Distinct pools of OXPAT suggest roles in lipid trafficking

Abstract

Muscle and liver tissues surfeited with neutral lipid have been implicated in the development of insulin resistance and type II diabetes. PAT proteins coat lipid storage droplets (LSDs) and regulate lipid storage. The most recently discovered PAT family member, OXPAT (also known as LSDP5 or MLDP), localizes to two distinct intracellular pools: the LSDs and a cytosolic pool. Characterization of the cytosolic pool reveals that OXPAT resides on a discreet structure. Sucrose gradient ultracentrifugation and non‐denaturing gradient gel electrophoresis indicate that the particles have a density of 1.10‐1.17 g/ml and a diameter of approximately 15 nm (575 kDa). Immunoprecipitation of these particles using an OXPAT specific antibody fails to precipitate ADRP. In contrast, both ADRP and OXPAT coexist on the more buoyant LSD. CHO cells ectopically expressing OXPAT have increased neutral lipid stores (1.5 fold more triacylglycerols and 3.8 fold more total cholesterol). Additionally, there is a change in the morphology of these LSDs (the size of the largest droplet in each cell increased from 1.5 to 3.1 microns when OXPAT was expressed). OXPAT shifts from the cytosol to the LSD upon treatment of cells with oleic acid to increase neutral lipid deposition. Collectively these data suggest a new role for OXPAT in neutral lipid trafficking and storage. This work was supported in part by a K award (HD049628) to WEA.