About Beta Amyloid Types, Functions, Monomeric vs Oligomeric Aβ in Alzheimer's Disease - Part 3
In this video, I will be explaining what Beta Amyloids are, their types, functions, and the distinction between monomeric and oligomeric Aβ- in relation to Alzheimer's Disease. You can learn more from my official article: https://therevisionist.org/reviews/th... | You can find the Alzheimer's Disease video series here: • Alzheimer's Disease Symptoms & Pathol... | The End of Alzheimer's: The First Program to Prevent and Reverse Cognitive Decline: https://amzn.to/2QnGu08
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What is beta-amyloid?
Amyloid beta (Aβ or Abeta) denotes peptides of 36–43 amino acids that are crucially involved in Alzheimer's disease as the main component of the amyloid plaques found in the brains of Alzheimer patients.
Beta-amyloid is a small piece of a larger protein called “amyloid precursor protein”
(APP). Although scientists have not yet determined APP’s normal function, they
know a great deal about how it appears to work. In its complete form, APP extends
from the inside of brain cells to the outside by passing through the fatty membrane
around the cell. When APP is “activated” to do its normal job, it is cut by other
proteins into separate, smaller sections that stay inside and outside cells. There are
several different ways APP can be cut; under some circumstances, one of the pieces
produced is beta-amyloid.
The peptides derive from the amyloid precursor protein (APP), which is cleaved by beta secretase and gamma secretase to yield Aβ. Aβ molecules can aggregate to form flexible soluble oligomers which may exist in several forms. It is now believed that certain misfolded oligomers (known as "seeds") can induce other Aβ molecules to also take the misfolded oligomeric form, leading to a chain reaction akin to a prion infection. The oligomers are toxic to nerve cells.
Why is beta-amyloid a prime suspect in Alzheimer’s disease?
Beta-amyloid is chemically “stickier” than other fragments produced when APP is
cut. It accumulates in stages into microscopic amyloid plaques that are considered a
hallmark of a brain affected by Alzheimer’s. The pieces first form small clusters
called oligomers, then chains of clusters called fibrils, then “mats” of fibrils called
beta-sheets. The final stage is plaques, which contain clumps of beta-sheets and other
substances.
According to the amyloid hypothesis, these stages of beta-amyloid aggregation
disrupt cell-to-cell communication and activate immune cells. These immune cells
trigger inflammation. Ultimately, the brain cells are destroyed.
Beta-amyloid monomers are neuroprotective.
The 42-aa-long beta-amyloid protein--Abeta(1-42)--is thought to play a central role in the pathogenesis of Alzheimer's disease (AD). Data from AD brain, transgenic APP (amyloid precursor protein)-overexpressing mice, and neuronal cultures treated with synthetic Abeta peptides indicate that self-association of Abeta(1-42) monomers into soluble oligomers is required for neurotoxicity. The function of monomeric Abeta(1-42) is unknown. The evidence that Abeta(1-42) is present in the brain and CSF of normal individuals suggests that the peptide is physiologically active. Here we show that synthetic Abeta(1-42) monomers support the survival of developing neurons under conditions of trophic deprivation and protect mature neurons against excitotoxic death, a process that contributes to the overall neurodegeneration associated with AD. The neuroprotective action of Abeta(1-42) monomers was mediated by the activation of the PI-3-K (phosphatidylinositol-3-kinase) pathway, and involved the stimulation of IGF-1 (insulin-like growth factor-1) receptors and/or other receptors of the insulin superfamily. Interestingly, monomers of Abeta(1-42) carrying the Arctic mutation (E22G) associated with familiar AD were not neuroprotective. We suggest that pathological aggregation of Abeta(1-42) may also cause neurodegeneration by depriving neurons of the protective activity of Abeta(1-42) monomers. This "loss-of-function" hypothesis of neuronal death should be taken into consideration when designing therapies aimed at reducing Abeta burden.
https://www.ncbi.nlm.nih.gov/pubmed/1...
Extra attribution: https://commons.wikimedia.org/wiki/Fi...
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