Traumatic injury elicits JNK-mediated human astrocyte retraction in vitro

Study of BBB Dysregulation in Neuropathogenicity Using Integrative Human Model of Blood-Brain Barrier

The blood-brain barrier (BBB) is a cellular and physical barrier with a crucial role in homeostasis of the brain extracellular environment. It controls the imports of nutrients to the brain and exports toxins and pathogens. Dysregulation of the blood-brain barrier increases permeability and contributes to pathologies, including Alzheimer's disease, epilepsy, and ischemia. It remains unclear how a dysregulated BBB contributes to these different syndromes. Initial studies on the role of the BBB in neurological disorders and also techniques to permit the entry of therapeutic molecules were made in animals. This review examines progress in the use of human models of the BBB, more relevant to human neurological disorders. In recent years, the functionality and complexity of in vitro BBB models have increased. Initial efforts consisted of static transwell cultures of brain endothelial cells. Human cell models based on microfluidics or organoids derived from human-derived induced pluripotent stem cells have become more realistic and perform better. We consider the architecture of different model generations as well as the cell types used in their fabrication. Finally, we discuss optimal models to study neurodegenerative diseases, brain glioma, epilepsies, transmigration of peripheral immune cells, and brain entry of neurotrophic viruses and metastatic cancer cells.

In Vitro Models of Traumatic Brain Injury: A Systematic Review

Traumatic brain injury (TBI) is a major public health challenge that is also the third leading cause of death worldwide. It is also the leading cause of long-term disability in children and young adults worldwide. Despite a large body of research using predominantly in vivo and in vitro rodent models of brain injury, there is no medication that can reduce brain damage or promote brain repair mainly due to our lack of understanding in the mechanisms and pathophysiology of the TBI. The aim of this review is to examine in vitro TBI studies conducted from 2008-2018 to better understand the TBI in vitro model available in the literature. Specifically, our focus was to perform a detailed analysis of the in vitro experimental protocols used and their subsequent biological findings. Our review showed that the uniaxial stretch is the most frequently used way of load application, accounting for more than two-thirds of the studies reviewed. The rate and magnitude of the loading were varied significantly from study to study but can generally be categorized into mild, moderate, and severe injuries. The in vitro studies reviewed here examined key processes in TBI pathophysiology such as membrane disruptions leading to ionic dysregulation, inflammation, and the subsequent damages to the microtubules and axons, as well as cell death. Overall, the studies examined in this review contributed to the betterment of our understanding of TBI as a disease process. Yet, our review also revealed the areas where more work needs to be done such as: 1) diversification of load application methods that will include complex loading that mimics in vivo head impacts; 2) more widespread use of human brain cells, especially patient-matched human cells in the experimental set-up; and 3) need for building a more high-throughput system to be able to discover effective therapeutic targets for TBI.

Pathophysiological Significance of WDR62 and JNK Signaling in Human Diseases

The c-Jun N-terminal kinase (JNK) is highly evolutionarily conserved and plays important roles in a broad range of physiological and pathological processes. The WD40-repeat protein 62 (WDR62) is a scaffold protein that recruits different components of the JNK signaling pathway to regulate several human diseases including neurological disorders, infertility, and tumorigenesis. Recent studies revealed that WDR62 regulates the process of neural stem cell mitosis and germ cell meiosis through JNK signaling. In this review we summarize the roles of WDR62 and JNK signaling in neuronal and non-neuronal contexts and discuss how JNK-dependent signaling regulates both processes. WDR62 is involved in various human disorders via JNK signaling regulation, and may represent a promising therapeutic strategy for the treatment of related diseases.

Assessment of the Effects of Stretch-Injury on Primary Rat Microglia

Mechanical stretch-injury is a prominent force involved in the etiology of traumatic brain injury (TBI). It is known to directly cause damage and dysfunction in neurons, astrocytes, and endothelial cells. However, the deleterious effects of stretch-injury on microglia, the brain's primary immunocompetent cell, are currently unknown. The Cell Injury Controller II (CICII), a validated cellular neurotrauma model, was used to induce a mechanical stretch-injury in primary rat microglia. Statistical analysis utilized Student's t test and one- and two-way ANOVAs with Tukey's and Sidak's multiple comparisons, respectively. Cells exposed to stretch-injury showed no signs of membrane permeability, necrosis, or apoptosis, as measured by media-derived lactate dehydrogenase (LDH) and cleaved-caspase 3 immunocytochemistry, respectively. Interestingly, injured cells displayed a functional deficit in nitric oxide production (NO), identified by media assay and immunocytochemistry, at 6, 12, 18, and 48 h post-injury. Furthermore, gene expression analysis revealed the expression of inflammatory cytokines IL-6 and IL-10, and enzyme arginase-1 was significantly downregulated at 12 h post-injury. Time course evaluation of migration, using a cell exclusion zone assay, showed stretch-injured cells display decreased migration into the exclusion zone at 48- and 72-h post-stretch. Lastly, coinciding with the functional immune deficits was a significant change in morphology, with process length decreasing and cell diameter increasing following an injury at 12 h. Taken together, the data demonstrate that stretch-injury produces significant alterations in microglial function, which may have a marked impact on their response to injury or their interaction with other cells.

JNK signaling as a target for anticancer therapy

The JNKs are members of mitogen-activated protein kinases (MAPK) which regulate many physiological processes including inflammatory responses, macrophages, cell proliferation, differentiation, survival, and death. It is increasingly clear that the continuous activation of JNKs has a role in cancer development and progression. Therefore, JNKs represent attractive oncogenic targets for cancer therapy using small molecule kinase inhibitors. Studies showed that the two major JNK proteins JNK1 and JNK2 have opposite functions in different types of cancers, which need more specification in the design of JNK inhibitors. Some of ATP- competitive and ATP non-competitive inhibitors have been developed and widely used in vitro, but this type of inhibitors lack selectivity and inhibits phosphorylation of all JNK substrates and may lead to cellular toxicity. In this review, we summarized and discussed the strategies of JNK binding inhibitors and the role of JNK signaling in the pathogenesis of different solid and hematological malignancies.

An Investigation of Dynamic Cerebral Autoregulation in Adolescent Concussion

PURPOSE

Although cerebrovascular impairments are believed to contribute to concussion symptoms, little information exists regarding brain vasomotor control in adolescent concussion, particularly autoregulatory control that forms a fundamental response mechanism during changes in blood pressure. This research tested the hypothesis that adolescent concussion is marked by impaired dynamic cerebral autoregulation.

METHODS

Nineteen concussed adolescents (15 ± 2 yr, 13 females) and 18 healthy controls (15 ± 2 yr, 9 females) completed two sit-to-stand trials. Brachial artery blood pressure and cerebral blood flow velocity in the right middle cerebral artery were measured continuously. Dynamic rate of regulation was calculated as the rate of change in cerebrovascular resistance relative to the change in arterial blood pressure. The concussed adolescents were followed through their rehabilitation for up to 12 wk.

RESULTS

At the first visit, the concussed adolescents demonstrated reduced rate of regulation compared with the healthy controls (0.12 ± 0.04 vs 0.19 ± 0.06 s, P ≤ 0.001). At the concussed adolescents final visit, after symptom resolution, the rate of regulation improved to levels that were not different from the healthy controls (n = 9; 0.15 ± 0.08 vs 0.19 ± 0.06 s, P= 0.06). Two distinct groups were observed at the final visit with some individuals experiencing recovery of dynamic cerebral autoregulation and others showing no marked change from the initial visit.

CONCLUSION

Adolescents demonstrate an impairment in dynamic cerebral autoregulation after concussion that improves along with clinical symptoms in some individuals and remains impaired in others despite symptom resolution.

Synergistic Inhibition of ERK1/2 and JNK, Not p38, Phosphorylation Ameliorates Neuronal Damages After Traumatic Brain Injury

Mitogen-activated protein (MAP) kinases are serine/threonine protein kinases that play a critical role in signal transduction and are activated by phosphorylation in response to a variety of pathophysiology stimuli. While MAP kinase signaling has a significant role in the pathophysiology of several neurodegenerative diseases, the precise function of activation of MAP kinase in traumatic brain injury (TBI) is unknown. Therefore, it is important to study the role of MAP kinase signaling in TBI-associated neurological ailments. In this study, using an in vitro stretch injury model in rat embryo neuronal cultures and the in vivo fluid percussion injury (FPI) model in rats, we explored the role of MAP kinase signaling in the mechanisms of cell death in TBI. Our study demonstrated that the stretch injury in vitro and FPI in vivo upregulated the phosphorylation of MAP kinase proteins ERK1/2 and JNK, but not p38. Using ERK1/2 inhibitor U0126, JNK inhibitor SP600125, and p38 inhibitor SB203580, we validated the role of MAP kinase proteins in the activation of NF-kB and caspase-3. By immunofluorescence and western blotting, further, we demonstrated the role of ERK1/2 and JNK phosphorylation in neurodegeneration by analyzing cell death proteins annexin V and Poly-ADP-Ribose-Polymerase p85. Interestingly, combined use of ERK1/2 and JNK inhibitors further attenuated the cell death in stretch-injured neurons. In conclusion, this study could establish the significance of MAP kinase signaling in the pathophysiology of TBI and may have significant implications for developing therapeutic strategies using ERK1/2 and JNK inhibitors for TBI-associated neurological complications.

Elevated Leukocyte Azurophilic Enzymes in Human Diabetic Ketoacidosis Plasma Degrade Cerebrovascular Endothelial Junctional Proteins

OBJECTIVE

Diabetic ketoacidosis in children is associated with vasogenic cerebral edema, possibly due to the release of destructive polymorphonuclear neutrophil azurophilic enzymes. Our objectives were to measure plasma azurophilic enzyme levels in children with diabetic ketoacidosis, to correlate plasma azurophilic enzyme levels with diabetic ketoacidosis severity, and to determine whether azurophilic enzymes disrupt the blood-brain barrier in vitro.

DESIGN

Prospective clinical and laboratory study.

SETTING

The Children's Hospital, London Health Sciences Centre.

SUBJECTS

Pediatric type 1 diabetes patients; acute diabetic ketoacidosis or age-/sex-matched insulin-controlled.

MEASUREMENTS AND MAIN RESULTS

Acute diabetic ketoacidosis in children was associated with elevated polymorphonuclear neutrophils. Plasma azurophilic enzymes were elevated in diabetic ketoacidosis patients, including human leukocyte elastase (p < 0.001), proteinase-3 (p < 0.01), and myeloperoxidase (p < 0.001). A leukocyte origin of human leukocyte elastase and proteinase-3 in diabetic ketoacidosis was confirmed with buffy coat quantitative real-time polymerase chain reaction (p < 0.01). Of the three azurophilic enzymes elevated, only proteinase-3 levels correlated with diabetic ketoacidosis severity (p = 0.002). Recombinant proteinase-3 applied to human brain microvascular endothelial cells degraded both the tight junction protein occludin (p < 0.05) and the adherens junction protein VE-cadherin (p < 0.05). Permeability of human brain microvascular endothelial cell monolayers was increased by recombinant proteinase-3 application (p = 0.010).

CONCLUSIONS

Our results indicate that diabetic ketoacidosis is associated with systemic polymorphonuclear neutrophil activation and degranulation. Of all the polymorphonuclear neutrophil azurophilic enzymes examined, only proteinase-3 correlated with diabetic ketoacidosis severity and potently degraded the blood-brain barrier in vitro. Proteinase-3 might mediate vasogenic edema during diabetic ketoacidosis, and selective proteinase-3 antagonists may offer future vascular- and neuroprotection.

New experimental models of the blood-brain barrier for CNS drug discovery

INTRODUCTION

The blood-brain barrier (BBB) is a dynamic biological interface which actively controls the passage of substances between the blood and the central nervous system (CNS). From a biological and functional standpoint, the BBB plays a crucial role in maintaining brain homeostasis inasmuch that deterioration of BBB functions are prodromal to many CNS disorders. Conversely, the BBB hinders the delivery of drugs targeting the brain to treat a variety of neurological diseases. Area covered: This article reviews recent technological improvements and innovation in the field of BBB modeling including static and dynamic cell-based platforms, microfluidic systems and the use of stem cells and 3D printing technologies. Additionally, the authors laid out a roadmap for the integration of microfluidics and stem cell biology as a holistic approach for the development of novel in vitro BBB platforms. Expert opinion: Development of effective CNS drugs has been hindered by the lack of reliable strategies to mimic the BBB and cerebrovascular impairments in vitro. Technological advancements in BBB modeling have fostered the development of highly integrative and quasi- physiological in vitro platforms to support the process of drug discovery. These advanced in vitro tools are likely to further current understanding of the cerebrovascular modulatory mechanisms.

Chronic traumatic encephalopathy: A paradigm in search of evidence?

Chronic traumatic encephalopathy (CTE) has been in the medical literature since the 1920s. It is characterized clinically by diverse neuropsychiatric symptoms, and pathologically by variable degrees of phosphorylated tau accumulation in the brain. The evolving paradigm for the pathogenesis of CTE suggests that concussion or subconcussion from athletic participation initiates a cascade of pathologic events, encompassing neuroinflammation and protein templating with trans-synaptic neurotoxicity. The end result is neurologic and neurobehavioral deterioration, often with self-harm. Although these concepts warrant further investigation, the available evidence permits no conclusions as regards the pathogenesis of the reported findings. Investigations into the role of premorbid or co-morbid neurodegenerative diseases has been limited to date, and in-depth genetic analyses have not been performed. The role of concussion or subconcussion if any, whether and how the condition progresses over time, the extent of phosphorylated tau in clinically normal athletes, the role of phosphorylated tau as a toxic species versus an inert disease response, and whether protein templating has any in vivo relevance remain to be elucidated.

The blood-brain barrier as a target in traumatic brain injury treatment

Traumatic brain injury (TBI) is one of the most frequent causes of death in the young population. Several clinical trials have unsuccessfully focused on direct neuroprotective therapies. Recently immunotherapeutic strategies shifted into focus of translational research in acute CNS diseases. Cross-talk between activated microglia and blood-brain barrier (BBB) could initiate opening of the BBB and subsequent recruitment of systemic immune cells and mediators into the brain. Stabilization of the BBB after TBI could be a promising strategy to limit neuronal inflammation, secondary brain damage and acute neurodegeneration. This review provides an overview on the pathophysiology of TBI and brain edema formation including definitions and classification of TBI, current clinical treatment strategies, as well as current understanding on the underlying cellular processes. A summary of in vivo and in vitro models to study different aspects of TBI is presented. Three mechanisms proposed for stabilization of the BBB, myosin light chain kinases, glucocorticoid receptors and peroxisome proliferator-activated receptors are reviewed for their influence on barrier-integrity and outcome after TBI. In conclusion, the BBB is recommended as a promising target for the treatment of traumatic brain injury, and it is suggested that a combination of BBB stabilization and neuroprotectants may improve therapeutic success.