The role of lipases and LRP in the catabolism of triglyceride-rich lipoproteins.

A strong candidate for the long searched CR receptor might be the a2MR/LRP. We oversee a whole series of in vitro experiments from different laboratories today which show that LRP expresses all features for being such a receptor protein. LRP is localized on the liver cell surface, as well as on most other animal cells. It recognizes apo E enriched lipoproteins, as beta-VLDL and CR. There is evidence that CR contains LPL and it has been demonstrated that LPL binds with high affinity to LRP. This has been shown in cell binding experiments with subsequent cross-linking and in direct binding assays on purified receptor protein. HL which is expressed in liver cells and localized at the liver cell surface is also able to bind to LRP. LRP is moreover found in endosomes and can mediate the uptake of beta-VLDL and CR. Further studies are necessary to evaluate its role in vivo as well as its regulation. The interplay between the different ligands of this large multifunctional receptor protein needs to be clarified. It should be emphasized here that by describing LPL as a new mediator of CR untake in the liver and providing evidence for an interaction between LPL and LRP the role of LRP in the remnant catabolism has become even more likely.