Repetitive mild brain trauma accelerates Abeta deposition, lipid peroxidation, and cognitive impairment in a transgenic mouse model of Alzheimer amyloidosis

The pathophysiology of concussions in youth

Mild traumatic brain injury, especially sport-related concussion, is common among young persons. Consequences of transient pathophysiologic dysfunction must be considered in the context of a developing or immature brain, as must the potential for an accumulation of damage with repeated exposure. This review summarizes the underlying neurometabolic cascade of concussion, with emphasis on the young brain in terms of acute pathophysiology, vulnerability, alterations in plasticity and activation, axonal injury, and cumulative risk from chronic, repetitive damage, and discusses their implications in the context of clinical care for the concussed youth, highlighting areas for future investigation.

A mouse model of human repetitive mild traumatic brain injury

A novel method for the study of repetitive mild traumatic brain injury (rmTBI) that models the most common form of head injury in humans is presented. Existing animal models of TBI impart focal, severe damage unlike that seen in repeated and mild concussive injuries, and few are configured for repetitive application. Our model is a modification of the Marmarou weight drop method and allows repeated head impacts to lightly anesthetized mice. A key facet of this method is the delivery of an impact to the cranium of an unrestrained subject allowing rapid acceleration of the free-moving head and torso, an essential characteristic known to be important for concussive injury in humans, and a factor that is missing from existing animal models of TBI. Our method does not require scalp incision, emplacement of protective skull helmets or surgery and the procedure can be completed in 1-2 min. Mice spontaneously recover the righting reflex and show no evidence of seizures, paralysis or impaired behavior. Skull fractures and intracranial bleeding are very rare. Minor deficits in motor coordination and locomotor hyperactivity recover over time. Histological analyses reveal mild astrocytic reactivity (increased expression of GFAP) and increased phospho-tau but a lack of blood-brain-barrier disruption, edema and microglial activation. This new animal model is simple and cost-effective and will facilitate characterization of the neurobiological and behavioral consequences of rmTBI. It is also ideal for high throughput screening of potential new therapies for mild concussive injuries as experienced by athletes and military personnel.

Repetitive closed-skull traumatic brain injury in mice causes persistent multifocal axonal injury and microglial reactivity

Repetitive mild or "concussive" traumatic brain injury (TBI) can cause substantial neurologic impairment, but the pathological features of this type of injury are not fully understood. We report an experimental model of TBI in which the closed skulls of anesthetized male C57BL/6J mice are struck with an electromagnetically controlled rubber impactor twice with an interval of 24 hours between impacts. The mice had deficits in Morris water maze performance in the first week after injury that only partially resolved 7 weeks later. By routine histology, there was no apparent bleeding, neuronal cell loss, or tissue disruption, and amyloid precursor protein immunohistochemistry demonstrated very few immunoreactive axonal varicosities. In contrast, silver staining revealed extensive abnormalities in the corpus callosum and bilateral external capsule, the ipsilateral cortex and thalamus, and the contralateral hippocampal CA1 stratum radiatum and stratum oriens. Electron microscopy of white matter regions demonstrated axonal cytoskeletal disruption, intra-axonal organelle compaction, and irregularities in axon caliber. Reactive microglia were observed in the same areas as the injured axons by both electron microscopy and Iba1 immunohistochemistry. Quantitative analyses of silver staining and Iba1 immunohistochemistry at multiple time points demonstrated transient cortical and thalamic abnormalities but persistent white matter pathology as late as 7 weeks after injury.Thus, prominent and long-lasting abnormalities in this TBI model were underestimated using conventional approaches. The model may be useful for mechanistic investigations and preclinical assessment of candidate therapeutics.

Autophagy is involved in traumatic brain injury-induced cell death and contributes to functional outcome deficits in mice

Previous data demonstrate that traumatic brain injury (TBI) activates autophagy, and increases microtubule-associated protein 1 light chain 3 (LC3) immunostaining mainly in neurons. However, the role of autophagy in traumatic brain damage remains elusive. The aim of the present study was to investigate the autophagic mechanisms participating in traumatic brain injury. The autophagy inhibitors 3-methyladenine (3-MA) and bafliomycin A1 (BFA) were administered with a single i.c.v. injection before TBI. We first examined the protein levels of Beclin-1 and LC3 II, which have been found to promote autophagy previously. Immunoblotting analysis showed that 3-MA pretreatment reduced post-TBI Beclin-1 and LC3-II levels, and maintained p62/SQSTM1 (p62) levels. In addition, double immunolabeling showed that the increased punctate LC3-II dots colocalizing with Propidium Iodide (PI)-stained nuclei at 24 h after injury, were partially inhibited by 3-MA pretreatment. Furthermore, inhibition of autophagy could reduce TBI-induced cell injury assessed with i.p. injection of PI and lesion volume, and attenuate behavioral outcome evaluated by motor test and Morris water maze. The neuroprotective effects were associated with an inhibition on TBI-induced up-regulation of LC3, Beclin-1, cathepsin B, caspase-3 and the Beclin-1/Bcl-2 ratio. Taken together, these data imply that the autophagy pathway is involved in the pathophysiologic responses after TBI, and inhibition of this pathway may help attenuate traumatic damage and functional outcome deficits.

The molecular pathophysiology of concussive brain injury

Concussion or mild traumatic brain injury (mTBI) is a condition that affects hundreds of thousands of patients worldwide. Understanding the pathophysiology of this disorder can help manage its acute and chronic repercussions. Immediately following mTBI, there are several metabolic, hemodynamic, structural, and electric changes that alter normal cerebral function. These alterations can increase the brain's vulnerability to repeat injury and long-term disability. This review evaluates current studies from the bench to the bedside of mTBI. Acute and chronic effects of concussion are measured in both animal and clinical studies. Also, the effect of repeat concussions is analyzed. Concussion-induced pathophysiology with regards to glucose metabolism changes, mitochondrial dysfunction, axonal injury, and structural damage are evaluated. Translational studies such as functional magnetic resonance imaging, magnetic resonance spectroscopy and diffusion tensor imaging prove to be effective clinical tools for both prognostic and treatment parameters. Understanding the neurobiology of concussion will lead to development and validation of physiological biomarkers of this common injury. These biomarkers (eg, laboratory tests, imaging, electrophysiology) will then allow for improved detection, better functional assessment and evidence-based return to play recommendations.

Modulation of ABCA1 by an LXR agonist reduces β-amyloid levels and improves outcome after traumatic brain injury

Traumatic brain injury (TBI) increases brain beta-amyloid (Aβ) in humans and animals. Although the role of Aβ in the injury cascade is unknown, multiple preclinical studies have demonstrated a correlation between reduced Aβ and improved outcome. Therefore, therapeutic strategies that enhance Aβ clearance may be beneficial after TBI. Increased levels of ATP-binding cassette A1 (ABCA1) transporters can enhance Aβ clearance through an apolipoprotein E (apoE)-mediated pathway. By measuring Aβ and ABCA1 after experimental TBI in C57BL/6J mice, we found that Aβ peaked early after injury (1-3 days), whereas ABCA1 had a delayed response (beginning at 3 days). As ABCA1 levels increased, Aβ levels returned to baseline levels-consistent with the known role of ABCA1 in Aβ clearance. To test if enhancing ABCA1 levels could block TBI-induced Aβ, we treated TBI mice with the liver X-receptor (LXR) agonist T0901317. Pre- and post-injury treatment increased ABCA1 levels at 24 h post-injury, and reduced the TBI-induced increase in Aβ. This reduction in Aβ was not due to decreased amyloid precursor protein processing, or a shift in the solubility of Aβ, indicating enhanced clearance. T0901317 also limited motor coordination deficits in injured mice and reduced brain lesion volume. These data indicate that activation of LXR can reduce Aβ accumulation after TBI, and is accompanied by improved functional recovery.

Cathepsin B contributes to traumatic brain injury-induced cell death through a mitochondria-mediated apoptotic pathway

It has been reported that lysosomal proteases play important roles in ischemic and excitotoxic neuronal cell death. We have previously reported that cathepsin B expression increased remarkably after traumatic brain injury (TBI). The present study sought to investigate the effects of a selective cathepsin B inhibitor (CBI) [N-L-3-trans-prolcarbamoyloxirane-2-carbonyl)-L-isoleucyl-L-proline] on cell death and behavioral deficits in our model. We examined the levels of cathepsin B enzymatic activity and its expression by double labelling damaged cells in the brain slice with propidium iodide (PI) and anticathepsin B. The results showed an elevated enzymatic activity associated with TBI-induced increase in a mature form of cathepsin B, suggesting that cathepsin B may play a role in TBI-induced cell injury. PI was found to label cells positive for the neuronal-specific nuclear marker NeuN, whereas fewer GFAP-positive cells were labelled by PI, suggesting that neurons are more sensitive to cell death induced by TBI. Additionally, we found that pretreatment with CBI remarkably attenuated TBI-induced cell death, lesion volume, and motor and cognitive dysfunction. To analyze the mechanism of action of cathepsin B in the cell death signaling pathway, we assessed DNA fragmentation by electrophoresis, Bcl-2/Bax protein expression levels, Bid cleavage, cytochrome c release, and caspase-3 activation. The results imply that cathepsin B contributes to TBI-induced cell death through the present programmed cell necrosis and mitochondria-mediated apoptotic pathways.

Traumatic brain injury: a disease process, not an event

Traumatic brain injury (TBI) is seen by the insurance industry and many health care providers as an "event." Once treated and provided with a brief period of rehabilitation, the perception exists that patients with a TBI require little further treatment and face no lasting effects on the central nervous system or other organ systems. In fact, TBI is a chronic disease process, one that fits the World Health Organization definition as having one or more of the following characteristics: it is permanent, caused by non-reversible pathological alterations, requires special training of the patient for rehabilitation, and/or may require a long period of observation, supervision, or care. TBI increases long-term mortality and reduces life expectancy. It is associated with increased incidences of seizures, sleep disorders, neurodegenerative diseases, neuroendocrine dysregulation, and psychiatric diseases, as well as non-neurological disorders such as sexual dysfunction, bladder and bowel incontinence, and systemic metabolic dysregulation that may arise and/or persist for months to years post-injury. The purpose of this article is to encourage the classification of TBI as the beginning of an ongoing, perhaps lifelong process, that impacts multiple organ systems and may be disease causative and accelerative. Our intent is not to discourage patients with TBI or their families and caregivers, but rather to emphasize that TBI should be managed as a chronic disease and defined as such by health care and insurance providers. Furthermore, if the chronic nature of TBI is recognized by government and private funding agencies, research can be directed at discovering therapies that may interrupt the disease processes months or even years after the initiating event.

Unusual cause of failure of end-to-end anastomotic urethroplasty for traumatic obliterative bulbar urethral stricture

End-to-end anastomotic urethroplasty (EEA) for traumatic bulbar urethral stricture has excellent long-term success rate. We encountered a patient with obliterative bulbar stricture and persistent phlegmon in perineum resulting from straddle injury. Phlegmon-excision and EEA was performed, which ended up in recurrence. Thorough excision of recurrent nodules & scar with stage-I urethroplasty was performed using 'scrotal shutter flap'. Histopathology of phlegmon of first surgery and nodules & urethral margins of second revealed amyloidosis. Stage-II urethroplasty was performed 3-months later after which he is well at 24 months follow-up. This is the first case of perineal-urethral amyloid associated with trauma. Etiology is elusive.

PKC activator therapeutic for mild traumatic brain injury in mice

Traumatic brain injury (TBI) is a frequent consequence of vehicle, sport and war related injuries. More than 90% of TBI patients suffer mild injury (mTBI). However, the pathologies underlying the disease are poorly understood and treatment modalities are limited. We report here that in mice, the potent PKC activator bryostatin1 protects against mTBI induced learning and memory deficits and reduction in pre-synaptic synaptophysin and post-synaptic spinophylin immunostaining. An effective treatment has to start within the first 8h after injury, and includes 5 × i.p. injections over a period of 14 days. The treatment is dose dependent. Exploring the effects of the repeated bryostatin1 treatment on the processing of the amyloid precursor protein, we found that the treatment induced an increase in the putative α-secretase ADAM10 and a reduction in β-secretase activities. Both these effects could contribute towards a reduction in β-amyloid production. These results suggest that bryostatin1 protects against mTBI cognitive and synaptic sequela by rescuing synapses, which is possibly mediated by an increase in ADAM10 and a decrease in BACE1 activity. Since bryostatin1 has already been extensively used in clinical trials as an anti-cancer drug, its potential as a remedy for the short- and long-term TBI sequelae is quite promising.

Gene-environment interaction research and transgenic mouse models of Alzheimer's disease

The etiology of the sporadic form of Alzheimer's disease (AD) remains largely unknown. Recent evidence has suggested that gene-environment interactions (GxE) may play a crucial role in its development and progression. Whereas various susceptibility loci have been identified, like the apolipoprotein E4 allele, these cannot fully explain the increasing prevalence of AD observed with aging. In addition to such genetic risk factors, various environmental factors have been proposed to alter the risk of developing AD as well as to affect the rate of cognitive decline in AD patients. Nevertheless, aside from the independent effects of genetic and environmental risk factors, their synergistic participation in increasing the risk of developing AD has been sparsely investigated, even though evidence points towards such a direction. Advances in the genetic manipulation of mice, modeling various aspects of the AD pathology, have provided an excellent tool to dissect the effects of genes, environment, and their interactions. In this paper we present several environmental factors implicated in the etiology of AD that have been tested in transgenic animal models of the disease. The focus lies on the concept of GxE and its importance in a multifactorial disease like AD. Additionally, possible mediating mechanisms and future challenges are discussed.

Genetic deletion and pharmacological inhibition of Nogo-66 receptor impairs cognitive outcome after traumatic brain injury in mice

Functional recovery is markedly restricted following traumatic brain injury (TBI), partly due to myelin-associated inhibitors including Nogo-A, myelin-associated glycoprotein (MAG) and oligodendrocyte myelin glycoprotein (OMgp), that all bind to the Nogo-66 receptor-1 (NgR1). In previous studies, pharmacological neutralization of both Nogo-A and MAG improved outcome following TBI in the rat, and neutralization of NgR1 improved outcome following spinal cord injury and stroke in rodent models. However, the behavioral and histological effects of NgR1 inhibition have not previously been evaluated in TBI. We hypothesized that NgR1 negatively influences behavioral recovery following TBI, and evaluated NgR1(-/-) mice (NgR1(-/-) study) and, in a separate study, soluble NgR1 infused intracerebroventricularly immediately post-injury to neutralize NgR1 (sNgR1 study) following TBI in mice using a controlled cortical impact (CCI) injury model. In both studies, motor function, TBI-induced loss of tissue, and hippocampal beta-amyloid immunohistochemistry were not altered up to 5 weeks post-injury. Surprisingly, cognitive function (as evaluated with the Morris water maze at 4 weeks post-injury) was significantly impaired both in NgR1(-/-) mice and in mice treated with soluble NgR1. In the sNgR1 study, we evaluated hippocampal mossy fiber sprouting using the Timm stain and found it to be increased at 5 weeks following TBI. Neutralization of NgR1 significantly increased mossy fiber sprouting in sham-injured animals, but not in brain-injured animals. Our data suggest a complex role for myelin-associated inhibitors in the behavioral recovery process following TBI, and urge caution when inhibiting NgR1 in the early post-injury period.

Traumatic brain injury and amyloid-β pathology: a link to Alzheimer's disease?

Traumatic brain injury (TBI) has devastating acute effects and in many cases seems to initiate long-term neurodegeneration. Indeed, an epidemiological association between TBI and the development of Alzheimer's disease (AD) later in life has been demonstrated, and it has been shown that amyloid-β (Aβ) plaques — one of the hallmarks of AD — may be found in patients within hours following TBI. Here, we explore the mechanistic underpinnings of the link between TBI and AD, focusing on the hypothesis that rapid Aβ plaque formation may result from the accumulation of amyloid precursor protein in damaged axons and a disturbed balance between Aβ genesis and catabolism following TBI.

Chronic traumatic encephalopathy (CTE) in a National Football League Player: Case report and emerging medicolegal practice questions

We present a case of chronic traumatic encephalopathy (CTE) in a retired National Football League (NFL) Player with autopsy findings, apolipoprotein E genotype, and brain tissue evidence of chronic brain damage. This 44-year-old retired NFL player manifested a premortem history of cognitive and neuropsychiatric impairment, which included in part, chronic depression, suicide attempts, insomnia, paranoia, and impaired memory before he finally committed suicide. A full autopsy was performed with Polymerase Chain Reaction-based analyses of his blood to determine the apolipoprotein genotype. Histochemical and immunohistochemical analyses were performed on topographical gross sections of the brain. Autopsy confirmed a fatal gunshot wound of the head. The apolipoprotein E genotype was E3/E3 and the brain tissue revealed diffuse cerebral taupathy (Neurofibrillary Tangles and Neuritic Threads). This will be the third case of CTE in a national football player, which has been reported in the medical literature. Omalu et al., reported the first two cases in 2005 and 2006. This case series manifested similar premortem history of neuropsychiatric impairment with autopsy evidence of cerebral taupathy without any neuritic amyloidopathy. For a definitive diagnosis of CTE to be made, and for medicolegal purposes, a full autopsy must be performed with histochemical and immunohistochemical analyses of the brain to identify the presence of Neurofibrillary Tangles (NFTs) and Neuritic Threads (NTs).

IMPLICATIONS

Further longitudinal prospective studies are required to confirm the common denominators and epidemiology of CTE in professional American football players, which have been identified by this case series.

Sodium channelopathy induced by mild axonal trauma worsens outcome after a repeat injury

There is great concern that one mild traumatic brain injury (mTBI) predisposes individuals to an exacerbated response with a subsequent mTBI. Although no mechanism has been identified, mounting evidence suggests traumatic axonal injury (TAI) plays a role in this process. By using a cell culture system, a threshold of mild TAI was found where dynamic stretch of cortical axons at strains lower than 5% induced no overt pathological changes. However, the axons were found to display an increased expression of sodium channels (NaChs) by 24 hr. After a second, identical mild injury, pathologic increases in [Ca(2+)](i) were observed, leading to axon degeneration. The central role of NaChs in this response was demonstrated by blocking NaChs with tetrodotoxin prior to the second injury, which completely abolished postinjury increases in [Ca(2+)](i). These data suggest that mild TAI induces a form of sodium channelopathy on axons that greatly exaggerates the pathophysiologic response to subsequent mild injuries.

Thiamine deficiency induces oxidative stress and exacerbates the plaque pathology in Alzheimer's mouse model

Mitochondrial dysfunction, oxidative stress and reductions in thiamine-dependent enzymes have been implicated in multiple neurological disorders including Alzheimer's disease (AD). Experimental thiamine deficiency (TD) is an established model for reducing the activities of thiamine-dependent enzymes in brain. TD diminishes thiamine-dependent enzymes throughout the brain, but produces a time-dependent selective neuronal loss, glial activation, inflammation, abnormalities in oxidative metabolism and clusters of degenerating neurites in only specific thalamic regions. The present studies tested how TD alters brain pathology in Tg19959 transgenic mice over expressing a double mutant form of the amyloid precursor protein (APP). TD exacerbated amyloid plaque pathology in transgenic mice and enlarged the area occupied by plaques in cortex, hippocampus and thalamus by 50%, 200% and 200%, respectively. TD increased Abeta(1-42) levels by about three fold, beta-CTF (C99) levels by 33% and beta-secretase (BACE1) protein levels by 43%. TD-induced inflammation in areas of plaque formation. Thus, the induction of mild impairment of oxidative metabolism, oxidative stress and inflammation induced by TD alters metabolism of APP and/or Abeta and promotes accumulation of plaques independent of neuron loss or neuritic clusters.

Linking vascular disorders and Alzheimer's disease: potential involvement of BACE1

The etiology of Alzheimer's disease (AD) remains unknown. However, specific risk factors have been identified, and aging is the strongest AD risk factor. The majority of cardiovascular events occur in older people and a close relationship between vascular disorders and AD exists. Amyloid plaques, composed of the beta amyloid peptide (Abeta), are hallmark lesions in AD and evidence indicates that Abeta plays a central role in AD pathophysiology. The BACE1 enzyme is essential for Abeta generation, and BACE1 levels are elevated in AD brain. The cause(s) of this BACE1 elevation remains undetermined. Here we review the potential contribution of vascular disease to AD pathogenesis. We examine the putative vasoactive properties of Abeta and how the cellular changes associated with vascular disease may elevate BACE1 levels. Despite increasing evidence, the exact role(s) vascular disorders play in AD remains to be determined. However, given that vascular diseases can be addressed by lifestyle and pharmacologic interventions, the potential benefits of these therapies in delaying the clinical appearance and progression of AD may warrant investigation.

Chronic traumatic encephalopathy in athletes: progressive tauopathy after repetitive head injury

Since the 1920s, it has been known that the repetitive brain trauma associated with boxing may produce a progressive neurological deterioration, originally termed dementia pugilistica, and more recently, chronic traumatic encephalopathy (CTE). We review 48 cases of neuropathologically verified CTE recorded in the literature and document the detailed findings of CTE in 3 profession althletes, 1 football player and 2 boxers. Clinically, CTE is associated with memory disturbances, behavioral and personality changes, parkinsonism, and speech and gait abnormalities. Neuropathologically, CTE is characterized by atrophy of the cerebral hemispheres, medial temporal lobe, thalamus, mammillary bodies, and brainstem, with ventricular dilatation and a fenestrated cavum septum pellucidum. Microscopically, there are extensive tau-immunoreactive neurofibrillary tangles, astrocytic tangles, and spindle-shaped and threadlike neurites throughout the brain. The neurofibrillary degeneration of CTE is distinguished from other tauopathies by preferential involvement of the superficial cortical layers, irregular patchy distribution in the frontal and temporal cortices, propensity for sulcal depths, prominent perivascular, periventricular, and subpial distribution, and marked accumulation of tau-immunoreactive astrocytes. Deposition of beta-amyloid, most commonly as diffuse plaques, occurs in fewer than half the cases. Chronic traumatic encephalopathy is a neuropathologically distinct slowly progressive tauopathy with a clear environmental etiology.

Targeted knock-down of neuronal nitric oxide synthase expression in basal forebrain with RNA interference

Nitric oxide (NO) is a gas messenger with diverse physiological roles in the nervous system, from modulation of synaptic plasticity and neurogenesis to the mediation of neuronal death. NO production in the brain is catalyzed by three isoforms of NO synthase (NOS) including neuronal NOS (nNOS), inducible NOS and endothelial NOS. In this report, we demonstrate a method for in vitro and in vivo silencing of nNOS using RNAi strategies. Because of their efficiency in infecting postmitotic cells like neurons, lentiviral vectors were used as nNOS shRNA carriers. Of the siRNA sequences screened, one corresponding to exon 10 of the rat nNOS specifically and efficiently inhibited nNOS expression at the mRNA and protein level. In vitro experiments using rat cortical neurons showed the general efficacy of shRNA vectors in silencing constitutively expressed nNOS. To demonstrate the anatomical specificity of nNOS silencing in vivo, vectors were used to selectively knock-down the endogenous nNOS expression in cortical GABAergic interneurons of rat piriform cortex. Our findings show that the method reported here can achieve stable and highly effective nNOS suppression in an anatomically defined brain region. The ability of our nNOS silencing vectors to effectively and precisely silence nNOS expression shows their value as research tools for further studies of the role of nNOS in specific brain circuits. Furthermore, our findings raise the possibility for future considerations of lentiviral strategies as therapies for diseases of the nervous system involving NO neurotoxic cascades.

Molecular profiling reveals diversity of stress signal transduction cascades in highly penetrant Alzheimer's disease human skin fibroblasts

The serious and growing impact of the neurodegenerative disorder Alzheimer's disease (AD) as an individual and societal burden raises a number of key questions: Can a blanket test for Alzheimer's disease be devised forecasting long-term risk for acquiring this disorder? Can a unified therapy be devised to forestall the development of AD as well as improve the lot of present sufferers? Inflammatory and oxidative stresses are associated with enhanced risk for AD. Can an AD molecular signature be identified in signaling pathways for communication within and among cells during inflammatory and oxidative stress, suggesting possible biomarkers and therapeutic avenues? We postulated a unique molecular signature of dysfunctional activity profiles in AD-relevant signaling pathways in peripheral tissues, based on a gain of function in G-protein-coupled bradykinin B2 receptor (BKB2R) inflammatory stress signaling in skin fibroblasts from AD patients that results in tau protein Ser hyperphosphorylation. Such a signaling profile, routed through both phosphorylation and proteolytic cascades activated by inflammatory and oxidative stresses in highly penetrant familial monogenic forms of AD, could be informative for pathogenesis of the complex multigenic sporadic form of AD. Comparing stimulus-specific cascades of signal transduction revealed a striking diversity of molecular signaling profiles in AD human skin fibroblasts that express endogenous levels of mutant presenilins PS-1 or PS-2 or the Trisomy 21 proteome. AD fibroblasts bearing the PS-1 M146L mutation associated with highly aggressive AD displayed persistent BKB2R signaling plus decreased ERK activation by BK, correctible by gamma-secretase inhibitor Compound E. Lack of these effects in the homologous PS-2 mutant cells indicates specificity of presenilin gamma-secretase catalytic components in BK signaling biology directed toward MAPK activation. Oxidative stress revealed a JNK-dependent survival pathway in normal fibroblasts lost in PS-1 M146L fibroblasts. Complex molecular profiles of signaling dysfunction in the most putatively straightforward human cellular models of AD suggest that risk ascertainment and therapeutic interventions in AD as a whole will likely demand complex solutions.

T1rho MRI of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly. Classic symptoms of the disease include memory loss and confusion associated with the hallmark neuro-pathologic lesions of neurofibrillary tangles (NFT) and senile plaques (SP) and their sequelae, gray matter atrophy. Volumetric assessment methods measure tissue atrophy, which typically follows early biochemical changes. An alternate MRI contrast mechanism to visualize the early pathological changes is T1rho (or "T-1-rho"), the spin lattice relaxation time constant in the rotating frame, which determines the decay of the transverse magnetization in the presence of a "spin-lock" radio-frequency field. Macromolecular changes (in plaques and tangles) that accompany early AD are expected to alter bulk water T1rho relaxation times. In this work, we measure T1rho MRI on patients with clinically diagnosed AD, MCI and in age-matched cognitively normal control subjects in order to compare T1rho values with changes in brain volume in the same regions of the brain and demonstrate that T1rho can potentially constitute an important biomarker of AD.

Thrombin-induced oxidative stress contributes to the death of hippocampal neurons: role of neuronal NADPH oxidase

The present study investigated whether thrombin can induce the production of reactive oxygen species (ROS) through activation of neuronal NADPH oxidase and whether this contributes to oxidative damage and consequently to neurodegeneration. Immunocytochemical and biochemical evidence demonstrated that, in neuron-enriched hippocampal cultures, thrombin induces neurodegeneration in a dose-dependent manner. In parallel, ROS production was evident as assessed by analyzing DCF and hydroethidine. Real-time PCR analysis, at various time points after thrombin treatment, also demonstrated that expression of NADPH oxidase subunits (p47(phox) and p67(phox)) occurs. In addition, Western blot analysis and double-label immunocytochemistry showed an up-regulation in the expression of cytosolic components (Rac 1 and p67(phox)), the translocation of cytosolic proteins (p47(phox) and p67(phox)) to the membrane, and the localization of gp91(phox) or p47(phox) expression in hippocampal neurons of cultures and CA1 layer. The thrombin-induced ROS production, protein oxidation, and loss of cultured hippocampal neurons were partially attenuated by an NADPH oxidase inhibitor and/or by several antioxidants. Collectively, the present study is the first to demonstrate that, in cultured hippocampal neurons, thrombin-induced neurotoxicity is, at least in part, caused by neuronal NADPH oxidase-mediated oxidative stress. This strongly suggests that thrombin can act as an endogenous neurotoxin, and inhibitors of thrombin and/or antioxidants can be useful agents for treating oxidative stress-mediated hippocampal neurodegenerative diseases, such as Alzheimer's disease.

5-Lipoxygenase gene disruption reduces amyloid-beta pathology in a mouse model of Alzheimer's disease

5-Lipoxygenase (5LO), by producing leukotrienes, is a proinflammatory enzyme, and there is evidence suggesting that it is up-regulated with aging and may be involved in Alzheimer's disease (AD). In this paper, we studied the effect of 5LO-targeted gene disruption on the amyloid phenotype of a transgenic mouse model of AD, the Tg2576. Amyloid-beta (Abeta) deposition in the brains of Tg2576 mice lacking 5LO was reduced by 64-80% compared with Tg2576 controls. This reduction was associated with a similar significant decrease in Abeta levels measured by sandwich ELISA. Absence of 5LO did not induce any significant change in amyloid-beta precursor protein (APP) levels and processing, or Abeta catabolic pathways. Furthermore, in vitro studies showed that 5LO activation or 5LO metabolites increase, whereas 5LO inhibition decreases, Abeta formation, secondary to correspondent changes in gamma-secretase activity. These data establish for the first time a novel functional role for 5LO in the pathogenesis of AD-like amyloidosis, thereby modulating gamma-secretase activity. Our work suggests that pharmacological inhibition of 5LO could provide a novel therapeutic tool for AD.

Tissue transglutaminase, protein cross-linking and Alzheimer's disease: review and views

Extensive protein cross-linking and aggregation are some of the most common molecular events in the pathogenesis of Alzheimer's disease (AD). Both beta-amyloid (Abeta) plaques and neurofibrillary tangles, which are extracellular and intracellular proteinaceous aggregates, respectively, contribute to neuronal death and progressive cognitive decline. Although protein cross-linking has been recognized and extensively studied for many years, the underlying mechanisms are largely unknown. Recent data indicates that tissue transglutaminase (tTG), which catalyzes the cross-linking of a wide spectrum of proteins including Abeta, tau, alpha-synuclein and neurofilament proteins, may be involved in protein aggregation in AD. Many AD risk factors, such as trauma, inflammation, ischemia and stress, up-regulate tTG protein and activity levels. In this review, we summarize the evidence that tTG plays a role in AD, especially in cross-linking of Abeta, tau, alpha-synuclein and neurofilament proteins. An experimentally testable hypothesis is that tTG may play a central role in AD pathogenesis and that it provides a conceptual link between sporadic and familial AD through a shared pathogenic pathway.

Alzheimer disease models and human neuropathology: similarities and differences

Animal models aim to replicate the symptoms, the lesions or the cause(s) of Alzheimer disease. Numerous mouse transgenic lines have now succeeded in partially reproducing its lesions: the extracellular deposits of Abeta peptide and the intracellular accumulation of tau protein. Mutated human APP transgenes result in the deposition of Abeta peptide, similar but not identical to the Abeta peptide of human senile plaque. Amyloid angiopathy is common. Besides the deposition of Abeta, axon dystrophy and alteration of dendrites have been observed. All of the mutations cause an increase in Abeta 42 levels, except for the Arctic mutation, which alters the Abeta sequence itself. Overexpressing wild-type APP alone (as in the murine models of human trisomy 21) causes no Abeta deposition in most mouse lines. Doubly (APP x mutated PS1) transgenic mice develop the lesions earlier. Transgenic mice in which BACE1 has been knocked out or overexpressed have been produced, as well as lines with altered expression of neprilysin, the main degrading enzyme of Abeta. The APP transgenic mice have raised new questions concerning the mechanisms of neuronal loss, the accumulation of Abeta in the cell body of the neurons, inflammation and gliosis, and the dendritic alterations. They have allowed some insight to be gained into the kinetics of the changes. The connection between the symptoms, the lesions and the increase in Abeta oligomers has been found to be difficult to unravel. Neurofibrillary tangles are only found in mouse lines that overexpress mutated tau or human tau on a murine tau -/- background. A triply transgenic model (mutated APP, PS1 and tau) recapitulates the alterations seen in AD but its physiological relevance may be discussed. A number of modulators of Abeta or of tau accumulation have been tested. A transgenic model may be analyzed at three levels at least (symptoms, lesions, cause of the disease), and a reading key is proposed to summarize this analysis.

Alzheimer's disease-related changes in diseases characterized by elevation of intracranial or intraocular pressure

In this review, we focus on the coexistence of Alzheimer's disease-related changes in brain diseases, such as normal pressure hydrocephalus and traumatic brain injury, and in glaucoma at the level of the retinal ganglion cells. This is a group of diseases that affect central nervous system tissue and are characterized by elevation of intracranial or intraocular pressure and/or local shear stress and strain. In considering possible mechanisms underlying Alzheimer-type changes in these diseases, we briefly summarize recent evidence indicating that caspase activation and abnormal processing of beta-amyloid precursor protein, which are important events in Alzheimer's disease, may play a role both in glaucoma and following traumatic brain injury. With regard to normal pressure hydrocephalus, evidence suggests that changes in cerebrospinal fluid circulatory dynamics ultimately may result in reduced clearance of neurotoxins, such as beta-amyloid peptides and tau protein, that play a role in the pathogenesis of Alzheimer's disease. Data presented in this review could be interpreted to suggest that Alzheimer-type changes in these diseases may result at least in part from exposure of central nervous system tissue to increased levels of mechanical stress. Evidence for such a relationship is of major importance because it may support an association between elevated mechanical load and the development of Alzheimer-type lesions. Further studies are warranted, however, especially to elucidate the role of elevated mechanical forces in Alzheimer's disease neuropathogenesis.

Three weeks of running wheel exposure improves cognitive performance in the aged Tg2576 mouse

If begun early in life, exercise effectively reduces the development of cognitive deficits in transgenic mouse models of Alzheimer's disease (AD). However, the effectiveness of exercise, once the cognitive impairments are established, is not as clear. In terms of translating research in animal models to treatments involving exercise in Alzheimer's disease patients, it is critical to evaluate exercise intervention at time points that address not only prevention, but also treatment of cognitive decline. We provided exercise wheels to Tg2576 (TG) (n=12) and C57BL6 (WT) (n=17) mice at 16-18 months of age for three weeks. At this age animals have significant cognitive impairment and neuropathology consistent with AD. Age matched sedentary TG (n=13) and WT (n=12) mice were also included, as well as groups provided access to an immobile wheel (TG n=9, WT n=12). After three weeks, animals were evaluated in a radial arm water maze. Significant impairments were observed in the sedentary TG mice compared to WT in reference/long-term and working/short-term memory, as well as in probe trials. Exercised TG mice demonstrated improvements in memory, which made them indistinguishable from WT mice on all tasks. In addition, animals provided with an immobile wheel exhibited improvement in some, but not all cognitive measures. Our findings demonstrate that exercise can improve cognitive performance in a mouse model of AD even if applied after the development of pathology.

COG1410, a novel apolipoprotein E-based peptide, improves functional recovery in a murine model of traumatic brain injury

Traumatic brain injury (TBI) is a silent epidemic affecting approximately 1.4 million Americans annually, at an estimated annual cost of $60 billion in the United States alone. Despite an increased understanding of the pathophysiology of closed head injury, there remains no pharmacological intervention proven to improve functional outcomes in this setting. Currently, the existing standard of care for TBI consists primarily of supportive measures. Apolipoprotein E (apoE) is the primary apolipoprotein synthesized in the brain in response to injury, where it modulates several components of the neuroinflammatory cascade associated with TBI. We have previously demonstrated that COG133, an apoE mimetic peptide, improved functional outcomes and attenuated neuronal death when administered as a single intravenous injection at 30 min post-TBI in mice. Using the principles of rational drug design, we developed a more potent analog, COG1410, which expands the therapeutic window for the treatment of TBI by a factor of four, from 30 min to 2 h. Mice that received a single intravenous injection of COG1410 at 120 min post-TBI exhibited significant improvement on a short term test of vestibulomotor function and on a long term test of spatial learning and memory. This was associated with a significant attenuation of microglial activation and neuronal death in the hippocampus, the neuroanatomical substrate for learning and memory. Rationally derived apoE mimetic peptides have been demonstrated to exert neuroprotective and anti-inflammatory effects in vitro and in clinically relevant models of brain injury. This represents a novel therapeutic strategy in the treatment of TBI.

Long-lasting sleep patterns of adult patients with minor traumatic brain injury (mTBI) and non-mTBI subjects

BACKGROUND

Sleep disturbance is a common subjective complaint of minor traumatic brain-injured (mTBI) patients, but little is known about the characteristics of sleep disturbance in adults years after the injury.

METHODS

Polysomnographic (PSG) and multiple sleep latency test (MSLT) records of 26 mTBI adult patients with normal brain computerized tomography and negative encephalographic studies, no past history of CNS pathology, no premorbid or present major psychiatric diagnosis, and no sleep apnea syndrome were compared to a matched group of apparently healthy individuals (controls).

RESULTS

Sleep patterns were disturbed in the mTBI patients. Their sleep architecture was altered, with significantly higher light-sleep non-rapid eye movement (NREM) stage 2 scores compared to controls (54.5+/-13.4% vs. 46.6+/-10.4%, respectively, p=0.03) and significantly lower REM sleep scores (21.2+/-8.4% vs. 25.4+/-4.5%, respectively, p=0.05). The MSLT findings documented significant excessive daytime episodes of falling asleep.

CONCLUSIONS

Sleep disturbances of adult patients with chronic mTBI may manifest characteristic alterations in both timing and architecture of their sleep patterns. Sleep lab evaluations may help identify subgroups of mTBI patients who would probably benefit from treatment.

Electromagnetic controlled cortical impact device for precise, graded experimental traumatic brain injury

Genetically modified mice represent useful tools for traumatic brain injury (TBI) research and attractive preclinical models for the development of novel therapeutics. Experimental methods that minimize the number of mice needed may increase the pace of discovery. With this in mind, we developed and characterized a prototype electromagnetic (EM) controlled cortical impact device along with refined surgical and behavioral testing techniques. By varying the depth of impact between 1.0 and 3.0 mm, we found that the EM device was capable of producing a broad range of injury severities. Histologically, 2.0-mm impact depth injuries produced by the EM device were similar to 1.0-mm impact depth injuries produced by a commercially available pneumatic device. Behaviorally, 2.0-, 2.5-, and 3.0-mm impacts impaired hidden platform and probe trial water maze performance, whereas 1.5-mm impacts did not. Rotorod and visible platform water maze deficits were also found following 2.5- and 3.0-mm impacts. No impairment of conditioned fear performance was detected. No differences were found between sexes of mice. Inter-operator reliability was very good. Behaviorally, we found that we could statistically distinguish between injury depths differing by 0.5 mm using 12 mice per group and between injury depths differing by 1.0 mm with 7-8 mice per group. Thus, the EM impactor and refined surgical and behavioral testing techniques may offer a reliable and convenient framework for preclinical TBI research involving mice.

Experimental models of repetitive brain injuries

Repetitive traumatic brain injury (TBI) occurs in a significant portion of trauma patients, especially in specific populations, such as child abuse victims or athletes involved in contact sports (e.g. boxing, football, hockey, and soccer). A continually emerging hypothesis is that repeated mild injuries may cause cumulative damage to the brain, resulting in long-term cognitive dysfunction. The growing attention to this hypothesis is reflected in several recent experimental studies of repeated mild TBI in vivo. These reports generally demonstrate cellular and cognitive dysfunction after repetitive injury using rodent TBI models. In some cases, data suggests that the effects of a second mild TBI may be synergistic, rather than additive. In addition, some studies have found increases in cellular markers associated with Alzheimer's disease after repeated mild injuries, which demonstrates a direct experimental link between repetitive TBI and neurodegenerative disease. To complement the findings from humans and in vivo experimentation, my laboratory group has investigated the effects of repeated trauma in cultured brain cells using a model of stretch-induced mechanical injury in vitro. In these studies, hippocampal cells exhibited cumulative damage when mild stretch injuries were repeated at either 1-h or 24-h intervals. Interestingly, the extent of damage to the cells was dependent on the time between repeated injuries. Also, a very low level of stretch, which produced no cell damage on its own, induced cell damage when it was repeated several times at a short interval (every 2 min). Although direct comparisons to the clinical situation are difficult, these types of repetitive, low-level, mechanical stresses may be similar to the insults received by certain athletes, such as boxers, or hockey and soccer players. This type of in vitro model could provide a reliable system in which to study the mechanisms underlying cellular dysfunction following repeated injuries. As this area of TBI research continues to evolve, it will be imperative that models of repetitive injury replicate injuries in humans as closely as possible. For example, it will be important to model appropriately concussive episodes versus even lower level injuries (such as those that might occur during boxing matches). Suitable inter-injury intervals will also be important parameters to incorporate into models. Additionally, it will be crucial to design and utilize proper controls, which can be more challenging than experimental approaches to single mild TBI. It will also be essential to combine, and compare, data derived from in vitro experiments with those conducted with animals in vivo. These issues, as well as a summary of findings from repeated TBI research, are discussed in this review.

Traumatic brain injury and Alzheimer's disease: a review

In an effort to identify the factors that are involved in the pathogenesis of Alzheimer's disease (AD), epidemiological studies have featured prominently in contemporary research. Of those epidemiological factors, accumulating evidence implicates traumatic brain injury (TBI) as a possible predisposing factor in AD development. Exactly how TBI triggers the neurodegenerative cascade of events in AD remains controversial. There has been extensive research directed towards understanding the potential relationship between TBI and AD and the putative influence that apolipoprotein E (APOE) genotype has on this relationship. The aim of the current paper is to provide a critical summary of the experimental and human studies regarding the association between TBI, AD and APOE genotype. It will be shown that despite significant discrepancies in the literature, there still appears to be an increasing trend to support the hypothesis that TBI is a potential risk factor for AD. Furthermore, although it is known that APOE genotype plays an important role in AD, its link to a deleterious outcome following TBI remains inconclusive and ambiguous.

An apolipoprotein E-based therapeutic improves outcome and reduces Alzheimer's disease pathology following closed head injury: evidence of pharmacogenomic interaction

Apolipoprotein E (apoE) modifies glial activation and the CNS inflammatory response in an isoform-specific manner. Peptides derived from the receptor-binding region of apoE have been demonstrated to maintain the functional activity of the intact protein, and to improve histological and functional deficits after closed head injury. In the current study, APOE2, APOE3, and APOE4 targeted replacement (TR) mice expressing the human apoE protein isoforms (apoE2, apoE3 and apoE4) were used in a clinically relevant model of closed head injury to assess the interaction between the humanized apoE background and the therapeutic apoE mimetic peptide, apoE(133-149). Treatment with the apoE-mimetic peptide reduced microglial activation and early inflammatory events in all of the targeted replacement animals and was associated with histological and functional improvement in the APOE2TR and APOE3TR animals. Similarly, brain beta amyloid protein (Abeta)(1-42) levels were increased as a function of head injury in all of the targeted replacement mice, while treatment with apoE peptide suppressed Abeta(1-42) levels in the APOE2TR and APOE3TR animals. These results suggest a pharmacogenomic interaction between the therapeutic effects of the apoE mimetic peptide and the human apoE protein isoforms. Furthermore, they suggest that administration of apoE-mimetic peptides may serve as a novel therapeutic strategy for the treatment of acute and chronic neurological disease.

Impaired fibrinolysis and traumatic brain injury in mice

Traumatic brain injury (TBI) has been associated with intravascular coagulation, which may be a result of thromboplastin released following brain injury. Clots thus formed are lysed by plasmin, which is activated by tissue-type and urokinase-type plasminogen activators (uPA). To evaluate the association between traumatic intravascular coagulation and post-traumatic outcome, uPA knockout (uPA-/-) transgenic mice (n=12) or wild-type littermates (WT; n=12) were anesthetized and subjected to controlled cortical impact (CCI) brain injury. A second group of uPA-/- (n=12) and WT mice (n=12) were subjected to sham injury. Motor function was assessed over 2 weeks using the composite neuroscore test and cognition (learning) was assessed with the Morris Water Maze (MWM) at 2 weeks post-injury, whereupon the animals were sacrificed for cortical lesion volume analysis. Motor function was significantly worse in the brain-injured uPA-/- mice when compared to brain-injured WT mice at 48 h (p<0.05) and one week post-injury (p<0.05). These differences resolved by 2 weeks post-injury. There was no significant difference in post-injury cognitive function between uPA-/- mice and WT mice. However, at 2 weeks post-injury, the brain-injured uPA-/- had a significantly larger volume of cortical tissue loss than their WT counterparts (p<0.05). These results demonstrate that the absence of uPA in mice aggravates acute motor deficit and exacerbates cortical tissue loss following CCI brain injury, and suggests a neuroprotective role of the fibrinolytic process following TBI.

Oxidative stress in Alzheimer's disease

Oxidative damage is a major feature in the pathophysiology of Alzheimer's disease (AD). In this review, we discuss free radical-mediated damage to the biochemical components involved in the pathology and clinical symptoms of AD. We explain how amyloid beta-protein (Abeta), microtubule-associated protein tau, presenilins, apolipoprotein E, mitochondria and proteases play a role in increasing oxidative stress in AD. Abeta not only can induce oxidative stress, but its generation is also increased as a result of oxidative stress. Finally, a hypothetical model linking oxidative stress with beta-amyloid and neurofibrillary tangle pathology in AD is proposed.

Convergence of heat shock protein 90 with ubiquitin in filamentous alpha-synuclein inclusions of alpha-synucleinopathies

Heat shock proteins (Hsps) facilitate refolding of denatured polypeptides, but there is limited understanding about their roles in neurodegenerative diseases characterized by misfolded proteins. Because Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy are alpha-synucleinopathies characterized by filamentous alpha-synuclein (alpha-syn) inclusions, we assessed which Hsps might be implicated in these disorders by examining human brain samples, transgenic mouse models, and cell culture systems. Light and electron microscopic multiple-label immunohistochemistry showed Hsp90 was the predominant Hsp examined that co-localized with alpha-syn in Lewy bodies, Lewy neurites, and glial cell inclusions and that Hsp90 co-localized with alpha-syn filaments of Lewy bodies in PD. Hsp90 levels were most predominantly increased in PD brains, which correlated with increased levels of insoluble alpha-syn. These alterations in Hsp90 were recapitulated in a transgenic mouse model of PD-like alpha-syn pathologies. Cell culture studies also revealed that alpha-syn co-immunoprecipitated preferentially with Hsp90 and Hsc70 relative to other Hsps, and exposure of cells to proteasome inhibitors resulted in increased levels of Hsp90. These data implicate predominantly Hsp90 in the formation of alpha-syn inclusions in PD and related alpha-synucleinopathies.

Enhanced neurofibrillary tangle formation, cerebral atrophy, and cognitive deficits induced by repetitive mild brain injury in a transgenic tauopathy mouse model

Traumatic brain injury (TBI) is a risk factors for Alzheimer's disease (AD), and repetitive TBI (rTBI) may culminate in dementia pugilistica (DP), a syndrome characterized by progressive dementia, parkinsonism, and the hallmark brain lesions of AD, including neurofibrillary tangles (NFTs), formed by abnormal tau filaments and senile plaques (SPs) composed of Abeta fibrils. Previous study showed that mild rTBI (mrTBI) accelerated the deposition of Abeta in the brains of transgenic (Tg) mice (Tg2576) that over-express human Abeta precursor proteins with the familial AD Swedish mutations (APP695swe) and model of AD-like amyloidosis. Here, we report studies of the effects of mrTBI on AD-like tau pathologies in Tg mice expressing the shortest human tau isoform (T44) subjected to mrTBI, causing brain concussion without structural brain damage to simulate injuries linked to DP. Twelve-month-old Tg T44 (n = 18) and wild-type (WT; n = 24) mice were subjected to mrTBI (four times a day, 1 day per week, for 4 weeks; n = 24) or sham treatment (n = 18). Histopathological analysis of mice at 9 months after mrTBI revealed that one of the Tg T44 mice showed extensive telencephalic NFT and cerebral atrophy. Although statistical analysis of neurobehavioral tests at 6 months after mrTBI did not show any significant difference in any of groups of mice, the Tg T44 mouse with extensive NFT had an exceptionally low neurobehavioral score. The reasons for the augmentation of tau pathologies in only one T44 tau Tg mouse subjected to mrTBI remain to be elucidated.

Contributors to white matter damage in the frontal lobe in Alzheimer's disease

Abnormalities of cerebral white matter are present in a majority of patients with Alzheimer's disease (AD) and probably contribute to motor dysfunction and cognitive impairment. The white matter abnormalities are usually attributed to degenerative vascular disease and cerebral amyloid angiopathy (CAA) but the evidence is scanty or inconclusive. In the present study we examined sections of frontal lobe from 125 autopsy-confirmed cases of AD and assessed the relationship of degenerative large and small vessel disease, CAA, parenchymal Abeta load and APOE genotype, to several objective measures of white matter damage: extent of immunolabelling for glial fibrillary acidic protein (GFAP), axonal accumulation of amyloid precursor protein (APP), axon density in superficial and deep white matter, and intensity of staining for myelin. We found no association between atherosclerosis, arteriolosclerosis, CAA or APOE genotype and white matter damage. However, labelling of white matter for GFAP correlated strongly with the parenchymal Abeta load (P = 0.0003) and with APP accumulation (P = 0.008). Our findings suggest that severity of frontal white matter damage in AD is closely related to parenchymal Abeta load and that in most cases the contribution of degenerative vascular disease, CAA and APOE is relatively minor.

Impaired rapid eye movement sleep in the Tg2576 APP murine model of Alzheimer's disease with injury to pedunculopontine cholinergic neurons

Impaired rapid eye movement sleep (REMS) is commonly observed in Alzheimer's disease, suggesting injury to mesopontine cholinergic neurons. We sought to determine whether abnormal beta-amyloid peptides impair REMS and injure mesopontine cholinergic neurons in transgenic (hAPP695.SWE) mice (Tg2576) that model brain amyloid pathologies. Tg2576 mice and wild-type littermates were studied at 2, 6, and 12 months by using sleep recordings, contextual fear conditioning, and immunohistochemistry. At 2 months of age, REMS was indistinguishable by genotype but was reduced in Tg2576 mice at 6 and 12 months. Choline acetyltransferase-positive neurons in the pedunculopontine tegmentum of Tg2576 mice at 2 months evidenced activated caspase-3 immunoreactivity, and at 6 and 12 months the numbers of pedunculopontine tegmentum choline acetyltransferase-positive neurons were reduced in the Tg2576 mice. Other cholinergic groups involved in REMS were unperturbed. At 12 months, Tg2576 mice demonstrated increased 3-nitrotyrosine immunoreactivity in cholinergic projection sites but not in cholinergic soma. We have identified a population of selectively compromised cholinergic neurons in young Tg2576 mice that manifest early onset REMS impairment. The differential vulnerability of these cholinergic neurons to Abeta injury provides an invaluable tool with which to understand mechanisms of sleep/wake perturbations in Alzheimer's disease.

Experimental models of traumatic brain injury: do we really need to build a better mousetrap?

Approximately 4000 human beings experience a traumatic brain injury each day in the United States ranging in severity from mild to fatal. Improvements in initial management, surgical treatment, and neurointensive care have resulted in a better prognosis for traumatic brain injury patients but, to date, there is no available pharmaceutical treatment with proven efficacy, and prevention is the major protective strategy. Many patients are left with disabling changes in cognition, motor function, and personality. Over the past two decades, a number of experimental laboratories have attempted to develop novel and innovative ways to replicate, in animal models, the different aspects of this heterogenous clinical paradigm to better understand and treat patients after traumatic brain injury. Although several clinically-relevant but different experimental models have been developed to reproduce specific characteristics of human traumatic brain injury, its heterogeneity does not allow one single model to reproduce the entire spectrum of events that may occur. The use of these models has resulted in an increased understanding of the pathophysiology of traumatic brain injury, including changes in molecular and cellular pathways and neurobehavioral outcomes. This review provides an up-to-date and critical analysis of the existing models of traumatic brain injury with a view toward guiding and improving future research endeavors.

Dynamic complexity of the microglial activation response in transgenic models of amyloid deposition: implications for Alzheimer therapeutics

The presence of activated microglia in postmortem Alzheimer disease specimens is used to support the argument that inflammation contributes to Alzheimer pathogenesis. Transgenic mice overexpressing the amyloid precursor protein (APP) gene form amyloid plaques that are accompanied by local activation of microglia/macrophages in a manner similar to the human disease. Many markers of microglial activation and inflammation increase in an age-dependent manner in these mice. However, manipulation of these inflammatory reactions can lead to unexpected outcomes with several instances of reduced pathology when microglia/macrophages are activated further. In particular, anti-Abeta immunotherapy in amyloid-depositing transgenic mice causes a complex series of changes in microglial markers, negating the implicit belief that such activation is monotonic and represented equally well by any of several "activation" markers. A survey of the peripheral macrophage literature identifies at least 2 distinct activation states of macrophages with different consequences for the surrounding tissue. These different activation states can often be distinguished by the markers that are expressed. Several markers are identified from studies outside the brain that neuroscientists might consider evaluating when attempting to more definitively describe the activation state of the monocyte-derived cells in the brain.

Nature, nurture and neurology: gene-environment interactions in neurodegenerative disease. FEBS Anniversary Prize Lecture delivered on 27 June 2004 at the 29th FEBS Congress in Warsaw

Neurodegenerative disorders, such as Huntington's, Alzheimer's, and Parkinson's diseases, affect millions of people worldwide and currently there are few effective treatments and no cures for these diseases. Transgenic mice expressing human transgenes for huntingtin, amyloid precursor protein, and other genes associated with familial forms of neurodegenerative disease in humans provide remarkable tools for studying neurodegeneration because they mimic many of the pathological and behavioural features of the human conditions. One of the recurring themes revealed by these various transgenic models is that different diseases may share similar molecular and cellular mechanisms of pathogenesis. Cellular mechanisms known to be disrupted at early stages in multiple neurodegenerative disorders include gene expression, protein interactions (manifesting as pathological protein aggregation and disrupted signaling), synaptic function and plasticity. Recent work in mouse models of Huntington's disease has shown that enriching the environment of transgenic animals delays the onset and slows the progression of Huntington's disease-associated motor and cognitive symptoms. Environmental enrichment is known to induce various molecular and cellular changes in specific brain regions of wild-type animals, including altered gene expression profiles, enhanced neurogenesis and synaptic plasticity. The promising effects of environmental stimulation, demonstrated recently in models of neurodegenerative disease, suggest that therapy based on the principles of environmental enrichment might benefit disease sufferers and provide insight into possible mechanisms of neurodegeneration and subsequent identification of novel therapeutic targets. Here, we review the studies of environmental enrichment relevant to some major neurodegenerative diseases and discuss their research and clinical implications.

NADPH oxidase mediates hypersomnolence and brain oxidative injury in a murine model of sleep apnea

RATIONALE

Persons with obstructive sleep apnea may have significant residual hypersomnolence, despite therapy. Long-term hypoxia/reoxygenation events in adult mice, simulating oxygenation patterns of moderate-severe sleep apnea, result in lasting hypersomnolence, oxidative injury, and proinflammatory responses in wake-active brain regions. We hypothesized that long-term intermittent hypoxia activates brain NADPH oxidase and that this enzyme serves as a critical source of superoxide in the oxidation injury and in hypersomnolence.

OBJECTIVES

We sought to determine whether long-term hypoxia/reoxygenation events in mice result in NADPH oxidase activation and whether NADPH oxidase is essential for the proinflammatory response and hypersomnolence.

METHODS

NADPH oxidase gene and protein responses were measured in wake-active brain regions in wild-type mice exposed to long-term hypoxia/reoxygenation. Sleep and oxidative and proinflammatory responses were measured in adult mice either devoid of NADPH oxidase activity (gp91phox-null mice) or in which NADPH oxidase activity was systemically inhibited with apocynin osmotic pumps throughout hypoxia/reoxygenation.

MAIN RESULTS

Long-term intermittent hypoxia increased NADPH oxidase gene and protein responses in wake-active brain regions. Both transgenic absence and pharmacologic inhibition of NADPH oxidase activity throughout long-term hypoxia/reoxygenation conferred resistance to not only long-term hypoxia/reoxygenation hypersomnolence but also to carbonylation, lipid peroxidation injury, and the proinflammatory response, including inducible nitric oxide synthase activity in wake-active brain regions.

CONCLUSIONS

Collectively, these findings strongly support a critical role for NADPH oxidase in the lasting hypersomnolence and oxidative and proinflammatory responses after hypoxia/reoxygenation patterns simulating severe obstructive sleep apnea oxygenation, highlighting the potential of inhibiting NADPH oxidase to prevent oxidation-mediated morbidities in obstructive sleep apnea.

Traumatic brain injury: cause or risk of Alzheimer's disease? A review of experimental studies

Traumatic Brain Injury is the leading cause of death and disability among young individuals in our society. Moreover, according to some epidemiological studies, head trauma is one of the most potent environmental risk factors for subsequent development of Alzheimer's disease. Interestingly, pathological features that are present also in Alzheimer's disease (in particular deposition of beta-amyloid protein) were observed in traumatised brains already a few hours after the initial insult. The primary objective of this review is to present methodology and results of numerous recent human and animal studies dealing with this issue. Special emphasis was placed on head trauma experiments in transgenic mouse models of Alzheimer's disease. We further evaluate the connection between traumatic brain insults and subsequent development of dementia and try to differentiate between primary and secondary pathological mechanisms.