Tenascin-C induction exacerbates post-stroke brain damage

Intermittent fasting induced cerebral ischemic tolerance altered gut microbiome and increased levels of short-chain fatty acids to a beneficial phenotype

Preconditioning-induced cerebral ischemic tolerance is known to be a beneficial adaptation to protect the brain in an unavoidable event of stroke. We currently demonstrate that a short bout (6 weeks) of intermittent fasting (IF; 15 h fast/day) induces similar ischemic tolerance to that of a longer bout (12 weeks) in adult C57BL/6 male mice subjected to transient middle cerebral artery occlusion (MCAO). In addition, the 6 weeks IF regimen induced ischemic tolerance irrespective of age (3 months or 24 months) and sex. Mice subjected to transient MCAO following IF showed improved motor function recovery (rotarod and beam walk tests) between days 1 and 14 of reperfusion and smaller infarcts (T2-MRI) on day 1 of reperfusion compared with age/sex matched ad libitum (AL) controls. Diet influences the gut microbiome composition and stroke is known to promote gut bacterial dysbiosis. We presently show that IF promotes a beneficial phenotype of gut microbiome following transient MCAO compared with AL cohort. Furthermore, post-stroke levels of short-chain fatty acids (SCFAs), which are known to be neuroprotective, are higher in the fecal samples of the IF cohort compared with the AL cohort. Thus, our studies indicate the efficacy of IF in protecting the brain after stroke, irrespective of age and sex, probably by altering gut microbiome and SCFA production.

An interpretable machine learning-based cerebrospinal fluid proteomics clock for predicting age reveals novel insights into brain aging

Machine learning can be used to create "biologic clocks" that predict age. However, organs, tissues, and biofluids may age at different rates from the organism as a whole. We sought to understand how cerebrospinal fluid (CSF) changes with age to inform the development of brain aging-related disease mechanisms and identify potential anti-aging therapeutic targets. Several epigenetic clocks exist based on plasma and neuronal tissues; however, plasma may not reflect brain aging specifically and tissue-based clocks require samples that are difficult to obtain from living participants. To address these problems, we developed a machine learning clock that uses CSF proteomics to predict the chronological age of individuals with a 0.79 Pearson correlation and mean estimated error (MAE) of 4.30 years in our validation cohort. Additionally, we analyzed proteins highly weighted by the algorithm to gain insights into changes in CSF and uncover novel insights into brain aging. We also demonstrate a novel method to create a minimal protein clock that uses just 109 protein features from the original clock to achieve a similar accuracy (0.75 correlation, MAE 5.41). Finally, we demonstrate that our clock identifies novel proteins that are highly predictive of age in interactions with other proteins, but do not directly correlate with chronological age themselves. In conclusion, we propose that our CSF protein aging clock can identify novel proteins that influence the rate of aging of the central nervous system (CNS), in a manner that would not be identifiable by examining their individual relationships with age.

Loss of Epitranscriptomic Modification N6-Methyladenosine (m6A) Reader YTHDF1 Exacerbates Ischemic Brain Injury in a Sexually Dimorphic Manner

N6-Methyladenosine (m6A) is a neuronal-enriched, reversible post-transcriptional modification that regulates RNA metabolism. The m6A-modified RNAs recruit various m6A-binding proteins that act as readers. Differential m6A methylation patterns are implicated in ischemic brain damage, yet the precise role of m6A readers in propagating post-stroke m6A signaling remains unclear. We presently evaluated the functional significance of the brain-enriched m6A reader YTHDF1, in post-stroke pathophysiology. Focal cerebral ischemia significantly increased YTHDF1 mRNA and protein expression in adult mice of both sexes. YTHDF1-/- male, but not female, mice subjected to transient middle cerebral artery occlusion (MCAO) showed worsened motor function recovery and increased infarction compared to sex-matched YTHDF1+/+ mice. YTHDF1-/- male, but not female, mice subjected to transient MCAO also showed significantly perturbed expression of genes related to inflammation, and increased infiltration of peripheral immune cells into the peri-infarct cortex, compared with sex-matched YTHDF1+/+ mice. Thus, this study demonstrates a sexual dimorphism of YTHDF1 in regulating post-ischemic inflammation and pathophysiology. Hence, post-stroke epitranscriptomic regulation might be sex-dependent.

Epigenetic disruptions in the offspring hypothalamus in response to maternal infection

DNA methylation is an epigenetic modification that can alter gene expression, and the incidence can vary across developmental stages, inflammatory conditions, and sexes. The effects of viral maternal viral infection and sex on the DNA methylation patterns were studied in the hypothalamus of a pig model of immune activation during development. DNA methylation at single-base resolution in regions of high CpG density was measured on 24 individual hypothalamus samples using reduced representation bisulfite sequencing. Differential over- and under-methylated sites were identified and annotated to proximal genes and corresponding biological processes. A total of 120 sites were differentially methylated (FDR-adjusted p-value < 0.05) between maternal infection or sex groups. Among the 66 sites differentially methylated between groups exposed to inflammatory signals and control, most sites were over-methylated in the challenged group and included sites in the promoter regions of genes SIRT3 and NRBP1. Among the 54 differentially methylated sites between females and males, most sites were over-methylated in females and included sites in the promoter region of genes TNC and EIF4G1. The analysis of the genes proximal to the differentially methylated sites suggested that biological processes potentially impacted include immune response, neuron migration and ensheathment, peptide signaling, adaptive thermogenesis, and tissue development. These results suggest that translational studies should consider that the prolonged effect of maternal infection during gestation may be enacted through epigenetic regulatory mechanisms that may differ between sexes.

Post-stroke brain can be protected by modulating the lncRNA FosDT

We previously showed that knockdown or deletion of Fos downstream transcript (FosDT; a stroke-induced brain-specific long noncoding RNA) is neuroprotective. We presently tested the therapeutic potential of FosDT siRNA in rodents subjected to transient middle cerebral artery occlusion (MCAO) using the Stroke Treatment Academic Industry Roundtable criteria, including sex, age, species, and comorbidity. FosDT siRNA (IV) given at 30 min of reperfusion significantly improved motor function recovery (rotarod test, beam walk test, and adhesive removal test) and reduced infarct size in adult and aged spontaneously hypertensive rats of both sexes. FosDT siRNA administered in a delayed fashion (3.5 h of reperfusion following 1 h transient MCAO) also significantly improved motor function recovery and decreased infarct volume. Furthermore, FosDT siRNA enhanced post-stroke functional recovery in normal and diabetic mice. Mechanistically, FosDT triggered post-ischemic neuronal damage via the transcription factor REST as REST siRNA mitigated the enhanced functional outcome in FosDT-/- rats. Additionally, NF-κB regulated FosDT expression as NF-κB inhibitor BAY 11-7082 significantly decreased post-ischemic FosDT induction. Thus, FosDT is a promising target with a favorable therapeutic window to mitigate secondary brain damage and facilitate recovery after stroke regardless of sex, age, species, and comorbidity.

Therapeutic Potential of Intravenous miR-21 Mimic after Stroke Following STAIR Criteria

The microRNA-21 (miR-21) levels in the brain are crucial in determining post-stroke brain damage and recovery. The miR-21 exerts neuroprotection by targeting mRNAs that translate proteins that mediate brain damage. We currently determined the efficacy and efficiency of intravenously administered miR-21 mimic after focal cerebral ischemia in mice. Adult male mice were intravenously administered with either control mimic or miR-21 mimic at 5 min/2 h after reperfusion following 1 h transient middle cerebral artery occlusion to determine the therapeutic window of miR-21 mimic. Adult female, type-2 diabetic male, aged male, and aged female mice were administered with control/miR-21 mimic at 5 min after reperfusion following 35 min/1 h transient middle cerebral artery occlusion. Early administration of miR-21 mimic significantly reduced brain damage and promoted long-term recovery after stroke. Further, miR-21 mimic is more effective in males than in females subjected to stroke. However, delayed treatment with miR-21 mimic is not efficacious, and type-2 diabetic subjects show no improvement with miR-21 mimic treatment.

The extracellular matrix as modifier of neuroinflammation and recovery in ischemic stroke and intracerebral hemorrhage

Stroke is the second leading cause of death worldwide and has two major subtypes: ischemic stroke and hemorrhagic stroke. Neuroinflammation is a pathological hallmark of ischemic stroke and intracerebral hemorrhage (ICH), contributing to the extent of brain injury but also in its repair. Neuroinflammation is intricately linked to the extracellular matrix (ECM), which is profoundly altered after brain injury and in aging. In the early stages after ischemic stroke and ICH, immune cells are involved in the deposition and remodeling of the ECM thereby affecting processes such as blood-brain barrier and cellular integrity. ECM components regulate leukocyte infiltration into the central nervous system, activate a variety of immune cells, and induce the elevation of matrix metalloproteinases (MMPs) after stroke. In turn, excessive MMPs may degrade ECM into components that are pro-inflammatory and injurious. Conversely, in the later stages after stroke, several ECM molecules may contribute to tissue recovery. For example, thrombospondin-1 and biglycan may promote activity of regulatory T cells, inhibit the synthesis of proinflammatory cytokines, and aid regenerative processes. We highlight these roles of the ECM in ischemic stroke and ICH and discuss their potential cellular and molecular mechanisms. Finally, we discuss therapeutics that could be considered to normalize the ECM in stroke. Our goal is to spur research on the ECM in order to improve the prognosis of ischemic stroke and ICH.

Targeting Neutrophil α9 Improves Functional Outcomes After Stroke in Mice With Obesity-Induced Hyperglycemia

BACKGROUND

Obesity-induced hyperglycemia is a significant risk factor for stroke. Integrin α9β1 is expressed on neutrophils and stabilizes adhesion to the endothelium via ligands, including Fn-EDA (fibronectin containing extra domain A) and tenascin C. Although myeloid deletion of α9 reduces susceptibility to ischemic stroke, it is unclear whether this is mediated by neutrophil-derived α9. We determined the role of neutrophil-specific α9 in stroke outcomes in a mice model with obesity-induced hyperglycemia.

METHODS

α9Neu-KO (α9fl/flMRP8Cre+) and littermate control α9WT (α9fl/flMRP8Cre-) mice were fed on a 60% high-fat diet for 20 weeks to induce obesity-induced hyperglycemia. Functional outcomes were evaluated up to 28 days after stroke onset in mice of both sexes using a transient (30 minutes) middle cerebral artery ischemia. Infarct volume (magnetic resonance imaging) and postreperfusion thrombo-inflammation (thrombi, fibrin, neutrophil, phospho-nuclear factor kappa B [p-NFκB], TNF [tumor necrosis factor]-α, and IL [interleukin]-1β levels, markers of neutrophil extracellular traps) were measured post 6 or 48 hours of reperfusion. In addition, functional outcomes (modified Neurological Severity Score, rota-rod, corner, and wire-hanging test) were measured for up to 4 weeks.

RESULTS

Stroke upregulated neutrophil α9 expression more in obese mice (P<0.05 versus lean mice). Irrespective of sex, deletion of neutrophil α9 improved functional outcomes up to 4 weeks, concomitant with reduced infarct, improved cerebral blood flow, decreased postreperfusion thrombo-inflammation, and neutrophil extracellular traps formation (NETosis) (P<0.05 versus α9WT obese mice). Obese α9Neu-KO mice were less susceptible to thrombosis in FeCl3 injury-induced carotid thrombosis model. Mechanistically, we found that α9/cellular fibronectin axis contributes to NETosis via ERK (extracellular signal-regulated kinase) and PAD4 (peptidyl arginine deiminase 4), and neutrophil α9 worsens stroke outcomes via cellular fibronectin-EDA but not tenascin C. Obese wild-type mice infused with anti-integrin α9 exhibited improved functional outcomes up to 4 weeks (P<0.05 versus vehicle).

CONCLUSIONS

Genetic ablation of neutrophil-specific α9 or pharmacological inhibition improves long-term functional outcomes after stroke in mice with obesity-induced hyperglycemia, most likely by limiting thrombo-inflammation.

CDR1as regulates α-synuclein-mediated ischemic brain damage by controlling miR-7 availability

Transient focal ischemia decreased microRNA-7 (miR-7) levels, leading to derepression of its major target α-synuclein (α-Syn) that promotes secondary brain damage. Circular RNA CDR1as is known to regulate miR-7 abundance and function. Hence, we currently evaluated its functional significance after focal ischemia. Transient middle cerebral artery occlusion (MCAO) in adult mice significantly downregulated both CDR1as and miR-7 levels in the peri-infarct cortex between 3 and 72 h of reperfusion. Interestingly, neither pri-miR-7a nor 7b was altered in the ischemic brain. Intracerebral injection of an AAV9 vector containing a CDR1as gene significantly increased CDR1as levels by 21 days that persisted up to 4 months without inducing any observable toxicity in both sham and MCAO groups. Following transient MCAO, there was a significant increase in miR-7 levels and CDR1as binding to Ago2/miR-7 in the peri-infarct cortex of AAV9-CDR1as cohort compared with AAV9-Control cohort at 1 day of reperfusion. CDR1as overexpression significantly suppressed post-stroke α-Syn protein induction, promoted motor function recovery, decreased infarct size, and curtailed the markers of apoptosis, autophagy mitochondrial fragmentation, and inflammation in the post-stroke brain compared with AAV9-Control-treated cohort. Overall, our findings imply that CDR1as reconstitution is neuroprotective after stroke, probably by protecting miR-7 and preventing α-Syn-mediated neuronal death.

Tau and GSK-3β are Critical Contributors to α-Synuclein-Mediated Post-Stroke Brain Damage

Post-stroke secondary brain damage is significantly influenced by the induction and accumulation of α-Synuclein (α-Syn). α-Syn-positive inclusions are often present in tauopathies and elevated tau levels and phosphorylation promotes neurodegeneration. Glycogen synthase kinase 3β (GSK-3β) is a known promoter of tau phosphorylation. We currently evaluated the interaction of α-Syn with GSK-3β and tau in post-ischemic mouse brain. Transient focal ischemia led to increased cerebral protein-protein interaction of α-Syn with both GSK-3β and tau and elevated tau phosphorylation. Treatment with a GSK-3β inhibitor prevented post-ischemic tau phosphorylation. Furthermore, α-Syn interaction was observed to be crucial for post-ischemic GSK-3β-dependent tau hyperphosphorylation as it was not seen in α-Syn knockout mice. Moreover, tau knockout mice show significantly smaller brain damage after transient focal ischemia. Overall, the present study indicates that GSK-3β catalyzes the α-Syn-dependent tau phosphorylation and preventing this interaction is crucial to limit post-ischemic secondary brain damage.

Gene Silencing in the Brain with siRNA to Promote Long-Term Post-Stroke Recovery

RNA interference is a promising strategy to degrade target RNAs of interest after stroke using small interfering RNA (siRNA). An optimized targeting such as combining a siRNA with a nontoxic transfection reagent that facilitates the effective delivery of siRNAs to the brain and subsequent cellular uptake after stroke is needed. Furthermore, an appropriate route of administration such as intravenous (tail vein or retro-orbital sinus) or cerebroventricular injection has to be used. Using siRNAs tagged with fluorescent probes shows the cellular uptake of siRNA. Efficacy and window of opportunity for a siRNA needs to be determined by testing multiple doses and time frame that alters the long-term functional outcomes. Real-time PCR/western blots can be used to determine the siRNA efficiency by evaluating the knockdown of the RNA/protein of interest. In siRNA studies, it is also essential to identify a proper dose (efficacious, but not toxic) by histopathologic testing to identify any toxicity in the peripheral organs and CNS. This chapter describes the strategies to deliver siRNAs to treat stroke and to facilitate post-stroke long-term recovery.

MicroRNA miR-7 Is Essential for Post-stroke Functional Recovery

Transient focal ischemia induces a sustained downregulation of miR-7 leading to derepression of its target α-synuclein (α-Syn), which promotes neuronal death. We previously showed that treatment with miR-7 mimic prevents α-Syn induction and protects brain after stroke in rodents irrespective of age and sex. To further decipher the role of miR-7, we currently studied infarction and motor function in miR-7 double knockout mice (lack both miR-7a and miR-7b) subjected to focal ischemia. Adult miR-7^-/- mice showed similar motor and cognitive functions to miR-7^+/+ mice. However, when subjected to even a mild focal ischemia, the miR-7^-/- mice showed exacerbated brain damage and worsened motor function compared with the miR-7^+/+ mice. Replenishing miR-7 in miR-7^-/- mice (IV injection of miR-7 mimic) restored miR-7 mediated neuroprotection and motor recovery, potentially by preventing α-Syn protein induction. Thus, we show that miR-7 is an essential miRNA in the brain that prevents α-Syn translation and the ensuing brain damage after stroke.

Immediate outcome prognostic value of plasma factors in patients with acute ischemic stroke after intravenous thrombolytic treatment

In the present study, we explored multiple plasma factors to predict the outcomes of patients with AIS after IVT. Fifty AIS patients who received IVT with alteplase were recruited and divided into two groups according to their NIHSS scores. Serum from all subjects was collected to quantitatively analyze the levels of different plasma factors, IL-6, MMP-9, ADAMTS13, TNC, GSN and TRX, using Luminex assays or ELISA measurements. Compared with the levels assessed at the onset of AIS, the levels of MMP-9 (P < 0.001), ADAMTS13 (P < 0.001), and TRX (P < 0.001) significantly decreased after IVT. The level of IL-6 was significantly increased in the NIHSS > 5 group at admission (P < 0.001) compared to the NIHSS ≤ 5 group. AIS patients with a poor prognosis had lower levels of ADAMTS13 at 72 h post-IVT compared with patients with a good prognosis (P = 0.021). IL-6 also was notably higher in the poor outcome group (P = 0.012). After adjusting for confounders, ADAMTS13 at 72 h post-IVT was an independent protective factor for prognosis in AIS patients with an adjusted OR of 0.07 (P = 0.049), whereas IL-6 was an independent predictor of risk for AIS patients with an adjusted OR of 1.152 (P = 0.028). IVT decreased MMP-9, ADAMTS13, and TRX levels in the plasma of AIS patients. Patients with a NIHSS score of less than 5 exhibited lower IL-6 levels, indicating that increased levels of IL-6 correlated with AIS severity after IVT. Therefore, IL-6 and ADAMTS13 might be useful plasma markers to predict the prognosis in AIS patients at 90-days after IVT.