Palomino-Antolin, A. | bioRxiv Science

bioRxiv2020

Time-dependent dual effect of NLRP3 inflammasome in brain ischemia

Background and purposePost-ischemic inflammation contributes to worsening of ischemic brain injury and in this process, the inflammasomes play a key role. Inflammasomes are cytosolic multiprotein complexes which upon assembly activate the maturation and secretion of the inflammatory cytokines IL-1{beta} and IL-18. However, participation of the NLRP3 inflammasome in ischemic stroke remains controversial. Our aims were to determine the role of NLRP3 in ischemia and to explore the mechanism involved in the potential protective effect of the neurovascular unit. MethodsWT and NLRP3 knock-out mice were subjected to ischemia by middle cerebral artery occlusion (60 minutes) with or without treatment with MCC950 at different time points post-stroke. Brain injury was measured histologically with 2,3,5-triphenyltetrazolium chloride (TTC) staining. ResultsWe identified a time-dependent dual effect of NLRP3. While neither the pre-treatment with MCC950 nor the genetic approach (NLRP3 KO) proved to be neuroprotective, post-reperfusion treatment with MCC950 significantly reduced the infarct volume in a dose-dependent manner. Importantly, MCC950 improved the neuro-motor function and reduced the expression of different pro-inflammatory cytokines (IL-1{beta}, TNF-), NLRP3 inflammasome components (NLRP3, pro-caspase-1), protease expression (MMP9) and endothelial adhesion molecules (ICAM, VCAM). We observed a marked protection of the blood-brain barrier (BBB), which was also reflected in the recovery of the tight junctions proteins (ZO-1, Claudin-5). Additionally, MCC950 produced a reduction of the CCL2 chemokine in blood serum and in brain tissue, which lead to a reduction in the immune cell infiltration. ConclusionsThese findings suggest that post-reperfusion NLRP3 inhibition may be an effective acute therapy for protecting the blood-brain barrier in cerebral ischemia with potential clinical translation.

neuroscience↗

bioRxiv2020

Microglia-to-astrocyte communication modulates synaptic and cerebrovascular functions following traumatic brain injury

Background and purposeActivation of astrocytes contributes to synaptic remodeling, tissue repair and neuronal survival following traumatic brain injury (TBI). However, the mechanisms by which these cells interact to infiltrated inflammatory cells to rewire neuronal networks and repair brain functions remain poorly understood. Here, we explored how TLR4-induced astrocyte activation modified synapses and cerebrovascular integrity following TBI. Experimental approachWe used pharmacological and genetic approaches to determine how functional astrocyte alterations induced by activation of TLR4-pathway in inflammatory cells regulate synapses and neurovascular unit after TBI. For that, we used calcium imaging, immunofluorescence, flow cytometry, blood-brain barrier (BBB) integrity assessment and molecular and behavioral tools. Key resultsShortly after a TBI there is a recruitment of excitable and reactive astrocytes mediated by TLR4-pathway activation with detrimental effects on PSD-95/VGlut1 synaptic puncta, BBB integrity and neurological outcome. Pharmacological blockage of the TLR4-pathway with TAK242 partially reverted many of the observed effects. Synapses and BBB recovery after TAK242 administration were not observed in IP3R2-/- mice, indicating that effects of TLR4-inhibition depend on the subsequent astrocyte activation. In addition, TBI increased the astrocytic-protein thrombospondin-1 necessary to induce a synaptic recovery in a sub-acute phase. Conclusions and implicationsOur data demonstrate that TLR4-mediated signaling, most probably though microglia and/or infiltrated monocyte-astrocyte communication, plays a crucial role in the TBI pathophysiology and that its inhibition prevents synaptic loss and BBB damage accelerating tissue recovery/repair, which might represent a therapeutic potential in CNS injuries and disorders. Declaration of transparency and scientific rigourThis Declaration acknowledges that this paper adheres to the principles for transparent reporting and scientific rigour of preclinical research as stated in the BJP guidelines for Design & Analysis, Immunoblotting and Immunochemistry, and Animal Experimentation, and as recommended by funding agencies, publishers and other organisations engaged with supporting research. Bullet point summaryWhat is already known: O_LIAstrocytes and microglia participate in the early cerebral and synaptic response after traumatic brain injury. C_LIO_LITLR4 antagonism exerts neuroprotection in acute brain injuries. C_LI What this study adds: O_LIAcute astrocyte activation contributes to synaptic loss and BBB breakdown in the acute phase of TBI, and synaptic remodeling in the sub-acute phase. C_LIO_LIAstrocyte activation is mediated by microglia/infiltrating-monocytes activation through TLR4 receptors. C_LI Clinical significance: O_LIInhibition of astrocyte activation through TLR4 antagonism could be a promising option for TBI treatment. C_LI

neuroscience↗