Age-at-injury effects of microglial activation following traumatic brain injury： implications for treatment strategies

Traumatic brain injury（TBI）remains one of the leading causes of disability and death in infants and children.Studies have demonstrated that the youngest age group（especially≤4 years old）exhibit worse functional outcome following moderate to severe TBI compared to older children or adults（Anderson et al.,2005;Emami et al.,2017）.These data suggest that age-at-injury may be an important determinant of outcome,

Vav1 promotes inflammation and neuronal apoptosis in cerebral ischemia/reperfusion injury by upregulating microglial and NLRP3 inflammasome activation

Microglia,which are the resident macrophages of the central nervous system,are an important part of the inflammatory response that occurs after cerebral ischemia.Vav guanine nucleotide exchange factor 1(Vav1) is a guanine nucleotide exchange factor that is related to microglial activation.However,how Vav1 participates in the inflammato ry response after cerebral ischemia/reperfusion inj ury remains unclea r.In this study,we subjected rats to occlusion and repe rfusion of the middle cerebral artery and subjected the BV-2 mic roglia cell line to oxygen-glucose deprivatio n/reoxygenation to mimic cerebral ischemia/repe rfusion in vivo and in vitro,respectively.We found that Vav1 levels were increased in the brain tissue of rats subjected to occlusion and reperfusion of the middle cerebral arte ry and in BV-2 cells subjected to oxygen-glucose deprivation/reoxygenation.Silencing Vav1 reduced the cerebral infarct volume and brain water content,inhibited neuronal loss and apoptosis in the ischemic penumbra,and im p roved neurological function in rats subjected to occlusion and repe rfusion of the middle cerebral artery.Further analysis showed that Vav1 was almost exclusively localized to microglia and that Vav1 downregulation inhibited microglial activation and the NOD-like receptor pyrin 3(NLRP3) inflammasome in the ischemic penumbra,as well as the expression of inflammato ry facto rs.In addition,Vov1 knoc kdown decreased the inflammatory response exhibited by BV-2 cells after oxygen-glucose deprivation/reoxyge nation.Taken together,these findings show that silencing Vav1 attenuates inflammation and neuronal apoptosis in rats subjected to cerebral ischemia/repe rfusion through inhibiting the activation of mic roglia and NLRP3 inflammasome.

The role of general anesthetics and the mechanisms of hippocampal and extra-hippocampal dysfunctions in the genesis of postoperative cognitive dysfunction

Postoperative cognitive dysfunction （POCD） is a multifactorial process with a huge number of predisposing, causal, and precipitating factors. In this scenario, the neuroinflammation and the microglial activation play a pivotal role by triggering and amplifying a complex cascade involving the immuno-hormonal acti- vation, the micro circle alterations, the hippocampal oxidative stress activation and, finally, an increased blood-brain barrier＇s permeability. While the role of anesthetics in the POCD＇s genesis in humans is debated, a huge number of preclinical studies have been conducted on the topic and many mechanisms have been proposed to explain the potential neurodegenerative effects of general anesthetics. Probably, the problem concerns on what we are searching for and how we are searching and, surprisingly, preclinical studies showed that anesthetics may also manifest neuroprotective properties. The aim of this paper is to offer an overview on the potential impact of general anesthetics on POCD. Mechanisms of hippocampal and extra-hippocampal dysfunction due to neuroinflammation are discussed, whereas further research perspectives are also given.

Selective CDK inhibitors:promising candidates for future clinical traumatic brain injury trials

Traumatic brain injury induces secondary injury that contributes to neuroinflammation, neuronal loss, and neurological dysfunction. One important injury mechanism is cell cycle activation which causes neuronal apoptosis and glial activation. The neuroprotective effects of both non-selective （Flavopiridol） and selective （Roscovitine and CR-8） cyclin-dependent kinase inhibitors have been shown across mukiple experimental traumatic brain injury models and species. Cyclin-depen- dent kinaseinhibitors, administered as a single systemic dose up to 24 hours after traumatic brain injury, provide strong neuroprotection-reducing neuronal cell death, neuroinflammation and neurological dysfunction. Given their effectiveness and long therapeutic window, cyclin-dependent kinase inhibitors appear to be promising candidates for clinical traumatic brain injury trials.

The role of cofilin in age-related neuroinflammation

Aging brain becomes susceptible to neurodegenerative diseases due to the shifting of microglia and astrocyte phenotypes to an active“pro-inflammatory”state,causing chronic low-grade neuroinflammation.Despite the fact that the role of neuroinflammation during aging has been extensively studied in recent years,the underlying causes remain unclear.The identification of relevant proteins and understanding their potential roles in neuroinflammation can help explain their potential of becoming biomarkers in the aging brain and as drug targets for prevention and treatment.This will eventually reduce the chances of developing neurodegenerative diseases and promote healthier lives in the elderly.In this review,we have summarized the morphological and cellular changes in the aging brain,the effects of age-related neuroinflammation,and the potential role of cofilin-1 during neuroinflammation.We also discuss other factors contributing to brain aging and neuroinflammation.

Neuroprotective and anti-inflammatory effects of a therapy combining agonists of nicotinic α7 and σ1 receptors in a rat model of Parkinson’s disease

To date there is no treatment able to stop or slow down the loss of dopaminergic neurons that characterizes Parkinson’s disease.It was recently observed in a rodent model of Alzheimer’s disease that the interaction between the α7 subtype of nicotinic acetylcholine receptor(α7-nAChR)and sigma-1 receptor(σ1-R)could exert neuroprotective effects through the modulation of neuroinflammation which is one of the key components of the pathophysiology of Parkinson’s disease.In this context,the aim of the present study was to assess the effects of the concomitant administration of N-(3R)-1-azabicyclo[2.2.2]oct-3-yl-furo[2,3-c]pyridine-5-carboxamide(PHA)543613 as an α7-nAChR agonist and 2-(4-morpholinethyl)1-phenylcyclohexanecarboxylate(PRE)-084 as aσ1-R agonist in a well-characterized 6-hydroxydopamine rat model of Parkinson’s disease.The animals received either vehicle separately or the dual therapy PHA/PRE once a day until day 14 postlesion.Although no effect was noticed in the amphetamine-induced rotation test,our data has shown that the PHA/PRE treatment induced partial protection of the dopaminergic neurons(15-20%),assessed by the dopamine transporter density in the striatum and immunoreactive tyrosine hydroxylase in the substantia nigra.Furthermore,this dual therapy reduced the degree of glial activation consecutive to the 6-hydroxydopamine lesion,i.e,the 18 kDa translocation protein density and glial fibrillary acidic protein staining in the striatum,and the CD11b and glial fibrillary acidic protein staining in the substantia nigra.Hence,this study reports for the first time that concomitant activation of α7-nAChR andσ1-R can provide a partial recovery of the nigro-striatal dopaminergic neurons through the modulation of microglial activation.The study was approved by the Regional Ethics Committee(CEEA Val de Loire n°19)validated this protocol(Authorization N°00434.02)on May 15,2014.

Modulating poststroke inflammatory mechanisms: Novel aspects of mesenchymal stem cells, extracellular vesicles and microglia

Inflammation plays an important role in the pathological process of ischemic stroke,and systemic inflammation affects patient prognosis.As resident immune cells in the brain,microglia are significantly involved in immune defense and tissue repair under various pathological conditions,including cerebral ischemia.Although the differentiation of M1 and M2 microglia is certainly oversimplified,changing the activation state of microglia appears to be an intriguing therapeutic strategy for cerebral ischemia.Recent evidence indicates that both mesenchymal stem cells(MSCs)and MSC-derived extracellular vesicles(EVs)regulate inflammation and modify tissue repair under preclinical stroke conditions.However,the precise mechanisms of these signaling pathways,especially in the context of the mutual interaction between MSCs or MSC-derived EVs and resident microglia,have not been sufficiently unveiled.Hence,this review summarizes the state-ofthe-art knowledge on MSC-and MSC-EV-mediated regulation of microglial activity under ischemic stroke conditions with respect to various signaling pathways,including cytokines,neurotrophic factors,transcription factors,and microRNAs.

Association of Glial Activation and α-Synuclein Pathology in Parkinson's Disease

The accumulation of pathological α-synuclein(α-syn)in the central nervous system and the progressive loss of dopaminergic neurons in the substantia nigra pars compacta are the neuropathological features of Parkinson's disease(PD).Recently,the findings of prion-like transmission of α-syn pathology have expanded our understanding of the region-specific distribution ofα-syn in PD patients.Accumulating evidence suggests that α-syn aggregates are released from neurons and endocytosed by glial cells,which contributes to the clearance of α-syn.However,the activation of glial cells by α-syn species produces pro-inflammatory factors that decrease the uptake of α-syn aggregates by glial cells and promote the transmission of α-syn between neurons,which promotes the spread of α-syn pathology.In this article,we provide an overview of current knowledge on the role of glia and α-syn pathology in PD pathogenesis,highlighting the relationships between glial responses and the spread ofα-syn pathology.

Microglia in depression:current perspectives

Major depressive disorder(MDD)is a prevalent psychiatric disease that involves malfunctions of different cell types in the brain.Accumulating studies started to reveal that microglia,the primary resident immune cells,play an important role in the development and progression of depression.Microglia respond to stress-triggered neuroinflammation,and through the release of proinflammatory cytokines and their metabolic products,microglia may modulate the function of neurons and astrocytes to regulate depression.In this review,we focused on the role of microglia in the etiology of depression.We discussed the dynamic states of microglia;the correlative and causal evidence of microglial abnormalities in depression;possible mechanisms of how microglia sense depression-related stress and modulate depression state;and how antidepressive therapies affect microglia.Understanding the role of microglia in depression may shed light on developing new treatment strategies to fight against this devastating mental illness.

Recent developments on PET radiotracers for TSPO and their applications in neuroimaging

The 18 kDa translocator protein(TSPO),previously known as the peripheral benzodiazepine receptor,is predominately localized to the outer mitochondrial membrane in steroidogenic cells.Brain TSPO expression is relatively low under physiological conditions,but is upregulated in response to glial cell activation.As the primary index of neuroinflammation,TSPO is implicated in the pathogenesis and progression of numerous neuropsychiatric disorders and neurodegenerative diseases,including Alzheimer’s disease(AD),amyotrophic lateral sclerosis(ALS),Parkinson’s disease(PD),multiple sclerosis(MS),major depressive disorder(MDD)and obsessive compulsive disorder(OCD).In this context,numerous TSPO-targeted positron emission tomography(PET)tracers have been developed.Among them,several radioligands have advanced to clinical research studies.In this review,we will overview the recent development of TSPO PET tracers,focusing on the radioligand design,radioisotope labeling,pharmacokinetics,and PET imaging evaluation.Additionally,we will consider current limitations,as well as translational potential for future application of TSPO radiopharmaceuticals.This review aims to not only present the challenges in current TSPO PET imaging,but to also provide a new perspective on TSPO targeted PET tracer discovery efforts.Addressing these challenges will facilitate the translation of TSPO in clinical studies of neuroinflammation associated with central nervous system diseases.

The roles of microglia in viral encephalitis:from sensome to therapeutic targeting

Viral encephalitis is a devastating disease with high mortality,and survivors often suffer from severe neurological complications.Microglia are innate immune cells of the central nervous system(CNS)parenchyma whose turnover is reliant on local proliferation.Microglia express a diverse range of proteins,which allows them to continuously sense the environment and quickly react to changes.Under inflammatory conditions such as CNS viral infection,microglia promote innate and adaptive immune responses to protect the host.However,during viral infection,a dysregulated microglia-T-cell interplay may result in altered phagocytosis of neuronal synapses by microglia that causes neurocognitive impairment.In this review,we summarize the current knowledge on the role of microglia in viral encephalitis,propose questions to be answered in the future and suggest possible therapeutic targets.

Fluoxetine is Neuroprotective in Early Brain Injury via its Antiinflammatory and Anti-apoptotic Effects in a Rat Experimental Subarachnoid Hemorrhage Model

Fluoxetine, an anti-depressant drug, has recently been shown to provide neuroprotection in central nervous system injury, but its roles in subarachnoid hemorrhage(SAH) remain unclear. In this study, we aimed to evaluate whether fluoxetine attenuates early brain injury(EBI) after SAH. We demonstrated that intraperitoneal injection of fluoxetine(10 mg/kg per day) significantly attenuated brain edema and blood-brain barrier(BBB) disruption, microglial activation, and neuronal apoptosis in EBI after experimental SAH, as evidenced by the reduction of brain water content and Evans blue dye extravasation, prevention of disruption of the tight junction proteins zonula occludens-1, claudin-5, and occludin, a decrease of cells staining positive for Iba-1, ED-1, and TUNEL and a decline in IL-1 b, IL-6, TNF-a, MDA, 3-nitrotyrosine, and 8-OHDG levels. Moreover, fluoxetine significantly improved the neurological deficits of EBI and long-term sensorimotor behavioral deficits following SAH in a rat model. These results indicated that fluoxetine has a neuroprotective effect after experimental SAH.