Cholesterol-dependent homeostatic regulation of very long chain sphingolipid synthesis

Abstract

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.

Metabolic channeling of lipids via the contact zones between different organelles

“…[ 17 ] In S. cerevisiae , Svf1, a lipocalin‐like ceramide transfer protein, mediates the ER‐to‐cis‐Golgi transfer of ceramide, [ 40 ] and tricalbins (Tcb1p/Tcb2p/Tcb3p, the yeast orthologs of human extended synaptotagmins [E‐Syts]) mediate the ER‐to‐ medial ‐Golgi transfer, whereas no clear ortholog of Svf1 has been found in higher eukaryotes or it has not been determined whether mammalian E‐Syts mediate the ER‐to‐Golgi transfer of ceramide. Of note, CERT poorly transfers ceramide species with very long acyl chains due to the spatial limitation of the hydrophobic cavity in the LTD. [ 71,72 ] Thus, as described previously, [ 70,73 ] very long acyl‐chain ceramide may prefer a CERT‐independent and vesicular pathway to detach from the ER. This scenario can partly explain why GlcCer tends to have longer acyl chains than SM.…”

“…Both vesicular and non-vesicular pathways presumably operate in the ceramide delivery to the Golgi. [20,70] The budding yeast S. cerevisiae exceptionally does not have an ortholog of mammalian GlcCer synthase (UDP-glucose: ceramide glucosyltransferase: UGCG). Interestingly, S. cerevisiae was shown to mainly use the conventional vesicular pathway for the ER-Golgi transport of ceramide for the production of yeast glycophosphosphingolipids.…”

The molecular mechanism of on-demand sterol biosynthesis at organelle contact sites

“…Indeed, the strain overexpressing Yet3 was susceptible to fluconazole (Figure 3C). It was also shown that reduced sterols increase the levels of long-chain sphingolipids as a compensatory mechanism 59 . Indeed, lipidomic analysis demonstrated reduced sterol levels in strains overexpressing Yet3 (Figure S3A), and elevated levels of long-chain sphingolipids (Figure S3B) (Table S2).…”