Enterocyte Fatty Acid Handling Proteins and Chylomicron Formation

Dietary fats are the most concentrated caloric source in the human diet. In addition to their caloric content, fats also contain essential fatty acids and fat-soluble vitamins that are needed for good health. Normal dietary fat absorption is efficient but involves a complex and multilayered process. A major part of dietary fat is comprised of water insoluble triacylglycerols (TAG) that must be made to interact with water in order to be absorbed and processed by the intestine. The TAGs are hydrolyzed by pancreatic lipase to fatty acids and one sn-2-monoacylglycerol (MAG). These lipolytic products are absorbed through the apical membrane of enterocytes, directed to the endoplasmic reticulum (ER) where they are converted back to TAG to be packaged into chylomicrons, the intestine’s unique lipoproteins. The TAG is transported from the ER in a specialized vesicle, the pre-chylomicron transport vesicle, which is directed to the Golgi where the lipoproteins of the chylomicron are processed. The mature chylomicron is then incorporated into another vesicle for transport to the basolateral membrane where it is exocytosed into the lamina propria. The chylomicrons then enter the mesenteric lymph duct to be carried in the lymph system and enter the circulation in the left subclavian vein. This chapter reviews the basics of chylomicron synthesis and provides an updated overview of our current understanding regarding the apical membrane transporters, intracellular proteins, and organelles that facilitate lipid uptake and lipoprotein assembly in enterocytes.