Abstract
Dietary fat absorption by the small intestine is an efficient, multistep process that regulates the uptake and delivery of essential nutrients and energy. Fatty acids taken up by enterocytes, the absorptive cells of the small intestine, are resynthesized into triacylglycerol (TAG) and either secreted in chylomicrons or temporarily stored in cytoplasmic lipid droplets (CLDs). Proteins that associate with CLDs are thought to regulate the dynamics of TAG storage and mobilization. It is currently unclear what effect diet induced obesity (DIO) has on the balance between dietary fat storage and secretion. Specifically, there is limited knowledge of how DIO affects the level and diversity of proteins that associate with CLDs and regulate CLD dynamics. In the current study, we characterize CLDs from lean and DIO mice through histological and proteomic analyses. We demonstrate that DIO mice have larger intestinal CLDs compared to lean mice in response to dietary fat. Additionally, we identified 375 proteins in the CLD fraction isolated from enterocytes of lean and DIO mice. We identified a subgroup of lipid related proteins that are either increased or unique to the DIO CLD proteome. These proteins are involved in steroid synthesis, TAG synthesis, and lipolysis. This analysis expands our knowledge of the effect of DIO on the process of dietary fat absorption in the small intestine (D’Aquila, 2016).
Highlights
Enterocytes, the absorptive cells of the small intestine, are responsible for the uptake, repackaging, and secretion of dietary fat
We identified proteins involved in fatty acid oxidation in the cytoplasmic lipid droplet (CLD) fraction of only diet induced obesity (DIO) mice (Table 1). mRNA levels of genes involved in fatty acid oxidation (Kondo et al, 2006; de Wit et al, 2008; Douglass et al, 2012; Uchida et al, 2012) as well as fatty acid oxidation activity (Kondo et al, 2006) increases in enterocytes with chronic high fat feeding
We found that DIO alters CLD morphology and the CLD proteome in the postprandial response to dietary fat
Summary
Enterocytes, the absorptive cells of the small intestine, are responsible for the uptake, repackaging, and secretion of dietary fat. Enterocytes are capable of temporarily storing dietary fat in CLDs in the postprandial response to dietary fat (reviewed in Beilstein et al, 2016; D’Aquila et al, 2016). Dietary fat in the form of TAG is digested in the lumen of the small intestine producing free fatty acids and monoacylglycerols, which are incorporated into mixed micelles. Mixed micelles interact with the brush border membrane of enterocytes where free fatty acids and monoacylglycerols are absorbed. Free fatty acids and monoacylglycerols are resynthesized into TAG by acyl-CoA: monoacylglycerol acyltransferase and DGAT at the Abbreviations: CLD, cytoplasmic lipid droplet; DGAT, diacylglycerol O-acyltransferase; DIO, diet induced obesity; GO, Gene Ontology; Plin, perilipin; TAG, triacylglycerol. While there are structural and composition similarities between chylomicron particles and CLDs, these lipid containing particles differ in their synthesis and metabolism that allows chylomicrons to be secreted and requires further metabolism of CLDs before the stored lipids are used within or eventually secreted from cells (reviewed in Demignot et al, 2014)
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