VPS13A and VPS13C Influence Lipid Droplet Abundance

Abstract

Lipid transfer proteins mediate the exchange of lipids between closely apposed membranes at organelle contact sites and play key roles in lipid metabolism, membrane homeostasis, and cellular signaling. A recently discovered novel family of lipid transfer proteins, which includes the VPS13 proteins (VPS13A-D), adopt a rod-like bridge conformation with an extended hydrophobic groove that enables the bulk transfer of membrane lipids for membrane growth. Loss of function mutations in VPS13A and VPS13C cause chorea acanthocytosis and Parkinson's disease, respectively. VPS13A and VPS13C localize to multiple organelle contact sites, including endoplasmic reticulum (ER) – lipid droplet (LD) contact sites, but the functional roles of these proteins in LD regulation remains mostly unexplored. Here we employ CRISPR-Cas9 genome editing to generate VPS13A and VPS13C knockout cell lines in U-2 OS cells via deletion of exon 2 and introduction of an early frameshift. Analysis of LD content in these cell lines revealed that loss of either VPS13A or VPS13C results in reduced LD abundance under oleate-stimulated conditions. These data implicate two lipid transfer proteins, VPS13A and VPS13C, in LD regulation.

An Autopsy Series of Seven Cases of VPS13A Disease (Chorea‐Acanthocytosis)

“…VPS13A protein has been reported to localize to contact sites between the ER and mitochondria and to facilitate lipid transport resembling the ER‐mitochondria encounter systems seen in yeast, 17 in addition to playing an important role in formation of lipid droplets, which is critical for regulation of lipid metabolism 18 . Impairment of phosphorylation was noted in erythrocytes from patients with VPS13A disease 46 .…”

“…44,45 VPS13A protein has been reported to localize to contact sites between the ER and mitochondria and to facilitate lipid transport resembling the ERmitochondria encounter systems seen in yeast, 17 in addition to playing an important role in formation of lipid droplets, which is critical for regulation of lipid metabolism. 18 Impairment of phosphorylation was noted in erythrocytes from patients with VPS13A disease. 46 Recently, in silico prediction models have provided further details of the structure and apparent function of VPS13A in lipid transport between subcellular organelles, 13,47 as part of the group of related proteins (BLTPs) fulfilling similar functions.…”

“…Recent evidence from animal and cellular models suggests that VPS13A is involved in trafficking of lipids between subcellular organelles, including mitochondria, lipid droplets, and endoplasmic reticulum (ER) 11‐17 . Cell culture studies indicate that loss of VPS13A results in decreased levels of lipid droplets, which are involved in storage of lipids as a critical step in subcellular metabolism 18 . Our group has recently demonstrated significant alterations in lipid levels in human postmortem tissue from patients with VPS13A disease 19 .…”

“…[11][12][13][14][15][16][17] Cell culture studies indicate that loss of VPS13A results in decreased levels of lipid droplets, which are involved in storage of lipids as a critical step in subcellular metabolism. 18 Our group has recently demonstrated significant alterations in lipid levels in human postmortem tissue from patients with VPS13A disease. 19 Further work examining alterations in lipid processing after VPS13A mutation in the human brain has the potential to demonstrate mechanisms driving striatal degeneration.…”

The lipid droplet lipidome

“…Oxysterol binding related protein 5 (ORP5), a shuttling LTP, was localized at ER-LD contact sites upon oleate exposure, and was shown to regulate LD size presumably via counter transport of PS and phosphatidylinositol 4-phosphate (PI(4)P) to LDs and the ER, respectively [43]. Several bridge-like LTPs, including ATG2, VPS13A, and VPS13C, were identified at LD-ER contact sites, and have been proposed to facilitate bulk lipid transport of PC, PE, and cholesterol [44,45]. However, the molecular details of monolayer remodeling and enrichment in specific lipids via LTP action remain to be discovered.…”