The ARF-Like GTPase ARFRP1 Is Essential for Lipid Droplet Growth and Is Involved in the Regulation of Lipolysis

Abstract

ADP-ribosylation factor (ARF)-related protein 1 (ARFRP1) is a GTPase regulating protein trafficking between intracellular organelles. Here we show that mice lacking Arfrp1 in adipocytes (Arfrp1^ad−/−) are lipodystrophic due to a defective lipid droplet formation in adipose cells. Ratios of mono-, di-, and triacylglycerol, as well as the fatty acid composition of triglycerides, were unaltered. Lipid droplets of brown adipocytes of Arfrp1^ad−/− mice were considerably smaller and exhibited ultrastructural alterations, such as a disturbed interaction of small lipid-loaded particles with the larger droplets, suggesting that ARFRP1 mediates the transfer of newly formed small lipid particles to the large storage droplets. SNAP23 (synaptosomal-associated protein of 23 kDa) associated with small lipid droplets of control adipocytes but was located predominantly in the cytosol of Arfrp1^ad−/− adipocytes, suggesting that lipid droplet growth is defective in Arfrp1^ad−/− mice. In addition, levels of phosphorylated hormone-sensitive lipase (HSL) were elevated, and association of adipocyte triglyceride lipase (ATGL) with lipid droplets was enhanced in brown adipose tissue from Arfrp1^ad−/− mice. Accordingly, basal lipolysis was increased after knockdown of Arfrp1 in 3T3-L1 adipocytes. The data indicate that disruption of ARFRP1 prevents the normal enlargement of lipid droplets and produces an activation of lipolysis.

This work was supported by the Deutsche Forschungsgemeinschaft (Schu 750/5-2 and Schu 750/5-3) and the European Community's FP7 PREPROBEDIA (grant 201681).

We are grateful to Ronald M. Evans, Howard Hughes Medical Institute, The Salk Institute, La Jolla, CA, for providing the Cre-ap2 mouse and to Richard A. Kahn, Department of Biochemistry, Emory University School of Medicine, Atlanta, GA, for critical reading of the manuscript and helpful discussions. The skillful technical assistance of M. Fobker, W. Hanekamp, E. Meyer, B. Rischke, K. Schlattmann, A. Seelig, and D. Ziomek is gratefully acknowledged.

Conflict of interest statement: none declared.