Vascular Response to Spreading Depolarization Predicts Stroke Outcome

Background: Cortical spreading depolarization (CSD) is a massive neuro-glial depolarization wave, which propagates across the cerebral cortex. In stroke, CSD is a necessary and ubiquitous mechanism for the development of neuronal lesions that initiates in the ischemic core and propagates through the penumbra extending the tissue injury. Although CSD propagation induces dramatic changes in cerebral blood flow, the vascular responses in different ischemic regions and their consequences on reperfusion and recovery remain to be defined. Methods: Ischemia was performed using the thrombin model of stroke and reperfusion was induced by r-tPA (recombinant tissue-type plasminogen activator) administration in mice. We used in vivo electrophysiology and laser speckle contrast imaging simultaneously to assess both electrophysiological and hemodynamic characteristics of CSD after ischemia onset. Neurological deficits were assessed on day 1, 3, and 7. Furthermore, infarct sizes were quantified using 2,3,5-triphenyltetrazolium chloride on day 7. Results: After ischemia, CSDs were evidenced by the characteristic propagating DC shift extending far beyond the ischemic area. On the vascular level, we observed 2 types of responses: some mice showed spreading hyperemia confined to the penumbra area (penumbral spreading hyperemia) while other showed spreading hyperemia propagating in the full hemisphere (full hemisphere spreading hyperemia). Penumbral spreading hyperemia was associated with severe stroke-induced damage, while full hemisphere spreading hyperemia indicated beneficial infarct outcome and potential viability of the infarct core. In all animals, thrombolysis with r-tPA modified the shape of the vascular response to CSD and reduced lesion volume. Conclusions: Our results show that different types of spreading hyperemia occur spontaneously after the onset of ischemia. Depending on their shape and distribution, they predict severity of injury and outcome. Furthermore, our data show that modulating the hemodynamic response to CSD may be a promising therapeutic strategy to attenuate stroke outcome

Machine-guided design of cell-type-targeting cis-regulatory elements.

Cis-regulatory elements (CREs) control gene expression, orchestrating tissue identity, developmental timing and stimulus responses, which collectively define the thousands of unique cell types in the body1–3 . While there is great potential for strategically incorporating CREs in therapeutic or biotechnology applications that require tissue specificity, there is no guarantee that an optimal CRE for these intended purposes has arisen naturally. Here we present a platform to engineer and validate synthetic CREs capable of driving gene expression with programmed cell-type specificity. We take advantage of innovations in deep neural network modelling of CRE activity across three cell types, efficient in silico optimization and massively parallel reporter assays to design and empirically test thousands of CREs4–8 . Through large-scale in vitro validation, we show that synthetic sequences are more effective at driving cell-type- specific expression in three cell lines compared with natural sequences from the human genome and achieve specificity in analogous tissues when tested in vivo. Synthetic sequences exhibit distinct motif vocabulary associated with activity in the on-target cell type and a simultaneous reduction in the activity of off-target cells. Together, we provide a generalizable framework to prospectively engineer CREs from massively parallel reporter assay models and demonstrate the required literacy to write fit-for-purpose regulatory code

Characterization of spontaneous scillatory activity of the peri-lesional cortex during post-ischemic functional recovery

Malgré l’amélioration considérable dans les approches de traitement de l’AVC ischémique au cours des dernières décennies, une grande majorité des patients survivant à la phase aiguë présentent des séquelles neurologiques affectant considérablement leurs qualités de vie. L’ischémie cérébrale demeure donc un des principaux problèmes de santé publique. Pour rétablir les fonctions perdues chez les patients, les interventions de réhabilitation visent à renforcer la capacité de récupération du cerveau. Une cible particulièrement intéressante est la zone adjacente à l’infarctus (le cortex péri-infarci). Cette zone est un véritable réservoir de plasticité, mais la récupération est entravée par des processus cellulaires et moléculaires liés à la cicatrisation. Dans ce contexte, les oscillations neuronales, en particulier la puissance des oscillations gamma (30-50 Hz) qui organisent l’activité neuronale et favorisent la plasticité synaptique, sont spécifiquement diminuées dans le cortex péri-infarci pendant la récupération. Ainsi, pour comprendre leur importance dans la récupération, nous avons cherché à étudier l’origine du déficit des gamma dans un modèle expérimental d’AVC.Nos résultats reconfirment le déficit du gamma dans le cortex péri-infarci survenant à des périodes clés de la récupération spontanée. Grâce à une évaluation parallèle de la récupération de la dextérité de la patte avant et de l’activité oscillatoire, nous avons mis en évidence un lien entre la puissance des gammas dans la zone péri-lésionnelle et le niveau de récupération. Nous avons aussi mis en évidence que l’excès du GABA ambiant du cortex en récupération probablement causé par les astrocytes réactifs serait à l’origine de la réduction de la puissance des gammas. En modulant la signalisation GABAergique tonique avec des outils pharmacologiques, la puissance des oscillation gamma peut être boosté dans la zone perilésionnelle. À 4 mois, la restauration de de puissance des gammas est conjointe à la résolution de l’astrogliose réactive et à une normalisation de l’expression du GABA dans le cortex peri-infarci.Nos résultats suggèrent que les oscillations gamma jouent un rôle majeur dans le déroulement de la récupération fonctionnelle et peuvent être un biomarqueur potentiel pour la récupération. De plus, le niveau de GABA extracellulaire est déterminant pour la maintenance des oscillations gamma. Ainsi, une voie thérapeutique potentielle de récupération fonctionnelle post-ischémique pourrait être la stimulation des oscillations gamma.Even though acute stroke treatment has improved significantly over the last few decades, majority of patients to date suffer neurological disabilities which substantially impact their quality of life. Brain ischaemia thus remains one of the leading causes of burden to healthcare systems worldwide. To reinstate functions lost by patients, stroke intervention therapies aim at boosting the brain’s natural capacity to recover. A major approach is to target the area adjoining the infarct. Even though this zone represents a genuine reservoir of plasticity, recovery is hampered by cellular and molecular processes linked to lesion scarring. In this context, neural oscillations, in particular low gamma oscillations (30-50Hz) which organize neuronal activity into assemblies and favours synaptic plasticity is specifically diminished in the peri-infarct cortex during recovery. Thus, to understand their importance to recovery, we sought to investigate the origin of the low gamma deficit in an experimental stroke model.We reconfirm the low gamma power deficit in the peri-infarct cortex occurring at key periods of recovery. Simultaneous evaluation of forepaw dexterity recovery and Local field potential oscillatory activity reveal a correlation between peri-infarct low gamma power and the level of recovery. Furthermore, excessive tonic GABA in the perilesional area mediated by reactive astrocytes reduces low gamma oscillation power. Using pharmacological tools to modulate GABA signalling, low gamma oscillation power was rescued in the peri-infarct cortex. At 4 months restoration of baseline low gamma power coincides with resolution of reactive astrogliosis and evidently normalized GABA expression in the peri-infarct area.Our results suggest that low gamma oscillations play a major role in orchestrating functional recovery and may be a potential biomarker for recovery. Furthermore, the tonic GABAergic system is an active player in low gamma rhythmogenesis. Thus, a potential therapeutic avenue of stroke recovery might be to boost low gamma oscillations

Prolonged deficit of gamma oscillations in the peri-infarct cortex of mice after stroke

International audienceDays and weeks after an ischemic stroke, the peri-infarct area adjacent to the necrotic tissue exhibits very intense synaptic reorganization aimed at regaining lost functions. In order to enhance functional recovery, it is important to understand the mechanisms supporting neural repair and neuroplasticity in the cortex surrounding the lesion. Brain oscillations of the local field potential (LFP) are rhythmic fluctuations of neuronal excitability that synchronize neuronal activity to organize information processing and plasticity. Although the oscillatory activity of the brain has been probed after stroke in both animals and humans using electroencephalography (EEG), the latter is ineffective to precisely map the oscillatory changes in the peri-infarct zone where synaptic plasticity potential is high. Here, we worked on the hypothesis that the brain oscillatory system is altered in the surviving peri-infarct cortex, which may slow down the functional repair and reduce the recovery. In order to document the relevance of this hypothesis, oscillatory power was measured at various distances from the necrotic core at 7 and 21 days after a permanent cortical ischemia induced in mice. Delta and theta oscillations remained at a normal power in the peri-infarct cortex, in contrast to low gamma oscillations that displayed a gradual decrease, when approaching the border of the lesion. A broadband increase of power was also observed in the homotopic contralateral sites. Thus, the proximal peri-infarct cortex could become a target of therapeutic interventions applied to correct the oscillatory regimen in order to boost post-stroke functional recovery