Posted 5/27/2016 8:48 PM (GMT 0)
Another report that is new and addressing this same topic (Alz being caused by infections). Sorry it's long, but I'm assuming very few of us will have access to the Science Translational Medicine journal they appeared in:
"According to researchers, the expression of human amyloid beta protected against potentially lethal infections in mice, roundworms and cultured human brain cells. Source: Mass General.
Human amyloid-beta acts as natural antibiotic in the brains of animal models.
A new study from Massachusetts General Hospital (MGH) investigators provides additional evidence that
amyloid-beta protein – which is deposited in the form of beta-amyloid plaques in the brains of patients
with Alzheimer’s disease – is abnormal part of the innate immune system, the body’s first-line defense
against infection. Their study published in Science Translational Medicine finds that expression of human
amyloid-beta (A-beta) was protective against potentially lethal infections in mice, in roundworms and in
cultured human brain cells. The findings may lead to potential new therapeutic strategies and suggest
limitations to therapies designed to eliminate amyloid plaques from patient’s brains.
“Neuro degeneration in Alzheimer’s disease has been thought to be caused by the abnormal behavior of
A-beta molecules, which are known to gather into tough fibril-like structures called amyloid plaques
within patients’ brains,” says Robert Moir,MD, of the Genetics and Aging Research Unit in the Mass General
Institute for Neurodegenerative Disease (MGH-MIND), co-corresponding author of the paper. “This widely
held view has guided therapeutic strategies and drug development for more than 30 years, but our
findings suggest that this view is incomplete.”
A 2010 study co-led by Moir and Rudolph Tanzi, PhD, director of the MGH-MIND Genetics and Aging unit
and co-corresponding author of the current study, grew out of Moir’s observation that A-beta had many of
the qualities of an antimicrobial peptide (AMP), a small innate immune system protein that defends
against a wide range of pathogens. That study compared synthetic forms of A-beta with a known AMP
called LL-37 and found that A-beta inhibited the growth of several important pathogens, sometimes as
well or better than LL-37. A-beta from the brains of Alzheimer’s patients also suppressed the growth of
cultured Candida yeast in that study, and subsequently other groups have documented synthetic A-beta’s
action against influenza and herpes viruses.
The current study is the first to investigate the antimicrobial action of human A-beta in living models. The
investigators first found that transgenic mice that express human A-beta survived significantly longer
after the induction of Salmonella infection in their brains than did mice with no genetic alteration. Mice
lacking the amyloid precursor protein died even more rapidly. Transgenic A-beta expression also appeared
to protect C.elegans roundworms from either Candida or Salmonella infection. Similarly, human A-beta
expression protected cultured neuronal cells from Candida. In fact, human A-beta expressed by living cells
appears to be 1,000 times more potent against infection than does the synthetic A-beta used in previous
studies.
That superiority appears to relate to properties of A-beta that have been considered part of Alzheimer’s
disease pathology – the propensity of small molecules to combine into what are called oligomers and then
aggregate into beta-amyloid plaques. While AMPs fight infection through several mechanisms, a
fundamental process involves forming oligomers that bind to microbial surfaces and then clump together
into aggregates that both prevent the pathogens from attaching to host cells and allow the AMPs to kill
microbes by disrupting their cellular membranes. The synthetic A-beta preparations used in earlier studies
did not include oligomers; but in the current study, oligomeric human A-beta not only showed an even
stronger antimicrobial activity, its aggregation into the sorts of fibrils that form beta-amyloid plaques was
seen to entrap microbes in both mouse and roundworm models.
Tanzi explains, “AMPs are known to play a role in the pathologies of a broad range of major and minor
inflammatory disease; for example, LL-37, which has been our model for A-beta’s antimicrobial
activities, has been implicated in several late-life diseases, including rheumatoid arthritis, lupus and
atherosclerosis.The sort of dysregulation of AMP activity that can cause sustained inflammation
in those conditions could contribute to the neurodegenerative actions of A-betain Alzheimer’s disease.”
β-amyloidfibrils propagate from yeast surfaces and capture Candida albicans in culture medium. This
material relates to a paper that appeared in the May 25, 2016,issue of Science Translational
Medicine, published by AAAS. The paper, byD.K.V. Kumar at Massachusetts General Hospital in
Charlestown, Mass., and colleagues was titled, “Amyloid-ß peptide protects against microbial infection
in mouse and worm models of Alzheimer’s disease.” NeuroscienceNews.com image is credited to D.K.V.
Kumar et al. / Science Translational Medicine (2016).
Moir adds, “Our findings raise the intriguing possibility that Alzheimer’s pathology may arise when the
brain perceives itself to be under attack from invading pathogens, although further study will be required
to determine whether or not a bona fide infection is involved. It does appear likely that the inflammatory
pathways of the innate immune system could be potential treatment targets. If validated, our data also
warrant the need for caution with therapies aimed at totally removing beta-amyloid plaques.
Amyloid-based therapies aimed at dialing down but not wiping out beta-amyloid in the brain might be a
better strategy.”
Says Tanzi, “While our data all involve experimental models, the important next step is to search for
microbes in the brains of Alzheimer’s patients that may have triggered amyloid deposition as a
protective response, later leading to nerve cell death and dementia. If we can identify the culprits – be
they bacteria,viruses, or yeast – we may be able to therapeutically target them for primary
prevention of the disease.”
about this neurology research article:
Moir is an assistant professor of Neurology at Harvard Medical School (HMS), and Tanziis the Kennedy Professor of Neurology (Neuroscience) at HMS and vice-chair ofNeurology at MGH. The co-lead authors of the Science Translational Medicinepaper are Deepak K.V. Kumar, PhD, Se Hoon Choi, PhD, and Kevin Washicosky, ofthe MGH-MIND Genetics and Aging Unit. Additional co-authors are William A.Eimer, PhD, Stephanie Tucker, Jessica Ghofrani, and Aaron Lefkowitz, MGH-MIND;Gawain McColl, PhD, University of Melbourne, Australia, and Lee Goldstein, MD,Boston University.
Funding: This study was supported by National Institutes of Health grant 5R01 AI081990-02, the Cure Alzheimer’s Fund, and the Helmsley Charitable Trust.
Source: Terri Ogan – MassGeneral