Ying Peng

Amyloid beta protein dimer-containing human CSF disrupts synaptic plasticity: prevention by systemic passive immunization.

The current development of immunotherapy for Alzheimers disease is based on the assumption that human-derived amyloid β protein (Aβ) can be targeted in a similar manner to animal cell-derived or synthetic Aβ. Because the structure of Aβ depends on its source and the presence of cofactors, it is of great interest to determine whether human-derived oligomeric Aβ species impair brain function and, if so, whether or not their disruptive effects can be prevented using antibodies. We report that untreated ex vivo human CSF that contains Aβ dimers rapidly inhibits hippocampal long-term potentiation in vivo and that acute systemic infusion of an anti-Aβ monoclonal antibody can prevent this disruption of synaptic plasticity. Aβ monomer isolated from human CSF did not affect long-term potentiation. These results strongly support a strategy of passive immunization against soluble Aβ oligomers in early Alzheimers disease.

Complement C3 Deficiency Leads to Accelerated Amyloid β Plaque Deposition and Neurodegeneration and Modulation of the Microglia/Macrophage Phenotype in Amyloid Precursor Protein Transgenic Mice

Complement factor C3 is the central component of the complement system and a key inflammatory protein activated in Alzheimers disease (AD). Previous studies demonstrated that inhibition of C3 by overexpression of soluble complement receptor-related protein y in an AD mouse model led to reduced microgliosis, increased amyloid β (Aβ) plaque burden, and neurodegeneration. To further address the role of C3 in AD pathology, we generated a complement C3-deficient amyloid precursor protein (APP) transgenic AD mouse model (APP;C3−/−). Brains were analyzed at 8, 12, and 17 months of age by immunohistochemical and biochemical methods and compared with age-matched APP transgenic mice. At younger ages (8–12 months), no significant neuropathological differences were observed between the two transgenic lines. In contrast, at 17 months of age, APP;C3−/− mice showed significant changes of up to twofold increased total Aβ and fibrillar amyloid plaque burden in midfrontal cortex and hippocampus, which correlated with (1) significantly increased Tris-buffered saline (TBS)-insoluble Aβ42 levels and reduced TBS-soluble Aβ42 and Aβ40 levels in brain homogenates, (2) a trend for increased Aβ levels in the plasma, (3) a significant loss of neuronal-specific nuclear protein-positive neurons in the hippocampus, and (4) differential activation of microglia toward a more alternative phenotype (e.g., significantly increased CD45-positive microglia, increased brain levels of interleukins 4 and 10, and reduced levels of CD68, F4/80, inducible nitric oxide synthase, and tumor necrosis factor). Our results suggest a beneficial role for complement C3 in plaque clearance and neuronal health as well as in modulation of the microglia phenotype.

l-3-n-Butylphthalide ameliorates β-amyloid-induced neuronal toxicity in cultured neuronal cells

l-3-n-Butylphthalide (l-NBP), as an anti-cerebral ischemia agent, has been shown to have therapeutic effects on learning and memory deficits induced by chronic cerebral hypoperfusion and Abeta intracerebroventricular infusion in rats. In the present study, we investigated the neuroprotective effects of l-NBP on beta-amyloid (Abeta)25-35-induced neuronal death/apoptosis and potential mechanisms in rat hippocampal neurons and human neuroblastoma SH-SY5Y cells. Abeta25-35 significantly reduced cell viability and increased the number of apoptotic-like cells, indicating that Abeta25-35-induced neurotoxicity. In addition, tau protein hyperphosphorylation was found to increase after Abeta exposure. All of these phenotypes induced by Abeta25-35 were markedly reversed by l-NBP. Pretreatment with l-NBP prior to Abeta25-35 exposure significantly elevated cell viability, and reduced Abeta25-35-induced nuclear fragmentation and early apoptosis. Furthermore, immunoreactivity for hyperphosphorylation tau protein was significantly decreased by l-NBP treatment. Our results suggest that l-NBP may protect neurons against Abeta-induced neurotoxicity via inhibiting tau protein hyperphosphorylation.

L-3-n-butylphthalide improves cognitive impairment induced by intracerebroventricular infusion of amyloid-β peptide in rats

Alzheimers disease is the most common form of dementia. Amyloid-beta protein is considered as a key factor of pathogenesis of Alzheimers disease. l-3-n-butylphthalide (L-NBP), an anti-cerebral ischemia drug, has been shown to have therapeutic effects in vascular dementia animal models. In the present study, we investigated the potential of L-NBP to protect against cognitive impairment, oxidative damage and neuropathological changes induced by intracerebroventricular infusion of amyloid-beta peptide in rats. Daily treatments of 10 and 30 mg/kg L-NBP significantly improved spatial learning deficits and attenuated working memory deficits in Morris water maze task. L-NBP partially reversed the reduction of glutathione peroxidase activities and decreased malondialdehyde levels in the cortex and hippocampus. Furthermore, L-NBP markedly inhibited amyloid-beta-induced neuronal apoptosis, possibly by blocking caspase-3 activation. In addition, L-NBP reduced activation of glycogen synthase kinase-3beta and tau protein phosphorylation. Our results demonstrate that L-NBP protects against amyloid-beta-induced neurodegeneration and cognitive decline in a rat model, suggesting that it may have potential as a therapy for Alzheimers disease.

Huperzine A regulates amyloid precursor protein processing via protein kinase C and mitogen-activated protein kinase pathways in neuroblastoma SK-N-SH cells over-expressing wild type human amyloid precursor protein 695

Alpha-secretase (alpha-secretase), cleaves the amyloid precursor protein (APP) within the amyloid-beta (Abeta) sequence, resulting in the release of a secreted fragment of APP (alphaAPPs) and precluding Abeta generation. We investigated the effects of the acetylcholinesterase inhibitor, huperzine A (Hup A), on APP processing and Abeta generation in human neuroblastoma SK-N-SH cells overexpressing wild-type human APP695. Hup A dose-dependently (0-10 microM) increased alphaAPPs release. Therefore, we evaluated two alpha-secretase candidates, a disintegrin and metalloprotease (ADAM) 10 and ADAM17 in Hup A-induced non-amyloidogenic APP metabolism. Hup A enhanced the level of ADAM10, and the inhibitor of tumor necrosis factor-alpha converting enzyme (TACE)/ADAM17 inhibited the Hup A-induced rise in alphaAPPs levels, further suggesting Hup A directed APP metabolism toward the non-amyloidogenic alpha-secretase pathway. Hup A had no effect on Abeta generation in this cell line. The steady-state levels of full-length APP and cell viability were unaffected by Hup A. Alpha-APPs release induced by Hup A treatment was significantly reduced by muscarinic acetylcholine receptor antagonists (particularly by an M1 antagonist), protein kinase C (PKC) inhibitors, GF109203X and calphostin C, and the mitogen-activated kinase kinase (MEK) inhibitors, U0126 and PD98059. Furthermore, Hup A markedly increased the phosphorylation of p44/p42 mitogen-activated protein (MAP) kinase, which was blocked by treatment with U0126 and PD98059. In addition, Hup A inhibited acetylcholinesterase activity by 20% in neuroblastoma cells. Our results indicate that the activation of muscarinic acetylcholine receptors, PKC and MAP kinase may be involved in Hup A-induced alphaAPPs secretion in neuroblastoma cells and suggest multiple pharmacological mechanisms of Hup A regarding the treatment of Alzheimers disease (AD).

Effects of huperzine A on amyloid precursor protein processing and β-amyloid generation in human embryonic kidney 293 APP swedish mutant cells

The amyloid precursor protein (APP) is cleaved enzymatically by nonamyloidogenic and amyloidogenic pathways. α‐Secretase (α‐secretase), cleaves APP within the β‐amyloid (Aβ) sequence, resulting in the release of a secreted fragment of APP (αAPPs) and precluding Aβ generation. In this study, we investigated the effects of an acetylcholinesterase inhibitor, huperzine A (Hup A), on APP processing and Aβ generation in human embryonic kidney 293 cells transfected with human APP bearing the Swedish mutation (HEK293 APPsw). Hup A dose dependently (0–10 μM) increased αAPPs release and membrane‐coupled APP CTF‐C83, suggesting increased APP metabolism toward the nonamyloidogenic α‐secretase pathway. The metalloprotease inhibitor TAPI‐2 inhibited the Hup A‐induced increase in αAPPs release, further suggesting a modulatory effect of Hup A on α‐secretase activity. The synthesis of full‐length APP and cell viability were unchanged after Hup A incubation, whereas the level of AβTotal was significantly decreased, suggesting an inhibitory effect of Hup A on Aβ production. Hup A‐induced αAPPs release was significantly reduced by the protein kinase C (PKC) inhibitors GF109203X and Calphostin C. These data, together with the finding that the PKCα level was enhanced prior to the increase of αAPPs secretion, indicate that PKC may be involved in Hup A‐induced αAPPs secretion by HEK293 APPsw cells. Our data suggest alternative pharmacological mechanisms of Hup A relevant to the treatment of Alzheimers disease.

Cerebral amyloid-beta protein accumulation with aging in cotton-top tamarins: a model of early Alzheimer's disease?

Alzheimers disease (AD) is the most common progressive form of dementia in the elderly. Two major neuropathological hallmarks of AD include cerebral deposition of amyloid-beta protein (Abeta) into plaques and blood vessels, and the presence of neurofibrillary tangles in brain. In addition, activated microglia and reactive astrocytes are often associated with plaques and tangles. Numerous other proteins are associated with plaques in human AD brain, including Apo E and ubiquitin. The amyloid precursor protein and its shorter fragment, Abeta, are homologous between humans and non-human primates. Cerebral Abeta deposition has been reported previously for rhesus monkeys, vervets, squirrel monkeys, marmosets, lemurs, cynomologous monkeys, chimpanzees, and orangutans. Here we report, for the first time, age-related neuropathological changes in cotton-top tamarins (CTT, Saguinus oedipus), an endangered non-human primate native to the rainforests of Colombia and Costa Rica. Typical lifespan is 13-14 years of age in the wild and 15-20+ years in captivity. We performed detailed immunohistochemical analyses of Abeta deposition and associated pathogenesis in archived brain sections from 36 tamarins ranging in age from 6-21 years. Abeta plaque deposition was observed in 16 of the 20 oldest tamarins (>12 years). Plaques contained mainly Abeta42, and in the oldest animals, were associated with reactive astrocytes, activated microglia, Apo E, and ubiquitin-positive dystrophic neurites, similar to human plaques. Vascular Abeta was detected in 14 of the 20 aged tamarins; Abeta42 preceded Abeta40 deposition. Phospho-tau labeled dystrophic neurites and tangles, typically present in human AD, were absent in the tamarins. In conclusion, tamarins may represent a model of early AD pathology.

Novel Aβ Immunogens: Is Shorter Better?

Active and passive Aβ immunotherapy in Alzheimers disease (AD)-like mouse models lowers cerebral amyloid- β protein (Aβ) levels, especially if given early in the disease process, and improves cognitive deficits. In 2002, a Phase IIa clinical trial was halted due to meningoencephalitis in ∼6% of the AD patients. It is hypothesized that the immunogen, full-length Aβ1-42, may have led to an autoimmune response. Currently, we are developing novel Aβ peptide immunogens for active immunization in amyloid precursor protein transgenic mice (APP Tg) to target Aβ B cell epitopes (within Aβ1-15) and avoid Aβ-specific T cell epitopes (Aβ16-42) so as to generate a safe and effective AD vaccine. Intranasal immunization with dendrimeric Aβ1-15 (16 copies of Aβ1-15 on a lysine core) or a tandem repeat of Aβ1-15 joined by 2 lysines and conjugated to an RGD motif with a mutated form of an E. coli-derived adjuvant generated robust Aβ titers in both wildtype and APP Tg mice. The Aβ antibodies recognized a B cell epitope within Aβ1-7, were mostly T-helper 2 associated immunoglobulin isotypes, bound human AD and APP Tg plaques, and detected Aβ oligomers. Splenic T cells reacted to the immunogens but not full-length Aβ. Six months of intranasal immunization (from 6-to-12 months of age) of J20 mice with each immunogen lowered insoluble Aβ42 by 50%, reduced plaque burden and gliosis, and increased Aβ in plasma. Interestingly, Aβ antibody generation was influenced by route of immunization. Transcutaneous immunization with dβ1-15, but not full-length Abeta, led to high Aβ titers. In summary, our short Aβ immunogens induced robust titers of predominantly Th2 antibodies that were able to clear cerebral Aβ in the absence of Aβ-specific T cell reactivity, indicating the potential for a safer vaccine. We remain optimistic about the potential of such a vaccine for prevention and treatment of AD.

Complement C3 Deficiency Leads to Accelerated Amyloid Plaque Deposition and Neurodegeneration and Modulation of the Microglia/Macrophage Phenotype in Amyloid Precursor Protein Transgenic Mice

Complement factor C3 is the central component of the complement system and a key inflammatory protein activated in Alzheimers disease (AD). Previous studies demonstrated that inhibition of C3 by overexpression of soluble complement receptor-related protein y in an AD mouse model led to reduced microgliosis, increased amyloid β (Aβ) plaque burden, and neurodegeneration. To further address the role of C3 in AD pathology, we generated a complement C3-deficient amyloid precursor protein (APP) transgenic AD mouse model (APP;C3−/−). Brains were analyzed at 8, 12, and 17 months of age by immunohistochemical and biochemical methods and compared with age-matched APP transgenic mice. At younger ages (8–12 months), no significant neuropathological differences were observed between the two transgenic lines. In contrast, at 17 months of age, APP;C3−/− mice showed significant changes of up to twofold increased total Aβ and fibrillar amyloid plaque burden in midfrontal cortex and hippocampus, which correlated with (1) significantly increased Tris-buffered saline (TBS)-insoluble Aβ42 levels and reduced TBS-soluble Aβ42 and Aβ40 levels in brain homogenates, (2) a trend for increased Aβ levels in the plasma, (3) a significant loss of neuronal-specific nuclear protein-positive neurons in the hippocampus, and (4) differential activation of microglia toward a more alternative phenotype (e.g., significantly increased CD45-positive microglia, increased brain levels of interleukins 4 and 10, and reduced levels of CD68, F4/80, inducible nitric oxide synthase, and tumor necrosis factor). Our results suggest a beneficial role for complement C3 in plaque clearance and neuronal health as well as in modulation of the microglia phenotype.

Complement C3-Deficiency Leads to Accelerated Aβ Plaque Deposition and Neurodegeneration, and Modulation of the Microglia/Macrophage Phenotype in APP Transgenic Mice

Complement factor C3 is the central component of the complement system and a key inflammatory protein activated in Alzheimers disease (AD). Previous studies demonstrated that inhibition of C3 by overexpression of soluble complement receptor-related protein y in an AD mouse model led to reduced microgliosis, increased amyloid β (Aβ) plaque burden, and neurodegeneration. To further address the role of C3 in AD pathology, we generated a complement C3-deficient amyloid precursor protein (APP) transgenic AD mouse model (APP;C3−/−). Brains were analyzed at 8, 12, and 17 months of age by immunohistochemical and biochemical methods and compared with age-matched APP transgenic mice. At younger ages (8–12 months), no significant neuropathological differences were observed between the two transgenic lines. In contrast, at 17 months of age, APP;C3−/− mice showed significant changes of up to twofold increased total Aβ and fibrillar amyloid plaque burden in midfrontal cortex and hippocampus, which correlated with (1) significantly increased Tris-buffered saline (TBS)-insoluble Aβ42 levels and reduced TBS-soluble Aβ42 and Aβ40 levels in brain homogenates, (2) a trend for increased Aβ levels in the plasma, (3) a significant loss of neuronal-specific nuclear protein-positive neurons in the hippocampus, and (4) differential activation of microglia toward a more alternative phenotype (e.g., significantly increased CD45-positive microglia, increased brain levels of interleukins 4 and 10, and reduced levels of CD68, F4/80, inducible nitric oxide synthase, and tumor necrosis factor). Our results suggest a beneficial role for complement C3 in plaque clearance and neuronal health as well as in modulation of the microglia phenotype.