Tissue Expression of Endothelial Lipase and Its Implications

The size of expressed endothelial hpase was determined by immunoblot analysis of both HUVEC and HCAEC. Bands of 68 and 40 kDa were detected using an antibody directed against the amino-terminus of EL [3]. The expressed protein, based on amino acid translation of the EL cDNA, is predicted to be approximately 55 kDa. The 68 kDa form may represent the glycosylated full-length monomer, whereas the 40 kDa form may be the product of alternative splicing or a proteolytic cleavage product or both. 

The functional significance of the high EL expression in lung, placenta and thyroid is undetermined. Hirata et al. [4] noted that the distribution of EL in lung, as detected by in situ hybridization, suggested that EL expression may be locahzed to type 11 alveolar epithelial cells, which synthesize surfactant, a phosphatidylcholine-rich substance. EL might be involved in surfactant metabohsm. 

The character of HDL in cord blood is distinct from adult blood. Eetal HDL is apolipoprotein E-rich, with much lower esterified cholesterol. HDL represents fhe major lipoprotein class in cord blood, a marked change from the adult plasma h-poprotein profile. The phosphohpid content was the same as the HDL of adults [13]. A plausible hypothesis is fhat EL is directly involved in lipid metabolism and cholesterol transport in the developing fetus. 

Thyroid hormone decreases hepatic hpase activity [14] deficiency of thyroid hormone does not result in significant effects on HDL levels, however. Individuals wifh hypothyroidism have either unchanged or slightly elevated HDL levels [15]. It is possible fhat EL expression in the thyroid is regulated by thyroid hormone or that EL is involved in thyroid lipid metabolism. 

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