beta amyloid and nitric oxide : putative links umesh chaudhary
TRANSCRIPT
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Beta Amyloid and Nitric Oxide : Putative Links
Umesh Chaudhary
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Contents
• Introduction
• Current prospects in Alzheimer therapy
• B-Amyloid stimulation of iNOS :
TNF alpha and NF-kB dependent iNOS expression.
• Molecular basis of Alzheimer’s disease
• Nitric oxide and neurological functioning
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Nitric Oxide
A class of inter- and intra-cellular messenger molecules
– Small molecular weight, Highly diffusible, Gaseous, Highly reactive stable free radical
Second messenger role requires
•low concentrations of NO (<2M)
•occurs usually via guanylate cyclase.
Cytotoxic effects due to a combination of
•Elevated concentration (>10M)
•Formation of highly reactive peroxynitrite
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Free Radical Biology & Medicine, Vol. 25, Nos. 4/5, pp. 434–456, 1998
Direct Effects of Nitric Oxide Chemistry of Indirect Effects
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Properties of NOS Isozymes
Type I Type II Type III
Tissue in which first described
Cerebellum
Neuronal
Immunologically activated
Macrophages
Vascular Endothelial Cells
Tissue based terminology
nNOS iNOS eNOS
Expression Constitutive Inducible Constitutive
Intracellular free Calcium
Regulates No Effect Regulates
Size 161KDa 131KDa !33KDa
Location of Gene
Chrom-12 Chrom-17 Chrom-7
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Overall reaction Catalyzed and cofactors of NOS
Biochem. J. (2001) 357, 593-615
Nitric Oxide Biosynthesis
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Nitric Oxide and Nervous System
• Extensive distribution of NOS positive neuron
• Role in long term potentiation
• Learning and Memory
• Pain perception
• Neuromodulatory functions
• Host defense against pathogens
• Neurotoxicity
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Alzheimer’s Disease
Epidemiology• Most common Neurodegenerative disorder & dementia• Currently affecting nearly 5 million individuals in USA alone.
3
Symptoms Progressive cognitive decline affecting memory, learning,
emotions and behaviour
Pathology• Neurofibrillary Tangles, Senile Plaques and Synapse Loss• Mutation in one of the genes that codes for three transmembrane proteins-
APP, PS1 and PS2• APOe4 allele is higher
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Neuropathological Hallmarks
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Journal of Structural Biology
VARADARAJAN ET AL.
130, 184–208 (2000)
Central Role of Amyloid in Neurotoxicity
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Journal of Structural Biology
VARADARAJAN ET AL.
130, 184–208 (2000)
Amyloid Precursor Protein Processing
• APP is 770AA Transmembrane protein, Gene located on Chromosome 21
• Cleavage by and Secretase yields Amyloid
• Conversion of soluble forms to insoluble fibrils accounts for its toxicity
• Amyloid binding to RAGE leads to formation of plaque
• Amyloid can directly produce Hydrogen peroxide through metal ion reduction
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Presenilin 1 (PS1) on chromo 14 encodes 467 residue polypeptide & Presenilin 2 (PS2) on chromo 1 encodes for 448 residue polypeptide PS1 and PS2 are found in nuclear membrane ,ER and Golgi body Necessary for Neurogenesis and Neuronal survival 50 mutations of PS1 and 2 mutations of PS2 found in AD families
Mutations in Presenilin genes
All mutations enhances production of Fibrillar A 42 and Tau Hyper-phosphorylation leading to NFT’s
A plasma protein Involved in transport and metabolism of triglyceride and cholesterol e2, e3 and e4 allelic variantsApoE e4 allelic variant is high and linked with Alzheimer
Apolipoprotein E
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N- -CMicrotubule binding domain (MBD)
P sites
In AD Tau becomes hyper-phosphorylated
p p p p p p ppp
Neurofibrillary Tangles
Intra neuronal lesions in degenerating neurones
Composed of hyper-phosphorylated tau-protein organised in paired helical filaments
Tau is a soluble, microtubule-associated phospho-protein involved in neuronal stabilisation
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Law et al . / Brain Research Reviews 35 (2001) 73– 96
NO Neurotoxicity and Neuroprotection in AD
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-Amyloid Stimulation of Inducible Nitric-oxide Synthase in Astrocytes Is Interleukin-1- and Tumor Necrosis Factor- (TNF)-dependent, and Involves a TNF Receptor-associated Factor- and NFB-inducing Kinase-dependent Signaling Mechanism
(Keith T. Akama and Linda J. Van Eldik)From the ‡Department of Cell and Molecular Biology and §Northwestern Drug Discovery Program, NorthwesternUniversity Medical School, Chicago, Illinois 60611
The Journal of Biological Chemistry, Vol-275. No. 11, March 17, pp –7918-7924
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A- stimulated Cytokine production occurs before iNOS Production
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Protein synthesis inhibitor blocks A stimulated iNOS mRNA levels
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IL-1 Receptor antagonist Decreases the levels of Amyloid -stimulated i-NOS and Nitrite
Production
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Dominant Negative TRAF Proteins can Block NF-B Activation in Astrocytes
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Dominant Negative TRAF6 Inhibits iNOS Promoter Activation by A
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IL-1 Localizes to Microglia and iNOS Localizes to Astrocytes in A 42 Stimulated Glial Cultures
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SUMMARY• Amyloid activates Microglia to produce Pro-Inflammatory Cytokines such as IL-1 and TNF-
• These Cytokines in turn activate surrounding Astrocytes, which exacerbate the inflammation with the production of Neurotoxic Mediators such as iNOS.
• The resultant NO and Peroxynitrite ultimately damages local neurons and contributes to the Neurodegeneration observed in AD
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Evidence for NF-kB and Cytokine dependent iNOS induction
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Other Signaling Cascade Activated by Amyloid
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• Binding to Neurotrophin receptor leads to Apoptotic cell death
• Induction of Transcription of c-JUN mRNA and stimulates JUN Amino Terminal Kinase
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Neuroscience Letters 312 (2001) 177–179
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Science Vol 293, 21 September 2001 P- 2192-94
Amyloid can Directly activate Caspase 3 and induce Apoptosis in Neurons
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Potential Novel Therapeutic Approach
Focusing on -Amyloid plaques Enhance alpha-Secretase activity or inhibit beta or gamma-Secretase activity Correcting APP or presenilin mutationsAntioxidants such as Vitamin E and Extracts from roots of Ginko biloba Oestrogen modulate APP processing and reduce Amyloid- 42Vaccination with Amyloid Beta
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Focusing on Apolipoprotein E Replace ApoE e4 alleles with e2/3 alleles Cholesterol lowering drugs ( Lipitor )
Tau protein based therapies Prevent t-protein phosphorylation
Gene Therapy - Nerve Growth Factor, Propentophylline
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Conclusions
• Oxidative stress plays a vital role in Alzheimer Pathology
• Amyloid- can initiate a variety of signalling cascades leading to Neuronal cell death in AD
• Amyloid- can stimulate Pro inflammatory cytokines and ultimately contribute to Oxidative and Nitrosative Stress induced cell death and Apoptosis
• Further Detailed Studies needed to have a deeper Insight into Signal transduction pathways involved in Alzheimer Disease
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Twelve Alzheimer's patients injected with an experimental vaccine are suffering serious brain inflammation.
The vaccine's manufacturer halted the experiment last month when it discovered that the first four patients, all from France, were suffering the encephalitis-like reaction.
Since then, doctors have discovered eight more people with the apparent side effect, which can be hard to distinguish from worsening Alzheimer's.
TIMES - SUNDAY, FEBRUARY 24, 2002