Cholesterol depletion activates trafficking-coupled sphingolipid synthesis.

Area of Science:

• Cell Biology
• Lipid Metabolism
• Membrane Trafficking

Background:

• Homeostatic pathways regulate organelle membrane lipid composition.
• Mechanistic links between lipid sensing, synthesis, and trafficking remain unclear.
• Cell cholesterol depletion impacts sphingomyelin synthesis and plasma membrane cholesterol levels.

Purpose of the Study:

• To elucidate the mechanisms linking cholesterol homeostasis to lipid synthesis and trafficking.
• To identify the molecular players involved in very-long-chain (VLC) ceramide transport.
• To investigate the role of cTAGE5 in endoplasmic reticulum (ER)-to-Golgi transport.

Main Methods:

• Stable isotope metabolic analyses.
• Lipid trafficking assays.
• Protein localization and interaction studies (photochemical cross-linking).

Main Results:

• Acute cholesterol depletion increases VLC-sphingomyelin synthesis in the Golgi.
• This increase is driven by enhanced coatomer II-dependent VLC-ceramide trafficking from the ER to the Golgi.
• The integral membrane protein cTAGE5 is essential for ER-to-Golgi ceramide transport.
• cTAGE5 overexpression leads to ER network herniations and traps ceramide analogs.

Conclusions:

• cTAGE5 functions as a ceramide sensor at the ER exit site.
• cTAGE5 regulates the export of VLC-ceramide from the ER.
• This pathway links cellular cholesterol levels to the synthesis of VLC-sphingomyelin.