Yoo-Hun Suh

Nanotechnology, nanotoxicology, and neuroscience

Nanotechnology, which deals with features as small as a 1 billionth of a meter, began to enter into mainstream physical sciences and engineering some 20 years ago. Recent applications of nanoscience include the use of nanoscale materials in electronics, catalysis, and biomedical research. Among these applications, strong interest has been shown to biological processes such as blood coagulation control and multimodal bioimaging, which has brought about a new and exciting research field called nanobiotechnology. Biotechnology, which itself also dates back approximately 30 years, involves the manipulation of macroscopic biological systems such as cells and mice in order to understand why and how molecular level mechanisms affect specific biological functions, e.g., the role of APP (amyloid precursor protein) in Alzheimers disease (AD). This review aims (1) to introduce key concepts and materials from nanotechnology to a non-physical sciences community; (2) to introduce several state-of-the-art examples of current nanotechnology that were either constructed for use in biological systems or that can, in time, be utilized for biomedical research; (3) to provide recent excerpts in nanotoxicology and multifunctional nanoparticle systems (MFNPSs); and (4) to propose areas in neuroscience that may benefit from research at the interface of neurobiologically important systems and nanostructured materials.

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.

Block of LTP in rat hippocampus in vivo by β-amyloid precursor protein fragments

THE effects of β-amyloid precursor protein (β-APP) fragments on plasticity of glutamtatergic synaptic transmission were examined in the hippocampus of urethane anaesthetized rats. I.c.v. injection of β-amyloid (Aβ) 1–40 and 1–42 and the C-terminal fragment CT105 greatly shortened the duration of high frequency stimulation-induced long-term potentiation (LTP) of field excitatory postsynaptic potentials in the CA1 area. Whereas in vehicle injected animals LTP was stable over a 5 h recording period, doses of these peptides (Aβ1–40, 0.4 and 3.5 nmol; Aβ1–42, 0.01 nmol; CT105, 0.05 nmol) which did not affect baseline synaptic transmission abolished LTP within 3–5 h. The reduced duration of this form of synaptic plasticity may contribute to the cognitive deficits in Alzheimers disease.

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.

Use-Dependent Effects of Amyloidogenic Fragments of β-Amyloid Precursor Protein on Synaptic Plasticity in Rat Hippocampus In Vivo

The Alzheimers disease-related β-amyloid precursor protein (β-APP) is metabolized to a number of potentially amyloidogenic peptides that are believed to be pathogenic. Application of relatively low concentrations of the soluble forms of these peptides has previously been shown to block high-frequency stimulation-induced long-term potentiation (LTP) of glutamatergic transmission in the hippocampus. The present experiments examined how these peptides affect low-frequency stimulation-induced long-term depression (LTD) and the reversal of LTP (depotentiation). We discovered that β-amyloid peptide (Aβ1–42) and the Aβ-containing C -terminus of β-APP (CT) facilitate the induction of LTD in the CA1 area of the intact rat hippocampus. The LTD was frequency- and NMDA receptor-dependent. Thus, although low-frequency stimulation alone was ineffective, after intracerebroventricular injection of Aβ1–42, it induced an LTD that was blocked byd-(−)-2-amino-5-phosphonopentanoic acid. Furthermore, an NMDA receptor-dependent depotentiation was induced in a time-dependent manner, being evoked by injection of CT 10 min, but not 1 hr, after LTP induction. These use- and time-dependent effects of the amyloidogenic peptides on synaptic plasticity promote long-lasting reductions in synaptic strength and oppose activity-dependent strengthening of transmission in the hippocampus. This will result in a profound disruption of information processing dependent on hippocampal synaptic plasticity.

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.

Ionic effects of the Alzheimer's disease β-amyloid precursor protein and its metabolic fragments

Alzheimers disease is a progressive dementia characterized in part by deposition of proteinaceous plaques in various areas of the brain. The main plaque protein component is beta-amyloid, a metabolic product of the beta-amyloid precursor protein. Substantial evidence has implicated beta-amyloid (and other amyloidogenic fragments of the precursor protein) with the neurodegeneration observed in Alzheimers disease. Recently, beta-amyloid precursor protein and its amyloidogenic metabolic fragments have been shown to alter cellular ionic activity, either through interaction with existing channels or by de novo channel formation. Such alteration in ionic homeostasis has also been linked with cellular toxicity and might provide a molecular mechanism underlying the neurodegeneration seen in Alzheimers disease.

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.

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.