Amyloid-beta (Aβ or A-beta) is a peptide of 39–43 amino acids that seems to form the main composition of amyloid plaques seen in the brain of individuals with Alzheimer’s disease. This plaque is one of several neuritic plaques (structural abnormalities), found in the brain of autopsied Alzheimer’s patients.
At the center of these plaques is the A-beta protein, a protein that naturally circulates in the blood and cerebral spinal fluid. In Alzheimer’s disease, the beta amyloid protein deposits heavily in the cerebral cortex causing the classic symptoms of cognitive impairment – mainly memory and reasoning loss.
Amyloid-beta Protein – Waste Product of Alzheimer’s Disease or Cause?
For years scientists were unsure whether the beta-amyloid protein was a byproduct of the neurological progression of Alzheimer’s disease or the cause of it. In 2008, scientists isolated a toxic key from the protein that appeared to show that fragments from the protein may play a role in initiating the disease.
The study, “ Amyloid-ß protein dimers isolated directly from Alzheimer's brains impair synaptic plasticity and memory,” conducted by Shankar Ganesh M. & Selkoe Dennis J. et al, appeared in Nature Medicine on June 22, 2008. The National Institutes of Health director, Richard J. Hodes, M.D. said, "While more research is needed to replicate and extend these findings, this study has put yet one more piece into place in the puzzle that is Alzheimer's."
The latest study conducted by researchers at Massachusetts General Hospital, has now perhaps added one more piece to the puzzle of Alzheimer’s disease.
The Innate Immune System and the Amyloid-beta Protein
Massachusetts General Hospital's (MGH) team of researchers announced today that their study, “The Alzheimer's Disease-Associated Amyloid ß-Protein Is an Antimicrobial Peptide,” seems to show that the amyloid-beta protein is in fact an antimicrobial peptide that is part of the innate immune system. (PLoS ONE 5(3): e9505. doi:10.1371/journal.pone.000950 Soscia SJ, Kirby JE, Washicosky KJ, Tucker SM, Ingelsson M, et al. Mar. 3, 2010.)
Antimicrobial peptides are important parts of the body’s defense or immune system. Besides the ability to kill disease-causing microbes (germs) by acting as a naturally occurring antibiotic, they assist in inflammation functions, wound repair and help to regulate the immune system.
The immune system comprises two parts, the innate or non-specific immune system, which is the body’s first line of defense against invading organisms and the adaptive immune system, considered the second line of defense. Although each system’s function is different, they essentially play off one another and work hand-in-hand to protect the body.
MGH researchers noticed several chemical and biological likenesses between antimicrobial peptides and A-beta, especially when the protein was tested against fifteen significant pathogens. A-beta inhibited growth in eight of them. In the brain tissue of Alzheimer patient’s, significant antimicrobial activity actually correlated with the amount of A-beta present.
Future Research into A-beta Protein’s Role in Alzheimer’s Disease
The research study team concluded with the belief that a chronic infection of the central nervous system, may initiate the innate immune system into responding by producing higher levels of the A-beta protein, which in turn, could cause highly dangerous levels of inflammation in the brain.
Robert Moir, PhD, of the MGH-MIND Genetics and Aging Research Unit, said, “"Now we need to figure out what is triggering the innate immune system, particularly as we age, and what genes control A-beta's role in the innate response."
It is hoped that if studies can unlock what triggers the innate immune system response and specifically the genes that control the A-beta protein role within it, treatment options could be developed that curb or even control the response. It could well be one more step forward in the prevention of progression of Alzheimer’s disease.
Sources:
Massachusetts General Hospital website. News Releases. “Alzheimer's-associated protein may be part of the innate immune system. Understanding amyloid-beta's normal function could lead to preventive, therapeutic strategies.” Mar. 2, 2010. Accessed Mar. 3, 2010.
Alzheimer’s Organization website. “What is Alzheimer’s” Accessed Mar. 3, 2010.
Alzheimer’s Disease Research website. “Plaques and Tangles.” Accessed Mar. 3, 2010.
Elizabeth Batt - Elizabeth Batt is a former large animal nurse, certified NREMT, lover of equines and conservationist.
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