Lipids such as fatty acids and cholesterol are involved in innumerable cellular processes, including energy storage and production, membrane biogenesis, signal transduction, and the regulation of gene expression. Nevertheless, the mechanisms by which lipids are transported and targeted within cells remain largely unknown. Abnormal lipid trafficking, such as that occurring in lipid-storage diseases, can lead to severe cellular pathologies. The overall focus of research in this laboratory is on lipid traffic in cells, with particular emphasis on long-chain fatty acids, monoacylglycerols, and cholesterol. Ongoing efforts are addressing the following questions:

1. What are the functions of cytoplasmic fatty acid-binding proteins (FABP) in intracellular lipid transport and metabolism? Why do different cell types have different FABP?
2. What are the structural determinants of functional differences between members of the FABP gene family? What are the mechanisms of fatty acid and monoacylglycerol transport and utilization in polarized intestinal epithelial cells?
3. Fatty acids and monoacylglycerols delivered to the intestinal cell via the diet or via the bloodstream are metabolized differently--how is this 'metabolic polarity' established and maintained?
4. How does the intracellular cholesterol-binding protein, Niemann-Pick type C2 protein (NPC2), function in the transport of cholesterol out of endosomes and lysosomes?
   

Figure: Tertiary structure of the heart fatty acid binding protein. The helix-turn-helix domain (shown in pink) is hypothesized to be important in fatty acid (shown in blue) transfer to membranes.

The laboratory uses a combination of biochemical, biophysical, cell and molecular biological approaches to answer these questions. For example, fluorescence spectroscopic analysis of recombinant FABP is used to examine the interactions of fatty acids with FABP and the kinetics of fatty acid and monoacylglycerol transfer between FABP and membranes. The structural determinants of ligand-protein interactions and FABP-membrane interactions are probed using chemical modification and site-directed mutagenesis. Cell culture systems such as the Caco-2 human intestinal cell line and 3T3-L1 adipocytes are used to examine cellular lipid transport using biochemical methods and confocal microscopy. The functions of FABPs are also studied using transgenic mouse models in which specific FABP expression has been "knocked out" and in cultured cells by manipulation of FABP content. The metabolic polarity of fatty acid and monoacylglycerol in the intestinal cell is studied using a variety of mouse models and cell culture approaches. Human bibroblasts from patients with NPC disease are used to examine the function of the NPC2 protein in cholesterol trafficking.  These studies are providing fundamental information about the cellular trafficking of lipids , with the ultimate goal of enabling effective preventice and therapeutic approaches to a variety of pathologic conditions including obesity, cardiovascular disease, and lipid-storage diseases.

Glatz JFC, Storch J. Unraveling the significance of cellular fatty acid-binding proteins. Curr Opin Lipidol 12:267-274, 2001

Layne MD, Patel A, Chen YH, Rebel VI, Carvajal IM, Pellacani A, Ith B, Zhao D, Schreiber BM, Yet S-F, Lee, M-E, Storch J, Perrella MA. Role of macrophage-expressed fatty acid-binding protein in the development of accelerated atherosclerosis in hypercholesterolemic mice. FASEBJ. 15:2733-5, 2001

Ho SY, Delgado L, Storch J. Monoacylglycerol Metabolism in Human Intestinal Caco-2 Cells: Evidence for metabolic compartmentation and hydrolysis. J Biol Chem 277:1816-1823, 2002.

Corsico B, Liou H-L., Storch J. The α-helical domain of liver fatty acid binding protein is responsible for the diffusion-mediated transfer of fatty acids to phospholipid membranes. Biochemistry 43: 3600-3607, 2004.

Murota K and Storch J. Uptake of micellar long chain fatty acid and sn-2-monoacylglycerol into human intestinal Caco-2 cells exhibits characteristics of protein-mediated transport. J Nutrition, 135: 1626-1630, 2005.

Corsico B., Franchini GL, Hsu KT, Storch J. Electrostatic and hydrophobic interactions contribute to the collisional mechanism of fatty acid transfer from intestinal fatty acid binding protein to phospholipid membranes. J Lipid Res, 46:1765-72, 2005.

Abumrad NA and Storch J.  Fatty acid transport in the intestine.  In Physiology of the Gastrointestinal Tract, ed. 4,  R. Johnson, ed., Academic Press, pp. 1693-1709, 2006.

Cheruku SR, Xu Z, Dutia R, Lobel P and Storch J.  Mechanism of cholesterol transfer from the Niemann-Pick type C2 protein to model membranes supports a role in lysosomal cholesterol transport.  J Biol Chem 281: 31594-31604, 2006

Thumser AE and Storch J.  Characterization of a BODIPY-labeled fluorescent fatty acid analogue: Binding to fatty acid binding proteins, intracellular localization, and metabolism. Mol Cell Biochem 299:67-73, 2007