in aged mice. Interestingly, TREM2 deficiency in aged mice led to similar changes to LPS injection. This suggests that LPS injection likely mitigates aging-related demyelination and muscle denervation via Trem2 downregulation. Taken together, this study reveals the role of macrophage-driven inflammation as a pathogenic mediator in age-related peripheral neuropathy, and that targeting macrophages might be an option to mitigate peripheral neuropathies in aging individuals. Furthermore, this study shows that systemic inflammation may be an ambivalent modifier of age-related nerve damage, leading to a distinct type of axonal perturbation, but in addition to functionally counteracting, dampened demyelination and muscle denervation. Translationally, it is plausible to assume that tipping the balance of macrophage polarization to one direction or the other may determine the functional outcome in the aging peripheral nervous system of the elderly.Es ist bekannt, dass das Altern ein Risikofaktor für strukturelle Veränderungen und Funktionsstörungen des Nervensystems ist. Die Charakterisierung altersbedingter Veränderungen ist wichtig, um mögliche Wege zu identifizieren, um schädliche Auswirkungen zu überwinden und die Lebensqualität älterer Menschen zu verbessern. In dieser Studie wurde das periphere Nervensystem von 24 Monate alten gealterten C57BL/6-Mäusen untersucht und mit 12 Monate alten adulten Mäusen verglichen. Gealterte Mäuse zeigten ähnliche pathologische Veränderungen in ihren peripheren Nerven wie Nervenbiopsien älterer Menschen, wobei die Nervenfasern eine Demyelinisierung und axonale Schädigung zeigten. Bei den Nerven von adulten 12 Monate alten Mäusen und nicht gealterten Menschen fehlten solche Veränderungen. Darüber hinaus wiesen die neuromuskulären Endplatten von 24 Monate alten Mäusen im Vergleich zu adulten Mäusen eine erhöhte Denervation auf. Diese Veränderungen wurden von einer erhöhten Anzahl von Makrophagen in den peripheren Nerven gealterter Mäuse begleitet. Die neuroinflammatorischen Bedingungen waren mit einer Beeinträchtigung der Myelinintegrität, einer Abnahme der Nervenleitungseigenschaften und der Muskelkraft bei gealterten Mäusen verbunden. Um den pathologischen Einfluss von Makrophagen bei alternden Mäusen zu bestimmen, wurde die Makrophagen-Depletion bei Mäusen durch orale Verabreichung des CSF-1R-spezifischen Kinase-Inhibitors (c-FMS) PLX5622 (300 mg/kg Körpergewicht) durchgeführt, welche die Anzahl der Makrophagen in den peripheren Nerven um 70% reduzierte. Die behandelten Mäuse zeigten eine verminderte Demyelinisierung, eine reduzierte Muskeldenervation und einen Erhalt der Muskelkraft. Dies deutet darauf hin, dass die durch Makrophagen verursachte Entzündung in den peripheren Nerven teilweise für die altersbedingte Neuropathie bei Mäusen verantwortlich ist. Auf der Grundlage früherer Beobachtungen, dass systemische Entzündungen das Fortschreiten der Krankheit in Mausmodellen neurodegenerativer Erkrankungen beschleunigen können, wurde die Hypothese aufgestellt, dass systemische Entzündungen die periphere Neuropathie in gealterten Mäusen verschlimmern können. Um diese Hypothese zu untersuchen, wurde gealterten C57BL/6-Mäusen eine Einzeldosis Lipopolysaccharid (LPS; 500 μg/kg Körpergewicht) intraperitonal injiziert, um eine systemische Entzündung durch Nachahmung einer bakteriellen Infektion, meist über die Aktivierung von Toll-like-Rezeptoren (TLRs), zu induzieren. Eine veränderte endoneuriale Makrophagenaktivierung, die durch eine reduzierte Trem2-Expression hervorgehoben wird, konnte bei LPS-injizierten gealterten Mäusen einen Monat nach der Injektion gefunden werden. Dies ging einher mit einer bisher selten beobachteten Form der axonalen Perturbation, d.h. dem Auftreten von "dunklen Axonen", die sich durch ein geschädigtes Zytoskelett und eine erhöhte Gesamtelektronendichte des Axoplasmas auszeichnen. Gleichzeitig verringerte die LPS-Injektion jedoch die Demyelinisierung und Muskeldenervation bei gealterten Mäusen. Interessanterweise führte die TREM2 Defizienz bei gealterten Mäusen zu vergleichbaren Veränderungen wie die LPS-Injektion. Dies deutet darauf hin, dass die LPS-Injektion die alterungsbedingte Demyelinisierung und Muskeldenervierung über die Trem2 Herunterregulation abschwächt. Zusammenfassend zeigt diese Studie die Rolle der Makrophagen-getriebenen Entzündung als pathogener Mediator bei der altersbedingten peripheren Neuropathie. Zusätzlich deuten die Ergebnisse darauf hin, dass die gezielte Behandlung von Makrophagen eine Option zur Linderung peripherer Neuropathien bei alternden Menschen sein könnte. Darüber hinaus zeigt diese Studie, dass die systemische Entzündung ein ambivalenter Modifikator der altersbedingten Nervenschädigung sein kann, der zu einer bestimmten Art von axonaler Perturbation führt, aber zusätzlich zu einer funktionell entgegenwirkenden, weniger schweren Demyelinisierung und Muskeldenervation. Translatorisch ist es plausibel anzunehmen, dass eine Veränderung des Gleichgewichts der Makrophagenpolarisation in die eine oder andere Richtung das funktionelle Ergebnis im alternden peripheren Nervensystem der älteren Menschen bestimmen kann

Early targeting of endoneurial macrophages alleviates the neuropathy and affects abnormal Schwann cell differentiation in a mouse model of Charcot-Marie-Tooth 1A

We have previously shown that targeting endoneurial macrophages with the orally applied CSF-1 receptor specific kinase (c-FMS) inhibitor PLX5622 from the age of 3 months onwards led to a substantial alleviation of the neuropathy in mouse models of Charcot-Marie-Tooth (CMT) 1X and 1B disease, which are genetically-mediated nerve disorders not treatable in humans. The same approach failed in a model of CMT1A (PMP22-overexpressing mice, line C61), representing the most frequent form of CMT. This was unexpected since previous studies identified macrophages contributing to disease severity in the same CMT1A model. Here we re-approached the possibility of alleviating the neuropathy in a model of CMT1A by targeting macrophages at earlier time points. As a proof-of-principle experiment, we genetically inactivated colony-stimulating factor-1 (CSF-1) in CMT1A mice, which resulted in lower endoneurial macrophage numbers and alleviated the neuropathy. Based on these observations, we pharmacologically ablated macrophages in newborn CMT1A mice by feeding their lactating mothers with chow containing PLX5622, followed by treatment of the respective progenies after weaning until the age of 6 months. We found that peripheral neuropathy was substantially alleviated after early postnatal treatment, leading to preserved motor function in CMT1A mice. Moreover, macrophage depletion affected the altered Schwann cell differentiation phenotype. These findings underscore the targetable role of macrophage-mediated inflammation in peripheral nerves of inherited neuropathies, but also emphasize the need for an early treatment start confined to a narrow therapeutic time window in CMT1A models and potentially in respective patients

Statistical Characteristics of Mesoscale Convective Systems Initiated over the Tibetan Plateau in Summer by Fengyun Satellite and Precipitation Estimates

In order to investigate the key characteristics of mesoscale convective systems (MCSs) initiated over the Tibetan Plateau (TP) in recent years and the main differences in circulation and environmental factors between different types of MCSs, an automatic MCS identification and tracking method was applied based on the data from China’s Fengyun satellite and precipitation estimates. In total, 8820 MCSs were found to have been initiated over the TP during the summers from 2013 to 2019, and a total of 9.3% of them were able to move eastward out of the TP (EO). The number of MCSs showed a monthly variation, with a maximum in July and a minimum in June, while most EOs occurred in June. Compared with other types of MCSs, EOs usually had a lower cloud-top temperature, a greater rainfall intensity, a longer life duration, more rapid development, larger areas of rainfall and convective clouds, longer tracks and a wider influence range, indicating that EOs are more vigorous than the other types of MCSs. The movement of MCSs is mainly due to the mid- to high-level dynamic conditions, and moisture is an essential factor in their development and maintenance

Distinct roles of α‐ and β‐tubulin polyglutamylation in controlling axonal transport and in neurodegeneration

International audienc

H3K4me3 redistribution from TSS to miRNA-coding region affects miRNA expression in LPS-conditioned moDCs.

<p>(<b>A</b>) Proportion of H3K4me3 redistribution around the TSSs in the LPS- (LPS) or TGF-β(TGFβ)-upregulated miRNA with H3K4me3 modification. (<b>B</b>) H3K4me3 redistribution around the TSSs in the LPS-upregulated miRNA with H3K4me3 modification. For ChIP-Seq analysis, the MoDCs were exposed to LPS (100 ng/ml) for 24 hrs. The gene structure was downloaded from the UCSC Genome Brower. Enriched regions were found in the UCSC Genome Browser (<a href="http://genome.ucsc.edu" target="_blank">http://genome.ucsc.edu</a>.). Histone modification peaks were detected by CHIPOTle. The miRNA positions were predicted by Ensembl. The definitive and putative miRNATSSs were inferred from <a href="http://mirstart.mbc.nctu.edu.tw/browse.php" target="_blank">http://mirstart.mbc.nctu.edu.tw/browse.php</a>. (<b>C</b>) qRT-PCR analysis of microRNA in LPS-conditioned DCs. moDCs were exposed to LPS (100 ng/ml) for 24 hrs, and the total RNAs was extracted from LPS-conditioned DCs. R.E, relative expression. The qRT-PCR data were representative of three healthy donors. The arrow points in the direction of gene transcription. *, P<0.05; **, P<0.01.</p

LPS associated factors affects the expression of miRNAs with H3K4me3 redistribution.

<p>(<b>A</b>) qRT-PCR analyses of epigenetic factors RBBP4, RBBP7, HDAC1, MLL, RBBP5, EED, EZH2, JHM1D and SUZ12. Total RNA was extracted from moDCs following exposure to LPS (100 ng/ml) for 24 hrs and the expressions of RBBP4, RBBP7, HDAC1, MLL, RBBP5, EED, EZH2, JHM1D and SUZ12 were analyzed by qRT-PCR. (<b>B</b>) qRT-PCR analyses of miR-146a, miR-155, miR-29 and miR-210 in siRNA-transfected moDCs. MoDCs were transfected with siRNAs against RBBP4 (siRBBP4), RBBP7 (siRBBP7), HDAC1 (siHDAC1) or with control siRNA (siMock). After 48 hrs, total RNAs were extracted and analyzed by qRT-PCR. (<b>C</b>) qRT-PCR analyses of miR-146a and miR-155 in siRNA-transfected moDCs. moDCs were respectively transfected with siRNAs against p300 (siP300), p65 (sip65), p50 (siP50), or with control siRNA (siMock). After 48 hrs, total RNA was extracted and analyzed by qRT-PCR. (<b>D</b>) TNFα ELISA analyses of supernatants from siRBBP4 transfected moDCs. The supernatants were collected from siRBBP4 transfected moDCs and the TNFα concentrations were analyzed by ELISA (R&D, USA). (<b>E</b>) Flow cytometry analysis of CD86. siRBBP4 transfected moDCs were stained with anti-CD86 (IT2.2) and analyzed by flow cytometry. Grey, isotypic control. *, P<0.05; **, P<0.01.</p

Regulation of miRNA expression in LPS-conditioned moDCs.

<p>When moDCs are exposed to LPS, activated NF-κB p65 induces H3K4me3 redistribution from the TSS to miRNA-coding region by interacting with p300 and RBBP4/RBBP7. Meanwhile, activated NF-κB transcription factors (such as p65, p52, p50, C-rel and CrelB) bind to promoter regions and initiate miRNA expression. AP-1 components Jun and c-fos, which are activated by LPS, also bind with the miR-146a and miR-155 promoters to induce miR-155 and miR-146a gene expression.</p

In moDCs, active and repressive miRNAs are associated with H3K4me3 and H3K27me3 modification, respectively.

<p>(<b>A</b> and <b>B</b>) Proportion of moDCs-associated miRNAs with H3K4me3 or H3K27me3 modification. High, miRNAs with remarkable H3K4me3 or H3K27me3 modification; low, miRNAs with less H3K4me3 or H3K27me3 modification; no, miRNAs without H3K4me3 or H3K27me3 modification. (<b>C</b>) Repressive miRNAs with H3K27me3 modification. (<b>D</b>) Proportion of moDCs associated miRNAs with both H3K4me3 and H3K27me3 modification (Both). MoDCs were generated and visualized with anti-CD14, anti-CD83, anti-CD11c, anti-CD86, anti-CD80, anti-CD40 and anti-CD11b <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090231#pone.0090231-Huang1" target="_blank">[27]</a>. The gene structure was downloaded from the UCSC Genome Brower. Enriched regions were found in the UCSC Genome Browser (<a href="http://genome.ucsc.edu" target="_blank">http://genome.ucsc.edu</a>.). Histone modification peaks were detected by CHIPOTle. miRNA positions were predicted by Ensembl. The definitive and putative miRNA TSSs were inferred from <a href="http://mirstart.mbc.nctu.edu.tw/browse.php" target="_blank">http://mirstart.mbc.nctu.edu.tw/browse.php</a>. PTSS, putative transcription start site; DTSS, definitive transcription start site.</p