Induction of transforming growth factor beta receptors following focal ischemia in the rat brain

Amyloid beta accumulations and enhanced neuronal differentiation in cerebral organoids of Dutch-type cerebral amyloid angiopathy patients

Introduction

ADutch-type cerebral amyloid angiopathy (D-CAA) is a hereditary brain disorder caused by a point mutation in the amyloid precursor protein (APP) gene. The mutation is located within the amyloid beta (Aβ) domain of APP and leads to Aβ peptide accumulation in and around the cerebral vasculature. There lack of disease models to study the cellular and molecular pathological mechanisms of D-CAA together with the absence of a disease phenotype in vitro in overexpression cell models, as well as the limited availability of D-CAA animal models indicates the need for a D-CAA patient-derived model.

Methods

We generated cerebral organoids from four D-CAA patients and four controls, cultured them up to 110 days and performed immunofluorescent and targeted gene expression analyses at two time points (D52 and D110).

Results

D-CAA cerebral organoids exhibited Aβ accumulations, showed enhanced neuronal and astrocytic gene expression and TGFβ pathway de-regulation.

Conclusions

These results illustrate the potential of cerebral organoids as in vitro disease model of D-CAA that can be used to understand disease mechanisms of D-CAA and can serve as therapeutic intervention platform for various Aβ-related disorders.

The expression and phosphorylation of SMAD3 protein in microglia and astrocytes of the rat hippocampus after transient global cerebral ischemia

SMAD3 protein transduces signals from TGF-β and activins. In vitro studies have shown that SMAD3 plays an important role in regulating of micoglia and astrocytic function. However, there is little information on the association between SMAD3 signaling and the pathophysiology of the glial cells in the post-ischemic hippocampus. In this study, we examined the time-course changes in the expression and phosphorylation of SMAD3 in the rat hippocampus using a rat model of global cerebral ischemia. Most pyramidal neuronal cells in the CA1 region died within 7 days after ischemia. The number of SMAD3- or phosphorylated SMAD3 (p-SMAD3)-immunopositive microglia or astrocytes increased in the CA1 region 7 days after ischemia. Real-time PCR analysis showed an increase in the level of TGF-β1 mRNA in the hippocampus after ischemia. Intracerebroventricular injection of SB525334, a selective inhibitor of TGF-β receptor I kinase (ALK5), reduced the ischemia-induced p-SMAD3 immunoreactivity in the microglia and astrocytes. By contrast, intracerebroventricular injection of SB525334 did not affect the ischemia-induced neuronal cell death. These results suggest that ischemia-induced SMAD3 phosphorylation in the microglia and astrocytes of post-ischemic hippocampi is associated with tissue repair and not neuroprotection.

The promise of the TGF-β superfamily as a therapeutic target for Parkinson's disease

A large body of evidence underscore the regulatory role of TGF-β superfamily in the central nervous system. Components of the TGF-β superfamily modulate key events during embryonic brain development and adult brain tissue injury repair. With respect to Parkinson's disease (PD), TGF-ß signaling pathways are implicated in the differentiation, maintenance and synaptic function of the dopaminergic neurons, as well as in processes related to the activation state of astrocytes and microglia. In vitro and in vivo studies using toxin models, have interrogated on the dopaminotrophic and protective role of the TGF-β superfamily members. The evolution of genetic and animal models of PD that more closely recapitulate the disease condition has made possible the dissection of intracellular pathways in response to TGF-ß treatment. Although the first clinical trials using GDNF did not meet their primary endpoints, substantial work has been carried out to reappraise the TGF-β superfamily's clinical benefit.

TGFβ-Neurotrophin Interactions in Heart, Retina, and Brain

Ischemic insults to the heart and brain, i.e., myocardial and cerebral infarction, respectively, are amongst the leading causes of death worldwide. While there are therapeutic options to allow reperfusion of ischemic myocardial and brain tissue by reopening obstructed vessels, mitigating primary tissue damage, post-infarction inflammation and tissue remodeling can lead to secondary tissue damage. Similarly, ischemia in retinal tissue is the driving force in the progression of neovascular eye diseases such as diabetic retinopathy (DR) and age-related macular degeneration (AMD), which eventually lead to functional blindness, if left untreated. Intriguingly, the easily observable retinal blood vessels can be used as a window to the heart and brain to allow judgement of microvascular damages in diseases such as diabetes or hypertension. The complex neuronal and endocrine interactions between heart, retina and brain have also been appreciated in myocardial infarction, ischemic stroke, and retinal diseases. To describe the intimate relationship between the individual tissues, we use the terms heart-brain and brain-retina axis in this review and focus on the role of transforming growth factor β (TGFβ) and neurotrophins in regulation of these axes under physiologic and pathologic conditions. Moreover, we particularly discuss their roles in inflammation and repair following ischemic/neovascular insults. As there is evidence that TGFβ signaling has the potential to regulate expression of neurotrophins, it is tempting to speculate, and is discussed here, that cross-talk between TGFβ and neurotrophin signaling protects cells from harmful and/or damaging events in the heart, retina, and brain.

Changes in Smad1/5/9 expression and phosphorylation in astrocytes of the rat hippocampus after transient global cerebral ischemia

Smad proteins are known to transduce the actions of the transforming growth factor-β (TGF-β) family including TGF-βs, activins, and bone morphogenetic proteins (BMPs). We previously reported that Smad1/5/9 immunoreactivity was observed in astrocytes of various rat brain regions including the hippocampus, suggesting that Smad1/5/9 may be associated with the physiology of astrocytes. However, the Smad1/5/9 expression and activation in the hippocampal astrocytes after global cerebral ischemia has not been yet elucidated. In this study, we examined temporal changes in the expression and phosphorylation of Smad1/5/9 in the hippocampus using a rat model of global cerebral ischemia. Furthermore, we examined the candidate ligand involved in the phosphorylation of Smad1/5/9 in the hippocampus after ischemia. Pyramidal neuronal cell death in the CA1 regions was visible at 3 days, and maximum death occurred within 7 days after ischemia. At 7 days after ischemia, astrocytes that showed strong immunoreactivity for Smad1/5/9 were frequently observed in the CA1 region. Additionally, there was an increase in phosphorylated Smad1/5/9 (phospho-Smad1/5/9) -immunopositive astrocytes in the CA1 region 7 days after ischemia. Real-time PCR analysis showed an increase in the expression level of TGF-β1 mRNA in the hippocampus after ischemia. Intracerebroventricular injection of SB525334, an inhibitor of TGF-β/Smad signaling, reduced immunoreactivity for phospho-Smad1/5/9 in astrocytes. These results suggest that TGF-β1 may be a key molecule for ischemia-induced Smad1/5/9 phosphorylation in astrocytes, and TGF-β1-Smad1/5/9 signaling may play a role in post-ischemic events, including brain inflammation or tissue repair rather than neuroprotection of the hippocampus.

Triiodothyronine Aggravates Global Cerebral Ischemia-Reperfusion Injury in Mice

Thyroid hormones (THs) have been suggested to play an important role in both physiological and pathological events in the central nervous system. Hypothyroidism, which is characterized by low levels of serum THs, has been associated with aggravation of ischemic neuronal injuries in stroke patients. We hypothesized that administration of T3, the main active form of THs, may attenuate the ischemic neuronal injuries. In mice, global cerebral ischemia (GCI), which is induced by transient occlusion of the bilateral common carotid artery, causes neuronal injuries by inducing neuronal death and activating inflammatory responses after reperfusion in the hippocampus. In this study, we examined the effect of T3 administration on DNA fragmentation induced by neuronal death and the activation of inflammatory cells such as astrocytes and microglia in the hippocampus following GCI. The content of nucleosomes generated by DNA fragmentation in the hippocampus was increased by GCI and further increased by T3 administration. The protein expression levels of glial fibrillary acidic protein (GFAP), an astrocytic marker, and Ionized calcium binding adaptor protein 1 (Iba1), a microglial marker, in the hippocampus were also increased by GCI and further increased by T3 administration. The levels of T3 in both the serum and hippocampus were elevated by T3 administration. Our results indicate that T3 administration aggravates GCI-reperfusion injury in mice. There may be an increased risk of aggravation of ischemic stroke by the excessive elevation of T3 levels during the drug treatment of hypothyroidism.

Preventive and curative effects of grape seed powder on stroke using in vitro and in vivo models of cerebral ischemia/reperfusion

Stroke is a worldwide concern. Many studies pointed out relevant preventive effect of grape seed powder (GSP) against deleterious brain ischemia/reperfusion (I/R) injury, but curative effect has been scarcely approached. The present work aimed at studying the preventive and curative effect of GSP against stroke using in-vitro and in-vivo models. Primary neuron-astrocyte cocultures were used to evaluate in-vitro GSP protective and curative effect on oxygen-glucose-deprivation (OGD). A murine I/R model, in which GSP was administered as delayed post stroke drug, to evaluate its potential clinically translatable therapy was used and behavioral tests were conducted after 15 days. Ultra-structure of hippocampus dentate gyrus using Transmission Electron Microscopy (TEM) was also undertaken. GSP prevented OGD-induced toxicity and cell death in a dose dependent manner and was neuroprotective as assessed by sustained cell viability (70 % ±1 for OGD + GSP and 37 % ±2 for OGD) and modulated cytokines and brain derived neurotrophic factor (BDNF) expression. GSP also promoted behavioral outcomes by increasing step-down inhibitory time from 17s±4 to 50s±11 and rat overall activities by improving scores in open field test to near control level. Furthermore, GSP protected hippocampus dentate gyrus area from I/R-induced drastic alterations as assessed by reduced autophagic vacuoles.

Propolis ameliorates cerebral injury in focal cerebral ischemia/reperfusion (I/R) rat model via upregulation of TGF-β1

Neuroprotective impact of transforming growth factor β1 (TGF-β1) is increasingly recognized in different brain injuries. Propolis exhibits a broad spectrum of biological and pharmacological properties including neuroprotective action. The objective of the investigation was to explore the involvement of TGF-β1 signaling in the neuroprotective mechanism of propolis in I/R rats. In this study, focal cerebral ischemia model was built by middle cerebral artery occlusion (MCAO) for 2 h followed by reperfusion. The investigation was carried out on 48 rats that were arranged into four groups (n = 12): the sham group, I/R control group, I/R + propolis (50 mg/kg) group and I/R + propolis (100 mg/kg) group. The results revealed that propolis preserved rats against neuronal injury induced by cerebral I/R. It significantly reduced neurological deficit scores and improved motor coordination and locomotor activity in I/R rats. Propolis antagonized the damage induced by cerebral I/R through suppression of malondialdehyde (MDA) and elevation of reduced glutathione (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), brain-derived neurotropic factor (BDNF) and dopamine levels in the brain homogenates of I/R rats. Other ameliorations were also observed based on reduction of neurodegeneration and histological alterations in the brain tissues. These results also proposed that the neuroprotective effect of propolis might be related to upregulation of TGF-β1 and suppressed matrix metallopeptidase-9 (MMP9) mRNA expression.

The interrelationship between cerebral ischemic stroke and glioma: a comprehensive study of recent reports

Glioma and cerebral ischemic stroke are two major events that lead to patient death worldwide. Although these conditions have different physiological incidences, ~10% of ischemic stroke patients develop cerebral cancer, especially glioma, in the postischemic stages. Additionally, the high proliferation, venous thrombosis and hypercoagulability of the glioma mass increase the significant risk of thromboembolism, including ischemic stroke. Surprisingly, these events share several common pathways, viz. hypoxia, cerebral inflammation, angiogenesis, etc., but the proper mechanism behind this co-occurrence has yet to be discovered. The hypercoagulability and presence of the D-dimer level in stroke are different in cancer patients than in the noncancerous population. Other factors such as atherosclerosis and coagulopathy involved in the pathogenesis of stroke are partially responsible for cancer, and the reverse is also partially true. Based on clinical and neurosurgical experience, the neuronal structures and functions in the brain and spine are observed to change after a progressive attack of ischemia that leads to hypoxia and atrophy. The major population of cancer cells cannot survive in an adverse ischemic environment that excludes cancer stem cells (CSCs). Cancer cells in stroke patients have already metastasized, but early-stage cancer patients also suffer stroke for multiple reasons. Therefore, stroke is an early manifestation of cancer. Stroke and cancer share many factors that result in an increased risk of stroke in cancer patients, and vice-versa. The intricate mechanisms for stroke with and without cancer are different. This review summarizes the current clinical reports, pathophysiology, probable causes of co-occurrence, prognoses, and treatment possibilities.

Complement component 1q subcomponent binding protein in the brain of the rat

Complement component 1q subcomponent binding protein (C1qbp) is a multifunctional protein involved in immune response, energy homeostasis of cells as a plasma membrane receptor, and a nuclear, cytoplasmic or mitochondrial protein. Recent reports suggested its neuronal function, too, possibly in axon maintenance, synaptic function, and neuroplasticity. Therefore, we addressed to identify C1qbp in the rat brain using in situ hybridization histochemistry and immunolabelling at light and electron microscopic level. C1qbp has a topographical distribution in the brain established by the same pattern of C1qbp mRNA-expressing and protein-containing neurons with the highest abundance in the cerebral cortex, anterodorsal thalamic nucleus, hypothalamic paraventricular (PVN) and arcuate nuclei, spinal trigeminal nucleus. Double labelling of C1qbp with the neuronal marker NeuN, with the astrocyte marker S100, and the microglia marker Iba1 demonstrated the presence of C1qbp in neurons but not in glial cells in the normal brain, while C1qbp appeared in microglia following their activation induced by focal ischemic lesion. Only restricted neurons expressed C1qbp, for example, in the PVN, magnocellular neurons selectively contained C1qbp. Further double labelling by using the mitochondria marker Idh3a antibody suggested the mitochondrial localization of C1qbp in the brain, confirmed by correlated light and electron microscopy at 3 different brain regions. Post-embedding immunoelectron microscopy also suggested uneven C1qbp content of mitochondria in different brain areas but also heterogeneity within single neurons. These data suggest a specific function of C1qbp in the brain related to mitochondria, such as the regulation of local energy supply in neuronal cells.

Silencing of TGFβ signalling in microglia results in impaired homeostasis

TGFβ1 has been implicated in regulating functional aspects of several distinct immune cell populations including central nervous system (CNS) resident microglia. Activation and priming of microglia have been demonstrated to contribute to the progression of neurodegenerative diseases and, thus, underlie stringent control by endogenous regulatory factors including TGFβ1. Here, we demonstrate that deletion of Tgfbr2 in adult postnatal microglia does neither result in impairment of the microglia-specific gene expression signatures, nor is microglial survival and maintenance affected. Tgfbr2-deficient microglia were characterised by distinct morphological changes and transcriptome analysis using RNAseq revealed that loss of TGFβ signalling results in upregulation of microglia activation and priming markers. Moreover, protein arrays demonstrated increased secretion of CXCL10 and CCL2 accompanied by activation of immune cell signalling as evidenced by increased phosphorylation of TAK1. Together, these data underline the importance of microglial TGFβ signalling to regulate microglia adaptive changes.

Comparing Effects of Transforming Growth Factor β1 on Microglia From Rat and Mouse: Transcriptional Profiles and Potassium Channels

The cytokine, transforming growth factor β1 (TGFβ1), is up-regulated after central nervous system (CNS) injuries or diseases involving microglial activation, and it has been proposed as a therapeutic agent for treating neuroinflammation. Microglia can produce and respond to TGFβ1. While rats and mice are commonly used for studying neuroinflammation, very few reports directly compare them. Such studies are important for improving pre-clinical studies and furthering translational progress in developing therapeutic interventions. After intracerebral hemorrhage (ICH) in the rat striatum, the TGFβ1 receptor was highly expressed on microglia/macrophages within the hematoma. We recently found species similarities and differences in response to either a pro-inflammatory (interferon-γ, IFN-γ, +tumor necrosis factor, TNF-α) or anti-inflammatory interleukin-4 (IL-4) stimulus. Here, we assessed whether rat and mouse microglia differ in their responses to TGFβ1. Microglia were isolated from Sprague-Dawley rats and C57BL/6 mice and treated with TGFβ1. We quantified changes in expression of >50 genes, in their morphology, proliferation, apoptosis and in three potassium channels that are considered therapeutic targets. Many inflammatory mediators, immune receptors and modulators showed species similarities, but notable differences included that, for some genes, only one species responded (e.g., Il4r, Il10, Tgfbr2, colony-stimulating factor receptor (Csf1r), Itgam, suppressor of cytokine signaling 1 (Socs1), toll-like receptors 4 (Tlr4), P2rx7, P2ry12), and opposite responses were seen for others (Tgfb1, Myc, Ifngr1). In rat only, TGFβ1 affected microglial morphology and proliferation, but there was no apoptosis in either species. In both species, TGFβ1 dramatically increased Kv1.3 channel expression and current (no effects on Kir2.1). KCa3.1 showed opposite species responses: the current was low in unstimulated rat microglia and greatly increased by TGFβ1 but higher in control mouse cells and decreased by TGFβ1. Finally, we compared TGFβ1 and IL10 (often considered similar anti-inflammatory stimuli) and found many different responses in both species. Overall, the numerous species differences should be considered when characterizing neuroinflammation and microglial activation in vitro and in vivo, and when targeting potassium channels.

Distribution of Smad mRNA and proteins in the rat brain

Smad proteins are known to transduce the action of TGF-β superfamily proteins including TGF-βs, activins, and bone morphogenetic proteins (BMPs). In this study, we examined the expression of Smad1, -2, -3, -4, -5, and -8 mRNA in the rat brain by means of RT-PCR and in situ hybridization (ISH). In addition, we examined the nuclear accumulation of Smad1, -2, -3, -5, and -8 proteins after intracerebroventricular injection of TGF-β1, activin A, or BMP6 with immunohistochemistry to investigate whether TGF-β, activin, and/or BMP activate Smads in the rat brain. RT-PCR analysis revealed that Smad1, -2, -3, -4, -5, and -8 mRNA was expressed in the brain and that the Smad3 and Smad8 mRNA differed in the expression level between brain regions. For example, there were high levels of expression of Smad3 mRNA in the cerebral cortex, caudate putamen/globus pallidus, and cerebellum, but low levels in the thalamus and midbrain. Expression of Smad8 mRNA was higher in the midbrain, cerebellum, and pons/medulla oblongata in comparison to the olfactory bulb, cerebral cortex, caudate putamen/globus pallidus, hippocampus/dentate gyrus, and thalamus. ISH signals for Smad1 mRNA were widely detected in the brain except for a small number of regions including the olfactory tubercle, posterior region of hypothalamus, and cerebellar nuclei. ISH signals for Smad2 mRNA were abundantly observed in several brain regions including the olfactory bulb, piriform cortex, basal ganglia, cingulate cortex, epithalamus, including the pineal gland and medial habenular nuclei, hypothalamus, inferior colliculi of the midbrain, and some nuclei in the pons, cerebellar cortex, and choroid plexus. ISH signals for Smad3 mRNA were also abundantly observed in several brain regions. Especially strong signals for Smad3 mRNA were observed in the olfactory tubercle, piriform cortex, basal ganglia, dentate gyrus, and cingulate cortex. ISH signals for Smad5 and Smad8 mRNA were restricted to a small number of brain regions, the signal intensity of which was weak. ISH signals for Smad4 mRNA were detected in all regions examined. Intracerebroventricular injection of activin A induced nuclear accumulation of Smad2 and Smad3 immunoreactivity in neurons. In contrast, intracerebroventricular injection of TGF-β1 or BMP6 did not induce nuclear accumulation of the immunoreactivity for any Smad in neurons. These results suggest that activin-Smad signaling plays an important role in brain homeostasis.

TGFβ pathway deregulation and abnormal phospho-SMAD2/3 staining in hereditary cerebral hemorrhage with amyloidosis-Dutch type

Hereditary cerebral hemorrhage with amyloidosis‐Dutch type (HCHWA‐D) is an early onset hereditary form of cerebral amyloid angiopathy (CAA) pathology, caused by the E22Q mutation in the amyloid β (Aβ) peptide. Transforming growth factor β1 (TGFβ1) is a key player in vascular fibrosis and in the formation of angiopathic vessels in transgenic mice. Therefore, we investigated whether the TGFβ pathway is involved in HCHWA‐D pathogenesis in human postmortem brain tissue from frontal and occipital lobes. Components of the TGFβ pathway were analyzed with quantitative RT‐PCR. TGFβ1 and TGFβ Receptor 2 (TGFBR2) gene expression levels were significantly increased in HCHWA‐D in comparison to the controls, in both frontal and occipital lobes. TGFβ‐induced pro‐fibrotic target genes were also upregulated. We further assessed pathway activation by detecting phospho‐SMAD2/3 (pSMAD2/3), a direct TGFβ down‐stream signaling mediator, using immunohistochemistry. We found abnormal pSMAD2/3 granular deposits specifically on HCHWA‐D angiopathic frontal and occipital vessels. We graded pSMAD2/3 accumulation in angiopathic vessels and found a positive correlation with the CAA load independent of the brain area. We also observed pSMAD2/3 granules in a halo surrounding occipital vessels, which was specific for HCHWA‐D. The result of this study indicates an upregulation of TGFβ1 in HCHWA‐D, as was found previously in AD with CAA pathology. We discuss the possible origins and implications of the TGFβ pathway deregulation in the microvasculature in HCHWA‐D. These findings identify the TGFβ pathway as a potential biomarker of disease progression and a possible target of therapeutic intervention in HCHWA‐D.

Delayed ALK5 inhibition improves functional recovery in neonatal brain injury

Neuroinflammation subsequent to developmental brain injury contributes to a wave of secondary neurodegeneration and to reactive astrogliosis that can inhibit oligodendrocyte progenitor differentiation and subsequent myelination. Here we evaluated the therapeutic efficacy of a small molecule antagonist for a TGFß receptor in a model of moderate perinatal hypoxia-ischemia (H-I). Osmotic pumps containing SB505124, an antagonist of the type 1 TGFß1 receptor ALK5, or vehicle, were implanted three days after H-I induced at postnatal day 6. Perinatal H-I induced selective neuronal death, ventriculomegaly, elevated CNS levels of IL-6 and IL-1α, astrogliosis, and fewer proliferating oligodendrocyte progenitors. Myelination was reduced by ∼50%. Anterograde tracing revealed extensive axonal loss in the corticospinal tract. These alterations correlated with functional impairments across a battery of behavioral tests. All of these parameters were brought back towards normal levels with SB505124 treatment. Notably, SB505124 preserved neurons in the hippocampus and thalamus. Our results indicate that inhibiting ALK5 signaling, even as late as three days after injury, creates an environment that is more permissive for oligodendrocyte maturation and myelination producing significant improvements in neurological outcome. This new therapeutic would be especially appropriate for moderately preterm asphyxiated infants, for whom there is presently no FDA approved neuroprotective therapeutic.

TGF-β1/Smad3 Signaling Pathway Suppresses Cell Apoptosis in Cerebral Ischemic Stroke Rats

BACKGROUND We desired to observe the changes of transforming growth factor-β1/drosophila mothers against decapentaplegic protein (TGF-β1/Smad3) signaling pathway in the hippocampus region of cerebral ischemic stroke rats so that the effects of this pathway on nerve cells can be investigated. MATERIAL AND METHODS The ischemic stroke models were built by middle cerebral artery occlusion (MCAO) in vivo and oxygen-glucose deprivation (OGD) in vitro. TGF-β1 and TGF-β1 inhibitors were injected into rat models while TGF-β1, TGF-β1 siRNA, Smad3, and Smad3 siRNA were transfected into cells. Infarct sizes were measured using triphenyltetrazolium chloride (TTC) staining, while the apoptosis rate of cells were calculated by Annexin V-fluorescein isothiocyanate/propidium iodide (Annexin V-FITC/PI) staining. Levels of TGF-β1, Smad3, and Bcl-2 were examined by real-time polymerase chain reaction (RT-PCR), immunohistochemical, and Western blot analysis. RESULTS The expressions of TGF-β1/Smad3 signal pathway were significantly increased in both model rats and BV2 cells, whereas the expression of Bcl-2 was down-regulated (P<0.05). The TGF-β1/Smad3 signal pathway exhibited protective effects, including the down-regulation of infarction size in cerebral tissues and the down-regulation of apoptosis rate of BV2 cells by increasing the expression of Bcl-2 (P<0.05). In addition, these effects could be antagonized by the corresponding inhibitors and siRNA (P<0.05). CONCLUSIONS The TGF-β1/Smad3 signaling pathway was up-regulated once cerebral ischemic stroke was simulated. TGF-β1 may activate the expression of Bcl-2 via Smad3 to suppress the apoptosis of neurons.

TGF-β1 modulates microglial phenotype and promotes recovery after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating form of stroke that results from the rupture of a blood vessel in the brain, leading to a mass of blood within the brain parenchyma. The injury causes a rapid inflammatory reaction that includes activation of the tissue-resident microglia and recruitment of blood-derived macrophages and other leukocytes. In this work, we investigated the specific responses of microglia following ICH with the aim of identifying pathways that may aid in recovery after brain injury. We used longitudinal transcriptional profiling of microglia in a murine model to determine the phenotype of microglia during the acute and resolution phases of ICH in vivo and found increases in TGF-β1 pathway activation during the resolution phase. We then confirmed that TGF-β1 treatment modulated inflammatory profiles of microglia in vitro. Moreover, TGF-β1 treatment following ICH decreased microglial Il6 gene expression in vivo and improved functional outcomes in the murine model. Finally, we observed that patients with early increases in plasma TGF-β1 concentrations had better outcomes 90 days after ICH, confirming the role of TGF-β1 in functional recovery from ICH. Taken together, our data show that TGF-β1 modulates microglia-mediated neuroinflammation after ICH and promotes functional recovery, suggesting that TGF-β1 may be a therapeutic target for acute brain injury.

Monocyte-Derived Macrophages Contribute to Spontaneous Long-Term Functional Recovery after Stroke in Mice

Stroke is a leading cause of disability and currently lacks effective therapy enabling long-term functional recovery. Ischemic brain injury causes local inflammation, which involves both activated resident microglia and infiltrating immune cells, including monocytes. Monocyte-derived macrophages (MDMs) exhibit a high degree of functional plasticity. Here, we determined the role of MDMs in long-term spontaneous functional recovery after middle cerebral artery occlusion in mice. Analyses by flow cytometry and immunocytochemistry revealed that monocytes home to the stroke-injured hemisphere., and that infiltration peaks 3 d after stroke. At day 7, half of the infiltrating MDMs exhibited a bias toward a proinflammatory phenotype and the other half toward an anti-inflammatory phenotype, but during the subsequent 2 weeks, MDMs with an anti-inflammatory phenotype dominated. Blocking monocyte recruitment using the anti-CCR2 antibody MC-21 during the first week after stroke abolished long-term behavioral recovery, as determined in corridor and staircase tests, and drastically decreased tissue expression of anti-inflammatory genes, including TGFβ, CD163, and Ym1. Our results show that spontaneously recruited monocytes to the injured brain early after the insult contribute to long-term functional recovery after stroke.

SIGNIFICANCE STATEMENT

For decades, any involvement of circulating immune cells in CNS repair was completely denied. Only over the past few years has involvement of monocyte-derived macrophages (MDMs) in CNS repair received appreciation. We show here, for the first time, that MDMs recruited to the injured brain early after ischemic stroke contribute to long-term spontaneous functional recovery through inflammation-resolving activity. Our data raise the possibility that inadequate recruitment of MDMs to the brain after stroke underlies the incomplete functional recovery seen in patients and that boosting homing of MDMs with an anti-inflammatory bias to the injured brain tissue may be a new therapeutic approach to promote long-term improvement after stroke.

Microglial Cells Prevent Hemorrhage in Neonatal Focal Arterial Stroke

Perinatal stroke leads to significant morbidity and long-term neurological and cognitive deficits. The pathophysiological mechanisms of brain damage depend on brain maturation at the time of stroke. To understand whether microglial cells limit injury after neonatal stroke by preserving neurovascular integrity, we subjected postnatal day 7 (P7) rats depleted of microglial cells, rats with inhibited microglial TGFbr2/ALK5 signaling, and corresponding controls, to transient middle cerebral artery occlusion (tMCAO). Microglial depletion by intracerebral injection of liposome-encapsulated clodronate at P5 significantly reduced vessel coverage and triggered hemorrhages in injured regions 24 h after tMCAO. Lack of microglia did not alter expression or intracellular redistribution of several tight junction proteins, did not affect degradation of collagen IV induced by the tMCAO, but altered cell types producing TGFβ1 and the phosphorylation and intracellular distribution of SMAD2/3. Selective inhibition of TGFbr2/ALK5 signaling in microglia via intracerebral liposome-encapsulated SB-431542 delivery triggered hemorrhages after tMCAO, demonstrating that TGFβ1/TGFbr2/ALK5 signaling in microglia protects from hemorrhages. Consistent with observations in neonatal rats, depletion of microglia before tMCAO in P9 Cx3cr1(GFP/+)/Ccr2(RFP/+) mice exacerbated injury and induced hemorrhages at 24 h. The effects were independent of infiltration of Ccr2(RFP/+) monocytes into injured regions. Cumulatively, in two species, we show that microglial cells protect neonatal brain from hemorrhage after acute ischemic stroke.

Microglial Cells Prevent Hemorrhage in Neonatal Focal Arterial Stroke

Perinatal stroke leads to significant morbidity and long-term neurological and cognitive deficits. The pathophysiological mechanisms of brain damage depend on brain maturation at the time of stroke. To understand whether microglial cells limit injury after neonatal stroke by preserving neurovascular integrity, we subjected postnatal day 7 (P7) rats depleted of microglial cells, rats with inhibited microglial TGFbr2/ALK5 signaling, and corresponding controls, to transient middle cerebral artery occlusion (tMCAO). Microglial depletion by intracerebral injection of liposome-encapsulated clodronate at P5 significantly reduced vessel coverage and triggered hemorrhages in injured regions 24 h after tMCAO. Lack of microglia did not alter expression or intracellular redistribution of several tight junction proteins, did not affect degradation of collagen IV induced by the tMCAO, but altered cell types producing TGFβ1 and the phosphorylation and intracellular distribution of SMAD2/3. Selective inhibition of TGFbr2/ALK5 signaling in microglia via intracerebral liposome-encapsulated SB-431542 delivery triggered hemorrhages after tMCAO, demonstrating that TGFβ1/TGFbr2/ALK5 signaling in microglia protects from hemorrhages. Consistent with observations in neonatal rats, depletion of microglia before tMCAO in P9 Cx3cr1(GFP/+)/Ccr2(RFP/+) mice exacerbated injury and induced hemorrhages at 24 h. The effects were independent of infiltration of Ccr2(RFP/+) monocytes into injured regions. Cumulatively, in two species, we show that microglial cells protect neonatal brain from hemorrhage after acute ischemic stroke.

MicroRNA involvement in mechanism of endogenous protection induced by fastigial nucleus stimulation based on deep sequencing and bioinformatics

BACKGROUND

Neurogenic neuroprotection is a promising approach for treating patients with ischemic brain lesions. Fastigial nucleus stimulation (FNS) has been shown to reduce the tissue damage resulting from focal cerebral ischemia in the earlier studies. However, the mechanisms of neuroprotection induced by FNS remain unclear. MicroRNAs (miRNAs) are a newly discovered group of non-coding small RNA molecules that negatively regulate target gene expression and involved in the regulation of pathological process. To date, there is a lack of knowledge on the expression of miRNA in response to FNS. Thus, we study the regulation of miRNAs in the rat ischemic brain by the neuroprotection effect of FNS.

METHODS

In this study, we used an established focal cerebral ischemia/reperfusion (IR) model in rats. MiRNA expression profile of rat ischemic cortex after 1 h of FNS were investigated using deep sequencing. Microarray was performed to study the expression pattern of miRNAs. Functional annotation on the miRNA was carried out by bioinformatics analysis.

RESULTS

Two thousand four hundred ninety three miRNAs were detected and found to be miRNAs or miRNA candidates using deep sequencing technology. We found that the FNS-related miRNAs were differentially expressed according microarray data. Bioinformatics analysis indicated that several differentially expressed miRNAs might be a central node of neuroprotection-associated genetic networks and contribute to neuroprotection induced by FNS.

CONCLUSIONS

MiRNA acts as a novel regulator and contributes to FNS-induced neuroprotection. Our study provides a better understanding of neuroprotection induced by FNS.

Altering 5-hydroxymethylcytosine modification impacts ischemic brain injury

Epigenetic modifications such as cytosine methylation and histone modification are linked to the pathology of ischemic brain injury. Recent research has implicated 5-hydroxymethylcytosine (5hmC), a DNA base derived from 5-methylcytosine (5mC) via oxidation by ten-eleven translocation (Tet) enzymes, in DNA methylation-related plasticity. Here we show that 5hmC abundance was increased after ischemic injury, and Tet2 was responsible for this increase; furthermore, inhibiting Tet2 expression abolished the increase of 5hmC caused by ischemic injury. The decrease in 5hmC modifications from inhibiting Tet2 activity was accompanied by increased infarct volume after ischemic injury. Genome-wide profiling of 5hmC revealed differentially hydroxymethylated regions (DhMRs) associated with ischemic injury, and DhMRs were enriched among the genes involved in cell junction, neuronal morphogenesis and neurodevelopment. In particular, we found that 5hmC modifications at the promoter region of brain-derived neurotrophic factor (BDNF) increased, which was accompanied by increased BDNF mRNA, whereas the inhibition of Tet2 reduced BDNF mRNA and protein expression. Finally, we show that the abundance of 5hmC in blood samples from patients with acute ischemic stroke was also significantly increased. Together, these data suggest that 5hmC modification could serve as both a potential biomarker and a therapeutic target for the treatment of ischemic stroke.

Revisiting Cerebral Postischemic Reperfusion Injury: New Insights in Understanding Reperfusion Failure, Hemorrhage, and Edema

Cerebral postischemic reperfusion injury is defined as deterioration of ischemic brain tissue that parallels and antagonizes the benefits of restoring cerebral circulation after therapeutic thrombolysis for acute ischemic stroke. To understand the paradox of injury caused by treatment, we first emphasize the phenomenon in which recanalization of an occluded artery does not lead to tissue reperfusion. Additionally, no-reflow after recanalization may be due to injury of the neurovascular unit, distal microthrombosis, or both, and certainly worsens outcome. We examine the mechanism of molecular and sub-cellular damage in the neurovascular unit, notably oxidative stress, mitochondrial dysfunction, and apoptosis. At the level of the neurovascular unit, which mediates crosstalk between the damaged brain and systemic responses in blood, we summarize emerging evidence demonstrating that individual cell components play unique and cumulative roles that lead to damage of the blood–brain barrier and neurons. Furthermore, we review the latest developments in establishing a link between the immune system and microvascular dysfunction during ischemic reperfusion. Progress in assessing reperfusion injury has also been made, and we review imaging studies using various magnetic resonance imaging modalities. Lastly, we explore potential treatment approaches, including ischemic preconditioning, postconditioning, pharmacologic agents, and hypothermia.