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Wall Street Journal, November 9, 2012, 10:36 p.m. ET

An Outcast Among Peers Gains Traction on Alzheimer's Disease


..A protein called tau—which forms twisted fibers known as tangles inside the brain cells of Alzheimer's patients— may be largely responsible for driving the disease. ...

Although interest in tau is building, opinions about the cause of Alzheimer's remain deeply divided. Some scientists believe an interaction between beta amyloid and tau plays a central role. Others think there are many possible triggers, including some beyond beta amyloid or tau. ...

The disease was first identified in 1906 by German physician Alois Alzheimer, who studied the brain of a deceased woman who had suffered from dementia and documented the [amyloid] plaques and [tau] tangles that riddled the tissue. ...

Like all of the body's proteins, tau has a normal, helpful function—working inside neurons to help stabilize the fibers that connect nerve cells. But when it misfires, tau can clump together to form harmful tangles that kill brain cells. ...

In the early 1990s, Dr. Wischik and his colleagues compared the postmortem brains of Alzheimer's sufferers against those of people who had died without dementia, to see how their levels of amyloid and tau differed. They found that both healthy brains and Alzheimer's brains could be filled with amyloid plaque, but only Alzheimer's brains contained aggregated tau. What's more, as the levels of aggregated tau in a brain increased, so did the severity of dementia....
[end quote]

The rest of the article is about the scientific controversy and about drug development.

Both amyloid and tau are proteins that are normally soluble in the cell's liquid internal environment. However, they change their configuration to become insoluble. Then they clump.

Alzheimer's disease resembles prion diseases in that the symptoms are caused by a buildup of misfolded, insoluble proteins.

The root cause of many diseases that are caused by misfolded proteins may be a defective proteasome, the complex mechanism for removing defective (including misfolded) proteins.

The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that carry out such reactions are called proteases. Proteasomes are part of a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. The degradation process yields peptides of about seven to eight amino acids long, which can then be further degraded into amino acids and used in synthesizing new proteins.[end quote]

The proteasome (which essentially takes out and recycles trash) is so complex that there are many ways that it could become less effective.

Like the nature/ nurture debate, the answer to the tau/ amyloid debate may be "both."

Research on drugs that affect the proteasome involve inhibiting it, for example in cancer cells.

Nature Reviews Drug Discovery 5, 596-613 (July 2006) | doi:10.1038/nrd2056

Drug discovery in the ubiquitin–proteasome system

Grzegorz Nalepa1, Mark Rolfe & J. Wade Harper

...The malfunction of the ubiquitin–proteasome pathway leading to improper handling of misfolded proteins likely contributes to the pathogenesis of Parkinson's disease. ...

There is ongoing debate as to whether this collapse of the UPS in patients' brains is a consequence of genetic insults, environmental influences such as oxidative stress or toxin exposure, or both. Since Parkinson's disease most probably represents a constellation of diverse neurodegenerative syndromes that result in clinically similar outcomes rather than a single pathological entity, both hypotheses seem to be true, at least in some cases. ...
[end quote]

J Cell Mol Med. 2008 Apr;12(2):363-73. Epub 2008 Feb 8.
The ubiquitin-proteasome system in Alzheimer's disease.
Oddo S.

Department of Neurobiology and Behavior University of California, Irvine, CA 92697-4545, USA.

Accumulation of proteins is a recurring event in many neurodegenerative diseases, including Alzheimer's disease (AD). Evidence has suggested that protein accumulation may result from a dysfunction in the ubiquitin proteasome system (UPS). Indeed, there is clear genetic and biochemical evidence of an involvement of the ubiquitin proteasome system in AD. This review summarizes the data supporting an involvement of the UPS in the pathogenesis of AD, focusing on the data showing the relationship between Abeta and tau, the two hallmark lesions of AD, and the UPS.
[end quote]

Also see
Exp Biol Med (Maywood). 2011 Mar 1;236(3):268-76. Epub 2011 Mar 7.
The role of the ubiquitin proteasome system in Alzheimer's disease.
Riederer BM, Leuba G, Vernay A, Riederer IM.
[end quote]

... early-onset Alzheimer’s [caused by a genetic mutation] involves an overproduction of amyloid, while late onset involves a problem clearing amyloid from the brain. ...
[end quote]

The N.Y. Times article did not mention tau.

It is possible that the obvious plaques and tangles in brains affected by Alzheimer's disease have attracted researchers' attention. Drug development efforts have been targeted to reducing the observable amount of amyloid, even though there is no evidence that this helps. The researcher who is focused on tau may have a more destructive target than amyloid, but he is also focused on the visible symptom.

I was not able to find any research on drug development that specifically targeted the proteasome in Alzheimer's disease (e.g. stimulating it to work more efficiently in older patients).

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