Amyloid bPeptide Impairs IonMotive ATPase: Evidence of a Role in Loss of Ca2 Homeostasis and Cell De

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Amyloid b-Peptide Impairs Ion-Motive ATPase
Evidence of a Role in Loss of Ca2 Homeostasis
and Cell Death

• Literature Review
• Presentation by Joanna Leung

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Overview of Presentation

• The Facts on Alzheimers Disease
• Causes at the Cellular Level
• The Research Question
• Experiments in this Paper
• Summary of Findings and Pertinence

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Alzheimers Disease

• Affects 4.5 million Americans (primarily found in
  elderly population with onset after 60 years of
  age)
• Symptomology includes forgetfulness (dementia),
  inability to speak, write, recognize people and
  places, daily function
• Risk determinants risk for AD age, family
  history, ApoE4 gene
• Neurodegeneration attributed to b-amyloid plaque
  formation

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Amyloid Plaques
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b-Amyloid Peptide (Ab)

• 40-42 amino acids derived from Amyloid Precursor
  Protein (APP)
• Exposure to Ab 1-40 or Ab 25-35 to plasma
  membranes of neurons causes loss of Ca2
  homeostasis and cell death
• 2 possible mechanisms
• Influx of Ca2
• ROS byproducts

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The Foundations

• Ab accumulation impairs Na2/KATPase which
  causes an influx of Na2 ions and cell
  depolarization
• Also produces ROS byproducts
• Na./Ca2 exchanger and Ca2-ATPase responds with
  influx of Ca2 ions. Too high levels neurotoxic
• Cell apoptosis fragmentation, condensation,
  shrinkage, blebbing

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So what is this paper about?!

• Research Goal Explore how Ab impairs, by an
  oxidative mechanism, the function of plasma
  membrane proteins involved in regulation of ion
  homeostasis
• Looking at 3 ion-motive ATPases
• Use cultured 18-day embryonic rat hippocampal
  neurons and hippocampal slices from 4 postmortem
  adult humans

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Rat Hippocampal Neurons

• Prepared on Eagles MEM supplemented with 10
  heat inactivated fetal bovine serum, KCl, and
  pyruvate
• Composition 80-90 neurons, rest were astrocytes
• Different conditions ouabain, tetrodoxin, Ca2
  deficient medium, or Na deficient medium
• ATPase activity Na/Ca2 exchange activity
  assays conducted and free calcium levels
  determined

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Postmortem Human Hippocampal Tissue

• Homogenized, isolated through a sucrose gradient,
  ATPase activity assays, staining with Hoescht dye
  and fluorescence imaging to visualize nuclear
  condensation and DNA fragmentation

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Comparing neuronal survival under exposure to Ab
Mark RJ, Hensley K, Butterfield DA, and Mattson
MP. (1995). Amyloid b-peptide impairs
ion-motive ATPase Activities. Journal of
Neuroscience, 15(9), 6241.
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Comparing Na2/KATPase activity and examining
sequence specificity
Mark RJ, Hensley K, Butterfield DA, and Mattson
MP. (1995). Amyloid b-peptide impairs
ion-motive ATPase Activities. Journal of
Neuroscience, 15(9), 6241.
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Comparing different levels of ouabain and their
effect on neuronal survival
Mark RJ, Hensley K, Butterfield DA, and Mattson
MP. (1995). Amyloid b-peptide impairs
ion-motive ATPase Activities. Journal of
Neuroscience, 15(9), 6243.
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Determining whether Ca2 is mediated by Na
influx
Mark RJ, Hensley K, Butterfield DA, and Mattson
MP. (1995). Amyloid b-peptide impairs
ion-motive ATPase Activities. Journal of
Neuroscience, 15(9), 6243.
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Other questions answered

• Use of TTX in presence of Ab 25-35 increases
  neuronal survival compared to exposure to Ab
  25-35 only
• Ouabain visualizations of neurons undergoing
  apoptosis
• Metal ions such as iron amplify ROS
• Combat ROS species with antioxidants vitamin E
  and propylgallate

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Summary and Questions?

• So what exactly again is the process of neural
  degeneration starting with exposure to Ab 25-35?
• Hint plaque, Na2/KATPase, Ca2 response,
  apoptosis
• Relevance to class P-Type ATPases, active
  transport, proteins