Allows transport of water insoluble fats through blood plasma.
Outer shell
- Apolipoprotein
- Phospholipids
The number and type of apolipoproteins determine the function of the lipoprotein.
Inner (hydrophobic) core:
- triglycerides
- cholesterol
Categorized by density
- Chylomicrons (ULDL) transport dietary fats from intestines throughout the body
- VLDL are assembled from triglycerides in the liver and go to adipose tissue
- IDL
- LDL (correlate with atherosclerosis progression)
- HDL collect fat and transport back to liver ("good")
Breakdown of dietary fats. Involves mainly chylomicrons:
- Triglycerides assemble with apolipoprotein B to form precursor chylomicrons
- Precursor chylomicrons move through lymph duct directly into bloodstream
- Precursor chylomicrons receive APOC and APOE and become mature
- Mature chylomicrons release in interaction with lipoprotein lipase
- Hydrolysis of triglycerides releases fatty acids and glycerol
- Chylomicron remnants interact (with APOE) with receptors in liver where the are degraded and used for energy
- Nascent VLDL are assembled in hepatocytes with APOB
- Nascent VLDL receive APOE and APOC from HDL and become mature
- Mature VLDL release free fatty acids and glycerol from LPL (lipoprotein lipase)
- Remnant VLDLs are called IDL
- IDL can be hydrolyzed once more to create LDL
Interaction with innate immune system - some fraction of LDLs interact with scavenger receptors on macrophages and are ingested via phagocytosis. Cholesterol laden macrophages become foam cells, die and deposit as atherosclerotic plaques.
- HDL assembled in liver
- HDL collect cholesterol in different tissues and deposit elsewhere
High levels of lipoproteins can lead to abnormal hardening of the blood vessels, called atherosclerosis.