Alzheimer Disease: Tan J

Giunta B, Fernandez F, Nikolic WV, Obregon D, Rrapo E, Town T, Tan J. · Neuroimmunology Laboratory, Department of Psychiatry, Behavioral Medicine, Institute for Research in Psychiatry, University of South Florida, College of Medicine, Tampa, FL 33613, USA. · J Neuroinflammation. · Pubmed #19014446 links to  free full text

Abstract: Recently, the term "inflammaging" was coined by Franceshci and colleagues to characterize a widely accepted paradigm that ageing is accompanied by a low-grade chronic up-regulation of certain pro-inflammatory responses. Inflammaging differs significantly from the traditional five cardinal features of acute inflammation in that it is characterized by a relative decline in adaptive immunity and T-helper 2 responses and is associated with increased innate immunity by cells of the mononuclear phagocyte lineage. While the over-active innate immunity characteristic of inflammaging may remain subclinical in many elderly individuals, a portion of individuals (postulated to have a "high responder inflammatory genotype") may shift from a state of "normal" or "subclinical" inflammaging to one or more of a number of age-associated diseases. We and others have found that IFN-gamma and other pro-inflammatory cytokines interact with processing and production of Abeta peptide, the pathological hallmark feature of Alzheimer's disease (AD), suggesting that inflammaging may be a "prodrome" to AD. Although conditions of enhanced innate immune response with overproduction of pro-inflammatory proteins are associated with both healthy aging and AD, it is suggested that those who age "well" demonstrate anti-inflammaging mechanisms and biomarkers that likely counteract the adverse immune response of inflammaging. Thus, opposing the features of inflammaging may prevent or treat the symptoms of AD. In this review, we fully characterize the aging immune system. In addition, we explain how three novel treatments, (1) human umbilical cord blood cells (HUCBC), (2) flavanoids, and (3) Abeta vaccination oppose the forces of inflammaging and AD-like pathology in various mouse models.

Town T, Tan J, Flavell RA, Mullan M. · Section of Immunobiology, Yale University School of Medicine, New Haven, CT 06520, USA. · Neuromolecular Med. · Pubmed #16247185 No free full text.

Abstract: Alzheimer's disease (AD) is the most common dementing illness and is pathologically characterized by deposition of the 40-42 amino acid peptide, amyloid-beta (Abeta), as senile plaques. It is well documented that brain inflammatory mechanisms mediated by reactive glia are activated in response to Abeta plaques. A number of reports further suggest that T-cells are activated in AD patients, and that these cells exist both in the periphery and as infiltrates in the brain. We explore the potential role of T-cells in the AD process, a controversial area, by reviewing reports that show disturbed activation profiles and/or altered numbers of various subsets of T-cells in the circulation as well as in the AD brain parenchyma and in cerebral amyloid angiopathy. We also discuss the recent Abeta immunotherapy approach vis-à-vis the activated, autoaggressive T-cell infiltrates that contributed to aseptic meningoencephalitis in a small percentage of patients, and present possible alternative approaches that may be both efficacious and safe. Finally, we explore the use of mouse models of AD as a system within which to definitively test the possible contribution of T-cells to AD pathogenesis.

Morgan D, Gordon MN, Tan J, Wilcock D, Rojiani AM. · Department of Pharmacology, University of South Florida, Tampa, 33612, USA. · J Neuropathol Exp Neurol. · Pubmed #16141783 No free full text.

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

Tan J, Town T, Mullan M. · The Roskamp Institute, Department of Psychiatry, University of South Florida, 3515 East Fletcher Avenue, Tampa, Florida 33613, USA. · Curr Opin Pharmacol. · Pubmed #12127879 No free full text.

Abstract: Increasing evidence supports a role of the CD40 receptor-CD40 ligand (CD40-CD40L) interaction in the pathogenesis of Alzheimer's disease (AD). It has previously been shown that this dyad acts synergistically with the Alzheimer amyloid-beta peptide to promote microglial activation. Reactive microglia produce potentially neurotoxic substances such as tumor necrosis factor alpha and the reactive oxygen species nitric oxide, which can induce bystander neuronal injury at high levels. When a transgenic mouse model of AD is crossed with an animal deficient in CD40L, the resulting phenotype is deficient in the gliosis observed in a mouse model of AD in which CD40L is present. Additionally, these crossed animals have complete absence of AD-like neuronal Tau hyperphosphorylation, a marker of the preneuronal tangle pathology in AD patients. This suggests that the CD40-CD40L system is a critical enhancer of microglial activation in an AD transgenic mouse model and that such activation is associated with an increase in a key indicator of neuronal stress. Conversely, the finding that reduced CD40-CD40L interaction is associated with reduced chronic microgliosis and Tau hyperphosphorylation supports the view that, in general, mechanisms that reduce microgliosis will be beneficial in AD.

Town T, Tan J, Mullan M. · Department of Psychiatry, Roskamp Institute, University of South Florida, 3515 E. Fletcher Avenue, Tampa, FL 33613, USA. · Neurochem Int. · Pubmed #11578772 No free full text.

Abstract: The interaction between CD40 and its cognate ligand, CD40 ligand, is a primary regulator of the peripheral immune response, including modulation of T lymphocyte activation, B lymphocyte differentiation and antibody secretion, and innate immune cell activation, maturation, and survival. Recently, we and others have identified CD40 expression on a variety of CNS cells, including endothelial cells, smooth muscle cells, astroglia and microglia, and have found that, on many of these cells, CD40 expression is enhanced by pro-inflammatory stimuli. Importantly, the CD40-CD40 ligand interaction on microglia triggers a series of intracellular signaling events that are discussed, beginning with Src-family kinase activation and culminating in microglial activation as evidenced by tumor necrosis factor-alpha secretion. Based on the involvement of microglial activation and brain inflammation in Alzheimer's disease pathogenesis, we have investigated co-stimulation of microglia, smooth muscle, and endothelial cells with CD40 ligand in the presence of low doses of freshly solubilized amyloid-beta peptides. Data reviewed herein show that CD40 ligand and amyloid-beta act synergistically to promote pro-inflammatory responses by these cells, including secretion of interleukin-1 beta by endothelial cells and tumor necrosis factor-alpha by microglia. As these cytokines have been implicated in neuronal injury, a comprehensive model of pro-inflammatory CD40 ligand and amyloid-beta initiated Alzheimer's disease pathogenesis (mediated by multiple CNS cells) is proposed.

Zhu Y, Bickford PC, Sanberg P, Giunta B, Tan J. · Rashid Laboratory for Developmental Neurobiology, Silver Child Development Center, Department of Psychiatry and Behavioral Medicine, University of South Florida College of Medicine, Tampa, Florida 33613, USA. · Rejuvenation Res. · Pubmed #18789000 No free full text.

Abstract: Alzheimer's Disease (AD) is the most common age-related dementia, with a current prevalence in excess of five million individuals in the United States. The aggregation of amyloid-beta (A beta) into fibrillar amyloid plaques is a key pathological event in the development of the disease. Microglial proinflammatory activation is widely known to cause neuronal and synaptic damage that correlates with cognitive impairment in AD. However, current pharmacological attempts at reducing neuroinflammation mediated via microglial activation have been largely negative in terms of slowing AD progression. Previously, we have shown that microglia express proinflammatory cytokines and a reduced capacity to phagocytose A beta in the context of CD40, A beta peptides and/or lipopolysaccharide (LPS) stimulation, a phenomenon that can be opposed by attenuation of p44/42 mitogen-activated protein kinase (MAPK) signaling. Other groups have found that blueberry (BB) extract both inhibits phosphorylation of this MAPK module and also improves cognitive deficits in AD model mice. Given these considerations and the lack of reduced A beta quantities in behaviorally improved BB-fed mice, we wished to determine whether BB supplementation would alter the microglial proinflammatory activation state in response to A beta. We found that BB significantly enhances microglial clearance of A beta, inhibits aggregation of A beta(1-42), and suppresses microglial activation, all via suppression of the p44/42 MAPK module. Thus, these data may explain the previously observed behavioral recovery in PSAPP mice and suggest a means by which dietary supplementation could mitigate an undesirable microglial response toward fibrillar A beta.

Town T, Laouar Y, Pittenger C, Mori T, Szekely CA, Tan J, Duman RS, Flavell RA. · Department of Immunobiology, Yale University School of Medicine, 300 Cedar Street, New Haven, Connecticut 06520-8011, USA. · Nat Med. · Pubmed #18516051 links to  free full text

Abstract: Alzheimer's disease is the most common dementia and is pathologically characterized by deposition of amyloid-beta peptide (Abeta) into beta-amyloid plaques, neuronal injury and low-level, chronic activation of brain immunity. Transforming growth factor-betas (TGF-betas) are pleiotropic cytokines that have key roles in immune cell activation, inflammation and repair after injury. We genetically interrupted TGF-beta and downstream Smad2/3 signaling (TGF-beta-Smad2/3) in innate immune cells by inducing expression of CD11c promoter-driven dominant-negative TGF-beta receptor type II in C57BL/6 mice (CD11c-DNR), crossed these mice with mice overexpressing mutant human amyloid precursor protein, the Tg2576 Alzheimer's disease mouse model, and evaluated Alzheimer's disease-like pathology. Aged double-transgenic mice showed complete mitigation of Tg2576-associated hyperactivity and partial mitigation of defective spatial working memory. Brain parenchymal and cerebrovascular beta-amyloid deposits and Abeta abundance were markedly (up to 90%) attenuated in Tg2576-CD11c-DNR mice. This was associated with increased infiltration of Abeta-containing peripheral macrophages around cerebral vessels and beta-amyloid plaques. In vitro, cultures of peripheral macrophages, but not microglia, from CD11c-DNR mice showed blockade of classical TGF-beta-activated Smad2/3 but also showed hyperactivation of alternative bone morphogenic protein-activated Smad1/5/8 signaling and increased Abeta phagocytosis. Similar effects were noted after pharmacological inhibition of activin-like kinase-5, a type I TGF-beta receptor. Taken together, our results suggest that blockade of TGF-beta-Smad2/3 signaling in peripheral macrophages represents a new therapeutic target for Alzheimer's disease.

Rezai-Zadeh K, Arendash GW, Hou H, Fernandez F, Jensen M, Runfeldt M, Shytle RD, Tan J. · Rashid Laboratory for Developmental Neurobiology, Silver Child Development Center, Department of Psychiatry and Behavioral Medicine, and Department of Neurosurgery, University of South Florida, Tampa, FL 33613, USA. · Brain Res. · Pubmed #18457818 No free full text.

Abstract: We previously reported that intraperitoneal (i.p.) injection (20 mg/kg) of (-)-epigallocatechin-3-gallate (EGCG), the main polyphenolic constituent of green tea, decreased beta-amyloid (Abeta) levels and plaques via promotion of the non-amyloidogenic alpha-secretase proteolytic pathway in "Swedish" mutant amyloid precursor protein overexpressing (APPsw, Tg) mice. Here, we find that EGCG administered orally in drinking water (50 mg/kg) similarly reduces Abeta deposition in these mice. Following a six month treatment of an 8 month old cohort, immunohistochemical analysis of coronal sections reveals that plaque burdens were reduced in the cingulate cortex, hippocampus, and entorhinal cortex by 54%, 43%, and 51%, respectively. Congo red plaque burdens were decreased in the cingulate cortex, hippocampus, and entorhinal cortex by 53%, 53%, and 58%, respectively as well. ELISA of brain homogenates of the treatment Tg mice revealed consistent reductions in both Abeta1-40 and 1-42 soluble and insoluble forms. In the present study we also investigated the effect EGCG administration had on tau pathology and cognition in Tg mice. Both i.p. and orally-treated Tg animals were found to have modulated tau profiles, with markedly suppressed sarkosyl-soluble phosphorylated tau isoforms. Radial arm water maze (RAWM) testing for working memory indicated that EGCG provided cognitive benefit to Tg mice with both i.p. and oral administration, although i.p.-treated animals showed a more pronounced benefit because of the greater impairment of their Tg controls at the time of testing. Taken together, these data further the notion of EGCG dietary supplementation as a potentially safe and effective prophylaxis for Alzheimer's disease.

Nikolic WV, Hou H, Town T, Zhu Y, Giunta B, Sanberg CD, Zeng J, Luo D, Ehrhart J, Mori T, Sanberg PR, Tan J. · Rashid Laboratory for Developmental Neurobiology, Silver Child Development Center, Department of Psychiatry & Behavioral Medicine, University of South Florida, Tampa, FL 33613, USA. · Stem Cells Dev. · Pubmed #18366296 links to  free full text

Abstract: Modulation of immune/inflammatory responses by diverse strategies including amyloid-beta (Abeta) immunization, nonsteroidal anti-inflammatory drugs, and manipulation of microglial activation states has been shown to reduce Alzheimer's disease (AD)-like pathology and cognitive deficits in AD transgenic mouse models. Human umbilical cord blood cells (HUCBCs) have unique immunomodulatory potential. We wished to test whether these cells might alter AD-like pathology after infusion into the PSAPP mouse model of AD. Here, we report a marked reduction in Abeta levels/beta-amyloid plaques and associated astrocytosis following multiple low-dose infusions of HUCBCs. HUCBC infusions also reduced cerebral vascular Abeta deposits in the Tg2576 AD mouse model. Interestingly, these effects were associated with suppression of the CD40-CD40L interaction, as evidenced by decreased circulating and brain soluble CD40L (sCD40L), elevated systemic immunoglobulin M (IgM) levels, attenuated CD40L-induced inflammatory responses, and reduced surface expression of CD40 on microglia. Importantly, deficiency in CD40 abolishes the effect of HUCBCs on elevated plasma Abeta levels. Moreover, microglia isolated from HUCBC-infused PSAPP mice demonstrated increased phagocytosis of Abeta. Furthermore, sera from HUCBC-infused PSAPP mice significantly increased microglial phagocytosis of the Abeta1-42 peptide while inhibiting interferon-gammainduced microglial CD40 expression. Increased microglial phagocytic activity in this scenario was inhibited by addition of recombinant CD40L protein. These data suggest that HUCBC infusion mitigates AD-like pathology by disrupting CD40L activity.

Obregon D, Hou H, Bai Y, Nikolic WV, Mori T, Luo D, Zeng J, Ehrhart J, Fernandez F, Morgan D, Giunta B, Town T, Tan J. · Neuroimmunology Laboratory, Institute for Research in Psychiatry, Department of Psychiatry and Behavioral Medicine, USA. · Neurobiol Dis. · Pubmed #18055209 No free full text.

Abstract: Amyloid-beta (Abeta) immunization efficiently reduces amyloid plaque load and memory impairment in transgenic mouse models of Alzheimer's disease (AD). Active Abeta immunization has also yielded favorable results in a subset of AD patients. However, a small percentage of patients developed severe aseptic meningoencephalitis associated with brain inflammation and infiltration of T-cells. We have shown that blocking the CD40-CD40 ligand (L) interaction mitigates Abeta-induced inflammatory responses and enhances Abeta clearance. Here, we utilized genetic and pharmacologic approaches to test whether CD40-CD40L blockade could enhance the efficacy of Abeta(1-42) immunization, while limiting potentially damaging inflammatory responses. We show that genetic or pharmacologic interruption of the CD40-CD40L interaction enhanced Abeta(1-42) immunization efficacy to reduce cerebral amyloidosis in the PSAPP and Tg2576 mouse models of AD. Potentially deleterious pro-inflammatory immune responses, cerebral amyloid angiopathy (CAA) and cerebral microhemorrhage were reduced or absent in these combined approaches. Pharmacologic blockade of CD40L decreased T-cell neurotoxicity to Abeta-producing neurons. Further reduction of cerebral amyloidosis in Abeta-immunized PSAPP mice completely deficient for CD40 occurred in the absence of Abeta immunoglobulin G (IgG) antibodies or efflux of Abeta from brain to blood, but was rather correlated with anti-inflammatory cytokine profiles and reduced plasma soluble CD40L. These results suggest CD40-CD40L blockade promotes anti-inflammatory cellular immune responses, likely resulting in promotion of microglial phagocytic activity and Abeta clearance without generation of neurotoxic Abeta-reactive T-cells. Thus, combined approaches of Abeta immunotherapy and CD40-CD40L blockade may provide for a safer and more effective Abeta vaccine.

Cracchiolo JR, Mori T, Nazian SJ, Tan J, Potter H, Arendash GW. · The Johnnie B. Byrd Alzheimer's Center and Research Institute, Tampa, FL 33613, USA. · Neurobiol Learn Mem. · Pubmed #17714960 links to  free full text

Abstract: Although social, physical, and cognitive activities have each been suggested to reduce the risk of Alzheimer's disease (AD), epidemiologic studies cannot determine which activity or combination of activities is most important. To address this question, mutant APP transgenic AD mice were reared long-term in one of four housing conditions (impoverished, social, social+physical, or complete enrichment) from 1(1/2) through 9 months of age. Thus, a stepwise layering of social, physical, and enhanced cognitive activity was created. Behavioral evaluation in a full battery of sensorimotor, anxiety, and cognitive tasks was carried out during the final 5 weeks of housing. Only AD mice raised in complete enrichment (i.e., enhanced cognitive activity) showed: (1) protection against cognitive impairment, (2) decreased brain beta-amyloid deposition, and (3) increased hippocampal synaptic immunoreactivity. The protection provided by enhanced cognitive activity spanned multiple cognitive domains (working memory, reference learning, and recognition/identification). Cognitive and neurohistologic benefits of complete enrichment occurred without any changes in blood cytokine or corticosterone levels, suggesting that enrichment-dependent mechanisms do not involve changes in the inflammatory response or stress levels, respectively. These results indicate that the enhanced cognitive activity of complete enrichment is required for cognitive and neurologic benefit to AD mice-physical and/or social activity are insufficient. Thus, our data suggest that humans who emphasize a high lifelong level of cognitive activity (over and above social and physical activities) will attain the maximal environmental protection against AD.

Nikolic WV, Bai Y, Obregon D, Hou H, Mori T, Zeng J, Ehrhart J, Shytle RD, Giunta B, Morgan D, Town T, Tan J. · Department of Psychiatry and Behavioral Medicine, University of South Florida, Tampa, FL 33613, USA. · Proc Natl Acad Sci U S A. · Pubmed #17264212 links to  free full text

Abstract: Alzheimer's disease (AD) immunotherapy accomplished by vaccination with beta-amyloid (Abeta) peptide has proved efficacious in AD mouse models. However, "active" Abeta vaccination strategies for the treatment of cerebral amyloidosis without concurrent induction of detrimental side effects are lacking. We have developed a transcutaneous (t.c.) Abeta vaccination approach and evaluated efficacy and monitored for deleterious side effects, including meningoencephalitis and microhemorrhage, in WT mice and a transgenic mouse model of AD. We demonstrate that t.c. immunization of WT mice with aggregated Abeta(1-42) plus the adjuvant cholera toxin (CT) results in high-titer Abeta antibodies (mainly of the Ig G1 class) and Abeta(1-42)-specific splenocyte immune responses. Confocal microscopy of the t.c. immunization site revealed Langerhans cells in areas of the skin containing the Abeta(1-42) immunogen, suggesting that these unique innate immune cells participate in Abeta(1-42) antigen processing. To evaluate the efficacy of t.c. immunization in reducing cerebral amyloidosis, transgenic PSAPP (APPsw, PSEN1dE9) mice were immunized with aggregated Abeta(1-42) peptide plus CT. Similar to WT mice, PSAPP mice showed high Abeta antibody titers. Most importantly, t.c. immunization with Abeta(1-42) plus CT resulted in significant decreases in cerebral Abeta(1-40,42) levels coincident with increased circulating levels of Abeta(1-40,42), suggesting brain-to-blood efflux of Abeta. Reduction in cerebral amyloidosis was not associated with deleterious side effects, including brain T cell infiltration or cerebral microhemorrhage. Together, these data suggest that t.c. immunization constitutes an effective and potentially safe treatment strategy for AD.

Arendash GW, Schleif W, Rezai-Zadeh K, Jackson EK, Zacharia LC, Cracchiolo JR, Shippy D, Tan J. · The Byrd Alzheimer's Center and Research Institute, Tampa, FL 33647, USA. · Neuroscience. · Pubmed #16938404 No free full text.

Abstract: A recent epidemiological study suggested that higher caffeine intake over decades reduces the risk of Alzheimer's disease (AD). The present study sought to determine any long-term protective effects of dietary caffeine intake in a controlled longitudinal study involving AD transgenic mice. Caffeine (an adenosine receptor antagonist) was added to the drinking water of amyloid precursor protein, Swedish mutation (APPsw) transgenic (Tg) mice between 4 and 9 months of age, with behavioral testing done during the final 6 weeks of treatment. The average daily intake of caffeine per mouse (1.5 mg) was the human equivalent of 500 mg caffeine, the amount typically found in five cups of coffee per day. Across multiple cognitive tasks of spatial learning/reference memory, working memory, and recognition/identification, Tg mice given caffeine performed significantly better than Tg control mice and similar to non-transgenic controls. In both behaviorally-tested and aged Tg mice, long-term caffeine administration resulted in lower hippocampal beta-amyloid (Abeta) levels. Expression of both Presenilin 1 (PS1) and beta-secretase (BACE) was reduced in caffeine-treated Tg mice, indicating decreased Abeta production as a likely mechanism of caffeine's cognitive protection. The ability of caffeine to reduce Abeta production was confirmed in SweAPP N2a neuronal cultures, wherein concentration-dependent decreases in both Abeta1-40 and Abeta1-42 were observed. Although adenosine A(1) or A(2A) receptor densities in cortex or hippocampus were not affected by caffeine treatment, brain adenosine levels in Tg mice were restored back to normal by dietary caffeine and could be involved in the cognitive protection provided by caffeine. Our data demonstrate that moderate daily intake of caffeine may delay or reduce the risk of AD.

Mori T, Town T, Tan J, Yada N, Horikoshi Y, Yamamoto J, Shimoda T, Kamanaka Y, Tateishi N, Asano T. · Institute of Medical Science, Saitama Medical School, 1981 Kamoda, Kawagoe, Saitama 350-8550, Japan. · J Pharmacol Exp Ther. · Pubmed #16709678 links to  free full text

Abstract: Like microglia, reactive astrocytes produce a myriad of neurotoxic substances in various brain pathologies, such as Alzheimer's disease (AD), trauma, and cerebral ischemia. Among the numerous products of reactive astrocytes, attention has recently been directed toward the possible detrimental role of S100B, because the protein has been shown to be highly expressed along with the progression of brain damage and to exert neurotoxic effects at high concentrations. The present study aimed to examine the possible role of astrocyte-derived S100B in the progression of cerebral amyloidosis and gliosis in transgenic mice overproducing mutant amyloid precursor protein (Tg APP(sw) mice, line 2576). For this purpose, arundic acid (Ono Pharmaceutical Co., Ltd., Mishima, Osaka, Japan), which is known to negatively regulate astrocyte synthesis of S100B, was orally administered to Tg APP(sw) mice for 6 months from 12 months of age, and the effects of the agent on the above parameters were examined. Here, we report that beta-amyloid deposits along with amyloid-beta peptide/S100B levels, as well as beta-amyloid plaque-associated reactive gliosis (astrocytosis and microgliosis), were significantly ameliorated in arundic acid-treated Tg APP(sw) mice relative to vehicle-treated Tg APP(sw) mice at 19 months of age. Based on the above results, arundic acid is considered to deserve further exploration as a promising therapeutic agent for AD.

Obregon DF, Rezai-Zadeh K, Bai Y, Sun N, Hou H, Ehrhart J, Zeng J, Mori T, Arendash GW, Shytle D, Town T, Tan J. · Neuroimmunology Laboratory, Silver Child Development Center, Department of Psychiatry and Behavioral Medicine, The Byrd Alzheimer's Center and Research Institute, 3515 E. Fletcher Avenue, Tampa, FL 33647, USA. · J Biol Chem. · Pubmed #16624814 links to  free full text

Abstract: Recently, we have shown that green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) exerts a beneficial role on reducing brain Abeta levels, resulting in mitigation of cerebral amyloidosis in a mouse model of Alzheimer disease. EGCG seems to accomplish this by modulating amyloid precursor protein (APP) processing, resulting in enhanced cleavage of the alpha-COOH-terminal fragment (alpha-CTF) of APP and corresponding elevation of the NH(2)-terminal APP product, soluble APP-alpha (sAPP-alpha). These beneficial effects were associated with increased alpha-secretase cleavage activity, but no significant alteration in beta-or gamma-secretase activities. To gain insight into the molecular mechanism whereby EGCG modulates APP processing, we evaluated the involvement of three candidate alpha-secretase enzymes, a-disintegrin and metalloprotease (ADAM) 9, 10, or 17, in EGCG-induced non-amyloidogenic APP metabolism. Results show that EGCG treatment of N2a cells stably transfected with "Swedish" mutant human APP (SweAPP N2a cells) leads to markedly elevated active ( approximately 60 kDa mature form) ADAM10 protein. Elevation of active ADAM10 correlates with increased alpha-CTF cleavage, and elevated sAPP-alpha. To specifically test the contribution of ADAM10 to non-amyloidogenic APP metabolism, small interfering RNA knockdown of ADAM9, -10, or -17 mRNA was employed. Results show that ADAM10 (but not ADAM9 or -17) is critical for EGCG-mediated alpha-secretase cleavage activity. In summary, ADAM10 activation is necessary for EGCG promotion of non-amyloidogenic (alpha-secretase cleavage) APP processing. Thus, ADAM10 represents an important pharmacotherapeutic target for the treatment of cerebral amyloidosis in Alzheimer disease.

Town T, Nikolic V, Tan J. · Section of Immunobiology, Yale University School of Medicine, 300 Cedar St, New Haven, CT 06520-8011, USA. · J Neuroinflammation. · Pubmed #16259628 links to  free full text

Abstract: Microglia are innate immune cells of myeloid origin that take up residence in the central nervous system (CNS) during embryogenesis. While classically regarded as macrophage-like cells, it is becoming increasingly clear that reactive microglia play more diverse roles in the CNS. Microglial "activation" is often used to refer to a single phenotype; however, in this review we consider that a continuum of microglial activation exists, with phagocytic response (innate activation) at one end and antigen presenting cell function (adaptive activation) at the other. Where activated microglia fall in this spectrum seems to be highly dependent on the type of stimulation provided. We begin by addressing the classical roles of peripheral innate immune cells including macrophages and dendritic cells, which seem to define the edges of this continuum. We then discuss various types of microglial stimulation, including Toll-like receptor engagement by pathogen-associated molecular patterns, microglial challenge with myelin epitopes or Alzheimer's beta-amyloid in the presence or absence of CD40L co-stimulation, and Alzheimer disease "immunotherapy". Based on the wide spectrum of stimulus-specific microglial responses, we interpret these cells as immune cells that demonstrate remarkable plasticity following activation. This interpretation has relevance for neurodegenerative/neuroinflammatory diseases where reactive microglia play an etiological role; in particular viral/bacterial encephalitis, multiple sclerosis and Alzheimer disease.

Rezai-Zadeh K, Shytle D, Sun N, Mori T, Hou H, Jeanniton D, Ehrhart J, Townsend K, Zeng J, Morgan D, Hardy J, Town T, Tan J. · Silver Child Development Center, Department of Psychiatry and Behavioral Medicine, University of South Florida, Tampa, Florida 33613, USA. · J Neurosci. · Pubmed #16177050 links to  free full text

Abstract: Alzheimer's disease (AD) is a progressive neurodegenerative disorder pathologically characterized by deposition of beta-amyloid (Abeta) peptides as senile plaques in the brain. Recent studies suggest that green tea flavonoids may be used for the prevention and treatment of a variety of neurodegenerative diseases. Here, we report that (-)-epigallocatechin-3-gallate (EGCG), the main polyphenolic constituent of green tea, reduces Abeta generation in both murine neuron-like cells (N2a) transfected with the human "Swedish" mutant amyloid precursor protein (APP) and in primary neurons derived from Swedish mutant APP-overexpressing mice (Tg APPsw line 2576). In concert with these observations, we find that EGCG markedly promotes cleavage of the alpha-C-terminal fragment of APP and elevates the N-terminal APP cleavage product, soluble APP-alpha. These cleavage events are associated with elevated alpha-secretase activity and enhanced hydrolysis of tumor necrosis factor alpha-converting enzyme, a primary candidate alpha-secretase. As a validation of these findings in vivo, we treated Tg APPsw transgenic mice overproducing Abeta with EGCG and found decreased Abeta levels and plaques associated with promotion of the nonamyloidogenic alpha-secretase proteolytic pathway. These data raise the possibility that EGCG dietary supplementation may provide effective prophylaxis for AD.

Townsend KP, Town T, Mori T, Lue LF, Shytle D, Sanberg PR, Morgan D, Fernandez F, Flavell RA, Tan J. · Neuroimmunology Laboratory, Department of Psychiatry, University of South Florida College of Medicine, Tampa, USA. · Eur J Immunol. · Pubmed #15688347 No free full text.

Abstract: Although deposition of amyloid beta-peptide (Abeta) as Abeta plaques involves activation of microglia-mediated inflammatory responses, activated microglia ultimately fail to clear Abeta plaques in the brains of either Alzheimer's disease (AD) patients or AD mouse models. Mounting evidence suggests that chronic microglia-mediated immune response during Abeta deposition etiologically contributes to AD pathogenesis by promoting Abeta plaque formation. However, the mechanisms that govern microglia response in the context of cerebral Abeta/beta-amyloid pathology are not well understood. We show that ligation of CD40 by CD40L modulates Abeta-induced innate immune responses in microglia, including decreased microglia phagocytosis of exogenous Abeta(1-42) and increased production of pro-inflammatory cytokines. CD40 ligation in the presence of Abeta(1-42) leads to adaptive activation of microglia, as evidenced by increased co-localization of MHC class II with Abeta. To assess their antigen-presenting cell (APC) function, cultured microglia were pulsed with Abeta(1-42) in the presence of CD40L and co-cultured with CD4(+) T cells. Under these conditions, microglia stimulate T cell-derived IFN-gamma and IL-2 production, suggesting that CD40 signaling promotes the APC phenotype. These data provide a mechanistic explanation for our previous work showing decreased microgliosis associated with diminished cerebral Abeta/beta-amyloid pathology when blocking CD40 signaling in transgenic Alzheimer's mice.

Zhao G, Mao G, Tan J, Dong Y, Cui MZ, Kim SH, Xu X. · Department of Pathobiology, College of Veterinary Medicine, The University of Tennessee, Knoxville, Tennessee 37996, USA. · J Biol Chem. · Pubmed #15485850 links to  free full text

Abstract: Gamma-secretase cleavage of beta-amyloid precursor protein (APP) is crucial in the pathogenesis of Alzheimer disease, because it is the decisive step in the formation of the C terminus of beta-amyloid protein (Abeta). To better understand the molecular events involved in gamma-secretase cleavage of APP, in this study we report the identification of a new intracellular long Abeta species containing residues 1-46 (Abeta46), which led to the identification of a novel zeta-cleavage site between the known gamma- and epsilon-cleavage sites within the transmembrane domain of APP. Our data clearly demonstrate that the new zeta-cleavage is a presenilin-dependent event. It is also noted that the new zeta-cleavage site at Abeta46 is the APP717 mutation site. Furthermore, we show that the new zeta-cleavage is inhibited by gamma-secretase inhibitors known as transition state analogs but less affected by inhibitors known as non-transition state gamma-secretase inhibitors. Thus, the identification of Abeta46 establishes a system to determine the specificity or the preference of the known gamma-secretase inhibitors by examining their effects on the formation or turnover of Abeta46.

Todd Roach J, Volmar CH, Dwivedi S, Town T, Crescentini R, Crawford F, Tan J, Mullan M. · Roskamp Institute, 2040 Whitfield Avenue, Sarasota, FL 34243, USA. · Brain Res. · Pubmed #15223380 No free full text.

Abstract: We have shown that, when an amyloid-beta peptide (Abeta) overproducing transgenic mouse model (PSAPP) of Alzheimer's disease (AD) is treated with a depleting antibody against CD40L, it causes marked attenuation of Abeta pathology associated with decreased amyloidogenic processing of amyloid precursor protein (APP) and increased cerebral clearance of Abeta. Here, we report that, when PSAPP mice receive a regimen of anti-CD40L antibody commencing at an age associated with initial Abeta deposition, they demonstrate superior spatial memory on the standard water maze and radial arm water maze tasks, as well as exhibiting superior non-spatial memory in the object recognition test, as compared to control PSAPP mice. Furthermore, PSAPP mice treated with an anti-CD40L antibody regimen commencing at an age associated with extensive Abeta deposition demonstrate superior spatial memory on the standard water maze task, as compared to control PSAPP mice. Disruption of CD40L activity has beneficial effects on pathology and cognitive behavior in the PSAPP mouse model, providing support for the therapeutic potential of interrupting the CD40-CD40L interaction in AD.

Tan J, Town T, Abdullah L, Wu Y, Placzek A, Small B, Kroeger J, Crawford F, Richards D, Mullan M. · Department of Psychiatry, Roskamp Institute, University of South Florida, 3515 E. Fletcher Ave., Tampa, FL 33613, USA. · J Neuroimmunol. · Pubmed #12417447 No free full text.

Abstract: Aging represents the greatest risk for development of Alzheimer's disease (AD), and changes in peripheral immune cell phenotypes have been found to be associated with aging. Using flow cytometry, we measured the relative expression levels of CD45 isoforms, a marker of nai;ve versus memory CD4+ T cell status, on isolated CD4+ T lymphocytes from patients with a clinical diagnosis of probable Alzheimer's disease, normal elderly, cognitively abnormal elderly, and patients with clinically diagnosed other forms of dementia. Data show significantly lower levels of CD45RA, and an increase in the CD45RO/CD45RA ratio, on CD4+ T cells in patients diagnosed with probable Alzheimer's disease (n=46) and in cognitively abnormal individuals (n=37) compared to age-matched normal participants (n=90). Patients diagnosed with other forms of dementia (n=19) did not significantly differ from normal individuals. Both CD45RA and the CD45RO/CD45RA ratio had higher positive and negative predictive values and were more sensitive biomarkers of probable AD than the apolipoprotein E epsilon 4 allele, and had greater predictive ability for probable AD by regression analyses. Additionally, a testing strategy employing apolipoprotein E genotyping and CD45RA or the CD45RO/CD45RA ratio revealed increased sensitivity, positive and negative predictive values, and predictive ability over the apolipoprotein E epsilon 4 allele. These data show altered peripheral immunity in AD patients, and raise the possibility that a testing strategy using CD45 isoform alteration on CD4+ T cells and apolipoprotein E genotype may be clinically valuable for diagnosing probable AD.

Town T, Vendrame M, Patel A, Poetter D, DelleDonne A, Mori T, Smeed R, Crawford F, Klein T, Tan J, Mullan M. · Roskamp Institute, University of South Florida, 3515 E. Fletcher Avenue, Tampa, FL 33613, USA. · J Neuroimmunol. · Pubmed #12417433 No free full text.

Abstract: It has been demonstrated that immunization of transgenic mouse models of Alzheimer's disease (AD) with amyloid-beta(1-42) peptide (Abeta(1-42)) results in prevention of Abeta plaque formation and amelioration of established plaques in the brain. As the response of the T lymphocyte helper (Th) arm of the immune response had not yet been investigated after Abeta immunization, we i.p. immunized C57BL/6 mice with Abeta(1-42), Abeta(1-40), or phosphate-buffered saline (PBS), and examined markers of Th1 and Th2 immune responses in spleen and in splenocytes from these mice. Spleens from Abeta(1-42)-immunized mice demonstrated decreased interleukin-12 receptor beta chain expression compared to mice immunized with Abeta(1-40) or PBS. Consistently, following stimulation with concanavalin A or anti-CD3 antibody, primary splenocytes from Abeta(1-42)-immunized mice demonstrated elevated secretion of interleukin-4 and interleukin-10, and decreased levels of interferon-gamma. To validate this Th1-->Th2 shift in a transgenic mouse model of AD, we immunized Tg APP(sw) mice (line 2576) with Abeta(1-42) and found decreased Th1 (interleukin-2 and interferon-gamma) and elevated Th2 (interleukin-4 and interleukin-10) cytokines in their stimulated primary splenocytes. Interferon-gamma was markedly reduced and interleukin-10 was increased in blood plasma from these mice, effects that were associated with dramatically mitigated Abeta deposition after Abeta(1-42) immunization. Taken together, these results show enhanced Th2 and down-regulated Th1 immunity following immune challenge with Abeta(1-42).

Tan J, Town T, Crawford F, Mori T, DelleDonne A, Crescentini R, Obregon D, Flavell RA, Mullan MJ. · The Roskamp Institute, Department of Psychiatry, University of South Florida, 3515 East Fletcher Avenue, Tampa, Florida 33613, USA. · Nat Neurosci. · Pubmed #12402041 No free full text.

Abstract: We have shown that interaction of CD40 with CD40L enables microglial activation in response to amyloid-beta peptide (Abeta), which is associated with Alzheimer's disease (AD)-like neuronal tau hyperphosphorylation in vivo. Here we report that transgenic mice overproducing Abeta, but deficient in CD40L, showed decreased astrocytosis and microgliosis associated with diminished Abeta levels and beta-amyloid plaque load. Furthermore, in the PSAPP transgenic mouse model of AD, a depleting antibody against CD40L caused marked attenuation of Abeta/beta-amyloid pathology, which was associated with decreased amyloidogenic processing of amyloid precursor protein (APP) and increased circulating levels of Abeta. Conversely, in neuroblastoma cells overexpressing wild-type human APP, the CD40-CD40L interaction resulted in amyloidogenic APP processing. These findings suggest several possible mechanisms underlying mitigation of AD pathology in response to CD40L depletion, and validate the CD40-CD40L interaction as a target for therapeutic intervention in AD.

Town T, Tan J, Sansone N, Obregon D, Klein T, Mullan M. · The Roskamp Institute, University of South Florida, 3515 E. Fletcher Avenue, Tampa, FL 33613, USA. · Neurosci Lett. · Pubmed #11427310 No free full text.

Abstract: It has been demonstrated that immunization of transgenic mouse models of Alzheimer's disease (AD) with amyloid-beta1-42 peptide (Abeta1-42) results in amelioration of AD-like pathology, including reduced soluble and deposited beta-amyloid and decreased cognitive impairment. Based on the proposed importance of immunoglobulin G (IgG) anti-Abeta antibodies (Abs) in these effects, we sought to characterize these Abs in splenocytes from mice immunized with Abeta1-42. Data show that a more aggregated preparation of Abeta1-42 gives a robust IgG anti-Abeta Ab response, while these Abs are almost undetectable when a less aggregated preparation of Abeta1-42 is used as the immunogen. Importantly, IgG anti-Abeta Ab production is detected after just 12 weeks of Abeta1-42 treatment. Analysis of anti-Abeta Ab IgG isotypes reveals that the majority of these Abs are IgG1, with significantly fewer Abs of the IgG2a or IgG2b isotypes (IgG1>IgG2a>IgG2b), suggesting a T lymphocyte helper type II response after Abeta1-42 immunization. To determine the epitope of Abeta recognized by IgG anti-Abeta Abs, intact Abeta and Abeta peptide fragments were analyzed for their ability to bind these Abs. Data show that these Abs specifically recognize an amino-terminal epitope of Abeta between amino acids one and twelve, with higher affinity for a more soluble preparation of Abeta1-42. These data further indicate the immunogenic potential of Abeta1-42 and offer insight into the nature of the IgG anti-Abeta Ab response.

Tan J, Town T, Mori T, Wu Y, Saxe M, Crawford F, Mullan M. · The Roskamp Institute, Department of Psychiatry, University of South Florida, Tampa, Florida 33613, USA. · J Neurosci. · Pubmed #11027218 links to  free full text

Abstract: Reactive microglia have been suggested to play a role in the Alzheimer's disease (AD) process, and previous studies have shown that expression of CD45, a membrane-bound protein-tyrosine phosphatase (PTP), is elevated in microglia in AD brain compared with controls. To investigate the possible role of CD45 in microglial responsiveness to beta-amyloid (Abeta) peptides, we first co-treated primary cultured microglia with a tyrosine phosphatase inhibitor [potassium bisperoxo (1,10-phenanthroline) oxovanadate (phen), 5 micrometer] and freshly solubilized Abeta peptides (1000 nm). Data show synergistic induction of microglial activation as evidenced by tumor necrosis factor alpha (TNF-alpha) production and nitric oxide (NO) release, both of which we show to be dependent on activation of p44/42 mitogen-activated protein kinase (MAPK). Furthermore, co-treatment with phen and Abeta peptides results in microglia-induced neuronal cell injury. Stimulation of microglial CD45 by anti-CD45 antibody markedly inhibits these effects via inhibition of p44/42 MAPK, suggesting that CD45 is a negative regulator of microglial activation. Accordingly, primary cultured microglia from CD45-deficient mice demonstrate hyper-responsiveness to Abeta, as evidenced by TNF-alpha release, NO production, and neuronal injury after stimulation with Abeta peptides. As a validation of these findings in vivo, brains from a transgenic mouse model of AD [transgenic Swedish APP-overexpressing (Tg APP(sw)) mice] deficient for CD45 demonstrate markedly increased production of TNF-alpha compared with Tg APP(sw) mice. Taken together, these results suggest that therapeutic agents that stimulate the CD45 PTP signaling pathway may be effective in suppressing microglial activation associated with AD.