- Research Scientist, Immunobiology
- Research Assistant Professor, Neurology
For my doctoral dissertation at the University of Southern California, I identified and characterized the mechanisms of sex steroid hormone induced neuroprotection against apoptosis associated with Alzheimer's disease. I identified an anti-apoptotic mechanism of testosterone- and dihydrotestosterone-induced protection in neuron cultures, utilizing biochemical and morphological markers of apoptosis and pharmacological cell death agents. I determined that androgen receptor-modulating drugs flutamide and cyproterone acetate are both androgen receptor agonists (neuroprotective) and antagonists (inhibit gene transcription), using neuron and cell line cultures. I discovered a neuroprotective mechanism (mitogen-activated protein kinase/ribosomal S6 kinase/Bcl-2-associated death protein) mediated by testosterone and dihydrotestosterone against beta-amyloid-induced apoptosis, using neuron and cell line cultures, and I identified an alternative mechanism (protein kinase C/cyclic AMP response element-binding protein) of androgen-mediated neural functions.
During my postdoctoral work at the Buck Institute, I investigated a novel, amyloid precursor protein dependent signal transduction pathway involved in the pathogenesis of Alzheimer’s using postmortem Alzheimer's disease human brain tissue and transgenic mouse models. I Identified the domain in a novel human protein (netrin-1) required for amyloid precursor protein binding and beta-amyloid suppression, employing deletion mutant designs in cell culture. I determined the role of mitogen-activated protein kinase kinase-6 and tau phosphorylation in neurofibrillary tangle pathology via the genotypic identification and phenotypic characterization of a novel, inducible transgenic mouse model of Alzheimer’s disease (NSE-rtTA-Cre+Prp-LoxP-MKK6 x PDAPP). Finally, I determined the role of the amyloid precursor protein and p21-activated kinase in Alzheimer’s disease, using postmortem human brains of early, moderate, and severe neuropathology and a transgenic PDAPP mouse model of Alzheimer's disease.
While at Stanford University as a Senior Research Scientist in the laboratory of Dr. Frank Longo, I tested and demonstrated the therapeutic effectiveness of small molecule ligands for the p75 neurotrophin receptor on memory deficits and degeneration of cholinergic neurons using pre-clinical mouse models of Alzheimer's disease and Down syndrome. Specifically, I assessed the therapeutic efficacy of small molecule ligands for the p75 neurotrophin receptor on the Alzheimer’s disease phenotype, including cholinergic neuronal degeneration, beta-amyloid and tau pathology, inflammatory responses, and cognitive behavioral deficits in an amyloid precursor protein mutant (Thy1-hAPPLond/Swe) mouse model. This lead ligand is currently in Phase II of clinical trials. I also assessed the effects of p75 neurotrophin receptor ligands on noradrenergic neuronal degeneration and psychiatric-related behaviors such as depression, anxiety, aggression, social withdrawal, and sensorimotor gating deficit in Thy1-hAPPLond/Swe mice. I evaluated positron emission tomography (PET) imaging of activatedmicroglia and deoxyglucose uptake in the brain as a translatable tool for Alzheimer’s disease therapy monitoring using p75 neurotrophin receptor ligands in Thy1-hAPPLond/Swe mice. I also assessed the therapeuticefficacy of p75 neurotrophin receptor ligands on the Down syndrome phenotype, including cholinergic andnoradrenergic neuronal degeneration, dendritic spine abnormalities, and cognitive behavioral deficits in asegmentally trisomic (Ts65Dn) mouse model.
My current research program at the University of Arizona is focused on mixed dementia, which is a condition in which pathology characteristic of more than one type of dementia co-exists in an individual, for example stroke infarcts alongside the neuropathology characteristic of Alzheimer's disease. Specifically, my research is centered on determining the impact of the following four sequelae of stroke on the development of Alzheimer's disease: axonal degeneration, chronic neuroinflammation, chronic blood brain barrier dysfunction, and impaired paravascular clearance. Recently, my research team developed two new mouse models of post-stroke mixed dementia. Currently, the mice are in use to determine the role of a beta-secreatase 1-dependent myelin repair pathway in driving Alzheimer's disease mixed dementia pathology after stroke, and also to pre-clinically test a Phase 2a therapeutic compound that targets fundamental mechanisms relevant to Alzheimer's pathogenesis in post-stroke mixed dementia.
- Ph.D. Neuroscience
- University of Southern California, Los Angeles, California, United States
- B.S. Psychobiology
- University of California, Los Angeles, Los Angeles, California, United States
- Immunbiology (2013 - Ongoing)
- University of Arizona, Tucson, Arizona (2013 - Ongoing)
- Stanford University, Stanford, California (2008 - 2013)
- Buck Institute for Age Research (2005 - 2008)
- RO1. Title: The interactions between the chronic sequlae of stroke and Azheimer's disease
- NIH/NIA, Fall 2019
- Research Project Grant Parent R01
- NIH/NIA, Fall 2016
- Ruth L. Kirschstein National Research Service Award Fellowship
- NIH-NIA, Fall 2007
As a Ph.D. trained neuroscientist, my research interest lies is uncovering mechanisms of age-related neurodegenerative diseases, and applying therapeutic strategies to the treatment thereof. I have extensive experience in investigating mechanisms of neuroprotection and cell loss, developing animal models, and preclinical testing of compounds in models of aging and neurodegeneration, which includes conducting motor, cognitive, and psychiatric behavioral tests in rodents.
Directed ResearchNSCS 392 (Spring 2020)
Curr Rsrch Vis+NeurodegenPSIO 696E (Fall 2019)
Immunity & Biology of AgingIMB 695L (Fall 2019)
- Chung, A. G., Frye, J. B., Zbesko, J. C., Constantopoulos, E., Hayes, M., Figueroa, A. G., Day, A. W., Konhilas, J. P., Mckay, B. S., Nguyen, T. V., & Doyle, K. P. (2018). Liquefaction of the brain following stroke shares a similar molecular and morphological profile with atherosclerosis and mediates secondary neurodegeneration in an osteopontin-dependent mechanism. eNeuro, 5(5), ENEURO.0076-18.2018.
- Doyle, K. P., Nguyen, T. V., Mckay, B. S., Konhilas, J. P., Day, A. W., Figueroa, A., Hayes, M., Constantopoulos, E., Zbesko, J., Frye, J., & Chung, A. (2018). Liquefaction of the brain following stroke shares a similar molecular and morphological profile with atherosclerosis and mediates secondary neurodegeneration in an osteopontin dependent mechanism. eNeuro.
- Felix, K. M., Jaimex, I. A., Nguyen, T. V., Ma, H., Raslan, W. A., Klinger, C. N., Doyle, K. P., & Wu, H. J. (2018). Gut Microbiota Protects Immunocompromised Hosts Against Pneumococcal Pneumonia. Frontiers in Cellular and Infection Microbiology, 8, 118.
- Nguyen, T. V., Hayes, M., Zbesko, J. C., Congrove, N. R., Belichenko, N. P., McKay, B. S., Longo, F. M., & Doyle, K. P. (2018). Alzheimer's associated amyloid and tau deposition co-localizes with a homeostatic myelin repair pathway in two mouse models of post-stroke mixed dementia.. Acta Neuropathological Communications, 6(1), 100.
- Zbesko, J. C., Nguyen, T. V., Yang, T., Frye, J. B., Hussain, O., Hayes, M., Chung, A., Day, W., Stepanovic, K., Krumberger, M., Mona, J., & Doyle, K. (2018). Glial Scars are permeable to neurodegenerative factors present in chronic stroke infarcts.. Neurobiology of Disease.
- Branca, C., Ferreira, E., Nguyen, T., Doyle, K., Caccamo, A., & Oddo, S. (2017). Genetic reduction of Nrf2 exacerbates cognitive deficits in a mouse model of Alzheimer’s disease. Human Molecular Genetics, 26(24), 4823-4835. doi:10.1093/hmg/ddx361
- Danilo, C. A., Constantopoulos, E., McKee, L. A., Chen, H., Regan, J. A., Lipovka, Y., Lahtinen, S., Stenman, L. K., Nguyen, T., Doyle, K., Slepian, M. J., Khalpey, Z. I., & Konhilas, J. P. (2017). Bifidobacterium animalis subsp. lactis 420 mitigates the pathological impact of myocardial infarction in the mouse.. Benef Microbes, 8(2), 257-269. doi:10.3920/BM2016.0119
- James, M. L., Belichenko, N. P., Shuhendler, A. J., Hoehne, A., Andrews, L. E., Condon, C., Nguyen, T. V., Reiser, V., Jones, P., Trigg, W., Rao, J., Gambhir, S. S., & Longo, F. M. (2017). [18F]GE-180 PET detects reduced microglia activation after LM11A-31 therapy in a mouse model of Alzheimer’s disease. Theranostics.
- Nguyen, T. V., Frye, J. B., Zbesko, J. C., Stepanovic, K., Hayes, M., Urzua, A., Serrano, G., Beach, T. G., & Doyle, K. P. (2016). Multiplex immunoassay characterization and species comparison of inflammation in acute and non-acute ischemic infarcts in human and mouse brain tissue. Acta neuropathologica communications, 4(1), 100.More infoThis study provides a parallel characterization of the cytokine and chemokine response to stroke in the human and mouse brain at different stages of infarct resolution. The study goal was to address the hypothesis that chronic inflammation may contribute to stroke-related dementia. We used C57BL/6 and BALB/c mice to control for strain related differences in the mouse immune response. Our data indicate that in both mouse strains, and humans, there is increased granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin-6 (IL-6), interleukin-12 p70 (IL-12p70), interferon gamma-induced protein-10 (IP-10), keratinocyte chemoattractant/interleukin-8 (KC/IL-8), monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), macrophage inflammatory protein-1β (MIP-1β), regulated on activation, normal T cell expressed and secreted (RANTES), and Tumor necrosis factor-α (TNF-α) in the infarct core during the acute time period. Nevertheless, correlation and two-way ANOVA analyses reveal that despite this substantial overlap between species, there are still significant differences, particularly in the regulation of granulocyte colony-stimulating factor (G-CSF), which is increased in mice but not in humans. In the weeks after stroke, during the stage of liquefactive necrosis, there is significant resolution of the inflammatory response to stroke within the infarct. However, CD68+ macrophages remain present, and levels of IL-6 and MCP-1 remain chronically elevated in infarcts from both mice and humans. Furthermore, there is a chronic T cell response within the infarct in both species. This response is differentially polarized towards a T helper 1 (Th1) response in C57BL/6 mice, and a T helper 2 (Th2) response in BALB/c mice, suggesting that the chronic inflammatory response to stroke may follow a different trajectory in different patients. To control for the fact that the average age of the patients used in this study was 80 years, they were of both sexes, and many had suffered from multiple strokes, we also present findings that reveal how the chronic inflammatory response to stroke is impacted by age, sex, and multiple strokes in mice. Our data indicate that the chronic cytokine and chemokine response to stroke is not substantially altered in 18-month old compared to 3-month old C57BL/6 mice, although T cell infiltration is attenuated. We found a significant correlation in the chronic cytokine response to stroke in males and females. However, the chronic cytokine response to stroke was mildly exacerbated by a recurrent stroke in both C57BL/6 and BALB/c mice.
- Doyle, K. P., Quach, L. N., Solé, M., Axtell, R. C., Nguyen, T. V., Soler-Llavina, G. J., Jurado, S., Han, J., Steinman, L., Longo, F. M., Schneider, J. A., Malenka, R. C., & Buckwalter, M. S. (2015). B-lymphocyte-mediated delayed cognitive impairment following stroke. The Journal of neuroscience : the official journal of the Society for Neuroscience, 35(5), 2133-45.More infoEach year, 10 million people worldwide survive the neurologic injury associated with a stroke. Importantly, stroke survivors have more than twice the risk of subsequently developing dementia compared with people who have never had a stroke. The link between stroke and the later development of dementia is not understood. There are reports of oligoclonal bands in the CSF of stroke patients, suggesting that in some people a B-lymphocyte response to stroke may occur in the CNS. Therefore, we tested the hypothesis that a B-lymphocyte response to stroke could contribute to the onset of dementia. We discovered that, in mouse models, activated B-lymphocytes infiltrate infarcted tissue in the weeks after stroke. B-lymphocytes undergo isotype switching, and IgM, IgG, and IgA antibodies are found in the neuropil adjacent to the lesion. Concurrently, mice develop delayed deficits in LTP and cognition. Genetic deficiency, and the pharmacologic ablation of B-lymphocytes using an anti-CD20 antibody, prevents the appearance of delayed cognitive deficits. Furthermore, immunostaining of human postmortem tissue revealed that a B-lymphocyte response to stroke also occurs in the brain of some people with stroke and dementia. These data suggest that some stroke patients may develop a B-lymphocyte response to stroke that contributes to dementia, and is potentially treatable with FDA-approved drugs that target B cells.
- James, M. L., Belichenko, N. P., Nguyen, T. V., Andrews, L. E., Ding, Z., Liu, H., Bodapati, D., Arksey, N., Shen, B., Cheng, Z., Wyss-Coray, T., Gambhir, S. S., Longo, F. M., & Chin, F. T. (2015). PET imaging of translocator protein (18 kDa) in a mouse model of Alzheimer's disease using N-(2,5-dimethoxybenzyl)-2-18F-fluoro-N-(2-phenoxyphenyl)acetamide. Journal of nuclear medicine : official publication, Society of Nuclear Medicine, 56(2), 311-6.More infoHerein we aimed to evaluate the utility of N-(2,5-dimethoxybenzyl)-2-(18)F-fluoro-N-(2-phenoxyphenyl)acetamide ((18)F-PBR06) for detecting alterations in translocator protein (TSPO) (18 kDa), a biomarker of microglial activation, in a mouse model of Alzheimer's disease (AD).
- Nguyen, T. V., Shen, L., Vander Griend, L., Quach, L. N., Belichenko, N. P., Saw, N., Yang, T., Shamloo, M., Wyss-Coray, T., Massa, S. M., & Longo, F. M. (2014). Small molecule p75NTR ligands reduce pathological phosphorylation and misfolding of tau, inflammatory changes, cholinergic degeneration, and cognitive deficits in AβPP(L/S) transgenic mice. Journal of Alzheimer's disease : JAD, 42(2), 459-83.More infoThe 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.
- Knowles, J. K., Simmons, D. A., Nguyen, T. V., Vander Griend, L., Xie, Y., Zhang, H., Yang, T., Pollak, J., Chang, T., Arancio, O., Buckwalter, M. S., Wyss-Coray, T., Massa, S. M., & Longo, F. M. (2013). Small molecule p75NTR ligand prevents cognitive deficits and neurite degeneration in an Alzheimer's mouse model. Neurobiology of aging, 34(8), 2052-63.More infoThe p75 neurotrophin receptor (p75(NTR)) is associated with multiple mechanisms linked to Alzheimer's disease (AD); hence, modulating its function might confer therapeutic effects. In previous in vitro work, we developed small molecule p75(NTR) ligands that inhibited amyloid-β-induced degenerative signaling and prevented neurite degeneration. In the present study, a prototype p75(NTR) ligand, LM11A-31, was administered orally to the Thy-1 hAPP(Lond/Swe) (APP(L/S)) AD mouse model. LM11A-31 reached brain concentrations known to inhibit degenerative signaling without toxicity or induction of hyperalgesia. It prevented deficits in novel object recognition after 2.5 months and, in a separate cohort, deficits in Y-maze performance after 3 months of treatment. Stereology studies found that the number and size of basal forebrain cholinergic neurons, which are normal in APP(L/S) mice, were unaffected. Neuritic dystrophy, however, was readily apparent in the basal forebrain, hippocampus and cortex, and was significantly reduced by LM11A-31, with no effect on amyloid levels. These studies reveal that p75(NTR) is an important and tractable in vivo drug target for AD, with LM11A-31 representing a novel class of therapeutic candidates.
- Faizi, M., Bader, P. L., Saw, N., Nguyen, T. V., Beraki, S., Wyss-Coray, T., Longo, F. M., & Shamloo, M. (2012). Thy1-hAPP(Lond/Swe+) mouse model of Alzheimer's disease displays broad behavioral deficits in sensorimotor, cognitive and social function. Brain and behavior, 2(2), 142-54.More infoAlzheimer'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-hAPP(Lond/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-hAPP(Lond/Swe+) mice. We found hyperactivity in a novel environment as well as significant deficits in spontaneous alternation behavior. In fear conditioning (FC), Thy1-hAPP(Lond/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-hAPP(Lond/Swe+) mice. Lastly, in the social novelty session of a three-chamber test, Thy1-hAPP(Lond/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-hAPP(Lond/Swe+) mouse model of AD displayed a behavioral phenotype that resembles, in part, the cognitive and psychiatric symptoms experienced in AD patients.
- Nguyen, T. V., Jayaraman, A., Quaglino, A., & Pike, C. J. (2010). Androgens selectively protect against apoptosis in hippocampal neurones. Journal of neuroendocrinology, 22(9), 1013-22.More infoAndrogens can protect neurones from injury, although androgen neuroprotection is not well characterised in terms of either specificity or mechanism. In the present study, we compared the ability of androgens to protect neurones against a panel of insults, empirically determined to induce cell death by apoptotic or non-apoptotic mechanisms. Three criteria defining but not inclusive of apoptosis are: protection by caspase inhibition, protection by protein synthesis inhibition and the presence of pyknotic nuclei. According to these criteria, beta-amyloid, staurosporine, and Apoptosis Activator II induced cell death involving apoptosis, whereas hydrogen peroxide (H(2)O(2)), iron, calcium ionophore and 3-nitropropionic acid induced cell death featuring non-apoptotic characteristics. Pretreatment of hippocampal neurones with testosterone or dihydrotestosterone attenuated cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but none of the other insults. The anti-oxidant Trolox did not reduce cell death induced by beta-amyloid, staurosporine and Apoptosis Activator II, but did protect against H(2)O(2) and iron. Similarly, a supra-physiological concentration of oestrogen reduced cell death induced by H(2)O(2) and iron, an effect not observed with androgens. We also show that activation of oestrogen pathways was not necessary for androgen neuroprotection. These data suggest that androgens directly activate a neuroprotective mechanism specific to inhibition of cell death involving apoptosis. Determining the specificity of androgen neuroprotection may enable the development of androgen compounds for the treatment of neurodegenerative disorders.
- Knowles, J. K., Rajadas, J., Nguyen, T. V., Yang, T., LeMieux, M. C., Vander Griend, L., Ishikawa, C., Massa, S. M., Wyss-Coray, T., & Longo, F. M. (2009). The p75 neurotrophin receptor promotes amyloid-beta(1-42)-induced neuritic dystrophy in vitro and in vivo. The Journal of neuroscience : the official journal of the Society for Neuroscience, 29(34), 10627-37.More infoOligomeric forms of amyloid-beta (Abeta) are thought to play a causal role in Alzheimer's disease (AD), and the p75 neurotrophin receptor (p75(NTR)) has been implicated in Abeta-induced neurodegeneration. To further define the functions of p75(NTR) in AD, we examined the interaction of oligomeric Abeta(1-42) with p75(NTR), and the effects of that interaction on neurite integrity in neuron cultures and in a chronic AD mouse model. Atomic force microscopy was used to ascertain the aggregated state of Abeta, and fluorescence resonance energy transfer analysis revealed that Abeta oligomers interact with the extracellular domain of p75(NTR). In vitro studies of Abeta-induced death in neuron cultures isolated from wild-type and p75(NTR-/-) mice, in which the p75(NTR) extracellular domain is deleted, showed reduced sensitivity of mutant cells to Abeta-induced cell death. Interestingly, Abeta-induced neuritic dystrophy and activation of c-Jun, a known mediator of Abeta-induced deleterious signaling, were completely prevented in p75(NTR-/-) neuron cultures. Thy1-hAPP(Lond/Swe) x p75(NTR-/-) mice exhibited significantly diminished hippocampal neuritic dystrophy and complete reversal of basal forebrain cholinergic neurite degeneration relative to those expressing wild-type p75(NTR). Abeta levels were not affected, suggesting that removal of p75(NTR) extracellular domain reduced the ability of excess Abeta to promote neuritic degeneration. These findings indicate that although p75(NTR) likely does not mediate all Abeta effects, it does play a significant role in enabling Abeta-induced neurodegeneration in vitro and in vivo, establishing p75(NTR) as an important therapeutic target for AD.
- Nguyen, T. V., Yao, M., & Pike, C. J. (2009). Dihydrotestosterone activates CREB signaling in cultured hippocampal neurons. Brain research, 1298, 1-12.More infoAlthough androgens induce numerous actions in brain, relatively little is known about which cell signaling pathways androgens activate in neurons. Recent work in our laboratory showed that the androgens testosterone and dihydrotestosterone (DHT) activate androgen receptor (AR)-dependent mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling. Since the transcription factor cyclic AMP response element binding protein (CREB) is a downstream effector of MAPK/ERK and androgens activate CREB in non-neuronal cells, we investigated whether androgens activate CREB signaling in neurons. First, we observed that DHT rapidly activates CREB in cultured hippocampal neurons, as evidenced by CREB phosphorylation. Further, we observed that DHT-induced CREB phosphorylation is AR-dependent, as it occurs in PC12 cells stably transfected with AR but in neither wild-type nor empty vector-transfected cells. Next, we sought to identify the signal transduction pathways upstream of CREB phosphorylation using pharmacological inhibitors. DHT-induced CREB phosphorylation in neurons was found to be dependent upon protein kinase C (PKC) signaling but independent of MAPK/ERK, phosphatidylinositol 3-kinase, protein kinase A, and Ca(2+)/calmodulin-dependent protein kinase IV. These results demonstrate that DHT induces PKC-dependent CREB signaling, which may contribute to androgen-mediated neural functions.
- Nguyen, T. V., Galvan, V., Huang, W., Banwait, S., Tang, H., Zhang, J., & Bredesen, D. E. (2008). Signal transduction in Alzheimer disease: p21-activated kinase signaling requires C-terminal cleavage of APP at Asp664. Journal of neurochemistry, 104(4), 1065-80.More infoThe deficits in Alzheimer disease (AD) stem at least partly from neurotoxic beta-amyloid peptides generated from the amyloid precursor protein (APP). APP may also be cleaved intracellularly at Asp664 to yield a second neurotoxic peptide, C31. Previously, we showed that cleavage of APP at the C-terminus is required for the impairments seen in APP transgenic mice, by comparing elements of the disease in animals modeling AD, with (platelet-derived growth factor B-chain promoter-driven APP transgenic mice; PDAPP) versus without (PDAPP D664A) a functional Asp664 caspase cleavage site. However, the signaling mechanism(s) by which Asp664 contributes to these deficits remains to be elucidated. In this study, we identify a kinase protein, recently shown to bind APP at the C-terminus and to contribute to AD, whose activity is modified in PDAPP mice, but normalized in PDAPP D664A mice. Specifically, we observed a significant increase in nuclear p21-activated kinase (isoforms 1, 2, and or 3; PAK-1/2/3) activation in hippocampus of 3 month old PDAPP mice compared with non-transgenic littermates, an effect completely prevented in PDAPP D664A mice. In contrast, 13 month old PDAPP mice displayed a significant decrease in PAK-1/2/3 activity, which was once again absent in PDAPP D664A mice. Similarly, in hippocampus of early and severe AD subjects, there was a progressive and subcellular-specific reduction in active PAK-1/2/3 compared with normal controls. Interestingly, total PAK-1/2/3 protein was increased in early AD subjects, but declined in moderate AD and declined further, to significantly below that of control levels, in severe AD. These findings are compatible with previous suggestions that PAK may be involved in the pathophysiology of AD, and demonstrate that both early activation and late inactivation in the murine AD model require the cleavage of APP at Asp664.
- Pike, C. J., Nguyen, T. V., Ramsden, M., Yao, M., Murphy, M. P., & Rosario, E. R. (2008). Androgen cell signaling pathways involved in neuroprotective actions. Hormones and behavior, 53(5), 693-705.More infoAs a normal consequence of aging in men, testosterone levels significantly decline in both serum and brain. Age-related testosterone depletion results in increased risk of dysfunction and disease in androgen-responsive tissues, including brain. Recent evidence indicates that one deleterious effect of age-related testosterone loss in men is increased risk for Alzheimer's disease (AD). We discuss recent findings from our laboratory and others that identify androgen actions implicated in protecting the brain against neurodegenerative diseases and begin to define androgen cell signaling pathways that underlie these protective effects. Specifically, we focus on the roles of androgens as (1) endogenous negative regulators of beta-amyloid accumulation, a key event in AD pathogenesis, and (2) neuroprotective factors that utilize rapid non-genomic signaling to inhibit neuronal apoptosis. Continued elucidation of cell signaling pathways that contribute to protective actions of androgens should facilitate the development of targeted therapeutic strategies to combat AD and other age-related neurodegenerative diseases.
- Yao, M., Nguyen, T. V., Rosario, E. R., Ramsden, M., & Pike, C. J. (2008). Androgens regulate neprilysin expression: role in reducing beta-amyloid levels. Journal of neurochemistry, 105(6), 2477-88.More infoAge-related testosterone depletion in men is a risk factor for Alzheimer's disease. Prior studies suggest that androgens affect Alzheimer's disease risk by regulating accumulation of beta-amyloid protein (Abeta) by an undefined mechanism. In this study, we investigated the role of the Abeta-catabolizing enzyme neprilysin (NEP) in this process. First, we observed that androgens positively regulate neural expression of NEP in adult male rats. Next, we investigated androgen regulatory effects on both NEP expression and Abeta levels using cultured hippocampal neurons and neuronally differentiated rat pheochromocytoma cell 12 with or without androgen receptor (AR). Dihydrotestosterone (DHT) induced a time-dependent increase in NEP expression. DHT also significantly decreased levels of Abeta in AR-expressing cells transfected with amyloid precursor protein, but did not affect levels of either full-length or non-amyloidogenic, soluble amyloid precursor protein. Importantly, the DHT induced decrease of Abeta was blocked by pharmacological inhibition of NEP. The DHT-mediated increase in NEP expression and decrease in Abeta levels were (i) not observed in rat pheochromocytoma cell 12 lacking AR and (ii) blocked in AR-expressing cells by the antagonists, cyproterone acetate and flutamide. Together, these findings suggest that androgen regulation of Abeta involves an AR-dependent mechanism requiring up-regulation of the Abeta catabolizing enzyme NEP.
- Chen, M. J., Nguyen, T. V., Pike, C. J., & Russo-Neustadt, A. A. (2007). Norepinephrine induces BDNF and activates the PI-3K and MAPK cascades in embryonic hippocampal neurons. Cellular signalling, 19(1), 114-28.More infoBoth antidepressant treatment and physical exercise have been shown to increase circulating levels of norepinephine (NE) and hippocampal brain-derived neurotrophic factor (BDNF). Increases in BDNF have been shown to be associated with enhanced dendritic arborization and neuronal survival, which forms the theoretical basis of the Neurotrophin Hypothesis of antidepressant action. Using isolated embryonic hippocampal neurons and immunoblotting, we show that application of NE increases BDNF and phosphorylated Trk, and that these increases can be prevented by ERK and PI-3K inhibitors. In addition, NE-induced increases in phospho-ERK2 and PI-3K were each suppressed by a PI-3K and MAPK inhibitor, respectively. Furthermore, phosphorylation of cAMP-response element binding (CREB) protein was also increased by NE and brought down to baseline levels by MAPK and PI-3K inhibitors. And finally, because both the MAPK and PI-3K inhibitors suppress phosphorylation of both TrkB (upstream) and CREB (downstream), these results indicate that NE-induced BDNF expression follows a cyclic pathway, reminiscent of a positive feedback loop. The results of this study provide an in vitro model of the intracellular signaling mechanisms activated by NE, via ligand-G-protein-coupled receptor (GPCR)-to-BDNF-RTK transactivation, that is putatively thought to occur in vivo as a result of excitatory neural activity.
- Nguyen, T. V., Yao, M., & Pike, C. J. (2007). Flutamide and cyproterone acetate exert agonist effects: induction of androgen receptor-dependent neuroprotection. Endocrinology, 148(6), 2936-43.More infoAndrogens can exert profound effects on the organization, development, and function of the nervous system through activation of androgen receptors (ARs). Nonsteroidal and steroidal antiandrogens antagonize AR-mediated, classic genomic actions of androgens. However, emerging studies in nonneuronal cells indicate that antiandrogens can act as partial agonists for the AR. Here we investigated the effects of the antiandrogens flutamide and cyproterone acetate on neuroprotection induced by dihydrotestosterone (DHT). We observed that, although flutamide and cyproterone acetate blocked androgen-induced gene expression, they failed to inhibit DHT protection against apoptotic insults in cultured hippocampal neurons. Interestingly, flutamide and cyproterone acetate alone, like DHT, significantly reduced apoptosis. Furthermore, the protective actions of flutamide and cyproterone acetate were observed specifically in AR-expressing cell lines, suggesting a role for AR in the agonist effects of antiandrogens. Our results indicate that, in contrast to the classic antiandrogen properties of flutamide and cyproterone acetate, these AR modulators display agonist activities at the level of neuroprotection. These findings provide new insight into the agonist vs. antagonist properties of antiandrogens, information that will be crucial to understanding the neural implications of clinically used AR-modulating drugs.
- Yao, M., Nguyen, T. V., & Pike, C. J. (2007). Estrogen regulates Bcl-w and Bim expression: role in protection against beta-amyloid peptide-induced neuronal death. The Journal of neuroscience : the official journal of the Society for Neuroscience, 27(6), 1422-33.More infoEstrogen is neuroprotective against a variety of insults, including beta-amyloid peptide (Abeta); however, the underlying mechanism(s) is not fully understood. Here, we report that 17beta-estradiol (E2) selectively regulates neuronal expression of the Bcl-2 family (bcl-2, bcl-x, bcl-w, bax, bak, bad, bik, bnip3, bid, and bim). In primary cerebrocortical neuron cultures under basal conditions, we observe that E2 upregulates expression of antiapoptotic Bcl-w and downregulates expression of proapoptotic Bim in an estrogen receptor (ER)-dependent manner. In the presence of toxic levels of Abeta, we observe that E2 attenuates indices of neuronal apoptosis: c-Jun N-terminal kinase (JNK)-dependent downregulation of Bcl-w and upregulation of Bim, mitochondrial release of cytochrome c and Smac, and cell death. These neuroprotective effects of E2 against Abeta-induced apoptosis are mimicked by the JNK inhibitor SP600125 (anthra[1,9-cd]pyrazol-6(2H)-one). In addition, E2 attenuates Abeta-induced JNK phosphorylation in an ER-dependent manner, but does not affect basal levels of JNK phosphorylation. These results suggest that E2 may reduce Abeta-induced neuronal apoptosis at least in part by two complementary pathways: (1) ER-dependent, JNK-independent upregulation of Bcl-w and downregulation of Bim under basal conditions, and (2) ER-dependent inhibition of Abeta-induced JNK activation and subsequent JNK-dependent downregulation of Bcl-w and upregulation of Bim, resulting in mitochondrial release of cytochrome c and Smac and eventual cell death. These data provide new understanding into the mechanisms contributing to estrogen neuroprotection, a neural function with potential therapeutic relevance to Alzheimer's disease.
- Pike, C. J., Rosario, E. R., & Nguyen, T. V. (2006). Androgens, aging, and Alzheimer's disease. Endocrine, 29(2), 233-41.More infoTestosterone depletion is a normal consequence of aging in men that is associated with senescent effects in androgen- responsive tissues. We discuss new evidence that one consequence of testosterone depletion in men is an increased risk for the development of Alzheimer's disease (AD). Furthermore, we discuss two candidate mechanisms by which testosterone may affect AD pathogenesis. First, testosterone has been identified as an endogenous regulator of beta-amyloid, a protein that abnormally accumulates in AD brain and is implicated as a causal factor in the disease. Second, findings from several different paradigms indicate that testosterone has both neurotrophic and neuroprotective functions. These new findings support the clinical evaluation of androgen-based therapies for the prevention and treatment of AD.
- Nguyen, T. V., Yao, M., & Pike, C. J. (2005). Androgens activate mitogen-activated protein kinase signaling: role in neuroprotection. Journal of neurochemistry, 94(6), 1639-51.More infoRecent evidence indicates that testosterone is neuroprotective, however, the underlying mechanism(s) remains to be elucidated. In this study, we investigated the hypothesis that androgens induce mitogen-activated protein kinase (MAPK) signaling in neurons, which subsequently drives neuroprotection. We observed that testosterone and its non-aromatizable metabolite dihydrotestosterone (DHT) rapidly and transiently activate MAPK in cultured hippocampal neurons, as evidenced by phosphorylation of extracellular signal-regulated kinase (ERK)-1 and ERK-2. Importantly, pharmacological suppression of MAPK/ERK signaling blocked androgen-mediated neuroprotection against beta-amyloid toxicity. Androgen activation of MAPK/ERK and neuroprotection also was observed in PC12 cells stably transfected with androgen receptor (AR), but in neither wild-type nor empty vector-transfected PC12 cells. Downstream of ERK phosphorylation, we observed that DHT sequentially increases p90 kDa ribosomal S6 kinase (Rsk) phosphorylation and phosphorylation-dependent inactivation of Bcl-2-associated death protein (Bad). Prevention of androgen-induced phosphorylation of Rsk and Bad blocked androgen neuroprotection. These findings demonstrate AR-dependent androgen activation of MAPK/ERK signaling in neurons, and specifically identify a neuroprotective pathway involving downstream activation of Rsk and inactivation of Bad. Elucidation of androgen-mediated neural signaling cascades will provide important insights into the mechanisms of androgen action in brain, and may present a framework for therapeutic intervention of age-related neurodegenerative disorders.
- Yao, M., Nguyen, T. V., & Pike, C. J. (2005). Beta-amyloid-induced neuronal apoptosis involves c-Jun N-terminal kinase-dependent downregulation of Bcl-w. The Journal of neuroscience : the official journal of the Society for Neuroscience, 25(5), 1149-58.More infobeta-Amyloid protein (Abeta) has been implicated as a key molecule in the neurodegenerative cascades of Alzheimer's disease (AD). Abeta directly induces neuronal apoptosis, suggesting an important role of Abeta neurotoxicity in AD neurodegeneration. However, the mechanism(s) of Abeta-induced neuronal apoptosis remain incompletely defined. In this study, we report that Abeta-induced neuronal death is preceded by selective alterations in expression of the Bcl-2 family of apoptosis-related genes. Specifically, we observe that Abeta significantly reduces expression of antiapoptotic Bcl-w and Bcl-x(L), mildly affects expression of bim, Bcl-2, and bax, but does not alter expression of bak, bad, bik, bid, or BNIP3.Abeta-induced downregulation of Bcl-w appears to contribute to the mechanism of apoptosis, because Abeta-induced neuronal death was significantly increased by Bcl-w suppression but significantly reduced by Bcl-w overexpression. Downstream of Bcl-w, Abeta-induced neuronal apoptosis is characterized by mitochondrial release of second mitochondrion-derived activator of caspase (Smac), an important precursor event to cell death. We observed that Smac release was potentiated by suppression of Bcl-w and reduced by overexpression of Bcl-w. Next, we investigated the upstream mediator of Abeta-induced Bcl-w downregulation and Smac release. We observed that Abeta rapidly activates c-Jun N-terminal kinase (JNK). Pharmacological inhibition of JNK effectively inhibited all measures of Abeta apoptosis: Bcl-w downregulation, Smac release, and neuronal death. Together, these results suggest that the mechanism of Abeta-induced neuronal apoptosis sequentially involves JNK activation, Bcl-w downregulation, and release of mitochondrial Smac, followed by cell death. Complete elucidation of the mechanism of Abeta-induced apoptosis promises to accelerate development of neuroprotective interventions for the treatment of AD.
- Nguyen, T., & Doyle, K. (2015, October). Advancing neuroimmunology: Untangling biomarkers in the brain. Science.More infoAdvancing neuroimmunology:Untangling biomarkers in the brainPDF icon Download Slidesaudio This event occurred onWednesday, October 28, 2015Unraveling how the immune and nervous systems interact has helped advance our understanding of many mechanisms within the brain, from development to diseases. Inflammation and immune responses in the nervous system have been linked to a variety of brain disorders, including neurodegeneration, traumatic brain injury, stroke, and cognitive decline. Our knowledge of immune-related pathologies in the brain and the ability to identify biomarkers for disease and inflammation are key for forming meaningful mechanistic conclusions. In this webinar, our expert panel will share their experience researching neuroinflammation and neurodegeneration-related biomarkers, and will discuss methodologies for tracking pathological changes and quantifying specific inflammatory mediators, such as T cells, cytokines, and antibodies. During this webinar, the speakers will discuss:Best practices and the challenges of studying biomarkers in the brainTechniques for measuring immune-related moleculesProtocols for analyzing human samples as well as rodent models
- Doyle, K., Nguyen, T., Hayes, M. I., Zbesko, J. C., Becktel, D. A., Frye, J. B., Chung, A., & Calderon, K. (2019, January/Winter). Cyclodextrin treatment substantially alters the inflammatory response to stroke. 30th Annual Undergraduate Biology Research Program Conference. University of Arizona: University of Arizona Undergraduate Biology Research Program.More infoThe goal of this study is to investigate cyclodextrin as a pharmacological approach for improving recovery from ischemic stroke. Approximately 800,000 people suffer a stroke each year in the United States, many of whom later develop long-term disabilities, such as post-stroke dementia and Alzheimer’s disease. Ischemic stroke accounts for around 87% of all stroke cases and occurs when an artery that supplies blood to the brain is blocked or restricted by a thrombosis, embolism, or systemic hypoperfusion. Reduced blood supply results in insufficient levels of oxygen and nutrients to maintain cellular homeostasis, thereby causing excitotoxicity, oxidative stress, apoptosis, and inflammation in the surrounding tissue. In response to this damage, brain tissue undergoes liquefactive necrosis, a process through which proteinases and other enzymes degrade tissue and transform it into a viscous mass. In prior studies, we demonstrated that stroke infarcts in the stage of liquefactive necrosis are sites of chronic inflammation, which we suspect prolongs the healing process and contributes to secondary neurodegeneration, the probable cause of long-term disabilities in stroke victims. In a mouse model of stroke, we previously found a second wave of inflammation between 4 and 8 weeks post-stroke, as demonstrated by elevated cytokine and chemokine expression and which coincided with an accumulation of cholesterol crystals within the infarct. Cholesterol crystals form within the lysosomes of a foamy macrophage when cholesterol ingested by the foamy macrophage from myelin debris exceeds the efflux capacity of the cell. The formation of cholesterol crystals destabilizes the lysosome, which produces a signal that activates the NLRP3 inflammasome. Activation of the NLRP3 inflammasome leads to the secretion of IL-1, one cytokine that prolongs inflammation. Because of this association between cholesterol crystal accumulation and chronic inflammation, we hypothesize that stroke recovery in mice can be improved by preventing cholesterol overloading within phagocytic cells through treatment with cyclodextrin, an FDA-approved drug shown to increase cholesterol solubility, promote removal of cholesterol from foamy macrophages, and initiate anti-inflammatory mechanisms.
- Chung, A., Frye, J. B., Zbesko, J. C., Constantopoulos, E., Hayes, M. I., Figueroa, A. G., Day, W. A., Konhilas, J. P., Mckay, B. S., Nguyen, T., & Doyle, K. (2018, June). Liquefaction of the brain following stroke shares a similar molecular and morphological profile with atherosclerosis and mediates secondary neurodegeneration in an osteopontin dependent mechanism. Keystone Symposia Conference: New Frontiers in Neuroinflammation: What Happens when CNS and Periphery Meet?. Keystone, Colorado: Keystone Symposia Conference.
- Chung, A., Frye, J. B., Zbesko, J. C., Constantopoulos, E., Hayes, M. I., Figueroa, A. G., Day, W. A., Konhilas, J. P., Mckay, B. S., Nguyen, T., & Doyle, K. (2018, November). Liquefaction of the brain following stroke shares characteristics with atherosclerosis. Society for Neuroscience Conference. San Diego, California: Society for Neuroscience.
- Nguyen, T. V. (2018, November). Alzheimer’s disease pathology is a chronic sequela of ischemic stroke in two mouse models of mixed dementia. Society for Neuroscience. San Diego, CA.
- Nguyen, T., Hayes, M. I., Frye, J. B., Zbesko, J. C., Belichenko, N. P., Longo, F. M., & Doyle, K. (2018, November). Alzheimer’s disease pathology is a chronic sequela of ischemic stroke in two mouse models of mixed dementia. Society for Neuroscience Conference. San Diego, California: Society for Neuroscience.
- Zbesko, J. C., Nguyen, T., Yang, T., Frye, J., Hussein, O., Hayes, M. I., Chung, A., Day, W. A., Stepanovic, K., Krumberger, M., Mona, J., Longo, F. M., & Doyle, K. (2018, March). Glial scars are permeable to the neurotoxic environment of chronic stroke infarcts. American Society for Neurochemistry. Riverside, California: American Society for Neurochemistry.
- Zbesko, J. C., Nguyen, T., Hussain, O., Day, W. A., Frye, J., Hayes, M. I., Krumberger, M., Mona, J. K., Stepanovic, K., & Doyle, K. (2017, June). Glial Scars are permeable to neurodegenerative factors present in areas of liquefactive necrosis following stroke. Neuroinflammation: Concepts, Characteristics, Consequences. Keystone Symposia Conference. Keystone, Colorado: Keystone Symposia.
- Doyle, K., Nguyen, T., Calderon, K., Chung, A., Frye, J. B., Zbesko, J. C., & Becktel, D. A. (2019, June/Summer). Cyclodextrin treatment substantially attenuates the chronic inflammatory response to ischemic stroke in mice. Neurodegenerative Diseases: New Insights and Therapeutic Opportunities. Keystone, Colorado: Keystone Symposia.More infoIschemic stroke is a leading cause of physical disability and dementia for Americans, and a stroke occurs every 40 seconds in the United States. In response to ischemia, the brain degenerates by the process of liquefactive necrosis. Liquefactive necrosis is a chronic inflammatory response that occurs for unknown reasons, exacerbates post-stroke injury, and persists for months following stroke. Our published data indicate that liquefactive necrosis shares a similar molecular and morphological profile with atherosclerosis. We hypothesize that following stroke, cholesterol derived from myelin debris overwhelms the processing capability of phagocytic cells in the brain, leading to the formation of lipid-laden foam cells, generation of intracellular cholesterol crystals, secretion of pro-inflammatory cytokines, and production of degradative enzymes. Furthermore, we propose that this sustained inflammatory response, coupled with concurrent cell death, causes post-stroke secondary neurodegeneration and impairs functional recovery. Therefore, the goal of this research was to determine whether cyclic oligosaccharide 2-hydroxypropyl-β-cyclodextrin (CD), an FDA-approved drug that can solubilize and entrap lipophilic substances, prevents the accumulation of cholesterol within foamy macrophages and initiates anti-inflammatory mechanisms after ischemic stroke. To accomplish this goal, we utilized a mouse model of chronic stroke in conjunction with immunostaining, multiplex immunoassays, RNA sequencing, lipidomics, and behavioral analyses. We discovered that treatment with CD for six weeks following stroke significantly reduced the area of liquefactive necrosis, decreased T-lymphocyte, B-lymphocyte, and plasma cell accumulation in the infarct, and attenuated the expression of multiple degradative enzymes. We also found that cyclodextrin-treated mice had improved cognitive function at 7 weeks following stroke compared to vehicle-treated mice. These findings suggest that CD treatment may help the immune system process lipid debris following stroke, and may be a potential method of enhancing stroke recovery and preventing the development of post-stroke dementia.