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Introduction Elevated circulating IL-6 levels are associated with poorer outcomes after stroke, and increased serum IL-6 levels are linked to a higher risk of stroke. IL-6 binds to soluble IL-6 receptors (sIL-6R) and subsequently to ubiquitously expressed gp130, initiating proinflammatory trans-signaling. This study tested the hypothesis that inhibiting IL-6 trans-signaling by administering soluble (s) gp130 improves long-term functional outcomes in young mice after stroke. Methods Recombinant mouse gp130Fc chimera (sgp130) was administered one hour after middle cerebral artery occlusion (MCAO) followed by twice-weekly administration for 2 weeks in mice (8–15 weeks old). Behavioral assessments were done on days 7 and 28 post-MCAO for chronic studies. Flow cytometry was performed on days 3 (blood) and 7 (spleen and brain) to assess IL-6, mIL-6R, and phosphorylated STAT3 expression. Results Improved long-term functional outcomes were observed in male, but not female mice. To investigate the differential response in females, ELISA analyses revealed that plasma IL-6 levels increased in both sexes after MCAO, with a more pronounced induction in females. Additionally, circulating sIL-6R levels were significantly higher in females compared to males ( p  < 0.05) at 24 h post-MCAO. Administering a higher dose of sgp130 (1 mg/kg) to females improved long-term functional outcomes, suggesting that a higher dose is needed to inhibit IL-6 trans-signaling in females effectively. Mechanistically, sgp130 treatment reduced phosphorylated STAT3 expression in brain F4/80 macrophages and increased the expression of mIL-6R on splenic immune cells at day 7 post-MCAO in both sexes. Conclusion These findings demonstrate that inhibition of IL-6 trans-signaling with gp130Fc improves long-term functional outcomes in both male and female mice, albeit in a dose-dependent manner. This study provides novel insights into potential therapeutic strategies targeting IL-6 signaling pathways following stroke.

Inflammation is a significant driver of ischemic stroke pathology in the brain. To identify potential regulators of inflammation, we performed single-cell RNA sequencing (scRNA-seq) of young and aged mouse brains following stroke and found that interferon alpha-inducible protein 27 like 2   A ( Ifi27l2a ) was significantly up-regulated, particularly in microglia of aged brain. Ifi27l2a is induced by interferons for viral host defense and has been linked with pro-inflammatory cellular mechanisms. However, its potential role in neurodegeneration is unknown. Using a combination of cell culture, experimental stroke models in mice, and human autopsy brain samples, we demonstrated that induction of Ifi27l2a occurs in microglia in response to aging, ischemic stroke, and pro-inflammatory molecules. We further showed that induction of Ifi27l2a in microglia was sufficient to stimulate mitochondrial ROS production and promote a pro-inflammatory phenotype. Lastly, using an ischemic stroke model, we demonstrated that hemizygous deletion of Ifi27l2a ( Ifi27l2a +/- mice) reduced gliosis (microgliosis and astrogliosis), acute and chronic brain injury, and motor function deficits. Together, these findings identify Ifi27l2a as a critical neuroinflammatory mediator in ischemic stroke and provide support for the therapeutic strategy of disrupting Ifi27l2a to attenuate inflammation in the post-stroke brain. The role of Ifi27l2a, an interferon-induced gene, remains poorly understood in diseased brains. Here, authors show age and stroke-dependent upregulation of Ifi27l2a in microglia, and that reduction of Ifi27l2a leads to reduced brain injury and functional deficits after ischemic stroke.

Alzheimer’s disease (AD) is the leading cause of dementia globally. The accumulation of amyloid and tau proteins, neuronal cell death and neuroinflammation are seen with AD progression, resulting in memory and cognitive impairment. Microglia are crucial for AD progression as they engage with neural cells and protein aggregates to regulate amyloid pathology and neuroinflammation. Recent studies indicate that microglia contribute to the propagation of amyloid beta (Aβ) via their immunomodulatory functions including Aβ phagocytosis and inflammatory cytokine production. Three-dimensional cell culture techniques provide the opportunity to study pathophysiological changes in AD in human-derived samples that are difficult to recapitulate in animal models (e.g., transgenic mice). However, these models often lack immune cells such as microglia, which play a critical role in AD pathophysiology. In this study, we developed a neuroimmune assembloid model by integrating cerebral organoids (COs) with induced microglia-like cells (iMGs) derived from human induced pluripotent stem cells from familial AD patient with PSEN2 mutation. After 120 days in culture, we found that iMGs were successfully integrated within the COs. Interestingly, our assembloids displayed histological, functional and transcriptional features of the pro-inflammatory environment seen in AD, including amyloid plaque-like and neurofibrillary tangle-like structures, reduced microglial phagocytic capability, and enhanced neuroinflammatory and apoptotic gene expression. In conclusion, our neuroimmune assembloid model effectively replicates the inflammatory phenotype and amyloid pathology seen in AD.

Introduction Acute stroke leads to the activation of myeloid cells. These cells express adhesion molecules and transmigrate to the brain, thereby aggravating injury. Chronically after stroke, repair processes, including angiogenesis, are activated and enhance post-stroke recovery. Activated myeloid cells express CD13, which facilitates their migration into the site of injury. However, angiogenic blood vessels which play a role in recovery also express CD13. Overall, the specific contribution of CD13 to acute and chronic stroke outcomes is unknown. Methods CD13 expression was estimated in both mice and humans after the ischemic stroke. Young (8–12 weeks) male wild-type and global CD13 knockout (KO) mice were used for this study. Mice underwent 60 min of middle cerebral artery occlusion (MCAO) followed by reperfusion. For acute studies, the mice were euthanized at either 24- or 72 h post-stroke. For chronic studies, the Y-maze, Barnes maze, and the open field were performed on day 7 and day 28 post-stroke. Mice were euthanized at day 30 post-stroke and the brains were collected for assessment of inflammation, white matter injury, tissue loss, and angiogenesis. Flow cytometry was performed on days 3 and 7 post-stroke to quantify infiltrated monocytes and neutrophils and CXCL12/CXCR4 signaling. Results Brain CD13 expression and infiltrated CD13 + monocytes and neutrophils increased acutely after the stroke. The brain CD13 + lectin + blood vessels increased on day 15 after the stroke. Similarly, an increase in the percentage area CD13 was observed in human stroke patients at the subacute time after stroke. Deletion of CD13 resulted in reduced infarct volume and improved neurological recovery after acute stroke. However, CD13KO mice had significantly worse memory deficits, amplified gliosis, and white matter damage compared to wild-type animals at chronic time points. CD13-deficient mice had an increased percentage of CXCL12 + cells but a reduced percentage of CXCR4 + cells and decreased angiogenesis at day 30 post-stroke. Conclusions CD13 is involved in the trans-migration of monocytes and neutrophils after stroke, and acutely, led to decreased infarct size and improved behavioral outcomes. However, loss of CD13 led to reductions in post-stroke angiogenesis by reducing CXCL12/CXCR4 signaling.

Stroke is the most common cause of long-term disability and places a high economic burden on the global healthcare system. Functional outcomes from stroke are largely determined by the extent of ischemic injury, however, there is growing recognition that systemic inflammatory responses also contribute to outcomes. Mast cells (MCs) rapidly respond to injury and release histamine (HA), a pro-inflammatory neurotransmitter that enhances inflammation. The gut serves as a major reservoir of HA. We hypothesized that cromolyn, a mast cell stabilizer that prevents the release of inflammatory mediators, would decrease peripheral and central inflammation, reduce MC trafficking to the brain, and improve stroke outcomes. We used the transient middle cerebral artery occlusion (MCAO) model of ischemic stroke in aged (18 mo) male mice to investigate the role of MC in neuroinflammation post-stroke. After MCAO we treated mice with 25 mg/kg body weight of cromolyn (MC stabilizer) by oral gavage. Cromolyn was administered at 3 h, 10 h, 24 h and every 24 h for 3 days post-stroke. Three control groups were used. One group underwent a sham surgery and was treated with cromolyn, one received sham surgery with PBS vehicle and the third underwent MCAO with PBS vehicle. Mice were euthanized at 24 h and 3 days post-stroke. Cromolyn administration significantly reduced MC numbers in the brain at both 24 h and 3 days post-stroke. Infarct volume was not significantly different between groups, however improved functional outcomes were seen at 3 days post-stroke in mice that received cromolyn. Treatment with cromolyn reduced plasma histamine and IL-6 levels in both the 24-h and 3-day cohorts. Gut MCs numbers were significantly reduced after cromolyn treatment at 24 h and 3 days after stroke. To determine if MC trafficking from the gut to the brain occurred after injury, GFP + MCs were adoptively transferred to c-kit −/− MC knock-out animals prior to MCAO. 24 h after stroke, elevated MC recruitment was seen in the ischemic brain. Preventing MC histamine release by cromolyn improved gut barrier integrity and an improvement in stroke-induced dysbiosis was seen with treatment. Our results show that preventing MC histamine release possesses prevents post-stroke neuroinflammation and improves neurological and functional outcomes. Graphical abstract

Recent studies have highlighted the crucial role of microglia (MG) and their interactions with the gut microbiome in post-stroke neuroinflammation. The activation of immunoregulatory pathways, including the aryl hydrocarbon receptor (AHR) pathway, is influenced by a dynamic balance of ligands derived from both the host and microbiota. This study aimed to investigate the association between stroke-induced dysbiosis and the resultant imbalance in AHR ligand sources (loss of microbiota-derived [indole-based] and increase of host-derived [kynurenine-based]) after stroke. Microbiota-derived AHR ligands decreased in human plasma and remained low for days following an ischemic stroke highlighting the translational significance. Transient-middle-cerebral-artery-occlusion was performed in aged wild-type and germ-free male mice. MG-AHR expression and activity increased in both in vivo and ex vivo stroke models. Germ-free mice showed altered neuroinflammation and antigen presentation while aged mice showed reduced infarct volume and neurological deficits following treatment with microbiota-derived AHR ligands after stroke. Restoring a balanced pool of host- and microbiota-derived AHR ligands may be beneficial after stroke and may represent a therapeutic target. Peesh et al . show that ischemic stroke reduces microbiota-derived and increases host-derived aryl (AHR) hydrocarbon ligands. Post-stroke treatment with indole-based AHR ligands improved microglia-mediated antigen processing and co-stimulatory immune functions.

Changes in cAMP signalling in the brain influence mood and responses to stress. Here, the authors found that Cdk5 regulates cAMP degradation by PDE4 phosphodiesterases in the mouse ventral striatum. Targeting this mechanism in striatum or D1 dopamine receptor–expressing neurons improved behavioral responses to acute and chronic stressors. These results suggest an alternative strategy for the treatment of mental illnesses like depression where stress is a risk factor. The cAMP and cAMP-dependent protein kinase A (PKA) signaling cascade is a ubiquitous pathway acting downstream of multiple neuromodulators. We found that the phosphorylation of phosphodiesterase-4 (PDE4) by cyclin-dependent protein kinase 5 (Cdk5) facilitated cAMP degradation and homeostasis of cAMP/PKA signaling. In mice, loss of Cdk5 throughout the forebrain elevated cAMP levels and increased PKA activity in striatal neurons, and altered behavioral responses to acute or chronic stressors. Ventral striatum– or D1 dopamine receptor–specific conditional knockout of Cdk5, or ventral striatum infusion of a small interfering peptide that selectively targeted the regulation of PDE4 by Cdk5, produced analogous effects on stress-induced behavioral responses. Together, our results demonstrate that altering cAMP signaling in medium spiny neurons of the ventral striatum can effectively modulate stress-induced behavioral states. We propose that targeting the Cdk5 regulation of PDE4 could be a new therapeutic approach for clinical conditions associated with stress, such as depression.

Direct or indirect exposure to an explosion can induce traumatic brain injury (TBI) of various severity levels. Primary TBI from blast exposure is commonly characterized by internal injuries, such as vascular damage, neuronal injury, and contusion, without external injuries. Current animal models of blast-induced TBI (bTBI) have helped to understand the deleterious effects of moderate to severe blast forces. However, the neurological effects of mild blast forces remain poorly characterized. Here, we investigated the effects caused by mild blast forces combining neuropathological, histological, biochemical and neurophysiological analysis. For this purpose, we employed a rodent blast TBI model with blast forces below the level that causes macroscopic neuropathological changes. We found that mild blast forces induced neuroinflammation in cerebral cortex, striatum and hippocampus. Moreover, mild blast triggered microvascular damage and axonal injury. Furthermore, mild blast caused deficits in hippocampal short-term plasticity and synaptic excitability, but no impairments in long-term potentiation. Finally, mild blast exposure induced proteolytic cleavage of spectrin and the cyclin-dependent kinase 5 activator, p35 in hippocampus. Together, these findings show that mild blast forces can cause aberrant neurological changes that critically impact neuronal functions. These results are consistent with the idea that mild blast forces may induce subclinical pathophysiological changes that may contribute to neurological and psychiatric disorders.

Background Intraventricular hemorrhage (IVH) remains a major complication in preterm infants with lifelong sequelae. There is no effective treatment for IVH other than supportive care and surgery for post-hemorrhagic hydrocephalus. We previously reported that the innate neuroimmune response in an animal model of IVH was dependent on developmental stage, only occurring in older animals. Methods This study utilized a lysed-blood injection model of IVH in rats. This model specifically captures the effects of blood products released by IVH on brain parenchyma. We performed RNAseq and differential gene expression analysis on CD11b/c-positive cells in the brain (microglia/macrophages) to define gene expression in innate immune cells after IVH. We examined CD68 expression, a marker of activated microglia/infiltrating macrophages, in the periventricular white matter after IVH over 90 days. Using IBA1 staining with skeletonized branch analysis and secondary individual cell Sholl analysis, we characterized morphological changes in innate immune cells after IVH. Glial fibrillary protein (GFAP) staining was used to assess astrogliosis and chronic glial scar formation after IVH. We also examined CD68 expression in brain samples from human infants with or without IVH. Results RNAseq of isolated innate immune cells showed significant differences in cytokine-mediated gene expression at 24 h in IVH versus control animals. CD68 expression in white matter decreased overall with time and was elevated at 7 days in the IVH group compared to controls. IBA1 labeling, when analyzed across all time points, showed significant changes to microglial/macrophage branch number, branch area, and soma area after IVH. Sholl analysis of individual IBA1 labeled cells showed an effect of time but not IVH on microglial/macrophage morphology. At the chronic timepoint of 90 days, IVH induced astrogliosis at the margin of the lateral ventricle. A brain sample from a human infant with IVH showed increased CD68 expression throughout the occipital cortex compared with a non-IVH control, indicating immune activation in brain parenchyma after IVH. Conclusions Intraventricular blood products induce a robust innate immune response shortly after injection. RNAseq and CD68 counts are more sensitive to differences between groups than morphological immune cell analysis. Gliosis at the edge of ependyma occurs over time. These results help establish the timeline of inflammation after IVH to better define the window for treating IVH-associated inflammation and subsequent brain injury.

Pancreatic neuroendocrine tumors (PanNETs) are a heterogeneous population of neoplasms that arise from hormone-secreting islet cells of the pancreas and have increased markedly in incidence over the past four decades. Non-functional PanNETs, which occur more frequently than hormone-secreting tumors, are often not diagnosed until later stages of tumor development and have poorer prognoses. Development of successful therapeutics for PanNETs has been slow, partially due to a lack of diverse animal models for pre-clinical testing. Here, we report development of an inducible, conditional mouse model of PanNETs by using a bi-transgenic system for regulated expression of the aberrant activator of Cdk5, p25, specifically in β-islet cells. This model produces a heterogeneous population of PanNETs that includes a subgroup of well-differentiated, non-functional tumors. Production of these tumors demonstrates the causative potential of aberrantly active Cdk5 for generation of PanNETs. Further, we show that human PanNETs express Cdk5 pathway components, are dependent on Cdk5 for growth, and share genetic and transcriptional overlap with the INS-p25OE model. The utility of this model is enhanced by the ability to form tumor-derived allografts. This new model of PanNETs will facilitate molecular delineation of Cdk5-dependent PanNETs and the development of new targeted therapeutics.