How APOE4 Neurons Burn Through Their Own Membranes

A self-reinforcing loop in APOE4 brains—calcium, cPLA2, DHA loss, AA/AdA backfill—silently arms neuronal membranes with ferroptotic substrates over decades, with no internal off switch.

Diagram 3 — The Engine: The Loop That Never Stops —

The first article in this series showed a fork: the same enzyme, cPLA2, cleaving the same membrane — but producing opposite outcomes depending on whether arachidonic acid or DHA sits at sn-2. The second article showed a supply chain — and a hallway: six places DHA gets lost between the capsule and the membrane, including three post-entry fates that consume, misroute, or trap DHA even after it crosses the blood-brain barrier. This article connects them. The diagram above is the engine that drives the APOE4 brain from one state to the other — and it explains why the transition takes decades, runs silently, and has no internal off switch.

The engine doesn’t just strip DHA and leave a weaker membrane. It replaces DHA with specific fatty acids — arachidonic acid and its elongation product adrenic acid — and loads them into a specific phospholipid class through enzymatic machinery that is structurally biased to do exactly that. The membrane that results is not weakened. It is armed. Armed with the precise substrates of a death program that Diagram 4 (coming up soon) calls “The Kill Switch”.