L-FABP directly interacts with PPARα in cultured primary hepatocytes

Although studies with liver type fatty acid binding protein (L-FABP) gene ablated mice demonstrate a physiological role for L-FABP in hepatic fatty acid metabolism, little is known about the mechanisms whereby L-FABP elicits these effects. Studies indicate that L-FABP may function to shuttle lipids to the nucleus, thereby increasing the availability of ligands of nuclear receptors, such as peroxisome proliferator-activated receptor-alpha (PPAR alpha). The data herein suggest that such mechanisms involve direct interaction of L-FABP with PPAR alpha. L-FABP was shown to directly interact with PPAR alpha in vitro through co-immunoprecipitation (co-IP) of pure proteins, altered circular dichroic (CD) spectra, and altered fluorescence spectra. In vitro fluorescence resonance energy transfer (FRET) between Cy3-labeled PPAR alpha and Cy5-labeled L-FABP proteins showed that these proteins bound with high affinity (K-d approximately 156 nM) and in close proximity (intermolecular distance of 52 angstrom). This interaction was further substantiated by co-IP of both proteins from liver homogenates of wild-type mice. Moreover, double immunogold electron microscopy and FRET confocal microscopy of cultured primary hepatocytes showed that L-FABP was in close proximity to PPAR alpha (intermolecular distance 40-49 angstrom) in vivo. Taken together, these studies were consistent with L-FABP regulating PPAR alpha transcriptional activity in hepatocytes through direct interaction with PPAR alpha. Our in vitro and imaging experiments demonstrate high affinity, structural molecular interaction of L-FABP with PPAR alpha and suggest a functional role for L-FABP interaction with PPAR alpha in long chain fatty acid (LCFA) metabolism. Hostetler, H. A., A. L. McIntosh, B. P. Atshaves, S. M. Storey, H. R. Payne, A. B. Kier, and F. Schroeder. L-FABP directly interacts with PPAR alpha in cultured primary hepatocytes. J. Lipid Res. 2009. 50: 1663-1675.