Cheol Hyoung Park

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.

α-Synuclein regulates neuronal survival via Bcl-2 family expression and PI3/Akt kinase pathway

α‐Synuclein (α‐SN) is a ubiquitous protein that is especially abundant in the brain and has been postulated to play a central role in the pathogenesis of Parkinsons disease, Alzheimers disease, and other neurodegenerative disorders. However, little is known about the neuronal functions of α‐SN and the molecular and cellular mechanisms underlying neuronal loss. Here, we show that α‐SN plays dual roles of neuroprotection and neurotoxicity depending on its concentration or level of expression. At nanomolar concentrations, α‐SN protected neurons against serum deprivation, oxidative stress, and excitotoxicity through the PI3/Akt signaling pathway, and its protective effect was increased by Bcl‐2 overexpression. Conversely, at both low micromolar and overexpressed levels in the cell, α‐SN resulted in cytotoxicity. This might be related to decreased Bcl‐xL expression and increased bax expression, which is subsequently followed by cytochrome c release and caspase activation and also by microglia‐mediated inflammatory responses via the NFκB and mitogen‐activated protein kinase pathways.

Chronic stress accelerates learning and memory impairments and increases amyloid deposition in APPV717I-CT100 transgenic mice, an Alzheimer’s disease model

Although chronic stress is known to be linked with memory and other neurological disorders, little is known about the relationship between chronic stress and the onset or development of Alzheimers disease (AD). In this study, we investigated the effects of long‐term stress on the onset and severity of cognitive deficits and pathological changes in APPV717I‐CT100 mice overexpressing human APP‐CT100 containing the London mutation (V717I) after exposure to immobilization stress. We found that chronic immobilization stress accelerated cognitive impairments, as accessed by the Passive avoidance and the Social Transfer of Food Preference (STFP) tests. Moreover, the numbers and densities of vascular and extracellular deposits containing amyloid beta peptide (Aβ) and carboxyl‐terminal fragments of amyloid precursor protein (APP‐CTFs), which are pathologic markers of AD, were significantly elevated in stressed animals, especially in the hippocampus. Moreover, stressed animals, also showed highly elevated levels of neurodegeneration and tau phosphorylation and increased intraneuronal Aβ and APP‐CTFs immunoreactivities in the hippocampus and in the entorhinal and piriform cortex. This study provides the first evidence that chronic stress accelerates the onset and severity of cognitive deficits and that these are highly correlated with pathological changes, which thus indicates that chronic stress may be an important contributor to the onset and development of AD.

The postnatal environment can counteract prenatal effects on cognitive ability, cell proliferation, and synaptic protein expression

Many environmental factors during the pre‐ or postnatal period can affect an individuals cognitive function and neural development throughout life. Little is known, however, about the combined effects of the pre‐ and postnatal environments on cognitive function of adult offspring and structural alterations in the adult brain. In this study, we confirmed that pre‐ or postnatal stress impaired learning and memory performance of rats. Conversely, pre‐ or postnatal enriched housing improved behavioral performance. These experience‐dependent behavioral alterations were consistent with changes in 5‐bromo‐2′‐deoxyuridine‐labeled cell number in the granule cell layer of the hippocampus and in the expression level of synaptic markers such as neuronal cell adhesion molecule and synaptophysin, and expression of a neurotrophic factor, brain‐derived neurotrophic factor. Postnatal stress appeared to have no influence on cell proliferation, however. We did find that postnatal environment could attenuate prenatal effects partly via a longitudinal cross‐housing study, in which pups born to mothers housed under enriched conditions were reared under stressful conditions and vice versa. These results suggest that postnatal environmental manipulations can counteract the cognitive alterations in early adulthood and the structural changes in the young adult brain induced by prenatal experience.

Novel cognitive improving and neuroprotective activities of Polygala tenuifolia Willdenow extract, BT-11.

We carried out this study to search a new active constituent that had cognitive enhancing activity and low side effects from natural source. We found that the extract of dried root of Polygala tenuifolia Willdenow (BT‐11, 10 mg/kg, i.p.) could significantly reverse scopolamine‐induced cognitive impairments in rat, using a passive avoidance and a water maze test. We also investigated the effects of BT‐11 on neurotoxicity induced by glutamate (Glu) and toxic metabolites of amyloid precursor protein (APP) such as amyloid β protein (Aβ) and C‐terminal fragment of APP (CT) in primary cultured neurons of rat. The pretreatment of BT‐11 (0.5, 3, and 5 μg/ml) significantly reduced cell death induced by Glu (1 mM), Aβ (10 μM) and CT105 (10 μM) in a dose‐dependent manner. In addition, BT‐11 inhibited acetylcholinesterase (AChE) activity in a dose‐dependent and non‐competitive manner (IC50 value; 263.7 μg/ml). Our novel findings suggest the possibility that this extract may have some protective effects against neuronal death and cognitive impairments in Alzheimers disease (AD), or other neurodegenerative diseases related to excitotoxicity and central cholinergic dysfunction.

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.

Carboxyl-terminal fragment of Alzheimer’s APP destabilizes calcium homeostasis and renders neuronal cells vulnerable to excitotoxicity

Numerous lines of evidence indicate that some of the neurotoxicity associated with Alzheimers disease (AD) is due to proteolytic fragments of the amyloid precursor protein (APP). Most research has focused on the amyloid β peptide (Aβ). However, the possible role of other cleaved products of APP is less clear. We have previously shown that a recombinant carboxy‐terminal 105 amino acid fragment (CT 105) of APP induced strong nonselective inward currents in Xenopus oocyte; it also revealed neurotoxicity in PC12 cells and primary cortical neurons, blocked later phase of long‐term potentiation in rat hippocampus in vivo, and induced memory deficits and neuropathological changes in mice. We report here that the pretreatment with CT 105 for 24 h at a 10 μM concentration increases intracellular calcium concentration by about twofold in SK‐N‐SH and PC 12 cells, but not in U251 cells, originated from human glioblastoma. In addition, the calcium increase and toxicity induced by CT 105 were reduced by cholesterol and MK 801 in SK‐N‐SH and PC 12 cells, whereas the toxicity of Aβ1–42 was attenuated by nifedipine and verapamil. CT 105 rendered SK‐N‐SH cells and rat primary cortical neurons more vulnerable to glutamate‐induced excitotoxicity. Also, conformational studies using circular dichroism experiments showed that CT 105 has ~15% of β‐sheet content in phosphate buffer and aqueous 2,2,2‐trifluoroethanol solutions. However, the content of β‐sheet conformation in dodecyl phosphocholine micelle or in the negatively charged vesicles, is increased to 22%‐23%. The results of this study showed that CT 105 disrupts calcium homeostasis and renders neuronal cells more vulnerable to glutamate‐induced excitotoxicity, and that some portion of CT 105 has partial β‐sheet conformation in various environments, which may be related to the self‐aggregation and toxicity. This may be significantly possibly involved in inducing the neurotoxicity characteristic of AD.–Kim, H.‐S., Park, C. H., Cha, S. H., Lee, J.‐H., Lee, S., Kim, Y., Rah, J.‐C., Jeong, S.‐J., Suh, Y.‐H. Carboxyl‐terminal fragment of Alzheimers APP destabilizes calcium homeostasis and renders neuronal cells vulnerable to excitotoxicity. FASEB J. 14, 1508–1517 (2000)

Flunarizine induces Nrf2-mediated transcriptional activation of heme oxygenase-1 in protection of auditory cells from cisplatin

We investigated the cytoprotective mechanisms of flunarizine in cisplatin-induced death of auditory cells. Concomitant with an increase in viability, treatment with flunarizine resulted in a marked dissociation of Nrf2/Keap1 and subsequent intranuclear translocation of Nrf2, which was mediated by PI3K-Akt signaling. Overexpression of Nrf2 protected cells from cisplatin along with transcriptional activation of ARE to generate heme oxygenase-1 (HO-1). Pretreatment with flunarizine predominantly increased the transcriptional activity of HO-1 among Nrf2-driven transcripts, including HO-1, NQO1, GCLC, GCLM, GSTμ-1, and GSTA4. Furthermore, both pharmacological inhibition and siRNA transfection of HO-1 completely abolished the flunarizine-mediated protection of HEI-OC1 cells and the primary rat (P2) organ of Corti explants from cisplatin. These results suggest that Nrf2-driven transcriptional activation of ARE through PI3K-Akt signaling augments the generation of HO-1, which may be a critically important determinant in cellular response toward cisplatin and the cytoprotective effect of flunarizine against cisplatin.

α-Synuclein induces apoptosis by altered expression in human peripheral lymphocyte in Parkinson’s disease

Though the etiology of Parkinson’s disease (PD) remains unclear, α‐synuclein (α‐SN) is regarded as a major causative agent of PD. Several lines of evidence indicate that immunological abnormalities are associated with PD for unknown reasons. The present study was performed to assess whether peripheral blood mononuclear cells (PBMCs) show altered α‐SN expression in PD patients and to identify its functions, which may be related to peripheral immune abnormalities in PD. α‐SN was found to be expressed more in 151 idiopathic PD (IPD) patients than in 101 healthy controls, who nevertheless showed as age‐dependent increases. By in vitro transfection, α‐SN expression was shown to be correlated with glucocorticoid sensitive apoptosis, possibly caused by the enhanced expression of glucocorticoid receptor (GR), caspase activations (caspase‐8, caspase‐9), CD95 up‐regulation, and reactive oxygen species (ROS) production. An understanding of the correlation between α‐SN levels and apoptosis in the presence of the coordinated involvement of multiple processes would provide an insight into the molecular basis of the disease. The present study provides a clue that the α‐SN may be one of the primary causes of the immune abnormalities observed in PD and offers new targets for pharmacotherapeutic intervention.

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.