Publications by authors named "Pramod K Dash"

115 Publications

4R-cembranoid confers neuroprotection against LPS-induced hippocampal inflammation in mice.

J Neuroinflammation 2021 Apr 19;18(1):95. Epub 2021 Apr 19.

Department of Biochemistry, Universidad Central del Caribe School of Medicine, Av. Sta. Juanita, Bayamón, 00960, Puerto Rico.

Background: Chronic brain inflammation has been implicated in the pathogenesis of various neurodegenerative diseases and disorders. For example, overexpression of pro-inflammatory cytokines has been associated with impairments in hippocampal-dependent memory. Lipopolysaccharide (LPS) injection is a widely used model to explore the pathobiology of inflammation. LPS injection into mice causes systemic inflammation, neuronal damage, and poor memory outcomes if the inflammation is not controlled. Activation of the alpha-7 nicotinic receptor (α7) plays an anti-inflammatory role in the brain through vagal efferent nerve signaling. 4R-cembranoid (4R) is a natural compound that crosses the blood-brain barrier, induces neuronal survival, and has been shown to modulate the activity of nicotinic receptors. The purpose of this study is to determine whether 4R reduces the deleterious effects of LPS-induced neuroinflammation and whether the α7 receptor plays a role in mediating these beneficial effects.

Methods: Ex vivo population spike recordings were performed in C57BL/6J wild-type (WT) and alpha-7-knockout (α7KO) mouse hippocampal slices in the presence of 4R and nicotinic receptor inhibitors. For in vivo studies, WT and α7KO mice were injected with LPS for 2 h, followed by 4R or vehicle for 22 h. Analyses of IL-1β, TNF-α, STAT3, CREB, Akt1, and the long-term novel object recognition test (NORT) were performed for both genotypes. In addition, RNA sequencing and RT-qPCR analyses were carried out for 12 mRNAs related to neuroinflammation and their modification by 4R.

Results: 4R confers neuroprotection after NMDA-induced neurotoxicity in both WT and α7KO mice. Moreover, hippocampal TNF-α and IL-1β levels were decreased with 4R treatment following LPS exposure in both strains of mice. 4R restored LPS-induced cognitive decline in NORT. There was a significant increase in the phosphorylation of STAT3, CREB, and Akt1 with 4R treatment in the WT mouse hippocampus following LPS exposure. In α7KO mice, only pAkt levels were significantly elevated in the cortex. 4R significantly upregulated mRNA levels of ORM2, GDNF, and C3 following LPS exposure. These proteins are known to play a role in modulating microglial activation, neuronal survival, and memory.

Conclusion: Our results indicate that 4R decreases the levels of pro-inflammatory cytokines; improves memory function; activates STAT3, Akt1, and CREB phosphorylation; and upregulates the mRNA levels of ORM2, GDNF, and C3. These effects are independent of the α7 nicotinic receptor.
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http://dx.doi.org/10.1186/s12974-021-02136-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8054431PMC
April 2021

Selective Endothelial Hyperactivation of Oncogenic KRAS Induces Brain Arteriovenous Malformations in Mice.

Ann Neurol 2021 05 22;89(5):926-941. Epub 2021 Mar 22.

Vivian L. Smith Department of Neurosurgery, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX.

Objective: Brain arteriovenous malformations (bAVMs) are a leading cause of hemorrhagic stroke and neurological deficits in children and young adults, however, no pharmacological intervention is available to treat these patients. Although more than 95% of bAVMs are sporadic without family history, the pathogenesis of sporadic bAVMs is largely unknown, which may account for the lack of therapeutic options. KRAS mutations are frequently observed in cancer, and a recent unprecedented finding of these mutations in human sporadic bAVMs offers a new direction in the bAVM research. Using a novel adeno-associated virus targeting brain endothelium (AAV-BR1), the current study tested if endothelial KRAS mutation induces sporadic bAVMs in mice.

Methods: Five-week-old mice were systemically injected with either AAV-BR1-GFP or -KRAS . At 8 weeks after the AAV injection, bAVM formation and characteristics were addressed by histological and molecular analyses. The effect of MEK/ERK inhibition on KRAS -induced bAVMs was determined by treatment of trametinib, a US Food and Drug Administration (FDA)-approved MEK/ERK inhibitor.

Results: The viral-mediated KRAS overexpression induced bAVMs, which were composed of a tangled nidus mirroring the distinctive morphology of human bAVMs. The bAVMs were accompanied by focal angiogenesis, intracerebral hemorrhages, altered vascular constituents, neuroinflammation, and impaired sensory/cognitive/motor functions. Finally, we confirmed that bAVM growth was inhibited by trametinib treatment.

Interpretation: Our innovative approach using AAV-BR1 confirms that KRAS mutations promote bAVM development via the MEK/ERK pathway, and provides a novel preclinical mouse model of bAVMs which will be useful to develop a therapeutic strategy for patients with bAVM. ANN NEUROL 2021;89:926-941.
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http://dx.doi.org/10.1002/ana.26059DOI Listing
May 2021

P-glycoprotein Expression Is Upregulated in a Pre-Clinical Model of Traumatic Brain Injury.

Neurotrauma Rep 2020 18;1(1):207-217. Epub 2020 Nov 18.

Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, Mississippi, USA.

Athletes participating in contact sports are at risk for sustaining repeat mild traumatic brain injury (rmTBI). Unfortunately, no pharmacological treatment to lessen the pathophysiology of brain injury has received U.S. Food and Drug Administration (FDA) approval. One hurdle to overcome for potential candidate agents to reach effective therapeutic concentrations in the brain is the blood-brain barrier (BBB). Adenosine triphosphate (ATP)-binding cassette (ABC) transporters, such as P-glycoprotein (Pgp), line the luminal membrane of the brain capillary endothelium facing the vascular space. Although these transporters serve to protect the central nervous system (CNS) from damage by effluxing neurotoxicants before they can reach the brain, they may also limit the accumulation of therapeutic drugs in the brain parenchyma. Thus, increased Pgp expression following brain injury may result in reduced brain availability of therapeutic agents. We therefore questioned if repeat concussive injury increases Pgp expression in the brain. To answer this question, we used a rodent model of repeat mild closed head injury (rmCHI) and examined the messenger RNA (mRN) and protein expression of both isoforms of rodent Pgp (Abcb1a and Abcb1b). Compared with sham-operated controls ( 5), the mRNA levels of both Abcb1a and Abcb1b were found to be increased in the hippocampus at day 1 ( 5) and at day 5 ( 5) post-injury. Using a validated antibody, we show increased immunolabeling for Pgp in the dorsal cortex at day 5 and in the hippocampus at day 1 ( 5) and at day 5 ( 5) post-injury compared with sham controls ( 6). Taken together, these results suggest that increased expression of Pgp after rmCHI may reduce the brain accumulation of therapeutic drugs that are Pgp substrates. It is plausible that including a Pgp inhibitor with a candidate therapeutic agent may be an effective approach to treat the pathophysiology of rmCHI.
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http://dx.doi.org/10.1089/neur.2020.0034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7703495PMC
November 2020

A method for assessing tissue respiration in anatomically defined brain regions.

Sci Rep 2020 08 6;10(1):13179. Epub 2020 Aug 6.

Department of Neurobiology and Anatomy, The University of Texas McGovern Medical School, Houston, TX, 77030, USA.

The survival and function of brain cells requires uninterrupted ATP synthesis. Different brain structures subserve distinct neurological functions, and therefore have different energy production/consumption requirements. Typically, mitochondrial function is assessed following their isolation from relatively large amounts of starting tissue, making it difficult to ascertain energy production/failure in small anatomical locations. In order to overcome this limitation, we have developed and optimized a method to measure mitochondrial function in brain tissue biopsy punches excised from anatomically defined brain structures, including white matter tracts. We describe the procedures for maintaining tissue viability prior to performing the biopsy punches, as well as provide guidance for optimizing punch size and the drug doses needed to assess various aspects of mitochondrial respiration. We demonstrate that our method can be used to measure mitochondrial respiration in anatomically defined subfields within the rat hippocampus. Using this method, we present experimental results which show that a mild traumatic brain injury (mTBI, often referred to as concussion) causes differential mitochondrial responses within these hippocampal subfields and the corpus callosum, novel findings that would have been difficult to obtain using traditional mitochondrial isolation methods. Our method is easy to implement and will be of interest to researchers working in the field of brain bioenergetics and brain diseases.
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http://dx.doi.org/10.1038/s41598-020-69867-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7413397PMC
August 2020

Early versus Late Profiles of Inflammatory Cytokines after Mild Traumatic Brain Injury and Their Association with Neuropsychological Outcomes.

J Neurotrauma 2021 01 5;38(1):53-62. Epub 2020 Aug 5.

Department of Neurosurgery, Baylor College of Medicine, Houston, Texas, USA.

Despite pre-clinical evidence for the role of inflammation in traumatic brain injury (TBI), there is limited data on inflammatory biomarkers in mild TBI (mTBI). In this study, we describe the profile of plasma inflammatory cytokines and explore associations between these cytokines and neuropsychological outcomes after mTBI. Patients with mTBI with negative computed tomography and orthopedic injury (OI) controls without mTBI were prospectively recruited from emergency rooms at three trauma centers. Plasma inflammatory cytokine levels were measured from venous whole-blood samples that were collected at enrollment (within 24 h of injury) and at 6 months after injury. Neuropsychological tests were performed at 1 week, 1 month, 3 months, and 6 months after the injury. Multivariate regression analysis was performed to identify associations between inflammatory cytokines and neuropsychological outcomes. A total of 53 mTBI and 24 OI controls were included in this study. The majority of patients were male (62.3%), and injured in motor vehicle accidents (37.7%). Plasma interleukin (IL)-2 ( = 0.01) and IL-6 ( = 0.01) within 24 h post-injury were significantly higher for mTBI patients compared with OI controls. Elevated plasma IL-2 at 24 h was associated with more severe 1-week post-concussive symptoms ( = 0.001). At 6 months, elevated plasma IL-10 was associated with greater depression scores ( = 0.004) and more severe post-traumatic stress disorder (PTSD) symptoms ( = 0.001). Plasma cytokine levels (within 24 h and at 6 months post-injury) were significantly associated with early and late post-concussive symptoms, PTSD, and depression scores after mTBI. These results highlight the potential role of inflammation in the pathophysiology of post-traumatic symptoms after mTBI.
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http://dx.doi.org/10.1089/neu.2019.6979DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7757539PMC
January 2021

Traumatic brain injury and hippocampal neurogenesis: Functional implications.

Exp Neurol 2020 09 3;331:113372. Epub 2020 Jun 3.

The Department of Neurobiology and Anatomy, University of Texas McGovern Medical School, Houston, TX 77030, United States of America. Electronic address:

In the adult brain, self-renewing radial-glia like (RGL) progenitor cells have been shown to reside in the subventricular zone and the subgranular zone of the hippocampus. A large body of evidence shows that experiences such as learning, enriched environment and stress can alter proliferation and differentiation of RGL progenitor cells. The progenitor cells present in the subgranular zone of the hippocampus divide to give rise to newborn neurons that migrate to the dentate gyrus where they differentiate into adult granule neurons. These newborn neurons have been found to have a unique role in certain types of hippocampus-dependent learning and memory, including goal-directed behaviors that require pattern separation. Experimental traumatic brain injury (TBI) in rodents has been shown to alter hippocampal neurogenesis, including triggering the acute loss of newborn neurons, as well as progenitor cell hyper-proliferation. In this review, we discuss the role of hippocampal neurogenesis in learning and memory. Furthermore, we review evidence for the molecular mechanisms that contribute to newborn neuron loss, as well as increased progenitor cell proliferation after TBI. Finally, we discuss strategies aimed at enhancing neurogenesis after TBI and their possible therapeutic benefits.
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http://dx.doi.org/10.1016/j.expneurol.2020.113372DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7803458PMC
September 2020

Sarm1 loss reduces axonal damage and improves cognitive outcome after repetitive mild closed head injury.

Exp Neurol 2020 05 18;327:113207. Epub 2020 Jan 18.

Department of Neurobiology and Anatomy, the University of Texas McGovern Medical School, Houston, TX 77225, United States of America. Electronic address:

One of the consistent pathologies associated with both clinical and experimental traumatic brain injury is axonal injury, especially following mild traumatic brain injury (or concussive injury). Several lines of experimental evidence have demonstrated a role for NAD+ metabolism in axonal degeneration. One of the enzymes that metabolizes NAD+ in axons is Sarm1 (Sterile Alpha and TIR Motif Containing 1), and its activity is thought to play a key role in axonal degeneration. Using a Sarm1 knock-out mouse, we examined if loss of Sarm1 offers axonal injury protection and improves cognitive outcome after repeated mild closed head injury (rmCHI). Our results indicate that rmCHI caused white matter damage that can be observed in the corpus callosum, cingulum bundle, alveus of the hippocampus, and fimbria of the fornix of wild-type mice. These pathological changes were markedly reduced in injured Sarm1 mice. Interestingly, the activation of astrocytes and microglia was also attenuated in the areas with white matter damage, suggesting reduced inflammation. Associated with these improved pathological outcomes, injured Sarm1 mice performed significantly better in both motor and cognitive tasks. Taken together, our results suggest that strategies aimed at inhibiting Sarm1 and/or restoring NAD+ levels in injured axons may have therapeutic utility.
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http://dx.doi.org/10.1016/j.expneurol.2020.113207DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7959192PMC
May 2020

Loss of PTEN-induced kinase 1 (Pink1) reduces hippocampal tyrosine hydroxylase and impairs learning and memory.

Exp Neurol 2020 01 23;323:113081. Epub 2019 Oct 23.

Department of Neurobiology and Anatomy, The University of Texas McGovern Medical School, Houston, TX 77225, United States of America. Electronic address:

Phosphatase and tensin homolog (PTEN)-induced kinase 1 (Pink1) is involved in mitochondrial quality control, which is essential for maintaining energy production and minimizing oxidative damage from dysfunctional/depolarized mitochondria. Pink1 mutations are the second most common cause of autosomal recessive Parkinson's disease (PD). In addition to characteristic motor impairments, PD patients also commonly exhibit cognitive impairments. As the hippocampus plays a prominent role in cognition, we tested if loss of Pink1 in mice influences learning and memory. While wild-type mice were able to perform a contextual discrimination task, age-matched Pink1 knockout (Pink1) mice showed an impaired ability to differentiate between two similar contexts. Similarly, Pink1 mice performed poorly in a delayed alternation task as compared to age-matched controls. Poor performance in these cognitive tasks was not the result of overt hippocampal pathology. However, a significant reduction in hippocampal tyrosine hydroxylase (TH) protein levels was detected in the Pink1 mice. This decrease in hippocampal TH levels was also associated with reduced DOPA decarboxylase and dopamine D2 receptor levels, but not post-synaptic dopamine D1 receptor levels. These presynaptic changes appeared to be selective for dopaminergic fibers as hippocampal dopamine beta hydroxylase, choline acetyltransferase, and tryptophan hydroxylase levels were unchanged in Pink1 mice. Administration of the dopamine D1 receptor agonist SKF38393 to Pink1 mice was found to improve performance in the context discrimination task. Taken together, our results show that Pink1 loss may alter dopamine signaling in the hippocampus, which could be a contributing mechanism for the observed learning and memory impairments.
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http://dx.doi.org/10.1016/j.expneurol.2019.113081DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6984002PMC
January 2020

Mild Traumatic Brain Injury Decreases Spatial Information Content and Reduces Place Field Stability of Hippocampal CA1 Neurons.

J Neurotrauma 2020 01 11;37(2):227-235. Epub 2019 Oct 11.

Department of Neurobiology and Anatomy, The University of Texas McGovern Medical School, Houston, Texas.

Both clinical and experimental studies have reported that mild traumatic brain injury (mTBI) can result in cognitive impairments in the absence of overt brain damage. Whether these impairments result from neuronal dysfunction/altered plasticity is an area that has received limited attention. In this study, we recorded activity of neurons in the cornu Ammonis (CA)1 subfield of the hippocampus in sham and mild lateral fluid percussion injured (mFPI) rats while these animals were performing an object location task. Electrophysiology results showed that the number of excitatory neurons encoding spatial information (i.e., place cells) was reduced in mFPI rats, and that these cells had broader and less stable place fields. Additionally, the in-field firing rate of place cells in sham operated, but not in mFPI, animals increased when objects within the testing arena were moved. Immunostaining indicated no visible damage or overall neuronal loss in mFPI brain sections. However, a reduction in the number of parvalbumin-positive inhibitory neurons in the CA1 subfield of mFPI animals was observed, suggesting that this reduction could have influenced place cell physiology. Alterations in spatial information content, place cell stability, and activity in mFPI rats coincided with poor performance in the object location task. These results indicate that altered place cell physiology may underlie the hippocampus-dependent cognitive impairments that result from mTBI.
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http://dx.doi.org/10.1089/neu.2019.6766DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6964805PMC
January 2020

Traumatic Brain Injury Induces Tau Aggregation and Spreading.

J Neurotrauma 2020 01 28;37(1):80-92. Epub 2019 Aug 28.

Mitchell Center for Alzheimer's Disease and Related Brain Disorders, Department of Neurology, The University of Texas Health Science Center at Houston, Houston, Texas.

The misfolding and aggregation of tau protein into neurofibrillary tangles is the main underlying hallmark of tauopathies. Most tauopathies have a sporadic origin and can be associated with multiple risk factors. Traumatic brain injury (TBI) has been suggested as a risk factor for tauopathies by triggering disease onset and facilitating its progression. Several studies indicate that TBI seems to be a risk factor to development of Alzheimer disease and chronic traumatic encephalopathy, because there is a relationship of TBI severity and propensity to development of these illnesses. In this study, we evaluated whether moderate to severe TBI can trigger the initial formation of pathological tau that would induce the development of the pathology throughout the brain. To this end, we subjected tau transgenic mice to TBI and assessed tau phosphorylation and aggregation pattern to create a spatial heat map of tau deposition and spreading in the brain. Our results suggest that brain injured tau transgenic mice have an accelerated tau pathology in different brain regions that increases over time compared with sham mice. The appearance of pathological tau occurs in regions distant to the injury area that are connected synaptically, suggesting dissemination of tau aggregates. Overall, this work posits TBI as a risk factor for tauopathies through the induction of tau hyperphosphorylation and aggregation.
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http://dx.doi.org/10.1089/neu.2018.6348DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6921297PMC
January 2020

Coordinating what we've learned about memory consolidation: Revisiting a unified theory.

Neurosci Biobehav Rev 2019 05 18;100:77-84. Epub 2019 Feb 18.

Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center, Houston, TX, 77030, USA.

According to traditional systems consolidation theories neocortical long-term plasticity (i.e., cellular consolidation) lags behind, and is dependent upon, hippocampal long-term plasticity. In this review, we examine accumulating evidence that local neocortical and hippocampal cellular consolidation occurs with a similar time-course. The implication is that the rate-limiting step for systems consolidation is the time it takes for cellular consolidation in longer connections throughout a more distributed extra-hippocampal system that comes to coordinate distributed neocortical activity during recall. The hippocampus is, thus, crucial for the development of this extra-hippocampal coordinating system, and acts to coordinate activities crucial for recall until it develops. Recent work on schema formation, engram cells, and the role of sleep in consolidation add substantial evidence for this "unified theory" of systems and cellular consolidation. Here, we discuss this evidence, its implications, and consider remaining questions.
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http://dx.doi.org/10.1016/j.neubiorev.2019.02.010DOI Listing
May 2019

Carnosic Acid Improves Outcome after Repetitive Mild Traumatic Brain Injury.

J Neurotrauma 2019 07 26;36(13):2147-2152. Epub 2019 Mar 26.

Department of Neurobiology and Anatomy, the University of Texas McGovern Medical School, Houston, Texas.

In the majority of cases, the cognitive and behavioral impairments resulting from a mild traumatic brain injury (TBI) (also referred to as concussion) wane within days to weeks. In contrast, these impairments can persist for months to years after repetitive mild TBI (rmTBI). The cellular and molecular mechanisms underlying these impairments are not well understood. In the present study, we examined the consequences of rmTBI (three weight drops each separated by 72 h) on brain tissue respiration, pathology, and cognitive performance in mice. The transcription factor nuclear factor-erythroid 2-realted factor 2 (Nrf2) has been demonstrated to enhance the expression of numerous cytoprotective genes. Carnosic acid (CA) has been shown to activate Nrf2 and suppress the proinflammatory transcription factor nuclear factor kappa B (NF-κB). Because contemporaneous activation of cytoprotective genes and inhibition of proinflammatory genes can be beneficial, we questioned whether CA can be used to mitigate the pathobiology of rmTBI. The rmTBI increased hippocampal adenosine triphosphate-linked tissue respiration and proton leak that were unaffected by CA treatment. The rmTBI also caused significant motor and cognitive dysfunction, as tested using the foot fault, Barnes maze, and novel object recognition tasks. These impairments occurred in the absence of visible neuronal or dendritic loss. Post-rmTBI administration of CA significantly improved motor and cognitive function, and decreased Gfap and Iba1 immunoreactivities within white matter tracks. Taken together, these results show that rmTBI can cause cognitive impairments in the absence of overt neuronal pathologies, and post-injury treatment with CA can lessen some of these impairments.
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http://dx.doi.org/10.1089/neu.2018.6155DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6602106PMC
July 2019

Morphology of mitochondria in spatially restricted axons revealed by cryo-electron tomography.

PLoS Biol 2018 09 17;16(9):e2006169. Epub 2018 Sep 17.

Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, Texas, United States of America.

Neurons project axons to local and distal sites and can display heterogeneous morphologies with limited physical dimensions that may influence the structure of large organelles such as mitochondria. Using cryo-electron tomography (cryo-ET), we characterized native environments within axons and presynaptic varicosities to examine whether spatial restrictions within these compartments influence the morphology of mitochondria. Segmented tomographic reconstructions revealed distinctive morphological characteristics of mitochondria residing at the narrowed boundary between presynaptic varicosities and axons with limited physical dimensions (approximately 80 nm), compared to mitochondria in nonspatially restricted environments. Furthermore, segmentation of the tomograms revealed discrete organizations between the inner and outer membranes, suggesting possible independent remodeling of each membrane in mitochondria at spatially restricted axonal/varicosity boundaries. Thus, cryo-ET of mitochondria within axonal subcompartments reveals that spatial restrictions do not obstruct mitochondria from residing within them, but limited available space can influence their gross morphology and the organization of the inner and outer membranes. These findings offer new perspectives on the influence of physical and spatial characteristics of cellular environments on mitochondrial morphology and highlight the potential for remarkable structural plasticity of mitochondria to adapt to spatial restrictions within axons.
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http://dx.doi.org/10.1371/journal.pbio.2006169DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6160218PMC
September 2018

REST overexpression in mice causes deficits in spontaneous locomotion.

Sci Rep 2018 08 14;8(1):12083. Epub 2018 Aug 14.

Departments of Genetics, The University of Texas MD Anderson Cancer Center, Houston, TX, 77030, USA.

Overexpression of REST has been implicated in brain tumors, ischemic insults, epilepsy, and movement disorders such as Huntington's disease. However, owing to the lack of a conditional REST overexpression animal model, the mechanism of action of REST overexpression in these disorders has not been established in vivo. We created a REST overexpression mouse model using the human REST (hREST) gene. Our results using these mice confirm that hREST expression parallels endogenous REST expression in embryonic mouse brains. Further analyses indicate that REST represses the dopamine receptor 2 (Drd2) gene, which encodes a critical nigrostriatal receptor involved in regulating movement, in vivo. Overexpression of REST using Drd2-Cre in adult mice results in increased REST and decreased DRD2 expression in the striatum, a major site of DRD2 expression, and phenocopies the spontaneous locomotion deficits seen upon global DRD2 deletion or specific DRD2 deletion from indirect-pathway medium spiny neurons. Thus, our studies using this mouse model not only reveal a new function of REST in regulating spontaneous locomotion but also suggest that REST overexpression in DRD2-expressing cells results in spontaneous locomotion deficits.
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http://dx.doi.org/10.1038/s41598-018-29441-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6092433PMC
August 2018

Cell type-dependent effects of ellagic acid on cellular metabolism.

Biomed Pharmacother 2018 Oct 11;106:411-418. Epub 2018 Jul 11.

Department of Biochemistry and Molecular Biology, McGovern Medical School at UTHealth, 6431 Fannin Street, Houston, TX, 77030, United States. Electronic address:

Ellagic acid is a botanical polyphenol which has been shown to have numerous effects on cellular function. Ellagic acid can induce apoptosis and inhibit the proliferation of various cancer cell types in vitro and in vivo. As such, ellagic acid has attracted significant interest as a potential chemotherapeutic compound. One mechanism by which ellagic acid has been proposed to affect cellular physiology is by regulating metabolic pathways. Here we show the dose-dependent effects of ellagic acid on cellular energy production and downstream induction of the apoptotic program in HEK293, HeLa, MCF7, and HepG2 cells. At physiologically relevant doses, ellagic acid has pleiotropic and cell-type specific effects on mitochondrial function. At high doses ellagic acid can also influence glycolytic pathways and induce cell death. Our results demonstrate that ellagic acid can influence mitochondrial function at therapeutically relevant concentrations. The observed effects of ellagic acid on cellular respiration are complex and cell type-specific, which may limit the chemotherapeutic utility of this compound.
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http://dx.doi.org/10.1016/j.biopha.2018.06.142DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6115283PMC
October 2018

Endothelial Cell Dysfunction and Injury in Subarachnoid Hemorrhage.

Mol Neurobiol 2019 Mar 7;56(3):1992-2006. Epub 2018 Jul 7.

The Vivian L. Smith Department of Neurosurgery, University of Texas Health Science Center, 6431 Fannin St., Houston, TX, 77030, USA.

In the brain, vascular endothelial cells conserve blood viscosity, control blood flow, and form the interface between central nervous system and circulating blood. Clinical outcome after aneurysmal subarachnoid hemorrhage is linked to early brain injury, cerebral vasospasm, and other causes of delayed cerebral ischemia. The cerebral vasculature remains a unique target for therapies since it becomes rapidly disrupted after subarachnoid hemorrhage, and damage to the blood vessels continues into the delayed injury phase. The current failure of therapies to improve clinical outcome warrants a re-evaluation of current therapeutic approaches. The mechanisms of endothelial cell injury and blood-brain barrier breakdown are critical to the pathway of cerebral injury, and an improved understanding of these mechanisms may lead to novel therapeutic targets. This review provides an update on the current understanding of endothelial cell injury following aneurysmal subarachnoid hemorrhage, including blood-brain barrier dysfunction.
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http://dx.doi.org/10.1007/s12035-018-1213-7DOI Listing
March 2019

Unique Contribution of Haptoglobin and Haptoglobin Genotype in Aneurysmal Subarachnoid Hemorrhage.

Front Physiol 2018 31;9:592. Epub 2018 May 31.

Department of Anesthesiology, University of Florida, College of Medicine, Gainesville, FL, United States.

Survivors of cerebral aneurysm rupture are at risk for significant morbidity and neurological deficits. Much of this is related to the effects of blood in the subarachnoid space which induces an inflammatory cascade with numerous downstream consequences. Recent clinical trials have not been able to reduce the toxic effects of free hemoglobin or improve clinical outcome. One reason for this may be the inability to identify patients at high risk for neurologic decline. Recently, haptoglobin genotype has been identified as a pertinent factor in diabetes, sickle cell, and cardiovascular disease, with the Hp 2-2 genotype contributing to increased complications. Haptoglobin is a protein synthesized by the liver that binds free hemoglobin following red blood cell lysis, and in doing so, prevents hemoglobin induced toxicity and facilitates clearance. Clinical studies in patients with subarachnoid hemorrhage indicate that Hp 2-2 patients may be a high-risk group for hemorrhage related complications and poor outcome. We review the relevance of haptoglobin in subarachnoid hemorrhage and discuss the effects of genotype and expression levels on the known mechanisms of early brain injury (EBI) and cerebral ischemia after aneurysm rupture. A better understanding of haptoglobin and its role in preventing hemoglobin related toxicity should lead to novel therapeutic avenues.
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http://dx.doi.org/10.3389/fphys.2018.00592DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5991135PMC
May 2018

Increased Levels of Circulating Glial Fibrillary Acidic Protein and Collapsin Response Mediator Protein-2 Autoantibodies in the Acute Stage of Spinal Cord Injury Predict the Subsequent Development of Neuropathic Pain.

J Neurotrauma 2018 11 5;35(21):2530-2539. Epub 2018 Jul 5.

1 The Vivian L. Smith Department of Neurosurgery, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth) , Houston, Texas.

Neuropathic pain develops in 40-70% of spinal cord injury (SCI) patients and markedly compromises quality of life. We examined plasma from SCI patients for autoantibodies to glial fibrillary acidic protein (GFAP) and collapsin response mediator protein-2 (CRMP2) and evaluated their relationship to the development of neuropathic pain. In study 1, plasma samples and clinical data from 80 chronic SCI patients (1-41 years post-SCI) were collected and screened for GFAP autoantibodies (GFAPab). Results from study 1 indicated that GFAPab were present in 34 of 80 (42.5%) patients, but circulating levels did not correlate with the occurrence of neuropathic pain. In study 2, longitudinal plasma samples and clinical data were collected from 38 acute SCI patients. The level of GFAPab measured at 16 ± 7 days post-SCI was found to be significantly higher in patients that subsequently developed neuropathic pain (within 6 months post-SCI) than patients who did not (T = 219; p = 0.02). In study 3, we identified CRMP2 as an autoantibody target (CRMP2ab) in 23% of acute SCI patients. The presence of GFAPab and/or CRMP2ab increased the odds of subsequently developing neuropathic pain within 6 months of injury by 9.5 times (p = 0.006). Our results suggest that if a causal link can be established between these autoantibodies and the development of neuropathic pain, strategies aimed at reducing the circulating levels of these autoantibodies may have therapeutic value.
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http://dx.doi.org/10.1089/neu.2018.5675DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6909673PMC
November 2018

Endoplasmic Reticulum Stress Contributes to the Loss of Newborn Hippocampal Neurons after Traumatic Brain Injury.

J Neurosci 2018 02 31;38(9):2372-2384. Epub 2018 Jan 31.

Department of Neurobiology and Anatomy, the University of Texas McGovern Medical School, Houston, Texas 77225

Adult hippocampal neurogenesis has been shown to be required for certain types of cognitive function. For example, studies have shown that these neurons are critical for pattern separation, the ability to store similar experiences as distinct memories. Although traumatic brain injury (TBI) has been shown to cause the loss of newborn hippocampal neurons, the signaling pathway(s) that triggers their death is unknown. Endoplasmic reticulum (ER) stress activates the PERK-eIF2α pathway that acts to restore ER function and improve cell survival. However, unresolved/intense ER stress activates C/EBP homologous protein (CHOP), leading to cell death. We show that TBI causes the death of hippocampal newborn neurons via CHOP. Using CHOP KO mice, we show that loss of CHOP markedly reduces newborn neuron loss after TBI. Injured CHOP mice performed significantly better in a context fear discrimination task compared with injured wild-type mice. In contrast, the PERK inhibitor GSK2606414 exacerbated doublecortin cell loss and worsened contextual discrimination. Administration of guanabenz (which reduces ER stress) to injured male rats reduced the loss of newborn neurons and improved one-trial contextual fear memory. Interestingly, we also found that the surviving newborn neurons in brain-injured animals had dendritic loss, which was not observed in injured CHOP KO mice or in animals treated with guanabenz. These results indicate that ER stress plays a key role in the death of newborn neurons after TBI. Further, these findings indicate that ER stress can alter dendritic arbors, suggesting a role for ER stress in neuroplasticity and dendritic pathologies. The hippocampus, a structure in the temporal lobe, is critical for learning and memory. The hippocampus is one of only two areas in which neurons are generated in the adult brain. These newborn neurons are required for certain types of memory, and are particularly vulnerable to traumatic brain injury (TBI). However, the mechanism(s) that causes the loss of these cells after TBI is poorly understood. We show that endoplasmic reticulum (ER) stress pathways are activated in newborn neurons after TBI, and that manipulation of the CHOP cascade improves newborn neuron survival and cognitive outcome. These results suggest that treatments that prevent/resolve ER stress may be beneficial in treating TBI-triggered memory dysfunction.
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http://dx.doi.org/10.1523/JNEUROSCI.1756-17.2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5830522PMC
February 2018

A role for autophagy in long-term spatial memory formation in male rodents.

J Neurosci Res 2018 03 12;96(3):416-426. Epub 2017 Dec 12.

Department of Neurobiology and Anatomy, the University of Texas McGovern Medical School, Houston, Texas, USA.

A hallmark of long-term memory formation is the requirement for protein synthesis. Administration of protein synthesis inhibitors impairs long-term memory formation without influencing short-term memory. Rapamycin is a specific inhibitor of target of rapamycin complex 1 (TORC1) that has been shown to block protein synthesis and impair long-term memory. In addition to regulating protein synthesis, TORC1 also phosphorylates Unc-51-like autophagy activating kinase-1 (Ulk-1) to suppress autophagy. As autophagy can be activated by rapamycin (and rapamycin inhibits long-term memory), our aim was to test the hypothesis that autophagy inhibitors would enhance long-term memory. To examine if learning alters autophagosome number, we used male reporter mice carrying the GFP-LC3 transgene. Using these mice, we observed that training in the Morris water maze task increases the number of autophagosomes, a finding contrary to our expectations. For learning and memory studies, male Long Evans rats were used due to their relatively larger size (compared to mice), making it easier to perform intrahippocampal infusions in awake, moving animals. When the autophagy inhibitors 3-methyladenine (3-MA) or Spautin-1 were administered bilaterally into the hippocampii prior to training in the Morris water maze task, the drugs did not alter learning. In contrast, when memory was tested 24 hours later by a probe trial, significant impairments were observed. In addition, intrahippocampal infusion of an autophagy activator peptide (TAT-Beclin-1) improved long-term memory. These results indicate that autophagy is not necessary for learning, but is required for long-term memory formation.
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http://dx.doi.org/10.1002/jnr.24121DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6425965PMC
March 2018

Post-Injury Administration of Galantamine Reduces Traumatic Brain Injury Pathology and Improves Outcome.

J Neurotrauma 2018 01 18;35(2):362-374. Epub 2017 Dec 18.

Department of Neurobiology and Anatomy, The University of Texas McGovern Medical School , Houston, Texas.

Acetylcholine is an excitatory neurotransmitter in the central nervous system that plays a key role in cognitive function, including learning and memory. Previous studies have shown that experimental traumatic brain injury (TBI) reduces cholinergic neurotransmission, decreases evoked release of acetylcholine, and alters cholinergic receptor levels. Galantamine (U.S. Food and Drug Administration approved for the treatment of vascular dementia and Alzheimer's disease) has been shown to inhibit acetylcholinesterase activity and allosterically potentiate nicotinic receptor signaling. We investigated whether acute administration of galantamine can reduce TBI pathology and improve cognitive function tested days after the termination of the drug treatment. Post-injury administration of galantamine was found to decrease TBI-triggered blood-brain barrier (BBB) permeability (tested 24 h post-injury), attenuate the loss of both GABAergic and newborn neurons in the ipsilateral hippocampus, and improve hippocampal function (tested 10 days after termination of the drug treatment). Specifically, significant improvements in the Morris water maze, novel object recognition, and context-specific fear memory tasks were observed in injured animals treated with galantamine. Although messenger RNAs for both M1 (Nos2, TLR4, and IL-12ß) and M2 (Arg1, CCL17, and Mcr1) microglial phenotypes were elevated post-TBI, galantamine treatment did not alter microglial polarization tested 24 h and 6 days post-injury. Taken together, these findings support the further investigation of galantamine as a treatment for TBI.
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http://dx.doi.org/10.1089/neu.2017.5102DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5784795PMC
January 2018

Resuscitation of Hypotensive Traumatic Brain Injured Animals With Spray-Dried Plasma Does Not Adversely Alter Physiology and Improves Blood-Brain Barrier Function.

Mil Med 2017 07;182(7):e1706-e1711

Department of Neurobiology and Anatomy, The University of Texas McGovern Medical School Houston, 6431 Fannin, Houston, TX 77030-1501.

Introduction: According to the Defense and Veterans Brain Injury Center and the Armed Forces Health Surveillance Center, the number of soldiers who have sustained a traumatic brain injury (TBI) has risen dramatically over the past decade. Studies have shown that brain damage can be exacerbated if blood loss occurs (often occurring in polytrauma). As blood supply is critical for brain function and survival, TBI patients must be properly resuscitated to maintain blood volume, blood pressure, and cerebral perfusion. Recent studies have suggested that blood loss can damage the vascular endothelium and enhance blood-brain barrier (BBB) permeability. Brain endothelial cells and the tight junctions between them are key structural components of the BBB. As the BBB is critical for isolating the brain from potential pathogens and for regulating the influx of molecules into the brain, evaluation of resuscitation fluids for their efficacy to improve BBB function has clinical relevance. Although whole blood and fresh frozen plasma (FFP) contain the essential coagulation factors, ions, and other factors, the transport and storage of these products in remote, austere environments can be challenging. The use of spray-dried plasma (SDP) has several advantages including storage at ambient temperature, can be readily reconstituted before use, and infectious materials can be inactivated during the drying process. In this study, we compared FFP and SDP for their effects on blood pressure, cerebral blood flow, BBB integrity, and markers of endothelial cells and tight junction proteins, in TBI animals with blood loss.

Materials And Methods: All procedures were reviewed and approved by the UTHealth animal welfare committee. Sprague Dawley rats received controlled cortical impact brain injury followed by removal of 25% blood volume. Animals were resuscitated 40 minutes later with either FFP or concentrated SDP (Resusix) Heart rate and blood pressure were monitored continuously using catheters implanted into the femoral artery. Cerebral perfusion was assessed using a scanning laser Doppler device. Twenty-four hours after the injury and resuscitation with either FFP or SDP, BBB integrity were monitored by measuring the amount of Evans Blue dye in the injured brain following its intravenous administration. As this dye is excluded from the uninjured brain, its presence in the injured brain is an indicator of BBB breakdown. In addition, von Willebrand Factor immunohistochemistry was used to examine endothelial cell loss, whereas claudin-5 immunohistochemistry was used to assess the loss of tight junctions, in FFP- and SDP-resuscitated TBI animals.

Results: Our results show that post-TBI resuscitation with FFP and SDP had similar influences on cardiovascular physiology and cerebral perfusion. Resuscitation with SDP after TBI was found to decrease BBB permeability as indicated by reduced Evans Blue dye extravasation, and increased levels of von Willebrand Factor and claudin-5, as compared to resuscitation with FFP.

Conclusions: These preclinical results show that resuscitation with SDP may be superior to FFP, and support the further evaluation of this product as a resuscitation fluid for polytrauma patients with TBI.
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http://dx.doi.org/10.7205/MILMED-D-16-00185DOI Listing
July 2017

Mild Traumatic Brain Injury Reduces Spine Density of Projection Neurons in the Medial Prefrontal Cortex and Impairs Extinction of Contextual Fear Memory.

J Neurotrauma 2018 01 28;35(1):149-156. Epub 2017 Aug 28.

Department of Neurobiology & Anatomy, The University of Texas McGovern Medical School , Houston, Texas.

Epidemiology studies have found that a comorbidity exists between traumatic brain injury (TBI) and stress-related disorders. However, the anatomical and cellular bases for this association is poorly understood. An inability to extinguish the memory of a traumatic event lies at the core of many stress-related disorders. Experimental studies have shown that the medial pre-frontal cortex (mPFC), especially the infralimbic (IL) cortex, is required for extinction and for storing the memory of extinction. The output from the central nucleus of amygdala projects to the lateral hypothalamus, paraventricular nucleus, and central gray to regulate heart rate, stress hormone release, and freezing behavior, respectively. Projection neurons of the IL (layers II/III pyramidal neurons) are thought to stimulate GABAergic neurons in the amygdala, which, in turn, inhibit central amygdala output and reduce fear expression. Thus, loss and/or altered morphology of projection neurons of IL as a result of a mild TBI (mTBI) can compromise their ability to effectively inhibit the central amygdala, allowing the original fear memory to drive behavior. Using lateral mild fluid percussion injury (mFPI) in rats, we found that mFPI did not reduce neuronal numbers in the IL, but caused a significant reduction in overall dendritic spine density of both basal and apical dendrites on layer II/III pyramidal neurons. Spine numbers on layer V/VI pyramidal neurons were not significantly changed as a result of mFPI. The reduction in spine density on layer II/III pyramidal neurons we observed may diminish the efficacy of these neurons to inhibit the output of the central amygdala, thereby reducing the ability of the IL to suppress fear responses after extinction training. Consistent with this, mFPI rats display enhanced freezing behavior during and after extinction training as compared to sham-operated controls, although the ability to form contextual fear memories was not impaired. These results may have implications in stress-related disorders associated with mTBI.
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http://dx.doi.org/10.1089/neu.2016.4898DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5757078PMC
January 2018

Treatment of Severe Adult Traumatic Brain Injury Using Bone Marrow Mononuclear Cells.

Stem Cells 2017 04 23;35(4):1065-1079. Epub 2016 Nov 23.

Department of Neurosurgery, The University of Texas McGovern Medical School, Houston, Texas, USA.

Preclinical studies using bone marrow derived cells to treat traumatic brain injury have demonstrated efficacy in terms of blood-brain barrier preservation, neurogenesis, and functional outcomes. Phase 1 clinical trials using bone marrow mononuclear cells infused intravenously in children with severe traumatic brain injury demonstrated safety and potentially a central nervous system structural preservation treatment effect. This study sought to confirm the safety, logistic feasibility, and potential treatment effect size of structural preservation/inflammatory biomarker mitigation in adults to guide Phase 2 clinical trial design. Adults with severe traumatic brain injury (Glasgow Coma Scale 5-8) and without signs of irreversible brain injury were evaluated for entry into the trial. A dose escalation format was performed in 25 patients: 5 controls, followed 5 patients in each dosing cohort (6, 9, 12 ×10 cells/kg body weight), then 5 more controls. Bone marrow harvest, cell processing to isolate the mononuclear fraction, and re-infusion occurred within 48 hours after injury. Patients were monitored for harvest-related hemodynamic changes, infusional toxicity, and adverse events. Outcome measures included magnetic resonance imaging-based measurements of supratentorial and corpus callosal volumes as well as diffusion tensor imaging-based measurements of fractional anisotropy and mean diffusivity of the corpus callosum and the corticospinal tract at the level of the brainstem at 1 month and 6 months postinjury. Functional and neurocognitive outcomes were measured and correlated with imaging data. Inflammatory cytokine arrays were measured in the plasma pretreatment, posttreatment, and at 1 and 6 month follow-up. There were no serious adverse events. There was a mild pulmonary toxicity of the highest dose that was not clinically significant. Despite the treatment group having greater injury severity, there was structural preservation of critical regions of interest that correlated with functional outcomes. Key inflammatory cytokines were downregulated. Treatment of severe, adult traumatic brain injury using an intravenously delivered autologous bone marrow mononuclear cell infusion is safe and logistically feasible. There appears to be a treatment signal as evidenced by central nervous system structural preservation, consistent with previous pediatric trial data. Inflammatory biomarkers are downregulated after cell infusion. Stem Cells 2016 Video Highlight: https://youtu.be/UiCCPIe-IaQ Stem Cells 2017;35:1065-1079.
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http://dx.doi.org/10.1002/stem.2538DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5367945PMC
April 2017

Functional Connectivity Is Altered in Concussed Adolescent Athletes Despite Medical Clearance to Return to Play: A Preliminary Report.

Front Neurol 2016 25;7:116. Epub 2016 Jul 25.

Department of Physical Medicine and Rehabilitation, Baylor College of Medicine, Houston, TX, USA; Department of Neurology, Baylor College of Medicine, Houston, TX, USA.

Recovery following sports-related concussion (SRC) is slower and often more complicated in young adolescent athletes than in collegiate players. Further, the clinical decision to return to play is currently based on symptoms and cognitive performance without direct knowledge of brain function. We tested the hypothesis that brain functional connectivity (FC) would be aberrant in recently concussed, asymptomatic athletes who had been cleared to return to play. A seed-based FC analysis measured the FC of the default mode network (DMN) (seeds = anterior cingulate cortex, posterior cingulate cortex (PCC), right lateral parietal cortex, and left lateral parietal cortex) 30 days after SRC in asymptomatic high school athletes cleared to return to play (n = 13) and was compared to the FC of high school athletes with orthopedic injury (OI) (n = 13). The SRC group demonstrated greater FC than the OI group between the PCC and the ventral lateral prefrontal cortex, as well as between the right lateral parietal cortex and lateral temporal cortex (with regions both outside of and within the DMN). Additionally, the OI group demonstrated greater FC than the SRC group between right lateral parietal cortex and supramarginal gyrus. When relating the FC results to verbal memory performance approximately 1 week and 1 month after injury, significantly different between-group relations were found for the posterior cingulate and right lateral parietal cortex seeds. However, the groups did not differ in verbal memory at 1 month. We suggest that changes in FC are apparent 1-month post-SRC despite resolution of post-concussion symptoms and recovery of cognitive performance in adolescent athletes cleared to return to play.
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http://dx.doi.org/10.3389/fneur.2016.00116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4958621PMC
August 2016

Traumatic brain injury decreases AMP-activated protein kinase activity and pharmacological enhancement of its activity improves cognitive outcome.

J Neurochem 2016 10 1;139(1):106-19. Epub 2016 Aug 1.

Department of Neurobiology and Anatomy, McGovern Medical School, Houston, Texas, USA.

Prolonged metabolic suppression in the brain is a well-characterized secondary pathology of both experimental and clinical traumatic brain injury (TBI). AMP-activated kinase (AMPK) acts as a cellular energy sensor that, when activated, regulates various metabolic and catabolic pathways to decrease ATP consumption and increase ATP synthesis. As energy availability after TBI is suppressed, we questioned if increasing AMPK activity after TBI would improve cognitive outcome. TBI was delivered using the electromagnetic controlled cortical impact model on male Sprague-Dawley rats (275-300 g) and C57BL/6 mice (20-25 g). AMPK activity within the injured parietal cortex and ipsilateral hippocampus was inferred by western blots using phospho-specific antibodies. The consequences of acute manipulation of AMPK signaling on cognitive function were assessed using the Morris water maze task. We found that AMPK activity is decreased as a result of injury, as indicated by reduced AMPK phosphorylation and corresponding changes in the phosphorylation of its downstream targets: ribosomal protein S6 and Akt Substrate of 160 kDa (AS160). Increasing AMPK activity after injury using the drugs 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide or metformin did not affect spatial learning, but significantly improved spatial memory. Taken together, our results suggest that decreased AMPK activity after TBI may contribute to the cellular energy crisis in the injured brain, and that AMPK activators may have therapeutic utility. Increased phosphorylation of Thr172 activates AMP-activated protein kinase (AMPK) under conditions of low cellular energy availability. This leads to inhibition of energy consuming, while activating energy generating, processes. Hill et al., present data to indicate that TBI decreases Thr172 phosphorylation and that its stimulation by pharmacological agents offers neuroprotection and improves memory. These results suggest that decreased AMPK phosphorylation after TBI incorrectly signals the injured brain that excess energy is available, thereby contributing to the cellular energy crisis and memory impairments.
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http://dx.doi.org/10.1111/jnc.13726DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5037010PMC
October 2016

Traumatic Brain Injury Alters Methionine Metabolism: Implications for Pathophysiology.

Front Syst Neurosci 2016 29;10:36. Epub 2016 Apr 29.

Department of Neurobiology and Anatomy, UTHealth McGovern Medical School Houston, TX, USA.

Methionine is an essential proteinogenic amino acid that is obtained from the diet. In addition to its requirement for protein biosynthesis, methionine is metabolized to generate metabolites that play key roles in a number of cellular functions. Metabolism of methionine via the transmethylation pathway generates S-adenosylmethionine (SAM) that serves as the principal methyl (-CH3) donor for DNA and histone methyltransferases (MTs) to regulate epigenetic changes in gene expression. SAM is also required for methylation of other cellular proteins that serve various functions and phosphatidylcholine synthesis that participate in cellular signaling. Under conditions of oxidative stress, homocysteine (which is derived from SAM) enters the transsulfuration pathway to generate glutathione, an important cytoprotective molecule against oxidative damage. As both experimental and clinical studies have shown that traumatic brain injury (TBI) alters DNA and histone methylation and causes oxidative stress, we examined if TBI alters the plasma levels of methionine and its metabolites in human patients. Blood samples were collected from healthy volunteers (HV; n = 20) and patients with mild TBI (mTBI; GCS > 12; n = 20) or severe TBI (sTBI; GCS < 8; n = 20) within the first 24 h of injury. The levels of methionine and its metabolites in the plasma samples were analyzed by either liquid chromatography-mass spectrometry or gas chromatography-mass spectrometry (LC-MS or GC-MS). sTBI decreased the levels of methionine, SAM, betaine and 2-methylglycine as compared to HV, indicating a decrease in metabolism through the transmethylation cycle. In addition, precursors for the generation of glutathione, cysteine and glycine were also found to be decreased as were intermediate metabolites of the gamma-glutamyl cycle (gamma-glutamyl amino acids and 5-oxoproline). mTBI also decreased the levels of methionine, α-ketobutyrate, 2 hydroxybutyrate and glycine, albeit to lesser degrees than detected in the sTBI group. Taken together, these results suggest that decreased levels of methionine and its metabolic products are likely to alter cellular function in multiple organs at a systems level.
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http://dx.doi.org/10.3389/fnsys.2016.00036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4850826PMC
May 2016

Altered Mitochondrial Dynamics and TBI Pathophysiology.

Front Syst Neurosci 2016 30;10:29. Epub 2016 Mar 30.

Department of Neurobiology and Anatomy, McGovern Medical School, University of Texas Health Science Center at HoustonHouston, TX, USA; Vivian L. Smith Department of Neurosurgery, McGovern Medical School, University of Texas Health Science Center at HoustonHouston, TX, USA.

Mitochondrial function is intimately linked to cellular survival, growth, and death. Mitochondria not only generate ATP from oxidative phosphorylation, but also mediate intracellular calcium buffering, generation of reactive oxygen species (ROS), and apoptosis. Electron leakage from the electron transport chain, especially from damaged or depolarized mitochondria, can generate excess free radicals that damage cellular proteins, DNA, and lipids. Furthermore, mitochondrial damage releases pro-apoptotic factors to initiate cell death. Previous studies have reported that traumatic brain injury (TBI) reduces mitochondrial respiration, enhances production of ROS, and triggers apoptotic cell death, suggesting a prominent role of mitochondria in TBI pathophysiology. Mitochondria maintain cellular energy homeostasis and health via balanced processes of fusion and fission, continuously dividing and fusing to form an interconnected network throughout the cell. An imbalance of these processes, particularly an excess of fission, can be detrimental to mitochondrial function, causing decreased respiration, ROS production, and apoptosis. Mitochondrial fission is regulated by the cytosolic GTPase, dynamin-related protein 1 (Drp1), which translocates to the mitochondrial outer membrane (MOM) to initiate fission. Aberrant Drp1 activity has been linked to excessive mitochondrial fission and neurodegeneration. Measurement of Drp1 levels in purified hippocampal mitochondria showed an increase in TBI animals as compared to sham controls. Analysis of cryo-electron micrographs of these mitochondria also showed that TBI caused an initial increase in the length of hippocampal mitochondria at 24 h post-injury, followed by a significant decrease in length at 72 h. Post-TBI administration of Mitochondrial division inhibitor-1 (Mdivi-1), a pharmacological inhibitor of Drp1, prevented this decrease in mitochondria length. Mdivi-1 treatment also reduced the loss of newborn neurons in the hippocampus and improved novel object recognition (NOR) memory and context-specific fear memory. Taken together, our results show that TBI increases mitochondrial fission and that inhibition of fission improves hippocampal-dependent learning and memory, suggesting that strategies to reduce fission may have translational value after injury.
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http://dx.doi.org/10.3389/fnsys.2016.00029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4811888PMC
April 2016

Activation of Alpha 7 Cholinergic Nicotinic Receptors Reduce Blood-Brain Barrier Permeability following Experimental Traumatic Brain Injury.

J Neurosci 2016 Mar;36(9):2809-18

Department of Neurobiology and Anatomy, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, Texas 77030.

Unlabelled: Traumatic brain injury (TBI) is a major human health concern that has the greatest impact on young men and women. The breakdown of the blood-brain barrier (BBB) is an important pathological consequence of TBI that initiates secondary processes, including infiltration of inflammatory cells, which can exacerbate brain inflammation and contribute to poor outcome. While the role of inflammation within the injured brain has been examined in some detail, the contribution of peripheral/systemic inflammation to TBI pathophysiology is largely unknown. Recent studies have implicated vagus nerve regulation of splenic cholinergic nicotinic acetylcholine receptor α7 (nAChRa7) signaling in the regulation of systemic inflammation. However, it is not known whether this mechanism plays a role in TBI-triggered inflammation and BBB breakdown. Following TBI, we observed that plasma TNF-α and IL-1β levels, as well as BBB permeability, were significantly increased in nAChRa7 null mice (Chrna7(-/-)) relative to wild-type mice. The administration of exogenous IL-1β and TNF-α to brain-injured animals worsened Evans Blue dye extravasation, suggesting that systemic inflammation contributes to TBI-triggered BBB permeability. Systemic administration of the nAChRa7 agonist PNU-282987 or the positive allosteric modulator PNU-120596 significantly attenuated TBI-triggered BBB compromise. Supporting a role for splenic nAChRa7 receptors, we demonstrate that splenic injection of the nicotinic receptor blocker α-bungarotoxin increased BBB permeability in brain-injured rats, while PNU-282987 injection decreased such permeability. These effects were not seen when α-bungarotoxin or PNU-282987 were administered to splenectomized, brain-injured rats. Together, these findings support the short-term use of nAChRa7-activating agents as a strategy to reduce TBI-triggered BBB permeability.

Significance Statement: Breakdown of the blood-brain barrier (BBB) in response to traumatic brain injury (TBI) allows for the accumulation of circulating fluids and proinflammatory cells in the injured brain. These processes can exacerbate TBI pathology and outcome. While the role of inflammation in the injured tissue has been examined in some detail, the contribution of peripheral inflammation in BBB breakdown and ensuing pathology has not been well defined. We present experimental evidence to indicate that the stimulation of nicotinic acetylcholine α7 receptors (nAChRa7s) can reduce peripheral inflammation and BBB breakdown after TBI. These results suggest that activators of nAChRa7 may have therapeutic utility for the treatment of TBI.
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http://dx.doi.org/10.1523/JNEUROSCI.3197-15.2016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4879217PMC
March 2016