Regulation of lipoprotein lipase in rat adipose tissue ‐ a study of the role of angiopoietin‐like protein 4

Abstract

Lipoprotein lipase (LPL) plays a central role in hydrolysis of triglyceride‐rich lipoproteins. Rapid regulation of LPL activity by the nutritional status occurs mainly at the post‐translational level. Recent studies have demonstrated that angiopoietin‐like protein 4 (angptl4) controls lipoprotein metabolism via its ability to inhibit LPL. This occurs by direct binding of angptl4 to LPL resulting in conversion of active LPL dimers to inactive monomers. To further characterize the relationship between angptl4 and LPL, we studied the response of angptl4 mRNA and LPL activity in rat adipose tissue to different experimental conditions. Food withdrawal caused significant down‐regulation of LPL activity after 3 h, whereas angptl4 mRNA levels started to increase only after 4 h. During re‐feeding angptl4 mRNA expression was significantly decreased 1 h after feeding while a significant increase of LPL activity was not seen until after 2 h. Intraperitoneal injection of insulin caused a rapid increase in adipose tissue LPL activity after 30 min whereas the total mass of LPL protein remained the same. At this time (30 min) angptl4 mRNA levels had not changed significantly. We conclude that regulation of LPL activity in adipose tissue does not exactly correspond to changes in angptl4 mRNA levels. Thus, other mechanisms than transcriptional regulation of angptl4 must be involved in the control of LPL. Sponser: Swedich MRC.