Alzheimer’s amyloid-beta and tau proteins act as prions, study shows

Alzheimer’s disease may be a result of prions. Prions are self-propagating, misfolded proteins that are lethal and can spread through tissues like any other infection in the body. A recent study published in Science says that both amyloid beta (Aß) and tau proteins can act like prions in Alzheimer’s disease. The study has a striking conclusion that the prion conformers of these proteins are strongly associated with the age of the patients—its levels are higher in patients that died at younger age than those who died in older age.

Using novel lab tests, researchers from the University of California, San Francisco (UCSF) were able to detect and measure specific, self-propagating prion forms of Aß and tau proteins in brain tissue of 75 Alzheimer’s patients. In the study, the scientists combined two recently developed laboratory tests to rapidly measure prions in human tissue samples: a new Aß detection system and a tau prion assay.

Unlike earlier animal models that could take months to reveal the slow spread of Aß  and/or tau prions, these cell-based assays measure infectious prion levels in just three days, enabling the researchers to effectively quantify for the first time the levels of both tau and Aß prions in processed extracts from post-mortem brain samples. The brain tissues were collected from over 100 patients that died of Alzheimer’s disease and other neurodegenerative diseases from United States, Europe and Australia.

Out of the brain samples that were subjected to post mortem, 75 Alzheimer’s disease brains showed elevated levels of both Aß and tau proteins; 11 samples from patients with cerebral amyloid angiopathy (CAA), only amyloid beta prions could be observed; and in 10 samples from patients with fromtotemporal lobar degeneration (FTLD) only tau prions were detected. The CAA and the FTLD are both neuro-degenerative conditions and cause dementia like symptoms.

The most remarkable finding of the study is that the prion forms of both amyloid beta and tau proteins are present in formidably higher levels among the patients who died in early ages. Particularly, when they compared the overall tau build up, the researchers found that the relative abundance of prion tau in aged Alzheimer’s brains decrease exponentially. Relative to the overall tau levels, the tau prion levels in a patient that died at the age of 40 were averagely 32 times higher than a patient who died at 90.

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Source: UCSF News | May 1, 2019

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