Triacylglycerol Is Synthesized in a Specific Subclass of Caveolae in Primary Adipocytes

Anita Öst,Unn Örtegren,Johanna Gustavsson,Fredrik H Nystrom,Peter Strålfors

doi:10.1074/jbc.c400429200

Abstract

A principal metabolic function of adipocytes is to synthesize triacylglycerol (TG) from exogenous fatty acids. The level of fatty acids has to be tightly controlled in the adipocyte, as they can act as detergents that rapidly dissolve the plasma membrane, causing cell lysis if allowed to accumulate. Fatty acids therefore have to be efficiently converted to TG and stored in the central lipid droplet. We report that in intact primary adipocytes exogenous oleic acid was taken up and directly converted to TG in the plasma membrane, in a novel subclass of caveolae that specifically contains the protein perilipin. Isolated caveolae catalyzed de novo TG synthesis from oleic acid and glycerol 3-phosphate. Electron microscopy revealed the presence of caveolin and perilipin in caveolae and in lipid-laden bulbs in the plasma membrane, and fluorescence microscopy demonstrated colocalization of fatty acids/TG with caveolin and perilipin at the plasma membrane. A second caveolae fraction was isolated, which lacked perilipin and the triacylglycerol synthesizing enzymes. Both caveolae fractions contained caveolin-1 and the insulin receptor. The findings demonstrate that specific subclasses of caveolae carry out specific functions in cell metabolism. In particular, triacylglycerol is synthesized at the site of fatty acid entry in one of these caveolae classes.

Highlights

From the ‡Department of Cell Biology and Diabetes Research Centre, ¶Department of Medicine and Care, Linkoping University, SE58185 Linkoping, Sweden
The level of fatty acids has to be tightly controlled in the adipocyte, as they can act as detergents that rapidly dissolve the plasma membrane, causing cell lysis if allowed to accumulate
To gain knowledge of the biochemical pathways of fat metabolism in human physiology is central to understanding the derangements and pathology in the adipocyte handling of fatty acids associated with obesity and type 2 diabetes

Summary

Introduction

From the ‡Department of Cell Biology and Diabetes Research Centre, ¶Department of Medicine and Care, Linkoping University, SE58185 Linkoping, Sweden. The level of fatty acids has to be tightly controlled in the adipocyte, as they can act as detergents that rapidly dissolve the plasma membrane, causing cell lysis if allowed to accumulate. We report that in intact primary adipocytes exogenous oleic acid was taken up and directly converted to TG in the plasma membrane, in a novel subclass of caveolae that contains the protein perilipin.

Results

Conclusion