Mediates the transport of lipoprotein lipase LPL from the basolateral to the apical surface of endothelial cells in capillaries (PubMed:20620994). Anchors LPL on the surface of endothelial cells in the lumen of blood capillaries (PubMed:20620994, PubMed:24726386, PubMed:27811232). Thereby, plays an important role in lipolytic processing of chylomicrons by LPL, triglyceride metabolism and lipid homeostasis (PubMed:17403372). Binds chylomicrons and phospholipid particles that contain APOA5 (PubMed:18340083). Binds high-density lipoprotein (HDL) and plays a role in the uptake of lipids from HDL (PubMed:12496272). Mostly monomer, but also homodimer and homooligomer (PubMed:25387803). Interacts with lipoprotein lipase (LPL) (PubMed:17403372, PubMed:18340083, PubMed:19304573, PubMed:20620994, PubMed:25387803, PubMed:24726386, PubMed:27811232). Interacts with high affinity with high-density lipoprotein (HDL) (PubMed:12496272). Interacts with chylomicrons (PubMed:17403372). Interacts with APOA5 (PubMed:18340083). Detected in fat tissue (PubMed:18340083, PubMed:17403372). Detected on the luminal surface of capillary endothelial cells in heart, skeletal muscle and brown adipose tissue (at protein level) (PubMed:17403372, PubMed:20620994). Detected in heart and brown adipose tissue (PubMed:12496272, PubMed:17403372). Expressed at lower levels in lung and liver (PubMed:12496272). Induced by fasting. The N-terminal acidic region is intrinsically disordered (By similarity). This region contributes to LPL binding (PubMed:20620994). It stabilizes LPL and protects LPL against loss of activity (By similarity). Glycosylation of Asn-76 is critical for cell surface localization. Sulfation of a Tyr in the N-terminal acidic region increases the affinity for LPL. Adult mice display chylomicronemia when kept on a normal chow diet, with milky-looking blood plasma due to marked accumulation of chylomicrons in the plasma. Their plasma triglyceride levels are generally above 1000 mg/dl and can be as high as 5000 mg/dl. Mice display decreased plasma levels of lipoprotein lipase LPL (PubMed:17403372). Contrary to wild-type, LPL is not recruited to the apical surface of endothelial cell that faces the lumen of capillaries, but is mislocalized to the interstitial spaces surrounding myocytes and adipocytes (PubMed:20620994, PubMed:24726386, PubMed:27811232).