The GARP complex is required for cellular sphingolipid homeostasis.

Florian Fröhlich,Constance Petit,Romain Christiano,Nora Kory,Christer S Ejsing,Morven Graham,Xinran Liu,Hans-Kristian Hannibal-Bach,Robert V Farese,Tobias C Walther

doi:10.7554/elife.08712

Abstract

Sphingolipids are abundant membrane components and important signaling molecules in eukaryotic cells. Their levels and localization are tightly regulated. However, the mechanisms underlying this regulation remain largely unknown. In this study, we identify the Golgi-associated retrograde protein (GARP) complex, which functions in endosome-to-Golgi retrograde vesicular transport, as a critical player in sphingolipid homeostasis. GARP deficiency leads to accumulation of sphingolipid synthesis intermediates, changes in sterol distribution, and lysosomal dysfunction. A GARP complex mutation analogous to a VPS53 allele causing progressive cerebello-cerebral atrophy type 2 (PCCA2) in humans exhibits similar, albeit weaker, phenotypes in yeast, providing mechanistic insights into disease pathogenesis. Inhibition of the first step of de novo sphingolipid synthesis is sufficient to mitigate many of the phenotypes of GARP-deficient yeast or mammalian cells. Together, these data show that GARP is essential for cellular sphingolipid homeostasis and suggest a therapeutic strategy for the treatment of PCCA2.

Highlights

Eukaryotic membranes are composed of a complex mixture of lipids belonging to three major classes: sphingolipids, sterols, and glycerophospholipids
To identify genes involved in the regulation of sphingolipid homeostasis, we performed a quantitative, genome-wide screen in yeast for modulators of a growth defect caused by myriocin, an inhibitor of serine-palmitoyl transferase (SPT), which catalyzes the first and rate-limiting step of sphingolipid synthesis (Miyake et al, 1995)
We show that Golgi-associated retrograde protein (GARP) complex-mediated retrograde trafficking from endosomes to the Golgi is important for cellular sphingolipid homeostasis

Summary

Introduction

Eukaryotic membranes are composed of a complex mixture of lipids belonging to three major classes: sphingolipids, sterols, and glycerophospholipids. Sphingolipids make up between 10 and 20% of the mammalian plasma membrane (van Meer et al, 2008). They are generated in the ER and Golgi and are subsequently delivered to the plasma membrane by vesicular transport (Klemm et al, 2009). Sphingolipids can be recycled from endocytic vesicles back to the plasma membrane via the Golgi apparatus (Choudhury et al, 2002). Maintenance of membrane sphingolipid levels is important to ensure plasma membrane integrity and to facilitate normal membrane trafficking at the Golgi apparatus and throughout the endocytic pathway (Trajkovic et al, 2008; Klemm et al, 2009; Shen et al, 2014).

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Conclusion