Lipid Metabolism and Trafficking in the Golgi Apparatus

Sub-cellular biochemistry/Subcellular biochemistry · 2026-01-01

Cholesterol depletion activates trafficking-coupled sphingolipid synthesis

The Journal of Cell Biology · 2025-12-23

Homeostatic pathways maintain the lipid composition of organelle membranes, and mechanistic links between lipid sensing, synthesis, and trafficking are lacking. Acute depletion of cell cholesterol elicits an increase in the rate of very-long-chain (VLC) sphingomyelin synthesis in the Golgi apparatus, thereby promoting cholesterol retention in the plasma membrane. Stable isotope metabolic analyses and lipid trafficking assays showed that the increase in VLC-sphingomyelin results from an increase in the rate of coatomer II-dependent trafficking of VLC-ceramide from the endoplasmic reticulum to the Golgi apparatus. An integral membrane protein of the coatomer II network, cTAGE5, is required for endoplasmic reticulum-to-Golgi trafficking of ceramide and cTAGE5 overexpression caused herniations of the endoplasmic reticulum network that entrapped a synthetic ceramide analog to which cTAGE5 could be photochemically cross-linked. We propose that cTAGE5 is a ceramide sensor for export of VLC-ceramide from the endoplasmic reticulum exit site.

Abstract 1535 Regulation of Coatomer II-mediated ER-to-Golgi trafficking of sphingolipids

Journal of Biological Chemistry · 2025-05-01

Sphingomyelin plays a key role in cellular cholesterol homeostasis in part by binding to and sequestering cholesterol in organelle membranes. Using lipidomics and metabolic pulse-chase assays to monitor sphingolipid synthesis, we discovered that synthesis of very -long -chain (VLC) sphingomyelins is inversely regulated by cellular cholesterol levels; acute cholesterol depletion elicited a rapid induction of VLC--sphingolipid synthesis, increased trafficking of sphingolipids from the endoplasmic reticulum to the Golgi apparatus and plasma membrane, while cholesterol loading reduced VLC--sphingolipid synthesis.

Cholesterol depletion activates trafficking-coupled sphingolipid synthesis

bioRxiv (Cold Spring Harbor Laboratory) · 2025-02-16 · 1 citations

Within cellular membranes, sphingomyelin is associated with cholesterol and this complex facilitates homeostatic regulation of membrane viscosity. Acute cholesterol depletion increases the synthesis of very-long-chain (VLC) sphingomyelin, but a link between lipid sensing and sphingolipid synthesis is lacking. Using sphingolipid metabolic flux analysis, we observed that VLC-ceramide, the precursor to VLC complex sphingolipids that are produced in the Golgi apparatus, was rapidly consumed after cholesterol depletion, while synthesis of long-chain sphingolipids was unaffected. Sphingolipid trafficking assays showed that cholesterol depletion enhances VLC-Ceramide trafficking from the endoplasmic reticulum to the Golgi apparatus. Changes in the sizes of coatomer II ER exit sites were correlated with increased VLC-Ceramide trafficking and concomitant increase in sphingomyelin. Depletion of Sec16A, a component of the COPII network, abolished VLC-SM synthesis. This study reveals ER-to-Golgi trafficking of VLC-Ceramide as a key regulatory node in organelle membrane homeostasis pathways. Summary: In cellular membranes, sphingomyelin is associated with cholesterol. Metabolic flux analysis of sphingolipid metabolism showed that synthesis rate of sphingomyelin, but not ceramide, was increased after depletion of cholesterol due increased rate of COPII-dependent ER-to-Golgi transport of ceramide.

Bridge-like lipid transfer protein family member 2 suppresses ciliogenesis

Molecular Biology of the Cell · 2024-03-27 · 19 citations

Bridge-like lipid transfer protein family member 2 (BLTP2) is an evolutionary conserved protein with unknown function(s). The absence of BLTP2 in Drosophila melanogaster results in impaired cellular secretion and larval death, while in mice ( Mus musculus), it causes preweaning lethality. Structural predictions propose that BLTP2 belongs to the repeating β-groove domain-containing (also called the VPS13) protein family, forming a long tube with a hydrophobic core, suggesting that it operates as a lipid transfer protein (LTP). We establish BLTP2 as a negative regulator of ciliogenesis in RPE-1 cells based on a strong genetic interaction with WDR44, a gene that also suppresses ciliogenesis. Like WDR44, BLTP2 localizes to membrane contact sites involving the endoplasmic reticulum and the tubular endosome network in HeLa cells and that BLTP2 depletion enhanced ciliogenesis in RPE-1 cells grown in serum-containing medium, a condition where ciliogenesis is normally suppressed. This study establishes human BLTP2 as a putative LTP acting between tubular endosomes and ER that regulates primary cilium biogenesis.

Abstract 1621 Cholesterol-dependent homeostatic regulation of very long chain sphingolipid synthesis

Journal of Biological Chemistry · 2024-03-01

Author Reply to Peer Reviews of Bridge-like lipid transfer protein family member 2 suppresses ciliogenesis

2024-02-08

Bridge-like lipid transfer protein family member 2 suppresses ciliogenesis

bioRxiv (Cold Spring Harbor Laboratory) · 2023-12-12 · 2 citations

Abstract Bridge-like lipid transfer protein family member 2 (BLTP2) is an evolutionary conserved protein with unknown function(s). The absence of BLTP2 in Drosophila melanogaster results in impaired cellular secretion and larval death, while in mice ( Mus musculus ), it causes preweaning lethality. Structural predictions propose that BLTP2 belongs to the repeating β-groove domain-containing (also called the VPS13) protein family, forming a long tube with a hydrophobic core, suggesting that it operates as a lipid transfer protein (LTP). We establish BLTP2 as a negative regulator of ciliogenesis in RPE-1 cells based on a strong genetic interaction with WDR44 , a gene that also suppresses ciliogenesis. Like WDR44, BLTP2 localizes to membrane contact sites involving the endoplasmic reticulum and the tubular endosome network in HeLa cells and that BLTP2 depletion enhanced ciliogenesis by serum-fed RPE-1 cells, a condition where ciliogenesis is normally suppressed. This study establishes human BLTP2 as a putative lipid transfer protein acting between tubular endosomes and ER that regulates primary cilium biogenesis. Significance statement We show the involvement of an ER-localized bridge-like lipid transfer protein, BLTP2, in ciliogenesis and establish that BLTP2 is enriched at organelle-organelle membrane contact sites involving the endoplasmic reticulum (ER) and the tubular endosome network (TEN). These results implicate, for the first time, the involvement of bulk lipid transfer between the ER and TEN in regulating ciliogenesis.

Cholesterol-dependent homeostatic regulation of very long chain sphingolipid synthesis

The Journal of Cell Biology · 2023-10-03 · 11 citations

Sphingomyelin plays a key role in cellular cholesterol homeostasis by binding to and sequestering cholesterol in the plasma membrane. We discovered that synthesis of very long chain (VLC) sphingomyelins is inversely regulated by cellular cholesterol levels; acute cholesterol depletion elicited a rapid induction of VLC-sphingolipid synthesis, increased trafficking to the Golgi apparatus and plasma membrane, while cholesterol loading reduced VLC-sphingolipid synthesis. This sphingolipid-cholesterol metabolic axis is distinct from the sterol responsive element binding protein pathway as it requires ceramide synthase 2 (CerS2) activity, epidermal growth factor receptor signaling, and was unaffected by inhibition of protein translation. Depletion of VLC-ceramides reduced plasma membrane cholesterol content, reduced plasma membrane lipid packing, and unexpectedly resulted in the accumulation of cholesterol in the cytoplasmic leaflet of the lysosome membrane. This study establishes the existence of a cholesterol-sphingolipid regulatory axis that maintains plasma membrane lipid homeostasis via regulation of sphingomyelin synthesis and trafficking.

Lipid Sorting and Organelle Identity

Cold Spring Harbor Perspectives in Biology · 2023-07-24 · 18 citations

-Golgi network, which constitutes the interface between the two membrane territories. Organelle homeostasis is maintained by vesicle-mediated retrieval of bulk membrane from the distal organelles of each territory to the endoplasmic reticulum or plasma membrane and by soluble lipid transfer proteins that traffic particular lipids. The concept of cellular membrane territories emphasizes the contrasting features of organelle membranes of the secretory and endolysosome networks and the essential roles of lipid-sorting pathways that maintain organelle function.