Fatty acids (FA) and monoacylglycerol (MG), the hydrolytic products of triacylglycerol (TG), provide a major source of dietary energy. Nevertheless, substantial gaps remain in understanding the basic mechanisms of MG and FA assimilation. These include a molecular level understanding of the individual functions of two highly expressed enterocyte fatty acid-binding proteins (FABP), intestinal FABP and liver FABP. In addition, the mechanisms of differential trafficking of MG and FA added to the apical (AP) vs. basolateral (BL) poles of the enterocyte, where AP lipid is more highly incorporated into TG, and BL lipid into phospholipid, are not understood. In this proposal, we will use an integrated approach to address the cellular and molecular mechanisms that underlie the polarity of intestinal FA and MG transport and metabolism, and the specific roles of the two enterocyte FABPs in FA transport, lipid metabolism, and lipoportein secretion. Further, we will explore the regulation and function of monoacylglycerol lipase (MGL), which we have recently shown to be expressed in rat intestine.
The specific aims are 1) To determine the functions of IFABP and LFABP in cellular transport and metabolism of FA and MG: Structure-function studies in model systems, analysis of the apo- and holo-LFABP tertiary structures, and direct protein transfer of wild type and specific FABP mutant forms into cultured Caco-2 enterocytes, will allow us to determine the individual functions of IFABP and LFABP, and the structural basis for these functional properties; 2) To determine the cellular basis for metabolic compartmentation of FA and MG in the enterocyte. Studies in rats, mice null for specific enzymes and transport proteins, and Caco-2 cells, will allow us to examine the role of plasma membrane transporters, intracellular FABPs, and specific intracellular enzymes, in the underlying mechanisms of this metabolic divergence; and 3) To explore the role of intestinal monoacylglycerol lipase, using studies in rodents and cultured cells, MGL is higher in neonatal intestine and declines to lower levels in the adult animal, thus we will examine the mechanisms that underlie changes in MGL expression. The ultimate aim of this research program is to understand how to control the rate and extent of dietray lipid assimilation by modulating specific transport and metabolic processes. Such modulation has important implications for the treatment of obesity, diabetes, and hyperlipidemias.
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