Zebrafish fat-free, a novel Arf effector, regulates phospholipase D to mediate lipid and glucose metabolism

Zebrafish fat-free mutants (ffr) exhibit defective intestinal lipid metabolism and fat-free protein (Ffr) is involved in Golgi-related vesicular trafficking. In this study, we show that ffr mutants also display defective glucose metabolism. Using microarray and real-time PCR, we found that a ffr mutant with a nonsense mutation exhibits increased transcript level of ADP-ribosylation factor gene (arfs). Further analysis indicated that Ffr contains a putative Arf binding motif and can bind GTP-bound Arfs. In addition, ffr exhibited increased transcript and activity levels of the Arf downstream effector phospholipase D (PLD). Inhibition of PLD partially restored lipid and glucose metabolism in ffr, suggesting that Ffr is involved in a pathway regulating PLD activity by regulating Arfs. We propose that local over-production of phosphatidic acid (PA) by excess PLD promotes membrane curvature, which affects Golgi membrane structure and secretory processes, contributing to impairment of lipid and glucose metabolism.

Research Highlights
► Truncated Ffr binds and retains GTP-bound Arf at the Golgi, over-stimulating PLD.
► Excess local production of PA drives membrane curvature, resulting in swollen Golgi.
► Impaired exocytosis thereby affecting lipid and glucose metabolism.