The impact of phospholipid transfer protein (PLTP) on HDL metabolism

High-density lipoproteins (HDL) play a major protective role against the development of coronary artery disease. Phospholipid transfer protein (PLTP) is a main factor regulating the size and composition of HDL in the circulation and plays an important role in controlling plasma HDL levels. This is achieved via both the phospholipid transfer activity of PLTP and its capability to cause HDL conversion. The present review focuses on the impact of PLTP on HDL metabolism. The basic characteristics and structure of the PLTP protein are described. The two main functions of PLTP, PLTP-mediated phospholipid transfer and HDL conversion are reviewed, and the mechanisms and control, as well as the physiological significance of these processes are discussed. The relationship between PLTP and the related cholesteryl ester transfer protein (CETP) is reviewed. Thereafter other functions of PLTP are recapitulated: the ability of PLTP to transfer cholesterol, α-tocopherol and lipopolysaccharide (LPS), and the suggested involvement of PLTP in cellular cholesterol traffic. The discussion on PLTP activity and mass in (patho)physiological settings includes new data on the presence of two forms of PLTP in the circulation, one catalytically active and the other inactive. Finally, future directions for PLTP research are outlined.