Neurodegeneration as Proteostasis Failure | AI Learning Guide

The key point here is that the pathway has not changed. Chaperones, the proteasome, and autophagy are still doing what they always do. What has changed is that the load never stops, so the reserve keeps falling. And once aggregates begin to sequester chaperones and clog the clearance machinery, the response starts feeding its own activating signal. That is the self-amplifying loop from the last chapter, now running inside a single neuron. Notice the consequence for how we interpret surviving cells: the neurons that last longest are usually the ones with quiet stress signaling, because they never entered the loop.

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The reserve-versus-load prediction

A postmitotic neuron cannot dilute aggregates by division and cannot shed a damaged compartment. A continuous misfolding load therefore draws the chaperone, proteasome, and autophagy reserve down with no recovery interval, and the reserve-versus-load model predicts that reserve falls below load even if the load is constant.

How the loop closes

Aggregated protein sequesters chaperones and impairs proteasome and autophagy function. Reduced clearance raises the aggregate load further, so the response generates its own activating signal. This is the self-amplifying loop from Chapter 8, not a new mechanism.

Why surviving neurons look suppressed

Neurons that persist longest in affected regions often show reduced stress and apoptotic signaling. They are the cells that escaped the loop, not cells that won it. Enhanced protection is not what distinguishes them.