Note in Science page
Created Mar 05 10, Updated Oct 01 10 12:47
Amyloid beta protein: an antimicrobial peptide? go to comments

Researchers from the Massachusetts General Hospital provide data supporting an in vivo function for Amyloid beta (Aβ) – the primary constituent of the plaques found in the brains of Alzheimer’s disease (AD) patients – as an antimicrobial peptide (AMP)!
These small amyloid beta proteins might be part of the innate immune system, which provides broad defense against a wide range of pathogens.

Amyloid protein loop ©UCLA Newsroom

Amyloid beta is toxic to neurons, and the protein’s accumulation / clumping as plaques in the brains of Alzheimer’s patients is thought to induce the neurodegeneration characterizing the disorder. The protein is generated when a larger parent molecule called the amyloid precursorprotein (APP) is cleaved by enzymes. Several different types of Aβ can be generated by the cleavage; the more common Aβ 40 and Aβ 42 forms are particularly prone to aggregate into toxic plaques. It was thought for years that the amyloid beta were just metabolic garbage. The team found that Aβ 40 and mostly 42 have an anti-microbial activity (and has similarities with the human cathelicidin antimicrobial peptide LL-37).

Our findings suggest Aβ is a hitherto unrecognized AMP that may normally function in the innate immune system. This finding stands in stark contrast to current models of Aβ-mediated pathology and has important implications for ongoing and future AD treatment strategies.

It looks like factors that trigger hyperactivity of the innate immune system – not only infection but also traumatic brain injury and stroke, which are already known to increase the risk for Alzheimer’s – could cause excessive deposition of A-beta…

The Alzheimer’s Disease-Associated Amyloid β-Protein Is an Antimicrobial Peptide [PLoS one article]

Science Daily article

p.s. Sept 2010:
Function found for the amyloid precursor protein
is an iron oxidase! (n.b. the precursor, not the beta amyloid)

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