Keun-A Chang

C-terminal fragments of amyloid precursor protein exert neurotoxicity by inducing glycogen synthase kinase-3β expression

The AICD (amyloid precursor protein [APP] intracellular domain) and C31, the caspase‐cleaved C‐terminal fragment of APP, have been found in the brains of patients with Alzheimers disease (AD). Here, we demonstrate for the first time that the C‐terminal fragments of APP (AICD [C57, C59] and C31) exert neurotoxicity on differentiated PC 12 cells and rat primary cortical neurons by inducing the expression of glycogen synthase kinase 3β, forming a ternary complex with Fe65 and CP2/LSF/LBP1 in the nucleus, whereas deletion mutants and a point mutant with Y682G of the YENPTY domain, a Fe65 binding domain, do not. Moreover, expression of APP770 and Swedish mutant form of APP increased the levels of C‐terminal fragments of APP (APP‐CTs) in neuronal cells and also induced the up‐regulation of glycogen synthase kinase‐3β at both the mRNA and the protein levels. In addition, we show that CP2/LSF/LBP1 binding site (nt +0 to ∼+10) in human glycogen synthase kinase 3β promoter region is essential for the induction of the gene transcription by APP‐CTs. The neurotoxicities induced by APP‐CTs (AICD and C31) were accompanied by an increase in the active form of glycogen synthase knase‐3β, and by the induction of tau phosphorylation and a reduction in nuclear β‐catenin levels, and led to apoptosis.

Phosphorylation of amyloid precursor protein (APP) at Thr668 regulates the nuclear translocation of the APP intracellular domain and induces neurodegeneration.

ABSTRACT Amyloid precursor protein (APP) has eight potential phosphorylation sites in its cytoplasmic domain. Recently, it has demonstrated that the constitutive phosphorylation of APP at T668 (APP695 isoform numbering) was observed specifically in the brain. Neuron-specific phosphorylation of APP at T668 is thought to be important for neuronal functions of APP, although its exact physiological significance remains to be clarified. In this study, we show that the phosphorylation of the APP intracellular domain (AICD) at T668 is essential for its binding to Fe65 and its nuclear translocation and affects the resultant neurotoxicity, possibly mediated through the induction of glycogen synthase kinase 3β and tau phosphorylation by enhancing the formation of a ternary complex with Fe65 and CP2 transcription factor. Taken together, these results suggest that the phosphorylation of AICD at T668 contributes to the neuronal degeneration in Alzheimers disease (AD) by regulating its translocation into the nucleus and then affects neurodegeneration; therefore, the specific inhibitor of T668 phosphorylation might be the target of AD therapy.

Amyloid β peptide induces cytochrome c release from isolated mitochondria

Amyloid &bgr; peptide (A&bgr;) is a neurotoxic metabolic product of the amyloid precursor protein (APP). A&bgr; is strongly implicated in the pathology of Alzheimers disease (AD) and can be formed intracellularly. In this study, we show that the addition of A&bgr;1-42 to isolated mouse brain mitochondria can directly induce cytochrome c (Cyt c) release and mitochondrial swelling, which were partially inhibited by cyclosporin A (CsA). These results suggest that the A&bgr;accumulated intracellularly by APP processing might exert neurotoxicity by interacting with mitochondria and inducing mitochondrial swelling and release of Cyt c, which activates caspase-3 and finally can lead to apoptosis in neuronal cells and to neurodegeneration in AD.

The Preventive and Therapeutic Effects of Intravenous Human Adipose-Derived Stem Cells in Alzheimer’s Disease Mice

Alzheimer’s disease (AD) is characterized by the accumulation of amyloid plaques and neurofibrillary tangles accompanied by cognitive dysfunction. The aim of the present study was to elucidate preventive and therapeutic potential of stem cells for AD. Among stem cells, autologous human adipose-derived stem cells (hASCs) elicit no immune rejection responses, tumorigenesis, or ethical problems. We found that intravenously transplanted hASCs passed through the BBB and migrated into the brain. The learning, memory and pathology in an AD mouse model (Tg2576) mice greatly improved for at least 4 months after intravenous injection of hASC. The number of amyloid plaques and Aβ levels decreased significantly in the brains of hASC-injected Tg mice compared to those of Tg-sham mice. Here, we first report that intravenously or intracerebrally transplanted hASCs significantly rescues memory deficit and neuropathology, in the brains of Tg mice by up-regulating IL-10 and VEGF and be a possible use for the prevention and treatment of AD.

Effects of the monomeric, oligomeric, and fibrillar Aβ42 peptides on the proliferation and differentiation of adult neural stem cells from subventricular zone

The incidence of amyloid plaques, composed mainly of β‐amyloid peptides (Aβ), does not correlate well with the severity of neurodegeneration in patients with Alzheimer’s disease (AD). The effects of Aβ42 on neurons or neural stem cells (NSCs) in terms of the aggregated form remain controversial. We prepared three forms of oligomeric, fibrillar, and monomeric Aβ42 peptides and investigated their effects on the proliferation and neural differentiation of adult NSCs, according to the degree of aggregation or concentration. A low micromolar concentration (1 μmol/L) of oligomeric Aβ42 increased the proliferation of adult NSCs remarkably in a neurosphere assay. It also enhanced the neuronal differentiation of adult NSCs and their ability to migrate. These results provide us with valuable information regarding the effects of Aβ42 on NSCs in the brains of patients with AD.

S100a9 Knockdown Decreases the Memory Impairment and the Neuropathology in Tg2576 Mice, AD Animal Model

Inflammation, insoluble protein deposition and neuronal cell loss are important features in the Alzheimers disease (AD) brain. To investigate the regulatory genes responsible for the neuropathology in AD, we performed microarray analysis with APPV717I-CT100 transgenic mice, an animal model of AD, and isolated the S100a9 gene, which encodes an inflammation-associated calcium binding protein. In another AD animal model, Tg2576 mouse brain, and in human AD brain, induction of S100a9 was confirmed. The endogenous expression of S100a9 was induced by treatment with Aβ or CT peptides in a microglia cell line, BV2 cells. In these cells, silencing study of S100a9 showed that the induction of S100a9 increased the intracellular calcium level and up-regulated the inflammatory cytokines (IL-1β and TNFα) and iNOS. S100a9 lentiviral short hairpin RNA (sh-S100a9) was injected into the hippocampus region of the brains of 13-month-old Tg2576 mice. At two months after injection, we found that knockdown of S100a9 expression had improved the cognition decline of Tg2576 mice in the water maze task, and had reduced amyloid plaque burden. These results suggest that S100a9 induced by Aβ or CT contributes to cause inflammation, which then affects the neuropathology including amyloid plaques burden and impairs cognitive function. Thus, the inhibition of S100a9 is a possible target for AD therapy.

Mefenamic acid shows neuroprotective effects and improves cognitive impairment in in vitro and in vivo Alzheimer's disease models.

Nonsteroidal anti-inflammatory drugs (NSAIDs) exert anti-inflammatory, analgesic, and antipyretic activities and suppress prostaglandin synthesis by inhibiting cyclooxygenase, an enzyme that catalyzes the formation of prostaglandin precursors from arachidonic acid. Epidemiological observations indicate that the long-term treatment of patients suffering from rheumatoid arthritis with NSAIDs results in reduced risk and delayed onset of Alzheimers disease. In this study, we investigated the therapeutic potential for Alzheimers disease of mefenamic acid, a commonly used NSAID that is a cyclooxygenase-1 and 2 inhibitor with only moderate anti-inflammatory properties. We found that mefenamic acid attenuates the neurotoxicities induced by amyloid β peptide (Aβ)1–42 treatment and the expression of a Swedish double mutation (KM595/596NL) of amyloid precursor protein (Swe-APP) or the C-terminal fragments of APP (APP-CTs) in neuronal cells. We also show that mefenamic acid decreases the production of the free radical nitric oxide and reduces cytochrome c release from mitochondria induced by Aβ1–42, Swe-APP, or APP-CTs in neuronal cells. In addition, mefenamic acid up-regulates expression of the antiapoptotic protein Bcl-XL. Moreover, our study demonstrates for the first time that mefenamic acid improves learning and memory impairment in an Aβ1–42-infused Alzheimers disease rat model. Taking these in vitro and in vivo results together, our study suggests that mefenamic acid could be used as a therapeutic agent in Alzheimers disease.

Biphasic Electrical Currents Stimulation Promotes both Proliferation and Differentiation of Fetal Neural Stem Cells

The use of non-chemical methods to differentiate stem cells has attracted researchers from multiple disciplines, including the engineering and the biomedical fields. No doubt, growth factor based methods are still the most dominant of achieving some level of proliferation and differentiation control - however, chemical based methods are still limited by the quality, source, and amount of the utilized reagents. Well-defined non-chemical methods to differentiate stem cells allow stem cell scientists to control stem cell biology by precisely administering the pre-defined parameters, whether they are structural cues, substrate stiffness, or in the form of current flow. We have developed a culture system that allows normal stem cell growth and the option of applying continuous and defined levels of electric current to alter the cell biology of growing cells. This biphasic current stimulator chip employing ITO electrodes generates both positive and negative currents in the same culture chamber without affecting surface chemistry. We found that biphasic electrical currents (BECs) significantly increased the proliferation of fetal neural stem cells (NSCs). Furthermore, BECs also promoted the differentiation of fetal NSCs into neuronal cells, as assessed using immunocytochemistry. Our results clearly show that BECs promote both the proliferation and neuronal differentiation of fetal NSCs. It may apply to the development of strategies that employ NSCs in the treatment of various neurodegenerative diseases, such as Alzheimers and Parkinsons diseases.

BT-11 is effective for enhancing cognitive functions in the elderly humans.

Roots of Polygala tenuifolia Willdenow have been used in humans for centuries because of its sedative effects. We previously reported that BT-11, extracted from the roots of the plant, improved memory impairments in rats, enhanced memory in normal humans, and inhibited acetylcholinesterase activities in vitro. The present study was a randomized, double-blind, placebo-controlled comparison study to investigate whether BT-11 could enhance memory in the elderly humans. We used the Consortium to Establish a Registry for Alzheimers Disease Assessment Packet (CERAD) and the Mini-Mental State Examination (MMSE). In the elderly, the total CERAD scores were much more significantly increased in the BT-11-treated group (n=28) than in the placebo-treated group (n=25). Especially, the mean scores of word list recognition, constructional recall and praxis, and modified Boston naming test were markedly improved in BT-11-treated group than in placebo-treated group. In conclusion, BT-11 could enhance some cognitive functions including memory in the elderly humans and therefore may be used as nutraceuticals that provide health benefits, including disease prevention and/or treatment.

Effects of nicotine on APP secretion and Aβ- or CT105-induced toxicity

Several lines of evidence indicated that overexpression or aberrant processing of amyloid precursor protein (APP) is causally related to Alzheimers disease (AD). Amyloid precursor protein is principally cleaved within the amyloid beta protein domain to release a large soluble ectodomain (APPs), known to have a wide range of trophic functions. The central hypothesis guiding this review is that nicotine may play an important role in APP secretion and protection against toxicity induced by APP metabolic fragments (beta-amyloid [Abeta], carboxyl terminal [CT]). Findings from our experiments have shown that nicotine enhances the release of APPs, which has neurotrophic and neuroprotective activities in concentration-dependent (>50 micromol/L) and time-dependent (>2 hours) manners. In addition, pretreatment of nicotine (>10 micromol/L for 24 hours) partially prevented Abeta or CT(105)-induced cytotoxicity in primary cultured neuron cells, and the effects of nicotine-induced protection were inhibited by the pretreatment with a nicotine alpha-bungarotoxin. Nicotine (>10 micromol/L for 24 hours) partially inhibited CT(105)-induced cytotoxicity when PC12 cells was transfected with CT(105). From these results, we proposed that nicotine or nicotinic receptor agonist treatment might improve the cognitive functions not only by supplementation of cholinergic neurotransmission, but also by protecting Abeta- or CT(105)-induced neurotoxicity probably through the increased release of APPs and the activation of nicotinic receptors.