Intravascular triglyceride lipolysis becomes crystal clear

Abstract

The ability to store surplus calories as fat for use during fasting or periods of increased energy demands is a fundamental process required for survival of all species. Fat consumed in the diet is incorporated into triglyceride-rich lipoproteins (chylomicrons) in the intestine for delivery to peripheral tissues. The liver also secretes triglyceride-rich very low-density lipoproteins (VLDLs). Chylomicrons and VLDL triglycerides are hydrolyzed within capillaries by lipoprotein lipase (LPL) (1), releasing lipids for storage and utilization by vital tissues. The processing of lipoproteins by LPL has been studied intensively for more than a half century and has proved highly relevant to clinical medicine. A complete deficiency of LPL results in an inability to hydrolyze the triglycerides in chylomicrons and VLDLs, resulting in severe hypertriglyceridemia (chylomicronemia) and a substantial risk of acute pancreatitis (2). Partial deficiencies in LPL cause mild to moderate hypertriglyceridemia and increased risk for coronary artery disease (3, 4). The ability of LPL to hydrolyze plasma triglycerides is absolutely dependent on glycosylphosphatidylinositol (GPI)-anchored high-density lipoprotein–binding protein 1 (GPIHBP1), a GPI-anchored endothelial cell protein that binds LPL and tethers it to the luminal surface of capillaries (1). GPIHBP1 deficiency severely impairs triglyceride processing and causes severe hypertriglyceridemia (indistinguishable from that caused by LPL deficiency) (5, 6). Despite intensive research, structures for LPL and GPIHBP1 have been elusive. However, in PNAS, Birrane et al. (7) report the crystal structure of the LPL–GPIHBP1 complex. This accomplishment culminates a decade of collaborative studies by Stephen G. Young and collaborators that have focused on defining GPIHBP1 function in triglyceride metabolism. LPL activity was first reported by Hahn (8) in 1943, who described the appearance of a lipemia clearing factor in dogs after an injection of heparin. The activity of LPL is regulated by apolipoproteins on the surface of lipoproteins (most notably … [↵][1]1Email: jay.horton{at}utsouthwestern.edu. [1]: #xref-corresp-1-1