Impaired expression of neuroprotective molecules in the HIF-1alpha pathway following traumatic brain injury in aged mice

Age dictates brain functional connectivity and axonal integrity following repetitive mild traumatic brain injuries in mice

Traumatic brain injuries (TBI) present a major public health challenge, demanding an in-depth understanding of age-specific symptoms and risk factors. Aging not only significantly influences brain function and plasticity but also elevates the risk of hospitalizations and death following TBIs. Repetitive mild TBIs (rmTBI) compound these issues, resulting in cumulative and long-term brain damage in the brain. In this study, we investigate the impact of age on brain network changes and white matter properties following rmTBI by employing a multi-modal approach that integrates resting-state functional magnetic resonance imaging (rsfMRI), graph theory analysis, diffusion tensor imaging (DTI), and neurite orientation dispersion and density imaging (NODDI). Our hypothesis is that the effects of rmTBI are worsened in aged animals, with this group showing more pronounced alterations in brain connectivity and white matter structure. Utilizing the closed-head impact model of engineered rotational acceleration (CHIMERA) model, we conducted rmTBIs or sham (control) procedures on young (2.5-3-months-old) and aged (22-months-old) male and female mice to model high-risk groups. Functional and structural imaging unveiled age-related reductions in communication efficiency between brain regions, while injuries induced opposhigh-risking effects on the small-world index across age groups, influencing network segregation. Functional connectivity analysis also identified alterations in 79 out of 148 brain regions by age, treatment (sham vs. rmTBI), or their interaction. Injuries exerted pronounced effects on sensory integration areas, including insular and motor cortices. Age-related disruptions in white matter integrity were observed, indicating alterations in various diffusion directions (mean diffusivity, radial diffusivity, axial diffusivity, and fractional anisotropy) and density neurite properties (dispersion index, intracellular and isotropic volume fraction). Neuroinflammation, assessed through Iba-1 and GFAP markers, correlated with higher dispersion in the optic tract, suggesting a neuroinflammatory response in injured aged animals compared to sham aged. These findings offer insight into the interplay between age, injuries, and brain connectivity, shedding light on the long-term consequences of rmTBI.

Age dictates brain functional connectivity and axonal integrity following repetitive mild traumatic brain injuries

Traumatic brain injuries (TBI) present a major public health challenge, demanding an in-depth understanding of age-specific signs and vulnerabilities. Aging not only significantly influences brain function and plasticity but also elevates the risk of hospitalizations and death following repetitive mild traumatic brain injuries (rmTBIs). In this study, we investigate the impact of age on brain network changes and white matter properties following rmTBI employing a multi-modal approach that integrates resting-state functional magnetic resonance imaging (rsfMRI), graph theory analysis, diffusion tensor imaging (DTI), and Neurite Orientation Dispersion and Density Imaging (NODDI). Utilizing the CHIMERA model, we conducted rmTBIs or sham (control) procedures on young (2.5-3 months old) and aged (22-month-old) male and female mice to model high risk groups. Functional and structural imaging unveiled age-related reductions in communication efficiency between brain regions, while injuries induced opposing effects on the small-world index across age groups, influencing network segregation. Functional connectivity analysis also identified alterations in 79 out of 148 brain regions by age, treatment (sham vs. rmTBI), or their interaction. Injuries exerted pronounced effects on sensory integration areas, including insular and motor cortices. Age-related disruptions in white matter integrity were observed, indicating alterations in various diffusion directions (mean, radial, axial diffusivity, fractional anisotropy) and density neurite properties (dispersion index, intracellular and isotropic volume fraction). Inflammation, assessed through Iba-1 and GFAP markers, correlated with higher dispersion in the optic tract, suggesting a neuroinflammatory response in aged animals. These findings provide a comprehensive understanding of the intricate interplay between age, injuries, and brain connectivity, shedding light on the long-term consequences of rmTBIs.

Role of hypoxia-inducible factor in postoperative delirium of aged patients: A review

Postoperative delirium is common, especially in older patients. Delirium is associated with prolonged hospitalization, an increased risk of postoperative complications, and significant mortality. The mechanism of postoperative delirium is not yet clear. Cerebral desaturation occurred during the maintenance period of general anesthesia and was one of the independent risk factors for postoperative delirium, especially in the elderly. Hypoxia stimulates the expression of hypoxia-inducible factor-1 (HIF-1), which controls the hypoxic response. HIF-1 may have a protective role in regulating neuron apoptosis in neonatal hypoxia-ischemia brain damage and may promote the repair and rebuilding process in the brain that was damaged by hypoxia and ischemia. HIF-1 has a neuroprotective effect during cerebral hypoxia and controls the hypoxic response by regulating multiple pathways, such as glucose metabolism, angiogenesis, erythropoiesis, and cell survival. On the other hand, anesthetics have been reported to inhibit HIF activity in older patients. So, we speculate that HIF plays an important role in the pathophysiology of postoperative delirium in the elderly. The activity of HIF is reduced by anesthetics, leading to the inhibition of brain protection in a hypoxic state. This review summarizes the possible mechanism of HIF participating in postoperative delirium in elderly patients and provides ideas for finding targets to prevent or treat postoperative delirium in elderly patients.

c-Jun N-terminal kinase signaling in cellular senescence

Cellular senescence leads to decreased tissue regeneration and inflammation and is associated with diabetes, neurodegenerative diseases, and tumorigenesis. However, the mechanisms of cellular senescence are not fully understood. Emerging evidence has indicated that c-Jun N-terminal kinase (JNK) signaling is involved in the regulation of cellular senescence. JNK can downregulate hypoxia inducible factor-1α to accelerate hypoxia-induced neuronal cell senescence. The activation of JNK inhibits mTOR activity and triggers autophagy, which promotes cellular senescence. JNK can upregulate the expression of p53 and Bcl-2 and accelerates cancer cell senescence; however, this signaling also mediates the expression of amphiregulin and PD-LI to achieve cancer cell immune evasion and prevents their senescence. The activation of JNK further triggers forkhead box O expression and its target gene Jafrac1 to extend the lifespan of Drosophila. JNK can also upregulate the expression of DNA repair protein poly ADP-ribose polymerase 1 and heat shock protein to delay cellular senescence. This review discusses recent advances in understanding the function of JNK signaling in cellular senescence and includes a comprehensive analysis of the molecular mechanisms underlying JNK-mediated senescence evasion and oncogene-induced cellular senescence. We also summarize the research progress in anti-aging agents that target JNK signaling. This study will contribute to a better understanding of the molecular targets of cellular senescence and provides insights into anti-aging, which may be used to develop drugs for the treatment of aging-related diseases.

HIF-1α participates in secondary brain injury through regulating neuroinflammation

A deeper understanding of the underlying biological mechanisms of secondary brain injury induced by traumatic brain injury (TBI) will greatly advance the development of effective treatments for patients with TBI. Hypoxia-inducible factor-1 alpha (HIF-1α) is a central regulator of cellular response to hypoxia. In addition, growing evidence shows that HIF-1α plays the important role in TBI-induced changes in biological processes; however, detailed functional mechanisms are not completely known. The aim of the present work was to further explore HIF-1α-mediated events after TBI. To this end, next-generation sequencing, coupled with cellular and molecular analysis, was adopted to interrogate vulnerable events in a rat controlled cortical impact model of TBI. The results demonstrated that TBI induced accumulation of HIF-1α at the peri-injury site at 24 h post-injury, which was associated with neuronal loss. Moreover, gene set enrichment analysis unveiled that neuroinflammation, especially an innate inflammatory response, was significantly evoked by TBI, which could be attenuated by the inhibition of HIF-1α. Furthermore, the inhibition of HIF-1α could mitigate the activation of microglia and astrocytes. Taken together, all these data implied that HIF-1α might contribute to secondary brain injury through regulating neuroinflammation.

The role of SUMOylation in the neurovascular dysfunction after acquired brain injury

Acquired brain injury (ABI) is the most common disease of the nervous system, involving complex pathological processes, which often leads to a series of nervous system disorders. The structural destruction and dysfunction of the Neurovascular Unit (NVU) are prominent features of ABI. Therefore, understanding the molecular mechanism underlying NVU destruction and its reconstruction is the key to the treatment of ABI. SUMOylation is a protein post-translational modification (PTM), which can degrade and stabilize the substrate dynamically, thus playing an important role in regulating protein expression and biological signal transduction. Understanding the regulatory mechanism of SUMOylation can clarify the molecular mechanism of the occurrence and development of neurovascular dysfunction after ABI and is expected to provide a theoretical basis for the development of potential treatment strategies. This article reviews the role of SUMOylation in vascular events related to ABI, including NVU dysfunction and vascular remodeling, and puts forward therapeutic prospects.

Vitamin D Deficiency and Prognosis after Traumatic Brain Injury with Intracranial Injury: A Multi-Center Observational Study

Vitamin D may be important for neuroprotection after traumatic brain injury (TBI) by modifying the inflammatory response. The objective of this study was to evaluate the association between vitamin D deficiency and functional and survival outcomes in patients with TBI and intracranial injury. This study was a prospective multi-center cohort study conducted on adult TBI patients, with intracranial hemorrhage or diffuse axonal injury confirmed by radiological examination, admitted to five participating emergency departments (EDs) from December 2018 to June 2020. The study outcomes were good functional recovery at hospital discharge and survival at 6-months after injury. The primary exposure was serum vitamin D deficiency (0-10 ng/mL). Multi-level logistic regression analysis was performed to estimate the association between vitamin D deficiency and the study outcomes. Among 606 patients, 101 (16.7%) patients had vitamin D deficiency at the time of ED arrival. Good functional recovery was observed in 65.2% (395/606) of total population, and this proportion was significantly lower in the vitamin D deficiency group than the non-deficiency group (56.4 vs. 66.9%, p = 0.04, adjusted odds ratio (OR; 95% confidence interval [CI]): 0.56 (0.36-0.88)). Overall survival rate at 6 months after injury was 79.5% (434/546), and patients with vitamin D deficiency had significantly lower likelihood of survival at 6 months than patients without deficiency [75.0 vs. 80.3%, adjusted OR (95% CI): 0.59 (0.39-0.89)]. Vitamin D deficiency is associated with poor functional outcomes at hospital discharge and mortality at 6-months after injury in TBI patients with intracranial hemorrhage or diffuse axonal injury.

Aged Mouse Hippocampus Exhibits Signs of Chronic Hypoxia and an Impaired HIF-Controlled Response to Acute Hypoxic Exposures

Altered hypoxia-inducible factor-alpha (HIF-α) activity may have significant consequences in the hippocampus, which mediates declarative memory, has limited vascularization, and is vulnerable to hypoxic insults. Previous studies have reported that neurovascular coupling is reduced in aged brains and that diseases which cause hypoxia increase with age, which may render the hippocampus susceptible to acute hypoxia. Most studies have investigated the actions of HIF-α in aging cortical structures, but few have focused on the role of HIF-α within aged hippocampus. This study tests the hypothesis that aging is associated with impaired hippocampal HIF-α activity. Dorsal hippocampal sections from mice aged 3, 9, 18, and 24 months were probed for the presence of HIF-α isoforms or their associated gene products using immunohistochemistry and fluorescent in situ hybridization (fISH). A subset of each age was exposed to acute hypoxia (8% oxygen) for 3 h to investigate changes in the responsiveness of HIF-α to hypoxia. Basal mean intensity of fluorescently labeled HIF-1α protein increases with age in the hippocampus, whereas HIF-2α intensity only increases in the 24-month group. Acute hypoxic elevation of HIF-1α is lost with aging and is reversed in the 24-month group. fISH reveals that glycolytic genes induced by HIF-1α (lactose dehydrogenase-a, phosphoglycerate kinase 1, and pyruvate dehydrogenase kinase 1) are lower in aged hippocampus than in 3-month hippocampus, and mRNA for monocarboxylate transporter 1, a lactose transporter, increases. These results indicate that lactate, used in neurotransmission, may be limited in aged hippocampus, concurrent with impaired HIF-α response to hypoxic events. Therefore, impaired HIF-α may contribute to age-associated cognitive decline during hypoxic events.

Hypoxia Signaling in Parkinson's Disease: There Is Use in Asking "What HIF?"

Hypoxia is a condition characterized by insufficient tissue oxygenation, which results in impaired oxidative energy production. A reduction in cellular oxygen levels induces the stabilization of hypoxia inducible factor α (HIF-1α), master regulator of the molecular response to hypoxia, involved in maintaining cellular homeostasis and driving hypoxic adaptation through the control of gene expression. Due to its high energy requirement, the brain is particularly vulnerable to oxygen shortage. Thus, hypoxic injury can cause significant metabolic changes in neural cell populations, which are associated with neurodegeneration. Recent evidence suggests that regulating HIF-1α may ameliorate the cellular damage in neurodegenerative diseases. Indeed, the hypoxia/HIF-1α signaling pathway has been associated to several processes linked to Parkinson's disease (PD) including gene mutations, risk factors and molecular pathways such as mitochondrial dysfunction, oxidative stress and protein degradation impairment. This review will explore the impact of hypoxia and HIF-1α signaling on these specific molecular pathways that influence PD development and will evaluate different novel neuroprotective strategies involving HIF-1α stabilization.

Cerebral Hypoxia: Its Role in Age-Related Chronic and Acute Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) has been reported with widely varying frequency but appears to be strongly associated with aging. Outside of the surgical arena, chronic and acute cerebral hypoxia may exist as a result of respiratory, cardiovascular, or anemic conditions. Hypoxia has been extensively implicated in cognitive impairment. Furthermore, disease states associated with hypoxia both accompany and progress with aging. Perioperative cerebral hypoxia is likely underdiagnosed, and its contribution to POCD is underappreciated. Herein, we discuss the various disease processes and forms in which hypoxia may contribute to POCD. Furthermore, we outline hypoxia-related mechanisms, such as hypoxia-inducible factor activation, cerebral ischemia, cerebrovascular reserve, excitotoxicity, and neuroinflammation, which may contribute to cognitive impairment and how these mechanisms interact with aging. Finally, we discuss opportunities to prevent and manage POCD related to hypoxia.

M-CSF, IL-6, and TGF-β promote generation of a new subset of tissue repair macrophage for traumatic brain injury recovery

Traumatic brain injury (TBI) leads to high mortality rate. We aimed to identify the key cytokines favoring TBI repair and found that patients with TBI with a better outcome robustly increased concentrations of macrophage colony-stimulating factor, interleukin-6, and transforming growth factor-β (termed M6T) in cerebrospinal fluid or plasma. Using TBI mice, we identified that M2-like macrophage, microglia, and endothelial cell were major sources to produce M6T. Together with the in vivo tracking of mCherry+ macrophages in zebrafish models, we confirmed that M6T treatment accelerated blood-borne macrophage infiltration and polarization toward a subset of tissue repair macrophages that expressed similar genes as microglia for neuroprotection, angiogenesis and cell migration. M6T therapy in TBI mice and zebrafish improved neurological function while blocking M6T-exacerbated brain injury. Considering low concentrations of M6T in some patients with poor prognostic, M6T treatment might repair TBI via generating a previously unidentified subset of tissue repair macrophages.

The multiple organs insult and compensation mechanism in mice exposed to hypobaric hypoxia

This study was first and systematically conducted to evaluate the hypoxia response of the brain, heart, lung, liver, and kidney of mice exposed to an animal hypobaric chamber. First, we examined the pathological damage of the above tissues by Hematoxylin & eosin (H&E) staining. Secondly, biochemical assays were used to detect oxidative stress indicators such as superoxide dismutase (SOD), malondialdehyde (MDA), reduced glutathione (GSH), and oxidized glutathione (GSSG). Finally, the hypoxia compensation mechanism of tissues was evaluated by expression levels of hypoxia-inducible factor 1 alpha (HIF-1α), erythropoietin (EPO), and vascular endothelial growth factor (VEGF). During the experiment, the mice lost weight gradually on the first 3 days, and then, the weight loss tended to remain stable, and feed consumption showed the inverse trend. H&E staining results showed that there were sparse and atrophic neurons and dissolved chromatin in the hypoxia group. And hyperemia occurred in the myocardium, lung, liver, and kidney. Meanwhile, hypoxia stimulated the enlargement of myocardial space, the infiltration of inflammatory cells in lung tissue, the swelling of epithelial cells in hepatic lobules and renal tubules, and the separation of basal cells. Moreover, hypoxia markedly inhibited the activity of SOD and GSH and exacerbated the levels of MDA and GSSG in the serum and five organs. In addition, hypoxia induced the expression of HIF-1α, EPO, and VEGF in five organs. These results suggest hypoxia leads to oxidative damage and compensation mechanism of the brain, heart, lung, liver, and kidney in varying degrees of mice.

Designing neuroreparative strategies using aged regenerating animal models

In our ever-aging world population, the risk of age-related neuropathies has been increasing, representing both a social and economic burden to society. Since the ability to regenerate in the adult mammalian central nervous system is very limited, brain trauma and neurodegeneration are often permanent. As a consequence, novel scientific challenges have emerged and many research efforts currently focus on triggering repair in the damaged or diseased brain. Nevertheless, stimulating neuroregeneration remains ambitious. Even though important discoveries have been made over the past decades, they did not translate into a therapy yet. Actually, this is not surprising; while these disorders mainly manifest in aged individuals, most of the research is being performed in young animal models. Aging of neurons and their environment, however, greatly affects the central nervous system and its capacity to repair. This review provides a detailed overview of the impact of aging on central nervous system functioning and regeneration potential, both in non-regenerating and spontaneously regenerating animal models. Additionally, we highlight the need for aging animal models with regenerative capacities in the search for neuroreparative strategies.

Relationship between HIF-1α and apoptosis in rats with traumatic brain injury and the influence of traditional Chinese medicine Sanqi

Objective To explore the expression of HIF-1α, neuronal apoptosis and the influence of traditional Chinese medicine Sanqi on hematoma after brain injury in rats. Methods Ninety SD rats were divided into 3 groups randomly: blank control group, traumatic brain injury (TBI) group and Sanqi intervention group, and they were decapitated after brain injury at different time points: 6 h, 1 d, 2 d, 3 d, 5 d, 7 d. The model of cerebral hemorrhage was made by autologous non-coagulation in stereotactic locator, the expression of HIF-1α and TUNEL-positive cells (apoptotic cells) in the perihematomal area was detected by immunohistochemistry. Results In blank control group, a small amount of HIF-1α was expressed and apoptotic cells were observed. The expression of HIF-1α was up-regulated in the brain injury group from 6 h, and the apoptotic cells increased in abundance. The peak of HIF-1α was reached at 3 d, then decreased, and remained at the high level on the 7 d. Compared with blank control group, the TBI group was statistically significant (P < 0.05). The Chinese medicine Sanqi intervention group significantly up-regulated HIF-1α'expression and decreased neuronal apoptosis, which was statistically significant (P < 0.05). Conclusion HIF-1α's expression was up-regulated around the hematoma after brain injury, and the apoptosis of nerve cells was obviously increased. The traditional Chinese medicine Sanqi can significantly increase the expression of HIF-1α, reduce the apoptosis around the hematoma, and thus play a neuroprotective role.

Models of Traumatic Brain Injury in Aged Animals: A Clinical Perspective

Traumatic brain injury (TBI) is a major cause of morbidity and mortality in the United States, with advanced age being one of the major predictors of poor prognosis. To replicate the mechanisms and multifaceted complexities of human TBI and develop prospective therapeutic treatments, various TBI animal models have been developed. These models have been essential in furthering our understanding of the pathophysiology and biochemical effects on brain mechanisms following TBI. Despite these advances, translating preclinical results to clinical application, particularly in elderly individuals, continues to be challenging. This review aims to provide a clinical perspective, identifying relevant variables currently not replicated in TBI animal models, to potentially improve translation to clinical practice, especially as it applies to elderly populations. As background for this clinical perspective, we reviewed articles indexed on PubMed from 1970 to 2019 that used aged animal models for studying TBI. These studies examined end points relevant for clinical translation, such as neurocognitive effects, sensorimotor behavior, physiological mechanisms, and efficacy of neuroprotective therapies. However, compared with the higher incidence of TBI in older individuals, animal studies on the basic science of aging and TBI remain remarkably scarce. Moreover, a fundamental disconnect remains between experiments in animal models of TBI and successful translation of findings for treating the older TBI population. In this article, we aim to provide a clinical perspective on the unique attributes of TBI in older individuals and a critical appraisal of the research to date on TBI in aged animal models as well as recommendations for future studies.

Regulation of BACE1 expression after injury is linked to the p75 neurotrophin receptor

BACE1 is a transmembrane aspartic protease that cleaves various substrates and it is required for normal brain function. BACE1 expression is high during early development, but it is reduced in adulthood. Under conditions of stress and injury, BACE1 levels are increased; however, the underlying mechanisms that drive BACE1 elevation are not well understood. One mechanism associated with brain injury is the activation of injurious p75 neurotrophin receptor (p75), which can trigger pathological signals. Here we report that within 72 h after controlled cortical impact (CCI) or laser injury, BACE1 and p75 are increased and tightly co-expressed in cortical neurons of mouse brain. Additionally, BACE1 is not up-regulated in p75 null mice in response to focal cortical injury, while p75 over-expression results in BACE1 augmentation in HEK-293 and SY5Y cell lines. A luciferase assay conducted in SY5Y cell line revealed that BACE1 expression is regulated at the transcriptional level in response to p75 transfection. Interestingly, this effect does not appear to be dependent upon p75 ligands including mature and pro-neurotrophins. In addition, BACE1 activity on amyloid precursor protein (APP) is enhanced in SY5Y-APP cells transfected with a p75 construct. Lastly, we found that the activation of c-jun n-terminal kinase (JNK) by p75 contributes to BACE1 up-regulation. This study explores how two injury-induced molecules are intimately connected and suggests a potential link between p75 signaling and the expression of BACE1 after brain injury.

A Network Pharmacology Analysis to Explore the Effect of Astragali Radix-Radix Angelica Sinensis on Traumatic Brain Injury

Traumatic brain injury (TBI) is a critical public health and socioeconomic problem worldwide. The herb pair Astragali Radix (AR)-Radix Angelica Sinensis (RAS) is a common prescribed herbal formula or is added to other Chinese medicine prescriptions for traumatic brain injury (TBI) treatment. However, the underlying mechanisms are unclear. In this study, we aimed to explore the active ingredients and action targets of AR-RAS based on the combined methods of network pharmacology prediction and experimental verification. Furthermore, the corresponding potential mechanisms of “multicomponents, multitargets, and multipathways” were disclosed. Methods. A network pharmacology approach including ADME (absorption, distribution, metabolism, and excretion) filter analysis, target prediction, known therapeutic targets collection, Gene Ontology (GO), pathway enrichment analysis, and network construction was used in this study. Further verification experiments were performed to reveal the therapeutic effects of AR-RAS in a rat model of TBI. Results. The comprehensive systematic approach was to successfully identify 14 bioactive ingredients in AR-RAS, while 33 potential targets hit by these ingredients related to TBI. Based on GO annotation analysis, multiple biological processes were significantly regulated by AR-RAS. In addition, 89 novel signaling pathways (P<0.05) underlying the effects of AR-RAS for TBI treatment were identified by DAVID. The neurotrophin signaling pathway was suggested as the major related pathway targeted by AR-RAS to improve axonal growth. The animal experiment confirmed that AR-RAS significantly induced tissue recovery and improved neurological deficits on the 14th day (P<0.01). Treatment with AR-RAS markedly reduced the protein and mRNA expression level of NogoA in the hippocampus of TBI rats. Conclusion. Our work illuminates the “multicompounds, multitargets, and multipathways” curative action of AR-RAS in the treatment of TBI by network pharmacology. The animal experiment verifies the effects of AR-RAS on neurological function improvement and axonal outgrowth via downregulation of NogoA expression, providing a theoretical basis for further research on treatment of TBI.

Astrocyte HIF-2α supports learning in a passive avoidance paradigm under hypoxic stress

BACKGROUND

The brain is extensively vascularized, useŝ20% of the body's oxygen, and is highly sensitive to changes in oxygen. While synaptic plasticity and memory are impaired in healthy individuals by exposure to mild hypoxia, aged individuals appear to be even more sensitive. Aging is associated with progressive failure in pulmonary and cardiovascular systems, exposing the aged to both chronic and superimposed acute hypoxia. The HIF proteins, the "master regulators" of the cellular response to hypoxia, are robustly expressed in neurons and astrocytes. Astrocytes support neurons and synaptic plasticity via complex metabolic and trophic mechanisms. The activity of HIF proteins in the brain is diminished with aging, and the increased exposure to chronic and acute hypoxia with aging combined with diminished HIF activity may impair synaptic plasticity.

PURPOSE

Herein, we test the hypothesis that astrocyte HIF supports synaptic plasticity and learning upon hypoxia.

MATERIALS AND METHODS

An Astrocyte-specific HIF loss-of-function model was employed, where knock-out of HIF-1α or HIF-2α in GFAP expressing cells was accomplished by cre-mediated recombination. Animals were tested for behavioral (open field and rotarod), learning (passive avoidance paradigm), and electrophysiological (long term potentiation) responses to mild hypoxic challenge.

RESULTS

In an astrocyte-specific HIF loss-of-function model followed by mild hypoxia, we identified that the depletion of HIF-2α resulted in an impaired passive avoidance learning performance. This was accompanied by an attenuated response to induction in long-term potentiation (LTP), suggesting that the hippocampal circuitry was perturbed upon hypoxic exposure following HIF-2α loss in astrocytes, and not due to hippocampal cell death. We investigated HIF-regulated trophic and metabolic target genes and found that they were not regulated by HIF-2α, suggesting that these specific targets may not be involved in mediating the phenotypes observed.

CONCLUSION

Together, these results point to a role for HIF-2α in the astrocyte's regulatory role in synaptic plasticity and learning under hypoxia and suggest that even mild, acute hypoxic challenges can impair cognitive performance in the aged population who harbor impaired HIF function.

Response of the cerebral vasculature following traumatic brain injury

The critical role of the vasculature and its repair in neurological disease states is beginning to emerge particularly for stroke, dementia, epilepsy, Parkinson's disease, tumors and others. However, little attention has been focused on how the cerebral vasculature responds following traumatic brain injury (TBI). TBI often results in significant injury to the vasculature in the brain with subsequent cerebral hypoperfusion, ischemia, hypoxia, hemorrhage, blood-brain barrier disruption and edema. The sequalae that follow TBI result in neurological dysfunction across a host of physiological and psychological domains. Given the importance of restoring vascular function after injury, emerging research has focused on understanding the vascular response after TBI and the key cellular and molecular components of vascular repair. A more complete understanding of vascular repair mechanisms are needed and could lead to development of new vasculogenic therapies, not only for TBI but potentially vascular-related brain injuries. In this review, we delineate the vascular effects of TBI, its temporal response to injury and putative biomarkers for arterial and venous repair in TBI. We highlight several molecular pathways that may play a significant role in vascular repair after brain injury.

MicroRNAs as diagnostic markers and therapeutic targets for traumatic brain injury

Traumatic brain injury (TBI) is characterized by primary damage to the brain from the external mechanical force and by subsequent secondary injury due to various molecular and pathophysiological responses that eventually lead to neuronal cell death. Secondary brain injury events may occur minutes, hours, or even days after the trauma, and provide valuable therapeutic targets to prevent further neuronal degeneration. At the present time, there is no effective treatment for TBI due, in part, to the widespread impact of numerous complex secondary biochemical and pathophysiological events occurring at different time points following the initial injury. MicroRNAs control a range of physiological and pathological functions such as development, differentiation, apoptosis and metabolism, and may serve as potential targets for progress assessment and intervention against TBI to mitigate secondary damage to the brain. This has implications regarding improving the diagnostic accuracy of brain impairment and long-term outcomes as well as potential novel treatments. Recent human studies have identified specific microRNAs in serum/plasma (miR-425-p, -21, -93, -191 and -499) and cerebro-spinal fluid (CSF) (miR-328, -362-3p, -451, -486a) as possible indicators of the diagnosis, severity, and prognosis of TBI. Experimental animal studies have examined specific microRNAs as biomarkers and therapeutic targets for moderate and mild TBI (e.g., miR-21, miR-23b). MicroRNA profiling was altered by voluntary exercise. Differences in basal microRNA expression in the brain of adult and aged animals and alterations in response to TBI (e.g., miR-21) have also been reported. Further large-scale studies with TBI patients are needed to provide more information on the changes in microRNA profiles in different age groups (children, adults, and elderly).

Oxidative stress response and Nrf2 signaling in aging

Increasing oxidative stress, a major characteristic of aging, has been implicated in a variety of age-related pathologies. In aging, oxidant production from several sources is increased, whereas antioxidant enzymes, the primary lines of defense, are decreased. Repair systems, including the proteasomal degradation of damaged proteins, also decline. Importantly, the adaptive response to oxidative stress declines with aging. Nrf2/EpRE signaling regulates the basal and inducible expression of many antioxidant enzymes and the proteasome. Nrf2/EpRE activity is regulated at several levels, including transcription, posttranslation, and interactions with other proteins. This review summarizes current studies on age-related impairment of Nrf2/EpRE function and discusses the changes in Nrf2 regulatory mechanisms with aging.

Modeling Chronic Traumatic Encephalopathy: The Way Forward for Future Discovery

Despite the extensive media coverage associated with the diagnosis of chronic traumatic encephalopathy (CTE), our fundamental understanding of the disease pathophysiology remains in its infancy. Only recently have scientific laboratories and personnel begun to explore CTE pathophysiology through the use of preclinical models of neurotrauma. Some studies have shown the ability to recapitulate some aspects of CTE in rodent models, through the use of various neuropathological, biochemical, and/or behavioral assays. Many questions related to CTE development, however, remain unanswered. These include the role of impact severity, the time interval between impacts, the age at which impacts occur, and the total number of impacts sustained. Other important variables such as the location of impacts, character of impacts, and effect of environment/lifestyle and genetics also warrant further study. In this work, we attempt to address some of these questions by exploring work previously completed using single- and repetitive-injury paradigms. Despite some models producing some deficits similar to CTE symptoms, it is clear that further studies are required to understand the development of neuropathological and neurobehavioral features consistent with CTE-like features in rodents. Specifically, acute and chronic studies are needed that characterize the development of tau-based pathology.

Phosphodiesterase inhibitors as therapeutics for traumatic brain injury

Developing therapeutics for traumatic brain injury remains a challenge for all stages of recovery. The pathological features of traumatic brain injury are diverse, and it remains an obstacle to be able to target the wide range of pathologies that vary between traumatic brain injured patients and that evolve during recovery. One promising therapeutic avenue is to target the second messengers cAMP and cGMP with phosphodiesterase inhibitors due to their broad effects within the nervous system. Phosphodiesterase inhibitors have the capability to target different injury mechanisms throughout the time course of recovery after brain injury. Inflammation and neuronal death are early targets of phosphodiesterase inhibitors, and synaptic dysfunction and circuitry remodeling are late potential targets of phosphodiesterase inhibitors. This review will discuss how signaling through cyclic nucleotides contributes to the pathology of traumatic brain injury in the acute and chronic stages of recovery. We will review our current knowledge of the successes and challenges of using phosphodiesterase inhibitors for the treatment of traumatic brain injury and conclude with important considerations in developing phosphodiesterase inhibitors as therapeutics for brain trauma.

Heart-Specific Knockout of the Mitochondrial Thioredoxin Reductase (Txnrd2) Induces Metabolic and Contractile Dysfunction in the Aging Myocardium

BACKGROUND

Ubiquitous deletion of thioredoxin reductase 2 (Txnrd2) in mice is embryonically lethal and associated with abnormal heart development, while constitutive, heart-specific Txnrd2 inactivation leads to dilated cardiomyopathy and perinatal death. The significance of Txnrd2 in aging cardiomyocytes, however, has not yet been examined.

METHODS AND RESULTS

The tamoxifen-inducible heart-specific αMHC-MerCreMer transgene was used to inactivate loxP-flanked Txnrd2 alleles in adult mice. Hearts and isolated mitochondria from aged knockout mice were morphologically and functionally analyzed. Echocardiography revealed a significant increase in left ventricular end-systolic diameters in knockouts. Fractional shortening and ejection fraction were decreased compared with controls. Ultrastructural analysis of cardiomyocytes of aged mice showed mitochondrial degeneration and accumulation of autophagic bodies. A dysregulated autophagic activity was supported by higher levels of lysosome-associated membrane protein 1 (LAMP1), microtubule-associated protein 1A/1B-light chain 3-I (LC3-I), and p62 in knockout hearts. Isolated Txnrd2-deficient mitochondria used less oxygen and tended to produce more reactive oxygen species. Chronic hypoxia inducible factor 1, α subunit stabilization and altered transcriptional and metabolic signatures indicated that energy metabolism is deregulated.

CONCLUSIONS

These results imply a novel role of Txnrd2 in sustaining heart function during aging and suggest that Txnrd2 may be a modifier of heart failure.

Exercise preconditioning improves traumatic brain injury outcomes

PURPOSE

To determine whether 6 weeks of exercise performed prior to traumatic brain injury (TBI) could improve post-TBI behavioral outcomes in mice, and if exercise increases neuroprotective molecules (vascular endothelial growth factor-A [VEGF-A], erythropoietin [EPO], and heme oxygenase-1 [HO-1]) in brain regions responsible for movement (sensorimotor cortex) and memory (hippocampus).

METHODS

120 mice were randomly assigned to one of four groups: (1) no exercise+no TBI (NOEX-NOTBI [n=30]), (2) no exercise+TBI (NOEX-TBI [n=30]), (3) exercise+no TBI (EX-NOTBI [n=30]), and (4) exercise+TBI (EX-TBI [n=30]). The gridwalk task and radial arm water maze were used to evaluate sensorimotor and cognitive function, respectively. Quantitative real time polymerase chain reaction and immunostaining were performed to investigate VEGF-A, EPO, and HO-1 mRNA and protein expression in the right cerebral cortex and ipsilateral hippocampus.

RESULTS

EX-TBI mice displayed reduced post-TBI sensorimotor and cognitive deficits when compared to NOEX-TBI mice. EX-NOTBI and EX-TBI mice showed elevated VEGF-A and EPO mRNA in the cortex and hippocampus, and increased VEGF-A and EPO staining of sensorimotor cortex neurons 1 day post-TBI and/or post-exercise. EX-TBI mice also exhibited increased VEGF-A staining of hippocampal neurons 1 day post-TBI/post-exercise. NOEX-TBI mice demonstrated increased HO-1 mRNA in the cortex (3 days post-TBI) and hippocampus (3 and 7 days post-TBI), but HO-1 was not increased in mice that exercised.

CONCLUSIONS

Improved TBI outcomes following exercise preconditioning are associated with increased expression of specific neuroprotective genes and proteins (VEGF-A and EPO, but not HO-1) in the brain.

The Temporal Pattern of Changes in Serum Biomarker Levels Reveals Complex and Dynamically Changing Pathologies after Exposure to a Single Low-Intensity Blast in Mice

Time-dependent changes in blood-based protein biomarkers can help identify the ­pathological processes in blast-induced traumatic brain injury (bTBI), assess injury severity, and monitor disease progression. We obtained blood from control and injured mice (exposed to a single, low-intensity blast) at 2-h, 1-day, 1–week, and 1-month post-injury. We then determined the serum levels of biomarkers related to metabolism (4-HNE, HIF-1α, ceruloplasmin), vascular function (AQP1, AQP4, VEGF, vWF, Flk-1), inflammation (OPN, CINC1, fibrinogen, MIP-1a, OX-44, p38, MMP-8, MCP-1 CCR5, CRP, galectin-1), cell adhesion and the extracellular matrix (integrin α6, TIMP1, TIMP4, Ncad, connexin-43), and axonal (NF-H, Tau), neuronal (NSE, CK-BB) and glial damage (GFAP, S100β, MBP) at various post-injury time points. Our findings indicate that the exposure to a single, low-intensity blast results in metabolic and vascular changes, altered cell adhesion, and axonal and neuronal injury in the mouse model of bTBI. Interestingly, serum levels of several inflammatory and astroglial markers were either unchanged or elevated only during the acute and subacute phases of injury. Conversely, serum levels of the majority of biomarkers related to metabolic and vascular functions, cell adhesion, as well as neuronal and axonal damage remained elevated at the termination of the experiment (1 month), indicating long-term systemic and cerebral alterations due to blast. Our findings show that the exposure to a single, low-intensity blast induces complex pathological processes with distinct temporal profiles. Hence, monitoring serum biomarker levels at various post-injury time points may provide enhanced diagnostics in blast-related neurological and multi-system deficits.

Differential response of miRNA-21 and its targets after traumatic brain injury in aging mice

The present study investigated the possible role of miR-21, a miRNA that has known prosurvival function, in poor outcomes in the elderly following traumatic brain injury compared to adults. Controlled cortical impact injury was induced in adult (5-6 months) and aged (22-24 months) C57/BL6 mice. miR-21 and four of its targets (PDCD4, TIMP3, RECK, PTEN) were analyzed at 1, 3, 7 days post injury in samples of injured cortex using real-time PCR analysis. Basal miR-21 expression was higher in the aged brain than in the adult brain. In the adult brain, miR-21 expression increased in response to injury, with the maximum increase 24 hours after injury followed by a gradual decrease, returning to baseline 7 days post-injury. In contrast, in aged mice, miR21 showed no injury response, and expression of miR-21 target genes (PTEN, PDCD4, RECK, TIMP3) was up-regulated at all post injury time points, with a maximal increase at 24 hours post injury. Based on these results, we conclude that the diminished miR21 injury response in the aged brain leads to up-regulation of its targets, with the potential to contribute to the poor prognosis following TBI in aging brain. Therefore, strategies aimed at up-regulation of miR-21 and/or down regulation of its targets might be useful in improving outcomes in the elderly following TBI.

Early expressions of hypoxia-inducible factor 1alpha and vascular endothelial growth factor increase the neuronal plasticity of activated endogenous neural stem cells after focal cerebral ischemia

Endogenous neural stem cells become “activated” after neuronal injury, but the activation sequence and fate of endogenous neural stem cells in focal cerebral ischemia model are little known. We evaluated the relationships between neural stem cells and hypoxia-inducible factor-1α and vascular endothelial growth factor expression in a photothromobotic rat stroke model using immunohistochemistry and western blot analysis. We also evaluated the chronological changes of neural stem cells by 5-bromo-2′-deoxyuridine (BrdU) incorporation. Hypoxia-inducible factor-1α expression was initially increased from 1 hour after ischemic injury, followed by vascular endothelial growth factor expression. Hypoxia-inducible factor-1α immunoreactivity was detected in the ipsilateral cortical neurons of the infarct core and peri-infarct area. Vascular endothelial growth factor immunoreactivity was detected in bilateral cortex, but ipsilateral cortex staining intensity and numbers were greater than the contralateral cortex. Vascular endothelial growth factor immunoreactive cells were easily found along the peri-infarct area 12 hours after focal cerebral ischemia. The expression of nestin increased throughout the microvasculature in the ischemic core and the peri-infarct area in all experimental rats after 24 hours of ischemic injury. Nestin immunoreactivity increased in the subventricular zone during 12 hours to 3 days, and prominently increased in the ipsilateral cortex between 3–7 days. Nestin-labeled cells showed dual differentiation with microvessels near the infarct core and reactive astrocytes in the peri-infarct area. BrdU-labeled cells were increased gradually from day 1 in the ipsilateral subventricular zone and cortex, and numerous BrdU-labeled cells were observed in the peri-infarct area and non-lesioned cortex at 3 days. BrdU-labeled cells rather than neurons, were mainly co-labeled with nestin and GFAP. Early expressions of hypoxia-inducible factor-1α and vascular endothelial growth factor after ischemia made up the microenvironment to increase the neuronal plasticity of activated endogenous neural stem cells. Moreover, neural precursor cells after large-scale cortical injury could be recruited from the cortex nearby infarct core and subventricular zone.

HIF-1α/COX-2 expression and mouse brain capillary remodeling during prolonged moderate hypoxia and subsequent re-oxygenation

Dynamic microvascular remodeling maintains an optimal continuous supply of oxygen and nutrients to the brain to account for prolonged environmental variations. The objective of this study was to determine the relative time course of capillary regression during re-oxygenation after exposure to prolonged moderate hypoxia and expression of the primary signaling factors involved in the process. Four-month old male C57BL/6 mice were housed and maintained in a hypobaric chamber at 290 Torr (0.4 atm) for 21 days and allowed to recover at normoxia (room air) for up to 21 days. The mice were either decapitated or perfused in-situ and brain samples collected were either homogenized for Western blot analysis or fixed and embedded in paraffin for immunohistochemistry. Hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) and erythropoietin (EPO) expression were increased during hypoxic exposure and diminished during subsequent re-oxygenation. However, cyclooxygenase-2 (COX-2) and angiopoietin-2 (Ang-2) were both elevated during hypoxia as well as subsequent re-oxygenation. Significantly increased capillary density at the end of the 3rd week of hypoxia regressed back toward normoxic baseline as the duration of re-oxygenation continued. In conclusion, elevated COX-2 and Ang-2 expression during hypoxia where angiogenesis occurs and re-oxygenation, when micro-vessels regress, identifies these proteins as vascular remodeling molecules crucial for angioplasticity.

Elucidating the severity of preclinical traumatic brain injury models: a role for functional assessment?

BACKGROUND

Concussion remains a symptom-based diagnosis clinically, yet preclinical studies investigating traumatic brain injury, of which concussion is believed to represent a "mild" form, emphasize histological end points with functional assessments often minimized or ignored all together. Recently, clinical studies have identified the importance of cognitive and neuropsychiatric symptoms, in addition to somatic concerns, following concussion. How these findings may translate to preclinical studies is unclear at present.

OBJECTIVE

To address the contrasting end points used clinically compared with those in preclinical studies and the potential role of functional assessments in a commonly used model of diffuse axonal injury (DAI).

METHODS

Animals were subjected to DAI by the use of the impact-acceleration model. Functional and behavioral assessments were conducted during 1 week following DAI before the completion of the histological assessment at 1 week post-DAI.

RESULTS

We show, despite the suggestion that this model represents concussive injury, no functional impairments as determined by using the common measures of motor, sensorimotor, cognitive, and neuropsychiatric function following injury over the course of 1 week. The lack of functional deficits is in sharp contrast to neuropathological findings indicating neural degeneration, astrocyte reactivity, and microglial activation.

CONCLUSION

Future studies are needed to identify functional assessments, neurophysiologic techniques, and imaging assessments more apt to distinguish differences following so-called "mild" traumatic brain injury in preclinical models and determine whether these models are truly studying concussive or subconcussive injury. These studies are needed not only to understand the mechanism of injury and production of subsequent deficits, but also to rigorously evaluate potential therapeutic agents.

Neuroglobin overexpression improves sensorimotor outcomes in a mouse model of traumatic brain injury

There is a significant need for novel treatments that will improve traumatic brain injury (TBI) outcomes. One potential neuroprotective mechanism is to increase oxygen binding proteins such as neuroglobin. Neuroglobin has a high affinity for oxygen, is an effective free radical scavenger, and is neuroprotective within the brain following hypoxia and ischemia. The purpose of this study was to determine whether neuroglobin overexpression improves sensorimotor outcomes following TBI in transgenic neuroglobin overexpressing (NGB) mice. Additional study aims were to determine if and when an endogenous neuroglobin response occurred following TBI in wild-type (WT) mice, and in what brain regions and cell types the response occurred. Controlled cortical impact (CCI) was performed in adult (5 month) C57/BL6 WT mice, and NGB mice constitutively overexpressing neuroglobin via the chicken beta actin promoter coupled with the cytomegalovirus distal enhancer. The gridwalk task was used for sensorimotor testing of both WT and NGB mice, prior to injury, and at 2, 3, and 7 days post-TBI. NGB mice displayed significant reductions in the average number of foot faults per minute walking at 2, 3, and 7 days post-TBI when compared to WT mice at each time point. Neuroglobin mRNA expression was assessed in the injured cortex of WT mice prior to injury, and at 1, 3, 7, and 14 days post-TBI using quantitative real time polymerase chain reaction (qRT-PCR). Neuroglobin mRNA was significantly increased at 7 days post-TBI. Immunostaining showed neuroglobin primarily localized to neurons and glial cells in the injured cortex and ipsilateral hippocampus of WT mice, while neuroglobin was present in all brain regions of NGB mice at 7 days post-TBI. These results showed that overexpression of neuroglobin reduced sensorimotor deficits following TBI, and that an endogenous increase in neuroglobin expression occurs during the subacute period. Increasing neuroglobin expression through novel therapeutic interventions during the acute period after TBI may improve recovery.

Early down regulation of the glial Kir4.1 and GLT-1 expression in pericontusional cortex of the old male mice subjected to traumatic brain injury

Astroglia play multiple roles in brain function by providing matrix to neurons, secreting neurotrophic factors, maintaining K(+) and glutamate homeostasis and thereby controlling synaptic plasticity which undergoes alterations during aging. K(+) and glutamate homeostasis is maintained by astrocytes membrane bound inwardly rectifying K(+) channel (Kir4.1) and glutamate transporter-1 (GLT-1 or EAAT-2) proteins, respectively in the synapse and their expression may be altered due to traumatic brain injury (TBI). Also, it is not well understood whether this change is age dependent. To find out this, TBI was experimentally induced in adult and old male AKR strain mice using CHI technique, and expression of the Kir4.1 and GLT-1 in the pericontusional cortex at various time intervals was studied by Western blotting and semi quantitative RT-PCR techniques. Here, we report that expression of both Kir4.1 and GLT-1 genes at transcript and protein levels is significantly down regulated in the pericontusional ipsi-lateral cortex of old TBI mice as compared to that in the adult TBI mice as function of time after injury. Further, expression of both the genes starts decreasing early in old mice i.e., from the first hour after TBI as compared to that starts from fourth hour in adult TBI mice. Thus TBI affects expression of Kir4.1 and GLT-1 genes in age- and time dependent manner and it may lead to accumulations of more K(+) and glutamate early in the synapse of old mice as compared to adult. This may be implicated in the TBI induced early and severe neuronal depolarization and excito-neurotoxicity in old age.

Molecular mechanisms of cognitive dysfunction following traumatic brain injury

Traumatic brain injury (TBI) results in significant disability due to cognitive deficits particularly in attention, learning and memory, and higher-order executive functions. The role of TBI in chronic neurodegeneration and the development of neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic Lateral Sclerosis (ALS) and most recently chronic traumatic encephalopathy (CTE) is of particular importance. However, despite significant effort very few therapeutic options exist to prevent or reverse cognitive impairment following TBI. In this review, we present experimental evidence of the known secondary injury mechanisms which contribute to neuronal cell loss, axonal injury, and synaptic dysfunction and hence cognitive impairment both acutely and chronically following TBI. In particular we focus on the mechanisms linking TBI to the development of two forms of dementia: AD and CTE. We provide evidence of potential molecular mechanisms involved in modulating Aβ and Tau following TBI and provide evidence of the role of these mechanisms in AD pathology. Additionally we propose a mechanism by which Aβ generated as a direct result of TBI is capable of exacerbating secondary injury mechanisms thereby establishing a neurotoxic cascade that leads to chronic neurodegeneration.

Peptidergic drugs for the treatment of traumatic brain injury

Traumatic brain injury (TBI) is a devastating medical condition that has an enormous socioeconomic impact because it affects more than 10 million people annually worldwide and is associated with high rates of hospitalization, mortality and disability. Although TBI survival has improved continuously for decades, particularly in developing countries, implementation of an effective drug therapy for TBI represents an unmet clinical need. All confirmatory trials conducted to date with drugs targeting a single TBI pathological pathway failed to show clinical efficacy, probably because TBI pathophysiology involves multiple cellular and molecular mechanisms of secondary brain damage. According to current scientific evidence of the participation of peptide-mediated mechanisms in the processes of brain injury and repair after TBI, peptidergic drugs represent a multimodal therapy alternative to improve acute outcome and long-term recovery in TBI patients. Preliminary randomized-controlled clinical trials and open-label studies conducted to date with the peptidergic drug Cerebrolysin® (Ever Neuro Pharma GmbH, Unterach, Austria) and with the endogenous neuropeptides progesterone and erythropoietin, showed positive clinical results. Cerebrolysin-treated patients had a faster clinical recovery, a shorter hospitalization time and a better long-term outcome. Treatment with progesterone showed advantages over placebo regarding TBI mortality and clinical outcome, whereas erythropoietin only reduced mortality. Further validation of these promising findings in confirmatory randomized-controlled clinical trials is warranted. This article reviews the scientific basis and clinical evidence on the development of multimodal peptidergic drugs as a therapeutic option for the effective treatment of TBI patients.

Traumatic brain injury in aged animals increases lesion size and chronically alters microglial/macrophage classical and alternative activation states

Traumatic brain injury (TBI) causes chronic microglial activation that contributes to subsequent neurodegeneration, with clinical outcomes declining as a function of aging. Microglia/macrophages (MG/Mɸ) have multiple phenotypes, including a classically activated, proinflammatory (M1) state that might contribute to neurotoxicity, and an alternatively activated (M2) state that might promote repair. In this study we used gene expression, immunohistochemical, and stereological analyses to show that TBI in aged versus young mice caused larger lesions associated with an M1/M2 balance switch and increased numbers of reactive (bushy and hypertrophic) MG/Mɸ in the cortex, hippocampus, and thalamus. Chitinase3-like 3 (Ym1), an M2 phenotype marker, displayed heterogeneous expression after TBI with amoeboid-like Ym1-positive MG/Mɸ at the contusion site and ramified Ym1-positive MG/Mɸ at distant sites; this distribution was age-related. Aged-injured mice also showed increased MG/Mɸ expression of major histocompatibility complex II and NADPH oxidase, and reduced antioxidant enzyme expression which was associated with lesion size and neurodegeneration. Thus, altered relative M1/M2 activation and an nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase)-mediated shift in redox state might contribute to worse outcomes observed in older TBI animals by creating a more proinflammatory M1 MG/Mɸ activation state.

Age-dependent alterations in cAMP signaling contribute to synaptic plasticity deficits following traumatic brain injury

The elderly have comparatively worse cognitive impairments from traumatic brain injury (TBI) relative to younger adults, but the molecular mechanisms that underlie this exacerbation of cognitive deficits are unknown. Experimental models of TBI have demonstrated that the cyclic AMP-protein kinase A (cAMP-PKA) signaling pathway is downregulated after brain trauma. Since the cAMP-PKA signaling pathway is a key mediator of long-term memory formation, we investigated whether the TBI-induced decrease in cAMP levels is exacerbated in aged animals. Aged (19 months) and young adult (3 months) male Fischer 344 rats received sham surgery or mild (1.4-1.6 atmospheres, atm) or moderate (1.7-2.1 atm) parasagittal fluid-percussion brain injury. At various time points after surgery, the ipsilateral parietal cortex, hippocampus, and thalamus were assayed for cAMP levels. Mild TBI lowered cAMP levels in the hippocampus of aged, but not young adult animals. Moderate TBI lowered cAMP levels in the hippocampus and parietal cortex of both age groups. In the thalamus, cAMP levels were significantly lowered after moderate, but not mild TBI. To determine if the TBI-induced decreases in cAMP had physiological consequences in aged animals, hippocampal long-term potentiation (LTP) in the Schaffer collateral pathway of the CA1 region was assessed. LTP was significantly decreased in both young adult and aged animals after mild and moderate TBI as compared to sham surgery animals. Rolipram rescued the LTP deficits after mild TBI for young adult animals and caused a partial recovery for aged animals. However, rolipram did not rescue LTP deficits after moderate TBI in either young adult or aged animals. These results indicate that the exacerbation of cognitive impairments in aged animals with TBI may be due to decreased cAMP levels and deficits in hippocampal LTP.

Depletion of GGA1 and GGA3 mediates postinjury elevation of BACE1

Traumatic brain injury (TBI) is one of the most robust environmental risk factors for Alzheimer's disease (AD). Compelling evidence is accumulating that a single event of TBI is associated with increased levels of Aβ. However, the underlying molecular mechanisms remain unknown. We report here that the BACE1 interacting protein, GGA3, is depleted while BACE1 levels increase in the acute phase after injury (48 h) in a mouse model of TBI. We further demonstrated the role of GGA3 in the regulation of BACE1 in vivo by showing that BACE1 levels are increased in the brain of GGA3-null mice. We next found that head trauma potentiates BACE1 elevation in GGA3-null mice in the acute phase after TBI, and discovered that GGA1, a GGA3 homolog, is a novel caspase-3 substrate depleted at 48 h after TBI. Moreover, GGA1 silencing potentiates BACE1 elevation induced by GGA3 deletion in neurons in vitro, indicating that GGA1 and GGA3 synergistically regulate BACE1. Accordingly, we found that levels of both GGA1 and GGA3 are depleted while BACE1 levels are increased in a series of postmortem AD brains. Finally, we show that GGA3 haploinsufficiency results in sustained elevation of BACE1 and Aβ levels while GGA1 levels are restored in the subacute phase (7 d) after injury. In conclusion, our data indicate that depletion of GGA1 and GGA3 engender a rapid and robust elevation of BACE1 in the acute phase after injury. However, the efficient disposal of the acutely accumulated BACE1 solely depends on GGA3 levels in the subacute phase of injury.

Cervical spinal erythropoietin induces phrenic motor facilitation via extracellular signal-regulated protein kinase and Akt signaling

Erythropoietin (EPO) is typically known for its role in erythropoiesis but is also a potent neurotrophic/neuroprotective factor for spinal motor neurons. Another trophic factor regulated by hypoxia-inducible factor-1, vascular endothelial growth factor (VEGF), signals via ERK and Akt activation to elicit long-lasting phrenic motor facilitation (pMF). Because EPO also signals via ERK and Akt activation, we tested the hypothesis that EPO elicits similar pMF. Using retrograde labeling and immunohistochemical techniques, we demonstrate in adult, male, Sprague Dawley rats that EPO and its receptor, EPO-R, are expressed in identified phrenic motor neurons. Intrathecal EPO at C4 elicits long-lasting pMF; integrated phrenic nerve burst amplitude increased >90 min after injection (63 ± 12% baseline 90 min after injection; p < 0.001). EPO increased phosphorylation (and presumed activation) of ERK (1.6-fold vs controls; p < 0.05) in phrenic motor neurons; EPO also increased pAkt (1.6-fold vs controls; p < 0.05). EPO-induced pMF was abolished by the MEK/ERK inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4-bis(o-aminophenylmercapto)butadiene] and the phosphatidylinositol 3-kinase/Akt inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one], demonstrating that ERK MAP kinases and Akt are both required for EPO-induced pMF. Pretreatment with U0126 and LY294002 decreased both pERK and pAkt in phrenic motor neurons (p < 0.05), indicating a complex interaction between these kinases. We conclude that EPO elicits spinal plasticity in respiratory motor control. Because EPO expression is hypoxia sensitive, it may play a role in respiratory plasticity in conditions of prolonged or recurrent low oxygen.

Selective brain cooling in rats ameliorates intracerebral hemorrhage and edema caused by penetrating brain injury: possible involvement of heme oxygenase-1 expression

Brain edema formation associated with trauma-induced intracerebral hemorrhage (ICH) is a clinical complication with high mortality. Studies have shown that heme oxygenase-1 (HO-1) plays an important role in ICH-induced brain edema. In order to understand the role of HO-1 in the protective effect of selective brain cooling (SBC), we investigated the time course of HO-1 changes following penetrating ballistic-like brain injury (PBBI) in rats. Samples were collected from injured and control animals at 6, 24, 48, and 72 h, and 7 days post-injury to evaluate HO-1 expression, heme concentration, brain water content, and immunohistochemistry (IHC). Following a 10% frontal PBBI, HO-1 mRNA and protein was increased at all time points studied, reaching maximum expression levels at 24-48 h post-injury. An increase in the heme concentration and the development of brain edema coincided with the upregulation of HO-1 mRNA and protein during the 7-day post-injury period. SBC significantly decreased PBBI-induced heme concentration, attenuated HO-1 upregulation, and concomitantly reduced brain water content. These results suggest that the neuroprotective effects of SBC may be partially mediated by reducing the heme accumulation, which reduced injury-mediated upregulation of HO-1, and in turn ameliorated edema formation. Collectively, these results suggest a potential value of HO-1 as a diagnostic and/or therapeutic biomarker in hemorrhagic brain injury.

Traumatic brain injury: a risk factor for Alzheimer's disease

Traumatic brain injury (TBI) constitutes a major global health and socio-economic problem with neurobehavioral sequelae contributing to long-term disability. It causes brain swelling, axonal injury and hypoxia, disrupts blood brain barrier function and increases inflammatory responses, oxidative stress, neurodegeneration and leads to cognitive impairment. Epidemiological studies show that 30% of patients, who die of TBI, have Aβ plaques which are pathological features of Alzheimer's disease (AD). Thus TBI acts as an important epigenetic risk factor for AD. This review focuses on AD related genes which are expressed during TBI and its relevance to progression of the disease. Such understanding will help to diagnose the risk of TBI patients to develop AD and design therapeutic interventions.

Effects of aging on blood brain barrier and matrix metalloproteases following controlled cortical impact in mice

Aging alters the ability of the brain to respond to injury. One of the major differences between the adult and aged brain is that comparable injuries lead to greater blood brain barrier disruption in the aged brain. The goals of these studies were to quantify the effects of age on BBB permeability using high field strength MRI T1 mapping and to determine whether activation of matrix metalloproteases, their inhibitors, or expression of blood brain barrier structural proteins, occludin, zonnula occludins-1 (ZO-1) and claudin-5 were altered following injury to the aged C57/BL6 mouse brain. T1 mapping studies revealed greater blood brain barrier permeability in the aged (21-24 months old) brain than in the adult (4-6 months old) following controlled cortical impact. The increased blood brain barrier permeability in the pericontusional region was confirmed with IgG immunohistochemistry. MMP-9 activity was increased following controlled cortical impact in the aged brain, and this was accompanied by increased MMP-9 gene expression. MMP-2 activity was higher in the uninjured aged brain than in the adult brain. Occludin and ZO-1 mRNA levels were unchanged following injury in either age group, but claudin-5 mRNA levels were lower in the aged than the adult brain following injury. These results demonstrate quantitative increases in blood brain barrier permeability in the aged brain following injury that are accompanied by increased MMP-9 activation and decreased blood brain barrier repair responses.

Hypoxia-induced angiogenesis is delayed in aging mouse brain

Chronic moderate hypoxia results in systemic and central nervous system adaptations that allow acclimatization. Long-term responses to hypoxia involve systemic physiological changes, metabolic regulation, and vascular remodeling. To investigate whether aging affects systemic and cerebral angiogenic adaptational changes in response to prolonged hypoxia, the present study assessed the responses of 4month old ("young") C57BL/6 mice and 24month old ("aged") C57BL/6 mice to chronic hypobaric hypoxia of 0.4atm (290torr). Compared to young mice, delayed body weight-loss recovery and a lag in polycythemic response were observed in aged mice. As previously shown, hypoxia inducible factor-1α (HIF-1α) accumulation was attenuated and vascular endothelial growth factor (VEGF) expression was decreased in the cerebral cortex of aged mice. Conversely, cyclooxygenase-2 (COX-2), angiopoietin-2 (Ang-2), and peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) protein upregulation were not affected in the aged mice. Despite an initial delay in cerebral angiogenic response in aged mice in the first week of hypoxia, no significant differences were observed in microvascular density between young and aged mice in normoxia and at 2 and 3weeks of hypoxia. Taken together, these observations indicate that, even though the HIF-1 response to hypoxia is greatly attenuated, HIF-1 independent compensatory pathways are eventually able to maintain baseline and cerebral angiogenic adaptational changes to chronic hypoxia in aged mice. The delayed adaptive response, however, may result in decreased survival in the aged cohort.

Early and sustained increase in the expression of hippocampal IGF-1, but not EPO, in a developmental rodent model of traumatic brain injury

Pediatric traumatic brain injury (pTBI) is the leading cause of traumatic death and disability in children in the United States. Impaired learning and memory in these young survivors imposes a heavy toll on society. In adult TBI (aTBI) models, cognitive outcome improved after administration of erythropoietin (EPO) or insulin-like growth factor-1 (IGF-1). Little is known about the production of these agents in the hippocampus, a brain region critical for learning and memory, after pTBI. Our objective was to describe hippocampal expression of EPO and IGF-1, together with their receptors (EPOR and IGF-1R, respectively), over time after pTBI in 17-day-old rats. We used the controlled cortical impact (CCI) model and measured hippocampal mRNA levels of EPO, IGF-1, EPOR, IGF-1R, and markers of caspase-dependent apoptosis (bcl2, bax, and p53) at post-injury days (PID) 1, 2, 3, 7, and 14. CCI rats performed poorly on Morris water maze testing of spatial working memory, a hippocampally-based cognitive function. Apoptotic markers were present early and persisted for the duration of the study. EPO in our pTBI model increased much later (PID7) than in aTBI models (12 h), while EPOR and IGF-1 increased at PID1 and PID2, respectively, similar to data from aTBI models. Our data indicate that EPO expression showed a delayed upregulation post-pTBI, while EPOR increased early. We speculate that administration of EPO in the first 1-2 days after pTBI would increase hippocampal neuronal survival and function.

Perturbed cellular response to brain injury during aging

Old age is associated with an enhanced susceptibility to stroke and poor recovery from brain injury, but the cellular processes underlying these phenomena are only partly understood. Therefore, studying the basic mechanisms underlying structural and functional recovery after brain injury in aged subjects is of considerable clinical interest. Behavioral and cytological analyses of rodents that have undergone experimental injury show that: (a) behaviorally, aged rodents are more severely impaired by ischemia than are young animals, and older rodents also show diminished functional recovery; (b) compared to young animals, aged animals develop a larger infarct area, as well as a necrotic zone characterized by a higher rate of cellular degeneration and a larger number of apoptotic cells; (c) both astrocytes and macrophages are activated strongly and early following stroke in aged rodents; (d) in older animals, the premature, intense cytoproliferative activity following brain injury leads to the precipitous formation of growth-inhibiting scar tissue, a phenomenon amplified by the persistent expression of neurotoxic factors; (e) though the timing is altered, the regenerative capability of the brain is largely preserved in rats, at least into early old age. Whether endogenous neurogenesis contributes to spontaneous recovery after stroke has not yet been established. If neurogenesis from endogenous neuronal stem cells is to be used therapeutically, an individual approach will be required to assess the possible extent of neurogenic response as well as the possibilities to alter this response for functional improvement or prevention of further loss of brain function.

Redox control in mammalian embryo development

The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.

Postnatal erythropoietin treatment mitigates neural cell loss after systemic prenatal hypoxic-ischemic injury

OBJECT

Brain injury from preterm birth predisposes children to cerebral palsy, epilepsy, cognitive delay, and behavioral abnormalities. The CNS injury often begins before the early birth, which hinders diagnosis and concurrent treatment. Safe, effective postnatal interventions are urgently needed to minimize these chronic neurological deficits. Erythropoietin (EPO) is a pleiotropic neuroprotective cytokine, but the biological basis of its efficacy in the damaged developing brain remains unclear. Coordinated expression of EPO ligand and receptor expression occurs during CNS development to promote neural cell survival. The authors propose that prenatal third trimester global hypoxia-ischemia disrupts the developmentally regulated expression of neural cell EPO signaling, and predisposes neural cells to death. Furthermore, the authors suggest that neonatal exogenous recombinant human EPO (rhEPO) administration can restore the mismatch of EPO ligand and receptor levels, and enhance neural cell survival.

METHODS

Transient systemic hypoxia-ischemia (TSHI) on embryonic Day 18 in rats mimics human early-third trimester placental insufficiency. This model was used to test the authors' hypothesis using a novel clinically relevant paradigm of prenatal injury on embryonic Day 18, neonatal systemic rhEPO administration initiated 4 days after injury on postnatal Day 1, and histological, biochemical, and functional analyses in neonatal, juvenile, and adult rats.

RESULTS

The results showed that prenatal TSHI upregulates brain EPO receptors, but not EPO ligand. Sustained EPO receptor upregulation was pronounced on oligodendroglial lineage cells and neurons, neural cell populations particularly prone to loss from CNS injury due to preterm birth. Postnatal rhEPO administration after prenatal TSHI minimized histological damage and rescued oligodendrocytes and gamma-aminobutyric acidergic interneurons. Myelin basic protein expression in adult rats after insult was reduced compared with sham controls, but could be restored to near normal levels by neonatal rhEPO treatment. Erythropoietin-treated TSHI rats performed significantly better than their saline-treated peers as adults in motor skills tests, and showed significant seizure threshold restoration using a pentylenetetrazole increasing-dose paradigm.

CONCLUSIONS

These data demonstrate that neonatal rhEPO administration in a novel clinically relevant paradigm initiated 4 days after a global prenatal hypoxic-ischemic insult in rats rescues neural cells, and induces lasting histological and functional improvement in adult rats.

Hypoxia-inducible factor-1 improves inotropic responses of cardiac myocytes in ageing heart without affecting mitochondrial activity

Ageing reduces the ability of cardiac myocytes to respond to inotropic agents. We hypothesized that hypoxia-inducible factor-1 (HIF-1) would improve the functional and Ca(2+) transient responses of ageing myocytes to the inotropic agents and this would act, in part, through altered mitochondrial activity. Young (3-4 months) and older Fischer 344 rats (18-20 months) were used. Hypoxia-inducible factor-1alpha was upregulated with ciclopirox olamine (CPX, 50 mg kg(1) on 2 days). Hypoxia-inducible factor-1 upregulation was detected by Western blot. Cardiomyocyte contraction and Ca(2+) transients were measured at baseline and after forskolin and ouabain. We also measured mitochondrial complex activities and production of reactive oxygen species (ROS). In the young group, forskolin (31%) and ouabain (31%) significantly increased percentage shortening. Similar changes were observed in the young + CPX group. Calcium transients also responded in a similar manner. However, in the older group, forskolin (12%) and ouabain (6%) did not significantly increase myocyte contractility or Ca(2+) transients. In the older + CPX group, the effects of forskolin (34%) and ouabain (29%) were restored. In the young + CPX group, there was increased ROS production and mitochondrial complex I and III activity compared with the young group. These differences were not observed in older groups. These data demonstrate an impaired functional and Ca(2+) effect of positive inotropic agents in older myocytes. Upregulation of HIF-1 restored this blunted response, but this was not related to changed mitochondrial activity induced by HIF-1. Thus, we found that HIF-1 improved inotropy in older myocytes without requiring mitochondrial activity changes.

JNK contributes to Hif-1alpha regulation in hypoxic neurons

Hypoxia is an established factor of neurodegeneration. Nowadays, attention is directed at understanding how alterations in the expression of stress-related signaling proteins contribute to age dependent neuronal vulnerability to injury. The purpose of this study was to investigate how Hif-1alpha, a major neuroprotective factor, and JNK signaling, a key pathway in neurodegeneration, relate to hypoxic injury in young (6DIV) and adult (12DIV) neurons. We could show that in young neurons as compared to mature ones, the protective factor Hif-1alpha is more induced while the stress protein phospho-JNK displays lower basal levels. Indeed, changes in the expression levels of these proteins correlated with increased vulnerability of adult neurons to hypoxic injury. Furthermore, we describe for the first time that treatment with the D-JNKI1, a JNK-inhibiting peptide, rescues adult hypoxic neurons from death and contributes to Hif-1alpha upregulation, probably via a direct interaction with the Hif-1alpha protein.