1-Deoxysphingolipids dysregulate membrane properties and cargo trafficking in the early secretory pathway

1-Deoxysphingolipids are non-canonical sphingolipids linked to several diseases, but their cellular effects are poorly understood. Here, we utilize lipid chemical biology approaches to investigate the role of 1-deoxysphingolipid metabolism on the properties and functions of secretory membranes. We first applied organelle-specific bioorthogonal labeling to visualize the subcellular distribution of metabolically tagged 1-deoxysphingolipids in RPE-1 cells, observing that they are retained in the endoplasmic reticulum (ER). We found that 1-deoxysphingolipids can be transported by the non-vesicular transporter CERT in vitro but are retained at ER exit sites (ERES) in cells, suggesting that they do not efficiently sort into vesicular carriers. Cells expressing disease-associated variants of serine palmitoyl-CoA transferase (SPT) accumulated long-chain 1-deoxysphingolipids, which reduced ER membrane fluidity and enlarged ERES. We observed that the rates of membrane protein release from the ER were altered in response to mutant SPT expression, in a manner that was dependent on the cargo affinity for ordered or disordered membranes. We propose that dysregulation of sphingolipid metabolism alters secretory membrane properties, which can then modulate protein trafficking.