LCAT =  Lecithin–cholesterol acyltransferase

Key functions:

1. ApoA-I = LCAT activation (cholesterol esterification)
2. ApoB-48 = Chylomicron assembly and secretion by the intestine
3. ApoB-100 = LDL particle uptake by extrahepatic cells (binds LDL receptor)
4. ApoC-II = Lipoprotein lipase activation as a cofactor
5. ApoE-3 & -4 = VLDL and chylomicron remnant uptake by liver cells

Abetalipoproteinemia

Chylomicron and VLDL particles are synthesized within the ER as lipids accumulate around a single apoB molecule.

ApoB-100 is found in VLDL, and apoB-48 is present in chylomicrons. During synthesis of apoB-containing lipoproteins, microsomal triglyceride transfer protein (MTP) functions as a chaperone protein necessary for proper folding of apoB and also participates in the transfer of lipids to newly formed chylomicrons and VLDL particles.

Abetalipoproteinemia is autosomal recessive trait,

loss-of-function mutation in the MTP gene.

Jejunal biopsy shows enterocytes with foamy or clear cytoplasm, which is more prominent at the tips of the villi.

Familial dysbetalipoproteinemia

Type III hyperlipoproteinemia

characterized clinically by xanthomas and premature coronary and peripheral vascular disease.

Primary defect = ApoE3 and ApoE4, apolipoproteins found on chylomicrons and VLDL that are responsible for binding hepatic apolipoprotein receptors.