Tangles observed in the brains of Alzheimer's patients induce the formation of similar inclusions when injected into the brains of healthy mice, reports a study online this week in Nature Cell Biology. This indicates that the tangles have contagious properties and may be similar to prions, which are associated with infectious brain diseases such as 'mad cow disease' and human Creutzfeldt-Jakob disease (CJD).
Markus Tolnay and colleagues extracted sections of brain from mice expressing a mutant form of human tau protein, a component of the Alzheimer's neurofibrillary tangles. These brain extracts were injected into specific regions in the brains of wild-type mice. They observed that the brain extracts induced normal human tau proteins in the wild-type mice to assemble into neurofibrillary tangles. In addition, these newly formed tangles were able to spread to nearby regions in the brain.
Previously, the formation of tau inclusions observed in the neurodegenerative disease of the tauopathy family had not been thought to be contagious. Prion proteins are thought to infect and propagate by abnormally folding into a structure that is able to convert their normal counterparts into a similar abnormal structure.
This study opens new avenues in tauopathies research that will aim to understand how an abnormal form of tau can spread and how similar tauopathies and prion disease are.