Multimodal epigenetic changes and altered NEUROD1 chromatin binding in the mouse hippocampus underlie FOXG1 syndrome.

Forkhead box G1 (FOXG1) has important functions in neuronal differentiation and balances excitatory/inhibitory network activity. Thus far, molecular processes underlying FOXG1 function are largely unexplored. Here, we present a multiomics data set exploring how FOXG1 impacts neuronal maturation at the chromatin level in the mouse hippocampus. At a genome-wide level, FOXG1 i) both represses and activates transcription, ii) binds mainly to enhancer regions, iii) reconfigures the epigenetic landscape through bidirectional alteration of H3K27ac, H3K4me3, and chromatin accessibility, and iv) operates synergistically with NEUROD1. Interestingly, we could not detect a clear hierarchy of FOXG1 and NEUROD1, but instead, provide the evidence that they act in a highly cooperative manner to control neuronal maturation. Genes affected by the chromatin alterations impact synaptogenesis and axonogenesis. Inhibition of histone deacetylases partially rescues transcriptional alterations upon FOXG1 reduction. This integrated multiomics view of changes upon FOXG1 reduction reveals an unprecedented multimodality of FOXG1 functions converging on neuronal maturation. It fuels therapeutic options based on epigenetic drugs to alleviate, at least in part, neuronal dysfunction.

Pathological remodeling of reactive astrocytes: Involvement of DNA methylation and downregulation of homeostatic genes.

Astrocytes provide metabolic support to neurons, maintain ionic and water homeostasis, and uptake and recycle neurotransmitters. After exposure to the prototypical PAMP lipopolysaccharide (LPS), reactive astrocytes increase the expression of pro-inflammatory genes, facilitating neurodegeneration. In this study, we analyzed the expression of homeostatic genes in astrocytes exposed to LPS and identified the epigenetic factors contributing to the suppression of homeostatic genes in reactive astrocytes. Primary astrocytic cultures were acutely exposed to LPS and allowed to recover for 24, 72 h, and 7 days. As expected, LPS exposure induced reactive astrogliosis and increased the expression of pro-inflammatory IL-1B and IL-6. Interestingly, the acute exposure resulted in persistent hypermethylation of astroglial DNA. Similar hypermethylation was observed in highly reactive astrocytes from the traumatic brain injury (TBI) penumbra in vivo. Hypermethylation was accompanied by decreased expression of homeostatic genes including LDHA and Scl16a1 (MCT1) both involved in the lactate shuttle to neurons; glutamine synthase (GS) responsible for glutamate processing; Kcnj10 (Kir4.1) important for K+ homeostasis, and the water channel aquaporin-4 (Aqp4). Furthermore, the master regulator of DNA methylation, MAFG-1, as well as DNA methyl transferases DNMT1 and DNMT3a were overexpressed. The downregulation of homeostatic genes correlated with increased methylation of CpG islands in their promoters, as assessed by methylation-sensitive PCR and increased DNMT3a binding to the GS promoter. Treatment with decitabine, a DNMT inhibitor, prevented the LPS- and the HMGB-1-induced downregulation of homeostatic genes. Decitabine treatment also prevented the neurotoxic effects of these astrocytes in primary cortical cultures. In summary, our findings reveal that the pathological remodeling of reactive astrocytes encompasses not only the pro-inflammatory response but, significantly, also entails a long-term suppression of homeostatic gene expression with methylation of crucial CpG islands within their promoters.

Progression of reactive gliosis and astroglial phenotypic changes following stab wound-induced traumatic brain injury in mice.

Astrocytes are the main homeostatic cells in the central nervous system (CNS) and they have an essential role in preserving neuronal physiology. After brain injury, astrocytes become reactive, and that involves a profound change in the astroglial gene expression program as well as intense cytoskeleton remodeling that has been classically shown by the up-regulation of glial fibrillary acidic protein (GFAP), a pan-reactive gene over-expressed in reactive astrocytes, independently of the type of injury. Using the stab wound rodent model of penetrating traumatic injury in the cortex, we here studied the reactive astroglial morphology and reactive microgliosis in detail at 1, 3, 7, 14, and 28 days post-injury (dpi). By combining immunohistochemistry, morphometrical parameters, and Sholl analysis, we segmented the astroglial cell population into clusters of reactive astrocytes that were localized in the core, penumbra, and distal regions of the stab wound. Specifically, highly reactive clusters with more complex morphology, increased C3, decreased aquaporin-4 (AQP4), and glutamine synthetase (GS) expression, were enriched at 7 dpi when behavioral alterations, microgliosis, and neuronal alterations in injured mice were most significant. While pro-inflammatory gain of function with peripheral lipopolysaccharide (LPS) administration immediately after a stab wound expanded these highly reactive astroglial clusters, the treatment with the NF-κB inhibitor sulfasalazine reduced the abundance of this highly reactive cluster. Increased neuronal loss and exacerbated reactive microgliosis at 7 dpi were associated with the expansion of the highly reactive astroglial cluster. We conclude that highly reactive astrocytes found in stab wound injury, but expanded in pro-inflammatory conditions, are a population of astrocytes that become engaged in pathological remodeling with a pro-inflammatory gain of function and loss of homeostatic capacity. Controlling this astroglial population may be a tempting strategy to reduce neuronal loss and neuroinflammation in the injured brain.

Early life stress induces visual dysfunction and retinal structural alterations in adult mice.

Early life stress (ELS) is defined as a period of severe and/or chronic trauma, as well as environmental/social deprivation or neglect in the prenatal/early postnatal stage. Presently, the impact of ELS on the retina in the adult stage is unknown. The long-term consequences of ELS at retinal level were analyzed in an animal model of maternal separation with early weaning (MSEW), which mimics early life maternal neglect. For this purpose, mice were separated from the dams for 2 h at postnatal days (PNDs) 4-6, for 3 h at PNDs 7-9, for 4 h at PNDs 10-12, for 6 h at PNDs 13-16, and weaned at PND17. At the end of each separation period, mothers were subjected to movement restriction for 10 min. Control pups were left undisturbed from PND0, and weaned at PND21. Electroretinograms, visual evoked potentials, vision-guided behavioral tests, retinal anterograde transport, and retinal histopathology were examined at PNDs 60-80. MSEW induced long-lasting functional and histological effects at retinal level, including decreased retinal ganglion cell function and alterations in vision-guided behaviors, likely associated to decreased synaptophysin content, retina-superior colliculus communication deficit, increased microglial phagocytic activity, and retinal ganglion cell loss through a corticoid-dependent mechanism. A treatment with mifepristone, injected every 3 days between PNDs 4 and16, prevented functional and structural alterations induced by MSEW. These results suggest that retinal alterations might be included among the childhood adversity-induced threats to life quality, and that an early intervention with mifepristone avoided ELS-induced retinal disturbances.

An analysis from the CAPACITY database of outcomes of preoperative embolization before carotid body tumor surgery compared with resection alone.

OBJECTIVE: There is no definitive consensus on the impact of preoperative embolization on carotid body tumor (CBT) treatment. The objective of this study was to compare surgical outcomes of patients who underwent preoperative embolization before CBT resection vs patients who underwent resection alone. METHODS: The CAPACITY registry included 1432 patients with CBT from 11 medical centers in four different countries. The group of patients undergoing CBT resection with preoperative embolization was matched in a 1:6 ratio from a pool of patients from the CAPACITY database, using a generated propensity score with patients who did not underwent preoperative embolization. RESULTS: A total of 553 patients were included for analysis. Mean patient age was 56.23 ± 12.22 years. Patients were mostly female (n = 469; 84.8%). Bilateral CBT was registered in 60 patients (10.8%). Seventy-nine patients (14.3%) underwent preoperative embolization. Embolized patients had larger CBT sizes than non-embolized patients (33.8 mm vs 18.4 mm; P = .0001). Operative blood loss was lower in the embolized group compared with the non-embolized group (200 mL vs 250 mL; P = .031). Hematomas were more frequent in the non-embolized group (0% vs 2.7%; P = .044). Operative time, rates of stroke, cranial nerve injuries, and death were not statistically significant between groups. CONCLUSIONS: Embolization before CBT resection was associated with significantly lower blood loss and lower neck hematomas than patients who underwent resection alone. Operative time, stroke, cranial nerve injuries, and death were similar between groups.

Extensive deep vein thrombosis and pulmonary embolism as a unique clinical manifestation of COVID-19 in a young healthy patient.

BACKGROUND/OBJECTIVE: Deep vein thrombosis and pulmonary embolism have been described as complications in previously diagnosed COVID-19 patients, especially in those admitted in critical ill units, but, to our knowledge, there is no report of venous thromboembolism in an otherwise asymptomatic COVID-19 patient. METHODS: We report the case of a 22-year-old female, healthy patient with pulmonary embolism (Pulmonary Embolism Severity Index Score 22 points, low risk) and extensive proximal deep vein thrombosis as a unique clinical manifestation of the new coronavirus disease. RESULTS: The patient had no risk factors and no familial history of venous thromboembolism. All thrombophilia markers were negative. The patient was treated as first by an independent vascular team, performing vena cava filter placement and open thrombectomy. Her symptoms worsened, and after 3 weeks, she underwent US-enhanced thrombolysis and mechanical thrombectomy. She was isolated for 10 days and did not develop any other clinical manifestation of COVID-19 disease. During follow-up, she remained asymptomatic and complete patency of the venous system was achieved. Full oral anticoagulation was conducted for 6 months. CONCLUSION: COVID-19 appears to be a multi-symptomatic disease, and venous thromboembolism without any other previous described COVID-19 symptom could be considered one of its diverse clinical presentations and RT-PCR for SARS-CoV-2 tests emerge to be mandatory in patients with otherwise unexpected venous thrombosis.

DOT1L promotes progenitor proliferation and primes neuronal layer identity in the developing cerebral cortex.

Cortical development is controlled by transcriptional programs, which are orchestrated by transcription factors. Yet, stable inheritance of spatio-temporal activity of factors influencing cell fate and localization in different layers is only partly understood. Here we find that deletion of Dot1l in the murine telencephalon leads to cortical layering defects, indicating DOT1L activity and chromatin methylation at H3K79 impact on the cell cycle, and influence transcriptional programs conferring upper layer identity in early progenitors. Specifically, DOT1L prevents premature differentiation by increasing expression of genes that regulate asymmetric cell division (Vangl2, Cenpj). Loss of DOT1L results in reduced numbers of progenitors expressing genes including SoxB1 gene family members. Loss of DOT1L also leads to altered cortical distribution of deep layer neurons that express either TBR1, CTIP2 or SOX5, and less activation of transcriptional programs that are characteristic for upper layer neurons (Satb2, Pou3f3, Cux2, SoxC family members). Data from three different mouse models suggest that DOT1L balances transcriptional programs necessary for proper neuronal composition and distribution in the six cortical layers. Furthermore, because loss of DOT1L in the pre-neurogenic phase of development impairs specifically generation of SATB2-expressing upper layer neurons, our data suggest that DOT1L primes upper layer identity in cortical progenitors.

Different Flavors of Astrocytes: Revising the Origins of Astrocyte Diversity and Epigenetic Signatures to Understand Heterogeneity after Injury.

Astrocytes are a specific type of neuroglial cells that confer metabolic and structural support to neurons. Astrocytes populate all regions of the nervous system and adopt a variety of phenotypes depending on their location and their respective functions, which are also pleiotropic in nature. For example, astrocytes adapt to pathological conditions with a specific cellular response known as reactive astrogliosis, which includes extensive phenotypic and transcriptional changes. Reactive astrocytes may lose some of their homeostatic functions and gain protective or detrimental properties with great impact on damage propagation. Different astrocyte subpopulations seemingly coexist in reactive astrogliosis, however, the source of such heterogeneity is not completely understood. Altered cellular signaling in pathological compared to healthy conditions might be one source fueling astrocyte heterogeneity. Moreover, diversity might also be encoded cell-autonomously, for example as a result of astrocyte subtype specification during development. We hypothesize and propose here that elucidating the epigenetic signature underlying the phenotype of each astrocyte subtype is of high relevance to understand another regulative layer of astrocyte heterogeneity, in general as well as after injury or as a result of other pathological conditions. High resolution methods should allow enlightening diverse cell states and subtypes of astrocyte, their adaptation to pathological conditions and ultimately allow controlling and manipulating astrocyte functions in disease states. Here, we review novel literature reporting on astrocyte diversity from a developmental perspective and we focus on epigenetic signatures that might account for cell type specification.

DOT1L Activity Promotes Proliferation and Protects Cortical Neural Stem Cells from Activation of ATF4-DDIT3-Mediated ER Stress In Vitro.

Growing evidence suggests that the lysine methyltransferase DOT1L/KMT4 has important roles in proliferation, survival, and differentiation of stem cells in development and in disease. We investigated the function of DOT1L in neural stem cells (NSCs) of the cerebral cortex. The pharmacological inhibition and shRNA-mediated knockdown of DOT1L impaired proliferation and survival of NSCs. DOT1L inhibition specifically induced genes that are activated during the unfolded protein response (UPR) in the endoplasmic reticulum (ER). Chromatin-immunoprecipitation analyses revealed that two genes encoding for central molecules involved in the ER stress response, Atf4 and Ddit3 (Chop), are marked with H3K79 methylation. Interference with DOT1L activity resulted in transcriptional activation of both genes accompanied by decreased levels of H3K79 dimethylation. Although downstream effectors of the UPR, such as Ppp1r15a/Gadd34, Atf3, and Tnfrsf10b/Dr5 were also transcriptionally activated, this most likely occurred in response to increased ATF4 expression rather than as a direct consequence of altered H3K79 methylation. While stem cells are particularly vulnerable to stress, the UPR and ER stress have not been extensively studied in these cells yet. Since activation of the ER stress program is also implicated in directing stem cells into differentiation or to maintain a proliferative status, the UPR must be tightly regulated. Our and published data suggest that histone modifications, including H3K4me3, H3K14ac, and H3K79me2, are implicated in the control of transcriptional activation of ER stress genes. In this context, the loss of H3K79me2 at the Atf4- and Ddit3-promoters appears to mark a point-of-no-return that activates the death program in NSCs.

S100B protein activates a RAGE-dependent autocrine loop in astrocytes: implications for its role in the propagation of reactive gliosis.

Extracellular S100B dramatically increases after brain injury. While low S100B levels are neuroprotective, micromolar S100B levels have shown in vitro to activate microglia and facilitate neuronal death. In astrocytes, S100B exposure activates nuclear factor kappa B (NF-κB) and induces pro-inflammatory mediators. On microglia and neurons S100B effects are essentially mediated by receptor for advanced glycation end products (RAGE)/NF-κB, but it is not clear if these intracellular cascades are activated by different S100B levels in astrocytes and whether increased extracellular S100B is sufficient to induce reactive gliosis. A better understanding of these pathways is essential for developing successful strategies to preserve the beneficial S100B effects after brain injury. Here, we show that microglia-depleted cultured astrocytes exposed to S100B mimicked several features of reactive gliosis by activating RAGE/Rac-1-Cdc42, RAGE/Erk-Akt or RAGE/NF-κB-dependent pathways. S100B effects include RAGE/Rac1-Cdc42-dependent astroglial hypertrophy and facilitation of migration as well as increased mitosis. S100B exposure improved the astrocytic survival to oxidative stress, an effect that requires Erk/Akt. S100B also activates NF-κB in a dose-dependent manner; increases RAGE proximal promoter transcriptional activity and augmented endogenous RAGE expression. S100B-exposed astrocytes showed a pro-inflammatory phenotype with expression of Toll-like receptor 2 (TLR 2), inducible nitric oxide synthase (iNOS) and interleukin 1-beta (IL-1ß), and facilitated neuronal death induced by oxygen-glucose deprivation. In vivo, intracerebral infusion of S100B was enough to induce an astroglial reactive phenotype. Together, these findings demonstrate that extracellular S100B in the micromolar level activates different RAGE-dependent pathways that turn astrocytes into a pro-inflammatory and neurodegenerative phenotype. We propose that S100B turns astrocytes into a reactive phenotype in a RAGE-dependent manner but engaging different intracellular pathways. While both nanomolar and micromolar S100B turn astrocytes into a reactive phenotype, micromolar S100B induces a conversion into a pro-inflammatory-neurodegenerative profile that facilitates neuronal death of OGD-exposed neurons. We think that S100B/RAGE interaction is essential to expand reactive gliosis in the injured brain being a tempting target for limiting reactive gliosis to prevent the glial conversion into the neurodegenerative profile.

Nucleophosmin 1 cooperates with the methyltransferase DOT1L to preserve peri-nucleolar heterochromatin organization by regulating H3K27me3 levels and DNA repeats expression.

BACKGROUND: NPM1 is a phosphoprotein highly abundant in the nucleolus. However, additional nuclear functions have been attributed to NPM1, probably through interaction with other nuclear factors. DOT1L is one interaction partner of NPM1 that catalyzes methylation of histone H3 at lysine 79 (H3K79). DOT1L, playing functional roles in several biological processes, is known for its capability to organize and regulate chromatin. For example, DOT1L modulates DNA repeats expression within peri-nucleolar heterochromatin. NPM1 also affects peri-nucleolar heterochromatin spatial organization. However, it is unclear as of yet whether NPM1 and DOT1L functionally synergize to preserve nucleoli organization and genome stability, and generally, which molecular mechanisms would be involved. RESULTS: We characterized the nuclear function of NPM1 on peri-nucleolar heterochromatin organization. We show that (i) monomeric NPM1 interacts preferentially with DOT1L in the nucleus; (ii) NPM1 acts in concert with DOT1L to maintain each other's protein homeostasis; (iii) NPM1 depletion results in H3K79me2 upregulation and differential enrichment at chromatin binding genes including Ezh2; (iv) NPM1 and DOT1L modulate DNA repeats expression and peri-nucleolar heterochromatin organization via epigenetic mechanisms dependent on H3K27me3. CONCLUSIONS: Our findings give insights into molecular mechanisms employed by NPM1 and DOT1L to regulate heterochromatin activity and structural organization around the nucleoli and shed light on one aspect of the complex role of both proteins in chromatin dynamics.

Venous Thromboembolism in Hospitalized COVID-19 Patients Treated in a Single Academic Center in Mexico: A Case Series Study.

BACKGROUND: The increasing prevalence of venous thromboembolism (VTE) among patients with coronavirus disease 2019 (COVID-19) is a matter of concern as it contributes significantly to patients' morbidity and mortality. Data regarding the optimal anticoagulation regimen for VTE prevention and treatment remain scarce. This study describes the characteristics, treatment, and outcomes of COVID-19 patients with VTE treated in a single academic center in Mexico. METHODS: We conducted a retrospective study of all patients with a positive PCR test for SARS-CoV-2 hospitalized in a single academic center in Monterrey, Mexico, between March 2020 and February 2021, with a radiologically confirmed VTE, including deep venous thrombosis (DVT) and pulmonary embolism (PE). Informed consent was obtained from each patient before reviewing their medical records. RESULTS: Of the 2000 COVID-19 hospitalized patients, 36 (1.8%) developed VTE and were included in the analysis. The median age was 60 years (range 32-88 years), and up to 78% (n = 28) were males. Most patients (n = 34, 94%) had an underlying comorbidity and 47% (n = 17) had a BMI ≥ 30 kg/m2. In most cases (n=28, 78%), VTE presented as a PE, whereas the remaining 22% (n = 8) had a DVT. The median time between hospital admission and VTE was 8 days (range 0-33 days). Regarding the thromboprophylaxis regimen, 35/36 patients received low molecular weight heparin enoxaparin on admission, most commonly at a dose of 60 mg daily (n = 19, 53%). Other complications presented were superinfection (n = 19, 53%), acute kidney injury (n = 11, 31%), and septic shock (n = 5, 14%). A total of 69% of patients (n = 25) required intensive care unit admission, and patients' overall mortality was 55.6%. CONCLUSION: VTE remains a significant cause of increased morbidity and mortality among patients with COVID-19. The strikingly high mortality among patients with VTE highlights the need for further investigation regarding the best preventive, diagnostic, and treatment approaches.

S100B alters neuronal survival and dendrite extension via RAGE-mediated NF-κB signaling.

S100B is a soluble protein secreted by astrocytes that exerts pro-survival or pro-apoptotic effects depending on the concentration reached in the extracellular millieu. The S100B receptor termed RAGE (for receptor for advanced end glycation products) is highly expressed in the developing brain but is undetectable in normal adult brain. In this study, we show that RAGE expression is induced in cortical neurons of the ischemic penumbra. Increased RAGE expression was also observed in primary cortical neurons exposed to excitotoxic glutamate (EG). S100B exerts effects on survival pathways and neurite extension when the cortical neurons have been previously exposed to EG and these S100B effects were prevented by anti-RAGE blocking antibodies. Furthermore, nuclear factor kappa B (NF-κB) is activated by S100B in a dose- and RAGE-dependent manner and neuronal death induced by NF-κB inhibition was prevented by S100B that restored NF-κB activation levels. Together, these findings suggest that excitotoxic damage can induce RAGE expression in neurons from ischemic penumbra and demonstrate that cortical neurons respond to S100B through engagement of RAGE followed by activation of NF-κB signaling. In addition, basal NF-κB activity in neurons is crucial to modulate the extent of pro-survival or pro-death S100B effects.

Pathological Neuroinflammatory Conversion of Reactive Astrocytes Is Induced by Microglia and Involves Chromatin Remodeling.

Following brain injury or in neurodegenerative diseases, astrocytes become reactive and may suffer pathological remodeling, features of which are the loss of their homeostatic functions and a pro-inflammatory gain of function that facilitates neurodegeneration. Pharmacological intervention to modulate this astroglial response and neuroinflammation is an interesting new therapeutic research strategy, but it still requires a deeper understanding of the underlying cellular and molecular mechanisms of the phenomenon. Based on the known microglial-astroglial interaction, the prominent role of the nuclear factor kappa B (NF-κB) pathway in mediating astroglial pathological pro-inflammatory gain of function, and its ability to recruit chromatin-remodeling enzymes, we first explored the microglial role in the initiation of astroglial pro-inflammatory conversion and then monitored the progression of epigenetic changes in the astrocytic chromatin. Different configurations of primary glial culture were used to modulate microglia-astrocyte crosstalk while inducing pro-inflammatory gain of function by lipopolysaccharide (LPS) exposure. In vivo, brain ischemia by cortical devascularization (pial disruption) was performed to verify the presence of epigenetic marks in reactive astrocytes. Our results showed that 1) microglia is required to initiate the pathological conversion of astrocytes by triggering the NF-κB signaling pathway; 2) this interaction is mediated by soluble factors and induces stable astroglial phenotypic changes; 3) the pathological conversion promotes chromatin remodeling with stable increase in H3K9K14ac, temporary increase in H3K27ac, and temporary reduction in heterochromatin mark H3K9me3; and 4) in vivo reactive astrocytes show increased H3K27ac mark in the neuroinflammatory milieu from the ischemic penumbra. Our findings indicate that astroglial pathological pro-inflammatory gain of function is associated with profound changes in the configuration of astrocytic chromatin, which in turn are initiated by microglia-derived cues. These results open a new avenue in the study of potential pharmacological interventions that modify the initiation and stabilization of astroglial pathological remodeling, which would be useful in acute and chronic CNS injury. Epigenetic changes represent a plausible pharmacological target to interfere with the stabilization of the pathological astroglial phenotype.

Intermittent hypoxia during sleep induces reactive gliosis and limited neuronal death in rats: implications for sleep apnea.

Sleep apnea (SA) can be effectively managed in humans but it is recognized that when left untreated, SA causes long-lasting changes in neuronal circuitry in the brain. Recent neuroimaging studies gave suggested that these neuronal changes are also present even in patients successfully treated for the acute effects of SA. The cellular mechanisms that account for these changes are not certain but animal models of intermittent hypoxia (IH) during sleep have shown neuronal death and impairment in learning and memory. Reactive gliosis has a drastic effect on neuronal survival and circuitry and in this study we examined the neuro-glial response in brain areas affected by SA. Glial and neuronal alterations were analyzed after 1, 3, 5 and 10 days of exposure to IH (8 h/day during the sleep phase, cycles of 6 min each, 10-21% O2) and observed significant astroglial hyperplasia and hypertrophy in parietal brain cortex and hippocampus by studying gliofibrillary acidic protein, Vimentin, S100B and proliferating cell nuclear antigen expression. In addition, altered morphology, reduced dendrite branching and caspase activation were observed in the CA-1 hippocampal and cortical (layers IV-V) pyramidal neurons at short exposure times (1-3 days). Surprisingly, longer exposure to IH reduced the neuronal death rate and increased neuronal branching in the presence of persistent reactive gliosis. Up-regulation of hypoxia inducible factor 1 alpha (HIF-1alpha) and mdr-1, a HIF-1alpha target gene, were observed and increased expression of receptor for advanced end glycated products and its binding partner S100B were also noted. Our results show that a low number of hypoxic cycles induce reactive gliosis and neuronal death whereas continuous exposure to IH cycles reduced the rate of neuronal death and induced neuronal branching on surviving neurons. We hypothesize that HIF-1alpha and S100B glial factor may improve neuronal survival under hypoxic conditions and propose that the death/survival/re-growth process observed here may underlie brain circuitry changes in humans with SA.

Severe Acute Respiratory Syndrome Coronavirus 2 Impact on the Central Nervous System: Are Astrocytes and Microglia Main Players or Merely Bystanders?

With confirmed coronavirus disease 2019 (COVID-19) cases surpassing the 18 million mark around the globe, there is an imperative need to gain comprehensive understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although the main clinical manifestations of COVID-19 are associated with respiratory or intestinal symptoms, reports of neurological signs and symptoms are increasing. The etiology of these neurological manifestations remains obscure, and probably involves several direct pathways, not excluding the direct entry of the virus to the central nervous system (CNS) through the olfactory epithelium, circumventricular organs, or disrupted blood-brain barrier. Furthermore, neuroinflammation might occur in response to the strong systemic cytokine storm described for COVID-19, or due to dysregulation of the CNS rennin-angiotensin system. Descriptions of neurological manifestations in patients in the previous coronavirus (CoV) outbreaks have been numerous for the SARS-CoV and lesser for Middle East respiratory syndrome coronavirus (MERS-CoV). Strong evidence from patients and experimental models suggests that some human variants of CoV have the ability to reach the CNS and that neurons, astrocytes, and/or microglia can be target cells for CoV. A growing body of evidence shows that astrocytes and microglia have a major role in neuroinflammation, responding to local CNS inflammation and/or to disbalanced peripheral inflammation. This is another potential mechanism for SARS-CoV-2 damage to the CNS. In this comprehensive review, we will summarize the known neurological manifestations of SARS-CoV-2, SARS-CoV and MERS-CoV; explore the potential role for astrocytes and microglia in the infection and neuroinflammation; and compare them with the previously described human and animal CoV that showed neurotropism to propose possible underlying mechanisms.

p75 NTR expression is induced in isolated neurons of the penumbra after ischemia by cortical devascularization.

The p75 neurotrophin receptor (p75(NTR)) is involved in neuronal functions ranging from induction of apoptosis and growth inhibition to the promotion of survival. p75(NTR) expression is induced in the central nervous system (CNS) by a range of pathological conditions, where it seems to have a role in neuronal death and axonal growth inhibition. The cellular mechanisms driving p75(NTR) expression in cell lines and primary neurons is Sp1 dependent (Ramos et al. [2007] J. Neurosci. 27:1498). In this study, we analyzed the spatiotemporal profile of p75(NTR) expression after an ischemic lesion induced by cortical devascularization (CD). Our results show that p75(NTR) expression occurs in isolated neurons of the ischemic lesion site. The p75(NTR+) neurons presented morphological alterations and active caspase-3 staining. Some p75(NTR+) neurons were also positive for sortilin. The peak of p75(NTR) expression was localized 3 days postlesion (3DPL) in the penumbra. Sp1 transcription factor nuclear localization was observed in p75(NTR+) neurons. The overall level of Sp1 expression was increased until 14DPL on the ipsilateral hemisphere. With primary cortical neurons, we demonstrated that p75(NTR) expression is induced by excitotoxic stress and correlated with increased Sp1 abundance. We conclude that p75(NTR) expression is localized in selected neurons of the ischemic lesion and that these neurons are probably condemned to apoptotic cell death. In primary neuronal culture, it is clear that excitotoxicity and Sp1 are involved in induction of p75(NTR) expression, although, in vivo, some additional mechanisms are likely to be involved in the control of p75(NTR) expression in specific neurons in vivo.

Detrimental Effects of HMGB-1 Require Microglial-Astroglial Interaction: Implications for the Status Epilepticus -Induced Neuroinflammation.

Temporal Lobe Epilepsy (TLE) is the most common form of human epilepsy and available treatments with antiepileptic drugs are not disease-modifying therapies. The neuroinflammation, neuronal death and exacerbated plasticity that occur during the silent period, following the initial precipitating event (IPE), seem to be crucial for epileptogenesis. Damage Associated Molecular Patterns (DAMP) such as HMGB-1, are released early during this period concomitantly with a phenomenon of reactive gliosis and neurodegeneration. Here, using a combination of primary neuronal and glial cell cultures, we show that exposure to HMGB-1 induces dendrite loss and neurodegeneration in a glial-dependent manner. In glial cells, loss of function studies showed that HMGB-1 exposure induces NF-κB activation by engaging a signaling pathway that involves TLR2, TLR4, and RAGE. In the absence of glial cells, HMGB-1 failed to induce neurodegeneration of primary cultured cortical neurons. Moreover, purified astrocytes were unable to fully respond to HMGB-1 with NF-κB activation and required microglial cooperation. In agreement, in vivo HMGB-1 blockage with glycyrrhizin, immediately after pilocarpine-induced status epilepticus (SE), reduced neuronal degeneration, reactive astrogliosis and microgliosis in the long term. We conclude that microglial-astroglial cooperation is required for astrocytes to respond to HMGB-1 and to induce neurodegeneration. Disruption of this HMGB-1 mediated signaling pathway shows beneficial effects by reducing neuroinflammation and neurodegeneration after SE. Thus, early treatment strategies during the latency period aimed at blocking downstream signaling pathways activated by HMGB-1 are likely to have a significant effect in the neuroinflammation and neurodegeneration that are proposed as key factors in epileptogenesis.

FOXG1 Regulates PRKAR2B Transcriptionally and Posttranscriptionally via miR200 in the Adult Hippocampus.

Rett syndrome is a complex neurodevelopmental disorder that is mainly caused by mutations in MECP2. However, mutations in FOXG1 cause a less frequent form of atypical Rett syndrome, called FOXG1 syndrome. FOXG1 is a key transcription factor crucial for forebrain development, where it maintains the balance between progenitor proliferation and neuronal differentiation. Using genome-wide small RNA sequencing and quantitative proteomics, we identified that FOXG1 affects the biogenesis of miR200b/a/429 and interacts with the ATP-dependent RNA helicase, DDX5/p68. Both FOXG1 and DDX5 associate with the microprocessor complex, whereby DDX5 recruits FOXG1 to DROSHA. RNA-Seq analyses of Foxg1cre/+ hippocampi and N2a cells overexpressing miR200 family members identified cAMP-dependent protein kinase type II-beta regulatory subunit (PRKAR2B) as a target of miR200 in neural cells. PRKAR2B inhibits postsynaptic functions by attenuating protein kinase A (PKA) activity; thus, increased PRKAR2B levels may contribute to neuronal dysfunctions in FOXG1 syndrome. Our data suggest that FOXG1 regulates PRKAR2B expression both on transcriptional and posttranscriptional levels.

TGFß-Signaling and FOXG1-Expression Are a Hallmark of Astrocyte Lineage Diversity in the Murine Ventral and Dorsal Forebrain.

Heterogeneous astrocyte populations are defined by diversity in cellular environment, progenitor identity or function. Yet, little is known about the extent of the heterogeneity and how this diversity is acquired during development. To investigate the impact of TGF (transforming growth factor) ß-signaling on astrocyte development in the telencephalon we deleted the TGFBR2 (transforming growth factor beta receptor 2) in early neural progenitor cells in mice using a FOXG1 (forkhead box G1)-driven CRE-recombinase. We used quantitative proteomics to characterize TGFBR2-deficient cells derived from the mouse telencephalon and identified differential protein expression of the astrocyte proteins GFAP (glial fibrillary acidic protein) and MFGE8 (milk fat globule-EGF factor 8). Biochemical and histological investigations revealed distinct populations of astrocytes in the dorsal and ventral telencephalon marked by GFAP or MFGE8 protein expression. The two subtypes differed in their response to TGFß-signaling. Impaired TGFß-signaling affected numbers of GFAP astrocytes in the ventral telencephalon. In contrast, TGFß reduced MFGE8-expression in astrocytes deriving from both regions. Additionally, lineage tracing revealed that both GFAP and MFGE8 astrocyte subtypes derived partly from FOXG1-expressing neural precursor cells.