Tau: A Little Protein With Big Effects
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Methods used to diagnose Alzheimer’s disease are changing. In the past, the only definitive way to diagnose Alzheimer’s disease was after death, by an autopsy, which is not exactly helpful for treatment. The autopsy would reveal both amyloid plaques and tau tangles in the brain; these are hallmarks that characterize Alzheimer’s disease. Thankfully, science has drastically improved over the years. We currently have spinal fluid tests that look for these two key biomarkers and imaging tests that show changes in the brain.
A recent example of other evolving diagnosis methods is COVID-19. Early in the pandemic, when there were no COVID-19 tests, the only way to know if someone might have the virus was to check for a fever. Nowadays, we look for biomarkers – such as with a rapid antigen test – which can detect antigens to the virus even in asymptomatic people.
We now understand that a person can be suffering from the progressive nature of Alzheimer’s even if they do not yet show signs of cognitive impairment. Without biomarker testing, most patients’ first symptoms are memory loss, including long and short-term. Alzheimer’s is usually associated with increased age because the biological underpinnings of the disease accumulate over time. Diagnosis can be made by using something called the ATN framework. This framework describes the two major proteins involved, amyloid plaques and tau tangles, and the associated neurodegeneration – changes in the brain structure.
Let’s discuss the AT part of ATN: the two protein accumulations called amyloid plaques and tau tangles. It is no coincidence that these are also the biomarkers sought by scientists and doctors when diagnosing Alzheimer’s. Amyloid plaques are bundles of protein that build up outside of cells in the brain. They disrupt how cells connect and communicate with each other. Tau tangles are proteins found inside the neurons. In a healthy neuron, tau proteins help stabilize the microtubule that transfers nutrients. In Alzheimer’s patients, the tau proteins become corrupted and tangled, blocking the neuron’s transport system. This leads to cell death. As more cells die and neural network connections break down, areas in the brain begin to shrink. In the late stages of Alzheimer’s disease, there is widespread loss of brain volume.
The N of ATN is neurodegeneration which is the deterioration of neurons causing specific structural changes to the brain. A structural MRI and a radioactive PET scan are two classic methods of determining neurodegeneration. These are effective as staging tools, discovering how far along the disease has progressed. They are effective but can be expensive and time-consuming.
The good news is that researchers are currently working on blood tests that will hopefully be able to detect tau biomarkers quickly and easily. A blood test should be easy, cheap, and relatively simple. With luck, these early biomarker findings will also help drive the effectiveness of clinical therapies, paving the way for better Alzheimer’s treatments in the years to come.
By Benton Lowey-Ball, BS Behavioral Neuroscience
Sources:
Kandel, E. R., Schwartz, J. H., Jessell, T. M., Siegelbaum, S., Hudspeth, A. J., & Mack, S. (Eds.). (2000). Principles of neural science (Vol. 4, pp. 1149-1159). New York: McGraw-hill.
Largent, E. A., Wexler, A., & Karlawish, J. (2021). The Future Is P-Tau—Anticipating Direct-to-Consumer Alzheimer Disease Blood Tests. JAMA neurology, 78(4), 379-380. https://doi.org/10.1001/jamaneurol.2020.4835
Ossenkoppele, R., Reimand, J., Smith, R., Leuzy, A., Strandberg, O., Palmqvist, S., … & Hansson, O. (2021). Tau PET correlates with different Alzheimer’s disease‐related features compared to CSF and plasma p‐tau biomarkers. EMBO molecular medicine, 13(8), e14398. https://doi.org/10.15252/emmm.202114398
Peterson, R. C. [UCI MIND] (2019, April 3). Diagnosis of Alzheimer’s disease in the era of biomarkers – Ronald C. Petersen, MD, PhD [Video]. Youtube. https://www.youtube.com/watch?v=KtS5xynes2M
What Happens to the Brain in Alzheimer’s Disease? (2017, May 16) National Institute on Aging. https://www.nia.nih.gov/health/what-happens-brain-alzheimers-disease
