Mingyue Zhou

Dual actions of fibroblast growth factor 19 on lipid metabolism.

Elevated triglyceride (TG) and cholesterol levels are risk factors for cardiovascular disease and are often associated with diabetes and metabolic syndrome. Recent reports suggest that fibroblast growth factor (FGF)19 and FGF21 can dramatically improve metabolic dysfunction, including hyperglycemia, hypertriglyceridemia, and hypercholesterolemia. Due to their similar receptor specificities and co-receptor requirements, FGF19 and FGF21 share many common properties and have been thought to be interchangeable in metabolic regulation. Here we directly compared how pharmacological administration of recombinant FGF19 or FGF21 proteins affect metabolism in B6.V-Lepob/J leptin-deficient mice. FGF19 and FGF21 equally improved glucose parameters; however, we observed increased serum TG and cholesterol levels after treatment with FGF19 but not with FGF21. Increases in serum TGs were also observed after a 4-day treatment with FGF19 in C57BL6/J mice on a high-fat diet. This is in contrast to many literature reports that showed significant improvements in hyperlipidemia after chronic treatment with FGF19 or FGF21 in high-fat diet models. We propose that FGF19 has lipid-raising and lipid-lowering actions mediated through different FGF receptors and target tissues, and the results described here provide a potential mechanism that may explain the inconsistency in the reported effects of FGF19 on lipid metabolism.

The high-resolution crystal structure of human LCAT.

LCAT is intimately involved in HDL maturation and is a key component of the reverse cholesterol transport (RCT) pathway which removes excess cholesterol molecules from the peripheral tissues to the liver for excretion. Patients with loss-of-function LCAT mutations exhibit low levels of HDL cholesterol and corneal opacity. Here we report the 2.65 Å crystal structure of the human LCAT protein. Crystallization required enzymatic removal of N-linked glycans and complex formation with a Fab fragment from a tool antibody. The crystal structure reveals that LCAT has an α/β hydrolase core with two additional subdomains that play important roles in LCAT function. Subdomain 1 contains the region of LCAT shown to be required for interfacial activation, while subdomain 2 contains the lid and amino acids that shape the substrate binding pocket. Mapping the naturally occurring mutations onto the structure provides insight into how they may affect LCAT enzymatic activity.

Agonistic Human Antibodies Binding to Lecithin-Cholesterol Acyltransferase Modulate High Density Lipoprotein Metabolism.

Drug discovery opportunities where loss-of-function alleles of a target gene link to a disease-relevant phenotype often require an agonism approach to up-regulate or re-establish the activity of the target gene. Antibody therapy is increasingly recognized as a favored drug modality due to multiple desirable pharmacological properties. However, agonistic antibodies that enhance the activities of the target enzymes are rarely developed because the discovery of agonistic antibodies remains elusive. Here we report an innovative scheme of discovery and characterization of human antibodies capable of binding to and agonizing a circulating enzyme lecithin cholesterol acyltransferase (LCAT). Utilizing a modified human LCAT protein with enhanced enzymatic activity as an immunogen, we generated fully human monoclonal antibodies using the XenoMouseTM platform. One of the resultant agonistic antibodies, 27C3, binds to and substantially enhances the activity of LCAT from humans and cynomolgus macaques. X-ray crystallographic analysis of the 2.45 Å LCAT-27C3 complex shows that 27C3 binding does not induce notable structural changes in LCAT. A single administration of 27C3 to cynomolgus monkeys led to a rapid increase of plasma LCAT enzymatic activity and a 35% increase of the high density lipoprotein cholesterol that was observed up to 32 days after 27C3 administration. Thus, this novel scheme of immunization in conjunction with high throughput screening may represent an effective strategy for discovering agonistic antibodies against other enzyme targets. 27C3 and other agonistic human anti-human LCAT monoclonal antibodies described herein hold potential for therapeutic development for the treatment of dyslipidemia and cardiovascular disease.

BacMam production of active recombinant lecithin-cholesterol acyltransferase: Expression, purification and characterization.

Lecithin-cholesterol acyltransferase (LCAT) is a key enzyme in the esterification of cholesterol and its subsequent incorporation into the core of high density lipoprotein (HDL) particles. It is also involved in reverse cholesterol transport (RCT), the mechanism by which cholesterol is removed from peripheral cells and transported to the liver for excretion. These processes are involved in the development of atherosclerosis and coronary heart disease (CHD) and may have therapeutic implications. This work describes the use of baculovirus as a transducing vector to express LCAT in mammalian cells, expression of the recombinant protein as a high-mannose glycoform suitable for deglycosylation by Endo H and its purification to homogeneity and characterization. The importance of producing underglycosylated forms of secreted glycoproteins to obtain high-resolution crystal structures is discussed.