USE OF GENE-MANIPULATED MODELS TO STUDY THE PHYSIOLOGY OF LIPID TRANSPORT

1. In vivo and in vitro gene manipulated models were used to study the metabolism of chylomicron remnants. Transgenic mice expressing human apolipoprotein (Ape) A1 or E4, gene knockout mice deficient in ApoE or low density lipoprotein (LDL) receptors and antisense gene inhibition in HepG2 cells were used to evaluate the effect of gene manipulations on the metabolism of chylomicron remnants. 2. Mice transgenic for hum an ApoE4 showed accelerated clearance of chylomicron-like emulsions wh en animals were fed a low-fat diet. When challenged by a high-fat diet , remnant clearance in ApoE4 transgenic mice was delayed, as in normal or non-transgenic controls. However, unlike normal nontransgenic cont rols, in ApoE4 transgenic mice high density lipoprotein (HDL)-choleste rol levels remained high after high-fat feeding, which probably protec ted the animals from the development of atherosclerosis.(1) In contras t, clearance of chylomicron-like lipid emulsions was not affected by t he overexpression of human ApoAI in transgenic mice. 3. Gene knock-out mice deficient in ApoE or deficient in the LDL receptor were used to show that ApoE and LDL receptors are both essential for the normal, fa st catabolism of chylomicron remnants by the liver.(2) In the absence of the LDL receptor, an alternative ApoE-dependent pathway operates to clear chylomicrons from the plasma, with significantly delayed catabo lism. 4. Antisense gene inhibition techniques were used to suppress th e expression of syndecan, a core protein of heparan sulfate proteoglyc an, in HepG2 cells. Remnant uptake in cells transfected with the antis ense oligodeoxynucleotide complementary to a 20 nucleotide sequence up stream of the initiation site of syndecan cDNA markedly reduced the up take of chylomicron remnant.