Abstract:

Eukaryotic cells produce over 1000 different lipid species which tune organelle membrane properties, control signaling and store energy. Organelle-specific lipid distributions are maintained by local metabolism and transport of lipids via vesicular and non-vesicular routes. How lipids are sorted in these routes is largely unknown due to the difficulty to image lipid species in cells. We quantified the transport of individual phospholipids from the plasma membrane through the endomembrane system using pulse-chase fluorescence imaging of minimally modified lipid probes. Time resolved quantification of intracellular lipid distribution revealed strong differences in transport kinetics depending on acyl chain composition and headgroup identity. We found that non-vesicular lipid transport provides both higher molecular specificity and faster kinetics compared to vesicular lipid trafficking. By combining imaging with quantitative mass spectrometry, we determined that lipid transport is up to one order of magnitude faster than metabolism. Our findings thus suggest that non-vesicular lipid transport catalyzed by lipid transfer proteins is the main pathway for maintaining organelle membrane compositions and intracellular lipid homeostasis. We anticipate that our lipid imaging pipeline will facilitate a comprehensive structure-function analysis of the mammalian lipidome, which is required for understanding the molecular underpinnings of common lipid related diseases such as fatty liver disease and obesity.