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Symposium
on "Neurochemical aspects and approaches for neurological diseases"
Neuro 2004.
September 21-2, 2004, Osaka, Japan Organizer Purpose Summary Several different compounds and antibodies against prion protein have been reported to inhibit production of abnormal prion protein in vitro, however the mechanism of effect for most of those substances is unclear and there is still no effective drug in vivo. Because prion diseases occur as a result of conformational changes in the cellular prion protein, PrPC, it should be feasible to design drugs that interrupt the critical conversion process. We previously observed a partially denatured form of the prion protein using the high-pressure NMR and the CPMG relaxation dispersion methods, and hypothesized that slow exchange dynamics on the micro- to milliseconds time scale might be critical for the subsequent pathogenic conversion. Thus we incorporated the dynamical information in residue level into in silico screening and established a novel strategy termed "Dynamics Based Drug Design (DBDD)". According to this DBDD strategy, we could find several low-molecular weight anti-prion substances, by a combination of in silico and in vitro drug screening. These substances may stabilize the normal conformation of PrPC, with the result of reducing the population of the intermediate conformer, PrP*, thereby inhibiting its conversion to the pathogenic form.
Mechanisms that control
structure, function, and plasticity of the synapse are of utmost importance
for the adaptive functions of the neuronal circuitry that underlie the
brain's capacity for information processing. During the past years it
has been recognized that
Disfunction of endoplasmic reticulum (ER) provokes accumulation of unfolded proteins in the ER. Normal cells respond to ER stress by increasing transcription of genes encoding ER resident-chaperones to facilitate protein folding. This induction system is termed the unfolded protein response (UPR). Familial Alzheimer's disease-linked presenilin-1 (PS1) mutation downregulates the UPR signaling and leads to vulnerability to ER stress. The mechanisms by which mutant PS1 affects the ER stress response are attributed to the inhibited activation of ER stress sensors such as IRE1, PERK and ATF6. In this symposium, I will talk about the neuronal death induced by PS1 mutants during ER stress. Moreover, I will show the protective functions of a novel ER stress sensor, OASIS, in cell death induced by ER stress. OASIS is a transmembrane protein containing bZIP domain. The functional analyses of OASIS showed that 1) it was cleaved within the ER membrane in response to the ER stress. 2) overexpression of OASIS induced the transcription of GRP78/BiP mRNA through the activation of ER stress responsive element (ERSE), 3) its stable cell lines were resistant to ER stress compared with the control cells. These results indicate that the ER-resident transcription factor OASIS may be a candidate for leading cells protect against ER stress.
We have proposed that a nucleation-dependent polymerization model could explain the general mechanism of amyloid fibril formation in vitro. We will present our research to elucidate the molecular pathogenesis of Alzheimer's b-amyloidosis. First, we analyzed the kinetics of the extension and dissociation of b-amyloid fibrils in vitro, using a surface plasmon resonance biosensor. Both the extension and the slow-linear phase of the dissociation were consistent with a first-order kinetic model, with the critical monomer concentration to be 20 nM. Second, we investigated the effect of GM1 ganglioside, a major constituent of CNS caveola/DIG, on the formation of b-amyloid fibrils at pH 7.5 in vitro, using fluorometry with thioflavin T (ThT) and EM. The liposomes containing GM1 ganglioside and cholesterol induced the formation of b-amyloid fibrils from monomeric Ab peptides, without a lag phase and according to a first-order kinetic model. This may indicate that in vivo, GM1 ganglioside-bound Ab may act as an endogenous seed for the formation of b-amyloid fibrils. Finally, using ThT fluorometry and EM, we demonstrated that several antioxidants including nordihydroguaiaretic acid and other polyphenols inhibit the formation of b-amyloid fibrils as well as destabilize them in vitro. They could be key molecules for the development of therapeutics for human amyloidosis.
A major unanswered question in the biology of Alzheimer's disease (AD) concerns what mechanisms underlie the characteristically observed brain hypometabolism. Although mitochondrial dysfunction is a potential common denominator of in vivo and in vitro findings related to disturbed neuronal energy homeostasis in an amyloid-beta (Abeta)-rich environment, a direct link between mitochondrial function and Abeta has not been forthcoming. We hypothesized that Aß-binding alcohol dehydrogenase (ABAD), an intracellular target of Abeta present in mitochondria, might provide a direct connection between the amyloid peptide and mitochondrial properties. Our recent studies have demonstrated that Abeta is imported into mitochondria and can form a complex with ABAD in the mitochondrial matrix compartment. Formation of ABAD-Abeta complex decreases the enzymatic activity of ABAD, displaces cyclophilin D (cypD) from ABAD, and increases release of reactive oxygen species from mitochondria. We believe that diminished activity of ABAD has potentially deleterious consequences for neuronal function, especially in the context of the obligate role of ABAD in isoleucine catabolism. ABAD deficiency could lead to accumulation of the toxic agent tiglic acid. ABAD sequestration of cypD in mitochondrial matrix has a potentially protective effect by preventing its translocation to the inner mitochondrial membrane where it can promote opening of the membrane permeability transition pore. Finally, it is possible that ABAD-Abeta complex is a direct perturbant of mitochondrial function; diminished activity of mitochondrial respiratory complex IV in the presence of high levels of ABAD-Abeta complex leads to elaboration of reactive oxygen species from complex III. Based on these observations/predictions, it is not surprising that transgenic mice with targeted neuronal expression of ABAD and mutant amyloid precursor protein (these animals have high levels of neuronal ABAD-Abeta complex) display accelerated decline in behavioral and electrophysiologic function, as well as exaggerated neuropathologic findings. These observations suggest that ABAD might be a pathophysiologically significant mitochondrial target of Abeta.
Kazuo Kuwata Division
of Prion Research, Center for Emerging Infectious Diseases, Gifu University,
$500 |
