“Alzheimer's-in-a-Dish” Confirms Amyloid Hypothesis
An innovative laboratory culture system has succeeded, for the first time, in reproducing the full course of events underlying the development of Alzheimer’s disease. Using the system they developed, investigators from the Genetics and Aging Research Unit at Massachusetts General Hospital (MGH) now provide the first clear evidence supporting the hypothesis that deposition of beta-amyloid plaques in the brain is the first step in a cascade leading to the devastating neurodegenerative disease. They also identify the essential role in that process of an enzyme, inhibition of which could be a therapeutic target. The report received advance online publication on October 13th 2014 in Nature.
A release from the hospital quotes co-senior author Rudolph Tanzi, PhD, director of the MGH Genetics and Aging Research Unit, as saying, “Originally put forth in the mid-1980s, the amyloid hypothesis maintained that beta-amyloid deposits in the brain set off all subsequent events – the neurofibrillary tangles that choke the insides of neurons, neuronal cell death, and inflammation leading to a vicious cycle of massive cell death. One of the biggest questions since then has been whether beta-amyloid actually triggers the formation of the tangles that kill neurons. In this new system that we call ‘Alzheimer’s-in-a-dish,’ we’ve been able to show for the first time that amyloid deposition is sufficient to lead to tangles and subsequent cell death.”
The release notes that while the mouse models of Alzheimer’s disease that express the gene variants causing the inherited early-onset form of the disease do develop amyloid plaques in their brains and memory deficits, the neurofibrillary tangles that cause most of the damage do not appear. Other models succeed in producing tangles but not plaques. Cultured neurons from human patients with Alzheimer’s exhibit elevated levels of the toxic form of amyloid found in plaques and the abnormal version of the tau protein that makes up tangles, but not actual plaques and tangles.
Genetics and Aging Research Unit investigator Doo Yeon Kim, PhD, co-senior author of the Nature paper, realized that the liquid two-dimensional systems usually used to grow cultured cells poorly represent the gelatinous three-dimensional environment within the brain. Instead the MGH team used a gel-based, three-dimensional culture system to grow human neural stem cells that carried variants in two genes – the amyloid precursor protein and presenilin 1 – known to underlie early-onset familial Alzheimer’s Disease (FAD). Both of those genes were co-discovered in Tanzi’s laboratory.