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1.  ALK5-dependent TGF-β signaling is a major determinant of late stage adult neurogenesis 
Nature neuroscience  2014;17(7):943-952.
The transforming growth factor-β (TGF-β) signaling pathway serves critical functions in central nervous system (CNS) development, but apart from its proposed neuroprotective actions, its physiological role in the adult brain is unclear. We observed a prominent activation of TGF-β signaling in the adult dentate gyrus and expression of downstream Smad proteins in this neurogenic zone. Consistent with a function of TGF-β signaling in adult neurogenesis, genetic deletion of the TGF-β receptor ALK5 reduced the number, migration, and dendritic arborization of newborn neurons. Conversely, constitutive activation of neuronal ALK5 in forebrain caused a striking increase in these aspects of neurogenesis and was associated with higher expression of c-fos in newborn neurons and with stronger memory function. Our findings describe a new and unexpected role for ALK5-dependent TGF-β signaling as a regulator of the late stages of adult hippocampal neurogenesis which may have implications for changes in neurogenesis during aging and disease.
doi:10.1038/nn.3732
PMCID: PMC4096284  PMID: 24859199
2.  The future of blood-based biomarkers for Alzheimer’s disease 
Treatment of Alzheimer’s disease (AD) is significantly hampered by the lack of easily accessible biomarkers that can detect disease presence and predict disease risk reliably. Fluid biomarkers of AD currently provide indications of disease stage; however, they are not robust predictors of disease progression or treatment response, and most are measured in cerebrospinal fluid, which limits their applicability. With these aspects in mind, the aim of this article is to underscore the concerted efforts of the Blood-Based Biomarker Interest Group, an international working group of experts in the field. The points addressed include: (1) the major challenges in the development of blood-based biomarkers of AD, including patient heterogeneity, inclusion of the “right” control population, and the blood– brain barrier; (2) the need for a clear definition of the purpose of the individual markers (e.g., prognostic, diagnostic, or monitoring therapeutic efficacy); (3) a critical evaluation of the ongoing biomarker approaches; and (4) highlighting the need for standardization of preanalytical variables and analytical methodologies used by the field.
doi:10.1016/j.jalz.2013.01.013
PMCID: PMC4128378  PMID: 23850333
3.  Small Molecule p75NTR Ligands Reduce Pathological Phosphorylation and Misfolding of Tau, Inflammatory Changes, Cholinergic Degeneration, and Cognitive Deficits in AβPPL/S Transgenic Mice 
The p75 neurotrophin receptor (p75NTR ) is involved in degenerative mechanisms related to Alzheimer’s disease (AD). In addition, p75NTR levels are increased in AD and the receptor is expressed by neurons that are particularly vulnerable in the disease. Therefore, modulating p75NTR function may be a significant disease-modifying treatment approach. Prior studies indicated that the non-peptide, small molecule p75NTR ligands LM11A-31, and chemically unrelated LM11A-24, could block amyloid-β-induced deleterious signaling and neurodegeneration in vitro, and LM11A-31 was found to mitigate neuritic degeneration and behavioral deficits in a mouse model of AD. In this study, we determined whether these in vivo findings represent class effects of p75NTR ligands by examining LM11A-24 effects. In addition, the range of compound effects was further examined by evaluating tau pathology and neuroinflammation. Following oral administration, both ligands reached brain concentrations known to provide neuroprotection in vitro. Compound induction of p75NTR cleavage provided evidence for CNS target engagement. LM11A-31 and LM11A-24 reduced excessive phosphorylation of tau, and LM11A-31 also inhibited its aberrant folding. Both ligands decreased activation of microglia, while LM11A-31 attenuated reactive astrocytes. Along with decreased inflammatory responses, both ligands reduced cholinergic neurite degeneration. In addition to the amelioration of neuropathology in AD model mice, LM11A-31, but not LM11A-24, prevented impairments in water maze performance, while both ligands prevented deficits in fear conditioning. These findings support a role for p75NTR ligands in preventing fundamental tau-related pathologic mechanisms in AD, and further validate the development of these small molecules as a new class of therapeutic compounds.
doi:10.3233/JAD-140036
PMCID: PMC4278429  PMID: 24898660
Alzheimer’s disease; LM11A-31; LM11A-24; p75 neurotrophin receptor
4.  Young blood reverses age-related impairments in cognitive function and synaptic plasticity in mice 
Nature medicine  2014;20(6):659-663.
As human lifespan increases, a greater fraction of the population is suffering from age-related cognitive impairments, making it important to elucidate a means to combat the effects of aging1,2. Here we report that exposure of an aged animal to young blood can counteract and reverse pre-existing effects of brain aging at the molecular, structural, functional and cognitive level. Genome-wide microarray analysis of heterochronic parabionts—in which circulatory systems of young and aged animals are connected—identified synaptic plasticity–related transcriptional changes in the hippocampus of aged mice. Dendritic spine density of mature neurons increased and synaptic plasticity improved in the hippocampus of aged heterochronic parabionts. At the cognitive level, systemic administration of young blood plasma into aged mice improved age-related cognitive impairments in both contextual fear conditioning and spatial learning and memory. Structural and cognitive enhancements elicited by exposure to young blood are mediated, in part, by activation of the cyclic AMP response element binding protein (Creb) in the aged hippocampus. Our data indicate that exposure of aged mice to young blood late in life is capable of rejuvenating synaptic plasticity and improving cognitive function.
doi:10.1038/nm.3569
PMCID: PMC4224436  PMID: 24793238
5.  Microglial beclin 1 regulates retromer trafficking and phagocytosis and is impaired in Alzheimer’s disease 
Neuron  2013;79(5):873-886.
SUMMARY
Phagocytosis controls CNS homeostasis by facilitating the removal of unwanted cellular debris. Accordingly, impairments in different receptors or proteins involved in phagocytosis result in enhanced inflammation and neurodegeneration. While various studies have identified extrinsic factors that modulate phagocytosis in health and disease, key intracellular regulators are less understood. Here we show that the autophagy protein beclin 1 is required for efficient phagocytosis in vitro and in mouse brains. Furthermore, we show that beclin 1-mediated impairments in phagocytosis are associated with dysfunctional recruitment of retromer to phagosomal membranes, reduced retromer levels, and impaired recycling of phagocytic receptors CD36 and Trem2. Interestingly, microglia isolated from human Alzheimer’s disease (AD) brains show significantly reduced beclin 1 and retromer protein levels. These findings position beclin 1 as a link between autophagy, retromer trafficking, and receptor-mediated phagocytosis and provide insight into mechanisms by which phagocytosis is regulated and how it may become impaired in AD.
doi:10.1016/j.neuron.2013.06.046
PMCID: PMC3779465  PMID: 24012002
6.  TDP-43 Frontotemporal Lobar Degeneration and Autoimmune Disease 
Journal of neurology, neurosurgery, and psychiatry  2013;84(9):10.1136/jnnp-2012-304644.
Background
The aetiology and pathogenesis of non-genetic forms of frontotemporal dementia (FTD) is unknown and even with the genetic forms of FTD, pathogenesis remains elusive. Given the association between systemic inflammation and other neurodegenerative processes, links between autoimmunity and FTD need to be explored.
Objective
To describe the prevalence of systemic autoimmune disease in semantic variant primary progressive aphasia (svPPA), a clinical cohort, and in progranulin (PGRN) mutation carriers compared to neurologically healthy normal controls (NC) and Alzheimer’s disease (AD) as dementia controls.
Design
Case control.
Setting
Academic medical centres.
Participants
129 svPPA, 39 PGRN, 186 NC, and 158 AD patients underwent chart review for autoimmune conditions. A large subset of svPPA, PGRN, and NC cohorts underwent serum analysis for tumor necrosis factor α (TNF-α) levels.
Outcome Measures
Chi-square comparison of autoimmune prevalence and follow up logistic regression.
Results
There was a significantly increased risk of autoimmune disorders clustered around inflammatory arthritides, cutaneous disorders, and gastrointestinal conditions in the svPPA and PGRN cohorts. Elevated TNF-α levels were observed in svPPA and PGRN compared to NC.
Conclusions
svPPA and PGRN are associated with increased prevalence of specific and related autoimmune diseases compared to NC and AD. These findings suggest a unique pattern of systemic inflammation in svPPA and PGRN and open new research avenues for understanding and treating disorders associated with underlying transactive response DNA-binding protein 43 (TDP-43) aggregation.
doi:10.1136/jnnp-2012-304644
PMCID: PMC3840954  PMID: 23543794
7.  Antiviral drug ganciclovir is a potent inhibitor of microglial proliferation and neuroinflammation 
The antiviral drug ganciclovir inhibits microglial proliferation and protects against disease in mice with experimental autoimmunity encephalomyelitis.
Aberrant microglial responses contribute to neuroinflammation in many neurodegenerative diseases, but no current therapies target pathogenic microglia. We discovered unexpectedly that the antiviral drug ganciclovir (GCV) inhibits the proliferation of microglia in experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis (MS), as well as in kainic acid–induced excitotoxicity. In EAE, GCV largely prevented infiltration of T lymphocytes into the central nervous system (CNS) and drastically reduced disease incidence and severity when delivered before the onset of disease. In contrast, GCV treatment had minimal effects on peripheral leukocyte distribution in EAE and did not inhibit generation of antibodies after immunization with ovalbumin. Additionally, a radiolabeled analogue of penciclovir, [18F]FHBG, which is similar in structure to GCV, was retained in areas of CNS inflammation in EAE, but not in naive control mice, consistent with the observed therapeutic effects. Our experiments suggest GCV may have beneficial effects in the CNS beyond its antiviral properties.
doi:10.1084/jem.20120696
PMCID: PMC3920559  PMID: 24493798
8.  Parabiosis for the study of age-related chronic disease 
Swiss medical weekly  2014;144:w13914.
Summary
Modern medicine wields the power to treat large numbers of diseases and injuries most of us would have died from just a hundred years ago. In view of this tremendous achievement, it can seem as if progress has slowed, and we have been unable to impact the most devastating diseases of our time. Chronic diseases of age such as cardiovascular disease, diabetes, osteoarthritis, or Alzheimer’s disease turn out to be of a complexity that may require transformative ideas and paradigms to understand and treat them. Parabiosis, which mimics aspects of the naturally occurring shared blood supply in conjoined twins in humans and certain animals, may just have the power to be such a transformative experimental paradigm. Forgotten and now shunned in many countries, it has contributed to major breakthroughs in tumor biology, endocrinology, and transplantation research in the past century, and a set of new studies in the US and Britain report stunning advances in stem cell biology and tissue regeneration using parabiosis between young and old mice. We review here briefly the history of parabiosis and discuss its utility to study physiological and pathophysiological processes. We argue that parabiosis is a technique that should enjoy wider acceptance and application, and that policies should be revisited especially if one is to study complex age-related, chronic disorders.
doi:10.4414/smw.2014.13914
PMCID: PMC4082987  PMID: 24496774
9.  Long-Term Cognitive Impairments and Pathological Alterations in a Mouse Model of Repetitive Mild Traumatic Brain Injury 
Mild traumatic brain injury (mTBI, also referred to as concussion) accounts for the majority of all traumatic brain injuries. The consequences of repetitive mTBI have become of particular concern for individuals engaged in certain sports or in military operations. Many mTBI patients suffer long-lasting neurobehavioral impairments. In order to expedite pre-clinical research and therapy development, there is a need for animal models that reflect the long-term cognitive and pathological features seen in patients. In the present study, we developed and characterized a mouse model of repetitive mTBI, induced onto the closed head over the left frontal hemisphere with an electromagnetic stereotaxic impact device. Using GFAP-luciferase bioluminescence reporter mice that provide a readout of astrocyte activation, we observed an increase in bioluminescence relative to the force delivered by the impactor after single impact and cumulative effects of repetitive mTBI. Using the injury parameters established in the reporter mice, we induced a repetitive mTBI in wild-type C57BL/6J mice and characterized the long-term outcome. Animals received repetitive mTBI showed a significant impairment in spatial learning and memory when tested at 2 and 6 months after injury. A robust astrogliosis and increased p-Tau immunoreactivity were observed upon post-mortem pathological examinations. These findings are consistent with the deficits and pathology associated with mTBI in humans and support the use of this model to evaluate potential therapeutic approaches.
doi:10.3389/fneur.2014.00012
PMCID: PMC3912443  PMID: 24550885
mild traumatic brain injury; long-term; neurobehavior; bioluminescence; astrogliosis
10.  Inflammation and Alzheimer’s disease 
Neurobiology of aging  2000;21(3):383-421.
Inflammation clearly occurs in pathologically vulnerable regions of the Alzheimer’s disease (AD) brain, and it does so with the full complexity of local peripheral inflammatory responses. In the periphery, degenerating tissue and the deposition of highly insoluble abnormal materials are classical stimulants of inflammation. Likewise, in the AD brain damaged neurons and neurites and highly insoluble amyloid β peptide deposits and neurofibrillary tangles provide obvious stimuli for inflammation. Because these stimuli are discrete, microlocalized, and present from early preclinical to terminal stages of AD, local upregulation of complement, cytokines, acute phase reactants, and other inflammatory mediators is also discrete, microlocalized, and chronic. Cumulated over many years, direct and bystander damage from AD inflammatory mechanisms is likely to significantly exacerbate the very pathogenic processes that gave rise to it. Thus, animal models and clinical studies, although still in their infancy, strongly suggest that AD inflammation significantly contributes to AD pathogenesis. By better understanding AD inflammatory and immunoregulatory processes, it should be possible to develop anti-inflammatory approaches that may not cure AD but will likely help slow the progression or delay the onset of this devastating disorder.
PMCID: PMC3887148  PMID: 10858586
Alzheimer’s disease; Inflammation; Nervous system; Neuroinflammation; Complement; Cytokine; Chemokine; Acute phase protein; Microglia; Astrocyte; Neuron
11.  Colony-stimulating factor 1 receptor (CSF1R) signaling in injured neurons facilitates protection and survival 
Colony-stimulating factor 1 and IL-34 protect against and partially reverse neurodegeneration in mice in part via promoting CREB signaling.
Colony-stimulating factor 1 (CSF1) and interleukin-34 (IL-34) are functional ligands of the CSF1 receptor (CSF1R) and thus are key regulators of the monocyte/macrophage lineage. We discovered that systemic administration of human recombinant CSF1 ameliorates memory deficits in a transgenic mouse model of Alzheimer’s disease. CSF1 and IL-34 strongly reduced excitotoxin-induced neuronal cell loss and gliosis in wild-type mice when administered systemically before or up to 6 h after injury. These effects were accompanied by maintenance of cAMP responsive element–binding protein (CREB) signaling in neurons rather than in microglia. Using lineage-tracing experiments, we discovered that a small number of neurons in the hippocampus and cortex express CSF1R under physiological conditions and that kainic acid–induced excitotoxic injury results in a profound increase in neuronal receptor expression. Selective deletion of CSF1R in forebrain neurons in mice exacerbated excitotoxin-induced death and neurodegeneration. We conclude that CSF1 and IL-34 provide powerful neuroprotective and survival signals in brain injury and neurodegeneration involving CSF1R expression on neurons.
doi:10.1084/jem.20120412
PMCID: PMC3549715  PMID: 23296467
12.  Neural Progenitor Cells Regulate Microglia Functions and Activity States 
Nature neuroscience  2012;15(11):1485-1487.
We observed that mouse neural progenitor cells (NPCs) have a secretory protein profile distinct from other brain cells and modulate microglial activation, proliferation, and phagocytosis in culture and in vivo. NPC-derived vascular endothelial growth factor was necessary and sufficient to exert at least some of these effects in mice. Neural stem or precursor cells may thus not only be shaped by microglia but regulate in turn microglia functions and activity.
doi:10.1038/nn.3233
PMCID: PMC3495979  PMID: 23086334
13.  Immunotherapy of cereberovascular amloidosis in a transgenic mouse model 
Neurobiology of aging  2011;33(2):432.e1-432.e13.
Cerebrovascular amyloidosis is caused by amyloid accumulation in walls of blood vessel walls leading to hemorrhagic stroke and cognitive impairment. Transforming growth factor-β1 (TGF-β1) expression levels correlate with the degree of cerebrovascular amyloid deposition in Alzheimer s disease (AD) and TGF-β1 immunoreactivity in such cases is increased along the cerebral blood vessels. Here we show that a nasally administered proteosome-based adjuvant activates macrophages and decreases vascular amyloid in TGF-β1 mice. Animals were nasally treated with a proteosome-based adjuvant on a weekly basis for three months beginning at age 13 months. Using MRI we found that while control animals showed a significant cerebrovascular pathology, proteosome-based adjuvant prevents further brain damage and prevents pathological changes in the blood-brain barrier. Using an object recognition test and Y-maze, we found significant improvement in cognition in the treated group. Our findings support the potential use of a macrophage immuno-modulator as a novel approach to reduce cerebrovascular amyloid, prevent microhemorrhage and improve cognition.
doi:10.1016/j.neurobiolaging.2011.01.006
PMCID: PMC3136542  PMID: 21371785
cerebrovascular disease; congnitive impairment; intracerebral hemorrhage; macrophage; MRI; vaccine; therapy
14.  The role of inflammation in age-related disease 
Aging (Albany NY)  2013;5(1):84-93.
The National Institutes of Health (NIH) Geroscience Interest Group (GSIG) sponsored workshop, The Role of Inflammation in Age-Related Disease, was held September 6th-7th, 2012 in Bethesda, MD. It is now recognized that a mild pro-inflammatory state is correlated with the major degenerative diseases of the elderly. The focus of the workshop was to better understand the origins and consequences of this low level chronic inflammation in order to design appropriate interventional studies aimed at improving healthspan. Four sessions explored the intrinsic, environmental exposures and immune pathways by which chronic inflammation are generated, sustained, and lead to age-associated diseases. At the conclusion of the workshop recommendations to accelerate progress toward understanding the mechanistic bases of chronic disease were identified.
PMCID: PMC3616233  PMID: 23474627
15.  The immunology of neurodegeneration 
The Journal of Clinical Investigation  2012;122(4):1156-1163.
While immune responses in neurodegeneration were regarded as little more than a curiosity a decade ago, they are now increasingly moving toward center stage. Factors driving this movement include the recognition that most of the relevant immune molecules are produced within the brain, that microglia are proficient immune cells shaping neuronal circuitry and fate, and that systemic immune responses affect brain function. We will review this complex field from the perspective of neurons, extra-neuronal brain cells, and the systemic environment and highlight the possibility that cell intrinsic innate immune molecules in neurons may function in neurodegenerative processes.
doi:10.1172/JCI58656
PMCID: PMC3315444  PMID: 22466657
16.  Deficiency of terminal complement pathway inhibitor promotes neuronal tau pathology and degeneration in mice 
Background
The neuronal microtubule-associated protein tau becomes hyperphosphorylated and forms aggregates in tauopathies but the processes leading to this pathological hallmark are not understood. Because tauopathies are accompanied by neuroinflammation and the complement cascade forms a key innate immune pathway, we asked whether the complement system has a role in the development of tau pathology.
Findings
We tested this hypothesis in two mouse models, which expressed either a central inhibitor of complement or lacked an inhibitor of the terminal complement pathway. Complement receptor-related gene/protein y is the natural inhibitor of the central complement component C3 in rodents. Expressing a soluble variant (sCrry) reduced the number of phospho-tau (AT8 epitope) positive neurons in the brain stem, cerebellum, cortex, and hippocampus of aged P301L mutant tau/sCrry double-transgenic mice compared with tau single-transgenic littermates (JNPL3 line). CD59a is the major inhibitor of formation of the membrane attack complex in mice. Intrahippocampal injection of adeno-associated virus encoding mutant human P301L tau into Cd59a−/− mice resulted in increased numbers of AT8-positive cells compared with wild-type controls. This was accompanied by neuronal and synaptic loss and reduced dendritic integrity.
Conclusions
Our data in two independent mouse models with genetic changes in key regulators of the complement system support the hypothesis that the terminal pathway has an active role in the development of tau pathology. We propose that inhibition of the terminal pathway may be beneficial in tauopathies.
doi:10.1186/1742-2094-9-220
PMCID: PMC3511294  PMID: 22989354
Age-related neurodegeneration; Alzheimer’s disease; Complement system; Frontotemporal lobar degeneration; Innate immune system; Mouse models of tau pathology; Tauopathy
17.  Identification of a central role for complement in osteoarthritis 
Nature Medicine  2011;17(12):1674-1679.
Osteoarthritis, characterized by the breakdown of articular cartilage in synovial joints, has long been viewed as the result of “wear and tear”1. Although low-grade inflammation is detected in osteoarthritis, its role is unclear2–4. Here we identify a central role for the inflammatory complement system in the pathogenesis of osteoarthritis. Through proteomic and transcriptomic analyses of synovial fluids and membranes from individuals with osteoarthritis, we find that expression and activation of complement is abnormally high in human osteoarthritic joints. Using mice genetically deficient in C5, C6, or CD59a, we show that complement, and specifically the membrane attack complex (MAC)-mediated arm of complement, is critical to the development of arthritis in three different mouse models of osteoarthritis. Pharmacological modulation of complement in wild-type mice confirmed the results obtained with genetically deficient mice. Expression of inflammatory and degradative molecules was lower in chondrocytes from destabilized joints of C5-deficient mice than C5-sufficient mice, and MAC induced production of these molecules in cultured chondrocytes. Furthermore, MAC co-localized with matrix metalloprotease (MMP)-13 and with activated extracellular signal-regulated kinase (ERK) around chondrocytes in human osteoarthritic cartilage. Our findings indicate that dysregulation of complement in synovial joints plays a critical role in the pathogenesis of osteoarthritis.
doi:10.1038/nm.2543
PMCID: PMC3257059  PMID: 22057346
18.  The aging systemic milieu negatively regulates neurogenesis and cognitive function 
Nature  2011;477(7362):90-94.
Summary
In the central nervous system (CNS), aging results in a precipitous decline in adult neural stem/progenitor cells (NPCs) and neurogenesis, with concomitant impairments in cognitive functions1. Interestingly, such impairments can be ameliorated through systemic perturbations such as exercise1. Here, using heterochronic parabiosis we show that blood-borne factors present in the systemic milieu can inhibit or promote adult neurogenesis in an age dependent fashion in mice. Accordingly, exposing a young animal to an old systemic environment, or to plasma from old mice, decreased synaptic plasticity and impaired contextual fear conditioning and spatial learning and memory. We identify chemokines - including CCL11/Eotaxin – whose plasma levels correlate with reduced neurogenesis in heterochronic parabionts and aged mice, and whose levels are increased in plasma and cerebral spinal fluid of healthy aging humans. Finally, increasing peripheral CCL11 chemokine levels in vivo in young mice decreased adult neurogenesis and impaired learning and memory. Together our data indicate that the decline in neurogenesis, and cognitive impairments, observed during aging can be in part attributed to changes in blood-borne factors.
doi:10.1038/nature10357
PMCID: PMC3170097  PMID: 21886162
19.  Thy1-hAPPLond/Swe+ mouse model of Alzheimer's disease displays broad behavioral deficits in sensorimotor, cognitive and social function 
Brain and Behavior  2012;2(2):142-154.
Alzheimer's disease (AD), the most common form of dementia, is an age-dependent progressive neurodegenerative disorder. β-amyloid, a metabolic product of the amyloid precursor protein (APP), plays an important role in the pathogenesis of AD. The Thy1-hAPPLond/Swe+ (line 41) transgenic mouse overexpresses human APP751 and contains the London (V717I) and Swedish (K670M/N671L) mutations. Here, we used a battery of behavioral tests to evaluate general activity, cognition, and social behavior in six-month-old male Thy1-hAPPLond/Swe+ mice. We found hyperactivity in a novel environment as well as significant deficits in spontaneous alternation behavior. In fear conditioning (FC), Thy1-hAPPLond/Swe+ mice did not display deficits in acquisition or in memory retrieval in novel context of tone-cued FC, but they showed significant memory retrieval impairment during contextual testing in an identical environment. Surprisingly, in a standard hidden platform water maze, no significant deficit was detected in mutant mice. However, a delayed-matching-to-place paradigm revealed a significant deficit in Thy1-hAPPLond/Swe+ mice. Lastly, in the social novelty session of a three-chamber test, Thy1-hAPPLond/Swe+ mice exhibited a significantly decreased interest in a novel versus a familiar stranger compared to control mice. This could possibly be explained by decreased social memory or discrimination and may parallel disturbances in social functioning in human AD patients. In conclusion, the Thy1-hAPPLond/Swe+ mouse model of AD displayed a behavioral phenotype that resembles, in part, the cognitive and psychiatric symptoms experienced in AD patients.
doi:10.1002/brb3.41
PMCID: PMC3345358  PMID: 22574282
Alzheimer's disease; amyloid precursor protein; behavior; learning and memory; neurodegenerative disorder; social interaction
20.  Inflammation in Alzheimer Disease—A Brief Review of the Basic Science and Clinical Literature 
Biochemical and neuropathological studies of brains from individuals with Alzheimer disease (AD) provide clear evidence for an activation of inflammatory pathways, and long-term use of anti-inflammatory drugs is linked with reduced risk to develop the disease. As cause and effect relationships between inflammation and AD are being worked out, there is a realization that some components of this complex molecular and cellular machinery are most likely promoting pathological processes leading to AD, whereas other components serve to do the opposite. The challenge will be to find ways of fine tuning inflammation to delay, prevent, or treat AD.
Complex immune and inflammatory processes are activated during Alzheimer disease progression. Future trials of rationally selected anti-inflammatory drugs may help delay, prevent, or treat the disease.
doi:10.1101/cshperspect.a006346
PMCID: PMC3253025  PMID: 22315714
21.  Complement Receptor 2 is Expressed in Neural Progenitor Cells and Regulates Adult Hippocampal Neurogenesis 
Injury and inflammation are potent regulators of adult neurogenesis. As the complement system forms a key immune pathway that may also exert critical functions in neural development and neurodegeneration, we asked if complement receptors regulate neurogenesis. We discovered that complement receptor 2 (CR2), classically known as a co-receptor of the B lymphocyte antigen receptor, is expressed in adult neural progenitor cells (NPCs) of the dentate gyrus. Two of its ligands, C3d and interferon-α (IFN-α), inhibited proliferation of wildtype NPCs but not NPCs derived from mice lacking Cr2 (Cr2−/−) indicating functional Cr2 expression. Young and old Cr2−/− mice exhibited prominent increases in basal neurogenesis compared with wildtype littermates, while intracerebral injection of C3d resulted in fewer proliferating neuroblasts in wildtype than in Cr2−/− mice. We conclude that Cr2 regulates hippocampal neurogenesis and propose that increased C3d and IFN-α production associated with brain injury or viral infections may inhibit neurogenesis.
doi:10.1523/JNEUROSCI.3617-10.2011
PMCID: PMC3071463  PMID: 21411641
22.  Immune activation in brain aging and neurodegeneration: too much or too little? 
Neuron  2009;64(1):110-122.
Until recently the brain was studied almost exclusively by neuroscientists and the immune system by immunologists, fuelling the notion that these systems represented two isolated entities. However, as more data suggest an important role of the immune system in regulating the progression of brain aging and neurodegenerative disease, it has become clear that the crosstalk between these systems can no longer be ignored and a new interdisciplinary approach is necessary. A central question that emerges is whether immune and inflammatory pathways become hyperactivated with age and promote degeneration or whether insufficient immune responses, which fail to cope with age-related stress may contribute to disease. We try to explore here the consequences of gain- versus loss-of-function with an emphasis on microglia as sensors and effectors of immune function in the brain and we discuss the potential role of the peripheral environment in neurodegenerative diseases.
doi:10.1016/j.neuron.2009.08.039
PMCID: PMC2834890  PMID: 19840553
neurodegenerative disease; neuroimmunology; neuroinflammation; microglia
23.  Bioactive TGF-β can associate with lipoproteins and is enriched in those containing apolipoprotein E3 
Journal of neurochemistry  2009;110(4):1254-1262.
SUMMARY
Transforming growth factor-β1 (TGF-β1) has central functions in development, tissue maintenance, and repair and has been implicated in major diseases. We discovered that TGF-β1 contains several amphipathic helices and hydrophobic domains similar to apolipoprotein E (apoE), a protein involved in lipoprotein metabolism. Indeed, TGF-β1 associates with lipoproteins isolated from human plasma, cultured liver cells, or astrocytes, and its bioactivity was highest in high-density lipoprotein (HDL) preparations. Importantly, lipoproteins containing the apoE3 isoform had higher TGF-β levels and bioactivity than those containing apoE4, a major genetic risk factor for atherosclerosis and Alzheimer’s disease. Because TGF-β1 can be protective in these diseases an association with apoE3 may be beneficial. Association of TGF-β with different types of lipoproteins may facilitate its diffusion, regulate signaling, and offer additional specificity for this important growth factor.
doi:10.1111/j.1471-4159.2009.06222.x
PMCID: PMC2915937  PMID: 19549280
24.  Angiotensin II sustains brain inflammation in mice via TGF-β 
The Journal of Clinical Investigation  2010;120(8):2782-2794.
The renin-angiotensin-aldosterone system (RAAS) is a key hormonal system regulating blood pressure. However, expression of RAAS components has recently been detected in immune cells, and the RAAS has been implicated in several mouse models of autoimmune disease. Here, we have identified Ang II as a paracrine mediator, sustaining inflammation in the CNS in the EAE mouse model of MS via TGF-β. Ang II type 1 receptors (AT1Rs) were found to be primarily expressed in CNS-resident cells during EAE. In vitro, astrocytes and microglia responded to Ang II treatment by inducing TGF-β expression via a pathway involving the TGF-β–activating protease thrombospondin-1 (TSP-1). TGF-β upregulation in astrocytes and microglia during EAE was blocked with candesartan (CA), an inhibitor of AT1R. Treatment of EAE with CA ameliorated paralysis and blunted lymphocyte infiltration into the CNS, outcomes that were also seen with genetic ablation of AT1Ra and treatment with an inhibitor of TSP-1. These data suggest that AT1R antagonists, frequently prescribed as antihypertensives, may be useful to interrupt this proinflammatory, CNS-specific pathway in individuals with MS.
doi:10.1172/JCI41709
PMCID: PMC2912186  PMID: 20628203
25.  Regulation of Amyloid Precursor Protein Processing by the Beclin 1 Complex 
PLoS ONE  2010;5(6):e11102.
Autophagy is an intracellular degradation pathway that functions in protein and organelle turnover in response to starvation and cellular stress. Autophagy is initiated by the formation of a complex containing Beclin 1 (BECN1) and its binding partner Phosphoinositide-3-kinase, class 3 (PIK3C3). Recently, BECN1 deficiency was shown to enhance the pathology of a mouse model of Alzheimer Disease (AD). However, the mechanism by which BECN1 or autophagy mediate these effects are unknown. Here, we report that the levels of Amyloid precursor protein (APP) and its metabolites can be reduced through autophagy activation, indicating that they are a substrate for autophagy. Furthermore, we find that knockdown of Becn1 in cell culture increases the levels of APP and its metabolites. Accumulation of APP and APP C-terminal fragments (APP-CTF) are accompanied by impaired autophagosomal clearance. Pharmacological inhibition of autophagosomal-lysosomal degradation causes a comparable accumulation of APP and APP-metabolites in autophagosomes. Becn1 reduction in cell culture leads to lower levels of its binding partner Pik3c3 and increased presence of Microtubule-associated protein 1, light chain 3 (LC3). Overexpression of Becn1, on the other hand, reduces cellular APP levels. In line with these observations, we detected less BECN1 and PIK3C3 but more LC3 protein in brains of AD patients. We conclude that BECN1 regulates APP processing and turnover. BECN1 is involved in autophagy initiation and autophagosome clearance. Accordingly, BECN1 deficiency disrupts cellular autophagy and autophagosomal-lysosomal degradation and alters APP metabolism. Together, our findings suggest that autophagy and the BECN1-PIK3C3 complex regulate APP processing and play an important role in AD pathology.
doi:10.1371/journal.pone.0011102
PMCID: PMC2886067  PMID: 20559548

Results 1-25 (36)