Does any flagging take place in the brain at all? I have tried to keep up to date on Alzheimer's without knowing much about the human body. One thing I've thought about given the debate over whether Aβ is the culprit, one of many culprits, or just a visible sign of Alzheimer's got me thinking about it as a flagging mechanism. If a synapse is dead or in some way misbehaving it might be good to flag it as "corrupted", might that be what Aβ is doing at all? I mean system-wise it makes sense, but I know way too little about the human body or the brain.
There are lots of "damage-sensing" mechanisms at all scales within the body. These are how your skin knows to grow after an injury, how your immune system detects which cells are infected and need to be killed, and how your cells know which parts of themselves to digest via autophagy, among other things. At the single-protein level, there's ubiquination, which marks protein molecules for destruction, either because they are misfolded, damaged, or no longer needed. But this doesn't work when those misfolded proteins clump together into plaques. Then you need something like autophagy. But even that has limits, and a cell that lives for decades tends to reach those limits.
As for Aβ possibly being the body's way of flagging problem areas, that seems unlikely, because such a function probably would not involve drastically changing its 3-D structure (i.e. going from "correctly folded" state to "misfolded" state), and certainly would not involve forming plaques. These and many other observed features are better explained as features of the pathology and not just a kind of damage signal reporting on the existence of a problem.
