APOE: the pathway in the body

This page shows the biochemical pathway behind the laboratory value APOE genotype (genetics): which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Apolipoprotein E (ApoE) is a protein on the surface of the blood's fat-transport particles. It serves as a recognition tag through which the liver binds and internalises fat-rich remnant particles.

The pathway step by step

1. Dietary fats → Chylomicrons · ApoB-48 The intestinal cell packs the fats into large transport particles made of fat and protein. At first they carry ApoB-48; in the blood they pick up ApoE and ApoC-II from HDL particles. Source 5, 1
2. Chylomicrons → Chylomicron remnants Lipoprotein lipase · ApoC-II Lipoprotein lipase on the vessel wall splits off triglycerides; muscle and fat tissue absorb the fatty acids. Smaller remnants are left behind, with ApoE on their surface. Source 3, 4
3. Remnants with ApoE → Inside the liver cell LDL receptor, LRP1 The liver cell draws the bound particle inside. In the lysosome, proteins and fats are broken down; the cholesterol is then available to the cell again. Source 4
4. Inside the liver cell → VLDL The liver releases its own transport particles: VLDL. They carry ApoB-100 and also ApoE. Source 5
5. VLDL → IDL Lipoprotein lipase · ApoC-II Lipoprotein lipase also splits triglycerides off VLDL, producing IDL particles. Some of these bind to liver receptors via ApoE and are absorbed by the liver. Source 3, 1
6. IDL → LDL Hepatic lipase The rest of the IDL is converted to LDL. LDL carries hardly any ApoE; it binds to the LDL receptor via ApoB-100. Source 5, 2

Cofactors in this pathway

• ApoC-II — Activator of lipoprotein lipase, which splits triglycerides off chylomicrons and VLDL Source 3
• Triglycerides — Cargo of chylomicrons and VLDL; lipoprotein lipase splits them off at the vessel wall Source 3, 5In the ORY catalogue as a laboratory value: Triglyzeride
• Cholesterol — Cargo of the remnant particles that reaches the liver receptor via ApoE Source 1, 4In the ORY catalogue as a laboratory value: Cholesterin / Fettstoffwechsel
• Heparan sulfate proteoglycans — Binding sites on the liver cell where ApoE-rich remnant particles are first held Source 7
• Calcium — Holds the binding sites of the LDL receptor in shape; in the endosome the receptor releases it and lets go Source 8
• MTP (transfer protein) — Loads ApoB-48 with fat inside the gut cell; without this step no chylomicrons are formed Source 6
• GPIHBP1 — Carries lipoprotein lipase to the inner face of the vessel wall Source 3

Sources

1. Mahley RW. Apolipoprotein E: cholesterol transport protein with expanding role in cell biology. Science 1988 · PubMed 3283935
2. Weisgraber KH. Apolipoprotein E: structure-function relationships. Adv Protein Chem 1994 · PubMed 8154371
3. Kersten S. Physiological regulation of lipoprotein lipase. Biochim Biophys Acta 2014 · PubMed 24721265
4. Cooper AD. Hepatic clearance of plasma chylomicron remnants. Semin Liver Dis 1992 · PubMed 1334575
5. Mahley RW, Innerarity TL, Rall SC Jr et al. Plasma lipoproteins: apolipoprotein structure and function. J Lipid Res 1984 · PubMed 6099394
6. Hussain MM. Intestinal lipid absorption and lipoprotein formation. Curr Opin Lipidol 2014 · PubMed 24751933
7. Mahley RW, Ji ZS. Remnant lipoprotein metabolism: key pathways involving cell-surface heparan sulfate proteoglycans and apolipoprotein E. J Lipid Res 1999 · PubMed 9869645
8. Andersen CB, Moestrup SK. How calcium makes endocytic receptors attractive. Trends Biochem Sci 2014 · PubMed 24393667

Related pathways

• Cholesterol and lipoproteins — chylomicrons
• Triglycerides — chylomicrons
• Trans fatty acids — chylomicrons
• Vitamin E — chylomicrons

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert approval pending. Describes solely the role of ApoE in fat transport.
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