Multiple sclerosis | EPFL Graph Search

Multiple sclerosis (MS) is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This damage disrupts the ability of parts of the nervous system to transmit signals, resulting in a range of signs and symptoms, including physical, mental, and sometimes psychiatric problems. Specific symptoms can include double vision, visual loss, muscle weakness, and trouble with sensation or coordination. MS takes several forms, with new symptoms either occurring in isolated attacks (relapsing forms) or building up over time (progressive forms). In the relapsing forms of MS, between attacks, symptoms may disappear completely, although some permanent neurological problems often remain, especially as the disease advances. While the cause is unclear, the underlying mechanism is thought to be either destruction by the immune system or failure of the myelin-producing cells. Proposed caus

Epigenetic memory aids: Synaptic and molecular effects of HDAC inhibition that support memory formation

Allison Marie Burns

Learning and memory rely on synaptic communication in which intracellular signals are transported to the nucleus to stimulate transcriptional activation. Memory induced transcriptional increases are accompanied by alterations to the epigenetic landscape and can be pharmacologically mimicked to ameliorate memory in both healthy and cognitively impaired animals. Of particular interest in this regard is histone acetylation, as this epigenetic modification is enriched during memory formation and is readily amenable to pharmacological manipulation by means of histone deacetylase inhibitors (HDACis). Although multiple studies have shown that systemic HDACi administration can improve memory formation, their mode of action is not yet fully understood. In this study, we tested whether HDACis â given systemically â augment epigenetic, transcriptional and electrophysiological responses that are induced by learning, thus amplifying naturally occurring responses via cognitive epigenetic priming. To do this, we combined a system-wide HDACi treatment with a sub-threshold contextual fear conditioning (CFC) paradigm, a weakened Pavlovian modal that, alone, does not lead to long term memory formation. We found that, in combination, HDACi and CFC improve recent contextual memory that is accompanied by enhanced long-term potentiation in the hippocampus. Conversely, combined HDACi-CFC treatment induced no such synaptic strengthening in the striatum, a brain region that is not directly activated by fear conditioning. We then used bulk and single nuclear RNA-sequencing to show that HDACi activates unique transcriptional pathways, both between the two brain regions and between cell types within the hippocampus, indicating that HDACi does not act indiscriminatingly, but instead supports cellular processes that are already occurring in response to the conditioning. Finally, we show that HDACi treatment paired with contextual fear conditioning enriches H3K27ac at enhancers of known memory-related genes within the hippocampus but that not all these genes are necessarily more transcriptionally active at the same time point. These results indicate that systemic HDACi administration acts as a cognitive enhancer by amplifying brain-region specific processes that are naturally induced during memory formation but that these results may not be a direct effect of enhancer histone acetylation. These findings shed light on the mechanisms of HDACi-mediated cognitive epigenetic priming and help to pave the way for potential new therapies for memory-related disorders.

EPFL2022

Rhythmic and clock-dependent chromatin loops regulate circadian gene expression

Jérôme Mermet

In mammals the circadian clock drives daily behavioural and physiological changes that resonate with environmental cues, which can be observed, for example, in the intricate timing of rest during the night and activity during the day in humans. The circadian clock consists of a network of hierarchical clocks in which the central pacemaker is located in the suprachiasmatic nucleus, which is sensitive to external light and propagates time to the peripheral organ-based clocks. Within organs, clocks tick in each individual cell and are molecularly encoded in the genome as a network of dynamic feedback loops. By mediating the expression of the appropriate gene products at the correct moment of the day, the molecular clocks op-timize physiological functions of virtually every cell in our body, allowing us to synchronize with daily fluc-tuations in the environment. In mammalian cells the chromatin organization in the nucleus consists of a topological network, in which chromatin interactions between distal regulatory elements such as enhancers and target genes are essen-tial to regulate gene expression. Important questions remain: is the complex chromatin folding dynamic and if so on which genomic and temporal scales? In fact, dynamic rearrangements of the chromatin have been reported on multiple genomic and time scales, from the entire genome to enhancer-promoter con-tacts, across developmental transitions, cellular differentiation, and transcription cycles. With this per-spective in mind, the circadian oscillator provides a unique model to study the dynamics of genomic inter-actions in the context of fluctuating transcription. Here, we explored chromatin contacts of core-clock and clock-controlled gene promoters in the mouse. We aimed at evaluating the putative dynamics of chromatin contacts, at estimating their conservation across tissues, and at exploring the contribution of the circadian clock to this interaction network. To achieve this goal, we performed 4C-sequencing assays at two circadian time points in the liver and kidney of WT and clock-deficient animals. Overall, we observe that chromatin contacts are largely conserved across circadian time points and genetic backgrounds, and are tissue-specific. Our experiments reveal that the promoters of core-clock and clock-controlled genes contact distal genomic regions containing en-hancer chromatin signatures, suggesting a functional role of these distal sites in target gene regulation. Our data also suggest a clock-driven module of rhythmic genes that are colocalized in the nucleus. However, we also observe dynamic contacts between oscillating gene promoter and enhancer-like ge-nomic regions. In this thesis, we discuss in detail two examples of dynamic chromatin looping that are ob-served at the Cry1 and Gys2 loci. Our data reveal not only a dynamic coupling between the chromatin loop and the transcriptional state but also that the dynamic of chromatin looping depends on a functional clock. Furthermore, genome editing experiments using CRISPR-Cas9 tools reveal that the Cry1 distal site is essential for the transcriptional regulation of Cry1 and contributes to the circadian clock robustness both in-vivo and in cultured cells. These results demonstrate how local chromatin rearrangements take place in a 24-hour time-scale and set chromatin looping between gene promoters and distal regions as a new reg-ulatory layer for circadian gene expression.

EPFL2017

IL-17 controls central nervous system autoimmunity through the intestinal microbiome

Sandrine Natacha Isaac

Interleukin-17A- (IL-17A) and IL-17F-producing CD4(+) T helper cells (T(H)17 cells) are implicated in the development of chronic inflammatory diseases, such as multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). T-H 17 cells also orchestrate leukocyte invasion of the central nervous system (CNS) and subsequent tissue damage. However, the role of IL-17A and IL-17F as effector cytokines is still confused with the encephalitogenic function of the cells that produce these cytokines, namely, T-H 17 cells, fueling a long-standing debate in the neuroimmunology field. Here, we demonstrated that mice deficient for IL-17A/F lose their susceptibility to EAE, which correlated with an altered composition of their gut microbiota. However, loss of IL-17A/F in T-H cells did not diminish their encephalitogenic capacity. Reconstitution of a wild-type-like intestinal microbiota or reintroduction of IL-17A specifically into the gut epithelium of IL-17A/F-deficient mice reestablished their susceptibility to EAE. Thus, our data demonstrated that IL-17A and IL-17F are not encephalitogenic mediators but rather modulators of intestinal homeostasis that indirectly alter CNS-directed autoimmunity.

AMER ASSOC ADVANCEMENT SCIENCE2021