Clinical studies suggest that exposure to stress can increase risk for Alzheimer's disease (AD). ... more Clinical studies suggest that exposure to stress can increase risk for Alzheimer's disease (AD). Though the precise links between stress and vulnerability to develop AD remain unsettled, recent animal work suggests that stress may promote susceptibility to AD pathology by activating tau kinases and inducing tau phosphorylation (tau-P). Our previous findings indicate differential involvement of corticotropin-releasing factor receptors (CRFR1 and 2) in regulating tau-P in the hippocampus induced by acute restraint, an emotional stressor. To assess the generality of CRFR involvement in stress-induced tau-P and tau kinase activity, the present study extends our investigation to a well-characterized physiological stressor: immune challenge induced by bacterial lipopolysaccharide (LPS). Acute systemic administration of LPS (100 μg/kg) robustly increased hippocampal (but not isocortical or cerebellar) tau-P, peaking at 40-120 min postinjection and abating thereafter. Assessments of the genotype dependence of this effect yielded results distinct from the restraint model. Treatment with LPS increased phosphorylation in wild type, single and double CRFR knockouts with only subtle variation, which included a reliable exaggeration of tau-P responses in CRFR1-deficient mice. Parallel analyses implicate glycogen synthase kinase-3 and cyclin-dependent kinase 5 as likely cellular mediators of LPS-induced tau-P. Conversely, our data suggest that temperature-dependent fluctuations in tau phosphatase (PP2A) may not play a role in this context. Thus, neither the strict CRFR1-dependence of restraint-induced tau-P, nor the exaggeration of these responses in CRFR2 null mice, generalize to the LPS model. CRFR mediation of stress-induced hippocampal tau-P may be limited to emotional stressors.
Proceedings of the National Academy of Sciences, 2012
Exposure and/or sensitivity to stress have been implicated as conferring risk for development of ... more Exposure and/or sensitivity to stress have been implicated as conferring risk for development of Alzheimer's disease (AD). Although the basis for such a link remains unclear, we previously reported differential involvement of corticotropin-releasing factor receptor (CRFR) 1 and 2 in acute stress-induced tau phosphorylation (tau-P) and solubility in the hippocampus. Here we examined the role of CRFRs in tau-P induced by repeated stress and the structural manifestations of altered tau solubility. Robust tau-P responses were seen in WT and CRFR2 null mice exposed to repeated stress, which were sustained at even 24 h after the final stress exposure. A portion of phosphorylated tau in these mice was sequestered in detergent-soluble cellular fractions. In contrast, CRFR1 and CRFR double-KO mice did not exhibit repeated stress-induced alterations in tau-P or solubility. Similarly, treatment with CRFR1 antagonist attenuated repeated stress-induced tau-P. Using histochemical approaches in a transgenic CRFR1 reporter mouse line, we found substantial overlap between hippocampal CRFR1 expression and cells positive for phosphorylated tau after exposure to repeated stress. Ultrastructural analysis of negatively stained extracts from WT and CRFR2 null mice identified globular aggregates that displayed positive immunogold labeling for tau-P, as well as conformational changes in tau (MC1) seen in early AD. Given that repeated stress exposure results in chronic increases in hippocampal tau-P and its sequestration in an insoluble (and potentially prepathogenic) form, our data may define a link between stress and an AD-related pathogenic mechanism. neurofibrillary tangles | western blot | pathology | electron microscopy A lzheimer's disease (AD) is definitively characterized by the presence of β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs). NFTs are insoluble intracellular inclusions composed of aggregated hyperphosphorylated forms of the cytoskeletal protein tau that accumulate initially within the hippocampal formation (1). A critical step in NFT formation is thought to be the transition of these phosphorylated tau species into aggregated insoluble fibrils. Hyperphosphorylated tau has a reduced ability to bind microtubules and has been reported to self-aggregate into paired helical filaments (PHFs), which compose NFTs (2, 3). The development of NFTs is positively correlated with cognitive decline and neuronal loss in AD (4, 5).
Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemic... more Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemical and in situ hybridization. MCH-immunoreactive neurons were found in the lateral hypothalamus and dorsolateral zona incerta. MCH-ir fibers were seen in the medial mammillary nucleus, and in the median eminence, and very few fibers in the globus pallidus. This is the first report describing the MCH-ir cell and fiber distribution in the monkey brain.
To gain further knowledge on the preclinical phase of Alzheimer's disease (AD), we sought to ... more To gain further knowledge on the preclinical phase of Alzheimer's disease (AD), we sought to characterize cognitive performance, neuroimaging and plasma-based AD biomarkers in a cohort of non-demented adults with down syndrome (DS). The goal of the down syndrome biomarker Initiative (DSBI) pilot is to test feasibility of this approach for future multicenter studies. We enrolled 12 non-demented participants with DS between the ages of 30-60 years old. Participants underwent extensive cognitive testing, volumetric MRI, amyloid positron emission tomography (PET; 18F-florbetapir), fluorodeoxyglucose (FDG) PET (18F-fluorodeoxyglucose) and retinal amyloid imaging. In addition, plasma beta-amyloid (Aβ) species were measured and Apolipoprotein E (ApoE) genotyping was performed. Results from our multimodal analysis suggest greater hippocampal atrophy with amyloid load. Additionally, we identified an inverse relationship between amyloid load and regional glucose metabolism. Cognitive and ...
A randomized, placebo-controlled, double-blind, multicenter 52-week phase 2 trial of resveratrol ... more A randomized, placebo-controlled, double-blind, multicenter 52-week phase 2 trial of resveratrol in individuals with mild to moderate Alzheimer disease (AD) examined its safety and tolerability and effects on biomarker (plasma Aβ40 and Aβ42, CSF Aβ40, Aβ42, tau, and phospho-tau 181) and volumetric MRI outcomes (primary outcomes) and clinical outcomes (secondary outcomes). Participants (n = 119) were randomized to placebo or resveratrol 500 mg orally once daily (with dose escalation by 500-mg increments every 13 weeks, ending with 1,000 mg twice daily). Brain MRI and CSF collection were performed at baseline and after completion of treatment. Detailed pharmacokinetics were performed on a subset (n = 15) at baseline and weeks 13, 26, 39, and 52. Resveratrol and its major metabolites were measurable in plasma and CSF. The most common adverse events were nausea, diarrhea, and weight loss. CSF Aβ40 and plasma Aβ40 levels declined more in the placebo group than the resveratrol-treated gro...
We investigated the impact of APOE genotype on cerebral blood flow (CBF) in older and younger adu... more We investigated the impact of APOE genotype on cerebral blood flow (CBF) in older and younger adults. Forty cognitively normal older adults (16 ε4 carriers, 24 non-ε4 carriers) and 30 younger adults (15 ε4 carriers, 15 non-ε4 carriers) completed a resting-state whole-brain pulsed arterial spin labeling magnetic resonance scan. Main effects of aging were demonstrated wherein older adults had decreased gray matter CBF corrected for partial volume effects compared to younger adults in widespread brain regions. Main effects of APOE genotype were also observed wherein ε4 carriers displayed greater CBF in the left lingual gyrus and precuneus than non-carriers. An interaction between age and APOE genotype in the left anterior cingulate cortex (ACC) was characterized by reduced CBF in older ε4 carriers and increased CBF in young ε4 carriers. Increased CBF in the left ACC resulting from the interaction of age group and APOE genotype was positively correlated with executive functioning in you...
Alzheimer's disease (AD) is characterized by selective vulnerability of specific neuronal pop... more Alzheimer's disease (AD) is characterized by selective vulnerability of specific neuronal populations within particular brain regions. For example, hippocampal glutamatergic cell populations within the CA1/subicular pyramidal cell fields have been found to be particularly vulnerable early in AD progression. In contrast, hippocampal GABA-ergic neurons and receptors appear resistant to neurodegeneration. Despite relative sparing of GABA(A) receptors in AD, it is possible that the specific subunit composition of these receptors may undergo alterations with disease progression. In order to address this issue, we employed quantitative Western blot analysis to examine protein levels of GABA(A) receptor subunits alpha 1, alpha 5, beta 1, beta 2 in the hippocampus of subjects displaying increasing severity of AD neuropathology. Subjects were categorized into three groups based upon Braak staging pathologic criteria: pathologically mild (stages I/II, n=9); moderate (stages III/IV, n=8); ...
Clinical and basic science research suggests that stress and/or changes in central stress signali... more Clinical and basic science research suggests that stress and/or changes in central stress signaling intermediates may be involved in Alzheimer's disease (AD) pathogenesis. Although the links between stress and AD remain unsettled, data from our group and others have established that stress exposure in rodents may confer susceptibility to AD pathology by inducing hippocampal tau phosphorylation (tau-P). Work in our laboratory has shown that stress-induced tau-P requires activation of the type-1 corticotropin-releasing factor receptor (CRFR1). CRF overexpressing (CRF-OE) mice are a model of chronic stress that display cognitive impairment at 9-10 month of age. In this study we used 6-7 month old CRF-OE mice to examine whether sustained exposure to CRF and stress steroids would impact hippocampal tau-P and kinase activity in the presence or absence of the CRFR1-specific antagonist, R121919, given daily for 30 days. CRF-OE mice had significantly elevated tau-P compared to wild type ...
Journal of Alzheimer's disease : JAD, Jan 19, 2015
Stress exposure and the corticotropin-releasing factor (CRF) system have been implicated as mecha... more Stress exposure and the corticotropin-releasing factor (CRF) system have been implicated as mechanistically involved in both human Alzheimer's disease (AD) and associated rodent models. In particular, the major stress receptor, CRF receptor type 1 (CRFR1), modulates cellular activity in many AD-relevant brain areas, and has been demonstrated to impact both tau phosphorylation and amyloid-β (Aβ) pathways. The overarching goal of our laboratory is to develop and characterize agents that impact the CRF signaling system as disease-modifying treatments for AD. In the present study, we developed a novel transgenic mouse to determine whether partial or complete ablation of CRFR1 was feasible in an AD transgenic model and whether this type of treatment could impact Aβ pathology. Double transgenic AD mice (PSAPP) were crossed to mice null for CRFR1; resultant CRFR1 heterozygous (PSAPP-R1+/-) and homozygous (PSAPP-R1-/-) female offspring were used at 12 months of age to examine the impact...
In Alzheimer's disease (AD) it is well known that specific regions of the brain are particula... more In Alzheimer's disease (AD) it is well known that specific regions of the brain are particularly vulnerable to the pathologic insults of the disease. In particular, the hippocampus is affected very early in the disease and by end stage AD is ravaged by neurofibrillary tangles and senile plaques (i.e., the pathologic hallmarks of AD). Throughout the past several years our laboratory has sought to determine the molecular mechanisms underlying the selective vulnerability of neurons in AD. To this end, we employed immunohistochemical, biochemical, and in situ hybrization methods to examine glutamate and gamma-aminobutyric acid (GABAA) receptor subtypes in the hippocampus of patients displaying the full spectrum of AD pathology. Despite the fact that the hippocampus is characterized by a marked loss of neurons in the late stages of the disease, our data demonstrate a rather remarkable preservation among some glutamate and GABAA receptor subtypes. Collectively, our data support the vi...
Journal of Chemical Neuroanatomy - J CHEM NEUROANAT, 2004
We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal... more We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal mRNA expression of GABAA receptor subunits α1 and α5 in human subjects with progressing cognitive impairment. Included in this study were 17 participants of the Religious Order Study (ROS), who were categorized into three groups based upon degree of cognitive impairment: no cognitive impairment (n = 6); moderate cognitive impairment (n = 5); and probable Alzheimer’s disease (AD) (n = 6). While the levels of each specific subunit mRNA were relatively homogeneously distributed throughout the five hippocampal subregions analyzed (CA1–4, and the granule cell layer of the dentate gyrus), mRNA expression of the α1 receptor subunit was found to be 20% reduced in the moderate cognitive impairment group as compared to the no cognitive impairment group. In addition, α1 mRNA expression was 25% reduced in the probable Alzheimer’s disease group compared to the group with no cognitive impairment. Sim...
Alterations in corticotropin-releasing factor (CRF) signaling pathways have been implicated in ir... more Alterations in corticotropin-releasing factor (CRF) signaling pathways have been implicated in irritable bowel syndrome (IBS) pathophysiology. We aimed to: 1) determine the effect of the selective CRF receptor 1 antagonist (CRF 1 ), GW876008, relative to placebo, on regional activation and effective connectivity of a stress-related emotional-arousal circuit during expectation of abdominal pain using functional magnetic resonance imaging (fMRI) in human subjects with a diagnosis of IBS and healthy controls (HCs), and 2) examine GW876008 effects on state-trait anxiety and hypothalamic-pituitary-adrenal (HPA) axis response. While there were no drug-related effects on peripheral HPA activity, significant central effects were observed in brain regions associated with the stress response. Effective connectivity analysis showed druginduced normalizations between key regions of the emotional-arousal circuit in patients. During pain expectation, orally administered GW876008 relative to placebo produced significant blood oxygen level-dependent (BOLD) signal reductions in the amygdala, hippocampus, insula, anterior cingulate and orbitomedial prefrontal cortices across groups. Patients showed significantly greater BOLD responses in the left locus coeruleus and hypothalamus following placebo compared to HCs, and BOLD signal decreases in the left hypothalamus following drug. The inhibitory effects of GW876008 in the hypothalamus in patients were moderated by anxiety; patients having average and high levels of state anxiety showed drug-related BOLD decreases. GW876008 represents a novel tool for elucidating the neuronal mechanisms and circuitry underlying hyperactivation of CRF/CRF 1 signaling and its role in IBS pathophysiology. The unique state anxiety effects observed suggest a potential pathway for therapeutic benefit of CRF 1 receptor antagonism for patients with stress-sensitive disorders.
Alzheimer's disease (AD) is characterized by loss of specific cell populations within selective s... more Alzheimer's disease (AD) is characterized by loss of specific cell populations within selective subregions of the hippocampus. Excitotoxicity, mediated via ionotropic glutamate receptors, may play a crucial role in this selective neuronal vulnerability. We investigated whether alterations in NMDA receptor subunits occurred during AD progression. Employing biochemical and in situ hybridization techniques in subjects with a broad range of AD pathology, protein levels, and mRNA expression of NR1/2A/2B subunits were assayed. With increasing AD neuropathology, protein levels and mRNA expression for NR1/2B subunits were significantly reduced, while the NR2A subunit mRNA expression and protein levels were unchanged. Cellular analysis of neuronal mRNA expression revealed a significant increase in the NR2A subunit in subjects with moderate neurofibrillary tangle neuropathology. This investigation supports the hypothesis that alterations occur in the expression of specific NMDA receptor subunits with increasing AD pathologic severity, which is hypothesized to contribute to the vulnerability of these neurons. D
In this article we present a comprehensive review of relevant research and reports on the GABA A ... more In this article we present a comprehensive review of relevant research and reports on the GABA A receptor in the aged and Alzheimer's disease (AD) brain. In comparison to glutamatergic and cholinergic systems, the GABAergic system is relatively spared in AD, but the precise mechanisms underlying differential vulnerability are not well understood. Using several methods, investigations demonstrate that despite resistance of the GABAergic system to neurodegeneration, particular subunits of the GABA A receptor are altered with age and AD, which can induce compensatory increases in GABA A receptor subunits within surrounding cells. We conclude that although aging-and disease-related changes in GABA A receptor subunits may be modest, the mechanisms that compensate for these changes may alter the pharmacokinetic and physiological properties of the receptor. It is therefore crucial to understand the subunit composition of individual GABA A receptors in the diseased brain when developing therapeutics that act at these receptors.
Neurofibrillary tangles (NFTs) are composed of abnormal aggregates of the cytoskeletal protein ta... more Neurofibrillary tangles (NFTs) are composed of abnormal aggregates of the cytoskeletal protein tau. Together with amyloid β (Aβ) plaques and neuronal and synaptic loss, NFTs constitute the primary pathological hallmarks of Alzheimer disease (AD). Recent evidence also suggests that caspases are activated early in the progression of AD and may play a role in neuronal loss and NFT pathology. Here we demonstrate that tau is cleaved at D421 (ΔTau) by executioner caspases. Following caspase-cleavage, ΔTau facilitates nucleation-dependent filament formation and readily adopts a conformational change recognized by the early pathological tau marker MC1. ΔTau can be phosphorylated by glycogen synthase kinase-3β and subsequently recognized by the NFT antibody PHF-1. In transgenic mice and AD brains, ΔTau associates with both early and late markers of NFTs and is correlated with cognitive decline. Additionally, ΔTau colocalizes with Aβ 1-42 and is induced by Aβ 1-42 in vitro. Collectively, our data imply that Aβ accumulation triggers caspase activation, leading to caspase-cleavage of tau, and that this is an early event that may precede hyperphosphorylation in the evolution of AD tangle pathology. These results suggest that therapeutics aimed at inhibiting tau caspase-cleavage may prove beneficial not only in preventing NFT formation, but also in slowing cognitive decline.
We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal... more We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal mRNA expression of GABA(A) receptor subunits alpha1 and alpha5 in human subjects with progressing cognitive impairment. Included in this study were 17 participants of the Religious Order Study (ROS), who were categorized into three groups based upon degree of cognitive impairment: no cognitive impairment (n = 6); moderate cognitive impairment (n = 5); and probable Alzheimer's disease (AD) (n = 6). While the levels of each specific subunit mRNA were relatively homogeneously distributed throughout the five hippocampal subregions analyzed (CA1-4, and the granule cell layer of the dentate gyrus), mRNA expression of the alpha1 receptor subunit was found to be 20% reduced in the moderate cognitive impairment group as compared to the no cognitive impairment group. In addition, alpha1 mRNA expression was 25% reduced in the probable Alzheimer's disease group compared to the group with no cognitive impairment. Similarly, alpha5 subunit mRNA was reduced 32% between no cognitive impairment and moderate cognitive impairment groups, and 35% between no cognitive impairment and probable Alzheimer's disease groups. No significant reductions were found between moderate cognitive impairment and probable Alzheimer's disease groups for either subunit. Collectively, our data provide evidence for modest reductions in GABA(A) receptor subunit mRNAs, and suggest these changes occur very early in the progression of…
The Alzheimer's disease (AD) brain, characterized pathologically by the presence of senile plaque... more The Alzheimer's disease (AD) brain, characterized pathologically by the presence of senile plaques and neurofibrillary tangles, contains regions that are differentially prone toward development of AD pathology. Within these ''vulnerable'' regions, specific cell populations appear to be selectively affected; the pyramidal cells of the hippocampal subiculum subfield constitute such a vulnerable region. This study investigated whether the AMPA receptor subunit content (GluR1, GluR2, GluR2/3) within ''vulnerable'' vs. ''resistant'' sectors of the hippocampus is quantitatively altered with increasing AD neuropathology, as determined by Braak staging. We hypothesize that the glutamate-mediated vulnerability is highly influenced by the repertoire of glutamate receptors expressed on hippocampal neurons. Our results indicate that AMPA receptor subunit proteins are relatively spared across all Braak stages in resistant subfields (CA2/CA3/Dentate Gyrus). However, within vulnerable sectors, i.e., subiculum, GluR2, and GluR2/3 protein levels decreased 63.77% and 60.60%, respectively, in association with Braak stages I -II and stages III -IV, respectively. In Braak stages V -VI, GluR2 and GluR2/3 protein levels were similar to those of Braak stages I -II. In contrast to GluR2 and GluR2/3, GluR1 protein levels were unchanged within vulnerable sectors throughout all stages of the disease. In interpreting these data, it may be relevant to consider that the GluR2 subunit impedes the flow of Ca +2 through the AMPA receptor ion channel. Thus, we hypothesize that in resistant sectors, the presence of the GluR2 subunit may provide a neuroprotective role by limiting the flow of extracellular Ca +2 , whereas in vulnerable regions, the reduction of GluR2 may contribute to the vulnerability via a mechanism involving an increase in intracellular Ca +2 and destabilization of intracellular Ca +2 homeostasis. D
Pharmacological studies have documented that altered drug responses, particularly to benzodiazepi... more Pharmacological studies have documented that altered drug responses, particularly to benzodiazepines, are common in elderly populations. While numerous factors may contribute to changes in drug response, age-related alterations in the molecular composition of GABA A receptors may be a key factor in regulating these responses. We employed quantitative densitometry to examine the cytological features and density of highly prevalent hippocampal GABA A receptor subunits (α1 and β2/3) in young and aged rhesus monkeys. α1 and β2/3 subunit immunostaining was differentially distributed throughout the hippocampus. In addition, β2/3 immunolabeling in aged monkeys was characterized by marked intersubject variability in labeling intensity, with dramatic reductions present in 3 of 5 samples. α1 immunolabeling in aged monkeys was significantly reduced in the CA2 and CA3 subregions, and in hilus/polymorphic layer of the dentate gyrus. Collectively, our findings demonstrate that not only are GABA A receptor subunits differentially distributed throughout the hippocampus, but they are also differentially altered with increased age-changes that may have an important impact on the binding properties of GABA A receptor pharmacological agents.
Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemic... more Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemical and in situ hybridization. MCH-immunoreactive neurons were found in the lateral hypothalamus and dorsolateral zona incerta. MCH-ir fibers were seen in the medial mammillary nucleus, and in the median eminence, and very few fibers in the globus pallidus. This is the first report describing the MCH-ir cell and
Clinical studies suggest that exposure to stress can increase risk for Alzheimer's disease (AD). ... more Clinical studies suggest that exposure to stress can increase risk for Alzheimer's disease (AD). Though the precise links between stress and vulnerability to develop AD remain unsettled, recent animal work suggests that stress may promote susceptibility to AD pathology by activating tau kinases and inducing tau phosphorylation (tau-P). Our previous findings indicate differential involvement of corticotropin-releasing factor receptors (CRFR1 and 2) in regulating tau-P in the hippocampus induced by acute restraint, an emotional stressor. To assess the generality of CRFR involvement in stress-induced tau-P and tau kinase activity, the present study extends our investigation to a well-characterized physiological stressor: immune challenge induced by bacterial lipopolysaccharide (LPS). Acute systemic administration of LPS (100 μg/kg) robustly increased hippocampal (but not isocortical or cerebellar) tau-P, peaking at 40-120 min postinjection and abating thereafter. Assessments of the genotype dependence of this effect yielded results distinct from the restraint model. Treatment with LPS increased phosphorylation in wild type, single and double CRFR knockouts with only subtle variation, which included a reliable exaggeration of tau-P responses in CRFR1-deficient mice. Parallel analyses implicate glycogen synthase kinase-3 and cyclin-dependent kinase 5 as likely cellular mediators of LPS-induced tau-P. Conversely, our data suggest that temperature-dependent fluctuations in tau phosphatase (PP2A) may not play a role in this context. Thus, neither the strict CRFR1-dependence of restraint-induced tau-P, nor the exaggeration of these responses in CRFR2 null mice, generalize to the LPS model. CRFR mediation of stress-induced hippocampal tau-P may be limited to emotional stressors.
Proceedings of the National Academy of Sciences, 2012
Exposure and/or sensitivity to stress have been implicated as conferring risk for development of ... more Exposure and/or sensitivity to stress have been implicated as conferring risk for development of Alzheimer's disease (AD). Although the basis for such a link remains unclear, we previously reported differential involvement of corticotropin-releasing factor receptor (CRFR) 1 and 2 in acute stress-induced tau phosphorylation (tau-P) and solubility in the hippocampus. Here we examined the role of CRFRs in tau-P induced by repeated stress and the structural manifestations of altered tau solubility. Robust tau-P responses were seen in WT and CRFR2 null mice exposed to repeated stress, which were sustained at even 24 h after the final stress exposure. A portion of phosphorylated tau in these mice was sequestered in detergent-soluble cellular fractions. In contrast, CRFR1 and CRFR double-KO mice did not exhibit repeated stress-induced alterations in tau-P or solubility. Similarly, treatment with CRFR1 antagonist attenuated repeated stress-induced tau-P. Using histochemical approaches in a transgenic CRFR1 reporter mouse line, we found substantial overlap between hippocampal CRFR1 expression and cells positive for phosphorylated tau after exposure to repeated stress. Ultrastructural analysis of negatively stained extracts from WT and CRFR2 null mice identified globular aggregates that displayed positive immunogold labeling for tau-P, as well as conformational changes in tau (MC1) seen in early AD. Given that repeated stress exposure results in chronic increases in hippocampal tau-P and its sequestration in an insoluble (and potentially prepathogenic) form, our data may define a link between stress and an AD-related pathogenic mechanism. neurofibrillary tangles | western blot | pathology | electron microscopy A lzheimer's disease (AD) is definitively characterized by the presence of β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs). NFTs are insoluble intracellular inclusions composed of aggregated hyperphosphorylated forms of the cytoskeletal protein tau that accumulate initially within the hippocampal formation (1). A critical step in NFT formation is thought to be the transition of these phosphorylated tau species into aggregated insoluble fibrils. Hyperphosphorylated tau has a reduced ability to bind microtubules and has been reported to self-aggregate into paired helical filaments (PHFs), which compose NFTs (2, 3). The development of NFTs is positively correlated with cognitive decline and neuronal loss in AD (4, 5).
Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemic... more Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemical and in situ hybridization. MCH-immunoreactive neurons were found in the lateral hypothalamus and dorsolateral zona incerta. MCH-ir fibers were seen in the medial mammillary nucleus, and in the median eminence, and very few fibers in the globus pallidus. This is the first report describing the MCH-ir cell and fiber distribution in the monkey brain.
To gain further knowledge on the preclinical phase of Alzheimer's disease (AD), we sought to ... more To gain further knowledge on the preclinical phase of Alzheimer's disease (AD), we sought to characterize cognitive performance, neuroimaging and plasma-based AD biomarkers in a cohort of non-demented adults with down syndrome (DS). The goal of the down syndrome biomarker Initiative (DSBI) pilot is to test feasibility of this approach for future multicenter studies. We enrolled 12 non-demented participants with DS between the ages of 30-60 years old. Participants underwent extensive cognitive testing, volumetric MRI, amyloid positron emission tomography (PET; 18F-florbetapir), fluorodeoxyglucose (FDG) PET (18F-fluorodeoxyglucose) and retinal amyloid imaging. In addition, plasma beta-amyloid (Aβ) species were measured and Apolipoprotein E (ApoE) genotyping was performed. Results from our multimodal analysis suggest greater hippocampal atrophy with amyloid load. Additionally, we identified an inverse relationship between amyloid load and regional glucose metabolism. Cognitive and ...
A randomized, placebo-controlled, double-blind, multicenter 52-week phase 2 trial of resveratrol ... more A randomized, placebo-controlled, double-blind, multicenter 52-week phase 2 trial of resveratrol in individuals with mild to moderate Alzheimer disease (AD) examined its safety and tolerability and effects on biomarker (plasma Aβ40 and Aβ42, CSF Aβ40, Aβ42, tau, and phospho-tau 181) and volumetric MRI outcomes (primary outcomes) and clinical outcomes (secondary outcomes). Participants (n = 119) were randomized to placebo or resveratrol 500 mg orally once daily (with dose escalation by 500-mg increments every 13 weeks, ending with 1,000 mg twice daily). Brain MRI and CSF collection were performed at baseline and after completion of treatment. Detailed pharmacokinetics were performed on a subset (n = 15) at baseline and weeks 13, 26, 39, and 52. Resveratrol and its major metabolites were measurable in plasma and CSF. The most common adverse events were nausea, diarrhea, and weight loss. CSF Aβ40 and plasma Aβ40 levels declined more in the placebo group than the resveratrol-treated gro...
We investigated the impact of APOE genotype on cerebral blood flow (CBF) in older and younger adu... more We investigated the impact of APOE genotype on cerebral blood flow (CBF) in older and younger adults. Forty cognitively normal older adults (16 ε4 carriers, 24 non-ε4 carriers) and 30 younger adults (15 ε4 carriers, 15 non-ε4 carriers) completed a resting-state whole-brain pulsed arterial spin labeling magnetic resonance scan. Main effects of aging were demonstrated wherein older adults had decreased gray matter CBF corrected for partial volume effects compared to younger adults in widespread brain regions. Main effects of APOE genotype were also observed wherein ε4 carriers displayed greater CBF in the left lingual gyrus and precuneus than non-carriers. An interaction between age and APOE genotype in the left anterior cingulate cortex (ACC) was characterized by reduced CBF in older ε4 carriers and increased CBF in young ε4 carriers. Increased CBF in the left ACC resulting from the interaction of age group and APOE genotype was positively correlated with executive functioning in you...
Alzheimer's disease (AD) is characterized by selective vulnerability of specific neuronal pop... more Alzheimer's disease (AD) is characterized by selective vulnerability of specific neuronal populations within particular brain regions. For example, hippocampal glutamatergic cell populations within the CA1/subicular pyramidal cell fields have been found to be particularly vulnerable early in AD progression. In contrast, hippocampal GABA-ergic neurons and receptors appear resistant to neurodegeneration. Despite relative sparing of GABA(A) receptors in AD, it is possible that the specific subunit composition of these receptors may undergo alterations with disease progression. In order to address this issue, we employed quantitative Western blot analysis to examine protein levels of GABA(A) receptor subunits alpha 1, alpha 5, beta 1, beta 2 in the hippocampus of subjects displaying increasing severity of AD neuropathology. Subjects were categorized into three groups based upon Braak staging pathologic criteria: pathologically mild (stages I/II, n=9); moderate (stages III/IV, n=8); ...
Clinical and basic science research suggests that stress and/or changes in central stress signali... more Clinical and basic science research suggests that stress and/or changes in central stress signaling intermediates may be involved in Alzheimer's disease (AD) pathogenesis. Although the links between stress and AD remain unsettled, data from our group and others have established that stress exposure in rodents may confer susceptibility to AD pathology by inducing hippocampal tau phosphorylation (tau-P). Work in our laboratory has shown that stress-induced tau-P requires activation of the type-1 corticotropin-releasing factor receptor (CRFR1). CRF overexpressing (CRF-OE) mice are a model of chronic stress that display cognitive impairment at 9-10 month of age. In this study we used 6-7 month old CRF-OE mice to examine whether sustained exposure to CRF and stress steroids would impact hippocampal tau-P and kinase activity in the presence or absence of the CRFR1-specific antagonist, R121919, given daily for 30 days. CRF-OE mice had significantly elevated tau-P compared to wild type ...
Journal of Alzheimer's disease : JAD, Jan 19, 2015
Stress exposure and the corticotropin-releasing factor (CRF) system have been implicated as mecha... more Stress exposure and the corticotropin-releasing factor (CRF) system have been implicated as mechanistically involved in both human Alzheimer's disease (AD) and associated rodent models. In particular, the major stress receptor, CRF receptor type 1 (CRFR1), modulates cellular activity in many AD-relevant brain areas, and has been demonstrated to impact both tau phosphorylation and amyloid-β (Aβ) pathways. The overarching goal of our laboratory is to develop and characterize agents that impact the CRF signaling system as disease-modifying treatments for AD. In the present study, we developed a novel transgenic mouse to determine whether partial or complete ablation of CRFR1 was feasible in an AD transgenic model and whether this type of treatment could impact Aβ pathology. Double transgenic AD mice (PSAPP) were crossed to mice null for CRFR1; resultant CRFR1 heterozygous (PSAPP-R1+/-) and homozygous (PSAPP-R1-/-) female offspring were used at 12 months of age to examine the impact...
In Alzheimer's disease (AD) it is well known that specific regions of the brain are particula... more In Alzheimer's disease (AD) it is well known that specific regions of the brain are particularly vulnerable to the pathologic insults of the disease. In particular, the hippocampus is affected very early in the disease and by end stage AD is ravaged by neurofibrillary tangles and senile plaques (i.e., the pathologic hallmarks of AD). Throughout the past several years our laboratory has sought to determine the molecular mechanisms underlying the selective vulnerability of neurons in AD. To this end, we employed immunohistochemical, biochemical, and in situ hybrization methods to examine glutamate and gamma-aminobutyric acid (GABAA) receptor subtypes in the hippocampus of patients displaying the full spectrum of AD pathology. Despite the fact that the hippocampus is characterized by a marked loss of neurons in the late stages of the disease, our data demonstrate a rather remarkable preservation among some glutamate and GABAA receptor subtypes. Collectively, our data support the vi...
Journal of Chemical Neuroanatomy - J CHEM NEUROANAT, 2004
We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal... more We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal mRNA expression of GABAA receptor subunits α1 and α5 in human subjects with progressing cognitive impairment. Included in this study were 17 participants of the Religious Order Study (ROS), who were categorized into three groups based upon degree of cognitive impairment: no cognitive impairment (n = 6); moderate cognitive impairment (n = 5); and probable Alzheimer’s disease (AD) (n = 6). While the levels of each specific subunit mRNA were relatively homogeneously distributed throughout the five hippocampal subregions analyzed (CA1–4, and the granule cell layer of the dentate gyrus), mRNA expression of the α1 receptor subunit was found to be 20% reduced in the moderate cognitive impairment group as compared to the no cognitive impairment group. In addition, α1 mRNA expression was 25% reduced in the probable Alzheimer’s disease group compared to the group with no cognitive impairment. Sim...
Alterations in corticotropin-releasing factor (CRF) signaling pathways have been implicated in ir... more Alterations in corticotropin-releasing factor (CRF) signaling pathways have been implicated in irritable bowel syndrome (IBS) pathophysiology. We aimed to: 1) determine the effect of the selective CRF receptor 1 antagonist (CRF 1 ), GW876008, relative to placebo, on regional activation and effective connectivity of a stress-related emotional-arousal circuit during expectation of abdominal pain using functional magnetic resonance imaging (fMRI) in human subjects with a diagnosis of IBS and healthy controls (HCs), and 2) examine GW876008 effects on state-trait anxiety and hypothalamic-pituitary-adrenal (HPA) axis response. While there were no drug-related effects on peripheral HPA activity, significant central effects were observed in brain regions associated with the stress response. Effective connectivity analysis showed druginduced normalizations between key regions of the emotional-arousal circuit in patients. During pain expectation, orally administered GW876008 relative to placebo produced significant blood oxygen level-dependent (BOLD) signal reductions in the amygdala, hippocampus, insula, anterior cingulate and orbitomedial prefrontal cortices across groups. Patients showed significantly greater BOLD responses in the left locus coeruleus and hypothalamus following placebo compared to HCs, and BOLD signal decreases in the left hypothalamus following drug. The inhibitory effects of GW876008 in the hypothalamus in patients were moderated by anxiety; patients having average and high levels of state anxiety showed drug-related BOLD decreases. GW876008 represents a novel tool for elucidating the neuronal mechanisms and circuitry underlying hyperactivation of CRF/CRF 1 signaling and its role in IBS pathophysiology. The unique state anxiety effects observed suggest a potential pathway for therapeutic benefit of CRF 1 receptor antagonism for patients with stress-sensitive disorders.
Alzheimer's disease (AD) is characterized by loss of specific cell populations within selective s... more Alzheimer's disease (AD) is characterized by loss of specific cell populations within selective subregions of the hippocampus. Excitotoxicity, mediated via ionotropic glutamate receptors, may play a crucial role in this selective neuronal vulnerability. We investigated whether alterations in NMDA receptor subunits occurred during AD progression. Employing biochemical and in situ hybridization techniques in subjects with a broad range of AD pathology, protein levels, and mRNA expression of NR1/2A/2B subunits were assayed. With increasing AD neuropathology, protein levels and mRNA expression for NR1/2B subunits were significantly reduced, while the NR2A subunit mRNA expression and protein levels were unchanged. Cellular analysis of neuronal mRNA expression revealed a significant increase in the NR2A subunit in subjects with moderate neurofibrillary tangle neuropathology. This investigation supports the hypothesis that alterations occur in the expression of specific NMDA receptor subunits with increasing AD pathologic severity, which is hypothesized to contribute to the vulnerability of these neurons. D
In this article we present a comprehensive review of relevant research and reports on the GABA A ... more In this article we present a comprehensive review of relevant research and reports on the GABA A receptor in the aged and Alzheimer's disease (AD) brain. In comparison to glutamatergic and cholinergic systems, the GABAergic system is relatively spared in AD, but the precise mechanisms underlying differential vulnerability are not well understood. Using several methods, investigations demonstrate that despite resistance of the GABAergic system to neurodegeneration, particular subunits of the GABA A receptor are altered with age and AD, which can induce compensatory increases in GABA A receptor subunits within surrounding cells. We conclude that although aging-and disease-related changes in GABA A receptor subunits may be modest, the mechanisms that compensate for these changes may alter the pharmacokinetic and physiological properties of the receptor. It is therefore crucial to understand the subunit composition of individual GABA A receptors in the diseased brain when developing therapeutics that act at these receptors.
Neurofibrillary tangles (NFTs) are composed of abnormal aggregates of the cytoskeletal protein ta... more Neurofibrillary tangles (NFTs) are composed of abnormal aggregates of the cytoskeletal protein tau. Together with amyloid β (Aβ) plaques and neuronal and synaptic loss, NFTs constitute the primary pathological hallmarks of Alzheimer disease (AD). Recent evidence also suggests that caspases are activated early in the progression of AD and may play a role in neuronal loss and NFT pathology. Here we demonstrate that tau is cleaved at D421 (ΔTau) by executioner caspases. Following caspase-cleavage, ΔTau facilitates nucleation-dependent filament formation and readily adopts a conformational change recognized by the early pathological tau marker MC1. ΔTau can be phosphorylated by glycogen synthase kinase-3β and subsequently recognized by the NFT antibody PHF-1. In transgenic mice and AD brains, ΔTau associates with both early and late markers of NFTs and is correlated with cognitive decline. Additionally, ΔTau colocalizes with Aβ 1-42 and is induced by Aβ 1-42 in vitro. Collectively, our data imply that Aβ accumulation triggers caspase activation, leading to caspase-cleavage of tau, and that this is an early event that may precede hyperphosphorylation in the evolution of AD tangle pathology. These results suggest that therapeutics aimed at inhibiting tau caspase-cleavage may prove beneficial not only in preventing NFT formation, but also in slowing cognitive decline.
We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal... more We employed in situ hybridization and quantitative densitometry techniques to examine hippocampal mRNA expression of GABA(A) receptor subunits alpha1 and alpha5 in human subjects with progressing cognitive impairment. Included in this study were 17 participants of the Religious Order Study (ROS), who were categorized into three groups based upon degree of cognitive impairment: no cognitive impairment (n = 6); moderate cognitive impairment (n = 5); and probable Alzheimer's disease (AD) (n = 6). While the levels of each specific subunit mRNA were relatively homogeneously distributed throughout the five hippocampal subregions analyzed (CA1-4, and the granule cell layer of the dentate gyrus), mRNA expression of the alpha1 receptor subunit was found to be 20% reduced in the moderate cognitive impairment group as compared to the no cognitive impairment group. In addition, alpha1 mRNA expression was 25% reduced in the probable Alzheimer's disease group compared to the group with no cognitive impairment. Similarly, alpha5 subunit mRNA was reduced 32% between no cognitive impairment and moderate cognitive impairment groups, and 35% between no cognitive impairment and probable Alzheimer's disease groups. No significant reductions were found between moderate cognitive impairment and probable Alzheimer's disease groups for either subunit. Collectively, our data provide evidence for modest reductions in GABA(A) receptor subunit mRNAs, and suggest these changes occur very early in the progression of…
The Alzheimer's disease (AD) brain, characterized pathologically by the presence of senile plaque... more The Alzheimer's disease (AD) brain, characterized pathologically by the presence of senile plaques and neurofibrillary tangles, contains regions that are differentially prone toward development of AD pathology. Within these ''vulnerable'' regions, specific cell populations appear to be selectively affected; the pyramidal cells of the hippocampal subiculum subfield constitute such a vulnerable region. This study investigated whether the AMPA receptor subunit content (GluR1, GluR2, GluR2/3) within ''vulnerable'' vs. ''resistant'' sectors of the hippocampus is quantitatively altered with increasing AD neuropathology, as determined by Braak staging. We hypothesize that the glutamate-mediated vulnerability is highly influenced by the repertoire of glutamate receptors expressed on hippocampal neurons. Our results indicate that AMPA receptor subunit proteins are relatively spared across all Braak stages in resistant subfields (CA2/CA3/Dentate Gyrus). However, within vulnerable sectors, i.e., subiculum, GluR2, and GluR2/3 protein levels decreased 63.77% and 60.60%, respectively, in association with Braak stages I -II and stages III -IV, respectively. In Braak stages V -VI, GluR2 and GluR2/3 protein levels were similar to those of Braak stages I -II. In contrast to GluR2 and GluR2/3, GluR1 protein levels were unchanged within vulnerable sectors throughout all stages of the disease. In interpreting these data, it may be relevant to consider that the GluR2 subunit impedes the flow of Ca +2 through the AMPA receptor ion channel. Thus, we hypothesize that in resistant sectors, the presence of the GluR2 subunit may provide a neuroprotective role by limiting the flow of extracellular Ca +2 , whereas in vulnerable regions, the reduction of GluR2 may contribute to the vulnerability via a mechanism involving an increase in intracellular Ca +2 and destabilization of intracellular Ca +2 homeostasis. D
Pharmacological studies have documented that altered drug responses, particularly to benzodiazepi... more Pharmacological studies have documented that altered drug responses, particularly to benzodiazepines, are common in elderly populations. While numerous factors may contribute to changes in drug response, age-related alterations in the molecular composition of GABA A receptors may be a key factor in regulating these responses. We employed quantitative densitometry to examine the cytological features and density of highly prevalent hippocampal GABA A receptor subunits (α1 and β2/3) in young and aged rhesus monkeys. α1 and β2/3 subunit immunostaining was differentially distributed throughout the hippocampus. In addition, β2/3 immunolabeling in aged monkeys was characterized by marked intersubject variability in labeling intensity, with dramatic reductions present in 3 of 5 samples. α1 immunolabeling in aged monkeys was significantly reduced in the CA2 and CA3 subregions, and in hilus/polymorphic layer of the dentate gyrus. Collectively, our findings demonstrate that not only are GABA A receptor subunits differentially distributed throughout the hippocampus, but they are also differentially altered with increased age-changes that may have an important impact on the binding properties of GABA A receptor pharmacological agents.
Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemic... more Melanin-concentrating hormone was identified in the brain of Cebus monkey using immunohistochemical and in situ hybridization. MCH-immunoreactive neurons were found in the lateral hypothalamus and dorsolateral zona incerta. MCH-ir fibers were seen in the medial mammillary nucleus, and in the median eminence, and very few fibers in the globus pallidus. This is the first report describing the MCH-ir cell and
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Papers by Robert Rissman