Evidence that hepatic lipase and endothelial lipase have different substrate specificities for high-density lipoprotein phospholipids

Hepatic lipase (HL) and endothelial lipase (EL) are both members of the triglyceride lipase gene family. HL hydrolyzes phospholipids and triglycerides in triglyceride-rich lipoproteins and high-density lipoproteins (HDL). EL hydrolyzes HDL phospholipids and has low triglyceride lipase activity. The aim of this study was to determine if HL and EL hydrolyze different HDL phospholipids and whether HDL phospholipid composition regulates the interaction of EL and HL with the particle surface. Spherical, reconstituted HDL (rHDL) containing either 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), 1-palmitoyl-2-linoleoylphosphatidylcholine (PLPC), 1-palmitoyl-2-arachidonylphosphatidylcholine (PAPC), or 1-palmitoyl-2-docosahexanoylphosphatidylcholine (PDPC) as the only phospholipid, apolipoprotein A-I as the only apolipoprotein, and either cholesteryl esters (CE) only or mixtures of CE and triolein (TO) in their core were prepared. The rHDL were similar in size and had comparable core lipid/apoA-I molar ratios. The CE-containing rHDL were used to determine the kinetics of HL- and EL-mediated phospholipid hydrolysis. For HL the V-max of phospholipid hydrolysis for (POPC)rHDL > (PLPC)rHDL similar to (PDPC)rHDL > (PAPC)rHDL, while the K-m(app) for (POPC)rHDL > (PDPC)rHDL > (PLPC)rHDL > (PAPC)rHDL. For EL the V-max for (PDPC)rHDL > (PAPC)rHDL > (PLPC)rHDL similar to (POPC)rHDL, while the K-m(app) for (PAPC)rHDL similar to (PLPC)rHDL > (POPC)rHDL > (PDPC)rHDL. The kinetics of EL- and HL-mediated TO hydrolysis was determined using rHDL that contained TO in their core. For HL the V-max of TO hydrolysis for (PLPC)rHDL > (POPC)rHDL > (PAPC)rHDL > (PDPC)rHDL, while the K-m(app) for (PLPC)rHDL > (POPC)rHDL similar to (PAPC)rHDL > (PDPC)rHDL. For EL the V-max and K-m(app) for (PAPC)rHDL > (PDPC)rHDL > (PLPC)rHDL > (POPC)rHDL. These results establish that EL and HL have different substrate specificities for rHDL phospholipids and that their interactions with the rHDL surface are regulated by phospholipids.