Membrane contacts between caveolae and the endoplasmic reticulum regulate uptake and metabolic trapping of long-chain fatty acids

The vital process of cellular fatty acid metabolism involves uptake, metabolic trapping and storage of long-chain fatty acids (LCFAs) in different lipid species. Although several different enzymes like transporters and acyl-CoA synthetases are involved, the sequential mechanistic steps of the process are poorly understood. Here, we have addressed the role of the caveola coat protein caveolin1 and the acyl-CoA synthetase FATP1 in the process as both have major impacts in the uptake and storage of fatty acids in vivo and in vitro. Using live cell microscopy and mass spectrometry-based quantification of LCFA metabolism, we found that FATP1-mediated uptake and metabolic processing of LCFAs is coupled to, and dependent on caveolin1. Furthermore, both proteins stimulate the incorporation of LCFA into phospholipids and triacylglycerol, but not in sphingolipids. Using correlative light and electron microscopy we found that membrane contact sites are formed between FATP1-enriched endoplasmic reticulum (ER) and caveolae. Analysis of their temporal stability showed that they are dynamic but frequently persist over minutes. We propose that caveolae directly couple the plasma membrane (PM) to the ER for directed LCFA transport and metabolic processing.