Vascular damage in the central nervous system: a multifaceted role for vascular-derived TGF-β

The Role of Neuroinflammatory Mediators in the Pathogenesis of Traumatic Brain Injury: A Narrative Review

Traumatic brain injury (TBI) is a debilitating acquired neurological disorder that afflicts nearly 74 million people worldwide annually. TBI has been classified as more than just a single insult because of its associated risk toward various long-term neurological and neurodegenerative disorders. This risk may be triggered by a series of postinjury secondary molecular and cellular pathology, which may be dependent on the severity of the TBI. Among the secondary injury mechanisms, neuroinflammation may be the most crucial as it may exacerbate brain damage and lead to fatal consequences when prolonged. This Review aimed to elucidate the influence of neuroinflammatory mediators on the TBI functional and pathological outcomes, particularly focusing on inflammatory cytokines which were associated with neuronal dysfunctions in the acute and chronic stages of TBI. These cytokines include interleukins (IL) such as IL-1(beta)β, IL-4, IL-6, IL8, IL-10, IL-18, IL-33 and tumor necrosis factor alpha (TNF-α), which have been extensively studied. Apart from these, IL-2, interferon gamma (IFN-γ), and transforming growth factor-beta (TGF-β) may also play a significant role in the pathogenesis of TBI. These neuroinflammatory mediators may trigger a series of pathological events such as cell death, microglial suppression, and increased catecholaminergic activity. Interestingly, in the acute phase of TBI, most of these mediators may also play a neuroprotective role by displaying anti-inflammatory properties, which may convert to a pro-inflammatory action in the chronic stages post TBI. Early identification and treatment of these mediators may help the development of more effective treatment options for TBI.

Involvement of Epigenetic Mechanisms and Non-coding RNAs in Blood-Brain Barrier and Neurovascular Unit Injury and Recovery After Stroke

Cessation of blood flow leads to a complex cascade of pathophysiological events at the blood-vascular-parenchymal interface which evolves over time and space, and results in damage to neural cells and edema formation. Cerebral ischemic injury evokes a profound and deleterious upregulation in inflammation and triggers multiple cell death pathways, but it also induces a series of the events associated with regenerative responses, including vascular remodeling, angiogenesis, and neurogenesis. Emerging evidence suggests that epigenetic reprograming could play a pivotal role in ongoing post-stroke neurovascular unit (NVU) changes and recovery. This review summarizes current knowledge about post-stroke recovery processes at the NVU, as well as epigenetic mechanisms and modifiers (e.g., DNA methylation, histone modifying enzymes and microRNAs) associated with stroke injury, and NVU repair. It also discusses novel drug targets and therapeutic strategies for enhancing post-stroke recovery.

Furin inhibition prevents hypoxic and TGFβ-mediated blood-brain barrier disruption

Hypoxic blood-brain barrier (BBB) dysfunction is a common feature of CNS diseases however mechanisms underlying barrier disturbance are still largely unknown. This study investigated the role of transforming growth factor β (TGFβ), a cytokine known to induce expression of the proprotein convertase Furin, in hypoxia-mediated barrier compromise. We show that exposure of brain endothelial cells (ECs) to hypoxia (1% O₂) rapidly stimulates their migration. Additional exogenous TGFβ (0.4 nM) exposure potentiated this effect and increased Furin expression in a TGFβ type I receptor activin-like kinase 5 (ALK5) - dependent manner (prevented by 10 μM SB431542). Furin inhibition prevented hypoxia-induced EC migration and blocked TGFβ-induced potentiation suggesting existence of a feedback loop. TGFβ and Furin were also critical for hypoxia-induced BBB dysfunction. TGFβ treatment aggravated hypoxia-induced BBB permeability but ALK5 or Furin blockade reversed injury-induced permeability changes. Thus during insult Furin compromises endothelial integrity by mediating the effects of TGFβ. Targeting the Furin or ALK5 pathway may offer novel therapeutic strategies for improving BBB stability and CNS function during disease.

Cytokine Responses in Severe Traumatic Brain Injury: Where There Is Smoke, Is There Fire?

This scoping review will discuss the basic functions and prognostic significance of the commonly researched cytokines implicated in severe traumatic brain injury (sTBI), including tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, tissue inhibitor of matrix metalloproteinases-1 (TIMP-1), transforming growth factor-β (TGF-β), substance P, and soluble CD40 ligand (sCD40L). A scoping review was undertaken with an electronic search for articles from the Ovid MEDLINE, PUBMED and EMBASE databases from 1995 to 2017. Inclusion criteria were original research articles, and reviews including both animal models and human clinical studies of acute (< 3 months) sTBI. Selected articles included both isolated sTBI and sTBI with systemic injury. After applying the inclusion criteria and removing duplicates, 141 full-text articles, 126 original research articles and 15 review articles, were evaluated in compiling this review paper. A single reviewer, CC, completed the review in two phases. During the first phase, titles and abstracts of selected articles were reviewed for inclusion. A second evaluation was then conducted on the full text of all selected articles to ensure relevancy. From our current understanding of the literature, it is unlikely a single biomarker will be sufficient in accurately prognosticating patients with sTBI. Intuitively, a more severe injury will demonstrate higher levels of inflammatory cytokines which may correlate as a marker of severe injury. This does not mean, necessarily, these cytokines have a direct and causal role in the poor outcome of the patient. Further research is required to better delineate the complex systemic inflammatory and CNS interactions that occur during sTBI before they can be applied as a reliable prognostic tool.

Cerebral ischemia/repefusion injury: From bench space to bedside

While stroke research represents the primary interface between circulation and brain research, the hemostasis system also carries a pivotal role in the mechanism of vascular brain injury. The complex interrelated events triggered by the energy crisis have a specific spatial and temporal pattern arching from the initial damage to the final events of brain repair. The complexity of the pathophysiology make it difficult to model this disease, therefore it is challenging to find appropriate therapeutic targets. The ever-persistent antagonism between the positive results of drug candidates in the experimental stroke models and the failures of the clinical trials prompts changes in the research strategy, especially in the field of potential neuroprotective therapies. System biology approach could initiate new directions in the future for both preclinical and clinical research. Incentive methods aimed at anti-apoptosis mechanisms and the augmentation of post-ischemic brain repair could benefit the facts, that these processes can be targeted much longer following the cell-necrosis in the hyper-acute phase. Sequential monitoring of candidate genes and proteins responsible for stroke progression and post-stroke repair seems to be useful both in therapeutic target-identification, and in clinical testing. Understanding the mechanism behind the effect of selegiline and other drugs capable of activating the anti-apoptotic gene expression could help to find new approaches to enhance the regenerative potential in the remodeling of neuronal and microvascular networks.

Targeting the neurovascular unit in brain trauma

Although the neurovascular unit was originally developed as a conceptual framework for stroke, it is now recognized that these cell-cell interactions play critical roles in many other CNS disorders as well. In brain trauma, perturbations within the neurovascular unit may be especially important. Changes in neurovascular coupling may disrupt blood flow and metabolic regulation. Disruption of transmitter release-reuptake kinetics in neurons and astrocytes may augment excitotoxicity. Alterations in gliovascular signaling may underlie blood-brain barrier disruptions and traumatic edema. Perturbations in cell-cell signaling between all neuronal, glial, and vascular compartments may increase susceptibility to cell death. Finally, repairing the brain after trauma requires the integrated restoration of all neural, glial, and vascular connectivity for effective functional recovery. Just as in stroke, saving neurons alone may also be insufficient for treating brain trauma. In this minireview, we attempt to briefly highlight some of these pathways to underscore the importance of rescuing the entire neurovascular unit in brain trauma.

Structural brain abnormalities in patients with inflammatory illness acquired following exposure to water-damaged buildings: a volumetric MRI study using NeuroQuant®

Executive cognitive and neurologic abnormalities are commonly seen in patients with a chronic inflammatory response syndrome (CIRS) acquired following exposure to the interior environment of water-damaged buildings (WDB), but a clear delineation of the physiologic or structural basis for these abnormalities has not been defined. Symptoms of affected patients routinely include headache, difficulty with recent memory, concentration, word finding, numbness, tingling, metallic taste and vertigo. Additionally, persistent proteomic abnormalities in inflammatory parameters that can alter permeability of the blood-brain barrier, such as C4a, TGFB1, MMP9 and VEGF, are notably present in cases of CIRS-WDB compared to controls, suggesting a consequent inflammatory injury to the central nervous system. Findings of gliotic areas in MRI scans in over 45% of CIRS-WDB cases compared to 5% of controls, as well as elevated lactate and depressed ratios of glutamate to glutamine, are regularly seen in MR spectroscopy of cases. This study used the volumetric software program NeuroQuant® (NQ) to determine specific brain structure volumes in consecutive patients (N=17) seen in a medical clinic specializing in inflammatory illness. Each of these patients presented for evaluation of an illness thought to be associated with exposure to WDB, and received an MRI that was evaluated by NQ. When compared to those of a medical control group (N=18), statistically significant differences in brain structure proportions were seen for patients in both hemispheres of two of the eleven brain regions analyzed; atrophy of the caudate nucleus and enlargement of the pallidum. In addition, the left amygdala and right forebrain were also enlarged. These volumetric abnormalities, in conjunction with concurrent abnormalities in inflammatory markers, suggest a model for structural brain injury in "mold illness" based on increased permeability of the blood-brain barrier due to chronic, systemic inflammation.

Effects of acupuncture at GV20 and ST36 on the expression of matrix metalloproteinase 2, aquaporin 4, and aquaporin 9 in rats subjected to cerebral ischemia/reperfusion injury

Background/Purpose

Ischemic stroke is characterized by high morbidity and mortality worldwide. Matrix metalloproteinase 2 (MMP2), aquaporin (AQP) 4, and AQP9 are linked to permeabilization of the blood-brain barrier (BBB) in cerebral ischemia/reperfusion injury (CIRI). BBB disruption, tissue inflammation, and MMP/AQP upregulation jointly provoke brain edema/swelling after CIRI, while acupuncture and electroacupuncture can alleviate CIRI symptoms. This study evaluated the hypothesis that acupuncture and electroacupuncture can similarly exert neuroprotective actions in a rat model of middle cerebral artery occlusion (MCAO) by modulating MMP2/AQP4/APQ9 expression and inflammatory cell infiltration.

Methods

Eighty 8-week-old Sprague-Dawley rats were randomly divided into sham group S, MCAO model group M, acupuncture group A, electroacupuncture group EA, and edaravone group ED. The MCAO model was established by placement of a suture to block the middle carotid artery, and reperfusion was triggered by suture removal in all groups except group S. Acupuncture and electroacupuncture were administered at acupoints GV20 (governing vessel-20) and ST36 (stomach-36). Rats in groups A, EA, and ED received acupuncture, electroacupuncture, or edaravone, respectively, immediately after MCAO. Neurological function (assessed using the Modified Neurological Severity Score), infarct volume, MMP2/AQP4/AQP9 mRNA and protein expression, and inflammatory cell infiltration were all evaluated at 24 h post-reperfusion.

Results

Acupuncture and electroacupuncture significantly decreased infarct size and improved neurological function. Furthermore, target mRNA and protein levels and inflammatory cell infiltration were significantly reduced in groups A, EA, and ED vs. group M. However, MMP2/AQP levels and inflammatory cell infiltration were generally higher in groups A and EA than in group ED except MMP2 mRNA levels.

Conclusions

Acupuncture and electroacupuncture at GV20 and ST36 both exercised neuroprotective actions in a rat model of MCAO, with no clear differences between groups A and EA. Therefore, acupuncture and electroacupuncture might find utility as adjunctive and complementary treatments to supplement conventional therapy for ischemic stroke.

Immunological demyelination triggers macrophage/microglial cells activation without inducing astrogliosis

The glial scar formed by reactive astrocytes and axon growth inhibitors associated with myelin play important roles in the failure of axonal regeneration following central nervous system (CNS) injury. Our laboratory has previously demonstrated that immunological demyelination of the CNS facilitates regeneration of severed axons following spinal cord injury. In the present study, we evaluate whether immunological demyelination is accompanied with astrogliosis. We compared the astrogliosis and macrophage/microglial cell responses 7 days after either immunological demyelination or a stab injury to the dorsal funiculus. Both lesions induced a strong activated macrophage/microglial cells response which was significantly higher within regions of immunological demyelination. However, immunological demyelination regions were not accompanied by astrogliosis compared to stab injury that induced astrogliosis which extended several millimeters above and below the lesions, evidenced by astroglial hypertrophy, formation of a glial scar, and upregulation of intermediate filaments glial fibrillary acidic protein (GFAP). Moreover, a stab or a hemisection lesion directly within immunological demyelination regions did not induced astrogliosis within the immunological demyelination region. These results suggest that immunological demyelination creates a unique environment in which astrocytes do not form a glial scar and provides a unique model to understand the putative interaction between astrocytes and activated macrophage/microglial cells.

Astrocytes specifically remove surface-adsorbed fibrinogen and locally express chondroitin sulfate proteoglycans

Surface-adsorbed fibrinogen (FBG) was recognized by adhering astrocytes, and was removed from the substrates in vitro by a two-phase removal process. The cells removed adsorbed FBG from binary proteins' surface patterns (FBG+laminin, or FBG+albumin) while leaving the other protein behind. Astrocytes preferentially expressed chondroitin sulfate proteoglycan (CSPG) at the loci of fibrinogen stimuli; however, no differences in overall CSPG production as a function of FBG surface coverage were identified. Removal of FBG by astrocytes was also found to be independent of transforming growth factor type β (TGF-β) receptor based signaling as cells maintained CSPG production in the presence of TGF-β receptor kinase inhibitor, SB 431542. The inhibitor decreased CSPG expression, but did not abolish it entirely. Because blood contact and subsequent FBG adsorption are unavoidable in neural implantations, the results indicate that implant-adsorbed FBG may contribute to reactive astrogliosis around the implant as astrocytes specifically recognize adsorbed FBG.

TGF-β superfamily gene expression and induction of the Runx1 transcription factor in adult neurogenic regions after brain injury

Traumatic brain injury (TBI) increases neurogenesis in the forebrain subventricular zone (SVZ) and the hippocampal dentate gyrus (DG). Transforming growth factor-β (TGF-β) superfamily cytokines are important regulators of adult neurogenesis, but their involvement in the regulation of this process after brain injury is unclear. We subjected adult mice to controlled cortical impact (CCI) injury, and isolated RNA from the SVZ and DG at different post-injury time points. qPCR array analysis showed that cortical injury caused significant alterations in the mRNA expression of components and targets of the TGF-β, BMP, and activin signaling pathways in the SVZ and DG after injury, suggesting that these pathways could regulate post-injury neurogenesis. In both neurogenic regions, the injury also induced expression of Runt-related transcription factor-1 (Runx1), which can interact with intracellular TGF-β Smad signaling pathways. CCI injury strongly induced Runx1 expression in activated and proliferating microglial cells throughout the neurogenic regions. Runx1 protein was also expressed in a subset of Nestin- and GFAP-expressing putative neural stem or progenitor cells in the DG and SVZ after injury. In the DG only, these Runx1+ progenitors proliferated. Our data suggest potential roles for Runx1 in the processes of microglial cell activation and proliferation and in neural stem cell proliferation after TBI.

Neurotrophic molecules in the treatment of neurodegenerative disease with focus on the retina: status and perspectives

Neurotrophic factors are operationally defined as molecules that promote the survival and differentiation of neurons. Chemically, they belong to divergent classes of molecules but most of the classic neurotrophic factors are proteins. Together with stem cells, viral vectors and genetically engineered cells, they constitute important tools in neuroprotective and regenerative neurobiology. Protein neurotrophic molecules signal through receptors located on the cell membrane. Their downstream signaling exploits pathways that are often common to chemically different factors and frequently target a relatively restricted set of transcription factors, RNA interference and diverse molecular machinery involved in the life vs. death decisions of neurons. Application of neurotrophic factors with the aim of curing or, at least, improving the outcome of neurodegenerative diseases requires (1) profound knowledge of the complex molecular pathology of the disease, (2) the development of animal models as closely as possible resembling the human disease, (3) the identification of target cells to be addressed, (4) intense efforts in chemical engineering to ensure the stability of molecules or to design carriers and small analogs with the ability to cross the blood-brain barrier and (5) scrutinity with regard to possible side effects. Last, but not least, engineering efforts to optimize administration, e.g., by designing the right canulae and infusion devices, are important for the successful translation of preclinical advances into clinical benefit. This article presents selected examples of neurotrophic factors that are currently being tested in animal models or developed for transfer to the clinic, with a major focus on factors with the potential of becoming applicable in various forms of retinal degeneration.

Isolation and culture of mouse cortical astrocytes

Astrocytes are an abundant cell type in the mammalian brain, yet much remains to be learned about their molecular and functional characteristics. In vitro astrocyte cell culture systems can be used to study the biological functions of these glial cells in detail. This video protocol shows how to obtain pure astrocytes by isolation and culture of mixed cortical cells of mouse pups. The method is based on the absence of viable neurons and the separation of astrocytes, oligodendrocytes and microglia, the three main glial cell populations of the central nervous system, in culture. Representative images during the first days of culture demonstrate the presence of a mixed cell population and indicate the timepoint, when astrocytes become confluent and should be separated from microglia and oligodendrocytes. Moreover, we demonstrate purity and astrocytic morphology of cultured astrocytes using immunocytochemical stainings for well established and newly described astrocyte markers. This culture system can be easily used to obtain pure mouse astrocytes and astrocyte-conditioned medium for studying various aspects of astrocyte biology.